CN104215176A - High accuracy optical interval measurement device and method - Google Patents
High accuracy optical interval measurement device and method Download PDFInfo
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- CN104215176A CN104215176A CN201410472652.5A CN201410472652A CN104215176A CN 104215176 A CN104215176 A CN 104215176A CN 201410472652 A CN201410472652 A CN 201410472652A CN 104215176 A CN104215176 A CN 104215176A
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Abstract
Disclosed are a high accuracy optical interval measurement device and a high accuracy optical interval measurement method. The high accuracy optical interval measurement device comprises a short coherent light source, a laser length measurement light source, an illumination indication light source, a first optical fiber coupler, a second optical fiber coupler, a measurement light path, a reference mirror light path, a delayed scanning light path, a wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, connection optical fibers and an environment sensor. According to the high accuracy optical interval measurement device and the high accuracy optical interval measurement method, a time domain optical coherence chromatographic technique is adopted, a broadband light source and the high accuracy delayed scanning light path are used to achieve noncontact measurement of optical element intervals, a common optical path length measurement technique is used to obtain accurate displacement of the delayed scanning light path, measurement errors are eliminated and measurement accuracy is improved by using an extraction algorithm enveloped with five step phase shift interference fringes and through environment compensation, the internal measurement accuracy in a measurement range can reach the submicron level, and simultaneously measurement can be performed in real time and measurement efficiency is improved during the installation adjustment process of an optical instrument.
Description
Technical field
The present invention relates to field of optical measurements, be specifically related to a kind of non-contacting measurement mechanism based on optical fiber Michelson interference principle and measuring method is measured lens center thickness and lens separation.
Background technology
In optical field, lens are as the most basic optical element of composition optical system, and the mismachining tolerance of its center thickness will directly have influence on the image quality of whole optical system.Debug in process at optical instrument, position of optical element error is larger on the impact of complete machine optics assembly quality, also be error more rambunctious, particularly in the assembling process of exposure system of photo-etching machine, aerial survey camera lens, interferometer standard lens, the contour performance precision optical system of laserresonator, have very strict control overflow to interval, lens center, the little by little deviation at its interval, lens center all may cause the deterioration of image quality.The positional precision how solving optical element is the key point ensureing its optical property.
In traditional optical measurement, great majority adopt dial gauge or clock gauge etc. to carry out contact type measurement or measure with the pure optical means of indirect type at present.The major defect of contact type measurement is the anti-reflection film of easy snag lens surface, and ergometry easily makes piece surface damage, and therefore measuring accuracy is lower.And indirect type is measured, because of needs reduced parameter, its precision is reduced.Further, above-mentioned two kinds of methods measure all more difficult practical center accurately finding lens, and therefore measuring accuracy is not high, is not suitable for the dress school of high-performance objective.
In the prior art, in " optical lens center thickness measuring system and method " (see Chinese patent CN102435146A), disclose a set of noncontact lens center thickness measuring system based on the confocal method of optics, it measures simple and fast, but its measurement range is little, be subject to the restriction of minimal wave length in light source and most long wavelength's focal length, be applicable to signal-lens measurement, its precision is subject to the restriction of measurement range and spectrometer optical resolution.
Summary of the invention
The object of the invention is to the measuring accuracy and the efficiency that improve optical interval in optical measurement, and a kind of high-precision optical interval measurement apparatus and method based on optical fiber Michelson interference principle are provided, adopt Time Domain Optical coherence tomography techniques, wideband light source and high precision delaying sweep light path is utilized to realize the non-cpntact measurement at optical element interval, the precise displacement of optical delay circuit is obtained by common light path Laser technique in dimensional metrology, adopt the extraction algorithm of five step phase shift interference fringe envelopes and pass through ambient compensation, eliminate measuring error, improve measuring accuracy, in measurement range, interval measurement precision can reach submicron order, debug in process at optical instrument simultaneously and can realize real-time measurement.
Technical solution of the present invention is specific as follows:
A kind of high-precision optical interval measurement device, for two fiber coupler structure, specifically comprise: short-coherence light source, laser length measurement light source, illumination instruction light source, the first fiber coupler, the second fiber coupler, optical path, reference mirror light path, delaying sweep light path, wavelength division multiplexer, the first photodetector, the second photodetector, connecting fiber, environmental sensor.
Short-coherence light source and the second fiber coupler are connected to two ports of the side of the first fiber coupler, laser length measurement light source and optical path are connected to two ports of the opposite side of the first fiber coupler, and illumination instruction light source is connected with optical path; Reference mirror light path and delaying sweep light path are connected to two ports of the opposite side of the second fiber coupler, wavelength division multiplexer is connected with a port of the side of the second fiber coupler, and the first and second photodetectors are connected with two output ports of wavelength division multiplexer respectively.
Described short-coherence light source is super-radiance light emitting diode (Superluminescent LED), is wideband light source, has very little coherent length, as the interference signal measurement light source of device.
Described laser length measurement light source is distributed feedback laser (Distributed FeedBack Laser), has extraordinary monochromaticity, the long positioned light source of the survey as device.
Described illumination instruction light source is laser diode, sends visible ray in order to coordinate the adjustment of determinand optical axis position.
Described optical path comprises four-dimensional adjustment rack, adjustable focus optical fiber amasthenic lens, determinand and erecting frame.Optical path is connected with the first fiber coupler by adjustable focus optical fiber amasthenic lens, the measuring beam that short-coherence light source sends enters the adjustable focus optical fiber amasthenic lens in optical path through the first fiber coupler, each surface in determinand reflected, and enters the second fiber coupler after getting back to the first fiber coupler.Erecting frame is for adjusting and fixing the position of determinand, and four-dimensional adjustment rack is fixed adjustable focus optical fiber amasthenic lens and points to and position adjustments, ensures the optical axis coincidence of its optical axis and determinand.Adjustable focus optical fiber amasthenic lens is positioned over optical path foremost, by the focal position of adjustment adjustable focus optical fiber amasthenic lens outgoing beam, can ensure that the light beam major part that in determinand, each surface reflection is returned is got back in adjustable focus optical fiber amasthenic lens.
Described reference mirror light path comprises an optical fiber retroeflector, is connected with the second fiber coupler by connecting fiber, reflects the folded light beam on surface each in determinand in optical path.The position of optical fiber retroeflector should be arranged in the initial position (from the position that fiber optic collimator camera lens is nearest) of the removable scanning reflection mirror of corresponding delaying sweep light path, and namely in optical fiber retroeflector and delaying sweep light path, the initial position of removable scanning reflection mirror is aplanatic.
Described delaying sweep light path comprises fiber optic collimator camera lens, removable scanning reflection mirror and motor and drives mobile platform.Fiber optic collimator camera lens is positioned over delaying sweep light path foremost, delaying sweep light path is connected with the second fiber coupler by fiber optic collimator camera lens, short coherent measurement light beam and laser length measurement light beam, by incide after fiber optic collimator camera lens collimation on removable scanning reflection mirror and to reflect, are got back in the second fiber coupler.Removable scanning reflection mirror is arranged on a motor and drives on mobile platform, with certain speed uniform motion in measuring process, the interference signal measurement that its position mobile message is produced in the folded light beam of reference mirror light path and removable scanning reflection mirror respectively by laser length measurement light beam obtains.
Described wavelength division multiplexer is 1310/1550nm wavelength division multiplexer, for being separated by the interference signal of two kinds of different wave lengths, is divided into two-way, enters the first and second photodetectors respectively.
The interference signal that the laser length measurement light beam that first, second described photodetector is used for the short coherent measurement light beam and wavelength 1550nm receiving wavelength 1310nm respectively produces, and be connected with computing machine and show.
Described connecting fiber is single-mode polarization maintaining fiber, avoids the measuring error because polarization mode dispersion causes.
Described environmental sensor detects the inside temperature in temperature, air pressure, relative humidity and delaying sweep light path under the present circumstances respectively, is applied to the compensation of refractive index calculated value in algorithm, ensures the precision of interval measurement.
Utilize above-mentioned optical interval measurement device to treat the measuring method at object test light interval, the method comprises the following steps:
1. by illumination instruction light source by Fiber connection in optical path, light source is opened, determinand is fixed by erecting frame, by the position regulating four-dimensional adjustment rack to regulate adjustable focus optical fiber amasthenic lens, according to the luminous point that surface reflection each in determinand is returned, regulate the outgoing beam of adjustable focus optical fiber amasthenic lens to determinand) center, namely in the optical axis of determinand and optical path measuring beam optical axis coincidence;
2. illumination instruction light source is closed, the optical fiber of connection first fiber coupler the 4. port is replaced the connecting fiber of illumination instruction light source and optical path, open short-coherence light source and laser length measurement light source, regulate the adjustable focus optical fiber amasthenic lens in optical path, make the stiffness of coupling of each surface reflection in determinand large as far as possible;
3. the motor controlled in described delaying sweep light path drives mobile platform at the uniform velocity to drive removable scanning reflection mirror to move, the interference signal input computing machine that the first photodetector and the second photodetector will record respectively;
4. computing machine carries out data processing, draws the optical interval of determinand:
Utilize the five step phase shift nonlinear algorithms based on movable phase interfere to carry out the extraction of interference signal, calculate the tangent value of the phase place of each sampled point by following formula,
Wherein I
1, I
2, I
3, I
4, I
5be respectively the light intensity value of five neighbouring sample points,
Edlen formula is utilized to revise the refractive index of air and group index:
n
15-1＝[8342.13+2406030(130-σ
2)
-1+15997(38.9-σ
2)
-1]×10
-8
n
t,p,f＝n
t,p-f(5.7224-0.0457σ
2)×10
-8
What utilize optical path and optics group delay in delaying sweep light path compares the optical interval D drawn in determinand
mea,
n
g,air(λ
1,T
ref,p,RH)·D
ref＝n
g,air(λ
1,T
mea,p,RH)·D
mea
In formula, n
airwith n
g, airrepresent refractive index and the group index of air respectively, they are by wavelength (λ
1or λ
2), temperature (the temperature T in delaying sweep light path
refor the temperature T in optical path
mea), air pressure p and relative humidity RH determined, the computing formula of its refractive index is edlen formula:
n
15-1＝[8342.13+2406030(130-σ
2)
-1+15997(38.9-σ
2)
-1]×10
-8
n
t,p,f＝n
t,p-f(5.7224-0.0457σ
2)×10
-8
In formula: (n
15-1) be that σ is the wave number in vacuum, is the inverse of wavelength X in a standard atmospheric pressure, refractive index at 15 DEG C in air, unit is μm
-1, (n
t,p-1) for being subject to the refractive index of temperature and barometric pressure effect in normal air, n
t, p, ffor being subject to the refractive index of temperature, air pressure and steam dividing potential drop impact in normal air, t is temperature DEG C, and p is air pressure Torr, f is steam dividing potential drop Torr, by n
t, p, frefractive index n can be obtained
airand the dispersion relation of wavelength, utilize the formula of group index
namely corresponding group index n can be drawn
g, air.
With compared with first technology, the present invention has following technological merit:
1) the high-precision optical interval measurement apparatus and method based on optical fiber Michelson interference principle that the present invention proposes belong to non-contact measurement, effectively can solve contact and indirect type and measure the shortcoming that optical interval brings, measurement range is large, measurement efficiency is high, disposablely can complete the measurement at many group intervals in one group of optical system.
2) the present invention adopts two fiber coupler structure, under making the light path of generation interference signal two light beam be positioned at the same environment of device, eliminate reference path and optical path in single fiber coupler structure and lay respectively in device and environmental impact factor outside device.
3) the present invention adopts optical interval measurement signal and laser length measurement signal to be total to the version of light path, and eliminate the errors in position measurement of removable scanning reflection mirror, achieve the accurate measurement of its shift length, interval measurement precision can reach submicron order.
Accompanying drawing explanation
Fig. 1 is that the high-precision optical interval measurement device based on optical fiber Michelson interference principle of the present invention is always schemed.
In figure:
1 is short-coherence light source;
2 is laser length measurement light sources;
3 is illumination instruction light sources;
4 is first fiber couplers;
5 is second fiber couplers;
6 is optical paths;
601 is four-dimensional adjustment racks;
602 is adjustable focus optical fiber amasthenic lens;
603 is determinands;
604 is erecting frames;
7 is reference mirror light paths;
701 is optical fiber retroeflectors;
8 is delaying sweep light paths;
801 is fiber optic collimator camera lenses;
802 is removable scanning reflection mirrors;
803 is that motor drives mobile platform;
9 is wavelength division multiplexers;
10 is first photodetectors;
11 is second photodetectors;
12 is connecting fibers;
13 is environmental sensors.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail, but should limit the scope of the invention with this.
As shown in Figure 1, high-precision optical interval measurement device of the present invention mainly consists of the following components: short-coherence light source 1, laser length measurement light source 2, illumination instruction light source 3, first fiber coupler 4, second fiber coupler 5, optical path 6, reference mirror light path 7, delaying sweep light path 8, wavelength division multiplexer 9, first photodetector 10, second photodetector 11, connecting fiber 12, environmental sensor 13.
Short-coherence light source 1 and the second fiber coupler 5 are connected to two ports of the side of the first fiber coupler 4, laser length measurement light source 2 and optical path 6 are connected to two ports of the opposite side of the first fiber coupler 4, and illumination instruction light source 3 is connected with optical path 6; Reference mirror light path 7 and delaying sweep light path 8 are connected to two ports of the opposite side of the second fiber coupler 5, wavelength division multiplexer 9 is connected with a port of the side of the second fiber coupler 5, and the first photodetector is connected with two output ports of wavelength division multiplexer 9 respectively with the second photodetector 10,11.
Described short-coherence light source 1 is super-radiance light emitting diode (SLED), minimum output power 15mW, central wavelength lambda
1=1310nm, half-peak band width Δ λ=50nm, coherent length is about 15 μm.
Described laser length measurement light source 2 is distributed feedback laser, central wavelength lambda
2=1550nm ,-3dB live width is 2MHz, and output power can reach 30mW.
Described illumination instruction light source 3 is laser diode, and central wavelength lambda=655nm, half-peak band width δ λ=30nm, output power is 0.676mW.
The measuring beam that short-coherence light source 1 sends is coupled in the optical fiber 12 be connected with optical path 6 by the first described fiber coupler 4, and makes the folded light beam on each surface in determinand 603 be coupled in the optical fiber 12 be connected with the second fiber coupler 5; The laser length measurement light beam coupling that simultaneously laser length measurement light source 2 can be sent is in the optical fiber 12 be connected with the second fiber coupler 5.
The second described fiber coupler 5 is respectively by through the measuring beam of determinand 603 kinds of each surface reflections and laser length measurement light beam, be beamed into two-beam respectively and enter reference mirror light path 7 and delaying sweep light path 8 respectively, the light beam coupling simultaneously also reflected with reference to mirror light path 7 and delaying sweep light path 8 is in the optical fiber 12 be connected with wavelength division multiplexer 9.
Described optical path 6 comprises four-dimensional adjustment rack 601, adjustable focus optical fiber amasthenic lens 602, determinand 603 and erecting frame 604.Optical path 6 is connected with the first fiber coupler 4 by adjustable focus optical fiber amasthenic lens 602, the measuring beam that short-coherence light source 1 sends enters the adjustable focus optical fiber amasthenic lens 602 in optical path 6 through the first fiber coupler 4, in determinand 603, each surface reflected, and enters the second fiber coupler 5 after getting back to the first fiber coupler 4.Erecting frame 604 is for adjusting and fixing the position of determinand 603, and four-dimensional adjustment rack 601 pairs of adjustable focus optical fiber amasthenic lens 602 are fixed and point to and position adjustments, ensures the optical axis of focusing optical fiber amasthenic lens 602 and the optical axis coincidence of determinand 603.Adjustable focus optical fiber amasthenic lens 602 is positioned over optical path 6 foremost, by the focal position of adjustment adjustable focus optical fiber amasthenic lens 602 outgoing beam, ensures that the first photodetector 10 can obtain a very strong interference signal.
Described reference mirror light path 7 comprises an optical fiber retroeflector 701, is connected with the second fiber coupler 5 by connecting fiber 12, reflects the folded light beam on surface each in determinand 603 in optical path 6.The position of optical fiber retroeflector 701 should be arranged in the initial position (from the position that fiber optic collimator camera lens 801 is nearest) of the removable scanning reflection mirror of corresponding delaying sweep light path 8 802, and namely optical fiber retroeflector 701 is aplanatic with the initial position of removable scanning reflection mirror 802 in delaying sweep light path 8.
Described delaying sweep light path 8 comprises fiber optic collimator camera lens 801, removable scanning reflection mirror 802 and motor and drives mobile platform 803.Fiber optic collimator camera lens 801 is positioned over delaying sweep light path 8 foremost, delaying sweep light path 8 is connected with the second fiber coupler 5 by fiber optic collimator camera lens 801, short coherent measurement light beam and laser length measurement light beam to be incided after being collimated by fiber optic collimator camera lens 801 on removable scanning reflection mirror 802 and reflect, and get back in the second fiber coupler 5.Removable scanning reflection mirror 802 is arranged on a motor and drives on mobile platform 803, with certain speed uniform motion in measuring process, the interference signal measurement that its position mobile message is produced in the folded light beam of reference mirror light path 7 and removable scanning reflection mirror 802 respectively by laser length measurement light beam obtains.
Described wavelength division multiplexer 9 is 1310/1550nm wavelength division multiplexer, for being separated by the interference signal of two kinds of different wave lengths, is divided into two-way, enters the first photodetector 10 and the second photodetector 11 respectively.
The first described photodetector 10 and the second photodetector 11 are two photodiodes, spectral response range is 950 ~ 1650nm, the interference signal that the laser length measurement light beam of the short coherent measurement light beam and wavelength 1550nm that receive wavelength 1310nm respectively produces, and be connected with computing machine and show.
Described connecting fiber 12 is single-mode polarization maintaining fiber, and cutoff wavelength is 1260nm.
Described environmental sensor 13 detects the inside temperature in temperature, air pressure, relative humidity and delaying sweep light path 8 under the present circumstances respectively, is applied to the compensation of refractive index calculated value in algorithm, ensures the precision of interval measurement.
The short coherent measurement light beam that in device, short-coherence light source 1 sends enters into optical path 6 through the first fiber coupler 4, the reflected light on each two surfaces in determinand 603, two bundles are divided into through the second fiber coupler 5, light beam enters reference mirror light path 7, and another light beam enters in delaying sweep light path 8.In delaying sweep light path 8, light beam after fiber optic collimator camera lens 801 reflect by removable scanning reflection mirror 802.Each folded light beam turns back in the second fiber coupler 5, enters wavelength division multiplexer 9.Now, in the folded light beam of removable scanning reflection mirror 802 and reference mirror light path 7, the folded light beam of optical fiber retroeflector 701 interferes generation interference signal, through algorithm process after being detected, obtains the intensity distributions of interference signal by the first photodetector 10.Simultaneously, the laser length measurement light beam that laser length measurement light source 2 sends, two bundles are divided into respectively through after the first fiber coupler and the second fiber coupler 4,5, enter reference mirror light path 7 and delaying sweep light path 8 respectively, the interference signal that in two light paths, folded light beam produces is obtained by the second photodetector 11, because it is identical with the sample frequency that short coherent measurement light beam produces interference signal, the relative position that short coherent measurement light beam produces the removable scanning reflection mirror 802 corresponding to interference signal extreme value place namely can be obtained.Be there is the difference of the position of removable scanning reflection mirror 802 in delaying sweep light path 8 corresponding to maximum position by interference signal respectively, namely can calculate the optical interval of determinand 603.
In systematic survey process, high-precision optical interval measurement device of the present invention and measuring method, comprise the following steps:
1. by illumination instruction with light source 3 by Fiber connection to the adjustable focus optical fiber amasthenic lens 602 in optical path 6, light source is opened, determinand 603 is fixed by erecting frame 604, by the position regulating four-dimensional adjustment rack 601 to regulate adjustable focus optical fiber amasthenic lens 602, according to the luminous point that surface reflection each in determinand 603 is returned, regulate the center of outgoing beam to determinand 603 of adjustable focus optical fiber amasthenic lens 602, i.e. the optical axis of determinand 603 and the optical axis coincidence of adjustable focus optical fiber amasthenic lens 602 outgoing measuring beam;
2. illumination instruction light source 3 is closed, the optical fiber of connection first fiber coupler 4 the 4. port is replaced the connecting fiber of illumination instruction light source 3 and adjustable focus optical fiber amasthenic lens 602 in optical path 6, open short-coherence light source 1 and laser length measurement light source 2, regulate the adjustable focus optical fiber amasthenic lens 602 of optical path 6, make the stiffness of coupling of each surface reflection in determinand 603 large as far as possible;
3. the motor in control lag scanning optical path 8 drives mobile platform 803 at the uniform velocity to drive removable scanning reflection mirror 802 to move, and the interference signal that the laser length measurement light beam of short coherent measurement light beam and wavelength 1550nm that the first photodetector 10 and the second photodetector 11 receive wavelength 1310nm respectively produces inputs computing machine;
4. described computing machine carries out to interference signal the optical interval that data processing draws determinand 603:
Whole device is actually and carries out measuring with comparing of optical path 6 and optics group delay in delaying sweep light path 8, and optics group delay is defined as n
gd, wherein n
gfor group index, under setted wavelength, it is defined as
d is physical distance.When systematic survey, removable scanning reflection mirror 802 in delaying sweep light path 8 carries out uniform rectilinear scanning along the direction being parallel to optical axis with certain speed on electrically driven (operated) mobile platform, simultaneously, the computing machine be connected with the second photodetector 11 with the first photodetector 10 constantly gathers and processes the interference signal that the short coherent measurement light beam of the wavelength 1310nm obtained in scanning process and wavelength 1550nm laser length measurement light beam produce, the five step phase shift nonlinear algorithms based on movable phase interfere are utilized to carry out the extraction of interference signal, good precision and repeatability is had under actual noise grade.In interference signal, the degree of modulation of certain given sampled point can be defined by following formula:
wherein I
1, I
2, I
3, I
4, I
5be respectively the light intensity value of five neighbouring sample points, the phase value of each sampled point can be calculated by following formula,
Make the phase-shift phase in phase shift algorithm
wherein v is the translational speed of removable scanning reflection mirror 802 in delaying sweep light path 8, f
sfor system sampling frequency, be also the sample frequency of laser length measurement beam interference signal simultaneously, can v=30mms be obtained
-1, f
s=180kHz.So when scanning reflection mirror 802 removable in delaying sweep light path 8 moves to a certain position, when making the folded light beam group delay difference of optical fiber retroeflector 701 in its folded light beam and reference mirror light path 7 be zero, interference signal is peak value; When removable scanning reflection mirror 802 move to make optical fiber retroeflector 701 in its folded light beam and reference mirror light path 7 folded light beam group delay difference for n
gduring the position of D, an interference peak signal (wherein n will be obtained again
gfor the group index of medium between surface each in determinand 603, D is the optical interval in determinand 603 between two surfaces).If determinand 603 comprises organize optical interval more, then in single pass process, multiple peak value will be there will be in the first photodetector 10, the position of removable scanning reflection mirror 802 in delaying sweep light path 8 corresponding to each peak value, is each optical mirror plane vertex position in optical path 6 in determinand 603.Below it is further described: the relative position Z of removable scanning reflection mirror 802
refcan be defined by following formula:
wherein
be to wavelength X in the second photodetector 11
2the laser length measurement beam interference signal measurement of=1550nm the phase value obtained by algorithm process.Wavelength X
1measurement interference signal and wavelength X
2laser length measurement interference signal be with identical sample frequency f
sobtain, therefore measure the relative distance D of removable scanning reflection mirror 802 movement in distance in interference signal between two peak values and delaying sweep light path 8
ref, also just correspond to the optical interval D of optical element in determinand 603 in optical path 6
mea.Can represent with following two formula:
(1)
n
g,air(λ
1,T
ref,p,RH)·D
ref＝n
g,air(λ
1,T
mea,p,RH)·D
mea (2)
In formula, suppose that the medium of determinand 603 optical interval in optical path 6 is air, otherwise the n of this right of formula
g, airshould replace by the group index of this medium.
In formula, n
airwith n
g, airrepresent refractive index and the group index of air respectively, they are by wavelength (λ
1or λ
2), temperature (the temperature T in delaying sweep light path 8
refor the temperature T in optical path 6
mea), air pressure p and relative humidity RH determined, the reason that in Here it is device, environmental sensor 13 exists.The computing formula of its refractive index is edlen formula:
n
15-1＝[8342.13+2406030(130-σ
2)
-1+15997(38.9-σ
2)
-1]×10
-8
n
t,p,f＝n
t,p-f(5.7224-0.0457σ
2)×10
-8
In formula: (n
15-1) be that σ is the wave number in vacuum, is the inverse of wavelength X in a standard atmospheric pressure, refractive index at 15 DEG C in air, unit is μm
-1, (n
t,p-1) for being subject to the refractive index of temperature and barometric pressure effect in normal air, n
t, p, ffor being subject to the refractive index of temperature, air pressure and steam dividing potential drop impact in normal air, t is temperature DEG C, and p is air pressure Torr, f is steam dividing potential drop Torr.By n
t, p, frefractive index n can be obtained
airand the dispersion relation of wavelength, utilize the formula of group index
namely corresponding group index n can be drawn
g, air.
So the optical interval D determinand 603 can be drawn from formula (1), (2)
meaformula:
From then on the optical interval D in determinand 603 can be found out in formula
meabe proportional to the wavelength X of laser instrument in laser length measurement light source 2
2divided by wavelength X
2under air refraction n
air(λ
2, T
ref, p, RH), therefore need before measuring to calibrate this wavelength and its time stability.(thermal expansivity is about 0.05 × 10 to utilize a heat-staple gauged distance block
-6k
-1) carry out Measurement and calibration, if D
exactfor the accurate distance of this gauged distance block, then the precision laser wavelength after calibration is
laser wavelength lambda is supposed in this formula
2be in close proximity to (a few nanometer) accurate wavelength X
2, exact.
Claims (8)
1. a high-precision optical interval measurement device, is characterized in that, for two fiber coupler structure, comprising short-coherence light source (1), laser length measurement light source (2), illumination instruction is with light source (3), first fiber coupler (4), second fiber coupler (5), optical path (6), reference mirror light path (7), delaying sweep light path (8), wavelength division multiplexer (9), first photodetector (10), second photodetector (11), connecting fiber (12) and environmental sensor (13), described optical path (6) comprises four-dimensional adjustment rack (601), adjustable focus optical fiber amasthenic lens (602), determinand (603) and erecting frame (604), described adjustable focus optical fiber amasthenic lens (602) is placed on four-dimensional adjustment rack (601), described determinand (603) is placed on erecting frame (604), described reference mirror light path (7) comprises an optical fiber retroeflector (701), and described delaying sweep light path (8) comprises fiber optic collimator camera lens (801), removable scanning reflection mirror (802) and motor drive mobile platform (803), described removable scanning reflection mirror (802) is placed in described motor and drives on mobile platform (803), and the position relationship of above-mentioned component is as follows:
The output terminal of described short-coherence light source (1) by optical fiber and the first described fiber coupler (4) 1. port be connected, the output terminal of described laser length measurement light source (2) by optical fiber and the first fiber coupler (4) 3. port be connected, adjustable focus optical fiber amasthenic lens (602) in described optical path (6) by optical fiber and described the first fiber coupler (4) 4. port be connected, to first aim at the optical axis of determinand (603) measuring beam in described optical path (6) before measurement starts, now described illumination instruction light source (3) is connected with the adjustable focus optical fiber amasthenic lens (602) in described optical path (6) by optical fiber,
Described the first fiber coupler (4) 2. port through optical fiber and the second fiber coupler (5) 1. port be connected, second fiber coupler (5) 3. port be connected with described optical fiber retroeflector (701) through optical fiber, the other end of the 4. connecting fiber of port of the second fiber coupler (5) is placed in the front focus of the fiber optic collimator camera lens (801) of described delaying sweep light path (8), second fiber coupler (5) 2. port be connected through the input end of optical fiber with described wavelength division multiplexer (9), two output terminals of this wavelength division multiplexer (9) are connected with the second photodetector (11) with described the first photodetector (10) respectively, described the first photodetector (10) is connected with the input end of computing machine with the output terminal of the second photodetector (11).
2. high-precision optical interval measurement device according to claim 1, is characterized in that described short-coherence light source (1) is super-radiance light emitting diode, central wavelength lambda
sLED=1310nm, coherent length is 15 μm.
3. high-precision optical interval measurement device according to claim 1, is characterized in that described laser length measurement light source (2) is distributed feedback laser, central wavelength lambda
lASER=1550nm ,-3dB live width is 2MHz.
4. high-precision optical interval measurement device according to claim 1, is characterized in that described illumination instruction light source (3) is laser diode, central wavelength lambda=655nm.
5. high-precision optical interval measurement device according to claim 1, is characterized in that described wavelength division multiplexer (9) is 1310/1550nm wavelength division multiplexer.
6. high-precision optical interval measurement device according to claim 1, the spectral response range that it is characterized in that described the first photodetector (10) and the second photodetector (11) is 950 ~ 1650nm, the interference signal that the laser length measurement light beam of the short coherent measurement light beam and wavelength 1550nm that receive wavelength 1310nm respectively produces.
7. high-precision optical interval measurement device according to claim 1, it is characterized in that described connecting fiber (12) is single-mode polarization maintaining fiber, cutoff wavelength is 1260nm.
8. utilize the optical interval measurement device described in claim 1 to treat the measuring method at object test light interval, it is characterized in that the method comprises the following steps:
1. by illumination instruction with light source (3) by Fiber connection in optical path (6), light source is opened, by the fixing determinand (603) of erecting frame (604), by the position regulating four-dimensional adjustment rack (601) to regulate adjustable focus optical fiber amasthenic lens (602), according to the luminous point that each surface reflection in determinand (603) is returned, regulate the center of outgoing beam to determinand (603) of adjustable focus optical fiber amasthenic lens (602), namely in the optical axis of determinand (603) and optical path (6) measuring beam optical axis coincidence,
2. illumination instruction is closed with light source (3), the optical fiber of connection first fiber coupler (4) the 4. port is replaced the connecting fiber of illumination instruction light source (3) and optical path (6), open short-coherence light source (1) and laser length measurement light source (2), regulate the adjustable focus optical fiber amasthenic lens (602) in optical path (6), make the stiffness of coupling of each surface reflection in determinand (603) large as far as possible;
3. the motor controlled in described delaying sweep light path (8) drives mobile platform (803) at the uniform velocity to drive removable scanning reflection mirror (802) mobile, the interference signal input computing machine that the first photodetector (10) and the second photodetector (11) will record respectively;
4. computing machine carries out data processing, draws the optical interval of determinand (603):
Utilize the five step phase shift nonlinear algorithms based on movable phase interfere to carry out the extraction of interference signal, calculate the tangent value of the phase place of each sampled point by following formula,
Wherein I
1, I
2, I
3, I
4, I
5be respectively the light intensity value of five neighbouring sample points,
Edlen formula is utilized to revise the refractive index of air and group index:
n
15-1＝[8342.13+2406030(130-σ
2)
-1+15997(38.9-σ
2)
-1]×10
-8
n
t,p,f＝n
t,p-f(5.7224-0.0457σ
2)×10
-8
What utilize the middle optics group delay of optical path (6) and delaying sweep light path (8) compares the optical interval D drawn in determinand (603)
mea,
n
g,air(λ
1,T
ref,p,RH)·D
ref＝n
g,air(λ
1,T
mea,p,RH)·D
mea
In formula, n
airwith n
g, airrepresent refractive index and the group index of air respectively, they are by wavelength X
1or λ
2, temperature, air pressure p and relative humidity RH determined, the computing formula of its refractive index is edlen formula:
n
15-1＝[8342.13+2406030(130-σ
2)
-1+15997(38.9-σ
2)
-1]×10
-8
n
t,p,f＝n
t,p-f(5.7224-0.0457σ
2)×10
-8
In formula: (n
15-1) be that σ is the wave number in vacuum, is the inverse of wavelength X in a standard atmospheric pressure, refractive index at 15 DEG C in air, unit is μm
-1, (n
t,p-1) for being subject to the refractive index of temperature and barometric pressure effect in normal air, n
t, p, ffor being subject to the refractive index of temperature, air pressure and steam dividing potential drop impact in normal air, t is temperature DEG C, and p is air pressure Torr, f is steam dividing potential drop Torr, by n
t, p, frefractive index n can be obtained
airand the dispersion relation of wavelength, utilize the formula of group index
namely corresponding group index n can be drawn
g, air.
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