JPH01267853A - Optical pickup - Google Patents

Abstract

PURPOSE:To decrease manday by locating a laser element and photodetectors on the sides of both the main faces of a transparent plate and making only the two parallel main faces of the transparent plate into optical faces. CONSTITUTION:A laser element 3 and photodetectors 5a and 5b are located on the sides of both main faces 8a and 8b of a transparent plate 7, and a half mirror film 9 to reflect a laser beam from the laser element 3 to the side of a recording medium and transmit return light from the recording medium and another mirror film 11 are provided only on the main faces 8a and 8b of the transparent plate 7. Gratings 10 and 12 to put downward light emitted from the transparent plate 7 and lead it to the photodetectors 5a and 5b is provided on the face of the transparent plate 7 on the side of the photodetectors 5a and 5b. Thus, for example, the work of lapping the end faces of the transparent plate 7 in the state of small pieces of individual transparent plates 7 becomes unnecessary and the manday can be decreased.

Description

[Detailed description of the invention] The present invention will be described in the following order.

A. Industrial field of application B6 Overview of the invention C1 Prior art [Fig. 2 D1 Problem to be solved by the invention E0 Means for solving the problem F0 Effect G. Examples [Fig. 1] H0 Invention Effects (A, Industrial Application Field) The present invention relates to an optical pickup, in particular, a method that includes a laser element and a photodetector on one semiconductor substrate, and reflects the laser light from the laser element toward a recording medium to emit light from the recording medium. The present invention relates to an optical pickup equipped with a transparent plate that is a prism that guides returned light to a photodetector.

(B. Summary of the Invention) In the above-mentioned optical pickup, the present invention includes a laser element and a photodetector on both principal surfaces of the transparent plate in order to make it easier to manufacture the transparent plate, which is a prism, and to reduce the cost of the optical pickup. A half-mirror film or other mirror film is provided only on the main surface of the transparent plate to reflect the laser light from the laser element toward the recording medium and to transmit the return light from the recording medium. A grating that guides the emitted light downward to the photodetector is provided on the surface of the transparent plate on the photodetector side.

(C, Prior Art) [FIG. 2] Semiconductor laser devices are increasingly used as light sources in optical heads that optically record and reproduce information on optical recording media. Conventional optical heads generally transmit light from a light source to an optical recording medium (e.g. compact disc, video disc, etc.) using an objective lens.
The returning light from the optical recording medium is reflected by a beam splitter to the light receiving device, and the returned light is detected by the light receiving device.

However, in order to meet the demands for downsizing and simplifying the structure of optical heads, the semiconductor laser element and the light receiving element are placed close together, and the laser light emitted from the semiconductor laser element is transferred to the optical head on the surface where the light receiving element is formed. Research has been conducted on reading signals by detecting the returned light from the optical recording medium with a light-receiving element, which is reflected on the recording medium side.
It is introduced in the publication No.-158970.

As a further development of the technology described in the above-mentioned publication, the applicant company fixes a semiconductor laser element on the area where the light-receiving element is not formed on the semiconductor substrate on which the light-receiving element is formed, and Developed a device in which a prism was fixed on the light-receiving element forming area of a substrate, and applied related technology in Japanese Patent Applications No. 61-38576 and No. 61-385.
75, Japanese Patent Application No. 61-126318, etc.

FIG. 3 shows an example of such an optical integrated circuit device. In the drawing, a is a semiconductor substrate, b and b are photodetectors constituted by algebraic photodiodes c and c"", which perform servo operations such as focusing and tracking, and signal reading. d is a submount fixed on a region different from the photodetector b of the semiconductor substrate a, and e is a semiconductor laser element chip-bonded onto the submount d, with the laser beam emitting end face facing the photodetector side. Pounded to face.

Reference numeral f denotes a prism made of glass with a trapezoidal side surface shape, and is bonded to the photodetectors b and b of the semiconductor substrate a at the bottom surface thereof, with the inclined end face g of the prism facing toward the semiconductor laser element e. A half-mirror film is formed on the inclined end surface g and on the bottom surface corresponding to the photodetector b on the right side in FIG. Further, a full mirror film i is formed approximately in the middle of the upper surface of the prism f. These mirror films are formed in a two-layer structure, for example, by an amorphous silicon layer and a Ti0 layer.

In this optical pickup shown in FIG. 2, the laser beam emitted from the semiconductor laser element e is reflected by the inclined end face g of the prism f toward the upper side of the recording medium (not shown), and the return light from the recording medium is A part of the returned light is received by the right photodetector b, and the rest is reflected diagonally upward by the half mirror film on the bottom of the prism 6. This reflected return light is reflected by the full mirror film i on the upper surface of the prism f and is received by the left photodetector b.

