CN112082734B - Calibration method for Y waveguide reflection characteristic test - Google Patents
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Abstract
The invention provides a calibration method for a Y waveguide reflection characteristic test, which comprises an implemented device structure and a calibration method flow. The embodiment adopts a 3dB coupler and a variable attenuator to construct a calibration device, improves the calibration precision of the reflection characteristic test result of the Y waveguide by adjusting the loss of the calibration device, and realizes the synchronous operation of the test and the calibration. The patent establishes a calibration device and a calibration method for the internal reflection characteristic test result of a Y waveguide device, and can calibrate the reflectivity of the existing chip and coupling point in the Y waveguide.
Description
Technical Field
The invention relates to a calibration method for testing reflection characteristics of a Y waveguide, and belongs to the technical field of measurement of polarizing optical devices.
Background
The fiber-optic gyroscope is a non-mechanical angular velocity measuring instrument based on the Sagnac effect invented in the seventies of the twentieth century. The interference type Fiber Optic gyroscope (IFOG) has the characteristics of low cost, small volume, light weight, low power consumption and the like, and is fast to start, large in dynamic range, strong in corrosion resistance and noise resistance, high in sensitivity, good in working stability and high in reliability. The interference type fiber-optic gyroscope can accurately measure the angular velocity and the angular acceleration of an object, and can obtain the information of the motion state, the track, the advancing direction and the like of the object through calculation according to the measurement result, so the interference type fiber-optic gyroscope has important status and huge application value in the directions of the aerospace field, the military field, the sensing field and the like. The main components of the interference type fiber optic gyroscope comprise a multifunctional integrated optical device (commonly called as a Y waveguide) and a long-distance fiber optic sensing ring, and the extinction ratio of a Y waveguide chip can influence the random walk of the fiber optic gyroscope, so that the important method for optimizing the performance of the fiber optic gyroscope at home and abroad at present is to test the extinction ratio of the Y waveguide chip and the reflection of the Y waveguide chip which form the fiber optic gyroscope, and the optimal process is found through optimization iteration.
Generally, the extinction ratio of a Y waveguide chip is mainly tested by a polarization extinction ratio measuring instrument, but the extinction ratio of the Y waveguide chip used for a high-precision optical fiber gyroscope in the 21 st century can reach over 80 dB. For example: a method (CN 201310185490.2) for improving extinction ratio of Y waveguide chip for fiber-optic gyroscope proposed by Huayong, Shuping, etc. of forty-fourth institute of China electronic technology group company has improved extinction ratio of waveguide chip to over 80 dB. But the method is limited by the performance of a testing instrument and a testing method, and accurate measurement of the extinction ratio of the Y waveguide chip with the high extinction ratio cannot be realized at present. The extinction ratio tester, a common polarization performance tester, is only 72dB of a Model4810 type polarization extinction ratio measuring instrument developed by American dBm Optics with the highest resolution, and besides, the ERM102 type of the American General Photonics company, the ER2200 type of the Korean Fiberpro company and the PEM-330 type of the Japanese Santec company can only reach about 50dB of the highest extinction ratio, and cannot meet the testing requirement of a Y waveguide device with the high extinction ratio of more than 80 dB. The existing method for testing the high extinction ratio polarizer is to use optical coherence domain polarization measurement (OCDP) to perform measurement. In the early 90 s of the 20 th century, HerveLefevre et al, France, for the first time, disclosed an OCDP system (USpatent: 4893931) based on the principle of white light interference, which used a superluminescent light emitting diode (SLD) as a light source and a spatial interference light path as an optical path correlation measurement structure. According to the patent technology, French Photonetics company develops two models of OCDP test systems, WIN-P125 and WIN-P400, mainly used for polarization characteristic analysis of short (500m) and long (1600m) polarization-maintaining fibers. The main performance is that the polarization crosstalk sensitivity is-70 dB, the dynamic range is 70dB, and then the sensitivity and the dynamic range are respectively improved to-80 dB and 80dB through improvement. 2011, tsuneka et al, tsujin university, discloses a method and an apparatus for detecting polarization extinction ratio of an optical polarizer (chinese patent application No. 201110052231.3), which also adopts a spatial interference light path as a core device of OCDP, and derives the polarization extinction ratio by detecting the coupling strength of a coupling point. The dynamic range of the device is 75dB, and the device is suitable for measurement of various optical polarization devices such as polarization maintaining optical fibers, polarization maintaining optical fiber couplers, polarizers and the like. In 2012, the polar army et al, the university of harbin engineering, proposed a polarization crosstalk testing apparatus (chinese patent application No. CN201210379406.6) based on an all-fiber optical path and a method for improving the polarization crosstalk measurement performance of an optical device (chinese patent application No. CN201210379407.0), and adopted the technical scheme of the all-fiber optical path and suppressing beat noise, so as to greatly suppress the noise amplitude, increase the sensitivity of the polarization optical device in extinction ratio measurement to-95 dB above, and simultaneously, the dynamic range can be correspondingly maintained at 95dB, and the volume of the testing system is reduced, and the measurement stability is increased. In 2016, the Dynamic range of OCDP instrument measurement was theoretically and experimentally improved to 100dB by a Li-created form paper (Dynamic range beyond 100dB for polarization mode based on white light interferometer) at Harbin engineering university.
