CN112082651A - Polarization characteristic measurement method for assembling full polarization-maintaining Sagnac closed light path - Google Patents
Polarization characteristic measurement method for assembling full polarization-maintaining Sagnac closed light path Download PDFInfo
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Abstract
The invention provides a polarization characteristic measurement method for assembly of a full-polarization-maintaining Sagnac closed light path, which comprises the following steps: the Y waveguide and the polarization-maintaining optical fiber ring which are used for assembling the full-polarization-maintaining Sagnac closed optical path are connected into a non-closed optical path and a closed optical path in sequence, and are respectively connected into an optical coherence domain polarization measuring instrument for measurement, and by combining a second-order polarization crosstalk effect, all polarization characteristic information such as first-order polarization crosstalk of all connection points in the closed optical path, distributed polarization crosstalk of the full length of the polarization-maintaining optical fiber ring, extinction ratio of a Y waveguide chip and the like can be obtained. The method realizes the measurement of the polarization characteristic in the assembly process of the full polarization-preserving Sagnac closed optical path, can be widely used for monitoring and evaluating the distributed polarization crosstalk of all optical devices and connecting points in the closed optical path, and has important significance for the development of high-performance interference optical sensors.
Description
Technical Field
The invention relates to a polarization characteristic measuring method for assembling a full polarization-preserving Sagnac closed light path, and belongs to the technical field of measurement of optical devices and light path components.
Background
The fiber Sagnac interferometer was proposed and proven more than 40 years ago, and was originally a closed optical path formed by connecting a common coupler and an optical fiber and used for measuring the angular velocity of rotation relative to the inertial space, namely, the optical path structure adopted by the original fiber optic gyroscope. Through years of research and development, a full polarization-maintaining scheme formed by connecting a Y waveguide and a polarization-maintaining optical fiber ring is generally adopted in the current Sagnac closed optical path structure, wherein the Y waveguide is a highly integrated optical chip and has the functions of optical beam splitting, beam combining, polarization, modulation and the like, and the polarization-maintaining optical fiber ring is formed by winding hundreds of meters or even thousands of meters of polarization-maintaining optical fibers according to a certain process and is used for sensing external environment changes. The application field of the full polarization-maintaining Sagnac closed optical path is not limited to the optical fiber gyroscope, and the full polarization-maintaining Sagnac closed optical path is widely applied to the fields of optical fiber hydrophones, optical fiber current transformers, detectors and the like. The scheme has the advantages that the polarization fading effect can be inhibited, and the measurement sensitivity of various interference type optical sensors is further improved. The problem of the scheme is generally shown in that the polarization phase error is introduced by the defect of the polarization characteristics of the optical device and the connecting point in the closed optical path, and the measurement accuracy of the sensor is directly influenced. Therefore, it is necessary to fully monitor the polarization characteristics of Sagnac in the process of assembling the fully-polarization-maintaining closed optical path, so as to ensure that the polarization characteristics of the optical devices and the connection points in the closed optical path meet the use requirements of the high-performance optical sensor.
The fiber optic gyroscope is the most mature type of optical sensor applied to Sagnac interferometer, and taking the assembly of the fiber optic gyroscope as an example, core devices such as a Y waveguide, a polarization maintaining fiber ring and the like are usually tested and screened separately, and the testing method is already mature. For example: in 2008, yao xiao tian et al, suzhou halo technology ltd, disclosed a method and an apparatus for measuring the quality of an optical fiber ring for an optical fiber gyro (chinese patent application No. CN 200810119075.6), in which the quality of an optical fiber sensitive ring was evaluated from the viewpoint of temperature conductivity; in 2013, the inventor of Harbin engineering university discloses a dual-channel optical performance testing device of an integrated waveguide modulator and a polarization crosstalk identification and processing method thereof (Chinese patent application No. CN201310744466.8), and a white light interferometer is used for realizing the test of Y-waveguide dual-channel distributed polarization crosstalk. And directly putting the screened qualified device into a fiber-optic gyroscope system for testing after welding, and evaluating the testing performance of the whole fiber-optic gyroscope. For example: in 2017, YaoXIANG day of Suzhou halo technology, Inc. discloses a testing method, a testing device, a storage medium and a computer device (Chinese patent application No. CN201710867702.3) of a fiber-optic gyroscope, and the testing result of the polarization characteristic of a core device is brought into a calculation model to obtain the gyroscope quality parameters such as phase error caused by polarization crosstalk and zero-offset stability in a fiber-optic gyroscope system. The method directly tests a single device to a system complete machine, and neglects the polarization characteristic of a connection point between the devices. In order to fully obtain the optical path connection state, an optical path level test is required to be added between the device level test and the system level test. For the connection state test of the sensitive closed optical path, the connection loss test and the polarization characteristic test are mainly divided. In 2018, a light path performance test system for a fiber-optic gyroscope (chinese patent application No. CN201810996752.6) was disclosed by promised people of the optical-electrical technology limited company in the time of beijing aerospace, and the test system can test the connection loss and total loss of a light path of an optical device in a closed light path. However, there is still no effective method for polarization characteristic test of closed optical path.
With the rapid development of high-precision fiber optic gyroscopes, numerous researchers have proposed schemes for direct coupling of the Y waveguide and the polarization maintaining fiber optic ring, so as to reduce the number of connection points in a closed optical path and reduce the phase error of the gyroscope introduced by polarization crosstalk. For example: in 2013, Liuyin et al, of Weitong science and technology GmbH, Beijing, disclose a fiber optic gyroscope without optical fiber fusion points and a method for manufacturing the fiber optic gyroscope (Chinese patent application No. CN 201310410382.0); in the same year, Huoshan et al, the sixth and eighth institute of the China aviation industry, disclose a fusion-free manufacturing method of a high-precision fiber-optic gyroscope (Chinese patent application No. CN201310676683.8), wherein a holding device and an adhesion method are mentioned, in which a Y waveguide and a polarization-maintaining fiber ring are directly coupled, and adjustment, alignment, dispensing and fixation can be performed only by means of imaging, positioning and calibration. The alignment condition is not visually monitored through the connection point polarization crosstalk information, and large alignment deviation is easy to generate. In 2016, Yuanyonghui Gui et al of Harbin engineering university disclose a method for assembling a core sensitive optical path of a fiber-optic gyroscope (Chinese patent application No.: CN201610265230.X), which monitors the pair-axis condition of a connection point by measuring polarization crosstalk, but only can measure the polarization crosstalk of the connection point in a non-closed state, but cannot measure the polarization crosstalk when the optical path is in a closed state, and is only suitable for assembling the fiber-optic gyroscope. In summary, there is still a lack of an effective method for measuring the polarization characteristics of all the optical devices and joints in a fully-polarization-preserving Sagnac closed optical path.
