SU1702258A1 - Optical fiber refractometer - Google Patents

Abstract

The invention relates to a measurement technique and can be applied to measure the refractive index of liquids during chemical and biological research, fuel analysis. The purpose of the invention is to simplify the design of an optical fiber refractometer and to reduce the consumption of liquid for analysis. The goal is achieved by the fact that in a fiber-optic refractometer, the measuring section is a transmitting and receiving surface micro-inhomogeneous fiber-optic elements that are bare sections of optical fiber of the same length, located in the horizontal plane in parallel, directed towards each other and offset relative to each other. a friend by an amount b, equal to a / tg a, where a is the distance between the bare sections of the optical fiber; tg a is the tangent of the aperture angle, while the receiving element is located in the light flux formed by the modes flowing through the side surface of the transmitting element, and the distance between the bare sections of the optical fiber keeps the drop of the liquid under study between them. 2 silt, (L S

Description

The invention relates to a measurement technique and can be applied to measure the refractive index of liquids during chemical and biological research, fuel analysis.

The purpose of the invention is to simplify the design of the refractometer and reduce the amount of liquid required for analysis.

Figure 1 shows a diagram of a fiber refractometer; figure 2 is the same, top view.

The refractometer contains a radiation source 1, a fiber-optic light guide 2, a transmitting element 3. a receiving element 4, a radiation receiver 5. The receiving and transmitting elements are surface-micro-inhomogeneous segments of the fiber of the same length, located in the horizontal plane, parallel to each other directed towards each other and displaced relative to each other by the distance b a / tg a, where a is the aperture angle; a is the distance between them.

Refractometer works as follows.

A drop of the test liquid is placed between the transmitting element 3 and the receiving element 4 and spreads along the entire length of the elements. The light from the source 1 through the fiber-optic light guide 2 enters the transmitting element 3. Part of the light

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about

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goes out through the end of the fiber, and the os-, aerial part (flowing out modes) passes through the liquid under study and enters the receiving element 4. At the same time, the amount of light that falls on the receiving element 4 depends on the refractive index of the liquid under study. The light from the receiving element 4 passes through the fiber-optic light guide 2 to the radiation receiver 5, where the luminous flux power is recorded, which is a function of the refractive index of the liquid under study.

The exposed areas of the fiber give the luminous flux a diffuse character of scattering and reception into and out of the medium through the lateral surface of the fibers due to the presence of surface microneutronodes on the fiber core. The refractometer uses the phenomenon of the attenuation coefficient of the luminous flux going along the transmitting surface of an o-micronerodner element represented by a bare fiber on surface micro-anion-single affinity, depending on the refractive index of the fluid, followed by perception of the radiation produced by the resulting modes. In this case, the perception is also carried out through the side surface of the surface-micro-inhomogeneous surface and, similarly, the light flux flows, formed by flowing modes on the surface microheterogeneity of the receiving element. The presence of surface micronomicities of the core of the fiber in the measuring section causes an exponential nature of the attenuation and transition of the light flux into the medium due to losses

Р рое-2 Ц

where P is the power of the light flux at the entrance of the fiber of the transmitting element;

Ro is the power of the light flux at the entrance;

L is the length of the measuring section,; - attenuation coefficient on the surface microheterogeneities x

Analyzing this formula, it can be assumed that the power of the light flux formed by the resulting modes will be equal to

RVM P-P,

where Rv m - the power of the luminous flux of the flowing modes of the transmitting element,

Thus, the greatest flow, and hence the sensitivity will be the maximum approximation Рвм to Р0

This is possible if the luminous flux completely passes into the medium, i.e. it is necessary either to increase the number of inhomogeneities or to increase the length

sensitive element of the measuring section.

The perception of the luminous flux of the receiving element is diffuse, therefore, for a more complete transition of the luminous flux, it is necessary to concentrate on the receiving element. This is only possible by creating an optically dense medium between the elements to improve the light coupling.

In this connection, it can be said that the maximum sensitivity of the refractometer will lie within the limits of § 1.4. to which most hydrocarbon fuels and glycerin belong.

The nature of perception on the receiving element also follows an exponential law and will depend on the length of the receiving element and the coefficient of surface micro-inhomogeneities on the element. The transmitting and receiving elements are chosen of the same length for a more complete transition of the luminous flux from the transmitting to the receiving element

When placed on or analyzed by

the fluid ™ between the transmitting and receiving elements is influenced by the force of gravity, under the action of which the wolfon is enveloped, therefore, for uniform enveloping of the elements, they

Dislocation in a horizontal plane parallel to each other. With such an arrangement of the fibers, the wettability and coating of the fibers will be uniform for both elements, which

affects the accuracy of the device.

The nature of the input spreading and outflow through the side surface of the luminous flux obeys optical laws, therefore, if we take ideally

5 smooth fiber, the angle of light output through the side surface of the transmitting element will not be greater than the angle of entry - the aperture angle. Thus, in order to take into account this feature, the fibers are displaced relative to each other by the magnitude b. At the same time, a mathematical analysis of the arrangement of elements and the nature of the propagation of the light flux shows that b will be equal to the ratio

5, where a is the distance between the exposed areas of the optical fiber; tg a - tangent of aperture angle.

In a multimode fiber, as the beam enters, the modes propagate inside

fibers at different angles. The following modes are used in the refractometer, i.e. the propagation vector of electromagnetic waves that are not parallel to the optical axis of the fiber. The outflow of such modes occurs through the side surface of the transmitting element and is diffuse. Therefore, to register this light flux, the receiving element must be in the light flux formed by the modes flowing through the side surface of the transmitting element.

The choice of the distance between the fibers is related to the physical properties of the fluids, since the analyzed fluid is acted upon by surface tension, as a result of experimental studies, the optimal value of the distance between the fibers at which the fluid with the lowest surface tension coefficient was found

uniformly wetted both elements and held onto these elements.

Claims (1)

Invention Formula Fiber optic refractometer containing a radiation source, an optical fiber with a sensitive element in the form of a surface-micro-inhomogeneous part of the fiber and a receiver radiation, characterized in that, in order to simplify the constuction and reduce the flow of liquid for analysis, the sensing element is designed as transmitting and receiving segments of the same length, located in the same plane with the device axis parallel to each other, directed towards each other and displaced relative to each other by the value of ba / tg and where about. aperture angle; a is the distance between the segments, which ensures the retention of a drop of the test liquid between them. FIG. 7