JP2002246699A - Laser module and optical information processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of aberration caused by oblique incidence from at least one of two semiconductor laser chips in a two-wavelength laser module in which the two semiconductor laser chips with different wavelengths are integrated in a single package. SOLUTION: A micromachine rotating stage 105 having a 45 deg. mirror 106 mounted thereon is formed on a silicon substrate 101 while being integrated with two semiconductor lasers 102 and 103 and an optical sensor, the micromachine rotating stage is rotated, and a laser beam with a necessary wavelength is selected and is raised by 90 deg.. Therefore, it is possible to conform the optical axes of the two wavelengths to each other and to suppress increase in aberration of an objective lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compact disc (CD) and a digital versatile disc (DV).
D) An optical information processing apparatus for reproducing or recording / reproducing an optical disk such as a rewritable DVD (DVD-RAM) and a laser module used therein.

[0002]

2. Description of the Related Art In a DVD, it is necessary to ensure compatibility with a CD, and recently, compatibility with a CD-R which can be recorded only once is also essential. The laser wavelength used for DVD reproduction is about 650 nm red, but recording and reproduction of CD-R requires 780 nm infrared light, and most recent DVD drive devices use a red laser and infrared light. Both lasers are mounted. However, when an optical pickup is configured in a state where semiconductor lasers of respective wavelengths are separately packaged, a prism or the like for synthesizing the optical paths is required, and there is a disadvantage that the optical head is large and heavy.

In order to reduce the size and weight of such a DVD drive device, for example, a technique described in Japanese Patent Application Laid-Open No. Hei 9-120568 has been developed. Here, a red semiconductor laser chip and an infrared semiconductor laser chip are arranged side by side with a photodetector in one package. By doing so, the optical paths of the light beams of the two wavelengths are shared, which is effective for reducing the size and weight of the optical head.

[0004] On the other hand, however, since the two light emitting points are always mounted at a certain distance from each other, there is a disadvantage that the optical axes of the light beams of the respective wavelengths do not exactly coincide.
At this time, a light beam of at least one wavelength is obliquely incident on the objective lens for condensing on the disk recording film, and aberration occurs in the objective lens. For this reason, the light spot to be condensed becomes blurred and large, and there is a possibility that recording and reproduction on the optical disk become impossible.

[0005] For example, Japanese Patent Laid-Open No. Hei 10-261240 discloses a conventional technique for solving this problem. Here, a hologram element for compensating for aberrations generated in the obliquely incident light beam is added. This makes it possible to obtain a good light spot for each of the two wavelengths.

[0006]

The second conventional example described above has a drawback that the light utilization efficiency is reduced because a hologram element is used. The hologram element can ideally obtain a diffraction efficiency close to 100% for light of the required diffraction order. However, for this purpose, it is necessary to make the hologram grating saw-toothed,
It is difficult to manufacture, and it tends to increase the manufacturing cost. If a hologram having a substantially rectangular lattice cross section is used to avoid this, the diffraction efficiency will decrease. Also, at this time, unnecessary diffracted light is generated both when the light emitted from the semiconductor laser is directed to the disk and when the light is reflected by the disk and directed to the photodetector. It is likely to increase. Furthermore, since the number of components is increased by newly using a hologram, there is also a problem that the size, weight, and manufacturing cost of the optical head increase due to this.

In view of the above-mentioned problems, an object of the present invention is to provide a module in which two semiconductor lasers having different wavelengths are integrated in one package so that the optical axes of the light having the two wavelengths coincide with each other and additional optical components are provided. It is to provide a small and inexpensive laser module without using it. It is another object of the present invention to provide an optical information processing device having a mechanism required to realize the above.

[0008]

In order to solve the above-mentioned problems, the present invention employs a micromachine technique as described in Optics Letters, Vol. 21, No. 2, (1996), pp. 155 to 157. Here, a principle experiment aiming at miniaturization of an optical head by micromachine technology is shown, and a rotating beam splitter formed on a silicon substrate is used as an actuator for tracking. In the present invention, this rotating mirror is used.

In the present invention, a base substrate made of silicon or the like and at least two semiconductor laser chips having different wavelengths are mounted, and a 45 ° mirror which turns up the emitted light by 90 ° and rises perpendicularly to the substrate is provided. The rotary beam splitter is mounted on a rotary stage instead of the beam splitter. By using this, one of the two wavelengths can be selectively activated by rotation of the rotary stage. At the same time, a photodetector is integrally packaged on the same substrate to form a laser module.

In order to use this as an optical information device, the optical disk inserted into the device must be a DVD or
It is necessary to discriminate whether the disc is a CD and drive the rotary stage accordingly. Therefore, in addition to the laser module, an optical system such as a collimator lens or an objective lens for condensing the laser light on the optical information recording medium, and a spindle motor for scanning the optical information recording medium with respect to the condensed spot And a mechanism capable of discriminating at least two types of information recording media and detecting the disc as a medium discrimination signal.
A control mechanism for driving a mirror to rotate any one of the laser light emitted from the two semiconductor laser chips so as to selectively reflect the laser light in a direction perpendicular to the surface of the base substrate. Is configured.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a basic embodiment of a laser module according to the present invention. A red semiconductor laser chip 102 and an infrared semiconductor laser chip 1 on a silicon substrate 101
03 is implemented. The red semiconductor laser chip 102 is DVD, and the infrared semiconductor laser chip 103 is C
D is used for recording and reproduction, respectively. However, here, the case of DVD recording and reproduction is assumed, and the laser radiation 104
Are emitted from the red semiconductor laser chip 102.
This light is reflected by a 45 ° reflecting mirror 106 mounted on the micromachine rotation stage 105 and vertically rises from within the plane of the silicon substrate 101. Here, since the light emitting point of the semiconductor laser is on the side closer to the substrate from the viewpoint of adjustment accuracy and heat radiation characteristics, the 45 ° reflecting mirror is etched from the surface on which the semiconductor laser chip is mounted in order to start up the laser light efficiently. It is manufactured on the surface dug down by the process of (1). The tracking / RF signal detection photodetector 107 for receiving the laser radiation 104 raised as described above when the laser radiation 104 is condensed on an optical disk (not shown), reflected and returned,
A defocus detecting photodetector 108 is formed on the surface of the silicon substrate 101 around the semiconductor laser chip. Here, as an example, four photodetectors 107 are arranged around the red semiconductor laser chip 102 as photodetectors for tracking and detection of a reproduction signal. This is a DVD
This is because the reflected light flux needs to be divided into four and received in the ROM for tracking detection by the phase difference method. Four photodetectors 108 are arranged around the infrared semiconductor laser chip 103 with two divided light receiving areas as one set. This is a light receiving area for detecting a defocus, and is a light receiving area for receiving the reflected light divided into four for the tracking detection and detecting the defocus by the knife edge method. The photocurrent from each light receiving area is extracted from a bonding pad 109 wired from the light receiving area from a bonding line (not shown) bonded here.

FIG. 2 shows an embodiment in which the laser radiation 104 is switched to the light from the infrared semiconductor laser chip 103 in the laser module of FIG. By rotating the micromachine rotation stage 105 by 180 °, the vertically rising light can be switched to the infrared side.
As a result, the optical axes from the two semiconductor laser chips can be matched, and the incident light to the objective lens can be perpendicularly projected at the two wavelengths without adding an additional optical component such as a hologram outside the laser module. And increase in aberration can be suppressed.

In manufacturing such a laser module, at least basically, first, a photodetector is formed on a silicon substrate, and then a protective film for protecting the photodetector is formed on a center rotating stage. A film is formed leaving a portion, a rotary stage manufacturing portion is etched with potassium hydroxide or the like, and then a rotary stage and a 45 ° mirror are manufactured in this portion using the technology shown in the above-mentioned document, The protective film of the photodetector is removed, and the two semiconductor lasers are mounted by soldering.

FIG. 3 is a diagram showing the laser module of FIG. 1 or 2 mounted on a package 301. The bonding pad and the package electrode are connected with a gold wire or the like. Thereafter, a cap (not shown) is put on the cover and sealed with nitrogen or the like to prevent oxidation.

FIG. 4 shows an embodiment in which an optical disk drive as an optical information processing apparatus is constituted by using the packaged laser module shown in FIG. The light emitted from the laser module 301 is a collimating lens 401
Is turned into a parallel light beam by
The optical path is folded back, the diffraction grating 403, the objective lens 404
After that, the light is focused on the optical disk 405. Diffraction grating 40
The lens 3 and the objective lens 404 are mounted on a lens actuator 406 and driven integrally. When a polarizing diffraction grating and a λ / 4 plate are integrally used for the diffraction grating 403, the diffraction grating does not act on the light going to the disk, but acts only on the light that is reflected and returns to the laser module. The reflected light can be branched. Also, a compatible lens capable of recording and reproducing signals on both CD and DVD is used as the objective lens. The optical disk 405 is a spindle motor 40
7 and rotate. The light reflected from the optical disk 405 and returned to the laser module 301 is focused on a light receiving area, converted into a photocurrent proportional to the light intensity, and sent to a detection circuit system. At least the laser module 301, the collimating lens 401, and the rising mirror 40
2. An optical head 408 is constituted by the diffraction grating 403, the objective lens 404, and the lens actuator 406. Of the detected photocurrents, those in the photodetection area for focus detection are converted by the focus detection circuit 409 into defocus signals. Based on the output, the disc discrimination circuit 410 discriminates whether the disc is a DVD or a CD based on, for example, the amplitude of the defocus signal, and drives the micromachine rotary stage based on the discrimination result to select a desired light source. Therefore, before the discrimination, either the red semiconductor laser or the infrared semiconductor laser is turned on regardless of the type of the disc, and only the defocus signal is detected. As a result, if necessary, the micromachine rotating stage is driven so as to select a correct semiconductor laser. On the other hand, the defocus signal is
The focus is fed back to 6 to perform focus control. The tracking signal output from the laser module and the photocurrent from the reproduction signal light receiving area are converted into a reproduction signal by the controller circuit 412 and a tracking signal by the tracking circuit 413. The tracking signal is fed back to the lens actuator 406 and used as a drive signal in the radial direction of the disk.
The tracking circuit drives the feed motor 414 based on the read address instruction from the controller and the tracking error signal, thereby positioning the optical head 408 at an appropriate disk radial position. The reproduction signal detected by the controller circuit is output as user data 415. Alternatively, user data 415 is input to the controller circuit 412,
In response, the controller circuit 412 controls the laser drive circuit 411, controls the light emission of the semiconductor laser chip, and records information on the optical disc.

FIG. 5 is a diagram showing the problems of the conventional two-wavelength laser module. Two semiconductor laser chips 102,
Assuming that rays emitted from 103 and passing through the center of the objective lens are the optical axes 501 and 502 of the respective semiconductor lasers, they enter the objective lens at different incident angles. Therefore, even if the semiconductor laser chip or the objective lens 404 is arranged so that the optical axis of the light beam of one of the wavelengths coincides with the optical axis 503 of the objective lens, the other does not necessarily coincide with the objective axis, and the objective is not changed. It will be incident on the lens. As a result, aberrations such as astigmatism and coma occur in the condensed light spot, and the size increases. Therefore, there is a possibility that the quality of a signal that can be recorded on and reproduced from the optical disc 405 is degraded.

FIG. 6 shows an embodiment of a micromachine rotary stage. This example is based on the Technical Digest of Annual International Workshop
On Micro Electro Mechanical Systems, 1998, pp. 116-120.
The micromachine rotary stage includes a rotor 601 having eight projections and twelve stators 602. The stator is electrically insulated from the substrate, and alternately applies alternating voltages having a phase shift of 120 ° to adjacent stators. The rotor electrically connected to the substrate is grounded to the ground level. With the above configuration, the rotary stage can be rotated. The rotation speed is determined by the frequency of the applied AC voltage. What is necessary is just to fix the rotating mirror of this application to a rotor.

FIG. 7 shows a manufacturing process of the micromachine rotary stage. First, using a SOI substrate (Silicon On Insulator) 701 having an SiO2 layer 702 in the middle of the substrate, a bottom portion of the rotor is patterned by a recess pattern and etched (a). Next, a pattern for reducing contact resistance and conducting with the substrate is formed by anisotropic dry etching (b), a pattern of the rotor and the stator is drawn (c), and SiO2 in the wafer is formed by reactive ion etching. To form a rotor and a stator (d). Next, after doping with phosphorus, the rotor and the stator are separated by dicing, and the stator 6 is removed.
In the case of 02, SiO2 of the mounting portion of the rotor is etched. The rotor 601 has SiO2 dissolved by hydrofluoric acid etching, separated from the substrate, and rinsed with pure water.
Further, a rotor is mounted on the shaft 703 of the stator.

[0020]

According to the present invention, two semiconductor lasers can be combined with one another.
In an optical information processing apparatus using a packaged laser module, the optical axes of the two wavelengths can be matched without using any additional optical components outside the laser module, and the aberration in the objective lens increases. Thus, an inexpensive and high-performance optical information processing apparatus can be provided.

[Brief description of the drawings]

FIG. 1 shows a basic embodiment of a laser module according to the present invention.

FIG. 2 shows an embodiment in which laser radiation 104 is switched to light from an infrared semiconductor laser chip 103 in the laser module of FIG.

FIG. 3 is a package mounting diagram of the laser module of the present invention.

FIG. 4 is an embodiment of an optical information processing apparatus according to the present invention.

FIG. 5 is a diagram showing a problem of a conventional two-wavelength laser module.

FIG. 6 is an embodiment of a micromachine rotary stage.

FIG. 7 shows a manufacturing process of a micromachine rotary stage.

[Explanation of symbols]

101 {silicon substrate, 102} red semiconductor laser chip, 103 {infrared semiconductor laser chip, 104}
{Laser radiation, 105} micro-machine rotating stage, 106 ‥‥ 45 ° reflection mirror, 107 ‥‥ photodetector for tracking / RF signal detection, 108 ‥‥ photodetector for defocus detection, 109 ‥‥ bonding pad, 301
{Laser module package, 401} Collimating lens, 402} Rising mirror, 403} Diffraction grating, 404} Objective lens, 405} Optical disk,
406 lens actuator, 407 spindle motor, 408 optical head, 409 focus detection circuit, 410 disk discrimination circuit, 411 laser drive circuit, 412 controller circuit, 413 tracking circuit , 414 feed motor, 415 user data, 501 red semiconductor laser optical axis, 501
{Optical axis of infrared semiconductor laser, 503} Optical axis of objective lens, 601 {rotator, 602} stator, 701}
{SOI substrate, 702} SiO2 layer, 703} Shaft.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 5/022 H01L 31/02 D

Claims (2)

[Claims] 1. A base substrate, at least two semiconductor laser chips having different wavelengths mounted on the base substrate, a rotary 45 ° mirror formed on the base substrate, and a periphery of the rotary 45 ° mirror. A laser module, wherein an arranged photodetector is packaged integrally. 2. The laser module according to claim 1, an optical system for converging the laser beam on an optical information recording medium, a mechanism for scanning the optical information recording medium with respect to the converged spot, A mechanism capable of discriminating at least two types of information recording media and detecting the disc as a medium discrimination signal; and driving the rotary 45 ° mirror in response to the medium discrimination signal to generate the laser light emitted from the two semiconductor laser chips. A control mechanism for rotating any one of them so as to selectively reflect the light in a direction perpendicular to the surface of the base substrate;