The invention provides a polarization characteristic measuring method for assembling a full polarization-preserving Sagnac closed optical path, aiming at the problems, which is characterized by comprising the following steps of: the Y waveguide and the polarization-maintaining optical fiber ring which are used for assembling the full-polarization-maintaining Sagnac closed optical path are connected into a non-closed optical path and a closed optical path in sequence, and are respectively connected into an optical coherence domain polarization measuring instrument for measurement, and by combining a second-order polarization crosstalk effect, all polarization characteristic information such as first-order polarization crosstalk of all connection points in the closed optical path, distributed polarization crosstalk of the full length of the polarization-maintaining optical fiber ring, extinction ratio of a Y waveguide chip and the like can be obtained. The method realizes the measurement of the polarization characteristic in the assembly process of the full polarization-preserving Sagnac closed optical path, can be widely used for monitoring and evaluating the distributed polarization crosstalk of all optical devices and connecting points in the closed optical path, and has important significance for the development of high-performance interference optical sensors.
Disclosure of Invention
The invention aims to provide a polarization characteristic measuring method for assembling a full-polarization-maintaining Sagnac closed optical path, which is used for monitoring and evaluating distributed polarization crosstalk of all optical devices and connecting points in the closed optical path and can comprehensively improve the polarization performance of the closed optical path.
The purpose of the invention is realized as follows: the method comprises the following steps:
(1) selecting a Y waveguide 206 for assembling a full polarization-maintaining Sagnac closed optical path, and measuring the lengths of a Y waveguide input polarization-maintaining tail fiber 204, a Y waveguide first output polarization-maintaining tail fiber 208 and a Y waveguide second output polarization-maintaining tail fiber 217 to be l1，l2，l3And require | l3-l2If is greater than 10cm, a connection point B205 is formed between the Y waveguide 206 and the Y waveguide input polarization-maintaining tail fiber 204, a connection point C207 is formed between the Y waveguide first output polarization-maintaining tail fiber 208, and a connection point F216 is formed between the Y waveguide second output polarization-maintaining tail fiber 217;
(2) selecting a polarization maintaining fiber ring 211 for assembling a full polarization maintaining Sagnac closed light path, and carrying out 0-degree axial welding on a first port 210 of the polarization maintaining fiber ring and a first output polarization maintaining tail fiber 208 of a Y waveguide to form a connecting point D209;
(3) selecting a 45-degree polarizer 201, and measuring the length l of the 45-degree polarizer polarization-maintaining tail fiber 202pSelecting a 45-degree analyzer 215, and measuring the length l of the 45-degree analyzer polarization-maintaining pigtail 214a；
(4) Carrying out 0-degree axial fusion on a 45-degree polarizer polarization-maintaining tail fiber 202 and a Y waveguide input polarization-maintaining tail fiber 204 to form a connection point A203, and connecting a 45-degree polarizer single-mode tail fiber 218 with an SLD (narrow-band light-emitting diode) broad-spectrum light source 220;
(5) carrying out 0-degree axial welding on a polarization maintaining tail fiber (214) of the 45-degree polarization analyzer and a second port (212) of a polarization maintaining optical fiber ring to form a connection point E (213), and connecting a single-mode tail fiber (219) of the 45-degree polarization analyzer with an optical coherence domain polarization measuring instrument (221);
(6) distributed polarization crosstalk measurement is carried out on a non-closed optical path, first-order polarization crosstalk of a connection point A, B, C, D, E, distributed polarization crosstalk of the full length of a polarization-maintaining optical fiber ring and extinction ratio measurement information of a Y waveguide chip are extracted from a measurement map at one time, the position of each interference signal peak can be calculated based on the length of each section of polarization-maintaining tail fiber, and the birefringence of the polarization-maintaining optical fiber in the optical path is assumedIs Δ nfBirefringence of the Y waveguide chip is DeltanYThe Y waveguide 206 has a length lYThe polarization maintaining fiber ring 211 has a length lfThen the peak positions of the interference signals representing the first order polarization crosstalk of connection point A, B, C, D, E are: sA＝Δnf·lp，SB＝Δnf·(lp+l1)，SC＝Δnf·(l2+lf+la)，SD＝Δnf·(lf+la)，SE＝Δnf·laThe first-order polarization crosstalk intensity is CTA，CTB，CTC，CTD，CTEThe peak position of the interference signal representing the extinction ratio of the Y waveguide chip is SY＝Δnf·(lp+l1+l2+lf+la)+ΔnY·lYIntensity of extinction ratio of CTYThe full-length distributed polarization crosstalk information of the polarization maintaining optical fiber ring 211 appears between the first-order polarization crosstalk interference signal peaks of the connection point D209 and the connection point E213, and the lumped extinction ratio of the polarization maintaining optical fiber ring 211 is calculated to be CT through the full-length distributed polarization crosstalk informationcoil；
(7) Judging CTBAnd CTCWhether it is better than-40 dB and CTYWhether the power is better than 50dB or not, if not, returning to the step (1) and replacing the Y waveguide 206, and if so, performing the next step;
(8) judging whether the distributed polarization crosstalk of the full length of the polarization maintaining optical fiber ring 211 is better than-50 dB, if not, returning to the step (2) and replacing the polarization maintaining optical fiber ring 211, and if so, performing the next step;
(9) judging CTDWhether the current time is better than-40 dB or not is judged, if not, the step (2) is returned to and the connecting point D209 is welded again, and if so, the next step is carried out;
(10) disconnecting the connection point E213, removing the 45-degree polarization analyzer 215, and carrying out 0-degree axial alignment fusion on the polarization-maintaining optical fiber ring second port 212 and the Y waveguide second output polarization-maintaining tail fiber 217 to form a connection point G301;
(11) selecting a 1 × 2 single-mode coupler 302, connecting a first port 303 of the 1 × 2 single-mode coupler with a 45-degree polarizer single-mode pigtail 218, connecting a second port 304 of the 1 × 2 single-mode coupler with an SLD (super line stop) wide-spectrum light source 220, and connecting a third port 305 of the 1 × 2 single-mode coupler with an optical coherence domain polarization measuring instrument 221;
(12) distributed polarization crosstalk measurement is carried out on the closed optical path, second-order polarization crosstalk between the connection point D209 and the connection point F216 and second-order polarization crosstalk measurement information between the connection point D209 and the connection point G301 are respectively extracted from a measurement map spectrum, and the positions of interference signal peaks are SDF＝Δnf·(lf+l3) And SDG＝Δnf·lfThe second order polarization crosstalk intensity is CTDFAnd CTDGAnd the first-order polarization crosstalk intensity of the connection point F216 is calculated to be CTF＝CTDF-CTDThe first-order polarization crosstalk intensity of the connection point G301 is CTG＝CTDG-CTD；
(13) Judging CTFWhether the power is better than-40 dB or not is judged, if not, the step (1) is returned and the Y waveguide 206 is replaced, and if so, the next step is carried out;
(14) judging CTGAnd (4) whether the measured value is better than-40 dB, if not, returning to the step (10) and welding the connecting point G301 again, and if so, ending the measurement.
The invention also includes such structural features:
1. step (2) requires la-lp-l1＞10cm。
2. The 45-degree polarizer 201 and the 45-degree polarization analyzer 215 used in the optical path are both dual-port optical devices, one end of each dual-port optical device is a polarization-maintaining pigtail, the other end of each dual-port optical device is a single-mode pigtail, the Y waveguide 206 is a three-port optical device, the input pigtail and the output pigtail of each dual-port optical device are polarization-maintaining optical fibers, and all the polarization-maintaining optical fibers in the optical path are common panda type polarization-maintaining optical fibers.
3. The 1 × 2 single-mode coupler 302 in step (9) may be replaced by a three-port single-mode fiber circulator or a2 × 2 single-mode coupler.
4. In the step (10), the second-order polarization crosstalk between the connection point C207 and the connection point F216, and the connection point C207 and the connection point G may be extracted from the measurement spectrum301, the positions of interference signal peaks are SCF＝Δnf·(l2+lf+l3) And SCG＝Δnf·(l2+lf) The second order polarization crosstalk intensity is CTCFAnd CTCGTherefore, the first-order polarization crosstalk intensity at the connection point F216 is calculated as CTF＝CTCF-CTCThe first-order polarization crosstalk intensity of the connection point G301 is CTG＝CTCG-CTC。
Compared with the prior art, the invention has the beneficial effects that: the invention provides a polarization characteristic measurement method for assembling a full-polarization-preserving Sagnac closed optical path, which can realize monitoring and evaluation of distributed polarization crosstalk of all optical devices and connecting points in the closed optical path, and compared with the prior art, the polarization characteristic measurement method has the advantages that:
(1) the non-closed light path and the closed light path are measured once respectively, so that distributed polarization crosstalk information of all optical devices and connection points can be obtained, the separate testing and screening processes of the optical devices are omitted, the testing method is simple, and the testing efficiency is high;
(2) when the optical path is in a closed state, the first-order polarization crosstalk of all the connection points can be calculated by measuring the second-order polarization crosstalk between the connection points in the closed optical path and combining the test result of the non-closed optical path, so that the problem that the closed optical path cannot be measured is effectively solved;
(3) the method is also suitable for measuring the polarization crosstalk of the connecting point when the Y waveguide and the polarization-maintaining optical fiber ring are directly coupled, and compared with the traditional imaging positioning method, the method can more intuitively obtain the polarization axis alignment information of the connecting point, has higher precision and provides an effective monitoring means for the direct coupling technology.
Drawings
FIG. 1 is a flow chart of polarization characteristic measurement for a fully-polarization-preserving Sagnac closed-path setup;
FIG. 2 is a diagram of a distributed polarization crosstalk measurement apparatus for non-closed optical paths;
FIG. 3 is a diagram of transmission paths of optical signals in a non-closed optical path;
FIG. 4 is a diagram of a distributed polarization crosstalk measurement apparatus for a closed optical path;
fig. 5 is a transmission path diagram of an optical signal in a closed optical path.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The invention provides a polarization characteristic measuring method for assembling a full polarization-preserving Sagnac closed optical path, which comprises the following steps of:
1) selecting a Y waveguide (206) for assembling a full polarization-maintaining Sagnac closed optical path, and measuring the lengths of an input polarization-maintaining tail fiber (204) of the Y waveguide, a first output polarization-maintaining tail fiber (208) of the Y waveguide and a second output polarization-maintaining tail fiber (217) of the Y waveguide to be l respectively1，l2，l3And require | l3-l2If the length is more than 10cm, a connection point B (205) is formed between a Y waveguide (206) and a Y waveguide input polarization-maintaining tail fiber (204), a connection point C (207) is formed between the Y waveguide first output polarization-maintaining tail fiber (208), and a connection point F (216) is formed between the Y waveguide second output polarization-maintaining tail fiber (217);
2) selecting a polarization-maintaining optical fiber ring (211) for assembling a full-polarization-maintaining Sagnac closed optical path, and carrying out 0-degree axial welding on a first port (210) of the polarization-maintaining optical fiber ring and a first output polarization-maintaining tail fiber (208) of a Y waveguide to form a connecting point D (209), wherein the optical path is a first step in the assembling process of the full-polarization-maintaining Sagnac closed optical path and is called as a non-closed optical path;
3) selecting a 45-degree polarizer (201), and measuring the length l of the polarization-maintaining tail fiber (202) of the 45-degree polarizerp. Selecting a 45-degree analyzer (215), and measuring the length l of the polarization-maintaining tail fiber (214) of the 45-degree analyzeraAnd requires la-lp-l1＞10cm；
4) Carrying out 0-degree in-axis welding on a 45-degree polarizer polarization-maintaining tail fiber (202) and a Y waveguide input polarization-maintaining tail fiber (204) to form a connection point A (203), and connecting a 45-degree polarizer single-mode tail fiber (218) with an SLD (narrow-band light source) 220;
