JPH11110779A - Optical head - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize an optical head that is small and stable against wavelength fluctuation. An optical head including a transparent substrate provided with a light propagation path through which light propagates between upper and lower surfaces in a zigzag manner, a light source, a photodetector, a light condensing means, and a position signal detecting optical means. In the above, the light emitting portion of the substrate to the optical disk is notched obliquely, and the zigzag light is deflected and emitted vertically to the upper and lower surfaces of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used for reading out a signal from an optical disk and optically tracking a magnetic disk.

[0002]

2. Description of the Related Art FIG. 14 is a block diagram of a conventional optical head disclosed in, for example, "Optical Disc Technology", published by Radio Technology Co., supervised by Morio Onoe. The laser light output from the semiconductor laser 4 as a light source becomes parallel light by the coupling lens 11, is reflected by the beam splitter 7, changes its direction, and is focused on the optical disk 10 by the objective lens 3. The light reflected by the optical disk 10 is converted into parallel light by the objective lens 3,
Passes through the optical system and enters the position signal detecting optical means 9 composed of a condensing lens, a cylindrical lens, and the like, and is condensed on the detector 5. In such a conventional general optical head, it is necessary to position and assemble a large number of components with high accuracy, and it is difficult to assemble and to reduce the size and weight.

Further, as a conventional general optical head which alleviates such a problem, there has been proposed a flat plate integrated type optical head as shown in FIG. 15 in which elements are integrated on a flat plate. JP-A-4-219640).
Laser light output from a semiconductor laser as a light source is guided to a substrate 1 which is a light propagation path through which light propagates in a zigzag shape, and is condensed on a disk 10 by a condensing means 3 on the substrate. The light reflected by the disk 10 passes through the second condensing unit 12, enters the position signal detecting optical unit 9, and is guided to the photodetector 5. In the optical head proposed here, since light propagates obliquely in the light transmission path substrate, light incident on the light transmission path substrate from the light source and light emitted from the light transmission path substrate to the disk are also transmitted through the light transmission path substrate. The incident light is not perpendicular to, but obliquely incident on, and is obliquely emitted. In such an arrangement, since light is obliquely applied to the disk, it is difficult to guide the reflected light from the disk to the same condensing means as the outward path, so that it is necessary to provide separate optical paths for the outward path and the return path. In addition, the light source and the photodetector must be installed to be inclined with respect to the light propagation path substrate, which causes a problem that the arrangement becomes complicated.

As an example of avoiding such a problem (Japanese Patent Laid-Open Publication No. Hei 4-219640, as shown in FIG. 16, the condensing means 3 and the coupling lens 11 formed on a substrate are used).
There has been proposed an optical head that uses an off-axis type diffractive lens that also has a function of deflecting light, and that allows light to enter and exit the light propagation path substrate perpendicularly, but an off-axis type Fresnel lens has been proposed. Has both the effect of condensing light and the effect of deflecting light, making it difficult to design and manufacture, such as narrowing the period of the diffraction grating.Because it deflects light by diffraction, it can respond to slight wavelength variations of the light source. As a result, the diffraction angle changes sensitively, so that the optical head may lack stability.

[0005]

Since the conventional flat-plate integrated optical head is configured as described above, the structure for obliquely entering and exiting light becomes complicated, resulting in a reduction in size and cost. There have been problems such as difficulty or lack of stability because light is deflected using a diffraction grating.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a small, low-cost, and stable optical head.

[0007]

According to a first aspect of the present invention, there is provided an optical head comprising: a transparent substrate having a light propagation path through which light propagates between upper and lower surfaces in a zigzag manner; a light source; When,
An optical head comprising a light condensing means and a position signal detecting optical means, wherein a light emitting portion of the substrate to the disk is obliquely notched, and the zigzag light is deflected and emitted perpendicular to the upper and lower surfaces of the substrate. It is.

An optical head according to a second configuration of the present invention is a transparent substrate having a light propagation path through which light propagates between upper and lower surfaces in a zigzag manner, a light source, a photodetector, and a light collector. Means and a position signal detecting optical means, wherein the surface of the substrate facing the light emitting portion to the disc is notched obliquely, a reflection layer is formed in the notched portion, and the light of the zigzag is formed. The light in the propagation path is deflected and reflected, and the reflected light is emitted perpendicularly to the upper and lower surfaces of the substrate.

An optical head according to a third configuration of the present invention is provided with an aperture made of a diffraction grating for defining a focused spot diameter of a light beam at a specific value on an upper surface or a lower surface of a substrate.

