JPS62197931A - Focus detecting device - Google Patents

Abstract

PURPOSE:To miniaturize a device and to reduce the cost by making focus detection that uses tow photodetectors possible by single prism and integrating plural optical parts. CONSTITUTION:The prism 37 of a focus detecting device 30 is provided with the first and second semitransparent reflecting faces, and the single prism 37 is made to have the function of a beam splitter that separates a beam 45 for projecting an optical recording medium 16 from a beam 45 from the optical recording medium 16 and the function of a beam splitter that separates the beam 45 to detect the beam 45 from the optical recording medium 16 around the convergent point. A semiconductor laser 31, the prism 37 and the first and second light detector 33, 34 are integrated, and plural optical parts are arranged on the same plane of a semiconductor substrate 32. Thus, the number of parts is decreased, and the device can be miniaturized and low cost is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus detection device for detecting the focusing state of an optical recording medium.

[Summary of the invention]

The present invention enables focus detection using a single prism to perform focus detection using two photodetectors before and after the convergence point of a beam from an optical recording medium in a focus detection device such as the one described above. By integrating these optical components and arranging them on the same plane of the semiconductor substrate, the device can be made compact and low in cost.

[Conventional technology]

A focus error signal indicating the focusing state of an optical recording medium is required to have symmetry with respect to a zero-crossing point, linearity in the vicinity of the zero-crossing point, and elimination of read signal leakage.

JP-A-60-217535 discloses a focus detection device 10 as shown in FIG. 8A as a focus detection device that satisfies the above requirements.

This focus detection device 10 makes a beam 12 emitted from a light source 11 such as a laser diode pass through a beam splinter 13, a collimator lens 14, and an objective lens 15, enters an optical recording medium 16, and is reflected by this optical recording medium 16. The beam 17 transmitted through the objective lens 15 and collimator lens 14 and further reflected by the beam splitter 13 is split into first and second beams 22 and 23 by the beam splitter 21, and from the convergence point of the first beam 22. Also, a first photodetector 24 is arranged at a distance from the optical recording medium 16, and a second photodetector 25 is arranged closer to the optical recording medium 16 than the convergence point of the second beam 23. As shown in FIGS. 8B and 8C, the sum of the detection signals from the photodetectors 24a and 24c on both sides of the first photodetector 24 and the detection signal from the center photodetector 25b of the second photodetector 25, The central photodetector 2 of the first photodetector 24
The focus error signal is obtained by comparing the detection signal from the second photodetector 4b and the sum of the detection signals from the photodetectors 25a and 25c on both sides of the second photodetector 25.

[Problem that the invention seeks to solve]

However, such a focus detection device 10 requires two beam splinters 13.21, and moreover, a light source 11, a beam splitter 13.21, and a photodetector 24.21.
25 are arranged separately from each other and are not easy to assemble, making the device large and expensive.

[Means for solving problems]

Focus detection device 30.60.70.8 according to the invention
0 is a semiconductor laser 3 fixed to a semiconductor substrate 32
1 and a prism 3 fixed to the semiconductor substrate 32.
7.61.71, a first transflective surface formed on the surface 37a of this prism 37.61.71 facing the semiconductor laser 31, and the prism 37.
．． 61. A second semi-transmissive reflection formed on the surface 37c of 71 that is in contact with the semiconductor substrate 32 and at a position where the beam after passing through the first semi-transmissive reflection surface is incident. the second surface of the semiconductor substrate 32;
the semiconductor substrate 32;
It has three photodetectors 34a to 34c formed at a position where the beam after being reflected by the second semi-transmissive reflective surface is incident and arranged in the predetermined direction. a second photodetector 34, which irradiates the optical recording medium 16 with a beam 45 emitted from the semiconductor laser 31 and reflected by the first semi-transparent reflective surface; The optical recording medium 16 transmitted through the reflective surface
After reflecting the beam 45 from the second semi-transmissive reflective surface and before entering the second photodetector 34, the beam 45 is converged, and the light beams on both sides of the first photodetector 33 are converged. The sum of the detection signals from the detection sections 33a, 33c and the central photodetection section 34b of the second photodetector 34, and the sum of the detection signals from the central photodetection section 33b and the second photodetector 33 of the first photodetector 33, respectively. The focus error signal of the optical recording medium 16 is obtained by comparing the sum of detection signals from the photodetectors 34a and 34C on both sides of the photodetector 34.

[Effect]

Focus detection device 30.60.70.8 according to the invention
0, the prism 37 has first and second transflective surfaces, so that the beam splinter separates the beam 45 for irradiating the optical recording medium 16 and the beam 45 from the optical recording medium 16. A single prism 37 has the function of a beam splitter to separate the beam 45 from the optical recording medium 16 for detection before and after its convergence point.

Moreover, the semiconductor laser 31, the prisms 37, 61, 71, and the first and second photodetectors 33, 34 are integrated, and furthermore, these plural optical components can be arranged on the same plane of the semiconductor substrate 32.

〔Example〕

Hereinafter, first to fourth embodiments of the present invention will be described with reference to FIGS. 1 to 7.

FIG. 1 shows a first embodiment. The focus detection device 30 of the first embodiment has a laser diode 31 fixed to a Si substrate 32 with tin solder or the like, and
Photodetectors 33 to 36 are formed on a substrate 32, and a prism 37 having a trapezoidal cross section consisting of B and 7 is fixed onto the photodetectors 33 to 35 with an adhesive.

The prism 37 has a surface 37a facing the laser diode 31 and a surface 37 facing the Si substrate 32.
The portion of portion b other than the vicinity of the photodetector 35 is a semi-transmissive reflective surface, and the surface 37c facing the surface 21b is a reflective surface.

As shown in FIG. 2, the photodetectors 33 and 34 include three photodetectors 33a to 33c and 34a to 34a arranged in a fixed direction.
34c. In addition, these photodetectors 33a to 3
3c, 34a-34c are connected to operational amplifiers 41-43.

The photodetector 35 has four photodetectors arranged as shown in FIG. 8, and is used for tracking detection. Further, the photodetector 36 is used for automatic output control of the laser diode 31.

Note that the focus detection device 30 is enclosed in a cap 44, as shown in FIG.

In the focus detection device 30 of the first embodiment, a portion of the beam 45 emitted from the laser diode 31 is reflected by the surface 37a, passes through the objective lens 46, and irradiates the optical recording medium 16.

A portion of the beam 45 reflected by the optical recording medium 16, transmitted through the objective lens 46, and incident on the surface 37a is transmitted through this surface 37a and incident on the surface 37b. However, surface 37
Since the area b near the photodetector 33 is a semi-transmissive reflective surface, a part of the beam 45 passes through the surface 37b and reaches the photodetector 3.
3, and the remainder is reflected by surface 37b.

The beam 45 reflected by the surface 37b is reflected by the surface 37c and enters the surface 37a again. and,
A portion of the beam 45 incident on the surface 37a is incident on the photodetector 34, and the remaining portion is reflected by the surface 37a and the surface 37c and incident on the photodetector 35.

In the focus detection device 30 of this first embodiment,
The size etc. of the prism 37 are selected so that when the optical recording medium 16 is located at the convergence point of the beam 45, the conjugate point of this convergence point is located on the surface 37c.

Therefore, as shown in FIG. 2, the beam nozzles 47 of the beam 45 on the photodetectors 33, 34 have the same size when the optical recording medium 16 is located at the convergence point of the beam 45. As the optical recording medium 16 deviates from the convergence point of the beam 45, one becomes larger and the other becomes smaller.

As a result, from the operational amplifiers 41, 42, and 43, the curve 5
A signal designated 1.52.53 is obtained.

Therefore, if the signal obtained from the operational amplifier 43 is used as a focus error signal, this focus error signal has good symmetry with respect to the zero-crossing point, linearity near the zero-crossing point, and elimination of leakage of the reproduced signal. .

FIG. 5 shows a second embodiment. The focus detection device 60 of this second embodiment is substantially the same as the focus detection device 30 of the first embodiment described above, except that the prism 60 does not have a trapezoidal cross section and the beam 45 does not converge on the surface 61b. They may have similar configurations.

Therefore, in the focus detection device 60 of this second embodiment,
Even if there is a slight scratch on the portion of the surface 61b where the beam 45 is reflected, the beam 45 will not be affected by this scratch. For this reason, focus detection is performed stably.

FIG. 6 shows a third embodiment. The focus detection device 70 of the third embodiment has a prism 37 configured so that a beam 45 emitted from a laser diode 31 and directed toward a surface 37a is incident perpendicularly, and a beam 45 reflected by the surface 37a is emitted perpendicularly. The focus detection device 30 may have substantially the same configuration as the focus detection device 30 of the first embodiment described above, except that the prism 71 made of the same material, that is, BK7, is in close contact with the surface 37a of the prism 37. .

Therefore, in the focus detection device 70 of this third embodiment,
As is clear from FIG. 6, the beam 45 emitted from the laser diode 31 and transmitted through the surface 37a travels straight without being refracted. Therefore, less stray light enters the photodetectors 33 to 35, and focus detection is performed with high sensitivity.

FIG. 7 shows a fourth embodiment. The focus detection device 80 of this fourth embodiment is similar to the first embodiment described above, except that the line connecting the laser diode 31 and the photodetector 36 and the line connecting the photodetectors 33 to 35 intersect with each other. It may have substantially the same configuration as the focus detection device 30 of the embodiment.

Therefore, also in the focus detection device 80 of this fourth embodiment,
Since the beam 45 emitted from the laser diode 31 and transmitted through the surface 37a does not go to the photodetectors 33 to 35,
Less stray light enters these photodetectors 33-35.

〔Effect of the invention〕

In the focus detection device according to the present invention, focus detection using two photodetectors before and after the convergence point of the beam from the optical recording medium can be performed with a single prism, so the number of parts is small and the device is compact. Moreover, it is low cost.

Moreover, since multiple optical components are integrated, assembly is easy.Furthermore, since these multiple optical components can be placed on the same plane of the semiconductor substrate, manufacturing is extremely easy. The device is also low cost.

[Brief explanation of drawings]

Fig. 1 is a side view showing a first embodiment of the present invention, Fig. 2 is a schematic diagram showing a photodetector of the first embodiment and its circuit, and Fig. 3 is a side view showing an example of use of the first embodiment. 4 is a graph showing signals obtained from the circuit of FIG. 2, FIGS. 5 and 6 are side views showing the second and third embodiments of the present invention, respectively, and FIG.
The figure is a plan view showing a third embodiment of the present invention. FIG. 8 is a side view showing a conventional example of the present invention. In addition, in the symbols used in the drawings, 16--------・--・Optical recording medium 30.6
0,70.80 −・・・・−−−−−−−−−1・Focus detection device 31 −・−・・−・−・−・−・Laser diode 3
2.---------Si substrate 33.34------ one photodetector 33a to 33
=, 34a to 34c ------------------- Photodetector 37.
61. Tt--1-- Prism 37a, 37c--
・−・Face 45−−−−−・−・・−・・−・Beam.

Claims (1)

[Claims] A semiconductor laser fixed to a semiconductor substrate, a prism fixed to the semiconductor substrate, and a first prism formed on a surface facing the semiconductor laser of the prism. a second semi-transmissive reflective surface; a second surface of the prism that is in contact with the semiconductor substrate and is formed at a position where the beam after passing through the first semi-transmissive reflective surface is incident; a semi-transmissive reflective surface; and a third photodetector having three photodetectors formed in a position of the semiconductor substrate facing the second semi-transmissive reflective surface and arranged in a fixed direction. 1 photodetector, and three light beams formed in the semiconductor substrate at a position where the beam is incident after being reflected by the second semi-transmissive reflective surface and arranged in the certain direction. a second photodetector having a detection section, irradiating the optical recording medium with a beam emitted from the semiconductor laser and reflected by the first semi-transparent reflective surface; converging the beam from the optical recording medium that has passed through the semi-transparent reflective surface of the optical recording medium after being reflected by the second semi-transparent reflective surface and before entering the second photodetector; The sum of the detection signals from the photodetecting sections on both sides of the photodetector and the central photodetecting section of the second photodetector, and the sum of the detection signals from the photodetecting sections at the center of the first photodetector and the photodetecting section at the center of the first photodetector. A focus detection device that obtains a focus error signal of the optical recording medium by comparing the sum of detection signals from each of the photodetectors on both sides of a second photodetector.