JPH046632A - Focus detector - Google Patents

Abstract

PURPOSE:To reduce the cost and to detect a focus state always stably with high accuracy by detecting a focus state with respect to an object receiving a light of a convergence optical system based on an output of a photodetector section of a light emitting element and a light receiving element. CONSTITUTION:A light from an LD 51 of a light receiving and light emitting element 31 is reflected in a translucent face (1st face) 33 of a photodetector element 32 and converged to an object 35 receiving a light such as an optical disk via an objective lens 38. Then grating is applied to the translucent face 35 of the photodetector element 32 and generated + or -1st diffracted lights are projected to the object 35 receiving a light via the objective lens 38. Thus, three spots comprising a main beam spot 36 of the 0-th diffracted light and sub beam spots 37a, 37b of the + or -1st diffracted lights are formed on the object 35 receiving a light. Thus, the position alignment of the photodetector section with respect to the light emitting section is not required, the cost is reduced and the focal state is always stably detected with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a recording/reproducing device for recording and/or reproducing information on an optical information recording medium such as an optical disk, an optical cart, or a magneto-optical disk. The present invention relates to a focus detection device suitable for use in.

[Conventional technology]

As a conventional focus detection device, for example, Japanese Patent Application Laid-Open No. 565701
In Japanese Patent No. 3, a device as shown in FIGS. 8 and 9 is proposed. In the focus detection device shown in FIG.
After the light emitted from the laser diode (LD) 1 is reflected by the semi-transparent surface 3 of the parallel plate 2, it is converged on the disk 5 through the objective lens 4, and the reflected light is transmitted through the objective lens 4 to the parallel plate 2. After passing through the semi-transmissive surface 3, the light is reflected by the reflecting surface 6 of the parallel plate 2, and then transmitted through the semi-transmissive surface 3 again and received by the photodetector 7. Based on the output, the objective lens 4 The focus state for the disk 5, that is, the focus error signal (FES) is obtained. That is, in this focus detection device, the parallel plate 2 is used to give astigmatism to the return light from the disk 5 for FES detection, and the incident light to the disk 5 and the return light are separated, so that parts Efforts are being made to reduce the number of points and downsize the device.

In addition, in the focus detection device shown in FIG. 9, a wedge sandwich plate 8 is used in place of the parallel plate 2 shown in FIG. As a result, we are trying to downsize the - layer.

Furthermore, as another conventional focus detection device, Japanese Patent Laid-Open No. 1-2
Japanese Patent No. 29437 proposes a device as shown in FIG. This focus detection device includes an LDII on the same semiconductor substrate and a photodetector (PD) 12 on both sides of the LDII.
．． 13, 14, and 15 are integrally formed, the light from the LDII is converged and projected onto the optical disk 19 via the hologram element 17 and the objective lens 18, and the reflected light is transmitted via the objective lens 18. The ±1st-order diffracted light is made incident on the hologram element 17 and received by the PDs 1213 and 14.15, respectively, and
The hologram element 17 imparts astigmatism to the ±1st-order diffracted light so that the beam shapes of the ±1st-order diffracted light change in substantially opposite directions on PDs 12.13 and 14.15, thereby changing the outputs of PDs 12 to 15. The FES is obtained based on this.

That is, in this focus detection device, FIG.
As shown in FIG. 11C, the beam shapes of the ±1st-order diffracted lights 21 and 22 incident on the PDs 12.13 and 14.15 are as shown in FIG. are equal to each other,
When the optical disk 19 is closer to the objective lens 18 than the focal position of the objective lens 18, it becomes as shown in FIG. I'm trying to make it happen. In this way, the output of PD12 is A1, the output of PD13 is A2, the output of PD14 is A3, and the output of PD15 is A4.
When, FES is obtained by FES=(A++A3)-(Az+A4).

In this focus detection device, as described above, the LDII
By using the light receiving/emitting element 16 in which the PDs 12 to 15 are integrally formed on the same semiconductor substrate, the LD and PD
This eliminates the need for adjustment and makes the device more compact.

[Problem to be solved by the invention]

However, in the focus detection device shown in FIG.
Since the parallel plate 2 is used to obtain astigmatism for FES detection, a relatively thick parallel plate 2 is required, which makes it difficult to reduce the size and weight of the apparatus. In addition, in the case of using a wedge sandwich plate 8 instead of the parallel flat plate 2 as in No. 90, the processing cost of the wedge sandwich plate 8 is higher than that of the parallel flat plate 2, making the entire device expensive. There's a problem.

Furthermore, in the focus detection device shown in FIG.
Of the light emitted from II, return light from the optical disk 19 of the ±1st-order diffracted light generated when passing through the hologram element 17 passes through the hologram element 17 again and is transmitted to the PDs 12 to 1.
5 as stray light, the FES and reproduction signal (R
There is a problem in that it is not possible to stably obtain F) and a tracking error signal (TES).

The present invention has been made by focusing on the above-mentioned conventional problems.The present invention has been made by focusing on the above-mentioned problems of the conventional technology. The purpose is to provide equipment.

[Means and effects for solving the problem] In order to achieve the above object, the present invention provides a light emitting/receiving element having a light emitting part and a light receiving part formed on the same semiconductor substrate, and a light emitting/receiving element having a light emitting part and a light receiving part formed on the same semiconductor substrate. A converging optical system that converges light and projects it onto the object to be irradiated, and a light receiving/emitting element and the converging optical system. a first surface consisting of a semi-transparent surface that guides the irradiated object; and a first surface consisting of a partially reflective surface that reflects half of the pupil of the return light that is reflected by the irradiated object and passes through the converging optical system and guides it to the light receiving and emitting element. and a detection optical element having two surfaces, and is configured to detect the focal state of the converging optical system with respect to the irradiated object based on the output of the light receiving section of the light receiving and emitting element.

Further, in the present invention, a light receiving/emitting element having a light emitting part and a light receiving part formed on the same semiconductor substrate is disposed in an optical path between the light receiving/emitting element and an object to be irradiated, and light from the light receiving/emitting element is arranged. a first surface consisting of a semi-transparent surface that converges and guides the irradiated object to the irradiated object; and a partially reflective surface that reflects half of the pupil of the return light reflected from the irradiated object and converges and guides it to the light receiving and emitting element. a convergence detection optical element having a second surface consisting of a second surface, and is configured to detect a focus state of the convergence detection optical element with respect to the irradiated object based on the output of the light receiving section of the light receiving and emitting element.

〔Example〕

FIG. 1 shows a first embodiment of the invention. In this embodiment, as shown in FIG.
One LD 51 and six PDs on the same semiconductor substrate 61
52 to 57 are integrally formed.

In FIG. 2, the LD 51 has a striped double hetero (DH) structure, and has an n
A cladding layer 62 made of Ga, -XALXAs,
Active layer 63 made of aAs, P-type Ga1-x AL,
A cladding layer 64 made of As, a p-GaAs layer 65,
An oxide film 66 and an electrode metal 67 are sequentially laminated and provided,
An electrode metal 68 is provided on the other surface. That is, this LD 51 utilizes the open planes of the crystals of the cladding layers 62 and 64 to form a Fabry-Perot reflecting mirror that is optically parallel to the plane in the direction perpendicular to the pn junction plane.
By using a DI (DI) structure in which the active layer 63 is sandwiched between the cladding layers 62 and 64, both carrier confinement and light confinement effects are obtained. , is a typical gain waveguide type having no lateral refractive index distribution in the active layer 63, and the thickness of the active layer 63 is usually 0.1 to 0.5 μm, and the ground layer 62.64 The thickness of the p-GaAs layer 65 on the crat layer 64 is usually 1 to 2 μm.The p-GaAs layer 65 on the crat layer 64 is used to make it easier to take an electrode, and the oxide film 66 is used to partially conduct current to form a single layer. This is to obtain the fundamental transverse mode, and has a striped structure.The forward voltage of the LD51 configured in this way is approximately 2V, and the reverse breakdown voltage is 10V.
~50V.

PD52 to 57 are formed on the base 61 in the same manner as LD51, and between each of LD51 and PD52 to 57,
Grooves 69 to 7 are etched until they reach the base 61.
4 and electrically isolated. Note that P[1
52 to 57, an oxide film 66 having a stripe structure for partially flowing current as in the LD 51 is not provided.

In this way, the sensitivity of the active layer 63 can be made negative in the arrangement direction (x direction) of the LD 51 and PDs 52 to 57, and desirable characteristics as the light receiving/emitting element 31 can be obtained.

The manufacturing process, laser oscillation characteristics, and PD characteristics of such a light receiving/emitting element 31 are based on the "monosilicate integrated G
aALAs Laser/Detector Array j Institute of Electronics and Communication Engineers, QOE86-1~14. PP73-77.1986.
4.21.

As in the above-mentioned light receiving/emitting element 31, PO52 to PO57
The sensitivity characteristics of POs 52 to 57 in the thickness direction, that is, the y direction, when they are formed in the same way on the same semiconductor substrate 61 as the LD 51 are shown in FIG.
It can be controlled to some extent by the reverse voltage applied to O52 to O57.

In FIG. 1, the light from the LD 51 of the light receiving/emitting element 31 is reflected by the semi-transparent surface (first surface) 33 of the detection optical element 32, and then passes through the objective lens 38 and converges on the irradiated object 35 such as an optical disk. and project it. In this embodiment, a grating is formed on the semi-transparent surface 33 of the detection optical element 32, and the ±1st-order diffracted light generated here is also projected onto the irradiated object 35 via the objective lens 38. Therefore, three spots are formed on the irradiated object 35: the main beam spot 36 of the O-order diffracted light and the sub-beam spots 37a and 37b of the ±1st-order diffracted light. The grating formed on the semi-transparent surface 33 is formed so that the diffraction efficiency of the ±1st-order diffracted light during transmission is sufficiently smaller than that of the 0th-order diffracted light.

The reflected light of the main beam spond 36 on the irradiated object 35 is
Detection optical element 320 semi-transparent surface 33 via objective lens 38
The reflected light is diffracted by the grating and enters the light receiving/emitting element 31 as a first optical path, forming spots 1 to 80, 81, and 82 as shown in FIG.

Also, of the return light from the main beam spot 36, the light that has passed through the semi-transparent surface 33 of the detection optical element 32 enters the partially reflective surface (second surface) 34 of the detection optical element 320, and among this incident light, What is incident on the reflection area 34a is reflected,
The light passes through the semi-transparent surface 33 and enters the light receiving/emitting element 31 as a second optical path, forming a spot 78 as shown in FIG. The partially reflective surface 34 of the detection optical element 32 is configured with a reflective area 34a and a non-reflective area 34b, as shown in FIG. 5, in order to reflect half of the pupil of the returned light.

Also, the sub-beam beam at the irradiated object 35) 37a3
Similarly to the reflected light from the main beam spot 36, the reflected light from the main beam spot 36 also enters the light receiving/emitting element 31 through the first and second optical paths. That is, due to the reflected light of the sub beam spot 37a,
After passing through the first optical path, as shown in FIG.
A spot 77 is formed through the second optical path. Further, the reflected light from the sub-beam spot 37b forms spots 8082 and 76 on the light receiving/emitting element 31 via the above-mentioned first optical path, and forms a spot 79 via the second optical path.

In this embodiment, spot 7 is used to detect the FES and also to detect the reproduction signal (RFS). Here, the spot 78 is a spot formed through the partial reflection surface 34 of the detection optical element 32, and is a beam spot with half of the pupil cut off, so the spot shape in the focused and defocused states is , as shown in FIGS. 6A-C. That is, in the focused state, the spot center becomes a small spot that coincides with the center of PD55°56 as shown in FIG. 6B, and in the defocused state, the spot becomes a small spot as shown in FIG. As shown in P.D.
The result is a nearly semicircular spot biased toward either 55 or 56.

Therefore, the FES can be detected based on the output of PD55.56 using the knife edge method. Here, FES can be obtained by FES-5I 52 where the output of PD55 is So and the output of PD56 is 32.

Further, RFS can be determined from the change in the intensity of spot 78.
=St+52.

Furthermore, in this embodiment, the sub beam spot 37a,
A tracking error signal (TBS) is detected using spots 75, 76, 77, and 79 formed on the light receiving/emitting element 31 by the return light from the beam 37b. This TBS detection is based on a three-beam method, with sub-beam spot 37a3
7b is detected by the difference in intensity of the projected spot onto the PD. Here, since there are two optical paths, the first and second optical paths, which enter the light receiving/emitting element 31 via the detection optical element 32, as described above, the projection of the sub beam spots 37a and 37b onto the light receiving/emitting element 31 There are also two sets of spots (75, 76 and 77.79). Therefore, TES is PD52.
53. The outputs of 54 and 57 are respectively S:l+S4
+SS and S6, YES=53-5°TBS=55-56 TES can be obtained based on an arbitrary formula of -(S3+Ss)-(Sn+56).

As described above, in this embodiment, since the LD 51 and the PDs 52 to 57 are formed using the light receiving/emitting element 31 formed on the same semiconductor substrate, the entire structure can be made smaller and lighter. It becomes possible to integrally drive the entire device, and the PD5 for the LD51
No. 2 to 57 position adjustments are required, so the number of adjustment man-hours can be significantly reduced and the cost can be reduced.

Furthermore, since the detection optical element 32 consisting of the semi-transmissive surface 33 and the partially reflective surface 34 is used to branch the optical path of the incident light and the returning light to the irradiated object 35, the PD 52
57 can be reduced, and the movement of the spot due to wavelength fluctuations can be made extremely small, so that FES, RFS, and TES can always be detected stably and with high precision.

FIG. 7 shows a second embodiment of the invention. This embodiment replaces the detection optical element 32 and objective lens 38 of the first embodiment with a semi-transparent surface (first surface) 4 of an ellipsoid of revolution.
0 and a partially reflective surface (second surface) 41, which serves as the detection optical element 32 and the objective lens 38 of the first embodiment. And the operation is similar to that of the first embodiment.

In this way, if the convergence detection optical element 39 also functions as an objective lens, the configuration can be made simpler.
Moreover, it can be made at low cost and can be made extremely lightweight.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, in the embodiment described above, the LD 51 of the light receiving/emitting element 31 is
Although the active layer 63 is a typical gain waveguide type that does not have a lateral refractive index distribution, it is also possible to use a refractive index waveguide type that confines light by creating a lateral refractive index difference or a high frequency waveguide type. Distributed feedback type (DFB) allows oscillation in a single longitudinal mote without spectrum broadening even when modulated by
) or distributed reflection type (DBR).

Further, the semiconductor substrate 61 constituting the LD 51 and the PDs 52 to 57 is not limited to GaAs, but may also be made of Si. In this case, peripheral circuits such as a preamplifier can also be integrally formed on the Si substrate, making the configuration simpler. Furthermore, the semiconductor substrate 61 is not limited to n-type.
It can also be p-type.

〔Effect of the invention〕

As described above, according to the present invention, since the light emitting section and the light receiving section are formed using a light receiving/emitting element formed on the same semiconductor substrate, there is no need to adjust the position of the light receiving section with respect to the light emitting section, thus reducing the number of adjustment steps. It can be significantly reduced and the cost can be reduced.

In addition, a detection optical element having a first surface consisting of a semi-transmissive surface and a second surface consisting of a partially reflective surface splits the incident light to the irradiated object and the returning light, and also splits half of the pupil of the returned light. Since the light is guided to the light receiving section of the light receiving/emitting element, stray light to the light receiving section can be reduced, and therefore the focus state can always be detected stably and with high precision.

Furthermore, by providing the detection optical element with a light beam convergence function, the configuration can be made simpler and cheaper, and it can be made extremely lightweight.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a first embodiment of the present invention.
Figure 3 is a diagram showing the sensitivity characteristics in the thickness direction of the PD, and Figure 4 explains the spots formed on the receiver/emission element in Figure 1. Figure 5 is a diagram showing the configuration of the partial reflection surface of the detection optical element shown in Figure 1, Figure 6 A, B, and C are the P
A diagram for explaining the shape change of the focus detection beam incident on D, FIG. 7 is a diagram showing a second embodiment of the present invention, FIGS.
10 and 11A to 11C are diagrams for explaining the conventional technology. 31 - Receiving/emitting element 32 - Detection optical element 33 - Semi-transmissive surface (first surface) 34 Partially reflective surface (second surface) 34a
- One reflective area 34b - Non-reflective area 35 - Irradiated object 36 - Main beam spots 37a, 37b
- Sub-beam spot 38 - Objective lens 39 - Convergence detection optical element 40 - Semi-transparent surface (first surface) 41 Partially reflective surface (second surface) 51
--LD 52-57-POC3-Semiconductor substrate 75-82-Spot Figure 3 Figure 4 de Figure 1 Figure 2 Figure 8 Figure f6 Figure 11

Claims (1)

[Claims] 1. A light receiving/emitting element having a light emitting part and a light receiving part formed on the same semiconductor substrate, and a converging optical system that converges light from the light emitting part of the light receiving/emitting element and projects it onto an irradiated object. and a first surface made of a semi-transparent surface that is disposed in the optical path between the light receiving and emitting element and the converging optical system and guiding light from the light receiving and emitting element to the irradiated object via the converging optical system; a second surface comprising a partial reflection surface that reflects half of the pupil of the return light that is reflected by the irradiated object and passes through the converging optical system and guides it to the light receiving/emitting element; A focus detection device characterized in that the focus detection device is configured to detect a focus state of the converging optical system on the irradiated object based on an output of a light receiving section of a light receiving/emitting element. 2. A light receiving/emitting element having a light emitting part and a light receiving part formed on the same semiconductor substrate, and a light receiving/emitting element disposed in the optical path between the light receiving/emitting element and the irradiated object, converging the light from the light receiving/emitting element. a first surface consisting of a semi-transparent surface that guides the irradiated object; and a second surface consisting of a partially reflective surface that reflects half of the pupil of the return light reflected from the irradiated object and converges and guides it to the light receiving and emitting element. and a convergence detection optical element having a surface, the focus state being configured to detect the focus state of the convergence detection optical element with respect to the irradiated object based on the output of the light receiving section of the light receiving and emitting element. Detection device. 3. The focus detection device according to claim 1, wherein the light receiving/emitting element, the converging optical system, and the detecting optical system are configured to be driven integrally. 4. The focus detection device according to claim 2, wherein the light receiving/emitting element and the convergence detection optical element are configured to be driven integrally.