JP2002352458A - Optical head device, laser beam capturing device for power measurement, and optical disk device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the loss of laser light used in an objective lens, to increase the efficiency, and to increase the arrangement position of a photodetector and the degree of design freedom without complicating the configuration. A laser beam from a light source (201) is transmitted through a hologram (301), a dichroic PBS (302), a collimator lens (303), a tilt correction element (304), a λ / 4 plate (305), a reflection mirror (306), and an objective lens (307).
It is irradiated on the information recording surface of No. 0. The reflected light from the information recording surface is
The light is diffracted by the hologram 301 through the reverse path and enters the photodetector. The optical fiber has one end disposed in an area of non-effective light that does not enter the objective lens around an area of effective light in which an optical path is formed, in order to capture light for power measurement, and the other end. Are arranged on the light receiving surface of the photodetector 202.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for recording information on a recording medium using a light beam and for reading already recorded information from the recording medium, and such an optical head. The present invention relates to a laser light capturing device for power measurement which is effective for the device, and an optical disk device using such an optical head device.

[0002]

2. Description of the Related Art In recent years, in the field of recording media, the diameter of a conventional CD on which audio or digital data is recorded (1.
A digital versatile disk (DVD) that has the same size but is capable of high-density recording has been developed. Since DVDs have a high recording density, a beam having a wavelength (650 nm) shorter than the wavelength (780 nm) of light for reading CD data is required.

As a recording / reproducing apparatus, one capable of recording / reproducing both a CD system and a DVD system is desired. Therefore, as an optical head device (optical pickup) using a semiconductor array, a light source for DVD (wavelength 650 nm) (first light source) and a light source for CD (wavelength 78) are used.
0 nm) (second light source). As described above, the optical head device has the first light source (for DVD).
And a second light source (for CD).

A laser beam emitted from a first light source passes through a hologram and is capable of photosynthesis and light branching. The dichroic polarized beam splitter (dichroic beam splitter)
PBS). The laser light transmitted through the dichroic PBS passes through a collimator lens, becomes collimator light, and enters the objective lens. The light collected by the objective lens is applied to the recording surface of the disk. The light reflected from the disk passes through an objective lens, a collimator lens, and a dichroic prism, and enters a hologram.

The hologram diffracts reflected light and guides it to a photodetector using a photodiode. The photodetector has a focus error signal, a tracking error signal,
Outputs a read signal.

The laser light emitted from the second light source enters the dichroic PBS. The light beam reflected and emitted inside the dichroic PBS is:
The light passes through the collimator lens, becomes collimator light, and enters the objective lens. The light collected by the objective lens is applied to the recording surface of the disk. The light reflected from the disk passes through an objective lens, a collimator lens, and a dichroic PBS, and enters a hologram. The reflected light diffracted by the hologram is guided to the photodetector using a photodiode.

[0007]

In an apparatus using the above-described optical head device, an automatic power control (APC) is used to stabilize the intensity of a laser beam applied to a disk.
A circuit is provided. In this APC circuit, for example, reflected light from a disk is branched by a dichroic PBS, guided to a photodetector, and the amount of light is measured. Then, the driving power (supply current) of the light source currently used is controlled according to the result of the light quantity measurement, and the intensity of the light beam applied to the disk is stabilized.

According to the above-mentioned conventional APC circuit, since the light of the main system (irradiation path, reflection path) of the laser light is directly used, the power of the main system laser light is lost, and the efficiency tends to decrease. is there. In addition, when the photodetectors are arranged, there are restrictions on the arrangement positions, and the degree of freedom in designing the entire device is reduced. If an arrangement position of the photodetector is selected at an arbitrary position, components (prisms and lenses) for guiding light to the photodetector are required, which tends to complicate the entire configuration.

Accordingly, the present invention eliminates the loss of the backbone laser light (effective laser light employed in the objective lens), improves the efficiency, and allows the position of the photodetector to be arranged without complicating the configuration. Can be arbitrarily selected,
It is an object of the present invention to provide an optical head device, a laser beam capturing device for power measurement, and an optical disk device that can increase the degree of freedom in design.

[0010]

In order to achieve the above object, the present invention provides a light source for emitting laser light, and the light source and the light source for irradiating the disk with the laser light via an objective lens. An optical path component having an optical path formed between the objective lenses, and around a region of effective light having the optical path formed therein for capturing light for power measurement in order to control the power of the laser light, A light guide member having one end disposed in a region of non-effective light that does not enter the objective lens and the other end disposed on a light receiving surface of a photodetector.

The light guide member is an optical fiber, and the one end disposed in a light area leaking around the optical path (light area not incident on the objective lens) has an oblique angle with respect to the fiber axis. The light receiving surface is cut so as to become The area of the non-effective light where the one end is disposed is a part where the laser light has a radiation angle, and the light receiving surface refracts light in the light area in a direction away from the optical path. Are located in The light receiving surface;
It is arranged so that the angle formed by the boundary line of the effective light region (the inclined surface in the direction of the optical path located at the outermost periphery) is an acute angle.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1A and 1B show an embodiment of the present invention and show a basic configuration of an optical head device.
FIG. 1A is a plan view, and FIG. 1B is a side view.
Hereinafter, description will be made with reference to both figures.

On one side wall 102 of the chassis 101,
The first light source unit 201 is attached. Although not shown, the first light source unit 201 irradiates the reflected light from the disk by being diffracted by the hologram 301 and irradiates a reproduced signal, a format error signal,
A photodetector that performs photoelectric conversion to obtain a tracking error signal is provided.

The first light source unit 201 has a wavelength of 650
This is a DVD light source (first light source) that emits a laser beam of nm. Further, a second light source unit 202 is attached to the side wall 102 of the chassis 101.
The second light source unit 202 is a CD light source (second light source) that emits laser light having a wavelength of 780 nm.

As described above, the optical head device has the first light source (for DVD) and the second light source (for CD). The laser light emitted from the first light source is emitted on the plane of the chassis 101 in a direction substantially parallel to this plane, and the hologram 3
01 and enters the dichroic PBS 302. First
The laser light from the light source (1) goes straight through the dichroic PBS 302, becomes parallel light by the collimator lens 303, and enters the reflection mirror (prism) 306 via the tilt correction element 304 and the λ / 4 plate (polarization plate) 305. The light reflected by the reflection mirror 306 is incident on an objective lens 307 disposed above the reflection mirror 306.

The light focused by the objective lens 307 is applied to the reflective layer (information recording surface) of the disk 400 located above the objective lens 307. The light reflected on the information recording surface passes through the objective lens 307 and the reflection mirror 306 to have a wavelength of λ.
It returns to the / 4 plate 305. The light transmitted through the λ / 4 plate 305 passes through the tilt correction element 304 and is dichroic.
The light enters the PBS 302. The reflected light that has entered the dichroic PBS 302 travels straight and forms a hologram 301.
Is reproduced by the reproduction signal, the format error signal,
The light is incident on a photodetector (not shown) that performs photoelectric conversion to obtain a tracking error signal.

On a plane of the chassis 101 emitted from a CD light source (second light source), the light is radiated in a direction substantially parallel to the plane, and is passed through a λ / 2 plate 311 to a dichroic PB.
It is incident on S302. The laser light from the second light source is reflected inside the dichroic PBS 302, changed its direction, and enters the collimator lens 303. The laser light that has entered the collimator lens 303 becomes parallel light, and enters the reflection mirror (prism) 306 via the tilt correction element 304 and the λ / 4 plate (polarization plate) 305. The light reflected by the reflection mirror 306 is incident on an objective lens 307 disposed above the reflection mirror 306.

The light focused by the objective lens 307 is applied to a reflective layer (information recording surface) of the disk 400 located above the objective lens 307. The light reflected on the information recording surface passes through the objective lens 307 and the reflection mirror 306 to have a wavelength of λ.
It returns to the / 4 plate 305. The light transmitted through the λ / 4 plate 305 passes through the tilt correction element 304 and is dichroic.
The light enters the PBS 302. The reflected light that has entered the dichroic PBS 302 travels straight and forms a hologram 301.
Is reproduced by the reproduction signal, the format error signal,
The light is incident on a photodetector (not shown) that performs photoelectric conversion to obtain a tracking error signal.

Here, the optical head device of the present invention is provided with a means for detecting the power of a part of the laser light emitted from the light source for automatic power control.

That is, the photodetector 501 is attached to the side wall 104 of the chassis 101. This photodetector 501
For example, one end of the optical fiber 511 is opposed to the light receiving portion, and the other end of the optical fiber 511 is around the optical path of the laser light of the laser light output from the first light source 201. Are arranged in a light region of light that does not enter the objective lens 307. Thereby, the objective lens 307
The power of the laser light can be detected by using a part of the laser light without affecting the light amount incident on the laser light. The tip of the optical fiber 511 (end on the laser beam side)
It is held and stabilized by the positioning part 512 provided in the chassis 101.

