A wavelength-scan-based phase modulator half-wave voltage measuring device and method

Abstract

The application belongs to the technical field of optical fiber measurement, and provides a phase modulator half-wave voltage measuring device and method based on wavelength scanning, which comprises a tunable laser source module (1), a measuring module (2), an intensity correction module (3) and a signal acquisition and analysis module (4). The tunable laser (101) outputs linear frequency modulation continuous light (102), is injected into a Mach-Zehnder interferometer containing a phase modulator (204) and an internal modulation frequency shift unit (206), frequency shift of beat interference signals is realized by using an elongated optical fiber (206b), and finally the half-wave voltage is calculated through the beat main peak and sideband amplitude ratio. The application realizes heterodyne interference measurement of the phase modulator by using sweep laser, the half-wave voltage change in the working wavelength range can be obtained by single measurement, the test efficiency is high, the operation is simple, and the compatibility is strong.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber measurement technology, and specifically relates to a phase modulator half-wave voltage measurement device and method based on wavelength scanning. Background Technology

[0002] With the development of artificial intelligence, data centers, high-speed communications, and other fields, people's requirements for the efficiency and quality of information transmission are increasing, which is driving photonic integrated circuits (PICs) to become the core cornerstone of the next generation of information industry. PICs mainly miniaturize and integrate several active and passive optical devices on a common substrate to realize functions such as light generation, transmission, modulation, and detection. Among them, the straight waveguide lithium niobate electro-optic phase modulator is an important device in optical communication and high-power laser applications. Its modulation principle is the electro-optic effect, that is, using an external electric field to change the refractive index of the medium material and the light wave transmission characteristics, thereby achieving phase and polarization state modulation of the optical signal.

[0003] Half-wave voltage V π It is one of the key performance parameters of a phase modulator, referring to the phase change. π The required drive voltage is often used to evaluate the modulation capability and power consumption level of a device. For example, in X-cut and Y-transmission lithium niobate phase modulators, the half-wave voltage is defined as... ;in, l For the operating wavelength, G The distance between the electrodes. n e It is an unusual refractive index. Y 33 It is the electro-optic coefficient of lithium niobate. L Electrode length, C It is the electro-optic overlap factor. On the one hand, within the operating wavelength range of the phase modulator, the half-wave voltage... V π Will vary with wavelength l It increases with the increase of [something]. V π The relative change is approximately 5% or even higher. Current half-wave voltage testing methods are mostly single-wavelength tests. To evaluate... Vπ Follow l To obtain the change curve, multiple measurements are required, which is time-consuming and labor-intensive. On the other hand, due to factors such as impedance matching and speed matching during electro-optic modulation, the half-wave voltage... V π It will change with the frequency of the modulated electrical signal. f m It increases with the increase of [the quantity]. Existing technologies generally provide [the quantity] in the kHz range. V πHowever, from a practical application perspective, attention should be paid to the half-wave voltage performance in the MHz and GHz ranges. Therefore, in recent years, people have also been committed to the research of half-wave voltage testing methods in the high-frequency band.

[0004] The half-wave voltage testing methods for electro-optic phase modulators mainly fall into two categories: optical domain testing methods and electrical domain testing methods. Optical domain testing methods primarily include traditional spectrometer methods, which determine the modulation depth by analyzing the amplitude ratio between the optical carrier and the sidebands. m Then, based on the peak value of the modulated electrical signal at this time... V p To calculate half-wave voltage V π =V p / m While traditional spectrometer methods offer system simplicity, they are costly and limited by the GHz-level resolution of spectrometers, making it difficult to measure phase modulators with bandwidths less than 10 GHz, thus restricting the measurement range. Alternatively, applying Gaussian white noise to the phase modulator induces spectral broadening, and the half-wave voltage can be calculated using the degree of spectral broadening and the electrical noise power spectral density. V π However, this method has a large measurement error.

