JP2002092925A - Optical pickup unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the degradation of a signal reproduced by a return light beam from an optical recording medium to a light source without making the miniaturization and thickness reduction of a unit difficult. SOLUTION: The optical pickup unit has a light source 1, a composite optical element 2 which is constituted as a quarter wavelength plate by sticking quarts plates, on one surface of which a grating lattice is formed and which transmits luminous flux emitted from the light source, an objective lens 7 which converges the luminous flux transmitted through the composite optical element 2 on the signal recording surface of the optical recording medium 8, and a photodetecting means 10 which detects reflecting optical flux from the signal recording surface of the optical recording medium 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for writing and reading information signals on an optical recording medium.

[0002]

2. Description of the Related Art Hitherto, an optical pickup device for writing and reading information signals on and from an optical recording medium such as an optical disk has been proposed. As shown in FIGS. 5 and 6, this optical pickup device includes a semiconductor laser 101 serving as a light source, a grating 102, a beam splitter 103, and a front photodiode (FPD) 1.
04, a collimator lens 105, a mirror 106, an objective lens 107, a concave lens 109, and a photodetector (PD) 110.

In this optical pickup device, light emitted from a semiconductor laser 101 forms three light spots on an optical recording medium for detecting a tracking error signal by a so-called "three spot method" or "DPP method". Then, the light passes through a grating 102 serving as a means for performing the beam splitting, and then enters a beam splitter 103 for separating the forward and backward light beams to the optical recording medium.

[0004] In the beam splitter 103, a part of the incident light flux is transmitted through a reflection film formed on the surface,
The rest is reflected. The light beam transmitted through the beam splitter 103 enters a front photodiode 104 for monitoring the output power of the semiconductor laser 101. The luminous flux reflected by the beam splitter 103 is converted into divergent light by the collimator lens 105 into parallel light, and reflected by the mirror 106.
The light enters the objective lens 107. The objective lens 107 condenses the incident light beam on a signal recording surface of a disk 108 as an optical recording medium, and forms a minute light spot.

[0005] The reflected light from the disk 108 passes through the objective lens 107 and is reflected by the mirror 106, and then is converged by the collimator lens 105. Then, this light beam enters the beam splitter 103, and a part of the light is reflected by the reflection film of the beam splitter 103, and the rest is transmitted. The luminous flux transmitted through the beam splitter 103 generates astigmatism that can perform focus error detection by a so-called “astigmatism method” when transmitted through the beam splitter 103, and enters the photodetector 110 via the concave lens 109. Received. The output signal of the photodetector 110 becomes a reproduction signal from the disk 108.

[0006]

In the above-described optical pickup device, the characteristics of the reflection film of the beam splitter 103 include the reflectance Rp of P-polarized light, the reflectance Rs of S-polarized light, and the reflectance of P-polarized light. , The transmittance Ts of S-polarized light, for example, Rp ≒ Rs ≒ 85%, T
p ≒ Ts ≒ 15%. In this case, as shown in FIG.
15 is transmitted through the beam splitter 103, while the remaining 85% is reflected and reflected by the semiconductor laser 10.
It will return to 1.

When the output light from the semiconductor laser 101 is set to P-polarized light with respect to the beam splitter 103, the return light to the semiconductor laser 101 becomes P-polarized light, and similarly, the output light is set to S-polarized light. Return light is S
It becomes polarized light. That is, the emitted light and the return light have polarization components in the same direction. In this case, the semiconductor laser 101
There is a problem that the emitted light and the return light interfere with each other inside the chip to generate return light noise, and as a result, the reproduction signal from the disk 108 is deteriorated.

Therefore, as a countermeasure against returning light, for example, FIG.
8 and the mirror 106 and the objective lens 10 as shown in FIG.
An optical pickup device having an optical system in which a quarter wavelength plate 111 is added between the optical pickup device 7 and the optical pickup device 7 can be considered. The operation of the optical pickup device until the light emitted from the semiconductor laser 101 is reflected by the mirror 106 is described in FIG.
This is the same as that in the optical pickup device described above. The light beam reflected by the mirror 106 converts the linearly polarized light into circularly polarized light into a quarter wave plate 11.
1 and is converted into circularly polarized light, condensed by the objective lens 107, and forms a minute light spot on the disk.

