SU1432600A1 - Apparatus for automatic focusing of radiation at data surface of optical disk - Google Patents

Abstract

The invention relates to a technique of recording and reproducing an information source using optical radiation and allows for improved accuracy and noise immunity of focusing. The scan signal generator 5 through modulator 9 modulates the radiation wavelength of the semiconductor laser 1, which is focused by the zone plate (or hologram lens) 2 onto the information surface of the optical disk, and also scans along the normal to this surface due to the chromatism of the zone plate 2 Band-pass filter 7 performs spectral selection of the scanning signal with a frequency in the range of 10 ... 100 kHz, which allows to suppress the arising interference. The error of the focusing is controlled by the drive 4. Mathematical formulas are given that determine the focal distance of the zone plate or hologram lens and the distance between the minimum-3 cross-section of the field distribution in the laser resonator and the zone plate-hologram or hologram lens ., 1 Il.

Description

jL (l, ± JLlLl, -Jtlls - JjLLiL, i ii ((). z ,,, tgiyi / Aj Tj,

2.4

Obviously, with typical parameters of devices for reproducing information from optical disks, for example, 24-L,

50

heat care. wavelengths 7.5 they need easily realizable deviation of length uTic A (for typical fields: conductive

50

Mepj received when reproducing sound information from CDs: tgU -0,2; tgU 0.5 (-0.4); Lr 0.7-8 microns, 0.5 microns, the expression (2) takes the form

 O oi / u-xj. (3) 55 Therefore, S to obtain a given scanning amplitude of a focused n nTNa Zm at a maximum

) .z ,,, tgiyi / Aj Tj,

24-L

(2)

thermal care. wavelines &. 7.5, they need a technically feasible deviation of the wavelength uTic A (for typical injection fields: conductor lasers,

. used in devices for reproducing information from optical disks, the gradient of thermal leaving / dT is 0.25 nm / K; therefore, at L Hm 7.5 nm, the temperature range is dT

 ± 30, K, which corresponds to the operating temperature range specified in

technical conditions for information reproduction devices).

The distance d between the minimum field distribution in the laser cavity and the zone plate is determined from the ratio

1t, | u ft + fi + / J2 And V 3 () and T2

where ju "-l j

 - radiation wavelength of a semiconductor laser at an average temperature of the operating range,

and ensures the almost complete absence of spherocrotic aberracin, and therefore, diffraction

A device for automatic focusing, radiation on the information surface of an optical disk, containing optically coupled semiconductor laser, focusing optical system and photodetector combined in an optical head, equipped with a drive for working out a focus error, as well as a generator of a scanning signal and a synchronous detector, with the first input which is connected to the output of the scan signal generator, and

The limited focusing of laser radiation, d, the pin of which wave can be displaced by -20 ° is associated with the drive's drive from the calculated wavelength of the focusing error, which is about 4%. For example, if a zone plate is designed for a wavelength of 780 nm, then the mouth25

The device will function normally when a laser is installed in it, the length of the VRLGV4 radiation of which lies in the interval 750-810 mn.

The use of modulation of the radiation wavelength in conjunction with large chromatism, on the assigned zone plate or a hologram lens, provides scanning of the position of the transfer of a focused beam. Thanks

thirty

that, in order to increase the accuracy and interference of focusing with an increase in the signal-to-noise ratio of the reproduced signal, and to simplify the design,

A band-pass filter and a laser radiation wavelength modulator are entered into it, a bandpass filter input is connected to a photodetector output, an output is connected to a second input of a synchronous detector, and the output of the scanning sirnal generator is connected to a semiconductor laser through a laser radiation wavelength modulator, focusing

The electriioi scan is performed by the RVZ-35 optic system made in the form

to raise the frequency of the scanner, by-zone plate or hologram

to improve the accuracy and noise immunity of the lens with a focal length f, optic focusing, to increase the ratio between the

cash / disturbance of the information signal and reduce the drive power working off focusing errors.

Claims (1)

Invention Formula A device for automatic focusing, radiation on the information surface of an optical disk, containing optically coupled semiconductor laser, focusing optical system and photodetector combined in an optical head, equipped with a drive for working out a focus error, as well as a generator of a scanning signal and a synchronous detector, with the first input which is connected to the output of the scan signal generator, and ° is connected with the drive of the processing of a focusing error, which is ° is connected with the drive of the processing of a focusing error, which is that, in order to increase the accuracy and interference of focusing with an increase in the signal-to-noise ratio of the reproduced signal, and to simplify the design, A band-pass filter and a laser radiation wavelength modulator are entered into it, a bandpass filter input is connected to a photodetector output, an output is connected to a second input of a synchronous detector, and the output of the scanning sirnal generator is connected to a semiconductor laser through a laser radiation wavelength modulator, focusing focal length lenses determined by the ratio 2i.2L4 aa-ao ) (fBptg uTA Cr 7 () (G- (f) 5 tg uTMl TT where is the working wavelength of the band plates, E- tgU / tgU; and, and the input and output apertures of the zone plate ltk - the maximum increment of the wavelength of the radiation of a semiconductor laser within the specified operating temperature range of the device; VNIIPI Order 5450/46 Circulation 590 Random polygons pr-tie, Uzhgorod, st. Project, 4 aa-ao G- (f 45 laser and zone plate or hologram lens - from the relation: d 1 (C and + / 3 + g f 2 N 3 (G-7) 2 where p A / f,  - radiation wavelength of a semiconductor laser at an average temperature of the operating range, and the signal generator scans the scanning frequency in the range of 10 to 100 kHz. Subscription