JP2002334470A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head device capable of preventing fluctuation in the output of a laser diode by a return light by suppressing high frequency superimposition on power supply when laser beams of different wave lengths are converged on an optical recording medium by using a common optical lens to reproduce information or the like. SOLUTION: In the first and second laser diodes 11 and 12 of an optical head device 1, optical path lengths L1 and L2 from light emitting points 11a and 12a to the recording surface 7a of an optical recording medium are set to lengths which are multiplication of values (1/2+m1, 1/2+m2) obtained by adding 1/2 to optional integers to resonator optical path lengths n1d1 and n2d2 constituting the first and second diodes 11 and 12. Thus, since the first and second optical path lengths L1 and L2 are not integral multiples of the resonator optical lengths, fluctuation in the output of the laser diode by return light noise is prevented by suppressing high frequency superimposition on power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact disc (CD) and a digital versatile disc (DVD).
The present invention relates to an optical head device used for recording and reproduction of an optical recording medium such as an optical recording medium. More specifically, a laser beam having different wavelengths is focused on an optical recording medium using a common objective lens to thereby prevent fluctuations in the output of the laser diode due to return light when reproducing and recording information. The present invention relates to a head device.

[0002]

2. Description of the Related Art As an optical head device, a 650 nm band laser diode for DVD playback and a CD-R playback / read
2 equipped with a 780 nm band laser diode for recording
A device called a wavelength optical head device is known. An optical head device of this type is disclosed in, for example, Japanese Patent Publication No. 1-56455.
No. 6,086,045.

[0003] As disclosed in this publication,
In the two-wavelength optical head device, in order to reduce the size and size of the device, the optical system of each laser beam is shared to share the optical element. For example, first and second laser diodes that emit different laser beams are provided. The laser beams from these laser diodes are guided to a common optical path by a beam splitter that combines optical paths, and a common objective disposed on the common optical path. The light converges on an optical recording medium via a lens.

Here, a laser diode used in an optical head device has, for example, gallium aluminum arsenide (GaAlAs) on both sides of a gallium arsenide (GaAs) crystal.
A double hetero structure sandwiched in a sandwich is used. The central gallium arsenide layer is a laser medium that generates light by supplying power to the outer gallium aluminum arsenide. It has become. The generated light is amplified by the resonator and emitted from the light emitting point of the laser diode as laser light.

The positions of the first laser diode and the second laser diode in the two-wavelength optical head device are set based on the magnification of the optical system and the working distance (focal length) of the common objective lens. Generally, the first laser diode and the second laser diode are arranged at positions where the optical path length from the light emitting point to the recording surface of the optical recording medium is equal.

[0006]

However, when the optical path lengths from both laser diodes to the optical recording medium are equal, the optical path length from one laser diode to the optical recording medium is equal to the cavity optical path of the laser diode. May be an integral multiple of the length. In this case, since a resonator is formed between the laser diode and the optical recording medium, a standing wave (noise) is generated in the return light reflected by the optical recording medium and traveling toward the laser diode. When this noise returns to the laser diode, output fluctuation may occur in the laser diode.

In order to avoid this problem, conventionally, a high-frequency current is superimposed on a drive current of the laser diode so that return light noise does not adversely affect the laser diode resonator. However, as the weight depth increases, the return light noise decreases, but the generation of EMI (Electromagnetic Interference) noise increases, and a metal shield cover or a noise filter is required as a countermeasure.

Accordingly, an object of the present invention is to provide a method of reproducing information by converging laser beams having different wavelengths on an optical recording medium using a common objective lens without performing power supply by high frequency superposition. Another object of the present invention is to provide an optical head device capable of preventing output fluctuation of a laser diode due to return light by only performing high-frequency superimposition so as to suppress generation of EMI.

[0009]

According to the present invention, there is provided a first laser diode for emitting a first laser beam, and a second laser having a different wavelength from the first laser beam. An optical head device comprising: a second laser diode that emits light; and an optical system that guides the first laser light and the second laser light emitted from these laser diodes to an optical recording medium. The first optical path length L1 from the light emitting point of the laser diode to the recording surface of the optical recording medium is n1, the refractive index of the first resonator constituting the first laser diode is d1, and the length is d1. Is defined as L1 = (1/2 + m1) n1d1, and the optical path length L2 from the light emitting point of the second laser diode to the recording surface of the optical recording medium is defined by the second laser diode. The refractive index of the second resonator constituting the over de n2, the length and d2, the arbitrary integers and m2, is characterized by defined by L2 = (1/2 + m2) n2d2.

In the optical head device according to the present invention, the first and second laser diodes have an optical path length from each light emitting point to the recording surface of the optical recording medium, forming the first and second laser diodes. It is set so as not to be an integral multiple of the optical path length of the resonator. Therefore, output fluctuation of the laser diode due to return light noise can be prevented.

Here, if the optical system has a common objective lens for guiding both the first laser light and the second laser light to an optical recording medium, the optical system can be simplified. . Similarly, it is preferable that the optical system includes a common light receiving element that receives the first and second laser beams reflected by the optical recording medium.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an optical head device to which the present invention is applied will be described below with reference to the drawings.

(Overall Configuration) FIG. 1 is a schematic configuration diagram showing an optical system of an optical head device according to this embodiment. Optical head device 1 of this example
Is for reproducing information from a plurality of types of optical recording media 7 having different substrate thicknesses and recording densities, such as CDs, CD-Rs, and DVDs, and emits a first laser beam H1 having a wavelength of 780 nm. A common optical system Ho is provided with a first laser diode 11 that emits light, a second laser diode 12 that emits a second laser light H2 having a wavelength of 650 nm, and a common optical system Ho.

A magnification conversion lens 2 for converting the magnification of the first laser light emitted from the first laser diode is arranged between the first laser diode 11 and the common optical system Ho. Further, between the second laser diode 12 and the common optical system Ho, the reflection mirror 3 that changes the direction of the second laser light toward the common optical system Ho is arranged.

The first laser beam H1 whose magnification has been converted by the magnification conversion lens 2 is transmitted through the common optical system Ho.
Second laser beam H whose direction has been changed by reflection mirror 3
2, a collimator lens 5 for collimating the laser beams H1 and H2 guided by the beam splitter 4, and laser beams H1 and H2 emitted from the collimator lens 5 to the optical recording medium 7. The objective lens 6 that converges on the recording surface 7a is arranged.

The common optical system Ho includes an optical recording medium 7.
The first laser beam H1 and the second laser beam H2 that have passed through the beam splitter 4 after being reflected by the recording surface 7a of FIG.
Also, a common light receiving element (not shown) for receiving the return light is disposed.

In the optical head device 1 having this configuration, when information is reproduced from a CD-R as the optical recording medium 7, etc.
The first laser diode 11 emits a first laser beam H1 having a wavelength of 780 nm. This first laser beam H
1 is guided to the common optical system Ho via the beam splitter 4, converged by the objective lens 6 as a light spot on the recording surface of the CD-R, and reflected on the recording surface of the CD-R.
The return light of the laser beam H1 is focused on the common light receiving element, and the information detected and recorded on the CD-R is reproduced by the signal detected by the common light receiving element.

On the other hand, as the optical recording medium 7, a DVD
When reproducing information in the second laser diode 1
2 emits a second laser beam H2 having a wavelength of 650 nm. The second laser beam H2 is also transmitted to the beam splitter 4
And converged as a light spot on the recording surface of the DVD by the objective lens 6,
The return light of the second laser beam H2 reflected by the recording surface of (2) is focused on the common light receiving element. The information of the DVD is reproduced based on the signal detected by the common light receiving element.

(Arrangement Position of Laser Diode) Here,
The optical path length L1 from the light emitting point 11a of the first laser diode 11 to the recording surface 7a of the optical recording medium 7, and the light path length L1 from the light emitting point 12a of the second laser diode 11 to the recording surface 7 of the optical recording medium 7.
The optical path lengths L2 up to a are individually set.
In this example, the first optical path length L1 is shorter than the second optical path length L2. The optical path lengths L1 and L2 in the following description
Means the optical equivalent air length, and is shown in FIG. 1 ignoring the thickness of the optical component.

A magnification conversion lens 2 is arranged between the first laser diode 11 and the beam splitter 4,
By converting the magnification of the first laser beam H1, the first
The laser beam H1 and the second laser beam H2 are focused on the optical recording medium 7 using the common objective lens 6. The reason why the magnification conversion lens 2 is arranged only on one side is as follows. The first laser beam H1 used for CD-R recording is converted in magnification by the magnification conversion lens 2 so that more light is used to record information.
This is because light can be condensed. Further, the second laser beam H2 used for DVD reproduction is changed to the first laser beam H1.
If the magnification is changed to the same magnification, the light amount around the opening of the objective lens 6 will be attenuated, and the effective NA will decrease to deteriorate the reproduction quality. This is because it is desirable to condense light to

In this example, the first optical path length L1 is set as follows. Assuming that the refractive index of the resonator constituting the first laser diode 11 is n1 and the length is d1, the resonator optical path length of this laser diode is expressed as n1d1.
When the optical path length L1 becomes an integral multiple of the optical path length of the resonator, the output light of the laser beam fluctuates due to the return light noise. Therefore, assuming that an arbitrary integer is m1, the optical path length L1 is set by the following equation.