[0005] Electrical domain measurement methods mainly include PM-IM conversion and heterodyne methods. Compared to optical domain measurement methods, electrical domain measurement methods eliminate high-frequency optical carriers, further improving measurement resolution. PM-IM conversion methods are further subdivided into various techniques. For example, a phase modulator is connected in series with a time-delay interferometer to convert phase modulation into intensity modulation, and then the half-wave voltage is solved using the gain method, avoiding the influence of light source and device instability. However, this method is affected by the unevenness of the detector responsivity and introduces nonlinear conversion, making the measurement method more complex. The heterodyne method places the phase modulator in a Mach-Zehnder interferometer with an acousto-optic frequency shifter, using the frequency shifter to resolve the main peak of the beat frequency interference signal. However, the center frequency of the frequency shifter is usually tens or even hundreds of MHz, requiring a high-speed spectrum analyzer or detector, increasing the burden on the acquisition and detection system. Furthermore, the modulation-frequency shift method has a single and limited test wavelength, and the frequency shift is not flexible enough, resulting in low measurement efficiency, poor compatibility with different specifications of phase modulators, and the inability to obtain the half-wave voltage versus wavelength curve through a single measurement. Summary of the Invention

[0006] The first objective of this invention is to provide a phase modulator half-wave voltage measurement device based on wavelength scanning.

[0007] A second objective of the present invention is to provide a measurement method applicable to the above-mentioned half-wave voltage measuring device.

[0008] To achieve the first objective of this invention, this invention provides A phase modulator half-wave voltage measurement device based on wavelength scanning, characterized in that it includes a tunable laser source module, a measurement module, an intensity correction module, and a signal acquisition and analysis module; The tunable laser source module includes a tunable laser and a first coupler, wherein the tunable laser is connected to the input terminal of the first coupler; The measurement module includes a second coupler, a phase modulator, a signal generator, a third coupler, an internal modulation frequency shifting unit, and a first photodetector. The intensity correction module includes a second photodetector. The first output terminal of the first coupler is connected to the input terminal of the second coupler, the second output terminal of the first coupler is connected to the input terminal of the second photodetector, the first output terminal of the second coupler is connected to the input terminal of the phase modulator, the second output terminal of the second coupler is connected to the input terminal of the internal modulation frequency shifting unit, the output terminal of the phase modulator is connected to the first input terminal of the third coupler, the output terminal of the internal modulation frequency shifting unit is connected to the second input terminal of the third coupler, the output terminal of the third coupler is connected to the input terminal of the first photodetector, and the output terminals of the first photodetector and the second photodetector are connected to the signal acquisition and analysis module. The modulated electrical signal generated by the signal generator is input to the phase modulator for electro-optic modulation, and the modulated electrical signal generated by the signal generator is input to the signal acquisition and analysis module for real-time monitoring.

[0009] A further embodiment is that the internal modulation frequency shifting unit includes a tunable optical attenuator and an extended optical fiber, the second output terminal of the second coupler is connected to the input terminal of the tunable optical attenuator, and the output terminal of the tunable optical attenuator is connected to the second input terminal of the third coupler through the extended optical fiber.

[0010] A further embodiment is that the signal acquisition and analysis module includes a data monitoring and acquisition unit, a data post-processing unit, and a half-wave voltage calculation unit. The output terminals of the first photodetector and the second photodetector are connected to the input terminal of the data monitoring and acquisition unit. The modulated electrical signal generated by the signal generator is input to the input terminal of the data monitoring and acquisition unit. The output terminal of the data monitoring and acquisition unit is connected to the data post-processing unit. The data post-processing unit is connected to the half-wave voltage calculation unit.

[0011] To achieve the second objective of this invention, this invention provides a measurement method for a half-wave voltage measuring device applied to the above-described scheme. The measurement method includes: The tunable laser outputs linear frequency-modulated continuous light with a frequency that varies with time to the first coupler. The light is split into two beams by the first coupler. One beam is injected into the input of the second coupler through the first output of the first coupler, and the other beam is injected into the second photodetector through the second output of the first coupler. The light injected into the second coupler is split into two beams. One beam is input to the phase modulator, and the other beam is input to the inner modulation frequency shift unit. The light output from the phase modulator and the inner modulation frequency shift unit is combined in the third coupler and then output to the first photodetector. After photoelectric conversion by the first photodetector, the resulting time-domain interference signal is input to the signal acquisition and analysis module. The modulated electrical signal generated by the signal generator is divided into two beams. One beam of the modulated electrical signal is input to the phase modulator for electro-optic modulation, and the other beam of the modulated electrical signal is input to the signal acquisition and analysis module for real-time monitoring. After photoelectric conversion by the second photodetector, the resulting time-domain signal is injected into the signal acquisition and analysis module, which calculates the half-wave voltage.

