CN106691394B - High-resolution long-focal-depth OCT imaging system and method based on optical path coding - Google Patents

Abstract

The invention discloses a high resolution long focal depth OCT imaging system and method based on optical path coding. In the present invention, an optical path encoder is used to encode the output beam of the light source into multiple beams with different optical paths, and these beams are focused by the optical system at different depths of the sample for OCT imaging; and then the focal depth range of each beam in the OCT image is extracted The sample images obtained by irradiating the internal light and stitching can obtain high-resolution sample images in a large depth range. Due to the loss of part of the imaging range due to optical path encoding, an orthogonal dispersive spectrometer with ultra-high spectral resolution is used on the detection arm for detection. The interference spectrum signal obtained by the spectrometer is finally transmitted to the computer, and the high-resolution long-focus depth of the sample is realized on the computer. Fast reconstruction of images. The invention uses the ultra-long measurement range of the orthogonal dispersion spectrometer to distinguish the sample information obtained by beams focused at different depths under different coded optical paths, and can greatly increase the depth of focus.

Description

A high-resolution long-focus OCT imaging system and method based on optical path coding

technical field

The invention belongs to the technical fields of optical coherence tomography and optical microscopic imaging, and specifically relates to a high-resolution long-focus OCT imaging system and method based on optical path coding.

Background technique

Depth of focus (DOF) is an important parameter that affects the imaging quality of an optical system, and expanding the depth of focus is one of the important technologies to ensure that the imaging optical system has better imaging quality in a larger range. The relationship between the depth of focus DOF and the lateral resolution Δx can be expressed as: DOF=πΔx ² /2λ ₀ , where λ ₀ is the central wavelength of the light source. It can be seen that the depth of focus decreases with the increase of the lateral resolution. Using a focusing objective lens with a larger numerical aperture can improve the lateral resolution of the system, but at the same time it also reduces the depth of focus, resulting in lateral resolution outside the focal depth. rate will drop rapidly.

Optical coherence tomography (OCT) can realize non-contact, non-invasive, high-resolution imaging of tissue structure and physiological functions inside non-transparent high-scattering media. Compared with the OCT image obtained in the focal depth range of the beam, the OCT image obtained under the condition of beam defocus has a greater attenuation in resolution and contrast. Therefore, in order to obtain a good quality OCT image, the spot needs to be maintained in a longer range. Unchanged, but the long focal depth also means that the resolution of imaging is limited. In order to expand the focal depth of the OCT system, Schmitt et al. proposed a method of fixing the reference mirror to the translation stage of the imaging objective lens of the sample arm to achieve dynamic focusing, or by changing the shape of the MEMS deformable mirror and controlling the focus position in real time to achieve dynamic focusing. The structure of the method is relatively complicated, which limits the scanning speed. Z.Ding proposed an OCT system based on an axicon lens to achieve large depth of field and high lateral resolution imaging. Within the focal depth range of 6 mm, the lateral resolution is maintained at about 10 μm. However, the energy utilization efficiency of the axicon lens is relatively low, and the higher the focal depth expansion factor is, the lower the energy utilization efficiency is, so it is not suitable for biological samples that are sensitive to power.

Contents of the invention

The object of the present invention is to provide a high-resolution long-focus OCT imaging system and method based on optical path coding to address the deficiencies of the prior art. In the present invention, through parallel focused illumination at different depth positions of the sample, an orthogonal dispersive spectrometer with an ultra-long detection range is used on the detection arm to perform spectral detection to distinguish images obtained by multiple light beams encoded by the optical path, and high resolution of the sample can be achieved Long-range depth-of-focus OCT imaging.