5) carrying out 0-degree axial welding on a polarization maintaining tail fiber (214) of the 45-degree polarization analyzer and a second port (212) of a polarization maintaining optical fiber ring to form a connection point E (213), and connecting a single-mode tail fiber (219) of the 45-degree polarization analyzer with an optical coherence domain polarization measuring instrument (221);
6) and (3) carrying out distributed polarization crosstalk measurement on the non-closed optical path, and extracting the first-order polarization crosstalk of the connection point A, B, C, D, E, the distributed polarization crosstalk of the full length of the polarization-maintaining optical fiber ring and the extinction ratio measurement information of the Y waveguide chip from the measurement map at one time. The position of each interference signal peak can be calculated based on the length of each section of polarization-maintaining tail fiber, and the birefringence of the polarization-maintaining fiber in the optical path is assumed to be delta nfBirefringence of the Y waveguide chip is DeltanYThe Y-waveguide (206) has a length lYThe length of the polarization-maintaining fiber ring (211) is lf. Then the peak positions of the interference signal representing the first order polarization crosstalk of connection point A, B, C, D, E are: SA ═ Δ nf·lp，SB＝Δnf·(lp+l1)，SC＝Δnf·(l2+lf+la)，SD＝Δnf·(lf+la)，SE＝Δnf·laThe first-order polarization crosstalk intensity is CTA，CTB，CTC，CTD，CTE. The peak position of interference signal representing extinction ratio of Y waveguide chip is SY＝Δnf·(lp+l1+l2+lf+la)+ΔnY·lYIntensity of extinction ratio of CTY. The full-length distributed polarization crosstalk information of the polarization-maintaining optical fiber ring (211) appears between the first-order polarization crosstalk interference signal peaks of the connection point D (209) and the connection point E (213), and the lumped extinction ratio of the polarization-maintaining optical fiber ring (211) is calculated to be CT through the full-length distributed polarization crosstalk informationcoil；
7) Judging CTBAnd CTCWhether it is better than-40 dB and CTYWhether the power is better than 50dB or not, if not, returning to the step 1) and replacing the Y waveguide (206), and if so, performing the next step;
8) judging whether the distributed polarization crosstalk of the full length of the polarization maintaining optical fiber ring (211) is better than-50 dB, if not, returning to the step 2) and replacing the polarization maintaining optical fiber ring (211), and if so, performing the next step;
9) judging CTDWhether the current is better than-40 dB or not, if not, returning to the step 2) and welding the connecting point D (209) again, and if so, performing the next step;
10) disconnecting the connection point E (213), removing the 45-degree analyzer (215), and carrying out 0-degree axial welding on the second port (212) of the polarization-maintaining optical fiber ring and the second output polarization-maintaining tail fiber (217) of the Y waveguide to form a connection point G (301), wherein the optical path is the second step in the assembly process of the full-polarization-maintaining Sagnac closed optical path and is called as a closed optical path;
11) selecting a 1 × 2 single-mode coupler (302), connecting a first port (303) of the 1 × 2 single-mode coupler with a 45-degree polarizer single-mode pigtail (218), connecting a second port (304) of the 1 × 2 single-mode coupler with an SLD (super-low-power line) wide-spectrum light source (220), and connecting a third port (305) of the 1 × 2 single-mode coupler with an optical coherent domain polarization measuring instrument (221);
12) carrying out distributed polarization crosstalk measurement on the closed optical path, respectively extracting second-order polarization crosstalk between a connecting point D (209) and a connecting point F (216) and second-order polarization crosstalk measurement information between the connecting point D (209) and a connecting point G (301) from a measurement map spectrum, wherein the positions of interference signal peaks are SDF＝Δnf·(lf+l3) And SDG＝Δnf·lfThe second order polarization crosstalk intensity is CTDFAnd CTDG. Therefore, the first-order polarization crosstalk intensity at the connection point F (216) is calculated as CTF＝CTDF-CTDThe first-order polarization crosstalk intensity of the connection point G (301) is CTG＝CTDG-CTD；
13) Judging CTFWhether the power is better than-40 dB or not, if not, returning to the step 1) and replacing the Y waveguide (206), and if so, performing the next step;
14) judging CTGIf not, returning to the step 10) and welding the connecting point G again (301), and if so, finishing the measurement.
The polarization characteristic measurement method for assembling the full polarization-preserving Sagnac closed optical path is characterized by comprising the following steps of: a45-degree polarizer (201) and a 45-degree analyzer (215) used in the optical path are both dual-port optical devices, one end of each dual-port optical device is a polarization-maintaining tail fiber, and the other end of each dual-port optical device is a single-mode tail fiber. The Y-waveguide (206) is a three-port optical device with input and output pigtails that are polarization maintaining fibers. All polarization maintaining fibers in the optical path are common panda type polarization maintaining fibers.
The polarization characteristic measurement method for assembling the full polarization-preserving Sagnac closed optical path is characterized by comprising the following steps of: the 1 × 2 single-mode coupler (302) in the step 9) can also be replaced by a three-port single-mode fiber circulator or a2 × 2 single-mode coupler.
The polarization characteristic measurement method for assembling the full polarization-preserving Sagnac closed optical path is characterized by comprising the following steps of: step 10) may also extract, from the measurement map spectrum, second-order polarization crosstalk between the connection point C (207) and the connection point F (216), and second-order polarization crosstalk measurement information between the connection point C (207) and the connection point G (301), where interference signal peaks respectively appear at S positionsCF＝Δnf·(l2+lf+l3) And SCG＝Δnf·(l2+lf) The second order polarization crosstalk intensity is CTCFAnd CTCG. Therefore, the first-order polarization crosstalk intensity at the connection point F (216) is calculated as CTF＝CTCF-CTCThe first-order polarization crosstalk intensity of the connection point G (301) is CTG＝CTCG-CTC。
Fig. 2 shows a diagram of a distributed polarization crosstalk measurement apparatus for a non-closed optical path, where a portion in a dashed line frame is a non-closed optical path structure. When a non-closed optical path is measured, a 45-degree polarizer (201) and a 45-degree analyzer (215) are additionally used, wherein the 45-degree polarizer (201) is used for realizing that an optical signal is transmitted in an equivalent energy linear polarization state in an orthogonal polarization axis of a polarization-maintaining tail fiber (202) of the 45-degree polarizer, and the 45-degree analyzer (215) maps the optical signal transmitted in the orthogonal polarization axis of a polarization-maintaining tail fiber (214) of the 45-degree analyzer to the same polarization direction so as to facilitate interference between the signals. The SLD wide-spectrum light source (220) is generally a Gaussian low-polarization light source, the central wavelength of the light source is consistent with the working wavelength of an optical device in a closed light path, and the spectral width is generally larger than 40nm, so that the spatial resolution of distributed measurement is improved. The optical coherence domain polarization measuring instrument (221) is a self-research instrument of Harbin engineering university, a scanning type Michelson interferometer is integrated in the optical coherence domain polarization measuring instrument, the optical coherence domain polarization measuring instrument has an ultra-large space optical path scanning range of 6.4m, polarization maintaining optical fibers above 5km can be measured, the measurement space resolution is better than 10cm, the highest polarization crosstalk measurement sensitivity can reach-100 dB, and the measurement dynamic range is kept at 100 dB.
As shown in fig. 3, optical signal transmission paths when all first-order polarization crosstalk occurs in the non-closed optical path are enumerated. For simplicity of analysis, the polarizer and analyzer used in the test were considered to have polarization angles of ideally 45 °, and the Y-waveguide (206) had a splitting ratio of 50: 50. Taking the first-order polarization crosstalk of the connection point D (209) as an example, assume that its polarization coupling coefficient is ρDThe optical field amplitude of the input optical signal from the 45 DEG polarizer (201) is EinThen the optical field amplitude E of the reference optical signal when Path 1 is output from the 45 ° analyzer (215)refExpressed as:
optical field amplitude E of first order polarization crosstalk optical signal when path 5 is output from 45 DEG analyzer (215)cou-DExpressed as:
wherein the content of the first and second substances,
represents the phase difference between path 5 and path 1, and has:
wherein S isDThe position in the interference pattern where the interference signal peak representing the first order polarization crosstalk of the connection point D (209) appears is represented by the optical path difference between path 5 and path 1.
The responsivity of the photodetector is R, assuming that the splitting ratio of the coupler used in the optical coherence domain polarimeter (221) is 50: 50. The photocurrent intensity I of the interference between path 5 and path 1 is thencou-DExpressed as:
photocurrent intensity I of path 1 self-interferencerefExpressed as:
therefore, it represents the first-order polarization crosstalk intensity CT of the connection point D (209)DThe normalized logarithm of (d) is calculated as follows, here ignoring the direct current and phase terms of the interference signal:
similarly, the first-order polarization crosstalk intensity CT of the connection point a (203), the connection point B (205), the connection point C (207), and the connection point E (213)A，CTB，CTC，CTEAnd a chip extinction ratio CT of the Y waveguide (206)YAnd also according to the analysis and calculation process described above. Actually, there are numerous energy coupling defect points in the polarization-maintaining fiber ring (211), and the first-order polarization crosstalk intensity of any point where the energy-coupled optical signal interferes with the reference optical signal can be measured, so the above calculation formula is also applicable.
Fig. 4 shows a diagram of a distributed polarization crosstalk measurement apparatus with a closed optical path, where a part in a dashed box is a closed optical path structure. When measuring a closed optical path, a 45 DEG analyzer (215) is not needed, but a 1X 2 single mode coupler (302) is added. The function of the 1 x 2 single-mode coupler (302) is to inject the optical signal of the SLD wide-spectrum light source (220) into the closed optical path on the one hand, and to inject the polarization crosstalk signal generated in the closed optical path into the optical coherence domain polarization measurement instrument (221) on the other hand. In the closed optical path, the optical signal needs to pass through the Y-waveguide (206) twice, and since the Y-waveguide only allows fast axis light pass (slow axis extinction), only second order polarization crosstalk signals (higher order polarization crosstalk signals and their weak negligible) are present in the closed optical path.
As shown in fig. 5, optical signal transmission paths when all second-order polarization crosstalk occurs in a closed optical path are enumerated. Only the path of the optical signal transmitted clockwise after being split by the Y waveguide (206) is given here, and the path of the optical signal transmitted counterclockwise is similar to the path. Taking the second-order polarization crosstalk between the connection point D (209) and the connection point G (301) as an example, assume that the optical field amplitude of the input optical signal from the 45 DEG polarizer (201) is EinThen the light field amplitude E 'of the reference light signal when path 8 is again output from the 45 ° polariser (201)'refExpressed as:
let the polarization coupling coefficient of the connection point G (301) be ρGOptical field amplitude E 'of the second order polarized crosstalk optical signal when path 9 is again output from 45 DEG polarizer (201)'cou-DGExpressed as:
wherein the content of the first and second substances,
represents the phase difference between path 9 and path 8 and has:
photocurrent intensity I 'of interference between path 9 and path 8'cou-DGAnd photocurrent intensity I 'of path 8 self-interference'refRespectively expressed as:
therefore, the second-order polarization crosstalk intensity CT between the connection point D (209) and the connection point G (301) is representedDGThe normalized logarithm of (d) is calculated as follows, here ignoring the direct current and phase terms of the interference signal:
the first-order polarization crosstalk intensity CT of the connection point G (301) at this timeGCan be calculated by the following formula:
similarly, the polarization coupling coefficient of the connection point F (216) is assumed to be ρ in the same calculation stepFThen the interference between path 10 and path 8 can measure the second-order polarization crosstalk strength between connection point D (209) and connection point F (216): CTDF＝10·lg(ρD·ρF)2The optical path difference is: sDF＝Δnf·(lf+l3). The first-order polarization crosstalk intensity CT of the connection point F (216) at this timeFCan be calculated by the following formula:
as shown in fig. 5, the interference between the path 11 and the path 8 can measure the second-order polarization crosstalk strength between the connection point C (207) and the connection point G (301), and the interference between the path 12 and the path 8 can measure the second-order polarization crosstalk strength between the connection point C (207) and the connection point F (216). At this time, CTGAnd CTFCan also be calculated separately as follows:
CTG＝CTCG-CTC
CTF＝CTCF-CTC
based on the analysis and calculation, the first-order polarization crosstalk of all connection points in the optical path, the distributed polarization crosstalk of the full length of the polarization-maintaining optical fiber ring (211), the chip extinction ratio of the Y waveguide (206) and other all polarization characteristic information can be obtained by respectively carrying out distributed polarization crosstalk measurement on the non-closed optical path and the closed optical path once.
For clarity, the present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited thereby. The measurement is carried out according to a polarization characteristic measurement flow chart for the full-polarization-preserving Sagnac closed optical path assembly shown in the attached figure 1 by combining the parameters:
1) according to the step 101, a Y waveguide (206) for assembling a full-polarization-maintaining Sagnac closed optical path is selected, and the lengths of an input polarization-maintaining tail fiber (204) of the Y waveguide, a first output polarization-maintaining tail fiber (208) of the Y waveguide and a second output polarization-maintaining tail fiber (217) of the Y waveguide are measured to be l respectively1，l2，l3And require | l3-l2If the length is more than 10cm, a connection point B (205) is formed between a Y waveguide (206) and a Y waveguide input polarization-maintaining tail fiber (204), a connection point C (207) is formed between the Y waveguide first output polarization-maintaining tail fiber (208), and a connection point F (216) is formed between the Y waveguide second output polarization-maintaining tail fiber (217); the working wavelength of the Y waveguide (206) is 1550nm, and the fast axis passes light;
2) according to the step 102, selecting a polarization-maintaining optical fiber ring (211) for assembling the full-polarization-maintaining Sagnac closed optical path, and carrying out 0-degree in-axis welding on a first port (210) of the polarization-maintaining optical fiber ring and a first output polarization-maintaining tail fiber (208) of a Y waveguide to form a connecting point D (209), wherein the optical path is the first step in the assembling process of the full-polarization-maintaining Sagnac closed optical path and is called as a non-closed optical path; the working wavelength of the polarization-maintaining optical fiber ring (211) is 1550nm, and the length is less than 2 km;
3) according to step 103, a 45 ° polarizer (201) is selected and measuredThe length of the polarization-maintaining tail fiber (202) of the polarizer measuring 45 degrees is lp. Selecting a 45-degree analyzer (215), and measuring the length l of the polarization-maintaining tail fiber (214) of the 45-degree analyzeraAnd requires la-lp-l1More than 10 cm; the working wavelength of the 45-degree polarizer (201) and the 45-degree polarization analyzer (215) is 1550nm, the polarization extinction ratio is less than 0.2dB, and the insertion loss is less than 1 dB;
4) according to the step 104, carrying out 0-degree in-axis fusion on a 45-degree polarizer polarization-maintaining tail fiber (202) and a Y waveguide input polarization-maintaining tail fiber (204) to form a connection point A (203), and connecting a 45-degree polarizer single-mode tail fiber (218) with an SLD (super line driver) broad-spectrum light source (220); the central wavelength of the SLD wide-spectrum light source (220) is 1550nm, the half-spectrum width is more than 40nm, the fiber output power is more than 6mW, and the polarization extinction ratio is less than 0.2 dB;
5) according to the step 105, carrying out 0-degree in-axis fusion on a polarization maintaining tail fiber (214) of the 45-degree polarization analyzer and a second port (212) of a polarization maintaining optical fiber ring to form a connection point E (213), and connecting a single-mode tail fiber (219) of the 45-degree polarization analyzer with an optical coherence domain polarization measuring instrument (221); the optical coherence domain polarization measuring instrument (221) is internally integrated with a scanning type Michelson interferometer, has an ultra-large space optical path scanning range of 6.4m, the measuring sensitivity of polarization crosstalk can reach-100 dB, and the measuring dynamic range is kept at 100 dB;
6) according to step 106, distributed polarization crosstalk measurement is performed on the non-closed optical path, and first-order polarization crosstalk of the connection point A, B, C, D, E, distributed polarization crosstalk of the full length of the polarization-maintaining optical fiber ring, and extinction ratio measurement information of the Y waveguide chip are extracted from the measurement map at one time. The position of each interference signal peak can be calculated based on the length of each section of polarization-maintaining tail fiber, and the birefringence of the polarization-maintaining fiber in the optical path is assumed to be delta nfBirefringence of the Y waveguide chip is DeltanYThe Y-waveguide (206) has a length lYThe length of the polarization-maintaining fiber ring (211) is lf. Then the peak positions of the interference signal representing the first order polarization crosstalk of connection point A, B, C, D, E are: sA＝Δnf·lp，SB＝Δnf·(lp+l1)，SC＝Δnf·(l2+lf+la)，SD＝Δnf·(lf+la)，SE＝Δnf·laThe first-order polarization crosstalk intensity is CTA，CTB，CTC，CTD，CTE. The peak position of interference signal representing extinction ratio of Y waveguide chip is SY＝Δnf·(lp+l1+l2+lf+la)+ΔnY·lYIntensity of extinction ratio of CTY. The full-length distributed polarization crosstalk information of the polarization-maintaining optical fiber ring (211) appears between the first-order polarization crosstalk interference signal peaks of the connection point D (209) and the connection point E (213), and the lumped extinction ratio of the polarization-maintaining optical fiber ring (211) is calculated to be CT through the full-length distributed polarization crosstalk informationcoil；
7) According to step 107, CT is judgedBAnd CTCWhether it is better than-40 dB and CTYWhether the power is better than 50dB or not is judged, if not, the step 101 is returned and the Y waveguide is replaced (206), and if yes, the next step is carried out;
8) according to the step 108, judging whether the distributed polarization crosstalk of the full length of the polarization maintaining optical fiber ring (211) is better than-50 dB, if not, returning to the step 102 and replacing the polarization maintaining optical fiber ring (211), and if so, performing the next step;
9) according to step 109, CT is judgedDWhether the current is better than-40 dB or not, if not, returning to the step 102 and welding the connecting point D again (209), and if so, performing the next step;
10) according to the step 110, a connection point E (213) is disconnected, a 45-degree analyzer (215) is removed, and the polarization-maintaining optical fiber ring second port (212) and a Y waveguide second output polarization-maintaining tail fiber (217) are subjected to 0-degree axial fusion to form a connection point G (301), wherein the optical path is a second step in the assembly process of a full polarization-maintaining Sagnac closed optical path and is called a closed optical path;
11) according to the step 111, selecting a 1 × 2 single-mode coupler (302), connecting a first port (303) of the 1 × 2 single-mode coupler with a 45-degree polarizer single-mode pigtail (218), connecting a second port (304) of the 1 × 2 single-mode coupler with an SLD (super line stop) wide-spectrum light source (220), and connecting a third port (305) of the 1 × 2 single-mode coupler with an optical coherent domain polarization measuring instrument (221); the working wavelength of the 1 multiplied by 2 single-mode coupler (302) is 1550nm, the insertion loss is less than 1dB, and the splitting ratio is 50: 50;
12) according to step 112, distributed polarization crosstalk measurement is performed on the closed optical path, second-order polarization crosstalk between the connection point D (209) and the connection point F (216) and second-order polarization crosstalk measurement information between the connection point D (209) and the connection point G (301) are respectively extracted from the measurement map spectrum, and positions where interference signal peaks appear are SDF＝Δnf·(lf+l3) And SDG＝Δnf·lfThe second order polarization crosstalk intensity is CTDFAnd CTDG. Therefore, the first-order polarization crosstalk intensity at the connection point F (216) is calculated as CTF＝CTDF-CTDThe first-order polarization crosstalk intensity of the connection point G (301) is CTG＝CTDG-CTD；
13) According to step 113, CT is judgedFWhether the power is better than-40 dB or not is judged, if not, the step 101 is returned and the Y waveguide is replaced (206), and if yes, the next step is carried out;
14) according to step 114, CT is judgedGIf not, the step 110 is returned to and the connection point G is welded again (301), and if so, the measurement is finished.
In summary, the present invention provides a polarization characteristic measurement method for assembling a fully-polarization-maintaining Sagnac closed optical path, which is characterized in that: the Y waveguide and the polarization-maintaining optical fiber ring which are used for assembling the full-polarization-maintaining Sagnac closed optical path are connected into a non-closed optical path and a closed optical path in sequence, and are respectively connected into an optical coherence domain polarization measuring instrument for measurement, and by combining a second-order polarization crosstalk effect, all polarization characteristic information such as first-order polarization crosstalk of all connection points in the closed optical path, distributed polarization crosstalk of the full length of the polarization-maintaining optical fiber ring, extinction ratio of a Y waveguide chip and the like can be obtained. The method realizes the measurement of the polarization characteristic in the assembly process of the full polarization-preserving Sagnac closed optical path, can be widely used for monitoring and evaluating the distributed polarization crosstalk of all optical devices and connecting points in the closed optical path, and has important significance for the development of high-performance interference optical sensors.
Claims (5)
1. A polarization characteristic measurement method for full polarization-preserving Sagnac closed optical path assembly is characterized by comprising the following steps of: the method comprises the following steps:
(1) selecting a Y waveguide (206) for assembling a full polarization-maintaining Sagnac closed optical path, and measuring the lengths of an input polarization-maintaining tail fiber (204) of the Y waveguide, a first output polarization-maintaining tail fiber (208) of the Y waveguide and a second output polarization-maintaining tail fiber (217) of the Y waveguide to be l respectively1，l2，l3And require | l3-l2If the length is more than 10cm, a connection point B (205) is formed between a Y waveguide (206) and a Y waveguide input polarization-maintaining tail fiber (204), a connection point C (207) is formed between the Y waveguide first output polarization-maintaining tail fiber (208), and a connection point F (216) is formed between the Y waveguide second output polarization-maintaining tail fiber (217);
(2) selecting a polarization-maintaining optical fiber ring (211) for assembling a full-polarization-maintaining Sagnac closed optical path, and carrying out 0-degree in-axis fusion on a first port (210) of the polarization-maintaining optical fiber ring and a first output polarization-maintaining tail fiber (208) of a Y waveguide to form a connection point D (209);
(3) selecting a 45-degree polarizer (201), and measuring the length l of the polarization-maintaining tail fiber (202) of the 45-degree polarizerpSelecting a 45-degree analyzer (215), and measuring the length l of the polarization-maintaining tail fiber (214) of the 45-degree analyzera；
(4) Carrying out 0-degree in-axis welding on a 45-degree polarizer polarization-maintaining tail fiber (202) and a Y waveguide input polarization-maintaining tail fiber (204) to form a connection point A (203), and connecting a 45-degree polarizer single-mode tail fiber (218) with an SLD (narrow-band light source) 220;
(5) carrying out 0-degree axial welding on a polarization maintaining tail fiber (214) of the 45-degree polarization analyzer and a second port (212) of a polarization maintaining optical fiber ring to form a connection point E (213), and connecting a single-mode tail fiber (219) of the 45-degree polarization analyzer with an optical coherence domain polarization measuring instrument (221);
(6) distributed polarization crosstalk measurement is carried out on a non-closed optical path, first-order polarization crosstalk of a connection point A, B, C, D, E, distributed polarization crosstalk of the full length of a polarization-maintaining optical fiber ring and extinction ratio measurement information of a Y waveguide chip are extracted from a measurement map at one time, the position of each interference signal peak can be calculated based on the length of each section of polarization-maintaining tail fiber, and the birefringence of the polarization-maintaining optical fiber in the optical path is assumed to be delta nfBirefringence of the Y waveguide chip is DeltanYThe Y-waveguide (206) has a length lYPolarization maintaining optical fiberThe length of the ring (211) is lfThen the peak positions of the interference signals representing the first order polarization crosstalk of connection point A, B, C, D, E are: sA＝Δnf·lp，SB＝Δnf·(lp+l1)，SC＝Δnf·(l2+lf+la)，SD＝Δnf·(lf+la)，SE＝Δnf·laThe first-order polarization crosstalk intensity is CTA，CTB，CTC，CTD，CTEThe peak position of the interference signal representing the extinction ratio of the Y waveguide chip is SY＝Δnf·(lp+l1+l2+lf+la)+ΔnY·lYIntensity of extinction ratio of CTYThe full-length distributed polarization crosstalk information of the polarization-maintaining optical fiber ring (211) appears between the first-order polarization crosstalk interference signal peaks of the connection point D (209) and the connection point E (213), and the lumped extinction ratio of the polarization-maintaining optical fiber ring (211) is calculated to be CT through the full-length distributed polarization crosstalk informationcoil；
(7) Judging CTBAnd CTCWhether it is better than-40 dB and CTYWhether the power is better than 50dB or not is judged, if not, the step (1) is returned and the Y waveguide (206) is replaced, and if yes, the next step is carried out;
(8) judging whether the distributed polarization crosstalk of the full length of the polarization maintaining optical fiber ring (211) is better than-50 dB, if not, returning to the step (2) and replacing the polarization maintaining optical fiber ring (211), and if so, performing the next step;
(9) judging CTDWhether the current time is better than-40 dB or not is judged, if not, the step (2) is returned to and the connecting point D (209) is welded again, and if so, the next step is carried out;
(10) disconnecting the connection point E (213), removing the 45-degree polarization analyzer (215), and carrying out 0-degree axial fusion on the polarization-maintaining optical fiber ring second port (212) and the Y waveguide second output polarization-maintaining tail fiber (217) to form a connection point G (301);
(11) selecting a 1 × 2 single-mode coupler (302), connecting a first port (303) of the 1 × 2 single-mode coupler with a 45-degree polarizer single-mode pigtail (218), connecting a second port (304) of the 1 × 2 single-mode coupler with an SLD (super-low-power line) wide-spectrum light source (220), and connecting a third port (305) of the 1 × 2 single-mode coupler with an optical coherent domain polarization measuring instrument (221);
(12) carrying out distributed polarization crosstalk measurement on the closed optical path, respectively extracting second-order polarization crosstalk between a connecting point D (209) and a connecting point F (216) and second-order polarization crosstalk measurement information between the connecting point D (209) and a connecting point G (301) from a measurement map spectrum, wherein the positions of interference signal peaks are SDF＝Δnf·(lf+l3) And SDG＝Δnf·lfThe second order polarization crosstalk intensity is CTDFAnd CTDGThe first-order polarization crosstalk intensity of the connection point F (216) is calculated as CTF＝CTDF-CTDThe first-order polarization crosstalk intensity of the connection point G (301) is CTG＝CTDG-CTD；
(13) Judging CTFWhether the power is better than-40 dB or not is judged, if not, the step (1) is returned and the Y waveguide (206) is replaced, and if so, the next step is carried out;
(14) judging CTGIf not, the step (10) is returned to and the connection point G is welded again (301), and if so, the measurement is finished.
2. The polarization characteristic measurement method for the fully-polarization-preserving Sagnac closed optical path assembly according to claim 1, wherein: step (2) requires la-lp-l1＞10cm。
3. The polarization characteristic measurement method for the fully-polarization-preserving Sagnac closed optical path assembly according to claim 1 or 2, wherein: a45-degree polarizer (201) and a 45-degree polarization analyzer (215) used in an optical path are both dual-port optical devices, one end of each dual-port optical device is a polarization-maintaining pigtail, the other end of each dual-port optical device is a single-mode pigtail, a Y waveguide (206) is a three-port optical device, input and output pigtails of each dual-port optical device are polarization-maintaining optical fibers, and all polarization-maintaining optical fibers in the optical path are ordinary panda type polarization-maintaining optical fibers.
4. The polarization characteristic measurement method for the fully-polarization-preserving Sagnac closed optical path assembly according to claim 3, wherein: the 1 × 2 single-mode coupler (302) in step (9) may also be replaced by a three-port single-mode fiber circulator or a2 × 2 single-mode coupler.
5. The polarization characteristic measurement method for the fully-polarization-preserving Sagnac closed optical path assembly according to claim 1 or 4, wherein: step (10) may also extract, from the measurement map spectrum, second-order polarization crosstalk between the connection point C (207) and the connection point F (216), and second-order polarization crosstalk measurement information between the connection point C (207) and the connection point G (301), where interference signal peaks respectively appear at positions SCF＝Δnf·(l2+lf+l3) And SCG＝Δnf·(l2+lf) The second order polarization crosstalk intensity is CTCFAnd CTCGTherefore, the first-order polarization crosstalk intensity at the connection point F (216) is estimated to be CTF＝CTCF-CTCThe first-order polarization crosstalk intensity of the connection point G (301) is CTG＝CTCG-CTC。
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| 杨军等: "光学相干域偏振测量技术及其在高精度光纤陀螺器件测量中的应用", 《光学学报》 * |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113405566A (en) * | 2021-05-27 | 2021-09-17 | 广东工业大学 | Optical performance testing method of optical fiber sensitive ring based on distributed polarization crosstalk |
| CN113405566B (en) * | 2021-05-27 | 2023-05-16 | 广东工业大学 | Optical fiber sensitive ring optical performance test method based on distributed polarization crosstalk |
| CN115372880A (en) * | 2022-08-23 | 2022-11-22 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Light path testing system and fault point detection method of reflective all-fiber current transformer |
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