[0012] A further approach is that the center wavelength of the linearly frequency-modulated continuous light output by the tunable laser is l 0, the initial tuning wavelength is l 1. The termination tuning wavelength is l 2; Wavelength tuning range Δλ=λ 2 -l 1 =γΔt ; in Δt For scan time, c Wavelength scanning speed; The frequency tuning range is Δf=Δλc / λ 0 2 =νΔt ; n This refers to the frequency scanning speed.

[0013] A further proposed approach is that the ratio of the output optical power of the first output terminal and the second output terminal of the first coupler is x1:x2, and x1>x2.

[0014] A further proposed solution is that the phase modulator is a straight waveguide phase modulator, with an initial operating wavelength of... l 3. The cutoff wavelength is l 4. The center wavelength is l 5, l 3 ≤λ 1 <λ 2 ≤λ 4 and l5 =λ 0; The electro-optic bandwidth of the phase modulator is f 1. Half-wave voltage is V π Modulation depth is m=d / p ,in d It is the modulation coefficient.

[0015] A further approach is to determine the peak value of the modulated electrical signal output by the signal generator. V p =mV π modulation depth m>0 The frequency of the modulated electrical signal is f m , 0<f m ≤f 1.

[0016] A further approach is to require, in order to avoid aliasing of interference signals, f τ ≠xf m ,in x It is a positive integer. f m It is the frequency of the modulated electrical signal. f τ =nt It is the frequency shift amount of the extended optical fiber in the internal modulation frequency shift unit. t It extends the delay of the optical fiber.

[0017] A further approach involves the data post-processing unit first segmenting the time-domain interference signal according to time and wavelength, then correcting for intensity fluctuations during the light source wavelength scanning process; subsequently, after performing a Fourier transform, the amplitude ratio of the main peak to the first-order beat frequency sideband of each beat frequency interference signal segment can be obtained in the frequency domain. R And determine the modulation depth m ; The time-domain interference signal output by the first photodetector is A, the time-domain signal output by the second photodetector is B, and the corrected time-domain interference signal A' = A / B.

[0018] The beneficial effects of this invention are as follows: This invention utilizes the wavelength scanning method to measure the half-wave voltage of a phase modulator. A single measurement can acquire the half-wave voltage change within the operating wavelength range, eliminating the need for multiple tests at different wavelengths and significantly improving testing efficiency. Furthermore, compared to other electrical domain measurement methods, this invention removes the frequency shifter or FP cavity that limits the operating wavelength. Only a compatible light source and photodetector need to be replaced to perform phase modulator measurements in any wavelength band, making it simple to operate and highly compatible. Moreover, this invention uses a frequency-modulated continuous wave and a delay interferometer to replace the acousto-optic modulator in the traditional heterodyne method to achieve frequency shift. Replacing external modulation with internal modulation not only simplifies the optical path structure, enhances robustness, supports high-frequency half-wave voltage measurement, and improves signal quality, but also allows for flexible control of the frequency shift by adjusting the length of the extended optical fiber, enabling tests even at the kHz level. This greatly reduces the pressure on the acquisition and detection system and the hardware requirements. Attached Figure Description

[0019] Figure 1 This is an optical path diagram of an embodiment of the half-wave voltage measuring device of the present invention.

[0020] Figure 2 This is a schematic diagram of a frequency sweep signal based on a frequency-modulated continuous wave, representing an embodiment of the half-wave voltage measuring device of the present invention.

[0021] Figure 3 This is a schematic diagram of the beat frequency interference signal based on the frequency-modulated continuous wave in an embodiment of the half-wave voltage measuring device of the present invention.

[0022] Figure 4 These are curves showing the variation of the beat frequency main peak and beat frequency sideband intensity with modulation depth in an embodiment of the half-wave voltage measurement device of the present invention.

[0023] Figure 5 This is an optical path diagram of another embodiment of the half-wave voltage measuring device of the present invention.

[0024] Figure 6 This is a schematic diagram of the modulated electrical signal in another embodiment of the half-wave voltage measuring device of the present invention.

[0025] Figure 7 This is a schematic diagram of the time-domain beat frequency interference signal and its segmentation results in another embodiment of the half-wave voltage measuring device of the present invention.

[0026] Figure 8 This is a schematic diagram of the frequency domain beat frequency interference signal in another embodiment of the half-wave voltage measuring device of the present invention.

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0028] Reference Figure 1 to Figure 8The half-wave voltage measurement device for the phase modulator includes a tunable laser source module 1, a measurement module 2, an intensity correction module 3, and a signal acquisition and analysis module 4. The tunable laser source module 1 includes a tunable laser 101 and a first coupler 103, with the input terminal of the tunable laser 101 connected to the input terminal of the first coupler 103. The measurement module 2 includes a second coupler 201, a phase modulator 204, a signal generator 205, a third coupler 207, an internal modulation frequency shift unit 206, and a first photodetector 208. The intensity correction module 3 includes a second photodetector 301. The first output terminal 103a of the first coupler is connected to the input terminal of the second coupler 201, and the second output terminal 103b of the first coupler is connected to the second photodetector. The input terminal of 301 is connected, the first output terminal of the second coupler 201 is connected to the input terminal of the phase modulator 204, the second output terminal of the second coupler 201 is connected to the input terminal of the inner modulation frequency shift unit 206, the output terminal of the phase modulator 204 is connected to the first input terminal of the third coupler 207, and the output terminal of the inner modulation frequency shift unit 206 is connected to the second input terminal of the third coupler 207. The inner modulation frequency shift unit 206 includes a tunable optical attenuator 206a and an extension fiber 206b. The second output terminal of the second coupler 201 is connected to the input terminal of the tunable optical attenuator 206a, and the output terminal of the tunable optical attenuator 206a is connected to the second input terminal of the third coupler 207 through the extension fiber 206b.

[0029] The output of the third coupler 207 is connected to the input of the first photodetector 208. The output of the first photodetector 208 and the output of the second photodetector 301 are connected to the signal acquisition and analysis module 4. The modulated electrical signal generated by the signal generator 205 is input to the phase modulator 204 for electro-optic modulation. The modulated electrical signal generated by the signal generator 205 is input to the signal acquisition and analysis module 4 for real-time monitoring.

[0030] The signal acquisition and analysis module 4 includes a data monitoring and acquisition unit 401, a data post-processing unit 402, and a half-wave voltage calculation unit 403. The output terminal of the first photodetector 208 and the output terminal of the second photodetector 301 are connected to the input terminal of the data monitoring and acquisition unit 401. The modulated electrical signal generated by the signal generator 205 is input to the input terminal of the data monitoring and acquisition unit 401. The output terminal of the data monitoring and acquisition unit 401 is connected to the data post-processing unit 402. The data post-processing unit 402 is connected to the half-wave voltage calculation unit 403.

[0031] The tunable laser 101 in the tunable laser source module 1 outputs linearly frequency-modulated continuous light 102 whose frequency changes with time to the first coupler 103, which splits the light into two beams: the light from the first output terminal 103a of the first coupler is injected into the measurement module 2, and the light from the second output terminal 103b of the first coupler is injected into the intensity correction module 3.

[0032] The light from measurement module 2 is split into two beams after passing through the second coupler 201 and injected into measurement arm 202 and reference arm 203 respectively. The light in measurement arm 202 passes sequentially through phase modulator input pigtail 204a, phase modulator 204, and phase modulator output pigtail 204b, and then is injected into third coupler 207. The light in reference arm 203 passes sequentially through tunable optical attenuator 206a and extension fiber 206b in internal modulation frequency shift unit 206, and then is injected into third coupler 207. The output light from measurement arm 202 and reference arm 203 is combined in third coupler 207 and then photoelectrically converted by first photodetector 208. The resulting beat frequency interference signal is input to signal acquisition and analysis module 4. The modulated electrical signal generated by signal generator 205 is equally divided into two beams. One beam is input from first channel 205a to phase modulator 204 for electro-optic modulation, and the other beam is input from second channel 205b to signal acquisition and analysis module 4 for real-time monitoring.

[0033] The light injected into the intensity correction module 3 is received by the second photodetector 301 and converted into photoelectric signal, and then the resulting time-domain signal is injected into the signal acquisition and analysis module 4.

[0034] The electrical signal in the signal acquisition and analysis module 4 passes through the data monitoring and acquisition unit 401, the data post-processing unit 402, and the half-wave voltage calculation unit 403 in sequence, and finally the half-wave voltage is calculated.

[0035] The center wavelength of the linearly frequency-modulated continuous light output by the tunable laser 101 is l 0, the initial tuning wavelength is l 1. The termination tuning wavelength is l 2; Wavelength tuning range ; in Δt For scan time, c Wavelength scanning speed; The frequency tuning range is ; n This refers to the frequency scanning speed.

[0036] The insertion loss of the extension fiber 206b in the internal modulation frequency shift unit 206 is LOSS 1, length is L 0, latency is τ=L 0 n / a,in n The refractive index of the optical fiber. c The speed of light in a vacuum; the frequency shift caused by the extended optical fiber 206b is f τ =nt The scanning speed is determined by the fiber length and the frequency of the light source; to avoid aliasing of interference signals, it is required that... f τ ≠xf m ,in x It is a positive integer. f m It is the frequency of the modulated electrical signal.

[0037] The insertion loss of the tunable optical attenuator 206a in the internal modulation frequency shifting unit 206 is LOSS 2. To ensure the interference signal strength and measurement signal-to-noise ratio, it is required that... LOSS 1+ LOSS 2= LOSS 0, where LOSS 0 represents the insertion loss of the phase modulator 204.

[0038] The ratio of the output optical power of the first output terminal 103a and the second output terminal 103b of the first coupler is x1:x2, and x1>x2.

[0039] Phase modulator 204 is a straight waveguide phase modulator, with the modulation mechanism being the electro-optic effect, and the initial operating wavelength is... l 3. The cutoff wavelength is l 4. The center wavelength is l 5. Requirements l 3≤ l 1< l 2≤ l 4, and l 5= l 0, the electro-optic bandwidth of phase modulator 204 is f 1. Half-wave voltage is V π Modulation depth is m=d / p ,in d It is the modulation coefficient, the peak value of the modulated electrical signal output by the signal generator 205. V p =mV π modulation depth m>0 The frequency of the modulated electrical signal is f m , 0<f m ≤f 1.

[0040] The data monitoring and acquisition unit 401 can be a spectrum analyzer, oscilloscope, or data acquisition card, etc. The data post-processing unit 402 first segments the time-domain interference signal according to time and wavelength, and then corrects the intensity fluctuations caused by polarization state disturbances and frequency sweep nonlinearity during the wavelength scanning process of the light source to ensure the stability and accuracy of the test. After performing Fourier transform, the amplitude ratio of the main peak and the first-order beat frequency sideband of each beat frequency interference signal can be obtained in the frequency domain. R And determine the modulation depth m The time-domain interference signal output by the first photodetector 208 is A, and the time-domain signal output by the second photodetector 301 is B. The corrected time-domain interference signal A' = A / B. The half-wave voltage calculation unit 403 uses the peak value of the modulated electrical signal. V p With modulation depth m The half-wave voltage at different wavelengths was calculated. V π .

[0041] The principle and process of half-wave voltage measurement based on linear frequency modulated continuous wave and extended optical fiber phase modulator are as follows: The linearly frequency-modulated continuous light 102 output by the tunable laser 101 refers to the swept-frequency optical carrier 502 whose wavelength scans linearly with time, as shown in the attached figure. Figure 2 As shown, its light field E 0 (t,f 0 ) Represented as:

[0042] in A 0、 f 0 represents the amplitude and frequency of the input optical carrier. n It refers to the frequency scanning speed. F=νt It is the frequency scanning range. f 0 (t) yes t The phase of the light source fluctuates randomly at any given time. After the swept light passes through an extended 206b fiber, its output light field... E ref (t) Represented as:

[0043] in t This refers to extending the time delay of the optical fiber. The linear frequency-modulated time-delayed optical fiber 501 after extending the optical fiber is shown in the attached image. Figure 2 As shown.

[0044] Sine modulated signal electric field Loaded onto phase modulator 204, where A m and fm These are the amplitude and modulation frequency of the modulated electrical signal. After the swept light passes through the phase modulator 204 and undergoes electro-optic modulation, its output light field... E meas (t) The Bessel function, after expansion and simplification, is:

[0045] in d It is the modulation coefficient. n=0、±1、±2 ...represents the order. The positive first-order sideband of the sweep frequency is 503, and the negative first-order sideband is 504, as shown in the appendix. Figure 2 As shown. Therefore, the beat frequency interference signal after optical interference between the measuring arm 202 and the reference arm 203 of the Mach-Zehnder interferometer is expressed as:

[0046] in C=2πf 0 t+pnt 2 It is a constant. f τ =nt This refers to the frequency shift caused by extending the optical fiber. Therefore, for this internal modulation frequency shift method, the frequency shift is determined by both the frequency scanning speed of the light source and the length of the extended optical fiber. In contrast, the traditional heterodyne method uses an external modulation frequency shift method, where the frequency shift is directly determined by the frequency shifter.

[0047] Appendix Figure 2 After the linear frequency-modulated time-delayed light 501 interferes with the swept frequency optical carrier 502, the positive first-order sideband of the swept frequency 503, and the negative first-order sideband of the swept frequency 504, the following results can be obtained: Figure 3 The main beat frequency peak 601, the positive first-order beat frequency sideband 602, and the negative first-order beat frequency sideband 603 are shown.

[0048] By changing the amplitude of the modulated electrical signal A m To change the modulation coefficient d and modulation depth m This allows us to obtain the spectra of sideband intensity ratios at different beat frequencies. (See attached image) Figure 4 The solid line, dashed solid line, and double solid line shown represent the changes in light intensity with modulation depth for the beat frequency main peak 601, beat frequency positive first-order sideband 602, and beat frequency positive second-order sideband 604, respectively. a The dot represents the case where the amplitude of the main peak of the beat frequency and the amplitude of the positive first-order sideband of the beat frequency are the same. b The dot represents the case where the amplitude of the beat frequency peak is 0. The frequencies of the beat frequency peak and the beat frequency sidebands are determined by the length of the extended fiber 206b and the modulation frequency. f m Therefore, the modulation depth is obtained by measuring the beat frequency sideband intensity ratio. m Combined with the peak value of the electrical signal Vp Half-wave voltage can be obtained V π .

[0049] Of course, in addition to the above embodiments, as shown in the appendix Figure 5 As shown, the measurement module may further include a polarizer 211 and an analyzer 212. The polarizer 211 is connected between the second coupler 201 and the phase modulator 204, and the analyzer 212 is connected between the phase modulator 204 and the third coupler 207. The polarizer connects the single-mode optical path and the polarization-maintaining device, and converts the input light into linearly polarized light with a higher extinction ratio, reducing the impact of polarization state fluctuations on the accuracy of phase modulation and improving modulation efficiency and signal stability. Additionally, an oscilloscope 405 can be used for the data monitoring and acquisition unit.

[0050] The selection of the main optoelectronic devices and their performance parameters in this invention are as follows: 1) The tunable laser 101 outputs narrow linewidth laser light with a wavelength tuning range of 1530nm~1565nm, and the wavelength scanning speed is... c =20nm / s, frequency scanning speed n =2.5THz / s, scan time Δt =1.75s, such as using the TSL-510 laser from Santec Corporation of Japan.

[0051] 2) The operating wavelengths of the 0° polarizer 211 and the 45° analyzer 212 cover the 1550nm band. The input pigtail 211a of the polarizer and the output pigtail 212b of the analyzer are ordinary single-mode optical fibers, while the output pigtail 211b of the polarizer and the input pigtail 212a of the analyzer are panda-type polarization-maintaining optical fibers. The operating wavelengths of the second coupler 201 and the third coupler 207 cover the 1550nm band, and the pigtails are all ordinary single-mode optical fibers.

[0052] 3) The phase modulator 204 uses lithium niobate crystal and titanium diffusion process, Z-cut design, and has a working wavelength range of 1530nm~1565nm. The electro-optic bandwidth of -3dB is 10GHz, and the half-wave voltage specification at the 50kHz modulation frequency is 4V. For example, the PM10-C model phase modulator from Zhuhai Opto-Ku Technology can be used.

[0053] 4) Extend the fiber optic cable 206b to a length of L =1m, refractive index n The frequency shift introduced by a single-mode fiber with a resolution of 1.456 f τ =n= νLn / c ≈12.1kHz.

[0054] 5) The frequency of the sine wave output by signal generator 205 fm =50kHz, peak V p =1.7V, such as using an Agilent 33120A function generator.

[0055] 6) The oscilloscope 405 has a bandwidth of 350MHz, a total storage depth of 4Mpts, and a sampling rate of 1MS / s. If two channels are sampled, the sampling time is 2s, which is 1.75s longer than the scan time. The parameters are reasonably designed. For example, the Keysight DSOX3034A oscilloscope can be used.

[0056] 7) The modulated electrical signal received by computer 406 is shown in the attached figure. Figure 6 As shown, the measured frequency and peak value are consistent with the signal generator settings.

[0057] 8) Time-domain beat frequency interferometry signal 701 is attached. Figure 7 As shown, the time-domain signal is divided into two segments according to the wavelength scanning time. The wavelength tuning ranges of the first segment 702 and the second segment 703 are 1530~1547.5nm and 1547.5~1565nm, respectively.

[0058] 9) Next, taking the first signal 702 as an example, intensity correction and Fourier transform are performed to obtain the frequency domain beat frequency interference signal, as shown in the attached figure. Figure 8 As shown, the normalized main peak 605 and sideband peak 606 correspond to the attached peaks respectively. Figure 3 In the schematic diagram, the beat frequency main peak 601 and the beat frequency positive first-order sideband 602 have frequencies of 12.1kHz and 62.1kHz, respectively. The amplitude ratio between the normalized main peak 605 and the sideband peak 606 corresponds to the modulation depth. m =1 = 0.435, and thus the half-wave voltage at a wavelength of 1538.75nm can be calculated. V π1 = V p / m 1 = 3.91V, and similarly for the second signal 703, the modulation depth... m The formula 2 = 0.43 can be used to calculate the half-wave voltage at a wavelength of 1556.25 nm. V π2 = V p / m 2 = 3.95V; and the half-wave voltage increases with increasing wavelength, which is in line with theoretical expectations.

[0059] As can be seen from the above, this invention utilizes the wavelength scanning method to measure the half-wave voltage of a phase modulator. A single measurement can acquire the half-wave voltage change within the operating wavelength range, eliminating the need for multiple tests at different wavelengths and significantly improving testing efficiency. Furthermore, this invention uses a frequency-modulated continuous wave and a delay interferometer to replace the acousto-optic modulator in the traditional heterodyne method to achieve frequency shift. Replacing external modulation with internal modulation not only simplifies the optical path structure and improves signal quality, but also allows for flexible control of the frequency shift by adjusting the length of the extended optical fiber. Testing can even be conducted at the kHz level, greatly reducing the pressure on the acquisition and detection system and the hardware requirements.

Claims

1. A phase modulator half-wave voltage measurement device based on wavelength scanning, characterized in that, It includes a tunable laser source module, a measurement module, an intensity correction module, and a signal acquisition and analysis module; The tunable laser source module includes a tunable laser and a first coupler, wherein the tunable laser is connected to the input terminal of the first coupler; The measurement module includes a second coupler, a phase modulator, a signal generator, a third coupler, an internal modulation frequency shifting unit, and a first photodetector. The intensity correction module includes a second photodetector. The first output terminal of the first coupler is connected to the input terminal of the second coupler, the second output terminal of the first coupler is connected to the input terminal of the second photodetector, the first output terminal of the second coupler is connected to the input terminal of the phase modulator, the second output terminal of the second coupler is connected to the input terminal of the internal modulation frequency shifting unit, the output terminal of the phase modulator is connected to the first input terminal of the third coupler, the output terminal of the internal modulation frequency shifting unit is connected to the second input terminal of the third coupler, the output terminal of the third coupler is connected to the input terminal of the first photodetector, and the output terminals of the first photodetector and the second photodetector are connected to the signal acquisition and analysis module. The modulated electrical signal generated by the signal generator is input to the phase modulator for electro-optic modulation, and the modulated electrical signal generated by the signal generator is input to the signal acquisition and analysis module for real-time monitoring. The internal modulation frequency shifting unit includes a tunable optical attenuator and an extension optical fiber. The second output terminal of the second coupler is connected to the input terminal of the tunable optical attenuator, and the output terminal of the tunable optical attenuator is connected to the second input terminal of the third coupler through the extension optical fiber.

2. The half-wave voltage measuring device according to claim 1, characterized in that: The signal acquisition and analysis module includes a data monitoring and acquisition unit, a data post-processing unit, and a half-wave voltage calculation unit. The output terminals of the first photodetector and the second photodetector are connected to the input terminal of the data monitoring and acquisition unit. The modulated electrical signal generated by the signal generator is input to the input terminal of the data monitoring and acquisition unit. The output terminal of the data monitoring and acquisition unit is connected to the data post-processing unit. The data post-processing unit is connected to the half-wave voltage calculation unit.

3. A measurement method applied to the half-wave voltage measuring device according to claim 2, characterized in that: The measurement method includes: The tunable laser outputs linear frequency-modulated continuous light with a frequency that varies with time to the first coupler. The light is split into two beams by the first coupler. One beam is injected into the input of the second coupler through the first output of the first coupler, and the other beam is injected into the second photodetector through the second output of the first coupler. The light injected into the second coupler is split into two beams. One beam is input to the phase modulator, and the other beam is input to the inner modulation frequency shift unit. The light output from the phase modulator and the inner modulation frequency shift unit is combined in the third coupler and then output to the first photodetector. After photoelectric conversion by the first photodetector, the resulting time-domain interference signal is input to the signal acquisition and analysis module. The modulated electrical signal generated by the signal generator is divided into two beams. One beam of the modulated electrical signal is input to the phase modulator for electro-optic modulation, and the other beam of the modulated electrical signal is input to the signal acquisition and analysis module for real-time monitoring. After photoelectric conversion by the second photodetector, the resulting time-domain signal is injected into the signal acquisition and analysis module, which calculates the half-wave voltage.

4. The measurement method according to claim 3, characterized in that: The center wavelength of the linearly frequency-modulated continuous light output by the tunable laser is... λ 0, the initial tuning wavelength is λ 1. The termination tuning wavelength is λ 2; Wavelength tuning range Δλ=λ 2 -λ 1 =γΔt ; in Δt For scan time, γ Wavelength scanning speed; The frequency tuning range is Δf=Δλc / λ 0 2 =νΔt ; ν This refers to the frequency scanning speed.

5. The measurement method according to claim 3, characterized in that: The ratio of the output optical power of the first output terminal and the second output terminal of the first coupler is x1:x2, and x1>x2.

6. The measurement method according to claim 3, characterized in that: The phase modulator is a straight waveguide phase modulator, and the initial operating wavelength is... λ 3. The cutoff wavelength is λ 4. The center wavelength is λ 5, λ 3 ≤λ 1 <λ 2 ≤λ 4 and λ 5 =λ 0; The electro-optic bandwidth of the phase modulator is f 1. Half-wave voltage is V π Modulation depth is m=δ / π ,in δ It is the modulation coefficient.

7. The measurement method according to claim 3, characterized in that: The peak value of the modulated electrical signal output by the signal generator V p =mV π modulation depth m>0 The frequency of the modulated electrical signal is f m , 0<f m ≤f 1.

8. The measurement method according to claim 3, characterized in that: To avoid aliasing of interference signals, it is required f τ ≠xf m ,in x It is a positive integer. f m It is the frequency of the modulated electrical signal. f τ =ντ It is the frequency shift amount of the extended optical fiber in the internal modulation frequency shift unit. τ It extends the delay of the optical fiber.

9. The measurement method according to claim 3, characterized in that: The data post-processing unit first segments the time-domain interference signal according to time and wavelength, then corrects the intensity fluctuations during the wavelength scanning process of the light source; subsequently, after performing a Fourier transform, the amplitude ratio of the main peak to the first-order beat frequency sideband of each beat frequency interference signal segment can be obtained in the frequency domain. R And determine the modulation depth m ; The time-domain interference signal output by the first photodetector is A, the time-domain signal output by the second photodetector is B, and the corrected time-domain interference signal A' = A / B.

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