CN103837077B - Composite wave interferometry ranging distance system with two femtosecond laser frequency combs - Google Patents
Composite wave interferometry ranging distance system with two femtosecond laser frequency combs Download PDFInfo
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- CN103837077B CN103837077B CN201410106555.4A CN201410106555A CN103837077B CN 103837077 B CN103837077 B CN 103837077B CN 201410106555 A CN201410106555 A CN 201410106555A CN 103837077 B CN103837077 B CN 103837077B
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Abstract
The invention relates to a composite wave interferometry ranging distance system with two femtosecond laser frequency combs. The composite wave interferometry ranging distance system is characterized in that a first femtosecond laser frequency comb emits an optical pulse to a first spectroscope, the optical pulse reflected by the first spectroscope is transmitted to a first corner reflector, and the optical pulse reflected by the first corner reflector is transmitted to a second spectroscope through the first spectroscope. The optical pulse transmitted by the first spectroscope is transmitted to a second corner reflector, and the optical pulse reflected by the second corner reflector is reflected to the second spectroscope through the first spectroscope. A second femtosecond laser frequency comb emits an optical pulse to the second spectroscope, the optical pulse transmitted by the second spectroscope and an optical pulse emitted by a Michelson interference system are mixed and transmitted to a third spectroscope, the optical pulse transmitted by the third spectroscope is received by a first photoelectric detector in a detection mode through a first narrow-band band-pass filter, and the optical pulse reflected by the third spectroscope is received by a second photoelectric detector in a detection mode through a second narrow-band band-pass filter. The first photoelectric detector and the second photoelectric detector are connected with an A/ D converter connected with a signal processing unit through a corresponding data interface to process the received signal to obtain the required distance measuring value.
Description
Technical field
The present invention relates to a kind of laser distance measuring system, especially with regard to a kind of round trip flight being applied to absolute distance measurement
Second laser frequency comb composite wave interfeerometry ranging system.
Background technology
Traditional laser interferometry is a kind of range measurement mode of increment type, there is the non-fuzzy of 1/2nd wavelength
Distance.When tested distance be more than non-fuzzy apart from when, need between baseline and target object set up guide rail, mesh in measurement process
Mark object needs continuously to move along guide rail and then complete fringe count, realizes large range of range measurement.Laser definitely away from
From measurement (no guide rail range measurement) be a kind of direct measurement baseline between target object with a distance from method, with respect to the former tool
There are applied widely, simple operation and other advantages, therefore it has very strong application demand and a prospect in industry and space industry, one
Geometric sense in the big machinery change system such as high-speed railway, large aircraft, nuclear power and wind-powered electricity generation, to high-accuracy large-scale for the aspect
Carry out accurate measurement；On the other hand it is to realize high accuracy satellites formation it is also desirable to wide range, high-precision absolute distance measurement skill
Art is as guarantee.In recent years, the appearance of femtosecond laser frequency comb brings revolutionary breakthrough to laser absolute distance measurement.
Femtosecond laser frequency comb refers to the repetition rate (f of femtosecond pulse laserrep, abbreviation repetition) and phase offset
Frequency (fceo) with frequency reference source locking after device, the laser that it sends in time domain by a series of equally spaced ultrashort swash
Light pulse (pulsewidth is some femtoseconds) composition, there is a series of equally spaced discrete light spectral lines, adjacent spectrum line in corresponding frequency domain
Frequency interval be equal to femto-second laser repetition, these spectral line cover spectral region be tens nanometer.Fly existing
In second laser frequency comb range-measurement system, more conventional is that being had using two of proposing of Unite States Standard Weights and Measures Bureau (nist) is small
Repetition difference femtosecond laser frequency comb build range-measurement system, by the pulse of one of femtosecond laser frequency comb be used for reference and
Measurement, the pulse of another femtosecond laser frequency comb is used for sampling.In measurement process, sampling pulse and reference pulse and measurement
Pulse generation is periodically overlapping, then extracts range information from overlapping signal.This measuring method is divided into bigness scale and essence
Survey two steps: bigness scale is by, obtained by the femtosecond pulse flight-time information that extracts from overlapping bursts signal, typically enabling
Several microns of certainty of measurement；And accurate measurement is then by carrying out averagely to the result of multiple bigness scale, and precision is brought up to four/
Within one wavelength, so that it is determined that the integer level of interference fringe time (being commonly called as " several greatly " of interferometric phase), further according to the interference extracted
Phase place is refined to tested distance, realizes high-acruracy survey.The problem of this method is to be capable of very during only bigness scale
But high measuring speed precision is not high enough, and need to be entered by the method that multiple bigness scale is averaged when bigness scale is to accurate measurement transition
OK, greatly reduce the speed of range measurement.
