CN115452012A - An ultra-sensitive optical frequency-domain polarimeter for frequency-shift detection with polarization beam-splitting structure - Google Patents

Abstract

The invention belongs to the technical field of optical fiber measurement, and in particular relates to an optical frequency domain polarimeter for ultra-high sensitivity polarization beam splitting structure frequency shift detection. The interferometer module, the auxiliary interferometer module and the signal acquisition and analysis module are characterized in that: the frequency shifter contained in the polarization beam splitting frequency shifting interferometer module is used to move the signal to the high frequency, avoiding the noise mixing from the low frequency overlap problem; the main interference peak is suppressed by using a polarization beam splitter to separate the transmission mode and coupling mode light passing through the device under test, thereby increasing the sensitivity to -130dB, which greatly improves the speed and speed of polarization crosstalk measurement in principle. sensitivity. At the same time, the combination of the main extension fiber and the acousto-optic modulator is used to shift the frequency of the signal, which satisfies the acquisition of polarization crosstalk information during long-distance device testing.

Description

An ultra-sensitive optical frequency-domain polarimeter for frequency-shift detection with polarization beam-splitting structure

Technical field:

The design of the invention belongs to the technical field of optical fiber measurement, and in particular relates to an ultrahigh-sensitivity optical frequency domain polarimeter with a polarization beam splitting structure and frequency shift detection.

Background technique:

Polarization optical devices are an important part of high-precision optical measurement and sensing systems. With the improvement of polarization device technology and the improvement of precision, the extinction ratio peak of the device is getting lower and lower, and the polarization crosstalk is getting smaller and smaller. Technology continues to develop, and the existing optical coherent domain polarization measurement technology OCDP solution needs to be continuously improved to adapt to constantly updated device testing. Some extremely weak polarization mode couplings or extremely high polarization extinction ratios (>80dB) are highly susceptible to environmental noise. These small signals will be drowned in the noise floor, causing confusion in the identification of peak information. In the distributed polarization coupling measurement system, the measurement sensitivity and the dynamic range of the system are directly determined by the noise floor of the system itself. There are three typical types of noise in the system, optical shot noise, interferometric beat noise and circuit thermal noise. We need to suppress these noises to improve the dynamic range and detection sensitivity of polarization-mode coupled measurement systems.

In order to further improve the sensitivity, dynamic range and device measurement length of the test, Yang Jun et al. proposed to use a polarization beam splitter to separate the transmitted light and coupled light to suppress beat noise and improve the sensitivity, and use an attenuator to reasonably select the attenuation multiple to adjust the transmitted energy. Attenuation to reduce relative intensity noise (a noise suppression device and suppression method for distributed polarization crosstalk measurement of optical polarization devices, CN20510212810.8),

In 2021, Li Chuang and others proposed a polarization coupling measurement system and scheme based on PBS (Li Chuang. Research on ultra-high sensitivity polarization coupling measurement technology and Y waveguide test method [D]. Harbin Engineering University, 21.), using White light interferometry technology, after replacing the polarizing beam splitter with the coupler in the traditional solution, the transmitted light and coupled light from the device are completely separated, avoiding the influence of the noise caused by the interference beat.

Due to the low energy of the wide-spectrum light source used in the optical coherent domain polarization measurement technology OCDP, the signal-to-noise ratio is insufficient, and the dynamic range cannot be greatly improved. Moreover, since the optical path scanning is controlled by the scanning method of the mechanical displacement stage, the complexity of the system increases, the reliability decreases and the scanning time takes a long time.

Compared with the optical coherent domain polarization measurement technology OCDP, the polarization-sensitive optical frequency domain reflectometry (P-OFDR) makes full use of the characteristics of tunable lasers to greatly improve the measurement speed and signal-to-noise ratio, but it cannot correct the critical polarization crosstalk. parameters are measured. Compared with the well-developed Optical Coherent Domain Polarimetry (OCDP), Optical Frequency Domain Polarimetry (OFDP) has the advantages of short test time, large dynamic range, and high spatial resolution. Has been widely used.

In 2021, a fast measurement device for distributed polarization crosstalk based on optical frequency domain frequency shift interference was proposed (a fast measurement device for optical fiber distributed polarization crosstalk based on optical frequency domain interference, CN21110828166.2), the applicant used A high-coherence tunable laser light source is used for fast wavelength scanning, which eliminates the original mechanical scanning tester structure, and uses a Mach-Zehnder interferometer with an optical fiber extension arm as an auxiliary interferometer to correct fiber nonlinear noise. Stable and reliable, greatly improving the speed and dynamic range of polarization crosstalk measurements. In the same year, the applicant added a Mach-Zehnder interferometer with an optical fiber extension arm as the main interferometer to shift the beat frequency signal to a high frequency on the original basis, avoiding signal aliasing at low frequencies (a Distributed polarization crosstalk fast measurement device based on frequency shift interference in optical frequency domain, CN21110828088.6). In 2021, Wang Feng et al. of Nanjing University disclosed an acousto-optic modulator frequency shift method (an optical fiber parameter measurement device for correcting nonlinear tuning effects, CN202110135197.X) to shift the frequency of light waves and increase the frequency of beat signals.

With the continuous development of technology, the optical frequency domain polarimeter is still being updated and iterated, and there are still deficiencies. For example, the test requirements for long-distance devices force us to add an extension fiber to the interferometer arm to increase the beat frequency effect. To meet the requirements, the signal background will also be raised due to phase noise; at the same time, testing high extinction ratio devices requires the highest possible sensitivity.

In order to make up for the above-mentioned shortcomings, the present invention discloses an ultrahigh-sensitivity optical frequency domain polarimeter for frequency shift detection with a polarization beam splitting structure based on the improvement of the prior art. Compared with the traditional distributed polarization crosstalk fast measurement device based on optical frequency domain interference, the original 50:50 coupler is replaced by a polarization beam splitter in the polarization beam splitting interferometer, so that the orthogonal The transmission mode and coupling mode of the interferometer can be respectively injected into the reference arm and the coupling arm of the interferometer. At this time, the original main interference peak is suppressed, and higher sensitivity can be obtained; the invention uses the auxiliary interferometer to eliminate the frequency sweep of the light source The signal aliasing problem introduced by nonlinearity has the advantages of small size, reliable and stable system, and high sensitivity; in addition, the present invention uses the frequency shifter in the polarization beam splitting frequency shifting interferometer module to move the signal to the high frequency, avoiding the Noise aliasing problem from low frequency; meets requirements for testing polarization crosstalk information of long distance devices.

Invention content:

The purpose of the present invention is to provide an optical frequency domain polarimeter with ultra-high sensitivity polarization beam splitting structure frequency shift detection which can improve the sensitivity of polarization crosstalk test and overcome the problems of low frequency flicker noise and signal aliasing.

The object of the present invention is achieved through the following measures:

An ultra-high sensitivity optical frequency domain polarimeter with polarization beam splitting structure and frequency shift detection, including a tunable light source module 1, a device to be tested module 2, a polarization beam splitting frequency shift interferometer module 3, an auxiliary interferometer module 4 and a signal Acquisition and analysis module 5 is characterized in that:

