JPH02121131A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain a compact and light-weight optical pickup by setting a light source and plural photodetectors on a monolithic substrate and adding an error signal detecting hologram between the monolithic substrate and a luminous flux dividing hologram. CONSTITUTION:For instance, a 2nd hologram 12 divides the light returned from a recording medium 3 into a beam for detection of the focus error signal and a beam for detection of the tracking error signal. These divided beams are received by different photodetectors 5A-5C. Thus both focus and tracking error signals are detected independently of each other with no mutual interference. Furthermore a semiconductor laser 2 and those photodetectors 5A-5C are set on a monolithic substrate 6. Then the 3rd and 4th error signal detecting holograms 13 and 14 are set between the substrate 6 and the hologram 12. In such a constitution, a compact and light-weight optical pickup 1 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup using a hologram in an optical system.

[Prior art and problems to be solved by the invention] In recent years, the information-related industry has made remarkable progress, and the number of information records handled has also tended to increase. For this reason, instead of recording or reproducing devices that use conventional magnetic heads to record or reproduce information, we are now using optical beams to record information at high density on recording media, or to record information at high density on recording media. 2. Description of the Related Art Optical information recording and reproducing devices that can reproduce high-density recorded information at high speeds are attracting attention.

Incidentally, it is desirable that the optical pickup used in the optical information recording/reproducing device be small and lightweight in order to shorten access time. Therefore, recently, in order to make optical pickups smaller and lighter, for example, "Holographic optical elements for industry" published in "Optical Technology] Contact" magazine, December 1987 issue, pp. 698-707. Applied J
As shown in , an optical system using a hologram has been proposed.

In addition, as a means to further reduce the size and weight of the optical pickup, Japanese Patent Laid-Open Publication No. 62-162241 and Japanese Patent Laid-open No. 62-162
Japanese Patent No. 97141 discloses an optical pickup using a bologram in which a light source such as a semiconductor laser and a photodetector for detecting information and control signals are provided on the same substrate.

In the optical pickup disclosed in JP-A-62-162246, a photodetector is arranged on the outer periphery of the laser light source in a plane that includes the Rede light source and is perpendicular to the optical axis.
Two surface relief gratings (holograms) are arranged between the recording medium and the recording medium to converge the light beam from the laser light source onto the recording medium and to transmit the reflected light from the recording medium to a photodetector. The two holograms have different diffracted polarization directions, thereby separating the outgoing and returning light beams. In addition, for focus and tracking error signal detection, a four-part photodetector is placed around the outer periphery of the laser light source, and the focus and tracking error signals are obtained by balancing the output of each photodetector. There is.

Furthermore, in the optical pickup disclosed in Japanese Patent Application Laid-open No. 62-97111, a diffraction grating that splits the beam into two is arranged in the optical path of the returning light, and each of the split beams is divided into two. It is detected by a photodetector. Focus and tracking error signals are obtained by balancing the outputs of the four photodetectors.

However, the above-mentioned Japanese Patent Application Laid-Open No. 62-162246,
In the optical pickup disclosed in Japanese Unexamined Patent Application Publication No. 62-97141, all of the optical pickups are focused.

In tracking error signal detection, the beam for focus detection and the beam for tracking detection coexist, so the tracking error signal affects the focus offset, and conversely, the focus error signal affects the track offset. There is a problem in that it affects

In addition, in holograms, heat from the light source causes optical distortion, or wavefront aberration, which makes it difficult to focus.

There is a problem in that a tracking offset occurs.

Furthermore, when a surface relief type hologram is used, which affects polarization characteristics, the hologram has a problem in that it is susceptible to lumps and dust because the grating groove width of the grating is small. That is, if dust or dirt accumulates on the grating, the diffraction efficiency changes.

