CN113607277A - Narrow linewidth laser linewidth measuring system and adjusting method thereof - Google Patents
Narrow linewidth laser linewidth measuring system and adjusting method thereof Download PDFInfo
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Abstract
The invention relates to the field of laser line width measurement, in particular to a line width measurement system of a narrow line width laser and a mediation method thereof. The invention has reasonable design, and can measure the line width of the narrow-line-width laser without needing a very long optical fiber delay line and knowing the specific length of the optical fiber delay line.
Description
Technical Field
The invention relates to the field of laser line width measurement, in particular to a narrow line width laser line width measurement system and a mediation method thereof.
Background
Narrow-linewidth lasers play an extremely important role in the fields of coherent optical communication and optical fiber sensing, for example, in a Distributed acoustic wave sensor (DAS) based on a phase-sensitive optical time domain reflectometer (phi-OTDR), the linewidth of a laser directly affects the strain sensitivity of the DAS, and the narrower the linewidth of the laser, the higher the sensitivity of the DAS. At present, the linewidth of a Distributed Feedback (DFB) laser is generally in the khz level, while the linewidth of a fiber laser reaches the hundred hz level, which puts new requirements on the linewidth measurement technology of a narrow linewidth laser.
The precision of the spectrum analyzer is generally in the magnitude of 0.01nm, and the optical frequency resolution of a Fabry-Perot (F-P) scanning interferometer is in the magnitude of megahertz, which are difficult to meet the measurement precision requirements of the narrow linewidth lasers. The method for measuring the laser linewidth based on the Mach Zehnder Interferometer (MZI) requires that the length of the optical fiber delay line of the interferometer is far greater than the coherence length of the laser, generally more than 6 times, at this time, the Power Spectral Density (PSD) of the output signal of the interferometer is of a lorentz line type, and Half of the Full Width at Half Maximum (FWHM) is the laser linewidth. However, this method is limited in that when the line width of the laser is narrow, that is, the coherence length is long, the fiber delay line of the interferometer is very long, an excessively long fiber introduces a large optical power loss, and an excessively strong rayleigh stray light affects the final measurement accuracy. At present, a narrow linewidth laser linewidth measurement method based on a short delay line MZI is also available, but the length of the delay line needs to be accurately known, so that the measurement accuracy of the method is limited.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a narrow linewidth laser linewidth measuring system based on an optical fiber reflectometer and a mediation method thereof.
In order to realize the technical effects, the invention is realized by the following technical scheme:
the utility model provides a narrow linewidth laser linewidth measurement system, includes beam splitting module, light pulse generation module, optical fiber circulator, single mode fiber or weak reflection point array, coherent reception module, signal acquisition and processing module, beam splitting module links to each other with laser that awaits measuring and light pulse generation module respectively, light pulse generation module links to each other with optical fiber circulator, optical fiber circulator links to each other with single mode fiber or weak reflection point array, optical fiber circulator still links to each other with coherent reception module, coherent reception module links to each other with signal acquisition and processing module.
Further, the optical splitting module is a fiber coupler.
Further, the optical pulse generation module includes: the optical fiber spectrometer comprises an electric signal generator, an electric signal amplifier, an optical modulator and an optical amplifier, wherein the electric signal generator is connected with the electric signal amplifier, the electric signal amplifier is connected with the optical modulator, and the optical modulator is respectively connected with a light splitting module and the optical amplifier.
Further, the coherent receiving module comprises a splitting ratio 50/50 optical fiber coupler and a photodetector, and the 50/50 optical fiber coupler is respectively connected with the splitting module and the optical fiber circulator.
Furthermore, the signal acquisition and processing module comprises a data acquisition card and a data processor, and the data acquisition card is respectively connected with the coherent receiving module and the data processor.
