RU92180U1 - DEVICE FOR MEASURING PHYSICAL FIELD PARAMETERS - Google Patents

Abstract

1. A device for measuring the parameters of physical fields, containing a serially connected two-frequency laser emitter, an optical splitter, a first fiber optic cable, an optical sensor, a second fiber optic cable and a first photodetector, a second photodetector connected via a third fiber optic cable to a second output an optical splitter, as well as a controller for determining the parameter of the physical field, characterized in that a phase meter is introduced into it, while the outputs of the first and second photodetectors are connected respectively to the first and second inputs of the phase meter, and the output of the latter is connected to the input of the controller for determining the parameter of the physical field. ! 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. ! 5. The device according to claim 1, characterized in that the length of the third fiber optic cable is equal to the sum of the lengths of the first and second fiber optic cables.

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, a fiber optic cable, an optical sensor, a unit for spectral analysis of the received radiation and a photodetector unit connected to the input of the unit for determining the parameter of the physical field in which mathematical processing is performed spectral displacement, according to which, taking into account the calibration, the parameter of the physical field is determined, in this 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 appears 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 IPC 8 H04J 13/02, 08/09/2005), which contains a double-frequency laser connected in series an emitter, an optical splitter, a first optical fiber cable, an optical sensor, a second optical fiber cable and a first photodetector, a second photodetector connected through 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 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 is a device for measuring the parameters of physical fields, comprising a series-connected two-frequency laser emitter, an optical circulator, a first fiber optic cable, an optical sensor, a second fiber optic cable and a first photodetector, a second photodetector connected through a third fiber optic cable to the second output of the optical circulator, as well as the controller for determining the parameter of the physical field, is achieved by the fact that a phase meter is inserted into it, while the outputs of the first of the second and second photodetectors are connected respectively to the first and second inputs of the phase meter, and the output of the latter to the input of the controller determines the parameter of the physical field.

In some cases, the device may be implemented using an optical sensor based on a Bragg fiber grating.

In some cases, the device can be performed using an optical sensor based on a Fabry-Perot interferometer.

In some cases, the device may be implemented using an optical sensor based on a thin film filter.

In some cases, the device may be configured such that the length of the third fiber optic cable is equal to the sum of the lengths of the first and second fiber optic cables.

Figure 1 shows the structural diagram of the device.

Figure 2 shows the dependence of the phase difference between the envelope of the beats of the signals of the generated pair and the envelope of the beats of the signals of the pair passing through the optical sensor, from the generalized row bandwidth of the optical sensor for the case of applying to it a pair of signals of the same amplitude with an average frequency corresponding to the center frequency of its strip transmission at a given value of the parameter of the physical field, and a difference frequency equal to the half-width of the specified bandwidth.

A device for measuring the parameters of physical fields (Figs. 1, 2) contains a serially connected two-frequency laser emitter 1, an optical splitter 2, a first fiber optic cable 3, an optical sensor 4, a second fiber optic cable 5 and a first photodetector 6, a second photodetector 7 connected through the third fiber optic cable 8 to the second output of the optical splitter 2, as well as the controller 9 for determining the parameter of the physical field. A phase meter 10 is introduced into it, while the outputs of the first 6 and second 7 photodetectors are connected respectively to the first and second inputs of the phase meter 10, and the output of the phase meter 10 to the input of the controller 9 for determining the parameter of the physical field.

In some cases, the device may be implemented using an optical sensor 4 based on a Bragg fiber grating.

In some cases, the device can be performed using an optical sensor 4 based on a Fabry-Perot interferometer.

In some cases, the device may be implemented using an optical sensor 4 based on a thin film filter.

In some cases, the device may be configured such that the length of the third fiber optic cable 8 is equal to the sum of the lengths of the first 3 and second 5 fiber optic cables.

Figure 2 shows the dependence of the phase difference between the envelope of the beats of the signals of the pair generated by the dual-frequency laser emitter 1, and the envelope of the beats of the signals of the pair that passed through the optical sensor 4, on the generalized row bandwidth of the optical sensor 4 for the case when a pair of signals of the same amplitude the average frequency corresponding to the center frequency of its passband at a given value of the physical field parameter, and the difference frequency equal to the half width of the specified passband.

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

To measure the parameters of physical fields using a two-frequency laser emitter 1, a pair of signals of close amplitude with an average frequency corresponding to a certain frequency bandwidth of the optical sensor 4 is generated at a given (pre-set, calibration) value of the physical field parameter, and the difference frequency is narrow enough to so that both signals fall into the specified bandwidth. Then, the generated pair of signals is transmitted to the optical sensor 4 through the optical splitter 2 through the first optical medium, for which the first fiber-optic cable 3 is selected.

In the generated pair of signals passing through the optical sensor 4, 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, with the help of the first photodetector 6, a pair of signals passed through the optical sensor 4 is received, transmitted from it through the second optical medium, which is selected as the second fiber-optic cable 5. Using the second photodetector 7, the initial generated pair of signals is received, which is input to it through the second output of the optical splitter 2 and the third optical medium, which is selected as the third fiber optic cable 8. At the output of the photodetectors 7 and 6, signals corresponding to the beat envelope are generated the signals of the pair generated by the double-frequency laser radiation 1 and the envelope of the beats of the signals of the couple passed through the optical sensor 4. The difference between the phases of the phases of the envelope of the beats between the signals of the couple passed through the optical sensor 4 and the envelope of the beats between the signals of the couple generated by the two-frequency laser emitter 1 is produced in the phase meter 10.

Based on the value obtained and the controller’s determination of the physical field parameter 9 of the dependences of the phase difference between the beat envelope of the pair signals generated by the two-frequency laser emitter 1 and the beat envelope of the pair signals transmitted through the optical sensor 4 from the generalized bandwidth spacing of the optical sensor 4 (FIG. 2) and the dependence of the direction and magnitude of the frequency shift of the passband of the optical sensor 4 on the parameters of the physical field uniquely determine the measured parameter of the physical la.

Figure 2 shows the dependence of the phase difference between the envelope of the beats of the signals of the pair generated by the dual-frequency laser emitter 1, and the envelope of the beats of the signals of the pair that passed through the optical sensor 4, on the generalized detuning of the passband of the optical sensor 4. The dependence is constructed for the case of applying to the optical sensor 4 generated by a two-frequency laser emitter 1 pair of signals of the same amplitude with an average frequency corresponding to the center frequency of its passband for a given value of the parameter f field, and a difference frequency equal to half the width of the specified bandwidth. In this case, the device parameters that are optimal in sensitivity and steepness of the measurement conversion are provided.

In accordance with figure 2, the average generalized detuning of the passband of the optical sensor 4 is equal to 0 and corresponds to its center frequency and the average frequency generated by the two-frequency laser emitter 1 pair of signals. The detuning between the components of the generated signal pair is equal to 2 and corresponds to the half-width of the passband of the optical sensor 4. For other detuning values between the components of the generated signal pair, the phase difference values of the beat envelopes change, but the nature of the dependence does not change.

For a given (pre-established, calibration) parameter of the physical field, the average frequency of the generated signal pair will correspond to detuning 0, and the components of the pair will be located one with detuning - 1, the other with detuning 1. Their amplitudes will be equal, and the phase difference of the beat envelopes between the generated and passed through the optical sensor 4 pairs of signals will be equal to 0 (figure 2). With the frequency shift of the passband of the optical sensor 4 depending on changes in the physical field parameter, the position of the components of the generated signal pair relative to the passband will change and the phase difference of the beat envelope between the generated and transmitted through the optical sensor 4 signal pairs will change in accordance with the presented dependence.

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 phasemeter 10 information obtained on the phase difference between the beat envelope of the pair signals generated by the two-frequency laser emitter 1 and the beat envelope of the pair signals transmitted through the optical sensor 4, the generalized detuning of the passband of the optical sensor 4 is determined and then the dependence of the generalized detuning the passband of the optical sensor 4 from the parameter of the applied physical field in the controller 9 determines the parameter of the measured physical field.

The device can be implemented using various types of optical sensors 4, 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, a Fabry-Perot interferometer, or a thin-film filter.

Since it is essential for the device to measure phase relations, equalization of phase delays during the propagation of signal pairs through fiber optic cables 3, 5, 8 can be achieved by using a third fiber optic cable 8 in the device with a length equal to the sum of the lengths of the first 3 and second 5 fiber optical cables.

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:

- two-frequency laser emitter 1 - laser diode IDL10S-1300 Research Institute "Polyus";

- optical splitter 2 - optical splitter TELECOM-TEST 1 × 2 manufactured by LLC Production and Trade Company SOKOL;

- fiber-optic cables 3, 5, 8 - reference cords or cables TELECOM-TEST of the company "Production and Trade Company SOKOL";

- optical sensor 4 - Bragg fiber grating, Fabry-Perot interferometer, thin-film filters of IP NTsVO-Photonika LLC;

- photodetector 6, 7 - high-speed fiber-optic InGaAs / InP microwave broadband PIN photodetectors (receiving modules) of NPF DiLaz, for example, DFDMSh-40-16;

- controller 9 - microprocessor controller based on chips from Atmel, Microchip, etc .;

- phase meter 10 - microwave phase meter in the integrated performance of Booton, Vector.

To build a device for measuring the parameters of physical fields, all of these blocks of generation, reception and processing of signals can be performed on a single chip or in an 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 offset of their spectral characteristics depending on the parameters of the applied physical fields, the proposed device with dual-frequency sounding of an optical sensor and measuring the parameter of the physical field by the phase difference between the envelope of the beats of the reference pair of signals and the envelope of the beats of the measuring pa s signal 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;

thirdly, the use of amplitude analysis of measured values, which is subject to a significant influence of noise and interference of various nature.

Tests of the experimental device for measuring the parameters of physical fields were carried out on optical sensors made on Bragg fiber gratings made at the National Center for Optical Physics, IOF RAS (Moscow), calibrated on optical ANDO spectrum analyzers in the same place, calibration was confirmed on ANDO optical spectrum analyzers in the laboratory of the Volga State University of Telecommunications and computer science (Samara), and showed that the use of the method of two-frequency sounding of an optical sensor with the measurement of the parameter by the phase difference of the envelope The beating of the reference and measuring signals made it possible to achieve an error in measuring the temperature 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 solving the technical problem posed - cheaper, easier and more accurate devices for measuring the parameters of physical fields.

Claims (5)

1. A device for measuring the parameters of physical fields, containing a series-connected two-frequency laser emitter, an optical splitter, a first fiber optic cable, an optical sensor, a second fiber optic cable and a first photodetector, a second photodetector connected through a third fiber optic cable with a second output an optical splitter, as well as a controller for determining a parameter of a physical field, characterized in that a phase meter is inserted into it, while the outputs of the first and second photodetectors kov are connected respectively to the first and second inputs of the phase meter, and the output of the latter to the input of the controller determines the parameter of the physical field. 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. 5. The device according to claim 1, characterized in that the length of the third fiber optic cable is equal to the sum of the lengths of the first and second fiber optic cables.