CN103743553A - Double-channel optical performance testing device of integrated waveguide modulator and polarization crosstalk identification and processing method thereof - Google Patents

Abstract

The design of the invention belongs to the technical field of optical device measurement, and specifically relates to a dual-channel optical performance testing device of an integrated waveguide modulator and a polarization crosstalk identification and processing method thereof. The invention includes a high polarization stability wide-spectrum light source, an integrated waveguide modulator to be tested, an optical path demodulation device, and a polarization crosstalk detection and recording device. The device simplifies the system structure, enriches the test function, reduces the cost, improves the test efficiency, and can be widely used in the quantitative test of the optical performance of the integrated waveguide device above 80dB.

Description

A dual-channel optical performance test device with integrated waveguide modulator and its polarization crosstalk identification and processing method

technical field

The design of the invention belongs to the technical field of optical device measurement, and specifically relates to a dual-channel optical performance testing device of an integrated waveguide modulator and a polarization crosstalk identification and processing method thereof.

Background technique

Multifunctional integrated optical devices are commonly known as "Y waveguides", generally using lithium niobate materials as the substrate, which highly integrates single-mode optical waveguides, optical beam splitters, optical modulators and optical polarizers, forming an interference fiber optic gyroscope (FOG) and the core components of the fiber optic current transformer determine the measurement accuracy, stability, volume and cost of the fiber optic sensing system.

The important parameters of the Y waveguide device mainly include: the extinction ratio of the waveguide chip, the crosstalk of the pigtail, the optical path difference of the output channel, and the temperature characteristics of the above parameters. How to accurately and comprehensively test the optical properties of Y-waveguide devices is a very difficult problem encountered in the development and production of high-performance devices. The chip extinction ratio of the Y-waveguide used in the high-precision precision fiber optic gyroscope is required to reach more than 80dB. For example, a method (CN201310185490.2) proposed by Hua Yong and Shu Ping of the 44th Research Institute of China Electronics Technology Group Corporation to improve the extinction ratio of Y-waveguide chips used in fiber optic gyroscopes has achieved Y-waveguide devices above 80dB. And the commonly used polarization performance testing instrument—the extinction ratio tester, the Model 4810 polarization extinction ratio measuring instrument developed by the US dBmOptics company with the highest resolution is only 72dB; The highest extinction ratio of the PEM-330 type of Japan Santec Company can only reach about 50dB.

The Y waveguide device is composed of input optical fiber, waveguide chip, output optical fiber, modulation electrode, etc., and includes at least one input channel and two output channels. The complexity of the structure requires that in addition to the extinction ratio of the chip, the linear birefringence, pigtail crosstalk, insertion loss, optical path difference of the output channel, and the temperature characteristics and voltage characteristics of the other chips must also be measured. Parameter.

In the early 1990s, French Herve Lefevre et al. (US4893931) disclosed for the first time the OCDP system based on the principle of white light interference, which uses a superluminescent light-emitting diode (SLD) and a spatial interference optical path measurement structure. According to this patent, French Photonetics company has developed two types of OCDP test systems, WIN-P125 and WIN-P400, which are mainly used for the analysis of polarization characteristics of shorter (500m) and longer (1600m) polarization-maintaining optical fibers. Its main performance is that the polarization crosstalk sensitivity is -70dB and the dynamic range is 70dB. After improvement, the sensitivity and dynamic range are increased to -80dB and 80dB respectively. However, the measurement of Y-waveguide with high extinction ratio is not enough.

In 2002, Alfred Healy and others of Fibersense Technology Corporation of the United States disclosed a coupling method for input/output optical fibers of integrated waveguide chips (US6870628), using white light interferometry to realize the measurement of coupling crosstalk of input/output optical fibers of waveguide chips; In 2004, Yi Xiaosu and Xiao Wen of Beijing University of Aeronautics and Astronautics disclosed an online test method and test device for an integrated optical modulator for a fiber optic gyroscope (CN200410003424.X), which can realize optical parameters such as device loss and splitting ratio. In 2007, Yi Xiaosu and Xu Xiaobin of Beihang University disclosed a Y waveguide chip and polarization-maintaining optical fiber online alignment device and its online alignment method (CN200710064176.3), which is also realized by interference spectroscopy The measurement of crosstalk between waveguide chip and waveguide input/output fiber is carried out. But it does not involve the measurement of the extinction ratio of the waveguide chip.

In 2011, Zhang Hongxia of Tianjin University and others disclosed a detection method and detection device for the polarization extinction ratio of an optical polarization device (CN201110052231.3). The spatial interference optical path is also used as the core device of OCDP. By detecting the coupling strength of the coupling point, the derivation The polarization extinction ratio. The device is suitable for various optical polarization devices such as polarization-maintaining fiber, polarization-maintaining fiber coupler, and polarizer. Compared with the scheme of Herve Lefevre et al., the technical performance and indicators are similar.

In the same year, Yao Xiaotian and others from General Photonics Corporation of the United States disclosed an all-fiber measurement system for distributed polarization crosstalk measurement in polarization-maintaining optical fibers and optical birefringent materials (US20110277552, Measuring Distributed Polarization Crosstalk in Polarization Maintaining Fiber and Optical Birefringent Material), using an optical path retarder before the optical path correlator to suppress the number and magnitude of stray white light interference signals during polarization crosstalk measurements. This method can improve the polarization crosstalk sensitivity of the all-fiber measurement system to -95dB, but keep the dynamic range at 75dB.

In 2012, our research group proposed a polarization crosstalk measurement test device based on an all-fiber optical path (CN201210379406.6) and a method for improving the performance of polarization crosstalk measurements of optical devices (CN201210379407.0), using an all-fiber optical path and suppressing beat noise The technical solution greatly suppresses the noise amplitude, improves the sensitivity of polarization crosstalk measurement to over -95dB, and maintains the dynamic range at 95dB, reduces the volume of the test system, and increases the measurement stability. It lays the foundation for the characteristic measurement of high extinction ratio Y-waveguide devices.

The traditional view holds that the optical properties of the two output ends of the Y waveguide, such as chip extinction ratio and linear birefringence, are consistent. However, the actual test research shows that: limited by the material and manufacturing process of the Y waveguide, the optical performance of the two output channels may have a certain difference, which is of great significance for analyzing the manufacturing process and parameters of the waveguide; based on the principle of white light interferometry The Y-waveguide measurement system of the company only has the single-channel test capability. When it is necessary to measure the two output channels of the Y-waveguide, it must be measured twice; especially in the external environment parameters (such as temperature, etc.) or application parameters (such as When the electrode loading voltage of the waveguide chip, etc.) changes, two single-channel measurements and one dual-channel simultaneous measurement cannot be completely equivalent when there are differences in external loading conditions and measurement time. Therefore, the parameters of different output channels of Y-waveguide devices, such as the absolute value and difference value of optical characteristics such as waveguide chip extinction ratio, linear birefringence, insertion loss, and pigtail crosstalk, are of great practical value. However, at present, the testing device and method have not yet involved in the comprehensive testing and evaluation of the optical properties and differences of the different output channels of the Y waveguide device.