The laser with constant power and frequency generated by the laser to be tested is divided into two paths by the light splitting module, wherein one path has higher optical power and enters the optical pulse generating module as seed light, and the other path has lower optical power and enters the coherent receiving module as local light; the optical pulse generation module modulates the seed light into a high-power optical pulse string, and the optical pulse enters a weak reflection point array or a single-mode optical fiber through an optical fiber circulator; meanwhile, the optical pulse generating module sends a trigger signal to the signal acquisition and processing module; under the excitation of a high-power optical pulse train, each reflection point on the weak reflection point array can generate back scattered light, or rayleigh scattering points on a common single-mode optical fiber can also generate back scattered light, and the back scattered light returns to the coherent receiving module through the optical fiber circulator; the back scattering light interferes with the local light in a coherent receiving module, and an interference signal is photoelectrically converted into a current signal I (t); and finally, acquiring the current signal by the signal acquisition and processing module to obtain I (k), and processing data.
The optical pulse train comprises N pulses with the pulse width of taupA pulse repetition period of TcFrequency shift f0Of the light pulse of (2).
The interval between the reflection points of the weak reflection point array is required to be larger than c taupAnd/2, where c is the speed of light in the fiber.
A demodulation method of a line width measurement system of a narrow line width laser comprises the following steps:
step one, a data acquisition card acquires a current signal { I (k) } from a certain light pulse; k is 1, a, K, which is obtained by dividing the light pulse repetition period of the data acquisition card by the sampling rate; the data processor obtains an orthogonal signal (Q (k)) of the electric signal by using Hilbert transform; k is 1, a, K, and then a complex signal is synthesized by euler's formula
Wherein j is a plurality of flags; because of a total of N light pulses, their corresponding complex signals are labeled in emission time order
If ordinary single-mode optical fiber is used, the complex signal will have severe interference and polarization fading, i.e. at some k-values,
the mode of (2) is very small, and under the influence of additive noise, when the phase of a complex signal is extracted, very large noise is generated, which affects the measurement of line width, so that an additional processing step is required to remove fading noise. If the weak reflection point array is used, the fading problem does not exist, the following step two can be skipped, and the complex signal can be directly transmitted
Defined as synthesizing complex signals
Step two, obtaining a plurality of signals from the first light pulseConjugation of numbers
For reference, all the complex signals obtained by N optical pulses are subjected to phase rotation processing to obtain phase-rotated complex signals
The complex signal after phase rotation is processed by sliding average, the number of points of the sliding average is L, and then the comprehensive complex signal with interference fading and polarization fading mitigation can be obtained
Step three, taking a phase term of the comprehensive complex signal to obtain a phase signal { phi (n, k) ═ angle [ R (n, k) ]; n is 1, …, N; k is 1, …, K }. Where angle represents the angle.
Step four, calculating the variance of each point of the N phase signals obtained in the previous step to obtain a phase variance signal,
and performing linear fitting on the phase variance signal, wherein the slope after fitting is 2 pi · delta v, and the line width of the laser is delta v.
The scientific principle of the fourth step is explained as follows, the photoelectric field output by the laser is expressed as
Wherein j is
E0Is the amplitude of the electric field, ω0Is the central angular frequency of the laser and,
is phase random fluctuation, leads to laser line width broadening, wherein t is time, and can be analyzed according to the laser principle,
is a wiener process, i.e. a smooth independent incremental random process, the increments of which
Obeying a Gaussian distribution
The parameter Δ v is defined as the laser linewidth. Thus obtaining
The line width of the laser can be obtained by the variance and the s of the laser, but the s value is difficult to obtain accurately, and the measurement result is influenced. Another method is to obtain
The functional relationship (linear relationship) between the variance of (a) and(s) can be obtained by calculating the slope. The expression of the beat frequency signals of RBS and LO returned by a Rayleigh scattering point on the single-mode fiber or a weak reflection point on the weak reflection point array is
Wherein A is the amplitude, W is a rectangular window function, and the window function has a duration in the range of [ s, s + τ ]p]And s is the round-trip transmission time of light from the incident end of the fiber to the reflection point. Through Hilbert transform, the phase term of I (t) can be calculated, and if the system state is stable, the phase term is
Wherein C is a phase constant. Because the scattering points at different positions correspond to different s, phase terms of RBS and LO beat signals returned by the scattering points at various positions on the whole optical fiber are calculated, andcalculating the phase variance to obtain
And the linear function relation between the linear function relation and the s can obtain the line width delta v of the laser by calculating the slope of the phase variance.
