JPH0512703A - Optical head and second harmonic light source - Google Patents

Abstract

(57) [Abstract] [Purpose] In an optical head using a second harmonic light source, an optical head having a short optical path is formed by converting a second harmonic light beam generated from the light beam into diffused light. When a light beam 2 is incident on a second harmonic generation means 4, a solid-state laser element 5 is excited to generate a light beam 8. Next, when the light beam 8 is incident on the nonlinear optical element 6, the light beam 9 which is the second harmonic of the light beam 8 is generated by using this as the fundamental wave. The light beam 8 is amplified by the resonator constituted by the end surface 7a of the resonator element 7 and the end surface 5a of the solid-state laser element 5, and the light amount of the light beam 9 is increased. When the light beam 9 is transmitted through the resonant element 7, it is diffused by the concave surface 7b of the emitting surface and becomes a light beam 10. This light beam 10 is converted into an objective lens 12
By converging with, it is possible to construct a practical optical head with a short optical path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of an optical recording / reproducing apparatus for optically recording or reproducing information on an information recording medium and its light source.

[0002]

2. Description of the Related Art In an optical recording / reproducing apparatus, in order to improve the recording density, an optical head has been developed in which the wavelength is shortened by using the second harmonic of a light beam. An example of this is shown in FIG.

In FIG. 4, a light beam 42 emitted from a semiconductor laser 41 is focused by a converging lens 43 and is incident on a second harmonic generating means 44. The second harmonic generation means 44 includes a solid-state laser element 45, a non-linear optical element 46 having a non-linear optical effect, and a resonant element 47. The end face 47a of the resonant element 47 and the end face 45a of the solid-state laser element 45 constitute a resonator. is doing. Therefore, the light beam 42 incident on the second harmonic generation means 44 excites the solid-state laser element 45 to generate a light beam 48 which is a fundamental wave. Next, when the light beam 48 is incident on the nonlinear optical element 46, a light beam 49 that is the second harmonic thereof is generated. The light beam 48 of the fundamental wave is amplified by the resonator constituted by the end face 47a and the end face 45a, and the light beam 4 of the second harmonic wave is generated.
9 is transmitted through the resonance element 47 to become a parallel light beam 50. Since the light beam 48 spreads slightly, the resonance element 47
In many cases, the end surface 47a of the optical disk is made slightly concave so that the light does not diffuse, and the light beam 50 is a substantially parallel light beam.

As a concrete example of the second harmonic generating means 44, a solid-state laser element 45 using YAG (yttrium-aluminum-garnet crystal) and a nonlinear optical element 46 using KTP (KTiOPO ₄ ). It has been put to practical use. In this case, the wavelength of 8
When the 08 nm light beam 42 is emitted, a light beam 48 having a wavelength of 1064 nm is generated from the solid-state laser element 45, and a light beam 49 of 532 nm which is the second harmonic of the light beam 48 is generated from the nonlinear optical element 46. To do. Therefore, the light beam 50 becomes a parallel beam having a wavelength of 532 nm.

In this specification, the semiconductor laser 41,
The light beam 42, the converging lens 43, and the second harmonic generation means 44 are collectively referred to as a second harmonic light source.

Next, the beam diameter of the light beam 50 is expanded by a beam expander 53 composed of at least a concave lens 51 and a convex lens 52 to become a light beam 54. The diameter of the light beam 50 emitted from the second harmonic generation means 44 that is generally put to practical use is about 0.5 mm, and it is necessary to expand it by about 10 times in order to use it as an optical head. The expanded light beam 54 is P-polarized and enters a polarization beam splitter 55. Therefore, the light beam 54 is transmitted therethrough, passes through the quarter-wave plate 56 and the reflection mirror 57, and is narrowed down by the objective lens 58 to form a light spot 60 on the information recording medium 59. The light beam 61 reflected by the information recording medium 59 has an objective lens 58, a reflection mirror 57, 1 /
It passes through the four-wave plate 56 to become S-polarized light, which is reflected by the polarization beam splitter 55. The light beam 61 reflected here is a diaphragm lens 62 and a cylindrical lens 63.
The light is focused by and is received by the photodetector 64. Photo detector 64
Is configured to detect the focus error signal by the so-called astigmatism method and the tracking error signal by the push-pull method together with the reproduction signal. Reference numeral 65 denotes a focus driving means, which drives the objective lens 58 so that the light spot 60 is imaged on the recording information medium 59 by the focus error signal.

A tracking drive means (not shown) is driven by the tracking error signal so that the light spot 60 is focused on a certain track on the recording information medium 59.

