RU2491511C2 - Method to measure parameters of physical fields - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: pair of signals of close amplitude is generated with average frequency corresponding to the certain frequency of optical sensor pass band at the specified value of the physical field parameters, and a difference frequency, which is quite narrow so that both signals get into the specified pass band. The generated pair of signals is sent to the optical sensor along the first optical medium. Pairs of signals sent via an optical sensor and generated ones are received, being transmitted accordingly in the second and third optical media, and the physical field parameter is determined. The physical field parameter is determined, measuring difference of phases between the envelope of generated pair signal beats and the envelope of signal beats of the pair transmitted via the optical sensor.

EFFECT: higher accuracy of measurement due to elimination of sources of measurement errors.

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Description

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

A known method of measuring the parameters of physical fields (see electronic resource www.forc-photonics.ru, "Fiber Optic Probe Thermometer", file termometr_final.pdf, LLC IP NTsVO-Photonika, 10/14/2008), which consists in the fact that generate broadband radiation, transmit it to the optical sensor through the optical medium, receive the radiation converted in the sensor, 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 method is the need to use a complex expensive unit for spectral analysis of received radiation and a photodetector for recording spectral bias, as a rule, these are optical spectrum analyzers. Separate optoelectronic 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 invention is a method (see US Patent No. 7463832 B2 "Method and system for compensating thermal displacement for optical networks", 398/196 MPK8 H04J 13/02, 08/09/2005), which generate pairs of signals of a predetermined close amplitude with an average frequency corresponding to a certain frequency bandwidth of the optical sensor for 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 of signals to the optical sensor via the first optical medium, a pair of signals passed through it is transmitted through the second optical medium and the physical field parameter is determined by comparing the amplitude differences 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 a pair transmitted to the receiver via a third optical medium.

The disadvantage of the prototype method is the need to use a complex optical system for separate spectral reception of the individual components of the 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 the practical implementation of the method of measuring the parameters of physical fields.

The technical problem to be solved is in a method for measuring the parameters of physical fields, which consists in generating a pair of signals of close amplitude with an average frequency corresponding to a certain frequency of the passband of the optical sensor at a given value of the physical field parameter, and a difference frequency narrow enough so that both signals hit the specified bandwidth, transmit the generated pair of signals to the optical sensor through the first optical medium, take the passed through the optical sensor and the generated pair of signals transmitted respectively through the second and third optical media, and determine the parameter of the physical field, it is achieved by determining the parameter of the physical field by measuring the phase difference between the envelope of the beat of the signals of the generated pair and the envelope of the beat of the signals of the pair passed through the optical sensor.

In some cases, a pair of signals of the same amplitude is generated with an average frequency corresponding to the center frequency of the optical sensor passband at a given value of the physical field parameter and a difference frequency equal to half the width of the optical sensor passband.

Figure 1 shows a structural diagram of a device for implementing the method of measuring the parameters of physical fields.

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 that passed through the optical sensor on the generalized detuning of the passband 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 implementing the method of measuring the parameters of physical fields (FIGS. 1, 2) contains a serially connected dual-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, the second a photodetector 7 connected through a third fiber optic cable 8 to the second output of the optical splitter 2, and also a 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 various cases, the device can be performed using an optical sensor 4 based on a Bragg fiber grating, or a Fabry-Perot interferometer, or a thin-film filter. Typically, 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 two-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 implementation of the method.

To measure the parameters of physical fields using a two-frequency laser emitter 1, a pair of signals of close amplitude is generated with an average frequency corresponding to a certain frequency bandwidth of the optical sensor 4 at a given value of the physical field parameter, and a difference frequency narrow enough 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 envelope of the beats 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.

According to the obtained value and the phase difference dependencies in the controller 9 for determining the physical field dependence 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 mismatch of the passband 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 Olya.

Figure 2 shows the dependence of the phase difference between the envelope of the beats of the signals of the pair generated by the two-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 dual-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 values of the detuning 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 (calibration) parameter of the physical field, the average frequency of the generated signal pair will correspond to the detuning “0”, and the components of the pair will be located one with the detuning “-1”, the other with the detuning “1”. Their amplitudes will be equal, and the phase difference of the beat envelopes between the pairs of signals generated and transmitted through the optical sensor by 4 will be equal to zero (Fig. 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 detuning of the optical sensor passband on the value of the parameter of the applied physical field (for example, for the Bragg fiber optic array, typical detuning values 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 the 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.

A device for implementing the method of measuring the parameters of physical fields 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 implementation of the method to measure phase relations, equalization of phase delays during the propagation of signal pairs along fiber optic cables 3, 5, 8 can be achieved by using a third fiber optic cable 8 with a length equal to the sum of the lengths of the first 3 and second 5 fiber optic cables.

A device for implementing the method of measuring the parameters of physical fields can be created 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.

When implementing the method for constructing a sensor of parameters of physical fields, all of the indicated blocks for generating, receiving and processing signals can be performed on a single chip or in an integrated version.

Compared with existing methods 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 method of dual-frequency sensing of an optical sensor with measurement the parameter for the phase difference of the envelopes of the beats of the reference and measuring signals does not require:

firstly, the use of complex optical systems for determining the spectral displacement or separation 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 an experimental device for implementing the method of 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 ANDO optical spectrum analyzers in the same place, the calibration was confirmed on ANDO optical spectrum analyzers in the Povolzhsky laboratory State University of Telecommunications and Informatics (Samara), and showed that the use of a two-frequency sensing method of an optical sensor with measurement of pairs tra envelopes of the phase difference of the beats reference and measurement signals, allowed to reach a temperature measurement error 0,01 ° C in the range ± 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 - improving the accuracy of measurements, simplifying and cheapening devices for the practical implementation of the method of measuring the parameters of physical fields.

Claims (2)

1. A method of measuring the parameters of physical fields, which consists in generating a pair of signals of close amplitude with an average frequency corresponding to a certain frequency bandwidth of the optical sensor at a given value of the parameter of the physical field, and a difference frequency narrow enough for both signals to fall into the specified bandwidth, transmit the generated pair of signals to the optical sensor in the first optical medium, receive passed through the optical sensor and the generated pair of signals, transmitted respectively through the second and third optical media, and determine the parameter of the physical field, characterized in that the determination of the parameter of the physical field is made by measuring the phase difference between the envelope of the beat of the signals of the generated pair and the envelope of the beat of the signals of the pair passing through the optical sensor. 2. The method according to claim 1, characterized in that a pair of signals of the same amplitude is generated with an average frequency corresponding to the center frequency of the passband of the optical sensor at a given value of the physical field parameter and a difference frequency equal to the half-width of the passband of the optical sensor.

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