The reflected light from the disk 108 passes through the objective lens 107, then passes through a quarter-wave plate 111 which is means for converting circularly polarized light into linearly polarized light, becomes linearly polarized light, and is reflected by the mirror 106. You. The operation until the light beam reflected by the mirror 106 enters the photodetector 110 is the same as that in the above-described optical pickup device shown in FIG.

Here, the characteristics of the reflection film of the beam splitter 103 are, for example, RpＲRs ≒ 85%, Tp ≒ Ts ≒
If it is 15%, 15% of the light beam reflected by the disk 108 and incident on the beam splitter 103 is transmitted,
The remaining 85% is reflected and returns to the semiconductor laser 101 side.
However, when the light is transmitted back and forth through the quarter-wave plate 111, the polarization direction of the output light and the polarization direction of the return light are orthogonal to each other. For example, if the light emitted from the semiconductor laser 101 is set to be P-polarized light with respect to the beam splitter 103, the light returned to the semiconductor laser 101 will be S-polarized light, and the light emitted from the semiconductor laser 101 will be S-polarized light.
If it is set to be polarized light, the return light to the semiconductor laser 101 will be P-polarized light. In this case, the semiconductor laser 1
Since the emitted light and the return light do not interfere with each other inside the chip No. 01, good characteristics that no return light noise is generated and the reproduction signal from the disk 108 is not deteriorated can be realized.

However, since the configuration of this optical system is such that the quarter wavelength plate 111 is simply added to the conventional optical system, the number of parts increases, and the material cost and the processing cost for mounting increase. There was a problem that would.

Further, since a quarter-wave plate 111 is added between the mirror 106 and the objective lens 107, when the optical pickup device is to be made thinner, the quarter-wave plate 111 is not used. There was a problem that the thickness could not be reduced and the size could not be reduced. Also, a quarter-wave plate 11
Even when 1 is disposed between the collimator lens 105 and the mirror 106, there is still a problem that it is difficult to reduce the size of the optical pickup device.

Accordingly, the present invention has been proposed in view of the above-mentioned circumstances, and it is not difficult to reduce the size and thickness of the optical disk, and the reproduction signal is deteriorated by the return light from the optical recording medium to the light source. It is an object of the present invention to provide an optical pickup device in which is prevented.

[0014]

In order to solve the above-mentioned problems, an optical pickup device according to the present invention has a light source and a quartz plate attached to each other to form a quarter-wave plate, and has one surface. A grating grating is formed on top,
A composite optical element through which a light beam emitted from the light source passes, an objective lens for condensing the light beam transmitted through the composite optical element on a signal recording surface of the optical recording medium, and an objective lens on the signal recording surface of the optical recording medium. Light detecting means for detecting a reflected light flux of the light flux.

In the optical pickup device according to the present invention, a light source and a quartz plate are bonded to each other to form a quarter-wave plate, and a grating is formed on one surface and emitted from the light source. A composite optical element through which the light beam passes, a beam splitter into which the light beam transmitted through the composite optical element enters, an objective lens for condensing the light beam passing through the beam splitter on a signal recording surface of the optical recording medium, and an optical recording medium And a light detecting means for detecting a reflected light beam of the light beam on the signal recording surface on a light path different from the light path of incident light to the beam splitter via the beam splitter. In this optical pickup device, the composite optical element is provided on an optical path between the light source and the beam splitter.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, the optical system of the optical pickup device according to the present invention comprises a semiconductor laser (LD) 1 as a light source, a wave plate grating element 2 as a composite optical element, and a beam splitter (BS). 3, front photodiode 4, collimator lens 5, mirror 6,
Objective lens 7, concave lens 9, photo detector (PD)
It consists of 10 parts. As shown in FIG. 3, the wave plate grating element 2 includes two quartz plates 2a and 2b.
Are formed on the surface of a quarter-wave plate formed by bonding the optical axes so that the optical axes are orthogonal to each other.

In this optical pickup device, the light emitted from the semiconductor laser 1 is incident on the wave plate grating element 2 and is formed by a diffraction grating 2c formed on the surface of the wave plate grating element 2 by a so-called "3-spot method". Or three light beams for tracking error signal detection by the "DPP method" or the like. further,
At the stage of emission from the wavelength plate grating element 2, what was linearly polarized when emitted from the semiconductor laser 1 is converted to circularly polarized light.

By the way, if a quarter-wave plate composed of one quartz plate, which is usually used as a wave plate, is arranged in the divergent light from the semiconductor laser 1, as shown in FIG. Since the phase difference between the electromagnetic vector and the magnetic field vector greatly changes from 90 ° depending on the incident angle, the transmitted light is not completely circularly polarized. However, the wave plate grating element 2 of this optical pickup device is similar to that of FIG.
As shown in FIG. 2, since the two quartz plates 2a and 2b are quarter-wave plates formed by laminating the optical axes orthogonal to each other, even if the incident angle changes, the electromagnetic vector and the magnetic field vector do not change. The phase difference of 90 ° hardly changes from 90 °
The transmitted light is almost perfectly circularly polarized light.

The light beam transmitted through the wave plate grating element 2 is incident on a beam splitter 3 for separating the forward and return optical paths, and a part of the light is transmitted through a reflection film of the beam splitter 3 and the rest is reflected. The light transmitted through the beam splitter 3 enters a front photodiode 4 which is a means for monitoring the output power of the semiconductor laser 1. The light reflected by the beam splitter 3 is incident on a collimator lens 5, and the divergent light is converted by the collimator lens 5 into parallel light. And
The parallel light beam is reflected by the mirror 6 and is incident on the objective lens 7, and is condensed by the objective lens 7 to form a minute light spot on the signal recording surface of the disk 8 as an optical recording medium.

The reflected light from the disk 8 becomes circularly polarized light orthogonal to the circularly polarized light when it enters the disk 8, that is, circularly polarized light in the opposite direction, and re-enters the objective lens 7. Further, the light is reflected by the mirror 6, turned into convergent light by the collimator lens 5, and enters the beam splitter 3.

In the beam splitter 3, a part of the light beam is reflected and the rest is transmitted. The transmitted light of the beam splitter 3 generates astigmatism for detecting a focus error by a so-called “astigmatism method” when transmitting the beam splitter 3, and passes through a concave lens 9 to a photodetector 10 serving as light detecting means. It enters and is received. The output signal of the photodetector 10 becomes a reproduction signal from the disk 8.

Here, the characteristics of the reflection film of the beam splitter 3 are represented by the reflectance Rp of P-polarized light, the reflectance Rs of S-polarized light,
As the transmittance Tp of the P-polarized light and the transmittance Ts of the S-polarized light,
For example, if Rp ≒ Rs ≒ 85% and Tp ≒ Ts ≒ 15%, 15% of the light beam reflected by the disk 8 and incident on the beam splitter 3 is transmitted, but the remaining 85%
Is reflected and returns to the semiconductor laser 1 side.

However, in this optical pickup device, the light emitted from the semiconductor laser 1
The returning light to the disk 8
Since the light passes through the wave plate grating 2 on both of the returning light paths, the light emitted from the semiconductor laser 1 and the light returned from the disk 8 have orthogonal polarization directions. For example, the light emitted from the semiconductor laser 1 is emitted from the beam splitter 3
Is set to be P-polarized light, the return light to the semiconductor laser 1 is set to be S-polarized light, and the output light from the semiconductor laser 1 is set to be S-polarized light.
Return light to the P-polarized light.

Therefore, in this optical pickup device, the interference between the emitted light and the return light does not occur in the chip of the semiconductor laser 1, no return light noise occurs, and the reproduction signal from the disk 8 does not deteriorate. Good characteristics can be realized. In this optical pickup device, since the return light noise is suppressed, the S / N of the reproduction signal is improved, and the jitter is also reduced.

Further, in the optical system of the optical pickup device, since the grating and the quarter-wave plate are integrated, the number of parts may increase due to the provision of the quarter-wave plate. Therefore, it is not difficult to reduce the size, the processing cost for mounting does not increase, and the material cost can be reduced.

Further, in this optical pickup device, since the return light noise of the semiconductor laser is optically suppressed, a high frequency superimposing circuit for electrically suppressing the return light noise of the semiconductor laser can be omitted, and the material cost is reduced. In addition, processing costs can be reduced.

In this optical pickup device, return light noise at the time of recording on an optical recording medium can be prevented, and the occurrence of recording jitter components can be reduced by suppressing power fluctuation.

[0029]

As described above, in the optical pickup device according to the present invention, by integrating the grating and the quarter-wave plate, the optical system is compared with an optical system in which a quarter-wave plate is simply added. As a result, the number of parts can be reduced, processing costs such as mounting can be reduced, and material costs as parts costs can be reduced. Further, in this optical pickup device, miniaturization is easy.

In this optical pickup device, since the quarter wavelength plate is provided, the polarization directions of the reciprocating light are orthogonal to each other, and the interference of the semiconductor laser as the light source in the chip is prevented. Thus, the return light noise is suppressed, and the S / N of the reproduced signal is improved, thereby reducing the jitter.

Also, in this optical pickup device, since the return light noise of the semiconductor laser is suppressed optically, a high frequency superimposing circuit for electrically suppressing the return light noise of the semiconductor laser can be omitted, and the material cost is reduced. , The processing cost can be reduced.

Further, in this optical pickup device, return light noise during recording on the optical recording medium is prevented,
By suppressing the power fluctuation, the occurrence of the recording jitter component can be reduced.

That is, the present invention can provide an optical pickup in which a reproduction signal is prevented from being deteriorated by return light from an optical recording medium to a light source without making it difficult to reduce the size and thickness. is there.

[Brief description of the drawings]

FIG. 1 is a side view showing a configuration of an optical system of an optical pickup device according to the present invention.

FIG. 2 is a side view showing a polarization state of a light beam in the optical system of the optical pickup device.

FIG. 3 is a front view and a side view showing a configuration of a wave plate grating element constituting an optical system of the optical pickup device.

FIG. 4 is a graph showing an incident angle dependency of a phase difference in a wavelength plate.

FIG. 5 is a side view showing a configuration of an optical system of a conventional optical pickup device.

FIG. 6 is a side view showing a polarization state of a light beam in the optical system of the conventional optical pickup device.

FIG. 7 is a side view showing the configuration of an optical system of a conventional optical pickup device having a quarter-wave plate.

8 is a side view showing a polarization state of a light beam in the optical system of the optical pickup device shown in FIG.

[Explanation of symbols]

1 semiconductor laser, 2 wavelength plate grating element, 3
Beam splitter, 4 front photodiodes,
5 collimator lens, 6 mirror, 7 objective lens,
8 discs, 9 concave lenses, 10 photodetectors

Claims (3)

[Claims] 1. A composite optic in which a light source and a quartz plate are bonded to each other to form a quarter-wave plate, a grating is formed on one surface, and a light beam emitted from the light source is transmitted. An element, an objective lens for condensing a light beam transmitted through the composite optical element on a signal recording surface of the optical recording medium, and a light detecting unit for detecting a reflected light beam of the light beam on the signal recording surface of the optical recording medium. An optical pickup device comprising: 2. A composite optic in which a light source and a quartz plate are attached to each other to form a quarter-wave plate, a grating is formed on one surface, and a light beam emitted from the light source is transmitted. An element, a beam splitter on which a light beam transmitted through the composite optical element is incident, an objective lens for condensing the light beam passing through the beam splitter on a signal recording surface of an optical recording medium, and a signal recording surface of the optical recording medium A light detecting means for detecting, on the optical path different from the optical path of incident light to the beam splitter, via the beam splitter, the composite optical element includes the light source and the beam. An optical pickup device disposed on an optical path between the optical pickup and a splitter. 3. The optical pickup device according to claim 2, wherein the composite optical element is disposed with the surface on which the grating grating is formed facing the light source.