CN101181153A - Method for the tomography of high resolution optics coherence - Google Patents

Abstract

The invention relates to a high-resolution optical coherence tomography method, which adopts depth resolution dispersion compensation to more accurately compensate the dispersion in a compensation circuit and a sample, so as to eliminate the widening effect of the dispersion. The invention has the advantages that the dispersion compensation can be implemented without learning the materials and the structure information of the sample in advance, and the invention can not only compensate the dispersion mismatching of the two arms of an interference device, but can also compensate the internal dispersion of the sample; furthermore, the invention can adopt the corresponding dispersion coefficient to carry out the compensate against the different depth of the internal part of the sample, so as to achieve the best compensation effect and obtain optical coherence tomography images with high-resolution.

Description

The tomography of high resolution optics coherence method

Technical field

The present invention relates to a kind of domain optical coherence tomography (Fourier Domain OpticalCoherence Tomography is called for short FD-OCT) technology, relate in particular to a kind of high-resolution domain optical coherence tomography method.

Background technology

Optical coherent chromatographic imaging (OCT) is interfered (Low CoherenceInterferometry based on low-coherent light, be called for short LCI) principle, can carry out the micro-structure in the several mm depth scopes of scattering medium such as biological tissue inside non-invasive, real-time, at the tomography of body, have ultrahigh resolution (1 micron to 20 microns).Since people such as Huang in 1991 propose the OCT notion, and since it is applied to the tomography of human eye retina and coronary arterial wall, OCT is with its ultrahigh resolution, ultrafast image taking speed, radiationless damage, optical information diversity, and with the compatible advantage such as good of existing Medical Instruments, become by the extensive good optical image technology that has the important application prospect at biological tissue's imaging and medical science detection range.

Domain optical coherence tomography system (FD-OCT), it is a kind of New O CT system, by surveying interference spectrum and it being carried out the tomographic map that inverse Fourier transform obtains object, with respect to initial 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 detectivity is high advantage, be more suitable for the realtime imaging of biological tissue.

In order to carry out imaging, require the OCT system to have the spatial resolution of micron or sub-micrometer scale to micro-structure such as cell.In theory, vertical (degree of depth) resolution of OCT system depends primarily on the coherence length of light source, and the coherence length of light source and light source bandwidth are inversely proportional to, and in order to improve depth resolution, require system to use the more light source of high bandwidth.The OCT system generally adopts the super width of cloth to penetrate diode (SLD) as light source at present, is 830nm as adopting centre wavelength, and bandwidth is the SLD of 20nm, and depth resolution is about 15 μ m.Current domestic and international research mainly relies on raising light source bandwidth to improve longitudinal resolution, as adopt femto-second laser, and its bandwidth can reach the hundreds of nanometer, and resolution can reach several micron (referring to technology [1] formerly, R.A.Leitgeb, W.Drexler, A.Unterhuber et al., " Ultrahigh resolution Fourier domainoptical coherence tomography ", Opt.Express, 12,2156-2165,2004).But the longitudinal resolution of OCT system also is subjected to the influence of optical element and sample chromatic dispersion, when the chromatic dispersion mismatch of reference arm and sample arm, can cause true resolution less than theoretical value.High-resolution OCT system generally uses the ultra-wide spectrum light source at present, and the deterioration of the resolution that chromatic dispersion causes is serious, and dispersion compensation becomes the important step that realizes high-resolution OCT.At present, the method for dispersion compensation mainly is divided into two kinds of physical compensation and algorithm compensations.

Physical compensation is normally inserted dispersion compensation device in sample arm or reference arm, make the chromatic dispersion coupling of interferometer two arms, thereby the purpose that reaches dispersion compensation is (referring to technology [2] formerly, B.Bouma, G.J.Tearney, S.A.Boppart, M.R.Hee, M.E.Brezinski, and J.G.Fujimoto, " High-resolution optical coherence tomographic imaging using amode-lockedTi-Al2O3 laser source ", Opt.Lett.20,1486-1488,1995; C.K.Hizenberger, A.Baumgartner, W.Drexler, and A.F.Ferche; " Dispersion effects inpartial coherence interferometry:implications for intraocular ranging ", J.Biomed.Opt.4,144-151,1999).Optics rapid scanning delay line based on grating is a kind of physical dispersion compensation method commonly used, come compensation of dispersion (referring to technology [3] formerly by regulating balzed grating, with respect to the departing from of fourier transform lens focus (being defocusing amount), B.Golubovic, B.E.Bouma, G.J.Tearney, andJ.G.Fujimoto, " Optical frequency-domain reflectometry using rapid wavelengthtuning of a Cr4+:forsterite laser ", Opt.Lett.22,1704-1706,1997).Yet physical compensation need be used dispersion compensation device, has increased the complexity of system, and can only the chromatic dispersion of chromatic dispersion in the light path or specific sample be compensated, if sample chromatic dispersion character changes, needs dispersion compensation device is readjusted.

Algorithm compensation is realized dispersion compensation by the interference fringe of gathering is carried out post processing, mainly comprises iterative compensation algorithm, autofocus algorithm and convolution algorithm at present.Iterative algorithm hypothesis tomographic map is made up of different sharp keen interfaces, and set a sharp keen matrix equation and explain the sharp keen degree of tomographic map, by to second order and third-order dispersion coefficient iteration, feasible this sharp keen matrix equation maximum.Autofocus algorithm passes through the Renyi entropy minimum of the image after the feasible compensation of the different dispersion parameters of selection, and promptly picture contrast is the highest.These two kinds of algorithms to the chromatic dispersion of sample different depth all adopt unified abbe number compensate (referring to technology [4] formerly, M.Wojtkowski, V.J.Srinivasan, T.H.Ko, J.G.Fujimoto, A.Kowalczyk, and J.S.Duker, " " Opt.Express 12 for Ultrahigh resolution; high-speed, Fourier domain opticalcoherence tomography and methods for dispersion compensation, 2404-2422,2004; D.L.Marks, A.L.Oldenburg, J.J.Reynolds, and S.A.Boppart, " Autofocus algorithm for dispersion correction in optical coherence tomography, " Appl.Opt.42,3038-3046,2003).But actual sample, particularly human eye have multiple structure, and the abbe number between the different layers is widely different, can not all reach the The optimal compensation effect to each layer with unified abbe number compensation.Convolution algorithm is with time domain interference signal and a convolution kernel convolution, and this convolution kernel is the function of the degree of depth, thus realize depth resolution dispersion compensation (referring to technology [5] formerly, A.F.Ferche; C.K.Hitzenberger, M.Sticker, R.Zawadzki, B.Karamata, and T.Lasser, " Numerical dispersion compensation for partial coherence interferometry andoptical coherence tomography, " Opt.Express 9,2001).But the convolution kernel of the depth resolution that this method is used needs per sample material and Structure Calculation to obtain.Because the material and the structure of different samples generally are unpredictable, particularly human eye and skin, each detected object has different material characters and architectural feature, is difficult to obtain the convolution kernel of accurate depth resolution, thereby has limited the practical application of the dispersion compensation method of this depth resolution.

Find out also do not have a kind of dispersion compensation method automatic, depth resolution to be applied to OCT at present to realize high-resolution optical coherent chromatographic imaging by above analysis.

Summary of the invention

The objective of the invention is in order to overcome the deficiency of above-mentioned technology formerly, a kind of tomography of high resolution optics coherence method is provided, employing depth resolution dispersion compensation compensates the chromatic dispersion in light path and the sample more accurately, thereby eliminates the broadening effect of chromatic dispersion, obtains the tomographic map of high-resolution.The invention process dispersion compensation does not need to know in advance the material and the structural information of sample, chromatic dispersion between can compensating interferometer instrument two arms, can compensate the chromatic dispersion of sample interior again, and can the chromatic dispersion of sample interior different depth be compensated respectively, reach best compensation effect.

Technical solution of the present invention is as follows:

A kind of tomography of high resolution optics coherence method, this method comprises the following steps:

1. at first utilize high-resolution domain optical coherence tomography system each transversal scanning point to sample, the frequency domain interference spectrum signal of the photoelectronic detecting array record sample of this system is also sent into computer;

2. computer is done inverse Fourier transform to the interference spectrum signal of a certain crosswise spots of photoelectronic detecting array collection and is obtained this tomographic map;

3. adopt the airspace filter device to extract the complex amplitude and the phase place of the optical frequency territory interference signal of a certain degree of depth of this tomographic map;

4. adopt method of least square that described phase place is carried out match, obtain the 2nd order chromatic dispersion coefficient and the third-order dispersion coefficient of sample, and calculate the phase place distortion that chromatic dispersion causes at this degree of depth place; From described phase place, deduct this twist angle, obtain the phase place behind the dispersion compensation;

5. the Phase Build Out after utilizing complex amplitude and compensating goes out the optical frequency territory interference signal through dispersion compensation corresponding to this degree of depth;

6. 3. the tomographic map to different depth repeats the extremely 5. step, and the optical frequency territory interference signal at each degree of depth place is superposeed, and obtains the optical frequency territory interference signal through dispersion compensation of this crosswise spots;

7. the last optical frequency territory interference signal through dispersion compensation to this crosswise spots carries out inverse Fourier transform and obtains the tomographic map that this point is rebuild;

8. 2. repeating step is handled to the 7. interference spectrum signal to each crosswise spots of described frequency domain interference spectrum, obtains the two dimension or the three-dimensional tomographic map of this sample.

The choosing method of the window width of the airspace filter device of described a certain crosswise spots is:

The twice standard deviation sum of selecting the noise meansigma methods of frequency domain interference signal of this point and this signal is as threshold value;

Find each maximum that is higher than threshold value in this tomographic map;

With maximum is middle mind-set both sides extended window, and the width that equals preset threshold up to maximum both sides intensity is made as the window width of this maximum.

The characteristics of tomography of high resolution optics coherence method of the present invention are to have adopted the depth resolution dispersion compensation method, extract the complex amplitude and the phase place of the optical frequency territory interference signal of a certain degree of depth by airspace filter, utilize the phase place after least square fitting obtains dispersion compensation, further based on the optical frequency territory interference signal of this this degree of depth of Phase Build Out, at last inverse Fourier transform is done in the optical frequency territory interference signal stack behind the dispersion compensation of each degree of depth, obtained tomographic map.The depth resolution dispersion compensation method that adopts has compensated the chromatic dispersion in light path and the sample more accurately, has realized high-resolution optical coherent chromatographic imaging.

The principle of technical solution of the present invention:

Mobile example in the tomography of high resolution optics coherence system is to each transversal scanning point of sample, with spectrogrph record frequency domain interference fringe.Because spectrogrph has write down light intensity with wavelength change, rebuild tomographic map in order to utilize discrete Fourier transform (DFT) (DFT), need be to interference fringe in frequency domain (ω or k) uniform resampling, the interference fringe that obtains can be expressed as:

S _out(k)＝|E _R(k)| ²+2Re{E _R(k)*E _S(k)}+|E _S(k)| ² (1)

Wherein: k is a wave number, E _RBe the reference arm light field, E _SIt is the sample scattering light field.In general, the scattered light intensity of sample is very little with respect to the reference light intensity, so last can be ignored in (1) formula.In addition, from spectrum, deduct the spectral cterm (first) of reference arm, obtained having the two pure arm interference signal S of useful information _Int(k):

$S_{\mathrm{int}}\left(k\right)=2\mathrm{Re}\{E_R\left(k\right)*E_S\left(k\right)\}$

                

$=2\mathrm{Re}\left\{\underset{n}{\mathrm{\Σ}}\sqrt{I_n\left(k\right)I_r\left(k\right)}\exp \right[i({\mathrm{kz}}_n+\mathrm{\Φ}(k,z_n))\left]\right\}$ (2)

Wherein: I _n(k) be n layer scattered light intensity, I _r(k) be the reference arm reflective light intensity, z _nBe the optical path difference of n layer correspondence,  (k, z _n) be z _nThe phase contrast of place's reference arm and feeler arm, Ф (k, z _n) be z _nThe place is because the additive phase that chromatic dispersion causes.

From (2) formula as can be seen, interferometer two arm phase contrast  (k, z _n) by optical path difference kz _nThe additional phase error Ф (k, the z that cause with chromatic dispersion _n) two parts composition.The influence of chromatic dispersion is to have introduced an additional phase error, thereby makes phase distortion, and dispersion compensation is exactly in order to eliminate this additional phase error.Total phase contrast  (k, z _n) can be with Taylor series expansion:

                 

$=\{{\mathrm{\β}}_n\left(k_0\right)+{{\mathrm{\β}}_n}^{\′}\left(k_0\right)\×(k-k_0)+{{\mathrm{\β}}_n}^{\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^2}{2!}+{{\mathrm{\β}}_n}^{\′\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^3}{3!}+...\}{z}_n$

$=\{n_n\left(k_0\right)k_0+n_{g,n}\left(k_0\right)\×(k-k_0)+{{\mathrm{\β}}_n}^{\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^2}{2!}+{{\mathrm{\β}}_n}^{\′\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^3}{3!}+...\}{z}_n$ (3)

Wherein: β _n(k) be z _nThe propagation constant at place, n _nBe the phase refractive index of sample, n _{G, n}Be the group index of sample, β _n"=d ²β (k)/dk ²Be z _nThe 2nd order chromatic dispersion coefficient at place, β _n=d ³β (k)/dk ³Be z _nThe third-order dispersion coefficient at place.

Order $\sqrt{I_n\left(k\right)I_r\left(k\right)}=B_n\left(k\right),$ [n _n(k ₀)k ₀+n _g，n(k ₀)k ₀]×z _n＝φ _0，n， ${{\mathrm{\β}}_n}^{\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^2}{2!}={\mathrm{\φ}}_{\mathrm{GDD},n}\left(k\right),$ ${{\mathrm{\β}}_n}^{\′\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^3}{3!}={\mathrm{\φ}}_{\mathrm{TOD},n}\left(k\right),$ Then (2) formula is rewritten as:

$S_{\mathrm{int}}\left(k\right)=\mathrm{\Σ}{B}_n\left(k\right)\left\{\exp \right\{i[n_{g,n}\left(k_0\right)k+{\mathrm{\φ}}_{\mathrm{GDD},n}\left(k\right)+{\mathrm{\φ}}_{\mathrm{TOD},n}\left(k\right)+...]\×z_n\}$

                   

$+\exp \{-i[n_{g,n}\left(k_0\right)k+{\mathrm{\φ}}_{\mathrm{GDD},n}\left(k\right)+{\mathrm{\φ}}_{\mathrm{TOD},n}\left(k\right)+...]\×z_n\}\}\exp \left({\mathrm{i\φ}}_{0,n}\right)$ (4)

S _Int(k) for having the optical frequency territory interference signal of chromatic dispersion, the chromatic dispersion meeting causes the broadening of interfering envelope, thereby reduces the longitudinal resolution of optical coherent chromatographic imaging.From expression formula, it can also be seen that sample different depth z _nThere is different abbe number β at the place _n" and β _n adopts corresponding abbe number to compensate to the signal of different depth and just can reach best compensation effect.

The present invention realizes tomography of high resolution optics coherence by a kind of depth resolution dispersion compensation method, and concrete step is:

1, at first, S _Int(k) k is done inverse Fourier transform and obtains the time domain tomographic map:

$S_{\mathrm{int}}\left(z\right)=\underset{n}{\mathrm{\Σ}}{B}_n\left(z\right)\⊗\{\mathrm{\δ}(z+z_n)\⊗\mathrm{iFT}\{\exp \left[{\mathrm{i\φ}}_{\mathrm{GOD},n}\left(k\right)\right]\×z_n\}\⊗\mathrm{iFT}\{\exp [{\mathrm{i\φ}}_{\mathrm{TOD},n}\left(k\right)\×z_n]\⊗...\}+$

                

$\mathrm{\δ}(z-z_n)\⊗\mathrm{iFT}\left\{\exp \right[-{\mathrm{i\φ}}_{\mathrm{GOD},n}\left(k\right)\×z_n\left]\right\}\⊗\mathrm{iFT}\left\{\exp \right[-{\mathrm{i\φ}}_{\mathrm{TOD},n}\left(k\right)\×z_n\left]\right\}\⊗...\}\exp \left({\mathrm{i\φ}}_{0,n}\right)$ (5)

Here do not consider the mirror image problem, think z＞0, then:

$S_{\mathrm{int}}\left(z\right)$

(6)

$=\{\underset{n}{\mathrm{\Σ}}{B}_n\left(z\right)\⊗\mathrm{\δ}(z-z_n)\⊗\mathrm{iFT}\{\exp [-{\mathrm{i\φ}}_{\mathrm{GDD},n}\left(k\right)\×z_n]\}\⊗\mathrm{iFT}\{\exp [-{\mathrm{i\φ}}_{\mathrm{TOD},n}\left(k\right)\×z_n]\}\⊗...\}\×\exp (-{\mathrm{i\φ}}_{0,n})$ (6)

As can be seen from the above equation, to each position z _n, the modulation that its tomographic map not only is subjected to light source light spectrum (is reflected in B _n(z) on), the modulation that also is subjected to second order and high-order dispersion (is reflected in iFT{exp[-i φ _{GDD, n}(k) * z _n] etc. on).Wherein, 2nd order chromatic dispersion causes the broadening of interference fringe, and third-order dispersion causes the asymmetric of interference fringe, thereby because effect of dispersion causes systemic resolution to descend.

2, adopting width is that the window of Δ z is at z _nPlace's filtering obtains corresponding to z _nThe interferogram at place.Since broadening effect, z _nThe place interferogram may with neighbouring other the layer (as z _mLayer, z _n≈ z _m) interferogram have overlappingly, set window width Δ z _n, leach z _nLocate synergetic interferogram.If $\stackrel{\‾}{z_n}\≈z_n,$ And interferogram is the stack of i layer to the interferogram of j layer, then:

$S_{\mathrm{filter},n}\left(z\right)$

                    

$=\mathrm{rect}\left(\frac{z-z_n}{\mathrm{\Δn}}\right)\{\underset{n}{\mathrm{\Σ}}{B}_n\left(z\right)\⊗\mathrm{\δ}(z-z_n)\⊗\mathrm{iFT}\{\exp [-i+({\mathrm{\φ}}_{\mathrm{GDD},n}\left(k\right)+{\mathrm{\φ}}_{\mathrm{TOD},n}\left(k\right)+...)\×z_n]\}\×\exp (-{\mathrm{i\φ}}_{0,n})$

$=\underset{n=i}{\overset{j}{\mathrm{\Σ}}}{B}_n\left(z\right)\⊗\mathrm{\δ}(z-z_n)\⊗\mathrm{iFT}\left\{\exp \right[-i({\mathrm{\φ}}_{\mathrm{GDD},n}\left(k\right)+{\mathrm{\φ}}_{\mathrm{TOD},n}\left(k\right)+...)\×\stackrel{\‾}{z_n}\left]\right\}\×\exp (-{\mathrm{i\φ}}_{0,n})$ (7)

Window width choose particular importance because this method compensates according to identical abbe number the signal in the window width, if window width is too wide, and the abbe number in this window is inconsistent, will weaken the effect of depth resolution dispersion compensation; Window width is too narrow, and the interferogram that leaches includes only the part of certain one deck interferogram, causes the weakening or the distortion of this layer information.This method at first finds each maximum that is higher than threshold value in the tomographic map, is the expansions of middle mind-set both sides with each maximum, and the width when both sides intensity equals preset threshold is as window width.Here the setting of threshold value is also very important, if too high (being higher than some maximum) may make some layer information dropout, if the too low window width that may cause is too wide.This method selects the twice standard deviation sum of the noise meansigma methods of frequency domain interference signal of each crosswise spots and this signal as threshold value.

3, S _{Filter, n}(z) z is done Fourier transform, obtain corresponding to z _nThe optical frequency territory interference signal S at place _{Filter, n}(k):

$S_{\mathrm{filter},n}\left(k\right)$

                     

$=\underset{n=i}{\overset{j}{\mathrm{\Σ}}}{B}_n\left(k\right)\exp \{-i[n_n\left(k_0\right)k_0+n_{g,n}\left(k_0\right)\×(k-k_0)+{{\mathrm{\β}}_n}^{\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^2}{2!}+{{\mathrm{\β}}_n}^{\′\′\′}\left(k_0\right)\×\frac{{(k-k_0)}^3}{3!}+...]\×\stackrel{\‾}{z_n}\}$ (8)

Because dispersive influence is the phase place of interference signal, dispersion compensation is that phase place is compensated, then the complex amplitude by signal and compensate after the interference signal of bit recovery mutually.So, the complex amplitude and the PHASE SEPARATION of this signal to be kept complex amplitude here, by next step phase place is carried out dispersion compensation then.This signal complex amplitude and phase place be:

4, adopt NUMERICAL MATCH METHOD FOR that the phase place of distortion is carried out dispersion compensation.With (k-k ₀) be independent variable, to  _{Filter, n}(k) carry out numerical fitting, obtain z _nThe second order and the third-order dispersion factor beta at place _n" (k ₀) and β _n (k ₀).Here only consider second order and third-order dispersion, ignore more high-order dispersion.Then the phase place distortion is:

Phase place is carried out dispersion compensation, promptly from  _{Filter, n}(k) deduct  in _{Disp, n}(k) obtain phase place behind the dispersion compensation:

5, utilize complex amplitude A _{Filter, n}(k) and phase place  _{Comp, n}(k) recover z _nThe optical frequency territory interference signal at place:

$S_{\mathrm{comp},n}=\underset{n=i}{\overset{j}{\mathrm{\Σ}}}{B}_n\left(k\right)\×\exp \{-i[n_n\left(k_0\right)k_0+n_{g,n}\left(k_0\right)\×(k-k_0)]\×\stackrel{\‾}{z_n}\}---\left(12\right)$

So far, obtained z _nThe optical frequency territory interference signal of place's dispersion compensating.To different z _nThe place carried out for 2 to 5 steps respectively, then the result was superposeed, and obtained the optical frequency territory interference signal of this crosswise spots through dispersion compensation:

$S_{\mathrm{comp}}\left(k\right)=\underset{n}{\mathrm{\Σ}}{B}_n\left(k\right)\×\exp \left\{i\right[n_n\left(k_0\right)k_0+n_{g,n}\left(k_0\right)\×(k-k_0)]\×z_n\}---\left(13\right)$

6, last, S _Comp(k) k is done inverse Fourier transform, and delivery, obtains the tomographic map of this transversal scanning point dispersion compensating:

$S_{\mathrm{comp}}\left(z\right)=\underset{n}{\mathrm{\Σ}}{B}_n\left(z\right)\⊗\mathrm{\δ}(z-z_n)---\left(14\right)$

7, each transversal scanning point is carried out above dispersion compensation step respectively, obtain the two dimension or the three-dimensional tomographic map of this sample.

Implement the high-resolution domain optical coherence tomography system of said method, comprise low-coherence light source, on the illumination direction of this low-coherence light source, place collimator and extender device, Michelson's interferometer in turn, incident illumination is divided into detection light with the beam splitter of this Michelson's interferometer and reference light enters feeler arm and reference arm respectively, the end of reference arm light path is a reference mirror, the end of feeler arm light path is a sample, and sample is placed on the accurate translation stage of three-dimensional; The Michelson's interferometer outfan connects a spectrogrph, and this spectrogrph is connected with computer by image pick-up card.

Described low-coherence light source is a broad spectrum light source, and its spectrum typical case half width is tens and arrives hundreds of nanometers, as super-radiance light emitting diode or femto-second laser etc.

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

Described Michelson's 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.It can be the bulk optics system, as be made of reference arm and feeler arm two-way light path the Amici prism beam split; Also can be fiber optic system, as by two output optical fibre light paths of 2 * 2 fiber couplers respectively as with reference to arm and feeler arm light path.

Described spectrogrph is by diffraction grating, and condenser lens and photodetector array are formed.

Described photodetector array is that CCD or photodiode array or other have the detector array of photosignal translation function.

The accurate translation stage of described three-dimensional can be done the translation of micron dimension precision along three mutually perpendicular directions.

The working condition of this system is as follows:

The light that low-coherence light source sends is behind collimator and extender device collimator and extender, in Michelson's interferometer, be divided into two bundles, a branch of light incides the reference mirror surface through reference arm, a branch of in addition light is in feeler arm incides sample, light of returning from the reference mirror surface reflectance and the light that different depth reflection or backscattering are returned in the sample are collected and return along reference arm and feeler arm, in Michelson's interferometer, interfere, enter the spectrogrph beam split again and computer sent in record, spectroscopic data obtains sample along the tomographic map of surveying the light optical axis direction after through the depth resolution dispersion compensation.By the accurate translation stage of three-dimensional transversal scanning is done with surveying the vertical plane of light optical axis in the sample edge, obtain the two dimension or the three-dimensional tomographic map of sample

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

When adopting wideband light source, use the depth resolution dispersion compensation method, can be at different depth, adopt different dispersion parameters to compensate respectively, obtain more accurate compensation effect, make the OCT system can adopt the more light source of high bandwidth, obtain higher longitudinal resolution.

The dispersion compensation process does not need to know in advance the material and the architectural characteristic of sample, highly versatile.

System does not need to increase extra dispersion compensation device, and is simple in structure.

Description of drawings

Fig. 1 is the bulk optics system block diagram of domain optical coherence tomography system.

Fig. 2 is an embodiment structures of samples sketch map.

Fig. 3 is the flow chart of the depth resolution dispersion compensation of a crosswise spots.

Fig. 4 is the embodiment sample tomographic map that does not pass through dispersion compensation.

Fig. 5 is the sample tomographic map that the embodiment sample is carried out the dispersion compensation of depth resolution according to the present invention program.

Fig. 6 is the sample tomographic map that the embodiment sample is carried out dispersion compensation according to unified abbe number.

The specific 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, Fig. 1 is the bulk optics system block diagram of domain optical coherence tomography system.Wherein 1 is low-coherence light source, on the low-coherence light source illumination direction, place collimator and extender device 2 successively, Michelson's interferometer 3, the beam splitter 4 of this Michelson's interferometer 3 is divided into incident illumination surveys light and reference light, place object lens 5 and reference mirror 6 on the reference light direction of propagation successively, survey light and focused on the sample 9 by object lens 8 after reflecting mirror 7 reflections, sample 9 is placed on the D translation platform 10.Michelson's interferometer 3 outfans connect a spectrogrph 11, and this spectrogrph 11 comprises diffraction grating 12, lens 13 and photoelectronic detecting array 14, and spectrogrph is connected with computer 20 by image pick-up card 15.

Low-coherence light source 1 sends low-coherent light and enter Michelson's interferometer 3 behind collimator and extender device 2 collimation, is divided into two bundles through beam splitter 4, and a branch of light focuses on the reference mirror 6 by the object lens in the reference arm 5, returns beam splitter 4 through reference mirror 6 reflections; Another Shu Guang is by sample arm, after object lens 8 focus on the sample 9, sample 9 is placed on the D translation platform 10 and realizes two-dimensional scan through reflecting mirror 7 reflections.Converge and interfere at beam splitter 4 from the light of reference mirror 6 reflection and different depth reflection or backscattering are returned in the sample 9 light, this interference light incides on the diffraction grating 12 in the spectrogrph 11 diffraction takes place, diffraction light is imaged on the photoelectronic detecting array 14 by lens 13 and converts the signal of telecommunication to, obtain optical frequency territory interference signal data through image pick-up card 15 and send into computer 20, this optical frequency territory interference signal obtains frequency domain interference signal corresponding to different depth through airspace filter device 16, then by phase place recovery algorithms 17 obtain dispersion compensating optical frequency territory interference signal phase place, reconstruction 18 by optical frequency territory interference signal obtains the optical frequency territory interference signal corresponding to the dispersion compensating of each degree of depth, obtains final tomographic map by inverse Fourier transformer 19 at last.By the scanning that moving three dimension translation stage 10 is realized sample, obtain the two dimension or the three-dimensional tomographic map of sample 9.Move and the spectrogrph collection of platform want consistent, and promptly the interference signal of Cai Jiing is corresponding with the sample position of scanning.Here by circuit gated sweep platform uniform motion, the interference signal and the corresponding relation of sample position that the movement velocity by computing platform and the acquisition rate of spectrogrph obtain gathering, thus rebuild the two-dimentional or three-dimensional tomographic map of sample.

Fig. 2 is the embodiment sample drawing, and this sample is formed by three layers, and the superiors are that thickness is the air layer about 250 μ m, and the intermediate layer is that thickness is the water of 1500 μ m, and lower floor is that thickness is the K9 glass of 1000 μ m.

In OCT, coherence length l _cBe inversely proportional to the light source bandwidth Delta lambda:

$l_c=\frac{4\mathrm{<figure-callout\; id="2"\; label="ln"\; filenames="S200710172096XE00031.png,S200710172096XE00051.png"\; state="\{\{state\}\}">ln</figure-callout>}2}{\mathrm{\&pi;}}\frac{{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}^2}{\mathrm{\&Delta;\&lambda;}}---\left(15\right)$

Wherein: Δ λ is the light source bandwidth,

Be centre wavelength.Systemic resolution δ z=l _c/ 2.In this enforcement, the light source bandwidth is 100nm, and centre wavelength is 750nm, and coherence length is 4.96 μ m.In water and glass, corresponding coherence length is about 3.4 μ m.

To each transversal scanning point, with spectrogrph record frequency domain interference fringe, in frequency domain (ω or k) uniform resampling, the interference fringe that obtains can be expressed as (1) formula to interference fringe.Removed between background noise and the sample interior different layers after the coherent superposition item, the optical frequency territory interference signal that obtains is:

$S_{\mathrm{int}}\left(k\right)=\underset{n=1}{\overset{3}{\mathrm{\&Sigma;}}}{B}_n\left(k\right)\left\{\exp \right\{i[n_{g,n}\left(k_0\right)k+{\mathrm{\&phi;}}_{\mathrm{GDD},n}\left(k\right)+{\mathrm{\&phi;}}_{\mathrm{TOD},n}\left(k\right)+...]\&times;z_n\}$

$+\exp \{-i[n_{g,n}\left(k_0\right)k+{\mathrm{\&phi;}}_{\mathrm{GDD},n}\left(k\right)+{\mathrm{\&phi;}}_{\mathrm{TOD},n}\left(k\right)+...]\&times;z_n\}\}\exp -\left({\mathrm{i\&phi;}}_{0,n}\right)$ (16)

In the formula: z ₁, z ₂And z ₃Be respectively water layer front surface, water and the corresponding optical path difference of glass interface and position, glass rear surface.

1. do not consider the mirror image problem, think z＞0, S _Int(k) k is done the sample tomographic map (Fig. 4) that Fourier transform is not passed through dispersion compensation:

$S_{\mathrm{int}}\left(z\right)=\{\underset{n=1}{\overset{3}{\mathrm{\&Sigma;}}}{B}_n\left(z\right)\&CircleTimes;\mathrm{\&delta;}(z-z_n)\&CircleTimes;\mathrm{iFT}\{\exp [-i\left({\mathrm{\&phi;}}_{\mathrm{GDD},n}\left(k\right){+\mathrm{\&phi;}}_{\mathrm{TOD},n}\left(k\right)\right)\&times;z_n]\}\&CircleTimes;...\}\&times;\exp \left({\mathrm{i\&phi;}}_{0,n}\right)---\left(17\right)$

2. find z ₁, z ₂And z ₃The peaked correspondence position z of place's interference fringe _{1, max}, z _{2, max}And z _{3, max},, ask for the filter window width Delta z of space filter by method noted earlier ₁, Δ z ₂With Δ z ₃Respectively with z _{1, max}, z _{2, max}And z _{3, max}Being the center, is Δ z with width ₁, Δ z ₂With Δ z ₃Window filtering, obtain the striped of three broadenings:

S _filter，n(z)

＝B _n(z)δ(z-z _n)iFT{exp[-i(φ _GDD，n(k)+φ _TOD，n(k)+...)×z _n]}×exp(-iφ _0，n) n＝1，2，3 (18)

3.S _{Filter, n}(z) z is done Fourier transform, obtain corresponding to z _nThe optical frequency territory interference signal S at place _{Filter, n}(k):

$S_{\mathrm{filter},n}\left(k\right)=B_n\left(k\right)\&times;$

                                                          

$\exp \{-i[n_n\left(k_0\right)k_0+n_{g,n}\left(k_0\right)\&times;(k-k_0)+{{\mathrm{\&beta;}}_n}^{\&prime;\&prime;}\&times;\frac{{(k-k_0)}^2}{2!}+{{\mathrm{\&beta;}}_n}^{\&prime;\&prime;\&prime;}\left(k_0\right)\&times;\frac{{(k-k_0)}^3}{3!}+...]\&times;z_n\}n=\mathrm{1,2,3}$ (19)

Extract the complex amplitude and the phase place of this signal:

4. with (k-k ₀) be independent variable, to  _{Filter, n}(k) numerical fitting obtains z _nThe second order and the third-order dispersion factor beta at place _n" (k ₀) and β _n (k ₀).Calculating the phase place distortion is:

Phase place is carried out dispersion compensation, from  _{Filter, n}(k) deduct  in _{Disp, n}(k) obtain phase place behind the dispersion compensation:

 _comp，n(k)＝-[n _n(k ₀)k ₀+n _g，n(k ₀)×(k-k ₀)]×z _n n＝1，2，3 (22)

5. by complex amplitude A _{Filter, n}(k) and phase place  _{Comp, n}(k) recover z _nThe optical frequency territory interference signal at place:

S _comp，n(k)＝B _n(k)×exp{-i[n _n(k ₀)k ₀+n _g，n(k ₀)×(k-k ₀)]×z _n} n＝1，2，3 (23)

6. three place's signal stacks obtain the optical frequency territory interference signal of the sample of dispersion compensating:

$S_{\mathrm{comp}}\left(k\right)=\underset{n=1}{\overset{3}{\mathrm{\&Sigma;}}}{B}_n\left(k\right)\&times;\exp \left\{i\right[n_n\left(k_0\right)k_0+n_{g,n}\left(k_0\right)\&times;(k-k_0)]\&times;z_n\}---\left(24\right)$

7.S _Comp(k) k is done inverse Fourier transform and delivery, obtains the sample tomographic map (Fig. 5) of dispersion compensating:

$S_{\mathrm{comp}}\left(z\right)=\underset{n=1}{\overset{3}{\mathrm{\&Sigma;}}}{B}_n\left(z\right)\&CircleTimes;\mathrm{\&delta;}(z-z_n)---\left(25\right)$

Fig. 3 is the flow chart of the depth resolution dispersion compensation of a crosswise spots.

As seen from Figure 4, because air does not have chromatic dispersion, z ₁Place's width of fringe is near calculated value.And the interface z of water and glass ₂And the rear surface z of glass ₃The place is owing to effect of dispersion, and striped has obvious broadening.

As seen from Figure 5, carry out after the dispersion compensation of depth resolution, width of fringe approaches calculated value, and systemic resolution increases substantially.

In (21) formula, adopt z ₃The abbe number β at place ₃" (k ₀) and β ₃ (k ₀) compensation z ₁And z ₂Striped, obtain the sample tomographic map (Fig. 6) that compensates according to unified abbe number.Because z ₃The abbe number maximum at place, and z ₁The place does not have chromatic dispersion, z ₂Place's abbe number is less, so this compensation method has caused z ₁And z ₂The overcompensation at place causes z ₁Place's striped broadening, z ₂Place's striped improves poor effect.

By Fig. 3, Fig. 4 and Fig. 5 as can be seen, on the basis of adopting the ultra-wide spectrum light source, the present invention has adopted the depth resolution dispersion compensation method, has compensated the broadening effect of chromatic dispersion effectively, has realized a kind of tomography of high resolution optics coherence method.

Claims (2)

1. a tomography of high resolution optics coherence method is characterised in that this method comprises the following steps:

1. at first utilize high-resolution domain optical coherence tomography system each transversal scanning point to sample, the frequency domain interference spectrum signal of the photoelectronic detecting array record sample of this system is also sent into computer;

2. computer is done inverse Fourier transform to the interference spectrum signal of a certain crosswise spots of photoelectronic detecting array collection and is obtained this tomographic map;

3. adopt the airspace filter device to extract the complex amplitude and the phase place of the optical frequency territory interference signal of a certain degree of depth of this tomographic map;

4. adopt method of least square that described phase place is carried out match, obtain the 2nd order chromatic dispersion coefficient and the third-order dispersion coefficient of sample, and calculate the phase place distortion that chromatic dispersion causes at this degree of depth place; From described phase place, deduct this twist angle, obtain the phase place behind the dispersion compensation;

5. the Phase Build Out after utilizing complex amplitude and compensating goes out the optical frequency territory interference signal through dispersion compensation corresponding to this degree of depth;

6. 3. the tomographic map to different depth repeats the extremely 5. step, and the optical frequency territory interference signal at each degree of depth place is superposeed, and obtains the optical frequency territory interference signal through dispersion compensation of this crosswise spots;

7. the last optical frequency territory interference signal through dispersion compensation to this crosswise spots carries out inverse Fourier transform and obtains the tomographic map that this point is rebuild;

8. 2. repeating step is handled to the 7. interference spectrum signal to each crosswise spots of described frequency domain interference spectrum, obtains the two dimension or the three-dimensional tomographic map of this sample.

2. tomography of high resolution optics coherence method according to claim 1 is characterized in that the choosing method of window width of the airspace filter device of described a certain crosswise spots is:

The twice standard deviation sum of selecting the noise meansigma methods of frequency domain interference signal of this point and this signal is as threshold value;

Find each maximum that is higher than threshold value in this tomographic map;

With maximum is middle mind-set both sides extended window, and the width that equals preset threshold up to maximum both sides intensity is made as the window width of this maximum.

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