JP3010032B2 - Optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical head for optically recording or reproducing information.

[0002]

2. Description of the Related Art In recent years, the information industry has been remarkably progressing, and the amount of information handled tends to increase. For this reason, instead of a recording or reproducing apparatus that records and reproduces information using a conventional magnetic head, a light beam is irradiated to record information at a high density on a recording medium or to record at a high density on a recording medium. An optical information recording / reproducing apparatus capable of reproducing information recorded at a high speed at a high speed has been attracting attention.

Incidentally, it is desirable that the optical head used in the optical information recording / reproducing apparatus be small and light in order to shorten the access time. Therefore, recently, in order to reduce the size and weight of the optical head, for example, Japanese Patent Application Laid-Open
As disclosed in Japanese Patent No. 32743, an optical system using a hologram has been proposed.

An outline of an example of a conventional optical head as disclosed in the above publication will be described with reference to FIG. This optical head is for magneto-optical (thermomagnetic) recording. A laser beam 172 emitted from a semiconductor laser 170 is converged by a lens 174, then diverges again, passes through a hologram lens 178, and passes through an objective lens. 182 converges on a magneto-optical (thermomagnetic) medium 184. The medium 18
The reflected light from 4 enters the hologram lens 178 via the objective lens 182. This hologram lens 17
The eight pairs of diffracted lights 188 and 190 are converged on a pair of photodetectors 192 and 194, respectively. This photodetector 19
Just before 2,194, a polarizing lens 196 is provided. The polarizing lens 196 is composed of, for example, a hologram lens, and guides two polarized beams orthogonal to each other to the photodetectors 192 and 194, respectively. The outputs of the photodetectors 192 and 194 obtain a focus and tracking error signal and an information signal. The semiconductor laser 17
Behind 0, a photodetector that detects the light behind the semiconductor laser 170 is provided. Then, for example, the output of the photodetector is used for APC (automatic light control) of the semiconductor laser 170.

[0005]

However, in the magneto-optical (thermomagnetic) optical head, the information signal of the magneto-optical (thermomagnetic) medium is minute, and a part of the reflected light from the medium returns to the semiconductor laser. . Therefore, the APC using the rear light of the semiconductor laser cannot be accurately detected because of the influence of the noise (backtalk noise) of the semiconductor laser, and cannot perform accurate control. This problem is not limited to the magneto-optical (thermomagnetic) optical head, but is a write-once (DR)
AW) or a read-only optical head. That is, in these optical heads, for example, the reflected light is prevented from returning to the semiconductor laser by changing the polarization direction by 90 degrees between the outgoing light and the reflected light toward the recording medium. This is because part of the reflected light returns to the semiconductor laser due to the influence of birefringence.

Therefore, as shown in FIG. 9, it is conceivable to monitor the forward light (outgoing light toward the recording medium) of the semiconductor laser. In the example of FIG. 9, the semiconductor laser 170
Is emitted to the half mirror 200, and a part of the light transmitted through the half mirror 200 is received by the front monitor photodetector 202. The half mirror 2
The light reflected at 00 passes through a hologram lens 178 and is converged on a medium 184 by an objective lens 182. The reflected light from the medium 184 is
, And enters the hologram lens 178. The pair of diffracted lights of the hologram lens 178 are reflected by the half mirror 200, respectively, and the pair of photodetectors 192, 1
94 is converged.

However, when a part of the forward light of the semiconductor laser 170 is separated and monitored by the half mirror 200 as described above, the substrate on which the semiconductor laser 170 and the photodetectors 192 and 194 are disposed and the front monitor The wiring of the front monitor photodetector 202 is troublesome because the photodetector 202 is away from the monitor photodetector 202.

The semiconductor laser 170 and the photodetector 1
Since the substrate on which the sensors 92 and 194 are provided is separated from the front monitor photodetector 202, it is disadvantageous to reduce the size of the optical head.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made capable of monitoring forward light of a semiconductor laser, that is, light emitted toward a recording medium, and having a small size and easy assembly. It is intended to provide an optical head.

[0010]

An optical head according to the present invention comprises:
In order to achieve the above object, a light source that emits light applied to a recording medium, and an optical member on which a hologram is formed that diffracts reflected light from the recording medium and directs the light in a different direction from the light source An optical head comprising: a first photodetector that receives light diffracted by the hologram; and a second photodetector that receives a part of light emitted from the light source. A photodetector and a second photodetector are provided on the same substrate, a part of light emitted from the light source is reflected, and a reflection hologram guided to the second photodetector is directly formed on the optical member. Provided.