Except that OCDP with high precision and large dynamic range is adopted to test extinction ratio of Y waveguide chip of fiber-optic gyroscope, the reflection of Y waveguide chip can be tested by optical low-coherence reflectometer, which originates from the end of 20 century 80 years. Takada and Hewlett-Packard et al, both in the laboratory of electronic communications for the Japanese telegraph telephone company (NTT), made an excellent contribution to the development of optical low coherence reflectometers, studied in detail the noise impact of optical low coherence reflectometers, and promoted the sensitivity of reflection intensity to-160 dB, while extending the measurement length to several meters or even nearly one hundred meters, making the optical low coherence reflectometer system initially practical. Thereafter, the united states HP company introduced HP8504B optical low coherence reflectometer, which can achieve-160 dB reflection intensity sensitivity while ensuring stable and reliable testing, and the japan itanium company also introduced AQ7410B, which is a similar performance instrument.
For an optical low coherence reflectometer, when the reflectometer is used for a Y waveguide test, the test result is the reflection intensity of a reflection point inside a Y waveguide, and when the quality of the Y waveguide is actually evaluated, the reflection intensity needs to be converted into the reflectivity of a chip, so that the process of calibrating the reflection intensity of a Y waveguide chip is involved. The Y waveguide integrates a polarization function, the loss is large (generally greater than 3dB), so the calibration precision of the Y waveguide is influenced by the loss, and until now, a better method is not provided for accurately calibrating the reflection intensity of a Y waveguide chip.
Disclosure of Invention
The invention aims to provide a calibration method for a Y waveguide reflection characteristic test.
The purpose of the invention is realized as follows: the method comprises the following steps:
the method comprises the following steps: manufacturing the calibration device 20 according to the calibration device manufacturing method, and debugging the insertion loss of the calibration device 20;
step two: the Y waveguide 204 is connected to the calibration device 20 in a forward manner;
step three: the low-coherence reflectometer 500 is connected with a matched length optical fiber 501 with proper length, a variable attenuator 3502 and a polarization state controller 503, and the calibration device 20 is connected with the low-coherence reflectometer 500;
step four: starting the low-coherence reflectometer 500 to perform forward test on the Y waveguide 204, and adjusting the variable attenuator 3502 and the polarization state controller 503 to make the amplitude of the reflection peak of the Y waveguide 204 be maximum;
step five: recording the amplitude of the reflection peak of the forward reflection point of the Y waveguide 204 as A1；
Step six: re-coupling the Y waveguide 204 into the calibration apparatus 20 in a reverse manner;
step seven: starting the low-coherence reflectometer 500 to perform reverse test on the Y waveguide 204, and adjusting the variable attenuator 3502 and the polarization state controller 503 to make the amplitude of the reflection peak of the reflection point of the Y waveguide 204 maximum;
step eight: record the reflection peak amplitude of the backward reflection point of the Y waveguide 204 as A2；
Step nine: using a loss meterAccording to the formula, the forward reflection peak amplitude of the Y waveguide 204 is A1 and the backward reflection peak amplitude of the Y waveguide 204 is A2Calculating the forward and backward reflection losses delta of the reflection point of the Y waveguide 2041And delta2；
Step ten: the Y waveguide 204 is connected into the calibration device 20 in a forward mode;
step eleven: adjusting the variable attenuator 2107 of the calibration arm 106 to adjust the loss of the calibration arm 106 to delta1；
Step twelve: calculating the length S of calibration fiber 108 required to test Y-waveguide 2041Adjusting the length of the calibration fiber 108;
step thirteen: starting the low-coherence reflectometer 500 to perform Y waveguide 204 test;
fourteen steps: observing whether the reflection peak and the calibration peak of the Y waveguide 204 appear simultaneously in the test result;
step fifteen: if the judgment in the step fourteen is no, recalculating and adjusting the length S of the calibration optical fiber 1081And returning to the step thirteen;
sixthly, the steps are as follows: if the judgment in the step fourteen is yes, recording Y waveguide 204 and calibration peak reflection intensity test data;
seventeen steps: and comparing the calibration result with the Y waveguide 204 test result, and calculating the reflectivity of the reflection point of the Y waveguide 204.
The invention also includes such structural features:
1. the calibration device comprises an SLD light source 100, a flange plate 101, a coupler input tail fiber 102, a single-mode coupler 103, a test arm 104, a calibration arm 106, a variable attenuator 1105, a test module 114, a test arm debugging module 115, a variable attenuator 2107, a calibration optical fiber 108, an output collimating mirror 110, a calibration arm debugging module 116 and a calibration module 117, wherein the SLD light source 100 is connected with the coupler input tail fiber 102 through the flange plate 101, and the length of the coupler input tail fiber 102 is L1(ii) a One arm of the output end of the single-mode coupler 103 is used as a test arm 104, and the other arm is used as a calibration arm 106; the variable attenuator 1105 is mounted on the test arm 104, the test arm 104 is connected to the test arm debug module 115 or the test module 114 through the welding point A201, and the test arm 104 has a length L2(ii) a Calibration arm 106 is connected to calibration fiber 108 through solder joint E111, and variable attenuator 2107 is mounted on calibration fiber 108; the tail end of the calibration optical fiber 108 is connected with an output collimating mirror 110, the calibration arm transmission light 109 is output to a calibration arm debugging module 116 or a calibration module 117, and the test module 114 is a Y waveguide 204 of various types; the calibration module 117 is composed of a movable platform 112 and a coating reflection mirror 123, the coating reflection mirror 123 is installed on the movable platform 112, the direction faces the output collimating mirror 110, and the coating reflection mirror 123 is different coated lenses with known reflectivity.
2. The test arm debugging module 115 comprises a single mode fiber 124, a fiber union 121 and an optical power meter 1122, wherein the single mode fiber 124 is connected to the optical power meter 1122 through the fiber union 121, and the optical power meter 1122 is used for measuring the output optical power of the test arm 104.
3. Calibration arm debugging module 116 includes a receiving collimator 120, a collimator pigtail 125, and an optical power meter 2126, where receiving collimator 120 is connected to optical power meter 2126 through collimator pigtail 125, and optical power meter 2126 is used to measure the output optical power of calibration arm 106.
4. The manufacturing and debugging steps of the calibration device are as follows:
Compared with the prior art, the invention has the beneficial effects that: 1. the calibration device has simple structure, convenient operation, reliability and stability. The optical devices required by the calibration device only need one single-mode coupler, one variable attenuator, one coating reflection mirror and one output collimating mirror, even the calibration can be realized only by the single-mode coupler and the variable attenuator under the condition of not needing high calibration precision, and the device has small volume, low manufacturing cost and excellent performance. 2. The calibration device can realize that when the low-coherence reflectometer is used for carrying out Y waveguide test, the test and the calibration are carried out simultaneously, and the calibration result and the test result can be processed simultaneously, so that the test time is saved, and the test efficiency is improved. 3. When the calibration device is used, the loss of the reflection point in the Y waveguide can be accurately calculated by adopting a special calibration method, so that the calibration precision can be improved, and a large calibration range can be maintained under the high calibration precision.
Drawings
FIG. 1 is a diagram of a Y-waveguide calibration apparatus;
FIG. 2 is a flow chart of a method for manufacturing and debugging a Y waveguide calibration device;
FIG. 3 is a schematic diagram of a forward and reverse test of a Y waveguide;
FIG. 4 is a flow chart of Y waveguide calibration;
FIG. 5 is a diagram of a calibration setup for testing the Y-waveguide with a low coherence reflectometer.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
A calibration for a reflection characteristic test of a Y waveguide comprises the following steps:
1) as can be seen from step (601), the calibration device 20 is manufactured according to the calibration device manufacturing method, and the insertion loss of the calibration device 20 is adjusted.
2) As can be seen from step (602), Y waveguide 204 is coupled into calibration apparatus 20 in a forward manner.
3) As shown in the step (603), the low coherence reflectometer 500 is connected to the matched fiber 501, the variable attenuator 3502 and the polarization state controller 503 with appropriate length, and the calibration apparatus 20 is connected to the low coherence reflectometer 500 as shown in the step (603).
4) Step (604), the low coherence reflectometer 500 is started to perform the forward test of the Y waveguide 204, and the variable attenuator 3502 and the polarization state controller 503 are adjusted to maximize the amplitude of the reflection peak of the reflection point of the Y waveguide 204.
5) From step (605), the amplitude of the reflection peak of the forward reflection point of the Y waveguide 204 is recorded as a1。
6) As seen in step (606), Y waveguide 204 is re-inserted into calibration apparatus 20 in a reverse manner.
7) In step (607), the low coherence reflectometer 500 is started to perform the reverse test of the Y waveguide 204, and the variable attenuator 3502 and the polarization state controller 503 are adjusted to maximize the amplitude of the reflection peak at the reflection point of the Y waveguide 204.
8) From step (608), the amplitude of the reflection peak of the point of the backward reflection of the Y waveguide 204 is recorded as A2。
9) From step (609), using a loss calculation formula, the forward reflection peak amplitude of Y waveguide 204 is a1And the amplitude of the back reflection peak of the Y waveguide 204 is A2Calculating the forward and backward reflection losses delta of the reflection point of the Y waveguide 2041And delta2。
10) As shown in step (610), the Y waveguide 204 is re-inserted into the calibration apparatus 20 in a forward manner.
11) From step (611), the variable attenuator 2107 of the calibration arm 106 is adjusted to adjust the loss of the calibration arm 106 to δ1。
12) From step (612), the length S of calibration fiber 108 required to test Y-waveguide 204 is calculated1And adjusting the length of the calibration fiber 108.
13) From step (613), the low coherence reflectometer 500 is started for the Y waveguide 204 test.
14) From step (614), it is observed whether the reflection peak and calibration peak of the Y waveguide 204 appear simultaneously in the test result.
15) As shown in step 615, if the determination in step 614 is negative, the length S of the calibration fiber 108 is recalculated and adjusted1And returns to step (613).
16) As seen from step 616, if step 614 determines yes, Y waveguide 204 and the calibration peak reflection intensity test data are recorded.
17) In step (617), the calibration result is compared with the test result of the Y waveguide 204, and the reflectivity of the reflection point of the Y waveguide 204 is calculated.
The invention provides a calibration device and a calibration method for Y waveguide reflection characteristic test, which are used for accurately calibrating the reflectivity of a Y waveguide reflection point in a Y waveguide test result of a low-coherence reflectometer by constructing the calibration device and adopting a special calibration method and a calculation formula.
The Y waveguide calibration device is shown in the attached figure 1.
The calibration device 20 is composed of an SLD light source 100, a flange plate 101, a coupler input pigtail 102, a single-mode coupler 103, a test arm 104, a calibration arm 106, a variable attenuator 1105, a test module 114, a test arm debugging module 115, a variable attenuator 2107, a calibration optical fiber 108, an output collimating mirror 110, a calibration arm debugging module 116, and a calibration module 117.
SLD light source 100 is connected to coupler input pigtail 102 via flange 101, and coupler input pigtail 102 has length L1。
One arm of the output end of the single-mode coupler 103 is used as a test arm 104, and the other arm is used as a calibration arm 106.
The variable attenuator 1105 is mounted on the test arm 104, the test arm 104 is connected to the test arm debugging module 115 or the test module 114 through the welding point A201, and the length of the test arm 104 is L2。
The tail end of the calibration fiber 108 is connected to an output collimating mirror 110, and outputs the calibration arm transmission light 109 to a calibration arm debugging module 116 or a calibration module 117.
The test arm debugging module 115 comprises a single mode fiber 124, a fiber union 121 and an optical power meter 1122, wherein the single mode fiber 124 is connected to the optical power meter 1122 through the fiber union 121, and the optical power meter 1122 is used for measuring the output optical power of the test arm 104.
Calibration arm debugging module 116 includes a receiving collimator 120, a collimator pigtail 125, and an optical power meter 2126, where receiving collimator 120 is connected to optical power meter 2126 through collimator pigtail 125, and optical power meter 2126 is used to measure the output optical power of calibration arm 106.
The flow of the manufacturing and debugging method of the Y waveguide calibration device is shown in figure 2.
From step (401), the device is selected first, and the single-mode coupler 103 with the splitting ratio of exactly 50:50 is selected as much as possible, because it is necessary to ensure that the input light intensities of the test arm 104 and the calibration arm 106 are consistent.
As shown in step (402), after the device is selected, the corresponding device is connected according to the device connection mode, the test arm 104 is connected to the test arm debugging module 115, and the calibration arm 106 is connected to the calibration arm debugging module 116, so as to start debugging the calibration apparatus 20.
As shown in step (403), the first step of debugging is to adjust the variable attenuators 1105 and 2107 to a relaxed and non-attenuated state, so as to ensure that the attenuators do not bring additional loss.
In step (404), the second step is to weld a single mode fiber 124 to the testing end, and the single mode fiber 124 is connected to the optical power meter 1122 through the fiber union 121, so as to manufacture the testing arm debugging module 115.
As shown in step (405), in the third step, a receiving collimator 120 is placed in parallel after the collimator 110 is output from the calibration end, and the optical power meter 2126 is connected to the collimator tail fiber 125 to manufacture the calibration arm debugging module 116.
As seen from step (406), the output light intensity I received by the optical power meter 1122 at the time of recording is recorded1And the output intensity I of the optical power meter 21262。
As shown in step 407, the fourth step is to compare the output intensity I1And output light intensity I2If the magnitudes are equal, then step 409 is entered, if not, then step 408 is entered.
As seen in step (408), the fifth step is to adjust the variable attenuators 1105 and 2107 to output intensities I1And output light intensity I2Are equal.
As shown in step 409, the debugging is completed, the state is fixed, and the test arm debugging module 115 is replaced with the test module 114 composed of the Y waveguide 204.
In step (410), the welding point a201 of the testing end is disconnected, the calibration arm debugging module 116 is replaced with the calibration module 117 composed of the coated mirror 123 with known reflectivity, and the manufacturing of the calibration device 20 is completed.
The forward and reverse test structure of the Y waveguide is shown in figure 3.
The Y waveguide forward and reverse test structure is composed of a calibration device 20, a Y waveguide forward test structure 21 and a Y waveguide reverse test structure 22.
