RU2100831C1 - Optical radiation modulator - Google Patents

Abstract

FIELD: data indication devices; magnetic field sensors. SUBSTANCE: optical radiation modulator has two sections of transparent sphere, on the interface boundary of which condition of full internal reflection is satisfied, and magnetic field source. Particles or fibres of magnetically hard, magnetically soft or magnetostrictive material are introduced on interface boundary of media sections or in close vicinity of it to create mechanical stresses under the effect of magnetic field. Two sections of transparent media may be made as fibre light guide. EFFECT: improved indication process. 2 cl, 2 dwg

Description

 The invention relates to techniques for modulating optical radiation and can be used both for modulating light and for visual display of information, as well as for indicating a magnetic field.

Numerous radiation modulation devices are known, some of which are described in [1]
Acoustic sensor on microbends of fiber [1] p. 101, is a fiber light guide enclosed between a movable and a stationary deformer, which creates a periodic curvature during mutual approach, as a result of which energy is transferred from the core modes to the clad modes.

 Microbending strain gauge, [1] p. 108, the optical scheme is not different from the above acoustic sensor, however, the deformer is made in the form of a tensile chain. As the measured strain increases, the amplitude of the microbends of the optical fiber freely placed inside the chain links increases. In this case, when microbends occur, not only does a part of the radiation transfer to the cladding, but also there is a back reflection from sections of the fiber subjected to microbends.

 Interoferometric magnetic field sensor [1] p. 160, the sensitive element of which is a fiber light guide with a magnetostrictive material glued to it or applied to it. In this case, deformations of the magnetostrictive material are transformed into deformations of the fiber waveguide, which change the optical path of the light, and also cause the effect of photoelasticity in the fiber.

 The closest set of features to the claimed invention is a modulator of optical radiation [5] prototype. It consists of two optical prisms, the planes of which are located in parallel with a fixed gap between them. The plane of the first prism is irradiated from the side opposite the gap with light, which in the initial state of the device is completely reflected from it, and on the plane of the second prism is a layer of elastic material. The device also includes a pressure member capable of mechanically acting on the layer of elastic material thereby deforming it. When a pressure element is applied to the elastic material, the latter is pressed inside the gap, reducing it. In this case, part of the light penetrates beyond the plane of the first prism and either propagates into the second, if the elastic element is transparent, or is absorbed by it.

 The action of the prototype is based on the violation of total internal reflection when approaching the reflecting plane from an area in which light does not propagate, a material with optical properties different from the properties of this area.

 A common feature of these devices is that they both contain two sections of transparent media, at the interface of which the condition of total internal reflection is satisfied.

 The work of the prototype, as well as the claimed device, is based on the joint use of the effects of total internal reflection and its violation by mechanical action on the optical medium near the boundary of reflection.

 Analogs and a prototype of the invention do not provide the ability to control optical radiation due to the violation of the total internal reflection at the interface in the optical medium under the influence of a magnetic field.

This goal is achieved by the fact that particles 3 of a ferromagnetic or magnetostrictive material are introduced into a transparent medium having an interface at which the condition of total internal reflection is satisfied, for example, an optical fiber, which create mechanical stresses under the influence of a magnetic field. It is known ([1] [2]) that the boundaries L in the medium between sections 1 and 2 with optical densities n ₁ and n _2, respectively, where n _{1 is} less than n ₂ , is able to completely reflect the optical radiation coming from section 2 back to this plot, if the angle between normal to the interface and the direction of radiation lies in the range from Q to 90 ^o inclusive, where Q is the critical angle of incidence equal to arcsin (n ₂ / n ₁ ), [1] sec. 19. If particles of a material interacting with a magnetic field are located in the immediate vicinity of this boundary or even on it itself, when this field is applied, such particles create mechanical stresses in the optical medium, providing the effect of photoelasticity and deformation of the boundary [2]
In the event that these particles cause scattering or absorption of radiation, they are placed outside the region of propagation of radiation with total internal reflection. The essence of this proposal is illustrated in FIG. 1, where it is shown that magnetically sensitive particles are located on one side of the interface.

Let L be the boundary at which total internal reflection of light with wavelength λ incident at an angle a to the normal to the interface L. occurs. For definiteness, we assume that the boundary is sharp, although in the general case it can represent a smooth, gradient transition from a region with optical density p ₁ to the region with optical density n ₂ .

где ω угловая частота падающего излучения,
с скорость света в вакууме.It is known ([5] p. 109.113, files 4.6, 4.7) that with total internal reflection, a light wave penetrates into an optically less dense medium, a phenomenon called impaired total internal reflection. The intensity of the light wave penetrating beyond the interface decreases exponentially with distance from the boundary. The effective penetration depth H _{e is the} distance at which the light intensity decreases e times the quantitative characteristic of total internal reflection:

where ω is the angular frequency of the incident radiation,
with the speed of light in a vacuum.

The thickness of a layer of material with an optical density n adjacent directly to the boundary L can be determined in the following way: by calculating or modeling a particular case with specific materials and particle sizes, find the maximum distance from the particle to the boundary L at which the stresses and strains caused by it for a given magnetic field, sufficient to violate the total internal reflection. This distance H _{max is the} maximum possible thickness N.

The minimum possible thickness H _min depends on the level of scattering loss. The thickness of the layer with magnetic particles should not significantly exceed the dimensions of the particles themselves due to the fact that the particles closest to the boundary L produce a greater effect, and a large layer thickness n ₂ will lead to large losses in the absorption and scattering of light passing through the boundary L. Mechanical fiber strength can be enhanced by adding an external fourth layer of transparent material, possibly with the addition of a light-accumulating substance phosphor or by enclosing the fiber in a transparent or translucent material. If a phosphor is to be used, one of its functions is to change the direction of radiation and make the radiation pattern from each point more uniform.