The tunable laser source module 1 sends chirped continuous light 60, which is injected into the first coupler 61 from the first coupler input port 61a and divided into two beams; the beam in the first coupler 61 is first output through the first coupler The pigtail 61b is injected into the device under test module 2; the beam output from the device under test module 2 is injected into the polarization beam splitting frequency shifting interferometer module 3, and then injected into the polarization beam splitter 31 by the input pigtail 30 of the polarization beam splitter therein And be divided into two beams of orthogonal state light, one beam is injected into the reference arm 32 as the reference beam, and the other beam is injected into the delay arm 33 as the test beam, and the light beams output by the reference arm 32 and the delay arm 33 are carried out in the second coupler 35 The beams are combined and then divided into two beams, and then differentially detected by the first balance detector 36; the beam in the first coupler 61 is injected into the auxiliary interferometer module 4 after passing through the second output pigtail 61c of the first coupler; polarization beam splitting The polarization beam-splitting frequency-shifting interferometer signal 37 output by the frequency-shifting interferometer module 3 and the auxiliary interferometer signal 46 output by the auxiliary interferometer module 4 are jointly injected into the acquisition unit 50 in the signal acquisition and analysis module 5 for acquisition, and the obtained signal is then Enter the signal processing unit 51 for data analysis and processing.

When light is injected into the DUT module 2, it passes through the polarizer input pigtail 20a, the polarizer 20, the polarizer output pigtail 20b, the first connection point 21, and the DUT input pigtail of the DUT module 2 in sequence. 23a, the second connection point 22, the device under test 23, the third connection point 24, the output pigtail 23b of the device under test and the fourth connection point 25;

When the parameter to be measured of the device under test 23 includes a high extinction ratio, the fusion angle of the first connection point 21 is θ ₁ =45°, and the parameter to be measured of the device under test 23 is the polarization crosstalk of the general coupling point , the welding angle of the first connection point 21 is θ ₁ =0°±2° or θ ₁ =90°±2°; the welding angle of the fourth connection point 25 is θ ₂ =0°±2° or θ ₂ =90°±0°; the optical path difference of the module 2 of the device under test is X ₁ , and the frequency shift is f ₁ ;

After the light is injected into the device under test, the coupling mode and the transmission mode are in an orthogonal state at the input end of the polarization beam splitter 30, and the polarization beam splitter 31 completely separates them and injects them into the reference arm 32 and the delay arm of the interferometer respectively. In 33, due to the presence of frequency shifter 34 in the delay arm, with the injection of light, a certain time delay will be generated in the delay arm; the polarization beam splitter 31 and the second coupler 35 are connected to the fifth The connection point 32a and the sixth connection point 33a adjust the polarization state of the polarization beam splitting interferometer through the polarization controller 33b to obtain a signal with as large a magnitude as possible; the optical path difference of the polarization beam splitting frequency shifting interferometer module 3 is X ₂ , after the light passes through the frequency shifter 34, the amount of frequency shift f ₂ is generated. According to the relationship between optical path difference and time delay τ ₂ =X ₂ /c and the amount of time delay τ ₂ =1/f ₂ , f ₂ =c/ X ₂ ; in the same way, the frequency shift of the module (2) of the device under test can be obtained as f ₁ =c/X ₁ , and then the frequency shift introduced by the frequency shifter and the frequency shift introduced by the device under test can be known from X ₂ > 2X ₁ The relationship of the frequency shift amount is 2f ₂ <f ₁ ;

The light beam injected into the third coupler 40 is divided into two beams of light, one beam is injected into the reference arm 41 as a reference beam, and the other beam is injected into the delay arm 42 as the test light, and passes through the test fiber 43, the reference arm 41 and the delay arm therein. The light beam output by 42 is combined in the fourth coupler 44 and then divided into two beams, and then differentially detected by the second balance detector 45; the optical path difference of the auxiliary interferometer module 4 is X ₃ , X ₃ > 2X2 _;

The signal acquisition unit 50 converts the received analog signal auxiliary interferometer signal 46 and the polarization beam splitting frequency-shifting interferometer signal 37 into digital signals, and the two are jointly input to the signal processing unit 51; the parameter setting needs of the acquisition software and the hardware parameter setting Consistent, to realize the complete acquisition of data; The method of the processing data of signal processing unit 51 is to carry out the non-linear correction of light source to polarization beam splitting frequency shifting interferometer signal 37 according to the auxiliary interferometer signal 46 that gathers, filter out frequency sweep Most of the intensity noise inside the light source intercepts the corrected signal to extract effective information, and then uses Fourier transform to demodulate the position and intensity information of polarization crosstalk in the frequency domain signal, and finally obtain a signal that meets the test requirements .

