JP2008004136A - Two-wave optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a two-wave optical pickup which uses a leakage prism to separate a proper amount from the light emitted by the laser diodes in 650 nm, and 780 nm bands to input to the front monitor. <P>SOLUTION: This two-wave optical pickup has light sources to emit light in two wave lengths; diffraction gratings matching respective two wave lengths; an objective lens to focus the light from the light sources on an optical recording medium; a photodetector to detect the amount of the light from the light sources; and a light sensor to detect the return light from the optical recording medium, and records or reproduces the information detected by the photodetector on the optical recording medium. It is built by disposing a leakage prism in the light path between the light sources and the objective lens to separate the light from the light sources to input to the photodetector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an optical pickup used for recording and reproduction of both CD (Compact Disc) and DVD (Digital Versatile Disc) optical discs, and more particularly to a two-wavelength optical pickup using a leakage prism for light quantity separation for monitoring.

In recent years, an optical pickup used in an optical disk recording / reproducing apparatus is a CD (780 nm band).
In addition, an optical pickup in which a plurality of laser beams having different wavelengths are integrated according to applications such as DVD (650 nm band) is employed. An example using a CD / DVD both-recording type optical pickup is disclosed in Patent Document 1. FIG. 8 is a schematic diagram showing a configuration of a two-wave (CD, DVD) optical pickup 31, which includes semiconductor laser diodes (hereinafter referred to as LDs) 32 and 35, diffraction gratings 33 and 36, and first and second elements. Polarization beam splitters (hereinafter referred to as PBS) 34, 38
A front monitor 37, a quarter-wave plate 39, a collimating lens 40, a rising mirror 41, an objective lens 42, a sensor lens 43, and a photodetector 44.

FIG. 9A is a diagram showing the spectral characteristics of the polarizing film 34a of the first PBS 34, and about 10% of the amount of P-polarized light having a wavelength of about 780 nm used for CD is transmitted by the polarizing film 34a. A light amount of about 90% is reflected. About 90% of the light amount of P-polarized light having a wavelength of about 650 nm used for DVD is transmitted by the polarizing film 34a, and about 10% of the light amount is reflected. FIG. 9B is a diagram showing the spectral characteristics of the polarizing film 38a of the second PBS 38, in which P-polarized light is transmitted and S-polarized light is reflected.

The P-polarized light in the wavelength band of 780 nm emitted from the LD 32 in FIG. 8 is divided into three beams by the diffraction grating 33, enters the first PBS 34, and about 90% of the light quantity is reflected by the polarizing film 34a. , The traveling direction is changed by 90 degrees and the light is incident on the second PBS 38. About 10% of P-polarized light that has passed through the polarizing film 34 a enters the front monitor 37. On the other hand, P-polarized light having a wavelength of 650 nm band emitted from the LD 35 is divided into three beams by the diffraction grating 36, and the first P
About 90% of the amount of light is incident on the BS 34 and transmitted by the polarizing film 34a, and the second PBS.
Proceed to 38. About 10% of P-polarized light reflected by the polarizing film 34 a enters the front monitor 37. Nearly 100% of the P-polarized light having a wavelength of about 650 nm and 780 nm incident on the second PBS 38 is transmitted by the characteristics of the polarizing film 38a, enters the quarter-wave plate 39, is converted into circularly polarized light, and is further collimated. The light is converted into parallel light by the lens 40, converted upward 90 degrees by the rising mirror 41, collected by the objective lens 42, and focused on the surface of the optical disk (not shown).

The reflected light from the surface of the optical disk becomes reversely polarized circularly polarized light, enters the quarter-wave plate 39 through the objective lens 42, the rising mirror 41, and the collimating lens 40, and is converted into S-polarized light. 2 enters the PBS 38. The incident S-polarized light is the polarizing film 38 of the second PBS 38.
The light is totally reflected by a, enters the photodetector 44 through the sensor lens 43, and the information is decoded. In addition, about 10% of the amount of light emitted from the LDs 32 and 35 is guided to the monitor 37. By an APC (auto power controller) connected to the front monitor 37,
The drive signal levels of the drivers of the LDs 32 and 35 are controlled so that the signal level of the front monitor 37 becomes the reference level. APC including this monitor is described in detail in Patent Document 2.
JP 2004-110897 A JP 2002-185073 A

However, the conventional polarizing film 34a of the optical pickup PBS 34 for two wavelengths of DVD and CD is composed of several tens of layers, and transmits about 95% (reflects about 5%) of 650 nm band laser light for DVD, and 780 nm for CD. When manufacturing a polarizing film that reflects about 95% of the laser beam in the band (transmits about 5%), the film thickness accuracy of each layer is extremely strict, and the polarizing film is wavelength-dependent and the manufacturing yield is poor. was there.
An object of the present invention is to provide a two-wave optical pickup using a leakage prism that reflects about 5% of light emitted from light emitting diodes of DVD and CD and transmits about 95%.

The present invention is characterized in that a two-wave optical pickup is configured by using a leakage prism that separates the monitoring light quantity of the optical pickup for two wavelengths.
A light source that emits light of two different wavelengths, a diffraction grating corresponding to two different wavelengths, an objective lens that collects light emitted from the light source onto an optical recording medium, and a light amount emitted from the light source are detected. A light amount detecting means, and a light detecting means for detecting reflected light from the optical recording medium,
A two-wavelength optical pickup that records or / and reproduces information detected by the light detection means on the optical recording medium, and is emitted from the light source in an optical path between the light source and the objective lens. A two-wave optical pickup in which a leakage prism that splits the emitted light to the light amount detecting means is arranged.
When the two-wave optical pickup is configured as described above, a light quantity separation device can be easily configured, and an optical pickup having good wavelength dependency and good separation accuracy can be obtained, and characteristics of the APC function are improved.

Adhering parts placed adjacent to each other in the optical component are bonded together using an optical adhesive.
Construct wave pickup. By configuring the two-wave optical pickup in this way, there is an effect that the optical pickup can be reduced in size.

Embodiments according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a dual-wavelength two-wave optical pickup (hereinafter simply referred to as an optical pickup) 1 of a 780 nm band CD and a 650 nm band DVD according to the present invention. Two laser diodes (LD) 2 and 6, two diffraction gratings 3 and 7 for CD and DVD, and CD
, A wavelength synthesis prism 4 for synthesizing light for DVD, a leakage prism 5, CD, DV
A PBS 8 for D, a quarter-wave plate 9, a collimating lens 10, a photodetector 12, and a front monitor 13 are provided. Here, from the two LDs 2 and 6 for CD and DVD, S
It is assumed that polarized laser beams S1 and S2 are emitted.

Before describing the operation of the optical pickup 1 shown in FIG. 1, an optical device used for this will be described. FIG. 2 is a perspective view showing a configuration of the leakage prism 5. A hexahedral prism (leakage prism) in which two triangular prisms each having an angle of 45 degrees with an inclined surface are bonded to each other with an optical adhesive is shown in FIG.
As shown in Example 1 of this example, the leakage prism is provided with a SiO ₂ thin film of approximately 52 nm. The spectral characteristics of this leakage prism are from 370 nm to 850 n as shown by Ts in FIG.
The leakage prism is characterized by transmitting about 95% of S-polarized laser light of m and reflecting about 5% of S-polarized laser light as indicated by Rs in the spectral characteristics of FIG. Tp and Rp are P-polarized light transmittance (%) and reflectance (%). As is clear from this figure, the separation characteristics are very good and there is almost no wavelength dependency.

4 and 5 are spectral characteristics of the wavelength combining prism 4 and the PBS 8, respectively, and are examples of those designed by a well-known optical filter theory. As shown in the spectral characteristics of FIG. 4, the wavelength combining prism 4 reflects the S-polarized laser light S1 in the 780 nm band (for CD) and transmits the S-polarized laser light S2 in the 650 nm band (for DVD). It is configured. And PB
S8 is configured to reflect S-polarized laser beams S1 and S2 for CD and DVD and transmit P-polarized laser beams P1 and P2 as shown in the spectral characteristics of FIG. Here, FIG.
Rs represents the reflectance of S-polarized light, and Tp represents the transmittance of P-polarized light.

S-polarized laser light S 1 emitted from the LD 2 for CD shown in FIG. 1 passes through the diffraction grating 3 and enters the wavelength combining prism 4. S-polarized laser light S incident on the wavelength combining prism 4
1 is reflected by the polarizing film 4 a of the wavelength combining prism 4 and enters the leakage prism 5 while changing the traveling direction by 90 degrees. On the other hand, S-polarized laser light S2 emitted from the LD 6 for DVD
Enters the wavelength combining prism 4, passes through the polarizing film 4 a, and enters the leakage prism 5.

S-polarized laser beams S1 and S2 for CD and DVD incident on the leakage prism 5 transmit about 95% of the amount of incident light as shown by Ts in the spectral characteristics of FIG. 8 is incident. On the other hand, as indicated by Rs in the spectral characteristics of FIG. 3, about 5% of the incident light quantity is reflected and enters the front monitor 13. CD and DVD incident on PBS8
The S-polarized laser beam for use is almost totally reflected by the polarizing film 8a and changes the traveling direction by 90 degrees.
When the light enters the four-wave plate 9 and is transmitted through it, it is converted into circularly polarized light. The circularly polarized light emitted from the quarter-wave plate 9 is converted into parallel light by the collimator lens 10, collected by an objective lens (not shown), and focused on the surface of the optical disk 11.

Circularly polarized light reflected from the surface of the optical disk 11 becomes reversely rotated circularly polarized light, enters a quarter-wave plate 9 through an objective lens and a collimator lens 10 (not shown), and transmits a P-polarized laser. It is converted into light (P1, P2) and enters the PBS 8. The P-polarized laser beams P1 and P2 incident on the PBS 8 are transmitted through the polarizing film 8a as indicated by Tp in FIG.
And the information is deciphered. On the other hand, as described in the prior art, the light incident on the front monitor 13 is used to control the drive signal levels of the drivers of the LDs 2 and 6 so that the signal level of the front monitor 13 becomes the reference level.

Conventionally, about 10% of the amount of light was separated by PBS and made incident on the front monitor. However, when a polarizing film of PBS corresponding to two wavelengths of CD and DVD is manufactured, several dozen layers of dielectric thin films are laminated. In addition, the film thickness required strict accuracy. In addition, the polarizing film has wavelength dependency and it is extremely difficult to satisfy the required specifications. The feature of the two-wavelength optical pickup of the present invention is that the amount of light for front monitoring can be easily separated by using a leakage prism formed with a single SiO ₂ thin film of approximately 52 nm. As shown in FIG. 3, the leakage prism is characterized by excellent wavelength dependency and easy manufacture.

In addition to the 52 nm SiO ₂ thin film of Example 1 shown in FIG. 2, a leakage prism having a thin film configuration of Examples 2, 3 and the like shown in FIG. Example 2 is a leakage prism with a three-layer thin film configuration.
SiO ₂ of 100nm on the slopes of the prism, 22 nm of Al ₂ O _3, is formed by laminating SiO ₂ of 62 nm. The spectral characteristics of Example 2 are shown in FIG. Ts and Rs are transmittances of S-polarized light (%
) And reflectance (%). As is apparent from this figure, the transmittance Ts (%) and the reflectance Rs (%) are about 95% and about 5% for S-polarized light with a wavelength of 370 nm to 850 nm, respectively. The transmittance (%) and reflectance (%) for P-polarized light are indicated by Tp and Rp.

Example 3 is a 6-layer thin film leakage prism, with 9 nm Al ₂ O ₃ , 9 nm on the slope of the prism.
9 nm lanthanum aluminate (mixed oxide of La and Al ₂ O ₃ ), 35 nm SiO ₂
53 nm Al ₂ O ₃ , 49 nm SiO ₂ , and 15 nm Al ₂ O ₃ .
The spectral characteristics of Example 3 are shown in FIG. The spectral characteristics of FIG. 7 also show substantially the same characteristics as the spectral characteristics shown in FIG.

In the present embodiment, the leakage prism 5 is arranged at the subsequent stage of the wavelength combining prism 4. However, this is merely an example, and the leakage prism 5 is provided between the objective lens (not shown) and the wavelength combining prism 4. It can be arranged at any position in the optical path.

The two-wave optical pickup shown in FIG. 1 is shown individually to explain the function of each optical component. However, the pickup can be reduced in size by attaching two or more components together. In FIG. 1, three prisms, that is, the wavelength combining prism 4, the leakage prism 5, and the polarization beam splitter 8 are used. For example, the wavelength combining prism 4 and the leakage prism 5 may be bonded together. The leakage prism 5 and the polarizing beam splitter 8 may be bonded together. Further, the polarizing beam splitter 8 and the quarter wavelength plate 9 may be bonded together.

1 is a schematic configuration diagram showing a configuration of a two-wave optical pickup according to the present invention. Perspective view showing the configuration of the leakage prism The spectral characteristic figure of a leakage prism. The spectral characteristic figure of a wavelength synthesis prism. The spectral characteristic figure of a polarization beam splitter. The spectral characteristic figure of a leakage prism. The spectral characteristic figure of a leakage prism. The schematic block diagram which showed the structure of the conventional optical pick-up. (A), (b) is a spectral characteristic figure of a polarization beam splitter, respectively.

Explanation of symbols

1 2-wave optical pickup, 2, 6 laser diode, 3, 7 diffraction grating, 4 wavelength synthesis prism, 4a, 5a, 8a polarizing film, 5 leakage prism, 8 polarizing beam splitter, 9 1/4 wavelength plate, 10 collimating lens, 11 optical disc, 12 photodetector, 13 front monitor, S1, S2 S polarized light, P1, P2 P polarized light, Ts S polarized light transmittance, Rs S polarized light reflectance, Tp P polarized light transmittance

Claims (2)

A light source that emits light of two different wavelengths, a diffraction grating corresponding to two different wavelengths, an objective lens that collects light emitted from the light source onto an optical recording medium, and a light amount emitted from the light source are detected. A light amount detecting means, and a light detecting means for detecting reflected light from the optical recording medium,
A two-wave optical pickup for recording or / and reproducing information detected by the light detection means on the optical recording medium,
A two-wave optical pickup, wherein a leakage prism that disperses light emitted from the light source to the light amount detecting means is disposed in an optical path between the light source and the objective lens. 2. The two-wave optical pickup according to claim 1, wherein the components arranged adjacent to each other in the optical component are bonded together using an optical adhesive.

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