JPH04319543A - Optical information recording/reproducing device - Google Patents

Abstract

PURPOSE:To obtain the optical information recording/reproducing device provided with an optical pickup of a waveguide type for reducing a shift of a condensing point caused by a fluctuation of light source wavelength, and the influence exerted on a focus error signal by placing in parallel two pairs of waveguide mirrors of the same type. CONSTITUTION:An emitted light from a light source is condensed to an optical information recording medium through an optical system, and a reflected return light from the optical information recording medium is coupled to an optical waveguide layer 8 by a coupler 3. The coupled luminous flux is propagated into the optical waveguide layer 8, made incident on two waveguide concave mirrors 13a, 13b of the same type placed in parallel and divided into two. Subsequently, two luminous fluxes reflected and focused by the concave mirrors 13a, 13b are made incident on waveguide convex mirrors 14a, 14b and reflected, and photodetected by photodetectors 11a, 11b and 11c, 11d provided in a substrate 10. Accordingly, a shift of a condensing point caused by a fluctuation of light source wavelength and the influence exerted on a focus error signal are reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording/reproducing apparatus, and more particularly to an optical information recording/reproducing apparatus equipped with a waveguide type optical pickup.

0002

2. Description of the Related Art Conventionally, optical information recording and reproducing apparatuses have been put into practical use that use optical information recording media such as optical disks and magneto-optical disks as information recording media for image signals, audio signals, etc. As an optical pickup, one using an optical waveguide (waveguide element) has been proposed (for example, Japanese Patent Laid-Open No. 63-61430). Here, FIG. 5 shows an example of an optical pickup using a conventional optical waveguide, and this conventional technique will be explained below. In FIG. 5, emitted light 115 from a light source 116 passes through a collimator lens 117 , transmits through a transparent substrate 123 , passes through an objective lens 118 , and is focused on a recording medium surface 114 on an optical disk 113 . Then, recording medium side 1
The reflected return light 115' from 14 returns to the objective lens 11.
8 and enters the two-part condensing grating couplers 131 and 132 on the transparent substrate 123 , and is coupled to the optical waveguide layer 122 on the transparent substrate 123 by diffraction. The process after this combination will be explained with reference to FIG. In FIG. 7, the condensing grating coupler 131,1
The two beams 115' in the optical waveguide layer 122 that are divided into two parts and focused by the photodiode PD
The light is condensed at the center of a photodetector 124 consisting of photodiodes PD3 and PD2, and a photodetector 125 consisting of photodiodes PD3 and PD4, respectively. Then, photodiodes PD1, PD2, and P constituting each photodetector
When the optical outputs of D3 and PD4 are A, B, C, and D, respectively, the focus error signal ΔF is given by ΔF=(A+D)−(B+C), and the tracking error signal ΔT is given by ΔT=(A
+B)-(C+D), and the recording signal S is given as S=A+B+C+D. Next, FIG. 6 shows another example of an optical pickup according to the prior art, and the optical pickup shown in FIG. 7 is an example in which an opaque semiconductor substrate 150 is used instead of the transparent substrate 123 of FIG. , in this case,
The emitted light 115 from the light source 116 passes through the collimating lens 117 and then passes through the optical waveguide layer 122 and the substrate 150.
This is different from the example shown in FIG. However, the other configuration is shown in Figure 5.
This is the same as shown in .

0003

[Problems to be Solved by the Invention] By the way, in the optical pickup according to the above-mentioned prior art, the optical waveguide layer 122
Convergence of the light coupled to is performed by condensing grating couplers 131 and 132. For this reason, the focal position of the light beam changes greatly due to wavelength fluctuations of the light source 116, making it impossible to detect a focus error signal. Moreover, since the condensing grating couplers 131 and 132 serve as both a waveguide coupler and a condensing optical system for the waveguide, the degree of freedom in arranging the optical system is small. The present invention has been made in view of the above circumstances, and is an optical information recording and reproducing device equipped with a waveguide type optical pickup having a focal position detection means that is less affected by wavelength fluctuations of a light source and operates stably. The purpose is to provide

0004

[Means for Solving the Problems] In order to achieve the above object, an optical information recording/reproducing apparatus according to the invention as set forth in claim 1 includes a light source and an optical system that focuses light from the light source onto an optical information recording medium. , a coupler that couples the reflected return light from the optical information recording medium to the optical waveguide, an optical waveguide, two pairs of waveguide mirrors that focus the guided light from the coupler, and two pairs of waveguide mirrors. The two pairs of waveguide mirrors are of the same type and are arranged in parallel, and the coupler, the optical waveguide,
A feature is that the waveguide mirror and the photodetector are integrally formed on the substrate. Furthermore, the invention according to claim 2 is as follows:
The optical information recording and reproducing apparatus described above is characterized in that a focal position detection signal, a tracking error signal, and a recording signal are simultaneously detected by two pairs of waveguide mirrors and a photodetector.

[0005]

[Operation] In the optical information recording/reproducing device of the present invention, the light emitted from the light source is focused on the optical information recording medium via the optical system, and the reflected return light from the optical information recording medium is coupled to the optical waveguide by the coupler. be done. The guided light from the coupler is divided into two parts and focused by two pairs of waveguide mirrors of the same type and arranged in parallel, and each light is received by a photodetector. Therefore, in the optical information recording and reproducing apparatus of the present invention, the shift of the focal point due to fluctuations in the light source wavelength and its influence on the focus error signal are reduced compared to the case where the conventional condensing grating coupler is used. Ru.

[0006] Incidentally, the light emitted from the light source is focused on an optical information recording medium via an optical system, and the reflected return light from the optical information recording medium is coupled to an optical waveguide by a coupler. The present inventors have already proposed a technique for condensing light into two parts using a set of waveguide optical systems, receiving the light using two sets of photodetectors, and detecting a focus error signal, a tracking error signal, and a recording signal. (For example, Japanese Patent Application Hei 2-17
No. 6728), in this prior art, two sets of waveguide optical systems are arranged symmetrically with respect to the center, so the positional shift during the fabrication of the waveguide optical system occurs symmetrically, so the focal position shift due to this is also contrasting. This will occur. Therefore, the distance between the focal positions of the two light beams changes greatly due to the positional shift of the waveguide optical system, and an offset may occur when detecting the focus error signal. On the other hand, in the present invention, two pairs of waveguide mirrors are of the same type and arranged in parallel as a waveguide optical system, so the change in the focal distance of the two light beams caused by the error in the manufacturing position of the waveguide mirrors However, it is difficult to change compared to the center-symmetrical optical system arrangement of the prior art. Therefore, the offset when detecting the focus error signal is smaller than in the prior art, and the tolerance for manufacturing position errors can be increased.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 3 are a plan view and a side view of an optical pickup showing a first embodiment of the present invention. In FIGS. 1 and 3, light emitted from a light source 1 is converted into parallel light by a collimating lens 2, and enters a trapezoidal prism coupler 3. The light reflected from the bottom surface of the prism coupler 3 is focused by an objective lens 4 onto a recording medium layer 6 of an optical disk 5, which is an optical information recording medium. Then, the reflected return light from the recording medium layer 6 passes through the objective lens 4 again and enters the trapezoidal prism coupler 3 again. Here, a part of the returned light passes through the gap layer 7 and is coupled to the optical waveguide layer 8 . The combined light beam propagates through the optical waveguide layer 8, enters two waveguide concave mirrors 13a and 13b arranged in parallel, and is split into two. The two light beams reflected and focused by the waveguide concave mirrors 13a and 13b are then reflected by the waveguide convex mirrors 14a and 13b.
14b and are reflected, and are received by photodetectors 11a, 11b and 11c, 11d provided in substrate 10. The optical elements of the photodetectors 11a, 11b and the photodetectors 11c, 11d are arranged so that the light beams are converged in the middle when in focus.

Here, as the light source 1, a semiconductor laser,
It is desirable to use various solid-state and gas lasers, SHG light sources, LEDs, and other devices with good spatial coherence and temporal coherence. Further, although the collimating lens 2 and the objective lens 4 are normal lenses, they may be an aspheric lens, a Fresnel lens, a distributed refractive index lens, other lenses, or a combination thereof. Furthermore, although the prism coupler 3 is a trapezoidal prism coupler, it may also be a triangular prism coupler. As for the waveguide element 12, a semiconductor substrate such as Si or GaAs is used as the substrate 10. However, other organic materials such as glass, ceramics, dielectric crystals, plastics, and resins can be considered. The optical waveguide layer 8 and the buffer layer 9 are made of a material transparent to the light source wavelength by methods such as vapor deposition, sputtering, CVD, coating, oxidation, and diffusion, and the refractive index of the buffer layer 9 is the same as the optical waveguide. It needs to be lower than layer 8. Furthermore, if the substrate 10 is made of a transparent material, or if loss due to absorption by the substrate 10 is not considered, the buffer layer 9 is not necessary. The gap layer 7 may be filled with an air layer or other transparent material, but its refractive index must be lower than that of the trapezoidal prism coupler 3 and the optical waveguide layer 8. Further, the refractive index of the trapezoidal prism coupler 3 needs to be higher than the refractive index of the optical waveguide layer 8. Furthermore, a grating coupler can be used in place of the trapezoidal prism coupler.

Next, for the waveguide concave mirrors 13a, 13b and the waveguide convex mirrors 14a, 14b, only the optical waveguide layer 8 or part of the buffer layer 9 is removed by dry or wet etching, cutting, ion sealing, etc. It can be formed by removing the entire portion, or by diffusing a low refractive index material. In addition, when forming by removing, even if the end face is in direct contact with the air layer, the end face may be coated with a high reflectance metal or the like, or may be filled with a low refractive index material. Also, Figure 3
Now, the waveguide concave mirrors 13a and 13b and the waveguide convex mirror 1
The end faces of 4a and 14b are perpendicular to the optical waveguide layer 8, but may be oblique or tapered laterally. Moreover, the photodetectors 11a, 11b and 11c,
Regarding 11d, an example of a photodiode manufactured by impurity diffusion, ion implantation, etc. is shown, but this may also be a Schottky type photodiode. In addition, the substrate 10
If the substrate is not a semiconductor substrate, an α-Si photodiode or the like can be applied.

Next, as is clear from FIG. 1, in the configuration of the present invention, the two pairs of waveguide mirrors are of the same type and are arranged in parallel, that is, one pair of waveguide concave mirror 13a A feature is that the positional relationship with the waveguide convex mirror 14a is equal to the positional relationship with the waveguide concave mirror 13b and the waveguide convex mirror 14b of the other set. Therefore, if the incident light beam to each waveguide mirror is a parallel light beam, there are two sets of the same optical system, and changes in light focusing performance due to manufacturing errors such as etching will occur in the same way for the two sets. It has the characteristic that the distance between the focal points of the light beam does not easily change.

Next, various signal detection methods using the optical pickup having the above configuration will be described. First, as shown in FIG. The two luminous fluxes are detected by the photodetector 11.
a, 11b and 11c, 11d, a trapezoidal prism coupler 3, a waveguide concave mirror 13a
, 13b, waveguide convex mirrors 14a, 14b, and photodetectors 11a, 11b, 11c, 11d are arranged. Here, when the recording medium layer 6 of the optical disk 5 moves away from the focus position of the objective lens 4 with respect to the objective lens 4, the light beam incident on the waveguide element 12 becomes almost convergent, and the waveguide concave mirrors 13a, 13b and the guide Wave path convex mirror 14a
, 14b in the optical waveguide layer 8 are located in front of the photodetectors 11a, 11b, 11c, and 11d. Here, the photodetectors 11a, 11b and 11
Letting the optical outputs of c and 11d be A, B, C, and D, respectively, B>A and C>D. Therefore, when the focus error signal ΔF is set as ΔF=(A+D)−(B+C), ΔF<0. Further, when the recording medium layer 6 approaches the objective lens 4 side from the focal position of the objective lens 4, the light beam incident on the waveguide element 12 becomes almost divergent, and the waveguide concave mirrors 13a, 13b
The focal positions of the two light beams in the optical waveguide layer 8 separated by the waveguide convex mirrors 14a and 14b are located at the photodetectors 11a and 11b.
, 11c, 11d, and A>B and D
>C. Therefore, the focus error signal becomes ΔF>0. Further, at the time of focusing shown in FIG. 1, the adjustment is made so that A=B and C=D, so ΔF=0. Therefore, the positive/negative of ΔF is detected by a circuit similar to that shown in FIG. 7, this is fed back to the control device, and the position of the objective lens 4 is adjusted by an actuator (not shown) so that ΔF=0. Alternatively, autofocusing becomes possible by adjusting the position of the entire optical pickup using an actuator (not shown).

Next, the tracking error signal ΔT is expressed as ΔT
= (A+B) - (C+D) Then, the positive or negative of ΔT is detected by the push-pull method, etc., this is fed back to the control device, and the objective lens 4 or the entire optical pickup is controlled by the actuator (Fig. (not shown) etc., auto-tracking becomes possible. Next, the recording signal S is
It can be detected by setting S=A+B+C+D.

The signal detection method has been explained above, but as mentioned above, in the present invention, two sets of waveguide optical systems of the same type (waveguide concave mirrors 13a and 13b and waveguide convex mirror 1) are used.
4a and 14b) are arranged in parallel, the deviation due to manufacturing errors in the focal positions of the two light beams is considered to be approximately the same degree and in the same direction because they are the same optical system, and the manufacturing error in the distance between the focal points of the two light beams is considered to be the same. It is thought that there is little change due to For this reason,
Offset when focusing when detecting focus error signal (
(origin position deviation error) can be reduced. Next, to describe the features of this embodiment, in this embodiment, waveguide concave mirrors 13a and 13b are used as the first mirror, and waveguide convex mirrors 14a and 14b are used as the second mirror, so that the optical system is has a telephoto configuration in which the focal length is longer than the distance from the optical system to the focal position. Therefore, since the focal length can be long relative to the length of the optical system, the focus position detection sensitivity can be increased when compared with an optical system of the same size and conventional configuration using the same objective lens.

Next, a second embodiment of the present invention will be explained. Here, FIGS. 2 and 4 are a plan view and a side view of an optical pickup showing a second embodiment of the present invention. The planar configuration shown in FIG. 2 is similar to that shown in FIG. 1, but in the case of this embodiment, the waveguide convex mirrors 13a' and 13b' are arranged first, and then the waveguide concave mirrors 14a' and 14b' are arranged. are doing. This configuration is effective in reducing coma aberration, has little change in the incident angle of the focal spot diameter, and can detect the focus error signal more stably. Note that, as in FIG. 1, this is a combination of two sets of waveguide mirrors of the same type. others,
In this embodiment, a grating coupler 3' is used instead of the trapezoidal prism coupler shown in FIGS. 1 and 3.

Further, as shown in FIG. 4, a transparent substrate is used as the substrate 10, and the light from the light source 1 is collimated into a parallel beam by the collimating lens 2, and then is passed through the waveguide element 12 from the bottom of the substrate 10. , and is focused onto the recording medium 6 of the optical disk 5 by the objective lens 4. Then, the reflected return light from the recording medium 6 is coupled to the optical waveguide layer 8 by the grating coupler 3'. In addition, the photodetectors 11a, 11
As b, 11c, and 11d, loaded α-Si photodiodes are used. Incidentally, in the case of this embodiment, the gap layer 7 and the buffer layer 9 are not necessary. Further, various signal detection methods are the same as those in the embodiments shown in FIGS. 1 and 3, and the manufacturing method of each element is also the same. Regarding the grating coupler 3', although the illustrated example shows an example of an evenly spaced loading type, it may have an unevenly spaced curved shape, and a blaze type and volume phase type are also applicable.

