CN115427766A - Fabry-Perot sensor cavity length demodulation system and Fabry-Perot sensor cavity length demodulation method - Google Patents
Fabry-Perot sensor cavity length demodulation system and Fabry-Perot sensor cavity length demodulation method Download PDFInfo
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Abstract
A Fabry-Perot sensor cavity length demodulating system and a Fabry-Perot sensor cavity length demodulating method are provided, wherein the demodulating system comprises: a light source (1); a circulator (2) having a first port (21), a second port (22) and a third port (23), the circulator (2) being arranged to receive light emitted from the light source via the first port (21) and to transmit the light to the Fabry-Perot sensor (3) via the second port (22); a Fabry-Perot sensor (3) arranged to receive light from the second port (22), to reflect the light at the first and second planes of the Fabry-Perot sensor (3) respectively to cause multibeam interference, and to return the interference light to the second port (22) of the circulator (2) and to transmit from the second port (22) to the third port (23); a detector (4) arranged to receive the interfering light from the third port (23) and to form a curve of the intensity of the interfering light with respect to the cavity length of the fabry-perot sensor (3); a processor (5) arranged to receive the curve and to divide the curve into a integer wavelength part and an non-integer wavelength part, for the integer wavelength part the processor (5) calculating the number of integer wavelengths comprised by the integer wavelength part and further calculating a first cavity length variation, for the non-integer wavelength part the processor (5) calculating a second cavity length variation based on a function of the light intensity and the cavity length, calculating a total cavity length variation by adding the first cavity length variation and the second cavity length variation.
Description
The invention relates to a Fabry-Perot sensor cavity length demodulation system and a Fabry-Perot sensor cavity length demodulation method.
The fiber Fabry-Perot (F-P) sensor has the advantages of small volume, high sensitivity, good stability, electromagnetic interference resistance and the like, and is widely applied to the measurement fields of strain, temperature, pressure and the like. The fiber Fabry-Perot sensor senses the measured quantity through the change of the measurement cavity length, and the speed and the accuracy of cavity length demodulation directly influence the speed and the accuracy of measurement. Therefore, the fast and accurate demodulation of the cavity length of the fiber Fabry-Perot sensor is of great significance.
In the application of optical fiber sensing, a demodulation system is responsible for continuously sending optical signals to an optical fiber sensor and receiving returned optical signals carrying information to be measured, and the information required by people is extracted after photoelectric conversion, signal acquisition and signal conditioning. The research on the fabry-perot cavity sensor demodulation system is represented by FISO corporation in canada, and essens corporation in canada in the united states. The former two companies adopt non-scanning type related scanning technology, the Opsens company adopts white light polarization interference technology, the two technologies need to manufacture fine optical wedges and linear array CCDs, the cost is high, and the demodulation rate cannot be increased due to the need of acquiring spectral images, so that the two technologies are not suitable for measuring rapidly changing signals, such as the measurement of explosion pressure. The intensity demodulation method is the oldest and simplest method adopted by the optical fiber Fabry-Perot sensor, obtains cavity length information of the optical fiber Fabry-Perot sensor by measuring the change of output light intensity, and has the characteristics of low cost and high demodulation rate. In the experiment, a monochromatic light source is adopted, and a photoelectric detector is directly used for receiving reflected light. As the cavity length changes, the sensor output intensity changes. The relationship between the reflected light intensity and the cavity length is as follows:
wherein I R For reflected light intensity, L is the cavity length.
The cavity length is used as an abscissa, the reflected light intensity is used as an ordinate, and the reflected light intensity and the cavity length are in a sine relationship.
Disclosure of Invention
The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
Fig. 1 is a schematic diagram showing a fabry-perot sensor cavity length demodulation system according to a first embodiment of the present invention.
Fig. 2 shows a curve obtained by the fabry-perot sensor cavity length demodulation system according to the first embodiment of the present invention.
Fig. 3 is a schematic diagram showing a fabry-perot sensor cavity length demodulation system according to a second embodiment of the present invention.
Fig. 4a and 4b show a first curve and a second curve, respectively, obtained by a fabry-perot sensor cavity length demodulation system according to a second embodiment of the present invention.
Fig. 5 shows a third curve obtained by a fabry-perot sensor cavity length demodulation system according to a second embodiment of the invention.
Like elements in different figures are denoted by like reference numerals.
In order to make the objects, technical solutions and advantages of the technical solutions of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of specific embodiments of the present invention. Like reference symbols in the various drawings indicate like elements. It should be noted that the described embodiments are only some embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without inventive step, are within the scope of protection of the invention.
Unless defined otherwise, technical or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the description and claims of the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not necessarily denote a limitation of quantity. The word "comprising" or "comprises", and the like, means that the element or item preceding the word comprises the element or item listed after the word and its equivalent, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.
Hereinafter, a Fabry-Perot sensor cavity length demodulation system of the present invention will be described in detail with reference to the accompanying drawings.
< first embodiment >
Fig. 1 is a schematic diagram showing a fabry-perot sensor cavity length demodulation system according to a first embodiment of the present invention. Fig. 2 shows a curve obtained by the fabry-perot sensor cavity length demodulation system according to the first embodiment of the present invention.
As shown in fig. 1, the fabry-perot sensor cavity length demodulation system includes a light source 1 (e.g., a semiconductor laser) that emits light having a wavelength preferably in the range of 640nm to 660nm, more preferably 650nm. The light emitted by the light source 1 is transmitted to the first port 21 of the circulator 2, which also has a second port 22 and a third port 23, and the light is transmitted from the first port 21 to the second port 22 and further to the fabry perot sensor 3. The Fabry-Perot sensor is provided with a cavity and a diaphragm, light received by the Fabry-Perot sensor is reflected at the bottom of the cavity and the diaphragm respectively, and therefore the bottom of the cavity and the diaphragm are called a first plane and a second plane respectively. At the Fabry-Perot sensor, light is reflected at the first plane and the second plane of the Fabry-Perot sensor respectively to generate multi-beam interference, and the interference light returns to the second port of the circulator and is further transmitted to the third port. The interfering light exiting the third port is transmitted to a detector 4 (e.g., a photodetector) which receives the interfering light and forms a plot of the intensity of the interfering light versus the cavity length of the fabry perot sensor, as shown in figure 2. The processor 5 receives the curve and divides the curve into a whole wavelength part and a non-whole wavelength part, for the whole wavelength part, the processor calculates the number of whole wavelengths included in the whole wavelength part and further calculates a first cavity length variation, for the non-whole wavelength part, the processor calculates a second cavity length variation based on a function of the light intensity and the cavity length, and calculates a total cavity length variation by adding the first cavity length variation and the second cavity length variation. For example, in fig. 2, the wavelength part from point a to point B is denoted as n, the first cavity length variation amount is n λ/2, the wavelength part from point B to point C is not n, the second cavity length variation amount is calculated based on a function of the light intensity and the cavity length, and finally the first cavity length variation amount and the second cavity length variation amount are added to obtain the total cavity length variation amount. Methods for calculating the amount of change in the second cavity length based on a function of the light intensity and the cavity length are well known to those skilled in the art, for example, the cavity length is abscissa, the reflected light intensity is ordinate, and the reflected light intensity and the cavity length are in a sinusoidal relationship from which the cavity length change can be derived from the light intensity, where one light intensity corresponds to one cavity length.
A polarizer 6 may also be provided between the light source and the circulator to form linearly polarized light from the light source which is transmitted to the circulator, which in this case is a polarization-maintaining circulator.
The light source in the application emits 650nm wavelength light, and under the condition that the cavity length changes the same, the short wavelength light source forms more interference fringes, so that the demodulation is more accurate. In addition, the principle of linearly polarized light interference superposition is adopted, incoherent superposition between unpolarized light is avoided, and the contrast of interference fringes is improved, so that the sensitivity of the optical fiber F-P demodulation system is improved. The Fabry-Perot sensor used in the present application is preferably large in cavity diameter and thin in membrane, so that the Fabry-Perot cavity has high sensitivity as can be seen from the Fabry-Perot cavity sensitivity calculation formula (1).
Wherein S is the sensitivity, a is the membrane diameter, mu is the Poisson 'S ratio, E is the Young' S modulus, and h is the membrane.
< second embodiment >
Fig. 3 is a schematic diagram showing a fabry-perot sensor cavity length demodulation system according to a second embodiment of the present invention. Fig. 4a and 4b show a first curve S1 and a second curve S2, respectively, obtained by a fabry-perot sensor cavity length demodulation system according to a second embodiment of the invention. Fig. 5 shows a third curve S3 obtained by the fabry-perot sensor cavity length demodulation system according to the second embodiment of the present invention.
The second embodiment differs from the first embodiment in that a quarter-wave plate 7 is arranged between the polarizer 6 and the polarization maintaining circulator 2, a polarization splitting prism 8 is arranged downstream of the third port 23 of the polarization maintaining circulator, and the detectors comprise a first detector 41 and a second detector 42. Light emitted by the light source 1 passes through the polarizer to form linearly polarized light. The direction of the polarizer and the fast and slow axes of the quarter-wave plate form an included angle of 45 degrees, so that linearly polarized light can be changed into circularly polarized light after passing through the quarter-wave plate. The circularly polarized light enters the Fabry-Perot sensor through the polarization-maintaining circulator, and multi-beam interference occurs between two parallel surfaces of the Fabry-Perot sensor. The interference light is transmitted to the polarization beam splitter prism 8 through the third port of the polarization maintaining circulator, and the circularly polarized light is split into two beams of linearly polarized light, namely a first light beam L1 and a second light beam L2, through the polarization beam splitter prism. The first and second beams have a phase difference of pi/2, are received by the first and second detectors, respectively, to form first and second curves of light intensity versus cavity length, and the first curve of light intensity versus cavity length formed by the first beam is proportional to sin (wt + phi 1), as shown in fig. 4a, and the second curve of light intensity versus cavity length formed by the second beam is proportional to cos (wt + phi 1), as shown in fig. 4 b. The first and second curves are input to the processor 5 and divided by the processor to obtain a third curve proportional to tan (wt + φ 1), as shown in FIG. 5. The third curve is steeper than the first curve and the second curve, which is beneficial to improving the demodulation accuracy.
Next, the processor divides the third curve into a whole wavelength portion and a non-whole wavelength portion, for the whole wavelength portion, the processor calculates the number of whole wavelengths (for example, 19 in fig. 5) included in the whole wavelength portion, and further calculates a first cavity length variation, for the non-whole wavelength portion (point a to point B and point C to point D), the processor calculates a second cavity length variation based on a function of the light intensity and the cavity length, and calculates a total cavity length variation by adding the first cavity length variation and the second cavity length variation.
The operational steps of the Fabry-Perot sensor cavity length demodulation method according to the invention are as follows: directing light from a light source to a circulator having a first port, a second port, and a third port, the light entering the circulator from the first port and being transmitted to a Fabry-Perot sensor via the second port; reflecting the light at the first plane and the second plane of the Fabry-Perot sensor respectively to generate multi-beam interference to form interference light, and returning the interference light to the second port of the circulator and transmitting the interference light from the second port to the third port; receiving the interference light from the third port of the circulator by using a detector to form a curve of the light intensity of the interference light relative to the cavity length of the Fabry-Perot sensor; and receiving the curve by using a processor, dividing the curve into a whole wavelength part and a non-whole wavelength part, calculating the whole wavelength quantity contained in the whole wavelength part by the processor for the whole wavelength part, further calculating a first cavity length variation, calculating a second cavity length variation for the non-whole wavelength part based on a function of the light intensity and the cavity length, and calculating the total cavity length variation by adding the first cavity length variation and the second cavity length variation.
Additionally, the demodulation method further comprises the steps of arranging a polarizer between the light source and the circulator, arranging a quarter-wave plate between the polarizer and the polarization-maintaining circulator, and arranging a polarization splitting prism downstream of the third port 23 of the polarization-maintaining circulator. In the case of a polarizer, the circulator is a polarization-maintaining circulator. And the detectors are arranged as a first detector and a second detector to receive the first light beam and the second light beam split by the polarization splitting prism, respectively.
The method divides a curve of light intensity relative to cavity length into an integer wave part and a non-integer wave part, calculates the number of the whole wavelengths in the integer wave part, obtains a first cavity length variation, and calculates a second cavity length variation in the non-integer wave part. Therefore, the demodulation speed is ensured, the demodulation precision is improved, and the high-speed and accurate demodulation of the Fabry-Perot sensor is realized.
While the best modes for carrying out the various aspects of the present teachings have been described in detail, those familiar with the art to which this invention relates will recognize various alternative modifications and changes may be made to the specific embodiments described above, and various combinations of features and structures described herein may be made without departing from the spirit and scope of the invention.
Claims (14)
- A fabry-perot sensor cavity length demodulation system, the demodulation system comprising:a light source;a circulator having a first port, a second port, and a third port, the circulator arranged to receive light emitted from the light source via the first port and transmit the light to the fabry-perot sensor via the second port;a Fabry-Perot sensor arranged to receive light from the second port, such that the light is reflected at the first and second planes of the Fabry-Perot sensor, respectively, to cause multi-beam interference to occur, and to return the interference light to the second port of the circulator and transmit from the second port to a third port;a detector arranged to receive the interfering light from the third port, forming a curve of light intensity of the interfering light relative to a cavity length of the fabry-perot sensor;a processor arranged to receive the curve and to divide the curve into a integer wavelength part, for which the processor calculates the number of integer wavelengths comprised in the integer wavelength part and further calculates a first cavity length variation, and a non-integer wavelength part, for which the processor calculates a second cavity length variation based on a function of the light intensity and the cavity length, the total cavity length variation being calculated by adding the first cavity length variation and the second cavity length variation.
- The demodulation system of claim 1 wherein said demodulation system further comprises:a polarizer arranged such that it receives light from the light source, forms linearly polarized light, and transmits the linearly polarized light to the circulator, the circulator being a polarization-preserving circulator.
- The demodulation system of claim 2 wherein said demodulation system further comprises:a quarter wave plate arranged to receive the linearly polarized light from the polarizer, convert the linearly polarized light to circularly polarized light, and transmit the circularly polarized light to the polarization maintaining circulator.
- The demodulation system of claim 3 wherein said demodulation system further comprises:a polarization splitting prism arranged to receive the interference light from the third port, split the interference light into a first beam and a second beam,wherein the detector comprises a first detector and a second detector arranged to receive the first light beam and the second light beam, respectively, and to form a first curve of the first light beam and a second curve of the second light beam,wherein the processor receives the first curve and the second curve, and divides the first curve and the second curve to obtain a third curve,the processor divides the third curve into a whole wavelength part and a non-whole wavelength part, for the whole wavelength part, the processor calculates the whole wavelength quantity contained in the whole wavelength part and further calculates a first cavity length variation, for the non-whole wavelength part, the processor calculates a second cavity length variation based on a function of the light intensity and the cavity length, and the total cavity length variation is calculated by adding the first cavity length variation and the second cavity length variation.
- The demodulation system of claim 4 wherein said first curve is a sine curve, said second curve is a cosine curve, and said third curve is a tangent curve.
- The demodulation system of claim 1 wherein the light source emits light having a wavelength in the range of 640nm to 660 nm.
- The demodulation system of claim 6 wherein the light source emits light having a wavelength of 650nm.
- A Fabry-Perot sensor cavity length demodulation method is characterized by comprising the following steps:directing light from a light source to a circulator, the circulator having a first port, a second port, and a third port, the light entering the circulator from the first port and being transmitted to a fabry-perot sensor via the second port;reflecting the light at the first plane and the second plane of the Fabry-Perot sensor respectively to generate multi-beam interference to form interference light, and returning the interference light to the second port of the circulator and transmitting the interference light from the second port to the third port;receiving the interference light from the third port of the circulator by using a detector to form a curve of the light intensity of the interference light relative to the cavity length of the Fabry-Perot sensor;and receiving the curve by using a processor, dividing the curve into a whole wavelength part and a non-whole wavelength part, calculating the whole wavelength quantity contained in the whole wavelength part by the processor for the whole wavelength part, further calculating a first cavity length variation, calculating a second cavity length variation for the non-whole wavelength part based on a function of the light intensity and the cavity length, and calculating the total cavity length variation by adding the first cavity length variation and the second cavity length variation.
- The demodulation method according to claim 8, wherein the demodulation method further comprises: the polarizer is arranged between the light source and the circulator, receives light from the light source, forms linearly polarized light and transmits the linearly polarized light to the circulator, and the circulator is a polarization-maintaining circulator.
- The demodulation method of claim 9 further comprising disposing a quarter wave plate between the polarizer and the polarization maintaining circulator, receiving the linearly polarized light from the polarizer, configured to convert the linearly polarized light into circularly polarized light, and transmitting the circularly polarized light to the polarization maintaining circulator.
- The demodulating method according to claim 10, further comprising disposing a polarization splitting prism downstream of the third port of the polarization maintaining circulator, which receives the interference light from the third port of the polarization maintaining circulator, and splits the interference light into the first light beam and the second light beam;wherein the detector comprises a first detector and a second detector for receiving the first light beam and the second light beam, respectively, and forming a first curve of the first light beam and a second curve of the second light beam,wherein the processor is used for receiving the first curve and the second curve and dividing the first curve and the second curve to obtain a third curve,the third curve is divided into a whole wavelength part and a non-whole wavelength part by the processor, for the whole wavelength part, the processor calculates the whole wavelength quantity contained in the whole wavelength part and further calculates a first cavity length variation, for the non-whole wavelength part, the processor calculates a second cavity length variation based on a function of the light intensity and the cavity length, and the total cavity length variation is calculated by adding the first cavity length variation and the second cavity length variation.
- The demodulation method of claim 11 wherein the first curve is a sine curve, the second curve is a cosine curve, and the third curve is a tangent curve.
- The demodulation method of claim 8 wherein the light source emits light having a wavelength in the range of 640nm to 660 nm.
- The demodulation method of claim 13 wherein the light source emits light having a wavelength of 650nm.
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| CN115931022B (en) * | 2023-01-04 | 2023-05-23 | 北京佰为深科技发展有限公司 | Demodulation system of optical fiber Fabry-Perot sensor |
| CN117130006B (en) * | 2023-08-24 | 2024-05-03 | 光维(广东)科技有限公司 | Automatic aliasing elimination double-optical comb ranging device and method |
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| CN102519498B (en) * | 2011-12-07 | 2014-06-04 | 天津大学 | Low coherence interference demodulation method based on any extreme value |
| CN102607612B (en) * | 2012-03-22 | 2014-12-17 | 天津大学 | Low-coherence interference demodulation method based on monochrome frequency absolute phase |
| CN103697923A (en) * | 2013-12-20 | 2014-04-02 | 北京航空航天大学 | Method for demodulating extrinsic fiber Fabry-Perot interferometer cavity length |
| CN104215368A (en) * | 2014-09-15 | 2014-12-17 | 江苏昂德光电科技有限公司 | F-P cavity optical fiber pressure sensing device and demodulation method thereof |
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