(D. Problem that the invention attempts to solve) By the way, the second
In the optical integrated circuit device shown in the figure, the prism f reflects, enters, and emits light on three surfaces: the inclined end surface g, the bottom surface, and the top surface, so these three surfaces must be finished as optical surfaces. . In addition, a reflective film 9a is provided on the three surfaces.
, 9b, 9C must be formed. This is very troublesome, and it is also difficult to miniaturize the prism f. This is because lapping is necessary because the surface roughness is too large to form an optical surface just by cutting the glass, and lapping of the inclined end face g of the prism f is extremely difficult. That is, one possible method for forming the prism f is to form a transparent plate into a wafer shape and then dice it. In this case, before dicing (in other words, at the wafer stage), the top and bottom surfaces are If the prism is wrapped, there is no need to wrap the top and bottom surfaces of the prism in a state where it is cut into pieces, and therefore there is no problem that lapping the top and bottom surfaces of the prism is particularly troublesome. Furthermore, it is not difficult to form a half mirror or a full mirror on the top and bottom surfaces of the prism since it can be done in the form of a wafer. However, lapping to make the inclined end face g an optical surface and formation of a reflective film after lapping can only be performed after dicing a wafer-shaped transparent plate into individual prisms, and It is not easy to wrap the end face of the prism and form a reflective film while the prism is in a stained state. Therefore, it is troublesome to form the prism, and the manufacturing cost of the prism increases, leading to an increase in the price of the optical pickup.

The present invention has been made in order to solve these problems, and makes it possible to manufacture the prisms to be used in a mass-producible manner, further reducing the manufacturing cost of the prisms, and further improving the optical pickup. The aim is to reduce the price of.

(E. Means for Solving the Problems) In order to solve the above problems, the optical pickup of the present invention has a laser element and a photodetector located on both main surfaces of the transparent plate, and only the main surface of the transparent plate A grating is provided with a half mirror film or other mirror film that reflects the laser light from the laser element toward the recording medium and transmits the return light from the recording medium, and also directs the light emitted from the transparent plate downward to the photodetector. is provided on the photodetector side surface of the transparent plate.

(F. Effect) According to the optical pickup of the present invention, only the two parallel principal surfaces of the transparent plate need to be used as optical surfaces. If both principal surfaces of the transparent wafer are lapped to form an optical surface, there is no need to perform the work of finishing the transparent wafer into an optical surface after dicing. Therefore, it is no longer necessary to wrap the end faces of each transparent plate after it has been cut into pieces, and the manufacturing cost of the transparent plate is reduced accordingly. Furthermore, the number of man-hours required to form the reflective film and grating on the optical surface can be similarly reduced, contributing to a reduction in manufacturing costs. Even if laser light is generated from the laser element at a position higher than the surface of the semiconductor substrate, it is bent downward by the grating provided on the transparent plate, so that the laser light is guided to the photodetector formed on the surface of the semiconductor substrate. You can do it like this.

(G. Embodiment) [FIG. 1] Hereinafter, the optical pickup of the present invention will be explained in detail according to the illustrated embodiment.

FIG. 1 is a perspective view showing one embodiment of the optical pickup of the present invention.

1 is a semiconductor substrate; 2 is a submount made of, for example, a silicon semiconductor, disposed on the surface of the semiconductor substrate 1; 3 is a semiconductor laser element provided on the submount 2; 4;
is a monitor photodetector formed on the surface of the submount 2. The semiconductor laser element 3 is disposed at a location appropriately shifted to the left side in FIG. 1 from the center of the semiconductor substrate 1, and its optical axis is parallel to the surface of the semiconductor substrate 1 (that is, horizontal), and the optical axis is parallel to the surface of the semiconductor substrate 1, and It is made to be diagonal with respect to each side of the semiconductor substrate 1, which faces diagonally to the right and toward the front.

5a and 5b are photodetectors formed on the surface of the right side of the semiconductor substrate 1 in FIG.
Two photodiodes formed parallel to each other 6.6.
Consists of 6. The photodetector 5a is the first photodetector of the semiconductor substrate l.
A photodetector 5b is located approximately at the center in the front and back direction in the figure.
is located slightly further back than photodetector a.

Reference numeral 7 denotes a rectangular parallelepiped-shaped transparent plate forming a prism, which is fixed onto the semiconductor substrate 1 so as to divide the semiconductor substrate 1 into left and right halves at approximately the center. 8a and 8b are main surfaces finished as optical surfaces by wrapping the transparent plate 7, and are parallel to each other. is semiconductor substrate 1
is fixed to.

Reference numeral 9 denotes a half mirror film formed on the main surface 8a of the transparent plate 7 on the side of the semiconductor laser element 3, which is located on the opposite side in FIG. Light is incident diagonally to the right (from the perspective of the half mirror film 9), and the laser beam is directed diagonally to the left (from the perspective of the half mirror film 9).
The light is reflected onto a recording medium (not shown), such as a laser disc or a compact disc (not shown) located at the half-mirror film 9. Since the half mirror film 9 allows the return light to pass through, the return light is incident on the transparent plate 7. 10 is the main surface 8 of the transparent plate 7 on the photodetector side.
With the grating and half mirror film formed in b,
It is provided at a position to receive the returned light that has passed through the half mirror film 9 and entered the transparent plate 7. The grating and half-mirror film 10 are formed by forming a grating made of unevenness on the main surface 8b of the transparent plate 7, and forming a half-mirror film on the uneven grating. Part of the returned light that has passed through the half mirror film 9 and entered the grating and the half mirror film 10 is reflected, and the rest is bent downward by the grating, exits the transparent plate 7, and is received by the photodetector 5a.

A full mirror film 1 is formed on the main surface 8a of the transparent plate 7, and is formed at a position that receives laser light from the grating and the half mirror film 10, which is approximately in the center of the main surface 8a. The laser beam from the grating and half mirror film 10 is reflected.

Reference numeral 12 denotes a grating formed on the main surface 8b of the transparent plate 7, and is provided at a position to receive the returned light reflected by the full mirror film 11, and bends the returned light appropriately downward and emits it to the photodetector 5b. so that the light is received by the

In addition, detection of focus error by reading signals recorded on the recording medium from the amount of light received by the photodetectors 5a and 5b;
Tracking errors are detected.

The reason why gratings are provided on the main surface 8b on the photodetector side in the transparent plate 7 corresponding to each of the photodetectors 5a and 5b is as follows.

That is, the optical axis of the laser beam emitted from the semiconductor laser element 3 is parallel to the surface of the semiconductor substrate 1, and the optical path is formed on one plane parallel to the surface of the semiconductor substrate 1 at a position higher than the surface. If left as is, the returned light will reach the photodetectors 5a and 5 formed on the surface of the semiconductor substrate 1.
This means that the light will not be received by b. Therefore, a grating that bends the light obliquely downward is provided in the portion of the transparent plate 7 that emits the laser light toward the photodetectors 5a and 5b so that the light is received by the photodetectors 5a and 5b.

(H, Effect of the Invention) As described above, the optical pickup of the present invention includes a laser element disposed on a portion of the semiconductor substrate, and a plurality of photodetectors provided on the surface of the other portion of the semiconductor substrate. , a transparent plate having both principal surfaces parallel to each other is formed between a portion of the semiconductor substrate where the laser element is arranged and a portion where the photodetector is provided; The transparent plate has a surface on the laser element side that reflects the laser light from the laser element toward the recording medium and allows the return light from the recording medium to pass through. a first half-mirror film provided on the photodetector side, and a second half-mirror provided on the photodetector side that reflects a part of the light that passes through the first half-mirror film and enters the transparent plate. a grating formed in a portion provided on the second half-mirror film that diffracts the light transmitted through the half-mirror film and guides it to a part of the photodetector; A mirror film provided on the surface on the laser element side that reflects the reflected light, and a grating provided on the laser element side that diffracts the light reflected by the mirror film and guides it to another photodetector. It is characterized by having at least the following.

Therefore, according to the optical pickup of the present invention, only the parallel double cloth of the transparent plate needs to be used as the optical surface, so the transparent plate is formed by dicing a transparent wafer, and in order to form the transparent plate, If both principal surfaces of the transparent wafer are lapped to form an optical surface, there is no need to perform the work of finishing the transparent wafer into an optical surface after dicing. Therefore, it is no longer necessary to wrap the end faces of each transparent plate after it has been cut into pieces, and the manufacturing cost of the transparent plate is reduced accordingly. Furthermore, the number of man-hours required to form the reflective film and grating on the optical surface can be similarly reduced, contributing to a reduction in manufacturing costs. Even if laser light is generated from the laser element at a position higher than the surface of the semiconductor substrate, it is bent downward by the grating provided on the transparent plate, so that the laser light is guided to the photodetector formed on the surface of the semiconductor substrate. You can do it like this.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the optical pickup of the present invention, and FIG. 2 is a perspective view showing a conventional technique. Explanation of symbols 1... Semiconductor substrate, 3... Laser element, 5a, 5b
...Photodetector, 7...Transparent plate, 8a, 8b...Main surface, 9...First
10... Grating (and second half mirror film), 11... Mirror film, 12... Grating. 5a, 5b Photo holder

Claims (1)

[Claims] (1) A laser element is placed on a portion of the semiconductor substrate,
A plurality of photodetectors are provided on a surface portion of another portion of the semiconductor substrate, and both main surfaces are parallel to each other between a portion of the semiconductor substrate where the laser element is arranged and a portion where the photodetector is provided. The transparent plate formed on the optical surface is
The transparent plate is arranged so that its main surfaces face the laser element side and the photodetector side, and the transparent plate reflects the laser light from the laser element toward the recording medium side and allows the return light from the recording medium side to pass through. However, there is a first half mirror film provided on the surface on the laser element side, and a second half mirror film provided on the photodetector side that reflects a part of the light that passes through the half mirror film and enters the transparent plate. a second half-mirror film, a grating formed in a portion provided on the second half-mirror film that diffracts the light transmitted through the half-mirror film and guides it to a part of the photodetector; A mirror film provided on the laser element side where the light reflected by the half mirror film is reflected, and a mirror film provided on the laser element side where the light reflected by the mirror film is diffracted and guided to another photodetector. An optical pickup characterized in that it has at least a grating provided therein.