JPH0973648A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a substrate formable by a simple semiconductor substrate working process and to provide an inexpensively semiconductor laser device by using a semiconductor substrate without having a mirror surface for polarizing a laser beam. SOLUTION: A semiconductor laser element 2 is arranged and fixed on the base 1a of the recessed part 5 of the substrate 1 and is so arranged that the end face on the side opposite to the end face 2a to emit the laser beam faces the inclined flank 1b, of the recessed part 5. Plural PD elements 4, 6 as photodetectors are arranged on the slope 3 of the substrate 1 and the flank 1b2 of the recessed part 5. The element 4 among these elements receives the reflected light from a disk and exists in a positional relation optical conjugate with the exit end face 2a of the laser beam. On the other hand, the element 6 receives the output light from the backward end face of the element 2 and faces the end face of the element 2 in proximity thereto and, therefore, the high coupling efficiency is obtd. with a small area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor for an optical pickup for recording and reading information stored in an information recording medium such as an optical disk or a magneto-optical disk by using coherent light from a semiconductor laser element. The present invention relates to a laser device.

[0002]

2. Description of the Related Art In a CD (compact disc),
The record information is accumulated as a pit row arranged along a track provided on the disc surface. When the pit row (information track) is irradiated with coherent light collected by the objective lens, if the spot position hits the edge of the pit, the reflected light with a phase difference will cause an interference effect, except for the pit area. The amount of reflected light is reduced compared to the case where the light is reflected on a flat place. In the optical pickup, the attenuated pulse of the reflected light amount corresponding to this pit train is converted into an electric pulse signal by the photodetector and output.

By the way, it is extremely difficult to obtain the ideal flatness of an actual optical disc without any warp or distortion on the surface, and when the inclination of the rotation axis of the driver due to a mounting error is taken into consideration, In order to read information accurately, the positional relationship between the objective lens of the pickup and the disk surface must be controlled so that it is always appropriate. That is, it is necessary to perform position control in the tracking direction so that the irradiation light from the laser does not diverge from the pit train (information track) and focusing control for always matching the focal position of the laser beam with the information surface of the disc.

The current position information for performing such control needs to be detected for two independent systems of the tracking displacement signal and the focusing displacement signal, and an optical system in which various optical elements are precisely arranged is constructed. I had to do it. For this reason, the optical pickup requires a relatively large capacity optical element arrangement space, and it is also necessary to perform complicated adjustment work for each part during assembly. These have hindered the demands for improvement of optical pickups that are compact and lightweight for high-speed access and need no adjustment for cost reduction.

In order to solve such obstacles, various attempts have conventionally been made to reduce the number of parts by combining the optical element functions of a hologram element to reduce the size and weight of the optical pickup head. In addition, in order to make the size and weight more effective and to reduce the number of adjustment points, the semiconductor laser device (LD; LD;
Efforts have also been made to integrate a laser diode) and a photodetector (PD; photo diode).

FIG. 4 shows an example of a hybrid mounting integration of such a semiconductor laser and a photodetector. Silicon (S
Photodetectors 17 and 18 for detecting an RF information signal, an error signal, and an LD power monitor signal are formed on a semiconductor substrate 14 made of i) or the like by a multi-divided pn junction. A recess 14a is formed in the center of the semiconductor substrate 14 by etching or the like.
A semiconductor laser device (LD) 15 is formed on the bottom surface of the recess 14a.
Are arranged. One surface 16 of the side surfaces forming the recess 14a is inclined and is used as a deflection mirror for the emitted light of the LD 15. Therefore, the laser light emitted from the LD 15 in a direction horizontal to the surface of the semiconductor substrate 14 and the bottom surface of the recess 14a has its optical axis in a direction substantially perpendicular to the surface of the semiconductor substrate 14 due to the inclined surface 16 as a deflection mirror. That is why it is biased.

The package form of this hybrid element is as schematically shown in FIG. 5, in which laser light is emitted through a transparent window provided on the entrance / exit surface 20 on the upper side of the package 19 in the figure, and the hybrid element serves as an information recording medium. Similarly, the reflected light from the optical disk is incident on the entrance / exit surface 20 of the package.

Next, FIG. 6 shows a schematic diagram of an optical system of an optical pickup using this hybrid element. According to a general design method of an optical pickup which is made thin, the optical path to the raising mirror 22 arranged directly below the objective lens 23 is made parallel to the pickup base surface 21. That is, the laser light emitted from the LD 15 is deflected by the deflection mirror 16 and forms an optical path in parallel with the pickup base surface 21 from the transparent window provided on the upper surface of the package 19. Then, the laser light is vertically deflected by the rising mirror 22, condensed by the objective lens 23, and applied to the information track of the rotating optical disk. The reflected light from the optical disk passes through the objective lens 23 and the rising mirror 22 in the opposite optical path, and then is divided into a plurality of pieces by the hologram element 25 that forms diffracted light, and the photodetector 17 provided on the semiconductor substrate 14 is provided. It is designed to be received by.

[0009]

By the way, in order to read the high-density pit information on the optical disk surface without error,
The quality of the light spot at the focal position is important, and when the inclined surface 16 of the semiconductor substrate is used as a deflection mirror for laser light, high surface accuracy is required for the mirror surface. Further, in order to obtain a high reflectance from this deflecting mirror, it was necessary to strictly control the conditions for forming the reflective film. Therefore, in the method of using such a semiconductor substrate mirror as a laser emission light deflection mirror, strict process control is required for processing the substrate, and it is difficult to reduce the cost.

Further, in the case of constructing an optical pickup optical system as shown in FIG. 6, the LD / PD hybrid device package 19 emits laser light in a direction perpendicular to an entrance / exit surface 20 provided with a transparent window. Therefore, this entrance / exit surface 20
Must be raised so as to be orthogonal to the pickup base surface 21. However, in such a case, as shown in the figure, a height corresponding to the height dimension w1 of the package 19 is required, which is a factor of increasing the thickness of the entire pickup device without utilizing the lowest height dimension w2 of the package 19. It was

[0011]

A semiconductor laser device in an optical pickup according to the present invention comprises a semiconductor laser element for irradiating a track of an information recording medium with a laser beam, and a light detection for detecting a reflected light from the information recording medium. And a semiconductor substrate on which the semiconductor laser element and the photodetector are arranged, the semiconductor substrate is a recess having a bottom surface, a side surface, and an open portion in which at least a part of the side surface is open. , And an inclined surface formed non-parallel to the bottom surface, the semiconductor laser,
It is characterized in that it is fixed to the bottom surface of the concave portion of the semiconductor substrate and emits laser light from the open portion side, and the photodetector is formed on the inclined surface of the semiconductor substrate. Further, the semiconductor substrate is mounted on a package, and when the package is arranged at the lowest height, laser light is emitted and incident from a side surface portion thereof.

In the semiconductor laser device in the optical pickup according to the present invention, the laser light is emitted without being deflected, and the reflected light from the disk, that is, the signal light is received by the PD as a photodetector formed on the inclined surface of the semiconductor substrate. It is configured to
Since the inclined surface is not used as the deflecting mirror, it is not necessary to form the deflecting mirror surface as in the conventional case, and the process control such as surface accuracy of semiconductor substrate processing can be loose. In addition, when the hybrid-mounted package is placed at the lowest height, the structure allows laser light to enter and exit from the side of the package, so this thin package should be installed in the direction parallel to the pickup base surface. Can be made thinner.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a semiconductor laser device according to the present invention will be described below in detail with reference to the drawings.

[0014]

1 is a perspective view showing the structure of a main part of a semiconductor laser device for an optical pickup according to an embodiment of the present invention. In the figure, reference numeral 1 is a semiconductor substrate made of silicon (Si), and a step having a predetermined shape is formed by etching. Inside this step, there is a bottom surface 1a having a depth of several tens of μm and a side surface 1b having a longitudinal direction of several hundreds of μm.
₁ and includes a recess 5 having an opening portion 1c which part of the side is opened. The shape of the step region seen from the upper surface is substantially convex, and the protrusion amount of the step region in the protruding portion is set to be slightly longer than the chip length of the semiconductor laser element 2. Further, as a step other than the concave portion 5, there is an inclined surface 3 which is formed at the edge of the semiconductor substrate 1 and communicates with the open portion 1c.
It is formed non-parallel to a. The bottom surface 1a and the surface 1d of the semiconductor substrate 1 are parallel to each other.

The semiconductor laser element 2 is disposed on the bottom surface 1a of the recess 5 and is fused and fixed with a low melting point metal.
The end surface on the opposite side of the end surface 2a from which the laser light is emitted is a recess 5
It is arranged so as to face the inclined side surface 1b _{2 of the} .

On the inclined surface 3 of the semiconductor substrate and the inclined side surface 1b ₂ of the recess 5, a plurality of PD elements 4 and 6 as photodetectors are arranged by pn junction in a predetermined selected region. Of these, P formed on the inclined surface 3
The D element 4 is for receiving the reflected light from the disc, and is in a position optically conjugate with the end face 2a from which the laser light is emitted. Since the PD element 4 is formed on the inclined surface 3 of the semiconductor substrate, that is, the inclined surface 3
Is not parallel to the surface of the semiconductor substrate 1 and the bottom surface 1a of the recess 5 but forms an angle, the reflected signal light returning substantially in the opposite direction to the light emitted from the end surface 2a of the semiconductor laser element 2 is PD element 4 formed on this inclined surface 3
Easily combined with.

From the output of the PD element 4, a focus error signal can be obtained by a known spot size method, a knife edge method, or the like, and a tracking error signal can be obtained by a known method such as a three-beam method or a push-pull method. At the same time, the RF information signal can be obtained.
Here, depending on the selection of the error signal detection method, the PD
By determining the detailed division pattern of the element 4, various detection methods can be supported.

On the other hand, the PD element 6 as a photodetector formed on the side surface 1b ₂ of the concave portion 5 is for receiving the output from the rear end surface of the semiconductor laser 2, and is provided on the end surface of the semiconductor laser 2. Since they face each other in close proximity, high coupling efficiency can be obtained in a small area. Taking advantage of the fact that the PD element 6 has a small area, that is, the PD element has a low junction capacitance characteristic, the PD element 6 is known as a SCOOP.
(S elf Co upled O ptical P ic
It has also become possible to use it for RF information signal detection of the kup) method.

FIG. 2 is a perspective view showing a state in which the semiconductor substrate 1 according to the present invention including the semiconductor laser 2 and the photodetector 4 is mounted on the package 7. According to the present embodiment, the laser light emitted from the semiconductor laser element 2 emitted in the horizontal direction to the surface of the semiconductor substrate 1 and the bottom surface 1a of the recess 5 to which the semiconductor laser element 2 is fixed is deflected by the deflection mirror. Without moving, it goes straight and is emitted from the side surface portion of the package 7. Further, the signal light reflected by the optical disk also enters from the side surface of the package 7. Reference numeral 8 is a transparent window that protects the semiconductor substrate 1 mounted on the package 7 and transmits laser light.

Picking up such a package 7
FIG. 3 is a schematic diagram of the optical system in a state of being attached to the base member 13.
Shown in 3A is a view as seen from a side surface direction orthogonal to the entrance / exit surface of the package 7, and FIG.
FIG. 7 is a plan view seen from xx ′ in FIG. The arrow indicating the optical path indicates the center of the light flux. In FIG. 3, the optical path of the laser light emitted from the package 7 follows the same optical path as that shown in FIG. 6 of the conventional example and is applied to the disk 12 as an information recording medium, and the reflected light also returns in the same optical path. , Package 7.

At this time, the package 7 is a pickup
It is arranged so as to have the lowest height with respect to the base member 13, and the laser light enters and exits from its side surface.
That is, the package 7 is arranged such that the height thereof is w2, and it is not necessary to set w1 to the height dimension as in the conventional example shown in FIG. Therefore, the overall thickness of the optical pickup can be reduced as compared with the conventional structure. In FIG. 3,
Reference numeral 13 is a hologram element that forms diffracted light. In the hologram element 13, the reflected light from the optical disk is distributed and coupled to the PD element 4 disposed near the semiconductor laser 2, and an error signal and an error signal are output from the PD output. A hologram pattern designed to obtain an RF information signal is formed. Further, reference numeral 10 is a rising mirror, reference numeral 11
Is an objective lens.

The formation of the semiconductor substrate in this embodiment can be performed by a known silicon processing process,
Since it is not necessary to form a deflecting mirror for deflecting the laser light from the semiconductor laser element, the surface precision control during etching processing may be more gradual than in the conventional example. Further, in the present embodiment, it is possible to form an integrated circuit for processing the signal received by the PD on the semiconductor substrate 1, in which case the optical pickup can be made smaller and lighter.

Further, in this embodiment, the end surface 2a of the semiconductor laser device 2 for emitting the laser beam and the light receiving surface on which the photodetector 4 is arranged are aligned with each other to have an optically conjugate positional relationship. However, the present invention is not limited to this, and the position of the etching surface, that is, the position of the PD element 4 as the photodetector and the fixation of the semiconductor laser element 2 are determined by the design specifications of the optical system such as HOE. The positional relationship can be set freely.

[0024]

As described above, according to the present invention,
By using a semiconductor substrate that does not have a mirror surface that deflects the laser light emitted from the semiconductor laser element, the substrate can be formed by a simple semiconductor substrate processing process,
It is possible to provide an inexpensive semiconductor laser device. Further, according to the present invention, when the package on which the semiconductor substrate is mounted is arranged at the lowest height, the laser light is incident and emitted from the side surface portion thereof, so that it is possible to reduce the thickness of the entire optical pickup. An effective semiconductor laser device can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of an embodiment of a semiconductor laser device according to the present invention.

FIG. 2 is a perspective view showing an embodiment of a semiconductor laser device according to the present invention.

FIG. 3 is a schematic diagram for explaining an optical system of an optical pickup using the semiconductor laser device according to the present invention,
(A) is a side view and (B) is a plan view.

FIG. 4 is a perspective view showing a main part of a conventional semiconductor laser device.

FIG. 5 is a perspective view showing a conventional semiconductor laser device.

FIG. 6 is a schematic diagram for explaining an optical system of an optical pickup using a conventional semiconductor laser device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 1a Bottom of recess 1b ₁ , 1b ₂ Side of recess 1c Open of recess 2 Semiconductor laser device (LD) 3 Inclined surface 4, 6 Photodetector (PD) 5 Recess 7 Package 12 Information recording medium

Claims (2)

[Claims] 1. A semiconductor laser element for irradiating a track of an information recording medium with a laser beam, a photodetector for detecting reflected light from the information recording medium, the semiconductor laser element and the photodetector are arranged. In a semiconductor laser device including a semiconductor substrate, the semiconductor substrate has a concave portion having a bottom surface, a side surface, and an open portion in which at least a part of the side surface is open, and an inclination formed non-parallel to the bottom surface. A surface, the semiconductor laser is fixed to the bottom surface of the recess of the semiconductor substrate, emits laser light from the open side, and the photodetector is formed on an inclined surface of the semiconductor substrate. A semiconductor laser device characterized by the above. 2. The semiconductor substrate is mounted on a package,
2. The semiconductor laser device according to claim 1, wherein when the package is arranged at the lowest height, the laser light is emitted / incident from a side surface portion thereof.