CN104792503B - A kind of device of optical polarization device distribution crosstalk measurement sensitivity enhancing - Google Patents

Abstract

The purpose of the present invention is to provide a device for enhancing the signal-to-noise ratio of the measurement signal, improving the sensitivity and dynamic range of polarization crosstalk measurement, and used for high-precision measurement and analysis of the polarization performance of optical devices . A device for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices, including a wide-spectrum light source, a polarizer, a polarization device to be measured, a first optical fiber rotary connector, a second optical fiber rotary connector, optical path demodulation and a signal detector , Signal detection and processing device. On the basis of the measurement limit of a single correlator, the present invention adopts the structure of synchronous measurement of two branches of the optical path correlator, and uses a polarization beam splitter to separate the signal light transmitted on the two polarization axes, and the two interference signals are linearly scanned after synchronous scanning. superimposition, to improve the measurement signal-to-noise ratio At the same time, it can measure the absolute strength of distributed crosstalk, greatly improving the sensitivity and accuracy of the measurement system.

Description

A device for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices

technical field

The design of the invention belongs to the technical field of optical fiber measurement, and in particular relates to a device for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices.

Background technique

Polarization optical devices are an important part of high-precision optical measurement and sensing systems. At present, the performance testing and evaluation methods and devices of optical devices are backward, which seriously hinders the development of high-precision optical measurement and sensing systems. For example, the chip extinction ratio of lithium niobate integrated waveguide modulator (commonly known as Y waveguide), the core device of high-precision fiber optic gyroscope, has reached more than 80dB; The ratio is about 50dB (according to the definition of energy, it is 10 ⁵ ), the highest resolution is Model 4810 polarization extinction ratio developed by dBm Optics in the United States, and the measurement limit of the measuring instrument is only 72dB.

Optical coherent domain polarization measurement technology (OCDP) is a high-precision distributed polarization coupling measurement technology. It is based on the principle of wide-spectrum light interference and uses scanning optical interferometers for optical path compensation to achieve interference between different polarization modes. The spatial position of the polarization crosstalk and the intensity of the polarization coupling signal are measured and analyzed with high precision, and then important parameters such as the extinction ratio and the beat length of the optical polarization device are obtained. As a very promising detection method for distributed optical polarization performance, OCDP technology is widely used in the fields of polarization-maintaining optical fiber manufacturing, accurate alignment of polarization-maintaining optical fiber, and device extinction ratio testing. Compared with other distributed detection methods and technologies such as Polarized Time Domain Reflectometry (POTDR), Optical Frequency Domain Reflectometry (OFDR), and Optical Coherent Domain Reflectometry (OCDR), OCDP technology has simple structure and high spatial resolution. (5 ~ 10cm), large measurement range (measurement length of several kilometers), ultra-high measurement sensitivity (coupling energy -80 ~ -100dB), ultra-large dynamic range (10 ⁸ ~ 10 ¹⁰ ), etc., it is very promising to develop into a High-precision, generalized testing technology and system. Because it most directly and truly describes the transmission behavior of signal light in the optical fiber optical path, it is especially suitable for testing and evaluating high-precision and ultra-high-precision interferometric optical fiber sensing optical circuits such as optical fiber devices, components, and fiber optic gyroscopes.

In the early 1990s, French Herve Lefevre et al [Method for the detection of polarization couplings in a birefringent optical system and application of this method to the assembling of the components of an optical system, US Patent 4865531] first disclosed OCDP based on the principle of white light interference The system adopts a superluminescent light emitting diode (SLD) as a light source and a spatial interference optical path as an optical path correlation measurement structure. According to this patent, the French Photonetics company has developed two types of OCDP test systems, WIN-P 125 and WIN-P 400, which are mainly used for the analysis of the 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.

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 (Chinese patent application number: 201110052231.3), which also uses the spatial interference optical path as the core device of OCDP, by detecting the coupling of the coupling point Intensity, the polarization extinction ratio is derived. 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 index are similar.

In the same year, people such as Yao Xiaotian of General Photonics Corporation of the United States disclosed an all-fiber measurement system (US20110277552, Measuring Distributed Polarization Crosstalk in PolarizationMaintaining Fiber) for distributed polarization crosstalk measurement in polarization-maintaining optical fibers and optical birefringent materials. and Optical Birefringent Material), by adding an optical path retarder before the optical path demodulation and signal detector, to suppress the quantity and amplitude of stray white light interference signals in the measurement of polarization crosstalk. This method can improve the polarization crosstalk sensitivity of the all-fiber measurement system to -95dB, but maintain the dynamic range at 75dB.

In 2012, the applicant of the present invention proposed a device and method for improving the measurement performance of polarization crosstalk of optical devices (Chinese Patent Application No. .6), using all-fiber optical path demodulation and signal detector structure, adding polarization beam splitting and online rotating connection functions, suppressing beat noise, improving measurement sensitivity, and adding Faraday rotators in the correlator to increase the stability of the light source. Compared with General Optoelectronics Corporation of the United States, the polarization crosstalk sensitivity of the measurement system can be increased to -95dB while maintaining the dynamic range at better than 95dB. The sensitivity is close to the measurement limit, and it will be difficult to significantly improve the measurement signal-to-noise ratio and sensitivity without changing the optical path structure and the measurement idea.

In 2013, the applicant of the present invention proposed a large scanning range optical coherence domain polarization measurement device (Chinese patent application number CN201310739313.4), using multiple continuous optical path extension units cascaded, and making the scanning optical device in the unit They appear in pairs to realize the expansion of optical path scanning and suppress the influence of scanner intensity fluctuation on measurement. The main problem to be solved is how to improve the accuracy and stability of polarization crosstalk measurement, and the measurement sensitivity performance has not been improved.