[0008]

In the conventional structure as described above, since the diameter of the light beam emitted from the second harmonic generation means is small, a beam expander having a relatively large expansion rate is required. The beam expander is composed of at least two or more lens groups, and the optical path length becomes long when the expansion ratio is large. Therefore, there has been a big problem in reducing the size and weight of the optical head. In addition, it is difficult to reduce the cost because the number of optical components increases.

[0009]

In order to solve the above problems, the optical head of the present invention comprises a second harmonic light source for emitting diffused light, an objective lens for converging the diffused light on an information recording medium, and information. The light separating means for separating the reflected light from the recording medium and the light detecting means for detecting the separated reflected light are provided.

As the second harmonic light source, (1) a solid-state laser element that emits a fundamental wave by being excited by laser light, a non-linear optical element that emits a second harmonic of the fundamental wave, and a fundamental wave And a resonance element forming a resonator, and the resonance element is configured so that the second harmonic wave emitted from the resonance element becomes diffused light.

(2) A solid-state laser element that emits a fundamental wave by being excited by laser light, a nonlinear optical element that emits a second harmonic of the fundamental wave, and the solid-state laser element generate a fundamental wave. The resonance element is formed of a resonance element forming a resonator, and the second harmonic wave emitted from the resonance element is diffused light.

(3) A solid-state laser element that emits a fundamental wave by being excited by a laser beam, a non-linear optical element that emits a second harmonic of this fundamental wave, and a resonance element that forms a resonator of the fundamental wave. And a lens for diffusing the second higher harmonic wave emitted from the resonant element, and the second higher harmonic wave is emitted as diffused light.

[0013]

According to the present invention, with the above-described structure, in the optical head using the second harmonic light source, the beam diameter necessary for the optical head can be secured without using the beam expander such as the beam expander. The optical head can be easily configured by the optical path.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention and shows the configuration of an optical head and a second harmonic light source.

In FIG. 1, a light beam 2 emitted from a semiconductor laser 1 is focused by a converging lens 3 and is incident on a second harmonic generation means 4. Second harmonic generation means 4
Is a solid-state laser element 5 that emits a fundamental wave, a nonlinear optical element 6 that emits a second harmonic, and a resonant element 7,
The end face 7a of the resonator element 7 and the end face 5a of the solid-state laser element 5 form a resonator for a fundamental wave. Where the light beam 2
Is excited, the solid-state laser element 5 is excited to generate a light beam 8 which is a fundamental wave. Next, when the light beam 8 is incident on the nonlinear optical element 6, a light beam 9 which is the second harmonic of the light beam 8 is generated. The light beam 8 is amplified by the resonator constituted by the end face 7a and the end face 5a, and the light amount of the light beam 9 emitted from the nonlinear optical element 6 is increased. The light beam 9 is transmitted through the resonant element 7 and is refracted by the concave surface 7b which is the exit surface thereof to become diffused light. Therefore, the light beam 10 emitted from the second harmonic generation means 4 becomes diffused light. The amount of the light beam 10 can be increased by forming a reflection film for the light beam 9 that is the second harmonic on the end face 6a of the nonlinear optical element 6. Further, if the element material forming the second harmonic generation means 4 is the same as in the conventional example, the wavelength 80 of the light beam 2 is
The wavelength of the light beam 10 becomes 532 nm with respect to 8 nm.

Next, a part of the light beam 10 is reflected by the half mirror 11 and focused by the objective lens 12 to form a light spot 14 on the information recording medium 13. The light beam 15 reflected by the information recording medium 13 passes through the objective lens 12 again and enters the half mirror 11. A part of the light beam 15 is reflected here, but a part is transmitted here. Light beam 15
Has astigmatism by passing through the half mirror 11. Therefore, a photodetector 16 for detecting this light beam 15
Like the conventional example, can be configured to detect the focus error signal by the astigmatism method and the toking error signal by the push-pull method together with the reproduction signal.

Reference numeral 17 denotes a focus driving means, which causes the light spot 14 to move to the recording information medium 1 according to the focus error signal.
The objective lens 12 is driven so as to form an image on the surface 3.
Further, a tracking drive means (not shown) is driven by the tracking error signal so that the light spot 14 is imaged on a certain track on the recording information medium 13.

FIG. 2 and FIG. 3 show the construction of the second harmonic light source in the embodiments of claims 3 and 6, respectively. Further, those having the same numbers as those in FIG. 1 have the same functions and operations.

In FIG. 2, a light beam 2 emitted from a semiconductor laser 1 is focused by a converging lens 3 and is divided into 2
It is incident on the second harmonic generation unit 1. The second harmonic generation means 21 includes a solid-state laser element 22 that emits a fundamental wave, a nonlinear optical element 23 that emits the second harmonic, and resonant elements 24 and 25. The resonant elements 24 and 25 form the fundamental wave. Of the resonator. When the light beam 2 is incident on this, the solid-state laser element 22 is excited to generate a light beam 26 which is a fundamental wave. Next, when the light beam 26 is incident on the nonlinear optical element 23, the light beam 27 which is the second harmonic thereof is generated. The light beam 26 is a resonant element 24, 25.
The light amount of the light beam 27 amplified by the resonator constituted by the end face 24a and the end face 25a and emitted from the nonlinear optical element 23 is increased. The light beam 27 passes through the resonance element 25 and is refracted by the concave surface 25b, which is the exit surface, to become diffused light. Therefore, the light beam 10 becomes diffused light.

In FIG. 3, the light beam 2 emitted from the semiconductor laser 1 is focused by the converging lens 3 and is incident on the second harmonic generating means 31. Second harmonic generation means 31
Is a solid-state laser element 32, a non-linear optical element 33, a resonator element 34, and a concave lens 35, and has an end face 34a and an end face 32a.
And constitute a resonator. When the light beam 2 is incident on this, the solid-state laser element 32 is excited to generate a light beam 36, and the nonlinear optical element 33 generates a light beam 37 that is the second harmonic. The light beam 36 is amplified by the resonator to increase the light beam 37,
Is transmitted through the resonance element 34 and diffused by the concave lens 35. Therefore, the light beam 10 becomes diffused light.

As described above, according to the present invention, the light head emitted from the second harmonic wave generating means is diffused light, so that the optical head can be constructed without expansion. Therefore, unlike the conventional example, a beam expander having a long optical path is not required. Further, the diffused light is directly incident on the objective lens and converged on the information recording medium, whereby an optical head suitable for the second harmonic light source can be configured.

[0022]

With the above-described structure, in the optical head using the second harmonic light source, the light beam of the second harmonic generated from the optical head is used as the diffused light, and the conventional beam expanding means is used. Is no longer needed. In the present invention, it is only necessary to collect the diffused light from the second harmonic light source, and the optical head can be constructed with a short optical path.

Therefore, the optical head can be downsized, the number of optical components is small, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a principle diagram of an optical head and a second harmonic light source according to a first embodiment of the present invention.

FIG. 2 is a principle diagram of a second harmonic light source according to a second embodiment of the present invention.

FIG. 3 is a principle diagram of a second harmonic light source according to a third embodiment of the present invention.

FIG. 4 is a principle diagram of a conventional optical head.

[Explanation of symbols]

1 Semiconductor laser 3 Converging lens 4 Second harmonic generation means 5 Solid-state laser device 6 Non-linear optical element 7 Resonance element 8 light beams 9 light beam 10 light beams 11 half mirror 12 Objective lens 13 Information recording medium 16 Photodetector

Claims (6)

[Claims] 1. A second harmonic light source that emits diffused light, an objective lens that converges the diffused light onto an information recording medium, and a light separating unit that separates reflected light from the information recording medium, and the separated light. An optical head comprising a light detecting means for detecting reflected light. 2. A half mirror is used as the light separating means, the diffused light emitted from the second harmonic light source is reflected by the half mirror, and the reflected light from the information recording medium is transmitted. The optical head according to claim 1. 3. A solid-state laser element that emits a fundamental wave when excited by a laser beam, a nonlinear optical element that emits a second harmonic of this fundamental wave, and a resonant element that forms a resonator of the fundamental wave. The second harmonic light source is characterized in that the resonance element is configured such that the second harmonic emitted from the resonance element becomes diffused light. 4. A solid-state laser element that emits a fundamental wave when excited by a laser beam or the like, a nonlinear optical element that emits a second harmonic of the fundamental wave, and the resonance of the fundamental wave between the solid-state laser element. Second resonance light source, characterized in that the resonance element is configured so that the second harmonic wave emitted from the resonance element becomes diffused light. 5. The third harmonic wave emitting surface of the resonant element is a concave surface, and the second harmonic wave emitted from the optical element is a diffused light by the concave surface. The second harmonic light source described. 6. A solid-state laser element that emits a fundamental wave when excited by laser light or the like, a nonlinear optical element that emits a second harmonic of the fundamental wave, and a resonance element that forms a resonator of the fundamental wave. A second harmonic light source, comprising a lens for diffusing the second harmonic emitted from the resonant element, the second harmonic being configured to be emitted as diffused light.