Optical device and method

Abstract

A hyperspectral imaging apparatus (100) is provided, comprising an entrance element (102) for receiving a light field from a scene (106), an encoder (108), at least one dispersive element (110, 112), at least one array detector (114, 116), and a processor (118). The encoder (108) is arranged to receive at least a portion of the light field from the entrance element (102) and to transform it to provide a first encoded light field (120) and a second encoded light field (122) having different spatial patterns. The at least one dispersive element (110, 112) is arranged to apply a spectral shear to the first encoded light field (120) and the second encoded light field (122), respectively, to provide a first sheared light field (124) and a second sheared light field (126). The at least one array detector (114, 116) is arranged to detect the first sheared light field (124) and the second sheared light field (126). The processor (118) is arranged to process output information of the at least one array detector (114, 116) to determine a datacube (128) corresponding to a hyperspectral image of the scene.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a hyperspectral imaging apparatus and a hyperspectral image acquisition method. BACKGROUND

[0002] Hyperspectral imaging involves acquiring a three-dimensional datacube of a scene, collecting intensity through one spectral domain and two spatial domains. The datacube has the format I(x,y, ). Each slice of the datacube comprises an xy image corresponding to light of a particular wavelength. Conventional hyperspectral imagers rely on two main methods of capture: either a scanned 2D sensor is used to capture the datacube, or the spectral information to be retrieved is spatially multiplexed after processing. Scanned imagers are limited in direction and must be scanned (hence the name), a process that takes a considerable amount of time and introduces motion artifacts. Multiplexed imagers largely avoid the errors introduced by scanning, but require a large sacrifice of spatial information or complex sensors to achieve hyperspectral imaging. Multiplexed imagers have limited resolution and / or are difficult to manufacture.

[0003] In order to achieve single-shot hyperspectral capture and avoid the resolution sacrifice of multiplexed spectrometers, algorithmic imaging approaches have been attempted. The most famous example is the coded aperture snapshot spectral imager (CASSI) and its variants. CASSI relies on compressive sensing - a signal processing framework for reconstructing underdetermined linear systems. By processing the input signal into a format that can be used for compressive sensing reconstruction, CASSI can reconstruct a hyperspectral datacube from a signal obtained from a single exposure of a conventional two-dimensional detector. However, while CASSI achieves single-shot imaging without a significant sacrifice of spatial resolution or complex multiplexing, it can only capture datacubes at a limited resolution, with occasional artifacts.

[0004] It is an object of the present disclosure to overcome or at least ameliorate the disadvantages associated with known hyperspectral imaging apparatuses and hyperspectral imaging methods. SUMMARY

[0005] According to a first aspect of the present disclosure, there is provided a hyperspectral imaging apparatus comprising an entrance element for receiving a light field from a scene, an encoder, at least one dispersive element, at least one array detector, and a processor. The encoder is arranged to receive at least a portion of the light field from the entrance element and to transform it to provide a first encoded light field and a second encoded light field having different spatial patterns. The at least one dispersive element is arranged to apply a second spectral shear to the first encoded light field and the second encoded light field respectively to provide a first sheared light field and a second sheared light field. The at least one array detector is arranged to detect the first sheared light field and the second sheared light field. The processor is arranged to process output information of the at least one array detector to determine a datacube corresponding to a hyperspectral image of the scene.

[0006] The imaging apparatus can be configured to obtain a datacube from a single photograph (e.g. one frame of data from the first array detector and the second array detector). In some embodiments, the imaging apparatus can be configured to obtain a datacube from more than one photograph (e.g. from two photographs, three photographs or more).

[0007] Providing more than one coded pattern in the detected light field enables tomographic reconstruction of the original hyperspectral datacube, improving the fidelity of the method of capturing data based on a single coded pattern.

[0008] In some embodiments, more than two coded light fields can be provided and detected, for example there can be four different coded light fields (and each coded light field can have a different code).

[0009] In some embodiments, there can be a single detector and a reconfigurable coder apparatus. In such embodiments, the first spatial pattern and the second spatial pattern can be separated in time, with the coder being reconfigured between detection of the first and second sheared light fields. A single dispersive element can be used in such embodiments (e.g. between the reconfigurable coder and the single detector).

[0010] In other embodiments, the coder can be arranged to provide spatially separated first and second coded light fields.

[0011] The first and second light fields can comprise complementary spatial patterns (whether the first and second coded light fields are spatially or temporally separated). The complementary spatial patterns can be complementary random or pseudo-random spatial patterns.

[0012] The coder can be configured to reflect the first and second coded light fields in different directions.

[0013] Some embodiments can combine spatial and temporal separation of coded light fields, detecting temporally and spatially separated coded light fields (e.g. by a reconfigurable coder providing spatially separated first and second light fields, and collecting more than one photograph from the detector with different coder patterns).

[0014] Advantageously, the generation of first and second copies of light fields that are coded with complementary spatial patterns and separately sheared prior to detection provides higher fidelity in the datacube reconstruction. This is analogous to tomography, whereby the first and second copies effectively correspond to projections of the datacube in different directions, providing additional information about the datacube rather than using only a single sheared and coded copy. The combination of coding and shearing with detection of two or more copies can be referred to as compressed tomography.

[0015] The at least one dispersive element can comprise a first dispersive element configured to apply a first spectral shearing to the first encoded light field and a second dispersive element configured to apply a second spectral shearing to the second encoded light field.

[0016] The at least one dispersive element can be or comprise a transmissive dispersive element. One or both of the first and second dispersive elements can be a transmissive dispersive element.

[0017] The first and second spectral shearing can have different magnitudes.

[0018] The first and second spectral shearing can have different spatial directions.

[0019] The encoder can comprise a digital micromirror device, a static mask, a liquid crystal device (e.g. liquid crystal on silicon).

[0020] The encoder can be or comprise a transmissive encoder. Both the encoder and the at least one dispersive element can be transmissive. The use of transmissive components can make the hyperspectral imaging device more amenable to miniaturization, in particular when performing compressed tomography.

[0021] The encoder can comprise a first encoder portion configured to provide the first encoded light field and a second encoder portion configured to provide the second encoded light field. The first and second encoder portions can be provided on or along respective first and second discrete imaging paths. The first and second discrete imaging paths can be parallel to each other. The discrete imaging paths can avoid the need for reflective elements such as beam splitters, which can further make the hyperspectral imaging device more amenable to miniaturization.

[0022] The first and second dispersive elements can be provided on respective first and second discrete imaging paths.

[0023] The hyperspectral imaging device can further comprise a spectral encoder configured to spectrally encode the first and second sheared light fields prior to detection thereof by the at least one array detector. This enables the hyperspectral imaging device to encode in both the spatial and spectral domains. This provides additional degrees of freedom in the encoding, thus allowing a higher degree of incoherence (randomness) in the sampling of the datacube, and in turn can improve the reconstruction of the datacube.

[0024] The spectral encoder can comprise a first spectral encoder portion configured to spectrally encode the first sheared light field, and a second spectral encoder portion configured to spectrally encode the second sheared light field. The first and second spectral encoder portions can be provided on or along the respective first and second discrete imaging paths. The spectral encoder can be a transmissive encoder.

[0025] The at least one array detector can comprise a first array detector and a second array detector arranged to detect the first and second sheared light fields, respectively.

[0026] The hyperspectral imaging apparatus can further comprise a beam splitter and a third array detector, wherein the beam splitter is arranged between the entrance element and the encoder and is arranged to provide a portion of the light field to the third array detector and a remaining portion of the light field to the encoder.

[0027] The portion of the light field provided to the third array detector can be unsheared (or spectrally non-dispersed).

[0028] The hyperspectral imaging apparatus can further comprise a focusing or relay element between the entrance element and the encoder.

[0029] The focusing element can be arranged to image the scene onto the encoder.

[0030] The at least one dispersive element can comprise a concave grating.

[0031] The at least one dispersive element can comprise a combination of a focusing element (e.g. a refractive or reflective element) and a planar grating. The planar grating can comprise a transmissive grating, a double Amici prism, or the like.

[0032] The at least one dispersive element can be arranged to image the first and second sheared light fields onto the at least one array detector, respectively. For example, the first and second dispersive elements can be configured to image the first and second sheared light fields onto the first and second array detectors, respectively.

[0033] The encoder and the at least one dispersive element can be integrated as a single component. The single component can be configured to provide the first and second sheared light fields that are encoded. This can further enable the hyperspectral imaging apparatus to be more miniaturized.

[0034] The integrated encoder and the at least one dispersive element can comprise an encoding pattern provided on the at least one dispersive element. The at least one dispersive element can be a diffractive grating. The encoding pattern can be lithographically printed onto the at least one dispersive element.

[0035] The processor can be arranged to determine the datacube by solving a minimization problem.

[0036] The minimization problem can comprise a regularization term that promotes sparsity.

[0037] The processor can be arranged to solve a minimization problem of the form:

[0038]

[0039] where S1 is the signal detected by the first detector, S2 is the signal detected by the second detector, k1 and k2 are weighting factors, o1 and o2 are measurement operators that depend on the encoders and the first and second dispersive elements, φ(I) is a regularization term that promotes sparsity, a is a regularization parameter, and ||.|| denotes a norm l 2 I = I(x, y, l) is the datacube.

[0040] The processor can be further arranged to process output information of a third detector together with the output information of the first and second detectors to determine the datacube. In such embodiments, the processor can be arranged to solve a minimization problem of the form:

[0041]

[0042] where S1 is the signal detected by the first detector, S2 is the signal detected by the second detector, S3 is the signal detected by the third detector, k1, k2 and k3 are weighting factors, o1, o2 and o3 are measurement operators that depend on the encoders, the first and second dispersive elements and the beam splitter, φ(I) is a regularization term that promotes sparsity, a is a regularization parameter, and ||.|| denotes a norm l 2 I = I(x, y, l) is the datacube.

[0043] According to a second aspect of the disclosure, there is provided a method of hyperspectral image acquisition, comprising:

[0044] receiving a light field from a scene;

[0045] transforming the light field to provide a first encoded light field and a second encoded light field having different spatial patterns;

[0046] applying spectral shearing to the first and second encoded light fields respectively to provide first and second sheared light fields;

[0047] detecting the first and second sheared light fields respectively to provide detection data; and

[0048] processing the detection data to determine a datacube corresponding to a hyperspectral image of the scene.

[0049] Features of any aspect, including optional features, can be combined as appropriate with features of any other aspect. Features described with reference to the imaging apparatus of the first aspect can be used in the method of the second aspect (e.g. the method can obtain a datacube from a single photograph etc.). BRIEF DESCRIPTION OF DRAWINGS

[0050] Example embodiments will be described, by way of example only, with reference to the accompanying drawings in which:

[0051] Figure 1 is a schematic diagram of a hyperspectral imaging apparatus according to an embodiment of the disclosure;

[0052] Figure 2 is a schematic diagram of a hyperspectral imaging apparatus according to another embodiment;

[0053] Figure 3 shows another embodiment of a hyperspectral imaging apparatus 300;

[0054] Figure 4 shows another embodiment of a hyperspectral imaging apparatus 400; and

[0055] Figure 5 shows an embodiment of a hyperspectral imaging apparatus 500.

[0056] It should be noted that the drawings are diagrammatic and are not drawn to scale. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments. DETAILED DESCRIPTION

[0057] Figure 1 A hyperspectral imaging apparatus 100 according to an embodiment of the disclosure is shown. The hyperspectral imaging apparatus 100 is capable of single-shot hyperspectral imaging. The hyperspectral imaging apparatus 100 comprises an entrance element 102 for receiving a light field 104 from a scene 106, an encoder 108, a first dispersive element 110 and a second dispersive element 112, a first array detector 114 and a second array detector 116, and a processor 118.