The Y waveguide forward test structure 21 and the Y waveguide reverse test structure 22 both comprise a welding point A201, a Y waveguide 204, a coupling point B208, a Y waveguide chip 205, a coupling point C209, a welding point D207, a Y waveguide input tail fiber 203 and a Y waveguide output tail fiber 206, wherein the coupling points are reflection points and can form corresponding reflection signals, and in addition, the Y waveguide input structure and the Y waveguide output structure are reflection points and can form corresponding reflection signalsThe length of the tail fiber 203 is L3Y waveguide 204 has a length L4The length of the Y waveguide output pigtail 206 is L5。
In the Y waveguide forward test structure 21, the Y waveguide 204 is connected with the calibration device 20 through a welding point A201, the end point of the test structure is a welding point D207, the light transmission mode is that the welding point A201, a coupling point B208, the Y waveguide 204, a Y waveguide chip 205, a coupling point C209 and a welding point D207 form a forward reflection signal 202 at a reflection point, and the magnitude of the forward reflection signal is A2011。
In the Y waveguide reverse test structure 22, the Y waveguide 204 is connected to the calibration device 20 through a solder point D207, the end point of the test structure is a solder point a201, the optical transmission mode is that the solder point D207, the coupling point C209, the Y waveguide chip 205, the Y waveguide 204, the coupling point B208 and the solder point a201 form a reverse reflection signal 210 at the reflection point, and the magnitude of the reverse reflection signal is a2。
When the calibration apparatus 20 is used, due to the existence of different reflection points inside the Y waveguide 204 and different losses between the different reflection points, for example, due to the existence of the Y waveguide 204 between the welding point a201 and the welding point D207, the loss of the input light between the two points may differ by about 3dB, which means that in order to ensure the calibration accuracy and the calibration precision, the same loss is required between calibration peaks of the welding point a201 and the welding point D207 during calibration. Therefore, to achieve accurate calibration of the test result of the Y waveguide, the loss of the input light in the Y waveguide 204 reaching each point needs to be accurately known, and then the loss of the input light in the Y waveguide 204 reaching each point can be solved by adopting forward and reverse tests and combining with a corresponding calculation formula.
The Y waveguide measurement and calibration process is shown in figure 4.
Step (601) is to fabricate the calibration device 20, and debug the insertion loss of the two arms of the calibration device 20 by using the test arm debugging module 115 and the calibration arm debugging module 116.
The steps (602) to (605) are to insert the Y waveguide 204 into the calibration apparatus 20 in a forward manner for forward test, during the test, the calibration apparatus 20 is first inserted into the low coherence reflectometer 500 and is adjusted, mainly the variable attenuator 3502 and the polarization state controller 503 are adjusted to make the Y waveguide 204 reflect the signal forward202 is the maximum, the measured reflection intensity is the true value at this time, and then the reflection peak amplitude of the forward reflected signal 202 of the Y waveguide 204 is recorded as a1And completing the forward test.
The steps (606) - (608) are to connect the Y waveguide 204 to the calibration device 20 in a reverse manner for reverse test, and during the test, the calibration device 20 is also connected to the low coherence reflectometer 500 for adjustment, mainly adjusting the variable attenuator 3502 and the polarization state controller 503 to make the amplitude of the reflection peak of the Y waveguide 204 retro-reflected signal 210 maximum, and then recording the amplitude of the reflection peak of the Y waveguide 204 retro-reflected signal 210 as a2And completing the reverse test.
Step (609) is to use a loss calculation formula according to the reflection peak amplitude A of the forward reflection signal 202 of the Y waveguide 2041And the reflection peak amplitude A of the Y waveguide 204 back reflected signal 2102The reflection loss delta of the forward and backward input light in the Y-waveguide 204 to each reflection point can be calculated1And delta2。
Steps (610) to (617) are the testing and calibrating processes of the Y waveguide 204, at this time, the Y waveguide 204 is firstly connected into the calibrating device 20 in a forward direction, and the loss δ of the Y waveguide 204 reaching the reflection point to be measured in the forward direction is calculated according to step (609)1To adjust the variable attenuator 2107 in the calibration arm 106 to increase the loss of the calibration arm 106 to delta1The purpose is to ensure consistent loss during testing and calibration. The length S of the calibration fiber 108 required for testing the Y waveguide 204 in the forward direction is then calculated1The purpose is to synchronize the result of the Y waveguide 204 with the calibration result, perform calibration while testing, and adjust the length of the calibration fiber 108. Starting the low-coherence reflectometer 500 to perform Y waveguide 204 test and observe whether the reflection peak and calibration peak of the Y waveguide 204 appear simultaneously in the forward test result, if not, recalculating and adjusting the length S of the calibration fiber 1081The test was repeated until both peaks appeared simultaneously. And finally, recording the reflection intensity test data of the Y waveguide 204 and the calibration peak, comparing the calibration result with the test result of the Y waveguide 204, and calculating the reflectivity of the reflection point of the Y waveguide 204 to finish the calibration of the Y waveguide 204.
According to the calibration device and method for the reflection characteristic test of the Y waveguide, disclosed by the invention, the calibration device is constructed by using the coupler with the splitting ratio of 50:50, the Y waveguide test and calibration are synchronously carried out, the loss of each reflection point of the Y waveguide is calculated by using the test results of forward reflection and backward reflection of the Y waveguide, and the calibration precision is improved.
The calibration principle of the device is as follows: assuming that the reflectivity of the coating mirror 123 in the calibration device 20 is 2%, the corresponding logarithm is-27 dB.
