Optical component and system for synchronous 3D hyperspectral imaging

Abstract

A compact structure for snapshot hyperspectral imaging may include an image splitter, an integral field-of-view unit, an integral field-of-view spectrometer, and a multiplexed integral field-of-view spectrometer. The image splitter includes: a first section having a first plurality of mirrors, each of the first plurality of mirrors having a predetermined inclination in a longitudinal direction; a second section having a second plurality of mirrors, each of the second plurality of mirrors having a predetermined inclination in the longitudinal direction; and a ridge extending laterally between the first section and the second section, the first section being at a first angle relative to the ridge, and the second section being at a second angle relative to the ridge opposite the first angle. The integral field-of-view unit light source includes a four-mirror design that includes an image splitter. The integral field-of-view spectrometer includes a spectrometer array and an image splitter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to provisional application serial number 63 / 391,107 filed on July 21, 2022, the entire contents of which are incorporated into this application.

[0003] Government power

[0004] This invention was made with government support under Grant No. 1727095 awarded by the National Science Foundation. The government has certain rights in this invention. Technical Field

[0005] The present disclosure relates to optical components and systems for simultaneous, real-time three-dimensional (two spatial dimensions [x, y] and one spectral dimension [λ]) hyperspectral imaging of a two-dimensional spatial field. Background Art

[0006] In many areas of business and science, cameras are used that have, in addition to spatial resolution, spectral resolution that often exceeds the red, green and blue light bands that the human eye can perceive. Spectrally high-resolution imaging techniques called "hyperspectral imaging" have been developed for these measurements. For example, such hyperspectral imaging allows the identification and differentiation of different chemical elements based on spatially resolved spectra.

[0007] Early hyperspectral imaging systems based on long-slit diffraction grating (or any dispersive element, such as a prism) spectrometers used so-called "push-broom" scanning, where one dimension was used for spatial determination and the other dimension was used for spectral determination on a two-dimensional image sensor. New methods of hyperspectral imaging and the development of higher resolution sensors and computer hardware have made snapshot full-frame hyperspectral systems possible.

[0008] Conventional hyperspectral imagers, also known as integral field spectrographs (IFS), consist of two parts: 1) an integral field unit (IFU), which reformats the two-dimensional (2D) spatial field formed by an imaging system (such as a telescope or microscope) into long narrow slices or sparsely distributed two-dimensional light source fields; and 2) a conventional grating spectrometer coupled to a two-dimensional sensor for synchronously recording the spectra of all field points. Three types of IFUs are commonly used to construct IFS: 1) microlens arrays; 2) coherent fiber arrays; and 3) machined or polished glass image slicers, each with its own advantages and limitations. The optical system of the spectrometer of a conventional IFS is usually huge because it needs to support extended long slits or large sparsely distributed small light sources formed by the IFU. Due to the huge spectrometers, the inherent spectral resolution that these spectrometers can achieve (limited by the illumination size of the grating) is usually far greater than the required resolution. Summary of the invention

[0009] One or more embodiments are directed to optical components and systems for snapshot hyperspectral imaging in a compact configuration.

[0010] One or more embodiments are directed to an image slicer for use with a multi-spectral light source, comprising: a first segment having a first plurality of mirrors, each of the first plurality of mirrors having a predetermined tilt in a longitudinal direction; a second segment having a second plurality of mirrors, each of the second plurality of mirrors having a predetermined tilt in the longitudinal direction; and a ridge extending laterally between the first segment and the second segment, the first segment being at a first angle relative to the ridge, and the second segment being at a second angle relative to the ridge opposite to the first angle.

[0011] Each of the first plurality of mirrors and the second plurality of mirrors may be a plane mirror.

[0012] One or more embodiments are directed to an integral field of view unit for use with a multi-spectral light source, having a four-mirror design, the four-mirror design comprising: an image splitter having a plurality of splitting mirrors to receive light from the multi-spectral light source and output a plurality of divergent light beams; a collimator mirror that collimates each of the plurality of divergent light beams from the plurality of splitting mirrors into a plurality of collimated light beams; a plurality of re-imaging mirrors that output an image of each splitting mirror onto an image sensor, and a plurality of folding mirrors that direct the plurality of collimated light beams from the collimator mirrors onto the plurality of re-imaging mirrors.

[0013] The image slicer may include: a first segment having a first plurality of mirrors, each having a predetermined inclination in a longitudinal direction; a second segment having a second plurality of mirrors, each having a predetermined inclination in the longitudinal direction; and a spine extending laterally between the first segment and the second segment, the first segment being at a first angle relative to the spine, and the second segment being at a second angle relative to the spine opposite to the first angle.

[0014] Each of the first plurality of mirrors and the second plurality of mirrors may be a plane mirror.

[0015] One or more embodiments are directed to an integral field of view spectrometer for use with a multi-spectral light source, comprising: an image slicer comprising a plurality of cutting mirrors; and an array of spectrometers, each spectrometer being associated with a corresponding one of the plurality of cutting mirrors, wherein the spectrometer array multiplexes multi-spectral data onto a two-dimensional image sensor.

[0016] Each spectrometer in the spectrometer array may include: a splitter mirror, which serves as an entrance slit of the spectrometer; a collimator mirror, which collimates the divergent light beam from the corresponding splitter mirror into a collimated light beam; a micro-grating, which receives the collimated light beam from the collimator mirror and diffracts the light into multiple wavelength bands; and a re-imaging mirror, which directs each of the multiple wavelength bands onto the two-dimensional image sensor.

[0017] Each collimating mirror may be an off-axis parabolic collimating mirror.

[0018] Each row of spectrometers in the spectrometer array may use a row of integrated off-axis parabolic collimating mirrors.

[0019] Each row of spectrometers in the spectrometer array may use a row of integrated micro-gratings.

[0020] Each row of spectrometers in the spectrometer array may use a row of integrated re-imaging mirrors.

[0021] The array of the integral field of view spectrometer can be a four-mirror design, including: a plurality of splitting mirrors in the image splitter to receive light from the multi-spectral light source and output a plurality of divergent light beams; a collimating mirror, which collimates each of the plurality of divergent light beams from the plurality of splitting mirrors into a plurality of collimated light beams; a plurality of folding mirrors; and a plurality of re-imaging mirrors to output an image of each splitting mirror to an image sensor, wherein the plurality of folding mirrors guide the plurality of collimated light beams from the collimating mirror to the plurality of re-imaging mirrors.

[0022] The image slicer may include: a first segment having a first plurality of mirrors, each of the first plurality of mirrors having a predetermined inclination in a longitudinal direction; a second segment having a second plurality of mirrors, each of the second plurality of mirrors having a predetermined inclination in the longitudinal direction; and a spine extending laterally between the first segment and the second segment, the first segment being at a first angle relative to the spine, and the second segment being at a second angle relative to the spine that is opposite to the first angle.

[0023] One or more embodiments are directed to a multiplexed integral field spectrometer, which includes a plurality of any of the integral field spectrometers described above.

[0024] The plurality of integral field spectrometers may receive light from a single source, and may further include a field divider to divide the light from the single source to be incident on each of the plurality of integral field spectrometers.

[0025] Each of the plurality of integrating field spectrometers receives light from a different source.

[0026] Each of the plurality of integrating field-of-view spectrometers may include an array of integrating field-of-view spectrometers, and may further include a field-of-view splitter to split light from each different light source to be incident on each of the array of integrating field-of-view spectrometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The scope of the present disclosure is best understood from the following detailed description of exemplary embodiments when read in conjunction with the accompanying figures.

[0028] Figure 1 is the perspective ray tracing graph, and Figure 2 Schematic perspective view of a machined image slicer integrating field unit (MISI) according to an embodiment.

[0029] Figure 3 is a perspective isometric view of an image slicer according to an embodiment.

[0030] Figure 4 is a perspective schematic diagram of a machined image slicer compact spectrometer (MICS) according to an embodiment.

[0031] Figure 5 is a perspective view of a MICS according to an embodiment.

[0032] Figure 6 Perspective ray tracing diagram of the MICS for the chief ray of a single beam.

[0033] Figures 7 to 9 Different perspectives of the MICS for the chief ray of the full beam.

[0034] Fig.10 Schematic side view of the full-beam MICS.

[0035] Fig.11 Schematic diagram of the top view of the full beam MICS.

[0036] Fig.12 A perspective ray tracing diagram of a configuration with four MICS sharing a common light feed according to an embodiment.

[0037] Fig.13 is a schematic perspective view of a configuration with a plurality of MICS each having a dedicated light source supply according to an embodiment. DETAILED DESCRIPTION

[0038] An integrating field unit is an optical device that divides a two-dimensional spatial field into a two-dimensional array of image elements (pixels) or long narrow slices, and uses a re-imaging system to reformat the spatial field into sparsely distributed point sources or long slits to form an input source, usually called the "entrance slit" of a diffraction grating spectrometer, for injection into a diffraction spectrometer for use with a multi-spectral light source.

[0039] like Figure 1 and Figure 2 As shown, a machined image slicer integrating field unit (MISI) 100 includes a machined image slicer 110, an image slicer 110 including a plurality of slice mirrors 115, a collimator 120, a plurality of fold mirrors 130, a plurality of re-imaging mirrors 140, and an array of exit field stops or exit slits, i.e., an exit port 150, which has a corresponding plurality of images of the slice mirrors 115, which are then output to a focal plane array 160 at a sensor. Therefore, the re-imaging system of the MISI 100 is a four-mirror design, i.e., the fold mirror 130 between the slice mirror 115, the collimator 120, and the re-imaging mirror 140.

[0040] The plurality of cutting mirrors 115 in the image slicer 110 reflect the incident light beam I into a plurality of divergent light beams B' toward the collimating mirror 120, which in turn collimates the divergent light beams B' into collimated light beams B and directs the collimated light beams B to a corresponding one of the folding mirrors 130. The light output from each folding mirror 130 is reflected and focused by a corresponding one of the re-imaging mirrors 140 to image each cutting mirror 115 at and through each exit slit 150.

[0041] In particular, each micro-slicing mirror 115 is re-imaged to a designated position in the outlet 150 using a collimating mirror 120 (e.g., an off-axis parabolic collimating mirror) to collimate the divergent beam from the slicing mirror 115, and then refocused to the focal plane array by a corresponding folding mirror 130 (e.g., a micro-flat folding mirror) and a re-imaging mirror 140 (e.g., a micro-spherical mirror). In particular, each re-imaging mirror 140 may be approximately one focal length away from the middle pupil of each collimated beam B formed by the parabolic collimating mirror 120, so that the exiting beam is effectively telecentric.

[0042] If you can Figure 3 As seen in , the image slicer 110 is divided into two sections defined by a ridge 112. The slicer mirror 115 includes a first plurality of slicer mirrors 114 and a second plurality of slicer mirrors 116 divided by the ridge 112. The first plurality of slicer mirrors 114 have a general tilt angle to direct the light beam upward, while the second plurality of slicer mirrors 116 have a general tilt angle in the opposite direction of the general tilt angle of the first plurality of slicer mirrors to direct the light beam downward. Dividing the image slicer into two sections reduces the depth of the valley of each section. The valleys of a conventional image slicer (i.e., an image slicer without a ridge) would have to be very deep, making the manufacture of the image slicer impractical. However, by including the ridge 112, the depth of the valley can be reduced. The ridge 112 allows the image slicer 110 to direct the image of the slicer mirror 116 to different folding mirror 130 / re-imaging mirror 140 configurations arranged in an array. The specific design of the image slicer 110 depends on the arrangement of these other components of the MISI 100, and the ridges 112 are used to keep the angles small and the focal plane size of the sensor.

[0043] In a specific example, the image slicer 110 may include 56×2 slice mirrors, for example, each having a size of 0.036 mm×2.664 mm, to divide the field of view into a total of 112 sub-fields of view (only 6 of which are shown for clarity). The design of the image slicer 110 depends on the downstream configuration and may include additional sections with additional ridges.

[0044] Figures 4 to 11 A machined image slicer compact spectrometer (MICS) 200 is shown according to an embodiment. Figure 4 and Figure 6 For Figures 7 to 11The actual configuration shown in the figure is rotated to better illustrate the array. As can be seen therein, MICS200 uses the machined image slicer 110 design and the re-imaging system of MISI 100, but replaces the common collimator mirror 120 with a separate collimator mirror and replaces the folding mirror 130 with a grating. Thus, the integrating field unit of MISI 100 is converted into a miniature spectrometer array of MICS200. By incorporating the grating directly into the integrating field unit, the MICS design eliminates the need to have a large common spectrometer behind the integrating field unit, thereby greatly reducing the size of the integrating field spectrometer. The optical design of the MICS according to different configurations is described below, one with a single MICS and one with four MICS, to demonstrate the flexibility and scalability of the design.

[0045] The MICS 200 includes an image slicer 110, which includes a plurality of slicer mirrors 115, a plurality of off-axis parabolic mirrors (OAPs) 220, a plurality of micro gratings 230, a plurality of re-imaging mirrors 140, and a focal plane array 160. Figure 4 As can be seen in FIG. 1 , the plurality of splitter mirrors 115 in the image splitter 110 reflects the incident light beam I into a plurality of divergent light beams B′ toward each of the plurality of OAPs 220 , which in turn collimate the light beams B′ into collimated light beams B and direct the collimated light beams B onto a corresponding one of the gratings 130 .

[0046] If you can Figure 6 As can be seen in the illustration, the micro grating 230 diffracts each collimated light beam B into a plurality of component light beams λ1 to λ n , for example, for white light, three light beams (red, green, blue), which are then focused into light beams Bg on the focal plane array 160. The light output from the micro grating 230 (here a reflective grating) is reflected by the corresponding re-imaging mirror 140 toward the focal plane array 160. Again, the specific design of the image slicer 110 will be dictated by the arrangement of these other components of the MICS 200 and the focal plane size of the sensor.

[0047] Replacing the folding mirror 130 with a grating 230 converts each of the 4-mirror re-imaging systems of MISI 100 into a micro-spectrometer. In addition, while the re-imaging system of MISI 100 has a common parabolic collimator mirror 120 (which results in a variable reflection angle between the incident beam on the folding mirror 130 and the outgoing beam), MICS 200 uses a separate off-axis parabolic mirror 220 (with the vertex of the mother parabola located at the center of the corresponding splitting mirror) to collimate the beam reflected by each splitting mirror 115. This design causes the collimated beam from each of the splitting mirrors 115 to propagate in parallel toward each corresponding micro-grating 230 to maintain a constant reflection angle (or spectrometer angle) for all micro-spectrometers. Therefore, Figures 4 to 10 The single MICS 200 shown includes an array of spectrometers, one for each cutting mirror 115 of the image slicer 110 .

[0048] If you can Figure 4-11 As can be seen in the specific example shown, the image slicer 110 may include 12×2 slice mirrors, for example, each with a size of 20 μm×0.84 mm, forming a 4×6 spectrometer array, as can be seen in FIG. Figure 4 . All micro-spectrometers can have the same grating α angle and spectrometer angle ψ=α-β, where α is the angle of incidence of the light beam of the micro-grating 230 relative to the grating normal, and β is the exit angle of the diffracted light beam relative to the grating normal. All micro-gratings can have the same blazing angle. In this particular example, each micro-grating can be grouped as part of a grating 235, each grating 235 containing 14 micro-gratings for the 14 micro-spectrometers in the row. In addition, as can be seen therein, each collimator 220, each grating 230, and each re-imaging mirror 140 can be integrated along one direction in the array (here, the row direction).

[0049] The MICS200 is designed to exploit modern large format focal plane arrays (FPAs) with large multiplexing capabilities to simultaneously acquire high quality spectral information over a 2D field in a compact space. Given an FPA of certain physical size and pixel format, the instantaneous spatial and spectral sampling size as well as the hyperspectral field of view (nx, ny, nλ) can be adjusted depending on the requirements of the measurement. For example, larger size optics can be used to achieve higher spectral resolution. However, this will reduce the number of micro-spectrometers that can be accommodated on the sensor and the instantaneous spatial field of view coverage of the IFS. Nevertheless, the compact size of the MICS allows the use of multiple MICS in a single instrument, allowing the field of view to be easily doubled or quadrupled, such as Fig.12 shown.

[0050] Fig.12An example system 300 is shown comprising four MICS 200a to 200d fed by a common light source (eg, telescope 10). A 2x2 field of view divider 320 divides the telescope focal plane into four sub-fields of view, one for each MICS. Fig.12 The inset diagram in shows details of the field of view divider 320. Four 2-lens folded relay systems direct the four sub-fields of view to corresponding MICSs in the four MICSs 200a to 200d. In this particular example, the telescope field of view is divided twice, first into four sub-fields of view by the field of view divider 320, and each sub-field of view is divided by the image divider in the corresponding MICS 200a to 200d. Additional field of view dividers can be connected in series and additional MICSs can be included as needed. The image divider 110 of the MICS will be located at the focus of the telescope 10 directly or through an optical relay.

[0051] exist Fig.13 The middle figure shows another way of multiplexing to increase the hyperspectral field of view, where the system 400 includes an array of smaller telescopes 20, an array of corresponding MICS 220 for each telescope 20, and an array of corresponding image sensors 30. Each MICS 220 covers a mosaic field of view, and the mosaic fields of view of all MICS are combined to form an image of the entire field of view. Similarly, the image slicer 110 of the MICS will be located at the focus of each telescope 20 directly or through an optical relay.

[0052] Alternatively, each MICS 200 in the array may include multiple MICS 200a to 200d together with a field of view divider 320 for each telescope 220, i.e., using Fig.12 system 300.

[0053] The present disclosure is not limited to the above-mentioned embodiments which are merely exemplary. It will be appreciated by those skilled in the art that the disclosed systems and / or methods can be implemented in other specific forms without departing from the gist of the present disclosure or its basic features. Therefore, the embodiments disclosed at present are considered to be illustrative rather than restrictive. The present disclosure is not exhaustive and should not be interpreted as limiting the claimed invention to the specifically disclosed embodiments. In view of the present disclosure, it will be appreciated by those skilled in the art that modifications and variations may be made according to the above teachings, or modifications and variations may be obtained by practicing the present disclosure.

[0054] The scope of the invention is indicated by the appended claims rather than by the foregoing description.

Claims

1. An image segmenter for use with a multi-spectral light source, the image segmenter comprising: a first section having a first plurality of mirrors, each mirror of the first plurality of mirrors having a predetermined tilt in a longitudinal direction; a second section having a second plurality of mirrors, each mirror of the second plurality of mirrors having a predetermined tilt in the longitudinal direction; and A spine extends transversely between the first section and the second section, the first section being at a first angle relative to the spine, and the second section being at a second angle relative to the spine opposite the first angle.

2. The image slicer of claim 1, wherein each of the first plurality of mirrors and the second plurality of mirrors is a plane mirror.

3. An integrating field of view unit for use with a multi-spectral light source, comprising: Four-mirror design, the four-mirror design includes an image splitter having a plurality of splitter mirrors to receive light from the multi-spectral light source and output a plurality of divergent light beams; a collimating mirror that collimates each of the plurality of divergent light beams from the plurality of cleaving mirrors into a plurality of collimated light beams; a plurality of re-imaging mirrors that output the image of each slicing mirror onto an image sensor, and A plurality of folding mirrors direct the plurality of collimated light beams from the collimating mirror to the plurality of re-imaging mirrors.

