JPS60179949A - Optical disk reproducer - Google Patents

Abstract

PURPOSE:To reproduce an optical disk which is recorded with high density by applying laser light to a nonlinear optical crystal matter from a semiconductor laser to produce an optical higher harmonic wave containing a 2omega component and then reading the pit information out of the optical disk with the light containing the 2omega component. CONSTITUTION:The type and the direction are selected for a crystal which can have 90 deg. phase matching with a frequency omega. Thus the light of wavelength omega is converted into the light of double frequency, i.e., the 2nd higher harmonic wave. The light of 2omega condensed on an optical lens 10 passes through again an objective lens 11 and 1/4lambda plate 10 to be reflected by 90 deg. by the 2nd polarized beam splitter 9 with modulation and dispersion done by the pit information and is made incident on a photodetecting element 13 via a BPF12 which transmits only the light of 2omega. The element 13 uses a PIN diode or an avalanche diode and produces an RF signal corresponding to the bit information read out by the light of 2omega. Thus it is possible to reproduce an optical disk which is recorded with high density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an original disc reproducing device equipped with an optical system that allows bit information of a commercial density to be read out.

[Background technology and its problems]

The reading limit of concave recorded information (bit information) recorded on the original disc is generally two-layer wave fe = 2NA
/λ.

Here, NA is the aperture ratio of the lens, and λ is the original wavelength of the original disk VC irradiation (860 nm with a semiconductor laser).
) is shown.

Therefore, if the numerical aperture NA of the lens is increased, the spatial frequency fe at which readout can be performed will be high (which will exceed it in response to high-density recording, but the influence of the skew of the original Since the influence of uneven thickness of the disk becomes noticeable, NA-i-0.5 is the limit in current mechanical technology.

Moreover, the wavelength λ of the laser beam is argon, He-Cd
[Equivalent σ] Gas lasers can obtain wavelengths of 400 nm to 500 nm, but gas lasers require large equipment, so
It cannot be said to be suitable as a light source for general consumer equipment.

Therefore, at present, in the original disk playback device using a semiconductor laser as the light source, 1e=2 xo, slo,
7 B==1.3 x 10' 1300 lines/m
A spatial frequency of m, that is, a bit length of about 0.6 μm or less cannot be read, and the recording density is restricted.

[Purpose of the invention]

This invention was made in view of the actual situation.
By generating original harmonics using a nonlinear optical crystal, the original disc reproduction ferl! , is provided.

[Summary of the invention]

The present invention provides an original disk reproducing device that uses a semiconductor laser as a light emitting source and reads information recorded on the original disk, by making a conductor laser beam enter a nonlinear optical crystal body, so that the wavelength in the direction of movement is 1/2. The second-order original harmonic wave is outputted, and the bit information of the original disk is read using the second-order original harmonic wave.

Therefore, the spatial frequency that indicates the reading limit is almost doubled, making it possible to read pinpoint information that is considered to be of higher density.

〔Example〕

FIG. 181 is a schematic diagram of the original pickup part in the original disc playback device of the present invention.

In this figure, 1 is a semiconductor laser that outputs a coherent beam, 2 is a collimator for making a parallel light beam, and 3 is a beam shaping prism for correcting the anisotropy of the semiconductor laser 1.

A uniform laser source output from the beam shaping prism 3 is focused by a compling lens 4 and is incident on a nonlinear optical crystal S.

As the nonlinear optical crystal 5, one is selected and used that has a crystal type and orientation that achieves a 90° phase matching with the frequency ω and the 90° phase matching with respect to the wavelength (860 nm) K of the semiconductor laser 1, as will be described later. From KotoK (e.g. K Nb
O, ), and the light having a wavelength of ω is gradually converted into an element with twice the frequency, that is, a second harmonic, while propagating in the crystal.

