JP2008204510A - Light receiving/emitting element and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and highly accurate light receiving/emitting element using a short-wavelength semiconductor laser, and an optical pickup device. <P>SOLUTION: The light receiving/emitting element is provided with: a light source 1; a reflection mirror 2 equipped with a reflective film 2a; and a substrate 9. The light source 1 is disposed so as to emit illumination light in parallel to the substrate 9. The reflection mirror 2 is disposed so as to reflect the illumination light upward vertically to the surface of the substrate 9. A reflectance X(%) of the reflective film 2a satisfies X≈C/(A×B), where A(W) is an output at which the quantum noise of the light source 1 is sufficiently reduced, B(%) is light transmission efficiency from the reflection mirror 2 to an optical disk 7, and C(W) is a reproduction output necessary for reproducing the optical disk. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting / receiving element used for reproducing information recorded on an information recording medium such as an optical disk, an optical pickup device, and a semiconductor laser device used therefor, and in particular, when a short wavelength semiconductor laser is used as a light source. It is suitable for.

  The optical memory technology using an optical disk having a pit-like pattern as a high-density and large-capacity storage medium is expanding its applications such as digital audio disk, video disk, document file disk, and data file. In this optical memory technology, information is recorded / reproduced with high accuracy and reliability on an optical disc through a finely focused light beam. This recording / reproducing operation depends solely on the optical system. The basic functions of the optical head device, which is the main part of the optical system, can be broadly divided into condensing to form a diffraction-limited micro spot, focus control and tracking control of the optical system, and detection of a pit signal. These functions are realized by a combination of various optical systems and photoelectric conversion detection methods according to the purpose and application. In particular, in recent years, as the amount of information to be recorded on the information recording medium has increased, an information recording medium having a larger capacity has been demanded. In order to increase the capacity of an information recording medium, when recording information on the information recording medium and reproducing information recorded on the information recording medium, a light spot formed by light irradiated on the information recording medium It is necessary to increase the recording density of information by reducing the value of. For this purpose, the light spot can be reduced by shortening the wavelength of the semiconductor laser as the light source and increasing the numerical aperture (NA) of the objective lens. For example, an optical head device capable of recording or reproducing information with respect to a DVD (digital versatile disk) uses a semiconductor laser light source having a wavelength of 660 nm and an objective lens having an NA of 0.6. For example, the wavelength is 405 nm. By using the semiconductor laser light source and the objective lens having an NA of 0.85, a recording density equivalent to about 5 times the recording density in DVD can be achieved.

  However, in the optical disk apparatus using a short-wavelength semiconductor laser as a light source as described above, the reproduction power margin in the semiconductor laser is reduced due to the problem of quantum noise of the semiconductor laser. An optical pickup that addresses the problem of quantum noise of the semiconductor laser is described in Patent Document 1. The optical pickup described in Patent Document 1 realizes good reproduction characteristics while keeping the light power on the optical disk board surface low and suppressing the quantum noise of the semiconductor laser to a sufficiently low power.

  FIG. 4 shows a configuration of a conventional optical pickup. In FIG. 4, a light source 101 is a GaN-based semiconductor laser emitting blue light. The intensity filter 203 is an optical element having a film that absorbs light. In the optical system disclosed in Patent Document 1, the intensity filter 203 is mechanically inserted into and removed from the optical path.

  When recording information on the optical disc 107, the intensity filter 203 is disposed outside the optical system as indicated by reference numeral 203a. Thereby, the light irradiated from the light source 101 reaches the beam splitter 202 as it is. The light reflected by the beam splitter 202 is converted into parallel light by passing through the collimator lens 105. The parallel light is reflected by the rising mirror 201 and collected by the objective lens 106, and a light spot is formed on the optical disk 107. Information can be recorded by changing the state of the recording layer of the optical disc 107 by the energy of light in the light spot.

  Next, when reproducing the information recorded on the optical disc 107, the intensity filter 203 is arranged in the optical path. Thereby, the light emitted from the light source 101 is attenuated when passing through the intensity filter 203. The attenuated light is condensed on the recording layer of the optical disc 107 through the beam splitter 202, the collimator lens 105, the rising mirror 201, and the objective lens 106, as in the above-described recording operation.

  The light reflected from the recording layer reaches the objective lens 106 again by the reflectivity according to the state of the recording layer of the optical disc 107. Next, the light that has passed through the rising mirror 201 and the collimator lens 105 passes through the multi lens 204 and is condensed on the photodiode 205. The photodiode 205 generates a focus error signal and a tracking error signal in order to extract information recorded on the optical disc 107. The focus error signal is generated using an astigmatism method. Based on the focus error signal, the position of the objective lens 106 is controlled so that the light beam is condensed on the recording layer of the optical disc 107. Further, based on the tracking error signal, the objective lens 106 is controlled in the position in the board direction of the optical disc 107 so that the light beam is focused on a desired track on the optical disc 107. The focus control and tracking control as described above are performed, and the light collected at the target position on the optical disc 107 reaches the photodiode 205 while retaining the information recorded on the optical disc 107 and is converted into an electric signal. As a result, the recorded information on the optical disc 107 is reproduced.