Although waveguide convex mirrors (13a', 13b' or 14a, 14b) are used in each of the embodiments shown in FIGS. 1 and 2, in reality these are straight waveguide mirrors (waveguide plane mirrors). ), or these may be used as waveguide concave mirrors. That is, the two pairs of waveguide mirrors may be concave waveguide mirrors, or one of the pair may be a straight waveguide mirror. Furthermore, the photodetectors 11a, 11b and 11
Although c and 11d are two parallel-type photodiodes, one may be arranged so as to block the light flux, and the other may receive the remaining light flux. However, it is desirable that the two sets have the same arrangement.

[0017]

As explained above, in the optical information recording and reproducing apparatus according to claim 1, the light emitted from the light source is focused on the optical information recording medium through the optical system, and the light emitted from the optical information recording medium is The reflected return light is coupled to the optical waveguide by a coupler, and the guided light from the coupler is divided into two parts and focused by two pairs of waveguide mirrors of the same type and arranged in parallel, and each light is received by a photodetector. Because of its configuration, compared to the case of using conventional focusing grating couplers, it is possible to reduce the shift of the focusing point due to fluctuations in the light source wavelength and its effect on the focus error signal, and it is expected to reduce signal noise. . In addition, because the waveguide optical system has a configuration in which two pairs of waveguide mirrors are of the same type and are arranged in parallel, changes in the focal length of the two light beams caused by errors in the manufacturing position of the waveguide mirrors may occur in the prior patent application mentioned above. It is less likely to change compared to the center-symmetrical optical system arrangement like the technology, and therefore the offset when detecting the focus error signal is smaller than the prior technology, allowing for greater tolerance for errors in the manufacturing position. The cost of the device can be reduced. Furthermore, since the coupler, optical waveguide, waveguide mirror, and photodetector are integrally formed on the substrate, the optical pickup section can be made more compact. In addition, as in the invention as claimed in claim 2, if the focal position detection signal, the tracking error signal, and the recording signal can be detected simultaneously by the two pairs of waveguide mirrors and the photodetector, it is possible to reduce the It is possible to realize an optical information recording and reproducing device that includes an optical pickup with noise and an optical pickup that has a high tolerance to manufacturing errors and can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an optical pickup showing a first embodiment of the present invention.

FIG. 2 is a plan view of an optical pickup showing a second embodiment of the invention.

FIG. 3 is a side view of an optical pickup showing a first embodiment of the present invention.

FIG. 4 is a side view of an optical pickup showing a second embodiment of the present invention.

FIG. 5 is a side view of an optical pickup showing an example of the prior art.

FIG. 6 is a side view of an optical pickup showing another example of the prior art.

FIG. 7 is a schematic diagram showing an example of a planar configuration of a waveguide element section of an optical pickup and an example of a signal detection circuit according to the prior art.

[Explanation of symbols]

1... Light source 2... Collimating lens 3... Prism coupler 3'... Grating coupler 4... Objective lens 5... Optical disc 6... Recording medium layer 8... Optical waveguide layer 10 ... Waveguide elements 11a, 11b, 11c, 11d ... Photodetector 12
···substrate

Claims (2)

[Claims] Claim 1: A light source, an optical system that focuses light from the light source onto an optical information recording medium, a coupler that couples reflected return light from the optical information recording medium to an optical waveguide, an optical waveguide, and a coupler. two pairs of waveguide mirrors that focus the guided light of;
an optical pickup having a photodetector that receives light from each pair of waveguide mirrors; the two pairs of waveguide mirrors are of the same type and are arranged in parallel; An optical information recording/reproducing device characterized in that a waveguide, a waveguide mirror, and a photodetector are integrally formed on a substrate. 2. The optical information recording and reproducing apparatus according to claim 1, wherein a focus position detection signal, a tracking error signal, and a recording signal are simultaneously detected by two pairs of waveguide mirrors and a photodetector. An optical information recording/reproducing device characterized by: