SU1509996A1 - Device for reproducing information - Google Patents

Abstract

The invention relates to instrumentation, in particular, to disk optical storage devices. To improve the quality and reliability of information reproduction, the device compensates for the difference in thickness of the substrate of information carrier 7. This is achieved by using a compensator of two optical wedges 11 and 12, a focusing lens 10 and a quarter-wave plate 9. Compensating for the difference in thickness of the substrate of information carrier 7 makes it possible to significantly reduce the spherical aberration and improve the quality of information reproduction. 1 p. F-ly, 3 ill.

Description

fug.1

The invention relates to instrumentation, in particular to disk optical storage devices with bitwise representation of information.

The purpose of the invention is to improve the quality and reliability of reproduction of information.

Fig. 1 schematically shows an information reproducing apparatus; Fig. 2 illustrates the equivalent optical design of the device and the path of the beams in it when the thickness of the substrate of the information carrier is increased in comparison with the nominal one; in FIG. 3 - the same, when an increase in the thickness of the substrate of the information carrier is compensated by a decrease in the thickness of the streamer

variable thickness plates

cherish us.

The device contains a semiconductor laser 1, a collimating optical system 2, a beam splitter 3, a polarization beam splitter 4, focusing the LENS 5, a floating element 6, a carrier 7 of information with a photosensitive layer q, a focus sensor 8, a quarter-wave plate 9, an additional focus lens 10, an optical the wedge 11, the optical wedge 12 coated on the outer surface (and the drive 13 of the transparent wedge 12.

The device works as follows.

The linearly polarized radiation of a semiconductor laser 1 (Fig. 1) is converted by an optical collimation system 2, for example, consisting of a micro-lens and a cylindrical beam expander into a parallel beam with a circular cross section that passes through the beam splitter 3, which is an amplitude beam divider falls on the polarisable beam splitter 4, and then on the quarter-wave plate 9, which transforms the linearly polarized radiation into it into linearly polarized radiation, and is focused by an additional the focusing lens 10 through a plane-parallel plate formed by optical wedges 11 and 12 on the reflective coating applied to the outer surface of the transparent wedge 12. The beam reflected from the reflective coating transforms the additional focusing

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lens 10 in a parallel beam, the polarization of which after passing through a quarter-wave plate 9 becomes linear and orthogonal to the polarization of the beam incident on the quarter-wave plate from the semiconductor laser 1. The beam is reflected by a polarization beam splitter 4 and hits the focus lens 5 which focuses the radiation through the transparent substrate of the information carrier 7 on the photosensitive layer. "

The distance between the upper surface of the information carrier and the focusing lens 5, which is connected to the floating element 6, is kept constant due to the airbag, which occurs either when the air is forced into the floating element from an overpressure source (not shown) or when moving information carrier due to the aerodynamic effect. The beam reflected from the photosensitive layer a is transformed by a focusing lens 5, reflected by a polarization beam splitter 4, passes through a quarter-wave plate 9, is focused by an additional focusing lens 10 through optical wedges 11 and 12 on the surface of the reflective coating cG. After reflection, the beam is converted by an additional focusing lens 10 and passes through a quarter-wave plate 9, at the output of which the beam polarization becomes linear and orthogonal polarization of the beam reflected from the carrier 7, therefore, the beam passes through the polarization beam splitter 4 and a part of it is reflected by the beam splitter 3 to a focusing sensor 8, which can be made, for example, in the form of successively placed prisms of a critical angle and a split photodetector (not shown).

If the thickness of the substrate portion of the information carrier 7, which is currently at the moment of time opposite to the focusing lens 5, corresponds to the nominal one, then the optical system is in a balanced state, i.e. the spherical aberration is zero, a parallel beam of rays falls on the focusing sensor 8 and the output signal of this sensor is zero. In this case, the drive 13 is de-energized and the optical wedge 12 occupies the initial position at which the best focusing of the radiation of the semiconductor laser 1 on the photosensitive layer a of the information carrier 7 is achieved.

