CN101832817B - Parallel complex frequency domain optical coherence tomography method and system - Google Patents

Abstract

A parallel complex frequency domain optical coherence tomography method and system, based on the parallel frequency domain optical coherence tomography method, the method replaces the reference plane reflector of the interference reference arm with an inclined reflection grating, and makes the first-order diffracted light of the incident reference light return in the reverse direction along the original incident light path, so as to introduce linear spatial phase modulation in the parallel detection direction of the two-dimensional frequency domain interference fringes obtained by the two-dimensional photodetector array, that is, introduce a spatial carrier in the two-dimensional frequency domain interference fringes; then the two-dimensional frequency domain interference fringes containing the spatial carrier are Fourier transformed along the parallel detection direction, and then the two-dimensional complex frequency domain interference fringes are obtained by filtering with a frequency domain filter window, coordinate translation and inverse Fourier transform along the frequency spectrum direction, and finally the tomogram of the object to be measured is obtained by inverse Fourier transform along the optical frequency direction. The present invention has a simple structure and a fast imaging speed, and the tomogram of the object to be measured can be obtained with only one exposure.

Description

Parallel complex frequency domain optical coherence tomography imaging method and system

Technical field

The present invention relates to domain optical coherence tomography (Fourier-Domain Optical CoherenceTomography, be called for short FD-OCT), relate in particular to a kind of parallel complex frequency domain optical coherence tomography imaging method and system based on spatial carrier (spatial carrier).

Background technology

Optical coherent chromatographic imaging (Optical Coherence Tomography, be called for short OCT) be a kind of optical tomography technology that development in recent years is got up, it can carry out the imaging of high resolving power non-intruding to the micro-structure in the several mm depth scopes of high scattering medium such as biological tissue inside, is with a wide range of applications in fields such as biological tissue's living imaging and imaging of medical diagnosis.

Domain optical coherence tomography system (FD-OCT) is an a kind of New O CT system, it is by surveying interference spectum and it is obtained the tomographic map of object do inverse Fourier transform, with respect to previous time domain optical coherence tomography system (Time-Domain Optical Coherence Tomography, be called for short TD-OCT) have and need not depth direction scanning, image taking speed is fast and detection sensitivity is high advantage, can satisfy the real-time requirement of biological tissue's living imaging and imaging of medical diagnosis better.

The domain optical coherence tomography system mainly is made up of low-coherence light source (broad spectrum light source), Michelson interferometer and spectrometer (core parts are spectro-grating, condenser lens and ccd detector) three parts, send into spectrometer by the wide spectral light that low-coherence light source is sent through the interference signal that Michelson interferometer produces, obtain the intensity distributions (interference spectum) that interference signal changes with wavelength (λ), obtain interference signal in frequency domain (ν territory after then it being done conversion reciprocal, ν=1/ λ) intensity distributions, i.e. frequency domain interference fringe.Principle based on the different frequency of the corresponding frequency domain interference fringe of the degree of depth at each layer light reflection in the object under test or backscattering interface, FD-OCT obtains light reflectivity or backscattering rate distribution, the i.e. tomographic map of object under test along the depth resolution of illumination light optical axis direction to the frequency domain interference fringe do inverse Fourier transform.But, comprising some parasitic images in the tomographic map that FD-OCT obtains, limited the application of FD-OCT.These parasitic images are respectively: the direct current background, and from coherent noise and complex conjugate mirror image.Wherein, direct current background and reduced the signal to noise ratio (S/N ratio) of FD-OCT from the existence of coherent noise has influenced image quality; And the existence of complex conjugate mirror image makes FD-OCT can't distinguish positive and negative optical path difference (surveying the optical path difference of light path relative reference light path), and object under test can only place a side of zero optical path difference position during measurement, causes effective investigation depth scope to reduce half.

Complex frequency domain optical coherence tomography imaging is by rebuilding the complex analytic signal of frequency domain interference fringe, this is resolved the frequency domain interferometric fringe signal obtains object do inverse Fourier transform tomographic map again, can eliminate the parasitic image that exists in the tomographic map of traditional F D-OCT reconstruction, complex conjugate mirror image particularly, thereby make FD-OCT can distinguish positive and negative optical path difference, the investigation depth expanded range is original 2 times, realizes full depth finding.At present, the complex frequency domain OCT method that has proposed mainly comprises based on the movable phase interfere art with based on the complex frequency domain OCT of difference interference art.

Complex frequency domain OCT based on movable phase interfere art (phase-shifting interferometry)

2002, people such as A.F.Fercher rebuild the complex frequency domain interference fringe based on the movable phase interfere art the earliest, realized complex frequency domain OCT (referring to technology [1] formerly, M.Wojtkowski, A.Kowalczyk, R.Leitgeb andA.F.Fercher, " Full range complex spectral optical coherence tomographytechnique in eye imaging ", Optics Letters, Vol.27, No.16,1415-1417,2002).Yet, because the phase-shift interference that this method needs continuously or stepping collection at least 3 width of cloth have the fixed phase drift amount each other, reduced the image taking speed of frequency domain OCT, and interferometer and stability of sample have been proposed strict requirement, so this method is not suitable for the living imaging of biological tissue.2005, people such as Joseph A.Izatt propose to realize that based on the simultaneous phase-shifting interferometry complex frequency domain OCT is (referring to technology [2] formerly, M.V.Sarunic, M.A.Choma, C.Yang and J.A.Izatt, " Instantaneous complex conjugate resolved spectraldomain and swept-source OCT using 3 * 3 fiber couplers ", OpticsExpress, Vol.13, No.3,957-967,2005).Though obtain when this method can realize several movable phase interfere stripeds, but need to use N * N (N 〉=3) fiber coupler as the simultaneous phase-shifting device, the complicacy and the cost of system have been increased, and phase shifting accuracy is subjected to the influence of variation of ambient temperature easily, thereby influences the elimination effect of complex conjugate mirror image.

Complex frequency domain OCT based on difference interference art (heterodyne interferometry)

Realize the detection of complex frequency domain interference fringe based on the complex frequency domain OCT of difference interference art by introducing time in the frequency domain interference signal or spatial carrier, compare to have the advantage that is not subjected to the phase shifting accuracy restriction with complex frequency domain OCT based on the movable phase interfere art.2006, people such as Bachmann adopt two acousto-optic crsytals at the reference light of interferometer with survey that to introduce optical frequency in the light poor, produce a frequency domain interference fringe that contains free carrier wave, quadrature component by phase-locked detection frequency domain interference fringe is rebuild the complex frequency domain interference fringe (referring to technology [3] formerly then, A.H.Bachmann, R.A.Leitgeb and T.Lasser, " Heterodyne Fourier domainoptical coherence tomography for full range probing with high axialresolu

By above analysis, there are the problems such as synchronous scanning control that image taking speed is slow, system architecture is complicated, needs are complicated in complex frequency domain OCT at present, and these problems can solve by adopting parallel domain optical coherence tomography technology (parallel FD-OCT).Parallel frequency domain OCT is that with the key distinction of tradition based on the frequency domain OCT of single-point illumination it realizes the parallel detecting of frequency domain OCT two dimension tomographic map (B-scan) by adopting Line of light illumination sample.(referring to technology [5] formerly, Branislav Grajciar, Michael Pircher, Adolf F.Fercherand Rainer A.Leitgeb, " Parallel Fourier domain optical coherence tomographyfor in vivo measurement of the human eye ", Optics Express, Vol.13, No.4,2005).This method generally realizes the Line of light of object under test is thrown light on by add cylindrical mirror in light path, and utilize the frequency domain interference fringe of a plurality of lateral attitudes of object under test on the corresponding line illumination light of 2 D photoelectric detection array and the line item length direction, rebuild the two-dimentional tomographic map (B-scan) that obtains a width of cloth object under test.Parallel frequency domain OCT is owing to the horizontal mechanical scan of having avoided object under test, and image taking speed is fast, and is insensitive to motion blur.But still there are parasitic image problems such as complex conjugate mirror image in parallel frequency domain OCT.

Summary of the invention

The objective of the invention is to combine with parallel domain optical coherence tomography by spatial carrier difference interference art, a kind of method and system of parallel complex frequency domain optical coherence tomography imaging is provided in order to overcome the deficiency of above-mentioned technology formerly.The present invention only needs single exposure can realize the complex frequency domain optical coherence tomography imaging of the full degree of depth, have simple in structure, image taking speed fast, to the insensitive characteristics of motion blur.

Technical solution of the present invention is as follows:

A kind of method of parallel complex frequency domain optical coherence tomography imaging, this method is on the basis of parallel domain optical coherence tomography method, by replace interfering the reference planes catoptron of reference arm with the plane inclined reflective diffraction gratings, and the first-order diffraction light of incident reference light is returned along former input path is reverse, thereby modulate along introducing linear space phase on the parallel detecting direction in the two-dimensional frequency interference fringe that the 2 D photoelectric detector array obtains, promptly in the two-dimensional frequency interference fringe, introduce spatial carrier; Then the two-dimensional frequency interference fringe that contains spatial carrier is made Fourier transform along the parallel detecting direction, then pass through the process of the inverse Fourier transform of frequency domain filtering, coordinate translation and frequency domain successively, obtain two-dimentional complex frequency domain interference fringe, last again by with the wave number being the inverse Fourier transform acquisition object under test tomographic map of variable.

The concrete steps of the method for parallel complex frequency domain optical coherence tomography imaging of the present invention are as follows:

1. on the basis of parallel domain optical coherence tomography method, change tilted-putted flat reflective diffraction grating at the reference planes catoptron of interfering reference arm, make the first-order diffraction light of incident reference light return along original optical path is reverse, the incident angle θ that reference light incides on the flat reflective diffraction grating should satisfy relational expression (1):

$\sin \mathrm{\θ}=\frac{{\mathrm{\λ}}_0}{2d},---\left(1\right)$

Wherein: λ ₀Be the centre wavelength of low-coherence light source, d is the phase constant of flat reflective diffraction grating.

The frequency domain interference fringe of every bit, i.e. a width of cloth two-dimensional frequency interference fringe in the wire optical illumination zone on the corresponding testing sample of spectrometer and line item.Reference light incides on the flat reflective diffraction grating with incident angle θ, its first-order diffraction light returns along original optical path is reverse, in the two-dimensional frequency interference fringe, introduce linear space phase modulation ψ (x)=2kxtg θ/σ, promptly in the two-dimensional frequency interference fringe, introduce spatial carrier along the x direction of principal axis $f_{x0}=\frac{2\mathrm{tg\θ}}{\mathrm{\σ\λ}}.$

Wherein: λ represents wavelength, and k=2 π/λ represents wave number; Two dimensions of two-dimensional frequency interference fringe corresponding respectively the crosswise spots of testing sample upper edge wire illumination light length direction through the one-dimensional image system imaging lateral attitude that the 2 D photoelectric detector array lists in spectrometer (x axle) and optical source wavelength (y axle); The one-dimensional image system forms σ=F by the 3rd lens before the 2 D photoelectric detector array in second condenser lens and the spectrometer before first condenser lens and the testing sample before the Michelson interferometer midplane reflective diffraction gratings respectively ₂/ F ₁Represent the lateral magnification of one-dimensional image system, F ₁Represent in the Michelson interferometer focal length of first and second condenser lens before flat reflective diffraction grating and testing sample, F ₂Represent the focal length of the 3rd condenser lens in the spectrometer; X ' represents the lateral attitude of testing sample illumination light length direction along the line, x '=x/ σ;

2. after the system works, the two-dimensional frequency interferometric fringe signal that contains spatial carrier of described 2 D photoelectric detector array record as the formula (2):

$g(k,x)=S\left(k\right){\mathrm{\β}}_0+\underset{n}{\mathrm{\Σ}}S\left(k\right){\mathrm{\α}}_n\left(x\right)$

$+2\underset{n\≠m}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\cos \left[2k(z_n\left(x\right)-z_m\left(x\right))\right]---\left(2\right)$

$+2\underset{n}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\cos \left[2k(z_n\left(x\right)+x\·\mathrm{tg\θ}/\mathrm{\σ})\right],$

Wherein: S (k) represents the power spectrum density of low-coherence light source, and β 0 represents the equivalent reflectivity of flat reflective diffraction grating first-order diffraction, α _n(x), α _m(x) represent the 2 D photoelectric detector array to list reflectivity or backscattering rate that lateral attitude x ' on the testing sample of lateral attitude x correspondence locates n, the reflection of m layer or scattering interface, z _n(x), z _m(x) represent the 2 D photoelectric detector array to list vertical degree of depth that lateral attitude x ' on the testing sample of lateral attitude x correspondence locates n, the reflection of m layer or scattering interface.

Preceding two is respectively the catoptrical auto spectral density function of flat reflective diffraction grating and the auto spectral density function stack item of interior each layer depth place reflection of testing sample or back-scattering light in the formula (2), the 3rd is the mutual spectral density function stack of the reflection of different depth place or back-scattering light in the testing sample, and the 4th be the mutual spectral density function stack item of each layer depth place reflection or back-scattering light in flat reflective diffraction grating reflected light and the testing sample.

Formula (2) can be reduced to formula (3):

$g(k,x)=g_0(k,x)+2\underset{n}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_0\left(x\right){\mathrm{\β}}_0}\cos \left[2k(z_n\left(x\right)+x\·\mathrm{tg\θ}/\mathrm{\σ})\right],---\left(3\right)$

Wherein

$g_0(k,x)=S\left(k\right){\mathrm{\β}}_0+\underset{n}{\mathrm{\Σ}}S\left(k\right){\mathrm{\α}}_n\left(x\right)+2\underset{n\≠m}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\cos \left[2k(z_n\left(x\right)-z_m\left(x\right))\right]$ For DC component with from coherent noise, it is not subjected to the modulation of the spatial carrier of flat reflective diffraction grating introducing.

Formula (3) can be used formula (4) expression:

$g(k,x)=g_0(k,x)+\underset{n}{\mathrm{\Σ}}{b}_n(k,x)\exp \left[i2\mathrm{\π}{f}_{x0}x\right]+\underset{n}{\mathrm{\Σ}}{b}_n^{*}(k,x)\exp [-i2\mathrm{\π}{f}_{x0}x],---\left(4\right)$

Wherein: $b_n(k,x)=S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\exp \left[i{\mathrm{\φ}}_n(k,x)\right],$ φ _n(k, x)=2kz _n(x), * represents complex conjugate operation;

3. two-dimensional frequency interference signal formula (4) being done with x is that the Fourier transform of variable obtains formula (5):

$G(k,f_x)=G_0(k,f_x)+\underset{n}{\mathrm{\Σ}}{B}_n(k,f_x-f_{x0})+\underset{n}{\mathrm{\Σ}}{B_n}^{*}(k,f_x+f_{x0}),---\left(5\right)$

Wherein: the Fourier spectrum of G and B corresponding g of difference and b, f _xRepresent the spatial frequency spectrum of corresponding x axle, f _X0The spatial carrier frequency of representing the flat reflective diffraction grating to introduce; And $f_{x0}>\frac{{\mathrm{\ω}}_g+{\mathrm{\ω}}_b}{2},$ Wherein: ω _gAnd ω _bThe corresponding G of difference ₀With

Spectral bandwidth;

4. to step 3. the formula of gained (5) signal be multiplied by one earlier with f _X0Be the center, 2 ω _bRectangular window function for burst length $W\left(f_x\right)=\left\{\begin{array}{c}1,|f_x-f_{x0}|\≤{\mathrm{\ω}}_b\\ 0,|f_x-f_{x0}|>{\mathrm{\ω}}_b\end{array}\right.$ Carry out frequency domain filtering, obtain

5. will

At frequency domain coordinate f _xF moves to left on the axle _X0, it is on the frequency domain coordinate axis initial point, obtain

Again it is done with f _xBe the inverse Fourier transform of variable, promptly obtain a two-dimentional complex frequency domain interference fringe, as the formula (6):

$g_{\mathrm{comp}}(k,x)=\underset{n}{\mathrm{\Σ}}{b}_n(k,x)=\underset{n}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\exp \left[i{\mathrm{\φ}}_n(k,x)\right],---\left(6\right)$

6. to step 5. the two-dimentional complex frequency domain interferometric fringe signal (6) of gained to do with k be that the inverse Fourier transform of variable obtains formula (7):

Wherein: symbol

Expression is the inverse Fourier transform of variable with k; Γ represents the inverse Fourier transform of low-coherence light source power spectrum, i.e. the autocorrelation function of low-coherence light source.

Relational expression x '=x/ σ substitution formula (7) is obtained formula (8):

$\stackrel{\‾}{I}(x^{\′},z)=\underset{n}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x^{\′}\right){\mathrm{\β}}_0}\mathrm{\Γ}(z-2z_n\left(x^{\′}\right)),---\left(8\right)$

7. get

Amplitude information obtain the two-dimentional tomographic map of testing sample.

8. by accurate translation stage the vertical horizontal direction in plane that the testing sample edge and the optical axis of wire illumination light length direction and this wire illumination light constitute is made one-dimensional scanning, repeat the three-dimensional tomographic map that 2.～7. above step obtains testing sample.

The tomographic map that the inventive method obtains is compared with the parallel frequency domain OCT chromatography graphic (9) of not introducing the space phase modulation, has eliminated complex conjugate mirror image (I ₂), direct current background (I ₀) and from coherent noise (I ₁) three kinds of parasitic images, improved signal to noise ratio (S/N ratio), realized the parallel complex frequency domain optical coherence tomography imaging of full depth finding.

$={\mathrm{\β}}_0\mathrm{\Γ}\left(z\right)+\underset{n}{\mathrm{\Σ}}{\mathrm{\α}}_n\left(x\right)\mathrm{\Γ}\left(z\right)+\underset{n}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\mathrm{\Γ}(z+2z_n\left(x\right))+\underset{n}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\mathrm{\Γ}(z-2z_n\left(x\right))$

$+\underset{n\≠m}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\mathrm{\Γ}[z+2(z_n\left(x\right)-z_m\left(x\right))]+\underset{n\≠m}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\mathrm{\Γ}[z-2(z_n\left(x\right)-z_m\left(x\right))]$

$=I_0+I_1+I_2+\underset{n}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\mathrm{\Γ}(z-2z_n\left(x\right)),---\left(9\right)$

Wherein: $I_0={\mathrm{\β}}_0\mathrm{\Γ}\left(z\right)+\underset{n}{\mathrm{\Σ}}{\mathrm{\α}}_n\left(x\right)\mathrm{\Γ}\left(z\right)$ Represent the direct current background component,

$I_1=\underset{n\≠m}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\mathrm{\Γ}[z+2(z_n\left(x\right)-z_m\left(x\right))]+\underset{n\≠m}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\mathrm{\Γ}[z-2(z_n\left(x\right)-z_m\left(x\right))]$ Representative is from the coherent noise component, $I_2=\underset{n}{\mathrm{\Σ}}\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\mathrm{\Γ}(z+2z_n\left(x\right))$ Represent the complex conjugate image component.

The parallel complex frequency domain optical tomography system of implementing said method comprises low-coherence light source, order is placed collimator and extender device, cylindrical mirror, Michelson interferometer on the illumination direction of this low-coherence light source, the optical splitter of this Michelson interferometer is divided into feeler arm light path and reference arm light path with incident light, the end of reference arm light path is the flat reflective diffraction grating that a condenser lens and inclination are put, the end of feeler arm light path is a condenser lens and testing sample, and testing sample is placed on the precise mobile platform; The Michelson interferometer output terminal connects a spectrometer, and this spectrometer is by spectro-grating, and condenser lens and 2 D photoelectric detector array are formed; The 2 D photoelectric detector array is connected with computing machine by the image data acquiring card.The characteristics of this system are that described flat reflective diffraction grating tilts to put, and make the incident angle that reference light incides the flat reflective diffraction grating be $\mathrm{\θ}=\arcsin \frac{{\mathrm{\λ}}_0}{2d},$ Thereby making that the first-order diffraction light positive of incident light is good returns along former input path is reverse.

Described cylindrical mirror is converted into a wire focused light with a branch of incident directional light; The focal length of the condenser lens in the described Michelson interferometer before flat reflective diffraction grating and testing sample is identical; Condenser lens in described cylindrical mirror and the Michelson interferometer before flat reflective diffraction grating and testing sample is confocal relation; Condenser lens in the described Michelson interferometer before flat reflective diffraction grating and testing sample respectively with spectrometer in condenser lens be confocal relation; It is the object-image conjugate relation that described testing sample and plane reflective diffraction gratings are listed on the system light path with the 2 D photoelectric detector array respectively.

Described low-coherence light source is a wideband light source, and its spectrum typical case full width at half maximum is that tens nanometers are to the hundreds of nanometer, as light emitting diode (LED) or super-radiance light emitting diode (SLD) or femto-second laser or super continuum source etc.

Described collimator and extender device is made up of object lens and some lens.

Described Michelson interferometer, the one tunnel is the reference arm light path near aplanatic optical interference circuit to it is characterized in that having two, another road is the feeler arm light path.

Described 2 D photoelectric detector array is that area array CCD or face battle array CMOS or face battle array InGaAs or other have the two-way detector array of photosignal translation function.

Described precise mobile platform can be done the translation of micron order precision along three orthogonal directions.

The working condition of this system is as follows:

The light that low-coherence light source sends is after collimating apparatus expands bundle, again through cylindrical mirror at its converging action plane inner focusing, produce a wire focused light, in Michelson interferometer, wait to be divided into two bundles then, a branch of light incides on the flat reflective diffraction grating through reference arm, its first-order diffraction light returns along former input path is reverse, another Shu Guangjing feeler arm incides in the testing sample, diffraction light of returning from the flat reflective diffraction grating and the light wave that different depth reflection or backscattering are returned in the testing sample are waited to collect and are returned along reference arm and feeler arm, in Michelson interferometer, join and interfere, send into spectrometer beam split and record again, after the digital-to-analog conversion of image data acquiring card, send into computing machine and carry out data processing, obtain a two-dimentional tomographic map of testing sample shape illumination light along the line length direction and illumination light optical axis direction.By accurate translation stage testing sample edge and the wire illumination light length direction direction vertical with the illumination light optical axis done the one dimension transversal scanning, obtain the three-dimensional tomographic map of testing sample.

The beneficial effect that the present invention compared with prior art has is:

The characteristics of the method for parallel complex frequency domain optical coherence tomography imaging of the present invention are that spatial carrier difference interference art is used for parallel domain optical coherence tomography, on the parallel detecting direction, introduce spatial carrier by the plane inclined reflective diffraction gratings, utilize the spatial fourier transform analytical approach to rebuild the low-coherent light frequency domain and interfere the complex amplitude signal, eliminated the complex conjugate mirror image that exists in the FD-OCT imaging, direct current background and, realized the parallel complex frequency domain optical coherence tomography imaging of full depth finding from three kinds of parasitic images of coherent noise.

Compare with technology 1 formerly, the present invention only needs can obtain a width of cloth complex frequency domain interference fringe by single exposure, and is less demanding to interferometer and stability of sample.

Compare with technology 2 formerly, system architecture of the present invention is simple, and cost is low, and anti-environmental interference ability is strong.

Compare with 4 with technology 3 formerly, the present invention need not depth direction and horizontal mechanical scanning, can obtain the two-dimentional tomographic map of the full degree of depth of a width of cloth by single exposure, and image taking speed is fast; The present invention does not need complicated synchronous scanning control, and system architecture is simple, and has the insensitive advantage of motion blur.

Compare with technology 5 formerly, the present invention has solved parasitic image problems such as complex conjugate mirror image in conjunction with spatial carrier difference interference art and parallel frequency domain OCT, has realized that the parallel complex frequency domain OCT of the full degree of depth measures.

Description of drawings

Fig. 1 is the side-looking light path and the system architecture synoptic diagram of parallel complex frequency domain optical coherence tomography imaging of the present invention system.

Fig. 2 overlooks light path and system architecture synoptic diagram for parallel complex frequency domain optical coherence tomography imaging of the present invention system.

Embodiment

The invention will be further described below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this.

See also Fig. 1 and 2.Fig. 1 is the side-looking light path and the system architecture synoptic diagram of parallel complex frequency domain optical coherence tomography imaging of the present invention system.Fig. 2 overlooks light path and system architecture synoptic diagram for parallel complex frequency domain optical coherence tomography imaging of the present invention system.By Fig. 1 and 2 as seen, parallel complex frequency domain optical coherence tomography imaging of the present invention system comprises low-coherence light source 1, order is placed collimator and extender device 2 on the illumination direction of this low-coherence light source 1, cylindrical mirror 3, Michelson interferometer 4, the optical splitter 41 of this Michelson interferometer 4 is divided into feeler arm light path 44 and reference arm light path 42 with incident light, the end of reference arm light path 42 is the flat reflective diffraction grating 43 that first condenser lens 46 and inclination are put, the end of feeler arm light path is second condenser lens 47 and testing sample 45, and testing sample is placed on the precise mobile platform (not shown); The output terminal of Michelson interferometer 4 connects a spectrometer 5, and this spectrometer 5 is made up of spectro-grating 51, the three condenser lenses 52 and area array CCD detector 53; Area array CCD detector 53 is connected with computing machine 7 by image data acquiring card 6.The characteristics of this system are that described flat reflective diffraction grating 43 tilts to put, and make that the first-order diffraction light positive of incident light is good to return along former input path is reverse.

Described cylindrical mirror 3, it is converted into a wire focused light with a branch of incident directional light; The focal length of described first condenser lens 46, second condenser lens 47 is identical; First condenser lens 46, second condenser lens 47 in described cylindrical mirror 3 and the Michelson interferometer 4 are confocal relations; First condenser lens 46 in the described Michelson interferometer 4, second condenser lens 47 respectively with spectrometer 5 in the 3rd condenser lens 52 are confocal relations; Described testing sample 45 and plane reflective diffraction gratings 43 are the object-image conjugate relation on system light path with area array CCD detector 53 respectively.

The wide spectral light that low-coherence light source 1 sends is after collimating apparatus 2 expands bundle, in the side-looking light path plane, assemble (see figure 1) through cylindrical mirror 3 again, parallel transmission (see figure 2) in overlooking light path plane, produce a wire focused light, treat in Michelson interferometer 4 that then Amici prism 41 is divided into two bundles, a branch of transmitted light incides on the flat reflective diffraction grating 43 through reference arm light path 42, its first-order diffraction light returns along former input path is reverse, another bundle reflected light is in feeler arm light path 44 incides the testing sample 45 that is placed on the accurate translation stage (not shown), first-order diffraction light of returning from flat reflective diffraction grating 43 diffraction and the light wave that different depth reflection or backscattering are returned in the testing sample 45 are waited to collect and are returned along reference arm light path 42 and feeler arm light path 44 respectively, in Michelson interferometer 4, converge and interfere, send into spectrometer 5 again and treat spectro-grating 51 beam split, through the 3rd condenser lens 52, be imaged on area array CCD detector 53, after converting electric signal to, after 6 digital-to-analog conversions of image data acquiring card, send into computing machine 7 and carry out data processing, obtain a two-dimentional tomographic map of testing sample 45 shape illumination light length directions along the line and illumination light optical axis direction.

Described flat reflective diffraction grating 43 tilts to place, and the incident angle θ that reference light incides on the described flat reflective diffraction grating 43 is satisfied:

$\sin \mathrm{\θ}=\frac{{\mathrm{\λ}}_0}{2d},$

Wherein: λ ₀Be the centre wavelength of low-coherence light source 1, d is the grating phase constant of flat reflective diffraction grating 43.

Described spectrometer 5 and line item the frequency domain interference fringe of every bit, i.e. a width of cloth two-dimensional frequency interference fringe in the wire optical illumination zone on the corresponding testing sample 45.Reference light incides on the flat reflective diffraction grating 43 with incident angle θ, its first-order diffraction light returns along original optical path is reverse, in the two-dimensional frequency interference fringe, introduce linear space phase modulation ψ (x)=2kxtg θ/σ, promptly in the two-dimensional frequency interference fringe, introduce spatial carrier along the x direction of principal axis $f_{x0}=\frac{2\mathrm{tg\θ}}{\mathrm{\σ\λ}}.$ Wherein: λ represents wavelength, and k=2 π/λ represents wave number; Two dimensions of two-dimensional frequency interference fringe corresponding respectively on the testing sample 45 crosswise spots of illumination light length direction along the line through one-dimensional image the system imaging lateral attitude on the area array CCD detector 53 (x axle) and optical source wavelength direction (y axle) in spectrometer 5; The one-dimensional image system forms σ=F by the 3rd condenser lens 52 in first condenser lens 46 in the Michelson interferometer 4 and second condenser lens 47 and the spectrometer 5 respectively ₂/ F ₁Represent the lateral magnification of one-dimensional image system, F ₁Represent the focal length of condenser lens 46,47, F ₂Represent the focal length of the 3rd condenser lens 52; X ' represents the lateral attitude of testing sample 45 illumination light length directions along the line, x '=x/ σ.

The two-dimensional frequency interferometric fringe signal of described ccd detector 53 records is:

$g(k,x)=g_0(k,x)+2\underset{n}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_0\left(x\right){\mathrm{\β}}_0}\cos \left[2k(z_n\left(x\right)+x\·\mathrm{tg\θ}/\mathrm{\σ})\right],---\left(11\right)$

Wherein: S (k) represents the power spectrum density of low-coherence light source 1, β ₀Be the equivalent reflectivity of flat reflective diffraction grating 43 first-order diffraction, α _n(x), α _m(x) represent lateral attitude x ' on the testing sample 45 of x correspondence in lateral attitude on the ccd detector 53 to locate the reflectivity or the backscattering rate at n, the reflection of m layer or scattering interface, z _n(x), z _m(x) represent lateral attitude x ' on the testing sample 45 of x correspondence in lateral attitude on the ccd detector 53 to locate vertical degree of depth at n, the reflection of m layer or scattering interface.Wherein

$g_0(k,x)=S\left(k\right){\mathrm{\β}}_0+\underset{n}{\mathrm{\Σ}}S\left(k\right){\mathrm{\α}}_n\left(x\right)+2\underset{n\≠m}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\α}}_m\left(x\right)}\cos \left[2k(z_n\left(x\right)-z_m\left(x\right))\right]$ For DC component with from coherent noise, it is not subjected to the modulation of the spatial carrier of flat reflective diffraction grating introducing.

Formula (11) can be used formula (12) expression:

$g(k,x)=g_0(k,x)+\underset{n}{\mathrm{\Σ}}{b}_n(k,x)\exp \left[i2\mathrm{\π}{f}_{x0}x\right]+\underset{n}{\mathrm{\Σ}}{b}_n^{*}(k,x)\exp [-i2\mathrm{\π}{f}_{x0}x],---\left(12\right)$

Wherein: $b_n(k,x)=S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\exp \left[i{\mathrm{\φ}}_n(k,x)\right],$ φ _n(k, x)=2kz _n(x), * represents complex conjugate operation.

Then formula (12) being done with x is that the Fourier transform of variable obtains formula (13):

$G(k,f_x)=G_0(k,f_x)+\underset{n}{\mathrm{\Σ}}{B}_n(k,f_x-f_{x0})+\underset{n}{\mathrm{\Σ}}{B_n}^{*}(k,f_x+f_{x0}),---\left(13\right)$

Wherein: the Fourier spectrum of G and B corresponding g of difference and b, f _xRepresent the spatial frequency spectrum of corresponding x axle, f _X0The spatial carrier frequency of representing flat reflective diffraction grating 43 to introduce; And $f_{x0}>\frac{{\mathrm{\ω}}_g+{\mathrm{\ω}}_b}{2},$ Wherein: ω _gAnd ω _bThe corresponding G of difference ₀With

Spectral bandwidth.

Formula (13) is multiplied by one earlier with f _X0Be the center, 2 ω _bRectangular window function for burst length $W\left(f_x\right)=\left\{\begin{array}{c}1,|f_x-f_{x0}|\≤{\mathrm{\ω}}_b\\ 0,|f_x-f_{x0}|>{\mathrm{\ω}}_b\end{array}\right.$ Carry out frequency domain filtering, obtain

Follow it at frequency domain coordinate f _xF moves to left on the axle _X0, it is on the frequency domain coordinate axis initial point, obtain At last it is done with f _xBe the inverse Fourier transform of variable, obtain a two-dimentional complex frequency domain interference fringe, as the formula (14):

$g_{\mathrm{comp}}(k,x)=\underset{n}{\mathrm{\Σ}}{b}_n(k,x)=\underset{n}{\mathrm{\Σ}}S\left(k\right)\sqrt{{\mathrm{\α}}_n\left(x\right){\mathrm{\β}}_0}\exp \left[i{\mathrm{\φ}}_n(k,x)\right],---\left(14\right)$

It is that the inverse Fourier transform of variable obtains formula (15) that formula (14) is done with k:

Wherein: symbol

Expression is the inverse Fourier transform of variable with k; Γ represents the inverse Fourier transform of low-coherence light source 1 power spectrum, i.e. the autocorrelation function of low-coherence light source 1.

Relational expression x '=x/ σ substitution formula (15) is obtained formula (16):

$\tilde{I}(x^{\′},z)=\underset{n}{\mathrm{\Σ}}{\mathrm{\Γ}}_{\mathrm{nr}}(x^{\′},z-2z_n\left(x^{\′}\right)),---\left(16\right)$

Get

Amplitude information obtain a two-dimentional tomographic map of testing sample 45.

By accurate translation stage (not shown) the vertical horizontal direction in plane that testing sample 45 edges and the optical axis of wire illumination light length direction and this wire illumination light constitute is made one-dimensional scanning, repeat the three-dimensional tomographic map that above process obtains testing sample 45.

Claims (2)

1. the method for a parallel complex frequency domain optical coherence tomography imaging is characterized in that the concrete steps of this method are as follows:

1. on the basis of parallel domain optical coherence tomography method, will interfere the reference planes catoptron of reference arm to change tilted-putted flat reflective diffraction grating into, its pitch angle, promptly reference light incides the incident angle of flat reflective diffraction grating,

λ 0 represents the centre wavelength of low-coherence light source, d represents the grating phase constant of flat reflective diffraction grating, then the first-order diffraction light of incident reference light returns along former input path is reverse, thereby modulate ψ (x)=2kxtg θ/σ in the two-dimensional frequency interference fringe that the 2 D photoelectric detector array obtains along introducing linear space phase on the parallel detecting direction, promptly in the two-dimensional frequency interference fringe, introduce spatial carrier Wherein: λ represents wavelength, k=2 π/λ represents wave number, and x represents the lateral attitude of testing sample and interference reference arm flat reflective diffraction grating shape illumination light along the line length direction through the one-dimensional image system imaging lateral attitude that the 2 D photoelectric detector array lists in spectrometer; Described one-dimensional image system forms σ=F by the 3rd condenser lens before the 2 D photoelectric detector array in first condenser lens before the Michelson interferometer midplane reflective diffraction gratings and second condenser lens before the testing sample and the spectrometer respectively ₂/ F ₁Represent the lateral magnification of one-dimensional image system, F ₁Represent in the Michelson interferometer before the flat reflective diffraction grating focal length of second condenser lens before first condenser lens and testing sample, F ₂Represent the focal length of preceding the 3rd condenser lens of 2 D photoelectric detector array in the spectrometer; X ' represents the lateral attitude of testing sample shape illumination light along the line length direction, x '=x/ σ;

2. after the system works, described 2 D photoelectric detector array has write down the two-dimensional frequency interference signal that contains spatial carrier:

Wherein:

S (k) represents the power spectrum density of low-coherence light source, β ₀Represent the equivalent reflectivity of flat reflective diffraction grating first-order diffraction, α _n(x), α _m(x) represent the 2 D photoelectric detector array to list reflectivity or backscattering rate that lateral attitude x ' on the testing sample of lateral attitude x correspondence locates n, the reflection of m layer or scattering interface, z _n(x), z _m(x) represent the 2 D photoelectric detector array to list vertical degree of depth that lateral attitude x ' on the testing sample of lateral attitude x correspondence locates n, the reflection of m layer or scattering interface;

Following formula two-dimensional frequency interference signal can be expressed as again:

Wherein:

φ _n(k, x)=2kz _n(x), * represents complex conjugate operation;

3. to two-dimensional frequency interference signal g (k, x) doing with x is the Fourier transform of variable, obtains:

Wherein: the Fourier spectrum of G and B corresponding g of difference and b, f _xRepresent the spatial frequency spectrum of corresponding x axle;

4. with G (k, f _x) be multiplied by a rectangular window function and carry out frequency domain filtering, obtain

Wherein: rectangular window function is

ω _bFor

Spectral bandwidth;

5. will

At frequency domain coordinate f _xF moves to left on the axle _X0, obtain

Again with f _xFor variable obtains two-dimentional complex frequency domain interference signal g do inverse Fourier transform _Comp(k, x):

6. with two-dimentional complex frequency domain interference signal g _Comp(k is that variable is done inverse Fourier transform with k x), and substitution relational expression x '=x/ σ, obtains:

Wherein: Γ represents the inverse Fourier transform of low-coherence light source power spectrum, i.e. the autocorrelation function of low-coherence light source;

7. get

Amplitude information obtain the two-dimentional tomographic map of testing sample,

8. by accurate translation stage the vertical horizontal direction in plane that testing sample (45) edge and the optical axis of described wire illumination light length direction and this wire illumination light constitute is made one-dimensional scanning, repeat the three-dimensional tomographic map that 2.～7. above step obtains testing sample (45).

2. parallel complex frequency domain optical coherence tomography imaging system that realizes the described method of claim 1, comprise low-coherence light source (1), order is placed collimator and extender device (2) on the light beam working direction of low-coherence light source (1), cylindrical mirror (3), Michelson interferometer (4), the optical splitter (41) of this Michelson interferometer (4) is divided into feeler arm light path (44) and reference arm light path (42) with incident light, the end of reference arm light path (42) is first condenser lens (46) and plane reflective diffraction gratings (43), the end of feeler arm light path (44) is second condenser lens (47) and testing sample (45), and testing sample (45) is placed on the precise mobile platform; The output terminal of this Michelson interferometer (4) connects a spectrometer (5); This spectrometer (5) is made up of spectro-grating (51), the 3rd condenser lens (52) and 2 D photoelectric detector array (53); 2 D photoelectric detector array (53) is connected with computing machine (7) by image data acquiring card (6); It is characterized in that: described flat reflective diffraction grating (43), inclination is put, and makes the incident angle that reference light incides described flat reflective diffraction grating be

Described cylindrical mirror (3) is converted into a wire focused light with a branch of incident directional light; The focal length of described first condenser lens (46), second condenser lens (47) is identical; First condenser lens (46), second condenser lens (47) in described cylindrical mirror (3) and the Michelson interferometer (4) are confocal relations; First condenser lens (46) in the described Michelson interferometer (4), second condenser lens (47) respectively with spectrometer (5) in the 3rd condenser lens (52) be confocal relation; Described testing sample (45) and plane reflective diffraction gratings (43) are the object-image conjugate relation on system light path with 2 D photoelectric detector array (53) respectively.

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