JPH04311828A - Optical head and information recording device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head and information medium used in optical information processing devices such as optical disk devices, optical card devices, and optical tape devices.

0002

2. Description of the Related Art In an optical head used in an optical disk device, a beam emitted from a semiconductor laser or the like is irradiated onto an information medium such as an optical disk using a focus lens, and the beam reflected from the disk is focused again using a focus lens. The system separates the disc reflected beam from the semiconductor laser emitted beam, the separated disc reflected beam is received by a photodetector, a defocus detection signal and a track deviation detection signal are generated from the output of the photodetector, and these detection signals are is supplied to, for example, a two-dimensional lens actuator, and the focus lens is moved in the lens optical axis direction and the disk radial direction to perform focusing control and track alignment control. At the same time, an information reproduction signal is also generated from the photodetector output.

[0003] Usually, a semiconductor laser chip, which is a light source, is fixed to a package substrate to which lead wires for electrodes are attached, and is sealed with a cap with a glass window. We also provide semiconductor laser packages, beam separation optical systems,
The photodetector, two-dimensional lens actuator, etc. are firmly fixed to the housing (body) of the optical head. However, in order to achieve focusing control and tracking control, the focus lens is movably supported via a spring of a two-dimensional lens actuator fixed to the optical head housing. Therefore, the entire optical head is not hermetically sealed.

In addition, many of the defocus detection methods used in conventional optical heads such as optical disks utilize the fact that the shape and light intensity distribution of the disk reflected light change due to defocus, and detect a multi-segment photodetector. The unbalance of the direct current output signal was used as the defocus detection signal.

For example, in the astigmatism method described in Japanese Patent Application Laid-Open No. 59-58537, when astigmatism is imparted to the disk reflected beam by an astigmatism element such as a cylindrical lens, the disk reflected beams are arranged in directions perpendicular to each other. Two focal lines are formed, and at the position of the circle of least confusion, which is approximately in the center, it becomes circular, so
The disk reflected light is received by a four-split photodetector. The shape of the reflected beam on the 4-split photodetector surface is approximately circular when the disk is at the focal position, and becomes linear in mutually orthogonal directions depending on the direction of the displacement when the disk is deviated from the focal position. Therefore, a defocus detection signal is obtained by adding the DC output signals of the photodetecting elements located diagonally to each other in the 4-split photodetector and taking the difference between the two DC summed signals.

On the other hand, what is the method of receiving the changes in the shape and light intensity distribution of the disk reflected light using a multi-segment photodetector and detecting the unbalance of the DC output signal, as in the first conventional example described above? Separately, a method for detecting a focus error using a diffraction grating that forms light spots at different positions in the focal depth direction has been proposed in Japanese Patent Laid-Open No. 1-303632.

According to an embodiment disclosed in Japanese Patent Application Laid-Open No. 1-303632, the diffraction grating is a part of a set of a plurality of concentric grooves whose grating groove intervals increase or decrease in sequence, and the +1st-order beam and −1-order beams are given positive and negative aberrations due to vertical movement of the image point (aberrations due to defocus). Also,
The diffraction grating uses a region where the center position of the concentric groove is eccentric from the position of the principal ray axis of the main beam, and radiates the +1st order beam and -1st order beam in opposite directions with respect to the principal ray axis of the main beam. . Therefore, the +1st-order beam and the -1st-order beam were focused by a focus lens into two side spots at different positions in the focal depth direction with respect to the main beam, and the amounts of reflected light from the two side spots were recorded on the optical disk. They are modulated by signals, and their degree of modulation is detected by a photodetector and an envelope detection circuit. 2
Since the degree of modulation by the two side spots changes depending on the defocus of the optical disc, a defocus detection signal can be obtained by taking the difference between the two degrees of modulation.

Furthermore, the beam separation optical system used in the conventional optical head uses a polarizing prism and a quarter wavelength plate, as described in, for example, Japanese Patent Laid-Open No. 59-58537. In this beam separation optical system, when the laser beam goes back and forth through the quarter-wave plate, the polarization direction of the linearly polarized beam is rotated by 90 degrees, so that the two beams can be completely separated by the polarizing prism. A commonly used polarizing prism is a cubic polarizing beam splitter in which a dielectric laminated film is sandwiched between two triangular prisms.
Separates the reflected beams at right angles.

Furthermore, in optical heads such as compact disks, in order to reduce the number of optical components, a quarter-wave plate is not used, but a half prism or half wave plate that separates approximately half of the disk reflected beam in the right angle direction is used. mirror is used.

[0010] Also, recently, Japanese Patent Application Laid-Open No. 2-216629
As described in the publication, by separating the disk reflected beam into a direction slightly different from that of the semiconductor laser using a diffraction grating or hologram element inserted between the semiconductor laser and the focus lens, the semiconductor laser and photodetection are performed. A small optical head in which the optical discs are mounted adjacent to each other has also been reported.

[0011]

However, when attempting to downsize the optical head, there is a problem in that the light source section of the conventional semiconductor laser sealed in a case becomes large. Therefore, it is conceivable to attach the semiconductor laser chip directly to the optical head housing. However, in conventional optical head housings, the inside of the optical head housing is not sealed, and the semiconductor laser chip is exposed to outside air containing moisture flowing in from the open part of the optical head housing or the spring part of the two-dimensional lens actuator. directly exposed. Therefore, if it is used for a long period of time or stored or used in a humid environment, the end face of the semiconductor laser chip deteriorates, making laser oscillation unstable, and furthermore, the performance of the optical head becomes unstable. arise.

[0012] Also, as in the astigmatism method described in the above-mentioned Japanese Patent Laid-Open No. 59-58537, the shape of the disk reflected light and the unbalance of the light intensity distribution are detected using a multi-segment photodetector. In the method of obtaining a defocus detection signal, for example, in order to focus the defocus detection optical system, the disc position where the data signal etc. is maximum or the disc position where the amount of reflected light returning to the light source is maximum is determined. , is detected by a measurement system separate from the focusing system, and at that disk position, each photodetection element of the 4-split photodetector receives an equal amount of light, and each photodetection element receives the same level of direct current. The positions of the four-split photodetector and the detection lens must be adjusted so that the defocus detection signal becomes zero level by outputting the signal. Therefore, there is a problem in that it takes time to assemble and adjust the optical head, making the optical head expensive. Further, there is a problem in that the optical head must be provided with a highly accurate optical component position adjustment mechanism, making it difficult to downsize the optical head.

Furthermore, if the mounting position of the optical component shifts due to a change in temperature, the position of the light beam on the surface of the multi-segment photodetector shifts, so a direct current amplifier is applied to the output of each photodetector element of the multi-segment photodetector. There is a problem in that balance occurs, and the disk position at which the defocus detection signal is at zero level deviates from the target point position for focusing, causing an offset in the defocus detection signal.

On the other hand, according to the embodiment disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 1-303632, the above-mentioned problems have been solved, but the pits are not suitable for obtaining the most stable defocus detection signal. The structure of the diffraction grating that determines the arrangement and the shape of the side spot has not been sufficiently studied, and the focus control pull-in operation may fail due to a decrease in the degree of modulation due to the relative positional shift between the side spot and the pit in the radial direction of the optical disk. There is a problem with stability. Normally, automatic focus control in an optical disc device should be performed before automatic tracking control, so it must not be affected by radial deviation of the optical disc.

This will be explained using FIG. 18. Figure 18
(1) and (2) show the spot shape and pits on the optical disc surface when a diffraction grating with a plurality of concentric grooves disclosed in Japanese Patent Application Laid-Open No. 1-303632 is used. 3
50a is a main spot on the optical disc surface, 350b and 350c are sub spots on the optical disc surface, 351 is a track, and 352 is a pit recorded on the track 351. The concentric groove diffraction grating gives the +1st order beam and the -1st order beam aberrations of positive and negative image point vertical movement (defocus aberrations), so the +1st order beam and the -1st order beam are
The focus lens narrows down the main beam to different positions in the depth of focus direction. Both (1) and (2) in Fig. 18 are shifted from the focal position of the main beam.
The spot shape at the focal position of the primary beam is shown, and the sub-spot 350c is the smallest. (1) is a case where three spots pass over the track 351, and the reflected light of the sub-spot 350c is largely modulated by the pit 352. Although not shown in FIG. 18, when the optical disc is displaced in the opposite direction and the sub-spot 350b becomes the smallest, the reflected light of the sub-spot 350b is significantly modulated by the pit 352. Therefore, when three spots pass over the track 351 as shown in (1), the defocus detection signal becomes a curve shown by the solid line 353 in (3) of FIG. On the other hand, (2) is a case where three spots pass between the tracks 351, and the reflected light of the sub-spot 350c is not significantly modulated by the pits 352, and is reduced to less than half of the case (1), for example. Although not shown in FIG. 18, even when the optical disc is misaligned in the opposite direction and the sub-spot 350b is the smallest, the pit 3 of the reflected light of the sub-spot 350b
For example, the modulation depth by 52 is reduced to less than half of that in case (1). Therefore, when three spots pass between the tracks 351 as shown in (2) of FIG. 18, the defocus detection signal is as shown in FIG.
As shown by the broken line 354 in 8(3), the peak decreases to less than half, and the detection sensitivity near the focal point also decreases to less than half. If the detection sensitivity decreases during the pull-in operation of automatic focusing control, there will be insufficient driving force to make the focus lens follow the disc displacement, and the movement of the focus lens will become slow, which may cause the pull-in operation to fail. be. Therefore, in the conventional example described above, there is a problem that the focus control pull-in operation becomes unstable.