The invention has the advantages that:
compared with the prior art, the invention can realize the measurement of the line width of the narrow-line-width laser by using shorter optical fibers without knowing the precise length of the optical fibers.
Compared with the prior art that the interferometer is adopted to measure the line width, the invention does not need a very long optical fiber delay line and can adopt a short optical fiber to measure.
Drawings
Fig. 1 is a diagram of a laser linewidth measurement system based on a fiber optic reflectometer.
Fig. 2 shows the phase signal output in example 1.
Fig. 3 is a phase variance signal output by embodiment 1.
In FIG. 1, 1-laser to be tested, 2-90/10 optical fiber coupler, 3-electrical signal generator, 4-electrical signal amplifier, 5-optical modulator, 6-optical amplifier, 7-optical fiber circulator, 8-single mode optical fiber or weak reflection point array, 9-50/50 optical fiber coupler, 10-photoelectric detector, 11-data acquisition card, 12-data processor.
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
Example 1
The utility model provides a narrow linewidth laser linewidth measurement system includes that beam split module, light pulse produce module, optical fiber circulator 7, single mode fiber or weak reflection point array 8, coherent reception module, signal acquisition and processing module, beam split module links to each other with laser 1 and the light pulse generation module that awaits measuring respectively, the light pulse generates the module and links to each other with optical fiber circulator 7, optical fiber circulator 7 links to each other with single mode fiber or weak reflection point array 8, optical fiber circulator 7 still links to each other with coherent reception module, coherent reception module links to each other with signal acquisition and processing module. In order to improve the system performance, the system can use all polarization maintaining optical fiber and polarization maintaining device, but the cost is increased.
Further, the optical splitting module is a fiber coupler, and preferably is a fiber coupler 2 with a splitting ratio of 90/10.
Further, the optical pulse generation module includes: the device comprises an electric signal generator 3, an electric signal amplifier 4, an optical modulator 5 and an optical amplifier 6, wherein the electric signal generator 3 is connected with the electric signal amplifier 4, the electric signal amplifier 4 is connected with the optical modulator 5, and the optical modulator 5 is respectively connected with an optical splitting module and the optical amplifier 6.
Further, the coherent receiving module comprises a splitting ratio 50/50 optical fiber coupler 9 and a photodetector 10, and the 50/50 optical fiber coupler 9 is respectively connected with the splitting module and the optical fiber circulator 7.
Further, the signal acquisition and processing module comprises a data acquisition card 11 and a data processor 12, and the data acquisition card 11 is connected with the coherent receiving module and the data processor 12 respectively.
The laser with constant power and frequency generated by the laser 1 to be tested is divided into two paths by the light splitting module, wherein one path has higher optical power and enters the optical pulse generating module as seed light, and the other path has lower optical power and enters the coherent receiving module as Local Oscillator (LO); the optical pulse generation module modulates the seed light into a high-power optical pulse string, and the optical pulse enters a weak reflection point array or a single-mode optical fiber through an optical fiber circulator 7; meanwhile, the optical pulse generating module sends a trigger signal to the signal acquisition and processing module; under the excitation of the high-power optical pulse train, each reflection point on the weak reflection point array can generate back scattering light RBS, or Rayleigh scattering points on the common single-mode optical fiber can also generate back scattering light (RBS), and the back scattering light RBS returns to the coherent receiving module through the optical fiber circulator 7; the back scattering light (RBS) interferes with the local light in a coherent receiving module, and the interference signal is photoelectrically converted into a current signal I (t); and finally, acquiring the current signal by the signal acquisition and processing module to obtain I (k), and processing data. Where t is the time of acquisition and k represents the numerical number of acquisition.
The optical pulse train comprises N pulses with the pulse width of taupA pulse repetition period of TcFrequency shift f0Of the light pulse of (2).
