SU1453328A1 - Fibre-optic velocity transducer - Google Patents

Abstract

The invention relates to a measurement technique and allows remote measurement and cont. the role of the speed of movement of the reflective surface, for example, the rotation of the shaft. The radiation from source 1, wavelength X, width of the spectral band 4-, through the beam splitter 2 enters the input end of the fiber optical fiber (VO) 3. The radiation coming out from the output end of the sun 3 3 is directed normally to the surface of the moving object 5. Reflected radiation from the surface is introduced in BC 4, made in the form of an open ring. The ends of the sun 4 are arranged symmetrically with respect to the output end of the sun 3, the optical axes of the sun 4 on the end side intersect at an angle, along the bisector of which the optical axis of the sun 3 is directed on the side of its output end. The reflected radiation propagates through the sun 4 in opposite directions, emerges from the conjugate ends of the sun 4, re-reflects from the moving surface and enters the sun 3 from its output end. A coherent addition of doubly reflected light waves occurs. As a source of radiation, brane has a weakly coherent LED, the length of the sun 4 is chosen from the condition 1. L L (nj ..), where M is the number of modal fiber groups; nj.,. - refractive indices of the core and cladding of the fiber. This makes it possible to eliminate the effect of the intermode noise of the fiber. The radiation emanating from the input end of the VS 3 is transmitted through a beam splitter to a photodetector 7, the frequency of the photocurrent at the output of which is determined by the doubled Doppler frequency shift - (L ate with co 00

Description

which determines the speed of the surface. The purpose of the invention is to improve the measurement accuracy by reducing the effect of intermode

optical fiber noise, as well as constructive simplification due to the possibility of using a low-coherent source. 1 il.

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The invention relates to a measurement technique and can be used in optical instrument making for creating systems for remote measurement and speed control of moving reflecting objects.

The aim of the invention is to improve the measurement accuracy by reducing the influence of inter mode noise in fiber optics and constructive simplification of the device.

The drawing shows a block diagram of the sensor.

The sensor contains a monochromatic radiation source 1, a beam splitter 2, a transceiver optical fiber (BC) .3, made in the form of an open ring, optical fiber 4, a reflecting surface 5 of a moving object, micro-lenses 6, a photodetector 7.

The sensor works as follows. A portion of the monochromatic radiation of the source 1 with the wavelength of the spectral bandwidth after passing through the beam splitter 2 is introduced, for example, by means of a micro-lens 6 into the sun 3 from its first end. At the output of BC 3, the radiation is directed normally to the surface of a moving object 5, for example, rotating with an angular velocity (O. The radiation reflected from the surface is introduced, for example, by means of micro lenses 6 into an optical fiber 4 that is open on one side of the ring the first and second ends, and at the same time, the end end performs the functions of both the input and output ends.

The Doppler frequency shift of the reflected light depends on the spatial conditions of the reception. With a symmetrical arrangement of the ends of the sun 4 relative to the output end of the sun 3 to ple ...

Q

five

5 o

35

40

dz

f .2-V-sinoi / Z equal to the frequency shift r i;: -,

where is the angle between the optical axes of the sun 4 from its ends; V is the linear velocity of the object's surface. If the distance between the ends of the BC 4 is 2d, and the distance from the second end of the BC 3 and the ends of the BC 4 to the surface is equal to h, the Doppler frequency shift at sinfl / 2 ti. tget / 2 equals

 f -i2d -h- A

BC 4 plays the role of a fiber ring interferometer in which the light fluxes propagate in opposite directions. The radiation emanating from each conjugate end of the sun 4 is again reflected from the object surface and is introduced into sun 3 from the side of its second end, where coherent addition of the secondary light streams passing through the sun 4 occurs. The interference structure resulting from the photomixing of light currents has a period.

The radiation transmitted by BS 3 in the direction opposite to the direction of propagation of the source's radiation passes through the light gap 2 to the photodetector 7. To ensure a sufficient depth of modulation of the photocurrent at the output of the photodetector, the spatial-frequency selective properties of the second end of the BC 3 used as input for reflected light, set in accordance with the period of the interference structure A.

For example, to increase the modulation depth of the photocurrent, the diameter of the cores of the sun 3 is chosen to be smaller than the width of one band from the condition a .: L / 2.

The interfering light waves pass through the same optical paths inside BC 4, which makes it possible to use as a source a low-coherent radiation source, a LED, which simplifies the design of the device. In this case, the coherent interaction of modes in the fiber is preserved only within the fiber length.

L

 Uc-njj

where P (., Pdu - refractive indices

cores and shell of the aircraft; M - the number of honey groups

in fiber.

The choice of the length of the light guide 4 from the condition makes it possible to exclude the influence of coherent intermode interference which determines the mode noise, which limits the accuracy of the sensor sensitivity. The frequency of the photocurrent at the output of the detector 7 is determined by twice the Doppler frequency shift 2fj) due to the double modulation of the moving object by the secondary reflection from its surface. Analyzing the frequency of the signal at the output of the sensor makes it possible to determine the speed of movement of the reflecting surface.

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Claims (1)

Invention Formula A fiber optic speed sensor containing a radiation source, the first and second fiber fibers and 145-3328, products, beam splitter, photodetector, with the first end of the first optical fiber optically matched to the radiation source and photodetecs 15 0 25 p five torus, and the second end of the second optical fiber is optically matched with the second end of the first optical fiber, characterized in that, in order to improve measurement accuracy by reducing the effect of intermode noise of optical fibers and simplifying the design, a low-coherent LED is selected as the radiation source, the light guide is made in the form of an open ring, while the end of the second fiber is optically matched with the second end of the first fiber, and the optical axes of the second optical fiber from the side the first- and second end faces lie in one plane and intersect at an angle, and the optical axis of the first optical fiber from the side of its second end aligned with the bisector of the angle, the length L of the second fiber is selected from the conditions y-lsp -n,) the refractive indices of the core and cladding of the fiber; M - the number of modal groups light guide; And L And - wavelength and width spectral line of radiation source. with .