CN101617935B - Method and system for wide-spectrum and high-resolution detection based on space-time light splitting in OCT - Google Patents

Abstract

The invention discloses a wide-spectrum high-resolution detection method and system based on time-space spectroscopy in OCT. The low-coherence light emitted from the broadband light source enters the broadband fiber coupler through the optical isolator, and then enters the scanning probe and the reference arm respectively after being split by the coupler. The returned light interferes in the broadband fiber coupler, and the detection arm will interfere After the signal is decomposed into different spectral components, it is detected and then transmitted to the computer to reconstruct the image of the sample. In the detection arm, the interference spectrum signal first passes through the time-domain spectroscopic device with low resolution and wide free spectral range, then passes through the space-domain spectroscopic device with high resolution and narrow free spectral range, and then is detected by the spectral imaging system. The present invention can reduce the field of view of the spectral imaging system on the premise of satisfying high spectral resolution, and avoid the problems of field curvature and spectral crosstalk in large field of view spectral imaging, thereby achieving high signal-to-noise ratio and high resolution spectral domain OCT imaging.

Description

Wide-spectrum high-resolution detection method and system based on space-time spectroscopy in OCT

technical field

The invention relates to optical coherence tomography (OCT) technology, in particular to a system of a wide-spectrum high-resolution detection method based on time-space spectroscopy in OCT.

Background technique

Optical coherence tomography (OCT) can perform non-contact, non-invasive, high-resolution in vivo imaging of internal tissue structures and physiological functions in vivo, and has a wide range of applications in the field of biomedical imaging.

The current spectral domain OCT system uses a high-speed linear array CCD to collect the spectral components of the interference signal in parallel, and can obtain the depth information of the sample without axial scanning. It has the characteristics of fast and high sensitivity. The core of the system is the fast spectrometer in the detection arm. . In the OCT system, the axial resolution of the system is inversely proportional to the bandwidth of the light source. The wider the bandwidth of the light source, the shorter the corresponding coherence length and the higher the axial resolution. In ophthalmology, skin, tumor and other disciplines, ultra-high resolution (2-3um) medical images are of great significance for clinical disease diagnosis. Therefore, spectral domain OCT must use a light source with a wider spectral range, and the grating spectrometer of the detection arm must detect wider spectral components in order to improve the axial resolution of the system. Many foreign scientific research institutions have carried out research in this area. For example, the N.A.Nassif group of Harvard Medical School in the United States has constructed an ultra-high resolution spectral domain OCT system based on an SLD (super radiance diode) light source with a center wavelength of 890nm and a bandwidth of 150nm. The resolution is 2.9um; the J.G.Fujimoto group of the Massachusetts Institute of Technology built an ultra-high resolution hyperspectral OCT system based on a femtosecond laser with a center wavelength of 850nm and a bandwidth of 144nm, with an axial resolution of 2.1um. In the detection arm part of the ultra-high resolution spectral domain OCT system, the traditional method is to use a linear array CCD with more pixels to detect more spectral components, or a linear array CCD based on a limited number of pixels to detect a wider spectral range , but sacrifices the spectral resolution of the spectrometer. Since the increase in the number of linear CCD pixels means an increase in the field of view, unless a more complex optical imaging system is designed, serious field curvature will inevitably appear on the image surface (CCD photosensitive surface), and due to the spectral range If it is too wide, the dispersion phenomenon is serious, resulting in different focusing positions of different colors of light, which makes the spectrometer unable to completely separate the various colors of light and introduces cross-talk (cross-talk), the detection signal-to-noise ratio decreases and the axial resolution of the system decreases, ultimately reducing the imaging quality . Reducing the spectral resolution of the spectrometer means reducing the imaging depth of spectral domain OCT. Therefore, how to make the grating spectrometer measure a wider spectral range with high resolution in the case of a limited imaging field of view is a major technical difficulty in the development of an ultra-high resolution spectral domain OCT system.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned technical difficulties, the purpose of the present invention is to provide a system of wide-spectrum high-resolution detection method based on time-space spectroscopy in OCT. In the detection arm part of the ultra-high-resolution spectral domain OCT system, time domain The ultra-broadband spectral detection with high spectral resolution is realized by the two-stage spectroscopic structure in the spatial domain and the spatial domain.