If the thickness of the substrate portion of the information carrier, which is currently opposite the focusing lens 5, differs from the nominal one, for example, increased by L, (FIG. 2), the beam c incident on the additional focusing lens 10 is reflected from the reflective coating cG, located in focus about the focusing lens 10, and is converted into a parallel beam of rays d, the rays of which coincide with the rays of the beam -c, but directed in the opposite direction. The beam d is focused by the focusing lens 5 at the point o, which is separated from the photosensitive layer a (shown by the dotted line) at a distance L ,. The reflected beam e comes from an imaginary source o, which is located at a distance of the photosensitive layer, and from a point o, at a distance of 2 L,. The focusing lens 5 converts the beam e into a converging beam, which is focused by an additional focusing lens at a point distant from / on the reflective coating f. In accordance with the reduction rule, the distance is

..,, n, g,

a beam, a part of which is diverted by the beam splitter 3 to the focusing sensor 8. The focus sensor signal becomes non-zero and the actuator 13 moves the optical wedge 12 until the defocus signal is zero, i.e. until the beam becomes parallel. In this case, the imaginary radiation source about the beam d is separated from the new position of the reflecting coating cG (Fig. 3, dashed line) at a distance of L ,, the focusing lens 10 converts the reflected beam

5 d into a diverging beam of rays, which is focused by a focusing lens 5 at point o on the photosensitive layer, which occupies a new position that is separated from the initial one by L. Reflected from the photosensitive layer, the beam e is converted by the focusing lens 5 into a convergent beam, and the beams d and e coincide, but are directed to the opposite sides. The beam e is focused by an additional focusing lens 10 at the point o, which coincides with the point o. Reflected from the reflective coating ff beam f is emitted from the mnir. mobile radiation source, which is located at a distance e from the new position of the reflective coating and lies in the plane of the initial position of the reflective coating. The magnitude of the compensating displacement of the reflecting coating L is associated with a deviation from the thickness of the substrate of the information carrier 7, l, by the expression

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BUT

  2 n, F;

where n is the index

media substrates; n - refractive index

a flat-plate plate formed by optical wedges 11 and 12; FJ is the focal length of the focusing lens 5; F is the focal distance of the additional focusing lens 10.

Reflected from the reflective coating from the beam f originates from an imaginary source, which is located at a distance cG from the reflecting coating. An additional focusing lens 10 converts the beam f into converging

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Spherical aberration compensation occurs as follows. The length of the 3rd order spherical aberration —S ,, arising with an increase in the thickness of the substrate of the information carrier 7 by D, is determined by the expression

one

nt - 1

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5sf, one

The magnitude of the longitudinal spherical aberration of the 3rd order cTS, which is. This is made by a plane-parallel plate consisting of optical wedges 11 and 12, with a decrease in its thickness by 2 × taking into account the double passage of the beam through this plate, is equal to

cfS

. P2-1 Fj sfg -pa

sin u.

the longitudinal spherical c4 with respect to the source image is equal to

l

,

/ n, - 1 pT

one

Fl)

wg

Thus, with full compensation of spherical aberration, the focal lengths of the focusing lenses and the refractive indices of the carrier substrate 7 {The information and optical wedges 11 and 12 must be related by the relation

B - slll.

one

P

( one)

Similarly, the compensation of defocusing and spherical aberration occurs with a decrease in the thickness of the substrate of the information carrier and a corresponding increase in the thickness of the plane-parallel plate formed by optical wedges.

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Claims (1)

Invention Formula An information reproducing apparatus comprising a sequentially mounted semiconductor laser, a collimating optical system, a beam splitter and a polarization beam splitter, with one output of which is optically coupled to a focusing lens installed in the floating element, as well as a focus sensor optically coupled to the beam splitter, characterized by , in order to increase the quality and reliability of information reproduction, optically coupled with another output of the polarization beam splitter is introduced into it - and Consequently, a quarter-wave plate, an additional focusing lens and two optical wedges installed in the form of a plane-parallel plate with a reflective coating on the surface furthest from the additional focusing lens, as well as a linear displacement drive associated with an optical wedge containing a reflective coating, This input of the optical wedge movement drive is connected to the output of the focus sensor. 7 / / 2 / 2 Phie.