On the other hand, in automatic tracking control,
A sample servo method using prewobble pits is a method in which target point alignment for track following is automatically performed and, in principle, no offset occurs even if the position of an optical component is shifted. The method for detecting track deviation in this method is that when the main spot passes through two sets of prewobbled pits that are arranged to be shifted by the same amount to the right and left with respect to the track center, the modulation level of the reflected beam is determined according to the amount of track deviation. The reflected beam is received by a photodetector, and the difference in modulation level is detected to obtain a track deviation detection signal. In this method, when the main spot passes through the center of the track, the track deviation detection signal automatically becomes zero level, so there is no need to adjust the position of the optical component to align the target point for track following. Further, the photodetector only needs to receive the entire amount of the reflected beam, and no offset occurs in the track deviation detection signal even if the mounting position of the optical component changes. However, in order to reduce the size and cost of the optical head, normally the same optical system is used for defocus detection and track misalignment detection, and the photodetecting element for defocus detection and the photodetecting element for tracking misalignment are also used. attached to the same photodetector package. Therefore,
When assembling an optical head, even though it is not necessary to adjust the position of the optical components for target point alignment for track following, highly accurate position adjustment of the optical components is still required for focusing. There was a problem that the advantages were not fully utilized.

[0017] Furthermore, if a beam separation optical system is used that uses a polarizing beam splitter, a half prism, or a half mirror to separate the disk reflected beam in the orthogonal direction, apart from the optical path of the focusing optical system from the semiconductor laser to the focus lens, This requires an optical path for the detection optical system from the beam splitter to the photodetector, which poses a problem in that it is not suitable for downsizing the optical head.

On the other hand, if a diffraction grating or a hologram element is used in the beam separation optical system, the optical path of the focusing optical system and the optical path of the detection optical system can be shared by mounting the semiconductor laser and the photodetector next to each other. This is effective in downsizing the optical head. However, since a diffraction grating or a hologram element cannot completely separate the semiconductor laser emitted beam and the disk reflected beam, the following problems arise. A semiconductor laser emitted beam also passes through a diffraction grating or a hologram element and is separated into a number of higher-order diffraction beams in addition to the zero-order diffraction beam, which causes a problem in that the light intensity of the main beam decreases. In addition, in order to prevent the extreme decrease in the light intensity of the main beam mentioned above,
Since the diffraction efficiency of the higher-order diffraction beam must be kept low, there is a problem that the beam separation efficiency of the disk reflected light is low and a sufficient detection signal cannot be obtained. Another problem is that most of the light reflected from the disk tends to return to the semiconductor laser, and laser noise is likely to occur.

An object of the present invention is to provide a compact optical head that can maintain stable performance for a long period of time by preventing deterioration of the semiconductor laser.

Another object of the present invention is that there is no need to adjust the position of optical components for focusing, there is no offset in the defocus detection signal even if the mounting position of the optical component changes, and the radius of the optical disc is An object of the present invention is to provide a small optical head using a defocus detection method that can achieve stable automatic focus pull-in operation without being affected by directional deviation. Another object of the present invention is to provide a compact optical head that uses an optical disk formatted for the sample servo method and uses the sample servo method for tracking control, making it possible to eliminate adjustment.

Another object of the present invention is to use a beam separation optical system that can completely separate the semiconductor laser emitted beam and the disc reflected beam, and that can share the optical path of the focusing optical system and the optical path of the detection optical system. The purpose of the present invention is to provide a compact optical head.

[0022]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor laser, particularly a semiconductor laser chip, and a focus that focuses an output beam emitted from the semiconductor laser onto the surface of an information medium such as a disk. An imaging optical system such as a lens, a beam separation optical system such as a diffraction grating, a beam splitter prism, or a half mirror that separates the output beam from the reflected beam reflected by the information medium, and a detection beam separated by the beam separation optical system. In an optical head consisting of a photodetector that receives light, a semiconductor laser, an imaging optical system, a beam separation optical system, and an optical head housing that fixes the photodetector, the imaging optical system or the beam separation optical system and the optical head housing are used. The semiconductor laser is hermetically sealed.

In a preferred embodiment (aspect 2) of the present invention, the space sealed by the imaging optical system or beam separation optical system and the optical head housing is replaced with dry nitrogen gas.

In another preferred embodiment (aspect 3) of the present invention, the space sealed by the imaging optical system or beam separation optical system and the optical head housing is replaced with a vacuum.

In a preferred embodiment (aspect 4) of the present invention, the imaging optical system or the beam separation optical system and the optical head housing are hermetically bonded together by sintering.

In a preferred embodiment (aspect 5) of the present invention, the position of the entire optical head housing is controlled in two directions using a two-dimensional lens actuator or the like in response to a focus shift detection signal or a track shift detection signal.

In a preferred embodiment (aspect 6) of the present invention, the beam separation optical system includes a first beam separation optical system that separates the output beam emitted from the semiconductor laser into a main beam and two sub-beams, and a first beam separation optical system that separates the output beam emitted from the semiconductor laser into a main beam and two sub-beams; and a second beam separation optical system that separates the plurality of reflected beams into a direction different from that of the output beam, and the first beam separation optical system separates the two sub-beams with positive astigmatism and negative astigmatism. The first diffraction grating or hologram element has marks on the information medium surface, such as pits with uneven shapes or pits with different reflectances, recorded in advance to modulate the amount of reflected light of the sub-beams. at least two photodetecting elements of a plurality of photodetectors or a split type photodetector for receiving the +1st-order sub-beam and -1st-order sub-beam separated by the second beam separation optical system, respectively; and two light detecting elements for receiving the sub-beams. Two amplitude detection circuits for detecting the magnitude of the amplitude modulated by the mark from the light amount signal output by the detection element, and a differential calculation circuit for subtracting the two amplitude detection signals output from the amplitude detection circuit. It consists of a defocus detection circuit.

In a further preferred embodiment (aspect 7) of the present invention, the first diffraction grating or hologram element is a set of a plurality of linear grooves in which the grating groove spacing increases or decreases sequentially. Further, the marks are arranged in a direction perpendicular to the direction of the track.

Another more preferred embodiment of the present invention (Embodiment 8)
), the first diffraction grating or hologram element is part of a set of a plurality of concentric elliptical grooves whose grating groove spacing increases or decreases sequentially, and furthermore, the center position of the concentric elliptical grooves is located at the main position of the zero-order beam. It is placed at a position eccentric from the position of the beam axis. Further, the marks are arranged in a direction perpendicular to the direction of the track.

Other more preferred embodiments of the present invention (Embodiment 9)
), the amplitude detection circuit includes a first sample and hold circuit that holds the output signal level of the photodetector when the +1st order beam or -1st order beam is between the marks, and a first sample and hold circuit that holds the output signal level of the photodetector element when the +1st order beam or -1st order beam A second sample and hold circuit that holds the output signal level of the photodetector when it is on the mark, and a differential operation that subtracts the output signal of the first sample and hold circuit and the output signal of the second sample and hold circuit. It consists of a circuit.

In another preferred embodiment (aspect 10) of the present invention, the amplitude detection circuit incorporates a switch circuit for always setting the polarity of the output signal of the amplitude detection circuit to a positive level or a negative level.

In another preferred embodiment (aspect 11) of the present invention, the mark is a first mark disposed at a certain distance on one side with respect to a predetermined track center line along which the main spot is guided on the information medium surface. It consists of a pit group and a second pit group placed equidistantly apart from each other on the opposite side with respect to the track center line, and the output signal level of the photodetecting element and the second pit group are A track deviation detection signal is obtained by comparing the output signal levels of the photodetecting elements when passing through two pits.

In another preferred embodiment (aspect 12) of the present invention, the second beam separation optical system that separates the reflected beam reflected by the information medium into a direction different from that of the emitted beam, comprises:
A diffraction grating plate having a second diffraction grating made of a birefringent material on at least one surface, and a polarization direction such that the reflected beam becomes an extraordinary ray (or ordinary ray) when it passes through the second diffraction grating. It consists of polarization rotation means such as a Faraday rotator and a quarter-wave plate for rotation, and the convex and concave portions of the second diffraction grating are such that the difference in optical path length with respect to the extraordinary ray (or ordinary ray) is an integer number of wavelengths. Double and half wavelengths, almost equal width.

[0034] In a preferred embodiment (aspect 13) of the present invention,
Furthermore, the difference in optical path length between the convex portion and the concave portion of the second diffraction grating with respect to the ordinary ray (or extraordinary ray) is an integral multiple of the wavelength.

In a preferred embodiment (aspect 14) of the present invention,
The polarization rotation means is a quarter wavelength plate.

In a preferred embodiment (aspect 15) of the present invention,
The diffraction grating plate and the quarter wavelength plate are integrated.

In a preferred embodiment (aspect 16) of the present invention,
The first diffraction grating is formed on the other surface of the diffraction grating plate having the second diffraction grating.

[0038] In a preferred embodiment (aspect 17) of the present invention,
The first diffraction grating is made of a birefringent material, and the convex portions and concave portions of the first diffraction grating have substantially equal widths with a difference in optical path length for the extraordinary ray (or ordinary ray) being an integral multiple of the wavelength.

[0039]

[Operation] In the present invention, since the semiconductor laser, particularly the semiconductor laser chip, is sealed by the imaging optical system or beam separation optical system and the optical head housing, it is free from moisture that flows in from outside the optical head housing. The semiconductor laser chip is not directly exposed to the outside air. Therefore, the laser oscillation does not become unstable due to deterioration of the end face of the semiconductor laser chip, so the performance of the optical head remains stable even if it is used for a long period of time or stored or used in a humid environment.

Furthermore, in the second or third aspect, since the semiconductor laser, particularly the semiconductor laser chip, is placed in a dry nitrogen gas atmosphere or in a vacuum from the beginning of manufacturing the optical head, the end face of the semiconductor laser chip is clean. can be maintained for a long time. Therefore, the optical head can be stored or used for a longer period of time.