The interval between the reflection points of the weak reflection point array is required to be larger than c taupWhere c is the speed of light in the fiber, about 2X 108m/s, the reflectivity of the weak reflection point is preferably-40 dB. The signal to noise ratio can be improved by using the weak reflection point array without the influence of fading noise, but the system cost can be improved by using the weak reflection point array; the use of single mode fiber is cheaper and more convenient, but because rayleigh scattering is weaker, the signal-to-noise ratio is lower, and fading noise is affected, additional algorithms are needed to solve the fading problem.
Example 2
A demodulation method of a line width measurement system of a narrow line width laser comprises the following steps:
step one, the data acquisition card 11 acquires a current signal { I (k) } from a certain light pulse; k is 1, a., K, which is obtained by dividing the repetition period of the light pulses of the data acquisition card 11 by the sampling rate; the data processor 12 obtains an orthogonal signal { q (k) of the electrical signal by using hilbert transform; k is 1, a, K, and then a complex signal is synthesized by euler's formula
Wherein j is a plurality of flags; because of a total of N light pulses, their corresponding complex signals are labeled in emission time order
If ordinary single-mode optical fiber is used, the complex signal will have severe interference and polarization fading, i.e. at some k-values,
the mode of (2) is very small, and under the influence of additive noise, when the phase of a complex signal is extracted, very large noise is generated, which affects the measurement of line width, so that an additional processing step is required to remove fading noise. If the weak reflection point array is used, the fading problem does not exist, the following step two can be skipped, and the complex signal can be directly transmitted
Defined as synthesizing complex signals
Step two, obtaining the conjugate of complex signal obtained by the first light pulse
For reference, all the complex signals obtained by N optical pulses are subjected to phase rotation processing to obtain phase-rotated complex signals
The complex signal after phase rotation is processed by sliding average, the number of points of the sliding average is L, and then the comprehensive complex signal with interference fading and polarization fading mitigation can be obtained
Step three, taking a phase term of the comprehensive complex signal to obtain a phase signal { phi (n, k) ═ angle [ R (n, k) ]; n is 1, …, N; k is 1, …, K }. Where angle represents the angle.
Step four, calculating the variance of each point of the N phase signals obtained in the previous step to obtain a phase variance signal,
and performing linear fitting on the phase variance signal, wherein the slope after fitting is 2 pi · delta v, and the line width of the laser is delta v.
The scientific principle of the fourth step is explained as follows, the photoelectric field output by the laser is expressed as
Wherein j is
E0Is the amplitude of the electric field, ω0Is the central angular frequency of the laser and,
is phase random fluctuation, leads to laser line width broadening, wherein t is time, and can be analyzed according to the laser principle,
is a wiener process, i.e. a smooth independent incremental random process, the increments of which
Obeying a Gaussian distribution
The parameter Δ v is defined as the laser linewidth. Thus obtaining
The line width of the laser can be obtained by the variance and the s of the laser, but the s value is difficult to obtain accurately, and the measurement result is influenced. Another method is to obtain
The functional relation between the variance and the s is a linear relation, and the line width of the laser can be obtained by calculating the slope. The expression of the beat frequency signals of RBS and LO returned by a Rayleigh scattering point on the single-mode fiber or a weak reflection point on the weak reflection point array is
Wherein A is the amplitude, W is a rectangular window function, and the window function has a duration in the range of [ s, s + τ ]p]And s is the round-trip transmission time of light from the incident end of the fiber to the reflection point. Through Hilbert transform, the phase term of I (t) can be calculated, and if the system state is stable, the phase term is
Wherein C is a phase constant. Because the scattering points at different positions correspond to different s, the phase terms of RBS and LO beat signals returned by the scattering points at all positions on the whole optical fiber are calculated, and the phase variance is calculated, so that the phase terms can be obtained
And the linear function relation between the linear function relation and the s can obtain the line width delta v of the laser by calculating the slope of the phase variance.
Example 3
As shown in fig. 1, the present embodiment includes: the device comprises a laser 1 to be tested, a light splitting module, a light pulse generating module, an optical fiber circulator 7, a common single-mode optical fiber 8, a coherent receiving module and a signal acquisition and processing module.
The light splitting module is an 90/10 optical fiber coupler 2.
