Endoscope imaging system and sapphire protective window design method

Abstract

The present application relates to a kind of endoscope imaging system and sapphire protective window design method.The endoscope imaging system includes shell, sapphire protective window, two imaging channels, linear polarization imaging unit and image processing host, two imaging channels are mutually parallel and arranged in shell, and the end of shell away from linear polarization imaging unit is encapsulated by sapphire protective window;Linear polarization imaging unit is installed in the back focal plane of the ocular of imaging channel, and includes image sensor and multiple micro-polarizer arrays, micro-polarizer array is integrated in the side of image sensor close to ocular, and is aligned with image sensor pixel by pixel, and image sensor is electrically connected with image processing host;By installing linear polarization imaging unit in the back focal plane of ocular, ocular directly images the emergent light of two imaging channels in different areas of linear polarization imaging unit, structure is relatively compact, can meet the miniaturization demand of endoscope imaging system.

Description

Technical Field

[0001] This invention relates to the field of endoscopic imaging technology, and in particular to an endoscopic imaging system and a design method for a sapphire protective window. Background Technology

[0002] Binocular endoscopes can provide surgeons with crucial three-dimensional information during minimally invasive surgery, including the three-dimensional shape of tissue surfaces and the spatial position of instruments. Acquiring high-quality three-dimensional information through endoscopy during surgery plays a vital role in the practice and development of minimally invasive surgical techniques. High-quality three-dimensional information of tissue surfaces not only provides objective evidence for the diagnosis of some lesions but also lays the foundation for the development of intelligent robotic minimally invasive surgery. Currently, three-dimensional image reconstruction methods based on feature detection and matching using ordinary binocular endoscopes are highly dependent on the texture features of the tissue itself, and the density and accuracy of the reconstruction are affected by tissue characteristics. Polarization imaging technology, however, can obtain the normal direction of each pixel without the existence of texture features or assumptions about the reflective properties of the tissue, providing important clues for dense three-dimensional reconstruction and improving the quality of three-dimensional reconstruction.

[0003] Existing binocular endoscopes are not suitable for polarization measurement imaging: 1) Ordinary binocular endoscopes have strong depolarization properties, making it impossible for the system to perform accurate polarization measurements; 2) Directly adding a polarization analyzer to the imaging end of the binocular endoscope to achieve polarization imaging would make the system too large and unable to meet the miniaturization requirements of minimally invasive surgical equipment. Summary of the Invention

[0004] Therefore, it is necessary to address the issue that adding a polarization analyzer to the imaging end of a binocular endoscope would result in an excessively large system size, and to provide a smaller endoscope imaging system suitable for polarization measurement imaging, as well as a sapphire protective window design method.

[0005] This application first provides an endoscopic imaging system, including a housing, a sapphire protective window, two imaging channels, a linear polarization imaging unit, and an image processing host. The two imaging channels are arranged parallel to each other within the housing, and the end of the housing away from the linear polarization imaging unit is encapsulated through the sapphire protective window. The linear polarization imaging unit is mounted on the back focal plane of the eyepiece of the imaging channel and includes an image sensor and a micro-polarizer array. The micro-polarizer array is integrated into the side of the image sensor near the eyepiece and is pixel-wise aligned with the image sensor. The image sensor is electrically connected to the image processing host.

[0006] In one embodiment, the sapphire protective window is a C-cut sapphire flat.

[0007] In one embodiment, the sapphire protective window includes a concentrically arranged connecting portion and a light-transmitting portion, the light-transmitting portion being located inside the connecting portion, and the thickness of the light-transmitting portion being less than the thickness of the connecting portion.

[0008] In one embodiment, the thickness of the light-transmitting portion is less than 0.2 mm.

[0009] In one embodiment, the endoscopic imaging system further includes a positive uniaxial crystal disposed between the sapphire protective window and the imaging channel.

[0010] In one embodiment, the endoscopic imaging system further includes a beam splitter disposed between the imaging channel and the linear polarization imaging unit.

[0011] In one embodiment, the micropolarizer array is a full Stokes micropolarizer array.

[0012] In one embodiment, the endoscopic imaging system further includes an illumination channel, a polarizing device, and a light source. The illumination channel is disposed within the housing, and the light generated by the light source illuminates the imaging target scene through the illumination channel. The polarizing device is disposed between the light source and the illumination channel. The illumination channel employs a polarization-maintaining light guide, and the polarizing device is a time-domain modulated all-Stokes polarizing device.

[0013] In one embodiment, the endoscopic imaging system further includes an illumination channel, a polarizing device, and a light source. The illumination channel is disposed within the housing, and the light generated by the light source illuminates the imaging target scene through the illumination channel. The polarizing device is disposed between the light source and the illumination channel. The illumination channel employs a polarization-maintaining light guide, and the polarizing device is a time-domain modulated linear Stokes polarizing device.

[0014] A second aspect of this application provides a method for designing a sapphire protective window in the aforementioned endoscopic imaging system, comprising the following steps:

[0015] a. The direction of anomalous light propagation in the sapphire protective window is determined by tracing the anomalous light using the following equation:

[0016]

[0017] Among them, [ξ e,o η e,o ζ e,o [αβγ] is the refraction direction vector of abnormal light and normal light, [αβγ] is the direction vector of the optical axis of the sapphire protective window, and the remaining parameters can be determined by the following equations;

[0018]

[0019]

[0020] α=αξ o +η o

[0021] b. Based on the propagation directions of normal and abnormal light, and combined with the optical axis direction of the sapphire protective window, the refractive index of the sapphire protective window for abnormal light propagation is calculated using the refractive index ellipsoid:

[0022]

[0023] Where θ is the angle between the direction of propagation of the anomalous light in the sapphire protective window and the optical axis of the crystal;

[0024] c. Calculate the phase difference between normal and abnormal light in the sapphire protective window using the following formula:

[0025]

[0026] Where δ is the phase difference between normal and abnormal light in the sapphire protective window, h is the crystal thickness of the sapphire protective window, λ is the wavelength of the incident light, and n o and n e θ represents the refractive index of normal and abnormal light in the sapphire protective window crystal. o and θ e The angles of refraction of normal and abnormal light in the sapphire protective window crystal;

[0027] d. Based on the size of the endoscope's field of view, substitute it into the formula in step c to obtain the phase difference δ between the normal and abnormal light. In the field of view, δ exhibits a ring-shaped interference fringe distribution. The thickness limit of the sapphire protective window should be the maximum thickness of a 0th-order fringe filling the entire field of view.

[0028]

[0029] Where δ0 is the phase difference within the 0th order stigma. Attached Figure Description

[0030] Figure 1 A three-dimensional structural diagram of a prior art binocular endoscopic imaging system;

[0031] Figure 2 This is a three-dimensional structural diagram of the endoscopic imaging system of this application;

[0032] Figure 3 for Figure 2 A magnified schematic diagram of the linear polarization imaging unit;

[0033] Figure 4 for Figure 3 A front view structural diagram;

[0034] Figure 5 This is a schematic diagram of the system setup for calibrating the endoscopic imaging system of this application;

[0035] Figure 6 for Figure 2 Enlarged structural diagram of the sapphire protective window.

[0036] Reference numerals: 10, Sapphire protective window; 11, Connecting part; 12, Light-transmitting part; 20, Imaging channel; 21, Eyepiece; 22, Relay lens; 23, Objective lens; 30, Linear polarization imaging unit; 31, Image sensor; 32, Micro polarizer array; 40, Image processing host; 50, Illumination channel; 60, Light source; 81, Polarizing light source; 82, Rotating linear polarizer. Detailed Implementation

[0037] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0042] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0043] Please refer to Figure 1 The existing binocular endoscopic imaging device mainly consists of the following components: a light source P60, a sapphire protective window P10, an illumination channel P50, an imaging channel P20, a beam splitter P70, an imaging unit P30, and an image processing host P40. The light source P60 illuminates the imaging target through the illumination channel P50. The returning light passes through the sapphire protective window P10, the imaging channel P20, and the beam splitter P70 before reaching the two imaging units P30, where it is converted into electrical signals and transmitted to the image processing host P40.

[0044] However, existing binocular endoscopes are not suitable for polarization measurement imaging: 1) Ordinary binocular endoscopes have strong depolarization properties, making it impossible for the system to perform accurate polarization measurements; 2) Directly adding a polarization analyzer to the imaging end of the binocular endoscope to achieve polarization imaging would make the system too large to meet the miniaturization requirements of minimally invasive surgical equipment.

[0045] Regarding the above issues, please refer to... Figure 2 , Figure 3 as well as Figure 4 As shown, this application first provides an endoscope imaging system, including a housing (not shown), a sapphire protective window 10, two imaging channels 20, a linear polarization imaging unit 30, and an image processing host 40. The two imaging channels 20 are arranged parallel to each other inside the housing, and the end of the housing away from the linear polarization imaging unit 30 is encapsulated by the sapphire protective window 10.

[0046] The linear polarization imaging unit 30 is mounted on the back focal plane of the eyepiece 21 of the imaging channel 20, and includes an image sensor 31 and a micro polarizer array 32. The micro polarizer array 32 is integrated on the side of the image sensor 31 near the imaging channel 20 and is aligned pixel by pixel with the image sensor 31. The image sensor 31 is electrically connected to the image processing host 40.

[0047] By mounting the linear polarization imaging unit 30 on the back focal plane of the eyepiece 21, the eyepiece 21 directly images the outgoing light from the two imaging channels 20 onto different areas of the linear polarization imaging unit 30. Compared to directly adding a polarization analyzer to the imaging end of the binocular endoscope, on the one hand, there is no need to set up an additional beam splitting structure, and on the other hand, the returned light can be directly analyzed and imaged in different areas of the same linear polarization imaging unit 30. The structure is relatively compact and can meet the miniaturization requirements of the endoscope imaging system.

[0048] In some embodiments, the imaging channel 20 consists of an eyepiece 21, a relay lens 22, and an objective lens 23, which are arranged sequentially. The sapphire protective window 10 is located on the side closer to the objective lens 23. The linear polarization imaging unit 30 is mounted on the back focal plane of the eyepiece 21. The two imaging channels 20 in the endoscopic imaging system can perform binocular imaging of the scene.

[0049] In some embodiments, the endoscopic imaging system further includes an illumination channel 50 and a light source 60. The illumination channel 50 and the imaging channel 20 are both fixed inside the housing and encapsulated by a sapphire protective window 10. The light generated by the light source 60 illuminates the imaging target scene through the illumination channel 50. The light reflected from the imaging scene passes through the imaging channel 20 and completes polarization imaging at the linear polarization imaging unit 30. The data is transmitted to the image processing host 40 to complete the polarization three-dimensional image reconstruction.

[0050] In some embodiments, the spatial period of the micro-polarizer array 32 is 2 pixels × 2 pixels, and the polarization detection directions of the four micro-polarizers in each spatial period are 0 and 1 respectively. ° 45 ° 135 ° and 90 ° .

[0051] Furthermore, after the image processing host 40 reconstructs the linear Stokes parameters (s0, s1, s2) of the scene, it uses two sets of s0 data from the stereo cameras, the triangular relationship between the stereo channels and the target, and the texture of the target to obtain sparse depth information within the scene. Using this depth information as a guide, it uses the measured s1 and s2 data to obtain the dense normal directions of the scene surface. Combined with the shape-from-polarization method algorithm, it can accurately supplement the depth information of the scene and reconstruct the dense three-dimensional shape of the scene.

[0052] Please refer to Figure 5 As shown, in some embodiments, the device performs system calibration using the eigenvalue calibration method; the polarization device consists of a polarization light source 81 and a rotating line polarizer 82; the line polarizers in the polarization device are respectively at 0... ° 45 ° 135 ° and 90 ° The position is used to analyze the polarized light and complete the system calibration.

[0053] Please refer to Figure 6 As shown, in some embodiments, the sapphire protective window 10 is a C-cut sapphire flat crystal, so that the thickness of the sapphire protective window 10 can be designed and calculated according to the field of view of the endoscope entrance pupil, so as to ensure that the endoscope imaging system has good polarization-maintaining properties.

[0054] Please refer to Figure 6 As shown, in some embodiments, the sapphire protective window 10 includes a connecting portion 11 and a light-transmitting portion 12 arranged concentrically. The light-transmitting portion 12 is located inside the connecting portion 11, and the thickness of the light-transmitting portion 12 is less than the thickness of the connecting portion 11.

[0055] To ensure that the thickness of the light-transmitting part 12 is relatively small, the thickness of the connecting part 11 is relatively large. Specifically, the relatively large thickness of the connecting part 11 can ensure that the sapphire protective window 10 is stably welded to the outer shell, while the relatively small thickness of the light-transmitting part 12 can ensure that the endoscope imaging system has good polarization-maintaining properties.

[0056] In some embodiments, the entrance pupil field of view of the endoscope is 70°, and the thickness of the light-transmitting part 12 is less than 0.2 mm.

[0057] In some embodiments, the endoscopic imaging system further includes a positive uniaxial crystal disposed between the sapphire protective window 10 and the imaging channel 20.

[0058] Since sapphire itself is a negative uniaxial crystal, by setting a positive uniaxial crystal corresponding to the sapphire protective window 10, the birefringence characteristics of the sapphire protective window 10 can be counteracted, avoiding the birefringence characteristics from generating complex polarization patterns in the field of view during polarization imaging, thus preventing the depolarization caused by the birefringence from affecting the polarization calibration of the system. This makes polarization imaging technology applicable to endoscopic imaging and provides more accurate polarization measurement results.

[0059] In some embodiments, the endoscopic imaging system further includes a beam splitter disposed between the imaging channel 20 and the linear polarization imaging unit 30.

[0060] In some embodiments, the micropolarizer array 32 is a full Stokes micropolarizer array, in which case the endoscopic imaging system of this application is a binocular full polarization imaging system.

[0061] In some embodiments, the endoscopic imaging system further includes an illumination channel 50, a polarizing device, and a light source 60. The illumination channel 50 is disposed within the housing, and the light generated by the light source 60 illuminates the imaging target scene through the illumination channel 50. The polarizing device is disposed between the light source 60 and the illumination channel 50. The illumination channel 50 adopts a polarization-maintaining light guide, and the polarizing device is a time-domain modulated all-Stokes polarizing device. In this case, the endoscopic imaging system of this application is a binocular linear Mueller polarization imaging system.

[0062] In some embodiments, the endoscopic imaging system further includes an illumination channel 50, a polarizing device, and a light source 60. The illumination channel 50 is disposed within the housing, and the light generated by the light source 60 illuminates the imaging target scene through the illumination channel 50. The polarizing device is disposed between the light source 60 and the illumination channel 50. The illumination channel 50 adopts a polarization-maintaining light guide, and the polarizing device is a linear Stokes polarizing device based on time-domain modulation. In this case, the endoscopic imaging system of this application is a binocular full Mueller polarization imaging system.

[0063] A second aspect of this application provides a method for designing a sapphire protective window in the aforementioned endoscopic imaging system, comprising the following steps:

[0064] a. The direction of anomalous light propagation in the sapphire protective window is determined by tracing the anomalous light using the following equation:

[0065]

[0066] Among them, [ξ e,o η e,o ζ e,o [α β γ] is the refraction direction vector of abnormal light and normal light, [α β γ] is the direction vector of the optical axis of the sapphire protective window, and the remaining parameters can be determined by the following equations;

[0067]

[0068]

[0069] α=αξ o +βη o

[0070] b. Based on the propagation directions of normal and abnormal light, and combined with the optical axis direction of the sapphire protective window, the refractive index of the sapphire protective window for abnormal light propagation is calculated using the refractive index ellipsoid:

[0071]

[0072] Where θ is the angle between the direction of propagation of the anomalous light in the sapphire protective window and the optical axis of the crystal;

[0073] c. Calculate the phase difference between normal and abnormal light in the sapphire protective window using the following formula:

[0074]

[0075] Where δ is the phase difference between normal and abnormal light in the sapphire protective window, h is the crystal thickness of the sapphire protective window, λ is the wavelength of the incident light, and n o and n e θ represents the refractive index of normal and abnormal light in the sapphire protective window crystal. o and θ e The angles of refraction of normal and abnormal light in the sapphire protective window crystal;

[0076] d. Based on the size of the endoscope's field of view, substitute it into the formula in step c to obtain the phase difference δ between the normal and abnormal light. In the field of view, δ exhibits a ring-shaped interference fringe distribution. The thickness limit of the sapphire protective window should be the maximum thickness of a 0th-order fringe filling the entire field of view.

[0077]

[0078] Where δ0 represents the phase difference within the 0th-order stain. Furthermore, considering the distribution of light source intensity according to wavelength, the thickness corresponding to the center wavelength needs to be calculated based on this distribution as the thickness of the sapphire protective window.

[0079] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0080] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An endoscopic imaging system, characterized in that, It includes a housing, a sapphire protective window (10), two imaging channels (20), a linear polarization imaging unit (30), and an image processing host (40). The two imaging channels (20) are arranged parallel to each other inside the housing, and the end of the housing away from the linear polarization imaging unit (30) is encapsulated through the sapphire protective window (10). The linear polarization imaging unit (30) is mounted on the back focal plane of the eyepiece (21) of the imaging channel (20), and includes an image sensor (31) and a micro polarizer array (32). The micro polarizer array (32) is integrated on the side of the image sensor (31) near the eyepiece (21) and is pixel-wise aligned with the image sensor (31). The image sensor (31) is electrically connected to the image processing host (40). The sapphire protective window (10) is a C-cut sapphire flat crystal; The endoscopic imaging system also includes a positive uniaxial crystal, which is disposed between the sapphire protective window (10) and the imaging channel (20).

2. The endoscopic imaging system according to claim 1, characterized in that, The sapphire protective window (10) includes a connecting part (11) and a light-transmitting part (12) arranged concentrically. The light-transmitting part (12) is located inside the connecting part (11), and the thickness of the light-transmitting part (12) is less than the thickness of the connecting part (11).

3. The endoscopic imaging system according to claim 2, characterized in that, The thickness of the light-transmitting part (12) is less than 0.2 mm.

4. The endoscopic imaging system according to claim 1, characterized in that, The endoscopic imaging system also includes a beam splitter, which is disposed between the imaging channel (20) and the linear polarization imaging unit (30).

5. The endoscopic imaging system according to claim 1, characterized in that, The micro-polarizer array (32) is a full Stokes micro-polarizer array.

6. The endoscopic imaging system according to claim 5, characterized in that, The endoscopic imaging system also includes an illumination channel (50), a polarizing device, and a light source (60). The illumination channel (50) is disposed inside the housing. The light generated by the light source (60) illuminates the imaging target scene through the illumination channel (50). The polarizing device is disposed between the light source (60) and the illumination channel (50). The lighting channel (50) adopts a polarization-maintaining light guide, and the polarization device is a time-domain modulated all-Stokes polarization device.

7. The endoscopic imaging system according to claim 1, characterized in that, The endoscopic imaging system also includes an illumination channel (50), a polarizing device, and a light source (60). The illumination channel (50) is disposed inside the housing. The light generated by the light source (60) illuminates the imaging target scene through the illumination channel (50). The polarizing device is disposed between the light source (60) and the illumination channel (50). The illumination channel (50) adopts a polarization-maintaining light guide, and the polarization device is a linear Stokes polarization device based on time-domain modulation.

8. A method for designing a sapphire protective window, used to design a sapphire protective window in the endoscopic imaging system according to any one of claims 1 to 7, characterized in that, Includes the following steps: a. The direction of anomalous light propagation in the sapphire protective window is determined by tracing the anomalous light using the following equation: Among them, [ξ e,o η e,o ζ e,o [αβγ] is the refraction direction vector of abnormal light and normal light, [αβγ] is the direction vector of the optical axis of the sapphire protective window, and the remaining parameters can be determined by the following equations; b. Based on the propagation directions of normal and abnormal light, and combined with the optical axis direction of the sapphire protective window, the refractive index of the sapphire protective window for abnormal light propagation is calculated using the refractive index ellipsoid: Where θ is the angle between the direction of propagation of the anomalous light in the sapphire protective window and the optical axis of the crystal; c. Calculate the phase difference between normal and abnormal light in the sapphire protective window using the following formula: Where δ is the phase difference between normal and abnormal light in the sapphire protective window, h is the crystal thickness of the sapphire protective window, λ is the wavelength of the incident light, and n o and n e θ represents the refractive index of normal and abnormal light in the sapphire protective window crystal. o and θ e The angles of refraction of normal and abnormal light in the sapphire protective window crystal; d. Based on the size of the endoscope's field of view, substitute it into the formula in step c to obtain the phase difference δ between normal and abnormal light in the sapphire protective window. In the field of view, δ exhibits a ring-shaped interference fringe distribution. The thickness limit of the sapphire protective window should be the maximum thickness of the 0th-order fringes filling the entire field of view. Where δ0 is the phase difference within the 0th order stigma.

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