The polarization beam splitting frequency-shifting interferometer module with polarization beam splitter 31 performs the distributed polarization crosstalk measurement process as follows: after the light passes through the device under test 23, the pigtail fiber 23b of the device under test carries the polarization crosstalk inside the device under test Information, most of the energy is transmitted in the transmission axis (fast axis) of the device, and a small part of the energy jumps from the transmission mode to the coupling mode due to the existence of internal defect points or coupling points. As the light propagates in the device under test, The waveforms 23c in the two modes will have a certain offset in position, that is, delay generation. The DUT output pigtail 23b and the polarization beam splitter input pigtail 30 are welded to the fourth connection point 25 by a polarization maintaining welding machine. The on-axis angle 300 of the two pigtails in the polarization-maintaining fusion splicer is 0°-0°. At this time, the light of the transmission mode and the coupling mode introduced by the device under test can be respectively injected into the Mach-Zehnder interference by the polarization beam splitter 31. In the reference arm 32 and the delay arm 33 of the instrument. Let the light transmitted in the reference arm 32 be 31b, and the light transmitted in the delay arm be 31c. After the light transmitted by the delay arm passes through the frequency shifter 34, the optical path difference between it and the reference arm increases, and then it is transferred from the distance domain to In the wavelength domain, the beat frequency effect will be significantly increased, and the requirements for the length of the device under test will also be significantly increased. The two beams of light finally combine at the second coupler 35 and interfere. After differential detection by the first balance detector 36, the acquisition card acquires a digital signal and converts it into an analog signal. After processing, the polarization inside the device under test can be obtained. Crosstalk coupling peak;

Use the polarization coupling measurement method calibrated by the polarization beam splitter 31 to obtain the relative dynamic range. The calibration of the coupling peak of the traditional polarization crosstalk measurement device is to obtain the dynamic range and sensitivity by normalizing the main peak, due to the use of the polarization beam splitter 31 The rear main interference peak is suppressed, so we use two different alignments for the pigtail of the device under test 23 and the pigtail of the polarization beam splitter 31 to calibrate. When the on-axis angle of the two is 0°-45°, the polarizing beam splitter 31 at this time is equivalent to a 50:50 coupler, and the information from the device to be tested can be injected uniformly after passing through the polarizing beam splitter 31. In the fast axis and the slow axis of the optical fiber, the fast axis and the slow axis in the reference arm 32 and the delay arm 33 interfere with each other to form the main interference peak we need. There will be a significant coupling peak at the symmetrical position of the main interference peak, and we choose this peak as the calibration peak. Align the axis again, and use the welding machine to make the axis angle 0°-0°. At this time, we infer from the actual length of the welding that the coupling peak next to the original main interference peak still exists, but the amplitude will change to a certain extent. By comparing the data obtained by the pigtail of the device under test and the pigtail of the polarization beam splitter with two different welding angles, the coupling peak is obtained with the on-axis angle of 0°-45° to calibrate the on-axis angle of 0°-0° Due to the use of the polarization beam splitter 31, the original main interference peak is suppressed, and the phase noise introduced by the main interference peak is also suppressed, so that the sensitivity can be greatly improved;

Compared with the prior art, the present invention has the advantages of:

1. The present invention is a device for fast measurement of low-noise distributed polarization crosstalk in the optical frequency domain. An auxiliary interferometer is used to correct the signal aliasing problem caused by the nonlinear frequency sweep of the light source, effectively improving the system signal-to-noise ratio.

2. Use the frequency shifter in the polarization beam splitting frequency shifting interferometer module to move the signal to the high frequency, eliminating the influence of the 1/f flicker noise at the low frequency and the influence of the DC component introduced by the acquisition signal system. The problem of noise aliasing from low frequencies also meets the requirements for testing long-distance devices. The frequency shifter is equivalent to increasing the length of the delay fiber, which can effectively improve the system sensing performance.

