RU122174U1 - DEVICE FOR MEASURING PHYSICAL FIELD PARAMETERS - Google Patents

Abstract

1. A device for measuring the parameters of physical fields, containing a series-connected source of laser radiation, the first fiber optic cable, an optical sensor, a second fiber optic cable and a photodetector, as well as a controller for determining the parameter of the physical field, characterized in that two selective filter and two amplitude detectors, wherein the laser radiation source is made four-frequency, and the output of the photodetector through the first selective filter and the first amplitude detector is connected to the first input of the controller for determining the parameter of the physical field and in parallel through the second selective filter and the second amplitude detector - to its second input. ! 2. The device according to claim 1, characterized in that the optical sensor is based on a fiber Bragg grating. ! 3. The device according to claim 1, characterized in that the optical sensor is based on a Fabry-Perot interferometer. ! 4. Device according to claim 1, characterized in that the optical sensor is based on a thin film filter.

Description

The technical solution relates to the technique of optical measurements, in particular to devices for measuring the parameters of physical fields (temperature, pressure, tension, etc.) using optical sensors, including sensors in integrated and fiber-optic design (Fabry-Perot interferometers, gratings Bragg, sensors on thin-film filters, etc.), in which there is a dependence of the frequency shift of their spectral, as a rule, band-resonance characteristic, depending on the parameters of the applied physical fields.

A device for measuring the parameters of physical fields is known (see electronic resource www.forc-photonics.ru, “Fiber Optic Probe Thermometer”, file termometr_final.pdf, LLC IP NTsVO-Photonika, October 14, 2008), which contains series-connected a broadband laser emitter, an optical splitter-circulator, an optical fiber cable, an optical sensor, a unit for spectral analysis of the received radiation, and a photodetector unit connected to the input of the controller for determining the parameter of the physical field in which the mathematical image is Botko spectral shift for which calibration is determined considering the physical parameter field, in case the temperature. Known similar devices for measuring parameters and other physical fields.

The device operates as follows. Generate broadband radiation in a laser emitter, transmit it to the optical sensor via a fiber optic cable, receive radiation converted in the optical sensor in the spectral analysis unit of the received radiation and the photodetector unit, and determine the parameters of the physical field by accurately recording the spectral shift of the resonant wavelength of the optical sensor .

The disadvantage of this device is the need to use complex expensive unit spectral analysis of received radiation and a photodetector unit for recording spectral bias (as a rule, these are optical spectrum analyzers). Optoelectronic spectral signal processing also seems to be complex and requires either tunable laser emitters, or complex spectral filtering systems, or several photodetectors, or, as an option, a system of CCD array receivers. All this leads to the appearance of additional sources of errors in the measurement of the parameters of physical fields and a decrease in their accuracy in general.

The prototype of the technical solution is a device for measuring physical fields (see US Patent No. 7463832 B2 “Method and system for compensating thermal displacements for optical networks”, 398/196 MPK8 H04J 13/02, 08/09/2005), which contains a double-frequency laser emitter connected in series , an optical splitter, a first optical fiber cable, an optical sensor, a second optical fiber cable and a first photodetector, a second photodetector connected via a third optical fiber cable to a second output of the optical splitter as well as a unit for comparing the amplitudes of each of the signals generated by a two-frequency laser emitter of a pair and a pair received after passing through the optical sensor, connected to a controller for determining the parameter of the physical field, in this case the temperature, while the outputs of the photodetectors are connected to the inputs of the amplitude comparison unit.

The prototype works as follows. In a two-frequency laser emitter, pairs of signals of a predetermined close amplitude are generated with an average frequency corresponding to a certain frequency bandwidth of the optical sensor at a given value of the physical field parameter, and a difference frequency narrow enough for both signals to fall into the specified bandwidth, transmit the generated pair signals to the optical sensor via the first fiber-optic cable, take a pair of si passed through the optical sensor on the first photodetector the signals transmitted to the second fiber-optic cable, and the physical field parameter is determined by comparing the differences in amplitudes between the signals of the pair received after passing through the optical sensor, or comparing their amplitudes with the amplitudes of the signals in the generated pair transmitted to the second photodetector via the third fiber-optic cable .