[0058] The entrance element 102 can comprise an aperture (e.g. or a slit) and is configured to direct light from the scene towards the encoder 108.

[0059] The encoder 108 is arranged to receive at least a portion of the light field 104 from the entrance and transform it to provide spatially separated first encoded light field 120 and second encoded light field 122, the first and second encoded light fields 120, 122 having complementary binary spatial patterns. The encoder 108 can be a binary encoder comprising an array of reflective elements (e.g. mirrors) that direct light in a first direction 120 or in a second direction 122 different from the first direction 120. For example, the encoder 108 can be composed of a plurality of first type of reflective elements and a plurality of second type of reflective elements. There can be a similar (e.g. equal) number of first type of reflective elements and second type of reflective elements, but this is not essential. The first type of elements can be configured to reflect light incident on the encoder 108 in the first direction 120. The second type of elements can be configured to reflect light incident on the encoder 108 in the second direction 122. Light reflected in the first direction 120 comprises the first encoded light field, light reflected in the second direction comprises the second encoded light field.

[0060] In some embodiments, the reflective elements can be fixed (e.g. the encoder 108 can comprise a fixed mirror array). In other embodiments, the pattern of first type of reflective elements and second type of reflective elements can be reconfigurable. For example, the encoder 108 can comprise a movable micro-mirror array, such as a digital micro-mirror device (which can be moved rapidly between a first angular position and a second angular position). A reconfigurable encoder 108 can be advantageous because additional information about a relatively slowly changing scene can be obtained by using different encoding patterns and combining the resulting data in order to obtain a hyperspectral image cube (i.e. using more than one shot).

[0061] In other embodiments, the encoder 108 can not be fully reflective. For example, in some embodiments, a beam splitter can be used to provide light to a first aperture array and a second aperture array complementary to the first array. The encoder in such embodiments comprises a first aperture array and a second aperture array. In some embodiments, a partially reflective encoder can be employed in which a portion (e.g. 50%) of the incident light is encoded and transmitted and another portion of the incident light is encoded and reflected.

[0062] Returning to Figure 1 The first and second dispersive elements 110, 112 are arranged to apply first and second spectral shears to the first and second encoded light fields, respectively, to provide first and second sheared light fields 124, 126. The dispersive elements 110, 112 can comprise reflective dispersive elements, such as diffraction gratings, but any dispersive elements (including transmissive dispersive elements) can be used. It can be advantageous for the first and second spectral shears to be different (e.g. positive and negative), but this is not essential.

[0063] The first and second dispersive elements 110 and 112 can be curved diffraction gratings configured to image the first and second sheared optical fields onto respective detectors. In other embodiments, the first and second dispersive elements 110 and 112 can each include a flat diffraction grating and a focusing element (e.g., a lens or mirror), where the focusing element is configured to image the sheared optical field onto the detector.

[0064] The first and second array detectors 114 and 116 are arranged to detect the first and second sheared optical fields, respectively. The processor 118 is arranged to process the output information of the first and second detectors 114 and 116 to determine a datacube 128 corresponding to a hyperspectral image of the scene.

[0065] The two sheared optical fields 124, 126 can be represented as:

[0066]

[0067]

[0068] where the subscripts 1 and 2 represent the first and second sheared optical fields, respectively, and the coefficient a represents system aberrations and filtering, and the coefficient c represents the dispersion from the respective dispersive element. Note that the coefficients c1 and c2 do not need to have opposite signs. I represents the input datacube I(x, y, l).

