CN116222404A - Sensing system for measuring difference between two arms of MZI and measuring method for difference between two arms of MZI - Google Patents
Sensing system for measuring difference between two arms of MZI and measuring method for difference between two arms of MZI Download PDFInfo
- Publication number
- CN116222404A CN116222404A CN202310003508.6A CN202310003508A CN116222404A CN 116222404 A CN116222404 A CN 116222404A CN 202310003508 A CN202310003508 A CN 202310003508A CN 116222404 A CN116222404 A CN 116222404A
- Authority
- CN
- China
- Prior art keywords
- mzi
- frequency
- module
- arms
- difference
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/14—Measuring arrangements characterised by the use of optical techniques for measuring distance or clearance between spaced objects or spaced apertures
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/02—Testing optical properties
- G01M11/0242—Testing optical properties by measuring geometrical properties or aberrations
- G01M11/0271—Testing optical properties by measuring geometrical properties or aberrations by using interferometric methods
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Geometry (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
The invention relates to a sensing system for measuring the difference between two arms of an MZI and a measuring method for the difference between two arms of the MZI, wherein the system comprises a narrow linewidth laser source module, a phase modulator module, a sensing module, a coherent receiving module, a photoelectric conversion module and a signal processing module which are sequentially connected, the method comprises the steps of modulating a single-frequency laser through a phase modulator, gradually increasing the modulation frequency from 0, shunting the modulated signal through an optical fiber coupler, then entering an unbalanced MZI to be measured, generating beat frequency optical signals after the two paths of laser output by the unbalanced MZI to be measured pass through the other optical fiber coupler, converting the beat frequency optical signals into electric signals through the photoelectric conversion module, performing digital processing after sampling, and recording the modulation signal frequency when the electric domain obtains a direct current signal for the first time as f m By the formula
And calculating to obtain the difference of the arm lengths of the two arms of the unbalanced MZI to be measured. The invention has high precision and is not limited by the range of the nonlinear frequency sweeping device and the external frequency sweeping device of the laser.
Description
Technical Field
The invention relates to a system and a method for measuring the difference between two arms of a MZI by single-frequency laser, belonging to the technical field of optical fiber sensors.
Background
Mach-Zehnder interferometers (Mach-Zehnder interferometer, MZIs) are a type of dual beam interferometer, which may also be referred to as phase modulated fiber sensors. The principle of the MZI is: coherent light emitted by the laser is respectively sent into two optical fibers, one is a detection arm, and the other is a reference arm. The two laser beams output from the two optical fibers are overlapped to generate interference effect, and the interference effect can be used for observing the relative phase shift change generated by different paths and the medium after the light beams emitted from the independent light sources are divided into two light beams. In the fields of distributed optical fiber acoustic wave sensors (Distributed Fiber-optic Acoustic Sensor, DAS), laser radars (Laser radars) and the like, it is important to accurately measure the distance between two points, and for mach-zehnder interferometer structures frequently used in these systems, unbalanced two-arm differences of the structures can be accurately and conveniently measured, so that the requirements are high in practical application scenes.
The current mainstream method for measuring the difference between two arms of the MZI is optical frequency domain reflectometer (Optical Frequency Domain Reflectometry, OFDR) technology, and the basic principle is as follows: the laser generates linear sweep frequency continuous light with high coherence, then enters the optical fiber coupler to be divided into two parts, one part is used as detection light to be emitted into the optical fiber to be detected, the other part is used as local reference light to enter the reference optical fiber, and the two light beams enter the optical fiber coupler again to generate interference phenomenon and then are received by the photoelectric balance detector to be converted into electric signals. Wherein the ideal electric field expression of the reference light is E 1 (t)＝E 1 expj(ω c t+2πf 0 t+πκt 2 ) Where κ is the sweep rate and the ideal electric field expression for the probe light is E 2 (t)＝E 2 expj{ω c (t-τ)+2πf 0 (t-τ)+πκ(t-τ) 2 And the current signal output by the local reference light and the detection light after beat frequency and photoelectric conversion is zi (t) =Asin < -2 pi kappa tau t+pi kappa tau 2 -2πf 0 τ-ω c τ]From this equation, it can be seen that in an ideal case, the beat frequency signals of the two beams of light are single-frequency sinusoidal signals with the frequency f=kτ, and the two-arm difference can be obtained by calculating the frequency obtained by fourier transform of the signals. However, in a practical system, due to the nonlinearity of the sweep frequency of the laser, phase noise and the like, the beat frequency signal obtained in practice is not a single frequency signal, but is a signal which is widened in frequency spectrum, which eventually results in that the OFDR cannot accurately detect the frequency of the signal, and thus the resolution of the two-arm difference measurement is seriously deteriorated. For this situation, the processing modes are generally divided into two types, one type is to use a laser with better linearity to sweep frequency or use an external sweep frequency device, and the devices generally have smaller sweep frequency range and high cost, and the resolution and the sweep frequency range are in a mutually restricted relation; another approach is to add an auxiliary interferometer to compensate for the desired better single frequency signal, but at the same time add complexity to the system. It can be seen that device performance and system complexity, etc., limit the accuracy of such a critical technique.
Disclosure of Invention
The invention aims to provide a sensing system for measuring the difference between two arms of an MZI and a measuring method for measuring the difference between two arms of the MZI, which have high precision and are not limited by the range of the nonlinear frequency sweeping device and the range of the external frequency sweeping device of a laser.
The main technical scheme of the invention is as follows:
the sensing system for measuring the two-arm difference of the MZI comprises a narrow-linewidth laser source module, a phase modulator module, a sensing module, a coherent receiving module, a photoelectric conversion module and a signal processing module which are sequentially connected, wherein the narrow-linewidth laser source module is used for generating ultra-narrow linewidth single-frequency laser, the phase modulator module is used for modulating the ultra-narrow linewidth single-frequency laser, the sensing module is an unbalanced MZI structure to be measured, and the coherent receiving module is used for receiving two paths of laser output by the unbalanced MZI structure to be measured and generating beat frequency optical signals; the photoelectric conversion module is used for converting beat frequency optical signals into electric signals, and the signal processing module is used for carrying out analog-to-digital conversion on the electric signals and processing the converted data.
The sensing module comprises a 50:50 optical fiber coupler and two common single-mode communication optical fibers.
The narrow linewidth laser source module adopts a narrow linewidth fiber laser.
The phase modulator module comprises a radio frequency signal generator and a phase modulator, wherein the radio frequency signal generator sends a sweep frequency signal to the phase modulator to carry out phase modulation of different frequencies continuously.
The coherent receiving module adopts a 50:50 optical fiber coupler.
The photoelectric conversion module adopts a balance detector.
A measuring method of two-arm difference of MZI, let single frequency laser go on sinusoidal signal modulation through a phase modulator, modulation frequency increases gradually from 0, enter to-be-measured unbalanced MZI after the signal after modulating is shunted through a fiber coupler, produce beat frequency optical signal after two-way laser that the unbalanced MZI to-be-measured outputs pass another fiber coupler, convert the said beat frequency optical signal into the electrical signal with the photoelectric conversion module, sample at this moment and carry on the digital processing; when the delay of the split laser in two arms of the unbalanced MZI to be measured is exactly equal to the integral multiple of the period of the modulation signal, two beams of coherent constructive laser which are completely matched are obtained, the signal obtained by the electric domain is a direct current signal, and the frequency of the modulation signal when the electric domain obtains the direct current signal for the first time is recorded as f m The two arm length difference of the unbalanced MZI to be measured is
Where is the propagation speed of light in the fiber.
The sensing system for measuring the difference between two arms of the MZI is adopted to carry out measurement, the phase modulator module adopts a radio frequency signal generator and a phase modulator which are connected, an output signal is generated by using an FPGA or in labview, and the output signal is introduced into the radio frequency signal generator.