The invention provides a dual-channel optical performance simultaneous testing device of a Y waveguide device. The design idea is: based on the all-fiber optical path structure, two sets of demodulation interferometers with independent functions are used for the two output channels of the Y waveguide device respectively. , using the principle of symmetry, through the organic compound and simplification of the test device structure, through the consistent setting of the optical path and device parameters, the comprehensive measurement of the optical characteristic parameters of the Y waveguide device is realized. The characteristics of the device include two demodulation interferometers with independent functions and the same optical path structure and parameters. They are respectively connected to the two output channels of the waveguide modulator and share the same optical path scanner. It is especially suitable for loading temperature, etc. Under the load of environmental parameters, the evaluation and analysis of the optical performance change and inconsistency of the output channel of the Y waveguide device can realize the extinction ratio of the waveguide chip between the two output channels of the integrated waveguide device, linear birefringence, insertion loss, pigtail crosstalk, etc. Simultaneous measurement of absolute and difference values of optical parameters. It has the advantages of comprehensive test parameters, high measurement accuracy, good stability, and simple optical path structure. It not only reduces the system cost, but also improves the test efficiency and saves the test cost. It can be widely used in the optics of integrated waveguide devices with high extinction ratio above 80dB. Quantitative testing of performance.

Contents of the invention

The purpose of the present invention is to provide a dual-channel optical performance testing device with integrated waveguide modulator, and the purpose of the present invention is also to provide a polarization crosstalk identification and processing method for the dual-channel optical performance testing device with integrated waveguide modulator.

The purpose of the present invention is achieved like this:

A dual-channel optical performance testing device for an integrated waveguide modulator, including a high polarization stability broadband light source, an integrated waveguide modulator to be tested, an optical path demodulation device, and a polarization crosstalk detection and recording device:

The first output channel and the second output channel of the integrated waveguide modulator to be tested are respectively connected to the first demodulation interferometer and the second demodulation interferometer of the optical path demodulation device; the polarization crosstalk detection and recording device is connected to the first The demodulation interferometer and the second demodulation interferometer, the photoelectric conversion and signal processing unit output white light interference signals from the first differential detector in the first demodulation interferometer and the second differential detector in the second demodulator Simultaneous processing and recording; the control computer uses the built-in polarization crosstalk identification and processing method of the integrated waveguide modulator to be tested to determine the waveguide chip extinction ratio and linearity between the first output channel and the second output channel of the integrated waveguide modulator to be tested. The absolute values of birefringence, insertion loss, and pigtail crosstalk are measured, stored, and displayed, and the performance differences when external environmental parameters or application parameters change are compared and displayed.

The first demodulation interferometer and the second demodulation interferometer: the first demodulation interferometer is connected with the first end of the first 2×2 fiber coupler by the first fiber analyzer, and the first 2×2 fiber coupler The second end of the second 2×2 fiber coupler is connected to the first end of the second 2×2 fiber coupler, the third end of the first 2×2 fiber coupler is connected to the fourth end of the second 2×2 fiber coupler through the first fiber circulator Connection, the fourth end of the first 2×2 fiber coupler is connected to the first DFB light source, the other end of the first fiber circulator is connected to the first fiber collimator lens, the second end of the second 2×2 fiber coupler and The third end is connected to the first differential detector;

The composition of the second demodulation interferometer is the same as that of the first demodulation interferometer, consisting of a second fiber analyzer, a third 2×2 fiber coupler, a fourth 2×2 fiber coupler, a second fiber circulator, It consists of a second fiber collimator lens, a second differential detector, and a second DFB light source.

The high polarization stability wide-spectrum light source is connected to the first photodetector through the first output end of the fiber coupler; after passing through the fiber isolator through the second output end, it is connected to the fiber polarizer.

The connection relationship between the integrated waveguide modulator to be tested and the wide-spectrum light source with high polarization stability and the optical path demodulation device is:

The output polarization-maintaining fiber of the optical fiber polarizer and the input polarization-maintaining pigtail fiber of the input channel of the integrated waveguide modulator to be tested have an axial angle of 0-45°;

The first output channel of the integrated waveguide modulator to be tested, the output polarization-maintaining pigtail of the second output channel, and the first and second optical fiber analyzers of the first demodulation interferometer and the second demodulation interferometer The on-axis angles of the input polarization-maintaining pigtails are 0-45°.

A polarization crosstalk identification and processing method for a dual-channel optical performance testing device integrating a waveguide modulator:

1) Detect the length l _{W- of the input polarization-maintaining pigtail,} and judge whether it satisfies:

S _Wi =l _Wi ×Δn _f >S _ripple

In the formula: Δn _f is the linear birefringence of the polarization-maintaining pigtail, and S _ripple is the maximum value of the optical path of the second-order coherence peak of the light source;

2) If not satisfied, weld a section of extended polarization-maintaining optical fiber l _fi , with the axis angle of 0°-0°, measure and record the length of the extended optical fiber l _fi and the theoretical optical path S _fi , and judge:

S _fi =l _fi ×Δn _f >S _ripple

3) Measure the length l _W of the waveguide chip;

4) Measure the length l _Wo-1 and l _Wo-2 of the first output channel pigtail and the second output channel pigtail, and judge:

S _Wo-1 =l _Wo-1 ×Δn _f and S _Wo-2 =l _Wo-1 ×Δn _f >S _W =l _W ×Δn _W

Where: the linear birefringence of Δn _W waveguide chip;

5) If the lengths l _Wo-1 and l _Wo-2 of the output channel pigtails do not meet the conditions of step 4), then weld two lengths of extension optical fiber l _fo-1 of the same length on the first output channel and the second output channel respectively , l _fo-2 , its angle to the axis is 0°-0°, and its length requirements meet:

S _fo-1 =l _fo-1 ×Δn _f and S _fo-2 =l _fo-1 ×Δn _f >S _W =l _W ×Δn _W , measure and record the extended optical fiber l _fo-1 and l _fo-2 ;

6) Connect the integrated waveguide modulator to be tested with the wide-spectrum light source and the optical path demodulation device, and its input and output angles on the axis are θ ₁ =45°, θ ₂ =45°;

7) Start the white light interferometer, and obtain two distributed polarization crosstalk measurement result curves of the first output channel and the second output channel at the same time;

8) Use the measured geometric lengths of each part of the device, including: input polarization-maintaining pigtail length l _Wi , input extension polarization-maintaining fiber length l _fi , waveguide chip length l _W , first output channel, second output channel pigtail Length l _Wo-1 , l _Wo-2 , length of output extension fiber l _fo-1 , l _fo-2 ; calculate the optical path delay, and arrange them in two rows according to the size:

