CN102657518B - Method of complex frequency-domain optical coherence tomography using differential sinusoidal phase modulation - Google Patents

Abstract

A method of complex frequency-domain optical coherence tomography using differential sinusoidal phase modulation includes: based on complex frequency-domain optical coherence tomography using differential sinusoidal phase modulation, introducing sinusoidal phase modulation to transverse scan interference signals, subjecting acquired interference spectral signals to inverse Fourier transform along the wave-number direction, using a phase difference of adjacent complex tomographic signals to replace phases of complex tomographic signals obtained in conversion so that new differential complex tomographic signals are formed, respectively subjecting a real part and an imagery part of each differential complex tomographic signal to phase demodulation prior to addition so as to obtain mirror-removed complex tomographic signals, and removing amplitude to obtain a full-depth structural tomographic map of a tested sample. By the method, complex conjugate mirror images, direct current background and autocorrelation noise in the frequency-domain optical coherence tomographic images are eliminated, sensitivity does not decrease with increase of transverse scanning distance, the affection of internal high-speed movement of a sample on mirror image elimination is reduced, and the method is applicable to in vivo imaging of biological samples.

Description

The complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation

Technical field

The present invention relates to domain optical coherence tomography (Fourier-Domain Optical Coherence Tomography is called for short FD-OCT), relate in particular to a kind of complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation.

Background technology

Optical coherent chromatographic imaging (Optical Coherence Tomography, abbreviation OCT) technology is the high-resolution formation method of a kind of non-intrusion type, can carry out being widely used in diagnosis and the research of a plurality of medical domains such as ophthalmology, skin at the body nondestructive tomographic imaging to a few mm depth scopes in biological tissue.

Domain optical coherence tomography (FD-OCT) is a kind of novel OCT imaging technique, the tradition time domain OCT utilizes the low-coherent light interfere measurement technique,, by sample is carried out mechanical scanning along depth direction, obtain the reflectivity information (A-line) of change in depth in sample; Then, by transversal scanning, obtain the tomographic map of corresponding different cross measure points on sample, the two-dimentional fault structure figure (B-scan) of a synthetic width sample depth direction.Frequency domain OCT technology is carried out Fourier transformation by collection interference spectrum signal to it just can obtain the tomographic map (A-line) of a depth resolution, need not to carry out the mechanical scanning of depth direction, have picking rate faster and higher sensitivity with respect to time domain OCT, be particularly useful for biological sample at health check-up survey and medical diagnosis.

Because the domain optical coherence tomography technology is to utilize the inverse Fourier transform method to analyze the interference spectrum signal that spectrogrph collects, the chromatography signal after conversion exists direct current background, Correlated noises and complex conjugate mirror image simultaneously except the structural information that comprises object.Wherein the former two has reduced the signal to noise ratio of system; The complex conjugate mirror image shows as real structure image with object about the symmetrical image in zero optical path difference position, and this is both overlapped when zero optical path difference is positioned at interior of articles.For fear of overlapping, object can only be placed in a side of zero optical path difference position, this will cause the system effective scope of detection to be reduced to original half.The complex conjugate mirror image can pass through to rebuild complex frequency domain interference spectrum signal, and its mode of carrying out inverse Fourier transform is eliminated, and this technology is complex frequency domain optical coherence tomography imaging.

The complex frequency domain optical coherence tomography imaging utilization is rebuild complex frequency domain interference spectrum signal and has been eliminated complex conjugate mirror image and other parasitic image, makes investigation depth expand as original 2 times, has realized full-depth probing.Complex frequency domain OCT mainly comprises based on the movable phase interfere art with based on difference interference art two classes at present.

1, based on the complex frequency domain OCT of movable phase interfere art (phase-shifting interferometry)

The people such as A.F.Fercher were used for the movable phase interfere art reconstruction of the multiple interference signal of frequency domain OCT at first in 1999, set up complex frequency domain OCT technology (referring to technology [1] formerly, A.F.Fercher, R.Leitgeb, C.K.Hitzenberger, H.Sattmann, and M.Wojtkowski, " Complex spectral interferometry OCT ", Proc.SPIE, Vol.3564,173-178,1998).The method, by the interference spectrum of mobile reference arm at adjacent phase difference such as several frames of sample same position continuous acquisition, utilizes the phase shift algorithm to rebuild multiple interference signal.This method has increased imaging time, and the stability of system and sample is proposed very high requirement, therefore is not suitable for the imaging of motion sample.After this OCT of the complex frequency domain based on simultaneous phase-shifting that develops, adopt dual-beam illumination and two cover interference signal receiving systems (referring to technology [2] P.Meemon formerly, Kye-Sung Lee, and J.P.Rolland, " Doppler imaging with dual-detection full-range frequency domain optical coherence tomography ", Biomed.Opt.Express 1 (2), 537-552,2010), or adopt the vertical two-beam in polarization direction to survey, thereby solved the impact of sample motion on image cancellation.Yet this method has increased the complexity of experimental provision.

2, based on the complex frequency domain OCT of difference interference art (heterodyne interferometry)

Complex frequency domain OCT based on the difference interference art makes the real structure picture that overlaps separate with the complex conjugate mirror image by introduce carrier wave in the frequency domain interference signal, and the recycling spectral window takes out the multiple interference signal of real structure.These class methods are not subject to the motion effects of sample, and experimental system is comparatively simple, has obtained more application.wherein a kind of mirror method that goes that is called synchronous B-M scanning method passes through in transversal scanning (B-scan) sample to introduce phase-modulation (M-scan) (referring to technology [3] K.Wang formerly, Z.Ding, Y.Zeng, J.Meng, and M.Chen, " Sinusoidal B-M method based spectral domain optical coherence tomography for the elimination of complex-conjugate artifact, " Opt.Express 2009, vol.17 (19): pp.16820-16833), make a transversal scanning just can obtain the B-scan figure of the full degree of depth of width.The method has shortened the interference signal acquisition time, makes it to be applied to the biological living imaging.Yet to the organism imaging time,, if there is the motion (as the blood flow motion) of higher speed sample inside, easily cause the image cancellation failure.Parabola BM scanning technique has been proposed (referring to technology [4] F.Jaillon formerly in order to address this problem the people such as Franck Jaillon, S.Makita, M.Yabusaki, and Y.Yasuno, " Parabolic BM-scan technique for full range Doppler spectral domain optical coherence tomography; " Opt.Express 2010, vol.18 (2): pp.1358-1372).The method is introduced the parabolic type phase-modulation when transversal scanning, and multiple interference signal is asked in filtering to differential signal, has reduced the impact of high-speed motion on the image cancellation effect, has eliminated and has gone the restriction of mirror image to the doppler velocity investigative range.Yet owing to adopting the parabolic type phase-modulation in transversal scanning, to cause the increase along with the transversal scanning distance, sample will be the highest with sensitivity the zero optical path difference position more and more far away, this sensitivity that can cause image reduces with the increase of transversal scanning distance.

The amplitude of sinusoidal phase modulation is less, and monotone increasing in time not, can make sample be in all the time the sensitivity upper zone.The sinusoidal phase modulation mode is not subject to the impact of PZT hysteresis effect in addition, relatively is fit to high-velocity scanning.At first the step people such as roc has rebuild complex frequency domain OCT signal (referring to technology [5] P.Bu formerly based on the method for sinusoidal phase modulation, X.Wang, and O.Sasaki, " Dynamic full-range Fourier-domain optical coherence tomography using sinusoidal phase-modulating interferometry; " Optical Engineering 2007, vol.46 (10): pp.105603-4; Go on foot roc, Wang Xiangchao. the method for the domain optical coherence tomography of full-depth probing and system thereof: China, 1877305A (patent) .2006-12-13).The method is obtained the complex frequency domain interference signal because needs carry out phase-modulation to each transversal scanning position, and the method has increased the sampling time of legacy data.The people such as wangkai combine the method for sinusoidal phase modulation and B-M scanning to have obtained sinusoidal B-M scan method (referring to technology [6] K.Wang formerly, Z.Ding, Y.Zeng, J.Meng, and M.Chen, " Sinusoidal B-M method based spectral domain optical coherence tomography for the elimination of complex-conjugate artifact; " Opt.Express 2009, vol.17 (19): pp.16820-16833).The method is carried out phase-modulation simultaneously in transversal scanning, has shortened the data sampling time.Yet the method extracts fundamental frequency by low pass filter and the frequency multiplication harmonic component is rebuild multiple interference spectrum signal, and is less to the redundancy of sample motion, is not suitable for the biological sample living imaging.

Summary of the invention

The present invention is in order to overcome the deficiency of above formerly technology, a kind of complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation is provided, the method has reduced the impact of sample interior high-speed motion on the image cancellation effect, and sample is near the higher zero optical path difference position of sensitivity all the time, and sensitivity does not reduce apart from increase with transversal scanning.

Technical solution of the present invention is as follows:

a kind of complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation, characteristics are that the method is on the basis of sinusoidal phase modulation complex frequency domain optical coherence tomography imaging method, introduce sinusoidal phase modulation in the transverse scanning interference signal, the interference spectrum signal that gathers is carried out inverse Fourier transform along wave number, the phase place of the multiple chromatography signal that obtains after conversion is replaced with the phase contrast of adjacent multiple chromatography signal, form the multiple chromatography signal of difference, the real part of the multiple chromatography signal of difference and imaginary part are carried out respectively addition after phase demodulating obtain the multiple chromatography signal of mirror image, take out its amplitude, can recover the full depth structure tomographic map of sample.

The complex frequency domain optical coherence tomography imaging method of described difference sinusoidal phase modulation is characterized in that the concrete steps of the method are as follows:

1. on the basis of sinusoidal phase modulation complex frequency domain optical coherence tomography imaging method, adopt the domain optical coherence tomography system (referring to technology 5 formerly) of full-depth probing, when utilizing 2-D vibration mirror to carry out transversal scanning along detection light optical axis vertical direction, drive reference mirror and do sinusoidal vibration along optical axis direction under the driving of sinusoidal phase modulation device, introduce sinusoidal phase modulation in the interference signal of the different horizontal detection positions of sample, the amplitude a of reference mirror sinusoidal vibration should meet a=2.63/ (2k ₀ω _c), k wherein ₀For wave number corresponding to the centre wavelength of light source light spectrum, ω _cAngular frequency for reference mirror sinusoidal vibration;

2. the interference spectrum signal I (k, t) that adds sinusoidal phase modulation of described detector record is:

$I(k,t)=I_0\left(k\right)+2S\left(k\right)\underset{n}{\mathrm{\Σ}}\sqrt{R_{\mathrm{Sn}}{R}_R}\cos \left[2k(z_n\left(t\right)+A\cos ({\mathrm{\ω}}_{c}t+\mathrm{\θ}))\right],$

Wherein, I ₀(k) be self correlation item between the inner different depth reflecting surface of direct current background in the interference spectrum signal and sample, S (k) is the light source light spectrum density function, R _SnWith R _RBe respectively the reflectance of testing sample n layer reflecting surface and the reflectance of reference mirror, z _n(t) be the optical path difference of testing sample n layer reflecting surface and reference mirror reflecting surface, t represents that detecting light beam scans the different corresponding times of horizontal detection point of sample, A=2ka is the modulation depth that reference mirror is done the sinusoidal vibration phase-modulation, and a is the amplitude of reference mirror vibration, ω _c=2 π f _cFor angular frequency, f _cFor frequency, θ is initial phase;

3. above-mentioned interference spectrum signal I (k, t) is done inverse Fourier transform along wave number k, obtains the chromatography signal I (z, t) of testing sample along detection light optical axis direction:

In formula,

The inverse Fourier transform of wave number k is done in expression, and Γ (z) is the inverse Fourier transform of light source light spectrum density function, The expression convolution, δ is Dirac function, and second, equation right side is the mutual coherent term of sample reflected signal and reference mirror reflected signal, and this reflectance that has reflected sample inside distributes; The 3rd, equation right side is and second picture about zero optical path difference position symmetry, the distribution of this and fict interior of articles reflectance, but Fourier transformation produces because the real number interference spectrum signal that detector is collected carries out, and is called mirror image;

4. the phase place of following formula is taken out, the adjacent signals phase place is done difference, obtain that adjacent phase is poor is:

Δφ(z，t)＝2k ₀(dz _n(t)-Aω _csin(ω _ct+θ))Δt，

Wherein: dz _n(t) over time, Δ t represents that detector gathers the interval of adjacent two signals to the optical path difference of expression reference mirror reflecting surface and detected sample position n layer reflecting surface;

5. form new chromatography signal with the amplitude in original chromatography signal and the phase contrast of obtaining:

Make z _n'=z _n(t)+Acos (ω _cT+ θ), new modulation depth is A '=A ω _c, new initial phase is θ '=θ+pi/2, the following formula abbreviation is:

Wherein,

Self correlation between the different reflectings surface of the direct current background while having reflected sample in measurement and sample interior, utilize the two-dimensional scan galvanometer along with the optical axis vertical direction, carrying out transversal scanning, and gather the interference spectrum signal of different lateral attitudes on sample with detector, obtain a frame two dimension interference spectrum signal, after doing on average to the time it, obtain an one dimension interference spectrum signal, it is cut from each interference signal of former interference spectrum, can remove direct current background and Correlated noises, after removing, new chromatography signal representation is:

$I^{\′}(z,t)=\underset{n}{\mathrm{\Σ}}(\mathrm{\Γ}\left({z_n}^{\′}\right)+\mathrm{\Γ}(-{z_n}^{\′}))\cos \left({2k}_0\mathrm{\Δt}({\mathrm{dz}}_n\left(t\right)+A^{\′}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\θ}}^{\′}))\right)$

$+i\underset{n}{\mathrm{\Σ}}(\mathrm{\Γ}\left({z_n}^{\′}\right)-\mathrm{\Γ}\left({{-z}_n}^{\′}\right))\sin \left({2k}_0\mathrm{\Δt}({\mathrm{dz}}_n\left(t\right)+A^{\′}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\θ}}^{\′}))\right)$

6. the real part in formula and imaginary part are carried out respectively phase demodulating, obtain:

With top two formula additions divided by the multiple chromatography signal of the mirror image that is eliminated after 2, be:

$\tilde{I}(z,t)=\underset{n}{\mathrm{\Σ}}\mathrm{\Γ}\left({z_n}^{\′}\right)\exp (-i{2k}_0\mathrm{\Δ}{\mathrm{tdz}}_n\left(t\right)),$

7. again according to the relation of z and z ', z _n'=z _n(t)+Acos (ω _cT+ θ), z ' is reduced into each measures the real depth position z of t constantly, the amplitude in the multiple chromatography signal of elimination mirror image is taken out and can be obtained the one dimension tomographic map that reflects the sample structural information and do not comprise mirror image:

$\tilde{I}(z,t)=\underset{n}{\mathrm{\Σ}}\mathrm{\Γ}(z_n\left(t\right)+A\cos ({\mathrm{\ω}}_{c}t+\mathrm{\θ}))\exp (-i{2k}_0\mathrm{\Δ}{\mathrm{tdz}}_n\left(t\right));$

The full degree of depth two-dimensional structure figure that can form sample after 8. 4.～7. each the interference spectrum signal in a described frame two dimension interference spectrum signal being processed according to above-mentioned steps.

Utilize the two-dimensional scan galvanometer to scan simultaneously along two-dimensional directional, obtain a frame two dimension interference spectrum signal of different longitudinal position, after 3.～8. carrying out date processing by step claimed in claim 2, obtain the three-dimensional full depth structure figure of testing sample.

The complex frequency domain optical coherence tomography imaging system of implementing said method comprises low-coherence light source, and the light of light source output is coupled in Michelson's interferometer, and Michelson's interferometer is divided into two-way with incident illumination, incides respectively in reference arm and sample arm.Light beam in reference arm optical fiber is radiated on reference mirror after the optical fiber collimator collimation.Be focused in sample after 2-D vibration mirror after the optical alignment of sample arm optical fiber output.The outfan of Michelson's interferometer connects a spectrogrph, and the interference spectrum that spectrogrph collects is inputted in computer by image pick-up card.The characteristics of this system are that 2-D vibration mirror rotates along the vertical direction of optical axis, obtain the interference signal of different cross measures position on sample, described reference mirror is fixed on a sinusoidal phase modulation device, rotate when on sample, different cross measures position is scanned from galvanometer, this sinusoidal phase modulation device drives described reference mirror and does sinusoidal vibration.

Described low-coherence light source is wide spectral bandwidth light source, and its spectral bandwidth is tens to the hundreds of nanometer, as super-radiance light emitting diode (SLD) or femto-second laser or super continuum source etc.

Described Michelson's interferometer is characterized in that having two and makes reference respectively arm and sample arm near aplanatic optical interference circuit.

Described spectrogrph is by collimating lens, spectro-grating, and condenser lens and photodetector array form.

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

Described sinusoidal phase modulation device is comprised of SIN function electric signal generator and the piezoelectric ceramic actuator that is fixed on described reference mirror, and the time SIN function driving signal of telecommunication that described SIN function electric signal generator sends drives described reference mirror by piezoelectric ceramic actuator and does sinusoidal vibration.

The working condition of this system is as follows:

the light that low-coherence light source sends is coupled in Michelson's interferometer, Michelson's interferometer is divided into reference path and sample light path with incident illumination, light in reference path is radiated on the reference mirror that is fixed on the sinusoidal phase modulation device after collimation, being focused mirror through 2-D vibration mirror after optical alignment in the sample light path focuses in sample, the back-scattering light of the reflected light of reference mirror and sample interior different depth is collected back in reference arm and sample arm again, be admitted in spectrogrph after converging in Michelson's interferometer, the interference spectrum signal that spectrogrph will record is sent into computer by image pick-up card and is carried out date processing, obtain the tomographic map of sample along depth direction.Do transversal scanning by 2-D vibration mirror along the optical axis vertical direction and obtain the tomographic map of diverse location on sample, obtain two dimension or the three-dimensional tomographic map of sample.The sinusoidal phase modulation device is fixed on reference mirror, when galvanometer carries out transversal scanning along the optical axis vertical direction, this device drives reference mirror and does sinusoidal vibration under the driving of the signal of telecommunication of a sinusoidal variations, introduce sinusoidal phase modulation in the interference signal of the different detecting locations of sample that spectrogrph collects.

The present invention compared with prior art useful effect is:

The complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation of the present invention is on the basis of sinusoidal phase modulation complex frequency domain optical coherence tomography imaging method, with the multiple former chromatography signal reconstruction of the chromatography signal substituting complex frequency domain interference signal of difference.The present invention has eliminated complex conjugate mirror image and direct current background and the Correlated noises in the domain optical coherence tomographic map, reduced the impact of sample interior high-speed motion on the image cancellation effect, be more suitable for the imaging in vivo for biological sample, and because sample is near the higher zero optical path difference position of sensitivity all the time, sensitivity does not reduce apart from increase with transversal scanning.

System does not need to increase extra means, and is simple in structure.

Description of drawings

Fig. 1 is the fiber optic system structural representation of complex frequency domain optical coherence tomography imaging system.

The specific embodiment

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

See also Fig. 1, Fig. 1 is the structural representation of the optical fiber complex frequency domain optical coherence tomography imaging system that adopts of the complex frequency domain optical coherence tomography imaging method embodiment of difference sinusoidal phase modulation of the present invention.The complex frequency domain optical coherence tomography imaging system, comprise low-coherence light source 1, place Michelson's interferometer 2 on the illumination direction of low-coherence light source, the beam splitter 21 of Michelson's interferometer is divided into reference arm light path 22 and sample arm light path 23 with incident illumination, the end of reference arm light path is reference mirror 24, is followed successively by two-dimensional scan galvanometer 25, focus lamp 26 and testing sample 27 along light beam incident direction of advance in the sample arm light path; The outfan of described Michelson's interferometer connects a spectrogrph 4, and this spectrogrph 4 is connected with computer 6 by image pick-up card 5, and described spectrogrph 4 is comprised of spectro-grating 41, condenser lens 42 and detector 43; Described reference mirror 24 connects a sinusoidal phase modulation device 3, described sinusoidal phase modulation device 3 is comprised of SIN function electric signal generator and the piezoelectric ceramic actuator that is fixed on described reference mirror 24, and the SIN function signal of telecommunication that described SIN function electric signal generator sends drives described reference mirror 24 by piezoelectric ceramic actuator and does sinusoidal vibration.

the wide spectral light that low-coherence light source 1 sends is coupled in Michelson's interferometer 2, be divided into two bundles by beam splitter 21, a branch ofly through reference arm light path 22, incide reference mirror 24 surfaces, another is restrainted after sample arm light path 23 collimations by two-dimensional scan galvanometer 25, be focused mirror 26 and focus on the interior diverse location of testing sample 27, the light of returning from reference mirror 24 surface reflections and from the light that the inner different depth backscattering of testing sample 27 is returned is collected back reference arm light path 22 and sample arm light path 23 again, produce and interfere after beam splitter 21 places converge in Michelson's interferometer 2, this interference light is admitted to spectrogrph 4, after spectro-grating 41 light splitting, being focused lens 42 is imaged on detector 43, after converting the signal of telecommunication to, send into computer 6 and carry out date processing after image pick-up card 5 digital-to-analogue conversions, obtain testee 27 along the tomographic map of surveying the light optical axis direction.

Do transversal scanning by 25 pairs of testing samples 27 of two-dimensional scan galvanometer along the optical axis vertical direction and obtain two dimension or the three-dimensional tomographic map of testee 27.Described sinusoidal phase modulation device 3 is connected with the reference mirror 24 in Michelson's interferometer 2, when two-dimensional scan galvanometer 25 carries out transversal scanning along the optical axis vertical direction, described reference mirror 24 drives reference mirror 24 and does sinusoidal vibration under the driving of the signal of telecommunication of the sinusoidal variations of described sinusoidal phase modulation device 3, therefore introduce sinusoidal phase modulation in the interference signal of the different detecting locations of testee that spectrogrph 4 collects.The amplitude that described reference mirror 24 is done sinusoidal vibration is a=2.63/ (2k ₀ω _c), k wherein ₀Send the wave number corresponding to centre wavelength of spectrum for light source 1, ω _cAngular frequency for reference mirror sinusoidal vibration.

The interference spectrum signal I (k, t) of described detector 43 records is:

$I(k,t)=I_0\left(k\right)+2S\left(k\right)\underset{n}{\mathrm{\Σ}}\sqrt{R_{\mathrm{Sn}}{R}_R}\cos \left[2k(z_n\left(t\right)+A\cos ({\mathrm{\ω}}_{c}t+\mathrm{\θ}))\right]---\left(1\right)$

Wherein, I ₀(k) be self correlation item between the inner different depth reflecting surface of direct current background in the interference spectrum signal and sample, S (k) is the light source light spectrum density function, R _SnWith R _RBe respectively the reflectance of testing sample 27 n layer reflecting surface and the reflectance of reference mirror 24, z _n(t) be the optical path difference of testing sample 27 n layer reflecting surface and reference mirror 24 reflectings surface, t represents that detecting light beam scans the different corresponding times of horizontal detection point of sample, A=2ka is the modulation depth that reference mirror 24 is done the sinusoidal vibration phase-modulation, and a is the amplitude of reference mirror 24 vibrations, ω _c=2 π f _cFor angular frequency, f _cFor frequency, θ is initial phase.

Interference spectrum signal I (k, t) is done inverse Fourier transform along wave number k, obtains the chromatography signal (A-line signal) of testing sample 27 along detection light optical axis direction:

In formula, The inverse Fourier transform of wave number k is done in expression, and Γ (z) is the inverse Fourier transform of light source light spectrum density function, The expression convolution, δ is Dirac function.Second, equation right side is the mutual coherent term of sample reflected signal and reference mirror reflected signal, and this reflectance that has reflected sample inside distributes; The 3rd, equation right side is and second picture about zero optical path difference position symmetry, this is the distribution of fict interior of articles reflectance also, but Fourier transformation produces because the real number interference spectrum signal that detector is collected carries out, and is called complex conjugate picture or mirror image.

The phase place of (2) formula is taken out, the phase place of adjacent multiple chromatography signal is done difference, the phase contrast that obtains adjacent multiple chromatography signal is:

Δφ(z，t)＝2k ₀(dz _n(t)-Aω _csin(ω _ct+θ))Δt (3)

Wherein: dz _n(t) over time, Δ t represents that detector gathers the interval of adjacent two signals to the optical path difference of expression reference mirror reflecting surface and detected sample position n layer reflecting surface.

Form the multiple chromatography signal of new difference with the phase contrast that amplitude and (3) formula of the multiple chromatography signal in (2) formula are obtained:

Make z _n'=z _n(t)+Acos (ω _cT+ θ), new modulation depth is A '=A ω _c, new initial phase is θ '=θ+pi/2, and its substitution following formula can be obtained:

Wherein,

Self correlation between the different reflectings surface of the direct current background while having reflected sample in measurement and sample interior, can utilize two-dimensional scan galvanometer 25 along with the optical axis vertical direction, carrying out transversal scanning, and gather the interference spectrum signal of different lateral attitudes on sample with detector, a frame two dimension interference spectrum signal that obtains, after doing on average to the time it, obtain an one dimension interference spectrum signal, it is cut from each interference signal of former interference spectrum, can remove direct current background and Correlated noises.New chromatography signal can be re-expressed as:

$I^{\′}(z,t)=\underset{n}{\mathrm{\Σ}}(\mathrm{\Γ}\left({z_n}^{\′}\right)+\mathrm{\Γ}(-{z_n}^{\′}))\cos \left({2k}_0\mathrm{\Δt}({\mathrm{dz}}_n\left(t\right)+A^{\′}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\θ}}^{\′}))\right)$

$\left(6\right)$

$+i\underset{n}{\mathrm{\Σ}}(\mathrm{\Γ}\left({z_n}^{\′}\right)-\mathrm{\Γ}\left({{-z}_n}^{\′}\right))\sin \left({2k}_0\mathrm{\Δt}({\mathrm{dz}}_n\left(t\right)+A^{\′}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\θ}}^{\′}))\right)$

Utilize respectively the method in technology [5] formerly to carry out phase demodulating to the real part in (6) formula and imaginary part, can obtain:

With (7) formula with (8) formula phase adduction divided by 2, the multiple chromatography signal of the mirror image that is eliminated is:

$\tilde{I}(z,t)=\underset{n}{\mathrm{\Σ}}\mathrm{\Γ}\left({z_n}^{\′}\right)\exp (-i{2k}_0\mathrm{\Δ}{\mathrm{tdz}}_n\left(t\right))---\left(9\right)$

According to z _n' with z _nRelation, with the z in (9) formula _n' be reduced into each to measure the real depth position z of t constantly _n, then will eliminate amplitude in the multiple chromatography signal of mirror image and take out and can obtain the one dimension tomographic map that reflects the sample structural information and do not comprise mirror image.The full degree of depth two-dimensional structure figure that can form sample 27 after each the interference spectrum signal in one frame two dimension interference spectrum signal is processed according to above-mentioned steps.Utilize two-dimensional scan galvanometer 25 to scan simultaneously along two-dimensional directional, obtain the two-dimentional interference spectrum signal of different longitudinal position,, through above-mentioned processing, namely obtain the three-dimensional full depth structure figure of testing sample 27.

Claims (3)

1. the complex frequency domain optical coherence tomography imaging method of a difference sinusoidal phase modulation, be characterised in that the method is on the basis of sinusoidal phase modulation complex frequency domain optical coherence tomography imaging method, introduce sinusoidal phase modulation in the transverse scanning interference signal, the interference spectrum signal that gathers is carried out inverse Fourier transform along wave number, the phase place of the multiple chromatography signal that obtains after conversion is replaced with the phase contrasts of two adjacent multiple chromatography signals, form the multiple chromatography signal of difference, the real part of the multiple chromatography signal of difference and imaginary part are carried out respectively addition after phase demodulating obtain the multiple chromatography signal of mirror image, take out its amplitude, be the full depth structure tomographic map of sample.

2. the complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation according to claim 1 is characterized in that the concrete steps of the method are as follows:

1. on the basis of sinusoidal phase modulation complex frequency domain optical coherence tomography imaging method, adopt the domain optical coherence tomography system of full-depth probing, when utilizing 2-D vibration mirror to carry out transversal scanning along detection light optical axis vertical direction, drive reference mirror and do sinusoidal vibration along optical axis direction under the driving of sinusoidal phase modulation device, introduce sinusoidal phase modulation in the interference signal of the different horizontal detection positions of sample, the amplitude a of reference mirror sinusoidal vibration should meet a=2.63/ (2k ₀ω _c), k wherein ₀For wave number corresponding to the centre wavelength of light source light spectrum, ω _cAngular frequency for reference mirror sinusoidal vibration;

2. the interference spectrum signal I (k, t) that adds sinusoidal phase modulation of detector record is:

$I(k,t)=I_0\left(k\right)+2S\left(k\right)\underset{n}{\mathrm{\Σ}}\sqrt{R_{\mathrm{Sn}}{R}_R}\cos \left[2k(z_n\left(t\right)+A\cos ({\mathrm{\ω}}_{c}t+\mathrm{\θ}))\right],$

Wherein, I ₀(k) be self correlation item between the inner different depth reflecting surface of direct current background in the interference spectrum signal and sample, S (k) is the light source light spectrum density function, R _SnWith R _RBe respectively the reflectance of testing sample n layer reflecting surface and the reflectance of reference mirror, z _n(t) be the optical path difference of testing sample n layer reflecting surface and reference mirror reflecting surface, t represents that detecting light beam scans the different corresponding times of horizontal detection point of sample, A=2ka is the modulation depth that reference mirror is done the sinusoidal vibration phase-modulation, and a is the amplitude of reference mirror vibration, ω _c=2 π f _cFor angular frequency, f _cFor frequency, θ is initial phase;

3. above-mentioned interference spectrum signal I (k, t) is done inverse Fourier transform along wave number k, obtains the chromatography signal I (z, t) of testing sample along detection light optical axis direction:

In formula,

The inverse Fourier transform of wave number k is done in expression, and Γ (z) is the inverse Fourier transform of light source light spectrum density function,

The expression convolution, δ is Dirac function, and second, equation right side is the mutual coherent term of sample reflected signal and reference mirror reflected signal, and this reflectance that has reflected sample inside distributes; The 3rd, equation right side is and second picture about zero optical path difference position symmetry, the distribution of this and fict interior of articles reflectance, but Fourier transformation produces because the real number interference spectrum signal that detector is collected carries out, and is called mirror image;

4. the phase place of described chromatography signal I (z, t) is taken out, the adjacent signals phase place is done difference, obtain that adjacent phase is poor is:

Δφ(z,t)＝2k ₀(dz _n(t)-Aω _csin(ω _ct+θ))Δt，

Wherein: dz _n(t) optical path difference of expression reference mirror reflecting surface and detected sample position n layer reflecting surface over time,

△ t represents that detector gathers the interval of adjacent two signals;

5. form new chromatography signal with the amplitude in original chromatography signal and the phase contrast of obtaining:

Make z _n'=z _n(t)+Acos (ω _cT+ θ), new modulation depth is A'=A ω _c, new initial phase is θ '=θ+pi/2, the following formula abbreviation is:

Wherein, Self correlation between the different reflectings surface of the direct current background while having reflected sample in measurement and sample interior, utilize the two-dimensional scan galvanometer along with the optical axis vertical direction, carrying out transversal scanning, and gather the interference spectrum signal of different lateral attitudes on sample with detector, obtain a frame two dimension interference spectrum signal, after doing on average to the time it, obtain an one dimension interference spectrum signal, it is cut from each interference signal of former interference spectrum, can remove direct current background and Correlated noises, after removing, new chromatography signal representation is:

$I^{\′}(z,t)=\underset{n}{\mathrm{\Σ}}(\mathrm{\Γ}\left({z_n}^{\′}\right)+\mathrm{\Γ}\left({{-z}_n}^{\′}\right))\cos \left({2k}_0\mathrm{\Δt}({\mathrm{dz}}_n\left(t\right)+A^{\′}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\θ}}^{\′}))\right)$ ；

$+i\underset{n}{\mathrm{\Σ}}(\mathrm{\Γ}\left({z_n}^{\′}\right)-\mathrm{\Γ}(-{z_n}^{\′}))\sin \left({2k}_0\mathrm{\Δt}({\mathrm{dz}}_n\left(t\right)+A^{\′}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\θ}}^{\′}))\right)$

6. to described I'(z, t) real part and imaginary part carry out respectively phase demodulating, obtain:

With top two formula additions divided by the multiple chromatography signal of the mirror image that is eliminated after 2, be:

$\tilde{I}(z,t)=\underset{n}{\mathrm{\Σ}}\mathrm{\Γ}\left({z_n}^{\′}\right)\exp \left({-i2k}_0\mathrm{\Δ}{\mathrm{tdz}}_n\left(t\right)\right),$

7. again according to the relation of z and z ', z _n'=z _n(t)+Acos (ω _cT+ θ), z ' is reduced into each measures the real depth position z of t constantly, the amplitude in the multiple chromatography signal of elimination mirror image is taken out, be the one dimension tomographic map that reflects the sample structural information and do not comprise mirror image:

$\tilde{I}(z,t)=\underset{n}{\mathrm{\Σ}}\mathrm{\Γ}(z_n\left(t\right)+A\cos ({\mathrm{\ω}}_{c}t+\mathrm{\θ}))\exp (-{i2k}_0\mathrm{\Δ}{\mathrm{tdz}}_n\left(t\right));$

8. after 4.～7. each the interference spectrum signal in a described frame two dimension interference spectrum signal being processed according to above-mentioned steps, form the full degree of depth two-dimensional structure figure of sample.

3. the complex frequency domain optical coherence tomography imaging method of difference sinusoidal phase modulation according to claim 2, it is characterized in that utilizing the two-dimensional scan galvanometer to scan simultaneously along two-dimensional directional, obtain the two-dimentional interference spectrum signal of different longitudinal position, 3.～8. after carrying out date processing by step claimed in claim 2, obtain the three-dimensional full depth structure figure of testing sample.

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