CN113804405A - Micro optical fiber dispersion measuring device based on double-coupler ring optical path structure - Google Patents
Micro optical fiber dispersion measuring device based on double-coupler ring optical path structure Download PDFInfo
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Abstract
The invention discloses a micro optical fiber dispersion measuring device based on a double-coupler annular optical path structure, which can be used for high-precision dispersion measurement of optical fibers and devices with small dispersion coefficients or short lengths and belongs to the technical field of optical fiber measurement. The device comprises a wide-spectrum light source, an interferometer, a double-coupler loop structure, a detection module and a dispersion calculation module, and is characterized in that: the wide-spectrum light source provides a light source for the interferometer, the double-coupler loop structure is connected to a measuring arm of the interferometer, interference signals with dispersion information can be obtained by adjusting the optical path of a reference arm, and finally, the dispersion information in the interference signals is extracted by using a dispersion calculation module. On one hand, the double-coupler loop structure additionally provides a power coupling proportion parameter which can be adjusted, on the other hand, under the condition of the same system dynamic range, the double-coupler loop structure can support more circulation times of the optical wave train, and further improves the dispersion measurement precision. The invention solves the problem that the prior art is difficult to measure the micro dispersion of the optical fiber and the device thereof with high precision.
Description
Technical Field
The invention belongs to the technical field of optical fiber measurement, and particularly relates to an optical fiber device micro-chromaticity dispersion measuring device based on a ring light path structure.
Background
Optical fiber communication has become an important part of communication systems due to the characteristics of large transmission capacity and strong anti-interference capability. With the development of society, the amount of various information is increasing, which requires a higher-speed communication system, and in the high-speed optical fiber communication system, the presence of chromatic dispersion causes intersymbol interference, so chromatic dispersion compensation is required for the optical fiber communication system. The dispersion compensation is performed, and the dispersion value of the optical fiber communication system needs to be known first, so that the dispersion measurement becomes an indispensable link. Common dispersion measurement methods include time delay methods, phase shift methods, interferometry, and the like.
For the time delay method, the basic principle is to inject the light pulses with different wavelengths into the optical fiber and the device to be measured respectively, the arrival time of the light pulses with different wavelengths at the other end is different due to the existence of dispersion, and the dispersion value can be calculated by measuring the arrival time difference of the light pulses with different wavelengths. For example, U.S. Pat. No. 20040169848, also referred to in the literature "Comparison of Single-mode fiber dispersion measurement techniques" (Lightwave technique, vol.3, No.5, pp.958-966, 1985), has a measurement accuracy of chromatic dispersion of around 1ps/nm, which is very low because it is difficult to obtain a delay value accurately. The time delay method for measuring dispersion requires that the length of the optical fiber to be measured is in km level to accumulate enough dispersion amount, so that the arrival time difference between different pulses can be relatively accurately distinguished, and therefore, the method cannot be used for measuring the dispersion of a short optical fiber.
The phase shift method is to modulate the light with sine intensity and inject the modulated light signal into the fiber and device to be measured, and the light signal will have delay due to the dispersion effect, and the modulated light signals with different frequency components will have different delays, so the dispersion value can be calculated from the delay among the light signals with different frequencies. Phase Shift methods have been well studied, for example, Francois Babin et al, USA, propose an apparatus and method for measuring the Phase difference of intensity modulated Optical signals (US6429929), and for example, BRUNO COSTA et al, in the document "Phase Shift Technique for the Measurement of Chromatic Dispersion in Optical Fibers Using LED's" (IEEE Transactions on Microwave Theory and Techniques, vol.30, No.10, pp.1497-1503, 1982), measure the Chromatic Dispersion of Optical Fibers with an accuracy of 1ps/nm Using a Phase Shift method based on an LED light source. By observing various phase shifting methods and improved phase shifting methods, it is known that the minimum measurement length of the phase shifting method is dozens of meters, and the dispersion of a short optical fiber (less than 1m) cannot be accurately measured.
The basic principle of the time domain interference method is that the wavelength of a light source is fixed, the optical path difference between two arms is changed, so that an interference signal related to time is obtained, Fourier transformation is carried out on the time domain interference signal, phase information is obtained, then the phase is differentiated to obtain a dispersion value, and the measurement precision can reach 0.0015 ps/nm. Carlos Palavicini et al measured dispersion of photonic crystal fiber of 81.4cm length using an optical low coherence interferometer in the literature "Phase-sensitive optical low-coherence technique to the characterization of photonic crystal fibers (Opti Lett, vol.30, No.4, p.361, 2005)". Although the general time domain interferometry can measure the dispersion of a short fiber (less than 1m), the measurement accuracy of some fiber with extremely small dispersion coefficient is rapidly reduced. For the chinese patent (202110827979.X), a chromatic dispersion measuring device based on a ring optical path structure is proposed, which can perform chromatic dispersion measurement on optical fibers and devices with small dispersion coefficient and short length, but the loop structure only uses one coupler, and the straight arm is directly connected with the interferometer, so that useless optical signals directly enter the detector, the signal-to-noise ratio of the interference signals is reduced, and the precision of chromatic dispersion measurement is reduced.
The spectral domain interferometry is to fix the length of two arms of an interferometer and change the wavelength of a light source so as to obtain an interference spectrum. Due to the existence of dispersion, the optical path difference of light with different wavelengths passing through the interferometer is different (the lengths of the two arms are fixed, and different refractive indexes exist when the wavelengths are different), so that different wavelengths are displayed on an interference spectrum and correspond to different intensities. MITSUHULURO TATEDA et al measured the Dispersion of a Single Mode Optical Fiber of less than 1m in the literature "Interferometric Method for Chromatic Dispersion Measurement in a Single-Mode Optical Fiber" (Journal of Quantum Electronics, Vol.17, pp.404-4071981). Another example, US patent (US20100134787) measures the dispersion of an 11.9cm long fiber using spectral domain interferometry. The method can measure the optical fiber with the diameter less than 1m, and the measurement precision of the chromatic dispersion of the method can reach 0.0001ps/nm for an unbalanced spectral domain interference method, and can reach 0.00007ps/nm for a balanced spectral domain interference method. However, for a micro-dispersion-coefficient optical fiber (e.g., a hollow fiber), the measurement accuracy of the spectral domain interferometry is greatly reduced due to the small dispersion amount, and the dispersion of the optical fiber and the device with small dispersion coefficient and short length cannot be accurately measured.
The time delay method and the phase shift method cannot perform high-precision dispersion measurement on short-length optical fibers, and although the common time domain interferometry and the spectral domain interferometry can measure short optical fibers, the measurement precision of some optical fibers with small dispersion coefficients can be greatly reduced, so that the device for performing dispersion measurement on optical fibers and devices with micro-dispersion is very important. In the single coupler loop structure based on the optical fiber resonant cavity type, as the useless optical signals of the coupler straight-through arm directly enter the detector, larger noise is introduced into the acquired interference signals, the signal-to-noise ratio is reduced, and the dispersion measurement accuracy is degraded, so that a loop structure capable of eliminating the influence of the useless optical signals of the coupler straight-through arm is needed. In view of the above problems, the double-coupler-based loop structure provided by the invention can amplify the dispersion amount through optical circulation to improve the measurement accuracy, and can eliminate the noise influence of the coupler straight arm to improve the signal-to-noise ratio, thereby further improving the accuracy of dispersion measurement. Therefore, the dispersion measuring device with the double-coupler-based loop structure can perfectly solve the problem that the method cannot measure the optical fiber and the device with small dispersion coefficient and short length, and can support more optical wave circulation times under the condition of the same system dynamic range, thereby further improving the dispersion measuring precision.
Disclosure of Invention
The invention aims to provide a micro optical fiber dispersion measuring device based on a double-coupler ring optical path structure, which solves the problem that the dispersion of optical fibers and devices with small dispersion coefficient and short length is difficult to accurately measure in the background technology, and meanwhile, the double-coupler ring optical path structure can support optical wave arrays with more ring times under the condition of the same system dynamic range, thereby further improving the dispersion measuring precision.
A micro optical fiber dispersion measuring device based on a double-coupler ring optical path structure is characterized in that: the wide-spectrum light source 10, the interferometer 20, the double-coupler loop structure 30, the detection module 60 and the dispersion calculation module 80 form the device, wherein:
1) light emitted by the broad spectrum light source 10 is injected into the interferometer 20, the double-coupler loop structure 30 is connected into the interferometer 20, the output light of the interferometer 20 is detected by the detection module 60, and an interference signal detected by the detection module 60 is sent to the dispersion calculation module 80;
2) in the double-coupler loop structure 30, light is injected into the second coupler 31 from the first input end 311 of the second coupler, after splitting, one path is output from the second output end 314 of the second coupler, the other path is output from the first output end 313 of the second coupler, and is injected into the third coupler 32 through the optical fiber to be tested and the device 33 and the first input end 321 of the third coupler, after splitting, one path is output from the second output end 324 of the third coupler, the other path is output from the first output end 323 of the third coupler and is injected into the second coupler 31 through the second input end 312 of the second coupler, and a circuit is completed for one time, and the circuit is performed again according to the path;
3) in the dispersion calculation module 80, the data acquisition card 81 acquires the interference signal from the detection module 60, and then intercepts two interference peaks by the interference peak intercepting unit 82, wherein the first interference peak 885 is input to the first dispersion coefficient extracting unit 83 for dispersion coefficient extraction, the second interference peak 884 is input to the second dispersion coefficient extracting unit 84 for dispersion coefficient extraction, and the dispersion coefficients of the two interference peaks are input to the dispersion difference unit 85 for difference operation, so as to obtain the dispersion coefficients of the optical fiber to be detected and the device 33.
The interferometer 20 is characterized in that: light is injected into the first coupler 21 from the first input end 211 of the first coupler and is divided into two paths, one path enters the fourth coupler 26 through the second output end 214 of the first coupler, the loop structure 30 of the double coupler and the second input end 262 of the fourth coupler, wherein the m-th wave packet 251 is circularly output for m times in the loop structure 30 of the double coupler, the m + 1-th wave packet 252 is circularly output for m +1 times, and the m + 2-th wave packet 253 is circularly output for m +2 times; the other path enters the fourth coupler 26 through the first coupler first output end 213, the reference fiber 22, the optical path correlator 23 and the fourth coupler first input end 261; the two light beams are combined at the fourth coupler 26.
The interferometer 20 is characterized in that: the length of the second output terminal 214 of the first coupler is L214Refractive index n, and length L of the fourth coupler second input 262262Refractive index n, length L of first coupler first output end 213213Refractive index n and length L of the fourth coupler first input 261261Refractive index n, length L of reference fiber 2222Refractive index n, maximum delay length Δ L of the optical path correlator 2323(max)。
The double-coupler loop structure 30 is characterized in that: the length of the first input 311 of the second coupler is L311Refractive index n, length L of second coupler second input end 312312Refractive index n, length L of the first output end 313 of the second coupler313Refractive index n, length L of the first input end 321 of the third coupler321Refractive index n, length L of the first output 323 of the third coupler323Refractive index n, and length L of second output end 324 of third coupler324Refractive index n, length L of the optical fiber to be measured and the device 3333Refractive index of n33。
The optical path correlator 23 is characterized in that: light can enter from the first collimating lens 231 and sequentially pass through the first reflecting mirror 233, the second reflecting mirror 234 and the second collimating lens 232; the light can also enter from the second collimating lens 232 and pass through the second reflecting mirror 234, the first reflecting mirror 233 and the first collimating lens 231 in sequence; moving the first mirror 233 and the second mirror234, the optical path optical length can be changed, and the maximum optical length is: Δ L23(max)。
The reference optical fiber 22 is characterized in that: the reference fiber 22 has a refractive index n and a length L22It should satisfy:
where m is the number of circulations of light in the dual-coupler loop structure 30.
The double-coupler loop structure 30 is characterized in that: if the first input 311 of the second coupler is used as the optical input, the ratio of the output optical power of the first output 313 of the second coupler to the output optical power of the second output 314 of the second coupler is a; if the second coupler second input end 312 is used as the optical input end, the ratio of the output optical power of the second coupler first output end 313 to the output optical power of the second coupler second output end 314 is
If the third coupler first input end 321 is used as the optical input end, the ratio of the output optical power of the third coupler first output end 323 to the output optical power of the third coupler second output end 324 is b; if the third coupler second input end 322 is used as the optical input end, the ratio of the output optical power of the third coupler first output end 323 to the output optical power of the third coupler second output end 324 is
The output power of the second output terminal 324 of the third coupler is:
a and b are selected to satisfy Pout，m≥PBPDWherein P isBPDIndicating the minimum detectable optical power of the detection module 60.
The above-mentionedThe dual coupler loop structure 30, characterized by: the splitting ratio parameter a of the second coupler 31 and the splitting ratio parameter b of the third coupler 32 should satisfy
The double-coupler loop structure 30 is characterized in that: the second coupler first input 311 and the second coupler first output 313 do not form a through arm.
In the double-coupler loop structure 30, the first input end 311 of the second coupler and the second output end 314 of the second coupler form a straight-through arm, the optical wave train output at the second output end 314 of the second coupler belongs to a useless optical signal, in order to exclude the useless optical signal from the interferometer, the second output end 314 of the second coupler is suspended, and the third coupler 32 is added as the optical wave train output end of the loop structure, so that the structure can support optical wave trains with more ring times under the condition of the same system dynamic range, and further the dispersion measurement precision is improved.
The invention provides a micro optical fiber dispersion measuring device based on a double-coupler annular optical path structure. By introducing the loop structure based on the double couplers, the dispersion of the optical fiber and the device can be amplified, and meanwhile, the influence of optical noise in the straight arm of the couplers can be eliminated, so that the dispersion measurement precision can be greatly improved. The invention has the advantages of high precision, small measurable dispersion amount, low cost and the like, and can be widely used for dispersion measurement of optical fibers and devices with small dispersion coefficient and short length.
The invention relates to a micro optical fiber dispersion measuring device based on a double-coupler annular light path structure based on a time domain interference method. The basic principle of the time domain interference method is that when light fields with different frequencies are transmitted in a medium, different phase velocities exist, and after wide-spectrum light is transmitted for a certain time, the equal phase surfaces of the light fields with different frequencies can be located at different positions, so that the whole wave packet is widened, and the widening degree of the wave packet corresponds to the dispersion amount one by one. According to the principle, narrow-band light with different central wavelengths can be injected into the time domain interferometer respectively, corresponding interferograms are recorded respectively, and the dispersion value can be calculated by utilizing the time delay difference among the interferograms, so that the method is called as a direct time domain interferometry. The direct time domain interference method has high requirements on a light source and is time-consuming, so that light with multiple wavelengths (namely wide-spectrum light) can be injected into a time domain interferometer at one time to obtain an interference pattern formed by overlapping multiple single-wavelength interference signals, then the interference pattern is subjected to Fourier transform to be decomposed into single-wavelength interference signals, and a dispersion value can be obtained from a phase spectrum obtained by the Fourier transform.