3. The present invention uses a polarization beam splitter to inject the orthogonal transmission mode and coupling mode from the device under test into the reference arm and the delay arm of the interferometer respectively, and the phase noise introduced by the interference main peak is suppressed along with the interference main peak, only The interference peaks of the coupling of two modes exist, and by using the coupling peaks for calibration, the sensitivity of the device can be increased to -130dB, which provides more options for testing devices with high extinction ratios.

4. The present invention uses a device for fast measurement of distributed polarization crosstalk with a polarization beam splitter, which overcomes the limitation brought by phase noise, and the sensitivity can increase with the increase of the light intensity detected by the detector under the premise that the light intensity is sufficiently large. keep improving.

Description of drawings:

Fig. 1 is a schematic diagram of an ultra-high sensitivity optical frequency domain polarimeter for polarization beam splitting structure frequency shift detection.

Fig. 2 is a schematic diagram of the working principle of the polarization beam splitting frequency shifting interferometer in an optical frequency domain polarimeter for ultra-high sensitivity polarization beam splitting structure frequency shift detection.

Fig. 3 is a schematic diagram of an optical frequency domain polarimeter for performing frequency shift detection of an ultra-high sensitivity polarization beam splitting structure on a Y waveguide.

In order to more clearly illustrate an optical frequency domain polarimeter and method for ultra-high sensitivity polarization beam splitting structure frequency shift detection proposed by the present invention, the present invention will be further described below in conjunction with the embodiments and accompanying drawings, but it should not be Limit the protection scope of the present invention.

Specific implementation method, an optical frequency domain polarimeter for performing an ultra-sensitive polarization beam splitting structure frequency shift detection on the Y waveguide in the optical frequency domain, as shown in Figure 3:

It consists of four parts: tunable laser source module 1, device under test module 2, polarization beam splitting frequency shifting interferometer module 3, auxiliary interferometer module 4 and signal acquisition and analysis module 5, among which:

1) The tunable laser source module 1 outputs linear frequency modulated continuous light 60, which is injected into the first coupler 61 from the first coupler input port 61a and divided into two beams of light;

2) The light beam output by the first output pigtail 61b of the first coupler is injected into the DUT module 2;

3) The light beam output from the device-to-be-tested module 2 is injected into the polarization beam splitting frequency-shifting interferometer module 3, and injected into the polarization beam splitter 31 by the polarization beam splitter input end 30 therein, and is divided into two beams of light in an orthogonal state, one beam As the reference light, it is injected into the reference arm 32, and another beam is injected into the delay arm 33 as the test light, and the light beams output by the reference arm 32 and the delay arm 33 are combined in the second coupler 35 and then divided into two beams, and then the first Balanced detector 36 for differential detection;

The light beam output by the second output pigtail 61c of the first coupler is injected into the auxiliary interferometer module 4;

The polarization beam splitting frequency shifting interferometer signal 37 output by the polarization beam splitting frequency shifting interferometer module 3 and the auxiliary interferometer signal 46 output by the auxiliary interferometer module 4 are jointly injected into the signal acquisition and analysis module 5 for data acquisition processing and demodulation. Signal acquisition and analysis module 5 is made up of acquisition unit 50 and signal processing unit 51; Acquisition unit 50 is programmed and controlled by Labview software, carries out synchronous acquisition and storage from the analog voltage signal that photoelectric conversion obtains from detector, converts into digital signal; Signal processing Unit 51 is used to control the generation and reception of signals, and to process and demodulate digital signals;

The selection and parameters of the main optoelectronic devices of this scheme are as follows:

1) The tunable laser source module 1 is a narrow linewidth tunable laser capable of continuous wavelength scanning, the wavelength tuning range is 1480-1640nm, the coherent mode is turned on, the wavelength scanning rate is 40nm/s, and the wavelength scanning time is 4s;

2) The photosensitive materials of the first balanced detector 36 and the second balanced detector 45 are both InGaAs, the common mode rejection ratio is 25dB, the optical detection range is 900-1700nm, the maximum detection bandwidth is 80MHz, and the saturated differential detection power is 55uW, The transimpedance gain is 50000V/A, and the minimum noise equivalent power is the peak responsivity of 1A/W, such as the 1817 balanced detector of NewFocus Company;

3) The 16-bit sampling rate of the acquisition unit 50 is 45MHz, and the sampling time is about 4s. Combined with the laser for external triggering, the sampling time is greater than the wavelength scanning time, and the parameter design is reasonable;

4) The light splitting ratio of the first coupler 61 is 5:95, the light splitting ratio of the second coupler 35, the third coupler 40, and the fourth coupler 44 is 50:50, the extinction ratio is greater than 20dB, and the insertion loss is less than 0.5dB, the working wavelength covers the 1550nm band, and all couplers are single-mode couplers; the output pigtail of the polarization beam splitter is a polarization-maintaining fiber, and the single-mode input pigtail of the second coupler 35 is connected to the first The fifth connection point 32a and the sixth connection point 33a, and the three-ring polarization controller 33b are used to control the polarization state of the polarization beam splitting frequency-shifting interferometer to make the signal as stable as possible to obtain a higher dynamic range.

5) The working wavelength of the polarizer 20 covers the 1550nm band, the polarizing angle is 0°, the insertion loss is less than 1dB, and the extinction ratio is greater than 30dB, the polarizer input pigtail 20a is a single-mode fiber, and the polarizer output pigtail 20b is For a Panda-type polarization-maintaining fiber with a diameter of 125um, the length of the polarization-maintaining pigtail is l ₁ =15m, and the corresponding optical path S ₁ =l ₁ ×Δn≈7.5×10 ³ um is calculated, where the linear birefringence Δn of the polarization-maintaining fiber is taken as 5×10 ^-4 ;

6) The working wavelength of the polarizing beam splitter 31 covers the 1550nm band, and the input pigtail 30 of the polarizing beam splitter is a panda-shaped polarization-maintaining fiber with a diameter of 125um. The length of the polarization-maintaining pigtail is l ₂ =10m, and the corresponding optical path S is calculated. ₂ = l ₂ ×Δn≈5×10 ³ um, where the linear birefringence Δn of the polarization-maintaining fiber is 5×10 ^-4 ;

7) The welding angle of the first connection point 21 is θ ₁ =45°, and the welding angle of the fourth connection point 25 is θ ₂ =0°;

8) The Y waveguide 23Y of the device to be tested uses lithium niobate crystal as the chip substrate, the extinction ratio is 90dB, and works on the fast axis. The geometric length of the Y waveguide input pigtail 23a is l ₃ =1m, and the diameter is 125um. Calculate the corresponding optical path S ₃ =l ₃ ×Δn=5×10 ² um, the geometric length of the Y waveguide output pigtail 23b is l ₄ =2m, and the diameter is 125um, calculate the corresponding optical path S ₄ =l ₄ ×Δn=1×10 ³ um, the length of the Y waveguide chip is l ₅ =0.04m, and the corresponding optical path S=S ₃ +S ₄ +S ₅ =l ₃ ×Δn+l ₄ ×Δn+l ₅ ×Δn _Y ≈5236um is calculated, where the polarization maintaining The linear birefringence Δn of the fiber is 5×10 ^-4 , and the linear birefringence Δn _Y of the Y waveguide chip is 9.34×10 ^-2 ;

9) The polarization beam splitting frequency shifting interferometer module 3 is a Mach-Zehnder fiber interferometer structure using a frequency shifter in one arm, and the optical path difference X ₂ corresponding to the polarization beam splitting frequency shifting interferometer module 3 in this embodiment is calculated = 11648000um; calculate the optical path difference X ₁ =S ₁ +S ₂ +S=17736um corresponding to the module 2 of the device under test in this embodiment, satisfy X ₂ >2X ₁ , and the parameter design is reasonable;

10) The auxiliary interferometer module 4 adopts the Mach-Zehnder fiber interferometer structure of extending the optical fiber 43 to l _ref =20m, and calculates the optical path difference corresponding to the auxiliary interferometer module 4 in this embodiment X ₃ =l _ref ×Δn=29.12× 10 ⁶ um, where the refractive index n of the single-mode fiber is 1.456; therefore, X ₃ >2X ₂ is satisfied, and the parameter design is reasonable;

11) The position corresponding to the characteristic peak of the extinction ratio interference is |X ₂ +S ₁ +S ₂ +S ₃ +S ₄ +S ₅ |=11665736um;

12) When the light beam is coupled once through the first connection point 21, the second connection point 22, the third connection point 24, and the fourth connection point 25, the positions of the corresponding four first-order polarization crosstalk interference characteristic peaks are respectively | X ₂ +S ₁ |=11655500um, |X ₂ +S ₁ +S ₃ |=11656000um, |X ₂ +S ₂ +S ₄ |=11654000um, |X ₂ +S ₂ |=11653000um, because l ₁ >l ₂ , so the position distribution of the interference peak is |X ₂ +S ₂ |<|X ₂ +S ₂ +S ₄ |<|X ₂ +S ₁ |<|X ₂ +S ₁ +S ₃ |;

13) When the light beam respectively passes through the first connection point 21 and the third connection point 24, the first connection point 21 and the fourth connection point 25, the second connection point 22 and the third connection point 24, the second connection point 22 and the fourth connection point After the connection point 25 is coupled twice, the positions of the corresponding four second-order polarization crosstalk interference characteristic peaks are respectively |X ₂ +S ₁ +S ₂ +S ₄ |=11661500um, |X ₂ +S ₁ +S ₂ | =11660500 um, |X ₂ +S ₁ +S ₂ +S ₃ +S ₄ |=11662000 um, |X ₂ +S ₁ +S ₂ +S ₃ |=11661000 um.

Excluding the time for changing the on-axis angle of the welding point between the output pigtail of the device under test and the input pigtail of the polarization beam splitter, the duration of a test is about 3.95s.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (6)