The first row corresponds to the first waveguide output channel: S _fi , (S _fi +S _Wi ), S _fo-1 , (S _fo-1 +S _Wo-1 ), (S _fo-1 +S _Wo-1 +S _fi +S _Wi +S _W-1 )

The second row corresponds to the second waveguide output channel: S _fi , (S _fi +S _Wi ), S _fo-2 , (S _fo-2 +S _Wo-2 ), (S _fo-2 +S _Wo-2 +S _fi +S _Wi +S _W-2 )

9) Compared with the theoretical formula, determine the characteristic peak of polarization crosstalk measured by the first output channel, specifically:

(1) The polarization crosstalk ρ _fi of the waveguide input extension fiber and the waveguide input pigtail;

(2) The polarization crosstalk ρ _Wi between the waveguide input pigtail and the waveguide chip;

(3) Polarized crosstalk ρ _fo-1 between the output extension fiber and the waveguide output pigtail of the first output channel;

(4) Polarized crosstalk ρ _Wo-1 between the waveguide output pigtail of the first output channel and the waveguide chip;

(5) Polarization crosstalk of the Y-waveguide chip measured in the first channel

Determine the characteristic peak of polarization crosstalk measured on the second output channel (2C), specifically:

(1) Polarized crosstalk ρ _fi between the waveguide input extension fiber and the waveguide input pigtail (21);

(2) Polarized crosstalk ρ _Wi between the waveguide input pigtail (21) and the waveguide chip (2D);

(3) Polarized crosstalk ρ _fo-2 between the output extension fiber and the second output channel waveguide output pigtail;

(4) Polarized crosstalk ρ _Wo-2 between the waveguide output pigtail of the second output channel and the waveguide chip (2D);

(5) Polarization crosstalk of the Y-waveguide chip measured by the second channel

与偏振串音

偏振串音ρ_W-o-2与偏振串音ρ_W-o-1；10) Contrasting polarized crosstalk

crosstalk with polarization

Polarized crosstalk ρ _Wo-2 and polarized crosstalk ρ _Wo-1 ;

11) Measured birefringence Δn _f and Δn _W based on the calculated polarization-maintaining fiber pigtail and waveguide chip; I(0) _out1 /I(0) _out2 represents the measured insertion loss of the first and second output channels of the waveguide device ratio;

12) When the external environment parameters or application parameters change, re-execute step 7) to measure the optical parameters of the Y waveguide. The parameters that can be measured also include the optical characteristic changes of the two output channels, including input/output optical fibers and waveguide chips. The coupling crosstalk changes with the temperature; the chip extinction ratio of the two output channels of the waveguide changes with the applied voltage.

The beneficial effects of the present invention are:

(1) As an all-round test device for the optical performance of Y-waveguide devices, it can measure the most and most comprehensive optical parameters, including the waveguide chip extinction ratio between the two output channels of the Y-waveguide device, linear birefringence, and pigtail crosstalk , Insertion loss, and the measurement of the consistency of the output channel, one scan can obtain the measurement of many parameters, the test efficiency is high, the stability is good, and the influence of the environment is small;

(2) Two sets of demodulation interferometers with completely independent functions can be used to measure the optical characteristics of the two output channels at the same time, which can realize different waveguide output channels in environmental parameters (such as temperature, etc.) Electrode loading voltage, etc.), the evaluation and analysis of the optical performance change and inconsistency of the Y waveguide device, which not only improves the test efficiency, but also saves the test cost;

(3) The same optical path design (including optical path structure and component parameters), sharing the same optical path scanner, reduces the system construction cost, improves the test speed, and reduces the measurement inconsistency between channels;

(4) It adopts all-fiber optical path, which has the advantages of small size, high measurement accuracy, good temperature stability and anti-vibration stability, etc.

Description of drawings

Figure 1 is a schematic diagram of the optical principle of distributed polarization crosstalk measurement of optical devices;

Figure 2 is a schematic diagram of the corresponding relationship between the interference signal amplitude and the optical path formed by polarization crosstalk;

Figure 3 is a schematic diagram of a dual-channel optical performance test device for a Y-waveguide device based on a Mach-Zehnder demodulation interferometer;

Figure 5 shows the measured cloth polarization crosstalk data (polarization crosstalk noise of the measurement device) when the slow axis of the waveguide pigtail is aligned with the fast axis of the waveguide chip, and the device is connected to the test device at 0° to 0°;

Figure 6 shows the distributed polarization crosstalk data measured from the first output channel 2B (optical characteristics of the Y waveguide device) when the input 0°-45° and output 45°-0° of the Y waveguide device are connected to the measurement device;

Fig. 7 shows the distributed polarization crosstalk data measured from the first output channel 2C (polarization crosstalk noise of the measuring device) when the Y waveguide device is connected to the test device at 90°-0°;

Fig. 8 is the variation of the power coupling crosstalk between Y waveguide input pigtail and waveguide chip with temperature;

Fig. 9 is the change of the power coupling crosstalk between the pigtail of the first output channel of the Y waveguide and the waveguide chip with temperature;

Figure 10 is the variation of the power coupling crosstalk between the pigtail of the second output channel of the Y waveguide and the waveguide chip with temperature;

Fig. 11 is the measurement data summary table of Y waveguide first output channel 2B;

Fig. 12 is the measurement data summary table of Y waveguide second output channel 2C;

Figure 13 is the measured linear birefringence of the first output channel 2B of the Y waveguide;

FIG. 14 is the linear birefringence of the second output channel 2C of the Y waveguide.

Detailed ways

A dual-channel optical performance simultaneous testing device for a Y waveguide device proposed by the present invention includes a high polarization stability wide-spectrum light source 1, an integrated waveguide modulator to be tested (Y waveguide) 2, an optical path demodulation device 3, and polarization crosstalk Detection and recording device 4 is characterized in that:

1) The first and second output channels 2B and 2C of the Y waveguide 2 are respectively connected to the first and second demodulation interferometers 31 and 32 of the optical path demodulation device 3;

2) The optical path structure, components and device parameters of the first demodulation interferometer 31 and the second demodulation interferometer 32 are the same, including the optical path difference between the arms of the first interferometer 31 and the second interferometer 32 and the connecting optical fiber 300, 320, 302, 322, 304, 324;

3) The fiber collimator lens 306 in the first demodulation interferometer 31 and the fiber collimator lens 326 in the second demodulation interferometer 32 share the same optical path scanner 310;

4) The polarization crosstalk detection and recording device 4 is simultaneously connected to the first and second demodulation interferometers 31 and 32, and the photoelectric conversion and signal processing unit 41 outputs white light to the first and second differential detectors 308 and 309, 328 and 329 Interference signal, processing and recording at the same time;

5) The control computer 42 utilizes data identification and processing algorithms to measure, store and display the optical properties of the first and second output channels 2B and 2C of the Y waveguide 2, and also to measure the performance differences of the output channels 2B and 2C , especially the performance under environmental conditions such as loading temperature and application conditions such as voltage are compared and displayed.

