Adjustable optical fiber delay line calibration device and method based on all-fiber interference

Abstract

The invention relates to the technical field of geometric quantity testing, and discloses an adjustable optical fiber delay line calibration device and method based on all-fiber interference, and the device comprises a laser transmitting module, a Michelson interferometer module, an optical modulation and demodulation module, and a metrological characteristic analysis module. The laser emitting module is used for emitting laser; the Michelson interferometer module is used for receiving the laser and then carrying out optical coupling to obtain an interference signal; the optical modulation and demodulation module is used for modulating laser, converting the interference signal into an electric signal and obtaining a phase variation based on the electric signal; and the metrological characteristic analysis module is used for calculating a measurement result from the phase change quantity to the light delay quantity, and completing the calibration of the adjustable optical fiber delay line based on all-fiber interference.

Description

Technical Field

[0001] This invention belongs to the field of geometric measurement technology, and particularly relates to an adjustable fiber delay line calibration device and method based on all-fiber interferometry. Background Technology

[0002] An adjustable fiber optic delay line consists of input and output fiber collimators and a motion mechanism. It projects light into free space and collects it back into the fiber. The optical delay time can be controlled by changing the propagation distance of the light through the motion mechanism. By controlling the relative distance between the input and output optical ports (single-pass) or the distance the light travels through a movable mirror (two-pass), the distance the light travels in free space can be precisely controlled. Essentially, it involves accurately measuring the spatial distance and the displacement within a variable range.

[0003] Currently, the performance testing methods for fiber optic delay lines mainly rely on estimations based on time reflection and displacement comparison. However, due to the low accuracy of absolute time delay measurement, which cannot meet technical requirements, there is still a lack of effective calibration methods. Consequently, traceability technology remains a gap, severely limiting the improvement of the quality and accuracy of fiber optic delay line-related products. This, in turn, makes it difficult to achieve qualitative breakthroughs in many key technologies or key technical indicators used in related industries. Summary of the Invention

[0004] The purpose of this invention is to alleviate the current difficulties in calibrating tunable fiber delay lines. It proposes a calibration device and method for tunable fiber delay lines based on all-fiber interferometry, which can accurately and efficiently calibrate tunable fiber delay lines. To achieve the above objective, this invention provides a calibration device and method for tunable fiber delay lines based on all-fiber interferometry. The device includes: a laser emission module, a Michelson interferometer module, an optical modulation and demodulation module, and a metrological characteristic analysis module. The laser emitting module is used to emit lasers; The Michelson interferometer module is used to receive the laser and then perform optical coupling to obtain an interference signal; The optical modulation and demodulation module is used to convert the interference signal into a sinusoidal modulation interference signal, and the sinusoidal modulation interference signal into an electrical signal, and demodulate the electrical signal to obtain the phase change. The metrological characteristic analysis module is used to calculate the measurement results of the phase change amount to the optical delay amount, and to complete the calibration of the adjustable fiber delay line based on all-fiber interferometry.

[0005] Optionally, the laser emitting module includes a laser and an optical isolator; The Michelson interferometer module includes a 2×2 fiber coupler, a fiber stretcher, a first reflector, an adjustable fiber delay line, and a second reflector. The optical modulation and demodulation module includes a photodetector, an AD module, a DA module, and an FPGA; The first and second ports of the 2×2 fiber coupler are connected to an optical isolator and a photodetector, respectively, and the third and fourth ports are connected to an adjustable fiber delay line and a fiber stretcher, respectively. The AD module of the optical modulation and demodulation module is connected to the photodetector and the FPGA respectively, and the DA module is connected to the modulation input port of the fiber stretcher and the FPGA respectively.

[0006] Optionally, the laser emitting module outputs laser light, which is input from the first port of the 2×2 fiber coupler and splits into two paths, output from the third and fourth ports. After being reflected by the first and second reflectors respectively, the laser light returns to the 2×2 fiber coupler, is re-beamed, and output from the second port to the photodetector.

[0007] Optionally, the fiber stretcher is connected to the second reflector, and the adjustable fiber delay line is connected to the first reflector.

[0008] This invention also discloses a method for calibrating tunable fiber delay lines based on all-fiber interferometry, the method comprising: The laser emits a laser beam, which is then input into a 2×2 fiber coupler after passing through an optical isolator. The beams are split into two optical signals, which are then input into an adjustable fiber delay line and a fiber stretcher for time delay and optical characteristic adjustment, respectively. After the time delay adjustment, the optical signal passes through the first reflector and forms a first optical signal of a specific wavelength. After the optical features are adjusted, the light signal is transformed into a second light signal of a specific wavelength after passing through the second reflecting mirror. The first optical signal returns from the adjustable fiber delay line to the 2×2 fiber coupler, and the second optical signal returns from the fiber stretcher to the 2×2 fiber coupler. The first and second optical signals in the 2×2 fiber coupler are combined to obtain a combined optical signal. The combined optical signal is acquired by a photodetector and converted into an analog electrical signal. The analog electrical signal is then converted into a digital signal by an AD module. The digital signal enters the FPGA and, in conjunction with a pre-set fiber stretching modulation digital signal, is processed to obtain the phase change. The optical delay is then obtained based on the phase change. The fiber stretching modulation digital signal is a pre-set digital signal in the FPGA. It is converted into a fiber stretching modulation analog signal by the DA module, and then controls the piezoelectric ceramic to drive the fiber stretcher to achieve phase modulation of the combined optical signal.

[0009] Optionally, the combined optical signal is an interference signal that needs to be resolved, specifically in the form of: ; in I 0 and I 1 represents the amplitude of the DC and AC terms of the interference signal, respectively. z For phase modulation depth, ω 0 and θ These represent the frequency and phase of the high-frequency modulated signal, respectively. ( t ) is the demodulated signal carrying the displacement information to be measured.

[0010] Optionally, the fiber stretcher is driven by piezoelectric ceramics, which stretches the fiber to change its length, causing a change in optical path and achieving phase modulation.

[0011] Optionally, the optical delay amount The calculations specifically include: ; in, Δ is the laser wavelength in the optical fiber. This is the phase change. It is the speed of light.

[0012] The beneficial effects of this invention are as follows: (1) The present invention uses a Michelson interferometer with an all-fiber structure to convert displacement into delay, which enriches the application field of laser interferometer.

[0013] (2) The present invention uses a phase generation carrier demodulation algorithm based on sinusoidal phase modulation method to demodulate the interference signal, which eliminates the influence of interference fringe contrast on the demodulation result. Moreover, the demodulation algorithm is simple in principle and fast in signal processing.

[0014] (3) The present invention uses a single detector to detect interference signals, which avoids the problem of unequal or non-ideal orthogonal gain of the two detectors in dual detector orthogonal detection, and the phase demodulation is not affected by the DC drift of the circuit.

[0015] (4) The measuring device of the present invention is simple and the measuring method is convenient, and the purpose of calibrating the optical delay of the adjustable fiber delay line is achieved. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic diagram of an adjustable fiber delay line calibration device based on all-fiber interferometry according to an embodiment of the present invention. Figure 2 This is a description of the port of the 2×2 fiber optic coupler in Embodiment 2 of the present invention; Explanation of reference numerals in the attached figures: 1-Laser, 2-Optical isolator, 3-2×2 fiber optic coupler, 4-Adjustable fiber optic delay line, 5-First reflector, 6-Fiber optic stretcher, 7-Second reflector, 8-Photodetector, 9-AD module, 10-DA module, 11-FPGA, 12-Host computer calibration software. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Example 1: like Figure 1 As shown, the present invention discloses an adjustable fiber delay line calibration device based on all-fiber interferometry, comprising: a laser emission module, a Michelson interferometer module, a delay adjustment module, and a metrological characteristic analysis module; Laser emission module, Michelson interferometer module, optical modulation and demodulation module, and metrological characteristic analysis module; The laser emitting module is used to emit laser light; the Michelson interferometer module is used to receive the laser light and perform optical coupling to obtain an interference signal; the optical modulation and demodulation module is used to convert the interference signal into an electrical signal and obtain the phase change based on the electrical signal; the metrological characteristic analysis module is used to calculate the measurement result of the phase change to the optical delay and complete the calibration of the tunable fiber delay line 4 based on all-fiber interference.

[0021] The laser emitting module includes a laser 1 and an optical isolator 2; the Michelson interferometer module includes a 2×2 fiber coupler 3, a fiber stretcher 6, a first reflector 5, an adjustable fiber delay line 4, and a second reflector 7; the optical modulation and demodulation module includes a photodetector 8, an AD module 9, a DA module 10, and an FPGA 11. The first and second ports of the 2×2 fiber coupler 3 of the Michelson interferometer module are connected to the optical isolator 2 of the laser emission module and the photodetector 8 of the optical modulation and demodulation module, respectively; the third and fourth ports of the 2×2 fiber coupler 3 are connected to the input ports of the adjustable fiber delay line 4 and the fiber stretcher 6, respectively; the output port of the adjustable fiber delay line 4 is connected to the first reflector 5, and the output port of the fiber stretcher 6 is connected to the second reflector 7; the AD module 9 of the optical modulation and demodulation module is connected to the photodetector 8 and the FPGA 11, respectively, and the DA module 10 is connected to the modulation input port of the fiber stretcher 6 and the FPGA 11, respectively.

[0022] The optical isolator 2, 2×2 fiber coupler 3, first reflector 5, fiber stretcher 6, second reflector 7, photodetector 8, AD module 9, DA module 10, and FPGA 11 are installed inside a separate instrument. Figure 1 As shown, the laser output port of laser 1 is connected to the optical signal input port of optical isolator 2. Optical isolator 2 is used to protect laser 1 by blocking the return light and inputting the obtained result into 2×2 fiber coupler 3. The first port of 2×2 fiber coupler 3 is connected to the optical signal output port of optical isolator 2. The second port of 2×2 fiber coupler 3 is connected to the input port of photodetector 8. After receiving the laser, photodetector 8 performs photoelectric conversion, converting the obtained interference signal containing sinusoidal phase modulation information into an electrical signal and outputting it to AD module 9 of FPGA 11. The third port of 2×2 fiber coupler 3 is connected to the fiber input port of fiber stretcher 6. Fiber stretcher 6 is used for sinusoidal phase modulation, obtaining a modulated signal by modulating the interference signal. The fourth port of 2×2 fiber coupler 3 is connected to the fiber input port of the adjustable fiber delay line 4 under test. Fiber stretcher 6 is an optical device for realizing phase modulation. Its modulated electrical signal input flyline is connected to the SMA output line of DA module 10 to receive the sinusoidal modulation signal generated by FPGA 11. In the Michelson interferometer, the reference arm consists of an optical fiber stretcher 6 and a first reflector 5, while the measuring arm consists of an adjustable optical fiber delay line 4 and a second reflector 7. The photodetector 8 converts the coupled interference light signal into an electrical signal, which is output to the AD module 9. The phase change is obtained by demodulation via the FPGA 11 and expressed using the following formula: ; in, Δ is the laser wavelength in the optical fiber. This is the phase change. Let be the speed of light. The optical delay can be calculated using the above formula. The measured optical delay is automatically saved to the calibration software.

[0023] Example 2: This invention also discloses a method for calibrating an tunable fiber delay line based on all-fiber interferometry, the method being as follows: Laser 1 emits a laser beam, which passes through optical isolator 2 and is then input into 2×2 fiber coupler 3 to split the laser beam into two optical signals, which are respectively input into adjustable fiber delay line 4 and fiber stretcher 6 for time delay adjustment and optical characteristic adjustment. The time-delayed optical signal is converted into a first optical signal of a specific wavelength after passing through the first reflector 5. The optical signal, after being adjusted by optical features, forms a second optical signal of a specific wavelength after passing through the second reflecting mirror 7; The first optical signal returns from the adjustable fiber delay line 4 to the 2×2 fiber coupler 3, and the second optical signal returns from the fiber stretcher 6 to the 2×2 fiber coupler 3. The first optical signal and the second optical signal in the 2×2 fiber coupler 3 are combined to obtain a combined optical signal. The combined optical signal is acquired by photodetector 8 and converted into analog electrical signal 1. The analog electrical signal 1 is converted into digital signal 1 by AD module 9. The digital signal 1 enters FPGA 11. In FPGA 11, it is combined with a pre-set fiber stretching modulation digital signal and processed to obtain the phase change. The optical delay is obtained based on the phase change. The fiber stretching modulation digital signal is a pre-set digital signal in FPGA11. It is converted into a fiber stretching modulation analog signal by DA module 10, and then controls the piezoelectric ceramic to drive the fiber stretcher 6 to achieve phase modulation of the combined light signal.

[0024] The photodetector 8 acquires the combined optical signal, wherein the combined optical signal includes a phase signal corresponding to the fiber delay and an optical signal formed by fiber stretching modulation. The collected combined optical signal is passed through AD module 9 to obtain an analog electrical signal; The analog electrical signal is input into FPGA11 to calculate the phase change. DA module 10 controls the fiber stretcher 6 to modulate the stretching optical signal by the phase change, thereby obtaining the fiber stretching modulation signal; The combined optical signal is an interference signal that needs to be solved, specifically in the following form: ; in I 0 and I 1 represents the amplitude of the DC and AC terms of the interference signal, respectively. z For phase modulation depth, ω 0 and θ These represent the frequency and phase of the high-frequency modulated signal, respectively. ( t) is the demodulated signal carrying the displacement information to be measured.

[0025] The optical fiber stretching and modulation signal is input into FPGA11 and then into the phase change quantity and the measurement characteristic analysis module to calculate the optical delay, thus completing the calibration of the adjustable optical fiber delay line 4 based on all-fiber interference.

[0026] After connecting laser 1 and adjustable fiber delay line 4 to the corresponding fiber input and output ports of the calibration device, connect them to the host computer calibration software 12 and turn on the device power. Then open the calibration software and set the adjustable fiber delay line 4 to zero.

[0027] According to the calibration requirements, the delay amount is set between the measurement start point and the measurement end point according to the set calibration delay interval, and the measurement begins. When the adjustable fiber delay line 4 under test reaches the set measurement point, the output value of the calibration device and the reading value of the adjustable fiber delay line 4 under test are collected at each measurement point. The designed calibration software system generates a data table, performs metrological characteristic analysis, obtains the calibration result, and completes the calibration.

[0028] In this embodiment, the laser emitted by laser 1 enters the Michelson interferometer. During the process of the adjustable fiber delay line 4 moving under the control of the host computer to generate a time delay, the return reference light and the return measurement light couple to generate an interference signal. The delay modulation and demodulation module converts the interference signal into an electrical signal through the photodetector 8. The AD module 9 collects the signal and demodulates the measured interference signal in the FPGA 11 to obtain the phase change. The calibration module performs phase to optical delay calculation and processing, records the delay measurement results, and performs metrological characteristic analysis in the host computer software to achieve calibration of the adjustable fiber delay line 4.

[0029] Furthermore, the all-fiber Michelson interferometer module includes an optical isolator 2, a 2×2 fiber coupler 3, a fiber stretcher 6, a first reflector 5, an adjustable fiber delay line 4, and a second reflector 7; wherein, the measurement optical path is laser 1—optical isolator 2—2×2 fiber coupler 3—adjustable fiber delay line 4—first reflector 5; the reference optical path is laser 1—optical isolator 2—2×2 fiber coupler 3—fiber stretcher 6—second reflector 7.

[0030] Furthermore, the delay modulation and demodulation module includes a photodetector 8, an FPGA 11, and a host computer. The photodetector 8 employs an avalanche diode capable of receiving weak light signals to receive the interference light signal generated by the interference module and convert it into an electrical signal.

[0031] Furthermore, in the delay modulation and demodulation module, the FPGA11 receives the interference signal converted by the photodetector 8 and performs signal processing, while working with the DA module 10 to generate the modulation signal of the fiber stretcher 6.

[0032] Furthermore, the delay modulation and demodulation module adopts the phase generation carrier PGC demodulation algorithm, which eliminates the influence of interference fringe contrast on the demodulation result. Moreover, the demodulation algorithm has a simple principle and high real-time signal processing performance.

[0033] Furthermore, during the delay process of the adjustable fiber delay line 4, the interference signal formed by the reference optical path and the measurement optical path is modulated and demodulated by the delay amount module to obtain the phase change amount, and the corresponding optical delay amount is calculated from this change amount.

[0034] Furthermore, apart from the FPGA11 and the host computer, the entire system is connected via optical fiber, and the interferometers of each component are connected using FC / APC optical fiber connectors.

[0035] Furthermore, the host computer calibration software 12 includes the calculation and processing of phase to optical delay, i.e. It records the results of delay measurements and performs analysis of metrological characteristics, including indication error, hysteresis error, and repeatability.

[0036] Furthermore, a complete calibration process mainly includes the following steps: Connect the laser 1 and the adjustable fiber delay line 4 to the corresponding fiber port of the calibration device. After the connection is completed and the power is turned on, the host computer performs operations such as returning the adjustable fiber delay line 4 to zero.

[0037] According to the calibration requirements, the delay amount is set between the measurement start point and the measurement end point according to the set calibration delay interval, and the measurement is started. When the adjustable fiber delay line 4 under test reaches the set measurement point, the output value of the calibration device and the output value of the adjustable fiber delay line 4 under test are collected by the adjustable fiber delay line 4 calibration device. The collected data is processed to complete the calibration of the adjustable fiber delay line 4.

[0038] In this embodiment, an optical fiber stretcher 6 is installed to change accordingly when the optical fiber delay line changes. Without the optical fiber stretcher 6 of the present invention, the 2×2 optical fiber coupler 3 would only receive the signal returned by the optical fiber delay line through the reflector. The signal obtained after the signal enters the photodetector 8 is not accurate for inferring the optical fiber delay line.

[0039] With the addition of the fiber optic stretcher 6, the photodetector 8 receives a real-time signal due to the real-time change of the simulated fiber delay line caused by the fiber optic stretcher 6. When the signal is processed by the photodetector 8, the real-time phase change is obtained, which is significantly more accurate than when the fiber optic stretcher 6 is not used.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An all-fiber interferometric tunable fiber delay line calibration apparatus, characterized in that, The device comprises: a laser emission module, a Michelson interferometer module, an optical modulation and demodulation module, and a metrological characteristic analysis module; the laser emission module is used for emitting laser; the Michelson interferometer module is used for receiving the laser and then performing optical coupling to obtain an interference signal; the optical modulation and demodulation module is used for converting the interference signal into a sinusoidal modulation interference signal, converting the sinusoidal modulation interference signal into an electrical signal, demodulating the electrical signal to obtain a phase change amount; the metrological characteristic analysis module is used for calculating a measurement result of the phase change amount to an optical delay amount, and completing adjustable optical fiber delay line calibration based on all-optical fiber interference.

2. The all-fiber interferometric based tunable fiber delay line calibration apparatus of claim 1, wherein, the laser emission module comprises a laser and an optical isolator; the Michelson interferometer module comprises a 2*2 optical fiber coupler, an optical fiber stretcher, a first mirror, an adjustable optical fiber delay line, and a second mirror; the optical modulation and demodulation module comprises a photodetector, an AD module, a DA module, and an FPGA; the first and second ports of the 2*2 optical fiber coupler are connected with the optical isolator and the photodetector respectively, and the third and fourth ports are connected with the adjustable optical fiber delay line and the optical fiber stretcher respectively; the AD module of the optical modulation and demodulation module is connected with the photodetector and the FPGA respectively, and the DA module is connected with the fiber stretcher modulation input port and the FPGA respectively.

3. The all-fiber interferometric based tunable fiber delay line calibration apparatus of claim 2, wherein, the laser emission module outputs laser, which is input from the first port of the 2*2 optical fiber coupler, then is divided into two paths and is output from the third and fourth ports, is reflected by the first and second mirrors respectively, returns to the 2*2 optical fiber coupler, and is output from the second port to the photodetector after recombining.

4. The all-fiber interferometric based tunable fiber delay line calibration apparatus of claim 3, wherein, the optical fiber stretcher is connected with the second mirror, and the adjustable optical fiber delay line is connected with the first mirror.

5. A method for calibrating a tunable fiber delay line based on all-fiber interferometry, the method being implemented by means of the device according to any one of claims 1-4, characterized in that the method comprises the steps of: the laser emits laser and inputs the laser into the 2*2 optical fiber coupler after passing through the optical isolator, and the laser is divided into two optical signals which are input into the adjustable optical fiber delay line and the optical fiber stretcher respectively to adjust the time delay and the optical characteristics; the optical signal after the time delay adjustment forms a first optical signal of a specific wavelength after passing through the first mirror; the optical signal after the optical characteristic adjustment forms a second optical signal of a specific wavelength after passing through the second mirror; the first optical signal returns to the 2*2 optical fiber coupler from the adjustable optical fiber delay line, and the second optical signal returns to the 2*2 optical fiber coupler from the optical fiber stretcher, the first optical signal and the second optical signal in the 2*2 optical fiber coupler are combined to obtain a combined optical signal; the combined optical signal is collected by the photodetector and is converted into an analog electrical signal, the analog electrical signal is converted into a digital signal by the AD module, and the digital signal enters the FPGA, in which the phase change amount is obtained by solving the pre-set optical fiber stretching modulation digital signal, and the optical delay amount is obtained based on the phase change amount; the optical fiber stretching modulation digital signal is a pre-set digital signal in the FPGA, which is converted into an optical fiber stretching modulation analog signal by the DA module, and then controls the piezoelectric ceramic to drive the optical fiber stretcher to act, so as to realize the phase modulation of the combined optical signal. the combined optical signal is an interference signal to be solved, and the specific form is:

6. The all-fiber interferometric based tunable fiber delay line calibration method of claim 5, wherein, ω ； wherein I 0 and I 1 are the amplitudes of the direct current and alternating current terms of the interference signal, respectively, z is the phase modulation depth, θ 0 and ​ are the frequency and phase of the high frequency modulation signal, respectively, t is the signal to be demodulated carrying the displacement information to be measured.​ 7. The all-fiber interferometric based tunable fiber delay line calibration method of claim 5, wherein, The fiber stretcher is driven by a piezoelectric ceramic, changes the length of the fiber by stretching the fiber, causes the change of the optical path, and realizes the phase modulation.

8. The all-fiber interferometric based tunable fiber delay line calibration method of claim 5, wherein, The light delay amount The calculation content specifically includes: ； wherein, is the laser wavelength in the optical fiber, Δ is the phase change amount, is the speed of light.

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