SU1422243A1 - Optical playback device - Google Patents

Abstract

Invention m. used in laser video and audio players and allows to increase the accuracy of information playback nyTeivi reduced light loss. The laser radiation 1 passes through an electro-optical modulator 2, made in the form of a phase modulator whose main planes coincide with the main planes of the polarization beam splitter 5. The change in the optical path length of the radiation in the electro-optical crystal of the modulator 2 is due to the linearly varying voltage applied to Oscillator 16. The interference interference is eliminated in the device by the notch filter 15 without distorting the reproducibility of my information. The description shows the relation from which the pulse frequency is determined. 2 Il.

Description

4 Yu Yu

to

four

WITH

The invention relates to the field of information storage, in particular, to devices for reproducing information from optical disk media, and can be used in laser video and audio players.

The aim of the invention is to improve the accuracy of information reproduction by reducing the light loss.

FIG. 1 shows a diagram of the device; in fig. 2 - diagrams, according to the principle of operation of the device.

The device (Fig. 1) contains a laser 1, an electro-optical modulator 2, a mirror 3, a corjiacyroiiiyio lens 4, a polarization beam splitter 5, a quarter-wave plate b, a positioning unit consisting of a mirror 7 and a drive 8, a lens 9 with a displacement drive 10, information carrier 11, photodetector unit 12, determination unit 13, focusing unit, information track tracking error unit 14, information notch filter 15 and linearly varying voltage generator 16.

The device works as follows.

Of the laser learning 1 (Fig. 1) passes through an electro-optical modulator 2, is reflected from a scanner 1) mirror 3, then a matching lens 4 passes, a polarization beam splitter 5, a quarter-wave plate 6, is reflected from a mirror 7 of a positioning unit, a lens 9 passes and focuses on the information carrier 11. The radiation reflected from the information carrier 11 passes for the second time the lens 9, is reflected from the mirror 7, passes the quarter-wave plate 6 and reflects the polarization beam splitter 5 to the photo-prism unit 12. Some of the radiation that passes through the polarization beam splitter 6 to the laser 1 is reflected from the latter and interferes with the initial laser radiation, which causes interference noise. The optical length of the electro-optic crystal of the modulator 2 varies from sawtooth to zero from the half-wheel by means of the generator 16 linearly varying voltage. The signal from the photonic receiver unit 12 passes through a notch (blocking) filter 15, which clears it of interference noise, and then goes to the information track tracking error detection unit 14 and the focus error detection unit 13. From block 4, the tracking signal is detected at the actuator 8 of the tracking mirror 7, eliminating the tracking error. From the focus error detection unit 13, the signal is fed to the drive 10 of the lens 9 to eliminate the focus error.

The interference noise is suppressed as follows. A linearly varying voltage is applied to the electro-optical crystal of the modulator 2 from generator 16. The range of variation of this voltage is from zero to half wave. According to the change in the applied voltage, the optical length of the radiation in the electro-optical crystal changes. The main planes of the electro-optical crystal coincide with the main planes of the polarization light.

The customer, which is necessary so that the magnitude of the polarization component of the laser radiation, which is parallel to the transmission plane of the polarization beam splitter, does not change when a voltage is applied.

2 Since the voltage to the crystal is brought from zero to half-wave, the radiation phase during its double passage varies from 0 to 2 liters. The frequency of linearly varying oscillations v is chosen so that the frequency v-f, where f is the maximum frequency of the interference noise, is higher than the frequency of the tracking error detection unit and the focus error detection unit, i.e. more than 30 kHz. The frequency v must be lower than the minimum frequency of the reproduced information. For video discs, the lower frequency of reproducible information is on the order of 1.5 MHz. Since the maximum frequency of the interference noise is about 40 kHz, the frequency v is chosen from 70 kHz

0 to 1.45 MHz.

