Fiber-optic sensor system

FIELD: electro-optical engineering.

SUBSTANCE: fiber-optic sensor system can be used in physical value fiber-optic converters providing interference reading out of measured signal. Fiber-optic sensor system has optical radiation laser detector, interferometer sensor, fiber-optic splitter, photodetector and electric signal amplifier. Interferometer sensor is equipped with sensitive membrane. Fiber-optic splitter is made of single-mode optical fibers. Connection between fiber-optic splitter and interferometer sensor is based upon the following calculation: l=0,125λn±0,075λ, where l is distance from edge of optical fiber of second input of fiber-optic splitter to light-reflecting surface of sensor's membrane (mcm); λ is optical radiation wavelength, mcm; n is odd number within [1001-3001] interval.

EFFECT: simplified design; compactness; widened sensitivity frequency range.

4 cl, 1 tbl, 3 dwg

 

The invention relates to opto-electronic instrumentation and can be used in the construction of fiber-optic transducers of physical quantities, providing interference eat the measured signal. The most effective to use in the design of devices microtechnological performance, especially micro receiver sound signals (microphones, hydrophones, steel, phonendoscopes etc).

Known fiber optic sensor system containing a broadband radiation source, fiber light guide (SU), completed with the formation of the measurement and reference optical channels, the polarization sensor intermode interference, the photodetector connected to the processing unit and displaying information, the scanning deformer installed in the aircraft, and the control unit of the scanning deformers (EN 2036419, G 01 B 21/00, 1995). For use as a microphone fiber-optic sensor system contains a diaphragm sensing element on the inner surface of which a spiral is a fiber-optical light guide, one end of which is through a focusing lens connected to a source of monochromatic radiation, and the other photodetector (EN 2047944, H 04 R 23/00, 1995).

However, these structures are bulky and have low what setting because of reading information in the form of changes in the amplitude used the information signal.

Among the specialized fiber-optic sensor systems known designed for temperature measurement, contains, jointly executed on the basis of fiber-optic laser (OX), the excitation channels and the interference information retrieval, microresonator modulation of the radiation of the OX, the sensor and the processing unit and displaying information (EN 2110049, G 01 K 11/32, G 02 B 6/00, 1998). To increase the sensitivity, accuracy and stability of the system one end of the optical fiber, the OX is associated with modified autocollimator interposed between this end and the microcavity with the formation in the plane of the reflective surface of the microcavity light spot of a given size, and the second is the output (EN 2161783, G 01 K 11/32, 2001).

However, these technical solutions are complicated to manufacture and operate, as they require regular adjustment of the nodes of the microcavity and the collimator. In addition, they have a preferred area of use of the temperature measurement.

Also known fiber-optic sensor system for measuring displacements containing the optical radiation source, the interferometric sensor of micrometric movements, fiber optic splitter, made of single-mode optical fibers, sensors, equipped with a bandpass optical filter, the control device is istwo and the piezoelectric actuator, installed with the possibility of displacement of the interferometric sensor, where the output optical radiation source connected to the first input fiber optic splitter, a second input fiber optical splitter connected to the interferometric sensor for transmitting light from a source of optical radiation and reception of optical interference signal from the sensor, the output optical fiber coupler is connected to the photodetector, the output of the photodetector is connected to the input of the control device, and the output control device connected to the electrical input of the piezoelectric actuator (P.G. Davis, I.J. Busch, Maurer G.S. Fiber Optic Displacement Sensor. - Fourth Pacific Northwest Optic Sensor Workshop, May 6, 1998 SPIE VOL TBD Courtesy Optiphase, Inc.).

The disadvantage of this device is the complexity of the node displacement of the interferometric sensor and a narrow dynamic range (not more than 200 μm) measured the micrometric movements.

Closest to the claimed is a fiber-optic sensor system containing the optical radiation source with a coherence length 80÷120 μm, the interferometric sensor, equipped with a sensitive membrane, fiber optic splitter, made of single-mode optical fiber, a photodetector and amplifier electrical signal, where the output and the source of optical radiation connected to the first input fiber optic splitter, the second input optical fiber coupler is connected to the interferometric sensor for transmitting light from a source of optical radiation and reception of optical interference signal from the sensor, the output of the fiber optic splitter is connected with the optical input of the photodetector, and the output of the photodetector is connected to the amplifier input electrical signal. For locking the position of the working point fiber optic sensor system is also equipped with dual-channel interferometric Converter reference signal, and the amplifier is electrically connected with the inputs of the first and second channels interferometric transducer and optical interferometric output of the Converter is implemented with the formation of the optical feedback of the transmitter with interferometric sensor (US 5094534, G 01 B 9/02, 1992).

However, the prototype device has a narrow frequency range, sensitivity, lack of, in particular, to work as a microphone that is exacerbated by the inertia of the elements of the dual interferometric transducer. In addition, it is cumbersome and difficult to manufacture and operate, requires careful initial and periodic adjustment of optical channels.

The technical task proposed is the first device is a simplification and miniaturization design, as well as extending the frequency range of sensitivity.

The solution of the stated technical problem is that in the construction of fiber-optic sensor system containing a source of optical radiation, an interferometric sensor, equipped with a sensitive membrane, fiber optic splitter, made of single-mode optical fiber, a photodetector and amplifier electrical signal, where the output optical radiation source connected to the first input fiber optic splitter, a second input fiber optical splitter connected to the interferometric sensor for transmitting light from a source of optical radiation and reception of optical interference signal from the sensor, the output of the fiber optic splitter is connected with the optical input of the photodetector, and the output of the photodetector connected to the amplifier input electrical signal is introduced the following change: as a source of optical radiation used laser.

The use of laser in this design it is necessary to extend the range of "vidnosti" interference pattern due to the increase of the coherence length of the radiation (not less than 4 times in comparison with the prototype). This conclusion can be justified by analysis of the well-known formula

where lwhenthe coherence length of the radiation source microns;

l - distance from the end face of the optical fiber of the second input optical fiber coupler to the reflective surface of the membrane interferometric sensor (μm).

From inequality (1) we can conclude that

i.e. the "area of vidnosti" the more, the more the coherence length of the radiation source. The increase in the "zone of vidnosti" leads to expansion of the range of acceptable displacement sensitive membrane, i.e. no need to stabilize the position of the working point on the static characteristic of the system. This allows you to simplify the system by removing part of the design of the prototype circuit-locked loop. This option (claim 1 of the formula) hereinafter referred to as the minimum. When the technical implementation of the distance l set of terms definition of the interference pattern at the output of the photodetector.

The optimal value of the parameter l (variant according to claim 2 of the formula) is observed for the

where λ - wavelength optical radiation microns;

n is an odd number of experimentally established interval [1001÷3001].

Further adjustment of the operating point of the system is understood as a particular value of l.

Formula (3) is convenient for adjusting the position of the corresponding end of the optical fiber relative to the membrane using system precision positioning. It can also be used to verify the optimality of the configuration options according to claim 1.

The achieved increase in the "zone of vidnosti provides, if necessary, the system can receive audio signals, i.e. work as a microphone. In this case, it uses an amplifier of electric signals and membrane interferometric sensor which is sensitive in the audio frequency range (variant according to claim 3 of the formula). To work as part of the design of this microphone, it is advisable to use a sensor with a sensitivity of membrane not less than 0.1 nm/PA in this frequency range.

In the proposed system can be used in the laser of any of the structural design, for example, gas or solid. The most appropriate use of a semiconductor laser optical radiation source with an electric power from the current regulator, which allows miniaturizing design and to reduce its power consumption. This variant may further comprise a circuit precision control of the position of the working point with the control effect on the temperature of the laser on the static component of the feedback signal from the photodetector (4 formulas). This option is useful in terms of the effect on the sensor intense disturbances (temperature, pressure, VI is the radio, and others), causing the offset position of the working point of the system. As a thermoregulatory organ in the circuit precision control of the position of the working point, it is advisable to use a Peltier element (5 formulas), which gives the opportunity to operate in the heating mode of the laser and cooling.

The principle variations in claims 4 and 5 of the formula is based on the first use of the dependence of the emission wavelength of the semiconductor laser from the temperature of this source of optical radiation for adjusting the position of the working point on the static characteristic of the system.

Figure 1 shows the minimum version of the fiber-optic sensor system; figure 2 shows a case where the system by regulating the position of the working point; figure 3 presents the amplitude-frequency response of the microphone is made on the basis of the proposed fiber-optic sensor systems.

The table shows the values of the technical characteristics of samples minimum system option.

Fiber-optic sensor system (figure 1) contains a laser source 1 optical radiation, the interferometric sensor 2, equipped with a sensitive membrane 3, the fiber optic splitter 4, is made of single-mode optical fiber, the photodetector 5 and the amplifier 6 electrical signal. You are the od source 1 optical radiation connected to the first input fiber optic splitter 4, the second input optical fiber coupler 4 is connected to the interferometric sensor 2 is able to transmit light from the light source 1 to the optical radiation and reception of the optical interference signal from the sensor 2. The output optical fiber coupler 4 is connected with the optical input of the photodetector 5, and the output of the photodetector 5 is connected to the amplifier 6 electrical signal. Depending on the destination system to the output of amplifier 6 is connected a corresponding recording device 7 (oscilloscope, computer, indicator light, speaker and so on). The distance l from the output end of the optical fiber to the membrane 3 of the sensor 2 is installed on the interference pattern, or by using the apparatus in accordance with formulas (2) and (3).

Laser radiation from the source 1 through the coupler 4, enters the interferometric sensor 2. Part of this radiation is reflected from the output end of the optical fiber, and the other part of the light distance l, and reflected from the membrane 3 of the sensor 2, is fed in the reverse direction at the specified end of the same optical fiber. Due to the fact that the setting value l does not exceed 0,5lwhen, these light fluxes are added coherently, thus forming an interference pattern, which is output splitter 4 is supplied to fo detector 5, which is accepted by the amplifier 6 electrical signal and supplied from the output of the latter on the recording unit 7.

The test results are minimal variants of the target structures with sources of optical radiation at a wavelength of λ=1.55 and of 1.30 μm is presented in table 1. As can be seen from the table, the threshold sensitivity of the samples of fiber-optic sensor systems maximum when installing the end face of the optical fiber sensor 2 at the optimal distance from the membrane 3, defined by the formula (3), namely l=0,125λwhen n is an odd value of n in the range [1001÷3001]. In this case, the threshold sensitivity is 0,008÷0.01 nm at λ1.55 microns and 0.005÷0,006 nm at λ=1,30 mm. When the output over a specified range of variation n the sensitivity of the system decreases due to the loss of contrast of the interference pattern. For even values of n the system insensitive due to the ingress of the working point on the insensitive area cosine interference dependence of the output signal of the system from the l value.

In a variant of the microphone (p.3 formula) distinguish between static and dynamic characteristics of the fiber-optic sensor systems. The static characteristic is a steady-state value of the output signal of the photodetector depending on the position of the working point for missing and interference. Dynamic characteristic is formed as a result of actions taken by the sound signal and depends on the amplitude-frequency characteristics (AFC) of the membrane of the sensor. Figure 3 shows the experimentally captured response fiber-optic sensor systems with wavelength λ1.55 microns of the semiconductor laser 1 with a capacity of 2 mW and a sample of the membrane of the sensor 3 a sensitivity of 1.5 nm/PA. The frequency response of such a system in the audio frequency range is uniform. Its irregularity is less than 3 dB with an average value of the frequency response equal to 135 dB.

The best option system, equipped with a semiconductor laser source 1 optical radiation with electric power from the current regulator, further comprises circuit 8 precision adjusting the position of the working point with the control effect on the temperature of the laser on the static component of the feedback signal from the photodetector, comprising an automatic controller 9 with the Executive mechanism and the regulatory body 10 (figure 2, item 4 of the formula). The input of the regulator 9 is connected with the output of the photodetector 5 directly, as shown in figure 2, or via the amplifier 6, the output of the controller 9 is connected using the enclosed structure of the actuator with the expansion body 10 mounted with the possibility of changing the temperature of the laser 1. temperature change of the laser 1 leads to a change in wavelength λ its radiation relative to the nominal value to compensate for the deviation of the operating point under the action of external interference on the sensor 2.

As the expansion body 10 may be used corresponding to the heater, for example, made in the form of nichrome spiral. It is also possible inclusion of the element 10 in the circuit of generator current regulator feeding the laser 1. The most useful within the expansion body 10 to use the Peltier element (5 formulas). This gives the opportunity to operate in the heating mode and the cooling laser, which expands the range of control actions.

As explained by the description, examples and graphics application, the use of the proposed fiber-optic sensor systems in comparison with the prototype allows to simplify and miniaturizing design of the target system by single execution path interferometric measurements and exceptions bulky Electromechanical node-locked loop position of the working point. In addition, there is an extension of the frequency range sensitivity, as evidenced by the frequency response variant of the system as a microphone. Achieved the life of the system in terms of the interference due to the first sales compensation interference by changing the wavelength of the radiation source.

T is Henichesk result derived from these results is to reduce the cost of the system by simplifying its construction and alignment.

1. Fiber-optic sensor system containing a laser optical radiation source, the interferometric sensor, equipped with a sensitive membrane, fiber optic splitter, made of single-mode optical fiber, a photodetector and amplifier electrical signal in which the output optical radiation source connected to the first input fiber optic splitter, a second input fiber optical splitter connected to the interferometric sensor is able to transmit light from the optical radiation source to the interferometric sensor, and the output of the photodetector is connected to the amplifier an electrical signal, characterized in that it uses a laser source with high coherence, the output of the fiber optic splitter directly connected with the optical input of the photodetector, and the connection of fiber-optic splitter to the interferometric sensor is made of calculation

l=0,125λn±0,075λ,

where l is the distance from the end face of the optical fiber of the second input optical fiber coupler to the reflective surface of the membrane integration of parametricheskogo sensor (μm);

λ - wavelength optical radiation microns;

n is an odd number from the interval [1001-3001],

for simultaneous reception of the optical interference signal from the sensor and transmit this signal to the input of the photodetector.

2. Fiber optic sensor system according to claim 1, characterized in that it is an amplifier of electric signals and membrane interferometric sensor are made sensitive in the audio frequency range.

3. Fiber optic sensor system according to claim 2, characterized in that when used as a source of optical radiation of a semiconductor laser it further comprises a circuit precision control of the position of the working point with the control effect on the temperature of the laser on the static component of the feedback signal from the photodetector.

4. Fiber optic sensor system according to claim 3, characterized in that the contour precision adjusting the position of the working point as the expansion body is equipped with a Peltier element.



 

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