CN109029271B - DFB array sweep light source optical fiber frequency domain interference ranging system and method - Google Patents
DFB array sweep light source optical fiber frequency domain interference ranging system and method Download PDFInfo
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Abstract
The invention belongs to a laser interference distance measurement technology, and aims to improve the contrast ratio of interference signals to the greatest extent and simultaneously have a wide sweep frequency range and good coherence, in the invention, a fiber frequency domain interference distance measurement system and a fiber frequency domain interference distance measurement method for a DFB array sweep frequency light source are characterized in that sweep frequency laser generated by the DFB array sweep frequency light source firstly enters a broadband fiber coupler with a splitting ratio of 20:80, and 20% of split light enters a reference Mach Zehnder interferometer MZI; the other 80% of light enters a reference arm in the two interference arms through a broadband optical fiber coupler with the splitting ratio of 10: 90; and the other 90% of the swept laser enters the test arm, the test arm adopts a three-terminal circulator structure, the swept laser enters the optical fiber probe from the three-terminal circulator and then is emitted to the surface of the workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the same optical fiber probe, and then enters the coupler for beam combination from the three-terminal circulator and interferes with reference light. The invention is mainly applied to laser interference distance measurement occasions.
Description
Technical Field
The invention belongs to the technical field of laser interference distance measurement, and particularly relates to a frequency domain interference gap measurement technology of a sweep frequency light source optical fiber. In particular to a fiber frequency domain interference ranging system based on a DFB array sweep light source.
Background
Many industrial, scientific and military systems require reliable high resolution methods to measure distance, while at the same time having stringent sensor size, power and complexity requirements. For example, clearance measurement in heavy equipment such as engines and turbines is widely used in national production and defense as one of the key parameters affecting the operational performance of large-scale equipment. As a core component of a thermal power generating unit, the axial clearance of a steam turbine is one of key indexes for improving the thermal performance of a supercritical steam turbine and influencing the operation safety of the supercritical steam turbine. The moving blade is used as a core acting element of the engine, and the running state parameters of the moving blade, particularly the change of the blade tip clearance of the moving blade directly influence the running state, the working efficiency and the safety performance of the whole engine system. In addition, airplanes and other heavy equipment are developing towards high-intelligence and high-performance manufacturing, and high requirements are placed on assembly of moving parts, effective control of axial distance between a rotor and a stator and the like, so that assembly standards and operation safety are guaranteed.
In recent years, a non-contact optical method is vigorously developed at home and abroad to measure the distance, and the sensor is arranged on the casing. The method mainly comprises the following steps: optical Time Domain Reflectometer (OTDR), Optical Frequency Domain Reflectometer (OFDR), white light interferometry, dual-frequency heterodyne interferometry, and swept-OCT. Optical Time Domain Reflectometry (OTDR) is widely used to locate breakpoints and other anomalies in fiber optic lines and networks. The method is simple and easy to implement, but the distributed sensing sensitivity is low, the measurement error is large, the general measurement range is km level, and the measurement spatial resolution of m level can be achieved. An optical frequency reflectometer (OFDR) realizes high-precision measurement based on an optical heterodyne detection method and light source linear frequency modulation. The method utilizes the frequency mixing of coherent light emitted by a linear frequency modulation light source to calculate the optical path difference. The optical fiber micro-nano-strip micro. The double-frequency heterodyne interferometry realizes large-size absolute distance measurement by using a multi-wavelength interferometry, has the advantages of insensitivity to light intensity fluctuation, high response speed, high signal-to-noise ratio and the like, is easy to realize high-precision measurement, and has the range of 100mm, the resolution ratio higher than 1nm and the precision better than 10 nm. The existing problem is that the method fundamentally depends on the frequency-stabilized laser with moderate spectral line distribution; different frequency stabilized lasers are suitable for different measuring ranges and precision requirements. The white light interference method has the advantages of high precision, quick detection and the like, but the measurement range can only reach 1um to 50 um. The method is suitable for measuring the absolute distance of an object with micron-scale, plane higher optical reflectivity and specular reflection or diffuse reflection. The principle of the frequency sweep OCT method is similar to that of an optical frequency domain reflectometer, and the method is based on the theory of optical low coherence interference and Fourier transform, is mainly applied to the mm-level detection range, and can reach the um-level measurement precision.
However, the optical measurement method mainly stays in the laboratory stage at present, and is rarely developed to be suitable for industrial field online detection. At present, a mature method mainly aims at a measuring range within 5mm, but few researches are carried out on gap measurement of a measuring range of about 10mm, and technical support is lacked. How to realize the precise field measurement of the medium clearance of about 10mm under the special operating environment has great significance for the field dynamic test technical blockade for breaking the foreign clearance.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a novel fiber frequency domain interference distance measurement method and device, which can improve the contrast of interference signals to the greatest extent, simultaneously have wide sweep frequency range and good coherence, and make equipment more compact and miniaturized. According to the technical scheme, sweep laser generated by a DFB array sweep light source enters a broadband fiber coupler with a light splitting ratio of 20:80, 20% of split light enters a reference Mach Zehnder interferometer MZI, interference signals collected by a photodiode PD2 of the MZI are reference clock signals with equal wave numbers, and the reference clock signals are used for signal reconstruction of a main interferometer at a later stage; the other 80% of light enters a reference arm of the two interference arms through a broadband optical fiber coupler with the splitting ratio of 10:90, the balance of the interference arms is adjusted by utilizing an optical fiber delay line with an electric displacement table, and meanwhile, the light intensity of the two interference lights is matched on line; the other 90% of the swept laser enters a test arm, the test arm adopts a three-terminal circulator structure, the swept laser enters the optical fiber probe from the three-terminal circulator and then is emitted to the surface of a workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the same optical fiber probe, and then enters a coupler for beam combination from the three-terminal circulator and interferes with reference light; the interference light is subjected to photoelectric conversion by an indium gallium arsenide InGaAs PIN type photoelectric detector, amplified by an amplifier and a filter, filtered and collected by an ADC (analog to digital converter), wherein a clock signal collected by the ADC is generated by a trigger signal clock of a swept-frequency light source, and the interference signal collected by a PD2 of a reference MZI interferometer is used as a clock signal for signal reconstruction.
The system also comprises a computer, which is used for carrying out fast Fourier transform on the obtained data to obtain a distance value to be measured.
The sweep frequency light source of the DFB array is a laser light source of a C-waveband DFB array module, a current control circuit board formed by an FPGA provides current for each DFB array module to scan, and the DFB array modules are connected to generate equivalent scanning by using the whole bandwidth of the array; the FPGA generates a PWM (pulse width modulation) error signal by comparing a reference clock with a signal obtained after MZI interference signal zero-crossing sampling, provides scanning current, and simultaneously outputs a TTL (transistor-transistor logic) trigger level signal according to the start of each current scanning for triggering a clock signal for data acquisition.
The optical fiber probe adopts a self-focusing lens, and the self-focusing lens is plated with an anti-reflection film, so that the influence of end face reflected light on interference is avoided; the self-focusing lens adopts a short focal length design.
The fiber frequency domain interference distance measurement method of the DFB array sweep light source comprises the steps that sweep laser generated by the DFB array sweep light source is sent into a broadband fiber coupler with the light splitting ratio of 20:80, 20% of split light enters a reference Mach-Zehnder interferometer MZI, interference signals collected by a photodiode PD2 of the MZI are reference clock signals with equal wave numbers and are used for signal reconstruction of a main interferometer at the later stage; the other 80% of light enters a reference arm of the two interference arms through a broadband optical fiber coupler with the splitting ratio of 10:90, the balance of the interference arms is adjusted by utilizing an optical fiber delay line with an electric displacement table, and meanwhile, the light intensity of the two interference lights is matched on line; the other 90% of the swept laser enters a test arm, the test arm adopts a three-terminal circulator structure, the swept laser enters the optical fiber probe from the three-terminal circulator and then is emitted to the surface of a workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the same optical fiber probe, and then enters a coupler for beam combination from the three-terminal circulator and interferes with reference light; the interference light is subjected to photoelectric conversion by an indium gallium arsenide InGaAs PIN type photoelectric detector, amplified by an amplifier and a filter, filtered and collected by an ADC (analog to digital converter), wherein a clock signal collected by the ADC is generated by a trigger signal clock of a swept-frequency light source, and the interference signal collected by a PD2 of a reference MZI interferometer is used as a clock signal for signal reconstruction.
The collected data are processed as follows: the distance between the end face of the optical fiber probe and the surface of the workpiece to be measured is d, the reflected light of the surface of the workpiece collected by the probe interferes with the reference light, and the interference formula is as follows:
The invention has the characteristics and beneficial effects that:
(1) the laser overcomes the defects that the conventional wavelength scanning laser sources such as micro-electro-mechanical systems (MEMS) external cavity lasers and electrically tunable semiconductor lasers have short coherence length (generally tens of micrometers), and when the ranging distance exceeds the coherence length, the interference signals are rapidly degraded. A sweep frequency light source based on a DFB array is adopted to replace an external cavity scanning type sweep frequency light source, and meanwhile, the sweep frequency light source has a wide sweep frequency range and good coherence, and the influence of interference signal degradation on measurement accuracy is avoided.
(2) The defect that the light intensity matching of the two interference arms cannot be adjusted on line under the field measurement condition in the design of the common-path interferometer is overcome, the light intensity of the two interference lights can be matched on line by adopting a non-common-path model, the actual situation that the surface reflectivity of a measured workpiece is different is adapted, and the contrast of interference signals is improved to the maximum extent.
(3) The defect that the efficiency of collecting the back scattering light is low when parallel light of a self-focusing lens of the optical fiber probe is irradiated to the surface of an object to be measured is overcome, and the light spot is more intensively irradiated to the surface to be measured by adopting the design of the short focal length of the self-focusing lens, so that the collection efficiency of the reflected light to be measured is improved.
(4) The device overcomes the defects of complex device for receiving interference signals and large volume, adopts a single photoelectric detector with wide bandwidth, greatly simplifies the device for receiving interference signals, and has more compact and miniaturized equipment and reduced cost.
Description of the drawings:
FIG. 1 shows a block diagram of a fiber frequency domain interference ranging system based on a DFB array swept-source.
Fig. 2 shows a functional block diagram of a DFB array swept source.
Fig. 3 shows a schematic design of a fiber optic self-focusing lens probe.
In fig. 1: 1 is DFB array sweep frequency light source; 2, a broadband coupler with the central wavelength of 1550nm and the splitting ratio of 20/80; the main interferometer is composed of 3, 4, 5, 6, 7, 8, and is used for real-time acquisition of interference light carrying distance information, wherein: 3 is a broadband coupler with the central wavelength of 1550nm, and the splitting ratio is 10/90; 4 is a three-terminal optical fiber circulator; the distance from the end face of the 5-bit optical fiber probe to the surface of the workpiece to be measured is a measured distance; 6 is an optical fiber delay line with an electric displacement platform; 7 is a broadband coupler with the central wavelength of 1550nm and is used for beam combination; 8 is a single-point InGaAs photodetector with response wavelength of 800-1700 nm; reference Mach-Zehnder interferometer (MZI) 9, it is made up of two 3dB couplers, the optical path difference of two fiber circles is the definite value, is used for producing the trigger signal sampled in the interval of equal wave number, carry on the signal reconstruction to the interference optical signal of the distance information that the main interferometer gathers; the device comprises an ADC (analog-to-digital converter) 10, an FPGA (field programmable gate array) 11, a USB (universal serial bus) chip 12 and a computer 13.
Detailed Description
The invention provides a distance measurement method of fiber frequency domain interference based on a DFB array sweep light source. It can overcome the following disadvantages: (1) the invention can overcome the defects that the conventional wavelength scanning laser source, such as a Micro Electro Mechanical System (MEMS) external cavity laser and an electrically adjustable semiconductor laser, has short coherence length (generally dozens of micrometers), and when the ranging distance exceeds the coherence length, an interference signal is rapidly degraded. (2) The invention can overcome the defect that the light intensity matching of the two interference arms can not be adjusted on line under the field measurement condition in the design of the common-path interferometer. (3) The invention can overcome the defect of low efficiency of collecting the back scattering light when the parallel light of the self-focusing lens of the optical fiber probe is emitted to the surface of the workpiece to be measured. (4) The invention can overcome the defects of complex device for receiving interference signals and large volume.
The invention has the following advantages: (1) the DFB array-based sweep frequency light source is adopted to replace an external cavity scanning type sweep frequency light source, and meanwhile, the DFB array-based sweep frequency light source has a wide sweep frequency range and good coherence, so that interference signal degradation is avoided; (2) by adopting the non-common-path model, the light intensity of the two interference lights can be matched on line, the different conditions of the reflectivity of the measured object are adapted, and the contrast of the interference signal is improved to the greatest extent. (3) The optical fiber probe adopts a self-focusing lens short focal length design, so that light spots are more intensively emitted to the surface to be measured, and the collection efficiency of reflected light to be measured is improved. (4) The single photoelectric detector with wide bandwidth is adopted, so that the device for receiving interference signals is greatly simplified, the equipment is more compact and miniaturized, and the cost is reduced.
The invention comprises the following steps:
(1) a fiber frequency domain interference ranging method of a sweep light source based on a distributed feedback laser (DFB) array is provided. Here we use a C-band DFB array module as the laser source for coherent scanning wavelength ranging, a custom current control circuit board provides a custom tailored current scan for each DFB element, and the measurement features from each element are connected to produce an equivalent scan using the entire bandwidth (>40nm) of the array. On one hand, the frequency sweeping light source has a wide frequency sweeping range and good coherence, and the influence of interference signal degradation on measurement precision is avoided; on the other hand, different wavelengths are separated in time by adopting a sweep frequency light source, so that the acquisition device can be simplified, a spectrometer is not needed, and only a photoelectric detector is needed for receiving.
(2) A measuring light path model of optical fiber frequency domain interference ranging is provided, wherein a Mach-Zenhder interferometer is adopted, and a reference arm and a test arm do not share a light path. In actual field measurement, because the surface reflectivity of a measured workpiece cannot be changed, the light intensity of two interference lights can be matched on line by adopting a non-common-path model, so that the contrast of interference signals is improved to the maximum extent.
(3) A design scheme of the optical fiber probe is provided under the condition that the reference arm and the test arm do not share the same optical path. The optical fiber probe is designed by adopting a self-focusing lens, on one hand, the self-focusing lens is plated with an anti-reflection film, and the influence of end face reflected light on interference is avoided; on the other hand, the design of short focal length is adopted, so that light spots are more intensively emitted to the surface to be measured, and the collection efficiency of reflected light to be measured is improved.
(4) An acquisition circuit design for a wide bandwidth single photodetector is presented. And calculating the bandwidth requirement of the photoelectric detector according to the scanning speed of the sweep frequency light source and the measured distance range, and adopting a detection scheme of a single photoelectric detector under the condition of medium and low frequency.
The technical scheme adopted by the invention is that the fiber frequency domain interference distance measuring system of the sweep light source based on the DFB array comprises:
(1) swept source for DFB array
A C-band DFB array module is adopted as a laser source for coherent scanning wavelength ranging, a customized current control circuit board provides customized current scanning for each DFB element, 12 DFB array elements with the line width of 1MHz are connected to generate equivalent scanning by using the whole bandwidth 1528-1568nm (total bandwidth of 40nm) of the array, and the scanning step is 1GHz (the C-band is 0.8 pm). The FPGA generates a PWM (pulse width modulation) error signal by comparing a reference clock with a signal obtained after zero-cross sampling of an interference signal of the MZI, so that a current driving circuit board is ensured to generate a stable set current scanning curve, and meanwhile, a TTL trigger level signal is output according to the start of each current scanning, so that the FPGA can be used for triggering a clock signal for data acquisition. The interferometer with two arms not sharing the same optical path is designed, the coupler is utilized to separate the two interference arms of the Mach-Zehnder interferometer, wherein the reference arm is an optical fiber delay line with an electric displacement table and is used for adjusting the balance of the interference arms, and meanwhile, the light intensity of two interference lights can be matched on line; the test arm adopts a three-terminal circulator, sweep light enters the optical fiber probe from the circulator and then is emitted to the surface of the workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the optical fiber probe and then enters the coupler for beam combination from the circulator to interfere with reference light.
(2) Short-focus self-focusing lens optical fiber probe
The distance measurement of the system is obtained by receiving a reflected light signal of the workpiece to be measured. The optical fiber probe has the double tasks of emitting sweep frequency laser signals and receiving reflected signals, and receives back scattered light and stray reflected light signals of a workpiece to be detected. The reflected light signal of the measured end face is influenced by the material reflectivity and temperature parameter change, and the improvement of the collection efficiency of the back scattering light on the reflecting surfaces of different objects to be measured is a vital research for improving the signal to noise ratio. Aiming at the measuring range of 10mm, the focal length of 7 +/-3 mm is adopted in the design, and compared with the design that collimated parallel light is emitted to the surface of a workpiece to be measured, the short focal length is adopted, limited laser power is converged on a small light spot, and the collection efficiency of reflected light is improved.
(3) Single photodetector detection
The PIN photodiode converts the acquired light intensity signal into an electric signal, converts the current signal into a voltage signal by using an I-V conversion circuit, and amplifies the weak signal. And calculating the bandwidth requirement of the photoelectric detector according to the scanning speed of the sweep frequency light source and the measured distance range, and adopting a detection scheme of a single photoelectric detector with a broadband under the condition of medium and low frequency.
In order to overcome the defects of the prior art, the method (1) overcomes the defects that the conventional wavelength scanning laser sources, such as micro-electro-mechanical systems (MEMS) external cavity lasers and electrically tunable semiconductor lasers, have short coherence length (generally tens of micrometers), and when the ranging distance exceeds the coherence length, the interference signal is rapidly degraded. (2) The defect that the light intensity matching of the two interference arms cannot be adjusted on line under the field measurement condition in the design of the common-path interferometer is overcome. (3) The defect that parallel light of a self-focusing lens of the optical fiber probe is emitted to the surface of a workpiece to be measured to collect back scattering light with low efficiency is overcome. (4) The defects of complex device for receiving interference signals and large volume are overcome.
The invention is realized by the following steps:
(1) swept optical source using DFB array
A C-band DFB array module is adopted as a laser source for coherent scanning wavelength ranging, a customized current control circuit board provides customized current scanning for each DFB element, 12 DFB array elements with the line width of 1MHz are connected to generate equivalent scanning by using the whole bandwidth 1528-1568nm (total bandwidth of 40nm) of the array, and the scanning step is 1GHz (the C-band is 0.8 pm). The FPGA generates a PWM (pulse width modulation) error signal by comparing a reference clock with a signal obtained after zero-cross sampling of an interference signal of the MZI, so that a current driving circuit board is ensured to generate a stable set current scanning curve, and meanwhile, a TTL trigger level signal is output according to the start of each current scanning, so that the FPGA can be used for triggering a clock signal for data acquisition.
(2) Interferometer design using two arms not sharing optical path
The two interference arms of the Mach-Zehnder interferometer are separated by using a coupler, wherein the reference arm is an optical fiber delay line with a dynamic displacement table and is used for adjusting the balance of the interference arms, and meanwhile, the light intensity of two interference lights can be matched on line; the test arm adopts a three-terminal circulator, sweep light enters the optical fiber probe from the circulator and then is emitted to the surface of the workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the optical fiber probe and then enters the coupler for beam combination from the circulator to interfere with reference light.
(3) Short-focus self-focusing lens optical fiber probe
The distance measurement of the system is obtained by receiving a reflected light signal of the workpiece to be measured. The optical fiber probe has the double tasks of emitting sweep frequency laser signals and receiving reflected signals, and receives back scattered light and stray reflected light signals of a workpiece to be detected. The reflected light signal of the measured end face is influenced by the material reflectivity and temperature parameter change, and the improvement of the collection efficiency of the back scattering light on the reflecting surfaces of different objects to be measured is a vital research for improving the signal to noise ratio. Aiming at the measuring range of 10mm, the focal length of 7 +/-3 mm is adopted in the design, and compared with the design that collimated parallel light is emitted to the surface of a workpiece to be measured, the short focal length is adopted, limited laser power is converged on a small light spot, and the collection efficiency of reflected light is improved.
(4) Single photodetector detection
The PIN photodiode converts the acquired light intensity signal into an electric signal, converts the current signal into a voltage signal by using an I-V conversion circuit, and amplifies the weak signal. And calculating the bandwidth requirement of the photoelectric detector according to the scanning speed of the sweep frequency light source and the measured distance range, and adopting a detection scheme of a single photoelectric detector with a broadband under the condition of medium and low frequency.
The invention is further described below with reference to the accompanying drawings and experiments.
In the invention, the sweep frequency light source uses a laser of a DFB array of a C wave band, the wavelength range is 1528-. Meanwhile, an FPGA (field programmable gate array) in the DFB generates a PWM (pulse-width modulation) error signal by comparing an internal reference clock with a signal obtained after MZI interference signal is subjected to zero-cross sampling, so that a current driving board is ensured to scan a waveform, and a corresponding TTL (transistor-transistor logic) level signal is output.
Furthermore, the sweep laser firstly enters the broadband fiber coupler 2 (the splitting ratio is 20:80), 20% of the sweep laser enters the MZI of the reference, and because the optical path difference of the interferometer is a fixed value, the interference signal collected by the PD2 is a reference clock signal with equal wave number, and the sweep laser can be used for signal reconstruction of a main interferometer at the later stage; the other 80 percent of the light enters the main interferometer, the two interference arms are separated by the broadband optical fiber coupler 3 (the splitting ratio is 10:90), wherein 10 percent of the light enters the reference arm, the balance of the interference arms is adjusted by utilizing the optical fiber delay line with the electric displacement table, and meanwhile, the light intensity of the two interference lights can be matched on line; and in addition, 90% of the light enters the test arm, a three-terminal circulator is adopted, the sweep light enters the optical fiber probe from the circulator and then is emitted to the surface of the workpiece to be tested, the reflected light from the surface of the workpiece to be tested is collected by the optical fiber probe and then enters the coupler for beam combination from the circulator, and the interference is generated between the reflected light and the reference light.
Further, the distance measurement of the system is obtained by receiving the reflected light signal of the workpiece to be measured. The fiber probe has the double tasks of emitting sweep frequency laser signals and receiving reflected signals, and receives back scattering light of a signal workpiece to be detected. Aiming at the measurement range of 10mm, the focal length of 7 +/-3 mm is adopted in the design, and compared with the design that collimated parallel light irradiates the surface of a workpiece to be measured and the short focal length, the limited laser power is converged on a small light spot, so that the collection efficiency of reflected light is improved.
Furthermore, as the sweep frequency light source separates the light with different wavelengths in time, a single InGaAs photodiode is adopted to convert the collected light intensity signal into an electric signal, and then an I-V conversion circuit is utilized to convert the current signal into a voltage signal and amplify the weak signal. According to the scanning rate of 1KHz of the sweep light source and the measuring distance range of 10mm, the bandwidth requirement of the photoelectric detector is selected to be more than 50MH under the condition of medium and low frequency, and the measuring requirement can be met.
Further, the reference light and the reflected light of the test arm interfere at the output of the broadband coupler. The InGaAs PIN photoelectric detector is used for carrying out photoelectric conversion, and the amplified and filtered signals are collected by the ADC. Wherein the clock signal collected by the ADC is generated by the trigger signal clock of the swept-frequency light source. And interference signals collected according to the PD2 of the reference MZI interferometer are used as clock signals for signal reconstruction, and the obtained data are transmitted to a computer by a USB chip for Fast Fourier Transform (FFT) to obtain a distance value to be measured (the distance from the end face of the optical fiber probe to the surface of a workpiece to be measured).
Claims (3)
1. A fiber frequency domain interference distance measurement system for a DFB array swept source is characterized in that swept laser generated by the DFB array swept source firstly enters a broadband fiber coupler with a splitting ratio of 20:80, 20% of split light enters a reference Mach-Zehnder interferometer MZI, interference signals collected by a photodiode PD2 of the reference Mach-Zehnder interferometer MZI are reference clock signals with equal wave numbers and are used for signal reconstruction of a main interferometer at a later stage; the other 80% of light enters a reference arm of the two interference arms through a broadband optical fiber coupler with the splitting ratio of 10:90, the balance of the interference arms is adjusted by using an optical fiber delay line with a dynamic displacement table, and meanwhile, the light intensity of the two interference lights is matched on line; the other 90% of the swept laser enters a test arm, the test arm adopts a three-terminal circulator structure, the swept laser enters the optical fiber probe from the three-terminal circulator and then is emitted to the surface of a workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the same optical fiber probe, and then enters a coupler for beam combination from the three-terminal circulator and interferes with reference light; the interference light is subjected to photoelectric conversion by an indium gallium arsenide InGaAs PIN type photoelectric detector, amplified and filtered by an amplifier and a filter, and then collected by an analog-to-digital converter (ADC), wherein a clock signal collected by the ADC is generated by a trigger signal clock of a sweep frequency light source, and the interference signal collected by a reference Mach Zehnder Interferometer (MZI) PD2 is used as a clock signal for signal reconstruction; the sweep frequency light source of the DFB array is a laser light source of a C-waveband DFB array module, a current control circuit board formed by an FPGA provides current for each DFB array module to scan, and the DFB array modules are connected to generate equivalent scanning by using the whole bandwidth of the array; the FPGA generates a Pulse Width Modulation (PWM) error signal by comparing a reference clock signal with a signal obtained by zero-crossing sampling of a reference Mach Zehnder Interferometer (MZI) interference signal, provides scanning current, and simultaneously outputs a transistor-transistor logic (TTL) trigger level signal according to the beginning of each current scanning to trigger a clock signal for acquiring data; the data of the FPGA are transmitted to the computer by the USB chip to be subjected to fast Fourier transform, and a distance value to be measured is obtained; the optical fiber probe adopts a self-focusing lens, and the self-focusing lens is plated with an anti-reflection film; the self-focusing lens adopts a short focal length design.
2. A fiber frequency domain interference distance measurement method for a DFB array swept source is characterized in that swept laser generated by the DFB array swept source is sent to a broadband fiber coupler with a splitting ratio of 20:80, 20% of split light enters a reference Mach-Zehnder interferometer MZI, interference signals collected by a photodiode PD2 of the reference Mach-Zehnder interferometer MZI are reference clock signals with equal wave numbers, and the reference clock signals are used for signal reconstruction of a main interferometer at a later stage; the other 80% of light enters a reference arm of the two interference arms through a broadband optical fiber coupler with the splitting ratio of 10:90, the balance of the interference arms is adjusted by utilizing an optical fiber delay line with an electric displacement table, and meanwhile, the light intensity of the two interference lights is matched on line; the other 90% of the swept laser enters a test arm, the test arm adopts a three-terminal circulator structure, the swept laser enters the optical fiber probe from the three-terminal circulator and then is emitted to the surface of a workpiece to be tested, reflected light from the surface of the workpiece to be tested is collected by the same optical fiber probe, and then enters a coupler for beam combination from the three-terminal circulator and interferes with reference light; the interference light is subjected to photoelectric conversion by an indium gallium arsenide InGaAs PIN type photoelectric detector, amplified by an amplifier and a filter, filtered and collected by an analog-to-digital converter (ADC), wherein a clock signal collected by the ADC is generated by a trigger signal clock of a sweep frequency light source, and the interference signal collected by a reference Mach Zehnder Interferometer (MZI) PD2 is used as a clock signal for signal reconstruction; the sweep frequency light source of the DFB array is a laser light source of a C-waveband DFB array module, a current control circuit board formed by an FPGA provides current for each DFB array module to scan, and the DFB array modules are connected to generate equivalent scanning by using the whole bandwidth of the array; the FPGA generates a Pulse Width Modulation (PWM) error signal by comparing a reference clock signal with a signal obtained by zero-cross sampling of a reference Mach Zehnder Interferometer (MZI) interference signal, provides scanning current, and simultaneously outputs a transistor-transistor logic (TTL) trigger level signal according to the beginning of each current scanning to trigger a clock signal for acquiring data.
3. A DFB array swept source fiber optic frequency domain interferometric ranging method as claimed in claim 2, characterized in that the collected data is processed as follows: the distance between the end face of the optical fiber probe and the surface of the workpiece to be measured is d, the reflected light of the surface of the workpiece collected by the probe interferes with the reference light, and the interference formula is as follows:
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