CN102183234B - Method and device for measuring frequency scanning absolute distance based on femtosecond optical frequency comb - Google Patents

Method and device for measuring frequency scanning absolute distance based on femtosecond optical frequency comb Download PDF

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CN102183234B
CN102183234B CN 201110068000 CN201110068000A CN102183234B CN 102183234 B CN102183234 B CN 102183234B CN 201110068000 CN201110068000 CN 201110068000 CN 201110068000 A CN201110068000 A CN 201110068000A CN 102183234 B CN102183234 B CN 102183234B
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frequency
laser
polarization
measuring
double
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CN102183234A (en
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吴学健
张继涛
李岩
尉昊赟
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Tsinghua University
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Tsinghua University
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Abstract

The invention relates to a device for measuring a frequency scanning absolute distance based on a femtosecond optical frequency comb and a method for measuring the absolute distance based on the device. The device comprises: a tunable laser (1), a polarization maintaining fiber system (2), a double-frequency heterodyne interferometer (3) and a system for measuring a laser frequency and an interferometric phase (4); the tunable laser (1) is used for generating single-frequency, single-line polarization laser, and an output laser frequency can be controlled by the working voltage and current ofthe tunable laser; the polarization maintaining fiber system (2) is used for coupling space laser with a polarization maintaining fiber in an unreflected way, and dividing the space laser into three paths of optical signals with equal optical intensity, and keeping an output laser polarization direction the same as an input laser polarization direction; the double-frequency heterodyne interferometer (3) is used for converting single-frequency laser into double-frequency orthogonal polarization laser, and converting distance information to be measured into phase information of a laser beat signal; and the system for measuring the laser frequency and the interferometric phase (4) is used for precisely measuring and locking and inputting the frequency of the laser, and measuring a phase different between the two paths of alternating current signals.

Description

Frequency sweeping absolute distance measurement method and device based on femtosecond optical frequency comb
Technical field
The present invention relates to a kind of absolute distance measurement method and device, particularly about a kind of frequency sweeping absolute distance measurement method and device based on femtosecond optical frequency comb.
Background technology
The laser interference range observation is by the phase differential of surveying reference path and optical path and according to the corresponding relation of interfering Wave-front phase and light path, obtains optical path with respect to the range difference of reference path.Wavelength is interfered in one of the every variation of reference path and optical path light path, and its phase differential just changes 2 π.The phase differential of reference path and optical path comprises integral part and the fraction part of phase place, i.e. the number of complete cycle and rest period decimal.According to the difference of detecting phase, the laser interference range observation can be divided into increment type laser interferometry and absolute distance laser interferometry two large classes.
The increment type laser interferometry, by fixed reference light path light path, continuously change the mode of optical path light path, the variable quantity of detecting phase, thus the relative distance that obtains reference path and optical path changes.The increment type laser interferometry have measuring accuracy high, measure the characteristics such as the large and measuring speed of range is fast, realize but the variable in distance of optical path depends on the high precision displacement guide rail.The absolute distance laser interferometry utilizes the principle of synthetic wavelength to increase the length of measuring wavelength, integral part and the fraction part of while detecting phase, thereby the absolute distance of acquisition optical path.The movement that the absolute distance laser interferometry need not optical path just can directly record absolute distance, all has a wide range of applications in fields such as industry and military affairs.
According to the difference of synthetic wavelength producing method, the absolute distance laser interferometry can be divided into phase shift interference method, multi-wavelength interference method and frequency scanning interference method etc.The phase shift interference method is to introduce the controllable variations of interference periods in an interference periods, accurately measures the phase place fraction part by corresponding algorithm, and the method can be used for length less than the absolute distance measurement of an interference periods.The multi-wavelength interference method is to adopt the laser beat frequency of a plurality of different wave lengths to produce wavelength much larger than the synthetic wavelength of single optical maser wavelength, thereby records the phase place integral part, realizes absolute distance measurement.Frequency scanning interference method is the continuous variation that utilizes tunable laser to produce laser frequency, forms synthetic wavelength to realize absolute distance measurement.
Frequency scanning interference method system based on tunable laser is simple, and its frequency sweeping variable range, measures range from several millimeters to tens meters, and measuring accuracy can reach micron dimension, and the method has become one of focus method of current absolute distance measurement research.The method sees document (1) for details: Distance measurement by the wavelength shift of laser diode light, H.Kikuta, K.Iwata and R.Nagata, Appl.Opt., 1986,25 (17): 2976-2980.In order to improve measuring accuracy and system stability, the normal Fabry-Perot-type cavity that adopts is controlled the sweep frequency of tunable laser, see document (2) for details: Accuracy of frequency-sweeping interferometry for absolute distance metrology, A.Cabral and J. Opt.Eng., 2007,46 (07): 073602.But Fabry-Perot-type cavity can only utilize the principle of multiple-beam interference that laser frequency is measured indirectly, and its measuring accuracy depends on the long degree of stability in physics chamber and the fineness of Fabry-Perot-type cavity.In addition, the frequency of operation of tunable laser also fails to contact with existing About Settling Measurement Standard, and the method fails to satisfy metrology to measuring the requirement that should have traceability.
Summary of the invention
For the problems referred to above, the purpose of this invention is to provide a kind of frequency stability is high and can trace to the source frequency sweeping absolute distance measurement method and device.
To achieve these goals, the present invention takes following technical scheme: a kind of frequency sweeping absolute distance measurement method based on femtosecond optical frequency comb is characterized in that may further comprise the steps: 1) a frequency sweeping absolute distance measurement device based on femtosecond optical frequency comb that comprises tunable laser, polarization maintaining optical fibre system, double frequency heterodyne ineterferometer and laser frequency and interferometric phase measuring system is set; Wherein, the shoot laser of tunable laser is incident to respectively wavemeter, the femtosecond optical frequency comb system of double frequency heterodyne ineterferometer and laser frequency and interferometric phase measuring system through the polarization maintaining optical fibre system; The two-way photodetector of double frequency heterodyne ineterferometer is electrically connected to the lock-in amplifier of laser frequency and interferometric phase measuring system, and the laser driver of laser frequency and interferometric phase measuring system is electrically connected to tunable laser; 2) regulate tunable laser and export a certain single-frequency laser, be locked to the femtosecond optical frequency comb system, and accurately record the work laser frequency of this moment and the two-way interference signal phase differential that the double frequency heterodyne ineterferometer is surveyed by laser frequency and interferometric phase measuring system; 3) continuously without the Output of laser frequency of the tuning tunable laser of mode hopping, the variable number of the integer phase place that is produced by the two-way interference signal phase differential of laser frequency and the detection of interferometric phase measuring system record double frequency heterodyne ineterferometer; 4) be tuned to another single-frequency when the tunable laser Output of laser, repeat 2) step, record the work laser frequency of this moment and the two-way interference signal phase differential that the double frequency heterodyne ineterferometer is surveyed; 5) scan, end frequency, interferometric phase integral part by the laser frequency that records and frequency sweeping rises, end the interferometric phase fraction part, calculate the absolute distance of light path reflecting surface to be measured.
A kind of frequency sweeping absolute distance measurement device based on femtosecond optical frequency comb is characterized in that, it comprises a tunable laser, a polarization maintaining optical fibre system, a double frequency heterodyne ineterferometer and a laser frequency and interferometric phase measuring system: wherein:
Described tunable laser output single-frequency, single linear polarization laser are by changing its Output of laser frequency of its working current or voltage continuously-tuning;
Described polarization maintaining optical fibre system comprises optoisolator, the first polarization maintaining optical fiber collimator, polarization maintaining optical fibre, polarization-maintaining fiber coupler and the second polarization maintaining optical fiber collimator that is successively set on the described tunable laser emitting light path; The input end of described polarization-maintaining fiber coupler is connected to polarization-maintaining fiber coupler by polarization maintaining optical fibre, and its output terminal is connected to respectively wavemeter, the femtosecond optical frequency comb system of the second polarization maintaining optical fiber collimator and laser frequency and interferometric phase measuring system by polarization maintaining optical fibre; Described polarization maintaining optical fibre system keeps laser polarization direction identical with the incident laser polarization direction;
Described double frequency heterodyne ineterferometer comprises the first semi-transparent semi-reflecting lens, first sound luminescent crystal, second sound luminescent crystal, the first catoptron, the second catoptron, the second semi-transparent semi-reflecting lens, 1/2 wave plate, polarization splitting prism, the first quarter wave plate, the second quarter wave plate, reference angle cone prism, measured angular cone prism, the first polaroid, the second polaroid, the first photodetector and the second photodetector that is successively set on described the second polarization maintaining optical fiber collimator emitting light path; The shoot laser of described polarization maintaining optical fiber collimator is the linearly polarized light of parallel paper direction; Described the first semi-transparent semi-reflecting lens, first sound luminescent crystal, second sound luminescent crystal, the first catoptron and the second catoptron form the Mach-Zehnder interferometer light path, first sound luminescent crystal and second sound luminescent crystal lay respectively at the two-way of Mach-Zehnder interferometer, only select respectively first sound luminescent crystal and second sound luminescent crystal+1 order diffraction light outgoing; Described 1/2 wave plate is with incident laser polarization state half-twist, and the shoot laser polarization direction is vertical paper direction; Described the second semi-transparent semi-reflecting lens is with the equicohesive two-way that is divided into of two-way incident beam, wherein one the tunnel behind described the first polaroid, be incident to described the first photodetector, described the first polaroid optical axis direction and two bundle laser polarization direction angles are 45 °, and another road is incident to described polarization splitting prism; Described polarization splitting prism reflects and transmission it respectively according to the difference of incident light polarization direction, wherein the light beam of the parallel paper in one tunnel polarization direction is after described polarization splitting prism reflection, be incident to described the first quarter wave plate, outgoing was to described reference angle cone prism after the polarization direction rotated 45 °, continue along 45 ° of former direction rotations by described the first quarter wave plate polarization direction after reflection, after described polarization splitting prism transmission is by described the second polaroid, be incident to described the second photodetector, the light beam of another vertical paper in polarization direction, road is after described polarization splitting prism transmission, be incident to described the second quarter wave plate, outgoing was to described measured angular cone prism after the polarization direction rotated 45 °, continue along 45 ° of former direction rotations by described the second quarter wave plate polarization direction after reflection, through the reflection of described polarization splitting prism through be incident to described the second photodetector after telling the second polaroid, the optical axis direction of described the second polaroid and two-way incident light polarization angular separation are 45 °;
Described laser frequency and interferometric phase measuring system comprise computing machine, wavemeter, femtosecond optical frequency comb system, laser driver and the large device of phasometer; The light input end of described wavemeter is connected to a certain exit end of described polarization maintaining optical fibre system by described polarization maintaining optical fibre, its output terminal is electrically connected to described computing machine; The light input end of described femtosecond optical frequency comb system is connected to a certain exit end of described polarization maintaining optical fibre system by described polarization maintaining optical fibre, its output terminal is electrically connected to described computing machine; Described laser driver is electrically connected to respectively described tunable laser and described computing machine; The two-way input end of described lock-in amplifier is electrically connected to respectively described first and second photodetector, and its PORT COM is electrically connected to described computing machine.
The modulating frequency of described first and second acousto-optic crsytal is different, and its frequency difference is less than the Measurement bandwidth of described phasometer.
The operation wavelength of described wavemeter covers all frequencies of described tunable laser, and its measuring accuracy is better than 100MHz.
The operation wavelength of described femtosecond optical frequency comb system covers all frequencies of described tunable laser, and its repetition frequency and offset frequency are locked to the microwave frequency reference signal.
Described phasometer has the two paths of signals input end, can measure the phase place that sinusoidal model is inputted on every road.
According to an aspect of the present invention, provide a kind of frequency sweeping absolute distance measurement device based on femtosecond optical frequency comb, it is characterized in that comprising:
Tunable laser, for generation of single-frequency, single linearly polarized laser, and the output laser frequency can be by its operating voltage and Current Control;
The polarization maintaining optical fibre system is used for the unreflected polarization maintaining optical fibre that is coupled into of space laser, and is divided into aplanatic three road light signals, and keeps the Output of laser polarization direction consistent with the input laser polarization direction;
The double frequency heterodyne ineterferometer is used for single-frequency laser is transformed into the double frequency orthogonal polarization laser, and will change with the confidence distance of measuring the phase information of laser beat frequency signal into;
Laser frequency and interferometric phase measuring system are used for the frequency of precision measurement and locking input laser, and measure the phase differential of two-way AC signal.
According to another aspect of the present invention, provide the frequency sweeping absolute distance measurement method based on femtosecond optical frequency comb based on said frequencies scanning absolute distance measurement device, it is characterized in that the method comprises:
A) regulate tunable laser, make it export a single-frequency laser, and with this laser lock-on to the femtosecond optical frequency comb system,
B) accurately record the work laser frequency of this moment and the two-way interference signal phase differential that the double frequency heterodyne ineterferometer is surveyed by laser frequency and interferometric phase measuring system,
C) continuous Output of laser frequency without the tuning tunable laser in mode hopping ground, the integer variable number that the two-way interference signal phase differential of being surveyed by laser frequency and interferometric phase measuring system record double frequency heterodyne ineterferometer produces,
D) Output of laser when tunable laser is tuned to another single-frequency, repeating step A), B), record the work laser frequency of this moment and the two-way interference signal phase differential that the double frequency heterodyne ineterferometer is surveyed,
E) stop frequency, interferometric phase integral part and frequency sweeping start-stop and stop the interferometric phase fraction part by the laser frequency scanning initial sum that records, calculate the absolute distance of optical path reflecting surface to be measured.
The present invention is owing to taking above technical scheme, it has the following advantages: 1, because the present invention adopts wavemeter and femtosecond optical frequency comb system to be used for the frequency of locking and measurement tunable laser, so laser frequency scans, end frequency and range of scanned frequencies can obtain the control and measurement of precision, thereby improved accuracy and the repeatability of system to absolute distance measurement.2, owing to the present invention repetition frequency and the offset frequency of femtosecond optical frequency comb are traced to the source to the microwave frequency benchmark, finally set up contacting of range measurements and microwave frequency benchmark by frequency sweeping absolute distance measurement method, realized tracing to the source of range measurements.
Description of drawings
Fig. 1 is the structural representation of device according to an embodiment of the invention.
Fig. 2 is frequency sweeping absolute distance measurement principle schematic according to an embodiment of the invention.
Embodiment
Below in conjunction with drawings and Examples the present invention is described in detail.
Frequency sweeping absolute distance measurement device based on femtosecond optical frequency comb according to an embodiment of the invention, as shown in Figure 1, comprise a tunable laser 1, a polarization maintaining optical fibre system 2, a double frequency heterodyne ineterferometer 3 and a laser frequency and interferometric phase measuring system 4.Wherein, the shoot laser of tunable laser 1 is incident to respectively wavemeter 401 and the femtosecond optical frequency comb system 402 of double frequency heterodyne ineterferometer 3 and laser frequency and interferometric phase measuring system 4 through polarization maintaining optical fibre system 2.The first photodetector 314 of double frequency heterodyne ineterferometer 3, the second photodetector 315 are electrically connected to the phasometer 404 of laser frequency and interferometric phase measuring system 4, and the laser driver 403 of laser frequency and interferometric phase measuring system 4 is electrically connected to tunable laser 1.
Frequency sweeping absolute distance measurement method based on femtosecond optical frequency comb according to an embodiment of the invention comprises:
A) regulate a certain single-frequency laser of tunable laser 1 output, be locked to femtosecond optical frequency comb system 402,
B) accurately record the work laser frequency of this moment and the two-way interference signal phase differential that double frequency heterodyne ineterferometer 3 is surveyed by laser frequency and interferometric phase measuring system 4.
C) continuously without the Output of laser frequency of the tuning tunable laser 1 of mode hopping, the integer variable number that is produced by the two-way interference signal phase differential of laser frequency and 3 detections of interferometric phase measuring system 4 record double frequency heterodyne ineterferometers.
D) be tuned to another single-frequency when tunable laser 1 Output of laser, repeat A), B) step, record the work laser frequency of this moment and the two-way interference signal phase differential that double frequency heterodyne ineterferometer 3 is surveyed.
E) stop frequency, interferometric phase integral part and frequency sweeping initial sum by the laser frequency scanning initial sum that records and stop the interferometric phase fraction part, calculate the absolute distance of optical path reflecting surface to be measured.
As shown in Figure 1, be used for output single-frequency, single linearly polarized laser based on the tunable laser 1 in the frequency sweeping absolute distance measurement device of femtosecond optical frequency comb.In the present embodiment, tunable laser 1 adopts external-cavity semiconductor laser, and its output wavelength is about 633nm, by changing its working current or operating voltage, can realize greater than 100GHz without the mode hopping frequency tuning.
As shown in Figure 1, comprise optoisolator 200, the first polarization maintaining optical fiber collimator 201, polarization maintaining optical fibre 202, polarization-maintaining fiber coupler 203 and the second polarization maintaining optical fiber collimator 204 based on the polarization maintaining optical fibre system 2 in the frequency sweeping absolute distance measurement device of femtosecond optical frequency comb, this system is used for the light beam one direction of tunable laser 1 output is transferred to respectively wavemeter 401, the femtosecond optical frequency comb 402 of double frequency heterodyne ineterferometer 3 and laser frequency and interferometric phase measuring system 4, and keeps laser polarization state constant.Wherein, the laser of tunable laser 1 output is through optoisolator 200 one way propagation to the first polarization maintaining optical fiber collimators 201, enter polarization maintaining optical fibre 202, its polarization direction remained unchanged when laser was propagated in polarization maintaining optical fibre 202, behind polarization-maintaining fiber coupler 203, be divided into aplanatic three road laser, be transmitted to the second polarization maintaining optical fiber collimator 203, wavemeter 401 and femtosecond optical frequency comb system 402 along polarization maintaining optical fibre 202 respectively.
As shown in Figure 1, comprise the first semi-transparent semi-reflecting lens 300 based on the double frequency heterodyne ineterferometer 3 in the frequency sweeping absolute distance measurement device of femtosecond optical frequency comb, first sound luminescent crystal 301, second sound luminescent crystal 302, the first catoptron 303, the second catoptron 304, the second semi-transparent semi-reflecting lens 305,1/2 wave plate 306, polarization splitting prism 307, the first quarter wave plate 308, the second quarter wave plate 309, reference angle cone prism 310, measured angular cone prism 311, the first polaroid 312, the second polaroid 313, the first photodetector 314 and the second photodetector 315, this system is used for utilizing the heterodyne Michelson Interference Principle absolute distance information to be measured to be converted into the phase information of interference signal.Wherein, the emitting laser polarization direction of the second polarization maintaining optical fiber collimator 203 is parallel to paper, the isocandela two bundle laser that are divided into transmission and reflection by the first semi-transparent semi-reflecting lens 300, after transmitted light is modulated by first sound luminescent crystal 301, its+1 order diffraction light reflexes to the second semi-transparent semi-reflecting lens 305 through the first catoptron 303, and the light beam polarization direction is parallel to paper; Reflected light by second sound luminescent crystal 302 modulation after, its+1 order diffraction light through the second catoptron 304 reflex to the rotation of 1/2 wave plate, 306 transmitted light beam polarization directions to the paper vertical direction, be incident to the second semi-transparent semi-reflecting lens 305.Two-way light after the second semi-transparent semi-reflecting lens 305 merges again isocandela be divided into two-way, wherein one the tunnel through the first polaroid 312, its optical axis direction and incident beam polarization direction angle are 45 °, are incident to the first photodetector 314 and are converted into electric signal; Another road vertical incidence is to polarization splitting prism 307, difference according to the incident beam polarization direction is reflected or transmission, wherein the light beam of the parallel paper in polarization direction reflexes to the first quarter wave plate 308 by polarization splitting prism 307, the outgoing beam polarization direction is incident to reference angle cone prism 310 after rotating 45 °, transmission the first quarter wave plate 308 after the reflection, the light beam polarization direction continues along 45 ° of former direction rotations, after polarization splitting prism 307 transmissions, be incident to the second polaroid 313, light beam transmission-polarizing Amici prism 307 to second quarter wave plates 309 of the vertical paper in polarization direction wherein, the outgoing beam polarization direction is incident to reference angle cone prism 311 after rotating 45 °, transmission the first quarter wave plate 309 after the reflection, the light beam polarization direction continues along 45 ° of former direction rotations, reflex to the second polaroid 313 through polarization splitting prism 307, the second polaroid 313 optical axis directions and two-way light beam polarization angular separation are 45 °, and the two-way light beam is incident to the second photodetector 315 and transforms electric signal behind the second polaroid 313.In the present embodiment, the modulating frequency of first sound luminescent crystal 301 is 80MHz, and the modulating frequency of second sound luminescent crystal 302 is 80.1MHz.
In double frequency heterodyne ineterferometer 3 according to an embodiment of the invention, the first semi-transparent semi-reflecting lens 300, first sound luminescent crystal 301, second sound luminescent crystal 302, the first catoptron 303, the second catoptron 303 and the second semi-transparent semi-reflecting lens 304 form the Mach-Zehnder interferometer, wherein the modulating frequency of first sound luminescent crystal 301 is 80MHz, and the modulating frequency of second sound luminescent crystal 302 is 80.1MHz; The first photodetector 314 is converted into the sinusoidal electric signals P that frequency is 100kHz with the two-way light beam beat signal that modulating frequency is respectively 80MHz and 80.1MHz; Polarization splitting prism 307, the first quarter wave plate 308, the second quarter wave plate 309, reference angle cone prism 310 and measured angular cone prism 311 form Michelson interferometer, the position of fixed reference prism of corner cube 310, for the position of a certain measured angular cone prism 311, by the second photodetector 315 modulating frequency is respectively the sinusoidal electric signals P ' that interference signal that the two-way light beam beat frequency of 80MHz and 80.1MHz produces is converted into 100kHz; The phase differential of P and P ' relatively just can obtain measuring the phase differential of light and reference light interference signal; 1/2 wave plate 306, the first quarter wave plate 308, the second quarter wave plate 309,312 of the first polarizations and the second polaroid 313 are used for changing laser polarization direction.
As shown in Figure 1, according to an embodiment of the inventionly comprise computing machine 400, wavemeter 401, femtosecond optical frequency comb system 402, laser driver 403 and phasometer 404 based on the laser frequency in the frequency sweeping absolute distance measurement device of femtosecond optical frequency comb and interferometric phase measuring system 4, this system is used for control and measures the Output of laser frequency of tunable laser 1 and the phase differential of measuring the two-way interference signal of double frequency heterodyne ineterferometer 3.Wherein, computing machine 400 be used for accepting wavemeter 401, femtosecond optical frequency comb system 402 and phasometer 404 output signal, and output is to the control signal of laser driver 403; The light input end of wavemeter 401 is connected to a certain fiber-optic output of polarization maintaining optical fibre system 2, and its output terminal is electrically connected to computing machine 400, is used for the Output of laser frequency of bigness scale tunable laser 1; The light input end of femtosecond optical frequency comb system 402 is connected to a certain fiber-optic output of polarization maintaining optical fibre system 2, and its output terminal is electrically connected to computing machine 400, is used for accurately measuring and locking the Output of laser frequency of tunable laser 1; Laser driver 403 input ends are electrically connected to computing machine 400, and its output terminal is electrically connected to tunable laser 1, are used for driving tunable laser 1 and controlling its Output of laser frequency and power; The two-way input end of phasometer 404 is electrically connected to respectively the first photodetector 312 and the second photodetector 313, and its output terminal is electrically connected to computing machine 400, is used for measuring the phase differential of two-way input exchange signal.
In laser frequency according to an embodiment of the invention and interferometric phase measuring system 4, aspect laser frequency measurement, wavemeter 401 carries out bigness scale based on principle of interference to the real-time laser frequency of tunable laser 1, its measuring accuracy is 60MHz, femtosecond optical frequency comb system 402 by with its repetition frequency and polarization Frequency Locking to the microwave frequency benchmark, the frequency of light wave of femtosecond optical frequency comb is traced to the source to the microwave frequency benchmark, by measuring frequency comb and testing laser beat frequency S, can accurately measure laser frequency, S be fed back to the Output of laser frequency of laser driver 403 lockable tunable laser 1; Aspect the interferometric phase measurement, photosignal P and P ' that the first photodetector 314 and the second photodetector 315 obtain input to phasometer 404, and the real-time phase that records P and P ' is poor And transmit it to computing machine 400.
As shown in Figure 1 and Figure 2, in the frequency sweeping absolute distance measurement device based on femtosecond optical frequency comb according to an embodiment of the invention,
The phase differential of reference arm and gage beam Can be expressed as
Wherein, L is the optical path difference of reference arm and gage beam, and λ is optical maser wavelength, and N is phase differential with respect to the integral part in 2 π cycles, and ε is the fractional part of phase differential with respect to 2 π cycles.Laser wavelength is changed to λ+Δ λ continuously from λ during frequency (wavelength) scanning survey, in like manner, and the phase differential of reference arm and gage beam Can be expressed as
Wherein, Be the phase differential of reference arm corresponding to λ and gage beam for optical maser wavelength, its phase place integral part is N 1, the phase place fraction part is ε 1, For optical maser wavelength is reference arm corresponding to λ+Δ λ and the phase differential of gage beam, its phase place integral part is N 2, the phase place fraction part is ε 2Can be got the variation of the reference arm that frequency sweeping causes and the phase differential of gage beam by above formula Can be expressed as
Wherein, Δ N and Δ ε are respectively integral part and the fraction part that reference arm that frequency sweeping causes and gage beam phase differential change, the instantaneous synthetic wavelength λ that frequency (wavelength) scanning causes s=λ (λ+Δ λ)/Δ λ, then following formula can be expressed as
Can get thus, the optical path difference L of reference arm and gage beam is
L = ( ΔN + Δϵ ) λ s = ( ΔN + Δϵ ) λ ( λ + Δλ ) Δλ - - - ( 6 )
Can get thus, integral part and fraction part by reference arm and the variation of gage beam phase differential in measurement laser initial sum termination wavelength and frequency (wavelength) scanning process, can get the optical path difference of reference arm and gage beam by formula (6), thereby obtain the absolute distance of object to be measured.
The present invention utilizes frequency sweeping absolute distance measurement principle, adopts wavemeter and femtosecond optical frequency comb system that laser frequency is carried out accurate control and measurement, can Effective Raise absolute distance measurement accuracy and repeatability.Simultaneously, the femtosecond optical frequency comb system building bridge of microwave frequency benchmark and laser frequency, final so that the absolute distance measurement result traces to the source to frequency reference, satisfy the metrology requirement.
The various embodiments described above only are used for explanation the present invention, and wherein the structure of each parts, connected mode etc. all can change to some extent, and every equivalents and improvement of carrying out on the basis of technical solution of the present invention all should do not got rid of outside protection scope of the present invention.

Claims (3)

1. based on the frequency sweeping absolute distance measurement device of femtosecond optical frequency comb, it is characterized in that comprising:
Tunable laser (1), for generation of single-frequency, single linearly polarized laser, and the output laser frequency can be by its operating voltage and Current Control;
Polarization maintaining optical fibre system (2) is used for the unreflected polarization maintaining optical fibre that is coupled into of space laser, and is divided into aplanatic three road light signals, and keeps the Output of laser polarization direction consistent with the input laser polarization direction;
Double frequency heterodyne ineterferometer (3) is used for single-frequency laser is transformed into double frequency cross polarization laser, and range information to be measured is changed into the phase information of laser beat frequency signal;
Laser frequency and interferometric phase measuring system (4) are used for the frequency of precision measurement and locking input laser, and measure the phase differential of two-way AC signal,
Wherein said laser frequency and interferometric phase measuring system (4) comprising:
Wavemeter (401) is used for bigness scale input laser frequency, and measuring accuracy is better than 100MHz;
Femtosecond optical frequency comb system (402) is used for precision measurement and locking input laser frequency, and measuring accuracy is better than 1kHz;
Be electrically connected to the laser driver (403) of tunable laser (1), Output of laser frequency and power that the operating voltage and the working current that are used for control tunable laser (1), laser driver (403) are used for driving tunable laser (1) and control tunable laser (1);
Phasometer (404) is for the phase differential of measuring the two-way AC signal;
Computing machine (400) is used for receiving the output signal of wavemeter (401), femtosecond optical frequency comb system (402) and phasometer (404), and exports the control signal to laser driver (403),
Wherein, polarization maintaining optical fibre system (2) is passed to respectively double frequency heterodyne ineterferometer (3), wavemeter (401) and femtosecond optical frequency comb system (402) with tunable laser (1) shoot laser.
2. frequency sweeping absolute distance measurement device according to claim 1 is characterized in that:
Double frequency heterodyne ineterferometer (3) is modulated to the double-frequency laser with the poor cross polarization of certain frequency with the single linearly polarized laser of single-frequency, comprising:
The first photodetector (314) is used for double frequency cross polarization laser is converted into electric signal;
The second photodetector (315) is used for and will be converted into electric signal with the double frequency cross polarization laser of testing distance information;
Wherein, the first photodetector (314) and the second photodetector (315) are electrically connected to respectively phasometer (404).
3. based on the frequency sweeping absolute distance measurement method of femtosecond optical frequency comb, it is characterized in that the method based on frequency sweeping absolute distance measurement device according to claim 1 and 2, is characterized in that comprising:
A) regulate tunable laser (1), make it export a single-frequency laser, and with this laser lock-on to femtosecond optical frequency comb system (402),
B) accurately record the work laser frequency of this moment and the two-way interference signal phase differential that double frequency heterodyne ineterferometer (3) is surveyed by laser frequency and interferometric phase measuring system (4),
C) continuously without the Output of laser frequency of the tuning tunable laser in mode hopping ground (1), the integer variable number that the two-way interference signal phase differential of being surveyed by laser frequency and interferometric phase measuring system (4) record double frequency heterodyne ineterferometer (3) produces,
D) Output of laser when tunable laser (1) is tuned to another single-frequency, repeating step A), B), record the work laser frequency of this moment and the two-way interference signal phase differential that double frequency heterodyne ineterferometer (3) is surveyed,
E) stop frequency, interferometric phase integral part and frequency sweeping start-stop and stop the interferometric phase fraction part by the laser frequency scanning initial sum that records, calculate the absolute distance of optical path reflecting surface to be measured.
CN 201110068000 2011-03-21 2011-03-21 Method and device for measuring frequency scanning absolute distance based on femtosecond optical frequency comb Expired - Fee Related CN102183234B (en)

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