The first interference peak 881, the second interference peak 882 and the third interference peak 883 generated by the device respectively contain m times, m +1 times and m +2 times of actual dispersion of the optical fiber and the device to be measured, two interference peaks are selected and the dispersion thereof is respectively calculated, the dispersion of the two interference peaks is subtracted, and finally the difference of the circulation times of the two interference peaks is divided, so that the actual dispersion of the optical fiber and the device to be measured can be obtained. Generally, m times of circular interference peaks (m is more than 2) and adjacent interference peaks are used for extracting the dispersion amount of the optical fiber and the device to be measured, the dispersion amount of the m times of circular interference peaks is m times of the actual dispersion amount of the optical fiber and the device to be measured, which is equivalent to m times of amplification of the dispersion amount of the optical fiber and the device to be measured, so that small dispersion amount is converted into large dispersion amount, and the measurement accuracy of a measurement system is improved. In addition, the loop structure based on the double couplers can effectively eliminate the optical noise influence of the straight arm of the coupler, so that the signal-to-noise ratio of an interference peak is improved, and the dispersion measurement precision is further improved.
The device in fig. 1 can obtain the optical wave packet circulating many times in the double-coupler loop structure 30, and the interference peak with specific circulating times can be obtained by matching the optical paths of the reference light and the test light by using the reference optical fiber 22 with corresponding length and adjusting the optical path of the optical path correlator 23, as shown in fig. 3. Intercepting the m-1 th and m-th circular interference peaks, respectively performing Fourier transform on the two interference peaks, and respectively performing weighted least square fitting on the phase spectrum according to the magnitude spectrum to obtain the phase spectrum phi of the m-1 th circular interference peakm-1Phase spectrum phi of (omega) th and mth circular interference peaksm(ω) on which derivation yields the correspondingGroup delay:
firstly, the group delay is converted from the frequency space to the wavelength space to obtain taum(lambda) and taum-1(λ), derived from which the group delay dispersion is obtained:
the group delay dispersion of the optical fiber and the device to be measured can be obtained by the subtraction of (5) and (6):
DDUT(λ)＝Dm(λ)-Dm-1(λ) (7)
in the process of obtaining the dispersion of the optical fiber and the device to be measured, m times of circular interference peaks (m is more than 2) and adjacent interference peaks are generally used for extracting the dispersion coefficient of the optical fiber and the device to be measured, the dispersion of the m times of circular interference peaks is m times of the actual dispersion of the optical fiber and the device to be measured, which is equivalent to m times of the amplification of the dispersion of the optical fiber and the device to be measured, so that small dispersion is converted into large dispersion (equivalent to the amplification effect), the sensitivity of a measuring system is improved, high-precision dispersion measurement is ensured, and the method is very suitable for the dispersion measurement of a micro-dispersion optical fiber and a device.
Compared with the prior art, the invention has the advantages that:
(1) the double-coupler loop structure can eliminate the optical noise influence of the straight arm of the coupler, so that the signal-to-noise ratio of the device is improved, and the dispersion measurement precision is further improved;
(2) the invention solves the problem that the prior art is difficult to carry out high-precision dispersion measurement on the optical fiber and the device thereof with small dispersion coefficient and short length;
(3) the optical fiber type interferometer has better stability;
(4) the invention only needs a cheap wide-spectrum light source and does not need an expensive spectrometer and the like, thereby realizing the dispersion measurement with low cost;
(5) the invention can be used for high-precision measurement of micro dispersion.
Drawings
FIG. 1 is a diagram of a double coupler loop configuration based microdispersion measurement apparatus;
FIG. 2 is a graph of the splitting ratio versus the output power of the loop structure (six cycles);
fig. 3 shows interference peaks in 5 and 6 rounds of loop.
Detailed Description
For clearly explaining the micro-fiber dispersion measuring device based on the dual-coupler loop optical path structure, the present invention is further described with reference to the embodiments and the drawings, but the protection scope of the present invention should not be limited thereby.
FIG. 1 is a diagram of an apparatus of the present invention in which the main optoelectronic devices are selected and parametered as follows:
1) the central wavelength of a wide-spectrum light source 10 is 1550nm, the spectrum width is 50nm, and the fiber output power range is from 0 to 10 mW;
2) the first coupler 21, the second coupler 31, the third coupler 32 and the fourth coupler 26 are all single-mode couplers, and the central working wavelength is 1550 nm;
3) the optical path scanning range of the optical path correlator is from 0 to 160 cm;
4) the optical fiber to be tested selects a single-mode optical fiber, the other connecting optical fibers are single-mode optical fibers, and the refractive index is 1.456;
if the interference peak is taken six times in a loop, in the dual-coupler loop structure 30, the optimal splitting ratios of the second coupler 31 and the third coupler 32 can be calculated according to the formula (2), and the relationships between the splitting ratio parameters a and b and the loop structure output power are shown in fig. 2. The optimal splitting ratio of the second coupler 31 is 85: 15, the optimal splitting ratio of the third coupler 31 is 85: 15, and the optical wave packet intensity of the loop structure outputting six circular times can be calculated according to the power distribution relation of the loop structure:
Pout，6＝0.0032Pin (8)
if the input light P is takeninAnd if the power is 1mW, the output power after twenty circulations is 0.0032mW, and the power can be detected by a detector.
In the interferometer 20, Δ L is taken23(max)＝1.6、L213＝1、L261＝1、L214＝1、L311＝1、L324＝1、L262＝1、L313＝0.1、L33＝0.13、L321＝0.1、L323＝0.1、L312The unit is 0.1, which is meters, and all the fibers except the fiber 33 to be measured are single-mode fibers, and the refractive index is n. To obtain six circular interference peaks, the length of the reference fiber 22 should be selected within a range of 3.88L or less based on the previous analysis22Less than or equal to 4.98, and the unit is meter; if the interference peak is obtained by five times of circular, the length of the reference fiber 22 should be selected within the range of 3.35L224.45 is less than or equal to the unit of meter, and therefore, the analysis shows that the length of the reference optical fiber is 3.9 meters, which can ensure that the optical path correlator scans to obtain two interference peaks, as shown in fig. 3.
After the reference optical fiber is selected, the device is started to obtain interference peaks, the obtained six-time and five-time annular interference peaks are put into the dispersion calculation module 80 to extract dispersion coefficients, and finally the chromatic dispersion of the optical fiber to be measured and the device 33 is 0.00495 ps/nm.
Claims (9)
1. A micro optical fiber dispersion measuring device based on a double-coupler ring optical path structure is characterized in that: this device is constituteed to broad spectrum light source (10), interferometer (20), double coupler loop structure (30), detection module (60) and dispersion calculation module (80), wherein:
1) light emitted by a wide-spectrum light source (10) is injected into an interferometer (20), a double-coupler loop structure (30) is connected into the interferometer (20), output light of the interferometer (20) is detected by a detection module (60), and an interference signal detected by the detection module (60) is sent to a dispersion calculation module (80);
2) in a double-coupler loop structure (30), light is injected into a second coupler (31) from a first input end (311) of the second coupler, after light splitting, one path of light is output from a second output end (314) of the second coupler, the other path of light is output from a first output end (313) of the second coupler, and is injected into a third coupler (32) through an optical fiber to be tested and a device (33) and a first input end (321) of the third coupler, after light splitting, one path of light is output from a second output end (324) of the third coupler, the other path of light is output from a first output end (323) of the third coupler and is injected into the second coupler (31) through a second input end (312) of the second coupler, primary circulation is completed, and circulation is performed again according to the path;
3) in a dispersion calculation module (80), a data acquisition card (81) acquires an interference signal from a detection module (60), the acquired interference signal intercepts two interference peaks through an interference peak intercepting unit (82), wherein a first interference peak (885) is input to a first dispersion coefficient extraction unit (83) for dispersion coefficient extraction, a second interference peak (884) is input to a second dispersion coefficient extraction unit (84) for dispersion coefficient extraction, and dispersion coefficients of the two interference peaks are input to a dispersion difference unit (85) for difference operation, so that dispersion coefficients of an optical fiber to be detected and a device (33) are obtained.
