JPH0766548B2 - Focus detection device - Google Patents

Description

The present invention relates to a focus detection device for detecting a focusing state of an optical recording medium.

[Outline of Invention]

The present invention enables focus detection using two photodetectors before and after the convergence point of a beam from an optical recording medium by a single prism in the focus detection device as described above, and further, a plurality of optical components can be provided. By integrating these optical components and disposing these optical components on the same plane of the semiconductor substrate, the device can be made small in size and low in cost.

[Conventional technology]

The focus error signal indicating the focusing state of the optical recording medium is required to have symmetry with respect to the zero cross point, linearity in the vicinity of the zero cross point, elimination of leakage of the reproduction signal, and the like.

Japanese Unexamined Patent Publication No. 60-217535 discloses a focus detecting device 10 as shown in FIG. 8A as a focus detecting device satisfying the above requirements.

The focus detection device 10 allows a beam 12 emitted from a light source 11 such as a laser diode to pass through a beam splitter 13, a collimator lens 14 and an objective lens 15 to enter an optical recording medium 16, and is reflected by the optical recording medium 16. The beam 17 transmitted through the objective lens 15 and the collimator lens 14 and further reflected by the beam splitter 13 is converted into the first and second beams 22, 23 by the beam splitter 21.
The optical recording medium is divided into
The first photodetector 24 is arranged apart from the optical axis 16 and is closer to the optical recording medium 16 than the convergence point of the second beam 23.
The photodetector 25 of FIG. 8 is arranged, and as shown in FIGS.
Of the detection signals by the photodetectors 24a and 24c on both sides of the photodetector 24 and the detection signal by the photodetector 25b at the center of the second photodetector 25 and the photodetection at the center of the first photodetector 24. The detection signal from the section 24b and the photodetectors 25 on both sides of the second photodetector 25
By comparing the sum of the detected signals by a, 25c,
The focus error signal is obtained.

[Problems to be solved by the invention]

However, such a focus detection device 10 requires two beam splitters 13 and 21, and the light source 11, the beam splitters 13 and 21, and the photodetectors 24 and 25 are arranged separately from each other, which facilitates assembly. Therefore, the device is large and costly.

[Means for solving problems]

The focus detection device 30, 60, 70, 80 according to the present invention includes a semiconductor laser 31 fixed to a semiconductor substrate 32, prisms 37, 61, 71 fixed to the semiconductor substrate 32, and the prisms 37, 61. , 71, a first semi-transmissive reflecting surface formed on a first surface 37a facing the semiconductor laser 31, and the prism 37, 61, 71 facing the semiconductor substrate 32. A second semi-transmissive anti-slope formed on the second surface 37b, which is formed at a position where the beam after passing through the first semi-transmissive reflective surface is incident, and the prism.
Formed at a position of the third surface 37c facing the second surface 37b of 37, 61, and 71, and at which the beam is incident after being reflected by the second semi-transparent anti-oblique surface. And the three photodetection sections 33a to 33c formed in a position facing the second semi-transmissive reflection surface of the semiconductor substrate 32 and aligned in a certain direction. Have first
Photodetector 33 and three photodetectors 34a formed in the semiconductor substrate 32 at positions where the beam after being reflected by the reflecting surface is incident and arranged in the predetermined direction.
A second photodetector 34 each having
The beam 45 emitted from the semiconductor laser 31 and reflected by the first semi-transmissive reflective surface irradiates the optical recording medium 16, and the beam from the optical recording medium 16 transmitted through the first semi-transmissive reflective surface. 45 is converged after being reflected by the second semi-transmissive reflecting surface and before being incident on the second photodetector 34, and the photodetection sections 33a on both sides of the first photodetector 33 are converged. , 33c and the sum of the detection signals by the central photodetector 34b in the second photodetector 34 and the central photodetector 33b and the second photodetector in the first photodetector 33, respectively. The photodetectors 34 on both sides of the container 34
The focus error signal of the optical recording medium 16 is obtained by comparing the sum of the detection signals of a and 34c.

[Action]

In the focus detection device 30, 60, 70, 80 according to the present invention,
Since the prism 37 has the first and second semi-transmissive reflecting surfaces, it has a beam splitter function for separating 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 which separates the beam 45 from the recording medium 16 in order to detect it before and after its convergence point.

Moreover, the semiconductor laser 31, the prisms 37, 61, 71 and the first
And the second photodetectors 33 and 34 are integrated, and 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 the first embodiment. In the focus detection device 30 of the first embodiment, a laser diode 31 is fixed to a Si substrate 32 by tin solder or the like, photodetectors 33 to 36 are formed on the Si substrate 32, and a prism 37 having a trapezoidal cross section made of BK7. Is fixed on the photodetectors 33 to 35 with an adhesive.

In the prism 37, a surface 37a facing the laser diode 31 and a part of the surface 37b facing the Si substrate 32 other than the vicinity of the photodetector 35 are semi-transmissive reflective surfaces, The surface 37c facing 37b is a reflecting surface.

As shown in FIG. 2, the photodetectors 33 and 34 have three photodetector sections 33a to 33c and 34a to 34c arranged in a fixed direction. Further, these photodetection units 33a to 33c and 34a to 34c are connected to the operational amplifiers 41 to 43.

The photodetector 35 has four photodetector sections arranged as shown in FIG. 7, and is used for tracking detection. The photodetector 36 is also used for automatic output control of the laser diode 31.

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 as described above, a part of the beam 45 emitted from the laser diode 31 is generated on the surface 37.
The optical recording medium 1 is reflected by a and passes through the objective lens 46.
Irradiate 6.

A part of the beam 45 transmitted through the objective lens 46 reflected by the optical recording medium 16 and incident on the surface 37a is transmitted through this surface 37a and incident on the surface 37b. However, in the surface 37b, the vicinity of the photodetector 33 is a semi-transmissive reflecting surface, so that part of the beam 45 passes through the surface 37b and is incident on the photodetector 33, and the rest is reflected by the surface 37b.

The beam 45 reflected by the surface 37b is reflected by the surface 37c and re-enters the surface 37b. Then, part of the beam 45 incident on the surface 37b is incident on the photodetector 34, and the rest is reflected by the surfaces 37b and 37c and is incident on the photodetector 35.

In the focus detection device 30 of the first embodiment, the size of the prism 37 is set 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. Etc. have been selected.

Therefore, as shown in FIG. 2, the spots 47 of the beam 45 on the photodetectors 33 and 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 shifts from the convergence point of the beam 45, one becomes larger and the other becomes smaller.

As a result, from the operation amplifiers 41, 42, 43, the curves 51, 52,
The signal indicated by 53 is obtained. Therefore, if the signal obtained from the operational amplifier 43 is used as the focus error signal, the focus error signal is good in symmetry with respect to the zero cross point, linearity in the vicinity of the zero cross point, elimination of leakage of the reproduced signal, and the like.

FIG. 5 shows the second embodiment. The focus detection device 60 of the second embodiment is different from the focus detection device 60 in that the prism 61 is not trapezoidal in cross section and the beam 45 does not converge on the surface 61b.
The focus detection device 30 of the first embodiment described above may have substantially the same configuration.

Therefore, in the focus detection device 60 of the second embodiment,
Even if there is a slight scratch in the part of the beam 61b where the beam 45 is reflected, the damage to the beam 45 is small.
Therefore, focus detection is stably performed.

FIG. 6 shows a third embodiment. In the focus detection device 70 of the third embodiment, the beam 45 emitted from the laser diode 31 and directed to the surface 37a is vertically incident and the surface 37a is
Of the first embodiment described above, except that the prism 71 made of the same material as the prism 37, that is, BK7, is closely attached to the surface 37a of the prism 37 so that the beam 45 reflected by is emitted vertically. It may have a configuration substantially similar to the focus detection device 30.

Therefore, in the focus detection device 70 of the third embodiment, the beam 45 emitted from the laser diode 31 and transmitted through the surface 37a goes straight without being refracted, as is apparent from FIG. Therefore, the stray light incident on the photodetectors 33 to 35 is small, and the focus detection is performed with high sensitivity.

FIG. 7 shows a fourth embodiment. The focus detecting apparatus 80 of the fourth embodiment is the same as 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. The focus detection device 30 of the embodiment may have substantially the same configuration.

Therefore, also in the focus detection device 80 of the fourth embodiment, the beam 45 emitted from the laser diode 31 and transmitted through the surface 37a does not go to the photodetectors 33 to 35, and is incident on these photodetectors 33 to 35. There is little stray light.

〔The invention's effect〕

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

Moreover, since the plurality of optical components are integrated, it is easy to assemble, and further, since the plurality of optical components can be arranged on the same plane of the semiconductor substrate, the manufacturing is very easy. Also, the cost of the device is low.

[Brief description of drawings]

FIG. 1 is a side view showing a first embodiment of the present invention, FIG. 2 is a schematic view showing a photodetector of the first embodiment and a circuit thereof, and FIG. 3 is a side view showing a use example of the first embodiment. FIGS. 4 and 5 are graphs showing signals obtained from the circuit of FIG. 2, FIGS. 5 and 6 are side views showing second and fourth embodiments of the present invention, respectively.
The drawing is a plan view showing a third embodiment of the present invention. FIG. 8 is a side view showing an embodiment of the present invention. In the reference numerals used in the drawings, 16 ... Optical recording medium 30, 60, 70, 80 ... Focus detection device 31 ... Laser diode 32 ... Si substrate 33, 34 ... Photodetector 33a-33c, 34a- 34c ...... Photodetector 37, 61, 71 ...... Prism 37a, 37c ...... Surface 45 ...... Beam.

Claims (1)

[Claims] 1. A semiconductor laser fixed to a semiconductor substrate, a prism fixed to the semiconductor substrate, and a prism formed on a first surface of the prism facing the semiconductor laser. 1 semi-transmissive anti-oblique surface, and a second surface of the prism that is in contact with the semiconductor substrate and is formed at a position where a beam after passing through the first semi-transmissive reflective surface is incident. A second semi-transparent anti-slope, and a third of the prisms facing the second surface.
And a reflecting surface formed at a position where the beam is incident after being reflected by the second semi-transmissive reflecting surface, and a second semi-transmissive anti-oblique surface of the semiconductor substrate. A first photodetector having three photodetection portions formed at positions facing each other and arranged in a certain direction, and after being reflected by the reflection surface of the semiconductor substrate A second photodetector having three photodetectors arranged at the position where the beam is incident and arranged in the constant direction, each of which emits light from the semiconductor laser. The optical recording medium is irradiated with the beam reflected by the first semi-transmissive reflective surface, and the beam from the optical recording medium transmitted through the first semi-transmissive anti-oblique surface is reflected by the second semi-transmissive reflective surface. And before the incidence on the second photodetector. The sum of detection signals by the photodetection units on both sides of the first photodetector and the photodetection unit at the center of the second photodetector and the center of the photodetector of the first photodetector. A focus detection device for obtaining a focus error signal of the optical recording medium by comparing the sum of detection signals by the photodetector and the photodetectors on both sides of the second photodetector.