Changes in the phase of the beam φ (1) with a frequency V and amplitude 2d, obtained as a result of the modulation of the optical length of an electro-optical crystal. The modulator is described by the relation

5f (1) 2ll-1-2lp,

where t is time;

 (PCh-1) T, p Oh, 1.2 ...;

T - period sawtooth oscillations. The radiation phase F (1) due to the oscillation 0 position of the information carrier 1 will change as follows:

f (1) 4 Dsoz (2l-ho1),

(2)

45

where D is the oscillation amplitude of the information carrier (on the order of 0.5 mm); l is the radiation wavelength (X

 0.63 microns);

co - oscillation frequency (for a video disc 50W - 25 Hz).

Thus, interference noise i will be recorded:

4l

i ioeos (-5: L-b Ф (1) + .cp (t)).

(3)

where io is the amplitude of the interference noise; L is the length of the optical path.

Substituting (I) and (2) into (3), we obtain i ioCOs (L + j4cos (2.T; tco) + 2nvt-2lp)

 ioCos ((2l; w) + 2nvi).

Therefore, the interference noise has a frequency varying from v-f to v-j-f,

one where f -j. For example, for v 150 kHz and

f 40 kHz, we have a PO-190 kHz interference noise band. Suppressed this frequency band by means of a rejector filter, we obtain a signal without interference noise.

The frequency transfer of the interference noise is illustrated graphically (Fig. 2). FIG. 2a shows the change in the radiation phase 0 with a fixed information carrier as a function of time t. Here d - broken line showing this change:

in 2.4vt - 2lp,

where V is the oscillation frequency of the linearly varying voltage; PT t (n + 1) T

T is the period of oscillation;

p - O, 1, 2, ...

Since the radiation phase is determined with an accuracy of 2 l, a broken line g is equivalent to the straight line, the equation of which

0 2nvt.

The phase change corresponds to the interference noise i (Fig. 26, curve g), the equation of which

i iocos (---),

where io is the amplitude of the interference schum;

FIG. 2c represents an equivalent change in the radiation phase introduced by an electro-optical crystal. The frequency of the change in the phase of the radiation introduced by the oscillations of the information carrier, f, is assumed to be constant. The change of the radiation phase at the expense of the information carrier corresponds to the right 3:

And - 9-t-f t

/ vl / 1L.

The total change in the phase of radiation (direct and) in this case is written down by the equation

6 2.4 (v-ff) t.

FIG. 2d shows interference noise, corresponding as a change in the radiation phase in the absence of carrier oscillations.

information (curve g), and the corresponding change in the phase of radiation, when the information carrier oscillates (curve k, T is the period of the curve W, T is the period of the curve k, and T D-; T is the -j-t -, - Thus , the interference noise in the device has a frequency v + Since the frequency f varies from O to f and at the same time

If Q is summed and subtracted from the frequency V, the interference noise in the device lies in the frequency range from v-f to v-ff and is eliminated by the notch filter 15 without distortion of the reproduced information.

Claims (1)

Invention Formula An optical playback device containing sequentially mounted 2) a laser, an electro-optical modulator with a control unit, a mirror, a matching lens, a polarization beam splitter, a quarter-wave plate, a drive positioning unit and a displacement drive lens, and a photodetector unit, 25 whose input is optically connected with a polarization beamsplitter.m, the focus error detection unit, the output of which is connected to the input of the lens drive, and the information track tracking error detection unit, the output of which is connected to the actuator input of the positioning unit, characterized in that in order to increase the accuracy of information reproduction by reducing light losses, a notch filter was inserted into it, the electro-optical modulator was designed as  the phase modulator and its main planes coincide with the main planes of the polarization beam splitter, and the modulator control unit is designed as a generator of linearly varying voltage 40 with a pulse repetition rate F determined from the ratio fc.i -4- f F fBoc - f, where f is the maximum frequency of the interference shchuma; feoc is the frequency of reproduced information; The fcji-working frequency of the error tracking unit for tracking the info track. 50, the output of the photodetector unit is connected with the inputs of the focus error detection unit and the error tracking unit for the information track through a notch filter. 9ig.2