1. An ultra-high sensitivity optical frequency domain polarimeter with polarization beam splitting structure and frequency shift detection, including a tunable light source module (1), a device module under test (2), and a polarization beam splitting frequency shift interferometer module (3) , auxiliary interferometer module (4) and signal acquisition analysis module (5), it is characterized in that: The tunable laser source module (1) sends linear frequency-modulated continuous light (60) into the first coupler (61) from the first coupler input port (61a) and is divided into two beams of light; the beam in the first coupler passes through the first coupler An output terminal (61b) is injected into the device under test module (2); the beam output from the device under test module (2) is injected into the polarization beam splitting frequency shifting interferometer module (3), and then input through the polarization beam splitter therein The pigtail (30) is injected into the polarization beam splitter (31) and is divided into two beams of orthogonal state light, one beam is injected into the reference arm (32) as a reference beam, and the other beam is injected into the delay arm (33) as a test beam, and the reference The beams output by the arm (32) and the delay arm (33) are combined in the second coupler (35) and then divided into two beams, and then differentially detected by the first balance detector (36); The light beam is injected into the auxiliary interferometer module (4) after the second output pigtail (61c) of the first coupler; the polarization beam splitting frequency shifting interferometer signal (37) output by the polarization beam splitting frequency shifting interferometer module (3) and The auxiliary interferometer signal (46) output by the auxiliary interferometer module (4) is jointly injected into the acquisition unit (50) in the signal acquisition and analysis module (5) for acquisition, and the obtained signal enters the signal processing unit (51) for further processing. Data analysis and processing. 2. by the described device under test module (2) of claim 1, it is characterized in that: When the light is injected into the device under test module (2), it passes through the device under test module (2) successively from the polarizer input pigtail (20a), the polarizer (20), the polarizer output pigtail (20b), the first Connection point (21), DUT input pigtail (23a), second connection point (22), DUT (23), third connection point (24), DUT output pigtail (23b) and the first Four connection points (25). 3. by the first connection point (21) and the 4th connection point (25) of the device under test module (2) described in claim 2, it is characterized in that: When the parameters to be measured of the device to be tested (23) include a high extinction ratio, the welding angle of the first connection point (21) is θ ₁ =45°±2°, and the parameters to be measured of the device to be tested (23) are When it is the polarized crosstalk of the general coupling point, the fusion angle of the first connection point (21) is θ ₁ =0°±2° or θ ₁ =90°±2°; the fusion angle of the fourth connection point (25) The angle is θ ₂ =0°±2° or θ ₂ =90°±2°; the optical path difference of the DUT module (2) is X ₁ , and the frequency shift is f ₁ . 4. by the polarization beam splitting frequency shifting interferometer (3) described in claim 1, it is characterized in that: After the light is injected into the device under test, the coupling mode and transmission mode are in an orthogonal state at the input end of the polarization beam splitter (30), and the polarization beam splitter (31) completely separates them and injects them into the reference arm of the interferometer respectively. (32) and in the delay arm (33), owing to the existence of the frequency shifter (34) in the delay arm, along with the injection of light, a certain time delay can be produced in the delay arm; the polarization beam splitter (31) and the first The two couplers (35) are connected to the fifth connection point (32a) and the sixth connection point (33a) through a flange, and the polarization state of the polarization beam splitting interferometer is adjusted by a polarization controller (33b) to obtain the maximum possible amplitude Large signal; the optical path difference of the polarization beam splitting frequency-shifting interferometer module (3) is X ₂ , and the light passes through the frequency shifter (34) to generate a frequency shift f ₂ , according to the corresponding relationship between the optical path difference and the time delay τ ₂ =X ₂ /c and time delay τ ₂ =1/f ₂ , f ₂ =c/X ₂ can be obtained; in the same way, the frequency shift of the DUT module (2) can be obtained as f ₁ =c/X ₁ , and from X ₂ >2X ₁ , it can be known that the relationship between the frequency shift introduced by the frequency shifter and the frequency shift introduced by the DUT is 2f ₂ <f ₁ . 5. by auxiliary interferometer module (4) described in claim 1, it is characterized in that: The light beam injected into the third coupler (40) is divided into two beams of light, one beam is injected into the reference arm (41) as the reference beam, and the other beam is injected into the delay arm (42) as the test beam, and passes through the extension fiber (43 ), the light beams output by the reference arm (41) and the delay arm (42) are combined in the fourth coupler (44) and then divided into two beams, and then differentially detected by the second balanced detector (45); auxiliary interference The optical path difference of the instrument module (4) is X ₃ , where X ₃ >2X ₂ . 6. the acquisition unit (50) and signal processing unit (51) of signal acquisition analysis module (5) according to claim 1, it is characterized in that: The signal acquisition unit (50) converts the received analog signal auxiliary interferometer signal (46) and polarization beam splitting frequency shifting interferometer signal (37) into a digital signal, and the two are jointly input to the signal processing unit (51); signal processing The data processing method of the unit (51) is to perform nonlinear phase correction of the light source on the polarization beam splitting frequency-shifting interferometer signal (37) according to the collected auxiliary interferometer signal (46), and use the deskewing filter algorithm to perform long-distance test The obtained signal is subjected to nonlinear correction, and then Fourier transform is used to demodulate the position and intensity information of polarization crosstalk in the frequency domain signal, and finally a signal that meets the test requirements is obtained.

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