JPS6258432A - Integrated optical pickup head - Google Patents

Abstract

PURPOSE:To reduce the cost by integrating a reflector which converts the optical path of the emitting light from a semiconductor laser to irradiate it toward an optical recording medium and a photodetector which receives the reflected light from the optical recording medium to detect information, on the same substrate. CONSTITUTION:In a laser area L, an n-type GaAlAs clad layer 12, an n-type GaAlAs active layer 13, a p-type GaAlAs clad layer 14, an n-type GaAs cap layer 15, an insulating layer (Si3N4)16, and electrodes 17a and 17b are formed on an n-type GaAs substrate 11. In a light detecting area D, the layer structure itself is approximately similar to that of the laser area L but parts on the cap layer 15 are removed by etching or the like and a photodetector 20 consisting of a photodiode is divided into four parts (a)-(d) by crossing separating zones 21 and is arranged on the clad layer 14. A laser emitting end face 22 and a reflecting face 23 are formed in the center separating part between the laser area L and the light detecting area D.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in an integrated optical pickup head for recording or reproducing information on or from an optical recording medium such as an optical video disk.

[Prior Art] Optical disk systems, which are high-density information recording systems using laser light, are attracting attention as information systems that will support the rapidly developing information society. Active research and development is being conducted to further improve the functionality of optical disc systems, including video discs, which have already been put into practical use. The optical pickup head in such an optical disc system corresponds to the pickup cartridge of an analog player, and can be said to be an extremely important component for the optical disc system.

All of the optical pickup heads that have been developed so far have individual optical elements such as semiconductor lasers, lenses, mirrors, polarized beam spurters, etc. arranged on a metal substrate. Therefore, it was difficult to make it smaller and lighter, and it had the disadvantage of having a large number of parts.

As a means to solve these problems, an optical pickup head using a guiding waveguide has been proposed, for example, as disclosed in Japanese Patent Application Laid-Open No. 59-151129.

FIG. 8 is a diagram showing the outline thereof. As shown in the figure, a LiNbO3 substrate 2 is placed on a silicon substrate 1, and a waveguide 2a is formed in its upper layer. A semiconductor laser 3 is arranged at the light input end of the waveguide 2a, and an integrated lens 4 is bonded to the light output end. and waveguide 2
In the middle of a, from the light input end side to the light output end side, there is a collimating lens 5 for collimating the emitted light from the semiconductor laser 3, and an elastic surface for Bragg diffracting the collimated light beam. Cross electrodes 6 for generating waves and grating lenses 7 for deflecting diffracted light within the cross section of the waveguide 2a are sequentially arranged. Further, a photodetector 8 consisting of six photodiodes is provided on one side of the silicon substrate l. A control circuit 9 composed of a microcomputer is provided on the upper surface of the silicon substrate 1, and is electrically connected to the integrated lens 4, the crossed electrodes 6, the grating lens 7, the photodetector 8, etc. In this way, the laser light emitted from the semiconductor laser 3 propagates through the waveguide 2a, and the propagated light beam is directed to the optical disk 1 by the integrated lens.
A pit (not shown) above 0 is focused and irradiated with light. The reflected light from the optical disc IO is received by a photodetector 8, and the state of the optical spot formed on the optical disc 10, ie, focusing information, tracking information, etc., is detected.

[Problems to be Solved by the Invention] However, in the conventional optical pickup head having the above configuration, it is difficult to match the silicon forming the substrate of the control circuit 9 with the LiNbO3 forming the substrate of the waveguide 2a. It has the disadvantage of poor performance. In addition, since the waveguide 2a is provided with intersecting electrodes 6 and grating lenses 7 for generating surface acoustic waves that cause Bragg diffraction of light, extremely complicated manufacturing processes are required, making it difficult to reduce costs. It had the disadvantage of being difficult to use. Furthermore, it is difficult to integrate the semiconductor laser 3 as a light source, the photodetector 8, etc. with the waveguide 2a on the same substrate, which also makes manufacturing difficult and increases costs. There was a problem.

Therefore, the present invention eliminates the problem of consistency between substrate materials, is small and lightweight, is extremely easy to manufacture, and can reduce costs.In addition, it is possible to integrate the optical recording medium so that the light from the optical recording medium does not return to the light source side. The purpose is to provide a type optical pickup head.

Means for Solving Problem E] The present invention is characterized by taking the following measures in order to solve the above problems and achieve the object. That is, a semiconductor laser having an emitted light deflection function, a reflector that converts the optical path of the emitted light from the semiconductor laser and irradiates it toward an optical recording medium, and a reflector that receives the reflected light from the optical recording medium and converts it into information. A photodetector for detection is integrated on the same substrate. As the reflector, a plane reflecting mirror or an elliptical mirror with a light condensing function is used. Further, as a photodetector, a plurality of light receiving elements arranged on the same plane is used so as to be able to detect tracking information and/or focusing information.

[Operation] By taking such measures, the semiconductor laser as a light source, the reflector, and the photodetector are integrally formed, so that the device is small and lightweight, and manufacturing is easy. Moreover, since the optical recording medium is irradiated by a reflector formed on the same substrate, there is no so-called return light.

[Embodiment 1] FIG. 1 is a perspective view showing the overall structure of a first embodiment of the present invention, and shows a semiconductor laser/photodiode integrated type optical pickup head.

This optical pickup head is divided into a laser region and a photodetection region by separating the central portion by etching or the like.

The laser region is formed as follows. In the figure, 11 is an n-type GaAs substrate, and on this substrate 11 is an n-type GaAs substrate.
, ffAs cladding layer 12, n-type GaA, 11'As active layer 13, p-type GaA/As cladding layer 14, n-type Ga
An As cap layer 15, an insulating layer (Si3Nt) 16, and electrodes 17a and 17b are formed. Note that the electrodes 17a and 17b are electrically separated by an electrode dividing portion 18. Another electrode 19 is formed on the other side of the substrate 11.

The photodetection area is formed as follows. The layer structure itself is almost the same as that of the laser region. However, the portion above the cap 515 has been removed by etching or the like, and a photodetector 20 consisting of a photodiode is placed on the cladding layer 14 by a cross-shaped separation band 21 a-d.
It is divided into four parts. The above separation strip 21
is formed by means such as etching or dry etching.

A laser emitting end surface 22 and a reflecting surface 23 are formed in a centrally separated portion between the laser region and the photodetection region. In FIG. 1, reference numeral 24 is an optical recording medium, which constitutes a muscanning semiconductor laser (hereinafter abbreviated as BSL). Therefore, BSL will be explained in detail below.

Semiconductor lasers are generally classified into two types depending on their waveguide mechanism: refractive index waveguide type and gain waveguide type.

The former has a mechanism in which light is guided by the refractive index in both directions perpendicular and parallel to the junction surface of the active layer of a semiconductor laser, whereas the latter has a mechanism in which light is guided by the refractive index in both directions perpendicular and parallel to the junction surface of the active layer of a semiconductor laser, whereas the latter has a mechanism in which light is guided by the refractive index The mechanism is based on the property that light is guided along areas where the gain is high depending on the .

BSL actively utilizes this gain waveguide mechanism. That is, the gain distribution in the active layer of a typical gain waveguide semiconductor laser is symmetrical with respect to the center of the active layer because the current injection electrode is uniformly formed on the active layer. On the other hand, in the case of BSL, two divided electrodes are formed on the active layer, and current can be injected into this pair of electrodes independently, making the gain distribution in the active layer asymmetrical. I can do it.

Figure 2 is a perspective view showing an example of the structure of BSL, and is
,R,5cif'res Appl phys Let
t 33 (8), 702°19784.

In order to correspond to the laser region in FIG. 1, the same functional parts are given the same reference numerals.

As shown in Fig. 2, an n-type G
a A As cladding layer 12, p-type 0.5
0.5 0.95 0.05 AS active layer 13, n-type Ga
A no Ga A no As cladding layer 14, n-type 0.5
A 0.5 GaAs cap layer 15 is sequentially formed. On this cap layer 25, electrodes 17a and 17b are provided which are divided into two with an insulating layer 16 for current narrowing interposed therebetween.

In other words, these electrodes 17a and 17b are connected to the electrode divided portion 18.
A pair of lead wires 19a, 1
Currents II and 12 can be injected independently through the terminals 9b. Further, the electrode 17a of the cap layer 15,
Zn diffusion regions 30a and 30b are provided in the portions in contact with electrodes 17b, respectively, so as to limit the current excitation region injected from electrodes 17a and 17b.

The asymmetric gain distribution in the active region 31 of the active layer 13 is
This is done by changing the ratio of the injection currents It and I2 mentioned above.

That is, if the injection current is made asymmetric (Il〆12),
The density of carriers injected into the active layer 13 is higher on the electrode side where the injection current is larger. For example, when 11>12, more carriers are injected from the electrode 17a side, and the gain in the active region 31 is higher on the II side. Therefore, a distribution as shown in FIG. 3(a) is shown in which the peak of the gain distribution is biased toward the 17a side.

Conversely, if 11<I2, the gain in the active region 3 is I
2 side is high, and the peak of the gain distribution is biased toward the 17b side, resulting in a distribution as shown in FIG. 3(b).

When the gain distribution shown in FIGS. 3(a) and 3(b) is formed, the phase of the wavefront of the optical mode of the active layer 23 is as shown in FIG. 4(a),
It can be seen that the wavefront is inclined as shown in (b).

The direction of the slope of the wavefront is determined by the ratio of the injection currents mI+ and I2. Note that the horizontal axis X in FIGS. 3 and 4 indicates a direction parallel to the bonding surface.

The direction of the laser emitted light depends on the tendency of the wavefront of the light in the active layer 13, and its far-field pattern is shown in FIGS. 5(a) and 5(b).
), it has a peak in a direction that is deflected at a predetermined angle with respect to the normal to the laser end face.

This emitted light peak position is determined by the injection current ratio 1 to the active layer 13.
By continuously changing 1/I2, it is possible to continuously move within a constant deflection angle range.

As shown in FIG. 6, the characteristics of BSL operation as a light source are as follows: The peak p of the intensity distribution of the emitted light is
The point is that it can be continuously deflected as shown by the arrow by variable operation No. 2.

Next, the operation of the optical pickup head constructed as described above will be explained.

When current is injected into the active layer 13 from the left and right electrodes 17a and 17b, laser oscillation is started in the laser region. The emitted light ■ emitted from the laser emitting end face 22 is
It is reflected from the reflective surface 23 provided on the side of the light detection area,
The light W incident on the optical disk 24 and reflected from the optical disk 24 is incident on the four-split photodetector 20, and photodetection is performed as follows.

The light incident on the photodetector 20 is transmitted through the cladding layer 14,
It reaches the vicinity of the active layer 13 and cladding layer 12 and is absorbed. Now, a reverse bias (lower than breakdown voltage) is applied to the pn junction formed by the active layer 13 and cladding layer 12.
(not shown), electrons and holes are generated in this light absorption region, and the electrons are transferred to the n region (cladding layer 12).
In addition, the holes move to the p region (active layer 13) and are detected as a current.

Tracking errors are detected by utilizing the fact that reflected light interferes with each other between parts of the optical disk 24 where there are bits and where there are no bits. That is, when the light spot deviates from the pit, nearly 100% of the light is reflected, whereas when the light spot irradiates a portion of the inside of the pit, the reflectance decreases and a change in the amount of reflected light occurs. Therefore, tracking errors can be detected by monitoring the change in the amount of light using the photodetector 20 and detecting the minimum amount of light. If a tracking error occurs, the emitted light V may be deflected by changing the injection current/ratio to the BSL and performing beam scanning, and the tracking correction of the light spot on the optical disk 24 may be performed.

In the present embodiment described above, the laser region as a light source and the photodetection region can be integrally formed on the same substrate, resulting in an extremely small and lightweight device. In addition, since the light V emitted from the laser region is made to enter the optical disk 24 through the reflective surface 23 formed on the same substrate, the great advantage is that the so-called return light from the optical disk 24 does not enter the laser region again. has.

Next, a second embodiment shown in FIG. 8 will be described. The difference between this second embodiment and the first embodiment is that in the above embodiment, a reflecting surface 23 which does not have the function of condensing the emitted light V from the laser is provided as a reflector, whereas in this embodiment In the example, an elliptical mirror 40 having a laser focusing function is provided.

In FIG. 8, reference numeral 40 denotes an elliptical mirror provided so as to face the other end face of the laser region, and is formed so that the laser emitting end face 41 and the recording surface of the optical disk 24 are each one of the focal points.

Therefore, the emitted light V from the laser is reflected by the elliptical mirror 40 to form a focal point on the optical disk 24, and the reflected light W forms a spot on the photodetector 20, which is formed around the photodetection area. Form. Since the photodetector 20 is divided into four parts by the separation band 21, tracking error detection can be performed efficiently by the same method as explained in the previous embodiment.

Focusing error detection can also be performed as follows.

That is, the recording surface of the optical disc 24 is
, the spot 25 formed on the photodetector 20'' by the reflected light W from the optical disk 24 is located mostly on the c and d sides, and the light on the c and d sides is The output becomes large. On the other hand, when the optical disk 24 is on the side B farther from the focal point of the elliptical mirror 40, the photodetector 20
The spot 25 formed on the top is biased toward the a and b sides, so the light output on the a and b sides is greater than the light output on the c and d sides. Therefore, focus errors can be detected.

In addition to the effects of the above-mentioned embodiments, the present embodiment described above has the advantage that tracking and focusing can be performed more accurately because a light condensing function is generated.

Note that the present invention is not limited to the above embodiments.

For example, in the above embodiment, an example was shown in which no external lens system was inserted between the integrated pickup head and the optical disk 24, but an external lens system may be provided to improve the focusing characteristics of the light spot. You can also do this. In this case, the first
In the second embodiment, a lens array in which convex lenses are arranged in an array is used, and in the second embodiment, an elliptical mirror 4o is used.
It is preferable to use a cylindrical lens array or a lenticular lens arranged orthogonally to the cylindrical lens array or lenticular lens.

In addition, in the examples, G is used as a laser material and a photodetector material.
AAs / GaAJAs material was used, but InP / InGaAsP
Other materials may also be used.

That is, the substrate 11 has an n-type 1nP layer and a cladding layer 1.
2 is an n-1nP layer, and the active layer 13 is an InGaAsP layer.

The cladding layer 14 may be made of n-1nGaAsP, and the cap layer 15 may be made of p-type 1nGaAsP. However, when an InGaAsP system is used, the laser oscillation wavelength is in the infrared region of 1.3 to 1.6p. The above-mentioned GaAs-based or InP-based materials can be used not only as light-emitting device materials but also as light-receiving devices, so by using semicircular compounds of these materials as substrates, semiconductor lasers, photodetectors, reflective mirrors, etc. It has the advantage that two optical systems can be integrated on the same substrate.

[Effects of the Invention] According to the present invention, the following effects are achieved. Since the semiconductor laser, photodetector, and reflector are integrally integrated on the same substrate, the device has good compatibility, is small and lightweight, and is easy to manufacture and inexpensive.

Furthermore, since the optical recording medium is irradiated with light from a reflector formed on the same substrate, there is no so-called return light and a good pickup function can be achieved. Furthermore, since a BSL is used as a light source, the optical spot can be tracked without using mechanical deflection means.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the overall configuration of the first embodiment of the present invention, FIG. 2 is a perspective view showing the BSL of the same embodiment, and FIG.
a) (b) to Fig. 5 (a) and (b) are diagrams showing the characteristics of the BSL, Fig. 6 (a) and (b) are diagrams showing the action of the BSL, and Fig. 7 is a diagram showing the characteristics of the BSL. FIG. 2 is a perspective view showing a second embodiment. FIG. 8 is a perspective view showing a conventional example. L... Laser area, D... Photo detection area, 11...
Substrate, 12... Cladding layer, 13... Active layer, 14
...Clad layer, 15...Cap layer, 16...
Insulating layer, 17a, 17b...electrode, 20...photodetector,...laser light emitting end surface, 23...reflecting surface, 2
4... Optical disk, 40... Elliptical mirror. Figure 1 Figure 2 (a) (b) Figure 3 (a) (b) Figure 4 (a) (b) Figure 6 Figure 2 Indication Patent Application No. 60-197136 2, Name of the invention Integrated optical pickup head 3, Relationship to the amended case Patent applicant (037) Olympus Optical Industry Co., Ltd. 4, Agent 1-chome, Toranomon, Minato-ku, Tokyo 26-5 No. 17 Mori Building 5,
Date of amendment order (shipment date) November 26, 1985, 1m! 7. Contents of amendment (1) “Figure 6 (a) (
b) Correct J to "Figure 6".

Claims (4)

[Claims] (1) A semiconductor laser having an emitted light deflection function, a reflector that converts the optical path of the emitted light from the semiconductor laser and irradiates it toward an optical recording medium, and a reflector that receives the reflected light from the optical recording medium to generate information. 1. An integrated optical pickup head characterized in that a photodetector for detecting 1 is integrated on the same substrate. (2) The integrated optical pickup head according to claim 1, wherein the reflector is an elliptical mirror that condenses and emits light emitted from the semiconductor laser. (3) The elliptical mirror is provided so that one focal point coincides with the light emitting end of the semiconductor laser and the other focal point coincides with the recording surface of the optical recording medium. The integrated optical pickup head according to scope 2. (4) The photodetector is comprised of a plurality of light receiving elements arranged in the same plane, and is provided to be able to detect tracking information and/or focusing information. The integrated optical pickup head according to item 2 or 3.