L1 = (1/2 + m1) n1d1 Similarly, the second optical path length L2 is obtained by multiplying the refractive index n2 of the resonator constituting the second laser diode 12 by the length d2. When the length becomes an integral multiple of n2d21, the output light of the laser beam fluctuates due to the return light noise. Thus, the optical path length L2 is set by the following equation, where m2 is an arbitrary integer.

L2 = (1/2 + m2) n2d2 As described above, in the optical head device 1, the first and second laser diodes 11 and 12 have the respective light emitting points 11a and 11a.
An optical path length L1 from 12a to the recording surface 7a of the optical recording medium,
L2 is set so as not to be an integral multiple of the optical path length of the resonator constituting each of the first and second laser diodes. Therefore, output fluctuation of the laser diode due to return light noise can be prevented.

Accordingly, there is no need to superimpose the power supply of the laser diode at a high frequency to make the return light noise in a strong oscillation state so as not to affect the amplification action in the resonator.
There is no need to take EMI countermeasures against high frequency superposition.

Further, by disposing the magnification conversion lens 2 on the optical path from the first laser diode 11 or the second laser diode 12 to the common objective lens 6, the first
And the second laser beams H1 and H2 to the common objective lens 6
The light can be condensed on the recording surface of the optical recording medium 7 in an optimal state by using.

The optical head device of the above embodiment is composed of two laser diodes individually arranged and one common light receiving element. An optical head device equipped with a laser, an optical head device in which two light receiving elements respectively corresponding to two laser diodes are arranged, an optical head device in which three or more laser diodes are arranged, and
In an optical head device including a plurality of objective lenses and / or a plurality of light receiving elements respectively corresponding to a plurality of laser diodes, the length of the optical path from the light emitting point to the optical recording medium is set to the resonator optical path length. By arranging them so that the length is obtained by multiplying an arbitrary integer by adding １, it is possible to prevent output fluctuation of the laser diode due to return light.

[0027]

As described above, in the optical head device according to the present invention, the first and second laser diodes have an optical path length from the light emitting point to the recording surface of the optical recording medium. The length is set so as not to be an integral multiple of the optical path length of the resonator constituting the two laser diodes. Therefore, output fluctuation of the laser diode due to return light noise can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical system of an optical head device to which the present invention has been applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical head device 2 Magnification conversion lens 3 Reflection mirror 4 Beam splitter 5 Collimator lens 6 Common objective lens 7 Optical recording medium 11 First laser diode 11a Light emission point 12 Second laser diode 12a Light emission point Ho Common optical system H1 First 1 laser beam H2 second laser beam L1 optical path length from first laser diode light emitting point to recording surface of optical recording medium L2 optical path length from second laser diode light emitting point to recording surface of optical recording medium

 ──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Daisuke Watanabe 5329 Shimosuwa-cho, Suwa-gun, Nagano Prefecture F-term in Sankyo Seiki Seisakusho Co., Ltd. 5D119 AA12 AA41 BA01 BB01 BB02 BB03 EC47 FA05 FA08 HA38 LB10

Claims (3)

[Claims] 1. A first laser diode for emitting a first laser light, and a second laser diode having a wavelength different from that of the first laser light.
An optical head device comprising: a second laser diode that emits a laser beam; and an optical system that guides the first laser beam and the second laser beam emitted from these laser diodes to an optical recording medium. The first optical path length L1 from the light emitting point of the first laser diode to the recording surface of the optical recording medium is such that the refractive index of the first resonator constituting the first laser diode is n1,
Assuming that the length is d1 and an arbitrary integer is m1, L1 = (1/2 + m1) n1d1 is defined by the following equation. Assuming that the refractive index of the second resonator constituting the second laser diode is n2, the length is d2, and an arbitrary integer is m2, L2 = (1/2 + m2) n2d2. Optical head device. 2. The optical head according to claim 1, wherein the optical system includes a common objective lens for guiding both the first laser light and the second laser light to an optical recording medium. apparatus. 3. The optical system according to claim 1, wherein the optical system includes a common light receiving element that receives the first and second laser beams reflected by the optical recording medium. Head device.