CN100464696C - Spectral coverage OCT imaging method based on optical scanning delay line and the system - Google Patents

Abstract

The invention discloses a spectrum OCT (optical coherent tomography) image method and relative system based on optical scanning delay line, wherein it arranges an optical scanning delay line in a reference arm of a spectrum OCT system, to realize scatter-free phase shift of reference light and system scatter compensation. And when guides in optical scanning delay line based on double gratings, the invention can generate group speed scatter and third-order scatter formed by any marks in large change range, to accurately match the scatters of reference arm and sample arm in spectrum OCT system. The scatter-free phase shift and scatter compensation can assure the axial resolution ratio of spectrum OCT system, eliminate coherent noise, and expand the image depth for one time. The invention is significant for dual-spectrum OCT system with ultra-high resolution ratio.

Description

A kind of spectral coverage OCT imaging method and system based on optical scan delay-line

Technical field

The present invention relates to optical coherent chromatographic imaging (OCT) technology, especially relate to a kind of spectral coverage OCT imaging method and system that uses based on optical scan delay-line.

Background technology

Optical coherent chromatographic imaging (Optical Coherence Tomography, be called for short OCT) be a kind of emerging optical image technology, can realize the organizational structure and the physiological function of live body inside are carried out noncontact, not damaged, high-resolution imaging, in the earlier detection of disease with in body biopsy field extensive application.

The spectral coverage OCT system comes the spectral components of parallel acquisition interference signal by high-speed CCD, need not the depth information that axial scan just can obtain sample, has quick and highly sensitive characteristics.But the shortcoming of spectral coverage OCT be mutual interference signal between its inherent each layer of sample and light source from coherent noises such as coherent interference signals.Simultaneously owing to the interference spectrum of the real number form that collects on the CCD is carried out contrary Fourier change and obtain depth information, and the result of the Fourier transform of real function is a Hermitian conjugate, it is symmetric having caused item of information, thereby has limited the investigation depth of spectral coverage OCT system.

The method of eliminating the coherent noise of spectral coverage OCT and expanding its investigation depth is to realize by the spectrum interference signal that constitutes plural form.Usually all be that the reflecting mirror that utilizes piezoelectric ceramic actuator to move reference arm is realized phase shift, usually adopt five step phase-shifting methods, by the interference spectrum signal that obtains after each phase shift reconstruct sample and reference arm between the complex values of spectral components of interference signal, carrying out contrary Fourier again changes, thereby eliminated coherent noise, and imaging depth has been expanded one times.

Because the OCT system adopts wideband light source to obtain micron-sized axial resolution, therefore adopt piezoelectric ceramic actuator to realize that inevitably there is the problem of chromatic dispersion in the spectral coverage OCT system of phase shift, can cause rebuilding after the phase shift error of interference spectrum complex signal, this is more obvious in super-resolution spectral coverage OCT system.For fear of because of system dispersion reduces axial resolution, adopt the spectral coverage OCT system of phase-shifting method to make the chromatic dispersion coupling of reference arm and sample arm reach optimum resolution simultaneously by follow-up numerical dispersion backoff algorithm.In the software dispersion compensation, make predefined image definition function reach maximum by iterative process, think this moment to have compensated system dispersion.But because the limitation of iterative algorithm has caused the real-time of software dispersion compensation algorithm also bad, software dispersion compensation algorithm can only bucking-out system chromatic dispersion in small range simultaneously.

Summary of the invention

The object of the present invention is to provide a kind of spectral coverage OCT imaging method and system based on optical scan delay-line.Reference arm place in the spectral coverage OCT system adopts fast optical delayed sweep line to realize dispersionless phase place modulation, uses fast optical delayed sweep line as dispersive compensation element simultaneously, can make the chromatic dispersion coupling of reference arm and sample arm.Especially, when the fast optical delayed sweep line that adopts based on double grating, can be in a big way system dispersion be compensated to three rank.

The objective of the invention is to be achieved through the following technical solutions:

One, a kind of spectral coverage OCT imaging method based on optical scan delay-line:

Introduce fast optical delayed sweep wire system at the reference arm of spectral coverage OCT system, realize simultaneously compensating to the phase place modulation of reference light with to the chromatic dispersion of system; When adopting the fast optical delayed sweep line of double grating, compare the optical scan delay-line of monochromatic light grid, in a wider context the fine compensation system dispersion especially; Its concrete steps are as follows:

1) make the galvanometer in the optical scan delay-line in the reference arm by synchronizing sequential circuit, the scanheads and the line array CCD in the probe unit of sample arm are synchronous, gather the interference spectrum signal;

2) by regulating the spacing x of galvanometer rotating shaft and optical axis in the optical scan delay-line ₀With the defocusing amount Δ z of grating, the chromatic dispersion phase place is synthetic to compensate system dispersion simultaneously in that reference light is not had; When adopting the fast optical delayed sweep line of double grating, regulate the spacing of two gratings, can produce the GVD and the third-order dispersion of the optional sign combination of comparing the bigger excursion of monochromatic light grid optics delayed sweep line, the chromatic dispersion of reference arm and sample arm is accurately mated;

3) in optical scan delay-line, in galvanometer scan period, gather the interference spectrum signal, import PC into by special purpose interface by the identical at interval interval of synchronizing sequential circuit control line array CCD; In PC, by existing various phase shift algorithms, reconstruct the complex expression of interference spectrum signal with three-step approach, four step rule, five-step approach, again by inverse Fourier transform, just draw the information of an axial scan.

Two, a kind of spectral coverage OCT imaging system based on optical scan delay-line:

Comprise wideband light source, optoisolator, broadband optical fiber coupler, four Polarization Controllers, scanheads, probe unit and optical scan delay-lines; The low-coherent light that comes out from wideband light source, incide broadband optical fiber coupler through first Polarization Controller, optoisolator, one the tunnel enters reference arm, another Lu Jingdi three Polarization Controllers of being made of optical scan delay-line through second Polarization Controller and enters scanheads after the beam split, the interference of light that two-way returns connects probe unit through the 4th Polarization Controller, handle reconstructed image at last at computer.

Described scanheads: comprise collimating lens, scanning galvanometer and condenser lens; Optical signal by the 3rd Polarization Controller enters shines on the sample through collimating lens, scanning galvanometer and condenser lens.

Described probe unit: comprise first collimating mirror, transmission grating, two gummed achromat and line array CCD; Interference light signal by the 4th Polarization Controller enters behind first collimating mirror, transmission grating, two gummed achromat, focuses on the line array CCD; The signal of telecommunication that produces on the line array CCD imports in the computer by image collection card.

Described optical scan delay-line: comprise first balzed grating,, second collimating mirror, first plane mirror, first fourier transform lens and first scanning galvanometer; Wherein first balzed grating, is parallel with first fourier transform lens, with the distance of its front focal plane be an adjustable defocusing amount Δ z; First scanning galvanometer is positioned on the back focal plane of first fourier transform lens; The angle of the normal of the normal of second collimating mirror and first plane mirror and first balzed grating, is the blaze angle of first balzed grating; Second collimating mirror be positioned at first plane mirror directly over; The spacing of the first scanning galvanometer rotating shaft and optical axis is an adjustable variable x ₀

Described optical scan delay-line: comprise second balzed grating,, the 3rd balzed grating,, the 3rd collimating mirror, second plane mirror, second fourier transform lens and second scanning galvanometer; Wherein the 3rd balzed grating, is parallel with second fourier transform lens, with the distance of its front focal plane be an adjustable defocusing amount Δ z; Second scanning galvanometer is positioned on the back focal plane of second fourier transform lens; The spacing of the second scanning galvanometer rotating shaft and optical axis is an adjustable variables x ₀Second balzed grating, and the 3rd balzed grating, are parallel to each other, and its groove is also parallel to each other, and spacing between the two is a scalable amount d simultaneously; The angle of the 3rd collimating mirror and the second balzed grating, normal is an adjustable inclination angle, and its size adjustment is λ to making centre wavelength ₀Light behind second balzed grating,, the 3rd balzed grating, diffraction along the optical axis direction outgoing; The 3rd collimating mirror be positioned at second plane mirror directly over; The spacing of the second scanning galvanometer rotating shaft and optical axis is an adjustable variable x ₀

Compare with background technology, the beneficial effect that the present invention has is:

1, realizes dispersionless phase shift.Can carry out dispersionless phase shift to reference light by optical scan delay-line, eliminate the phase shift error of coming, thereby avoided follow-up algorithmic error by the strip of light broadband.By no chromatic dispersion phase shift, can make up the sample of plural form and the interference light between the reference arm.Spectrum signal, thus coherent noise eliminated, and imaging depth has been expanded one times.

2, hardware compensating system dispersion.In optical scan delay-line, come the bucking-out system chromatic dispersion by regulating the grating defocusing amount.When using the optical scan delay-line of double grating, increased this independent variable of grating space especially, can produce interior GVD and the third-order dispersion that changes on a large scale, therefore can compensate to three rank system dispersion.Significant in the spectral coverage OCT system of ultrahigh resolution.

3, no chromatic dispersion phase shift and dispersion compensation are realized by optical scan delay-line simultaneously.Can realize the compactedness and the reliability of spectral coverage OCT system.

Description of drawings

Fig. 1 is the system schematic of the specific embodiment of the spectral coverage OCT imaging method based on optical scan delay-line of the present invention, and wherein reference arm is a monochromatic light grid optics delayed sweep line;

Fig. 2 is a spectral coverage OCT system reference arm when being double grating optics delayed sweep line, the structural representation of reference arm;

Fig. 3 is the control system block diagram of the present invention based on the spectral coverage OCT system of optical scan delay-line.

Among the figure: 1, wideband light source, 2, optoisolator, 3, broadband optical fiber coupler, 4, Polarization Controller, 5, collimating lens, 6, scanning galvanometer, 7, condenser lens, 8, sample, 9, balzed grating,, 10, collimating mirror, 11, plane mirror, 12, fourier transform lens, 13, scanning galvanometer, 14, collimating mirror, 15, transmission grating, 16, two gummed achromat, 17, line array CCD, 18, balzed grating,, 19, balzed grating,, 20, image pick-up card, 21, computer, 22, scanheads, 23, optical scan delay-line, 24, probe unit.

The specific embodiment

The invention will be further described below in conjunction with drawings and Examples.

As shown in Figure 1, the present invention includes wideband light source 1, optoisolator 2, broadband optical fiber coupler 3, four Polarization Controllers 4, scanheads 22, probe unit 24 and optical scan delay-lines 23; The low-coherent light that comes out from wideband light source 1, incide broadband optical fiber coupler 3 through first Polarization Controller 4, optoisolator 2, one the tunnel enters reference arm, another Lu Jingdi three Polarization Controllers 4 of being made of optical scan delay-line 23 through second Polarization Controller 4 and enters scanheads 22 after the beam split, the interference of light that two-way returns connects probe unit 24 through the 4th Polarization Controller 4, handle reconstructed image at last at computer 21.

Described scanheads 22: comprise collimating lens 5, scanning galvanometer 6 and condenser lens 7; Optical signal by the 3rd Polarization Controller 4 enters shines on the sample 8 through collimating lens 5, scanning galvanometer 6 and condenser lens 7.

Described probe unit 24: comprise first collimating mirror 14, transmission grating 15, two gummed achromat 16 and line array CCD 17; Interference light signal by the 4th Polarization Controller 4 enters behind first collimating mirror 14, transmission grating 15, two gummed achromat 16, focuses on the line array CCD 17; The signal of telecommunication that produces on the line array CCD 17 imports in the computer 21 by image collection card 20.

Described optical scan delay-line 23: comprise first balzed grating, 9, second collimating mirror 10, first plane mirror 11, first fourier transform lens 12 and first scanning galvanometer 13; Wherein first balzed grating, 9 is parallel with first fourier transform lens 12, with the distance of its front focal plane be an adjustable defocusing amount Δ z; First scanning galvanometer 13 is positioned on the back focal plane of first fourier transform lens 12; The angle of the normal of second collimating mirror 10 and first plane mirror 11 and the normal of first balzed grating, 9 is the blaze angle of first balzed grating, 9; Second collimating mirror 10 be positioned at first plane mirror 11 directly over; The spacing of 13 rotating shafts of first scanning galvanometer and optical axis is an adjustable variable x ₀

As shown in Figure 2, described optical scan delay-line 23: comprise second balzed grating, 18, the 3rd balzed grating, 19, the 3rd collimating mirror 10, second plane mirror 11, second fourier transform lens 12 and second scanning galvanometer 13; Wherein the 3rd balzed grating, 19 is parallel with second fourier transform lens 12, with the distance of its front focal plane be an adjustable defocusing amount Δ z; Second scanning galvanometer 13 is positioned on the back focal plane of second fourier transform lens 12; The spacing of 13 rotating shafts of second scanning galvanometer and optical axis is an adjustable variables x ₀Second balzed grating, 18 and the 3rd balzed grating, 19 are parallel to each other, and its groove is also parallel to each other, and spacing between the two is a scalable amount d simultaneously; The angle of the 3rd collimating mirror 10 and second balzed grating,, 18 normals is an adjustable inclination angle, and its size adjustment is λ to making centre wavelength ₀Light behind second balzed grating, 18, the 3rd balzed grating, 19 diffraction along the optical axis direction outgoing; The 3rd collimating mirror 10 be positioned at second plane mirror 11 directly over; The spacing of 13 rotating shafts of second scanning galvanometer and optical axis is an adjustable variable x ₀

As shown in Figure 1, the low-coherent light that sends from wideband light source 1, incide broadband optical fiber coupler 3 through Polarization Controller 4, optoisolator 2, enter reference arm and sample arm through Polarization Controller 4 respectively after the beam split, the light of reference arm collimates the back by the balzed grating, beam split through collimating mirror 10, each spectral components focuses on the scanning lens 13 by fourier transform lens 12, after scanning lens 13 modulation, return balzed grating, 9 by fourier transform lens 12 once more, and be incident upon on the plane mirror 11 once more behind the diffraction by balzed grating, 9.Each spectral components through plane mirror 11 reflections returns along Yuan Lu, finally synthesize with a branch of light and return broadband optical fiber coupler 3, after the interference of light of returning with sample arm, enter probe unit 24, be divided into each wavelength by transmission grating 15, focus on the line array CCD 17 by two gummed achromats 16 again.Last these interference spectrum components import in the computer 21 by image pick-up card 20 to be handled.

Reference light is through behind the optical scan delay-line 23 among Fig. 1, and wavelength is the light wave of λ, and its phase change amount is:

φ(k)＝2kδ+2kΔz?cos?β+2kx ₀θ-2kθ?f?sin?β (1)

Wherein k is wave number and k=2 π/λ, and δ is the initial light path difference, can think that δ=0, θ are the anglecs of rotation of scanning galvanometer 13, and f is the focal length of fourier transform lens 12, and β is by psin β=m (λ-λ ₀) decision, p is a grating constant, λ ₀Be centre wavelength, be φ (k) Taylor expansion:

$\mathrm{\φ}\left(k\right)=\mathrm{\φ}\left(k_0\right)+\mathrm{\φ}\′\left(k_0\right)(k-k_0)+\mathrm{\φ}\′\′\left(k_0\right)\frac{{(k-k_0)}^2}{2!}+\mathrm{\φ}\left(k_0\right)\′\′\′\frac{{(k-k_0)}^3}{3!}+\·\·\·\·\·\left(2\right)$

$\mathrm{\φ}\left(k\right)\≈(2\mathrm{\Δz}+2x_0\mathrm{\θ})k_0+(2\mathrm{\Δz}+2x_0\mathrm{\θ}+\frac{4\mathrm{\πm\θf}}{{\mathrm{pk}}_0})(k-k_0)+D_k\frac{{(k-k_0)}^2}{2!}+D_k^{\′}\frac{{(k-k_0)}^3}{3!}+\·\·\·\·\·\left(3\right)$

Wherein $D_k=-8{\mathrm{\&pi;}}^2{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C200710068210E00091.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\mathrm{\&Delta;z}/p^2{k_0}^3$ $D_k^{\&prime;}=24{\mathrm{\&pi;}}^2{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C200710068210E00091.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\mathrm{\&Delta;z}/p^2{k_0}^4,$ Change Δ z, just can change D _kWith

Size, thereby can compensate GVD in the system (GVD) and third-order dispersion (TOD).Place a plane mirror in sample arm, the interference spectrum signal is done inverse Fourier transform, obtain the value of A-scan, this moment is by regulating the width that Δ z changes envelope, when the coherence length of the half width of envelope and wideband light source 1 is mated substantially, can think that the Δ z of this moment has compensated the chromatic dispersion of system.Regulate x simultaneously ₀=-mf λ ₀/ p, φ (k) ≈ 2x at this moment ₀θ k ₀+ 2 Δ zk

Through the interference signal behind the dispersion compensation, after transmission grating 15 beam split, focus on the line array CCD 17 by two gummed achromats 16, the interference spectrum signal that line array CCD 17 any pixel collect is:

$I\left(k\right)=s\left(k\right)+s\left(k\right)\underset{i}{\mathrm{\&Sigma;}}2a_i\cos [2\mathrm{\&phi;}\left(k\right)-2{\mathrm{kz}}_i]+s\left(k\right)\underset{i}{\mathrm{\&Sigma;}}{a_i}^2+s\left(k\right)\underset{i\&NotEqual;j}{\mathrm{\&Sigma;}}2a_i{a}_j\cos \left(k2z_{\mathrm{ij}}\right)$

(4)

$=s\left(k\right)\underset{i}{\mathrm{\&Sigma;}}{a}_i\cos (4\mathrm{k\&Delta;z}+4x_0{k}_0\mathrm{\&theta;}-2{\mathrm{kz}}_i)+\mathrm{coherent\; noises}$

Interference spectrum component between reference arm and the sample arm as can be seen from the above equation, its phase term 4x ₀k ₀θ does not change with k, has therefore realized dispersionless phase place modulation.Control the scanning galvanometer 6 of reference arm simultaneously by synchronous circuit, the scanning galvanometer 13 in the optical scan delay-line 23, and the time of exposure of linear array CCD17 comes acquired signal in the probe unit.Frequency as scanning galvanometer in the sample arm 6 is made as 30Hz, the frequency of scanning galvanometer 13 is made as 500Hz in the optical scan delay-line 23, in optical scan delay-line 23 in the one-period of scanning galvanometer 13, by equal at interval 5 the interference spectrum signals of time collection of synchronous circuit control linear array CCD17, promptly obtain interference spectrum signal value under the different amount of phase shift, just can use this moment existing five step phase shift algorithm to calculate the phase place and the amplitude of interference spectrum signal, the interference spectrum signal that draws plural form is:

$I\left(k\right)=s\left(k\right)\underset{i}{\mathrm{\&Sigma;}}{a}_i\exp (4\mathrm{k\&Delta;z}-2{\mathrm{kz}}_i+4x_0{k}_0\mathrm{\&theta;})$

Carry out inverse Fourier transform just can the be eliminated depth information of an A-scan of mirror image and coherent noise with resulting plural interference spectrum signal this moment, and investigation depth has enlarged one times.

As shown in Figure 2, for reference arm be the sketch map of the optical scan delay-line of double grating.Wherein balzed grating, 18 and balzed grating, 19 parallel placements, and its groove is parallel to each other.Compare the optical scan delay-line of the monochromatic light grid shown in the reference arm among Fig. 1, reference light enters optical scan delay-line by collimating mirror 10, successively pass through balzed grating, 18 and balzed grating, 19 beam split, pass through fourier transform lens 12, scanning galvanometer 13 more successively and reflected the former road of tailing edge and return broadband optical fiber coupler 3 by plane mirror 11.Wave number is that the phase change amount φ (k) of light wave of k is relevant with the spacing d between two balzed grating,s.The optical scan delay-line of double grating can produce with grating defocusing amount Δ z by adjusting grating space d and compare the wider chromatic dispersion compensation quantity of monochromatic light grid optics delayed sweep line, simultaneously the GVD (GVD) and the third-order dispersion (TOD) of bucking-out system.

As shown in Figure 3, be control system block diagram based on the spectral coverage OCT system of optical scan delay-line.Wherein the interference spectrum signal that collects of line array CCD 17 imports in the computer 21 through image pick-up card 20.Computer 21 produces synchronous sequence simultaneously and controls in the optical scan delay-line 23 the scanning galvanometer 13 and the scanheads 22 of sample arm.In optical scan delay-line in the scan period of 23 scanning galvanometer 13, the 21 identical at interval times of control linear array CCD17 of computer are gathered 5 interference spectrum signals, after a scan period of scanning galvanometer 13 finishes, the next lateral attitude of computer 21 gated sweeps probe 22 scannings.

Claims (1)

1, a kind of spectral coverage OCT imaging method based on optical scan delay-line is characterized in that: introduce fast optical delayed sweep wire system at the reference arm of spectral coverage OCT system, realize simultaneously compensating to the phase place modulation of reference light with to the chromatic dispersion of system; When adopting the fast optical delayed sweep line of double grating, compare the optical scan delay-line of monochromatic light grid, in a wider context the fine compensation system dispersion; Its concrete steps are as follows:

1) make the galvanometer in the optical scan delay-line in the reference arm by synchronizing sequential circuit, the scanheads and the line array CCD in the probe unit of sample arm are synchronous, gather the interference spectrum signal;

2) by regulating galvanometer rotating shaft and the spacing x0 of optical axis and the defocusing amount Δ z of grating in the optical scan delay-line, the chromatic dispersion phase place is synthetic to compensate system dispersion simultaneously in that reference light is not had; When adopting the fast optical delayed sweep line of double grating, regulate the spacing of two gratings, the GVD and the third-order dispersion of the bigger excursion of monochromatic light grid optics delayed sweep line compared in generation, and the chromatic dispersion of reference arm and sample arm is accurately mated;

3) in optical scan delay-line, in galvanometer scan period, gather the interference spectrum signal, import PC into by special purpose interface by the identical at interval interval of synchronizing sequential circuit control line array CCD; In PC, by existing various phase shift algorithms, reconstruct the complex expression of interference spectrum signal with three-step approach, four step rule, five-step approach, again by inverse Fourier transform, just draw the information of an axial scan.

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