JPH03198225A - Optical reproducing device - Google Patents

Abstract

PURPOSE:To set the wavelength of playback beam light corresponding to recording density by providing a recording density detecting means which decides the recording density of an optical recording medium by detecting the track pitch. CONSTITUTION:When a disk D is irradiated with laser light C1 at right angles, the laser light is diffracted by a bit array formed on the disk D to generated diffracted light which is intensified in a direction determined by the track pitch. The direction is represented by a specific expression for the incidence direction and, for example, when a sensor 2 is at a distance of 50 mm from the disk D, the position where the diffracted light is made incident is 5 - 6 mm difference between 1.6 mum pitch and 1.4 mum pitch. For the purpose, the sensor 2 is constituted by arraying a position sensors or plural sensors to obtain an output corresponding to the track pitch of the disk D from the sensor 2. This output is applied to a pitch detecting circuit 3 to decide the track pitch according to the specific expression, thereby selecting the wavelength of the playback beam light corresponding to the recording density of the disk.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application Does the present invention have different recording densities? The present invention relates to an optical playback device capable of playing back several types of optical recording media.

(b) Prior Art Video discs and compact discs that reproduce video and audio information using laser light are well known. For video discs on which NTSC television signals are recorded, the recording linear velocity is 10.1 to 11.4 (m/s
e c ), and its track pitch is set to 1.4 to 2.0 (μm) according to the standard.

On the other hand, as one of the video discs, high-definition images are stored in TCI.
There are high-quality video discs in which a signal obtained by FM modulating a MUSE signal obtained by band compression using a multiple sub-Nyquist encoding method is recorded. This M IJ S E signal has a band of approximately 16 (MHz), so if you want to reproduce it using the same reproduction system as before, it is necessary to set the recording linear velocity to a large value. will be shortened. Therefore, the recording time can be lengthened by increasing the recording density by reducing the laser beam irradiation spot during recording. In this case, the wavelength of the laser light used will naturally be a short wavelength.

(C) Problem 4 to be Solved by the Invention If the wavelength of the laser beam is shortened for the purpose of reproducing a high-density recording disk for the reason stated above, the reproduction efficiency of a normal recording-density disk cannot be obtained sufficiently.

In other words, when information is recorded on a disk by forming four parts that are called pits, even if the large pits are irradiated with a short wavelength laser beam, no diffraction will occur. I can't play 7 minutes. Therefore, the present invention attempts to distinguish between differences in recording density.

(d) Means for Solving the Problems In the present invention, for an optical playback device capable of playing back multiple types of optical recording media with different recording densities, the recording density of the optical recording medium is detected by the track pitch. The configuration is such that a recording density detection means is provided for determining the recording density.

Further, a beam selection means is provided for selecting the wavelength of the reproduction light beam based on the detection output of the recording density detection means.

(E) Effect According to the above configuration, the recording density of the optical recording medium can be determined by detecting the track pitch, and reproduction can be performed according to the recording density of the optical recording medium. For example, by selecting the wavelength of the reproduction light beam, it is possible to efficiently reproduce data using a beam having an optimum wavelength according to the recording density.

(f) In the optical reproducing device of the embodiment shown in the embodiment diagram, F\l
-Ml; 5E4X at a recording linear velocity of 18 cm (m/
5ec), a standard disc recorded with a trunk pitch of 1.6 (#m), and a recording linear velocity of 15 cm (m/5ec).
), it is possible to reproduce high-density discs recorded at a track pitch of 1.4 (am), and the recording signal frequency is the same for both. Further, in this embodiment, it is assumed that a standard disk is reproduced by a first reproduction beam having a wavelength of 7,800 people, and a high-density recording disk is reproduced by a second reproduction beam having a wavelength of 6,700 people.

With the disk (D) attached, the laser C(1) is irradiated perpendicularly to the disk D. The laser beam is diffracted by the pit rows 5 formed on the disk (D), producing diffracted beams that intensify each other in a direction determined by the track pitch. The direction is θ=jan-'(λ2'F) with respect to the direction of incidence. Here, λ is the wavelength of the laser C (1), and p is the track pitch of the disk (D). For example, λ=7
800 people, p = 1.611m, θ” = 29
．． 2deg, and when p = 1.4μmm, θ'
xt becomes 33.9deg. For example, if the sensor (2) is at a distance of 50 mm from the disk (D), the position where the diffracted light enters will differ by 5 to 6 mm when the pitch is 1.6 μm and 1.4 μm. . Therefore, if this sensor (2) is a position sensor or a configuration in which a plurality of sensors are arranged in a line, an output corresponding to the track pinch of the disk (D) can be obtained from the sensor (2).

By applying this output to the pitch detection circuit (3), the track pitch can be determined based on the above equation. By using the output of the track pitch detection circuit (3), it is possible to select the wavelength of the reproduction beam according to the recording density of the disc.

The other configuration of the optical reproducing device shown in the figure is the same as that of a normal device. The pickup (4) has an objective lens and its actuator. Laser A (5) and laser B (6) having different wavelengths are selectively input to the pink-up (4). That is, the reproduction beam selection means (7) is driven by the output of the Sochi detection circuit (3), and the reproduction beam selection means (7) is
) is selected and inputted into the pickup (4).

The signal reproduced by the pickup (4) is sent to the reproduction circuit (8).
), one is input to the demodulation circuit (9) as an information signal, and the other is input to the disc motor (11).
) is input to the motor servo circuit (9) as a control signal. In the embodiment described above, the wavelength of the reproducing beam was selected, but when reproducing a high-density disc, a short-wavelength laser was used, and when reproducing a normal-density disc, a short-wavelength laser beam was used. Rather than irradiating the pit in a sufficiently focused state, the pit is irradiated in a slightly blurred state, that is, slightly out of focus, by increasing the beam diameter that corresponds to the focus. , - two short wavelength lasers can be used to reproduce both discs. In this case, either normal 7 orcus control is performed using the output of the track pitch detection circuit (3), or 7 orcus control is performed in a slightly blurred state (off 771 is added to the 7 orcus control signal). You will have to choose whether or not to perform orcus control.

(G) Effects of the Invention According to the present invention described above, the recording density of the disc to be reproduced can be automatically determined, and the reproduction state can be set according to the recording density.For example, the reproduction beam can be set according to the recording density. You can set the wavelength of light.

[Brief explanation of drawings]

The drawings are diagrams showing an embodiment of an optical reproducing device according to the present invention. 1.5.6 is a laser, 2 is a sensor, 3 is a track pitch detection means (recording density detection means), and 7 is a reproduction beam selection means.

Claims (2)

[Claims] (1) An optical playback device capable of playing back multiple types of optical recording media with different recording densities, including a recording density detection means for determining the recording density of the optical recording medium by detecting the track pitch. Characteristic optical playback device. (2) An optical playback device capable of playing back multiple types of optical recording media with different recording densities, comprising a recording density detection means for determining the recording density of the optical recording medium by detecting a track pitch; An optical reproducing device comprising a beam selection means for selecting a wavelength of a reproducing light beam based on the detection output of the density detection means.