Furthermore, in the optical pickup disclosed in Japanese Patent Application Laid-open No. 62-162246, the P-polarized light emitted from the semiconductor laser passes through a 1/4 wavelength plate, is reflected by the recording medium, and is again 1
After passing through a 74-wavelength plate, the light becomes S-polarized light, and is guided to a photodetector by a hologram that diffracts the S-polarized light. However, when a P-polarized component is generated due to the birefringence of the recording medium, some of the light returns to the semiconductor laser, increasing the noise of the semiconductor laser, which is a problem in the ΔPC circuit that uses the rear monitor light of the semiconductor laser. There is.

The present invention has been made in view of the above circumstances, and aims to provide an optical pickup that can be made smaller and lighter, and eliminate mutual interference between focus error signals and tracking error signals. .

A further object of the present invention is to provide an optical pickup that can prevent the hologram from being affected by the heat of the light source.

A further object of the present invention is to provide an optical pickup that can prevent a hologram from being affected by dust or dust.

A further object of the present invention is to provide an optical pickup capable of realizing a ΔPC circuit that is not affected by noise due to birefringence of a recording medium.

[Means for Solving the Problems] The optical pickup of the present invention is suitable for recording media! )J′! A light source that emits light that emits light, and a luminous flux that is emitted from the light source and reflected by the recording medium, so that each error signal of focus and tracking can be detected independently from each other,
a beam splitting hologram that splits the beam into at least two and guides each divided beam in a direction different from the light source; and a beam splitting hologram arranged on the optical path of at least one of the two beams split by the beam splitting hologram; An error signal detection hologram generates a light beam for detecting a focus or tracking error signal, and each light beam split by the light beam splitting hologram is received and information (
ffi, 4, as well as a plurality of photodetectors capable of independently detecting each focus and tracking error signal, and the light source and the plurality of photodetectors are integrated. The error signal detection hologram is provided on a substrate, and the error signal detection hologram is disposed between the integrated substrate and the light beam splitting hologram. For example, at least one of the error signal detection hologram and the beam splitting hologram is sealed with a transparent substrate.

Further, for example, an integrated substrate provided with the light source and a plurality of photodetectors is disposed on one side of a transparent substrate, and the error signal detection hologram and the light source are disposed on the other side of the transparent substrate. A photodetector for forward light monitoring is arranged.

[Function] In the present invention, the light emitted from the light source is reflected by the recording medium, split into at least two by the beam splitting hologram, and guided in a direction different from the light source. At least one of the two beams split by the beam splitting hologram is converted into a beam for detecting a focus or tracking error signal by an error signal detection hologram. Each of the beams divided by the beam splitting hologram is received by a plurality of photodetectors, and an information signal is detected, and each error signal of focus and tracking is detected independently of each other.

Furthermore, since the light source and the plurality of light beam detectors are provided on an integral long plate, and the error signal detection hologram is disposed between the integral substrate and the beam splitting hologram, the optical pickup can be Miniaturization.

It becomes possible to reduce the weight.

Furthermore, by sealing at least one of the error signal detection hologram and the beam splitting hologram with a transparent substrate, the hologram is prevented from being affected by the heat of the light source, clumps, and dust.

In addition, an integrated substrate provided with a light source and a plurality of photodetectors is placed on one side of a transparent substrate, and a hologram for detecting an error signal and a light source for monitoring the forward light of the light source are placed on the other side of the transparent substrate. By arranging the detector, the forward light of the light source can be monitored, and an APC circuit that is not affected by noise due to birefringence of the recording medium can be realized.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

Figures 1 to 6 relate to the first embodiment of the present invention.
The figure is an explanatory diagram showing the depiction of an optical pickup, Fig. 2 is an explanatory diagram showing the shape of the output beam of the semiconductor laser, Fig. 3 is a plan view showing the main parts of this embodiment, and Fig. 4 is an explanatory diagram showing the shape of the output beam of the semiconductor laser. FIG. 5 is a plan view showing the main parts of the circuit, FIG. 5 is a circuit diagram showing a circuit for detecting information signals, focus, and tracking error signals, and FIG.
Figure 6(a) is an explanatory diagram showing the shape of the light flux on each photodetector when in focus, and Figure 6(b) shows the shape of the light flux on each photodetector when the recording medium is farther than the focused point. FIG.

