CN115824277A - Multi-pulse frequency domain orthogonal demodulation system and method for phase noise fading suppression - Google Patents
Multi-pulse frequency domain orthogonal demodulation system and method for phase noise fading suppression Download PDFInfo
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Abstract
The invention discloses a multi-pulse frequency domain orthogonal demodulation system and a multi-pulse frequency domain orthogonal demodulation method for suppressing phase noise fading, wherein the system comprises a laser, an optical pulse modulation module, a first amplifier, a first transmission optical fiber, a first isolator, an interferometer, a second isolator, a second transmission optical fiber, a second amplifier, a detector, a data acquisition card, a signal demodulation and analysis module and a signal generator, wherein the laser, the optical pulse modulation module, the first amplifier, the first transmission optical fiber, the first isolator, the interferometer, the second isolator, the second transmission optical fiber, the second amplifier, the detector, the data acquisition card and the signal demodulation and analysis module are sequentially connected in series, and the signal generator is respectively connected to the optical pulse modulation module and the signal demodulation and analysis module. The invention can avoid phase noise fluctuation caused by phase fading, and particularly in system application of long distance, large scale and the like, the phase fading causes large change amplitude of optical signal power and signal-to-noise ratio after interference.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensors, and particularly relates to a multi-pulse frequency domain orthogonal demodulation system and method for phase noise fading suppression.
Background
The optical fiber sensing technology is a technology for sensing and measuring parameters such as external physical quantity, chemical quantity and the like by taking an optical fiber as a medium, and common optical fiber sensing technologies include an interference type sensing technology and a scattering type sensing technology. The interferometric sensing technology can sense the change of external physical and chemical parameters by utilizing structures such as a Fabry-Perot (F-P) cavity, a Michelson Interferometer (MI), a Mach-Zehnder interferometer (MZI), an optical fiber grating and the like. For the sensors, external physical and chemical parameter data can be acquired by combining with specific modulation and demodulation algorithms. Common demodulation methods include phase carrier demodulation (PGC), heterodyne demodulation, 3 × 3 coupler demodulation, and frequency domain quadrature demodulation techniques.
Among the demodulation methods, the PGC demodulation method has high carrier frequency requirement and small dynamic range; the heterodyne demodulation method is easily influenced by a frequency shift delay module and a transmission optical fiber; the 3 x 3 coupler demodulation method occupies a lot of hardware resources. The frequency domain demodulation technology is combined with the method, two paths of signal light with orthogonal phases on the time domain are constructed through frequency modulation, and phase information is demodulated. The method has the advantages of large achievable dynamic range and small link interference. However, due to the self-interference (homodyne) principle of the optical pulse, the interfered optical signal generates a phase fading phenomenon. The phenomenon that the power of an optical signal changes along with the signal-to-noise ratio of the signal is particularly obvious for a system with an amplifier, and finally, the demodulated phase noise fluctuates greatly in a time domain, and the noise stability is poor.
Disclosure of Invention
In order to solve the above technical problems in the prior art, the present invention provides a system and a method for multi-pulse frequency domain orthogonal demodulation with phase noise fading suppression, which can solve the influence of the phase fading phenomenon on noise variation.
The technical scheme of the technical problem of the invention is as follows: a multi-pulse frequency-domain quadrature demodulation system with phase noise fading suppression, comprising: the device comprises a laser, an optical pulse modulation module, a first amplifier, a first transmission optical fiber, a first isolator, an interferometer, a second isolator, a second transmission optical fiber, a second amplifier, a detector, a data acquisition card, a signal demodulation and analysis module and a signal generator, wherein the laser, the optical pulse modulation module, the first amplifier, the first transmission optical fiber, the first isolator, the interferometer, the second isolator, the second transmission optical fiber, the second amplifier, the detector, the data acquisition card and the signal demodulation and analysis module are sequentially connected in series, and the signal generator is respectively connected to the optical pulse modulation module and the signal demodulation and analysis module.
Further, the optical pulse modulation module includes an optical switch, a first coupler, a first delay optical fiber, a first frequency shifter, a second coupler, a second delay optical fiber, a second frequency shifter, and a third coupler, wherein an optical signal output by the laser is transmitted to the first coupler through the optical switch, the first coupler is divided into two paths, one path is transmitted to the second coupler through the first delay optical fiber, the other path is transmitted to the second coupler through the first frequency shifter, an output of the second coupler is divided into two paths, one path is transmitted to the third coupler through the second delay optical fiber, the other path is transmitted to the third coupler through the second frequency shifter, and the third coupler outputs an optical signal to the port.
Furthermore, the interferometer is an F-P cavity, an MI type interferometer, an MZI type interferometer or an optical fiber grating interferometer.
Further, the optical path difference generated by the interferometer is Δ L, and the optical path difference and the frequency of the pulse light generated by the optical pulse modulation module satisfy the following relationship
Wherein i is less than 4 and is a positive integer, and c is the speed of light.