The interference expression of the reflected signal is
The direct current quantity does not respond, and the alternating current quantity is directly considered. Since the low coherence reflectometer 500 typically employs a 99:1 coupler, IOn the upper part＝0.99I0,ILower part＝0.01I0Logarithmically varying the amplitude of the interference signal to:
when the calibration is performed, the reflectivity of the coating reflection mirror 123 is 2 per mill, IOn the upper part＝0.99I0×α1×cosθ1×0.002，ILower part＝0.01I0. Wherein alpha is1To calibrate arm 106 loss factor, cos θ1For the polarization phase difference of the calibration arm 106, logarithm is taken to obtain the calibration interference peak amplitude:
during measurement, let the reflection point of the Y waveguide 204 have a reflectivity of x and a loss of alpha2The polarization phase difference of the test arm 104 is cos θ2Then, there are:
obtained by the formulae (2) to (3):
an error term exists when the true reflectivity x of the reflection point of the Y waveguide (204) is calculated according to the formula (4):
the error term obtained from equation (5) is the loss factor α from calibration arm 1061 Y waveguide 204 reflection point loss α2And the polarization phase difference of the measurement arm 104 and the calibration arm 106, the calculation of the real reflectivity is influenced by the existence of the error term, and the calibration precision is reduced sharply.
The polarization state of the interference signal is controlled by tuning the polarization state controller 503 of the low coherence reflectometer 500 in the case of testing the Y waveguide 204 using the low coherence reflectometer 500, so the influence of the polarization state is not substantially considered, when the error term changes to:
from equation (6), the error term at this time is only found together with the loss factor α of calibration arm 1061Y waveguide 200 reflection point loss alpha2It is related.
In the case of calibration using the calibration device 20, the interference peak value of the calibration peak is logarithmically obtained:
wherein alpha is1To scale the loss of arm 106, ξ is the split ratio of coupler scaling arm 106.
During measurement, the reflectivity of the coating reflection mirror 123 is set as x, and the loss of the test arm 104 is set as alpha2The splitting ratio of the coupler test arm 104 is ζ, then：
Obtained by the formulae (7) to (8):
at this time, when the calibration apparatus 20 selects a single-mode coupler with a splitting ratio of 50:50, equation (9) becomes:
adjusting calibration arm loss α by variable attenuator 21072So that α is2＝α1So that equation (10) becomes:
it can be seen that, in the case of using the calibration device 20 proposed in the patent, the error term β can be eliminated by performing calibration and calculation according to the calibration method1And the accurate calibration of the test result of the Y waveguide 204 is realized.
The method for calculating the loss of any reflection point in the Y waveguide 204 by forward and reverse tests of the Y waveguide 204 comprises the following steps:
during forward test, the reflectivity of a reflection point is set as x, and the amplitude of an interference peak is set as follows:
during reverse test, the amplitude of the interference peak is as follows:
wherein, delta1For the positive test of the loss to point B, delta2The loss to point B was tested in reverse.
At this time, equations (12) to (13) can be obtained:
also, the total Y-waveguide 204 loss is generally known, assuming that its loss is δ, there is:
δ1+δ2＝δ (15)
the loss delta of the point B in the forward test can be solved by combining the two formulas (14) and (15)1The loss value of any point in the device to be tested can be obtained in an expanded mode through forward and reverse tests, and the Y waveguide 204 can be calibrated according to the loss value, but the method is not suitable for full-closed devices such as a fiber-optic gyroscope.
It should be noted that, when using the forward and reverse test method of the Y waveguide 204, the loss of the reflection point of the Y waveguide 204 cannot be too large, and assuming δ as the point B, the point B is taken as an example1、δ2All the loss is the loss to the point B, the loss of the point B is not included, and when the energy leaked from the point B is larger, the loss is larger, namely, delta is largerBThen, there are:
δ1+δ2＝δ-δB (16)
at this time, formula (16) replaces formula (15), and calculation and calibration are performed according to formula (15), so that a certain error exists, and the calibration accuracy is reduced.
For clearly illustrating the calibration of the low coherence reflectometer Y waveguide test results by the calibration apparatus of the present invention, the present invention is further described with reference to fig. 5, but the scope of the present invention should not be limited thereby.
The calibration device for testing the Y waveguide by the low-coherence reflectometer is shown in the attached figure 5, and the parameters of each component are selected as follows:
the Low-Coherence reflectometer 500 is an Optical Low Coherence Reflectometer (OLCR) based on the white light interference principle, and has a measurement fiber length of 0-50 cm (fiber refractive index of 1.456, single-mode fiber), a dynamic range of 0-100 dB, and a sensitivity of 130 dB.
The low coherence reflectometer 500 has three interfaces on the front panel, interface 1504 and interface 2505 for connecting appropriate length needed for testing the Y-waveguide 204, and interface 3506 for connecting with the calibration apparatus 20.
The matched length optical fiber 501 is a single mode jumper with a proper length, and the variable attenuator 3502 and the polarization state controller 503 are both installed on the matched length optical fiber 501.
The variable attenuators 1105, 2107, 3502 are all optomechanical attenuators, and the attenuation of the input light is achieved by changing the luminous flux by controlling the distance between the two optical fibers.
The polarization controller 503 is a three-ring polarization controller, and changes the polarization state of the input light by rotating the three disk rings.
The low-coherence reflectometer 500 is connected with the calibration device 20 through the flange plate 101, the calibration device 20 selects the single-mode coupler 103 with the splitting ratio of 50:50, and the working wavelength of the coupler is 1550 nm.
The test module 114 of the calibration apparatus 20 may be any type and configuration of Y-waveguide 204, and the loss of the Y-waveguide 204 needs to be known or forward and reverse tests need to be performed to calculate.
The output collimating mirror 110 of the calibration module 117 of the calibration arm 106 of the calibration device is a general fiber collimating mirror with high collimation and small divergence angle, and collimates the divergent light path output from the optical fiber into a parallel light path, and the reflecting structure is composed of a movable platform 112 and a coated reflecting mirror 123, wherein the coated reflecting mirror 123 is installed on the movable platform 112, and the direction faces the output collimating mirror 110, and the coated reflecting mirror 123 can be a lens with any reflectivity, preferably a reflecting mirror with a reflectivity of two thousandths.
The working mode of the calibration device is as follows: first, input light 507 of a size A is injected from an internal light source of the low coherence reflectometer 5000 Input light 507 enters single-mode coupler 103 through coupler input pigtail 102, enters test arm 104 and calibration arm 106 through two output arms of single-mode coupler 103, and enters test arm 104, the input light 507 passes through the reflection point of the Y waveguide 204 in the test module 114 to form a forward reflected signal 202 with a magnitude of a1At this time A1＝(A0/2)×α1×x，α1The loss from the Y-waveguide 204 to the reflection point, and x is the reflection point reflectivity. On the other hand, the input light 507 passes through the calibration arm 106 and is reflected by the coated mirror 123 to form a calibration signal 113 with a magnitude A3，A3＝(A0/2)×α2×0.002，α2To calibrate the arm 106 for wear. At this time, the variable attenuator 2107 is adjusted so as to be α2＝α1The reflectivity x of the reflection point of the Y waveguide 204 is calculated according to the formula (11), and the calibration signal 113 can realize accurate calibration of the forward reflection signal 202, thereby completing the whole test and calibration process.
In summary, the present invention provides a calibration apparatus and method for Y waveguide reflection characteristic test, including the apparatus structure and the calibration method flow. The embodiment adopts a 3dB coupler and a variable attenuator to construct a calibration device, improves the calibration precision of the reflection characteristic test result of the Y waveguide by adjusting the loss of the calibration device, and realizes the synchronous operation of the test and the calibration. The patent establishes a calibration device and a calibration method for the internal reflection characteristic test result of a Y waveguide device, and can calibrate the reflectivity of the existing chip and coupling point in the Y waveguide.
Claims (2)
1. A calibration method for testing the reflection characteristic of a Y waveguide is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: manufacturing the calibration device (20) according to the manufacturing method of the calibration device, and debugging the insertion loss of the calibration device (20); the manufacturing and debugging steps of the calibration device are as follows:
step 401, selecting a device, selecting a single-mode coupler (103) with a splitting ratio of just 50:50, and ensuring that the input light intensity of a test arm (104) is consistent with that of a calibration arm (106);
step 402, connecting corresponding devices according to the device connection mode, connecting a test arm debugging module (115) to a test arm (104), connecting a calibration arm (106) to a calibration arm debugging module (116), and starting debugging the calibration device (20);
step 403, adjusting the variable attenuators 1(105) of the test arm and the variable attenuators 2(107) of the calibration arm to a loose and attenuation-free state, so as to ensure that the attenuators do not bring additional loss;
step 404, welding a section of single mode fiber (124) at the testing end, connecting the single mode fiber (124) with the optical power meter 1(122) through the optical fiber loose joint (121), and manufacturing a testing arm debugging module (115);
step 405, a receiving collimating mirror (120) is arranged in parallel after the collimating mirror (110) is output from the calibration end, a tail fiber (125) of the collimating mirror is connected to the optical power meter 2(126), and a calibration arm debugging module (116) is manufactured;
step 406, recording the receiving output light intensity I of the optical power meter 1(122) at this time1And output light intensity I of optical power meter 2(126)2；
Step 407, comparing the output light intensity I1And output light intensity I2Whether the sizes are equal, if so, entering a step 409, and if not, entering a step 408;
step 408, adjusting the variable attenuators 1(105) and 2(107) to output intensities I1And output light intensity I2Equal;
step 409, completing debugging at the moment, fixing the state at the moment, and replacing the testing arm debugging module (115) with a testing module (114) consisting of a Y waveguide (204);
step 410, disconnecting a welding point A (201) at a test end, replacing a calibration arm debugging module (116) with a calibration module (117) composed of a coated reflector (123) with known reflectivity, and completing the manufacture of the calibration device (20);
step two: the Y waveguide (204) is connected into the calibration device (20) in a forward mode;
step three: the low coherence reflectometer (500) is connected into a matched length optical fiber (501) with proper length, a variable attenuator (3) (502) and a polarization state controller (503), and the calibration device (20) is connected into the low coherence reflectometer (500);
step four: starting a low-coherence reflectometer (500) to perform forward test on a Y waveguide (204), and adjusting a variable attenuator (3) (502) and a polarization state controller (503) to the maximum reflection peak amplitude value of a reflection point of the Y waveguide (204);
step five: recording the reflection peak amplitude of the forward reflection point of the Y waveguide (204) as A1；
Step six: re-connecting the Y waveguide (204) to the calibration device (20) in a reverse manner;
step seven: starting a low-coherence reflectometer (500) to perform reverse test on a Y waveguide (204), and adjusting a variable attenuator (3), (502) and a polarization state controller (503) to the maximum reflection peak amplitude value of a reflection point of the Y waveguide (204);
step eight: recording the amplitude of the reflection peak of the backward reflection point of the Y waveguide (204) as A2；
Step nine: using a loss calculation formula, according to the forward reflection peak amplitude of the Y waveguide (204) being A1 and the backward reflection peak amplitude of the Y waveguide (204) being A2Calculating forward and reverse reflection losses delta of reflection points of the Y-waveguide (204)1And delta2；
Step ten: the Y waveguide (204) is connected into the calibration device (20) again in a forward mode;
step eleven: adjusting the variable attenuator 2(107) of the calibration arm (106) and adjusting the loss value of the calibration arm (106) to delta1；
Step twelve: calculating the length S of the calibration fiber (108) required for testing the Y waveguide (204)1Adjusting the length of the calibration fiber (108);
step thirteen: starting a low-coherence reflectometer (500) to perform a Y waveguide (204) test;
fourteen steps: observing whether the reflection peak and the calibration peak of the Y waveguide (204) appear simultaneously in the test result;
step fifteen: if the step fourteen is judged to be no, recalculating and adjusting the length S of the calibration optical fiber (108)1And returning to the step thirteen;
sixthly, the steps are as follows: if the judgment in the step fourteen is yes, recording Y waveguide (204) and calibration peak reflection intensity test data;
seventeen steps: and comparing the calibration result with the Y waveguide (204) test result, and calculating the reflectivity of the reflection point of the Y waveguide (204).
2. The standard for testing reflection characteristics of Y waveguide as claimed in claim 1The method is characterized in that: the calibration device comprises an SLD light source (100), a flange plate (101), a coupler input tail fiber (102), a single-mode coupler (103), a test arm (104), a calibration arm (106), a variable attenuator 1(105), a test module (114), a test arm debugging module (115), a variable attenuator 2(107), a calibration optical fiber (108), an output collimating mirror (110), a calibration arm debugging module (116) and a calibration module (117), wherein the SLD light source (100) is connected with the coupler input tail fiber (102) through the flange plate (101), and the length of the coupler input tail fiber (102) is L1(ii) a One arm of the output end of the single-mode coupler (103) is used as a test arm (104), and the other arm is used as a calibration arm (106); the variable attenuator 1(105) is arranged on a test arm (104), the test arm (104) is connected with a test arm debugging module (115) or a test module (114) through a welding point A (201), and the length of the test arm (104) is L2(ii) a The calibration arm (106) is connected with the calibration optical fiber (108) through a welding point E (111), and the variable attenuator 2(107) is arranged on the calibration optical fiber (108); the tail end of the calibration optical fiber (108) is connected with an output collimating mirror (110), the calibration arm transmission light (109) is output to a calibration arm debugging module (116) or a calibration module (117), and the test module (114) is a Y waveguide (204) of various types; the calibration module (117) consists of a movable platform (112) and a coating reflection mirror (123), the coating reflection mirror (123) is installed on the movable platform (112) and faces the output collimating mirror (110) in the direction, and the coating reflection mirror (123) is different coated lenses with known reflectivity.
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| DE69801979T2 (en) * | 1998-07-15 | 2002-04-04 | Agilent Technologies Inc | Optical loss measurement |
| TWI242942B (en) * | 2004-02-17 | 2005-11-01 | Asia Optical Co Inc | Optical return loss detecting device |
| CN102288388B (en) * | 2011-05-09 | 2013-04-10 | 哈尔滨工程大学 | Device and method for improving polarization-maintaining optical fiber polarization coupling measurement precision and symmetry |
| CN103292976A (en) * | 2013-05-16 | 2013-09-11 | 北京航空航天大学 | Interferometry-based optical fiber Verdet constant measuring system |
| CN103743552B (en) * | 2013-12-30 | 2016-08-03 | 哈尔滨工程大学 | A kind of caliberating device of wide range continuous light path delay line |
| CN103900799B (en) * | 2014-03-28 | 2016-05-04 | 哈尔滨工程大学 | A kind of optical coherence polarimeter that suppresses interaction noise |
| CN103900797B (en) * | 2014-03-28 | 2016-05-04 | 哈尔滨工程大学 | With the optical coherence territory polarimeter of light path scanning position and velocity correction |
| CN104280215B (en) * | 2014-10-11 | 2017-02-15 | 哈尔滨工程大学 | Dual-channel optical performance bi-directional multi-alignment-angle automatic testing device for Y waveguide |
| CN105043718B (en) * | 2015-04-30 | 2017-11-21 | 哈尔滨工程大学 | A kind of Noise Suppression Device and suppressing method of the measurement of optical polarization device distributed polarization interference |
| CN105954004B (en) * | 2016-04-01 | 2018-10-26 | 哈尔滨工程大学 | A kind of back scattering random fit coherent noise tester |
| CN105784336B (en) * | 2016-04-26 | 2018-05-18 | 哈尔滨工程大学 | A kind of transmission of optical fibre device and reflecting properties test device and method |
| CN108956092B (en) * | 2018-05-23 | 2020-02-07 | 中国电子科技集团公司第四十一研究所 | Polarization coupling distribution calibrator and method based on integrated Y waveguide structure |
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