Further, in the fourth aspect, a sintered material having a melting point lower than that of the material of optical components such as a focus lens and a diffraction grating, such as cobalt glass (with a melting point of about 500 degrees Celsius), is used.
), etc., by heating and melting and slowly cooling it, it improves the airtightness of the joint that seals the semiconductor laser chip, and it also improves the airtightness of the joint part that seals the semiconductor laser chip.Furthermore, the end face of the semiconductor laser chip is The problem of deterioration is also solved.

In the fifth aspect, automatic focusing control and automatic tracking control are performed by controlling the position of the entire optical head housing in two directions using a two-dimensional lens actuator or the like according to the focal deviation detection signal and the tracking deviation detection signal. can be achieved.

Next, in order to explain the operation of the sixth aspect, the operation of the first diffraction grating and the defocus detection principle of the present invention will be explained using FIGS. 16 and 17. FIG. 16 is a basic configuration diagram of the optical head of the present invention, in which a laser beam 301 emitted from a conductive laser 300 is converted into a 0th-order beam 304a and a +1st-order beam 304b by a first diffraction grating 302.
It is separated into a primary beam 304c. +1st beam 304
The b and −1st order beams 304c are emitted in directions different from the 0th order beam 304a by small positive and negative angles. Furthermore, the first diffraction grating 302 used in the present invention is different from a normal evenly spaced straight groove type diffraction grating, and is a non-equally spaced straight groove type diffraction grating or a concentric elliptical arc type diffraction grating, and is for the +1st order beam. It acts as a positive cylindrical lens or toroidal lens with respect to the −1st order beam, and acts as a negative cylindrical lens or toroidal lens with respect to the -1st order beam. Therefore, positive and negative astigmatism with equal absolute values are given to the +1st-order beam and the -1st-order beam. Due to the action of the first diffraction grating 302, at least in the in-plane direction, the +1st-order beam 304b
is more focused than the zero-order beam 304a, and the -1st-order beam 304c is more divergent than the zero-order beam 304a. Each beam is focused by a focus lens 306. In the in-plane direction, the zero-order beam 304
Let 307a be the focal point of the beam a, 307b be the focal point of the +1st order beam 304b, and 307c be the focal point of the −1st order beam 304c. However, the focal points 307b and 307c are focal lines of the +1st-order beam 304b and the -1st-order beam 304c. Zero-order beam 304a from optical disk 308
The +1st order beam 304b and -1st order beam 304c are reflected by the optical disk 308, pass through the focus lens 306, are separated from the output beam 301 of the semiconductor laser 300 by the second diffraction grating 303, and reach the photodetector element. do. The photodetecting element 311b receives the +1st-order reflected beam 310b and outputs a light amount signal 312b, and the photodetecting element 311c
receives the −1st-order reflected beam 310c and outputs the light amount signal 312
Output c. The optical disc 308 has marks such as uneven pits. When the optical disk 308 moves in the horizontal direction on the paper, the light intensity of the +1st-order reflected beam 310b and the -1st-order reflected beam 310c are modulated by the marks.
The light amount signal 312b and the light amount signal 312c are also modulated. The magnitude of the modulation of the light amount signal 312b and the light amount signal 312c is
For example, it can be detected by an envelope detection circuit. The envelope detection circuit detects the upper level and lower level of the amplitude of the input signal, and outputs the difference therebetween, that is, the magnitude of modulation of the input signal. Therefore, the modulation degree signal 314
b indicates the magnitude by which the +1st-order reflected beam 310b is modulated by the mark, and the modulation degree signal 314c indicates the magnitude by which the +1st-order reflected beam 310c is modulated by the mark. The modulation degree signal 314b and the modulation degree signal 314c are input to the differential calculation circuit 315, and the output thereof is used as the defocus detection signal 31.
Set it to 6.

The most suitable position of the optical disk 308 (focusing target point position) for recording and reproducing information using the zero-order beam 304a is the position 309(2) of the focal point 307a of the zero-order beam 304a. The first diffraction grating 302 has a +1st order beam 304b and a −1st order beam 304c.
Since the astigmatism given to has opposite signs and equal absolute values,
The amount of deviation of the focusing point 306b and the focusing point 306c from the optical disk 308 is equal. Therefore, at this disk position,
+1st order reflected beam 310b and -1st order reflected beam 310c
are modulated by the marks to the same magnitude, the level of the modulation degree signal 314b and the level of the modulation degree signal 314c become equal, and the defocus detection signal 316 becomes zero level. When the optical disk 308 shifts toward position 309(1), the modulation degree of the +1st-order reflected beam 310b increases, and -
The degree of modulation of the primary reflected beam 310c becomes smaller, and the defocus detection signal 316 becomes a positive level. optical disc 308
is the position 309 of the focal point 307b of the +1st order beam 304b
In (1), the modulation degree of the +1st-order reflected beam 310b becomes maximum, and the defocus detection signal 316 becomes the maximum positive level. Conversely, when the optical disk 308 shifts toward position 309(3), the modulation degree of the +1st-order reflected beam 310b becomes smaller, the modulation degree of the -1st-order reflected beam 310c increases, and the defocus detection signal 316 becomes a negative level. become. The optical disc 308 is the focal point 307c of the -1st order beam 304c.
At position 309(3), -1st order reflected beam 310
The modulation degree of c becomes the maximum, and the defocus detection signal 316 becomes the maximum negative level.

17(1) and (2) show the optical disk surface when the optical disk 308 in FIG. 16 is shifted to position 309(3), 320a is the main spot, 320a is the main spot,
20b and 320c indicate sub-spots, 321 a track, and 322 a pit recorded on the track 321. The positions of the pits 322 are aligned in the radial direction of the disk over several tracks. (1) is a case where three spots pass over the track 321, and the reflected light of the sub-spot 320c is largely modulated by the plurality of pits 322. Although not shown in the figure, if the optical disc 308 in FIG. 16 shifts to position 309(1),
The reflected light of the sub-spot 320b is significantly modulated by the plurality of pits 322. Therefore, when three spots pass over the track 321 as shown in (1), the defocus detection signal becomes a curve shown by the solid line 323 in (3). A solid line 323 indicates that almost the same detection sensitivity as the solid line 353 in FIG. 18(3) can be obtained. In addition, (2) in FIG. 17 is a case where three spots pass between the tracks 321, and the reflected light of the sub-spot 320c is also largely modulated by the plurality of pits 322, so the degree of modulation is the same as in (1). It is obtained to the same extent as the case and does not decrease. Although not shown in the figure, even when the optical disc 308 in FIG. 16 is shifted to the position 309(1), the reflected light of the sub-spot 320b is modulated by the plurality of pits 322, and the degree of modulation is different from that in the case (1). It is obtained to the same extent and does not decrease. Therefore, as in (2), 3
Even when one spot passes between the tracks 321, the defocus detection signal is at almost the same level as the solid line 323, as shown by the broken line 324 in (3) of FIG. 17, and the detection sensitivity near the peak and focus also decreases. There's nothing wrong. Therefore, even if track deviation occurs, the pull-in operation for automatic focusing control can be performed stably.

As explained above, according to the present invention, the first
The astigmatism that the diffraction grating 302 gives to the +1st-order beam 304b and the -1st-order beam 304c has opposite signs and always has the same absolute value, so if the optical disk 308 is at the target point position for focusing, the astigmatism will be the same as the focusing point 307b. The amount of deviation at point 307c is always equal, and the +1st order reflected beam 3 due to the mark
The degree of modulation of the -1st-order reflected beam 310c is always equal to that of the reflected beam 10b, and the defocus detection signal 316 automatically becomes zero level. Therefore, according to the present invention, since the target point position for focusing is automatically set, there is no need to adjust the position of optical components for focusing. Further, in the present invention, the photodetecting element 311b and the photodetecting element 311c are +1
It is sufficient that the total amount of light of the secondary reflected beam 310b and the −1st-order reflected beam 310c is received, and each reflected beam may be located at any position on the light-receiving surface of the photodetector. Therefore, even if the position of the optical component shifts, no offset occurs in the defocus detection signal in principle. Furthermore, even if a track shift occurs, the pull-in operation for automatic focusing control can be performed stably.

In the seventh aspect, the first diffraction grating 302 or hologram element is a set of a plurality of linear grooves whose grating groove intervals increase or decrease in sequence, and the +1st-order beam and the −1st-order beam are directed in one direction. Positive and negative astigmatism that converges or diverges only is given to the beam, and the +1st-order beam and the -1st-order beam are emitted in opposite directions with respect to the principal ray axis of the 0th-order beam. Also,
The marks are arranged in a direction perpendicular to the track direction, so even if a track shift occurs, the focus shift detection signal will not decrease, and the pull-in operation for automatic focusing control can be performed stably. can.

In the eighth aspect, the first diffraction grating or hologram element is a part of a set of a plurality of concentric elliptical grooves whose grating groove spacing increases or decreases sequentially, and the first diffraction grating or hologram element is a part of a set of a plurality of concentric elliptical grooves whose grating groove spacing increases or decreases sequentially, Provides positive and negative astigmatism that converges or diverges in two directions. Furthermore, the center position of the concentric elliptical groove is placed at a position eccentric from the position of the principal ray axis of the 0th-order beam, and the +1st-order beam and -1st-order beam are emitted in opposite directions with respect to the principal ray axis of the 0th-order beam. do. In addition, since the marks are arranged in a direction perpendicular to the track direction, even if a track shift occurs, the focus shift detection signal will not decrease, and the pull-in operation for automatic focusing control will be performed stably. be able to.

In the ninth aspect, the amplitude detection circuit includes a first sample and hold circuit that holds the output signal level of the photodetecting element when the +1st order beam or the -1st order beam is between the marks, and the +1st order beam. or - a second one that maintains the output signal level of the photodetector when the primary beam is on the mark;
The photodetector element that receives the sub-beam outputs the sub-beam by comprising a sample-and-hold circuit and a differential calculation circuit that subtracts the output signal of the first sample-and-hold circuit and the output signal of the second sample-and-hold circuit. The magnitude of the amplitude modulated by the mark can be detected from the light amount signal.

[0050] In the tenth aspect, the amplitude detection circuit includes a switch circuit for always setting the polarity of the output signal of the amplitude detection circuit to a positive level or a negative level, so that the amplitude signal always has the same polarity positive. Therefore, as a result of performing these differential calculations, no malfunction occurs in the defocus detection signal.

[0051] In the eleventh aspect, the mark is located between the first pit group and the track center line, which are arranged at a certain distance on one side with respect to the predetermined track center line along which the main spot is guided on the information medium surface. The output signal level of the photodetecting element when the main spot passes through the first pit and when the main spot passes through the second pit is By comparing the output signal levels of the photodetecting elements, it is possible to use the sample servo method for tracking control using an optical disk formatted for the sample servo method, similar to the defocus detection method in the present invention, and to perform tracking control without any adjustment. It is possible to realize a compact optical head that can be

Next, in order to explain the operation of the twelfth aspect, the operation of the beam separation optical system consisting of the second diffraction grating and polarization rotation means will be explained. In FIG. 16, the semiconductor laser 30
A light source such as 0 emits a linearly polarized laser beam 301. The semiconductor laser emitted beam 301 passes through a second diffraction grating plate 303 made of a birefringent material, and then passes through a polarization rotation means 3 such as a Faraday rotator or a quarter-wave plate.
05 and reaches an information medium such as an optical disk 308. The reflected beam reflected by the information medium 308 passes through the polarization rotation means 305 again. Faraday rotator and 4
The polarization rotation means 305, such as a half-wave plate, can rotate the polarization direction of linearly polarized light by 90 degrees by reciprocating the laser beam. Therefore, for example, the emitted beam 301 from the light source 300 propagates in the second diffraction grating plate 303 as an ordinary ray, and the reflected beam from the disk 308 propagates in the second diffraction grating plate 303 as an extraordinary ray. The grating groove depth of the diffraction grating in the second diffraction grating plate 303 is such that the difference between the optical path length of the extraordinary ray that has passed through the convex portion and the optical path length of the extraordinary ray that has passed through the concave portion is an integral multiple of the wavelength and a half wavelength. is set to be. Furthermore, the width of the convex portion and the width of the concave portion of the lattice groove are approximately equal. Therefore, the beam that has passed through the convex portion and the beam that has passed through the concave portion have the same intensity and are shifted in phase by a half wavelength, so that they cancel each other out in the zero-order diffraction direction. On the other hand, in the ±1st-order diffraction direction, the diffraction beams strengthen each other, resulting in a strong ±1st-order diffraction beam, which reaches the photodetectors 311b and 311c arranged near the semiconductor laser 300. Therefore, the disk reflected beam can be completely separated, and a sufficient detection signal can be obtained. Further, the disk reflected beam does not return to the semiconductor laser 300,
The generation of laser noise is also reduced.

In the thirteenth aspect, the difference in optical path length between the convex portion and the concave portion of the second diffraction grating for the ordinary ray (or extraordinary ray) is set to be approximately an integral multiple of the wavelength. Since the phase of the beam passing through the convex portion of the second diffraction grating matches the phase of the beam passing through the concave portion, it does not act as a diffraction grating for the semiconductor laser output beam 301. Therefore, the semiconductor laser emitted beam 301
The main beam 304a is not separated by the first diffraction grating, but is separated by the first diffraction grating 303 and reaches the optical disk 308, so the light intensity of the main beam 304a does not decrease.

In the fourteenth aspect, by using a quarter wavelength plate for the polarization rotation means 305, the optical head can be made smaller and the cost of the optical head can be reduced.

In the fifteenth aspect, the diffraction grating plate and the quarter
By integrating the wavelength plate, the number of parts is reduced, making it easier to assemble the optical head, and the optical head can also be made smaller.

Furthermore, in the sixteenth aspect, since the first diffraction grating 302 is formed on the other surface of the diffraction grating plate 303, the number of optical components can be reduced and the optical head can be made smaller. . Furthermore, assembly of the optical head can be facilitated.

In the seventeenth aspect, the first diffraction grating 302 is further made of a birefringent material. Note that the convex portions and concave portions of the first diffraction grating 302 are used for extraordinary rays (or ordinary rays).
The difference in optical path length is approximately an integral multiple of the wavelength, and the widths are approximately equal. Therefore, the first diffraction grating 302 does not act as a diffraction grating on the disk reflected beam. Therefore, a plurality of beams 304a, 304b, and 304c are separated from the semiconductor laser emitted beam by the first diffraction grating 302.
is reflected by the disk and then re-applied to the first diffraction grating 302.
There will be no further separation even if it passes through.

[0058]

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 13.
This will be explained using FIG.

FIG. 1 is a block diagram of an optical head using the present invention. 1 is a semiconductor laser, 2 is a diffraction grating plate made of a birefringent material, 5 is a quarter wavelength plate, 6 is a focus lens, 7
A and 7B are three-split photodetectors, 8 is a photodetector for power monitoring of the semiconductor laser 1, and 9 is an arithmetic circuit for the photodetector output signal. A diffraction grating 3 is provided on the surface of the diffraction grating plate 2 on the semiconductor laser 1 side, and a diffraction grating 4 is provided on the surface on the focus lens 6 side. Beam 14 emitted from semiconductor laser 1
is separated by the diffraction grating 4 into a main beam 15a and sub-beams 15b and 15c. Reference numeral 16 indicates a reflected beam in which the main beam 15a and sub-beams 15b and 15c are reflected by an optical disk not shown in FIG. 1 and passed through a quarter wavelength plate. The reflected beam 16 is separated by the diffraction grating 3 into beams 17A and 17B. The reflected beam 16, beam 17A, and beam 17B each consist of a main beam 15a and two sub-beams 15b and 15c. The beam 17A is received by the 3-split photodetector 7A, and the beam 17B is received by the 3-split photodetector 7B. The semiconductor laser 1 and the photodetectors 7A and 7B are connected to the flange 10.
It is fixed onto the circular substrate 11 via. In addition, a power monitor photodetector 8 and an integrated electronic circuit 9 are also mounted on the circular substrate 1.
It is fixed on 1. 12 is a cylindrical optical head housing;
Inside the optical head housing 12, a focus lens 6, a quarter wavelength plate 5, a diffraction grating plate 2, and a circular substrate 11 are fixed via spacers 13a, 13b, and 13c.

FIG. 19 is an assembled view of this head. First, as shown in FIG. 19(a), a low melting point glass powder 400 such as cobalt glass is sandwiched between the optical head housing 12 and the focus lens 6 and heated in an oven. For example, cobalt glass melts at about 500 degrees Celsius. When the temperature is gradually returned to room temperature, the molten low melting point glass solidifies and forms the sintered glass 40, as shown in FIG. 19(b).
1, and the optical head housing 12 and focus lens 6 are hermetically bonded. The spacer 1 is attached to the optical head housing 12 to which the focus lens 6 is sintered and bonded in a dry nitrogen atmosphere.
3a, quarter wavelength plate 5, spacer 13b, diffraction grating plate 2, and spacer 13c are inserted in this order. Thereafter, a ring-shaped packing 402 made of soft metal such as copper is placed on the collar 403 of the optical head housing 12, and the circular board 11 is
, and while crushing the convex part of the metal packing 402 with the collar part 403 and the circular board 11 with a screw (not shown),
The circular substrate 11 is fixed. Through the above steps, the inside of the optical head housing 12 is filled with dry nitrogen gas and sealed from the outside air.

FIG. 2 is a mechanical configuration diagram of an optical disk device using the optical head shown in FIG. 21 is a device board;
22 is an optical disk, and 23 is a motor for rotating the optical disk 22. The optical head housing 12 is attached to a two-dimensional optical head actuator 25 via a spring 24. The two-dimensional optical head actuator 25 includes a focusing actuator 26 consisting of a coil and a magnet for performing focusing control by moving the entire optical head housing 12 in the vertical direction in the drawing, and a focusing actuator 26 that moves the entire optical head housing 12 in the horizontal direction in the drawing. It consists of a tracking actuator 27 consisting of a coil and a magnet for performing tracking control. Further, the carriage 28 moves the entire two-dimensional optical head actuator 25 in the radial direction of the optical disk 22,
Perform access control.

FIG. 3 is a block diagram of the structure of the three-part photodetectors 7A and 7B and the arithmetic circuit 9. The three-segment photodetector 7A includes three light receiving elements 7Aa, 7Ab,
7Ac, the light receiving element 7Aa receives the main beam 17Aa of the beam 17A, and the light receiving element 7Ab receives the main beam 17A of the beam 17A.
The light-receiving element 7Ac receives the sub-beam 17Ab of the beam 17A, and the sub-beam 17Ac of the beam 17A. The three-segment photodetector 7B includes three light receiving elements 7Ba, 7Bb, 7
Bc, the light receiving element 7Ba receives the main beam 17Ba of the beam 17B, and the light receiving element 7Bb receives the main beam 17B.
The light receiving element 7Bc receives the sub-beam 17Bb of the beam 17B. The adder circuit 30 adds the output signals of the light receiving elements 7Aa and 7Ba and outputs a light amount signal 31 of the main beam 15a. The sample servo circuit 32 generates a track deviation detection signal 33 from the light amount signal 31 of the main beam 15a. The track deviation detection signal 33 is supplied to the tracking actuator 27 in FIG. 2 to perform tracking control. The adder circuit 34b adds the output signals of the light receiving elements 7Ab and 7Bb and outputs a light amount signal 35b of the sub-beam 15b. The envelope detection circuit 36b generates a modulation degree signal 37b from the light amount signal 35b of the sub-beam 15b. The adder circuit 34c adds the output signals of the light receiving elements 7Ac and 7Bc and outputs a light amount signal 35c of the sub-beam 15c. The envelope detection circuit 36c generates a modulation degree signal 37c from the light amount signal 35c of the sub-beam 15c. The differential calculation circuit 38 subtracts the modulation degree signal 37b and the modulation degree signal 37c, and outputs a defocus detection signal. The focus shift detection signal 39 is supplied to the focusing actuator 26 in FIG. 2 to perform focusing control.

First, the operation of the beam separation optical system according to the present invention will be explained.

FIG. 4 is a diagram illustrating the structure of the diffraction grating plate 2. As shown in FIG. The diffraction grating plate 2 is, for example, LiNbO3 (lithium niobate). FIG. 4(a) shows a refractive index ellipsoid 40 of LiNbO3. LiNbO3 is a trigonal crystal and an optically negative uniaxial crystal. Therefore, the refractive index ellipsoid 40 has an optical axis (or the C axis of the crystal axis) 41
It is a rotationally symmetrical ellipsoid that is flat in the direction. FIG. 3(b) shows the optical axis 41 of the diffraction grating plate 2 and LiNbO3, and the polarization directions of the beams 14 and 16. The optical axis 41 is within the plane of the diffraction grating plate 2 . The shape of the cross section of the refractive index ellipsoid 40 perpendicular to the beam 14 or 16 is an ellipse whose minor axis is in the direction of the optical axis 41, as shown by an ellipse 42. The polarization direction 14' of the emitted beam 14 of the semiconductor laser 1 coincides with the direction of the optical axis 41. Therefore, the output beam 14 propagates through the diffraction grating plate 2 as an extraordinary ray. The beam 14 that has passed through the diffraction grating plate 2 becomes circularly polarized light by the quarter-wave plate 5, is reflected by the optical disk 22, becomes circularly polarized light in the opposite direction, and when it passes through the quarter-wave plate 5 again, it is emitted. The beam 14 becomes linearly polarized in a direction perpendicular to the polarization direction 14'. Therefore, the polarization direction 16' of the disk reflected beam 16 is an ellipse 42.
The disk reflected beam 16 propagates in the diffraction grating 2 as an ordinary ray. On the surface of the diffraction grating plate 2 on the semiconductor laser side, there is a diffraction grating 3 of an evenly spaced straight line type as shown in FIG. 4(c), and the groove depth of the diffraction grating 3 is, for example, 4.63 μm. Further, on the surface of the diffraction grating plate 2 on the focus lens side, there is a linear diffraction grating 4 with irregular intervals as shown in FIG. 4(d), and the groove depth of the diffraction grating 4 is 1.85 μm. be.

FIG. 5 is a diagram explaining the reason why the groove depths of the two diffraction gratings 3 and 4 are different. As shown in the upper diagram of FIG. 5, if the groove depth of the diffraction grating 51 made of a material 50 with a refractive index of n is d, the optical path length 52 of the convex portion is nd, and the surroundings of the diffraction grating are air. If it is surrounded, the optical path length of the recess is 5
Since 3 is d, the difference ΔOP in the optical path length between the convex part and the concave part is
ΔOP=(n-1)d. If ΔOP is an integral multiple of the wavelength, there is no phase shift between the beam passing through the convex portion and the beam passing through the concave portion, and there is no effect of the diffraction grating. When ΔOP deviates from an integer multiple of the wavelength, the phase of the beam passing through the convex portion and the phase of the beam passing through the concave portion are shifted, and the beam acts as a diffraction grating. In particular, if ΔOP is an integral multiple of the wavelength and a half wavelength, the phase of the beam passing through the convex portion and the phase of the beam passing through the concave portion are 1.
Since the beams deviated by 80 degrees and emitted in the 0th order diffraction direction cancel each other out, no 0th order diffraction beam is generated. Therefore,
The passing beam is mainly diffracted in the ±1st order diffraction directions. In the lower graph of FIG. 5, the horizontal axis is the groove depth d, and the vertical axis is the optical path length difference ΔOP/λ=(n-1)d/λ in units of wavelength. Li
The ordinary refractive index no and extraordinary ray refractive index ne of NbO3 near the wavelength 780 nm are: no=2.262 ne=2.179, and ΔOP/
λ is shown by a straight line 54, and ΔOP/λ obtained from the value of the extraordinary ray refractive index ne is shown by a straight line 55. As mentioned above, if the value on the vertical axis is just an integer, there is no effect of the diffraction grating. When the value on the vertical axis becomes a half-integer, there is no 0th-order diffraction beam, and the diffraction grating produces strong ±1st-order diffraction beams. For other values, the closer the value is to an integer, the stronger the 0th-order diffraction beam becomes, and the closer it is to a half-integer, the stronger the ±1st-order diffraction beam becomes. From the graph in Figure 5, when the groove depth is 4.63 μm, the difference in optical path length for extraordinary rays is exactly 7 times the wavelength, and the difference in optical path length for ordinary rays is 7.5 times the wavelength. Out. Therefore,
If the groove depth of the diffraction grating 4 on the semiconductor laser side surface of the diffraction grating plate 2 is 4.63 μm, the diffraction grating 4 will not act as a diffraction grating for the semiconductor laser emitted beam 14, and will reflect the disk. For beam 16, the diffraction grating produces no 0th-order diffraction beam but only ±1st-order diffraction beams. That is, the diffraction grating 3 and the quarter-wave plate 5 can completely separate the semiconductor laser emitted beam 14 and the disk reflected beam 16. In addition, the groove depth is 1.85 μm
In the case of , the difference in optical path length for ordinary rays is exactly three times the wavelength, and the difference in optical path length for extraordinary rays is 2.8.
It's double. Therefore, if the groove depth of the diffraction grating 4 on the focus lens side surface of the diffraction grating plate 2 is 1.85 μm, the diffraction grating 4 will produce a strong 0th-order diffraction beam and a weak ± It acts as a diffraction grating for producing the first-order diffraction beam, but does not act as a diffraction grating for the disc reflected beam 16. Therefore, the diffraction grating 4 is
It can be used as a diffraction grating for generating a main beam for recording and reproduction and two sub-beams for spot position control from the semiconductor laser emitted beam 14. Moreover,
There is an advantage that even if these beams pass through the diffraction grating 4 again after being reflected by the optical disk, they will not be separated into more beams as in a normal diffraction grating.

From the above explanation, in FIG. 1, the beam 14 emitted from the semiconductor laser 1 is divided into a main beam 15a, sub beams 15b and
optical disk 2, passes through a quarter-wave plate, and
2 (shown in Figure 2). The main beam 15a and sub beams 15b and 15c reflected by the optical disc 22 are 4
The beam 17 passes through the half-wave plate and is filtered by the diffraction grating 3.
A and beam 17B, and the semiconductor laser output beam 14
can be completely separated.

Next, the defocus detection method and focusing control in the optical head of this embodiment will be explained.

FIG. 6 is a diagram illustrating the structure and operation of the non-uniformly spaced linear type diffraction grating 4. The x-axis and y-axis are taken in the plane containing the diffraction grating 4, and the z-axis is taken in the direction of beam propagation,
Let O be the design coordinate origin. (1) in FIG. 6 shows the x-y plane, and the many grating grooves 60 of the diffraction grating 4 are part of a group of straight lines 61n (n=±1, ±2, ±3,...) parallel to the y-axis. be. Since the action of the diffraction grating 4 is uniform in the y-axis direction, its light condensing and diverging action will be explained using the xz cross section shown in FIG. Let P be a point on the z-axis that is away from the origin O by f, and let So be a circle with radius f centered on point P. Also, assuming the wavelength is λ, a circle with radius (f+nλ) centered on point P is Sn(n=
1, 2, 3,...). If the intersection of the circle Sn and the x-axis is a group of straight lines 61n, it is incident on the x-y plane and the group of straight lines 61n
The beams diffracted at and then focused on point P have the same phase at point P and strengthen each other, resulting in a +1st-order diffracted beam 15b. At the same time, the beam diffracted by the straight line group 61n in the opposite direction to the +1st-order diffracted beam is directed to a point Q on the z-axis, which is away from the origin O by -f, due to the symmetry of the diffraction angle by the diffraction grating.
It becomes a -1st-order diffracted beam 15c that diverges from. Therefore, the position Xn (n=1, 2, 3,...) of the straight line group 61n shown in FIG. 6 (1) from the origin O is

[0069]

[Math 1]

As shown in (2) of FIG.
5b, it acts as a positive cylindrical lens with a focal length f, giving positive astigmatism, and the +1st-order beam 15b has a focal line P.
Focus on x. Furthermore, it acts as a negative cylindrical lens with a focal length of -f to the -1st order diffracted beam, giving negative astigmatism, and the -1st order beam 15c becomes a beam that diverges from the focal line Qx.

FIG. 8 shows the information recording film surface of the optical disc 22. As shown in FIG. The data area of the optical disc 22 is divided into, for example, 32 sectors per round, and 43 segments per sector, and at the beginning of each segment there are uneven pits 93a and 93b on a track 92 indicated by a dashed line.
is located. Each pit 93a and pit 93b
The positions of are aligned within a range of at least several tracks along the radial direction of the disk (in the vertical direction on the paper). Also,
The spacing between the tracks 92 is 1.5 μm, and the pits 93a are shifted by about a quarter of a track in the upward direction on the paper.
3b is shifted by about 1/4 track toward the bottom of the paper. 9
1a is the spot of the main beam 15a of the 0th order diffraction, 91
b is the spot of the +1st-order diffraction sub-beam 15b, 91c
is the spot of the −1st-order diffraction sub-beam 15c. Pit 93a and 93b are spots 91a, 91b and 91
After passing through c, the main beam 16a and sub beam 16
The amounts of reflected light of the sub-beams 16b and 16c are respectively modulated. (2) in FIG. 8 shows that the optical disc 22 is connected to the main beam 15a.
The spot 91a is the smallest in the focal position, and is the disk position (focusing target point position) suitable for recording and reproducing information. The direction in which the diffraction grating 4 acts is the direction of the track 92. The sub beams 15b and 15c are
It focuses best in the direction perpendicular to the track, but not in the direction of the track. Therefore, the spots 91b and 91c have the same size and are long in the track direction, and the modulation degrees by the pits 93a and 93b of the sub-beams 16b and 16c are equal. (1) in Figure 8
is a case where the optical disc 22 is located at the focal line position of the -1st-order diffraction sub-beam 15c, the spot 91c becomes a vertically long focal line, and each pit 93a and pit 93b extends in the radial direction of the disc (up and down direction in the paper). Since the sub-beams 16c are aligned along the same axis, the sub-beams 16c are modulated the most. The spot 91b becomes laterally larger than in case (2), and the modulation degree of sub-beam 16b becomes smaller than in case (2). Conversely, (3) in FIG. 8 shows a case where the optical disc 22 is located at the focal line position of the +1st-order diffraction sub-beam 15b, and the spot 9
1b becomes a longitudinally long focal line, and sub-beam 16b is modulated most significantly. The spot 91c is laterally larger than in case (2), and the modulation degree of the sub-beam 16c is (
It is smaller than in case 2).

FIG. 9(1) shows changes in the degree of modulation of the light amount signal 35b and the light amount signal 35c due to the pits 93a and 93b, when the horizontal axis represents the change in the optical disk position. (1) on the horizontal axis is the focal line position of the -1st-order diffraction sub-beam 15c, (2) is the focal position of the main beam 15c and the target point position for focusing, and (3) is the +1st-order diffraction sub-beam 15b. is the focal line position of When the optical disc is in position (1), the sub-beam 15c is modulated the most, so the amplitude of the light amount signal 35c is maximum, and when the optical disc is in the position (3), the sub-beam 15b is modulated the most, so the amplitude of the light amount signal 35c is maximum. The amplitude will be maximum. Optical disc (2)
At the position, the amplitude of the light amount signal 35b and the amplitude of the light amount signal 35c are equal and are reduced to about half of the maximum amplitude. The light amount signal 35b and the light amount signal 35c are input to envelope detection circuits 36b and 36c shown in FIG. 3. The envelope detection circuit 36b detects the upper level 81b and the lower level 82b of the amplitude of the light amount signal 35b in (1) of FIG.
That is, a modulation degree signal 37b of the light amount signal 35b is output. The envelope detection circuit 36c detects an upper level 81c and a lower level 82c of the amplitude of the light amount signal 35c in (1) of FIG. 8, and outputs the difference therebetween, that is, a modulation degree signal 37c of the light amount signal 35c. (2) in FIG. 8 shows the modulation degree signals 37b and 37c obtained by the envelope detection circuit, the modulation degree signal 37c is maximum at disk position (1), and the modulation degree signal 37b is maximum at disk position (3). become. At the focus target point position (2), the modulation degree signals 37b and 3
7c is about half of the maximum value. Therefore, the modulation degree signal 37
If b and 37c are input to the differential arithmetic circuit 38, (
A defocus detection signal 39 as shown by the solid line in 3) is obtained. When the optical disc 22 is at the focusing target point position (2), the defocus detection signal amplitude signal 39 automatically becomes zero level. Therefore, using the focus shift detection signal 39, the focusing actuator 26 of the two-dimensional optical head actuator 25 moves the entire optical head toward the optical disk 22.
Focusing control can be performed by moving in a direction perpendicular to the plane.

FIG. 10 shows an example of a block diagram of envelope detection circuits 36b and 36c. After an input signal 100 is amplified by an amplifier 101 and differentiated by a differentiating circuit 103, high-frequency noise of the differentiated signal 104 is removed by a filter 105 and inputted to a bipolar zero comparator 106 to obtain a pulse signal 107. FIG. 11 (1) shows an example of the input signal 100, and (2) shows its differential signal 10.
4, and (3) shows the pulse signal 107. Figure 11
shows the same time course as a whole in the right direction on the page. When the input signal 100 reaches the minimum value or maximum value, the differential signal 1
04 becomes the zero level indicated by a dashed line 125, and the zero level comparator 106 outputs a pulse 126 every time the differential signal 104 passes through the zero level. The pulse signal 107 is input to the flip-flop circuit 108, and each time the pulse 126 is input to the flip-flop circuit 108, its Q terminal repeats either a high level state or a low level state. Therefore, Q terminal output and pulse signal 1
07 to the AND circuit 109, (4) in FIG.
A pulse signal 110 of every other pulse is obtained as shown in FIG. Therefore, if the sampling timing of the amplifier output 102 is determined by the pulse signal 110 using the sample and hold circuit 111, the sample and hold circuit 111 will be as shown in FIG.
A level signal 112 that maintains the lower level of amplitude shown by the circle point 113 in (1) is output. On the other hand, the Q bar terminal of the flip-flop circuit 108 repeats a high level state and a low level state, which are opposite to the Q terminal. Therefore, by inputting the Q-bar terminal output and the pulse signal 107 to the AND circuit 114, a pulse signal 115 of every other pulse, which is opposite to the pulse signal 110, as shown in (5) of FIG. 11 is obtained. Therefore, using the sample and hold circuit 116, the pulse signal 11
5, the sample and hold circuit 116 outputs a level signal 117 that maintains the upper level of the amplitude indicated by the triangular point 118 in (1) of FIG. Therefore, level signals 117 and 11
2 to the differential arithmetic circuit 118, the input signal 100
An amplitude signal 119 corresponding to the magnitude of the amplitude is obtained. However, depending on the timing of the pulse signals 110 and 115, the level signal 117 may hold the upper level of the amplitude of the input signal 100, the level signal 117 may hold the lower level of the amplitude, and the amplitude signal may become negative. Therefore, using a switch circuit 121 that selects the A terminal if the control signal is at a positive level and selects the B terminal if the control signal is at a negative level, an amplitude signal 119 is sent to the A terminal.
By inputting the amplitude signal 119 to the B terminal through the inverter 120, and further inputting the amplitude signal 119 to the control terminal, an output signal 122 that always indicates the magnitude of the amplitude as positive can be obtained.

[0074] In a normal optical disc device, the response frequency required for the automatic focus control system is about 2 kHz. On the other hand, if the number of segments in which the pits 93a and 93b are arranged is 32*43=1376 in one revolution, and the rotation speed of the optical disc 30 is 2400 rpm (40Hz), the sampling frequency of the defocus detection signal is approximately 55kHz. It is. Therefore, according to this embodiment, sufficiently stable automatic focus control can be achieved. In the defocus detection method of this embodiment, 3
Light receiving elements 7Ab and 7Ac of split type photodetectors 7A and 7B
, 7Bb, 7Bc are sub-beams 17Ab,
It is sufficient to receive the total amount of light of 17Ac, 17Bb, and 17Bc, and the target point for focusing can be self-adjusted without adjusting the position of a photodetector or the like. Furthermore, even if the mounting position of the photodetector or the like changes, no offset occurs in the defocus detection signal.

Next, tracking control will be explained using FIGS. 12 and 13.

FIG. 12 is a block diagram of the sample servo circuit 32 shown in FIG. 3. input signal 130
is amplified by an amplifier 131 and differentiated by a differentiating circuit 133, high-frequency noise of the differential signal 134 is removed by a filter 135, and inputted to a rising zero comparator 136 to obtain a pulse signal 137. (1) in FIG. 13 is the same as (1) in FIG.
Parts related to tracking control are shown on the same optical disk 22 surface as shown in 2). 91a is the spot of the main beam 15a, 92 is the center of the track, 93a is a pit that is shifted by a quarter track upwards in the page, and 93b is a pit that is shifted by a quarter track downwards in the page. , spot 91a is at the track center 9
2 (target point of tracking control) to the right on the paper. In (2) of FIG. 13, the input signal 13
0 is shown, (3) shows its differential signal 134, and (4) shows the pulse signal 137. FIG. 13 shows the same overall time course in the right direction on the paper. Input signal 1
30 reaches the local minimum value or maximum value, the differential signal 134 becomes the zero level shown by the dashed line 155, and the differential signal 134
The rising zero level comparator 136 outputs a pulse 156 each time the signal passes through the zero level 155 from a negative level to a positive level. The pulse signal 137 is input to the flip-flop circuit 138, and each time the pulse 156 is input to the flip-flop circuit 138, its Q terminal repeats either a high level state or a low level state. Therefore, by inputting the Q terminal output and the pulse signal 137 to the AND circuit 139, a pulse signal 140 of every other pulse as shown in (5) of FIG. 13 is obtained. Therefore, if the sampling timing of the amplifier output 132 is determined by the pulse signal 140 using the sample and hold circuit 141, the sample and hold circuit 141 will be able to obtain the sample timing of the amplifier output 132 using the pulse signal 140.
A level signal 142 holding the modulation level by the pit 93a indicated by 43 is output. On the other hand, the Q bar terminal of the flip-flop circuit 138 repeats a high level state and a low level state, which are opposite to the Q terminal. Therefore, if the Q bar terminal output and the pulse signal 137 are input to the AND circuit 144,
A pulse signal 145 of every other pulse, which is opposite to the pulse signal 140 as shown in (6) of FIG. 13, is obtained. Therefore,
Pulse signal 145 using sample and hold circuit 146
By determining the sampling timing of the amplifier output 132, the sample and hold circuit 146 obtains a level signal 147 that holds the modulation level due to the pit 93b indicated by the triangular point 148 in (2) of FIG. Therefore, the level signals 147 and 142 are input to the differential arithmetic circuit 148, and the output signal 149 is used as a track deviation detection signal. Pit 9
3a and 93b are arranged with the same amount of deviation from the center of the track 92, so when the spot 91a moves directly above the track 92 (target point of tracking control) as shown in (1) of FIG. are the modulation level 143 due to the pit 93a and the modulation level 148 due to the pit 93b.
become equal, and the track deviation detection signal 149 automatically becomes zero level. If the spot 91a shifts upward in the paper as shown in (1a) of FIG.
As shown in FIG. 2a), the modulation level 143 becomes a lower level due to the larger modulation in the pit 93a.
3b, there is less modulation and the modulation level 148 is a higher level. Therefore, the track deviation detection signal 149
becomes a negative level. Conversely, if the spot 91a is shifted downward in the plane of the paper as shown in (1b) of FIG.
As shown in 3(2b), the pit 93a is not modulated much and the modulation level 143 becomes a higher level, and the pit 93b is highly modulated and the modulation level 148 becomes a lower level. Therefore, the track deviation detection signal 14
9 is a positive level. Therefore, the track deviation detection signal 3
Tracking control can be performed by moving the entire optical head in the radial direction of the disk using the tracking actuator 27 of the two-dimensional optical head actuator 25.

[0077] In a normal optical disc device, the response frequency required for the tracking control system is about 8 kHz. On the other hand, the sampling frequency of the track deviation detection signal is about 55 kHz, the same as the defocus detection signal. Therefore, according to this embodiment, sufficiently stable automatic tracking control can be achieved. In the track deviation detection method of this embodiment, the light receiving elements 7Aa and 7Ba of the three-split photodetectors 7A and 7B only need to receive the entire amount of light of the main beams 17Aa and 17Ba, respectively, and the photodetectors, etc. You can self-adjust the tracking target point without having to adjust the position. Furthermore, even if the mounting position of the photodetector or the like changes, no offset occurs in the track deviation detection signal.

Information can be recorded and reproduced in the same manner as in a normal optical disc device. As an example, a case will be described in which a write-once optical disc is used. When recording information, a pulsed driving current is applied to the semiconductor laser 1 in accordance with the information to modulate the intensity of the laser beam in a pulsed manner, and the spot 91a of the main beam 15a is used to record a recording film on the surface of the optical disk 22. Record information by thermally drilling holes. When reproducing information, the semiconductor laser 1 is made to emit light at a constant low power, and the main beam 15a is also used.
Since the amount of reflected light of the reflected beams 17Aa and 17Ba of the spot 91a is modulated by the information recorded as the holes, the information can be reproduced from the light amount signal 31. When a phase change optical disk is used, the optical head of this embodiment can be used as is, with the only difference being that information is recorded as changes in the reflectance of the recording film rather than in the shape of holes.

A second embodiment of the present invention is shown in FIGS. 14 and 15.
Explain using. In the second embodiment, a concentric elliptical diffraction grating as shown in (1) of FIG. 14 is used instead of the nonuniformly spaced linear diffraction grating 4 of (1) of FIG. 6 used in the first embodiment. 201 is used. The other parts and operations are exactly the same as in the first embodiment, so their explanation will be omitted.

Grating grooves 20 of concentric elliptical diffraction grating 201
2 is a part (elliptic arc) of a concentric ellipse 203n (n=1, 2, 3, . . . ) centered on the origin O, as shown by the broken line in FIG. 14 (1). In the plane including the diffraction grating 201, the x-axis is taken in the long axis direction of the ellipse 203n, the y-axis is taken in the short-axis direction, the z-axis is taken in the direction in which the beam advances, and the coordinate origin is O. Radius RXn (n=1,
2, 3,…),

[0081]

[Math 2]

Radius RYn (n
=1,2,3,...),

[0083]

[Math 3]

(However, fy<fx). Then, in the x-z plane, +
The first-order diffraction beam 15b converges at a point on the z-axis that is away from the origin O by fx, and the -1st-order diffraction beam 15c diverges from a point on the z-axis that is away from the origin O by -fx. On the other hand, in the yz plane, the +1st order diffraction beam 15b
converges to a point on the z-axis that is fy away from the origin O, and -1
The next diffraction beam 15c diverges as if emerging from a point on the z-axis that is −fy away from the origin O. Therefore, (2
), the +1st order beam 15b has a focal line Px in the x direction, a focal line Py in the y direction, and -1st order beam 15b.
5c diverges in the x direction as if emerging from the focal line Qx, and diverges in the y direction as if emerging from the focal line Qy. Therefore, such a concentric elliptical diffraction grating 201 acts as a positive toroidal lens with focal lengths fx and fy for the +1st order diffraction beam, and acts as a positive toroidal lens with focal lengths fx and fy for the -1st order diffraction beam. acts as a negative toroidal lens of -fx and -fy. Therefore, the concentric elliptical diffraction grating 201 has astigmatism in two directions, positive and negative, which have equal absolute values in the +1st-order beam 15b and the -1st-order beam 15c (stronger in the short axis direction of the ellipse and weaker in the long axis direction). The +1st order beam 15b and the -1st order beam 15c are emitted in directions different from the 0th order beam 15a by small positive and negative angles.

Similar to FIG. 8, FIG. 15 shows the spot 91a of the main beam 15a of the 0th order diffraction on the surface of the optical disk 22 when the concentric elliptical diffraction grating 201 is used, and the +
The spot 91b of the first-order diffraction sub-beam 15b and -1
A spot 91c of the sub-beam 15c of the next diffraction is shown. The horizontal direction in the paper of FIG. 15 corresponds to the x direction (long axis direction of the ellipse 203) in FIG. 14, and the vertical direction in the paper corresponds to the y direction (short axis direction of the ellipse 203). Further, pits 93a and 93b on the track 92 indicated by the dashed line on the surface of the optical disk 22 have the same effect as that described in FIG. 8. (2 in Figure 14)
) is a case where the optical disc 22 is at the focal position of the main beam 15a, as in (2) of FIG. 8, and the spot 91a is the smallest and is the disc position suitable for recording and reproducing information (focusing target point position). . Sub beam 15b and 1
5c, due to the astigmatism given by the diffraction grating 201 which is strong in the vertical direction (y direction) of the paper and weak in the horizontal direction (x direction) of the paper, the convergence position shifts greatly in the vertical direction of the paper, and Since the convergence positions are slightly shifted, the spots 91b and 91c are vertically long elliptical spots of the same size. Therefore, the modulation degrees of the sub-beams 15b and 16c due to the pits 93a and 93b are equal. (1) in FIG. 15 is a case where the optical disc 22 is located at the x-direction focal line position of the -1st-order diffraction sub-beam 15c, as in (1) in FIG. 8, and since the sub-beam 15c is best focused in the horizontal direction, , the spot 91c becomes a vertically long spot, and each pit 9
Since the sub-beams 3a and the pits 93b are aligned along the radial direction of the disk (in the vertical direction of the paper), the sub-beam 15c is modulated most greatly. The spot 91b of the +1st-order diffraction sub-beam 15b becomes even larger than in case (2), and the modulation degree of sub-beam 15b becomes smaller than in case (2). (0) in FIG. 15 shows that the optical disk 22 is further away from the focus lens 8 and the -1st order diffraction sub-beam 1
5c, the sub-beam 15
Since c is now focused in the vertical direction, the spot 91c becomes a horizontally long spot, and the modulation degree of the sub-beam 15c is (
It will decrease compared to case 1). The spot 91b of the sub-beam 15b becomes even larger than in case (1), and the modulation degree of sub-beam 15b becomes even smaller than in case (1). On the other hand, in (3) of FIG. 15, the optical disk 22 is
Since the sub-beam 15b is best focused in the horizontal direction, the spot 91b becomes a vertically long spot, and each pit 93a and pit 93b is located in the radial direction of the disk (vertical direction in the paper). Since the sub-beams 15b are aligned along the sub-beam 15b, the sub-beams 15b are modulated the most. The spot 91c of the sub-beam 15c is even larger than in case (2), and the modulation degree of the sub-beam 15c is (2).
) will be smaller than in the case of (4) in FIG. 15 shows a case where the optical disk 22 further approaches the focus lens 8 and is located at the focal line position in the y direction of the sub-beam 15b of +1st order diffraction, and since the sub-beam 15b is now focused in the vertical direction, the spot 91b becomes a horizontally long spot, sub beam 1
The modulation depth of 5b is smaller than that of (3). The spot 91c of the sub-beam 15c becomes even larger than in case (3), and the modulation degree of sub-beam 15c becomes even smaller than in case (3). Therefore, when the change in the optical disk position is plotted on the horizontal axis, the change in the modulation degree of the light amount signal 35b and the light amount signal 35c due to the pits 93a and 93b is exactly the same as that shown in FIG. 9(1). That is, the amplitude of the light amount signal 35b is maximum at the disk position (3), the amplitude of the light amount signal 35c is maximum at the disk position (1), and the amplitude of the light amount signal 35b and the light amount signal 35c are the same at the disk position (2). The amplitudes will be equal. Furthermore, the modulation degree signals 37b and 37c output by the envelope detection circuits 36b and 36c become the same as (2) in FIG. When the shift detection signal 39 is obtained and the optical disc 22 is at the focusing target point position (2), the focus shift detection signal 39 automatically becomes zero level.

[0086] The diffraction grating plate 2 and quarter wavelength plate 5 shown in the first embodiment and the second embodiment can also be bonded together to form a single unit. As an example, a case will be described in which the diffraction grating 4 or the diffraction grating 201 on the surface of the diffraction grating plate 2 on the focus lens 6 side and the quarter wavelength plate 5 are bonded together using an infrared curable resin (UV resin). If the grooves of the diffraction grating are filled with UV resin with a refractive index of 1.5, the difference ΔOP in the optical path length between the convex and concave parts of the diffraction grating is ΔOP=(n-1
．． 5) It is d. As the refractive index within the diffraction grating, ΔOP/λ obtained from the ordinary ray refractive index no = 2.262 is expressed as a straight line 25
4, and ΔOP/λ obtained from the extraordinary ray refractive index ne=2.179 is shown by a straight line 255. Groove depth is 2.05μm
In the case of , the difference in optical path length for ordinary rays is exactly twice the wavelength, and the difference in optical path length for extraordinary rays is 1.8.
It's double. Therefore, the groove depth of the grating groove 60 of the diffraction grating 4 on the bonding surface side of the diffraction grating plate 2 or the grating groove 202 of the diffraction grating 201 may be set to 2.05 μm.

FIG. 20 is a diagram illustrating another embodiment of the present invention, in which parts having the same part numbers as those in FIG. 1 have the same functions. In the embodiment shown in FIG. 20, the area sandwiched between the diffraction grating plate 2 and the circular substrate 11 inside the optical head housing 12 is sealed. A ring-shaped rubber packing 4 is provided between the circular substrate 11 and the spacer 13d and between the diffraction grating plate 2 and the spacer 13d.
10 and tighten with screw 411 to seal it. The corner portion of the spacer 13d where the rubber packing 410 contacts is cut diagonally to maintain airtightness. Assembly work is performed in a dry nitrogen atmosphere. Alternatively, the assembly work up to just before tightening the screws 411 can be performed in advance in the atmosphere, and the screws 411 can be tightened by a motor in a vacuum bell jar of a vacuum device.
You can also tighten it.

[0088]

According to the present invention, it is possible to realize a compact optical head that can maintain stable performance for a long period of time without deterioration of the semiconductor laser. In addition, a beam separation optical system can be achieved that can completely separate the semiconductor laser emitted beam and the disc reflected beam, and can also share the optical path of the focusing optical system and the optical path of the detection optical system, which is effective for downsizing the optical head. .

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical head.

FIG. 2 is a configuration diagram of a mechanical system of an optical disc device.

FIG. 3 is a configuration diagram of a photodetector and an arithmetic circuit.

FIG. 4 is an explanatory diagram of the structure of a diffraction grating plate.

FIG. 5 is an explanatory diagram of grating groove depth and phase difference of a diffraction grating.

FIG. 6 is an explanatory diagram of the structure and operation of an unevenly spaced linear diffraction grating.

FIG. 7 is an explanatory diagram of the light focusing/diverging effect of the diffraction grating.

FIG. 8 is an explanatory diagram of spots and pits on the optical disc surface.

FIG. 9 is an explanatory diagram of defocus detection signal generation.

FIG. 10 is a configuration diagram of an envelope detection circuit.

FIG. 11 is an explanatory diagram of timing signal generation.

FIG. 12 is a configuration diagram of a sample servo circuit.

FIG. 13 is an explanatory diagram of track deviation detection signal generation.

FIG. 14 is an explanatory diagram of the structure and operation of a concentric elliptical diffraction grating.

FIG. 15 is an explanatory diagram of spots and pits on the optical disc surface.

FIG. 16 is a basic configuration diagram of an optical head of the present invention.

FIG. 17 is an explanatory diagram of spots and pits on the optical disc surface of the present invention.

FIG. 18 is an explanatory diagram of spots and pits on the surface of a conventional optical disc.

FIG. 19 is an explanatory diagram of an optical head assembly.

FIG. 20 is an explanatory diagram of an optical head assembly.

[Explanation of symbols]

1... Semiconductor laser, 2... Diffraction grating plate, 3... Diffraction grating, 4
... Diffraction grating, 5... Quarter wavelength plate, 6... Focus lens, 7A, 7B... 3-split photodetector, 12... Optical head housing, 22... Optical disk, 36b, 36c... Envelope detection circuit, 38... Difference Dynamic calculation circuit, 41...optical axis.

Claims (17)

[Claims] 1. A semiconductor laser, an imaging optical system that forms an image of an output beam emitted from the semiconductor laser on an information medium surface, and a beam separation optical system that separates a reflected beam reflected by the information medium and the output beam. a photodetector that receives the detection beam separated by the beam separation optical system, an optical head housing that fixes the semiconductor laser, the imaging optical system, the beam separation optical system, and the photodetector; 1. An optical head characterized in that the semiconductor laser is hermetically sealed by the imaging optical system or the beam separation optical system and the optical head housing. 2. The optical head according to claim 1, wherein a space sealed by the imaging optical system or the beam separation optical system and the optical head housing is replaced with nitrogen gas. light head. 3. The optical head according to claim 1, wherein a space sealed by the imaging optical system or the beam separation optical system and the optical head housing is replaced with a vacuum. light head. 4. The optical head according to claim 1, wherein the imaging optical system or the beam separation optical system and the optical head housing are hermetically sealed together by sintering. An optical head characterized by: 5. The optical head according to claim 1, wherein the entire optical head housing is positionally controlled in two directions. 6. A semiconductor laser, an imaging optical system that images an output beam emitted from the semiconductor laser on an information medium surface, and a beam separation optical system that separates the reflected beam reflected by the information medium and the output beam. a photodetector that receives the detection beam separated by the beam separation optical system, an optical head housing that fixes the semiconductor laser, the imaging optical system, the beam separation optical system, and the photodetector. , has an optical head in which the semiconductor laser is sealed by the imaging optical system or the beam separation optical system and the optical head housing, and the beam separation optical system converts the output beam emitted from the semiconductor laser into a main beam. and a second beam separating optical system that separates a plurality of reflected beams reflected by the information medium into two sub-beams in a direction different from that of the output beam. The beam separation optical means 1 includes a first diffraction grating or a hologram element that gives positive astigmatism and negative astigmatism to the two sub-beams, and the amount of reflected light of the sub-beams is reflected on the information medium surface. There is a mark recorded in advance for modulating the sub-beam, and the photodetector has two photodetecting elements that receive the sub-beam, and the light intensity signal output by the two photodetecting elements is modulated by the mark. a defocus detection circuit comprising two amplitude detection circuits for detecting the magnitude of the amplitude detected by the amplitude detection circuit; and a differential calculation circuit for subtracting the two amplitude detection signals output from the amplitude detection circuits. An information recording device characterized by: 7. The information recording device according to claim 6,
The first diffraction grating or hologram element is a collection of a plurality of linear grooves whose grating groove intervals increase or decrease in sequence, and the marks are arranged in a direction perpendicular to the direction of the track. An information recording device characterized by the following. 8. The information recording device according to claim 6,
The first diffraction grating or hologram element is a part of a set of a plurality of concentric elliptical grooves whose grating groove intervals increase or decrease sequentially, and the position of the concentric point of the concentric elliptical grooves corresponds to the principal ray of the main beam. An information recording device characterized in that the marks are eccentric from the position of the axis and are aligned in a direction perpendicular to the direction of the track. 9. The information recording device according to claim 6, wherein the amplitude detection circuit detects the light between the marks for each of the two sub-beams. a first sample and hold circuit that holds the output signal level of the element; a second sample and hold circuit that holds the output signal level of the photodetecting element when it is on the mark; output signal and the second
An information recording device comprising: a differential arithmetic circuit that subtracts an output signal of a sample and hold circuit. 10. The information recording device according to claim 9, wherein the amplitude detection circuit includes a switch circuit for always setting the polarity of the output signal of the amplitude detection circuit to a positive level or a negative level. An information recording device characterized by: 11. The information recording device according to claim 6, wherein the mark is aligned with a predetermined track center line along which the main spot is guided on the information medium surface. The main spot consists of a first pit group placed a certain distance apart on one side with respect to the track center line, and a second pit group placed an equal distance apart on the opposite side with respect to the track center line. A track deviation detection signal is obtained by comparing the output signal level of the photodetecting element when passing through the second pit with the output signal level of the photodetecting element when passing through the second pit. Information recording device. 12. The optical head according to any one of claims 1 to 5, wherein a second beam separation unit separates the reflected beam reflected by the information medium into a direction different from the output beam. The optical system includes a diffraction grating plate having a second diffraction grating made of a birefringent material on at least one surface;
a polarization rotation means for rotating the polarization direction so that the reflected beam becomes either an extraordinary ray or an ordinary ray when passing through the second diffraction grating, and a convex portion of the second diffraction grating; An optical head characterized in that the concave portion has a difference in optical path length for either an extraordinary ray or an ordinary ray by an integral multiple of a wavelength and a half wavelength, and has substantially equal widths. 13. The optical head according to claim 12,
The optical head is further characterized in that the convex portion and the concave portion of the second diffraction grating have a difference in optical path length with respect to either an ordinary ray or an extraordinary ray that is an integral multiple of a wavelength. 14. An optical head according to any one of claims 12 to 13, wherein the polarization rotating means has four polarization rotating means.
An optical head characterized by being a 1/2 wavelength plate. 15. The optical head according to claim 14,
The diffraction grating plate and the quarter wavelength plate are integrated.
An optical head characterized by: 16. The optical head according to claim 12, wherein the first diffraction grating is arranged on the other surface of the diffraction grating plate having the second diffraction grating. An optical head characterized in that: 17. The optical head according to claim 16,
The first diffraction grating is made of a birefringent material, and the convex portions and concave portions of the first diffraction grating have substantially equal widths with a difference in optical path length for either the extraordinary ray or the ordinary ray being an integral multiple of the wavelength. ,
An optical head characterized by: