JP2002025104A - Integrated optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form spots of three semiconductor lasers having different wavelengths on an optical disk with a low aberration in an optical head for recording and reproducing different kinds of optical disks such as CD, DVD and disk for flue-violet semiconductor laser with one device, and to realize miniaturization, thinning, and integration of the head simultaneously. SOLUTION: The positions of two light emitting points of a double wavelength monolithic GaAs semiconductor laser and a light emitting point of a GaN semiconductor laser having a wavelength of blue-violet are formed in left-right asymmetry, and the positions of three semiconductor laser light emitting points of different wavelengths are arranged closely, and thus the head is integrated by performing index-alignment on an OEIC, a PD pattern and a substrate with a reflecting mirror.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an apparatus for irradiating a semiconductor laser beam modulated by an electric signal onto an optical disk and recording or reproducing the same.

[0002]

2. Description of the Related Art Recently, a 780 nm wavelength CD, CD-ROM, CD-R, C
D-Rewritable specification, DVD, DVD-ROM, DVD-R with wavelength of 650nm
An optical disk device that can play any type of optical disk of the AM specification has appeared, but a light source unit and a photodetector are separated for each semiconductor laser having a different wavelength. In the future, blue or violet or shorter wavelength lasers with further improved recording density will be used, and an increase in the number of parts of the optical head is expected to be inevitable. For this reason, the mounting density of the light source and the photodetector has not been increased, and the miniaturization and thinning of the entire optical disc device have been hindered. For this reason, as described in JP-A-1-150244, Nikkei Electronics, Nov. 29, 1999 (No. 758), p49, attempts have been made to hybrid-integrate a photodetector portion of a reproducing head of an optical disc with a semiconductor laser. It has been done. But,
The above-mentioned known example only describes the necessity of reducing the positioning error of the semiconductor laser, but does not disclose any specific method for improving the positioning accuracy.

[0003]

In order to integrate an optical disk recording / reproducing head, three types of semiconductor lasers having different wavelengths are arranged in parallel, and one optical system is used to place three semiconductor laser spots on the optical disk. Need to be formed. However, the optical system has an objective lens having a relatively large numerical aperture, and the angle of view, that is, the angle of the central ray (the line connecting the object point and the image point) with respect to the optical axis direction that guarantees low aberration is finite. is there. In other words, even if one of the three semiconductor lasers can be formed as a spot with sufficient aberration on the optical disc, the other spot is blurred by the aberration. Another important issue is the relative alignment of the light emitting points of the three semiconductor lasers. Therefore, in the above-described conventional example, it is difficult to say that the problem of the thinning and miniaturization of the entire device has been completely solved.

[0004]

SUMMARY OF THE INVENTION The present invention solves these problems and provides a CD having a wavelength of 780 nm, a DVD having a wavelength of 650 nm, and a new ultra-high-density optical disk having a wavelength of around 400 nm.
An object of the present invention is to provide a breakthrough for reducing the size and thickness of a driver device capable of recording and reproducing various optical disks with compatibility. That is, a monolithic GaAs semiconductor laser having two light emitting portions having different wavelengths of 780 nm and 650 nm, and a GaN semiconductor laser having a wavelength of 410 nm are provided with an automatic focus detection and a photodetector for tracking detection having sensitivity to the corresponding wavelengths. In an apparatus for recording / reproducing an optical disk by an optical head equipped with an integrated module composed of a monolithically formed semiconductor substrate, the light emitting points of the two types of semiconductor lasers are shifted with respect to the center between the GaAs semiconductor laser and the GaN semiconductor laser. The light emitting points are arranged close to each other so as to be within an allowable range of the angle of view of the optical head optical system.

[0005] The details are as follows. The first means is a laser light source made monolithically of two types of GaAs semiconductor lasers having different wavelengths of 780 nm and 650 nm,
After the GaN semiconductor laser near m and the three types of photodetectors corresponding to these different wavelengths are aligned with the mask accuracy, the two semiconductor lasers are hybrid-integrated to reduce the number of parts to the level of a monolithic. In addition, an integrated module is provided in which the optical head, which has conventionally been a plurality of optical paths, is changed to a single optical path, and the light emitting points of the three semiconductor lasers are formed at asymmetric positions in the left and right directions, and the light emitting points are arranged close to each other. Is what you do.

A second means of the present invention is to apply an index mark for alignment to both a silicon substrate on which a photodetector is formed and a semiconductor laser, and to irradiate visible light or infrared light, The image is formed on a photoelectric conversion surface such as a CCD or image pickup tube, captured into a computer, and the center of gravity and shape of each mark are calculated to perform alignment. Due to the centroid calculation, alignment accuracy can be achieved on the order of sub-microns.

[0007] A third means of the present invention is to form a reflection mirror on a silicon substrate on which a photodetector is formed.
That is, an off-substrate near 9.7 degrees is prepared, a reflection mirror near 45 degrees is formed by anisotropic etching of silicon, and a beam from a semiconductor laser is reflected by this mirror. The beam is bent at right angles.

According to a fourth aspect of the present invention, an amplifier for electrically amplifying a photocurrent generated by a photodetector is monolithically formed on a silicon substrate on which a photodetector is formed, and a diagonal mirror and a positioning device are provided. An index mark is created.

According to a fifth aspect of the present invention, an index mark for positioning is provided on a substrate having a high thermal conductivity such as silicon carbide, and the two semiconductor lasers are accurately aligned.
This is a hybrid integration of a prism mirror for reflection, a photodetector, and an amplifier.

[0010]

FIG. 1 shows the structure of an optical head according to the present invention. That is, the laser light from the integrated module 100 composed of the semiconductor substrate 1, the two-wavelength monolithic GaAs semiconductor laser chip 4a, the one-wavelength GaN semiconductor laser 4b, the reflection mirror 5, the photodetectors 7, 8, 9 and the like is respectively a beam 6a , 6b, and 6c, which are collimated by the collimator lens 10, reach the objective lens 13 via the rising mirror 11, the diffraction grating plate 12, and the like, and are formed as spots 15a, 15b, and 16 on the optical disk 14 surface. When the objective lens 13 is composed of a plurality according to the wavelength of the semiconductor laser,
Alternatively, there is a case where a single substance capable of condensing light of a plurality of wavelengths is used. The lens is focused on the recording surface by the actuator 17 in accordance with the movement accompanying the rotation of the optical disk,
In addition, tracking, that is, tracking of the recording track 18 on the disk surface. Thus, a signal is recorded as an array of pits on the optical disk according to the ON / OFF of the semiconductor laser, or the pits already recorded are read out to reproduce the signal. in this way,
If a plurality of semiconductor lasers are integrated in the integrated module 100, the collimator lens 10, the objective lens 13, the rising mirror 11, and the like become one, and the optical path of the optical head can be unified. That is, if the present optical head is used, for example, a 1.2 mm thick CD or CD-R can be
Recording / reproducing at the light emitting portion of wavelength λa (= 780 nm) of a,
A 0.6 mm thick DVD or DVD-RAM is recorded / reproduced with the light emitting portion of wavelength λb (= 650 nm) of the GaAs semiconductor laser 4a.
Recording and reproduction can be performed by the GaN semiconductor laser 4b near the wavelength λc (= 400 nm).

FIG. 2 illustrates the diffraction grating 12. This is a composite element in which a polarizing four-divided diffraction grating 23 and a quarter-wave plate 24 are bonded and integrated, and the polarizing four-divided diffraction grating is arranged facing the semiconductor laser chip side. The polarizing four-divided diffraction grating is made of a birefringent optical crystal plate or a liquid crystal plate. When incident light is ordinary light, it is transmitted without refraction, and when incident light is extraordinary light, it acts as a diffraction grating. Linearly polarized beams 6a, 6 emitted from the semiconductor lasers 4a, 4b
b, 6c, when incident on the composite element 12 of the polarizing quarter-diffraction grating and the quarter-wave plate, when incident as ordinary light, is transmitted as it is without diffracting in the polarizing diffraction grating portion,
Circularly polarized light is produced by the quarter-wave plate of the composite element 12. The laser beams 6a, 6b, and 6c reflected by the optical disk become extraordinary rays by the quarter-wave plate of the composite element 12, and are diffracted by the polarizing four-division grating. The composite device shown in FIG. 2 is divided into four regions by boundaries 21 and 22. Yen 2
Numeral 0 denotes a laser beam 6a, 6b or 6c, which is divided into four + first-order diffracted lights and four first-order diffracted lights by a four-divided diffraction grating, and the photodetector part 7 or 8 of the semiconductor substrate 1 is separated.
, And are photoelectrically converted into an auto-focus signal, a tracking signal, and an information signal. This will be described in detail below.

FIG. 3A shows the surface of the semiconductor substrate 1 as viewed from the collimator lens 10 side. Eight black quarter circles indicated by 32a indicate the laser beams of the wavelength λa separated by the diffraction grating 23, and eight unfilled quarter circles indicated by 32b are separated by the diffraction grating. Wavelength λ
4B shows a laser beam. 32c corresponds to the wavelength λc. Reference numeral 7 denotes a photodetector for obtaining a defocus detection signal, which includes eight strip-shaped photodetectors 7a for receiving a laser beam 32a having a wavelength λa, and a laser beam 32b having a wavelength λb.
And eight strip-shaped photodetectors 7c for receiving the laser beam 32c of the wavelength λc.
Consists of The defocus detection method uses the knife edge method (Fouco method) using a four-divided beam, and if the wires are connected by a conductive thin film 33 of aluminum or the like as shown in FIG. And B
A signal for differential is obtained from the terminal. Reference numeral 8 denotes a photodetector for obtaining a track shift detection signal and an information reproduction signal. Output signals of the four photodetectors 8 pass through an amplifier 35 formed on a semiconductor substrate, and are connected to a D terminal, an E terminal, and an F terminal of a pad 34. And output from the G terminal. Reference numeral 9 denotes a photodetector for monitoring the amount of light emitted from the semiconductor laser chips 4a and 4b, and an output signal of the photodetector 9 is output from a terminal C of the pad 34. The points 31a, 31b and 31c correspond to the laser beams 6a, 6b and 6c emitted from the semiconductor laser chips 4a and 4b.
The reflection position on the surface of the semiconductor mirror 5 is shown.

For example, the diffraction grating pitches P of the four regions shown in FIG. 2 are all equal, and the directions of the diffraction gratings are + α, −α, + 3α, and −3α with respect to the vertical line 21. Assuming that the focal length of the lens is fc, the laser beam 32a of wavelength λa separated by the diffraction grating
The light is condensed on the circumference of a radius Ra = fc * λa / P centered on 1a at a position spaced by 2α degrees from the center. Similarly, the laser beam 32b of the wavelength λb separated by the diffraction grating is condensed on a circumference of a radius Rb = fc * λb / P centered on the point 31b and at a position spaced by 2α degrees from the center. The laser beam 32c of the wavelength λc separated by the diffraction grating is
Is condensed at a position at an interval of 2α degrees from the center on a circle having a radius Rc = fc * λc / P centered at. Points 31a and 31c
If the light emitting point distance D between the semiconductor laser chips 4a and 4b, which is the distance between the light emitting points, is approximately D ≒ fc * (λc−λa) / P,
The converging position of the laser beam of wavelength λa and the converging position of the laser beam of wavelength λc can be substantially matched, and as in this embodiment, the photodetector and the amplifier can be shared by beams of different wavelengths, Not only can the surface of the substrate 1 be saved, but also the number of pads for wire bonding and the number of output lines can be reduced, which is also effective in reducing the size of the package that houses the semiconductor substrate 1.

FIG. 3B shows a cross-sectional structure of the semiconductor substrate 1 at a position indicated by a dotted line AA ′ in FIG. The semiconductor mirror 5 is preferably formed at an angle of 45 degrees with respect to the laser chip mounting surface 2. For example, in processing a mirror surface using a silicon substrate, when the silicon (100) surface is etched with a potassium hydroxide-based aqueous solution, the etching rate of the (111) surface with respect to the (100) surface is almost two orders of magnitude slower. This is based on anisotropic etching in which a truncated quadrangular pyramid-shaped recess having the (111) plane as an inclined surface is formed. At this time, since the angle between the (111) plane and the (100) plane is about 54.7 °, in order to form a 45 ° semiconductor mirror,
For example, it is necessary to use a silicon substrate having an off-angle of about 9.7 degrees whose crystal axis is inclined with respect to the surface. However, the off-angle angle needs to be determined in consideration of the suitability of the semiconductor process for forming the photodetector and the electronic circuit, and the semiconductor mirror 5 may deviate from 45 degrees, and the laser beams 6a, 6b, and 6c Of the semiconductor substrate 1
May deviate from the vertical direction.

FIG. 4A shows an example in which a reflecting prism 50 is mounted as a reflecting mirror instead of processing by anisotropic etching. In general, a recording semiconductor laser for an optical disc has a higher output and a larger input power than a read-only semiconductor laser. For this reason, heat is generated, and it is necessary to adopt a structure for radiating the heat. Normally, silicon carbide is used for the submount of this type of semiconductor laser. In one embodiment of the present invention, the semiconductor lasers 4a and 4b are soldered on the silicon carbide substrate 51. The beam from the semiconductor laser is reflected by the reflecting mirror prism 50, and the signal is reproduced through the same optical path as described with reference to FIG. The silicon substrates 52 and 53 on which the photodetector groups 7 and 8 are formed are soldered to the silicon carbide substrate 51. At this time, relative alignment with the light emitting point of the semiconductor laser can be performed with high accuracy using a self-alignment method using the solder bump group 54. FIG. 4B is a sectional view taken along the line AA of FIG. FIG. 4 (c) is an elevation view of FIG. 4 (a).

FIG. 5 shows a light emitting point position of the semiconductor laser according to the present invention. That is, CD, CD-R, CD-Rewri
(4a) A semiconductor laser portion having an oscillation wavelength corresponding to the wavelength λa of the optical disk and a semiconductor laser portion having an oscillation wavelength corresponding to the wavelength λb of DVD and DVD-RAM optical disks are monolithically formed on the GaAs substrate. The two light emitting points 5a and 5b are usually formed at positions asymmetrical from the center, unlike the light emitting point positions 51a and 51b at the center of the semiconductor laser. On the other hand, the light emitting point 5c of the semiconductor laser 4b of the GaN substrate having a blue-violet oscillation wavelength around 400 nm is formed not to the normal light emitting position 51c but to the adjacent two-wavelength monolithic semiconductor laser side. Then, two types of semiconductor lasers are mounted in a direction in which both light emitting point positions approach. In this way, in the single-path optical system shown in FIG. 1, the angle of view formed by the three light emitting points can be made small, and the spots 15a, 15b, and 16 on the optical disk can be formed with low aberration. .

FIGS. 6A and 6B show a package for storing the semiconductor substrate 1. FIG. That is, the package substrate 200 includes the conductive pins 201 and the silicon substrate 202. FIG. 6B is a sectional view taken along the line AA in FIG. 6A and includes a cap 203 and a package sealing window 204. The package window 204 can also serve as the composite element 12 in FIG.

FIGS. 7A, 7B and 7C show another example of a package containing the semiconductor substrate 1. FIG. That is, FIG.
FIG. 3B is a sectional view taken along a broken line AA ′, and FIG. 3C is a sectional view taken along a broken line BB ′.
Reference numeral 42 denotes a lead wire which is connected to the pad 34 of the semiconductor substrate 1 by a bonding wire. The surface of the pedestal 43 on which the semiconductor substrate 1 is mounted is inclined such that the emission directions of the laser beams 6a and 6b are vertical. Reference numeral 44 denotes a glass cover for sealing the semiconductor substrate 1, and a reflection surface 45 for reflecting the outer peripheral portions of the laser beams 6a and 6b is provided inside the glass cover 44. The light beam reflected by the reflection surface 45 is received by the photodetector 9 of the semiconductor substrate 1, and a signal for monitoring the amount of light emitted from the semiconductor laser chips 4a and 4b is obtained.

Next, a method of mounting a plurality of semiconductor lasers on a silicon semiconductor substrate with high accuracy will be described with reference to FIGS.
This will be described with reference to FIGS. That is,
FIG. 8 shows a silicon substrate 1 having an index pattern 400 according to the present invention. Reference numeral 401 denotes a solder pattern, on which a semiconductor laser is bonded by soldering. An electrode pattern 402 is connected to the solder pattern 401.

FIG. 9 shows a corresponding semiconductor laser 4a,
4b, a solder pattern 501 formed on the back surface, and
This is an index pattern 502 for positioning. Figure 1
Numeral 0 describes a method of aligning the index pattern 400 on the substrate 1 with the index pattern 502 on the back surfaces of the semiconductor lasers 4a and 4b. That is, the surface of the substrate 1 and the semiconductor lasers 4a and 4b are
Alternatively, the light is illuminated from the back side, the reflected light or the transmitted light is received by the microscope 601, and the index pattern is enlarged and projected on the video monitor 602. Then, each index pattern 400, 502 is
Of the substrate 1 or the semiconductor laser until the displacement between the two centers becomes a constant value.
Finely move 4a or 4b. When the alignment is completed, tact bonding is performed, and the solder bonding is completed in a solder reflow furnace.

FIG. 11 is a cross-sectional view when the semiconductor lasers 4a and 4b are mounted on the mirror-attached substrate 1 by soldering.
Corresponding to '. An electrode 501 and an index pattern 502 for alignment are formed on the back surface of the semiconductor laser, and are soldered on the substrate 1 on which the electrode 402 and the solder 401 are formed. The alignment between the semiconductor laser and the substrate is performed between the index patterns 502 and 400. Beams from the semiconductor lasers 4a and 4b emit a light emitting point 704 and are reflected by the mirror 5 to reach a beam splitter, an objective lens, and an optical disk. A pedestal 705 is formed on the substrate 1 so that the beam from the light emitting point 704 is not kicked on the bottom surface of the substrate.

FIG. 12 shows another embodiment of the integrated module according to the present invention. That is, the amplifier 900 for amplifying the photocurrent from the photodetectors 32a, 32b, 32c is monolithically formed on the silicon or GaN substrate 1. Thus, it is possible to improve the degree of integration by reducing the number of components.

[0023]

As described above, according to the present invention,
An optical head on which a plurality of semiconductor lasers are mounted can be reduced in size and integrated, and the entire optical disk device can be reduced in size and thickness regardless of reproduction or recording, such as an optical disk compatible with CD, DVD, and blue-violet laser.

[Brief description of the drawings]

FIG. 1 is an optical head having a single optical path on which an integrated light source module according to the present invention is mounted.

FIG. 2 is a composite element for beam splitting.

FIG. 3 is a structural view of an integrated light source according to the present invention.

FIG. 4 is an integrated light source provided with a prism mirror.

FIG. 5 is a diagram showing a light emitting point position of a semiconductor laser.

FIG. 6 shows a package form of an integrated light source.

FIG. 7 is a diagram in which the integrated light source according to the present invention is mounted on a horizontal flat package.

FIG. 8 is a diagram showing an integrated substrate, an alignment index, a solder pattern, and electrodes of an integrated light source according to the present invention.

FIG. 9 is an index pattern for alignment applied to a semiconductor laser.

FIG. 10 shows a method of aligning a semiconductor laser light source with an index and an integrated substrate with a corresponding index pattern.

FIG. 11 is a sectional view taken along the line AA ′ of FIG.

FIG. 12 is a diagram showing a case where an OEIC (Optoelectric Integrated Circuit) such as an amplifier and a photodetector is monolithically integrated on an integrated substrate according to the present invention.

[Explanation of symbols]

1: semiconductor substrate, 2: semiconductor laser mounting surface, 4a:
2 wavelength monolithic semiconductor laser chip, 4b: 1 wavelength semiconductor laser chip, 5: reflection mirror, 6a, 6b, 6c: beam from semiconductor laser, 7: light detector, 8: light detector, 9: light monitor detector , 10: collimator lens,
11: rising mirror, 12: composite element of diffraction grating and wave plate, 13 objective lens, 14: optical disk, 15a, 1
5b, 16: light spot, 17: actuator, 1
8: Truck. 21: boundary line, 22: diffraction grating, 23:
Diffraction grating, 24: quarter wave plate. 31a, 31b, 31
c: spot on a mirror, 32a, 32b, 32c: light spot for automatic focus detection, 33: wiring, 34: electrode pad, 35: amplifier. 5a, 5b, 5c: emission point of the semiconductor laser according to the present invention, 51
a, 51b, 51c; light emitting point position of normal semiconductor laser, 20
0: package base, 201: conduction pin, 203: cap, 204: window. 41: case, 42: lead frame, 43: table, 44: window, 45: reflective film. 4
00: index mark, 401: solder pattern,
402: electrode pattern. 501: electrode pattern of the semiconductor laser, 502: index mark of the semiconductor laser. 6
00: infrared, 601: infrared camera, 602: monitor, 603: computer. 704: emission point of the semiconductor laser, 705: stage. 900: OEIC board with amplifier.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 5/022 H01S 5/022 5/026 5/026 (72) Inventor Ken Shimano Kenichi Higashi Koigakubo, Kokubunji-shi, Tokyo Chome 280 Hitachi Central Research Laboratory, Inc. (72) Inventor Shigeru Nakamura 1410 Inada, Hitachinaka-shi, Ibaraki Pref. Digital Media Products Division, Hitachi, Ltd. (72) Inventor Yasuyuki Arikawa 1410 Inada, Hitachinaka-shi, Ibaraki Stock Hitachi Digital Media Products Division F-term (reference) 5D119 AA02 AA41 BA01 CA10 EC45 EC47 FA05 FA08 JA57 LB04 MA09 NA05 5F073 AB06 AB27 AB29 CA01 EA04 FA13 FA23 FA27

Claims (9)

[Claims] 1. A monolithic GaAs semiconductor laser having two light emitting portions having different wavelengths of 780 nm and 650 nm, and a G laser having a wavelength of 410 nm.
aN semiconductor laser, automatic focus detection with sensitivity to the corresponding wavelength, and an optical head mounted with an integrated module consisting of a semiconductor substrate monolithically formed with a photodetector for tracking detection, in an apparatus for recording and reproducing optical disks, The emission points of the two types of semiconductor lasers are
The semiconductor laser and the GaN semiconductor laser are formed at right and left asymmetric positions with respect to the center, and the plurality of light emitting points are arranged close to each other so that the angle of view of the optical head optical system is within an allowable range. An integrated optical head device comprising: 2. An integrated optical head device according to claim 1, wherein said plurality of semiconductor lasers and / or one or both of said semiconductor substrates are provided with alignment marks. apparatus. 3. An integrated optical head device according to claim 1, wherein an oblique mirror is etched on said semiconductor substrate, and said plurality of semiconductor lasers and / or one or both of said semiconductor substrates are aligned. An integrated optical head device characterized by the following mark. 4. An integrated optical head device according to claim 1, wherein an amplifier for amplifying a photocurrent from said photodetector is monolithically formed on said semiconductor substrate, and said semiconductor substrate is processed with an oblique mirror. An integrated optical head device, wherein a mark for alignment is attached to one or both of the semiconductor lasers. 5. The integrated optical head device according to claim 1, wherein said photodetector and said photocurrent amplifier are formed monolithically, and said semiconductor substrate on which a diagonal mirror is processed and said semiconductor laser are aligned. Mark for the semiconductor laser and the surface in contact with the substrate, infrared transmitted light,
Alternatively, an integrated optical head device in which alignment is performed by image processing using reflected light. 6. An integrated optical head device according to claim 2, wherein a mark for positioning is provided, and a mark for positioning is provided on a substrate on which a photodetector is formed in a monolithic manner, and a 45 ° inclination is provided. An integrated optical head device, wherein a prism mirror having the following is hybrid-integrated on a heat sink substrate of silicon carbide. 7. The integrated optical head device according to claim 1, wherein a light emitting point of said GaAs semiconductor laser is formed closer to an end than a center of the GaAs laser chip. 8. The light emitting point of the GaN semiconductor laser is Ga
2. The integrated optical head device according to claim 1, wherein the N laser chip is formed closer to the end than the center. 9. An integrated optical head device according to claim 1, wherein an amplifier for amplifying a photocurrent from said photodetector is mounted on said semiconductor substrate in a hybrid manner, and said semiconductor substrate is formed with a diagonal mirror, and An integrated optical head device, wherein a mark for alignment is attached to one or both of the semiconductor lasers.