The optical pulse generation module comprises: an electric signal generator 3, an electric signal amplifier 4, an acousto-optic modulator 5 and an erbium-doped fiber amplifier.
The length of the single-mode optical fiber 8 is about 1.6 km.
The coherent receiving module comprises: 50/50 a fiber coupler 9 and a photodetector 10.
The signal acquisition and processing module comprises: a data acquisition card 11 and a data processor 12.
As shown in FIG. 1, the laser with constant power and frequency generated by the laser 1 to be tested enters the port a of the 90/10 fiber coupler 2, 90% of the light is output from the port b of the 90/10 fiber coupler 2 and enters the acousto-optic modulator 5 as seed light, and 10% of the light is output from the port 90/10Port c output of fiber coupler 2 goes as LO into 50/50 port b of fiber coupler 9; the electric signal generator 3 generates 500 pulse widths taupIs 100ns, and the pulse period Tc20 mus, frequency shift f0Sinusoidal pulses at 40 MHz; meanwhile, the electric signal generator 3 sends a trigger signal to the data acquisition card 11, and the trigger period is the same as Tc; the sine pulse train is amplified by an electric signal amplifier 4 and then input into an acousto-optic modulator 5; the acousto-optic modulator 5 is driven by the sine pulse train to modulate the seed light into an optical pulse train; the optical pulse train enters a port a of the optical fiber circulator 7 after being amplified by the erbium-doped optical fiber amplifier, and enters a single-mode optical fiber 8 from a port b of the optical fiber circulator 7; under the excitation of the high-power optical pulse train, the common single-mode fiber 8 generates an RBS, the RBS enters the port b of the fiber circulator 7, and enters 50/50 the port a of the fiber coupler 9 from the port c of the fiber circulator 7; RBS interferes with local light in 50/50 fiber coupler 9, the interference signal is converted to current signal i (t) by balanced photodetector 10; finally, the data acquisition card 11 acquires the discrete current signals I (k), and the data processor 12 processes the acquired I (k).
The embodiment relates to a demodulation method based on the system, which comprises the following steps:
step one, the data acquisition card 11 acquires a current signal { I (k) } from a certain light pulse; k is 1,.. K }, since the optical pulse repetition period is 20 μ s and the sampling rate of the data acquisition card 11 is 100MSa/s, K is 2000; the data processor 12 obtains an orthogonal signal { q (k) of the electrical signal by using hilbert transform; k is 1, a, K, and then a complex signal is synthesized by euler's formula
Since a total of 500 optical pulses, their corresponding complex signals are labeled in chronological order of transmission
Step two, because this embodiment uses a single mode fiber, it is necessary to remove the fading noise. Take the first light pulseObtaining the conjugate of a complex signal
For reference, all the complex signals obtained by N optical pulses are subjected to phase rotation processing to obtain phase-rotated complex signals
The complex signal after phase rotation is processed by sliding average, the number of points of the sliding average is L-10 points, and then the comprehensive complex signal with interference fading and polarization fading mitigation can be obtained
Taking a phase term of the comprehensive complex signal obtained in the previous step to obtain a phase signal { phi (n, k) ═ angle [ R (n, k) ]; n is 1, …, N; k is 1, …, K, and 500 phase signals are obtained as shown in fig. 2.
Step four, calculating the variance of each point of the N phase curves obtained in the previous step to obtain a phase variance signal,
the phase variance signal obtained by the calculation is shown in fig. 3. The slope of the phase variance signal is the line width of the laser, and Δ v is calculated to be 162 Hz.
The specification of the laser to be measured indicates that the line width is about 100Hz at an integration time of 120 μ s, the measurement result in this embodiment is 162Hz, and the reason why the measurement value is too large may be that the isolation effect of the measurement system is not ideal and the center frequency of the laser to be measured may be shifted due to the environmental influence.