The purpose of the present invention is achieved through the following technical solutions:

1. A wide-spectrum high-resolution detection method based on space-time spectroscopy in OCT:

The detection arm of the spectral domain OCT system adopts two-stage light splitting in the time domain and the spatial domain to realize broadband spectral high-resolution detection of spectral domain OCT; the specific steps are as follows:

1) In the detection arm of the spectral domain OCT system, the acousto-optic tunable filter (AOTF) with a large free spectral range and low spectral resolution is used as a first-level spectroscopic device to perform the first-level detection in the time domain. Spectral splitting, the broadband spectrum is divided into sequential narrowband spectra in time and output sequentially;

2) In the detection arm of the spectral domain OCT system, after the first-stage spectroscopic device, the second-stage spectroscopic device with high spectral resolution and narrow free spectral range is used to perform the second-stage spectroscopic splitting, and the sequence narrowband from the acousto-optic modulator The spectrum is further split in the spatial domain; the free spectral range of the virtual imaged phased array (Virtual Imaged Phased Array, VIPA) in the spatial domain is larger than the spectral resolution of the acousto-optic modulator;

3) In the detection arm of the spectral domain OCT system, spectral imaging and parallel detection are implemented through a spectral imaging system composed of a focusing lens and a high-speed linear array CCD using the spectrum after time-space splitting by a two-stage spectroscopic device.

2. A wide-spectrum high-resolution detection system based on space-time spectroscopy in OCT:

The invention includes a broadband light source, an optical isolator, a broadband fiber coupler, four polarization controllers, a reference arm, a scanning probe and a detection arm; the low coherent light from the broadband light source is incident through the first polarization controller and the optical isolator To the broadband fiber coupler, after light splitting, one path enters the scanning probe through the second polarization controller, and the other path enters the reference arm through the third polarization controller. After the returned light interferes in the broadband fiber coupler, it passes through the fourth polarization controller , enter the detection arm to decompose the interference signal into spectral signals, and finally these spectral signals are transmitted to the computer, processed in the computer, and the image is reconstructed by inverse Fourier transform. The detection arm: includes an acousto-optic modulator, a first collimating lens, a cylindrical focusing lens, a virtual image phased array, a first focusing lens and a high-speed linear array CCD; the interference light first passes through a large free spectral range and a low spectral resolution After the acousto-optic modulator, through the first collimating lens and cylindrical focusing lens, it enters a virtual image phased array with high spectral resolution and narrow free spectral range, and then is imaged by the first focusing lens and high-speed linear array CCD. Parallel detection realizes wide-spectrum high-resolution measurement of spectral-domain OCT.

The scanning probe: includes a third collimating lens, a scanning vibrating mirror and a second focusing lens; the light split by the broadband fiber coupler passes through the second polarization controller, the third collimating lens, the scanning vibrating mirror and the second focusing lens After the lens is irradiated to the sample, it returns from the original path to the broadband fiber coupler through the second polarization controller.

The reference arm: includes a second collimating lens, a dispersion compensator, a neutral filter, and a plane mirror; the light split by the broadband fiber coupler is passed through a third polarization controller, a second collimating lens, and a dispersion compensation Filter, neutral filter and plane reflector, return from the original path to the broadband fiber coupler through the third polarization controller.

The detection arm: consists of an acousto-optic modulator, a first collimating lens, a cylindrical focusing lens, a virtual image phased array, a first focusing lens and a high-speed linear array CCD; The acousto-optic modulator performs the first-order light splitting in the time domain, and divides the broadband spectrum into a sequence of narrow-band spectra in time and outputs them sequentially. The sequential narrow-band spectrum emitted from the acousto-optic modulator passes through the first collimating lens and the cylindrical focusing lens, and then enters a virtual image phased array with high spectral resolution and narrow free spectral range for second-stage light splitting in the spatial domain. The free spectral range of the virtual image phased array is greater than the spectral resolution of the AOM, and it splits the sequential narrowband spectrum output by the AOM with high spatial resolution. The spectrum after time-space splitting by the front and back two-stage spectroscopic devices is imaged by the first focusing lens, and a high-speed linear array CCD is used for parallel detection to realize wide-spectrum high-resolution measurement of spectral domain OCT. Finally, these spectral signals are transmitted to the computer, and the inverse Fourier transform and other processing are implemented in the computer to reconstruct the sample image.

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

1. Through the two-stage light splitting of the acousto-optic modulator and the virtual image phased array in the time domain and the space domain, broadband spectral detection with high spectral resolution can be realized. Compared with the traditional grating spectrometer, the spectral signal has been pre-processed in the time domain, thus reducing the field of view of the CCD in the spectral imaging system. Due to the smaller imaging field of view, it can eliminate the spectral crosstalk existing in the spectrometer of the traditional spectral domain OCT system when detecting in a large spectral range, as well as the defocus phenomenon caused by field curvature, distortion and dispersion in a large field of view, and can significantly improve spectral detection. signal-to-noise ratio. At the same time, because of the reduced field of view of spectral imaging, the entire spectral detection system is easier to realize miniaturization and integration.

2. Since the free spectral range of the acousto-optic modulator is very wide, and the spectral resolution of the virtual image phased array is very high, the space-time spectroscopic combination device formed by cascading the two can break through the constraints of the spectral range and spectral resolution of the traditional imaging spectrometer relationship to achieve high-resolution detection of broadband spectra.

3. The wide-spectrum high-resolution detection method and system proposed by the present invention can not only be applied to ultra-high resolution spectral domain OCT systems, but also can be applied to other spectral detection applications, such as astronomy, elemental analysis, and other spectral imaging systems .

Description of drawings

Fig. 1 is a schematic diagram of the system structure principle of the present invention.

Fig. 2 is an enlarged schematic view of the detection arm of the present invention.

Fig. 3 is a timing diagram of the present invention.

In the figure: 1. Broadband light source, 2. Optical isolator, 3. Broadband fiber coupler, 4. Polarization controller, 5. Collimator lens, 6. Scanning mirror, 7. Focusing lens, 8. Sample, 9. Collimating lens, 10, dispersion compensator, 11, neutral filter, 12, plane mirror, 13, acousto-optic modulator, 14, collimating lens, 15, cylindrical lens, 16, virtual image phased array, 17. Focusing lens, 18. High-speed linear array CCD, 19. Reference arm, 20. Scanning probe, 21. Detection arm.

Detailed ways

Below in conjunction with accompanying drawing and embodiment example, the present invention will be further described:

As shown in FIG. 1 and FIG. 2 , the present invention includes a broadband light source 1 , an optical isolator 2 , a broadband fiber coupler 3 , four polarization controllers 4 , a reference arm 19 , a scanning probe 20 and a detection arm 21 . The low-coherent light from the broadband light source 1 enters the broadband fiber coupler 3 through the first polarization controller 4 and the optical isolator 2. After splitting, it enters the scanning probe 20 through the second polarization controller 4 and is collimated. After the lens 5, the scanning galvanometer 6 and the focusing lens 7 irradiate the sample 8, the original path returns to the broadband fiber coupler 3 through the second polarization controller 4; the other path enters the reference arm 19 through the third polarization controller 4, and passes through the The collimating lens 9 , the dispersion compensator 10 , the neutral filter 11 and the flat mirror 12 return to the broadband fiber coupler 3 via the third polarization controller 4 through the original path. The light returned from the scanning probe 20 and the reference arm 19 is interfered in the broadband fiber coupler 3 , passes through the fourth polarization controller 4 , and enters the detection arm 21 .

In the detection arm 21, the interference light first enters the acousto-optic modulator 13, and by controlling the output frequency band of the acousto-optic modulator, the optical signal in the entire broadband spectral range is divided into a sequence of narrow-band spectra in time and output sequentially, realizing the time domain. The first split. The narrow-band spectrum output by the acousto-optic modulator is converged into a straight line through the collimating lens 14 and the incident cylindrical lens 15, and converges on the lower surface of the virtual image phased array 16. The free spectral range of the virtual image phased array 16 is larger than that of the acoustic wave. The spectral resolution of the light modulator 13. In addition to the incident window, the upper surface of the virtual image phased array 16 is coated with a reflective film with a reflectivity of 100%, and all the energy reflected by the lower surface is reflected back to the lower surface. The reflection forms a series of linear virtual images formed by the convergence of the parallel light focused by the cylindrical lens 15 , that is, a virtual image array. These virtual images interfere with each other to produce the effect of spatial light splitting. Utilize the spectrum after time-space splitting by the front and rear two-stage spectroscopic devices, and image it through the focusing lens 17, and use the high-speed linear array CCD 18 for parallel detection of the spectrum, so as to realize the high-resolution measurement of the ultra-broadband spectrum. Finally, the measurement results of these spectral signals are transmitted to the computer, and inverse Fourier transform and other processing are performed in the computer to reconstruct the sample image.

As shown in Fig. 3, in the detection arm, by controlling the radio frequency frequency loaded on the AOM 13, changing the output frequency band of the AOM 13, the optical signal in the entire broadband spectral range is divided in time Sequential narrowband spectra are output sequentially to realize the first time-domain splitting. The virtual image phased array 16 further spatially splits the narrowband output signal of each AOM 13 to realize wide-spectrum high-resolution time-space domain detection.

The function of the polarization controller 4 in the system is to facilitate the adjustment of the polarization mode of each channel, so as to minimize the influence of polarization mode dispersion and improve the imaging quality.

A wide-spectrum high-resolution detection method and system of spectral-domain OCT disclosed in the present invention can perform high-resolution measurement of an ultra-wide spectrum in the case of a limited field of view, thereby realizing ultra-high axial resolution of spectral-domain OCT At the same time, it can improve the problems of signal-to-noise ratio and axial resolution reduction caused by field curvature in the spectral detection of the traditional spectral domain OCT system. It is of great significance in the spectral detection of ultra-high resolution spectral domain OCT, and can also be used for other Wide-spectrum high-resolution detection system in the field.

Claims (4)

1. A wide-spectrum high-resolution detection method based on time-space spectroscopy in OCT, characterized in that: the detection arm of the spectral-domain OCT system adopts two-stage light-splitting in the time domain and spatial domain to realize broadband spectral high-resolution detection of spectral domain OCT ; The specific steps are as follows: 1) In the detection arm of the spectral domain OCT system, the acousto-optic modulator with a large free spectral range and low spectral resolution is used as a first-level spectroscopic device to perform the first-stage spectroscopic splitting in the time domain, and the broadband spectrum is divided into time-domain Sequential narrowband spectra are output sequentially; 2) In the detection arm of the spectral domain OCT system, after the first-stage spectroscopic device, the second-stage spectroscopic device with high spectral resolution and narrow free spectral range is used to perform the second-stage spectroscopic splitting, and the sequence narrowband from the acousto-optic modulator The spectrum is further split in the spatial domain; the free spectral range of the virtual image phased array of the spatial domain spectroscopic device is greater than the spectral resolution of the acousto-optic modulator; 3) In the detection arm of the spectral domain OCT system, spectral imaging and parallel detection are implemented through a spectral imaging system composed of a focusing lens and a high-speed linear array CCD using the spectrum after time-space splitting by a two-stage spectroscopic device. 2. a kind of system implementing the wide-spectrum high-resolution detection method based on time-space spectroscopic in a kind of OCT described in claim 1, comprises broadband light source (1), optical isolator (2), broadband optical fiber coupler (3), Four polarization controllers (4), a reference arm (19), a scanning probe (20) and a detection arm (21); the low coherent light coming out from the broadband light source (1) passes through the first polarization controller (4), light The isolator (2) is incident to the broadband fiber coupler (3), and after splitting, one path enters the scanning probe (20) through the second polarization controller (4), and the other path enters the reference arm ( 19), after the returned light interferes in the broadband fiber coupler (3), it enters the detection arm (21) through the fourth polarization controller (4) to decompose the interference signal into spectral signals, and finally these spectral signals are transmitted to the computer, Process in computer, reconstruct image by inverse Fourier transform; It is characterized in that, described detection arm (21): comprises acousto-optic modulator (13), first collimating lens (14), cylindrical focusing lens (15), A virtual image phased array (16), a first focusing lens (17) and a high-speed linear array CCD (18); the interference light first passes through the acousto-optic modulator (13) with a large free spectral range and low spectral resolution, and then passes through the first The collimating lens (14) and cylindrical focusing lens (15) are incident to a virtual image phased array (16) with high spectral resolution and narrow free spectral range, and then imaged by the first focusing lens (17) and high-speed linear array The CCD (18) performs parallel detection to realize wide-spectrum high-resolution measurement of spectral-domain OCT. 3. A system for implementing a wide-spectrum high-resolution detection method based on space-time spectroscopy in OCT according to claim 2, characterized in that: the reference arm (19) includes a second collimator lens (9), a dispersion compensation device (10), neutral filter (11) and plane mirror (12); the light after splitting is from the third polarization controller (4), through the second collimating lens (9), dispersion compensator ( 10), a neutral filter (11) and a plane reflector (12), return to the broadband fiber coupler (3) through the third polarization controller (4) by the original path. 4. A kind of system implementing the wide-spectrum high-resolution detection method based on space-time spectroscopic in OCT according to claim 2, is characterized in that: described scanning probe (20) comprises the 3rd collimating lens (5), scanning vibrator mirror (6) and the second focusing lens (7); the light after splitting passes through the third collimating lens (5), the scanning vibrating mirror (6) and the second focusing lens (7) from the second polarization controller (4) ) to irradiate the sample (8), and return to the broadband fiber coupler (3) through the second polarization controller (4) from the original path.

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