RU2338155C1 - Optic fiber displacement converter - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: Displacement converter includes spherical lens made of quartz glass with refraction factor, input and output optic fibers. Spherical lens is positioned between input and output optic fibers, so that optical axes of input and output optic fibers and lens coincide. Distances between input optic fiber and lens and between output optic fiber and lens are defined by formulae.

EFFECT: enhanced measurement accuracy, simplified construction.

3 dwg

Description

The invention relates to the field of measuring equipment, in particular to transducers of small displacements, and can be used in the development and manufacture of small-sized fiber-optic sensors for displacement, pressure, vibration displacement, angular displacement.

A device for monitoring vibration parameters containing a fiber optic ruler, which is a combination of light-conducting fiber discrete of equal thickness [Copyright certificate No. 962768, class. G01H 9/00, 1982. Device for controlling vibration]. The supply optical fiber (FOV), fixed in the inertial mass, moves under the influence of vibration of the housing relative to the optical fiber line. A narrow light beam of the light source is directed along the optical fiber to the sensing surface of the fiber-optic array, rigidly fixed in the housing. The light flux is transmitted through the optical fibers that are diverted to a photoelectric converter with a measuring unit.

The disadvantage of this device is the low reliability of the design due to the presence of the pendulum fastening of the inertial mass, in which backlash may appear over time, and the bends of the optical fiber, leading to a possible breakdown of the fiber.

The closest in technical essence to the invention is a device for measuring the displacement of an object, characterized in that the light flux from the light source, passing through the filter and the optical fiber, falls diverging beam onto a plano-convex lens [Copyright certificate No. 1516795A1, class. G01H 9/00, 1989. A device for measuring the movement of an object]. After refraction, the light beam is converted into a parallel one, which, partially reflected from the surface, passes into the air gap formed by a plane-convex lens and a plane-parallel plate. When reflected, it interferes with a light beam reflected from the flat surface of a plano-convex lens. Next, the luminous flux is focused on the input end of the output optical fiber (OOB). A photodetector registers the redistribution of energy in the interference pattern as a function of displacement.

The disadvantages of this device are large Fresnel losses at the interface of the device’s construction media and the need for very precise alignment of the structural elements relative to each other to obtain an interference pattern.

The invention is aimed at increasing the sensitivity of conversion of the light flux by reducing its loss in the measurement zone, simplifying the design of the fiber-optic converter.

According to the invention, a fiber-optic displacement transducer comprising a transparent spherical lens 2, leading 1 and leading 3 optical fibers, characterized in that the emitting end face of the leading optical fiber and the lens are at a distance relative to each other

where d _c is the diameter of the core of the optical fiber,

Θ _NA is the aperture angle of the optical fiber,

r _l is the radius of the spherical lens,

and the receiving end of the diverting optical fiber relative to the lens is at a distance

Where

Θ _in1 - the angle of input of radiation into the output optical fiber,

where n ₁ , n _l , n ₃ are the refractive indices of the media between the optical fiber and the lens, the lens material, between the lens and the optical fiber, respectively,

f is the rear focal length of the lens,

for spherical lens

Figure 1-3 shows geometric constructions explaining the location of the discharge 3 and supply 1 of the optical fibers relative to the spherical lens 2, moving in the direction of the X axis.

For uniform illumination and increased illumination, lens 2 should be located at a distance equal to two formation distances from the radiating end of POV 1 (Badeeva EA, Gorish A.V., Kotov A.N., Murashkina T.I., Pivkin A. G. The theoretical basis for the design of amplitude fiber-optic pressure sensors with an open optical channel: Monograph. - M .: MGUL, 2004. - 246 p.):

Since the increase in the distance between the emitting end face of the POV 1 and lens 2 can lead to the withdrawal of the spherical lens 1 from the lighting zone (Fig. 3), it is necessary to position it no further than

Where

The most optimal location of OOB 3 is in section AA (see FIG. 1). Such a technical solution is more preferable, since the distribution of illumination in the waist zone (at the focus of the lens) is uniform. Of equal intensity light fluxes will be formed if the location in the image plane 3 OOB emitting end PIW 1 will be a circle _of radius R equal to the radius R _s of the optical fiber, i.e. _from R _s = R. This is possible if the aperture angle Θ lens _L greater than the aperture angle Θ _NA, and the angle Θ to input radiation _Rin OOB smaller aperture angle Θ _NA, i.e.

In this case, POV 1 and OOB 3 are made of the same type of optical fiber.

Condition (8) and (9) is satisfied if

where the angle Θ _in1 is determined from the expression (3),

S _{f is} determined from expression (4).

The second component of expression (10) is insignificant, therefore, OOB 3 is located near the waist zone and, accordingly, the distribution of illumination in the plane of the receiving end of OOB 3 is almost uniform.

The principle of operation of the converter is as follows. Rays of light 4 and 5 of the emitting end of POV 1 exit at an aperture angle Θ _NA and fall at angles α ₁ and α ₂ onto the spherical surface of lens 2, where they are refracted, pass through the lens body at angles β ₁ and β _2, respectively, and secondarily fall onto the opposite the surface of the lens 2 at angles β ₁ and β ₂ are refracted and at angles γ ₁ and γ _{2 are} focused in the direction of the receiving end OOB 3. The image of the emitting end POW 1 in the plane AA, where the receiving end OOB 3 is located, is a round spot some area s _of .

The technical result of the proposed Converter is as follows. In the proposed fiber-optic displacement transducer, due to the new mutual arrangement of the optical elements, the conversion sensitivity is increased, the light flux loss in the measurement zone is reduced, the efficiency of using the light flux due to increased illumination and a decrease in the magnitude of the illuminated surface in the plane of the discharge optical fiber is increased.

Claims (1)

Fiber-optic displacement transducer containing a transparent spherical lens supplying and removing optical fibers, characterized in that the radiating end face of the supplying optical fiber and the lens are at a distance relative to each other

where d _c is the diameter of the core of the optical fiber, Θ _NA is the aperture angle of the optical fiber, r _l is the radius of the spherical lens, and the receiving end of the diverting optical fiber relative to the lens is at a distance l ₂ = S _t + b, Where

Θ _in1 - the angle of input of radiation into the output optical fiber,

where X _i is the measured displacement of the lens, n ₁ , n _l , n ₃ , are the refractive indices of the medium between the input, optical fiber and the lens, the lens material, the medium between the lens and the output optical fiber, respectively, f - back focal length of a spherical lens

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