Claims (12)
1. A narrow linewidth laser linewidth measurement system is characterized in that: the optical fiber ring device comprises a light splitting module, an optical pulse generating module, an optical fiber circulator (7), a single-mode optical fiber or weak reflection point array (8), a coherent receiving module and a signal collecting and processing module, wherein the light splitting module is respectively connected with a laser device (1) to be detected and the optical pulse generating module, the optical pulse generating module is connected with the optical fiber circulator (7), the optical fiber circulator (7) is connected with the single-mode optical fiber or the weak reflection point array (8), the optical fiber circulator (7) is also connected with the coherent receiving module, and the coherent receiving module is connected with the signal collecting and processing module.
2. A narrow linewidth laser linewidth measurement system according to claim 1, wherein: the light splitting module is an optical fiber coupler.
3. A narrow linewidth laser linewidth measurement system according to claim 2, wherein: the optical pulse generation module includes: the device comprises an electric signal generator (3), an electric signal amplifier (4), an optical modulator (5) and an optical amplifier (6), wherein the electric signal generator (3) is connected with the electric signal amplifier (4), the electric signal amplifier (4) is connected with the optical modulator (5), and the optical modulator (5) is respectively connected with a light splitting module and the optical amplifier (6).
4. A narrow linewidth laser linewidth measurement system according to claim 3, wherein: the coherent receiving module comprises a splitting ratio 50/50 optical fiber coupler (9) and a photoelectric detector (10), and the 50/50 optical fiber coupler (9) is respectively connected with the splitting module and the optical fiber circulator (7).
5. The narrow linewidth laser linewidth measurement system of claim 4, wherein: the signal acquisition and processing module comprises a block data acquisition card (11) and a data processor (12), wherein the data acquisition card (11) is respectively connected with the coherent receiving module and the data processor (12).
6. The narrow linewidth laser linewidth measurement system of claim 5, wherein: the laser with constant power and frequency generated by the laser device (1) to be tested is divided into two paths by the light splitting module, wherein one path has higher optical power and enters the optical pulse generating module as seed light, and the other path has lower optical power and enters the coherent receiving module as local light; the optical pulse generation module modulates the seed light into a high-power optical pulse string, and the optical pulse enters a weak reflection point array or a single-mode optical fiber through an optical fiber circulator (7); meanwhile, the optical pulse generating module sends a trigger signal to the signal acquisition and processing module; under the excitation of a high-power optical pulse train, each reflection point on the weak reflection point array can generate back scattering light, or Rayleigh scattering points on the common single-mode optical fiber can also generate back scattering light, and the back scattering light returns to the coherent receiving module through an optical fiber circulator (7); the back scattering light interferes with the local light in a coherent receiving module, and an interference signal is photoelectrically converted into a current signal I (t); and finally, acquiring the current signal by the signal acquisition and processing module to obtain I (k), and processing data, wherein t represents the acquisition time, and k represents the acquired digital serial number.
7. The narrow linewidth laser linewidth measurement system of claim 6, wherein: the optical pulse train comprises N pulses with the pulse width of taupA pulse repetition period of TcFrequency shift f0Of the light pulse of (2).
8. The narrow linewidth laser linewidth measurement system of claim 7, wherein: the interval between the reflection points of the weak reflection point array is required to be larger than c taupAnd/2, where c is the speed of light in the fiber.
9. A demodulation method of a line width measurement system of a narrow line width laser is characterized in that: the method comprises the following steps:
the data processor (12) converts the collected current signal I (k) into an orthogonal signal Q (k) through Hilbert conversion, and then obtains a complex signal by using an Euler formula
If an array of weak reflection points is used, complex signals are combined
Is that
If a single mode fiber is used, then a de-fading noise algorithm is required: taking the conjugate of the complex signal obtained by the first optical pulse as a reference, and performing phase rotation processing on the complex signals obtained by all the N optical pulses to obtain a phase-rotated complex signal; the complex signal after phase rotation is processed by moving average to obtain the comprehensive complex signal with fading noise alleviation
Taking a phase item of the comprehensive complex signal to obtain a phase signal; calculating the variance of each time position of the phase signal to obtain a phase variance signal; and performing linear fitting on the phase variance signal, calculating the slope, and converting to obtain the laser line width.