As shown in FIG. 1, for the recording medium 3 for recording and reproduction,
A write-once type (DRAW) or read-only type optical pickup 1 for recording and reproducing information is equipped with a semiconductor laser 2 as a light source, and between this semiconductor laser 2 and a recording medium 3, from the semiconductor laser 2 side, , a third hologram 13, a fourth hologram 14, a second hologram 12, a quarter wavelength plate 101, and a first hologram 11.

Further, on the side of the semiconductor laser 2, as shown in FIG. l
' Next, photodetectors 5A, 5B, and 5G provided on the semiconductor laser 2 and the integrated substrate 6 are arranged.

As shown in FIG. 4, the semiconductor laser 2 and the photodetector 1
The substrate 6 on which W5A, 5B, and 5C are provided is a transparent substrate 7.
As shown in FIG. 3, the third hologram 13 and the fourth hologram
The hologram 14 is sealed and the front monitor (
Photodetector) 8A.

8B is joined.

As shown in FIG. 2, the light beam emitted from the semiconductor laser 2 has an elliptical shape, and the short axis direction of the ellipse is the polarization plane of the P-polarized light.

The third hologram 13 and the fourth hologram 14 are arranged on both sides of the elliptical beam in the minor axis direction so as not to eclipse the elliptical beam of the semiconductor laser 2. Further, the front monitors 8A and 8B are placed on both sides of the elliptical beam in the long axis direction, at positions where they can receive light from both ends of the elliptical beam in the long direction. Furthermore, the elliptical beam of the semiconductor laser 2 is transmitted to the third hologram 13. Fourth hologram 14. When passing through the central portion surrounded by the front monitors 8A and 8B, both ends in the longitudinal direction are blocked by the front monitors 8A and 8B, and the beam is converted into a substantially circular beam.

The second hologram 12 is a surface relief hologram that transmits P-polarized light and diffracts S-polarized light. Further, the second hologram 12 divides the reflected light beam from the recording medium 3 into two, and sends one of the light beams to the third hologram 12.
3 and the other beam is diffracted so as to guide it to the fourth hologram 14. In addition, in Fig. 3, the symbol 1
5 is divided by the second hologram 12, and the third hologram 1
3 shows the light beam projected on the second hologram 12, and 16 shows the light beam projected on the second hologram 12.
The figure shows a beam of light that is divided by , and is projected onto the fourth hologram 14 .

In addition, the first hologram 11 has the function of an objective lens, and converges the light beam from the semiconductor laser 2 into a spot on the recording medium 3, and also converges the reflected light from the recording medium 3. It is designed to diffract as if

Further, as shown in FIG. 3, the third hologram 13 is divided into two parts, each of which uses a surface relief type hologram that diffracts S-polarized light, and the light beam 15 from the second hologram 12 is divided into two parts. , the - side luminous flux to the photodetector 5B,
The other beam is diffracted to a photodetector 5C.

Further, the fourth hologram 14 is a surface relief type hologram that diffracts S-polarized light, and is configured to diffract the light beam 16 from the second hologram 12 so as to guide it to the photodetector 5A. Further, the photodetector 5A includes 2
It has become a split photodetector.

Next, the operation of this embodiment will be explained.