According to the optical head of the prior art, the light emission power of the light source 101 can be maintained in a state where the quantum noise is sufficiently low during reproduction, and the power on the surface of the optical disk 107 can be kept low. Good reproduction can be realized without causing erroneous erasure.
Japanese Patent Laid-Open No. 2000-195086

  However, in the configuration disclosed in Patent Document 1, the strength filter 203 is necessary and a mechanism for mechanically moving the strength filter 203 is required, which increases the number of parts and increases the cost. .

  Further, there is a problem that assembly tolerance is generated by incorporating the strength filter 203 into the optical pickup, and the assembly margin of other optical members is reduced.

  The object of the present invention is to maintain the light emission power of the light source in a state where the quantum noise is sufficiently low, and to keep the power on the optical disk surface low, without causing deterioration of the optical disk and erroneous erasure of data. An object of the present invention is to provide an inexpensive and highly accurate light receiving / emitting element and optical pickup device that can realize reproduction.

In order to achieve the above object, a light receiving and emitting element of the present invention includes a light source, a mirror including a reflective film that reflects light emitted from the light source, the light source and the mirror, and a light receiving element on the surface. In the light emitting / receiving element including the substrate, the light source is disposed so as to irradiate the irradiation light in parallel to the substrate, and the mirror vertically extends the irradiation light to the surface of the substrate. The output that is arranged so as to reflect the light and the quantum noise of the light source is sufficiently reduced is A (W), and the transmission efficiency of light from the mirror to the optical disk is B (%). When the output is C (W), the reflectance X (%) of the reflective film is
X≈C / (A × B)
It is formed so as to satisfy the relationship.

The optical pickup device of the present invention includes a light source, a mirror having a reflective film that reflects light emitted from the light source, a substrate having the light source and the reflective mirror, and a light receiving element on the surface. And a light path branching means for transmitting the light from the mirror and splitting the return light from the optical disk side, and a light collecting means for condensing the light from the light path branching means on the information layer of the optical disk. In the pickup device, the light source is arranged to irradiate irradiation light in parallel to the substrate, and the mirror is arranged to reflect the irradiation light vertically upward with respect to the surface of the substrate. An output at which the quantum noise of the light source is sufficiently reduced is A (W), a light transmission efficiency from the mirror to the optical disk is B (%), and a reproduction output necessary for reproducing the optical disk is C (W When the reflectivity X (%) of the reflective film,
X≈C / (A × B)
It is formed so as to satisfy the relationship.

According to the present invention, it is not necessary to newly use an optical element such as a filter in order to reduce quantum noise that occurs with the shortening of the wavelength of the light source and is particularly problematic during reproduction.
As a result, the number of parts can be reduced, and there is no need to greatly change the conventional shape, and an inexpensive and highly accurate read-only light emitting / receiving element and optical pickup can be provided.

  In the light emitting / receiving element and the optical pickup device of the present invention, the light source can be composed of a semiconductor laser.

  The light source may be a semiconductor laser capable of emitting light in a wavelength range from green to ultraviolet.

  Further, the reflection film of the mirror can be composed of a light absorption film.

  The mirror may be formed by etching the substrate.

  Moreover, the said mirror can be set as the structure which has an angle of 40-50 degrees with respect to the irradiation light of the said light source.

(Embodiment 1)
FIG. 1 shows a schematic configuration of the light emitting / receiving element and the optical pickup device in the first embodiment. In FIG. 1, the light source 1 is constituted by a semiconductor laser. For example, the light source 1 is a semiconductor laser having an oscillation wavelength of 405 nm mounted on an optical pickup device compatible with an information medium such as a Blu-ray disc or HD-DVD, or a 650 nm CD (mounted on an optical pickup device compatible with DVD. It may be a semiconductor laser having an oscillation wavelength of 780 nm mounted on an optical pickup device compatible with a compact disk.

  Light emitted from the light source 1 in a direction parallel to the substrate 9 is reflected by the reflection film 2 a of the reflection mirror 2. The angle of the reflection surface of the reflection mirror 2 is preferably 45 degrees with respect to the optical axis of the light emitted from the light source 1, but may be 40 degrees to 50 degrees, and is not limited to this angle. The reflective film 2a is composed of a light absorbing film. The light absorbing film is, for example, an Au / Ti / Si substrate (reflectance of light with a wavelength of 405 nm: about 40%), a SiO / Al: Si / Au / Ti / Si substrate (reflectance of light with a wavelength of 405 nm: about 58). %). The film thickness of the light absorption film is, for example, 200 nm to 400 nm.

  The light reflected by the reflection mirror 2 passes through the diffraction element 4, the collimator lens 5, and the objective lens 6 and is collected on the optical disk 7. The light collected on the optical disk 7 is reflected by the reflection layer of the optical disk 7, passes through the objective lens 6 and the collimator lens 5, and enters the diffraction grating 4 (optical path branching means). The diffractive element 4 splits incident light to the two light receiving elements 3a and 3b. The light receiving elements 3a and 3b can reproduce the information recorded on the disk 7 by receiving the light split by the diffraction grating 4, converting it into an electric signal and outputting it.

  Here, FIG. 2 is a graph showing the relationship between the laser output of a semiconductor laser light source having an oscillation wavelength of 405 nm and the relative noise intensity. As shown in FIG. 2, it can be seen that when the output of the semiconductor laser decreases, the relative noise intensity increases rapidly. An increase in relative noise intensity causes a deterioration in reproduction signal characteristics of the optical disc.

The output of the light source 1 with a sufficiently small relative noise intensity is A (W), the light use efficiency of the optical pickup 8 including the diffraction grating 4, the collimator lens 5, the objective lens 6 and the like is B (%), and the optical disc 7 is reproduced. When the optimum reproduction signal output for the purpose is C (W), the reflectance X (%) of the reflective film 2a in the reflective mirror 2 is
X≈C / (A × B) (Formula 1)
Must be formed to satisfy the conditions. For example, when the output of the light source 1 is 2 mW, the light use efficiency of the optical pickup 8 is 25%, and the reproduction output of the optical disk 7 is 0.25 mW, the reflectance X of the reflection film 2a in the reflection mirror 2 is about 50%. Become.

  Note that な お used in Equation 1 represents that there is no problem with the characteristics of the present invention even if an error of about ± 5% is included.

  As described above, according to the first embodiment, the reflection mirror 2 includes the reflection film 2a having the reflectance expressed by Equation 1, so that the light emission power of the light source 1 is sufficiently reduced by quantum noise when the optical disk 7 is reproduced. Since the power can be attenuated to be low and the power on the surface of the optical disc 7 can be kept low, the optical disc 7 can be prevented from being deteriorated and erroneous erasure of data can be prevented. Further, since the conventional attenuation filter is not mounted, it can be realized with a simple configuration, the cost can be reduced, and the optical accuracy is not impaired.

(Embodiment 2)
FIG. 3 shows a schematic configuration of the light emitting / receiving element and the optical pickup device in the second embodiment.

  In FIG. 3, the light source 11 is composed of a semiconductor laser. The light source 11 is, for example, a semiconductor laser having an oscillation wavelength of 405 nm mounted on an optical pickup device compatible with an information medium such as a Blu-ray disc or HD-DVD, or 650 nm mounted on an optical pickup compatible with an information medium of DVD, You may comprise with the semiconductor laser of the oscillation wavelength of 780 nm mounted in the optical pick-up corresponding to the information medium of CD (compact disk).

  Light emitted from the light source 11 in a direction parallel to the substrate 19 is reflected by the reflective film 12. In the second embodiment, the reflective film 12 is formed on a part of the silicon substrate 19. Further, the angle of the reflection surface of the reflection film 12 is preferably 45 degrees with respect to the optical axis of the light emitted from the light source 11, but is not limited to this angle. The reflective film 12 is composed of a light absorbing film. The light absorption film is made of, for example, an Au / Ti / Si substrate (405 nm reflectance: about 40%), a SiO / Al: Si / Au / Ti / Si substrate (405 nm reflectance: about 58%), or the like. . The film thickness of the light absorption film is, for example, 200 nm to 400 nm. The reflective film 12 can also be formed by etching.

  The light reflected by the reflective film 12 passes through the diffraction element 14, the collimator lens 15, and the objective lens 16 and is collected on the optical disk 17. The light collected on the optical disc 17 is reflected by the reflection layer of the optical disc 17, passes through the objective lens 16 and the collimator lens 15, and enters the diffraction grating 14. The diffraction element 14 splits incident light toward the two light receiving elements 13a and 13b. The light receiving elements 13a and 13b can reproduce the information recorded on the disk 17 by receiving the light dispersed by the diffraction grating 14, converting it into an electric signal and outputting it.

  Here, FIG. 2 is a graph showing the relationship between the laser output of a semiconductor laser light source having an oscillation wavelength of 405 nm and the relative noise intensity. As shown in FIG. 2, it can be seen that when the output of the semiconductor laser decreases, the relative noise intensity increases rapidly. An increase in relative noise intensity causes a deterioration in reproduction signal characteristics of the optical disc.