The first and second demodulation interferometers 31, 32 are characterized in that:

1) The first demodulation interferometer 31 consists of a first fiber analyzer 301, a first 2×2 fiber coupler 303, a second 2×2 fiber coupler 307, a first fiber circulator 305, a first fiber quasi Composed of straight lens 306, first differential detectors 308, 309, and first DFB light source 311;

2) The second demodulation interferometer 32 consists of a second fiber analyzer 321, a third 2×2 fiber coupler 323, a fourth 2×2 fiber coupler 327, a second fiber circulator 325, a second fiber quasi Composed of straight lens 326, second differential detectors 328, 329, and second DFB light source 331;

3) The optical path structure, components and device parameters of the first demodulation interferometer 31 and the second demodulation interferometer 32 are the same, including the optical path difference between the two arms of the first interferometer 31 and the second interferometer 32 and the connection the lengths of optical fibers 300 and 320, 302 and 322, 304 and 324;

The described high polarization stability broadband light source 1 is characterized in that: the broadband light source 11 is connected to the first photodetector 14 through the first output end 13 of the fiber coupler 12; through the second output end 15 through the fiber isolator After 16, it is connected to the fiber polarizer 17.

The connection relationship between the Y waveguide 2 and the high polarization stability broadband light source 1 and the optical path demodulation device 3 is characterized in that:

1) The output polarization-maintaining fiber 18 of the polarizer 17 and the input polarization-maintaining pigtail 21 of the input channel 2A of the Y waveguide 2 have an axial angle of 0-45°;

2) The output polarization maintaining pigtails 22, 23 of the first and second output channels 2B, 2C of the Y waveguide and the first and second optical fiber analyzers 301, 321 of the first and second demodulation interferometers 31, 32 The axis-to-axis angles of the input polarization-maintaining pigtails 300 and 320 are respectively 0-45°.

The optical parameter measuring method of described Y waveguide 2 device is characterized in that:

1) The length l _Wi of the input polarization-maintaining pigtail 21 is required to satisfy the following formula:

S _Wi =l _Wi ×Δn _f >S _ripple (1)

In the formula: Δn _{f is} the linear birefringence of the polarization-maintaining pigtail, and S _ripple is the maximum value of the optical path of the second-order coherence peak of the light source 11.

2) If it is not satisfied, then weld a section of extended polarization maintaining optical fiber l _fi , the angle to the axis is 0°-0°, the length requirement is similar to formula (1), that is, formula (2) is satisfied, measure and record the length of the extended optical fiber l _fi and theoretical optical path S _fi ;

S _fi =l _fi ×Δn _f >S _ripple (2)

3) Measure the length l _W of the waveguide chip 2D;

4) Measure the lengths _lWo-1 and _lWo-2 of the first and second output channel pigtails 21 and 22 of the waveguide. The length requirements are similar to (1), that is, satisfy (3):

S _Wo-1 =l _Wo-1 ×Δn _f and S _Wo-2 =l _Wo-1 ×Δn _f >S _W =l _W ×Δn _W (3)

Where: Δn _W is the linear birefringence of the waveguide chip.

5) If the lengths l _Wo-1 and l _Wo-2 of the output pigtails 21 and 22 do not satisfy the formula (3), then weld two lengths of extension fibers l _fo-1 and l of the same length in the first and second output channels respectively _fo-2 , its on-axis angle is 0°-0°, and its length requirement is similar to formula (3), that is, to satisfy formula (4), measure and record the extended optical fibers l _fo-1 and l _fo-2 ;

S _fo-1 =l _fo-1 ×Δn _f and S _fo-2 =l _fo-1 ×Δn _f >S _W =l _W ×Δn _W (4)

6) Connect the Y waveguide 2 with the light source 1 and the optical path demodulation device 3, and the angles on the axis of its input and output are respectively θ ₁ =45°, θ ₂ =45°;

7) Start the white light interferometer and obtain two distributed polarization crosstalk measurement curves of the first and second output channels 2B and 2C at the same time;

8) Use the measured geometric lengths of each part of the device, including: input polarization maintaining pigtail 21 length l _Wi , input extension polarization maintaining fiber length l _fi , waveguide chip 2D length l _W , waveguide first and second output channel tails Fiber 21, 22 length lWo _-1 , lWo _-2 , output extension fiber length lfo _-1 , lfo _-2 ; calculate the optical path delay, and arrange them in two rows according to their size:

The first line (corresponding to the first waveguide output channel): S _fi , (S _fi +S _Wi ), S _fo-1 , (S _fo-1 +S _Wo-1 ), (S _fo-1 +S _Wo-1 +S _fi +S _Wi +S _W-1 )

The second row (corresponding to the second waveguide output channel): S _fi , (S _fi +S _Wi ), S _fo-2 , (S _fo-2 +S _Wo-2 ), (S _fo-2 +S _Wo-2 +S _fi +S _Wi +S _W-2 )

9) Compared with the formula (7) of the theoretical analysis results, according to the possible range of optical path delay, determine the meaning of each polarization crosstalk peak, including:

Determine the polarization crosstalk characteristic peak measured by the first output channel 2B, specifically:

(1) Polarized crosstalk ρ _fi between the waveguide input extension fiber and the waveguide input pigtail 21;

(2) polarization crosstalk ρ _Wi between the waveguide input pigtail 21 and the waveguide chip 2D;

(3) Polarized crosstalk ρ _fo-1 between the output extension fiber and the waveguide output pigtail 22 of the first output channel;

(4) Polarized crosstalk ρ _Wo-1 between the waveguide output pigtail of the first output channel and the waveguide chip 2D;

(5) Polarization crosstalk of the Y-waveguide chip measured in the first channel

Determine the polarization crosstalk characteristic peak measured by the second output channel 2C, specifically:

(1) Polarized crosstalk ρ _fi between the waveguide input extension fiber and the waveguide input pigtail 21;

(2) polarization crosstalk ρ _Wi between the waveguide input pigtail 21 and the waveguide chip 2D;

(3) Polarized crosstalk ρ _fo-2 between the output extension fiber and the waveguide output pigtail 23 of the second output channel;

(4) Polarized crosstalk ρ _Wo-2 between the waveguide output pigtail of the second output channel and the waveguide chip 2D;

(5) Polarization crosstalk of the Y-waveguide chip measured by the second channel

与

ρ_W-o-2与ρ_W-o-1，可知Y波导2两个输出通道2B、2C之间性能上的不一致；10) Contrast

and

ρ _Wo-2 and ρ _Wo-1 , it can be seen that the performance of the two output channels 2B and 2C of the Y waveguide 2 is inconsistent;

11) According to formulas (7) and (8), the measured birefringence Δn _f and Δn _W of polarization-maintaining fiber pigtails and waveguide chips can be calculated; I(0) _out1 /I(0) _out2 represent the first and second waveguide devices The insertion loss ratio measured by the two output channels;

12) When the external environmental parameters (such as temperature, etc.) or application parameters (such as the electrode loading voltage of the waveguide chip, etc.) change, go back to step 7) and measure the optical parameters of the Y waveguide again. The parameters that can be measured except the above In addition to the steps given, the optical properties of the two channels vary:

(1) The coupling crosstalk between input/output optical fiber and waveguide chip changes with temperature;

(2) The chip extinction ratio of the two output channels of the waveguide varies with the applied voltage.