The technical scheme adopted in the present invention is:

A high-resolution long-focus OCT imaging system based on optical path coding, including a broadband light source, a bandpass filter, a first mirror, a first broadband optical beam splitter, a second broadband optical beam splitter, and a first focusing lens , optical distance encoder, third broadband optical beam splitter, two-dimensional scanning galvanometer, second focusing lens, second mirror, third mirror, fourth mirror, one-dimensional precision translation stage, orthogonal dispersion spectrometer and computers;

The spatial light emitted by the broadband light source is reflected by the first reflector to the first broadband optical beam splitter after passing through the band-pass filter, and the light reflected by the first broadband optical beam splitter forms a sample optical path, which is split by the first broadband optical beam splitter The light transmitted by the beam filter forms the reference optical path.

The sample optical path: the transmitted light passing through the second broadband optical beam splitter is focused on the optical path encoder by the first focusing lens. The optical distance encoder is a glass plate coated on both sides, the beam incident surface is a high reflection film, and the other side is a total reflection film. The returned optical path coded light is reflected by the second broadband optical beam splitter and transmitted through the third broadband optical beam splitter, and then irradiates the sample to be tested after passing through the two-dimensional scanning galvanometer and the second focusing lens. The returned sample signal light is transmitted to the orthogonal dispersive spectrometer after being reflected by the second broadband optical beam splitter.

The reference optical path: the transmitted light passing through the first broadband optical beam splitter is reflected by the second reflector and then successively reflected by the third reflector and the fourth reflector, and then transmitted through the third broadband optical beam splitter and transmitted to the positive Cross-dispersive spectrometer. The third reflecting mirror and the fourth reflecting mirror are placed on a one-dimensional precision translation stage, and the optical path difference between the sample optical path and the reference optical path can be adjusted by moving the translation stage.

After the sample light interferes with the reference light, it enters the detection arm, is converted into an electrical signal by the orthogonal dispersive spectrometer, and is transmitted to a computer for processing.

The high-resolution long-focus OCT imaging method based on optical path coding includes the following steps:

Step 1: In the sample optical path of the high-resolution long-focus OCT imaging system, use an optical path encoder to modulate the illumination light of the sample to be tested, and the incident light forms multiple optical paths after multiple reflections on both sides of the optical path encoder Different virtual image light sources. These virtual image light sources are focused on different depth positions of the sample after being imaged by the optical system.

Step 2: In the detection arm of the high-resolution long-focus-depth OCT imaging system, an orthogonal dispersive spectrometer with ultra-high spectral resolution is used for detection. This spectrometer has an ultra-long measurement range and is used to distinguish sample information to realize longitudinal parallel detection of interference spectrum signals.

Step 3: Perform Fourier transform on the detected interference spectrum of the sample to be measured to obtain the image of the sample under multi-beam illumination conditions. The sample images obtained by different beams are distributed at different depth positions, and the sample images obtained by light within the focal depth range of each beam are selected and stitched together to obtain a sample image under high-resolution, long-focus deep beam illumination.

Compared with background technology, the present invention has following advantages:

1. The present invention uses the ultra-long measurement range of the orthogonal dispersive spectrometer to distinguish the sample information obtained by beams focused at different depths under different coded optical paths, which can greatly increase the depth of focus.

2. The present invention does not need to move the sample or the focusing lens when imaging, and can realize high-resolution long-focus OCT imaging of the sample with a single measurement, and has a relatively fast imaging speed.

3. Compared with methods such as axicon illumination and phase modulation, the beam quality of the present invention is higher, so the detection efficiency is also higher.

Description of drawings

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

Fig. 2 is a schematic diagram of optical path encoding in the present invention;

Fig. 3 is a schematic diagram of sample multi-focus illumination in the present invention;

4 is a schematic diagram of the distribution of multi-beam sample images in the coding space in the present invention;

Fig. 5 is a schematic diagram of sample image reconstruction in the present invention.

In the figure: 1. broadband light source, 2. bandpass filter, 3. first reflector, 4. first broadband optical beam splitter, 5. second broadband optical beam splitter, 6. first focusing lens, 7. Optical distance encoder, 8. Second reflector, 9. Third reflector, 10. Fourth reflector, 11. One-dimensional precision translation stage, 12. Third broadband optical beam splitter, 13. Two-dimensional Scanning galvanometer, 14, second focusing lens, 15, sample to be tested, 16, orthogonal dispersion spectrometer, 17, computer.

