RU1835556C - Determination method of phase shift value in optical information carrier and an appliance for its provision - Google Patents

Abstract

Usage: in the production of optical reflective media. SUMMARY OF THE INVENTION: The invention allows to reduce the threshold of sensitivity and increase the accuracy of measurements. This is achieved by the fact that when determining the main planes of the information carrier, the transmission coefficient of the first photodetector channel is made equal to zero at the maximum transmittance of the probe beam, and when measuring the phase shift of the information carrier, the transmission coefficient of the probe beam is changed with a simultaneous reverse change in the transmission coefficient of the first photodetector, after which subtraction between the signals of the first and second photodetector channels is performed, and the magnitude of the phase move in! determined by the magnitude of the gain of the first photodetector channel, at which the difference signal is zero. 2 s.p. f-ls, 1 ill.

Description

The invention relates to polarization. It can be used in the production of optical reflective storage media.

The purpose of the invention is to improve the accuracy of measurements.

The drawing shows a device for implementing the method.

The device consists of a first housing 1 with a first goniometric limb 2 and a second. bodies 6 with a second goniometric limb 7. Both bodies are rotatable around the axis of the beam. Moreover, the first housing 1 can rotate both in conjunction with the second housing 6, and independently. In the first building 1 in series

a laser 3 and a first polarizing beam splitter 4 are installed, as well as a first photodiode 5 optically coupled to the first polarizing beam splitter 4. Laser 3 is mounted so that the plane of polarization of its radiation coincides with the transmission plane of the first polarizing beam splitter 4. In the second housing 6 is equipped with a polarization beam splitter 8 and a second photodiode 9 optically coupled to it. After the second polarization beam splitter 8, a storage medium 10 is optically mounted on the beam axis. 5 of the first photodiode is connected to the direct input of the differential amplifier 11. inver00 SL 00

cl

SL

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the second input of this differential amplifier through the first output of the first switch 12 is connected to the second photodiode 9. In addition, the second photodiode 9 is electrically connected through the second output of the first switch 12 and the second output of the second switch 13 to the indicator zero 14.

The output of differential amplifier 11 is connected to the indicator zero 14 through the first output of the second switch 13. In this case, the second polarization beam splitter 8, the first polarization beam splitter 4, and the first photo diode 5 form the first photodetector, The second polarization beam splitter 8 and the second photo diode 9 form the second photodetector channel.

A method for measuring birefringence is implemented as follows. The probe laser beam passes through the first polarization beam splitter, the second polarization beam splitter and is reflected back from the information carrier. The reflected beam enters the second polarization beam splitter. Here, a part of the beam, with a polarization perpendicular to the transmission plane of the second polarizing beam splitter, is completely reflected by this beam splitter to the second photodiode. A part of the beam with parallel polarization passes through the second beam splitter and is reflected by the first beam splitter to the first photodiode. The signals from the first and second photodiodes are fed to the direct and inverse inputs of a differential amplifier. The differential signal from the differential amplifier is fed to the input of the zero indicator. In addition, a signal from the second photodiode can also be supplied to the input of the indicator zero.

It can be shown that the fluxes of the components of the reflected beam Φ1 and Φ2 that fall on the first and second photodiodes, respectively, are related to the flux of the initial laser radiation Φ0 by the following relations:

th (1 -sin2y sln22 (-i,)) COS29-slnJ0-r,. (1)

Фг sin2 - sin2 2 (# - Vo) cos2 in r Ф0.

where L is the magnitude of the phase shift of the information carrier with double passage of the beam,

Fo is the azimuth of the main plane of the information carrier.

the azimuth of the transmission plane of the second polarization beam splitter,

0-angle between the transmission planes of the first and second polarization beam splitters,

g is the reflection coefficient of the information carrier.

First, the orientation of the main plane of the information carrier is determined. To do this, a signal from the second photodiode is supplied to the indicator zero input, and the transmission planes of the first and second polarization beam splitters are set in parallel, i.e. at 0 °, in this

5

case we have:

Фг sin2 sin2 2 (V - Vb) g Фь.

By changing the azimuth t /, we reach Фг 0. In the obtained position, 1р р0.

To determine the magnitude of the phase shift, we set the azimuth of the plane

transmittance of the second beam splitter equal

f po + 45 °.

At the input of the indicator zero, we feed the difference signal from the photodetectors. Accordingly, the system of equations (1) is written:

 cos2f-cos2tfsin20-r-Ф0,

35

4 sin2 |

cos2 9 r Ф0

By changing the angle $ by turning the first beam splitter, we obtain the difference of the difference signal Фт-Ф2 0 to zero. The value of 40 phase shift is calculated by the formula:

45

D arctg

2tg |

1 + 4 $

ilm

.A 20.

Claims (2)

SUMMARY OF THE INVENTION T. A method for determining the phase shift of an optical information carrier, including the direction normal to the surface of the optical information carrier of linearly polarized light, and the light reflected from the surface of the optical information carrier with planes of polarization parallel and perpendicular to the plane of polarization of light directed to the surface of the optical information carrier in the first and second photodetector channels, respectively, determination of the main plane of the optical information carrier by minimizing the signal of the second photodetector channel when the plane of polarization of light is turned toward the surface of the optical information carrier, rotation of the plane of polarization of light directed toward the surface of the optical medium by 45 ° relative to the main plane of the optical information carrier, and determining the magnitude of the phase shift, such that. in order to increase the accuracy of measurements, after rotation of the plane of polarization of the light directed to the surface of the optical information carrier, the magnitude of the light flux directed to the first photodetector channel is changed at an angle of 45 ° relative to the main plane of the optical information carrier, at a constant value of the light flux, directed to the second photodetector channel, measure the value of the part of the light flux directed to the first photodetector channel from the light stream with the plane of polarization parallel to th plane of polarized light directed to the surface of the optical information carrier, wherein the signal values are equal to the first and second photo-reception channels. 2. A device for determining the phase shift of an optical medium information containing an optically coupled linearly polarized radiation source, a first and second beam splitter, the second beam splitter being polarized, and a first and second photo diode optically coupled to the first and second beam splitters, respectively, a differential amplifier, first and second photo diodes connected to the direct and inverse inputs of a differential amplifier, respectively, characterized in that. that the radiation source, the first beam splitter, the first photodiode are mounted on the first housing with the goniometer, the first beam splitter is polarized, and the transmission plane coincides with the plane of polarization of the radiation source, the second beam splitter and the second photodiode are installed in the second housing with the goniometer, the first and the second buildings can be rotated around a common axis parallel to the direction of radiation of the radiation source, both jointly and separately, an additional indicator zero, the second odiod connected to the differential amplifier via the first switch is further inputted, the second output of which is connected to the second output of the second switch, wherein the zero indicator is connected to the output of the differential amplifier via the second switch. her  s g / rzb 8 6. 2ZZ ZfezZZZZZz2JESXta3Sj . Y A / / / / / / / / / / / 10