With this configuration, a part of the light emitted from the light source is reflected by the reflection type hologram, and the reflected light is received by the second photodetector and monitored.
A PC can be realized. In addition, since the reflection hologram for directing a part of the emitted light to the second photodetector is provided directly on the optical member, there is no need to newly provide a space for the reflection hologram, which can contribute to downsizing. .

Further, since the reflection type hologram can freely set the direction of reflection when reflecting a part of the emitted light, the second photodetector can be arranged at a position which can contribute to miniaturization. It is preferable that the reflection hologram reflects the center including the optical axis of the emitted light.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 relate to a first embodiment of the present invention. FIG. 1A is an explanatory view showing an optical system for detecting an error signal and an information signal of an optical head, and FIG. 1B is a front view of the optical head. Explanatory diagram showing an optical system for optical monitoring, FIG.
Is an explanatory view showing a hologram lens, and FIG. 3 is a plan view of a substrate on which a semiconductor laser and a photodetector are arranged.

In this embodiment, as shown in FIGS. 1A and 1B, a write-once (DRAW) or read-only optical head for recording and reproducing information on a recording medium 4 for recording and reproduction. This is an example.

The optical head 10 includes a semiconductor laser 1 as a light source.
The hologram lens 2 and the objective lens 3 are disposed in this order from the semiconductor laser 1 side.

As shown in FIG. 2, the hologram lens 2 includes a diffraction hologram 21 disposed at the center, and two reflection holograms 22 as light reflecting means disposed on both sides of the diffraction hologram 21. Are formed on a single plate as an optical member. By the way, FIG.
As shown in the figure, the far field pattern of the emitted light beam 20 of the semiconductor laser 1 has an elliptical shape. The hologram lens 2 includes reflection holograms 22 on both ends in the major axis direction of the elliptical light beam 20 of the semiconductor laser 1.
22 are arranged. The size of the diffraction hologram 21 is substantially the same as the size of the light beam 20 in the minor axis direction. When the elliptical light beam 20 of the semiconductor laser 1 passes through the hologram lens 2, both ends in the long axis direction are shielded by the reflection hologram 22, and converted into a substantially circular beam. ing.

The diffraction hologram 21 can be formed, for example, by a double exposure method in which a photosensitive material is irradiated with object light and reference light. The reflection hologram 22 can be formed by coating a metal thin film on a diffraction grating similarly formed by the double exposure method.

As shown in FIG.
Are two error signal photodetectors (first photodetectors) 5
And two front monitor photodetectors (second photodetectors) 8
In addition, they are provided on the same substrate 7. On the substrate 7, a light emitting portion of the semiconductor laser 1 is disposed at a central portion, and on both sides of the light emitting portion of the semiconductor laser 1 in the X-axis direction, ± 1 order beams from the diffraction hologram 21 are detected. The error signal photodetectors 5 and 5 are respectively arranged at positions a few mm away from the light emitting section of the semiconductor laser 1. On both sides of the light emitting portion of the semiconductor laser 1 in the Y-axis direction, front monitor photodetectors 8, 8 for detecting zero-order beams of the reflection holograms 22, 22 are provided.
Each of them is arranged at a position several mm away from the light emitting section of the semiconductor laser 1. These photodetectors 5 and 8 are made of, for example, the same structure and material as the semiconductor substrate, and are provided with respective electrodes on the upper surface of the semiconductor substrate, the lower surface is a common electrode, the semiconductor laser 1 is forward biased, Units 5 and 8 are reverse biased. The structure of the same substrate 7 on which the semiconductor laser 1, two error signal photodetectors 5 and two front monitor photodetectors 8 are provided is described in JP-A-63-32743. May be used.

FIG. 1A shows an optical system including photodetectors 5 and 5 for error signals, and FIG. 1B shows an optical system including photodetectors 8 and 8 for forward monitoring. ing. From the same substrate 7 provided with the semiconductor laser 1, two error signal photodetectors 5 and two front monitor photodetectors 8,
The components up to the hologram lens 2 are formed in one package 6. The objective lens 3 is held by an actuator (not shown) that can move the objective lens 3 in the optical axis direction and in a direction orthogonal to the optical axis. The actuator including the objective lens 3 is replaceable. The actuator is driven via a drive circuit (not shown) based on the focus and tracking error signals obtained from the error signal photodetectors 5 and 5, whereby focus and tracking control is performed. .

The output of the front monitor photodetector 8 is sent to an APC circuit for automatically adjusting the light emission output of the semiconductor laser 1. Next, the operation of the present embodiment will be described.

As shown in FIG. 1A, a semiconductor laser 1
Is incident on the hologram lens 2, both ends in the long axis direction are reflected by the reflection holograms 22, 22, and the other portions pass through the diffraction hologram 21,
It is converted into a substantially circular beam. When passing through this diffraction hologram 21, the light beam is separated into zero-order and ± 1st-order diffraction beams, and the zero-order beam is incident on the objective lens 3 as it is without being diffracted, and converges on the recording medium 4. I do. The beam reflected by the recording medium 4 passes through the objective lens 3 and again enters the diffraction hologram 21 to generate zero-order and ± 1st-order diffracted beams, and the zero-order beam returns to the semiconductor laser 1. On the other hand, the ± first-order beams are converged on the error signal photodetectors 5 and 5 on the same substrate 7 as the semiconductor laser 1, and are received by the photodetectors 5 and 5 and photoelectrically converted. Then, from the outputs of the photodetectors 5 and 5, a focus and tracking error signal and an information signal are obtained.
The focus and tracking error signals can be obtained by an astigmatism method, a push-pull method, or the like, as shown in, for example, JP-A-63-32743.

On the other hand, as shown in FIG. 1B, the zero-order beams emitted from the semiconductor laser 1 and reflected by the reflection holograms 22, 22 are converged on the forward monitoring photodetectors 8, 8. The light is received by the photodetectors 8, 8 and photoelectrically converted. The output of the photodetector 8 is AP
It is sent to the C circuit, and the light emission output of the semiconductor laser 1 is automatically adjusted.

As described above, according to the present embodiment, a reflection hologram is provided between the semiconductor laser 1 and the objective lens 3 together with the diffraction hologram 21.
By receiving the diffracted light reflected by the light 2 by the front monitor photodetector 8, the front light of the semiconductor laser 1 can be monitored, and APC which is not affected by the back talk noise due to the reflected light can be realized.

Further, since the semiconductor laser 1, the photodetectors 5 and 5 for error signals, and the photodetectors 8 and 8 for forward monitoring are provided on the same substrate 7, all the wirings required on the same substrate 7 are required. The element is arranged, and it is not necessary to take out the signal line from the photodetector 8 from inside the package.
Is easy to assemble.

Since the semiconductor laser 1 and the photodetectors 5 and 8 are arranged on the same substrate 7 and the diffraction hologram 21 and the reflection hologram 22 are provided on a single plate, the configuration is simple. Thus, the size of the optical head 10 can be reduced. In particular, the reflection hologram 22 is
By providing the optical member 1 directly on a single plate, which is an optical member, there is no need to provide another optical member provided with the reflection hologram 22, which can contribute to miniaturization and thinning of the optical head.

FIGS. 4 and 5 relate to a second embodiment of the present invention. FIG. 4 is an explanatory view showing a hologram lens, and FIG. 5 is an explanatory view showing an optical system for monitoring a front light of an optical head.
The optical head 30 of the present embodiment is different from the first embodiment in the configuration of the hologram lens 2.

Hologram lens 2 in this embodiment
As shown in FIG. 4, a circular reflection type hologram 22 of about 1 mm is arranged at the center of the diffraction hologram 21. The grid lines of the reflection hologram 22 are formed so as to be substantially orthogonal (90 degrees) to the grid lines of the diffraction hologram 21. The reflection film of the reflection hologram 22 is coated with a metal thin film.

The size of the diffraction hologram 21 is substantially the same as the size of the light beam 20 emitted from the semiconductor laser 1 in the minor axis direction.
When passing through the hologram lens 2, both ends in the long axis direction are shielded by the frame of the hologram lens 2,
The beam is converted into a substantially circular beam.

In this embodiment, as shown in FIG. 5, the light beam emitted from the semiconductor laser 1 is incident on the hologram lens 2, the light beam irradiated on the diffraction hologram 21 is transmitted, and is located at the center. Light beam (light beam in the central part including the optical axis) applied to the reflective hologram 22
Are reflected to generate zero-order and ± 1st-order beams, the zero-order beam returns to the semiconductor laser 1, and the ± 1st-order beams are converged on the forward monitoring photodetectors 8, 8, and The light is received by the detectors 8, 8 and photoelectrically converted.