The elliptical beam from the P-polarized conductor laser 2 that vibrates within the plane of the paper passes through the transparent substrate 7 and is transmitted to the third hologram 13. Fourth
Hologram 14. And when passing through the central part surrounded by the front monitors 8A and 8B, it changes into a substantially circular beam!
9! be done. This circular beam passes through the second hologram 12, and is converted from linearly polarized P-polarized light to circularly polarized light by the quarter-wave plate 10. This circularly polarized beam is focused into a spot on the recording medium 3 by the first hologram 11 . The light reflected by this recording medium 3 is diffracted by the first hologram 11 so as to be converged, and again
The light passes through the /4 wavelength plate 1o and is converted from circularly polarized light to S-polarized linearly polarized light. The light that has passed through the quarter-wave plate 10 is split into two semicircular beams by the second hologram 12.
be divided.

One semicircular beam split by the second hologram 12 enters the third hologram 13 and is split into two quarter circular beams. One 174 circular beam is incident on the photodetector 5B, and the other 1/4 circular beam is incident on the photodetector 5B.
incident on C. A tracking error signal is generated from the output signals of the two photodetectors 5B and 5C.

Further, the other semicircular beam split by the second hologram 12 is incident on the fourth hologram 14 and diffracted,
The light is incident on the photodetector 5Δ. A focus error signal is generated from the output signal of the two-divided photodetector 5A.

As shown in FIG. 5, the tracking error signal is obtained by using a subtracter 21 to generate a difference signal between the outputs of the photodetectors 5B and 5C. Further, the focus error signal is subtracted by the subtracter 22 by generating a difference signal between the outputs of each of the photodetectors 5A1 and 5A2 of the photodetector 5A. Also, is the information signal added? , the sum signal of the outputs of the photodetectors 5B and 5C obtained by the i-device 23 and the sum signal of the outputs of the photodetectors 5A+ and 5A2 obtained by the adder 24 at t7 are added or subtracted by the adder 25. It is obtained by That is, the information signal is transmitted to all photodetectors 5
It is obtained from the sum of the outputs of A, 5B, and 5C.

Note that tracking error signal detection uses a method of detecting the deviation of the irradiated light spot with respect to the guide groove of the recording medium 3, and when the light spot is deviation with respect to the guide groove, the photodetector The sizes of the 1/4 circle light beams incident on 5B and 5C are shifted. However, 1/1 of the photodetector 5B
When 4 circles become larger, the 1/4 circle of the photodetector 5C becomes smaller, and conversely, when the 1/4 circle of the photodetector 5C becomes larger, the 1/4 circle of the photodetector 5B becomes smaller.

In addition, focus error signal detection is performed using the second hologram 1.
2 as a knife edge, and when the recording medium 3 is closer than the in-focus point, the recording medium 3 is in a defocused state, and as shown in FIG. A semicircle is projected. Further, as shown in FIG. 6(a), in the focused state, the photodetectors 5A, 5
B and 5C are both imaged and focused between photodetectors 5A+ and 5A2. Furthermore, if the recording medium 3 is farther than the in-focus point, the recording medium 3 will be in a defocused state, and a semicircle will be projected on the photodetector 5△2 side, as shown in FIG. 6(b). . At this time, the shape of the 1/4 circle projected onto the photodetector 58.5G is reversed (back side) to that in FIG. 5.

In addition, the output of the front monitors 8A and 8B is the output of the semiconductor laser 2.
The light is sent to the APC circuit, which automatically adjusts the light emission output.

As described above, according to this embodiment, the second hologram 12 separates the return light from the recording medium 3 into a beam for detecting a focus error signal and a beam for detecting a tracking error signal, and separates each beam. , separate photodetector 5A
Since the light is received by 5B and 5C, the focus and tracking error signals can be detected independently of each other, eliminating mutual interference.

Further, a semiconductor laser 2 and a plurality of photodetectors 5A.

5B and 5C are provided on the integrated substrate 6, and a third. Since the fourth holograms 13 and 14 are arranged between the integrated substrate 6 and the second hologram 12 for splitting the light beam, the optical pickup 1 can be made smaller and lighter.

Also, 3rd. The fourth hologram 13.14 is placed on the transparent substrate 7.
By sealing, it is possible to eliminate optical distortion of the holograms 13 and 14 due to heat from the semiconductor laser 2, that is, focus and tracking A offset caused by aberrations.

Also, 3rd. The fourth hologram 13.14 is placed on the transparent substrate 7.
By sealing the hologram, it is possible to prevent the hologram from being affected by lumps or dust when using a hologram with a narrow grid width, a polarization characteristic, and a high spatial frequency.

In addition, semiconductor laser 'f2 and photodetector Z5A, 5B.

5C is arranged on one side of the transparent substrate 7, and the third .5C is placed on the other side of the transparent substrate 7. By arranging the fourth hologram 13, 14 and the front monitors 8A and 8B, the forward light of the semiconductor laser 2 can be monitored, and an APC circuit that is not affected by noise due to birefringence of the recording medium 3 can be realized. .

In this embodiment, the fourth hologram 14 is not provided, and the semicircular beam divided by the second hologram 12'c is
The light may be directly incident on the photodetector 5Δ.

FIG. 7 is an explanatory diagram showing an optical pickup according to a second embodiment of the present invention.

In this embodiment, the first hologram 11 has the function of a collimator lens, and the first hologram 11
A separate objective lens 31 is provided between the recording medium 3 and the recording medium 3. Therefore, the light beam irradiated onto the recording medium is
The hologram 11 converts the light beam into a flat t1 light beam, which is focused onto the recording medium 3 by the objective lens 31. Further, the reflected light from the recording medium 3 is converged by the objective lens 31.

Further, the optical system other than the objective lens 31 is formed into a negative body. However, as in the first embodiment, the transparent L1 plate 7
A semiconductor laser 2 and photodetectors 5Δ, 5B,
The integrated substrate 6 provided with 5C is bonded, and the 3rd. Fourth hologram 13.14 and front monitor 8Δ
, 8B are provided.

Furthermore, another transparent substrate 32 is provided, and the second hologram 12 is sealed on one side of this transparent substrate 32, and the second hologram 12 is sealed on the other side.
A quarter wavelength plate 10 and a first hologram 11 are provided. A spacer 33 is provided between the transparent substrate 7 and the transparent substrate 32, and a space is provided between the transparent substrates 7 and 32. Furthermore, the transparent substrate 7 and the transparent substrate 32 are The optical system other than the objective lens 31 is integrated.

Only the objective lens 31 is movable to control focus and tracking.

According to this embodiment, since the second hologram 12 using a surface relief hologram is also sealed, this second hologram 12 is also protected from the heat of the semiconductor laser 2, dust, dirt, and the like.

In addition, since the optical system other than the objective lens 31 is integrated,
Optical pickups can be made smaller and lighter.

The other functions and effects of Structure 2 are the same as those of the first embodiment.

8 and 9 relate to a third embodiment of the present invention, FIG. 8 is an explanatory diagram showing the configuration of an optical pickup, and FIG. 9 is an explanatory diagram of a hologram.

In this embodiment, as in the second embodiment, the first hologram 11 has the function of a collimator lens, and a separate objective lens 31 is provided between the first hologram 11 and the recording medium 3. It is set up.

In addition, in this embodiment, the second, third, and third embodiments in the first embodiment are different from each other.
One hologram 41 serves as the fourth holograms 12, 13, and 14. This hologram 41 is sealed on one side of the transparent substrate 32.

As shown in FIG. 9, the hologram 41 has an inner portion 41Δ and two 1/4 inner portions 41B.

It is composed of 41G. Each part uses a surface relief type bologram that determines the polarization characteristic of diffracting S-polarized light, and the inner part 41A has 17
4 inner part 41B (1/4 inner part 41 to the photodetector 5B)
C is adapted to diffract so as to guide a light beam to the photodetector 5C.

According to this embodiment, there are 4 parts in the cylinder.

Other functions and effects of the configuration 1 are the same as those of the first embodiment.

It should be noted that the present invention is not limited to the above-mentioned embodiments, for example, the third embodiment. The fourth holograms 13 and 14 may also be holograms that do not have polarization properties.

[Effect of the Invention 1] As explained above, according to the present invention, a light source and a plurality of photodetectors are provided on an integrated substrate, and the error signal detection hologram is connected to the integrated substrate and the beam splitting hologram. Since it is placed between the two, it is possible to make the optical pickup smaller and lighter.Furthermore, the beam splitting hologram divides the focus and tracking error signals so that they can be detected independently of each other. Since each of the divided light beams is received by a plurality of photodetectors, the focus and tracking error signals can be detected independently from each other, and there is an effect that mutual interference between the error signals is eliminated.

In addition, by sealing at least one of the error signal detection hologram and the beam splitting hologram with a transparent substrate, the hologram is prevented from being exposed to heat from the light source, clumps, and dust. There is.

In addition, an integrated substrate provided with a light source and a plurality of photodetectors is arranged on one side of the transparent substrate, and a hologram for error detection and a front light monitor of the light source are placed on the other side of the transparent substrate. By arranging a photodetector, the forward light of the light source can be monitored, and an APC circuit that is not affected by noise due to birefringence of the recording medium can be realized.

[Brief explanation of drawings]

Figures 1 to 6 relate to the first embodiment of the present invention.
Figure 2 is an explanatory diagram showing the configuration of the optical pickup, Figure 2 is an explanatory diagram showing the shape of the emitted beam of the semiconductor laser, Figure 3 is a plan view showing the main parts of this embodiment, and Figure 4 is this embodiment. Fig. 5 is a plan view showing the main parts of the circuit; Fig. 5 is a circuit diagram showing the information signal, focus, and tracking error signal detection circuits;
Figure 6(a) is an explanatory diagram showing the shape of the light flux on each photodetector when in focus, and Figure 6(b) shows the shape of the light flux on each photodetector when the recording medium is farther than the focused point. FIG. 7 is an explanatory diagram showing an optical pickup according to a second embodiment of the present invention, FIGS. 8 and 9 relate to a third embodiment of the present invention, and FIG. 8 shows the configuration of an optical pickup. FIG. 9 is an explanatory diagram of a hologram. 1... Optical pickup 2... Semiconductor laser 5A
, 5B, 5C...Photodetector 6...Integrated substrate 7...Transparent substrate 8Δ, 8
B...Front monitor 11...First hologram 12...Second hologram 13...Third hologram 14...Fourth hologram Figure 1 Figure 2 Figure 3 Figure 7 Figure 5 C Figure 6 (a) (b)

Claims (3)

[Claims] (1) At least a light source that emits light to irradiate a recording medium, and a light beam emitted from the light source and reflected by the recording medium, so that each error signal of focus and tracking can be detected independently from each other. A beam splitting hologram that splits the beam into two and guides each divided beam in a direction different from the light source; and a beam splitting hologram arranged on the optical path of at least one of the two beams split by the beam splitting hologram, and focusing the beam. or an error signal detection hologram that generates a light beam for detecting a tracking error signal; and an error signal detection hologram that receives each light beam divided by the light beam splitting hologram and is capable of detecting information signals, as well as focusing and tracking errors. a plurality of photodetectors capable of detecting signals independently of each other; the light source and the plurality of photodetectors are provided on an integrated substrate; and the error signal detection hologram is disposed on the integrated substrate. An optical pickup characterized in that the optical pickup is disposed between the beam splitting hologram. (2) The optical pickup according to claim 1, wherein at least one of the error signal detection hologram and the beam splitting hologram is sealed with a transparent substrate. (3) The integrated substrate on which the light source and a plurality of photodetectors are provided is disposed on one side of a transparent substrate, and the error signal detection hologram is placed on the other side of the transparent substrate in front of the light source. 2. The optical pickup according to claim 1, further comprising a photodetector for optical monitoring.