Content of the invention
For the problems referred to above, it is an object of the invention to provide a kind of Double-femtosecond laser frequency comb composite wave interfeerometry ranging system
System, its be by the use of dual wavelength formed synthetic wavelength as bridge, will be straight to the bigness scale of Double-femtosecond laser frequency comb and interferometric phase
Connect and link up, that is, achieve the direct transition to accurate measurement for the bigness scale, thus avoiding repeatedly measuring averagely, realizing quick high accuracy and surveying
Amount.
For achieving the above object, the present invention takes technical scheme below: a kind of Double-femtosecond laser frequency comb synthesizes wave interference
Range-measurement system it is characterised in that: it includes the first femtosecond laser frequency comb, the second femtosecond laser frequency comb, Michelson interference
System, the second spectroscope, the 3rd spectroscope, the first narrow band filter, the second narrow band filter, the first photodetection
Device, the second photodetector, a/d transducer and signal processing unit；Wherein, described Michelson interference system includes first point
Light microscopic, the first corner reflector and the second corner reflector；Described first femtosecond laser frequency comb, as measurement signal source, sends light arteries and veins
Be flushed to described first spectroscope, the light pulse emission through described first dichroic mirror to described first corner reflector, through described
The light pulse of the first corner reflector reflection is transmitted to described second spectroscope through described first spectroscope again；Through described first light splitting
The light pulse emission of mirror transmission to described second corner reflector, again through described first light splitting after described second corner reflector reflection
Mirror reflexes to described second spectroscope；Described second femtosecond laser frequency comb, as oscillation signals according source, sends light pulse and arrives
Described second spectroscope, the light pulse through described second spectroscope transmission and the light arteries and veins through described Michelson interference system exit
Rush in row mixing, mixing light pulse emission is to described 3rd spectroscope；Light pulse through described 3rd spectroscope transmission is through described
Detected by described first photodetector after first narrow band filter and receive；Light pulse through described 3rd dichroic mirror
Detected by described second photodetector after described second narrow band filter and receive；Described first photodetector and
The outfan of two photodetectors is connected respectively to the input of described a/d transducer, and the outfan of described a/d transducer passes through
Corresponding data interface is connected to described signal processing unit to carry out processing the measurement distance value needed for obtaining by the signal of reception.
The spectral distribution of described first femtosecond laser frequency comb and the second femtosecond laser frequency comb must have larger width
Degree, and must have the larger overlapping region of ratio, this overlapping region accounts for more than half of the two itself spectral width.
The centre wavelength of described first narrow band filter and the second narrow band filter is respectively λ1And λ2, λ1With
λ2Must be in described greater overlap region, and λ1And λ2Selection need to meet following two conditions simultaneously: 1) according to bigness scale essence
Degree is chosen so that bigness scale precision is better than λs/ 4, λs=λ1λ2/(λ2-λ1), it is λ1And λ2Composite wave wavelength；2) according to interferometric phase
Certainty of measurement θ is chosen so that passing through composite wave λsThe precision of range finding is better than λ1/ 4 or λ2/ 4, wherein, composite wave λsThe essence of range finding
Spend for λs/ 2 (θ/360).
Described first narrow band filter and the second narrow band filter are all using Fiber Bragg Grating FBG.
Due to taking above technical scheme, it has the advantage that the 1, present invention passes through two narrow-band bandpass filters to the present invention
Ripple device selects to the centre wavelength of two femtosecond laser frequency comb, therefore after two narrow band filters, flies
Second light pulse broadening in time domain, sampling pulse can increase the points of sampling to reference and measurement pulse when sampling, improves
Signal quality；In addition, by the centre wavelength arranging different narrow band filters, suitable composite wave conduct can be obtained
Bridge, realizes bigness scale to the direct transition (need not be averagely) of accurate measurement.2nd, the synthetic wavelength that the present invention is formed by the use of dual wavelength as
Bridge, the bigness scale of Double-femtosecond laser frequency comb and interferometric phase are directly linked up, that is, achieve bigness scale direct to accurate measurement
Transition, thus avoid repeatedly measuring averagely, by the embodiment of the present invention, using the present invention in the bar not sacrificing measuring speed
Under part, directly bigness scale (several microns of precision) is transitioned into accurate measurement (nano level precision), be effectively ensured high measurement speed and
High measurement accuracy.The present invention can be widely applied in laser absolute distance measurement.
Brief description
To carry out detailed description to the present invention below in conjunction with accompanying drawing.It should be appreciated, however, that being provided only more of accompanying drawing
Understand the present invention well, they should not be interpreted as limitation of the present invention.
Fig. 1 is the light path schematic diagram of Double-femtosecond laser frequency comb composite wave interfeerometry ranging system of the present invention；
Fig. 2 is the light pulse schematic diagram of the present invention, and black is the first femtosecond laser frequency comb flfc1The light pulse sending,
Lycoperdon polymorphum Vitt is the second femtosecond laser frequency comb flfc2The light pulse sending；
Fig. 3 is normalization light spectral intensity schematic diagram of the present invention, and wherein, (a) is the first femtosecond laser frequency comb flfc1Light
Spectral structure, (b) is the second femtosecond laser frequency comb flfc2Spectral distribution, (c) is through the first narrow band filter bpf1Afterwards
Centre wavelength is λ1Narrow-band spectrum, (d) is through the second narrow band filter bpf2Rear center's wavelength is λ2Narrow-band spectrum；
Fig. 4 is the light pulse mixing schematic diagram of the present invention, and in lastrow, the hollow stick of fine line represents through the first corner reflection
Mirror cr1The light pulse returning, the solid stick of heavy line represents through the second corner reflector cr2Return light pulse, next line solid
The hollow stick of line represents the second femtosecond laser frequency comb flfc2The light pulse sending, dotted line frame represents optical pulse overlap position.
Specific embodiment
With reference to the accompanying drawings and examples the present invention is described in detail.
As shown in figure 1, the Double-femtosecond laser frequency comb composite wave interfeerometry ranging system of the present invention includes the first femtosecond laser
Frequency comb flfc1, the second femtosecond laser frequency comb flfc2, Michelson interference system, the second spectroscope bs2, the 3rd spectroscope
bs3, the first narrow band filter bpf1, the second narrow band filter bpf2, the first photodetector pd1, the second smooth electrical resistivity survey
Survey device pd2, a/d transducer 1 and signal processing unit 2；Wherein, Michelson interference system includes the first spectroscope bs1, first
Corner reflector cr1With the second corner reflector cr2；
First femtosecond laser frequency comb flfc1As measurement signal source, send light pulse to Michelson interference system
First spectroscope bs1, through the first spectroscope bs1The light pulse emission of reflection is to the first corner reflector cr1, through the first corner reflector
cr1The light pulse of reflection is again through the first spectroscope bs1It is transmitted to the second spectroscope bs2；Through the first spectroscope bs1The light arteries and veins of transmission
Punching is transmitted into the second corner reflector cr2, through the second corner reflector cr2Again through the first spectroscope bs after reflection1Reflex to the second light splitting
Mirror bs2；Second femtosecond laser frequency comb flfc2As oscillation signals according source, send light pulse to the second spectroscope bs2, through
Two spectroscope bs2The light pulse of transmission is mixed with the light pulse through Michelson interference system exit, and mixing light pulse is sent out
It is mapped to the 3rd spectroscope bs3；Through the 3rd spectroscope bs3The light pulse of transmission is through the first narrow band filter bpf1Afterwards by
One photodetector pd1Detect and receive；Through the 3rd spectroscope bs3The light pulse of reflection is through the second narrow band filter bpf2
Afterwards by the second photodetector pd2Detect and receive.First photodetector pd1With the second photodetector pd2Outfan respectively
It is connected to the input of a/d transducer 1, the outfan of a/d transducer 1 is connected to signal processing unit by corresponding data interface
The signal of reception is carried out processing measurement distance value l needed for obtaining by 2.
In a preferred embodiment, the first femtosecond laser frequency comb flfc1With the second femtosecond laser frequency comb flfc2
The repetition of existing Commercial fibers femto-second laser and phase offset frequency can be locked onto atomic clock to realize respectively, also may be used
Directly to adopt existing commercialization femtosecond laser frequency comb, both repetitions are in tens of mhz or hundred mhz magnitudes.Two femtoseconds swash
Optical frequency comb has that small repetition is poor, and their repetition periods (inverse of repetition) in time domain are designated as t respectivelyr1And tr2, repeat
Periodic inequality is designated as δ tr(as shown in Figure 2), the setting of two femtosecond laser frequency comb repetition differences should meet δ trSwash less than two femtoseconds
Light frequency pulse temporal width.
In a preferred embodiment, as shown in Fig. 3 (a) and (b), the first femtosecond laser frequency comb flfc1With second
Femtosecond laser frequency comb flfc2Spectral distribution must have larger width and (be generally chosen for more than 20nm, existing commercialization
Femtosecond laser frequency comb is attained by), and must have than larger overlapping region that (overlapping region accounts for the two spectral width itself
More than half, so make the selection of the centre wavelength of narrow band filter just have larger leeway), the first narrow-band bandpass
Wave filter bpf1With the second narrow band filter bpf2Centre wavelength be respectively λ1And λ2, light pulse is through this two arrowbands
In spectral distribution after band filter such as Fig. 3 shown in (c) and (d), λ1And λ2Must in above-mentioned larger overlapping region,
And λ1And λ2Selection should meet two conditions simultaneously: 1) according to bigness scale precision (typically several microns) choose so that bigness scale precision is excellent
In λs/ 4, wherein, λs=λ1λ2/(λ2-λ1), it is λ1And λ2Composite wave wavelength；2) (typically excellent according to interferometric phase certainty of measurement θ
In 0.5 °) choose so that passing through composite wave λsPrecision (the λ of range findings/ 2 (θ/360)) it is better than λ1/ 4 or λ2/4.Only simultaneously
Meet above-mentioned two condition and can ensure that will synthesize wave interference corresponding " several greatly " (interference fringe integer level time) during bigness scale determines
Standard, and according to the result of composite wave range finding, Single wavelength is interfered corresponding " several greatly " to fix.
In a preferred embodiment, two narrow band filters all can adopt Fiber Bragg Grating FBG, selects
It is after narrow band filter that the effect of narrow band filter has: one at 2 points, femtosecond pulse meeting broadening in time domain,
Current sampling pulse can increase the points of sampling to reference and measurement pulse when sampling, improves signal quality；Two is to pass through
The centre wavelength of different narrow band filters is set, suitable composite wave can be obtained as bridge, realize bigness scale to essence
The direct transition (need not be averagely) surveyed.
Further illustrate the concrete measuring principle of the LDMS of the present invention below by specific embodiment:
As shown in figures 1-4, the present invention is by the first corner reflector cr1With regard to the first spectroscope bs1Minute surface symmetric position fixed
Justice is for shown in baseline bl(Fig. 1 chain lines), the second corner reflector cr2It is measurement distance value to baseline bl apart from l.Work as l
During more than zero, from the first corner reflector cr1With the second corner reflector cr2There are intervals τ, simultaneously in the light pulse returning
Will be through the first corner reflector cr1The light pulse returning is defined as reference arm light pulse (the hollow stick of fine line as shown in Figure 4),
Will be through the second corner reflector cr2The light pulse returning is defined as measuring arm light pulse (the solid stick of heavy line as shown in Figure 4),
Will be through the second femtosecond laser frequency comb flfc2The light pulse sending is defined as local oscillation light pulse (heavy line as shown in Figure 4
Hollow stick).
Reference arm light pulse through Michelson interference system exit and measurement arm light pulse with through the second spectroscope bs2Thoroughly
The local oscillation light pulse penetrated mixes, due to the presence of two femtosecond laser frequency comb repetition differences, local oscillation light pulse
In each light pulse and reference arm light pulse in each pulse and measure each pulse in arm light pulse all can warp respectively
Go through and move closer to from being separated to, be then superimposed, then the process being gradually distance from, and often through one section of tupdate=tr1tr2δtr's
Time, said process can be repeated once, and by the first photodetector pd1With the second photodetector pd2Detect.First flies
Second laser frequency comb flfc1Pulse interval interval can be expressed as tr1The aerial light velocity of c, c pulse, the second femtosecond laser frequency
Rate combs flfc2Pulse interval be spaced apart tr2C, the convenience processing for follow-up data, the present invention is calculating seasonal ra1=tr1c/
2, ra2=tr2c/2.
When measurement distance l is less than ra1When, from the second corner reflector cr2The light pulse returning can be in the first corner reflector cr1
The first spectroscope bs is reached before the next pulse returning1, will not impulsing dislocation, therefore measurement obtain apart from l be
For actual distance value, when measurement distance l is more than ra1When, from the second corner reflector cr2The light pulse returning may be first
Corner reflector cr1Return next pulse after just reach, thus impulsing dislocation, then now measurement obtain apart from l
It is not actual distance value, need cumulative upper ra1Integral multiple just can access actual range, the concrete calculating process to l below
It is described in detail:
1) when measurement distance l is less than ra1When, the present invention is as follows to the signal processing of measurement distance l:
As shown in figure 4, in each tupdateIn time, local oscillation light pulse respectively with reference arm light pulse and measurement
Arm light pulse has been superimposed once (as shown in the dotted line frame in Fig. 4).For the first photodetector pd1The signal that detects and
Speech, the wherein a length of λ of cardiac wave1, corresponding mid frequency is ν1.Translate the theorem of corresponding frequency domain phase shift according to time domain, this two
In the superposed signal of individual position, frequency is ν11Phase delay (the ν of spectral line11Centered on frequency ν1Any one neighbouring spectrum
Line, its Phase delay is the spectral line ν in (a) and (b) position sensing signal in Fig. 411Corresponding phase contrast) δ φ11(ν11) with
Relation between reference arm light pulse and measurement arm light pulse delay, τ is:
δφ11(ν11)=(2 π τ) ν11(1)
Become by the Phase delay frequency corresponding with spectral line that formula (1) can obtain spectral line during optical pulse overlap twice
Direct ratio, the interference light signal of (a) that receive position and (b) position is carried out Fourier transformation by signal processing unit 2, and by two
The overlapping phase frequency spectrum of subpulse does difference operation, obtains the Phase delay of different spectral line, that is, obtain a series of difference light frequencies
With corresponding Phase delay (φ1i, ν1i), i represents the sequence number of spectral line, then by obtain some to (φ1i, ν1i)
Carry out fitting a straight line, the slope obtaining fitting a straight line is b1(b1=2 π τ), finally giving tested is that (delay, τ has corresponded to light apart from l
Coming and going in measurement distance):
l=cτ/2=b1C/4 π .(2)
In order to improve certainty of measurement further, it is possible to use the information of interferometric phase.Firstly for the first photodetector
For the signal that pd1 detects, the centre wavelength interfering light pulse is λ1, central wavelength lambda1Corresponding interferometric phase δ φ1,
According to principle of interference, light pulse central wavelength lambda1Interference phase difference δ φ in (a) and (b) position of pulse overlap1With found range
Relation between l is:
l=(δφ1/2π+m1) λ1/ 2 (3)
In formula, m1Be wavelength be λ1The interference of light corresponding integer level time (" several greatly "), be nonnegative integer.
Due to δ φ1Fourier transformation can be carried out by the interference light signal of (a) position and (b) position according to formula (1)
Phase place subtract each other again and obtain.If therefore can accurately obtain m1, then can obtain accurately apart from l, but generally will obtain
m1, the bigness scale distance value obtaining generally by formula (2) goes divided by λ1After/2, round is asking.In order to ensure to calculate
Do not produce deviation when rounding, then need the bigness scale precision meeting l to be better than λ1/ 4 condition, this with laser interferometry in precision by
The criterion that level is refined is similar.In order to meet this condition, existing the more commonly used method takes after being by multiple bigness scale all
To improve bigness scale precision, the precision after average reaches better than λ value1M is asked for again during/4 condition1, but measuring speed is significantly
Reduce.
For the second photodetector pd2For the signal detecting, the centre wavelength interfering light pulse is λ2, middle cardiac wave
Long λ2Corresponding interferometric phase δ φ2, according to principle of interference, light pulse central wavelength lambda2(a) and (b) position in pulse overlap
The interference phase difference δ φ putting2And tested relation between l is:
l=(δφ2/2π+m2) λ2/ 2 (4)
In formula, m2It is λ for wavelength2The interference of light corresponding integer level time (" several greatly "), be nonnegative integer.By formula (3) and
Formula (4) simultaneous abbreviation, will formula (3) and λ2The result being multiplied deducts formula (4) and λ1Obtain after the result being multiplied:
l=(δφs/2π+ms) λs/ 2 (5)
In formula, λs=λ1λ2/(λ2-λ1), it is λ1And λ2Composite wave wavelength；δφs=δφ1-δφ2, it is composite wave phase
Position；msFor the integer level time (" several greatly ") of composite wave, it is nonnegative integer.Due to λ1, λ2, δ φ1With δ φ2Be it is known that so
Composite wave wavelength XsWith synthesis wave phase δ φsAll can be calculated if it is possible to obtain accurate msValue, then can be by closing
Ripple wavelength and phase place is become to obtain tested distance by formula (5).The bigness scale value of the l in the present embodiment obtaining formula (2) substitutes into
Formula (5) calculates ms, and to msCarry out round.In order to ensure calculated msIt is accurate it is only necessary to meet l
Bigness scale precision be better than λs/ 4.Hereinbefore mention λ1And λ2Selection when need to meet this condition, this is to be easily done
, it is exemplified below:
With λ1=1.555 μm, λ2As a example=1.565 μm, composite wave wavelength Xs=243.36μm.And existing single bigness scale l
Precision is usually several microns, far superior to λs/ 4, therefore ensure enough to obtain accurate ms, by msIn generation, returns to formula (5) again, and
According to λsWith δ φsThen can be calculated more accurately apart from l.Taking 0.5 degree of phase accuracy as a example, the essence of the l now obtaining
Degree can reach λs/ 2 (0.5/360)=0.17 μm, it has been better than existing certainty of measurement λ1/4.Therefore will now more accurate l
Value is updated to formula (3), is calculated m1And round, then can get accurate m1Value.Again by m1In generation, returns to formula
(3), and according to λ1With δ φ1Then can recalculate and obtain accurate l value.Still taking 0.5 degree of phase accuracy as a example, the now essence of l
Degree can reach λ1/ 2 (0.5/360)=1.1nm.Can be seen by above-mentioned example, measurement can not sacrificed by this method
Under conditions of speed, directly bigness scale (several microns of precision) is transitioned into accurate measurement (nano level precision).
2) when measurement distance l is more than ra1When, can be measured by cursor principle, method particularly includes:
1. when measurement distance l is more than ra1When it is assumed that measurement arm light pulse k-th (k be any positive integer, represent pulse
Sequence number) pulse is from the first spectroscope bs1Travel to the second corner reflector cr2Again return to the first spectroscope bs1Period in, ginseng
Examine the kth of arm light pulse, k+1 ..., k+m(m is positive integer) individual pulse has been completed by the first spectroscope bs1Travel to
First corner reflector cr1Again return to the first spectroscope bs1Process, in other words, ginseng shown by lastrow as shown in Figure 4
Examine arm light pulse sequence and measurement arm light pulse sequence has occurred that the dislocation in m cycle, the dislocation in each cycle corresponds to
Distance be ra1, however, the measuring method of situation is planted it is impossible to come out the periodicity m of dislocation using above-mentioned 1st), according to
Method 1) time delay that measures is corresponding is between reference arm light pulse kth+m pulse and measurement k-th pulse of arm light pulse
Delay, the distance now surveyed is designated as d1, then actual tested can be write as l=mr apart from la1+d1Form, d1<ra1；
2. by the measuring method 1 of the present invention) measurement obtains distance value d1；
3. by the first femtosecond laser frequency comb flfc of the LDMS of the present invention1With the second femtosecond laser frequency comb
flfc2Swap it may be assumed that the second femtosecond laser frequency comb flfc2As measurement signal source, the first femtosecond laser frequency comb flfc1
As oscillation signals according source, using the measuring method 1 of the present invention) measurement obtain distance value d2, d2<ra2；
4. due to exchange before and after two femtosecond laser frequency comb measured be same apart from l, can be expressed as
Form:
l=mra1+d1=mra2+d2(6)
In formula, m is defined as above, and is the dislocation periodicity between reference arm pulse and measurement arm pulse, ra1And ra2It is
Datum, due to ra1And ra2There is small difference, and this difference can be embodied in d with the difference of m value1And d2Difference
On.Therefore according to the d recording1And d2M can be obtained, then m is substituted into formula (6), you can be calculated the distance value l of reality.
In order to ensure formula (6) both sides ra1And ra2Coefficient m identical, then need to meet l/ra1Round and l/ra2The knot rounding
Really identical it is therefore desirable to meet l < ra1ra1/(ra1-ra2).
The various embodiments described above are merely to illustrate the present invention, and wherein each optical element can be supported using conventional support
Fixing, and the position of optical element etc. all can be varied from, as long as meeting the paths condition of the present invention, all
The equivalents and improvement carrying out on the basis of technical solution of the present invention, all should not exclude protection scope of the present invention it
Outward.
Claims (2)
1. a kind of Double-femtosecond laser frequency comb composite wave interfeerometry ranging system it is characterised in that: it include first femtosecond laser frequency
Rate comb, the second femtosecond laser frequency comb, Michelson interference system, the second spectroscope, the 3rd spectroscope, the first narrow-band bandpass filter
Ripple device, the second narrow band filter, the first photodetector, the second photodetector, a/d transducer and signal processing list
Unit；Wherein, described Michelson interference system includes the first spectroscope, the first corner reflector and the second corner reflector；
Described first femtosecond laser frequency comb, as measurement signal source, sends light pulse to described first spectroscope, through described
The light pulse emission of one dichroic mirror is to described first corner reflector, the light pulse through described first corner reflector reflection and warp
Described first spectroscope is transmitted to described second spectroscope；Light pulse emission through described first spectroscope transmission is to described second
Corner reflector, to described second spectroscope after described second corner reflector reflection and through described first dichroic mirror；Described
Second femtosecond laser frequency comb, as oscillation signals according source, sends light pulse to described second spectroscope, through described second point
The light pulse of light microscopic transmission is mixed with the light pulse through described Michelson interference system exit, and mixing light pulse emission arrives
Described 3rd spectroscope；Light pulse through described 3rd spectroscope transmission is after described first narrow band filter by described
One photodetector detects and receives；Light pulse through described 3rd dichroic mirror quilt after described second narrow band filter
Described second photodetector detects and receives；The outfan of described first photodetector and the second photodetector connects respectively
To the input of described a/d transducer, the outfan of described a/d transducer is connected at described signal by corresponding data interface
The signal of reception is carried out processing the measurement distance value needed for obtaining by reason unit；
The spectral distribution of described first femtosecond laser frequency comb and the second femtosecond laser frequency comb must have larger width, and
Must there is the larger overlapping region of ratio, this overlapping region accounts for more than half of the two itself spectral width；
The centre wavelength of described first narrow band filter and the second narrow band filter is respectively λ1And λ2, λ1And λ2Necessary
In described greater overlap region, and λ1And λ2Selection need to meet following two conditions simultaneously:
1) chosen according to bigness scale precision so that bigness scale precision is better than λs/ 4, λs=λ1λ2/(λ2-λ1), it is λ1And λ2Composite wave ripple
Long；
2) chosen according to interferometric phase certainty of measurement θ so that passing through composite wave λsThe precision of range finding is better than λ1/ 4 or λ2/ 4, its
In, composite wave λsThe precision of range finding is λs/ 2 (θ/360).
2. as claimed in claim 1 a kind of Double-femtosecond laser frequency comb composite wave interfeerometry ranging system it is characterised in that: described
First narrow band filter and the second narrow band filter are all using Fiber Bragg Grating FBG.
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| CN111522018B (en) * | 2020-04-07 | 2022-05-10 | 清华大学深圳国际研究生院 | Double-femtosecond laser frequency comb distance measuring device and method |
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