The output of the light source 11 having a sufficiently small relative noise intensity is A (W), the light use efficiency of the optical pickup 18 including the diffraction grating 14, the collimator lens 15, the objective lens 16, and the like is B (%), and the optical disc 17 is reproduced. When the optimum reproduction signal output for C is (C), the reflectance X (%) of the reflective film 12 is
X≈C / (A × B) (Formula 2)
It is necessary to form so as to satisfy the conditions. For example, when the output of the light source 11 is 2 mW, the light utilization efficiency of the optical pickup 18 is 25%, and the reproduction output of the optical disk 17 is 0.25 mW, the reflectance of the reflective film 12 is about 50%.

  As described above, according to the second embodiment, by providing the reflective film 12 having the reflectance shown in Formula 2, the light emission power of the light source 11 is sufficiently reduced to reduce the quantum noise during reproduction of the optical disc 17. Since it can be attenuated and the power on the surface of the optical disk 17 can be kept low, it is possible to prevent the optical disk 17 from being deteriorated and erroneous data erasure. In addition, since a conventional filter is not mounted, it can be realized with a simple configuration, the cost can be reduced, and the optical accuracy is not impaired.

  Further, since the reflective film 12 is formed on a part of the substrate 19, it can be realized with a simple configuration and cost can be reduced.

  The light emitting / receiving element and the optical pickup device of the present invention are useful as an optical disc reproducing device, particularly a Blu-ray disc or HD-DVD reproducing device when a short wavelength semiconductor laser is used.

Schematic diagram of light receiving and emitting element and optical pickup device in Embodiment 1 Characteristic diagram showing correlation between laser output of semiconductor laser light source and relative noise intensity Schematic diagram of light emitting / receiving element and optical pickup device in Embodiment 2 Schematic diagram showing the configuration of a conventional optical pickup

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Reflecting mirror 2a Reflecting surface 3 Light receiving element 4 Diffraction grating 5 Collimator lens 6 Objective lens

Claims (12)

A light source;
A mirror provided with a reflective film for reflecting the irradiation light from the light source;
In the light emitting / receiving element including the light source and the mirror and a substrate having a light receiving element on the surface,
The light source is
Arranged to irradiate irradiation light parallel to the substrate,
The mirror is
The irradiation light is arranged to reflect vertically upward with respect to the surface of the substrate,
The output at which the quantum noise of the light source is sufficiently reduced is A (W), the light transmission efficiency from the mirror to the optical disk is B (%), and the reproduction output necessary for reproducing the optical disk is C (W). In this case, the reflectance X (%) of the reflective film is
X≈C / (A × B)
It is formed so that the relationship may be satisfied.   The light emitting / receiving element according to claim 1, wherein the light source includes a semiconductor laser.   The light emitting / receiving element according to claim 1, wherein the light source includes a semiconductor laser capable of emitting light in a wavelength region from green to ultraviolet.   The light receiving / emitting element according to claim 1, wherein the reflection film of the mirror is formed of a light absorption film.   The light emitting / receiving element according to claim 1, wherein the mirror is formed by etching the substrate.   The light receiving and emitting element according to claim 1, wherein the mirror has an angle of 40 to 50 ° with respect to the irradiation light of the light source. A light source;
A mirror having a reflective film for reflecting the irradiation light from the light source;
A substrate having the light source and the reflection mirror, and a light receiving element on the surface,
An optical path branching unit that transmits the light from the mirror and splits the return light from the optical disk side;
A light pickup device including a light collecting means for collecting light from the optical path branching means on an information layer of an optical disc,
The light source is
Arranged to irradiate irradiation light parallel to the substrate,
The mirror is
The irradiation light is arranged to reflect vertically upward with respect to the surface of the substrate,
The output at which the quantum noise of the light source is sufficiently reduced is A (W), the light transmission efficiency from the mirror to the optical disk is B (%), and the reproduction output necessary for reproducing the optical disk is C (W). In this case, the reflectance X (%) of the reflective film is
X≈C / (A × B)
An optical pickup device formed to satisfy the above relationship.   The optical pickup device according to claim 7, wherein the light source includes a semiconductor laser.   The optical pickup device according to claim 7, wherein the light source includes a semiconductor laser capable of emitting light in a wavelength region from green to ultraviolet.   The optical pickup device according to claim 7, wherein the reflection film of the mirror is formed of a light absorption film.   The optical pickup device according to claim 7, wherein the mirror is formed by etching the substrate.   The optical pickup device according to claim 7, wherein the mirror has an angle of 40 to 50 ° with respect to the irradiation light of the light source.

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