The disadvantage of the prototype device is the need to use a complex optical system for separate amplitude-spectral reception of individual components of signal pairs, requiring, as a rule, the presence of narrow-band interference filters, in turn, having a temperature dependence of spectral characteristics. Separate optoelectronic processing of the components is also complex and represents the processing of the absolute amplitude values of the received signals, subject to the effects of noise and interference of various nature. All this leads to the appearance of additional sources of errors in the measurement of the parameters of physical fields and a decrease in their accuracy in general.

The technical problem to be solved is to increase the accuracy of measurements, simplify and reduce the cost of devices for measuring the parameters of physical fields.

The technical problem to be solved in a device for measuring the parameters of physical fields, comprising a laser radiation source, a first fiber-optic cable, an optical sensor, a second fiber-optic sensor and a photodetector, and also a controller for determining a physical field parameter is achieved by introducing into it two selective filters and two amplitude detectors, the laser radiation source being made four-frequency, and the photodetector output through the first selective filter and the first the second amplitude detector is connected to the first input of the controller determining the parameter of the physical field and in parallel through the second selective filter and the second amplitude detector to its second input.

The device can be performed using an optical sensor based on a Bragg fiber grating.

The device can be performed using an optical sensor based on a Fabry-Perot interferometer.

The device can be performed using an optical sensor based on a thin-film filter.

Figure 1 shows the structural diagram of the device.

Figure 2 shows the dependences of the amplitudes of the beat envelope of the signals of the first and second pairs transmitted through the optical sensor and their difference from the generalized detuning of the passband of the optical sensor for the case of four signals of the same amplitude with an average frequency corresponding to the center frequency of its passband the specified value of the physical field parameter. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are not the same, and the difference between the average frequencies of the first and second pairs is equal to the half-width of the passband of the optical sensor. Dependencies are given under the assumption that the optical sensor has a triangular spectral characteristic, for example, a triangular Bragg grating.

A device for measuring the parameters of physical fields (1, 2) contains a series-connected laser source 1, a first fiber optic cable 2, an optical sensor 3, a second fiber optic cable 4 and a photodetector 5, as well as a controller for determining the parameter of the physical field 6 is achieved by the fact that two selective filters 7-8 and two amplitude 9-10 are introduced, while the laser radiation source 1 is made four-frequency, and the output of the photodetector 5 through the first selective filter 7 and the first amplitude detector 9 is connected to the first input of the controller parameter determining physical field 6 and parallel through a second selective filter 8 and the second amplitude detector 10 to its second input.

The device can be performed using an optical sensor 3 based on a Bragg fiber grating.

The device can be performed using an optical sensor 3 based on a Fabry-Perot interferometer.

The device can be performed using an optical sensor 3 based on a thin-film filter.

Figure 2 shows the dependences of the amplitudes of the beat envelope of the signals of the first and second pairs transmitted through the optical sensor 3, and their difference from the generalized detuning of the passband of the optical sensor 3 for the case when it receives four signals of the same amplitude with an average frequency from the laser source 1, the corresponding center frequency of its bandwidth for a given value of the parameter of the physical field. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are not identical, and the difference between the average frequencies of the first and second pairs is equal to the half-width of the passband of the optical sensor 3. The dependences are given under the assumption that the optical sensor has a triangular spectral characteristic, for example, a triangular Bragg grating.

Consider the operation of the device for measuring the parameters of physical fields.

To measure the parameters of physical fields using a four-frequency source of laser radiation 1 simultaneously generate four signals of the same amplitude with an average frequency corresponding to the center frequency of the passband of the optical sensor 3 at a given value of the parameter of the physical field. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are not the same, and the difference between the average frequencies of the first and second pairs is equal to the half-width of the passband of the optical sensor 3.

Then, the generated signal pairs are transmitted to the optical sensor 3 via the first optical medium, for which the first fiber-optic cable 2 is selected.

In the generated pairs of signals passing through the optical sensor 3, the amplitudes of the individual components change depending on the direction and magnitude of the frequency shift of its passband, caused by the applied physical field and uniquely determined by the parameter of this field.

Next, using the photodetector 5, pairs of signals transmitted through the optical sensor 3 are received, transmitted from the optical sensor 3 to the photodetector 5 via a second optical medium, for which a second fiber optic cable 4 is selected.

At the output of the photodetector 5, signals are generated corresponding to the beats of the signals of the first and second pairs, which are highlighted by the first 7, tuned to the frequency Ω1, and the second 8, tuned to the frequency Ω2, by selective filters. Then, in the first 9 and second 10 amplitude detectors, respectively, the amplitude of the envelopes of the first U _Ω1 and second U _Ω2 pairs is determined.

The difference in the amplitudes of the beat envelopes between the signals of the first and second pairs U _Ω1 -U _Ω2 , passed through the optical sensor 3, is measured in the controller for determining the parameter of the physical field 6.

1 Io the obtained values and embedded in the controller determine the parameter of the physical field 6, the dependence of the difference between the amplitudes of the envelopes of the beat of the signals of the first and second pairs U _Ω1 -U _Ω2 passed through the optical sensor 3, from the generalized detuning of the passband of the optical sensor 3 (figure 2) and the dependence the direction and magnitude of the frequency shift of the passband of the optical sensor 3 from the parameters of the physical field uniquely determine the measured parameter of the physical field.

Figure 2 shows the dependence of the difference between the amplitudes of the beat envelopes of the signals of the first and second pairs U _Ω1 -U _Ω2 transmitted through the optical sensor 3 from the generalized detuning of its passband for the case when four signals of the same amplitude with an average frequency are fed to it from the laser radiation source 1 corresponding to the center frequency of its bandwidth for a given value of the parameter of the physical field. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are not the same, and the difference between the average frequencies of the first and third pairs is equal to the half-width of the passband of the optical sensor 3. In this case, the device parameters that are optimal in sensitivity and steepness of the measurement conversion are provided.

For a given (calibration) parameter of the physical field, the average frequency of the generated four signals will correspond to the detuning “0”, the average frequency of the first pair will be located with the detuning “-1”, the average frequency of the second pair will be mismatching “+1”. Their amplitudes will be equal, and the difference frequencies of the pairs will not be the same and equal for the first pair Ω1, and the second - Ω2 (figure 2). With the frequency shift of the passband of the optical sensor 3, depending on the changes in the physical field parameter, the position of the components of the generated signal pair relative to the passband will change, the amplitudes of the envelopes of the beats of the pairs will change, and the differences between the amplitudes of the envelopes of the beats of the first and second pairs passing through the optical sensor 3 in accordance with the presented dependence U _Ω1 -U _Ω2 ( _figure 2).

With the known dependence of the magnitude of the detuning of the passband of the optical sensor on the value of the parameter of the applied physical field (for example, for the Bragg fiber optic array, typical values of the detuning depending on the temperature are ~ 0.01 nm / K and on the relative fiber elongation ~ 10 ³ ΔL / L (nm ) (S.A. Vasiliev, O.I. Medvedkov, I.G. Korolev, E.M. Dianov, Photoinduced fiber gratings of refractive index and their applications, Photon Express-Nauka, 6, pp. 163-183, 2004 )) determine the value of the parameter of the applied physical field.

Thus, from the obtained difference between the amplitudes of the envelopes of the beats of the first and second pairs U _Ω1 -U _Ω2 passing through the optical sensor 3, in accordance with the presented dependence, the generalized detuning of the passband of the optical sensor 3 is determined and then the dependence of the generalized detuning of the passband of the optical sensor 3 on parameter of the applied physical field in the controller determining the parameter of the physical field 10 uniquely determine the parameter of the measured physical field.

The device can be implemented using various types of optical sensors 3, the specific form of which is determined depending on the tasks to be solved and the nature of the applied physical field. It can be a Bragg fiber grating or a Fabry-Perot interferometer or a thin-film filter. Dependencies are given under the assumption that the optical sensor has a triangular spectral characteristic, for example, a triangular Bragg grating. When using the spectral characteristics of optical sensors with a non-linear shape, the form of the resulting characteristic U _Ω1 -U _Ω2 will also have non-linear sections, but this will not affect the unambiguity of determining the physical parameter.

A device for measuring the parameters of physical fields can be implemented on the following elements, designed to operate at a wavelength of 1300 nm (other wavelengths are possible):

- laser radiation source 1 - two two-frequency laser diodes IDL10S-1300 Research Institute "Polyus" or laser diodes DMPO131-22 LLC NPF "Dilaz", a single-frequency laser diode and modulators based on a Mach-Zehnder 500-x-13 interferometer Laser 2000;

- fiber-optic cables 2, 4 - reference cords or cables TELECOM-TEST of LLC Production and Trade Company SOKOL LLC;

- optical sensor 3 - Bragg fiber grating, Fabry-Perot interferometer, thin-film filters of IP NTsVO-Photonika LLC;

- photodetector 5 - high-speed fiber-optic InGaAs / InP microwave broadband PIN photodetectors (receiving modules) of NPF DiLaz, for example, DFDMSh-40-16;

- controller 10 - microprocessor controller based on chips from Atmel, Microchip, etc .;

- selective filters 6-7 - Agilent;

- amplitude detectors 8-9 - dual amplitude detector AD8302-a (Analog Devices).

To build a sensor of parameters of physical fields, all of these blocks of generation, reception and processing of signals can be performed on a single chip or in integral design.

Compared with existing devices for measuring the parameters of physical fields using optical sensors, including sensors in integrated and fiber-optic versions, in which there is a dependence of the frequency shift of their spectral characteristics depending on the parameters of the applied physical fields, the proposed device with four-frequency sounding of the optical sensor and measuring the parameter of the physical field according to the difference between the amplitudes of the envelopes of the beats of the pairs of signals transmitted through the optical sensors k does not require:

firstly, the use of complex expensive optical systems for determining the spectral bias or the allocation of individual spectral components for their further comparison, which significantly reduces the cost of the devices;

secondly, applications for the analysis of optical signals of selective elements, which have their own dependence on changes in the measured physical fields.

Tests of the experimental device for measuring the parameters of physical fields were carried out on optical sensors made on Bragg fiber gratings manufactured at Inversion-Fiber LLC (Novosibirsk), calibrated on optical spectrum analyzers EXFO in the laboratory of KNITU-KAI named after A.N. Tupolev (Kazan), and showed that the use of a four-frequency sensing device of an optical sensor with a parameter measurement by the difference in the amplitudes of the envelopes of the beats of the signal pairs made it possible to achieve a temperature measurement error of 0.01 ° C in the range of ± 60 ° C. In this case, the measurement error was determined mainly by the error of the ADC of the temperature determination controller.

All this allows us to talk about achieving a solution to the technical problem - simplification, increasing accuracy and cheaper devices for measuring the parameters of physical fields.

Claims (4)

1. A device for measuring the parameters of physical fields, containing a series-connected laser source, a first fiber optic cable, an optical sensor, a second fiber optic cable and a photodetector, as well as a controller for determining a parameter of the physical field, characterized in that two selective filter and two amplitude detectors, while the laser source is made four-frequency, and the output of the photodetector through the first selective filter and the first amplitude detector under It is connected to the first input of the controller determining the parameter of the physical field and in parallel through the second selective filter and the second amplitude detector to its second input. 2. The device according to claim 1, characterized in that the optical sensor is based on a Bragg fiber grating. 3. The device according to claim 1, characterized in that the optical sensor is based on a Fabry-Perot interferometer. 4. The device according to claim 1, characterized in that the optical sensor is based on a thin-film filter.