SU1697110A1 - Device for automatic focusing - Google Patents

Abstract

The invention relates to a technique for recording and reproducing information by optical means. To increase the reliability of information reproduction, part 5 of the splitter 3 is coated with a reflecting coating with a reflection coefficient R 0.99. This part of the splitter is optically coupled to the photodetector 7. The optical axes of the radiation source 1 and lens 6 are placed at a distance b determined from the relation b I, where I is the distance from the focal plane of lens 2 to the intersection point of the beam splitter 3 with the optical axis lens 6; / - Angular aperture of the lens 2. 2 Il.

Description

The invention relates to a technique for recording and reproducing information by optical means.

The aim of the invention is to increase -. the accuracy of the reproduction of information.

FIG. 1 shows a block diagram of the proposed device; figure 2 - the course of the beam of rays in the optical part of the circuit device.

The device (Fig. 1) contains a radiation source 1, a first lens 2, a beam splitter 3 with parts 4 and 5, of which part 4 has a translucent coating, and part 5 has a specular (R 0.99) lens 6 with a drive 7 moving , a unit for changing the position of the axis of the radiation pattern consisting of a second lens 8, a photodetector 9, a differential amplifier 10, a summing amplifier 11 and an analog divider 12. The device also includes a unit for defining the defocus amount of the lens, including a photodetector 13, a summing amplifier 14,

differential amplifier 15, analog divider 16. The outputs of analog dividers are connected to the inputs of differential amplifier 17. The output of source 18 of the reference voltage is connected to analog analog divider 20 via the summing amplifier 19, the output of which drives the drive 7 to move the lens 6 relative to the information carrier 21.

The device works as follows.

The radiation of the radiation source 1 passes the lens 2, is reflected from the part 4 with a translucent coating of the beam splitter 3 to the lens 8 of the repositioning block of the axis of the radiation pattern, and is focused on the sensitive elements of the two-element photodetector 9. The transmitted beam splitter part of the radiation is focused by the information carrier 21. Having reflected from the information carrier, the radiation again passes the lens 6 and, spreading (due to the displacement op (L

Os O 41

ABOUT

of the radiation source of the radiation source 1 relative to the optical axis of the lens 6) symmetrically with respect to the optical axis of the lens b, falls on part 5 of the beam splitter 3 with the reflection coefficient R 0.99, reflecting from which falls on the sensitive elements of the two-element photodetector 13 of the unit for determining the value lens defocus 6. Due to the high reflection coefficient and zero transmission of part 5, the reflected radiation does not enter the radiation source 1, which completely eliminates the noise caused by parasitic and amplitude modulated radiation of the radiation source 1. With a distance b between the optical axes of the radiation source 1 and the lens 6, determined from the ratio b I tg, where I is the distance from the focal plane of lens 2 to the intersection point of the plane of the splitter 3 with the optical axis of the lens 6; / 3-angle aperture lenses 2 (Fig. 2), the radiation beams are completely spatially separated, which eliminates the appearance of interference in the colliding beams.

The photodetector 13 is adjusted so that when the radiation beam is precisely focused on the surface of the information carrier 21, the axis of the reflected beam coincides with the boundary between the photosensitive elements of the photodetector. Due to the displacement of the axis of the radiation beam relative to the optical axis of the lens 6 during defocusing, the reflected beam is displaced in the direction perpendicular to the interface of the elements of the photodetector 13.

The difference signal from the elements of the photodetector 13, produced by the differential amplifier 15 and proportional to the magnitude of the displacement of the radiation beam in the plane of the photodetector 13, depends on the defocusing, the power of the beam and the radiation pattern of the radiation source. In the analog divider 16, the signal from the output of the differential amplifier 15 is divided into a total signal from the dual element photoreceiver 13 produced by the summing amp 14 and proportional only to the power of the radiation beam recording the out-of-focus. Consequently, the signal from the output of the analog divider 16 depends only on the defocusing and the drift of the axis of the radiation pattern of the radiation beam.

In the block for determining the defocus amount, the signal from the output of the analog divider 12 is proportional only to the value

The drift of the axis of the radiation pattern, and the output of the differential amplifier 17, in which the signal of the analog divider 12 is subtracted from the signal of the analog divider 16, produces a signal proportional to the amount of defocus.

The beam splitter 3 is in the form of a glass plate located under

an angle of 45 ° to the optical axis of the lens 6. On - part 4 of the splitter is applied a translucent, for example dielectric, coating, and part 5 on the side facing the lens 6 is a reflective, for example aluminum, coating with R 0.99. Due to the chosen ratio between the displacement of the axis of the radiation beam and the distance from the focal plane of the lens 2 to the splitter 3, the direct radiation beam passes

through the translucent part 4, and the beam reflected from the information carrier 21 hits the reflecting part 5. This completely excludes its penetration into the source 1 of the radiation and eliminates the noise caused by

spurious feedback.

Claims (1)

Invention Formula A device for automatic focusing containing a sequentially installed radiation source, a lens, a beam splitter, and a displacement drive lens, as well as optically coupled to the beam splitter through appropriate photoreceivers, the defocusing amount of the lens and the repositioning block of the axis of the radiation pattern, the outputs of which are connected to the differential inputs an amplifier whose output is connected to the input of an analog divider, another input of which is connected through the summing amplifier to the output of a voltage source, the output of the analog divider being connected to the input of a lens movement drive, another input of a summing amplifier, radiation directivity, and the optical axis of the source 0 radiation and the lens are parallel offset, characterized in that, in order to increase the reliability of reproduction of information, on the part of the beam splitter, optically connected with the photodetector 5 of the defocusing amount of the lens, a reflective coating is applied with a reflection coefficient R 0.99, and the optical axes of the radiation source and the lens are mounted between each other at a distance b, determined in- to the point of intersection of the plane by the beam split from the ratio b 2: 1 where I is the body with the optical axis of the objective; f is the angular distance from the focal plane of the lens and the aperture of the lens. YU 2 1