Further, the first amplifier and the second amplifier are erbium-doped fiber amplifiers, remote pump amplifiers, raman amplifiers or a combination of the amplifiers.
A multi-pulse frequency domain orthogonal demodulation method for phase noise fading suppression comprises the following steps:
wherein A is i For the i-th light pulse, the amplitude of the slowly varying light field, f i The frequency of the ith light pulse, t is a time parameter,
the initial phase of the ith optical pulse;
wherein D i As a DC bias of the interference signal, B i Is the degree of interference of the interference signal,
the phase change of the interference pulse caused by external signals;
and step 5, acquiring phase information by adopting arc tangent according to the orthogonal phase signal:
the invention has the beneficial effects that:
1. according to the invention, through carrying out frequency modulation on the optical signal, the interference signal of the phase reversal phase and the quadrature phase is constructed by utilizing the arm difference of the interferometer, the occupation of the optical signal connecting branch and the demodulation channel is reduced, and the consumption of hardware resources is reduced.
2. The invention can lock the interfered optical signals at a fixed phase by using optical frequency difference, the phase-reversed phase signal is used for carrying out difference to inhibit common-mode noise, and the quadrature phase signal acquires phase information by a phase demodulation method.
3. The invention can avoid phase noise fluctuation caused by phase fading. Particularly in the application of long-distance, large-scale and other systems, the phase fading causes the large change amplitude of the power and the signal-to-noise ratio of the interfered optical signal, and the invention can reduce the influence of the phase fading on the subsequent phase amplitude and phase noise solution.
Drawings
Fig. 1 is a block diagram of the present invention.
Fig. 2 is a flow chart of the present invention.
Fig. 3 is a schematic diagram of an optical pulse sequence output by the optical pulse modulation module according to the present invention.
Fig. 4 is a block diagram of the optical pulse modulation module according to embodiment 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, fig. 1 is a structural diagram of a multi-pulse frequency domain quadrature demodulation system for suppressing phase noise fading according to the present invention, which includes a laser 1, an optical pulse modulation module 2, an amplifier 3, a transmission fiber 4, an isolator 5, an interferometer 6, an isolator 7, a transmission fiber 8, an amplifier 9, a detector 10, a data acquisition card 11, a signal demodulation and analysis module 12, and a signal generator 13. Light generated by the laser 1 passes through the optical pulse modulation module 2 and is modulated into a pulse optical signal with a certain optical frequency difference. The optical signal is amplified by the optical amplifier 3, transmitted into the interferometer 6 through the transmission fiber 4 and the isolator 5, then output to the amplifier 9 through the isolator 7 and the transmission fiber 8, and the amplified optical signal is input to the detector 10. The optical power data acquired by the detector 10 is acquired by a data acquisition card 11, and processed by a signal demodulation and analysis module 12 to acquire the phase information detected by the detector 1. The signal generator 13 is used for synchronization of the optical pulse modulation module 2 and generation of radio frequency signals.
As shown in fig. 4, fig. 4 is a structural diagram of the optical pulse modulation module. Comprises an optical switch 14, a coupler 15, a delay optical fiber 16, a frequency shifter 17, a coupler 18, a delay optical fiber 19, a frequency shifter 20 and a coupler 21. The module includes three ports: optical input port (port 1), optical output port (port 2), radio frequency port (port 3).
The frequency shifter 17 can be realized by an optical fiber acousto-optic modulator or other devices, and has the function of generating a specific optical frequency difference for an optical pulse, wherein the frequency is Deltav 1 The length of the delay optical fiber 16 is L 1 Corresponding delay time of τ 1 。
The movementThe frequency shifter 20 has the same function as the frequency shifter 17, and the frequency shift frequency is Deltav 2 The length of the delay optical fiber 19 is L 2 Corresponding delay time of τ 2 . The frequencies of the frequency shifter 17 and the frequency shifter 20 and the delay information of the delay fiber 16 and the delay fiber 19 need to satisfy one of the following relations: relation 1) T/N t >2τ 2 ＝4τ 1 ＝4τ 0 >4τ 0 In which N is t For time division multiplexing, the time division is 1,f i+1 -f i ＝Δν 1 ，f i+2 -f i ＝Δν 2 (ii) a Relation 2) T/N t >2τ 1 ＝4τ 2 ＝4τ 0 >4τ 0 In which N is t For time division multiplexing, the time division is 1,f i+1 -f i ＝Δν 2 ，f i+2 -f i ＝Δν 1 。
The optical pulse modulation module 2 modulates the continuous signal light generated by the laser 1 into a periodic optical pulse sequence with a certain optical frequency difference, the period of the pulse sequence is T, and the width of a single pulse is tau 0 The adjacent pulses in the same period are delayed by tau d Optical frequency of f i The number of pulses is 4, and the schematic diagram of the optical pulse sequence is shown in fig. 3.
The interferometer 6 in the present invention may be an F-P cavity, MI type interferometer, MZI type interferometer, fiber grating or other type of structure interferometer. The optical path difference generated by the interferometer is Δ L, and the optical path difference and the pulse light frequency information generated by the light pulse modulation module need to satisfy the following relationship:
wherein i<4 and is a positive integer.
The amplifiers 3 and 9 of the present invention may be erbium doped fiber amplifiers, remote pump amplifiers, raman amplifiers or a combination of these.
The signal demodulation and analysis module 12 of the present invention has the functions of signal clock synchronization, modulation signal generation, electric signal filtering and amplification, phase information demodulation, etc.
The multi-pulse frequency domain orthogonal demodulation system not only can be applied to a single sensor system, but also can be applied to a time division multiplexing and wavelength division multiplexing optical fiber sensor array system. For the optical fiber sensor array system, the laser is replaced by a plurality of wavelength lasers and wavelength division multiplexers; the amplifier 3 is replaced by a peak shifting module and an amplifier, and the peak shifting module is used for adjusting pulse delay among wavelength channels; the interferometer is replaced by an interferometric sensor array.
The flow of the optical fiber sensing multi-pulse frequency domain orthogonal demodulation method is shown in fig. 2, and the method comprises the following steps:
and 3, detecting the interference light by a photoelectric detector to form an electric signal. By calibration or other means, solving for D in the above formula i And B i Obtaining a normalized signal expressed as:
and 4, after acquiring the normalized signals, respectively subtracting the interference signals with opposite phases to acquire two orthogonal phase signals, wherein the expression is as follows:
and step 5, acquiring phase information by adopting arc tangent according to the orthogonal phase signal:
it will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A multi-pulse frequency domain orthogonal demodulation system for suppressing phase noise fading is characterized by comprising a laser, an optical pulse modulation module, a first amplifier, a first transmission optical fiber, a first isolator, an interferometer, a second isolator, a second transmission optical fiber, a second amplifier, a detector, a data acquisition card, a signal demodulation and analysis module and a signal generator, wherein the laser, the optical pulse modulation module, the first amplifier, the first transmission optical fiber, the first isolator, the interferometer, the second isolator, the second transmission optical fiber, the second amplifier, the detector, the data acquisition card and the signal demodulation and analysis module are sequentially connected in series, and the signal generator is respectively connected to the optical pulse modulation module and the signal demodulation and analysis module.
2. The system according to claim 1, wherein the optical pulse modulation module modulates the continuous light generated by the laser into a periodic pulse sequence, the periodic pulse sequence includes 4 optical pulses, and the optical field is:
3. The system according to claim 1, wherein the optical pulse modulation module comprises an optical switch, a first coupler, a first delay fiber, a first frequency shifter, a second coupler, a second delay fiber, a second frequency shifter, and a third coupler, wherein an optical signal output from the laser is transmitted to the first coupler via the optical switch, the first coupler is divided into two paths, one path is transmitted to the second coupler via the first delay fiber, the other path is transmitted to the second coupler via the first frequency shifter, an output of the second coupler is divided into two paths, one path is transmitted to the third coupler via the second delay fiber, the other path is transmitted to the third coupler via the second frequency shifter, and the third coupler outputs an optical signal to the port.
4. The system of claim 1, wherein the interferometer is an F-P cavity, MI type interferometer, MZI type interferometer or fiber grating interferometer.
5. The system according to claim 1, wherein the optical path difference generated by the interferometer is Δ L, and the optical path difference and the frequency of the pulse light generated by the optical pulse modulation module satisfy the following relationship:
wherein i<4 and is a positive integer, k is an integer, f i Is the light frequency and c is the speed of light.
6. The phase noise fading suppressed multi-pulse frequency domain quadrature demodulation system of claim 1 wherein said first and second amplifiers are erbium doped fiber amplifiers, remote pumped amplifiers, raman amplifiers or a combination thereof.
7. A multi-pulse frequency domain orthogonal demodulation method for phase noise fading suppression is characterized by comprising the following steps:
step 1, an optical pulse modulation module modulates continuous light generated by a laser into a periodic pulse sequence, wherein the periodic pulse sequence comprises 4 optical pulses, and an optical field of the periodic pulse sequence is as follows:
step 2, the optical pulse sequence forms an orthogonal interference sequence pulse after passing through the interferometer, and the expression is as follows:
step 3, after the interference light is detected by the photoelectric detector, an electric signal is formed, and D in the formula is solved through calibration or other modes i And B i Obtaining a normalized signal expressed as:
step 4, after obtaining the normalized signal, respectively subtracting the interference signals with opposite phases to obtain two orthogonal phase signals, wherein the expression is as follows:
and step 5, acquiring phase information by adopting arc tangent according to the orthogonal phase signal:
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| CN116907627A (en) * | 2023-09-13 | 2023-10-20 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
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| CN116907627A (en) * | 2023-09-13 | 2023-10-20 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
| CN116907627B (en) * | 2023-09-13 | 2023-12-19 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
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