The sources of ω (fundamental wave) and 2ω (11 illv 4 waves) outputted from this nonlinear optical crystal 5 are made into parallel rays through a coupling Lemmelo, and then passed through a long wavelength cut filter 1 to a first beam splitter 8 (fundamental wave). wave ω) and a second polarizing beam splitter 9 (for harmonic wave 2ω) are incident on the VC, and are further irradiated onto the original disk through a 1/4 λ plate 10° objective lens 11.

Note that the aberration of the objective lens 11 needs to be removed for 2ω light, but it is preferable to design it so that it is removed under both 2ω and ω frequencies.

The 2ω element focused on the original disk D is modulated and scattered by the bit information, and is returned to the objective lens 11, 1/4
90 through the λ plate 10 and the second polarized beam splinter 8
The light enters the light receiving element 13 & through a bandpass interference filter 12 that allows only the reflected elements n and 2ω to pass through.

A normal PIN diode or avalanche diode is used as the receiving ftJ element 13, and an RF multiplied signal corresponding to readout rty:bit information is generated using 2ω light.

On the other hand, the source of ω (fundamental wave) is filtered by the long wavelength cut filter 1, and then sent to the first beam splitter 8 (which passes through almost completely for 2ω) and the second polarized beam. The original disk is focused through the splitter 9.1/4 λ plate 10° objective lens 11, but this irradiation spot is
As will be described later, the light is scattered and modulated by the preglobe of the original disk O on which bit information is formed, travels back along the original optical path, is changed in direction by 90 degrees by the first beam splinter 8, and is focused by the convex lens 14. Light receiving element 1 for saj servo
Enter 5.

As shown in FIG. 2, the servo light-receiving element 15 is formed by K, ttk, four-part receiver yt consisting of concentric circles divided in the longitudinal direction of the trunk, and surfaces A, B, C, and DK.
By the well-known “push-pull” method (A+D
Focus 1913 is detected from the calculation output of )-(B+C), and tracking error error signal is detected from the calculation output of (A+B)-(C+D). The detected f'I tile Eschera signal is passed through a servo circuit 16 to control the seven actuators 11 of the objective lens 11, and a focus servo and a tracking servo are added.

Here, ft, f isk DK is formed, the width of the bit is expressed as the spatial frequency (which is the original reading limit of ω (fundamental wave)) (
2NA/λ. ), the source of t or ω reflected by the first beam splitter 8 will be almost unaffected by the bit information (and tracking will be affected only by the pre-globe of the trunk). An error signal can be formed.

Therefore, the influence of bits does not affect the focus error signal, and even if the recorded information signal contains many KDC components and servo band components, it will not cause servo saturation or acoustic noise.

FIG. 3(m) shows the shape of the bit suitable for the original disk reproducing apparatus of the present invention and the dimensional relationship of the preglobe.

The bit width PW is 2ω light, that is, the wavelength λ(2ω)
Since 430 nm is irradiated, the VC can be reduced by 1/2 compared to the conventional one, to about 0.3 μm, which is 1/2 of the minimum bit length, so the recording density is 2
Double. Bit depth P and pregroup depth G
, are respectively λ in this method to form a tracking error signal in a push-pull manner. /8. λ. /12(λ0
- It is preferable to use the wavelength of the fundamental wave.

FIG. 3(b) shows an embodiment in which the preglobe is lifted up. In this case, it is appropriate to read out the focus.

Therefore, Pd2G,=λ. /8, which makes both the reading sensitivity (modulation degree) and the tracking detection sensitivity by the push-pull method optimal.

FIG. 4 is an explanatory diagram when extracting nine harmonics (2ω2) from the nonlinear optical crystal 5.
, ) are subjected to polling processing in the C-axis direction. Then, the light (λ=λ) from the semiconductor laser (1) is deflected in the b-axis direction and travels in the a-axis direction.

In this case, λ. =: 860 nm f: A room-temperature element is generated with respect to the original, and progresses in the a-axis direction.

This phenomenon is described in the publication rApp1. phya, 1et
The conversion efficiency of ω→2ω is as follows.

