JPH0636337A - Two-beam optical head - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to combine two reproducing and recording reflected beams with good performance without using two semiconductor lasers of different wavelengths and a wavelength selection mirror, and a simple and inexpensive optical system is provided. A two-beam optical head for an optical information recording / reproducing apparatus is obtained. In a two-beam optical head of an optical information recording / reproducing apparatus, a first light beam emitted from a first laser light source and a second light beam emitted from a second laser light source are combined. The synthesizing means is composed of a prism having an inclined surface that totally reflects the first light beam and refracts / transmits the second light beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-beam optical head in an optical information recording / reproducing apparatus.

[0002]

2. Description of the Related Art Conventional immediate RAW (Read After Write)
In an optical information recording / reproducing apparatus having a check function, two objective spots for recording / erasing and reproducing are formed on an optical disc medium by using one objective lens as shown in FIG. I had it. Therefore, the device is configured as follows.

Two laser beams respectively emitted from two semiconductor lasers having different wavelengths, for example, a semiconductor laser 20 having a wavelength of 830 nm for recording / erasing and a semiconductor laser 21 having a wavelength of 780 nm for reproducing are wavelength-selected. The objective lens 2 is synthesized by using the mirror 26.
7, two laser beams are focused on the optical disk medium 30 as a recording / erasing spot 28 and a reproducing spot 29.

The two laser beams are combined in the wavelength selection mirror 26 by utilizing the wavelength difference of 50 nm. For example, the long wavelength 830 nm laser beam is transmitted and the short wavelength 780 nm laser beam is reflected. The two laser beams were combined on the objective lens 27.

[0005]

However, in the conventional two-beam optical head having the above configuration, the wavelengths of the respective semiconductor lasers are practically 780 nm band and 830 nm.
Since the wavelength selection mirror is only in the nm band and the wavelength difference is very narrow, about 50 nm, it is difficult to say that the laser beam combining performance using the wavelength selection mirror is sufficient, and a wavelength selection mirror with good wavelength selection performance is used. It was difficult to produce, and the cost was high.

The present invention is capable of synthesizing two laser beams with good performance without using a wavelength selective mirror, and for optical recording / reproducing provided with a synthesizing means which can construct an optical system at low cost. The purpose is to obtain a two-beam optical head of the device.

[0007]

A two-beam optical head according to a first aspect of the present invention includes a first laser light source and a second laser light source.
Laser light source, combining means for combining the first light beam and the second light beam emitted from the respective laser light sources, and the first and second light beams combined by the combining means, respectively. In a two-beam optical head having a first spot and an objective lens for forming an image on a disk medium as a second spot, the synthesizing means totally reflects the first light beam and the second light beam. A prism having an inclined surface for refracting and transmitting is used.

Further, in the two-beam optical head according to the invention described in claim 2, in the two-beam optical head according to claim 1, the second light beam refracted / transmitted by the prism is an information beam. It is used for recording and erasing, and has a beam shaping function.

In the two-beam optical head according to the invention described in claim 3, in the two-beam optical head according to claim 1, the first light beam and the second light beam have the same wavelength. And

[0010]

In the present invention, one of the two laser beams from the two semiconductor lasers is incident on the prism slope surface at a larger angle than the critical angle for total reflection, and the other is incident at a smaller angle than the critical angle for transmission and refraction. The light is synthesized as a spot for erasing / recording and a spot for reproducing on the optical disk medium through the objective lens. Therefore, according to the present invention, since it is not necessary to use a wavelength selective mirror and semiconductor lasers having the same wavelength can be used, it is possible to construct an inexpensive optical system having good combining performance.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. Here, the signal detection optical system and the detector using the reflected beam from the optical disk medium 7 are omitted,
The process in which the two laser beams are combined and focused as a spot on the optical disk medium is shown.

In FIG. 1, the recording / erasing laser beam emitted from the semiconductor laser 1 is a collimating lens 3
And becomes a parallel light beam 10a and enters the prism 5. Since the angle of incidence on the slope A of the prism 5 is set to be smaller than the critical angle, the parallel light flux 10a is refracted on the slope A and passes through the prism 5. The prism 5 also has a beam shaping action for converting the parallel light flux 10a having an elliptical cross section into a circular shape.

On the other hand, the reproducing laser beam emitted from the semiconductor laser 2 is collimated by the collimator lens 4 into a parallel light beam 1.
It becomes 1a and enters the prism 5. Here prism 5
Since the incident angle on the slope A is set to be larger than the critical angle, the parallel light flux 11a is totally reflected on the slope A and then passes through the prism 5. The collimator lens 4 having a relatively small NA is used, and a part of the light beam is kicked so that the light beam 11
A is configured to be substantially circular. Even if a part of the reproducing laser beam is kicked by the collimator lens 4, it is sufficient that the intensity is about 1/5 to 1/10 of the intensity of the recording / erasing laser beam, so that the intensity is not insufficient.

The laser beam 10b and the laser beam 11b combined by the prism 5 as described above are then transmitted through the objective lens 6 and focused on the optical disk medium 7 as spots 8 and 9, respectively. When the optical disc medium 7 rotates in the direction of the arrow X in the figure, if the spot 9 is used for recording / erasing and the spot 8 is used for reproduction, the R
AW check can be realized.

Next, the design of the optical system in the case where two beams are combined by total reflection and refraction on the slope A of the prism 5 will be described with reference to FIG. When the refractive index of air is n ₀ = 1.0 and the refractive index of the prism is n ₁ = 1.4, the incident angle α of the parallel beam 20a of the recording / erasing laser beam on the prism slope A is α = 81.8. If set to °, n ₀ · sin α = n
_From the relationship of ₁ · sin β, β = 45 °.

On the other hand, in order to totally reflect the laser beam on the prism slope A, the incident angle must be larger than the critical angle θ. The critical angle θ is n ₀ · sin 90 ° = n
_{From 1} · sin θ, θ = 45.58 °. Therefore, for example, if the incident angle γ of the reproducing laser beam parallel light flux 11a on the prism slope A is set to γ = 45.7 °, the light flux 11a incident on the prism slope A is γ> θ and is totally reflected.

The angle δ between the beam 10b emitted from the prism 5 after being totally reflected on the slope A and the beam 11b emitted from the prism 5 after refraction / transmission is n ₁ · sin
From (γ−θ) = n ₀ · sin δ, δ = 1 °. Here, if the focal length f ₀ of the objective lens 6 is f ₀ = 3.9 mm, then 68 μm can be obtained as the distance between the spots 8 and 9 on the optical disk medium 7.

As described above, the present embodiment combines the two laser beams without using the wavelength selective mirror.
Therefore, it is possible to use the semiconductor laser 1 and the semiconductor laser 2 having the same wavelength.

In the above embodiment, the spot 8
The description of the signal detection optical system and the detector of the reflected beam of the spot 9 and the spot 9 on the optical disk medium 7 is omitted, but the conventional focus error and track error signal detection methods, the magneto-optical signal detector, etc. are used for these. it can.

[0020]

As described above, according to the present invention, since two laser beams are combined by utilizing the critical angle of the prism, it is not necessary to use a wavelength selection mirror and a semiconductor laser of the same wavelength can be used. There is an effect that it is possible to configure an optical head of an optical system that has good combining performance and is inexpensive.

[Brief description of drawings]

FIG. 1 is a schematic optical path diagram showing a configuration of a two-beam optical head according to an embodiment of the present invention.

FIG. 2 is a schematic optical path diagram for explaining two-beam combining by the prism 5 in the embodiment of FIG.

FIG. 3 is a schematic optical path diagram showing a configuration of a conventional two-beam optical head.

[Explanation of symbols]

 1, 2, 20, 21: Semiconductor laser 3, 4, 22, 23: Collimating lens 5: Prism 6, 27: Objective lens 7, 30: Optical disk medium 24, 25: Prism 26: Wavelength selection mirror

Claims (3)

[Claims] 1. A first laser light source, a second laser light source, a combining means for combining the first light beam and the second light beam emitted from each laser light source, and the combining means. In a two-beam optical head having an objective lens for forming an image of the combined first and second light beams on a disk medium as a first spot and a second spot, respectively, the combining unit includes: A two-beam optical head, which is a prism having a slanted surface for totally reflecting the light beam and refracting / transmitting the second light beam. 2. The two-beam according to claim 1, wherein the second light beam refracted and transmitted by the prism is used for recording and erasing information and has a beam shaping function. Optical head. 3. The two-beam optical head according to claim 1, wherein the first light beam and the second light beam have the same wavelength.