Detailed ways

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

As shown in Figure 1, the high-resolution long-focus OCT imaging system based on optical path coding includes 1. a broadband light source, 2. a bandpass filter, 3. a first mirror, 4. a first broadband optical beam splitter, 5. The second broadband optical beam splitter, 6. The first focusing lens, 7. Optical path encoder, 8. The second mirror, 9. The third mirror, 10. The fourth mirror, 11. One-dimensional precision translation stage, 12. third broadband optical beam splitter, 13. two-dimensional scanning galvanometer, 14. second focusing lens, 15. sample to be tested, 16. orthogonal dispersive spectrometer, 17. computer.

The spatial light emitted by the broadband light source 1 passes through the band-pass filter 2 and is reflected by the mirror 3 onto the broadband optical beam splitter 4. The transmitted light forms the reference light path.

The sample optical path: the transmitted light passing through the broadband optical beam splitter 5 is focused on the optical path encoder 7 by the focusing lens 6 . As shown in FIG. 2 , the optical distance encoder 7 is a glass plate coated on both sides, the incident surface of the light beam is a high reflection film, and the other side is a total reflection film. The incident light is reflected multiple times on both sides of the optical path encoder 7 to form a plurality of virtual image light sources with different optical paths and different positions, as shown in Figure 2, taking four virtual image light sources as an example: virtual image light source 1, virtual image light source 2, The virtual image light source 3 and the virtual image light source 4 correspond to the four coded beams returned respectively: beam 1, beam 2, beam 3, and beam 4. The coded light is reflected by the broadband optical beam splitter 5 and then transmitted through the broadband optical beam splitter 12. After passing through the two-dimensional scanning galvanometer 13 and the focusing lens 14, it is irradiated onto the sample to be measured 15 . The virtual image light source 1, the virtual image light source 2, the virtual image light source 3, and the virtual image light source 4 are respectively imaged at different depth positions of the sample, as shown in Figure 3, forming focus 1, focus 2, focus 3, and focus 4 in the sample space. The returned sample signal light is transmitted to the orthogonal dispersive spectrometer 16 after being reflected by the broadband optical beam splitter 12 .

The reference optical path: the transmitted light passing through the broadband optical beam splitter 4 is reflected by the mirror 8 and then successively reflected by the mirror 9 and the mirror 10, and then transmitted to the orthogonal dispersion spectrometer 16 after being transmitted through the broadband optical beam splitter 12 . The reflection mirror 9 and the reflection mirror 10 are placed on a one-dimensional precision translation stage 11, and the optical path difference between the sample optical path and the reference optical path can be adjusted by moving the translation stage.

After the sample light interferes with the reference light, it enters the detection arm, is converted into an electrical signal by the orthogonal dispersive spectrometer 16 and is transmitted to the computer 17 for processing.

The high-resolution long-focus OCT imaging method based on optical path coding includes the following steps:

Step 1: In the sample optical path of the high-resolution long-focus OCT imaging system, use an optical path encoder to modulate the illumination light of the sample to be tested, and the incident light forms multiple optical paths after multiple reflections on both sides of the optical path encoder Different virtual image light sources in different positions. These virtual image light sources are focused on different depth positions in the sample space after being imaged by the optical system, as shown in Figure 3, the distance between these focal points is determined by the distance between the virtual image light sources and the optical system composed of the focusing lens 6 and the focusing lens 14 , assuming that the thickness of the encoder is t, the refractive index is n, the focal length of the focusing lens 6 is f ₁ , and the focal length of the focusing lens 14 is f ₂ , the distance between adjacent focal points can be expressed as:

Δz _f =2tf ₂ ² /nf ₁ ² (1)

Step 2: In the detection arm of the high-resolution long-focus-depth OCT imaging system, an orthogonal dispersive spectrometer with ultra-high spectral resolution is used for detection. This spectrometer has an ultra-long measurement range and is used to distinguish sample information to realize longitudinal parallel detection of interference spectrum signals.

Step 3: Perform Fourier transform on the detected interference spectrum of the sample to be measured to obtain the image of the sample under multi-beam illumination conditions. As shown in Fig. 4, in the encoding space, four subimages obtained by four light beams: subimage 1, subimage 2, subimage 3 and subimage 4 are encoded at different optical path positions. The spacing between adjacent subgraphs can be expressed as:

Δz _s =nt (2),

In the sample space, only the sample within a certain focal depth range of the beam can be illuminated by the high-quality beam, and the resulting imaging result has high resolution. That is, each sub-image has a section of high-resolution imaging area, and the sample in this area is irradiated by the light within the focal depth range of the corresponding beam. The distance between the center positions of the high-resolution imaging area in the figure can be expressed as:

Δd=Δz _s -Δz _f (3),

By splicing the imaging results of the focal depth areas of the four sub-images together, as shown in Figure 5, the imaging results with a long depth range and high resolution can be reconstructed.

Claims (2)

1. A high-resolution long-focus OCT imaging system based on optical path coding, comprising a broadband light source, a bandpass filter, a first mirror, a first broadband optical beam splitter, a second broadband optical beam splitter, a first Focusing lens, optical path encoder, third broadband optical beam splitter, two-dimensional scanning galvanometer, second focusing lens, second mirror, third mirror, fourth mirror, one-dimensional precision translation stage, orthogonal Dispersion spectrometer and computer; The spatial light emitted by the broadband light source is reflected by the first reflector to the first broadband optical beam splitter after passing through the band-pass filter, and the light reflected by the first broadband optical beam splitter forms a sample optical path, which is split by the first broadband optical beam splitter The light transmitted by the beamer forms a reference optical path; The sample optical path: the transmitted light passing through the second broadband beam splitter is focused on the optical path encoder by the first focusing lens; the optical path encoder is a glass plate coated on both sides, and the incident surface of the beam is a high reflection film One side is a total reflection film; the returned optical path coded light is reflected by the second broadband optical beam splitter and then transmitted through the third broadband optical beam splitter, and then irradiates the sample to be tested after passing through the two-dimensional scanning galvanometer and the second focusing lens Above; the returned sample signal light is reflected by the second broadband optical beam splitter and then transmitted to the orthogonal dispersive spectrometer; The reference optical path: the transmitted light passing through the first broadband optical beam splitter is reflected by the second reflector and then successively reflected by the third reflector and the fourth reflector, and then transmitted through the third broadband optical beam splitter and transmitted to the positive In the cross-dispersion spectrometer; the third mirror and the fourth mirror are placed on a one-dimensional precision translation stage, and the optical path difference between the sample optical path and the reference optical path can be adjusted by moving the translation stage; After the sample light interferes with the reference light, it enters the detection arm, is converted into an electrical signal by the orthogonal dispersive spectrometer, and is transmitted to a computer for processing. 2. A kind of high-resolution long-focus OCT imaging method based on optical path encoding according to claim 1, characterized in that the method specifically comprises the following steps: Step 1: In the sample optical path of the high-resolution long-focus OCT imaging system, use an optical path encoder to modulate the illumination light of the sample to be tested, and the incident light forms multiple optical paths after multiple reflections on both sides of the optical path encoder Different virtual image light sources; these virtual image light sources are focused on different depth positions of the sample after being imaged by the optical system; Step 2: In the detection arm of the high-resolution long-focus-depth OCT imaging system, an orthogonal dispersive spectrometer with ultra-high spectral resolution is used for detection. This spectrometer has an ultra-long measurement range and is used to distinguish sample information to realize longitudinal parallel detection of interference spectrum signals; Step 3: Perform Fourier transform on the detected interference spectrum of the sample to be tested to obtain the sample image under multi-beam lighting conditions; the sample images obtained by different beams are distributed at different depth positions, and the focal depth range of each beam is selected The sample images obtained by light are stitched together to obtain a high-resolution, long-focus sample image under deep beam illumination.

Images