Here J d, □ is the nonlinear optical constant IPIII is the fundamental wave V
D) input power 1 wo is the spot size diameter due to the coupling lens, C is the speed of light in vacuum 1n+1. +n!
.

is the refractive index, l is the length of the crystal, and ε. is the vacuum dielectric constant.

When KNbO is used as the nonlinear optical crystal 5, d = 18.4 x 10-''m/V, so
Wo is 40ttm, l is 5.74 mm r P 6
1 is 196 mW, 292 μW is obtained as the original 7i7b harmonic output P2°.

This original harmonic output P! w (292 μW), which performs all of the information readout, focus error signal, and tracking error signal detection, is insufficient in power considering the loss of optical components in the middle, but as shown in Figure 1, the power of 2ω is insufficient. If only the pit information is read out from the source and an optical system is formed, a sufficient output level of RF (No. 1 can be obtained), as shown in Figure 3 (a) and (b).
It is possible to correspond to high-density recording using bits as shown in K.

FIG. 5 is a Glock diagram of an optical system showing another embodiment of the invention, in which the same functions as in FIG. 1 are designated by the same symbols. In this figure, 10a is a diffraction grating for 2ω light, and the 2ω source is the main spot and 2ω.
Three sub-spots are formed so as to irradiate the original disk D surface.

As is well known, the three reflected spots of n and 2ω are detected by the three light receiving elements 1 by the convex lens 12a.
3a, 13b, and 13cK images are formed, and the tracking error signal is detected by the 3-spot method, and the main spot (
An RF multiplied signal corresponding to the pit information is output from the light receiving element 13b).

Therefore, in the case of this embodiment, FIG. 3(a).

(b) It is necessary to provide a pre-globe as shown in VC. Also, in this embodiment, the focus error signal can be detected using the astigmatism method using the cylindrical lens 14a, the 4-split receiver shown in FIG. 6, and the element 15aVC. This shows the case where this is done.

The light that detects this focus error signal is the source of the fundamental wave (ω), as in the embodiment shown in Fig. 1, and the influence of the bit does not leak in, as in the embodiment shown in Fig. 1. It is.

The t'lyc focus error signal outputted from the four-divided receiving element 15a is inputted from the servo circuit 16a to the actuator 17a of the objective lens 11, where it is subjected to a f8 servo. Note that 17b is also an actuator.

〔Effect of the invention〕

As explained above, the original disk reproducing device of the present invention generates original harmonics having a 2ω component in addition to the laser source nonlinear crystal outputted from a semiconductor laser, and generates original harmonics with a 2ω component. Read out the focus information of 5KL4
．． : Therefore, the spatial frequency to be read out is higher than that of the conventional method, and there is an advantage that the original disk with high density recording can be played back.

[Brief explanation of the drawing]

Figure In1 is a schematic diagram of an optical system showing an embodiment of this invention,
Figure 2 is a diagram showing the dividing plane of the light receiving element, Figure 3 (a), (
b) is a perspective view of a briglobe and a pit, Fig. 4 is an explanatory diagram of a nonlinear optical crystal, Fig. 5 is a schematic diagram of an optical system showing another embodiment of the present invention, and Fig. 6 is a four-part receiving element. The child division plane is jIA. In the figure, 1 is a semiconductor laser, 3 is a beam shaping prism, 4
．． 6 is a campling lens, 5 is a nonlinear optical crystal, 8
is the first beam splitter, 9 is 2. A second polarizing beam splitter, 11, indicates an objective lens 8. 1st diagram 4th diagram w

Claims (1)

[Claims] In an original disc playback device that uses a semiconductor laser as a light emitting source to read information recorded on the original disc, the light output from the light emitting source is incident on a nonlinear optical crystal, and the light jt+! is output from the nonlinear optical crystal. 'Fr harmonics to read the bit information recorded on the original disk 41! An original disc playback device characterized by the following features: