CN110608761A - Optical fiber interference device and method capable of eliminating associated amplitude modulation - Google Patents
Optical fiber interference device and method capable of eliminating associated amplitude modulation Download PDFInfo
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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- G01D5/35322—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using interferometer with one loop with several directions of circulation of the light, e.g. Sagnac interferometer
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Abstract
The invention relates to an optical fiber interference device and a method capable of eliminating concomitant amplitude modulation, which comprises an optical fiber interferometer, wherein the optical fiber interferometer comprises a laser and a first coupler, the laser can transmit signals to the first coupler, the first coupler is connected with a probe part, it is characterized in that the output end of the probe part and the first coupler are respectively connected with a first mixer and a second mixer through a photoelectric detection piece, the first mixer and the second mixer are connected with a third mixer and a laser, the laser can output signals to the first mixer and the second mixer, the first mixer and the second mixer can output signals to the third mixer, the third mixer is connected with a controller, the photoelectric detection piece is also connected with the controller, and can convert optical signals output by the first coupler and the probe part into electric signals and transmit the electric signals to the controller.
Description
Technical Field
The invention relates to the technical field of optical fiber interferometers, in particular to an optical fiber interference device and method capable of eliminating associated amplitude modulation.
Background
The interference type optical fiber sensor utilizes light to perform light interference in an optical fiber, measures phase change of the interference light by utilizing an interference phenomenon of the light, and indirectly measures physical quantity including vibration, stress, displacement, speed and the like by measuring the phase change of the interference light. Typical applications of such fiber optic sensors include fiber optic gyroscopes, fiber optic vibration detectors, fiber optic hydrophones, fiber optic levels, fiber optic seismometers, fiber optic strain gauges, and the like. The optical fiber gyroscope can be applied to monitoring the flight state of a rocket, the running state of a satellite and the like; the optical fiber vibration detector can be applied to perimeter security protection and the like, the optical fiber seismometer can monitor large-amplitude signals such as earthquake, nuclear explosion and the like, and Zumberge and the like indicate that the dynamic range is about 180dB 1 kHz; the optical fiber hydrophone is mainly used for monitoring blind areas which cannot be detected by an underwater invisible target and a radar, and compared with the traditional hydrophone, the optical fiber hydrophone array has the characteristics of good directivity, large working bandwidth and the like; the optical fiber level meter is mainly applied to detecting the structural health of bridges, buildings and wind driven generators; the optical fiber strain gauge can measure ultra-low frequency physical processes, such as tide, and the working frequency band of the optical fiber strain gauge can reach 0.001Hz at the lowest. For the phase change in the optical path to be solved by a specific algorithm, a common phase demodulation algorithm can be divided into: active detection, passive detection, heterodyne detection, homodyne detection, and the like. The Phase Generation Carrier (PGC) algorithm in the active homodyne method has the characteristics of simple structure and high resolution, and is widely applied to sensors such as an optical fiber seismometer, an optical fiber hydrophone array and the like (CN200810117296. X). However, the fluctuation of light intensity caused by the unstable power of the laser injected by the high-frequency carrier alternating current in the internal modulation process is called as the associated amplitude modulation effect.
The inventor finds that, in the practical application process, the collection positions of the two detection signals on the optical path may be at a distance of more than ten roads or hundreds of kilometers, and at this time, the traditional method for compensating the associated amplitude modulation effect can cause the suppression signal distortion of the high-frequency direct current light intensity part, thereby causing the signal regulation distortion.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides the optical fiber interference device capable of eliminating the accompanying amplitude modulation, solves the problem of signal distortion inhibition of the high-frequency direct current light intensity part caused by different signal acquisition positions, and improves the stability and the practicability of the optical fiber interference device.
In order to achieve the purpose, the invention adopts the following technical scheme:
an optical fiber interference device capable of eliminating associated amplitude modulation comprises an optical fiber interferometer, wherein the optical fiber interferometer comprises a laser and a first coupler, the laser can transmit signals to the first coupler, the first coupler is connected with a probe part, an output end of the probe part and the first coupler are respectively connected with a first mixer and a second mixer through a photoelectric detection piece, the first mixer and the second mixer are connected with a third mixer and the laser, the laser can output signals to the first mixer and the second mixer, the first mixer and the second mixer can output signals to the third mixer, the third mixer is connected with a controller, the photoelectric detection piece is further connected with the controller, and optical signals output by the first coupler and the probe part can be converted into electric signals to be transmitted to the controller.
Furthermore, the controller is connected with the laser and can control the laser to send out a set signal.
Furthermore, the probe part comprises a second coupler and a third coupler, the second coupler and the third coupler are connected with two ends of the first interference arm and two ends of the second interference arm, the second interference arm is provided with a filtering piece, and the third coupler is connected with the photoelectric detection piece.
Furthermore, probe portion passes through the optical circulator and is connected with first coupler, the optical circulator is connected with the second photoelectric detector, probe portion includes the fourth coupler of being connected with the optical circulator, the fourth coupler is connected with the one end of third interference arm and fourth interference arm, and the other end that arm and fourth interference arm are interfered to the third is connected with first speculum and second mirror respectively, is provided with filtering member on the fourth interference arm, and first speculum and second mirror can transmit the light signal reflection for the optical circulator, the optical circulator is connected with photoelectric detection spare, can transmit the light signal reflection for photoelectric detection spare.
Furthermore, the photoelectric detection piece comprises a first photoelectric detector and a second photoelectric detector, the input end of the first photoelectric detector is connected with the first coupler, the output end of the first photoelectric detector is connected with the first frequency mixer and the controller, the input end of the second photoelectric detector is connected with the output end of the probe part, and the output end of the second photoelectric detector is connected with the second frequency mixer and the controller.
Further, the filtering element is a passive optical fiber filter or an active optical switch.
Furthermore, the probe part comprises a fifth coupler and a sixth coupler, a fifth interference arm and a sixth interference arm are connected between the fifth coupler and the sixth coupler, and the sixth interference arm is provided with a seventh coupler.
Furthermore, the photoelectric detector comprises a third photoelectric detector, a fourth photoelectric detector and a fifth photoelectric detector, the input end of the third photoelectric detector is connected with the first coupler, the output end of the third photoelectric detector is connected with the laser and the first mixer, the input end of the fourth photoelectric detector is connected with the seventh coupler, the output end of the fourth photoelectric detector is connected with the second mixer, the input end of the fifth photoelectric detector is connected with the sixth coupler, and the output end of the fifth photoelectric detector is connected with the controller.
The invention also discloses a working method of the optical fiber interference device capable of eliminating the associated amplitude modulation, wherein a laser, a first coupler and a photoelectric detection piece form a first light path, and the laser, the first coupler, a probe head part and the photoelectric detection piece form a second light path;
the laser sends a distance measurement modulation signal, the distance measurement modulation signal enters a first mixer through a first light path, the first mixer receives and mixes a signal of the laser and a signal of the first light path to obtain a first difference frequency signal, the second mixer receives and mixes a signal of the laser and a signal of a second light path to obtain a second difference frequency signal, the first difference frequency signal and the second difference frequency signal are transmitted to a third mixer to be mixed to obtain a difference frequency signal of an optical path difference delta L between the first light path and the second light path and transmitted to a controller, and the controller obtains a phase difference when the signals of the two light paths reach a photoelectric detection piece according to the difference frequency signal of the optical path difference
The laser emits optical signals, the controller receives the output optical signals of the first optical path and the second optical path through the photoelectric detection piece, and the obtained phase difference is obtainedIn the optical signal output by the photoelectric detection element brought into the first optical path, the data of the optical signal obtained by detecting the photoelectric detection element of the second optical path is divided by the data of the optical signal output by the photoelectric detection element of the first optical path and brought into the phase difference, so as to obtain the data of the interference optical signal.
Further, the method for calculating the phase difference comprises the following steps:
wherein, CnFor transmission of light in optical fibresThe conveying speed; v (t) is the optical frequency.
The invention has the beneficial effects that:
the optical fiber interference device capable of eliminating the accompanying amplitude modulation is provided with a first mixer, a second mixer and a third mixer, can obtain the optical path difference between a first optical path and a second optical path by utilizing a modulation signal output by a laser so as to obtain the phase difference of output signals of the two optical paths, when the laser sends out an optical signal, the acquired phase difference is brought into the optical signal output by the first optical path, then the optical signal data brought into the phase difference by the first optical path is divided by the output optical signal data of the second optical path so as to obtain interference data, the problem of signal distortion inhibition of a high-frequency direct current light intensity part caused by the phase difference of direct current light intensity caused by different signal acquisition positions is solved, the problem of distortion elimination caused by the accompanying amplitude modulation generated by the optical fiber interferometer in long-distance practical application is solved, and the phase difference caused by the different signal acquisition positions is measured, the normal work of the optical fiber interferometer in long-distance application is realized, and the stability and the practicability of the optical fiber interferometer are improved.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a schematic view of the overall structure of embodiment 1 of the present invention;
FIG. 2 is a schematic view of the overall structure of embodiment 2 of the present invention;
FIG. 3 is a schematic view of the overall structure of embodiment 3 of the present invention;
the optical fiber laser comprises a laser 1, a first coupler 2, a second coupler 3, a second coupler 4, a third coupler 5, a first interference arm 6, a second interference arm 7, a first optical fiber filter 8, a first photoelectric detector 9, a second photoelectric detector 10, a first mixer 11, a second mixer 12, a third mixer 13, a controller 14, an optical circulator 15, a fourth coupler 16, a third interference arm 17, a fourth interference arm 18, a first reflector 19, a second reflector 20, a second optical fiber filter 21, a fifth coupler 22, a sixth coupler 23, a fifth interference arm 24, a sixth interference arm 25, a seventh coupler 26, a fourth photoelectric detector 27, a third photoelectric detector 28 and a fifth photoelectric detector 28.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
For convenience of description, the words "up", "down", "left" and "right" in the present invention, if any, merely indicate correspondence with up, down, left and right directions of the drawings themselves, and do not limit the structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention.
As described in the background art, the present application provides an optical fiber interference device capable of eliminating the accompanying amplitude modulation, which is applied to the situation where the collection positions are far apart, and is liable to cause the phase difference of the dc light intensity, thereby causing the distortion of the suppression signal of the high-frequency dc light intensity.
In example 1, which is an exemplary embodiment of the present application, as shown in fig. 1, a fiber interferometer capable of eliminating the accompanying amplitude modulation includes a fiber interferometer, the fiber interferometer employs a mach-zehnder interferometer, the fiber interferometer includes a laser 1, the laser employs a DFB laser, the DFB laser is connected to a first coupler 2 through an optical fiber, the first coupler is capable of splitting an optical signal output by the DFB laser, a 99: 1X2 coupler is employed as the first coupler, 99% of a light-transmitting port of the first coupler is connected to a probe head portion, the probe head portion includes a second coupler 3 and a third coupler 4, the second coupler is connected to 99% of a light-transmitting port of the first coupler, the second coupler employs a 50:50 1X2 coupler, two light-transmitting ports of which are respectively connected to one end of a first interference arm 5 and one end of a second interference arm 6, the other ends of the first interference arm and the second interference arm are connected with a third coupler, and the third coupler adopts a 50:50 1X2 coupler.
The second interference arm is connected with a filtering piece, the filtering piece adopts a passive first optical fiber filter 7, the optical fiber filter can prevent the chirp signals from passing through but can not prevent optical signals for interference from passing through, and if interference signals exist during ranging, the ranging problem can not be solved, so that the optical fiber filter is arranged, and the interference of the signals during ranging is avoided.
The first coupler and the third coupler are both connected with the photoelectric detection piece, the photoelectric detection piece comprises a first photoelectric detector 8 and a second photoelectric detector 9, 1% of light through ports of the first coupler are connected with the input end of the first photoelectric detector, and the third coupler is connected with the input end of the second photoelectric detector.
The first photoelectric detector can receive signals transmitted by the first coupler, and the second photoelectric detector can receive signals transmitted by the third coupler, convert the signals into electric signals and output the electric signals.
The output of the first photodetector is connected to a first mixer 10, which can transmit the electrical signal to the first mixer, and the output of the second photodetector is connected to a second mixer 11, which can transmit the electrical signal to the second mixer.
The first mixer and the second mixer are both connected with the DFB laser and can receive the linear frequency modulation signal sent by the DFB laser.
The first mixer and the second mixer are both connected with a third mixer 12, and the third mixer is connected with a controller 13 and can send a difference frequency signal to the controller.
The first photoelectric detector and the second photoelectric detector are both connected with the controller and can transmit electric signals to the controller.
The controller is connected with the DFB laser and can control the DFB laser to send out a set chirp signal or an optical signal.
Example 2:
the embodiment discloses an optical fiber interference device capable of eliminating concomitant amplitude modulation, as shown in fig. 2, the optical fiber interferometer adopts a michelson interferometer, a probe part of the optical fiber interferometer is connected with 99% of a light-transmitting port of a first coupler through an optical circulator 14, the probe part comprises a fourth coupler 15, the fourth coupler adopts a 50:50 1X2 coupler, two light-transmitting ports of the fourth coupler are connected with one ends of a third interference arm 16 and a fourth interference arm 17, the other ends of the third interference arm and the fourth interference arm are respectively connected with a first reflector 18 and a second reflector 19, the fourth interference arm is provided with a passive second optical fiber filter 20, and the second optical fiber filter can prevent a chirp signal from passing through but cannot prevent an interference optical signal from passing through.
The optical circulator has three ports, one of which is connected to the 99% light-passing port of the first coupler, the other of which is connected to the light-passing port of the fourth coupler, the third port is used for receiving signals reflected by the first reflecting mirror and the second reflecting mirror and is connected to the second photodetector, and other structures are the same as those of embodiment 1, and are not described in detail herein.
Example 3
The embodiment discloses an optical fiber interference device capable of eliminating the satellite amplitude modulation, as shown in fig. 3, the optical fiber interferometer adopts a mach-zehnder interferometer, the probe part includes a fifth coupler 21 and a sixth coupler 22, the fifth coupler adopts a 40:60 1X2 coupler, the sixth coupler adopts a 50:50 1X2 coupler, a fifth interference arm 23 and a sixth interference arm 24 are connected between the fifth coupler and the sixth coupler, the sixth interference arm is provided with a seventh coupler 25, the seventh coupler and the sixth coupler are very close to each other on an optical path, 40% of a light-passing port of the fifth coupler is connected with the fifth interference arm, 60% of a light-passing port is connected with the sixth interference arm, 70% of the light-passing port of the seventh coupler adopts a 70:30 1X2 coupler, 70% of the light-passing port of the seventh coupler is connected with the sixth coupler, 30% of the light-passing port is connected with a fourth photoelectric detector 26, the light-through port of 1% of the first coupler connected with the probe part is connected with the third photoelectric detector 27, the sixth coupler is connected with the fifth photoelectric detector 28, the output end of the third photoelectric detector is connected with the first frequency mixer, the output end of the fourth photoelectric detector is connected with the second frequency mixer, the third photoelectric detector and the fourth photoelectric detector are both connected with the DFB laser, the first frequency mixer and the second frequency mixer are connected with the third frequency mixer, the third frequency mixer is connected with the controller, and the third photoelectric detector and the fourth photoelectric detector are both connected with the controller.
Example 4
The embodiment discloses a working method of an optical fiber interference device capable of eliminating associated amplitude modulation, which comprises the following steps:
in the optical fiber interference device according to embodiment 1, the laser, the first coupler, and the first photodetector form a first optical path, and the laser, the probe unit, and the second photodetector form a second optical path.
The DFB laser sends a ranging modulation signal under the control of the controller, the ranging modulation signal is a set chirp signal, a person skilled in the art can select a proper chirp signal according to actual conditions, the chirp signal passes through a first optical path (a first coupler-a first photoelectric detector), is output to a first mixer by a first photoelectric detector, and is also directly transmitted to the first mixer, the first mixer mixes the received signals of the laser and the first optical path to form a first difference frequency signal and outputs the first difference frequency signal to a third mixer, because a first optical fiber filter can prevent the chirp signal from passing through a second optical path (the first coupler-a second coupler-a first interference arm-a third coupler-a second photoelectric detector), and is output to the second mixer by a second photoelectric detector, meanwhile, the linear frequency modulation signal is also directly transmitted to a second mixer, the second mixer mixes the received signals of the laser and a second optical path to form a second difference frequency signal and outputs the second difference frequency signal to a third mixer, the third mixer mixes the first difference frequency signal and the second difference frequency signal to obtain a difference frequency signal of an optical path difference Delta L of a signal sent by the DFB laser and reaching the first photoelectric detector and the second photoelectric detector, the difference frequency signal of the optical path difference is transmitted to a controller, the controller calculates the difference frequency signal of the optical path difference to obtain a phase difference of the output signals of the first photoelectric detector and the second photoelectric detector
The specific calculation method comprises the following steps:
wherein, CnIs the speed of light transmission in the fiber; v (t) is the optical frequency.
The DFB laser emits optical signals for generating interference under the control of the controller, the optical signals pass through a first optical path and then are output by a first photoelectric detector and transmitted to the controller, the optical signals are transmitted in a first interference arm and a second interference arm of the probe part, the optical signals are transmitted by a third coupler after interference is generated and transmitted to the controller through a second photoelectric detector, the controller brings the obtained phase difference into the optical signals output by the first photoelectric detector, and then the signal data output by the second photoelectric detector is divided by the signal data output by the first photoelectric detector and brought into the phase difference, so that interference optical signal data are obtained.
The working method of the optical fiber interference device of the embodiment 2 is as follows:
the first light path is: the laser-first coupler-first photoelectric detector, the second light path is: the DFB laser emits chirp signals, the chirp signals are transmitted to the first mixer through the first coupler and the first photoelectric detector, meanwhile the chirp signals are directly transmitted to the first mixer, the first mixer carries out frequency mixing to obtain first difference frequency signals, the second optical fiber filter can prevent the chirp signals from passing through, therefore, the chirp signals are transmitted to the second mixer through the second photoelectric detector after passing through the optical circulator, the fourth coupler, the third interference arm, the first reflector, the optical circulator and the second photoelectric detector, meanwhile, the chirp signals are directly transmitted to the second mixer, the second mixer carries out frequency mixing to form second difference frequency signals, and the first difference frequency signals and the second difference frequency signals are transmitted to the third mixer, the third mixer mixes the first difference frequency signal and the second difference frequency signal to obtain a difference frequency signal of an optical path difference Delta L of a signal sent by the DFB laser reaching the first photoelectric detector and the second photoelectric detector, and transmits the difference frequency signal to the controller, and the controller calculates the difference frequency signal of the optical path difference to obtain a phase difference of output signals of the first photoelectric detector and the second photoelectric detector
The specific calculation method comprises the following steps:
wherein, CnIs the speed of light transmission in the fiber; v (t) is the optical frequency.
The DFB laser sends out optical signals for generating interference under the control of the controller, the optical signals are transmitted to the controller after passing through the first coupler and the first photoelectric detector, the other path of optical signals output by the first coupler enters the third interference arm and the fourth interference arm through the optical circulator, the interference is generated after the optical signals are reflected by the first reflecting mirror and the second reflecting mirror, the interfered signals are transmitted to the second photoelectric detector through the optical circulator, the second photoelectric detector transmits the interfered optical signals to the controller, the controller brings the obtained phase difference into the optical signals output by the first photoelectric detector, and then the signal data output by the second photoelectric detector is divided by the signal data output by the first photoelectric detector and brought into the phase difference, so that interference optical signal data are obtained.
The working method of the optical fiber interference device of the embodiment 3 is as follows:
the first light path is: the laser-first coupler-third photodetector, the second light path is: second light path I and second light path II constitute, second light path I is: the laser-first coupler-fifth coupler-seventh coupler-fourth photoelectric detector, the second optical path II is laser-first coupler-probe part-fifth photoelectric detector, the DFB laser emits chirp signal, and is transmitted to the first mixer through the first coupler and third photoelectric detector, the chirp signal is simultaneously and directly transmitted to the first mixer, the first mixer is mixed to obtain first difference frequency signal, the other path of chirp signal outputted by the first coupler is inputted to the fourth photoelectric detector through the fifth coupler and seventh coupler, the fourth photoelectric detector transmits signal to the second mixer, the second mixer receives chirp signal emitted by the DFB laser, the second mixer is mixed to form second difference frequency signal, the first difference frequency signal and the second difference frequency signal are transmitted to the third mixer for mixing, obtaining a difference frequency signal of an optical path difference Delta L of signals sent by the DFB laser and reaching the third photoelectric detector and the fourth photoelectric detector, transmitting the difference frequency signal to the controller, and calculating the difference frequency signal of the optical path difference by the controller to obtain a phase difference of output signals of the third photoelectric detector and the fourth photoelectric detector
The specific calculation method comprises the following steps:
wherein, CnIs the speed of light transmission in the fiber; v (t) is the optical frequency.
In this embodiment, since the optical paths of the seventh coupler and the sixth coupler are close, the optical path of the signal emitted by the laser to the fourth photodetector and the optical path to the fifth photodetector are approximately equal.
The DFB laser emits optical signals for interference, one path of the optical signals is transmitted to the controller through the first coupler and the third photoelectric detector, the other path of the optical signals is transmitted to the controller through the fifth photoelectric detector after interference is generated on the probe part, the controller brings the obtained phase difference into the optical signals output by the third photoelectric detector, and then the signal data output by the fifth photoelectric detector is divided by the signal data output by the third photoelectric detector and brought into the phase difference, so that interference optical signal data are obtained.
When two detection signals are adopted to compensate the accompanying amplitude modulation effect, when the optical path problem of the two detection signals is not considered, the light intensity I at the first photoelectric detector1(t) is expressed as
I0Is the direct current component of the light source; delta I0The amplitude of the variation of the light intensity along with the current variation; omegacAngular velocity being a wavelength; a time t;is the initial phase of the light source.
When the optical path problem of the two-way detection signal is not considered, assume I1(t) light emitted from the light source I0(t), light intensity I at the second photodetector2(t) is expressed as
A and B are fixed constants; v. of0Is a direct current frequency; Δ v is the amplitude of variation of the optical frequency; omegacAngular velocity being a wavelength; delta L is the optical path difference of the two interference arms; cnIs the speed of light transmission in the optical fiber.
As can be seen from formulas 1-1 and 1-2, the commonly used method for compensating the associated amplitude modulation effect is mainly based on the division of two detection signals to overcome the DC light intensity I0(t) the influence of the variation suppresses signal demodulation distortion.
However, when the two detection signals are separated by several tens or more of distances in the optical pathAt hundreds of kilometers, the intensity of light I detected at the first photodetector cannot be directly used1(t) emission light I as light source0(t) because of the intensity signal detected at the second photodetector and the outgoing light I from the light source0(t) there is a phase difference and direct division results in distortion of the signal demodulation.
When considering the optical path problem of the two detection signals, the phase difference between the upper measurement points must be considered. The light intensity I at the first photodetector1(t) is expressed as
I0Is the direct current component of the light source; delta I0The amplitude of the variation of the light intensity along with the current variation; omegacAngular velocity being a wavelength; t is time;is the initial phase of the light source;the amount of phase change added to the light from the light source arriving at the first photodetector.
Wherein
L1Is the optical path from the light source to the first photodetector; cnIs the speed of light transmission in the fiber; v (t) is the optical frequency.
When considering the optical path problem of the two detection signals. Light intensity I at the second photodetector2(t) is expressed as
A and B are fixed constants; i is0(t) is a light intensity expression of the emergent light of the light source reaching the second photoelectric detector; omegacAngular velocity being a wavelength; v. of0Is straightAn streamer frequency; Δ v is the amplitude of variation of the optical frequency; delta L is the optical path difference of the two interference arms; cnIs the speed of light transmission in the optical fiber.
Wherein
I0Is the direct current component of the light source; delta I0The amplitude of the variation of the light intensity along with the current variation; omegacAngular velocity being a wavelength; t is time;is the initial phase of the light source;the amount of phase change added to the light from the light source arriving at the second photodetector.
Wherein
L2Is the optical path from the light source to the second photodetector; cnIs the speed of light transmission in the fiber; v (t) is the optical frequency.
As shown above, when the optical path problem of the two detection signals is considered, the light intensity I at the first photodetector is determined1(t) is equal to the intensity of light I of the emergent light of the light source reaching the first photodetector0(t) according to formulas 1-3, 1-6; the phase difference of light emitted from the light source reaching the first photodetector and the second photodetector is
Can obtain the product
I0Is the direct current component of the light source; delta I0The variation of light intensity with currentAn amplitude value; omegacAngular velocity being a wavelength; t is time;is the initial phase of the light source;the phase variation quantity is increased when the emergent light of the light source reaches the first photoelectric detector;is the phase difference of the light from the emergent light of the light source reaching the first photodetector and the second photodetector.
That is, only the phase difference of the light from the light source reaching the first photodetector and the second photodetector needs to be measuredThe influence of light intensity change in the accompanying amplitude modulation effect can be overcome by dividing the two detection signals, and the purpose of signal demodulation is achieved.
Therefore, the device and the method of the embodiment solve the problem of signal distortion suppression of the high-frequency direct current light intensity part caused by the phase difference of the direct current light intensity due to the difference of the signal acquisition positions, and solve the problem of distortion elimination caused by the accompanying amplitude modulation generated in the long-distance practical application of the optical fiber interferometer.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. An optical fiber interference device capable of eliminating associated amplitude modulation comprises an optical fiber interferometer, wherein the optical fiber interferometer comprises a laser and a first coupler, the laser can transmit signals to the first coupler, the first coupler is connected with a probe portion, the optical fiber interference device is characterized in that the output end of the probe portion and the first coupler are respectively connected with a first mixer and a second mixer through a photoelectric detection piece, the first mixer and the second mixer are connected with a third mixer and the laser, the laser can output signals to the first mixer and the second mixer, the first mixer and the second mixer can output signals to the third mixer, the third mixer is connected with a controller, the photoelectric detection piece is further connected with the controller, and the optical signals output by the first coupler and the probe portion can be converted into electric signals to be transmitted to the controller.
2. The apparatus of claim 1, wherein the controller is coupled to the laser and is capable of controlling the laser to emit the set signal.
3. The apparatus of claim 1, wherein the probe unit comprises a second coupler and a third coupler, the second coupler and the third coupler are connected to two ends of the first interference arm and the second interference arm, the second interference arm is provided with a filter, and the third coupler is connected to the photodetector.
4. The optical fiber interference device capable of eliminating the concomitant amplitude modulation according to claim 1, wherein the probe unit is connected to the first coupler through an optical circulator, the optical circulator is connected to the second photodetector, the probe unit comprises a fourth coupler connected to the optical circulator, the fourth coupler is connected to one end of a third interference arm and one end of a fourth interference arm, the other end of the third interference arm and the other end of the fourth interference arm are respectively connected to the first reflector and the second reflector, the fourth interference arm is provided with a filtering member, the first reflector and the second reflector can reflect and transmit optical signals to the optical circulator, and the optical circulator is connected to the photodetector and can transmit the reflected optical signals to the photodetector.
5. An optical fiber interference device capable of canceling concomitant amplitude modulation according to claim 3 or 4, characterized in that: the photoelectric detection piece comprises a first photoelectric detector and a second photoelectric detector, the input end of the first photoelectric detector is connected with the first coupler, the output end of the first photoelectric detector is connected with the first frequency mixer and the controller, the input end of the second photoelectric detector is connected with the output end of the probe part, and the output end of the second photoelectric detector is connected with the second frequency mixer and the controller.
6. An optical fiber interference device capable of canceling concomitant amplitude modulation according to claim 3 or 4, characterized in that: the filtering part adopts a passive optical fiber filter or an active optical switch.
7. A fiber optic interference apparatus capable of canceling concomitant amplitude modulation according to claim 1, wherein: the probe part comprises a fifth coupler and a sixth coupler, a fifth interference arm and a sixth interference arm are connected between the fifth coupler and the sixth coupler, and the sixth interference arm is provided with a seventh coupler.
8. The apparatus of claim 7, wherein the photodetector comprises a third photodetector, a fourth photodetector and a fifth photodetector, the third photodetector has an input connected to the first coupler and an output connected to the laser and the first mixer, the fourth photodetector has an input connected to the seventh coupler and an output connected to the second mixer, the fifth photodetector has an input connected to the sixth coupler and an output connected to the controller.
9. A method of operating a fibre optic interferometric device capable of removing concomitant amplitude modulation according to any one of claims 1 to 8, in which the laser, the first coupler and the photodetecting element form a first optical path, and the laser, the first coupler, the probe section and the photodetecting element form a second optical path;
the laser sends a distance measurement modulation signal, the distance measurement modulation signal enters a first mixer through a first optical path, the first mixer receives and mixes a signal of the laser and a signal of the first optical path to obtain a first difference frequency signal, a second mixer receives and mixes a signal of the laser and a signal of a second optical path to obtain a second difference frequency signal, the first difference frequency signal and the second difference frequency signal are transmitted to a third mixer to be mixed to obtain a difference frequency signal delta L of an optical path difference between the first optical path and the second optical path and transmitted to a controller, and the controller obtains a phase difference when the signals of the two optical paths reach a photoelectric detection piece according to the difference frequency signal of the optical path difference
The laser emits optical signals, the controller receives the output optical signals of the first optical path and the second optical path through the photoelectric detection piece, and the obtained phase difference is obtainedIn the optical signal output by the photoelectric detection element brought into the first optical path, the data of the optical signal obtained by detecting the photoelectric detection element of the second optical path is divided by the data of the optical signal output by the photoelectric detection element of the first optical path and brought into the phase difference, so as to obtain the data of the interference optical signal.
10. The method of operation of claim 9 wherein said phase difference is calculated by:
wherein, CnIs the speed of light transmission in the fiber; v (t) is the optical frequency.
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