Similarly, means for detecting the power of the laser light from the second light source 202 is provided. That is, one end of the optical fiber 521 faces the light receiving unit of the photodetector 501. The other end of the optical fiber 511 is around the optical path of the laser light of the laser light output from the second light source 202 and is light that does not enter the objective lens 307 (light that is not used by the objective lens 307). Located in the area. Thus, the power of the laser light can be detected using a part of the laser light without affecting the amount of light incident on the objective lens 307. This optical fiber 5
The front end (end on the laser beam side) of the chassis 21
Is stabilized by being held by the positioning portion 522 provided in the first position. The positioning portions 512 and 522 have grooves that sandwich the optical fiber, where the optical fiber is disposed,
It is fixed with an adhesive or the like.

Although not shown, the objective lens 307 is not shown.
Is held by a lens holder. The lens holder is supported by one end of a plurality of wires, and can be finely controlled in a focus direction and a tracking direction. The plurality of wires are held by a wire holder attached to a chassis. Further, for example, a small permanent magnet for focus control and a permanent magnet for tracking control are attached to the lens holder. A focus control coil and a tracking control yoke coil are arranged on the chassis near the permanent magnets. Then, by supplying a focus control signal and a tracking control signal to the focus control coil and the tracking control yoke coil, respectively, the objective lens can be finely moved in the focus control direction and the tracking control direction.

First, with the optical head device having the above-described configuration, it is possible to eliminate the loss of the light beam of the main system (used in the objective lens). This means that the efficiency of using laser light can be improved. In addition, a part of the laser beam can be freely guided to the photodetector 501 by an optical fiber (or a light guide). As a result, the arrangement position of the photodetector can be arbitrarily selected without complicating the configuration of the entire apparatus, and the degree of design freedom can be increased.

In the above embodiment, when detecting the power of the laser light from the two light sources, it is possible to detect the power using one photodetector 501. However, the basic configuration of the present invention does not need to have a plurality of light sources, and is also effective for an optical head having one light source.

The apparatus according to the present invention is also characterized in the positional relationship between the light receiving surface of the optical fiber and the laser beam (method of capturing the amount of light into the fiber).

FIG. 2A shows the relationship between the laser light R emitted from the light source and the light receiving surface A at the end of the light guide (for example, the optical fiber 511).

The laser light emitted from the light source unit 201 is normally radiated and becomes an expanded laser light having an angle θ1. Here, the laser light R is converted into parallel light by a collimator lens around the optical axis. This parallel light enters the objective lens and is collected. Here, the light incident on the objective lens is a light beam in the range of the angle θ2.

For this reason, assuming that the light incident on the objective lens 307 is the light of the main system (the light path of the main system), the hatched portion of the light region outside the main system (FIG. 2A) (usually used). There is a light flux D that is not performed. Such light deviating from the basic optical path (or effective area) may be called stray light.

Therefore, in the present invention, the light flux (so-called stray light) in the light area D (or ineffective area) is effectively used. That is, the optical fiber 511 is located in this light region.
By arranging the light receiving surface A, a part of the laser beam R can be guided to the photodetector 501 without causing a loss to the light beam of the main system (without reducing the utilization rate of the light beam of the main system). .

Here, in the present invention, the optical fiber 51
Measures are taken so that the light-receiving surface at the tip of 1 can receive as much light flux in the light area (hatched area) as possible, and when the light in the light area enters the optical fiber 511, the refraction direction of the light fiber 511 We are taking measures to make it the direction. That is, the efficiency of the received light is increased.

In order to increase the efficiency of the received light, the light on the light receiving surface A of the optical fiber 511 is refracted in a direction away from the traveling direction of the laser light R in the emitting state. It is preferable to design the light receiving surface A. Therefore, preferably, as shown in an enlarged manner in FIG. 2B, when the stray light is taken into the optical fiber 511, the light receiving surface A is refracted in a direction parallel to the optical axis of the optical fiber 511.
It is better to set the slope. Further, in order to increase the light receiving efficiency, it is preferable that the diameter W of the light receiving surface A is arranged so as to be located over the entire cross section of the region D.

That is, according to the present invention, a light source for emitting laser light is provided. Similarly to the inside of the maximum spread angle θ1 of the laser light, an effective angle θ2 which is an optical path substantially utilizing the laser light is set. This depends on the optical components to be arranged.

Then, the light receiving surface A of the light guide member (optical fiber) enters into an ineffective area (oblique line) generated between the spread angle θ1 and the effective angle θ2. Here, the light receiving surface A is disposed at an acute angle with respect to the boundary formed by the divergence angle θ1, and the maximum entrance position is outside a region within the effective angle θ of the laser light. .

Next, the basic structure of an optical disk reproducing apparatus using the above-described optical head device will be described.

In FIG. 3, DT is a disk table for holding an optical disk as a storage medium. Although not shown, the disk table DT is rotated by a motor controlled by a servo circuit. Reference numeral 100 denotes an optical head device, as described with reference to FIG. 1, an optical disk O held by the disk table OD and rotated at a predetermined speed.
The recording surface of D is irradiated with a laser beam, the reflected laser beam reflected by the recording surface of the optical disk OD is taken in, and an electric signal corresponding to the light intensity of the reflected laser beam is output.

The optical head device 100 moves along a guide rail 600 provided in a predetermined positional relationship with the disk table DT in a direction perpendicular to the tangential direction of the track on the recording surface of the optical disk OD (in the radial direction of the optical disk OD). That is, it is possible to move in the tracking control direction). The optical head device 100 is reciprocated on a guide rail 600 by a linear motor (not shown).

An output signal from a photodetector (not shown) which is built in the first light source unit 201 of the optical head device 100 and receives light reflected from the disk is supplied to a signal processing circuit 7.
01, a tracking control circuit 702 and a focusing control circuit 703. The signal processing circuit 701 performs arithmetic processing for reproducing information recorded on a disk. The tracking control circuit 703 is a circuit that performs arithmetic processing on a signal reproduced from a disc to obtain a tracking error signal and obtain a tracking control signal.
The focusing control circuit 703 is a circuit that performs arithmetic processing on a signal reproduced from the disc to obtain a focusing error signal and generates a focusing control signal.

A detection signal from the photodetector 501, which is a feature of the present invention, is guided to the APC circuit 704. APC
The circuit 704 determines whether or not this detection signal is a signal of a preset level, and gives the obtained control signal to the laser drive circuit 705. Now, assuming that the first light source unit 201 is in the operating state, the laser driving circuit 705 controls the power of the laser light of the first light source unit 201 according to the control signal. Further, assuming that the second light source unit 203 is now in the operating state, the laser driving circuit 705 controls the power of the laser light of the second light source unit 201 according to the control signal.

As a result, the power of the output laser beam or the amount of the reflected light from the disk is automatically controlled so as to fall within a preset standard range.

The above first and second light source units 201,
In 202, a semiconductor laser device that emits a light beam (laser beam) having a predetermined wavelength is used.

The objective lens 307 is moved by a lens holder (not shown) in a direction perpendicular to the tangential direction of the track (radial direction of the optical disk OD) and in a direction in which the laser beam passes (direction perpendicular to the recording surface of the optical disk OD). ) Are movably supported. Optical disk OD
Is called a tracking control direction, and a direction orthogonal to the recording surface of the optical disc OD is called a focusing control direction.

The tracking control circuit 702 generates a tracking control signal from the tracking error signal,
Give to tracking coil. Further, the focusing control circuit 703 generates a focusing control signal from the focus error signal and supplies the signal to the focusing coil.

The switching control of the operation timing of the entire circuit and the operation conditions (parameters and the like) is performed by the system control unit 710.
It is set by the control signal from. Although not shown, the device includes a power supply device, a ROM (program memory) storing a program to be read when operating the device, and data read from the optical disk OD or a host computer (not shown). R for temporarily storing input data and control data, etc.
An AM (work memory) and the like are provided.

In the above description, the operation at the time of reproducing information from the optical disk has been described.
Of course, it can be applied to information recording on the M disk. At this time, the laser drive circuit 705 controls the modulation in accordance with the recording information and the APC circuit 70
4 controls the average power of the laser beam so as to reach the recording level.

Next, a signal processing circuit 701, a tracking control circuit 702, a focusing control circuit 703, and a
The relationship with the light detector housed in one light source unit 201 will be described. Note that the signal processing system described below includes:
This is an example, and does not limit the purpose of the present invention.

FIG. 4 shows an example of an electric signal system for processing a signal read by the optical head device.
Photodetectors 20 include photodiodes 6A, 6B, 6
C, 6D, 6E, and 6F are provided. The output of each photodiode 6A, 6B, 6C, 6D, 6E, 6F is
Buffer amplifiers 23a, 23b, 23c, 23
d, 23e and 23f. Each of the A to F signals output from the buffer amplifiers 23a, 23b, 23c, 23d, 23e, and 23f is calculated as follows.

The adder 234 generates an (A + C) signal,
The adder 235 generates a (B + D) signal. Adder 23
6 is the (A + C) signal from the adder 231 and the adder 2
(A + B) + (C + D)
+ D) signal. This (A + B) + (C +
D) The signal is output as a high-frequency signal HF via the equalizer 24 and processed by the signal processing circuit 701.

The (A + C) signal from the adder 234 and the (B + D) signal from the adder 235 are input to the phase difference detector 31. The output of the phase difference detector 31 is D
Used as a tracking error signal (DVD-TE) for VD. The (A + C) signal from the adder 234 and the (B + D) signal from the adder 235 are input to the subtractor 233. The (A + B)-(C + D) signal output from the subtracter 233 is used as a DVD or CD focus error signal (FE).

The subtractor 237 generates an (EF) signal. (E obtained based on the detection signal of this sub-beam
The -F) signal is ignored when the switch 322 is turned off during DVD reproduction.

The (EF) signal is used as a tracking error signal (CD-TE) for CD. That is, when the apparatus is in the CD playback mode, the switch 322 is turned on.

[0052]

As described above, according to the present invention, the loss of the backbone laser light (effective laser light used in the objective lens) is eliminated, the efficiency is improved, and the optical power is reduced without complicating the structure. The arrangement position of the detector can be arbitrarily selected, and the degree of freedom in design can be increased.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing an embodiment of an optical head device according to the present invention.

FIG. 2 is an explanatory diagram showing a main part of a power measurement laser beam capturing device according to the present invention.

FIG. 3 is an explanatory diagram showing a basic part of a reproducing apparatus according to the present invention.

FIG. 4 is a diagram showing an output signal processing unit of the photodetector according to the present invention.

[Explanation of symbols]

101: chassis, 201: first light source, 202: second light source, 301: hologram, 302: dichroic P
BS, 303: collimating lens, 304: tilt correction element, 305: λ / 4 plate, 306: reflection mirror, 307
... Objective lens, 400 ... Disc, 501 ... Photodetector,
511, 521: Optical fiber.

Claims (7)

[Claims] A light source that emits laser light; an optical path component that forms an optical path between the light source and the objective lens for irradiating the disk with the laser light via an objective lens; In order to take in light for power measurement in order to control the power of the optical path, one end is arranged around a region of the effective light where the optical path is formed and in a region of the non-effective light which does not enter the objective lens. And a light guide member having the other end disposed on a light receiving surface of the light detection element. 2. The optical head device according to claim 1, wherein the one end of the light guide member is arranged close to the light source. 3. The optical head device according to claim 1, wherein the one end of the light guide member is disposed close to the objective lens. 4. A light source for emitting laser light, an optical path component for forming an optical path between the light source and the objective lens for irradiating the disk with the laser light via an objective lens, and the laser light In order to take in light for power measurement in order to control the power of the optical path, one end is arranged around a region of the effective light where the optical path is formed and in a region of the non-effective light which does not enter the objective lens. An optical fiber, the other end of which is arranged on the light receiving surface of the light detecting element. 5. A light source for emitting laser light, and an optical component for setting an effective angle similar to the inside of the maximum spread angle of the laser light and further as an optical path substantially utilizing the laser light. A light receiving surface enters a region of non-effective light generated between the divergence angle and the effective angle, and the light receiving surface is arranged at an acute angle with respect to a boundary formed by the divergence angle. And a light guide member whose maximum entrance position is outside a region within an effective angle of the laser light. 6. The power measuring laser beam capturing device according to claim 5, wherein said light guide member is an optical fiber. 7. An information recording surface of an optical disk is irradiated with laser light from a light source via an optical path formed of optical components, and reflected light reflected on the information recording surface passes through the optical path. In the optical disc device for guiding the returned light to the photodetector via the hologram and reproducing the recorded information, the optical path is formed in order to take in the light for power measurement in order to control the power of the laser light. A light guide member having one end disposed in a non-effective region of light that does not enter the objective lens around the effective region of the light, and the other end disposed on a light receiving surface of a photodetector; A light detector to which the other end of the guide member is guided; and automatic power control means for controlling an amount of current supplied to the light source based on an output signal of the light detector. Optical disk device.