The choice of the highest concentration of particles can be carried out on the basis of various considerations. We can proceed from considerations of overlapping deformation fields of the optical medium between neighboring particles of the order of 10 μm, with the highest concentration of about 10 ¹² cm ^-3 . Another estimate can be made from those considerations so that radiation can pass between the particles, and this is achieved if the distance between them is not less than l, that is, for visible radiation the highest concentration is about 10 ⁹ cm ^-3 .

It does not make sense to evaluate the minimum concentration, since one particle may be enough for a large volume, 1 m ³ .

, а максимальный габарит определяется величиной светящейся точки, которую необходимо получить, и этот размер для больших табло может достигать порядка 10^-1 м.The minimum particle size is the size of a magnetic ion, which can be used as particles, not more than twice the distance between the nearest atoms of the basic substance, approximately

, and the maximum size is determined by the magnitude of the luminous point, which must be obtained, and this size for large displays can reach about 10 ^-1 m.

 The sources of the magnetic field that cause the effect used in the claimed device can be located outside, applied to the surface or embedded in the volume of the optical medium, for example, in the form of current conductors.

Let us analyze the attainability of the above effect. Take a transparent medium containing the boundary L of total internal reflection between sections 1 and 2. The following are the characteristics of areas [3] and [4] Section 1. Material 1 glass; optical density n ₁ 1.6109; coefficient of photoelasticity p ₁ 0.2; elastic modulus E ₁ = 7 • 10 ⁸ Pa. Section 2. Material 2 polystyrene; optical density n ₂ 1.60805; coefficient of photoelasticity p ₂ 0.3; elastic modulus E ₂ 0.32 • 10 ⁸ Pa.

Radiation with a wavelength λ equal to 0.568 μm at an angle a equal to 86 ^o to the normal to the boundary L is incident on the boundary L from section 1.

The critical angle of total internal reflection is Q 86.59 ^o . The radiation partially leaves region 1, if a is less than Q. We find the value of the mechanical stress s at which the radiation completely penetrates into section 2. In this case, the condition
n ₁ + Δn ₁ = n ₂ + Δn ₂ ,
where Δn ₁ and Δn ₂ changes the optical densities of sections 1 and 2, respectively, when a mechanical stress σ is applied to the medium.

Для того, чтобы лишь нарушить полное внутреннее отражение, достаточно меньшего напряжения.In the simple case

In order to only disrupt the total internal reflection, less stress is sufficient.

This effect can be realized using particles of a magnetically hard material with a coercive force Hc of at least 10 ³ A / m, or a soft magnetic material with a relative magnetic permeability μ of at least 10 ² , or a magnetostrictive material with a magnetomechanical coupling coefficient K of at least 0.2.

 Possible applications of the invention may be as follows. The described optical medium is a fiber in which section 1 is the core, and section 2 is the cladding, and particles 3 are located inside section 2. Such a fiber, combined with electric conductors, to which current pulses are generated, which create magnetic fields at the right points, can be a screen for outputting an image or a matrix for reading it, depending on whether the radiation sources or receivers are located at the ends of the fiber.

 In another embodiment, the optical medium may be a plane-parallel plate, the boundary L parallel to the surface of the plate, a conductor system is superimposed on section 2. This design can perform similar functions, radiation sources or receivers are located at the ends of the plate.

 In this case, the first and second embodiments of the device, devoid of current conductors, can play the role of a magnetic field sensor, the measured value in this case may be the intensity of the light transmitted through the boundary, or vice versa, reflected from it.

Technologically described device can be implemented by known methods [1]
For example, CVD is a process in which the chemical deposition of the main glass-forming oxide and doping oxides from a gas-vapor mixture is carried out, or by the method of manufacturing fiber from multicomponent glasses according to the double crucible method.

 In FIG. Figure 1 shows an optical medium with sections 1 and 2, the boundary L between them and ferromagnetic particles 3, which create mechanical stresses in the medium as a result of intrinsic deformation or displacements under the influence of magnetic field B. On the boundary L, radiation from section 1 is incident from wavelength l, while the critical angle of total internal reflection Q is less than a.

 In FIG. 2 shows an optical medium in the form of a fiber waveguide, where section 1 is the core and section 2 is the cladding.

LITERATURE
1. Fiber optics and instrument engineering, edited by M. Butusov L. Engineering, Leningrad. branch.

 2. The basics of optics, M. Born, E. Wolf. M. Science, 1973.

 3. Handbook of Physics, H. Kuchling. M. World, 1985.

 4. Physical Quantities Reference. M. Energoatomizdat, 1991.

 5. US patent N 4714326, CL. G 02 D 26/00, 1987.

Claims (2)

1. An optical radiation modulator containing two sections of a transparent medium, at the interface of which the condition of total internal reflection is fulfilled, characterized in that it is provided with a magnetic field source, while particles at the interface of the media sections or in the immediate vicinity of it are introduced

10 ^{- 1} m or fibers made of hard magnetic or soft magnetic material with a relative magnetic permeability of at least 10 ² or a magnetostrictive material with a concentration selected from the condition that the deformation fields of the optical medium overlap between adjacent particles to create mechanical stresses under the influence of a magnetic field.  2. The modulator according to claim 1, characterized in that the two sections of transparent media are made in the form of a fiber waveguide.

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