2. An interferometer (20) as claimed in claim 1, characterised by: light is injected into a first coupler (21) from a first input end (211) of the first coupler and is divided into two paths, one path enters a fourth coupler (26) through a second output end (214) of the first coupler, a double-coupler loop structure (30) and a second input end (262) of the fourth coupler, wherein an m-th wave packet (251) is circularly output in the double-coupler loop structure (30) for m times, an m + 1-th wave packet (252) is circularly output in an m + 1-th time, and an m + 2-th wave packet (253) is circularly output in an m + 2-th time; the other path enters a fourth coupler (26) through a first coupler first output end (213), a reference fiber (22), an optical path correlator (23) and a fourth coupler first input end (261); the two light beams are combined at a fourth coupler (26).
3. By claimThe interferometer (20) of claim 1, characterized by: the second output terminal (214) of the first coupler has a length L214Refractive index n, and length L of the fourth coupler second input end (262)262Refractive index n, length L of first output end (213) of first coupler213Refractive index n, and length L of the fourth coupler first input end 261261Refractive index n, length L of reference fiber (22)22The refractive index is n, and the maximum delay length of the optical path correlator (23) is Delta L23(max)。
4. The dual coupler loop architecture (30) of claim 1, wherein: the length of the first input terminal (311) of the second coupler is L311Refractive index n, length L of second input end (312) of second coupler312Refractive index n, length L of the first output end (313) of the second coupler313Refractive index n, length L of the first input end (321) of the third coupler321Refractive index n, length L of first output end 323 of the third coupler323Refractive index n, and length L of second output end (324) of third coupler324The refractive index is n, the length of the optical fiber to be measured and the device (33) is L33Refractive index of n33。
5. The optical path correlator (23) of claim 2 wherein: the light can enter from the first collimating lens (231) and sequentially passes through the first reflecting mirror (233), the second reflecting mirror (234) and the second collimating lens (232); the light can also enter from the second collimating lens (232) and sequentially pass through the second reflecting mirror (234), the first reflecting mirror (233) and the first collimating lens (231); by moving the first mirror (233) and the second mirror (234) simultaneously, the optical path length can be changed, and the maximum optical path length is: Δ L23(max)。
6. The reference fiber (22) of claim 2, wherein: the reference fiber (22) has a refractive index n and a length L22It should satisfy:
where m is the number of circulations of light in the dual-coupler loop structure (30).
7. The dual coupler loop architecture (30) of claim 1, wherein: if the first input end (311) of the second coupler is used as the optical input end, the ratio of the output optical power of the first output end (313) of the second coupler to the output optical power of the second output end (314) of the second coupler is a; if the second coupler second input terminal (312) is used as the optical input terminal, the ratio of the output optical power of the second coupler first output terminal (313) to the output optical power of the second coupler second output terminal (314) is
If the first input end (321) of the third coupler is used as the optical input end, the ratio of the output optical power of the first output end (323) of the third coupler to the output optical power of the second output end (324) of the third coupler is b; if the second input terminal (322) of the third coupler is used as the optical input terminal, the ratio of the output optical power of the first output terminal (323) of the third coupler to the output optical power of the second output terminal (324) of the third coupler is
The output power of the second output terminal (324) of the third coupler is:
a and b are selected to satisfy Pout，m≥PBPDWherein P isBPDIndicating the minimum detectable optical power of the detection module (60).
8. The dual coupler loop architecture (30) of claim 7, wherein: division of the second coupler (31)The light ratio parameter a and the splitting ratio parameter b of the third coupler (32) should satisfy
9. The dual coupler loop architecture (30) of claim 1, wherein: the second coupler first input (311) and the second coupler first output (313) do not form a pass-through arm.
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