The frequency step of the phase modulator is set according to the required resolution.
The beneficial effects of the invention are as follows:
the invention does not depend on laser sweep, but uses sine signals with gradually increased modulation frequency to modulate and replace single-frequency laser, thus being capable of immunizing sweep nonlinearity, phase noise and the like, and because the modulation is performed in an electric domain, the invention can accurately control, so that the measurement result has high precision and reliability, and the invention can simultaneously obtain the advantages of convenient measurement, high precision, low cost and the like.
Drawings
FIG. 1 is a schematic diagram of the sensing system for measuring the difference between two arms of a MZI according to the present invention;
FIG. 2 is a time-frequency spectrum diagram of a radio frequency signal from a radio frequency signal generator;
fig. 3 is a graph showing the variation of the root mean square value of the ac component of the detection result collected by the oscilloscope with the modulation frequency.
Reference numerals: 1. a narrow linewidth fiber laser; 2. a radio frequency signal generator; 3. a phase modulator; 4. a 50:50 fiber coupler; 5. a sensing optical fiber; 6. a balance detector; 7. a data acquisition card; 8. a data processor.
Detailed Description
The invention discloses a sensing system for measuring the difference between two arms of a MZI, which comprises a narrow linewidth laser source module, a phase modulator module, a sensing module, a coherent receiving module, a photoelectric conversion module and a signal processing module which are connected in sequence. The phase modulator module is used for modulating the signal of the ultra-narrow linewidth single-frequency laser, the sensing module is an unbalanced MZI structure to be tested, and the coherent receiving module is used for receiving two paths of laser output by the unbalanced MZI structure to be tested and generating beat frequency optical signals; the photoelectric conversion module is used for converting beat frequency optical signals into electric signals, and the signal processing module is used for carrying out analog-to-digital conversion on the electric signals and processing the converted data.
As shown in fig. 1, the sensing module includes one 50:50 fiber coupler 4 and two common single-mode communication fibers (collectively referred to as sensing fibers 5).
The narrow linewidth laser source module adopts a narrow linewidth optical fiber laser 1, and the center frequency of single-frequency laser emitted by the narrow linewidth optical fiber laser source module is f c 。
The phase modulator module comprises a radio frequency signal generator 2 and a phase modulator 3, the radio frequency signal generator sending a sweep signal (see fig. 2) to the phase modulator for phase modulation of successively different frequencies. The frequency step of the phase modulator can be set according to the required resolution, so that the full-automatic measurement of the difference between the two arms of the MZI is realized.
The coherent receiving module adopts a 50:50 optical fiber coupler 4.
The photoelectric conversion module adopts a balance detector 6. The balance detector 6 will extract the ac component alone.
The signal processing module comprises a data acquisition card 7 and a data processor 8 which are connected, the sampling rate of the data acquisition card is fs, and the data processor can adopt an FPGA, a CPU or a GPU.
The invention also discloses a method for measuring the difference between the two arms of the MZI, which comprises the following steps: the single-frequency laser is subjected to sinusoidal signal modulation by a phase modulator, the modulation frequency is gradually increased from 0, as shown in fig. 2, the smaller the step of the frequency increase is theoretically, but the smaller the step is, the longer the measurement time is, and in practical use, the adjustment can be performed according to the distance resolution required to be obtained. The modulated signals are branched through one optical fiber coupler and then enter an unbalanced MZI to be detected, two paths of laser output by the unbalanced MZI to be detected generate beat frequency optical signals after passing through the other optical fiber coupler, the beat frequency optical signals are converted into electric signals by using a photoelectric conversion module, at the moment, digital processing is carried out after sampling, and Fourier transformation is carried out, so that signal power corresponding to the modulation frequency is obtained; the modulation frequency is changed to obtain a variation curve of the signal power with the modulation frequency, as shown in fig. 3. Since the photoelectric conversion module extracts the ac component alone, the curve shown in fig. 3 is mainly the ac component, and contains no or only a small amount of dc component.
When the delay of the split laser in the two arms of the unbalanced MZI to be measured is exactly equal to the integral multiple of the period of the modulation signal, two beams of coherent constructive laser beams which are completely matched are obtained, the signal obtained by the electric domain is a direct current signal, and the signal power has the minimum value at the moment, as shown in the concave parts near 20MHz and 40MHz in figure 3. The frequency of the modulated signal when the DC signal is obtained for the first time in the electric domain is denoted as f m The two arm length difference of the unbalanced MZI to be measured is
Where v is the propagation speed of light in the fiber. In the present embodiment, according to the data of fig. 3, the frequency period of the modulated signal when the dc signal is obtained in the electric domain is f m =19.70 MHz, and the difference between the arm lengths of the two arms of the unbalanced MZI to be measured can be calculated as
When the delay of the split laser in the two arms of the unbalanced MZI to be measured is not equal to the integral multiple of the period of the modulation signal, the signal obtained by the electric domain contains an alternating current signal with strong frequency components of the modulation signal.
Continuing to increase the modulation frequency of the phase modulator, the signal obtained in the electric domain is periodically changed into a direct current signal, and the period is f m . Therefore, by increasing the frequency of the phase modulator, more modulation frequency values corresponding to the DC signal can be obtained, which is equal to the obtained multiple f m Any one of the different integer values is directly divided by the corresponding multiple to obtain f m The value of f corresponding to a plurality of different modulation frequencies is obtained firstly according to the same method m Recalculating f m Compared with the average value of the direct current signal obtained for the first time by directly taking the modulation frequency value corresponding to the direct current signal as f m The precision is higher.
The implementation of the method for measuring the difference between two arms of the MZI preferably adopts the sensing system for measuring the difference between two arms of the MZI.
Claims (9)
1. A sensing system for measuring a difference between two arms of a MZI, comprising: the device comprises a narrow linewidth laser source module, a phase modulator module, a sensing module, a coherent receiving module, a photoelectric conversion module and a signal processing module which are sequentially connected, wherein the narrow linewidth laser source module is used for generating ultra-narrow linewidth single-frequency laser, the phase modulator module is used for modulating the ultra-narrow linewidth single-frequency laser, the sensing module is an unbalanced MZI structure to be tested, and the coherent receiving module is used for receiving two paths of laser output by the unbalanced MZI structure to be tested and generating beat frequency optical signals; the photoelectric conversion module is used for converting beat frequency optical signals into electric signals, and the signal processing module is used for carrying out analog-to-digital conversion on the electric signals and processing the converted data.
2. The sensing system for measuring a difference between two arms of a MZI of claim 1, wherein: the sensing module comprises a 50:50 optical fiber coupler and two common single-mode communication optical fibers.
3. The sensing system for measuring a difference between two arms of a MZI of claim 1, wherein: the narrow linewidth laser source module adopts a narrow linewidth fiber laser.
4. The sensing system for measuring a difference between two arms of a MZI of claim 1, wherein: the phase modulator module comprises a radio frequency signal generator and a phase modulator, wherein the radio frequency signal generator sends a sweep frequency signal to the phase modulator to carry out phase modulation of different frequencies continuously.
5. The sensing system for measuring a difference between two arms of a MZI of claim 1, wherein: the coherent receiving module adopts a 50:50 optical fiber coupler.
6. The sensing system for measuring a difference between two arms of a MZI of claim 1, wherein: the photoelectric conversion module adopts a balance detector.
7. A method for measuring the difference between two arms of an MZI is characterized by comprising the following steps: sinusoidal signal modulation is carried out on single-frequency laser through a phase modulator, the modulation frequency is gradually increased from 0, the modulated signal enters an unbalanced MZI to be detected after being shunted through an optical fiber coupler, beat frequency optical signals are generated after two paths of laser output by the unbalanced MZI to be detected pass through the other optical fiber coupler, the beat frequency optical signals are converted into electric signals through a photoelectric conversion module, and digital processing is carried out after sampling; when the delay of the split laser in two arms of the unbalanced MZI to be measured is exactly equal to the integral multiple of the period of the modulation signal, two beams of coherent constructive laser which are completely matched are obtained, the signal obtained by the electric domain is a direct current signal, and the frequency of the modulation signal when the electric domain obtains the direct current signal for the first time is recorded as f m The two arm length difference of the unbalanced MZI to be measured is
Where v is the propagation speed of light in the fiber.
8. The method for measuring the difference between two arms of the MZI according to claim 7, wherein: the frequency step of the phase modulator is set according to the required resolution.
9. The method for measuring the difference between two arms of the MZI according to claim 7 or 8, wherein: continuing to increase the modulation frequency of the phase modulator, the signal obtained in the electric domain is periodically changed into a direct current signal, and the period is f m Further increasing f by increasing the frequency of the phase modulator m Is used for measuring the precision of the test piece.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310003508.6A CN116222404A (en) | 2023-01-03 | 2023-01-03 | Sensing system for measuring difference between two arms of MZI and measuring method for difference between two arms of MZI |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310003508.6A CN116222404A (en) | 2023-01-03 | 2023-01-03 | Sensing system for measuring difference between two arms of MZI and measuring method for difference between two arms of MZI |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116222404A true CN116222404A (en) | 2023-06-06 |
Family
ID=86583577
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310003508.6A Pending CN116222404A (en) | 2023-01-03 | 2023-01-03 | Sensing system for measuring difference between two arms of MZI and measuring method for difference between two arms of MZI |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN116222404A (en) |
-
2023
- 2023-01-03 CN CN202310003508.6A patent/CN116222404A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP6698164B2 (en) | Optical frequency domain reflection method and system based on frequency synthesis | |
| JP3667132B2 (en) | Brillouin gain spectrum measurement method and apparatus | |
| CN108801153B (en) | Optical fiber length measuring method and measuring device | |
| CN106643522A (en) | Optical-fiber low-coherence interference displacement demodulation device and method based on photoelectric oscillator | |
| JP6893137B2 (en) | Optical fiber vibration detection sensor and its method | |
| CN108827601A (en) | A kind of measuring device of fibre optic interferometer arm length difference | |
| WO2015176362A1 (en) | Light pulse compression reflector apparatus | |
| CN109547098B (en) | Microwave photon time delay measurement calibrating device | |
| CN110285843B (en) | Large-amplitude signal distributed weak grating array sensing system and demodulation method | |
| CN112129491A (en) | Optical fiber time delay measuring method and device based on single-optical-frequency comb interference | |
| CN111912516A (en) | Phase-synchronized optical fiber distributed vibration measurement device, driver and method | |
| JP3883458B2 (en) | Reflective Brillouin spectral distribution measuring method and apparatus | |
| CN116592986A (en) | Optical fiber distributed acoustic wave sensing device with adjustable dynamic strain range | |
| Sun et al. | Dynamic phase extraction in an ameliorated distributed vibration sensor using a highly stable homodyne detection | |
| CN110375779B (en) | Device and method for improving OFDR frequency domain sampling rate | |
| CN113340571A (en) | Optical time delay measuring method and device based on optical vector analysis | |
| CN108007307B (en) | Optical fiber measuring method and measuring device | |
| CN113607277B (en) | Demodulation method of narrow linewidth laser linewidth measurement system | |
| CN115900787A (en) | Method and system for realizing spectral domain reflectometer | |
| Soriano-Amat et al. | Millimetric spatial resolution time-expanded ϕ-OTDR | |
| CN112284511B (en) | Dynamic and static combined measurement distributed optical fiber sensing system | |
| CN213842395U (en) | Dynamic and static combined measurement distributed optical fiber sensing system | |
| CN213455339U (en) | Device for measuring optical fiber length | |
| Zhou et al. | Development of a variable and broad speed range all-fiber laser vibration measurement technology | |
| CN212254333U (en) | Phase synchronization optical fiber distributed vibration measuring device and driver |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |