Design method of achromatic focal depth expansion endoscopic optical coherence tomography probe

Abstract

The invention discloses an achromatic focal depth expansion endoscopic optical coherence tomography probe design method, and relates to the technical field of optical endoscopic probe design, and the method comprises the following steps: S100, structure initialization; s200, calculating emergent light field distribution and a quality factor function (FOM); s300, carrying out iterative calculation on a single circular ring; s400, height change disturbance stagnation is judged; s500, height change disturbance stagnation optimization is carried out; s600, retaining the structure; and S700, manufacturing a probe. According to the invention, achromatism and focal depth expansion are realized, and the assembly difficulty of the spliced endoscopic probe is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of optical endoscope probe design, and in particular to a design method of an achromatic focal depth extended endoscope optical coherence tomography probe. Background Art

[0002] When light of different wavelengths passes through the same focusing optical element, the focused light field will shift, that is, it cannot be focused to the same position, causing chromatic aberration. In the field of endoscopic optical coherence tomography, broadband light sources are usually used to obtain high longitudinal resolution, and broadband light sources will increase chromatic aberration, causing imaging artifacts and blur. In addition, during endoscopic surgery, the probe needs to operate in narrow tissues. The presence of chromatic aberration will increase the optical distortion caused by probe movement and change of viewing angle, reducing the accuracy of real-time imaging. Therefore, the achromatic probe can compensate and correct the chromatic aberration caused by the broadband light source, thereby allowing the wide spectrum signal to be effectively utilized without affecting the imaging accuracy, thereby improving the overall image quality. Most of the current achromatic design schemes focus on a single focal plane or achromatic design close to the diffraction limit, and such a design scheme usually brings a shorter depth of focus. In optical coherence tomography, the captured high-resolution image can only be maintained within the depth of focus. Once out of focus, the image resolution will drop sharply. Therefore, achieving achromatic aberration and depth of focus extension at the same time has become an urgent problem to be solved for endoscopic optical coherence tomography probes.

[0003] Therefore, technicians in this field are committed to developing a design method for an achromatic focal depth extended endoscopic optical coherence tomography probe. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to design an endoscopic optical coherence tomography probe that can achieve both achromatism and extended depth of focus.

[0005] Research has found that by considering achromatism while expanding the axial light field, it is possible to achieve achromatism while also expanding the depth of focus to a certain extent.

[0006] In one embodiment of the present invention, a method for designing an achromatic focal depth extended endoscopic optical coherence tomography probe is provided, comprising:

[0007] S100, initializing the structure, dividing the diffractive optical element with a diameter of 124 μm into T circular rings, setting the width and height of each circular ring, where T is a positive integer;

[0008] S200, calculating the output light field distribution and the quality factor function FOM, calculating the output light field distribution and the quality factor function FOM corresponding to the diffractive optical element with the structure initialized;

[0009] S300, iterative calculation of a single ring, traversing and selecting each ring and updating the height change Δh, updating the structure of the diffractive optical element, calculating the output light field distribution and the quality factor function FOM corresponding to each ring, and retaining the diffractive optical element structure that increases the quality factor function FOM;

[0010] S400, height change disturbance stagnation judgment, compare the quality factor function FOM of the first ring with the quality factor function FOM of the last ring, if the quality factor function FOM of the last ring is greater than the quality factor function FOM of the first ring, then re-execute step S300; otherwise, the height change Δh disturbance of each ring is stagnant, and execute step S500;

[0011] S500, height change disturbance stagnation optimization, the height change Δh is randomly updated within a specified range, and steps S300 to S400 are re-executed. If the height change Δh disturbance stagnation optimization exceeds a specified number of times, step S600 is executed;

[0012] S600, structure preservation, retaining the current diffractive optical element structure;

[0013] S700, probe production, using two-photon 3D printing technology, the diffraction optical element is printed on the end face of the optical fiber to complete the production of the endoscopic optical coherence tomography probe.

[0014] Optionally, in the endoscopic optical coherence tomography probe design method in the above embodiment, step S100 includes:

[0015] S110, ring width setting, set the width of each ring to

[0016] S120: Height setting: setting the height of each ring to a random value.

[0017] Preferably, in the endoscopic optical coherence tomography probe design method in the above embodiment, T is set to be 124, and the width of each circular ring is 0.5 μm.

[0018] Furthermore, in the endoscopic optical coherence tomography probe design method in the above embodiment, the range of the random value is between 1 μm and 15 μm.

[0019] Optionally, in the endoscopic optical coherence tomography probe design method in any of the above embodiments, step S200 includes:

[0020] S210, calculating the incident light field distribution of the diffractive optical element. The incident light of the diffractive optical element is Gaussian distribution, that is, the amplitude distribution of the fundamental mode light source emitted from the core of the single-mode optical fiber after passing through the beam expansion cylinder printed by two-photon 3D printing is Gaussian distribution. The formula is as follows:

[0021] A0(u,v,r)=U·exp[-(u 2 +v 2 ) / r 2 ]

[0022] Where U is the amplitude of the incident Gaussian light, r is the Gaussian light 1 / e 2 The radius of , (u,v) is the spatial coordinate;

[0023] S220, convert the phase into the corresponding phase distribution according to the geometric structure of the diffractive optical element The formula is as follows:

[0024]

[0025] Among them, n DOE is the refractive index of the photoresist used in two-photon printing, H(u,v) is the geometric height distribution of the diffractive optical element, and λ is the wavelength of the incident light;

[0026] S230, calculate the output light field distribution, calculate the output light field distribution corresponding to the diffractive optical element according to the Fresnel diffraction integral formula, and calculate the output light field distribution corresponding to the diffractive optical element at a distance z from the output surface of the diffractive optical element. n The light field distribution at is as follows:

[0027]

[0028] in, is an imaginary unit, is the wave number, λ m is the wavelength of the incident light, (x,y) is the exit surface z n The spatial coordinates at (u, v) are the spatial coordinates of the exit surface of the diffractive optical element. is the light field distribution on the exit surface of the diffractive optical element;

[0029] S240, calculate the quality factor function FOM, calculate the quality factor function FOM according to the light field distribution of the diffractive optical element, expand the focal depth of the focused light field corresponding to different wavelengths, and calculate the quality factor function FOM according to the light field distribution of the diffractive optical element. M ) corresponds to the same axial observation area (z1,z2,…z N ) are included in the FOM, and the formula is as follows:

[0030]

[0031] Where M is the number of discretized wavelengths within the incident light source bandwidth, N is the number of discretized observation planes within the axial observation area, and E desired (x,y,λ m ,z n)=exp[-(u 2 +v 2 ) / (λ m z n / 4r DOE )] indicates different z in the observation area j The light field distribution in the plane is at the diffraction limit, r DOE is the diameter of the designed diffractive optical element.

[0032] Preferably, in the endoscopic optical coherence tomography probe design method in any of the above embodiments, the height change Δh is 100 nm.

[0033] Optionally, in the endoscopic optical coherence tomography probe design method in any of the above embodiments, the iterative calculation traverses each ring from inside to outside or from outside to inside.

[0034] Optionally, in the endoscopic optical coherence tomography probe design method in any of the above embodiments, step S300 includes:

[0035] S310, calculating the output light field distribution and quality factor function FOM of the first circular ring, initially assigning i=1, selecting the i-th ring, increasing its height change by Δh, keeping the heights of the remaining rings unchanged, updating the structure of the diffractive optical element, and calculating the output light field distribution and quality factor function FOM;

[0036] S320, judging the quality factor function, if the current quality factor function FOM increases compared to the FOM before the diffractive optical element structure is updated, retaining the current diffractive optical element structure, and updating the quality factor function FOM to the current quality factor function FOM, i=i+1; otherwise, not retaining the current diffractive optical element structure, and not updating the quality factor function FOM;

[0037] S330, reducing the height change, reducing the height of the i-th ring by the same Δh, keeping the heights of the remaining rings unchanged, and calculating the output light field distribution and the quality factor function FOM;

[0038] S340, judging the quality factor function, if the current quality factor function FOM increases compared to the quality factor function FOM before the diffractive optical element structure is updated, then the current diffractive optical element structure is retained, and the quality factor function FOM is updated to the current quality factor function FOM, i=i+1; otherwise, the current diffractive optical element structure is not retained, and the quality factor function FOM is not updated, i=i+1;

[0039] S350, traverse all the rings, loop through steps S320 to S340, and traverse all the rings of the diffractive optical element.

[0040] Optionally, in the endoscopic optical coherence tomography probe design method in any of the above embodiments, the specified range is greater than or equal to 1 nm and less than or equal to 100 nm.

[0041] Preferably, in the endoscopic optical coherence tomography probe design method in the above embodiment, the specified number of times is 5 times.

[0042] The present invention focuses light of different wavelengths to the same position and extends the focal depth of the focused light field corresponding to different wavelengths. The establishment of the quality factor function FOM takes into account the light field distribution control at different axial positions at different wavelengths. It is directly printed on the optical fiber end face through two-photon printing technology, and simultaneously achieves achromatism and focal depth extension, reducing the difficulty of assembling the spliced ​​endoscopic probe.

[0043] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a flow chart illustrating a method of designing an endoscopic optical coherence tomography probe according to an exemplary embodiment;

[0045] Figure 2 is a rendering illustrating an endoscopic optical coherence tomography probe according to an exemplary embodiment;

[0046] Figure 3 is a schematic diagram illustrating an end-face image of an endoscopic optical coherence tomography probe according to an exemplary embodiment;

[0047] Figure 4 is a phase distribution diagram illustrating an end face image of an endoscopic optical coherence tomography probe according to an exemplary embodiment. DETAILED DESCRIPTION

[0048] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0049] In the drawings, components with the same structure are indicated by the same numerical reference numerals, and components with similar structures or functions are indicated by similar numerical reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the size and thickness of each component. In order to make the illustration clearer, the thickness of the components is schematically exaggerated in some places in the drawings.

[0050] The inventors have designed a method for designing an achromatic focal depth extended endoscopic optical coherence tomography probe, such as Figure 1As shown, the following steps are included:

[0051] In one embodiment of the present invention, a method for designing an achromatic focal depth extended endoscopic optical coherence tomography probe is provided, comprising:

[0052] S100, structural initialization, dividing the diffractive optical element with a diameter of 124 μm into T circular rings, setting the width and height of each circular ring, where T is a positive integer; including:

[0053] S110, ring width setting, set the width of each ring to Set T to 124 and the width of each ring to 0.5 μm;

[0054] S120 , height setting: setting the height of each ring to a random value, with the range of the random value being between 1 μm and 15 μm.

[0055] S200, calculating the output light field distribution and the quality factor function FOM, calculating the output light field distribution and the quality factor function FOM corresponding to the diffractive optical element with structure initialization; including:

[0056] S210, calculating the incident light field distribution of the diffractive optical element, the incident light of the diffractive optical element is Gaussian distribution, that is, the fundamental mode light source emitted from the core of the single-mode optical fiber is subjected to two-photon 3D imaging.

[0057] The amplitude distribution after the printed beam expansion cylinder is Gaussian distribution, and the formula is as follows:

[0058] A0(u,v,r)=U·exp[-(u 2 +v 2 ) / r 2 ]

[0059] Where U is the amplitude of the incident Gaussian light, r is the Gaussian light 1 / e 2 The radius of (u,v) is

[0060] Space coordinates;

[0061] S220, the conversion phase is respectively converted into

[0062] The phase distribution of The formula is as follows:

[0063]

[0064] Among them, n DOE is the refractive index of the photoresist used in two-photon printing, H(u,v) is the derivative

[0065] The geometric height distribution of the incident optical element, λ is the wavelength of the incident light;

[0066] S230, calculate the output light field distribution, calculate the output light field distribution corresponding to the diffractive optical element according to the Fresnel diffraction integral formula, and calculate the output light field distribution corresponding to the diffractive optical element at a distance z from the output surface of the diffractive optical element. n The light field distribution at is as follows:

[0067]

[0068] in, is an imaginary unit, is the wave number, λ m is the wavelength of incident light, (x,y)

[0069] is the exit surface z n The spatial coordinates at (u, v) are the spatial coordinates of the exit surface of the diffractive optical element.

[0070] is the light field distribution on the exit surface of the diffractive optical element;

[0071] S240, calculate the quality factor function FOM, calculate the quality factor function FOM according to the light field distribution of the diffractive optical element, expand the focal depth of the focused light field corresponding to different wavelengths, and calculate the quality factor function FOM according to the light field distribution of the diffractive optical element. M ) corresponds to the same axial observation area (z1,z2,…z N ) are included

[0072] In FOM, the formula is as follows:

[0073]

[0074] Where M is the number of discretized wavelengths within the incident light source bandwidth, N is the number of discretized observation planes within the axial observation area, and E desired (x,y,λ m ,z n )=exp[-(u 2 +v 2 ) / (λ m z n / 4r DOE )]

[0075] Indicates different z in the observation area j The light field distribution in the plane is at the diffraction limit, r DOE is the diameter of the designed diffractive optical element.

[0076] S300, iterative calculation of a single ring, traversing and selecting each ring and updating the height change Δh, in this embodiment, the height change Δh is 100nm, the structure of the diffractive optical element is updated, the output light field distribution and the quality factor function FOM corresponding to each ring are calculated, and the diffractive optical element structure that increases the quality factor function FOM is retained; the iterative calculation adopts an inside-to-outside method or an outside-to-inside method to traverse each ring, and this embodiment selects an inside-to-outside method; including:

[0077] S310, calculate the output light field distribution and quality factor function FOM of the first ring, initially assign i=1, select the i-th ring, increase its height change by Δh, keep the heights of the other rings unchanged, update the structure of the diffractive optical element, calculate the output light field distribution and quality factor function FOM,

[0078] Count FOM;

[0079] S320, judging the quality factor function, if the current quality factor function FOM increases compared to the FOM before the diffractive optical element structure is updated, then the current diffractive optical element structure is retained, and the quality factor function FOM is updated to the current quality factor function FOM, i=i+1; otherwise, the current diffractive optical element structure is not retained, and the quality factor function FOM is not updated.

[0080] new;

[0081] S330, reducing the height change, reducing the height of the i-th ring by the same Δh, keeping the heights of the remaining rings unchanged, and calculating the output light field distribution and the quality factor function FOM;

[0082] S340, judging the quality factor function, if the current quality factor function FOM increases compared to the quality factor function FOM before the diffractive optical element structure is updated, then retaining the current diffractive optical element structure, the quality factor function FOM is updated to the current quality factor function FOM, i=i+1; otherwise, not retaining the current diffractive optical element structure, the quality factor function FOM is updated to the current quality factor function FOM, i=i+1;

[0083] The prime factor function FOM is not updated, i=i+1;

[0084] S350, traverse all the rings, loop through steps S320 to S340, and traverse all the rings of the diffractive optical element.

[0085] S400, height change disturbance stagnation judgment, compare the quality factor function FOM of the first ring with the quality factor function FOM of the last ring, if the quality factor function FOM of the last ring is greater than the quality factor function FOM of the first ring, then re-execute step S300; otherwise, the height change Δh disturbance of each ring stagnates, and execute step S500.

[0086] S500, height change disturbance stagnation optimization, the height change Δh is randomly updated within the specified range, and steps S300-S400 are re-executed. If the height change Δh disturbance stagnation optimization exceeds the specified number of times, step S600 is executed, the specified range is greater than or equal to 1nm and less than or equal to 100nm, and the specified number of times is 5 times.

[0087] S600: retain the structure, and retain the current diffractive optical element structure.

[0088] S700, probe production, using two-photon 3D printing technology, the diffraction optical element is printed on the end face of the optical fiber to complete the production of the endoscopic optical coherence tomography probe.

[0089] In order to verify whether the method proposed in this patent can achieve dispersion correction while achieving extended depth of focus, a numerical simulation was carried out. The parameter settings are: M = 5, the expected achromatic bandwidth is 200nm, that is, λ1 = 750nm, λ2 = 800nm, λ3 = 850nm, λ4 = 900nm, λ5 = 950nm, N = 200, z1 = 1mm, z 200 =3mm, that is, the observation area is in the range of 1mm to 3mm in the axial direction and is divided into 200 observation planes at equal intervals. The diameter of the diffractive optical element is 124μm and is divided into 124 circular rings, and the width of each circular ring is 500nm. The control group uses the same aperture, central wavelength λ3=850nm, and focal length of 1.5mm for simulation. Similarly, the observation area is in the range of 1mm to 3mm in the axial direction and is divided into 200 observation planes at equal intervals. The results are shown in Figure 2 As shown in the figure, (a) is the light field distribution corresponding to the designed endoscopic optical coherence tomography probe at 5 discrete wavelengths. It can be seen that the position of the focused light field distribution does not change with the change of wavelength, and the dispersion is well corrected. In the control group (b), the focused light field obviously moves with the change of wavelength, and the dispersion effect is obvious. At the same time, the numerical simulation results show that the resolution of the focused light field in (a) and (b) is about 14μm, but the average focal depth at each wavelength in (a) is about 800μm, while the average focal depth in (b) is about 500μm, indicating that the designed endoscopic optical coherence tomography probe can not only realize dispersion correction well, but also extend the focal depth. Figure 3 To optimize the acquisition of endoscopic optical coherence tomography probe end-face images. Figure 4 is the corresponding phase distribution diagram.

[0090] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for designing an achromatic extended-depth-of-focus endoscopic optical coherence tomography probe, characterized in that: include: S100, initializing the structure, dividing the diffractive optical element with a diameter of 124 μm into T circular rings, setting the width and height of each circular ring, where T is a positive integer; S200, calculating the output light field distribution and the quality factor function FOM, calculating the output light field distribution and the quality factor function FOM corresponding to the diffractive optical element with the structure initialized; S300, iterative calculation of a single ring, traversing and selecting each ring and updating the height change Δh, updating the structure of the diffractive optical element, calculating the output light field distribution and the quality factor function FOM corresponding to each ring, and retaining the diffractive optical element structure that increases the quality factor function FOM; S400, height change disturbance stagnation judgment, compare the quality factor function FOM of the first ring with the quality factor function FOM of the last ring, if the quality factor function FOM of the last ring is greater than the FOM of the first ring, then re-execute step S300; otherwise, the height change Δh disturbance of each ring is stagnant, and execute step S500; S500, height change disturbance stagnation optimization, the height change Δh is randomly updated within a specified range, and steps S300 to S400 are re-executed. If the height change Δh disturbance stagnation optimization exceeds a specified number of times, step S600 is executed; S600, structure preservation, retaining the current diffractive optical element structure; S700, probe production: using two-photon 3D printing technology, printing the diffractive optical element onto the end face of the optical fiber to complete the production of the endoscopic optical coherence tomography probe.

2. The method for designing an endoscopic optical coherence tomography probe according to claim 1, characterized in that: The step S100 includes: S110, ring width setting, set the width of each ring to S120: Height setting: setting the height of each ring to a random value.

3. The method for designing an endoscopic optical coherence tomography probe according to claim 2, wherein: Set T to 124 and the width of each ring to 0.5 μm.

4. The method for designing an endoscopic optical coherence tomography probe according to claim 3, wherein: The random value ranges from 1 μm to 15 μm.

5. The method for designing an endoscopic optical coherence tomography probe according to claim 1, wherein: The step S200 includes: S210, calculating the incident light field distribution of the diffractive optical element, the incident light of the diffractive optical element is Gaussian distribution, that is, the amplitude distribution of the fundamental mode light source emitted from the core of the single-mode optical fiber after passing through the beam expansion cylinder printed by two-photon 3D printing is Gaussian distribution, the formula is as follows: A0(u,v,r)=U·exp[-(u 2 +v 2 ) / r 2 ]; S220, converting the phase into a corresponding phase distribution according to the geometric structure of the diffractive optical element The formula is as follows: S230, calculating the output light field distribution, according to the Fresnel diffraction integral formula, calculating the output light field distribution corresponding to the diffractive optical element, at a distance z from the output surface of the diffractive optical element n The light field distribution at is as follows: S240, calculating the quality factor function FOM, calculating the quality factor function FOM according to the light field distribution of the diffractive optical element, extending the focal depth of the focused light field corresponding to different wavelengths, and calculating the quality factor function FOM according to the light field distribution of the diffractive optical element ... M ) corresponds to the same axial observation area (z1,z2,…z N ) are included in the FOM, and the formula is as follows:

6. The method for designing an endoscopic optical coherence tomography probe according to claim 1, wherein: The height change Δh is 100 nm.

7. The method for designing an endoscopic optical coherence tomography probe according to claim 1, wherein: The iterative calculation traverses each ring from the inside to the outside or from the outside to the inside.

8. The method for designing an endoscopic optical coherence tomography probe according to claim 1, wherein: The step S300 includes: S310, calculating the output light field distribution and quality factor function FOM of the first circular ring, initially assigning i=1, selecting the i-th ring, increasing its height change by Δh, and keeping the heights of the remaining rings unchanged, updating the structure of the diffractive optical element, and calculating the output light field distribution and quality factor function FOM; S320, judging the quality factor function, if the current quality factor function FOM increases compared to the FOM before the diffractive optical element structure is updated, retaining the current diffractive optical element structure, and updating the quality factor function FOM to the current quality factor function FOM, i=i+1; otherwise, not retaining the current diffractive optical element structure, and not updating the quality factor function FOM; S330, reducing the height change, reducing the height of the i-th ring by the same Δh, keeping the heights of the remaining rings unchanged, and calculating the output light field distribution and the quality factor function FOM; S340, judging the quality factor function, if the current quality factor function FOM increases compared to the quality factor function FOM before the diffractive optical element structure is updated, retaining the current diffractive optical element structure, and updating the quality factor function FOM to the current quality factor function FOM, i=i+1; otherwise, not retaining the current diffractive optical element structure, and not updating the quality factor function FOM, i=i+1; S350, traverse all the circular rings, loop step S320 to step S340, and traverse all the circular rings of the diffractive optical element.

9. The method for designing an endoscopic optical coherence tomography probe according to claim 1, wherein: The specified range is greater than or equal to 1 nm and less than or equal to 100 nm.

10. The method for designing an endoscopic optical coherence tomography probe according to claim 1, wherein: The specified number of times is 5 times.

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