JPS62275332A - Optical head - Google Patents

Abstract

PURPOSE:To detect diffracted laser light reflected by the surface of an optical recording medium with high signal sensitivity despite the large floating value of an optical head, by providing a waveguide type microlens having an aperture larger than that of a laser light emitting path of a semiconductor laser part at the tip of this laser part or the side of said light emitting path. CONSTITUTION:A lens layer 15 (SiN) serving as a dielectric material having a higher refractive index the that of a waveguide layer 13 is laminated on the upper surface of the layer 13 and then etched by a dry etching process to form a Luneburg lens 16. This lens 16 has a circular periphery and a hemispherical surface together with an aperture larger than that of a laser output end of a semiconductor laser part 8A. The focal distance of the lens 16 is set so that the focal point of one side is set on the surface of an optical recording medium 40 with the focal point of other side set at the end face of the laser output of the part 8A. Thus it is possible to form a beam spot on the upper surface of the medium 40 with no aberration or to condense the reflected and diffracted light on the photodetecting parts 8B and 8C.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention <Industrial Application> The present invention uses a semiconductor laser to record information or record information on an optical recording medium such as an optical disk in a non-contact manner. In order to improve the reproducing optical head, the laser beam emitted from the semiconductor laser is reduced in spread due to the diffraction phenomenon due to the aperture of the laser beam output edge, and the signal reception sensitivity of the reflected diffracted light from the surface of the optical recording medium is reduced. The present invention aims to provide an optical head that can improve the performance.

TECHNICAL BACKGROUND An example of this type of optical head was previously proposed by the applicant of the present invention in Japanese Patent Application No. 186406/1983. The optical head proposed in Japanese Patent Application No. 59-186406 has a lower cladding layer 2, an active layer 3, and an upper cladding layer formed on the same semiconductor substrate 1 by liquid phase or vapor phase growth, as shown in FIG. Insulating grooves 5 are formed on both sides of the obtained semiconductor wafer except for the center part, from the top surface of the semiconductor wafer to a position slightly deeper than the bottom surface of the active layer 3, and the semiconductor wafers on both sides of the insulating grooves are photodetected. An optical head 30A integrally formed with parts 8B and 8C, and a semiconductor wafer in the central part as a semiconductor laser part 8A.
An upper electrode 9 is formed on the upper surface of the semiconductor laser section 8A.
3. Here, photodetecting electrodes 9a and 9b are provided on the upper surfaces of photodetecting sections 8B and 8C, respectively, and a common electric field 1) is provided on the opposite side of the semiconductor substrate 1 from these electric fields.

When using this optical head 30A in an optical disk device,
1) As shown in the figure, a gimbal spring (gi+mb
al) It is used by being set on the floating slider 33 attached to the slider 32. That is, the optical disc 40 floats close to a certain position on the optical disc 40 due to a pressure change in the air flow between the optical disc 40 and the optical disc 30A caused by the rotation of the optical disc 40, and the laser beam 21 emitted from the semiconductor laser section 8A is caused to fly onto the optical disc 40. The light is reflected and diffracted by the track guide groove (not shown), and the light receiving surface 3a of the light detecting portions 8B and 8C
, 3b, and a tracking error signal is obtained from the difference signal between the two, and a data signal is obtained from the sum signal.

<Problems to be Solved by the Invention> However, since the aperture of the laser beam emitting portion of the semiconductor laser portion of the optical head 30A having the above-described structure is minute with a thickness of 0.1 μm and a width of 1 μm, the emitted laser beam 21 spreads due to the diffraction phenomenon, and the spread of the laser light reflected and diffracted from the optical disk 40 surface becomes even larger.
The light intensity of the light receiving surfaces of B and 8C was weak, and the signal receiving sensitivity was significantly reduced. In order to eliminate such drawbacks, it is desirable to levitate the optical head as close to the optical disk surface as possible, but as the flying height becomes smaller, the distance from the optical disk 40 surface in the photodetectors 8B and 8C reflected diffraction laser beam 22 a, 22
It is necessary to bring the light receiving position of b closer to the laser beam emission opening, and the distance between the semiconductor laser section 8A and the light detection sections 8B and 8C @
d must be brought closer. For this reason, the width of the groove 5 must be set to 1 μm or more, and there are manufacturing difficulties such as the need for ultra-fine processing technology.

Furthermore, when the flying height is reduced, the probability of head crash increases, leading to a problem that significantly reduces the reliability of the optical disk device.

The present invention was made in order to eliminate such drawbacks in conventional optical heads using semiconductor lasers, and it reduces the spread of laser light emitted from the semiconductor laser as much as possible, and allows the laser light to be emitted from the optical recording medium surface. The purpose of this invention is to reduce the spread of the reflected diffraction laser beam, increase the intensity of the light received by the photodetector, and provide an optical head with excellent No. 48 light receiving sensitivity.

Another object of the present invention is to provide an optical head that can detect reflected and diffracted laser light from the surface of an optical recording medium with high signal sensitivity even if the flying height of the optical head is large.

Additionally, the present invention can cause head crashes during recording and playback.
The object of the present invention is to provide an optical head that is free from the risk of scratches.

Further, the present invention aims to provide an optical head having a structure that can be easily manufactured.

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have conducted various studies, and as a result, they have decided to use waveguide-type microlenses proposed for optical integrated circuits in optical heads. It has been found that it is possible to reduce the laser beam spot emitted from the semiconductor laser section of the laser beam onto the surface of the optical recording medium, and to efficiently receive the reflected diffracted light on the light receiving surface of the photodetector section. Waveguide-type microlenses are described, for example, in the academic journal "Applied Opt, 1cs" published by the American Physical Society, Vol. 13 (1974), p. 391,
The paper “Thin-Film Laser for Optical Fiber Couplers” reported by Mr. Boivin (English title: Thin-F
ilm La5er-to-Fiber Couple
er) In J, an aberration-free collimating type mode index lens (mode 1ndexlense)
states that the lens curve is parabolic and has no spherical aberration.

In addition, the academic journal “Journal of Optical Society of America” published by the Optical Society of America (English title: Journal of Optic
al 5ociety of As+area) J
Volume 67 (1977) Page 1004 t (8iT, l
f, H.

A paper reported by Mr. 5outh＊e l I “Analysis of homogeneous leading waveguide lens (English title: InhowlI
Geneous Optical Waveguide
In Lense Analysis) J, the Luneburg lens also has no spherical aberration, and the shape of the lens layer changes smoothly in the m-field, so there is no scattering or conversion in the guided light mode. I'm giving an explanation.

Based on the knowledge of the prior art, the present invention reduces the spread of the emitted laser light by providing a waveguide-shaped microlens at the tip of the semiconductor laser section of the optical head on the side of the laser light emission path, thereby reducing the spread of the emitted laser light and improving the optical recording medium surface. The reflected and diffracted light from the photodetector is designed to have high intensity and efficiency.

That is, the optical head according to the present invention includes a semiconductor laser section on a semiconductor substrate, and a photodetector section integrally formed with the semiconductor laser section on at least one side of the semiconductor laser section via an insulating groove. The head is characterized in that a waveguide-shaped microlens having a larger diameter than the diameter of the laser light output path of the semiconductor laser section is disposed at the tip of the semiconductor laser section on the side of the laser light output path.

The optical head of the present invention may have a structure in which a photodetecting section is provided on both sides of the semiconductor laser section through an insulating groove, or a photodetecting section may be provided on only one side of the semiconductor laser section via an insulating groove. It may be a configuration.

In the optical head of this OJI, a step index type mode index lens may be used as the guide type microlens.

In addition, in the optical head of the present invention, when a Lunebourg lens is used as the waveguide microlens, there is no spherical aberration (and the shape of the lens layer changes smoothly at the boundary, so there is no scattering in the leading wave mode). It is possible to collect light without any need for light.

Furthermore, when an aberration-free collimated mode index lens is used as the waveguide microlens of the optical head of the present invention, the lens curved surface is parabolic, so light can be focused without causing spherical aberration.

Furthermore, when the optical head of the present invention uses a Bragg type grating lens as the waveguide type microlens, it is possible to prevent the reflected and diffracted light from returning to the output end face of the semiconductor laser section, and to prevent the reflected and diffracted light from returning to the output end face of the semiconductor laser section. Light gathering performance can be improved.

As described above, in the optical head of the present invention, a waveguide-shaped microlens having a diameter larger than the diameter of the laser beam output/input path is disposed at the tip of the semiconductor laser section on the side of the laser beam output path. ,
The spread of the laser light emitted from the semiconductor laser section is reduced, and the beam spot on the surface of the optical recording medium can be narrowed down.

Therefore, the spread of reflection and diffraction from the surface of the optical recording medium is small, and since the light is focused on the photodetector through the waveguide microlens, the light can be focused with high intensity and efficiency, making it possible to extremely high signal sensitivity. .

Example of implementation Next, typical embodiments of the present invention will be described.

Embodiment 1 (1) Structure FIG. 1 is a perspective view showing the schematic structure of a first embodiment of the optical head of the present invention. This optical head 30B is a step type G
a Lower cladding N2 (n-
Ga AlAs layer), active R3 (n -Ga Aj A
s J! l) and cladding tank 4 (P-GaAJA
srfJ) are sequentially stacked and separated by an insulating groove 5.

It has photodetecting parts 8B and 8Ce, and a stripe (stripe) electrode 9a is provided on the upper surface of the semiconductor laser part 8A.

Electrodes 9b and 9c are provided on the entire upper surface of the photodetectors 8B and 8C, and a buffer f.12 (2 layers of Si) and a waveguide layer 13 (2 layers of Si-N or S502) are provided on the low base of the step-type GaAs substrate 1m. ) and a Luneburg lens 1G made of a dielectric material with a higher refractive index than the waveguide layer 13.

0 Manufacturing method The optical head 30B is made of a flat GaAs prepared in advance.
On the upper surface of the substrate 1a, n Ga kl As/IL2, - P - Ga AI As layer 3, P - Ga Aj Ax are formed by vapor phase growth (or liquid phase growth).
After the layers 4 are sequentially laminated, a stripe electrode is provided on the upper surface of the central portion of the formed semiconductor wafer, and photodetecting electrodes 9b and 9c are provided on the upper surface of the semiconductor wafers on both sides.

Thereafter, insulating grooves 5 are further formed from both upper surfaces of the central semiconductor wafer to a depth slightly exceeding the bottom of the active layer 3 (P-Ga Aj As, n 3 ). The depth of W5 is preferably as deep as possible. ), a semiconductor laser section 8A, and photodetector sections 8B and 8C were formed.

The obtained semiconductor laser section 8A, photodetector section 8B, 8
AZ resist film 1 is placed on the upper surface of C as shown in FIG.
4 coating makes the semiconductor laser part 8A and the photodetector part 8B
,8CQv,.

The upper surface of the unmasked side of the King 1 GaAs substrate 1a is etched by dry etching to a level deeper than the insulating groove 5 on the masking side described above.

After that, this etched GaAs substrate 1fi
Buffer layer 1 is formed on the top surface by CVD (chemical vapor deposition).
2 (8102N), the waveguide layer 13 (Si-N) is formed to the same height as the upper part of the active layer 3 on the masking side described above.

After that, a lens layer 15 (SiN) as a dielectric material having a higher refractive index than the waveguide layer 13 is laminated on the upper surface of the waveguide layer 13 (see FIG. As shown in Figure 1, a Lunebourg lens 16 having a larger aperture than the laser output end aperture of the semiconductor laser section 8A, a circular circumference, and a semicircular surface was formed.

After that, the AZ resist film 14 is removed, and the Ga A
A common electrode 1) was provided on the lower surface side of the s-substrate 1a.

The obtained Luneburg lens 16, as shown in FIG.
It is a lens with a centrally symmetrical refractive index portion, and has the property of being able to form a point image on the circumference of one of two concentric circles onto a point on the other circumference without aberration, as shown in Figure 3. If the laser output of the semiconductor laser unit is formed to have a focal length such that one focal point is placed on the surface of the optical recording medium 40 and the other focal point is placed on the end surface, the upper surface of the optical recording medium 40 can be formed without aberration. It is possible to create a beam spot, and to focus the reflected and diffracted light onto the photodetectors 8B and 8C.

Embodiment 2 FIG. 5 is a plan view showing the configuration of an optical head 30B according to a second embodiment of the present invention.

This optical head 30G was manufactured using the same structure and method as in Example 1, except that the waveguide-type microlens provided at the tip of the laser emission path of the semiconductor laser section 8A was constructed with an aberration-free collimating lens 17.

The lens surface of this aberration-free collimating lens 7 has a parabolic lens surface, and has the ability to image parallel light incident on the lens 17 without aberration, as shown in FIG.

Example 3 An optical head 30D according to a third example of the present invention had a configuration as shown in FIG.

This optical head 30D was fabricated using the same laminated structure and fabrication method as in Example 1, except that the step type mode index lens 18 was used as the waveguide type microlens provided at the tip of the laser input/output path of the semiconductor laser section 8A. It was done.

This step type mode index lens 18 is similar to a normal convex lens - one surface is flat and the other surface is a convex (or biconvex) spherical surface, and the incident laser beam is directed to one point (for example, the 40th surface of the optical recording medium). can be focused on.

Therefore, by forming one focal point of the lens 18 to be located on the laser output end face and the other focal point to be located on a predetermined optical recording medium surface, reflected and diffracted light can be efficiently received on the photodetectors 8B and 8C. Be able to do that.

Embodiment 4 As shown in FIG. 8, an optical head 30E according to a fourth embodiment of the present invention has a laser beam emitting path of a semiconductor laser section 8A.
A Bragg type grating lens 19 having a large aperture approximately equal to the width of the photodetecting sections 8B, 8C and the semiconductor laser section 8A was arranged so that its focal point was located on the optical recording medium surface and the laser output end surface. It is something.

This optical head 30E has the following features except that a Bragg type grating lens 19 is used as a waveguide type microlens.
It was manufactured using the same laminated structure and manufacturing method as in Example-1.

As shown in FIG. 9, this black type grating lens 19 is arranged so that the grating lines of each grating lens form a parabola group with the "0 point" as the focal point, and the grating lines of each grating lens are arranged in the traveling direction of the incident light. When a guided plane wave traveling in the X direction is incident on this lens 19, it undergoes Bragg diffraction and converges to the "0 point." A black-type grating lens can theoretically achieve a diffraction efficiency of 100% by appropriately selecting the lens thickness L.

In the above embodiments, the waveguide microlens is a Lunebourg lens, an aberration-free collimating lens,
Although the step type mode index lens and Bragg type grating lens are illustrated, the examples are not limited to these.
For example, a Fresnel zone lens can also be used.

In addition, GaAs is used as a material for forming the optical head.

Although Ga Aj As and the like have been exemplified, the present invention is not limited to these materials, and other semiconductor materials can be used.

Optical head 30B obtained as described above.

30G, 30D, and 30E are used for recording on or recording/reproducing optical recording media, such as optical discs.
When using the device as shown in the figure, the gimbal spring 3
The photodetectors 8B and 8C are mounted on the floating slider 33 provided in
The optical disc 40 is mounted so that the direction of the tracks is perpendicular to the direction of the tracks on the optical disc 40.

If the above waveguide-type microlens is used at the tip of the laser beam output path of the optical head, the emitted laser beam is a Gaussian beam, and if there is a beam waist on the focal length, the beam will be placed on the opposite focal length. Wes! Since the beam waist is formed exactly on the surface of the recording medium, theoretically, the spot diameter becomes the minimum and the light intensity becomes the maximum. On the other hand, since the reflected diffraction light is focused by the lens, the intensity of the light returned to the photodetector is strong, improving the signal reception efficiency, and after passing through the lens, it follows a line parallel to the emitted laser light, so it can be used as a semiconductor laser. Since the distance fid between the part and the photodetecting part can be sufficiently wide, the processing of the insulating groove 5 becomes easy. Further, by setting the focal length f to several tens of micrometers to several hundred micrometers, the flying height of the head can be increased, thereby eliminating the problem of head flash (and improving reliability significantly).

<Effects of the Invention> As is clear from the above description, the optical head according to the present invention has a waveguide-shaped microlens integrally formed at the tip of the laser light emission path of the semiconductor laser section, and the waveguide shape Since the aperture of the microlens is made larger than the aperture of the laser beam exit path, the spot diameter of the emitted laser beam formed on the optical recording medium surface is much smaller, and the reflected diffracted light is Since the light passes through the waveguide microlens again, the light can be efficiently focused on the light receiving surface of the photodetector with high light intensity, resulting in extremely high signal sensitivity.

Further, since the optical head of the present invention can be integrally formed on a predetermined semiconductor substrate through a series of steps, manufacturing can be extremely simple.

[Brief explanation of drawings]

1 is a perspective view showing a schematic configuration of an optical head according to a first embodiment of the present invention; FIG. 2 is a process diagram showing a procedure for manufacturing the optical head of FIG. 3 is a plan view of the optical head of FIG. 1, FIG. 4 is an explanatory diagram showing the recent bundle state of the Luneburg lens used in the optical head of FIG. 1, and FIG. 5 is a second embodiment of the present invention. FIG. 6 is an explanatory diagram showing the recent flux state of the non-acoustic collimating mode index lens used in the optical head of FIG. 5, and FIG. FIG. 8 is a plan view showing a schematic structure of an optical head according to a fourth embodiment of the present invention, and FIG. 9 is a plan view showing a schematic structure of an optical head according to a fourth embodiment of the present invention. Fig. 10 is a perspective view showing the schematic configuration of a conventional optical head; Fig. 1) is a main part of an optical disk device showing a state in which the optical head is installed. It is a perspective view.In the drawing, 1...Semiconductor substrate, 1a-=GaAs substrate, 2...Lower cladding layer, 3...Active layer, 4...Upper cladding layer, 8A...Semiconductor Laser, 8B, 8C... Photodetection section, 16... Lunebourg lens, 17... Aberration-free urimate lens, 18... Step mode index lens, 19
...Bragg type grating lens, 30A...
Conventional optical head, 30B, 30G, 30D, 30E... Optical head of the present invention, 40 Optical disk (optical recording medium). Patent applicant: Agent of Nippon Telegraph and Telephone Corporation

Claims (5)

[Claims] (1) In an optical head consisting of a semiconductor laser section on a semiconductor substrate and a photodetection section integrally formed with the semiconductor laser section on at least one side of the semiconductor laser section via an insulating groove, the semiconductor laser section An optical head characterized in that a waveguide-shaped microlens having a diameter larger than the diameter of the laser beam output path of a semiconductor laser section is disposed at the tip on the side of the laser beam output path. (2) The optical head according to claim (1), characterized in that a step index type mode index lens is used as the waveguide type microlens. (3) The optical head according to claim (1), characterized in that a Luneburg lens is used as the waveguide microlens. (4) The optical head according to claim (1), characterized in that an achromatic collimated mode index lens is used as the waveguide microlens. (5) The optical head according to claim (1), wherein a black grating lens is used as the waveguide microlens.