In an optical head according to a fourth aspect of the present invention, an aperture made of a diffraction grating is provided on the same surface of the substrate as the light collecting means.

In an optical head according to a fifth aspect of the present invention, the aperture formed by the diffraction grating is formed integrally with the position signal detecting optical means or the light condensing means.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is a plan view of an optical head according to a first embodiment of the present invention as viewed from above, FIG. 2 is a side view illustrating the optical head according to the first embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 2 is a plan view of the optical head 1 as viewed from below.

1, 2 and 3, 1 is a substrate, 3 is a light collecting means, 4 is a light source, 5 is a photodetector, 6 is a reflection layer, 7 is a beam splitter, 8 is a slope, and 9 is a position signal detector. The optical means 10 is a disk.

FIGS. 1, 2 and 3 show a first embodiment of the present invention.
1 shows the basic configuration of the optical head and how light is propagated and collected. As the substrate 1, for example, a thickness of 1.2 mm, a width of 2 mm,
An optical plastic having a length of 3 mm is used. The substrate itself is a light propagation path utilizing reflection on the upper and lower surfaces.
The light emitted from the light source 4 in the vertical direction (z-axis direction) from, for example, a semiconductor laser having a wavelength of 0.79 μm is obliquely cut (for example, 12.5 °) in the substrate by the oblique surface 8a which is an obliquely cut incident surface. ). This beam is incident on the position signal detecting optical means 9 formed on the upper surface of the substrate.
Here, assuming that, for example, a three-beam method is used as the position signal detecting means, the position signal detecting optical means is, for example, a diffraction grating for separating a beam into three beams.
This is a rectangular diffraction grating having a depth of 1 μm and a depth of 0.05 μm. Three beams can be obtained by the position signal detecting optical means. These three beams enter the beam splitter 7 formed on the lower surface, and the zero-order reflected light enters the condensing means 3 formed on the upper surface. This light collecting means is, for example, a Fresnel lens created by lithography technology. The light reflected by the light condensing means is reflected again by the reflection layer on the lower surface, and then exits in the vertical direction (z-axis direction) from the inclined surface 8b cut on the upper surface, for example, 2.3 m from the upper surface of the substrate.
Focus on the disk 10 m away. The light reflected by the disk surface again enters the element from the slope, and follows an optical path opposite to the outward path. The first-order diffracted light diffracted by the beam splitter is diffracted in a direction different from the outward path, and after the beam reflected by the reflection surface on the upper surface is emitted out of the substrate, the photodetector 5
Incident on.

In order to obtain a thin optical head by a flat plate integrated optical system in which light propagates in a zigzag manner, it is necessary to install substrates having optical elements formed on both sides in parallel with the disk. If the board is set parallel to the disc,
If the light propagating obliquely in the substrate is not emitted perpendicularly to the disk, the reflected light from the disk will not be able to propagate on the same optical path as the outward path, and it will be necessary to prepare another optical system for the return path . In order to emit light from the substrate perpendicular to the disk, a deflecting element that changes the direction of the light propagating obliquely is required. For this purpose, a method has been proposed in which a diffraction grating is used as a deflection element, and this diffraction grating is integrated with a light-collecting element to realize an off-axis Fresnel lens. However, the diffraction grating has a characteristic that the direction of deflection largely changes depending on the wavelength of the incident light, and unless a light source with extremely stable wavelength is used, a shift occurs in the direction of deflection. On the other hand, the prism-shaped inclined surface that deflects light by refraction has a smaller change in the deflection direction with respect to wavelength than the diffraction grating, and can maintain a stable emission angle with respect to the wavelength change of the light source. Etc. stability is increased. The angle of deflection by the diffraction grating changes approximately in proportion to the wavelength of light, but in the case of a prism, it depends on the wavelength dispersion of the refractive index and is much smaller.

Further, if the light is deflected not by refraction by the inclined surface but by reflection by the inclined surface as shown in FIG. 4, it is possible to completely eliminate the angle deviation due to wavelength fluctuation which remains slightly in the deflection method by refraction. It is possible.

In the optical head according to this embodiment, since the reflected light from the disk propagates in the same optical path as the outward path as described above, a small optical head can be constructed.

Embodiment 2 FIG. 5 is a plan view of the optical head according to the second embodiment of the present invention as viewed from above, FIG. 6 is a side view illustrating the optical head according to the second embodiment of the present invention, and FIG. 7 is an embodiment of the present invention. FIG. 3 is a plan view of the optical head 2 as viewed from below.

5, 6 and 7, 1 is a substrate, 2
Is an aperture formed by a diffraction grating, 3 is a light condensing means, 4
Is a light source, 5 is a photodetector, 6 is a reflection layer, 7 is a beam splitter, 8 is a slope, 9 is a position signal detecting optical means, and 10 is a disk.

FIGS. 5, 6, and 7 show a second embodiment of the present invention.
1 shows the basic configuration of the optical head and how light is propagated and collected. The function that light propagates in the substrate in a zigzag manner, is reflected by the disk, and returns to the photodetector is the same as that of the second embodiment, but the required effective diameter of the light incident on the lower surface of the substrate at the portion around the laser beam. A diffraction grating for diffracting the other part outside the effective area of the light propagation path is provided as an aperture, and only the central part of the laser beam propagates in the subsequent light path. Laser beam focusing spot diameter of the disk surface (1 / е becomes ² diameter 2 [omega intensity center portion), expressed as 2ω = 0.82λ / sinθ by the wavelength λ of the converging angle θ and the light by the lens. In order to detect the position signal, it is necessary to use a focused spot diameter corresponding to the track pitch of the disk, and therefore, it is necessary to provide an aperture for defining the focused angle in the optical path. In the flat plate integrated optical system, in order to form the aperture, a method of partially removing the reflective film or using a light absorbing film can be considered. However, in order to form a reflective film or a light absorbing film on the substrate surface as an aperture with high precision, it is necessary to add a process such as patterning by exposure and subsequent removal of the film, and the number of steps for manufacturing an element increases. In the present invention, the aperture is formed by diffracting unnecessary light out of the optical path by the diffraction grating. As a result, it is possible to form an aperture with high positional accuracy and shape accuracy by using a process similar to that of another beam splitter, Fresnel lens, or the like, thereby facilitating the manufacture of the element. Although the aperture is provided on the lower surface of the substrate in the present embodiment, the same effect can be obtained by providing the aperture on the upper surface.

Embodiment 3 FIG. 8 is a plan view of the optical head according to the third embodiment of the present invention as viewed from above, FIG. 9 is a side view illustrating the optical head according to the third embodiment of the present invention, and FIG.
FIG. 9 is a plan view of the optical head according to the third embodiment of the present invention as viewed from below.

8, 9 and 10, 1 is a substrate, 2 is an aperture formed by a diffraction grating, 3 is a light condensing means, 4 is a light source, 5 is a photodetector, 6 is a reflection layer, and 7 is a beam splitter. , 8 are slopes, 9 is position signal detecting optical means, and 10 is a disk.

FIGS. 8, 9 and 10 show the basic structure of an optical head according to a third embodiment of the present invention and how light is propagated and collected. As a substrate, for example, a thickness of 1.2 mm, a width of 2 mm,
An optical plastic having a length of 3 mm is used. The substrate itself is a light propagation path utilizing reflection on the upper and lower surfaces.
Light emitted in the vertical direction (z-axis direction) from, for example, a semiconductor laser having a wavelength of 0.79 μm, which is a light source, is obliquely (eg, 12.5 °) in the substrate due to the obliquely cut incident surface. Refracted. This beam is incident on the position signal detecting optical means 9 formed on the upper surface of the substrate. Here, assuming that, for example, a three-beam method is used as the position signal detecting optical means, the position signal detecting optical means is, for example, a diffraction grating for separating a beam into three beams, for example, at a pitch of 1.
This is a rectangular diffraction grating having a depth of 3.1 μm and a depth of 0.05 μm. The outer region is an aperture diffraction grating. For example, if the pitch is 1.5 μm and the depth is 0.13 μm, a portion other than the required effective diameter of the light incident on the aperture diffraction grating is diffracted outside the effective region of the light propagation path. Can be done.
By this position signal detecting optical means integrally formed with the aperture, three beams having a fixed beam diameter can be obtained.
These three beams enter the beam splitter 7 formed on the lower surface, and the zero-order reflected light enters the condensing means 3 formed on the upper surface. The light collecting means 3 is, for example, a Fresnel lens created by a lithography technique.
When the condensing means is formed by lithography in this way, the aperture diffraction grating can also be formed by lithography on the same mask, so that both can be aligned with high accuracy, for example, on the order of submicron. . The light reflected by the light condensing means is reflected again by the reflection layer 6b on the lower surface, then exits in the vertical z-axis direction from the inclined surface 8b cut on the upper surface, and is focused on a disk 2.3 mm away from the upper surface of the substrate, for example. . The light reflected by the disk surface again enters the element from the slope, and follows an optical path opposite to the outward path. The first-order diffracted light diffracted by the beam splitter is diffracted in a direction different from the outward path, and the reflected beam exits the substrate and then enters the photodetector.

If the central axes of the focusing means 3 and the aperture 2 in the optical path are displaced, the optical axis becomes oblique, so that the laser beam hitting the disk surface is inclined not perpendicularly to the disk. Will be. When the laser beam hitting the disc is tilted, the reflected light leaks out of the effective area of the optical path on the return path, and the light amount is lost,
Problems such as imbalance appearing in the position signal occur. Therefore, the aperture and the condensing means must be relatively positioned with extremely high precision. If the aperture and the condensing means are on the same surface of the substrate, if both are realized as diffractive optical elements, positioning can be performed with extremely high precision by drawing all at once when drawing a diffraction pattern, but both are positioned on different surfaces of the substrate. When arranged, positioning between different surfaces becomes difficult. By arranging the aperture and the light collecting means on the same surface of the substrate in this way,
The positioning of the mutual elements is facilitated and the fabrication is facilitated.

Embodiment 4 11 is a plan view of the optical head according to the fourth embodiment of the present invention as viewed from above, FIG. 12 is a side view illustrating the optical head according to the fourth embodiment of the present invention, and FIG. 13 is an embodiment of the present invention. FIG. 4 is a plan view of the optical head 4 as viewed from below.

In FIGS. 11, 12, and 13, reference numeral 1 denotes a substrate;
2 is an aperture formed by a diffraction grating, 3 is a light collecting means,
4 is a light source, 5 is a photodetector, 6 is a reflective layer, 7 is a beam splitter, 8 is a slope, 9 is a position signal detecting optical means, 10
Is a disk.

FIGS. 11, 12 and 13 show the basic structure of an optical head according to a fourth embodiment of the present invention and how light is propagated and collected. As a substrate, for example, a thickness of 1.2 mm and a width of 2 m
m, an optical plastic having a length of 3 mm is used. The substrate itself is a light propagation path utilizing reflection on the upper and lower surfaces. Light emitted in the vertical direction (z-axis direction) from, for example, a semiconductor laser having a wavelength of 0.79 μm, which is a light source, is obliquely (eg, 12.5 °) in the substrate due to a slope having an obliquely cut incident angle. Refracted. This beam is incident on the position signal detecting optical means 9 formed on the upper surface of the substrate.
Here, assuming that, for example, a three-beam method is used as the position signal detecting means, the position signal detecting optical means 9 is, for example, a diffraction grating for separating a beam into three beams.
This is a rectangular diffraction grating having a depth of 3.1 μm and a depth of 0.05 μm. Three beams can be obtained by this position signal detecting optical means. These three beams are incident on a beam splitter 7 formed on the lower surface, and the zero-order reflected light is incident on the condensing means 3 formed on the upper surface and formed integrally with the aperture. This light collecting means is, for example, a Fresnel lens created by lithography technology. The outer region is an aperture diffraction grating. For example, if the pitch is 1.5 μm and the depth is 0.13 μm, 90% or more of the light incident on the aperture diffraction grating can be diffracted outside the effective region of the light propagation path. it can. When the condensing means is formed by lithography in this way, the aperture diffraction grating can also be formed by lithography on the same mask, so that the alignment between the two can be performed with high accuracy, for example, on the order of submicron. . The light reflected by the light-collecting means integrally formed with the aperture is reflected again by the reflection layer on the lower surface, and then perpendicularly to the slope cut on the upper surface.
The light is emitted in the axial direction and is focused on a disk surface, for example, 2.3 mm away from the upper surface of the substrate. The light reflected by the disk surface again enters the element from the slope, and follows an optical path opposite to the outward path. The first-order diffracted light diffracted by the beam splitter is diffracted in a direction different from the outward path, and the reflected beam exits the substrate and then enters the photodetector.

Since the aperture diffraction grating of the optical head according to the second configuration is an element for diffracting unnecessary light out of the optical path, only the effective light such as another Fresnel lens or diffraction grating for three beams is used. It can be formed as an integrated element on one side with the working optical element. By integrally forming a plurality of elements as described above, mutual alignment becomes unnecessary, the number of reflection surfaces can be reduced, and manufacturing becomes easy.

[0029]

According to the optical head of the first structure of the present invention, a transparent substrate provided with a light propagation path through which light propagates between upper and lower surfaces in a zigzag manner, a light source, a photodetector, In an optical head provided with a light condensing means and a position signal detecting optical means, a light emitting portion of the substrate to the disk is notched obliquely so that the zigzag light is deflected and emitted perpendicular to the upper and lower surfaces of the substrate. Therefore, it is possible to realize a flat plate integrated optical head that is stable against wavelength fluctuations of the light source.

According to the optical head of the second configuration of the present invention, a transparent substrate provided with a light propagation path through which light propagates in a zigzag manner between the upper and lower surfaces, a light source, a photodetector, In the optical head including the light condensing means and the position signal detecting optical means, a surface of the substrate facing the light emitting portion to the disk is notched obliquely, and a reflection layer is formed on the notched portion,
A flat-plate integrated optical head that is stable against wavelength fluctuations of a light source that deflects and reflects the light in the zigzag light propagation path and emits the reflected light perpendicularly to the upper and lower surfaces of the substrate can be realized.

Further, according to the optical head of the third configuration of the present invention, since the aperture made of the diffraction grating for defining the focused spot diameter of the light beam to a specific value is provided on the upper surface or the lower surface of the substrate, The diameter of the focused spot on the disk can be defined.

Further, according to the optical head of the fourth configuration of the present invention, since the aperture composed of the diffraction grating is provided on the same surface as the light condensing means of the substrate, the displacement of each element is reduced. A highly stable flat plate integrated optical head can be realized.

Further, according to the optical head having the fifth configuration of the present invention, since the aperture formed by the diffraction grating is formed integrally with the position signal detecting optical means or the condensing means, the aperture diffraction grating is formed. And a small flat-plate integrated optical head.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical head according to a first embodiment of the present invention as viewed from above.

FIG. 2 is a side view showing the optical head according to the first embodiment of the present invention.

FIG. 3 is a plan view of the optical head according to the first embodiment of the present invention as viewed from below.

FIG. 4 is a side view showing another optical head according to the first embodiment of the present invention.

FIG. 5 is a plan view of the optical head according to the second embodiment of the present invention as viewed from above.

FIG. 6 is a side view showing an optical head according to a second embodiment of the present invention.

FIG. 7 is a plan view of the optical head according to the second embodiment of the present invention as viewed from below.

FIG. 8 is a plan view of the optical head according to the third embodiment of the present invention as viewed from above.

FIG. 9 is a side view showing an optical head according to a third embodiment of the present invention.

FIG. 10 is a plan view of the optical head according to the third embodiment of the present invention as viewed from below.

FIG. 11 is a plan view of an optical head according to a fourth embodiment of the present invention as viewed from above.

FIG. 12 is a side view showing an optical head according to a fourth embodiment of the present invention.

FIG. 13 is a plan view of the optical head according to the fourth embodiment of the present invention as viewed from below.

FIG. 14 is a configuration diagram of a conventional optical head.

FIG. 15 is a configuration diagram of a conventional flat plate integrated optical head.

FIG. 16 is a configuration diagram of a conventional flat plate integrated optical head.

[Explanation of symbols]

1 substrate, 2 aperture, 3 focusing means, 4 light sources,
5 photodetector, 6 reflection layer, 7 beam splitter,
8 slope, 9 position signal detecting optical means, 10 discs,
11 coupling lens, 12 second focusing means.

Claims (5)

[Claims] 1. An optical system comprising: a transparent substrate provided with a light propagation path through which light propagates between upper and lower surfaces in a zigzag manner; a light source; a photodetector; a condensing means; and a position signal detecting optical means. An optical head, wherein a light-emitting portion of the substrate to a disk is notched obliquely, and light in the zigzag light propagation path is deflected and emitted perpendicular to the upper and lower surfaces of the substrate. 2. An optical system comprising: a transparent substrate provided with a light propagation path through which light propagates between upper and lower surfaces in a zigzag manner; a light source; a photodetector; a condensing means; and a position signal detecting optical means. In the head, the surface of the substrate facing the light emitting portion to the disk is notched obliquely, a reflective layer is formed in the notched portion, and the light in the zigzag light propagation path is deflected and reflected,
An optical head for emitting the reflected light vertically to the upper and lower surfaces of the substrate. 3. The optical head according to claim 1, wherein an aperture made of a diffraction grating for defining a focused spot diameter of the light beam to a specific value is provided on an upper surface or a lower surface of the substrate. 4. The optical head according to claim 3, wherein an aperture made of the diffraction grating is provided on the same surface of the substrate as the light collecting means. 5. An optical head in which an aperture made of the diffraction grating is formed integrally with the position signal detecting means or the condensing means.