Method of adaptive processing of optical signal

FIELD: electro-optics.

SUBSTANCE: method can be used in optical filter constructions intended for processing of optical radiation under conditions of slow or single-time changes in processed signal, which changes are caused by non-controlled influence of environment. Optical signal is applied to entrance face of photo-refractive crystal where phase diffraction grating is formed by means of use of photo-refractive effect. Reflecting-type phase diffraction grating is formed. For the purpose the optical signal with duration to exceed characteristic time of phase diffraction grating formation, is applied close to normal line through entrance face of photo-refractive crystal of (100) or (111) cut onto its output face which is formed at angle of 10°to entrance face. Part of entrance signal, reflected by phase diffraction grating, is used as output signal. To apply optical signal to entrance face of photo-refractive crystal, it has to be transformed into quazi-flat wave which wave is later linearly polarized.

EFFECT: power independence of processing of optical signal.

2 cl, 2 dwg

 

The invention relates to the field of optoelectronics and can be used in the construction of optical filters designed to handle time-varying optical radiation output fiber-optic interferometer or specalog radiation obtained after the interaction of coherent laser radiation with the object under study, under conditions of slow or one-time changes of the processed signal, caused by uncontrolled external factors.

The known method adaptive processing an optical signal comprising its submission on the input face of the photorefractive crystal, in which a pre-form of the phase diffraction grating using the photorefractive effect, this provides for the supply of two optical signals, one of which is the carrier of the processed signal, and the other reference. Signals propagate in the crystal at a small angle, resulting in a crystal is formed of a diffraction grating is transmissive (see Hall, T.J., M.A. Fiddy, Ner M.S. Detector for an optical-fiber acoustic sensor using dynamic holographic interferometer // Optics Letters. - 1980. - Vol.5. - No.11. - P.485-487 or Delaye Ph., Blouin, A., Drolet D., de Montmorillon L.A., G. Roosen, Monchalin J.-P. Detection of ultrasonic motion of a scattering surface by photorefractive InP:Fe under an applied dc field // J. Opt, Soc. Am. B. - 1997. - Vol.14. - No.7. - P.1723-1734 or Honda T, Yamashita T., Matsumoto H. Optical measurement of ultrasonic nanoeter motion of rough surface by two-wave mixing in Bi 12SiO20// Japan J. Appl. Phys. - 1995. - Vol.34. - P.3737-3740 or Kamshilin A.A., Prokofiev V.V. Fast adaptive interferometer with a photorefractive GaP crystal // Optics Letters. - 2002. - Vol.27. - No.l9. - P.1711-1713).

The disadvantage of this technical solution is that the obligatory presence of an external reference wave, in addition, formed in the crystal diffraction grating is transmissive has a lower diffraction efficiency in comparison with a reflective grating, therefore, to improve the efficiency in use of an external constant or alternating electric field of 20 kV/see

There is also known a method of adaptive processing of the optical signal, including its filing on the input face of the photorefractive crystal, in which a pre-form of the phase diffraction grating using the photorefractive effect (see Kulchin YU.N., Romashko R.V., Piskunov N., Kamshilin. A.A. Multichannel correlation filter based on the photorefractive crystal to handle variable silovich fields // technical physics Letters. - 2000. Tom. 26. - P.23-27).

This method is based on the effect of fanning, known as the process of samedirection light wave introduced into a photorefractive crystal is pumping energy of this wave in the wave scattered by the self-consistent diffraction grating recorded in the crystal, in contrast to the analogues diffraction the second grating is formed without external reference wave.

The disadvantage of this technical solution is that due to the lack of diffraction efficiency of the generated lattice (transmissive) also requires the use of an external electric field.

Solved the technical problem is ensuring the independence of processing an optical signal (an exception is necessary, the application of an external electric field to the photorefractive crystal is used to implement the method).

The technical result obtained by the solution of the problem, which seeks to ensure the autonomy of the system, ensuring implementation of the method, because the high efficiency of interaction of oppositely propagating light waves (and thus, high diffraction efficiency, which is formed in a photorefractive crystal diffraction grating reflector type) is provided due to its small spatial period.

To solve the problem the way adaptive processing an optical signal comprising its submission on the input face of the photorefractive crystal, in which a pre-form of the phase diffraction grating using the photorefractive effect, characterized in that the shape of the phase diffraction grating reflective type, for which the optical signal, the duration of which exceeds the characteristic time is formirovaniya phase diffraction grating, serves close to normal through the input face of the photorefractive crystal slice (100) or (111), on its exit face formed at an angle of up to 10° to input, when the output signal using the input signal, the reflected phase diffraction grating. In addition, prior to the filing of the optical signal at the input face of the photorefractive crystal it is converted into quasilocal wave, which is then linearly polarize.

Comparative analysis of the characteristics of the claimed solution with the characteristics of the prototype and analogues demonstrates compliance of the claimed solution to the criterion "novelty".

Signs of a distinctive part of the formula of the invention provide a solution to the following functional tasks:

The sign "...form a phase diffraction grating reflective type..." provides high diffraction efficiency is formed in a photorefractive crystal diffraction grating, which allows to ensure the independence of processing an optical signal.

Signs "...optical signal, the duration of which exceeds the characteristic time of formation of the phase diffraction grating serves close to normal through the input face of the photorefractive crystal slice (100) or (111) at its exit face formed at an angle of up to 10° to input, ...determine the mu is necessary spatio-temporal parameters of the filing of the optical signal on the photorefractive crystal, when the observance of which is ensured by the occurrence of phase diffraction gratings "automodelismo" and "self-regulated" (supplied by the optical signal).

Signs "...as the output signal using the input signal, the reflected phase diffraction grating..." provide the possibility of detecting changes in the intensity of the input wave, i.e. the formation of information (measurement) signal, which indicates a change of the measured physical parameter field acting on the measuring section.

Signs of the second paragraph of the formula are improving the efficiency of processing the optical signal, as they provide its "harmonization".

The drawing shows a diagram of the installation, ensuring implementation of the method.

The drawing shows the setup for the adaptive processing of the optical signal that includes a lens system 1, a polarizer 2, a diaphragm 3, a photorefractive crystal 4, for example, made of Bi12TiO20containing the input line 5 (oriented as the cutoff (100) or (111) photorefractive crystal and the output line 6 (which is close to parallel with the input face is inclined to it at an angle of up to 10°). In addition, it is shown the phase diffraction grating 7 of the reflective type, the photo detector 8, such as a photodiode, the output is associated with selective voltmeter 9 (for visualization of the measurement results can be used and the means executed on another element base, mating with other nodes setup for adaptive processing of the optical signal). In addition, as shown in the drawing speciosae radiation 10 obtained after the interaction of coherent laser radiation with the object (or divergent optical radiation output fiber-optic interferometer), incoming (quasilocal) optical wave (signal) 11, the reflected optical wave (signal) 12. These elements do not differ from the well-known used for a similar purpose, except photorefractive crystal 4, which should be the distribution of the incoming (quasilocal) optical wave 11 along the crystallographic axis [100] or [111], which is its normal feed cutoff (100) or slice (111), i.e. one of these sections should be perpendicular to the direction of the incoming optical wave 11.

The claimed method is implemented as follows

Divergent optical radiation output fiber-optic interferometer or speciosae radiation obtained after the interaction of coherent laser radiation with the object, using the lens system 1 is converted into quasilocal wave, having in General a complex intensity distribution, which is after passing the polarizer 2 and the diaphragm 3 hits on the entrance face 5 of the photorefractive crystal 4 and extends in its thickness along the crystallographic axis [100] or [111]. After reflection part of the input wave from the output face 6 of the crystal in the last 4 covers two opposite mutually coherent optical waves (part 11 and reflected 12), interference which, due to the photorefractive effect, forms in the crystal 4 phase diffraction grating 7 of the reflective type. The grating 7 is formed in the crystal for a certain period of time (recording time), which depends on the type of crystal, the presence of impurities and of the total intensity of the input radiation. The occurrence of a crystal diffraction grating leads to diffraction on the input wave in the direction opposite to its spread (reflection on the grill). As the output signal using the input signal (incoming (quasilocal) optical wave 11), the reflected phase diffraction grating which receives the photodetector 8 and measure selective voltmeter 9 on whose testimony and judge about the changes in the intensity of reflected (difragirovavshej) optical wave 12.

The intensity of the scattered (difragirovavshej) wave grows to saturation during the time entry grid. If the intensity distribution of the input wave is changed in less recording time, the reflected wave causes a change in the total intensity or the polarization state (depending on when the state of polarization of the input wave). Changing the state of polarization is determined using the analyzer as shown in the drawing by the dotted line). All changes in the reflected wave occurs at the frequency of the second harmonic, if changes in the intensity of the input wave is sinusoidal. If changes of the input wave occur at times greater than the recording time of the lattice, the old grid will be erased in the crystal and recorded a new, appropriate to the new intensity distribution. In this case, the intensity (or the polarization state of the reflected wave will not change. This is the adaptability of the proposed filter, which is able to adapt to a slow or a one-time change of the processed signal, caused by the uncontrolled effects of external factors.

1. Method of adaptive processing of the optical signal, including its filing on the input face of the photorefractive crystal, in which a pre-form of the phase diffraction grating using the photorefractive effect, characterized in that the shape of the phase diffraction grating reflective type, for which the optical signal, the duration of which exceeds the characteristic time of formation of the phase diffraction grating serves close to normal through the input face of the photorefractive crystal slice (10) or (111) at its output face, formed at an angle of up to 10° to input, when the output signal using the input signal, the reflected phase diffraction grating.

2. The method according to claim 1, characterized in that prior to the filing of the optical signal at the input face of the photorefractive crystal it is converted into quasilocal wave, which is then linearly polarize.



 

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