The light emitted from the diffraction hologram 21 is converted into a substantially circular beam by shielding both ends of the elliptical beam by the frame of the hologram lens 21. Other configurations, operations, and effects are the same as those of the first embodiment.

FIGS. 6 and 7 relate to a third embodiment of the present invention. FIG. 6 (a) is an explanatory view showing an optical system for detecting an error signal and an information signal of an optical head, and FIG. 6 (b) is an optical system. FIG. 7 is an explanatory diagram showing an optical system for monitoring the front light of the head, and FIG. 7 is an explanatory diagram showing each optical element of the optical head.

The present embodiment is an example of a magneto-optical type optical head for recording and reproducing information on and from a magneto-optical medium. As shown in FIGS. 6A and 6B, the optical head 40
Comprises a semiconductor laser 1 as a light source, and a polarization hologram 47, a half-wave plate 46, a hologram lens 42, and an objective between the semiconductor laser 1 and the magneto-optical medium 44 in order from the semiconductor laser 1 side. A lens 43 is provided. The half-wave plate 46 and the hologram lens 42
Are provided on both end faces of the glass block 48, and the polarization hologram 47 is provided on an end face of the half-wave plate 46.

As shown in FIG. 7, the hologram lens 42 has a circular reflection hologram 22 disposed at the center of the diffraction hologram 21. The grid lines of the reflection hologram 22 are formed so as to be substantially perpendicular to the grid lines of the diffraction hologram 21. The reflection film of the reflection hologram 22 is coated with a metal thin film.

The polarization hologram 47 is provided with a space 47S having a width a of several mm from the center and having no grating formed, that is, having no polarization characteristics. In this polarization hologram 47, the grid lines of the polarization portions 47R and 47L on both sides of the space 47S are symmetrical with respect to the left and right lines, and are 45
It has a degree angle.

The half-wave plates 46, 46 are provided only in the portions corresponding to the polarization portions 47R, 47L of the polarization hologram 47, and the central portion is a space corresponding to the space 47S. . The half-wave plate 4
Nos. 6 and 46 have azimuths set to 22.5 degrees in order to rotate the polarization direction of the incident light by 45 degrees.

As in the first embodiment, the semiconductor laser 1 is provided on the same substrate 7 together with two error signal photodetectors 5 and two front monitor photodetectors 8. Next, the operation of the present embodiment will be described.

As shown in FIG. 6A, the semiconductor laser 1
For example, the P-polarized light beam emitted from the hologram lens passes through the space 47S of the polarization hologram 47 and the space between the half-wave plates 46, 46, enters the hologram lens 42, and irradiates the diffraction hologram 21. The beam is collimated by the diffraction hologram 21 and becomes parallel light. This parallel light is converged on the magneto-optical medium 44 by the objective lens 43. Information is recorded on the magneto-optical medium 44 by upward magnetization and downward magnetization. Accordingly, the P-polarized light incident on the magneto-optical medium 44 is
The polarization plane is rotated by the magneto-optical effect (Kerr effect) according to the magnetization direction of No. 4. For example, assuming that the polarization plane rotates by θ degrees with respect to the upward magnetization, the polarization plane rotates by −θ degrees with respect to the downward magnetization. As described above, the reflected light beam having the S-polarized light component whose polarization plane is rotated passes through the objective lens 43, and is incident on the diffraction hologram 21 again.
Generate a first order diffracted beam. This zero-order beam returns to the semiconductor laser 1. The ± 1st order beam is 1 /
After passing through the two-wavelength plates 46, 46, the light passes through the polarization portions 47R, 47L of the polarization hologram 47, is converged on the error signal photodetectors 5, 5, and is received by the photodetectors 5, 5.
Photoelectric conversion is performed. In FIG. 7, reference numeral 55a denotes the primary light of the diffraction hologram 21, and reference numeral 55b denotes the -1st light of the diffraction hologram 21. The polarization portion 47R,
Since 47L transmits only light in the polarization directions orthogonal to each other, an information signal can be obtained by outputting the output difference between the photodetectors 5 and 5 through a differential amplifier.

On the other hand, as shown in FIG. 6B, a light beam emitted from the semiconductor laser 1 and applied to the reflection type hologram 22 located at the center of the hologram lens 42 (the center light beam including the optical axis) ) Is reflected to generate zero-order and ± first-order beams, the zero-order beam returns to the semiconductor laser 1, and the ± first-order beams are transmitted to the half-wave plate 46,
The light passes through the space between the space 46 and the space 47S of the polarization hologram 47, is converged on the front monitoring photodetectors 8, 8, is received by the photodetectors 8, 8, and is photoelectrically converted. In FIG. 7, reference numeral 58a denotes primary light of the reflection hologram 22, and reference numeral 58b denotes -1st light of the reflection hologram 22.

The half-wave plates 46, 46 are for increasing the apparent Kerr rotation angle and are not always necessary. When the half-wave plates 46 are not provided, the polarization hologram 47 can be directly formed on the end face of the glass block 48 by a beam etching method or a transfer method. The hologram lens 42
May be directly formed on the end face of the glass block 48.

In place of the glass block 48, a plate or block made of a non-linear optical element may be used.
As described above, by forming the hologram lens 42 having the diffraction hologram 21 and the reflection hologram 22 and the polarization hologram 47 on both end surfaces of a plate or a block made of glass or a non-linear optical element, Because alignment can be done by manufacturing process work,
No adjustment is required. Further, since a mechanism for this adjustment is not required, the size of the optical head 40 can be reduced.

Other structures, operations and effects are the same as those of the first embodiment. Instead of the reflection hologram used in the present invention, a microprism may be provided, and the semicircular beam reflected by the microprism may be received by the front monitor photodetector. This microprism has a wedge (wedge) shape with respect to the beam irradiation surface, and is coated with a metal thin film or a dielectric multilayer film.

[0042]

As described above, according to the present invention, a part of the light emitted from the light source is reflected by the reflection hologram, and the reflected light is received by the second photodetector and monitored.
More accurate APC can be realized. In addition, since the reflection hologram for directing a part of the emitted light to the second photodetector is provided directly on the optical member, there is no need to newly provide a space for the reflection hologram, which can contribute to downsizing. .

By using a reflection type hologram,
Since the direction of reflection when reflecting part of the emitted light can be freely set, the second photodetector can be arranged at a position that can contribute to the miniaturization of the optical head, and the optical head can be miniaturized. Can be.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram showing an optical system for detecting an error signal and an information signal of an optical head, and FIG. 1B is an explanatory diagram showing an optical system for monitoring a front of the optical head.

FIG. 2 is an explanatory diagram showing a hologram lens.

FIG. 3 is a plan view of a substrate on which a semiconductor laser and a photodetector are arranged.

FIG. 4 is an explanatory diagram showing a hologram lens.

FIG. 5 is an explanatory diagram showing an optical system for monitoring the front of the optical head.

6A is an explanatory diagram showing an optical system for detecting an error signal and an information signal of the optical head, and FIG. 6B is an explanatory diagram showing an optical system for monitoring the front of the optical head.

FIG. 7 is an explanatory diagram showing each optical element of the optical head.

FIG. 8 is an explanatory view schematically showing an example of a conventional optical head.

FIG. 9 is an explanatory view schematically showing an optical head that separates and monitors a part of the forward light of the semiconductor laser by a half mirror.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 hologram lens 3 objective lens 4 recording medium 5 photodetector for error signal 7 substrate 8 photodetector for front monitor 10 optical head 21 diffraction hologram 22 reflection hologram

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 1-227289 (JP, A) JP-A 63-24132 (JP, A) JP-A 63-127442 (JP, A) JP 60-127 177441 (JP, A) JP-A-63-84184 (JP, A) JP-A-1-270382 (JP, A) JP-A-2-265036 (JP, A) JP-A-63-259847 (JP, A) JP-A-1-88926 (JP, A) JP-A-1-94541 (JP, A) JP-A-1-303639 (JP, A) JP-A-1-3131396 (JP, A) (58) (Int.Cl. ⁷ , DB name) G11B ^7/ 12-7/22 G11B 11/10 551 H01S 3/18

Claims (2)

(57) [Claims] An optical member having a hologram for diffracting reflected light from the recording medium and directing the reflected light from the recording medium in a direction different from the light source; and the hologram. An optical head comprising: a first photodetector that receives light diffracted by the first light detector; and a second photodetector that receives a part of light emitted from the light source. And a second photodetector are provided on the same substrate, and a reflection hologram that reflects a part of light emitted from the light source and guides the reflected light to the second photodetector is provided directly on the optical member. An optical head characterized in that: 2. An optical head according to claim 1, wherein said reflection hologram reflects a center including an optical axis of said outgoing light.