4. The integrating field of view unit according to claim 3, wherein the image segmentor comprises: a first section having a first plurality of mirrors, each having a predetermined tilt in a longitudinal direction; a second section having a second plurality of mirrors, each having a predetermined tilt in the longitudinal direction; and A spine extends transversely between the first section and the second section, the first section being at a first angle relative to the spine, and the second section being at a second angle relative to the spine opposite the first angle.

5. The image slicer of claim 4, wherein each of the first plurality of mirrors and the second plurality of mirrors is a plane mirror.

6. An integral field spectrometer for use with a multi-spectral light source, comprising: An image splitter, comprising a plurality of split mirrors; as well as A spectrometer array, each spectrometer is associated with a corresponding one of the plurality of cleaving mirrors, wherein the spectrometer array multiplexes multi-spectral data onto a two-dimensional image sensor.

7. The integral field spectrometer of claim 6, wherein each spectrometer in the spectrometer array comprises a cutting mirror, which serves as an entrance slit of the spectrometer; A collimator mirror, which collimates the divergent light beam from the corresponding splitter mirror into a collimated light beam; a micro grating that receives the collimated light beam from the collimator and diffracts the light into a plurality of wavelength bands; as well as A re-imaging mirror directs each of the plurality of wavelength bands onto the two-dimensional image sensor.

8. The integral field spectrometer of claim 7, wherein each collimator is an off-axis parabolic collimator.

9. The integrating field spectrometer of claim 8, wherein each row of spectrometers in the spectrometer array uses a row of integrated off-axis parabolic collimating mirrors.

10. An integrating field spectrometer as claimed in any one of claims 7 to 9, wherein each row of spectrometers in the spectrometer array uses a row of integrated micro-gratings.

11. An integrating field spectrometer as claimed in any one of claims 7 to 9, wherein each row of spectrometers in the spectrometer array uses a row of integrated re-imaging mirrors.

12. The integral field spectrometer as claimed in claim 6, wherein the array of the integral field spectrometer is a four-mirror design, comprising a plurality of splitter mirrors in the image splitter to receive light from the multi-spectral light source and output a plurality of divergent light beams; a collimating mirror that collimates each of the plurality of divergent light beams from the plurality of cleaving mirrors into a plurality of collimated light beams; Multiple folding mirrors; as well as A plurality of re-imaging mirrors are provided to output the image of each cutting mirror to the image sensor, wherein the plurality of folding mirrors guide the plurality of collimated light beams from the collimating mirror to the plurality of re-imaging mirrors.

13. The integral field spectrometer of claim 6, wherein the image slicer comprises: a first section having a first plurality of mirrors, each mirror of the first plurality of mirrors having a predetermined tilt in a longitudinal direction; a second section having a second plurality of mirrors, each mirror of the second plurality of mirrors having a predetermined tilt in the longitudinal direction; and A spine extends transversely between the first section and the second section, the first section being at a first angle relative to the spine, and the second section being at a second angle relative to the spine opposite the first angle.

14. A multiplexed integral field spectrometer, comprising a plurality of integral field spectrometers according to any one of claims 6 to 9.

15. The multiplexed integrating field-of-view spectrometer of claim 14, wherein the plurality of integrating field-of-view spectrometers receive light from a single light source, and further comprising a field-of-view splitter to split the light from the single light source to be incident on each of the plurality of integrating field-of-view spectrometers.

16. The multiplexed integrating field spectrometer of claim 14, wherein each of the plurality of integrating field spectrometers receives light from a different light source.

17. The multiplexed integrating field-of-view spectrometer of claim 16, wherein each of the plurality of integrating field-of-view spectrometers comprises an array of integrating field-of-view spectrometers, and further comprising a field-of-view splitter to split light from each different light source to be incident on each of the array of integrating field-of-view spectrometers.

Images