The invention is a technical improvement to the optical coherent domain polarization test system (OCDP) based on the principle of white light interference. The working principle of OCDP is shown in Figure 1. Taking the crosstalk performance test of the welding point of the polarization-maintaining fiber as an example, the highly stable wide-spectrum polarized light 501 emitted by the wide-spectrum light source is injected into the slow axis of the polarization-maintaining fiber 521 of a certain length ( Fast axis, the principle is the same). When the transmission light passes through the welding point 511 in the optical fiber 521, a part of the light energy of the signal light in the slow axis will be coupled into the orthogonal fast axis to form a coupling beam 503, and the remaining transmission beam 502 is still transmitted along the slow axis . When the transmitted light emerges from the other end of the optical fiber 521 (the transmission distance is l), due to the linear birefringence Δn (for example: 5×10 ^-4 ) existing in the optical fiber, the transmitted light 502 in the slow axis and the light in the fast axis There will be an optical path difference Δn1 between the coupled lights 503 . The light beams 502 and 503 pass through the welding point or the connecting head 512 rotated by 45°, and after being polarized by the analyzer 531 , they are divided into two parts uniformly by the beam splitter 532 . As shown in Figure 2, the reference beam is composed of transmitted light 601 and coupled light 602, transmitted in the fixed arm of the interferometer, and returned to the beam splitter 532 after being reflected by the fixed mirror 533; it is composed of transmitted light 603 and coupled light 604 The scanning light beam also returns to the beam splitter 532 after being reflected by the moving mirror 534, and the two parts of the light converge on the detector 537 to form a white light interference signal, which is received and converted into an electrical signal. After the signal is processed by the signal demodulation circuit 551, it is sent to the measurement computer 552; the measurement computer 552 is also responsible for controlling the moving mirror 534 to realize optical path scanning.

As shown in Figures 1 and 2, under the control of the measurement computer 552, the moving mirror 534 of the Michelson interferometer makes the optical path difference of the two arms of the interferometer pass through zero from Δnl and scan to -Δnl:

它与缺陷点的耦合幅度因子和光源强度成正比；(1) When the optical path difference is equal to Δnl, the coupling light 604 in the scanning beam matches the optical path of the transmission light 601 in the reference beam, and a white light interference signal is generated with a peak amplitude of

It is proportional to the coupling amplitude factor of the defect point and the intensity of the light source;

(2) When the optical path difference is zero, the optical paths of the reference beams 601 and 602 are matched with the transmission light 605 and the coupling light 606 in the scanning beam respectively, and white light interference signals are generated respectively, and their peak amplitudes are the superposition of the intensities of the two, Its magnitude is I _main ∝I ₀ , which is proportional to the input power of the light source. It can be seen from FIG. 2 that, compared with the previous white light interference signal, the optical path difference between the peaks of the two white light interference signals is just Δnl. If the linear birefringence Δn of the optical device is known, the position l of the defect point can be calculated, and the power coupling size ρ of the defect point can be calculated through the ratio of the peak intensity of the interference signal;

(3) When the optical path difference is equal to -Δnl, the optical paths of the transmitted light 607 in the scanning beam and the coupling light 602 in the reference beam match, and a white light interference signal is generated with a peak amplitude of It is the same as when the optical path difference is Δnl. As can be seen from the figure, compared with when the optical path difference is Δnl, the white light interference signal is symmetrical in the optical path, and the amplitude is the same.

The polarization crosstalk ρ can be calculated according to the polarization crosstalk signal amplitude I _coupling obtained when the optical path difference is Δnl or -Δnl, and the transmission optical signal amplitude I _main obtained when the optical path difference is zero:

$\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; coupling</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; main</span>}}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Since the general polarization crosstalk is much smaller than 1, formula (1) changes to:

$\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; coupling</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; main</span>}}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

In order to simultaneously obtain the optical characteristics of the two output channels of the Y-waveguide device, the test setup is shown in Figure 3. When the Y-waveguide device 2 is aligned with the wide-spectrum light source 1 and the optical path demodulation device 3 at an alignment angle of 0°-45°, 45°-0°, the polarization crosstalk detection and recording device 4 obtains the first and second The amplitude and optical path delay of the white light interference signals of output channels 2B and 2C all satisfy the formula (3):

$\left\{\begin{array}{c}\frac{\mathrm{<span\; class="notranslate">\; I</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&PlusMinus;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&PlusMinus;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&PlusMinus;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ \frac{\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; I</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; chip</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula: I(S _out1 ), I(S _out2 ) respectively represent the sum of the amplitudes of all white light interference signals detected by the first differential detector (308, 309) and the second differential detector (328, 329); S _out1 , S _out2 represent the optical path scanning delays of the first and second demodulation interferometers 31 and 32 respectively, and when the optical path difference of I(0) _out1 and I(0) _out2 is zero respectively, it represents the maximum peak value of the white light interference signal Amplitude; R(S) is the normalized autocoherence function of the broadband light source, R(0)=1, the white light interference peak signal amplitude of the transmitted light, and the optical path difference is zero; R(S)=0 (S>S ₀ , S ₀ is the coherence length of the broadband light source); S _fi , S _fo-1 , S _fo-2 , S _Wi , S _Wo-1 , S _Wo-2 , S _W-1 , S _W-2 respectively The input extension fiber, the first output channel extension fiber, the second output channel extension fiber, the waveguide input pigtail, the waveguide first output channel pigtail, the waveguide second output channel pigtail, the first output channel waveguide transmission optical path, the second The optical path delay corresponding to the waveguide transmission optical path of the two output channels, when the optical path of the slow axis is ahead of the optical path of the fast axis, the above delay is defined as +; when the optical path of the slow axis lags behind the optical path of the fast axis, the above delay is The quantity is defined as -, each optical path delay can be expressed as:

S _fi ＝l _fi ×Δn _f

S _Wi ＝l _Wi ×Δn _f

S _fo-1 = l _fo-1 ×Δn _f

S _fo-2 = l _fo-2 ×Δn _f (8)

S _Wo-1 ＝l _Wo-1 ×Δn _f

S _Wo-2 ＝l _Wo-2 ×Δn _f

S _W-1 = l _W-1 ×Δn _W

S _W-2 = l _W-2 ×Δn _W

分别为第一、第二通道测量的Y波导芯片偏振串音（消光比的倒数）。In the formula, l _fi , l _fo-1 , l _fo-2 , l _Wi , l _Wo-1 , l _Wo-2 , l _W-1 , l _W-2 are the input extension fiber and the first output channel extension fiber respectively , Length of second output channel extension fiber, waveguide input pigtail, waveguide first output channel pigtail, waveguide second output channel pigtail, first output channel waveguide chip, second output channel waveguide chip, Δn _f , Δn _W are the linear birefringence of _the polarization-maintaining _fiber and the waveguide chip _respectively ; The solder joint polarization crosstalk power factor of the extension fiber of the second output channel and the waveguide output pigtail, _ρWi , ρWo _-1 , ρWo _-2 are respectively the waveguide input, the first output pigtail, the second output pigtail and The polarization crosstalk power factor of the waveguide chip,

Y-waveguide chip polarization crosstalk (reciprocal of extinction ratio) measured for the first and second channels, respectively.

From (7) and (8), it can be seen that if the lengths of the input, first output, and second output extension fibers are known, the lengths of the input, first output, and second output waveguide pigtails, and the waveguide chip can be demodulated through the optical path The optical path scanning of device 3 and the collection and processing of polarization crosstalk detection and recording device 4 white light interference signal amplitude, when the optical path delay is 0, ±S _fi , ±S _fo-1 , ±S fo-2 , ±S _fo-2 , ± (S _fi +S _Wi ), ±(S _fo-1 +S _Wo-1 ), ±(S _fo-2 +S _Wo-2 ), ±(S _fo-1 +S _Wo-1 +S _fi +S _Wi +S _W-1 ), ±(S _fo-2 +S _Wo-2 +S _fi +S _Wi +S _W-2 ), respectively, the peak value of the white light interference signal can be obtained, and its amplitude corresponds to ρ _fi , ρ _fo-1 , ρ _fo-2 , ρ _Wi , ρ _Wo-1 , ρ _Wo-2 , and other optical parameters.

In order to clearly illustrate the device and method for simultaneous measurement of dual output channels of the integrated waveguide modulator (Y waveguide) of the present invention, the present invention will be further described in conjunction with the examples and accompanying drawings, but this should not limit the protection scope of the present invention.

Embodiment 1——Waveguide measurement device based on Mach-Zehnder demodulation interferometer

The device measurement device is shown in Figure 3. The device selection and parameters of the white light interferometry device are as follows:

(1) The central wavelength of the broadband light source 11 is 1550nm, the half-spectrum width is greater than 45nm, the output power of the fiber is greater than 2mW, the spectral ripple of the light source is <0.05dB (the peak amplitude is about -60dB), and the optical path range of the coherence peak is 4-7mm; DFB The half-spectrum width of the light source 311 is less than 50MHz, and the output power of the fiber is greater than 1mW;

(2) 2/98 fiber coupler 12 working wavelength 1550nm, splitting ratio 2:98;

(3) Optical fiber isolator 16 has a working wavelength of 1550nm, insertion loss of 0.8dB, and isolation >35dB;

(4) The optical fiber polarizer 17, the working wavelength of the first and second optical fiber analyzers 301 and 321 is 1550nm, the extinction ratio is 30dB, and the insertion loss is less than 1dB;

(5) The parameters of the first, second, third, and fourth fiber couplers 303, 307, 323, and 337 are the same, the operating wavelength is 1310/1550nm, and the splitting ratio is 50:50;

(6) The first and second optical fiber circulators 305 and 325 are three-port circulators with an insertion loss of 1dB and a return loss greater than 55dB;

(7) The working wavelength of the first and second collimating lenses 306 and 326 is 1550nm, and the optical path scanning distance between them and the optical path scanner 310 (the reflectivity is above 92%) varies from about 0 to 200mm , the average insertion loss is 2.0dB, the loss fluctuation is within ±0.2dB, and when the optical path scanner 310 is approximately at the 100mm position, the optical path difference between the two arms of the first and second demodulating interferometers 31, 32 is approximately zero;

(8) The photosensitive materials of the first and second differential detectors 308 and 309, 328 and 329 are all InGaAs, the light detection range is 1100-1700nm, and the responsivity is greater than 0.85;

(9) Select the Y waveguide device 2 to be tested, its working wavelength is 1550nm, the slow axis of the waveguide pigtail is aligned with the fast axis of the waveguide chip, and the length of the waveguide chip is 20mm.

The working process of the measuring device is as follows:

The output light of the broadband light source 11 becomes linearly polarized after being split by the fiber coupler 12, isolated by the fiber isolator 16 and polarized by the polarizer 17, and then passes through the polarization maintaining output fiber 18 and the polarization maintaining input tail of the Y waveguide 2 The 45° on-axis solder joint of the fiber 21, the light energy is evenly injected into the fast and slow axes of the waveguide chip 2D to be tested; the light signal is first divided into two beams and transmitted in 2B and 2C respectively, due to the existence of the extinction ratio of the Y waveguide , the signal light transmitted in the slow axis of the waveguide is greatly attenuated, while the light transmitted in the fast axis is slightly attenuated (corresponding to the insertion loss), and the light transmitted in the fast and slow axes is output from the first output channel 2B and the first output channel 2C of the Y waveguide together , injected into the pigtails 22 and 23, passed through the 45° solder joints of the pigtails 300 and 320 respectively, mixed in the first polarizer 301 and the second polarizer 321 respectively, and injected into the first demodulation interferometer respectively 31 and the second demodulation interferometer 32.

Taking the first demodulation interferometer 31 as an example, the signal light output from the slow axis of the Y waveguide 2 and the signal light output from the fast axis are evenly divided into two beams by 303, and one beam is transmitted in a fixed arm composed of an optical fiber 304. One beam is transmitted in a scanning arm consisting of a first circulator 305 , a first collimator 306 and an optical path scanner 310 . When the optical path scanner 310 moves to realize the optical path scanning, the optical path difference generated between the fixed arm and the scanning arm of the first demodulation interferometer 31 matches the optical path difference of the fast and slow axis output light of the Y waveguide 2 , the first differential detectors 308 and 309 will output white light interference signals, the white light interference peak value is inversely proportional to the extinction ratio of the waveguide chip, and the optical path scanning position corresponding to the peak value corresponds to the length of the waveguide chip. The above measurement process obtains the optical properties of the Y-waveguide 2 measured from the first output channel.

The second demodulation interferometer 32 shares the same optical path scanner 310 as the first demodulation interferometer. Therefore, when the optical path scanner 310 is working, the second demodulation interferometer 32 obtains the optical properties of the Y waveguide 2 measured from the first output channel almost simultaneously.

Embodiment 2——Double-channel simultaneous measurement of the Y-waveguide device with the slow axis of the pigtail and the fast axis of the waveguide chip

The measurement device diagram of the Y waveguide device is shown in Figure 3, and the optical performance measurement process is shown in Figure 4.

(1) From step 701, it can be seen that the length _lWi of the Y waveguide input pigtail is 1.53 meters;

(2) It can be seen from step 702 that the theoretical optical path of the input pigtail l _Wi (Δn _f is calculated as 5×10 ^-4 ) S _Wi =0.765mm; and S _ripple =4~7mm, it can be seen that the input extension fiber must be welded ;

(3) According to step 703, it can be seen that the length of the connecting extension optical fiber l _fi is at least 7×10 ⁻³ /5×10 ⁻⁴ =14 meters, and 15 meters is actually selected;

(4) According to step 704, it can be seen that the length of the measured waveguide chip is 20mm, its theoretical optical path (ΔnW is calculated as 8×10 ^-2 ) S _Wo =1.6mm, and the corresponding output pigtail length l _Wo =1.6×10 ^-3 /5×10 ^-4 =3.2 meters;

(5) According to step 705, it can be seen that the pigtail lengths l _Wo-1 and l _Wo-1 of the first and second output channels are measured to be 1.72 meters and 1.78 meters;

(6) From steps 706 to 707, it can be seen that the optical distances S _Wo-1 and S _Wo-1 of the output pigtails are both smaller than S _W . It can be seen that the output fiber must be extended, and the length of the welding extension fiber l _fo must be at least 3.2 meters. The actual selection 5.6 meters;

(7) Since this is the first measurement, adjust the angle of alignment between the input/output pigtail of the Y waveguide, the light source 1 and the optical path demodulation device 3 to 0°-0°, start the measurement, and obtain the measurement result as shown in Figure 5, 81 indicates 82 (82') and 83 (83') are the stray interference peaks of the optical path of the measurement device 3; 84 (84') are caused by the spectral ripple of the light source Higher-order coherence peak; 85 (85') is the polarization crosstalk noise floor of the measurement device 3, representing the measurement limit of the measurement device;

(8) From steps 708 to 709, it can be known that adjusting the input/output angles to 0°-45° and 45°-0° and restarting the test device can obtain the first output channel of the Y waveguide as shown in Figure 6 and Figure 7 2B, the measurement result of the second output channel 2C;

(9) From steps 710 to 711, it can be seen that according to the length of the optical fiber and waveguide chip, the optical path length of each part is calculated and sorted to obtain 8A to 8E (8A' to 8E' are respectively symmetric to 8A to 8E), 9A to 9E (9A '～9E' respectively 9A～9E symmetry) each has 10 characteristic peaks, and the meaning and specific amplitude of each polarization crosstalk peak are determined by formula (7), as shown in Figure 11 and Figure 12;

(10) It can be known from step 712 that the extinction ratios of the waveguide chip measured by the first output channel and the second output channel are 55.2±0.2dB and 52.3±0.2dB respectively, and the difference is 2.9dB;

(11) From steps 713 to 714, it can be known that the lengths of the input/output extension fibers are l _fi =15.00 meters, l _fo-1 =l _fo-2 =5.60 meters, and the input/output pigtails are respectively l _Wi =1.53 meters , l _Wo-1 = 1.72 meters, l _Wo-1 = 1.78 meters, the length of the waveguide chip is 20mm, and the linear birefringence of the optical fiber and waveguide can be calculated according to (7) and (8), see Figure 13 and Figure 14 for details ;

(12) According to the test data, the maximum value I(0) _out1 and I(0) _out2 of the peak value of the white light interference signal obtained from the first and second output channels are 2.8dBV and 3.9dBV respectively. It can be seen that the insertion loss of the two channels is different 1.1dB.

Embodiment 3——Measurement of the change of two output channels of Y waveguide device with temperature

The measurement device of the Y-waveguide device is still as shown in Figure 3, and the difference with Embodiment 2 is that another Y-waveguide 2 to be measured connected with the broadband light source 1 and the optical path demodulation device 3 is placed in the temperature control box Inside, change the temperature from -50°C to 80°C, follow the measurement process and data analysis method shown in Figure 4, and simultaneously obtain various optical changes of the Y waveguide device with temperature from the first measurement channel and the second measurement channel quantity.

The test results show that the crosstalk at the coupling point of the input/output pigtail and the waveguide chip is very sensitive to temperature. The power coupling crosstalk between fiber and waveguide chip varies with temperature. It can be seen from the figure that the changes of the three are not consistent. The waveguide input pigtail crosstalk and the first output channel pigtail crosstalk have a large change (above 20dB), while the second output channel pigtail crosstalk has a small change (10dB within). The magnitude of the crosstalk change and the temperature of the minimum crosstalk point are related to the materials and processes of the optical fiber and waveguide connection. Therefore, the analysis of the crosstalk curves of the first and second output channels with temperature has great guiding significance for the selection and optimization of Y-waveguide materials and processes.

Claims (5)

1. a binary channels optical performance test device for integrated waveguide modulator, comprises high polarization degree of stability wide spectrum light source (1), integrated waveguide modulator to be measured (2), light path demodulating equipment (3), polarization crosstalk detection and pen recorder (4), it is characterized in that:

The first output channel of integrated waveguide modulator to be measured (2) and the second output channel are connected to the first demodulated interferential instrument and the second demodulated interferential instrument of light path demodulating equipment (3); Polarization crosstalk detects and is connected the first demodulated interferential instrument and the second demodulated interferential instrument with pen recorder (4) simultaneously, and opto-electronic conversion and signal processing unit (41) are processed and record the white light interference signal of the second differential detector output in the first differential detector in the first demodulated interferential instrument and the second (FBG) demodulator simultaneously; Control polarization crosstalk identification and disposal route that computing machine (42) utilizes built-in integrated waveguide modulator to be measured (2), absolute value to the waveguide chip extinction ratio between the first output channel of integrated waveguide modulator to be measured (2) and the second output channel, linear birefrigence, insertion loss, tail optical fiber cross-talk is measured, Storage & Display, and the performance difference when external environment parameters or application parameter change is compared and shown.

2. the binary channels optical performance test device of a kind of integrated waveguide modulator according to claim 1, it is characterized in that: the first described demodulated interferential instrument and the second demodulated interferential instrument: the first demodulated interferential instrument (31) is connected with the first end of the one 2 * 2 fiber coupler (303) by the first optical fiber analyzer (301), the second end of the one 2 * 2 fiber coupler is connected with the first end of the 22 * 2 fiber coupler (307), the 3rd end of the one 2 * 2 fiber coupler is connected by the first optical fiber circulator (305) with the 4th end of the 22 * 2 fiber coupler (307), the 4th end of the one 2 * 2 fiber coupler is connected with a DFB light source (311), the other end of the first optical fiber circulator (305) connects the first fiber collimating lenses (306), the second end of the 22 * 2 fiber coupler (307) is connected the first differential detector with the 3rd end,

The second demodulated interferential instrument (32) is identical with the composition of the first demodulated interferential instrument, consists of respectively the second optical fiber analyzer (321), the 32 * 2 fiber coupler (323), the 42 * 2 fiber coupler (327), the second optical fiber circulator (325), the second fiber collimating lenses (326), the second differential detector, the 2nd DFB light source (331).

3. the binary channels optical performance test device of a kind of integrated waveguide modulator according to claim 1 and 2, it is characterized in that: described high polarization degree of stability wide spectrum light source (1), the first output terminal (13) by fiber coupler (12) is connected in the first photodetector (14); By the second output terminal (15), after fibre optic isolater (16), be connected in the optical fiber polarizer (17).

4. the binary channels optical performance test device of a kind of integrated waveguide modulator according to claim 3, is characterized in that: described integrated waveguide modulator to be measured (2) with the annexation of high polarization degree of stability wide spectrum light source (1) and light path demodulating equipment (3) is:

It is 0～45 ° to shaft angle degree that the output polarization maintaining optical fibre (18) of the optical fiber polarizer (17) is protected inclined to one side tail optical fiber (21) with the input of integrated waveguide modulator to be measured (2) input channel (2A);

What inclined to one side tail optical fiber and the first optical fiber analyzer of the first demodulated interferential instrument and the second demodulated interferential instrument were protected in first output channel (2B) of integrated waveguide modulator to be measured, the output of the second output channel (2C), inclined to one side tail optical fiber is protected in the input of the second optical fiber analyzer is respectively 0～45 ° to shaft angle degree.

5. the polarization crosstalk of the binary channels optical performance test device of integrated waveguide modulator is identified and a disposal route, it is characterized in that:

1) detect the length l that inclined to one side tail optical fiber (21) is protected in input _w-,, judge whether to meet:

S _W-i=l _W-i×Δn _f>S _ripple

In formula: Δ n _ffor protecting inclined to one side tail optical fiber linear birefrigence, S _ripplelight path maximal value for light source (11) Secondary coherence peak;

2) if do not met, weld an elongated segment polarization maintaining optical fibre l _f-i, to shaft angle degree, be 0 °-0 °, measure and record extended fiber l _f-ilength and theoretical light path S _f-i, judgement:

S _f-i=l _f-i×Δn _f>S _ripple

3) measure the length l of waveguide chip (2D) _w;

4) measure the length l of the first output channel tail optical fiber, the second output channel tail optical fiber _w-o-1, l _w-o-2, judgement:

S _w-o-1=l _w-o-1* Δ n _fand S _w-o-2=l _w-o-1* Δ n _f>S _w=l _w* Δ n _w

In formula: Δ n _wthe linear birefrigence of waveguide chip;

5) as the length l of output channel tail optical fiber _w-o-1, l _w-o-2do not meet the condition of step 4), in the first output channel, the second output channel, weld respectively the extended fiber l that two segment length are identical _f-o-1, l _f-o-2, it is 0 °-0 ° to shaft angle degree, its length requirement meets:

S _f-o-1=l _f-o-1* Δ n _fand S _f-o-2=l _f-o-1* Δ n _f>S _w=l _w* Δ n _w, measure and record extended fiber l _f-o-1, l _f-o-2;

6) integrated waveguide modulator to be measured (2) is connected with light path demodulating equipment (3) with wide spectrum light source (1), its input and and output shaft angle degree is respectively to θ ₁=45 °, θ ₂=45 °;

7) start white light interferometer, obtain two width distributed polarization crosstalk measurement result curve of the first output channel, the second output channel simultaneously;

8) utilize the geometrical length of the device each several part of having measured, comprising: inclined to one side tail optical fiber (21) length l is protected in input _w-i, input extends polarization maintaining optical fibre length l _f-i, waveguide chip (2D) length l _w, the first output channel, the second output channel tail optical fiber length l _w-o-1, l _w-o-2, output extended fiber length l _f-o-1, l _f-o-2; Calculate its optical path delay amount, and according to size, to be arranged in order be two row:

The corresponding first wave guide output channel of the first row: S _f-i, (S _f-i+ S _w-i), S _f-o-1, (S _f-o-1+ S _w-o-1), (S _f-o-1+ S _w-o-1+ S _f-i+ S _w-i+ S _w-1)

Corresponding the second waveguide output channel: the S of the second row _f-i, (S _f-i+ S _w-i), S _f-o-2, (S _f-o-2+ S _w-o-2), (S _f-o-2+ S _w-o-2+ S _f-i+ S _w-i+ S _w-2)

9) contrast with theoretical formula, determine the polarization crosstalk characteristic peak that the first output channel (2B) is measured, be specially:

(1) the polarization crosstalk ρ of waveguide input extended fiber and waveguide input tail optical fiber (21) _f-i;

(2) the polarization crosstalk ρ of waveguide input tail optical fiber (21) and waveguide chip (2D) _w-i;

(3) the polarization crosstalk ρ of output extended fiber and the first output channel waveguide output tail optical fiber _f-o-1;

The polarization crosstalk of (4) first output channel waveguide output tail optical fibers and waveguide chip (2D) _{ρ W-o-1};

(5) polarization crosstalk of the Y waveguide chip that first passage is measured

Determine the polarization crosstalk characteristic peak that the second output channel (2C) is measured, be specially:

(1) the polarization crosstalk ρ of waveguide input extended fiber and waveguide input tail optical fiber (21) _f-i;

(2) the polarization crosstalk ρ of waveguide input tail optical fiber (21) and waveguide chip (2D) _w-i;

(3) the polarization crosstalk ρ of output extended fiber and the second output channel waveguide output tail optical fiber _f-o-2;

The polarization crosstalk of (4) second output channel waveguide output tail optical fibers and waveguide chip (2D) _{ρ W-o-2};

(5) polarization crosstalk of the Y waveguide chip that second channel is measured

10) contrast polarization crosstalk

with polarization crosstalk

polarization crosstalk ρ _w-o-2with polarization crosstalk ρ _w-o-1;

11) according to the birefringence n of the polarization maintaining fiber pigtail calculating and waveguide chip actual measurement _f, Δ n _w; I (0) _out1/ I (0) _out2represent the insertion loss ratio that first, second output channel of waveguide device is measured;

12) when external environment parameters or application parameter variation, re-execute step 7), optical parametric to Y waveguide is measured, and the parameter that can measure also comprises the changes in optical properties of two output channels, comprises the coupling cross-talk variation with temperature of I/O optical fiber and waveguide chip; The chip extinction ratio of waveguide two output channels is with the variation of impressed voltage.

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