10. The demodulation method of the narrow linewidth laser linewidth measurement system according to claim 9, wherein: comprises the following specific steps
Step one, a data acquisition card (11) acquires a current signal { I (k) } from a certain light pulse; k is 1, a, K, K represents the acquired digital serial number, and K is obtained by dividing the light pulse repetition period of the data acquisition card (11) by the sampling rate; the data processor (12) obtains an orthogonal signal (Q (k)) of the electric signal by using Hilbert transform; k is 1, a, K, and then a complex signal is synthesized by euler's formula
Wherein j is a plurality of flags; because of a total of N light pulses, their corresponding complex signals are labeled in emission time order
Step two, if the common single mode fiber is used, extra processing steps are needed to remove the fading noise, and the conjugate of the complex signal obtained by the first optical pulse is taken
For reference, all the complex signals obtained by N optical pulses are subjected to phase rotation processing to obtain phase-rotated complex signals
The complex signal after phase rotation is processed by sliding average, the number of points of the sliding average is L, and then the comprehensive complex signal with interference fading and polarization fading mitigation can be obtained
If weak reflection point array is used, complex signal is directly transmitted
Defined as synthesizing complex signals
Step three, taking a phase term of the comprehensive complex signal to obtain a phase signal { phi (n, k) ═ angle [ R (n, k) ]; n is 1, …, N; k ═ 1, …, K }, where angle denotes angle;
step four, calculating the variance of each point of the N phase signals obtained in the previous step to obtain a phase variance signal,
and performing linear fitting on the phase variance signal, wherein the slope after fitting is 2 pi · delta v, and the line width of the laser is delta v.
11. The demodulation method of the narrow linewidth laser linewidth measurement system according to claim 10, wherein: in the fourth step, the photoelectric field expression output by the laser is as follows
Wherein j is
E0Is the amplitude of the electric field, ω0Is the central angular frequency of the laser and,
is phase random fluctuation, causes laser linewidth broadening, where t is time,
is the wiener process, an increment thereof
Obeying a Gaussian distribution
The parameter Δ v is defined as the laser linewidth and is thus obtained
The laser line width can be obtained by the variance sum s of the laser line width and the laser line width; or to obtain
The line width of the laser can be obtained by calculating the slope according to the functional relation between the variance of the (S) and the (S).
12. The demodulation method of the narrow linewidth laser linewidth measurement system according to claim 11, wherein: the expression of the beat frequency signal of the back scattering light returned by a Rayleigh scattering point on the single-mode fiber or a weak reflection point on the weak reflection point array and the local light is
Wherein A is the amplitude, W is a rectangular window function, and the window function has a duration in the range of [ s, s + τ ]p]S is the round-trip transmission time of the light from the incident end of the optical fiber to the reflection point; through Hilbert transform, the phase term of I (t) can be calculated, and if the system state is stable, the phase term is
C is a phase constant, and because s corresponding to scattering points at different positions is different, phase terms of backscattered light returned by the scattering points at all positions on the whole optical fiber and local optical beat frequency signals are calculated, and phase variance is calculated, so that the phase constant can be obtained
And the linear function relation between the linear function relation and the s can obtain the line width delta v of the laser by calculating the slope of the phase variance.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4830513A (en) * | 1986-11-24 | 1989-05-16 | Cselt - Centro Studi E Laboratori Telecomunicazioni S.P.A. | Distributed temperature sensor with optical-fiber sensing element |
| CN110487308A (en) * | 2019-08-27 | 2019-11-22 | 南京大学 | A kind of high-performance coherent detection type Φ-OTDR realization system and method based on PGC demodulation |
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| US4830513A (en) * | 1986-11-24 | 1989-05-16 | Cselt - Centro Studi E Laboratori Telecomunicazioni S.P.A. | Distributed temperature sensor with optical-fiber sensing element |
| CN110487308A (en) * | 2019-08-27 | 2019-11-22 | 南京大学 | A kind of high-performance coherent detection type Φ-OTDR realization system and method based on PGC demodulation |
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| CN115655663B (en) * | 2022-10-20 | 2024-02-06 | 中国航天三江集团有限公司 | Linewidth measurement method and system of all-fiber structure laser |
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