JPH05210859A - Optical reproducing device - Google Patents

Abstract

PURPOSE:To efficiently obtain a regenrative signal and a track deviation signal by using a second harmonic wave beam as the regenrative signal and a basic wave beam for a tracking servo in an SHG element. CONSTITUTION:The basic wave beam 2 and the second harmonic wave beam 3 of the SHG element are converged together on a recording disk 4 and a passing pit 5. The depth (d) of the pit is constituted so as to satisfy d=lambda1/8n regarding the wavelength of the basic wave as lambda1 and the refractive index of the disk 4 as (n). The depth (d) satisfies d=lambda2/4n for the wavelength of the second harmonic wave lambda2=lambda1/2 necessarily. Then, when the second harmonic wave beam is used as the regenerative signal and the basic wave beam is used for detecting the track deviation of a push-pull, the signals are obtained with optimum conditions in both cases. The track deviation is detected so that the reflected beam of the disk 4 is separated by wavelength classification lay a dichroic mirror 6 and the basic wave beam 2 is reflected and detected by the sensor 10 of a push-pull. Further, the second harmonic wave beam 3 transmits through the mirror 6 and is made incident on a sensor 13 for the regenrative signal and information is read.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing apparatus for reproducing information recorded on an optical recording medium with laser light.

[0002]

2. Description of the Related Art By utilizing a non-linear optical element,
In recent years, much research has been conducted on the generation of second-order harmonic laser light having a frequency twice that of the laser light incident on the device. Such a non-linear optical element is
(Second Harmonic GENERATE
r) It is called an element. Recently, the SHG element has been downsized, and an element combined with a semiconductor laser has been developed. If this is used as a light source for an optical disk reproduction pickup, the light spot diameter narrowed by the lens is proportional to the wavelength of the laser, so a minute light spot can be obtained by the second harmonic, and high resolution can be achieved. You can

[0003]

When reading the information recorded on the optical disk, the disk is rotated and the recording surface of the disk is scanned by the light spot, but the light spot always scans the track correctly. It is necessary to perform servo such as focus servo and tracking servo. The three-beam method and the push-pull method are often used for optical discs as the tracking deviation detection method for tracking servo. The former is a method in which the beam is divided into three parts using a diffraction grating and the track deviation is detected by using the intensity change of the diffracted light. While the servo stability is high, the optical system is complicated and adjustment is difficult. difficult. Also, light 3
In order to divide the light into two, the light intensity is required to sufficiently obtain the 0th-order light used for reproduction.

The latter is a method of detecting a track deviation by using a two-division sensor by a change in intensity distribution of reflected light, and has an advantage that the optical system is extremely simple. However, the size of the tracking signal obtained by the latter depends on the depth of the pit recorded as information on the disc, and the tracking signal is maximized when the pit depth is the laser wavelength ( It is widely known that it is 1/8 of λ). On the other hand, the reproduction signal becomes maximum when the pit depth is 1/4 of the laser wavelength, but the push-pull tracking signal becomes minimum at this time. Therefore, when this method is used, it is generally on the disc. By setting the depth of the pit of about λ / 6 and sacrificing the signal amount of both,
Each signal is configured to be obtained. Therefore,
The precision at the time of manufacturing the disk is required.

[0005]

Generally, when a laser beam is incident on an SHG element, both fundamental wave light (the same light as the incident light) and second harmonic light are obtained as emitted light. In the present invention, both the fundamental wave light and the second harmonic light of the light emitted from the SHG element are applied to the disc, light having a short wavelength (high frequency) is used as reproduction light, and wavelength is used as track deviation detection light. The tracking servo is performed by the push-pull method using light with a long wavelength (low frequency).
Further, the depth of the pit of the disc which is reproduced by using this reproducing apparatus is set to 1/4 of the wavelength of the reproducing light.

[0006]

According to the present invention, it is possible to simultaneously obtain the maximum value of the push-pull tracking signal and the maximum value of the reproduction signal without sacrificing the reproduction signal in order to obtain the signal for tracking servo. ..

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below with reference to FIGS. FIG. 1 is a schematic configuration diagram in which the fundamental wave light and the second harmonic light are condensed on the disk by the same lens.
Both the fundamental wave light 2 and the second harmonic light 3 are condensed by the objective lens 1 through the recording disk 4 into the pit 5. The pit depth d is configured to satisfy d = λ1 / 8n, where λ1 is the wavelength of the fundamental wave and n is the refractive index of the recording disk 4. The depth d of this pit is equal to the second harmonic (wavelength λ
For 2 = λ1 / 2), d = λ2 / 4n is inevitably satisfied. Therefore, if the second harmonic light is used for signal reproduction and the fundamental light is used for push-pull track deviation detection, it becomes possible to obtain signals under optimum conditions for both.

The tracking deviation is detected by separating the reflected light from the disk 4 into wavelengths by using the first dichroic mirror 6, etc., as is clear from the optical system of the optical reproducing apparatus shown in FIG. Mirror 1, λ1
It is possible to consider a method in which the light is incident on the track shift detection push-pull sensor 10 via the / 4 plate 8 and the deflection beam splitter 9 to detect the same. The second harmonic light 3 is the first
The light is transmitted through the dichroic mirror 6, passes through the λ2 / 4 plate 11 and the deflection beam splitter 12, and enters the reproduction signal sensor 13 to read information. In the figure, 14 is a semiconductor laser,
Reference numeral 15 is an SHG element, 16 is a second dichroic mirror, 17 is a mirror, and 18 is a lens.

In the embodiment of the present invention, the fundamental wave light and the second harmonic light are condensed on the disk surface by the same objective lens, but the optical path to the objective lens is not necessarily the same for each light. Not what you need.

[0010]

According to the present invention, the second harmonic light and the fundamental light using the SHG element using one light source,
This makes it possible to efficiently obtain the reproduction signal and the track shift signal. Further, since a minute spot can be obtained by using the second harmonic light for signal reproduction, it is also characterized in that it can be used for reproduction of a high density optical disc.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an optical reproducing apparatus of the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of an optical system of the optical reproducing apparatus of the present invention.

[Explanation of symbols]

 1 Objective Lens 2 Fundamental Wave Light 3 Second Harmonic Light 4 Recording Disc 5 Pit 6 First Dichroic Mirror 10 Track Deviation Detection Sensor 15 SHG Element

Claims (1)

[Claims] 1. In an optical reproducing device for reproducing an optical recording medium, two kinds of laser beams with different frequencies simultaneously emitted from one light source are simultaneously irradiated onto the recording medium and recorded on the recording medium. When reproducing information, an optical reproducing device characterized in that light having a high frequency is used for reproducing information and light having a low frequency is used for tracking servo.