In 2014, the applicant of the present invention proposed an optical coherent polarization measurement device that can suppress interference noise (Chinese patent application number CN201410120901.4), which uses an all-fiber polarization state controller to eliminate the residual light reflection of optical devices, and uses a Faraday rotator The optical path demodulation device overcomes the polarization fading effect in interference and effectively suppresses interference noise; proposes an optical coherent domain polarization measurement device with optical path scanning position and velocity correction (Chinese Patent Application No. CN201410120591.6), by adjusting the optical path The scanning correction improves the spatial precision and detection sensitivity of the polarization measurement device. However, none of the above devices can significantly improve the signal-to-noise ratio of the test system, and most of them use polarization-maintaining fibers, which will cause an increase in polarization crosstalk noise.

In order to further improve the test performance of polarization crosstalk, including measurement signal-to-noise ratio, sensitivity and dynamic range, etc., especially while ensuring the measurement length of the device and reducing the difficulty of test system construction, the signal-to-noise ratio of the measurement system is improved, thereby improving the measurement sensitivity. become a research hotspot. The enhancement range of the measurement interference signal light is higher than the enhancement range of the measurement system noise, so that the signal-to-noise ratio of the system can be further improved and the measurement sensitivity can be improved.

The present invention provides a device and method for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices. By performing polarization splitting on signal light, expanding the number of correlators, and superimposing two-way optical correlators, the signal strength is enhanced. , to improve the signal-to-noise ratio. The invention can be widely used in the high-precision measurement and analysis of the polarization performance of optical devices.

Contents of the invention

The purpose of the present invention is to provide a device for enhancing the signal-to-noise ratio of the measurement signal, improving the sensitivity and dynamic range of polarization crosstalk measurement, and used for high-precision measurement and analysis of the polarization performance of optical devices .

The purpose of the present invention is achieved like this:

A device for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices, including a wide-spectrum light source 501, a polarizer 511, a polarization device to be measured 522, a first optical fiber rotary connector 521, a second optical fiber rotary connector 523, an optical path solution Modulation and signal detector 530, signal detection and processing device 560;

The wide-spectrum light source 501 is connected to the polarization device 522 to be measured through the polarizer 511 and the first rotary connector 521 through a polarization-maintaining optical fiber. The first rotary connector 521 connects the output pigtail of the polarizer 511 to the The polarization characteristic axis of the input pigtail is aligned from 0° to 45°, and the linearly polarized light output by the polarizer 511 generates the same transmitted light components on the fast axis and the slow axis of the polarizing device 522 to be tested, and passes through the polarizing device 522 to be measured Finally, the transmitted light component of the linearly polarized light on the fast axis is coupled to the slow axis, and the transmitted light component of the linearly polarized light on the slow axis is coupled to the fast axis. The modulation is connected to the signal detector 530, and the second rotary connector 523 makes the output pigtail of the device to be measured and the optical path demodulation and the polarization axis of the input pigtail of the signal detector 530 realize 0°-0° alignment, so that the light The process demodulation and signal detector 530 inputs the transmitted light component in the fast axis of the pigtail and the coupled light on the slow axis to the fast axis, the transmitted light component in the slow axis and the coupled light on the fast axis in the slow axis Coupled light in the slow axis;

The optical path demodulation and signal detector 530 consists of a 1×2 polarization beam splitter 531, a first branch optical path demodulation and signal detector 540, a second branch optical path demodulation and signal detector 541 and a detector Composition, 1×2 polarization beam splitter 531 separates the optical path demodulation and signal detector 530 from the light beam in the fast axis and the slow axis in the input pigtail, and all the way outputs the transmitted light component in the fast axis and the slow axis to the fast axis The coupled light in the output, the transmitted light component in the slow axis and the coupled light from the fast axis to the slow axis;

The two split lights output by the 1×2 polarization beam splitter 531 are respectively transmitted to the first branch of the optical path demodulation and signal detector 540 and the second branch of the optical path demodulation and signal detector through the single-mode fiber In the optical path demodulation and signal detector 541, interference is carried out after transmission in the respective fixed-length optical path reference arms and length-variable optical path scanning arms of the two branch optical path demodulation and signal detectors, and the two branch optical path The optical path demodulator and the signal detector in the signal detector are connected with the signal detection and processing device 560, and the signals generated by the two branch optical path demodulation and signal detectors are linearly superimposed and processed and analyzed to obtain the final interference signal. The value of the signal is proportional to the product of the amplitude of the polarization crosstalk and the energy of the input light, and the scanning position of the optical path corresponds to the position where the polarization crosstalk occurs.

The optical path demodulation and signal detector 530, for the first branch optical path demodulation and signal detector and the second branch optical path demodulation and signal detector, the optical path scanning arm structure and parameters are the same, both The fixed-length optical path reference arm structure is the same as the parameters; the two branch optical path demodulation and signal detectors share the same optical path scanning delay line 549; when the optical path scanning delay line 549 is at the starting position of the movement, the optical path of each path The absolute optical path of the fixed reference arm is greater than the optical path correlation scanning arm; the optical path demodulation of the two branches and the detection signal of the signal detector are linearly superimposed.

The optical path demodulation and signal detector 530 is composed of a Michelson type optical path demodulation and detector 630, and the linearly polarized optical signal through the device under test and the rotary connector is injected into the 1×2 polarization beam splitter 631 The polarization-maintaining input port ps1, the first single-mode fiber output port ps2, and the second single-mode fiber output port ps3 are respectively injected into the first branch optical path demodulation and signal of Michelson-type optical path demodulation and signal detector 530 The detector 640 and the second branch optical path demodulation and signal detector 650, the signal light is injected into the first 2×2 fiber coupler 641 and the second 2×2 fiber coupler 651, and the first input port bs2 , the second input terminal bs5 is input, the first output port bs1 and the second output port bs6 respectively output two coherent branch signal lights, the first branch optical path demodulation and signal detector 640 and the second branch optical path demodulation and the signal detector 650 are composed of the first 2×2 fiber coupler 641, the second 2×2 fiber coupler 651, common single-mode fiber, the first Faraday rotating mirror 644, the second Faraday rotating mirror 654, the first Composed of a self-focusing collimating lens 643, a second self-focusing collimating lens 653, a first Faraday rotator 642, a second Faraday rotator 652, a movable optical mirror 649, a first detector 645, and a second detector 655; In the first branch of the Michelson-type optical path demodulation and detector 630, the first output end bs3 of the first coupler 641 is connected to the Faraday rotating mirror 644 to form a fixed-length optical path reference arm, and the first output end bs3 of the first coupler 641 The two output terminals bs4 are connected to the Faraday rotator 642 and form an optical path scanning arm with the self-focusing collimating lens 643 and the movable optical mirror 649. The two paths of light passing through the fixed-length optical path reference arm and the optical path scanning arm are sent to the first detector Receive at 645; in the second branch of the optical path demodulation and signal detector 630, the first output end bs7 of the second coupler 651 is connected to the Faraday rotator 652 and is connected with the self-focusing collimating lens 653 and the movable optical mirror 649 forms an optical path scanning arm, and the second output terminal bs8 of the second coupler 651 is connected to the Faraday rotating mirror 654 to form a fixed-length optical path reference arm. The two paths of light passing through the fixed-length optical path reference arm and the optical path scanning arm are Received on the second detector 654.

The optical path demodulator and signal detector 530 is composed of a Mach-Zehnder type optical path demodulator and detector 730, and the linearly polarized optical signal through the device under test and the rotary connector is injected into the 1×2 polarization beam splitter 731 The polarization-maintaining input port ps4, the first single-mode fiber output port ps5 and the second single-mode fiber output port ps6 are injected into the first branch optical path demodulation and detector 730 of the Mach-Zehnder type optical path demodulation and The signal detector 740, the second branch optical path demodulation and signal detector 750, the signal light is injected into the first 1×2 beam splitter 732 and the second 1×2 beam splitter 738, from the first input end bs9, the second input terminal bs16 input, the first branch correlator 740 and the second branch correlator 750 respectively have two output ports, and after differential processing, they are output as two coherent branch signal lights, and the first branch optical path solution The modulation and signal detector 740 and the second branch optical path demodulation and signal detector 750 are composed of 1×2 beam splitter, ordinary single-mode fiber, polarization state controller, 2×2 coupler, circulator, collimator Mirror, movable optical mirror 744 and detector, in the first branch of Mach-Zehnder optical path demodulation and detector 730, 1×2 beam splitter 732 splits the signal light passing through polarization beam splitter 731 There are two beams, one beam is connected to the polarization state controller through an ordinary single-mode optical fiber to form a fixed-length optical path reference arm, and the other beam passes through a collimating mirror 734 and a movable optical mirror 744 to form an optical path scanning arm, and the other beam passes through a fixed-length optical path reference arm. The two paths of light of the arm and the optical path scanning arm are differentially received on the first detector 736 and the second detector 737; in the second branch of the Mach-Zehnder optical path demodulation and detector 730, a 1×2 beam splitter 738 divides the signal light passing through the polarization beam splitter 731 into two beams, one beam is connected to a polarization state controller through a common single-mode fiber to form a fixed-length optical path reference arm, and the other beam passes through a collimating mirror 741 and a movable optical mirror 744 Composing the optical path scanning arm, the two paths of light passing through the fixed-length optical path reference arm and the optical path scanning arm are differentially received on the third detector 742 and the fourth detector 743 .

Polarizer 511, first rotary connector 521, second rotary connector 523, polarizer to be measured 522, optical path demodulation and signal detector 530, detector, the wavelength working range can cover the emission spectrum of the wide-spectrum light source 501 The output pigtail of the polarizer 511 and the input pigtail of the polarization beam splitter 531 all work in a single-mode, polarization-maintaining state; the output pigtail of the polarization beam splitter 531, the optical path demodulation and signal detector 530, and the detector are all Work in single-mode state.

The beneficial effects of the present invention are:

(1) On the basis of the measurement limit of a single correlator, the structure of two branches of optical path demodulation and signal detector is used for synchronous measurement, and a polarization beam splitter is used to separate the signal light transmitted on the two polarization axes, and the two paths interfere The signal is linearly superimposed after synchronous scanning, and the measurement signal-to-noise ratio is improved At the same time, it can measure the absolute strength of distributed crosstalk, greatly improving the sensitivity and accuracy of the measurement system.

(2) In addition to the connection between the wide-spectrum light source and the input pigtail of the polarization beam splitter in the optical path demodulation and signal detector, all optical fibers and devices in the optical path demodulation and signal detector need to use polarization-maintaining fibers All work in the common single-mode state, which reduces the requirements for optical devices and connecting optical fibers, and is conducive to the efficient construction of the measurement system.

(3) Use the same scanning platform to scan the correlators of the two coherent branches synchronously, avoiding the increase of system instability, volume and cost due to the addition of scanning platforms, and can expand the measurement support without adding additional optical delay lines Road, enhance the system signal-to-noise ratio.

Description of drawings

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

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

Fig. 3 is a schematic diagram of a technical scheme of a distributed crosstalk measurement sensitivity enhancement device of an optical polarization device;

Fig. 4 is a schematic diagram of the optical path of the optical device polarization crosstalk measurement using a single correlator;

Fig. 5 is a schematic diagram of the optical path of the enhanced optical device polarization crosstalk measurement scheme based on Michelson optical path demodulation and detector;

Fig. 6 is a schematic diagram of the technical scheme of Michelson-type optical path demodulation and detector;

Fig. 7 is a schematic diagram of the technical scheme of Mach-Zehnder optical path demodulation and detector;

Fig. 8 is a schematic diagram of a technical solution for measuring signal-to-noise ratio using Michelson-type optical path demodulation and detector enhanced optical device polarization crosstalk;

Fig. 9 is a schematic diagram of a technical solution for measuring signal-to-noise ratio using Mach-Zehnder optical path demodulation and detector enhancement optical device polarization crosstalk.

Detailed ways

In order to clearly illustrate the method and device of the present invention for improving the measurement performance of distributed polarization crosstalk of optical devices, the present invention will be further described in conjunction with the examples and accompanying drawings, but the protection scope of the present invention should not be limited by this.

The invention provides a device for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices, which is characterized in that linearly polarized light is injected into the fast and slow polarization axes of the device under test at the same time, and the energy of the signal light is transmitted on the fast and slow axes Equal, the polarization beam splitter connected after the device under test separates the optical signals transmitted in the two polarization axes (including transmitted light and coupled optical signals), and the demodulation of the two optical paths sharing the same optical delay line is simultaneously with the signal detector Realize the measurement of distributed polarization crosstalk in the two polarization axes of the fast axis and the slow axis, and improve the measurement sensitivity and dynamic range through the linear superposition processing of the measurement signal times. Based on the all-fiber polarization crosstalk measurement system, the device can achieve enhanced measurement sensitivity and dynamic range by optimizing the optical path structure and parameters of the measurement device. High-precision measurement and analysis of device polarization performance.

A device for enhancing the sensitivity of distributed crosstalk measurement of optical polarization devices, including a wide-spectrum light source, a polarizer, a polarization device to be measured, an optical fiber rotary connector, an optical path demodulation and signal detector, and a signal detection and processing device. Yes:

(1) The wide-spectrum light source is connected to the polarization device to be tested through the polarizer, the first rotary connector and the polarization maintaining fiber, and the first rotary connector makes the output pigtail of the polarizer and the input pigtail of the polarization device to be tested polarized The characteristic axis is aligned from 0° to 45°, and the linearly polarized light output by the polarizer generates the same transmitted light components on the fast axis and slow axis of the polarizing device to be tested. After passing through the polarizing device to be tested, the linearly polarized light is on the fast axis Part of the transmitted light component on the slow axis is coupled to the slow axis, and part of the transmitted light component of the linearly polarized light on the slow axis is coupled to the fast axis. 2. The rotary connector enables the output pigtail of the device to be measured to be aligned with the polarization axis of the optical path demodulator and the input pigtail of the signal detector to achieve 0°~0° alignment, so that the optical path demodulation and the input pigtail of the signal detector are fast The transmitted light component in the fast axis and the coupled light on the slow axis into the fast axis, the transmitted light component in the slow axis and the coupled light on the fast axis into the slow axis.

(2) Optical path demodulation and signal detector, composed of 1×2 polarization beam splitter, first and second branch optical path demodulation and signal detector and detector. The 1×2 polarization beam splitter separates the optical path demodulation and the light beam in the fast axis and the slow axis of the signal detector input pigtail, and outputs the transmitted light component in the fast axis and the coupling light from the slow axis to the fast axis. , one output the transmitted light component in the slow axis and the coupled light on the fast axis to the slow axis.

The two split lights output by the 1×2 polarization beam splitter are respectively transmitted to the first and second branches of the optical path demodulation and signal detector through the single-mode optical fiber. 1. Interference between the optical path demodulation of the second branch and the signal detector after transmission in the fixed-length optical path reference arm and the variable-length optical path scanning arm, the optical path demodulation of the first and second branches and the signal detector The detector in the device is connected to the signal detection and processing device, and the signals generated by the optical path demodulation of the first and second branches and the signal detector are linearly superimposed and analyzed to obtain the final interference signal. The value of the interference signal is proportional to the product of the amplitude of the polarization crosstalk and the energy of the input light, and its optical path scanning position corresponds to the position where the polarization crosstalk occurs.

The optical path demodulation and signal detector is characterized in that: for the first and second branch optical path demodulation and signal detectors, the structure and parameters of the optical path scanning arm are the same, and the structure and parameters of the two fixed-length optical path reference arms The same; the first and second branches of optical path demodulation and signal detector share the same optical path scanning delay line; when the optical path scanning delay line is at the starting position of the movement, the optical path of each path is fixed and the absolute optical path length of the reference arm is slightly Greater than the optical path correlation scanning arm; perform linear superposition processing on the optical path demodulation of the first and second branches and the detection signal of the signal detector. Typical structures include Michelson-type optical path demodulator and detector and Mach-Zehnder-type optical path demodulator and detector.

The optical path demodulation and signal detector is characterized by: it can be composed of Michelson type optical path demodulation and detector, and the linearly polarized light signal through the device under test and the rotary connector is injected into the polarization maintaining of the 1×2 polarization beam splitter The input end and the output end of the two single-mode optical fibers are respectively injected into the two optical path demodulation and signal detectors of the Michelson type optical path demodulation and signal detector. The signal light is injected into the 2×2 fiber coupler, input from the two input ports, and the two output ports respectively output the signal light of two coherent branches. Both optical path demodulation and signal detectors of the two branches are composed of 2×2 couplers, common single-mode optical fibers, Faraday rotating mirrors, self-focusing collimating lenses, Faraday rotators, movable optical mirrors and detectors. In the first branch of the Michelson-type optical path demodulation and detector, the first output end of the first coupler is connected to the Faraday rotating mirror to form a fixed-length optical path reference arm, and the second output end of the first coupler is connected to the Faraday The rotator forms an optical path scanning arm with a self-focusing collimating lens and a movable optical mirror, and the two-way light passing through the fixed-length optical path reference arm and the optical path scanning arm is received on the first detector; The second branch of the signal detector, the first output end of the second coupler is connected to the Faraday rotator and forms an optical path scanning arm with the self-focusing collimating lens and the movable optical mirror, the second output end of the second coupler The Faraday rotating mirror is connected to form a fixed-length optical path reference arm, and the two-way light passing through the fixed-length optical path reference arm and the optical path scanning arm is received on the second detector.

The optical path demodulation and signal detector is characterized by: it can be composed of Mach-Zehnder optical path demodulation and detector, and the linearly polarized optical signal through the device under test and the rotary connector is injected into the 1×2 polarization beam splitter The polarization-maintaining input end and the two single-mode fiber output ends are respectively injected into the two optical path demodulation and signal detectors of the Mach-Zehnder type optical path demodulator and detector. The signal light is injected into the 1×2 beam splitter and input from two input terminals, and the two output ports of the two branch correlators are differentially processed and then output as two coherent branch signal light. Both optical path demodulation and signal detectors are composed of 1×2 beam splitter, common single-mode fiber, polarization state controller, 2×2 coupler, circulator, collimating mirror, movable optical mirror and detection device composition. In the first branch of the Mach-Zehnder optical path demodulator and detector, the 1×2 beam splitter divides the signal light passing through the polarization beam splitter into two beams, and one beam is connected to the polarization state controller through a common single-mode fiber A fixed-length optical path reference arm is formed. One beam passes through a collimating mirror and a movable optical mirror to form an optical path scanning arm. Differential reception on the splitter; in the second branch of the Mach-Zehnder optical path demodulation and detector, the 1×2 beam splitter divides the signal light passing through the polarization beam splitter into two beams, and one beam passes through an ordinary single-mode fiber The polarization state controller is connected to form a fixed-length optical path reference arm, and one beam passes through a collimating mirror and a movable optical mirror to form an optical path scanning arm. Differential reception on the detector and the 4th detector.

The polarizer, the first and second rotary connectors, the polarizing device to be tested, the optical path demodulation and signal detector, and the detector are characterized in that: the wavelength working range can cover the emission spectrum of the wide-spectrum light source; the polarizer The output pigtail and the input pigtail of the polarization beam splitter all work in a single-mode, polarization-maintaining state; the output pigtail of the polarization beam splitter, the optical path demodulation and signal detector, and the detector all work in a single-mode state.

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 performance test of the polarization-maintaining fiber as an example, the highly stable wide-spectrum polarized light 101 emitted by the wide-spectrum light source is injected into the slow axis of the polarization-maintaining fiber 121 of a certain length (at the time of the fast axis, same principle). Due to defects in the geometric structure during fabrication, non-ideal effect of pre-applied stress, or under the action of external temperature and load, a certain defect point 111 exists in the optical fiber. When the signal light is transmitted along the slow axis, when the signal light is transmitted to the defect point 111, a part of the light energy in the slow axis will be coupled into the orthogonal fast axis to form a coupled beam 103, and the remaining transmitted beam 102 is still along the slow axis. shaft transmission. There is a linear birefringence Δn (for example: 5×10 ^-4 ) in the optical fiber, so that the refractive index of the slow axis is greater than the refractive index of the fast axis. When the other end of the fiber is output (the transmission distance is l), the transmitted light on the slow axis There will be an optical path difference Δnl between 102 and the coupled light 103 traveling on the fast axis. The above-mentioned light beams pass through the welding point or the rotary joint 112 , rotate the polarization state of the transmitted light and the coupled light by 45°, and then enter the optical path demodulation and signal detector 130 . In the optical path demodulation and signal detector 130, the optical beam splitter 132, the fixed reflector 133, and the movable reflector 134 form a Michelson optical interferometer. After the beams 102 and 103 are polarized by the analyzer 131 , they are uniformly divided into two parts by the beam splitter 132 . As shown in Figure 2, the reference beam is composed of transmitted light 201 and coupled light 202, transmitted in the fixed arm of the interferometer, and returned to the beam splitter 132 after being reflected by the fixed mirror 133; it is composed of transmitted light 203 and coupled light 204 The scanning beam also returns to the beam splitter 132 after being reflected by the moving mirror 134, and the two parts of the light converge on the detector 137 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 151, it is sent to the measurement computer 152; the measurement computer 152 is also responsible for controlling the moving mirror 134 to realize optical path scanning.

As shown in Figure 2, under the control of the measurement computer 152, the moving mirror 134 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:

(1) When the optical path difference is equal to Δnl, the coupling light 204 in the scanning beam matches the optical path of the transmission light 201 in the reference beam, then a white light interference signal is generated, and its peak amplitude is 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 201 and 202 are respectively matched with the transmission light 205 and the coupling light 206 in the scanning beam, and white light interference signals are generated respectively, and the peak amplitude is the superposition of the intensity of the two, Its magnitude is I _main ∝I ₀ , which is proportional to the input power of the light source. As can be seen from the figure, 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 transmission light 207 in the scanning beam matches the optical path of the coupling light 202 in the reference beam, 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:

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

In the optical coherent polarization test shown in Figure 1, the optical path adopts the method of equally dividing the energy of the transmitted light and the coupled light, P _x =P _r =P _s +P _c =P _s +ρP _s =P _s (1 +ρ), where P _s is the transmission light intensity, P _c is the coupling light intensity, and ρ is the coupling coefficient. Generally, ρ<<1.

The amplitude of the polarization-coupled signal can be expressed as:

It can be seen that when the optical coherent domain polarization test system (OCDP) based on the principle of white light interference uses an optical path demodulation and signal detector, without considering the thermal noise of the circuit, the detected signal-to-noise ratio is expressed as:

For the polarization crosstalk test scheme using optical path demodulation and signal detectors, when the first rotary connector 521 is aligned at 0°-45°, the polarized light emitted by the broadband light source 501 is injected into a certain length of In the optical fiber 522 (5A in Fig. 5), the polarized light has transmitted light components with the same magnitude in both the fast axis and slow axis directions, the transmitted light component in the fast axis direction is I _s1 , and the transmitted light component in the slow axis direction The component is I _s2 , due to the defects of the geometric structure during fabrication, the non-ideal effects of pre-applied stress, and the effects of external temperature and load, when the two transmitted light components are transmitted to the defect point, a part of the energy is coupled to the respective orthogonal axes ( As shown in 5B) in FIG. 5 , the coupled light beams I _c1 and I _c2 are formed, wherein I _c2 propagates in the direction of the fast axis, and wherein I _c1 propagates in the direction of the slow axis.

Due to the alignment of 0° to 45°, the two branches transmit light intensity components:

P _s1 =P _s2 (6)

Two branch coupled light components:

The signal amplitude measured on the two branch detectors can be expressed as:

For two detection branch noise:

Each branch of optical path demodulation and signal detector:

When the two branch signals are superimposed, since the amplitude of the two branches is the same, and the interference signal satisfies the characteristics of amplitude superposition, the signal amplitude after detection is detected:

The noise of the two branches of optical path demodulation and signal detector satisfies power superposition, so the final output of the correlator is:

Comparing Equation (5) and Equation (12), when the optical path demodulation is superimposed with the signal detector, due to the superposition of interference signal amplitude and noise power superposition, the improvement of signal strength is stronger than the increase of noise strength. Based on a single correlator structure, the signal-to-noise ratio of the system can be improved times, improving the sensitivity and dynamic range of the measurement system.

The distributed polarization crosstalk measurement scheme based on optical path demodulation and signal detector is shown in Figure 4. The selection of main optoelectronic devices and their parameters are as follows:

(1) The central wavelength of the broadband light source 501 is 1550nm, the half-spectrum width is greater than 45nm, the fiber output power is greater than 2mW, and the extinction ratio is greater than 6dB;

(2) The working wavelength of the fiber polarizer 511 is 1550nm, the extinction ratio is 30dB, the insertion loss is less than 1dB, the input end is a single-mode fiber, and the output is a panda-type polarization-maintaining fiber;

(3) The insertion loss of the first and second optical fiber rotary connectors 521 and 523 is 1dB; the polarization device 622 to be tested is a 200m panda-type polarization-maintaining optical fiber;

(4) The working wavelength of the 1×2 polarizing beam splitters 631 and 731 is 1550nm, the extinction ratio is greater than 20dB, and the insertion loss is less than 0.5dB;

(5) The operating wavelength of the Faraday rotating mirrors 644 and 654 is 1550nm, the optical rotation angle is 90±1°, and the insertion loss is less than 0.6dB;

(6) The working wavelength of the Faraday rotators 642 and 652 is 1550nm, the optical rotation angle is 45±1°, and the insertion loss is less than 0.3dB;

(7) The working wavelength of the 1×2 beam splitters 732 and 738 is 1550 nm and the insertion loss is less than 0.5 dB;

(8) The working wavelength of 2×2 fiber couplers 641, 651, 735, 741 is 1550nm, the input and output pigtails bs1~bs22 are all common optical fibers, the splitting ratio is 1:1, and the insertion loss is less than 0.1dB.

(9) The operating wavelength of the three-port circulators 733 and 739 is 1550nm, the insertion loss is 0.8dB, and the isolation is greater than 50dB;

(10) The working wavelength of the polarization state controllers 745 and 746 is 1550 nm, and the insertion loss is 0.5 dB;

(11) The operating wavelength of the self-focusing collimating lens 644, 654, 734, 741 is 1550nm, and the optical path scanning distance between them and the movable optical mirror 649, 744 (reflection rate is more than 92%) is about 0～ 400mm, the average insertion loss is 3.0dB;

(12) The operating wavelength of the mirrors 644 and 654 is 1550nm, and the insertion loss is less than 0.6dB;

(13) The photosensitive materials of photodetectors 651, 654, 736, 737, 742, and 743 are all InGaAs, and the light detection range is 1100-1700nm, such as the Nirvana ^TM series 2017 balance detector of New Focus Company.

The working process of the measuring device is as follows:

Device 1: Measuring Device for Polarization Crosstalk of Enhanced Optical Devices Based on Michelson-type Optical Path Demodulation and Detector

The output light of the wide-spectrum light source 501 becomes linearly polarized light through the polarizer 511, and is connected to the polarization device 522 to be measured through the first rotary connector 521, and the alignment angle of the first rotary connector 521 is adjusted to 0°-45°, so that The linearly polarized light is coupled into the two polarization characteristic axes of the polarizing device 522 to be tested, and becomes two transmitted light components with the same amplitude, as shown in 5A in FIG. 5 . During the transmission process of the two transmitted lights in the polarizing device 522 to be tested, the coupled light components on the respective orthogonal axes will be generated at the defect points. Adjust the alignment angle of the second rotary connector 523 to 0° to 0°, so that the two orthogonal signal lights with polarization are aligned with the two orthogonal directions of the input pigtail of the polarization beam splitter 631, and the two beam-splitting The signal light I _s1 , I _c2 and the coupled light I _s2 , I _c1 are respectively transmitted to the Michelson-type optical path demodulator and signal detector 630 in the two single-mode output pigtails of the polarization beam splitter 631 .

For the first branch optical path demodulation and signal detector 640, the signal light component transmitted in the ordinary single-mode optical fiber is divided into two beams of signal light through the 2×2 fiber coupler 641 and reaches the optical path scanning arm and the fixed reference arm respectively. The signal light in the fixed optical path reference arm passes through the Faraday rotating mirror 644 and returns to the 2×2 fiber coupler 641, and the signal light in the optical path scanning arm passes through the Faraday rotator 642 and the collimating mirror 643 and then shines on the movable optical mirror On 649, the reflected signal light passes through the collimating mirror 643 again, passes through the 2×2 fiber coupler and interferes with the signal light in the optical path scanning arm on the first detector 645;

For the second branch optical path demodulation and signal detector 650, the transmission light and coupling light components transmitted in the ordinary single-mode fiber are divided into two beams of signal light by the 2×2 fiber coupler 651 and reach the optical path scanning arm and the fixed beam respectively. Reference arm, fixed optical path The signal light in the reference arm passes through the Faraday rotating mirror 654 and returns to the 2×2 fiber coupler 651, and the signal light in the optical path scanning arm passes through the Faraday rotator 652 and the collimating mirror 653 and then shines on the movable On the optical reflection mirror 649 , the signal light after reflection passes through the collimating mirror 653 again, passes through the 2×2 fiber coupler and interferes with the signal light in the optical path scanning arm on the second detector 655 .

During the scanning and matching process of the two optical path scanning arms and the fixed optical path reference arm, the interference signals received on the first and second detectors are linearly superimposed on the signals to obtain the final measurement signal, so that the signal of the interference signal The noise ratio is further improved.

Device 2: Measuring Device for Polarization Crosstalk of Enhanced Optical Devices Based on Mach-Zehnder Optical Path Demodulation and Detector

The output light of the wide-spectrum light source 501 becomes linearly polarized light through the polarizer 511, and is connected to the polarizing device 522 to be measured through the first rotary connector 521, and the alignment angle of the first rotary connector 521 is adjusted to be 0°-45°. The alignment angle of the second rotary connector 523 is 0°～0°, so that the two orthogonal signal lights with polarization are aligned with the two orthogonal directions of the input pigtail of the polarization beam splitter 731, and the two signals after splitting The light I _s1 , I _c2 and the coupled light I _s2 , I _c1 are respectively transmitted in the two single-mode output pigtails of the polarization beam splitter 731 to the Mach-Zehnder optical path demodulation and signal detector 730 structure.

For the first branch optical path demodulation and signal detector 740, the signal light component transmitted in the ordinary single-mode optical fiber is divided into two beams of signal light by the 1×2 beam splitter 732 and reach the optical path scanning arm and the fixed reference arm respectively. The signal light in the fixed optical path reference arm is transmitted to the 2×2 fiber coupler 735 through the polarization state controller 745, the signal light in the optical path scanning arm passes through the circulator 733, and passes through the collimating mirror 734 and the movable optical mirror 744 Reflecting the signal light to the 2×2 fiber coupler 735, the signal light of the two arms is received on the detectors 736 and 737 to form a differential interference signal;

For the second branch optical path demodulation and signal detector, the signal light component transmitted in the ordinary single-mode optical fiber is divided into two beams of signal light by the 1×2 beam splitter 738 and reaches the optical path scanning arm and the fixed reference arm respectively. The signal light in the optical path reference arm is transmitted to the 2×2 fiber coupler 735 through the polarization state controller 746, the signal light in the optical path scanning arm passes through the circulator 739, and the collimating mirror 741 and the movable optical mirror 744 will The signal light is reflected to the 2×2 fiber coupler 735 , and the signal light of the two arms is received on the detectors 742 and 743 to form a differential interference signal.

The differential interference signal of the two branches can eliminate the influence of the DC light intensity, obtain the multiplied AC interference item, and then perform superposition processing on the differential interference signal to further improve the signal-to-noise ratio of the polarization crosstalk measurement.

Through the above two different optical path demodulation and signal detectors, it can be seen that for the device for enhancing the polarization crosstalk measurement signal-to-noise ratio of optical devices, for different optical path demodulation and signal detectors, after the above measurement process, the distribution can be obtained. Formula polarization crosstalk amplitude. Due to the use of optical path demodulation and signal detectors to make two-way synchronous measurement, the amplitude of interference signals is superimposed, and the energy of system noise is superimposed, which can improve the signal-to-noise ratio of the system compared with single-way measurement under the same structure. times, about 3dB.

Claims (1)

1. a kind of device of optical polarization device distribution crosstalk measurement sensitivity enhancing, including wide spectrum light source (501), the polarizer (511), polarizer (522) to be measured, the first fiber rotation connector (521), the second fiber rotation connector (523), light path Demodulation and signal sensor (530), signal detection and processing unit (560), it is characterised in that：

Wide spectrum light source (501) is logical by the polarizer (511), the first fiber rotation connector (521) and polarizer to be measured (522) Polarization maintaining optical fibre connection is crossed, the first fiber rotation connector (521) makes the output tail optical fiber of the polarizer (511) and polarizer to be measured (522) input tail optical fiber polarization characteristic axis completes 0 °~45 ° alignments, by the line polarisation of the polarizer (511) output in polarization to be measured Identical transmission light component is generated in the fast axle of device (522), slow axis, after polarizer to be measured (522), line polarisation is fast Transmission light component part on axis is coupled to slow axis, and transmission light component part of the line polarisation on slow axis is coupled to fast axle, to be measured Polarizer (522) is demodulated with light path by the second fiber rotation connector (523) and is connect with signal sensor (530), and second Fiber rotation connector (523) makes the output tail optical fiber of metering device to be measured input tail optical fiber with signal sensor (530) with light path demodulation Polarization sign axis realize 0 °~0 ° alignment, make light path demodulation with signal sensor (530) input tail optical fiber fast axle in transmission fast axle in Transmission light component and slow axis in the coupling light into fast axle, the transmission light component in slow axis in transmission slow axis and fast axle to slow Coupling light in axis；

Light path is demodulated with signal sensor (530) by the one 1 × 2nd polarization beam apparatus (531), the demodulation of first branch light path and signal Detector (540), the demodulation of the second branch light path are formed with signal sensor (541), and the one 1 × 2nd polarization beam apparatus (531) is by light Journey, which is demodulated, to be detached with fast axle in signal sensor (530) input tail optical fiber with the light beam in slow axis, exports the transmission in fast axle all the way Coupling light, exporting the coupling transmitted in light component and fast axle into slow axis in slow axis all the way into fast axle on light component and slow axis Closing light；

Light path demodulation is transmitted to by single mode optical fiber respectively via the two-way beam splitting light of the one 1 × 2nd polarization beam apparatus (531) output First branch light path demodulation with signal sensor (530) is visited with signal sensor (540), the demodulation of the second branch light path with signal It surveys in device (541), in two branch light path demodulation and the respective regular length light path reference arm of signal sensor (540,541) and length Interfered after being transmitted in degree variable light path scan arm, two branch light path demodulation and the spy in signal sensor (540,541) It surveys device and signal detection is connect with processing unit (560), and two branch light path demodulation are produced with signal sensor (540,541) Raw signal carries out linear superposition processing and analysis, obtains final interference signal, the numerical value of interference signal and the width of polarization interference Value, the product of input light energy are directly proportional, and light path scan position is corresponding with the position that polarization interference point occurs；

First branch light path demodulation and signal sensor (540) and second of the light path demodulation with signal sensor (530) Branch light path demodulates, two regular length light path reference arms identical as parameter as the light path of signal sensor (541) scanning arm configuration Structure is identical as parameter；Two branch light path demodulation share the same light path delayed sweep line with signal sensor (540,541) (549)；When light path delayed sweep line (549) is in movement start position, the absolute light path of the light path fixed reference arm per road is big In light path related scans arm；

The light path demodulation is demodulated with signal sensor (530) by Michelson formula light paths to be formed with detector (630), is led to The signal light for crossing polarizer to be measured (522) and the second fiber rotation connector (523) is injected into the 21 × 2nd polarization beam apparatus (631) polarization-maintaining input terminal (ps1), first branch single mode optical fiber output end (ps2), the second branch single mode optical fiber output end (ps3) first branch light path demodulation and signal sensor of the Michelson formula light paths demodulation with detector (630) are injected separately into (640) and the second branch light path demodulation with signal sensor (650), signal light be injected into the one 2 × 2nd fiber coupler (641), In 22 × 2nd fiber coupler (651), inputted from first input end (bs2), the second input terminal (bs5), the first output end Mouth (bs1), second output terminal mouth (bs6) export two-phase Heavenly Stems and Earthly Branches road signal light, the demodulation of first branch light path and signal detection respectively Device (640) is by the one 2 × 2nd fiber coupler (641), general single mode fiber, the first Faraday rotator (642), the first autohemagglutination Focus collimation lens (643), the first faraday rotator mirror (644), removable optical mirror (649) and the first detector (645) it forms；The second branch light path is demodulated with signal sensor (650) by the 22 × 2nd fiber coupler (651), general single mode Optical fiber, the second Faraday rotator (652), the second self-focusing collimation lens (653), the second faraday rotator mirror (654), Removable optical mirror (649) and the second detector (655) composition；In the demodulation of Michelson formula light paths and detector (630) the first output end (bs3) the first Faraday rotation of connection of the first branch, the one 2 × 2nd fiber coupler (641) is anti- Mirror (644) is penetrated, regular length light path reference arm, second output terminal (bs4) connection of the one 2 × 2nd fiber coupler (641) are formed First Faraday rotator (642) simultaneously forms light with the first self-focusing collimation lens (643) and removable optical mirror (649) Journey scan arm is received by the two-way light of regular length light path reference arm and light path scan arm on the first detector (645)； Michelson formula light paths demodulate and the second branch of signal sensor (630), and the first of the 22 × 2nd fiber coupler (651) Output end (bs7) the second Faraday rotator of connection (652) is simultaneously anti-with the second self-focusing collimation lens (653) and removable optics Mirror (649) composition light path scan arm is penetrated, the second output terminal (bs8) of the 22 × 2nd fiber coupler (651) connects second farad Rotating mirror (654) forms regular length light path reference arm, passes through regular length light path reference arm and light path scan arm Two-way light receives on the second detector (655)；

Or the light path demodulation is demodulated and detector (730) group with signal sensor (530) by Mach-Zehnder formula light paths At, by the signal light of polarizer to be measured (522) and the second fiber rotation connector (523) be injected into the 31 × 2nd polarization point The polarization-maintaining input terminal (ps4) of beam device (731), first branch single mode optical fiber output end (ps5) are exported with the second branch single mode optical fiber End (ps6) is injected separately into third branch light path demodulation and signal of the Mach-Zehnder formula light paths demodulation with detector (730) Detector (740), the demodulation of the 4th branch light path and signal sensor (750), signal light are injected into the one 1 × 2nd beam splitter (732), it in the 21 × 2nd beam splitter (738), is inputted from first input end (bs9), the second input terminal (bs16), third branch Light path is demodulated with signal sensor (740) by the one 1 × 2nd beam splitter (732), general single mode fiber, the first Polarization Controller (745), first annular device (733), third self-focusing collimation lens (734), removable optical mirror (649), the one 2 × 2nd Beam splitter (735) and third detector (736), the 4th detector (737) composition；4th branch light path demodulates and signal detection Device (750) is by the 21 × 2nd beam splitter (738), general single mode fiber, the second Polarization Controller (746), the second circulator (739), four selfs focussed collimated lens (740), removable optical mirror (649), the 22 × 2nd beam splitter (741) and the Five detectors (742), the 6th detector (743) composition；In the third of Mach-Zehnder formula light paths demodulation and detector (730) Branch, the one 1 × 2nd beam splitter (732) will be divided into two bundles by the signal light of the 31 × 2nd polarization beam apparatus (731), Yi Shutong Cross general single mode fiber connect the first polarization beat length device (745) constitute regular length light path reference arm, it is a branch of by third from Focussed collimated lens (734) and removable optical mirror (649) form light path scan arm, pass through regular length light path reference arm With the two-way light of light path scan arm on third detector (736) and the 4th detector (737) differential received；In Mach- Zehnder formula light paths demodulate the 4th branch with detector (730), and the 21 × 2nd beam splitter (738) will be by the 31 × 2nd partially The signal light of beam splitter (731) of shaking is divided into two bundles, and a branch of general single mode fiber that passes through connects second polarization beat length device (746) structure It is a branch of to pass through four selfs focussed collimated lens (740) and removable optical mirror (649) group at regular length light path reference arm At light path scan arm, by the two-way light of regular length light path reference arm and light path scan arm in the 5th detector (742) and Differential received on six detectors (743)；

The polarizer (511), the first fiber rotation connector (521), the second fiber rotation connector (523), polarizer to be measured (522) and light path demodulates the transmitting light that wide spectrum light source (501) can be covered with the wavelength wavelength operating range of signal sensor (530) Spectrum；The output tail optical fiber of the polarizer (511), the one 1 × 2nd polarization beam apparatus (531), the 21 × 2nd polarization beam apparatus (631), The input tail optical fiber of 31 × 2nd polarization beam apparatus (731) is operated in single mode, polarization hold mode；One 1 × 2nd polarization beam apparatus (531), the 21 × 2nd polarization beam apparatus (631), the output tail optical fiber of the 31 × 2nd polarization beam apparatus (731), light path demodulation with Signal sensor (530) is operated in single mode；

Demodulated using light path makes system signal noise ratio be promoted with signal sensor (530)Times.