[0069] The reconstruction of the hyperspectral datacube 128 can be performed by the processor 118. The data acquisition process can be represented as:

[0070] [S1, S2] T = [k1o1, k2o2] T I(x, y, l) (3)

[0072] where S is the signal detected at the respective detector, the coefficient k is a scaling factor to balance the intensity difference between the signals, and “o” represents the measurement operator of the signal. The image reconstruction within the compressive sensing framework can be performed by solving the minimization problem:

[0073]

[0074] where φ(I) is a regularization term that promotes sparsity, a is a regularization parameter, and ||.|| represents the l 2 norm. I = I(x, y, l) is the datacube. The minimization problem presented in (4) can be solved using existing methods (e.g., TwIST, LASSO, wavelet deconvolution, etc.).

[0075] Using a complementary coding scheme with two detectors enables to obtain a hyperspectral image in a single shot, where no incident light is wasted, and this enables to achieve efficient tomographic reconstruction of the hyperspectral datacube, since the coding of the light detected at the first and second detectors is complementary.

[0076] Figure 2 Another embodiment 200 is shown, in which also a beamsplitter 130 is provided. Further, lenses 134, 136 are included (not all lenses are labeled). Figure 1 The description of elements with the same reference numbers in Figure 2 .

[0077] The beamsplitter 130 splits the light field 104 into a first part 104a and a second part 104b. The second part 104b is directed to the encoder 108, while the first part 104a is directed to a third array detector 132. The third array detector 132 can be configured to take a direct image (i.e. the sum of intensities from an unclipped image over the full spectral range at each x,y pixel position). The signal detected by the third detector can be denoted as:

[0078]

[0079] The data acquisition process with the additional third detector can be denoted as:

[0080] [S1, S2,, S3] T = [k1o1, k2o2, o3] T I(x,y,λ) (6)

[0082] Reconstruction of the image datacube can be done by solving a minimization problem (which uses similar notation as (4)):

[0083]

[0084] In the embodiment of Figure 2 , a focusing lens 134 is shown, which focuses the light from the entrance 102 at the encoder 108 and the third detector 132. Such a focusing lens can also be used in the embodiment of Figure 1 , to focus the light at the encoder 108. Although a refractive lens is shown, a focusing element including a reflector can be used instead.

[0085] Adding a third detector that obtains a direct image provides more information for the reconstruction of the hyperspectral datacube. This direct image can also be directly visually compared to the output datacube to ensure that this is correct.

[0086] Figure 2 Also shown in FIG. 1 is two focusing lenses 136 for each optical path from the encoder 108 to the first array detector 114 and the second array detector 116. In Figure 1 A similar lens arrangement can also be used in the embodiment of FIG. 2. The lens between the encoder 108 and the first dispersive element 110 collimates the light from the encoder 108 at the first dispersive element 110. The other lens 136 between the first dispersive element 110 and the first array detector 114 focuses the light from the first diffraction element 110 at the first array detector 114. A similar arrangement is used for the other detection path (to the second array detector 116).

[0087] Preferably, the lenses are matched to a focal length f2 such that the distance from the dispersive elements 110, 112 to the encoder 108 and array detectors 114, 116 is the same (the lenses are placed midway between the encoder and the dispersive elements, and midway between the dispersive elements and the first array detector).

[0088] Although refractive lenses are depicted in the example embodiments of Figure 2 FIGS. 1 and 2 (which can be readily available, compact and low cost), reflective elements can alternatively be used, which can be advantageous as they will tend to not introduce any unwanted dispersion.

[0089] Figure 3 Another embodiment of a hyperspectral imaging apparatus 300 is shown. Figure 1 and Figure 2 The description of elements having the same or similar reference numerals in Figure 3 . The hyperspectral imaging apparatus 300 comprises an entrance element 102 for receiving a light field 104 from a scene 106, an encoder 308, first and second dispersive elements 310, 312, a first array detector 114, a second array detector 116 and a third array detector 132, and a processor 118. The hyperspectral imaging apparatus 300 works using the same principles as the hyperspectral imaging apparatuses 100, 200 described above, but utilises transmissive components instead of reflective components. By avoiding the use of reflective components (such as digital micromirror devices, beam splitters and reflective diffraction gratings), the use of transmissive components can make the hyperspectral imaging apparatus 300 more compact (and potentially lower cost), particularly when performing compressed tomography.

[0090] In the illustrated embodiment, the hyperspectral imaging device 300 includes a separate first discrete imaging path 301a, a separate second discrete imaging path 301b, and a separate third discrete imaging path 301c from the scene 106 to respective array detectors 114, 116, 132. In the illustrated embodiment, the discrete imaging paths 301a, 301b, 301c are parallel to one another to avoid the need for a beamsplitter, which can further enable the hyperspectral imaging device 300 to be more miniaturized. The arrow directions along each imaging path 301a, 301b, and 301c from the entrance element 102 are illustrative in nature and do not necessarily show the physical path of light through the hyperspectral imaging device 300.

[0091] The encoder 308 includes a first encoder portion 308a and a second encoder portion 308b. The first encoder portion 308a operates as part of the first discrete imaging path 301a with the first dispersive element 310 and the first array detector 314. In the illustrated embodiment, an imaging lens 340a is located between the entrance element 102 and the first encoder portion 308a, and a relay lens 342a is located between the first encoder portion 308a and the first dispersive element 310. In other embodiments, the imaging lens 340a and the relay lens 342a can be omitted. Similarly, the second encoder portion 308b operates as part of the second discrete imaging path 301b with the second dispersive element 312 and the second array detector 116. In the illustrated embodiment, an imaging lens 340b is located between the entrance element 102 and the second encoder portion 308b, and a relay lens 342b is located between the second encoder portion 308b and the second dispersive element 312. In other embodiments, the imaging lens 340b and the relay lens 342b can be omitted.

[0092] The first encoder portion 108a and the second encoder portion 108b are each arranged to receive at least a portion of the light field 104 from the entrance element 102 and transform it to provide respective first encoded light fields 120 and second encoded light fields 122. The first encoded light fields 120 and the second encoded light fields 122 have different spatial patterns. In the illustrated embodiment, the first encoder portion 308a and the second encoder portion 308b are transmissive encoders, such as first and second arrays of apertures or masks. In some embodiments, the first encoder portion 308a and the second encoder portion 108b are complementary to one another to produce the first encoded light fields 120 and the second encoded light fields 122 that include complementary spatial patterns, although this is not required.

[0093] The first and second dispersive elements 110 and 112 are arranged to apply first and second spectral shears to the first and second encoded light fields 120 and 122, respectively, to provide first and second sheared light fields 124 and 126. In the illustrated embodiment, the first and second dispersive elements 110 and 112 are each transmissive dispersive elements, such as transmissive diffraction gratings. It can be advantageous for the first and second spectral shears to be different (e.g., positive and negative), but this is not required.

[0094] The first and second array detectors 114 and 116 are arranged to detect the first and second sheared light fields 124 and 126, respectively. The processor 118 is arranged to process the output information of the first and second detectors 114 and 116 to determine a datacube 128 corresponding to a hyperspectral image of the scene. The processor 118 can reconstruct the hyperspectral datacube 128 according to Equations (1) through (7) discussed above.

[0095] A third discrete imaging path 301c extends from the entrance optic to a third array detector 132, which provides a direct image of the scene 106, which provides more information for the reconstruction of the hyperspectral datacube 128. The direct image is directly visually compared to the output datacube 128 to ensure that the datacube 128 is correct. In the illustrated embodiment, an imaging lens 340c is positioned between the entrance optic 102 and the third array detector 132. In some embodiments, the imaging lens 340c can be omitted. In some embodiments, the third imaging path 301c can not be present, or can not be utilized.

[0096] Figure 4 Another embodiment of a hyperspectral imaging apparatus 400 is shown. The hyperspectral imaging apparatus 400 is substantially similar to the hyperspectral imaging apparatus 300 described above, although imaging and relay lenses are not shown.

[0097] The hyperspectral imaging apparatus 400 further comprises a spectral encoder 440. The spectral encoder 440 is configured to spectrally encode the first and second sheared light fields 124, 126 prior to detection by the first and second array detectors 114, 116, respectively. In the illustrated embodiment, the spectral encoder 440 is arranged in the first and second imaging paths 301a, 301b after the respective dispersive elements 310, 312. In the illustrated embodiment, similar to the encoder 308, the spectral encoder 440 comprises a first spectral encoder portion 440a configured to spectrally encode the first sheared light field 124, and a second spectral encoder portion 440b configured to spectrally encode the second sheared light field 126. The first spectral encoder portion 440a works as part of the first imaging path 301a, while the second spectral encoder portion 440b works as part of the second imaging path 301b. In some embodiments, the first and second spectral encoder portions 440a, 440b are complementary to each other, although this is not essential.

[0098] In the illustrated embodiment, the spectral encoder 440 is a transmissive encoder, such as one or more aperture arrays. As mentioned above, the use of transmissive components can make the hyperspectral imaging apparatus 400 more amenable to miniaturization. In other embodiments, the spectral encoder can be a reflective encoder, such as a digital micromirror device.

[0099] The hyperspectral imaging apparatus 300 described above only uses the encoder 308 for encoding in the spatial domain. The spectral encoder 440 in combination with the encoder 308 enables the hyperspectral imaging apparatus 400 to encode in both the spatial and spectral domains. The additional degree of freedom in the encoding can allow a higher degree of incoherence (randomness / orthogonality) in the sampling of the datacube 128, which can improve the reconstruction.

[0100] Alternatively, the spectral encoder 440 can be used independently of the encoder 308 (which can be omitted from the hyperspectral imaging apparatus 400) in order to provide spectral encoding only. It will also be appreciated that a spectral encoder, such as the spectral encoder 440, can be implemented in the hyperspectral imaging apparatuses 100, 200 described above. The spectral encoder can be implemented as a single spectral encoder, or as multiple spectral encoder portions. For example, if the first and second encoded light fields 120, 122 (and hence the first and second sheared light fields 124, 126) are separated in time, a single spectral encoder 440 can be employed to spectrally encode the first and second sheared light fields 124, 126.

[0101] In the above embodiments, the encoding and the dispersion are performed by two separate, individual components, namely the encoders 108, 308 and the at least one dispersive element 110, 112, 310, 312. Figure 5 An embodiment of a hyperspectral imaging apparatus 500 is shown. The hyperspectral imaging apparatus 500 is similar to the embodiments shown in Figure 3 and Figure 4 .

[0102] However, in the embodiment shown in Figure 5 , the encoders 308 and the at least one dispersive element 310, 312 are integrated as a single component. This single component is an integrated encoder and dispersive element 550. The integrated encoder and dispersive element 550 provides a first encoded and sheared light field 552 and a second encoded and sheared light field 554. Effectively, the integrated encoder and dispersive element 550 provides both the first encoded light field 120 and the first sheared light field 124 as a single first encoded and sheared light field 552 (and correspondingly provides both the second encoded light field 122 and the second sheared light field 126 as a single second encoded and sheared light field 554).

[0103] In the embodiment shown, the first encoder portion 308a and the first dispersive element 310 on the first imaging path 301a have been replaced by a first integrated encoder and dispersive element 550a (and correspondingly, the second encoder portion 308b and the second dispersive element 312 on the second imaging path 301b have been replaced by an integrated encoder and dispersive element 550b).

[0104] In the embodiment shown, the integrated encoder and dispersive element 550 is a transmissive component. In some embodiments, the integrated encoder and dispersive element 550 can comprise a dispersive element (e.g., a diffractive grating, such as a transmissive diffractive grating) having an encoding pattern disposed thereon (e.g., using a photolithography process).

[0105] The integrated encoder and dispersive element 550 shortens the beam path in the discrete imaging paths 301a, 301b of the hyperspectral imaging apparatus 500, which can further enable the hyperspectral imaging apparatus 500 to be more miniaturized.

[0106] Optionally, a spectral encoder, such as the spectral encoder 440 described above, can be used in conjunction with the integrated encoder and dispersive element 550 in order to encode in both the spatial domain and the spectral domain.

[0107] Although the appended claims set forth particular combinations of features, it is understood that the scope of the disclosure of the present application extends to any novel feature or any novel combination of features disclosed herein, either explicitly or implicitly, whether or not it is referred to in a claim, and whether it is the same as any of the same features or combinations of features currently claimed in any claim, and whether it ameliorates any of the same technical problems as any of the same features or combinations of features currently claimed in any claim.

[0108] Features described in the context of separate embodiments can also be provided in combination in a single embodiment. Conversely, various features described in the context of a single embodiment can also be provided separately or in any suitable sub-combination. It is intended that each of the features reported herein can be addressed individually or in any combination by a claim in this or in any other patent application that issues from this application.

[0109] For the sake of completeness, it is also stated that the term "comprising" does not exclude other elements or steps, that the term "a" or "an" does not exclude a plurality, and that a reference to an item does not preclude that there is more than one of the same item present.

Claims

1. A hyperspectral imaging apparatus comprising an entrance for receiving a light field from a scene, an encoder, at least one dispersive element, at least one array detector, and a processor, wherein: the encoder is arranged to receive at least a portion of the light field from the entrance and to transform it to provide a first encoded light field and a second encoded light field having different spatial patterns; at least one dispersive element is arranged to apply a spectral shear to the first and second encoded light fields respectively to provide a first sheared light field and a second sheared light field; wherein the at least one dispersive element comprises a first dispersive element configured to apply a first spectral shear to the first encoded light field and a second dispersive element configured to apply a second spectral shear to the second encoded light field; at least one array detector is arranged to detect the first and second sheared light fields; wherein the at least one array detector comprises a first array detector and a second array detector arranged to detect the first and second sheared light fields respectively; and the hyperspectral imaging apparatus further comprises a third array detector arranged to receive an un-sheared portion of the light field; the processor is arranged to process output information from the third array detector together with output information from the at least one array detector to determine a datacube of a hyperspectral image corresponding to the scene.

2. The hyperspectral imaging device of claim 1, wherein, the encoder is arranged to provide spatially separated first and second encoded light fields having complementary spatial patterns.

3. The hyperspectral imaging apparatus of claim 2, wherein, the complementary spatial patterns are complementary random or pseudo-random spatial patterns, and / or wherein the spatial patterns are binary.

4. The hyperspectral imaging apparatus of claim 1, further comprising a beamsplitter, wherein, the beamsplitter is arranged between the entrance and the encoder and is arranged to provide a portion of the light field to the third array detector and a remaining portion of the light field to the encoder.

5. The hyperspectral imaging device of claim 1, wherein, the spectral shears applied to the first and second encoded light fields have different magnitudes and / or different spatial directions.

6. The hyperspectral imaging device of claim 1, wherein, the encoder comprises a digital micromirror device.

7. The hyperspectral imaging device of claim 1, wherein, one or both of the encoder and the at least one dispersive element are transmissive.

8. The hyperspectral imaging device of claim 1, wherein, the encoder comprises a first encoder portion configured to provide the first encoded light field and a second encoder portion configured to provide the second encoded light field.

9. The hyperspectral imaging device of claim 8, wherein, the first encoder portion is disposed on a first discrete imaging path and the second encoder portion is disposed on a second discrete imaging path.

10. The hyperspectral imaging device of claim 9, wherein, the first dispersive element is disposed on the first discrete imaging path and the second dispersive element is disposed on the second discrete imaging path.

11. The hyperspectral imaging device of claim 9, wherein, the first and second discrete imaging paths are parallel to each other.

12. The hyperspectral imaging apparatus of claim 9, further comprising a spectral encoder arranged to spectrally encode the first and second sheared light fields prior to detection of the first and second sheared light fields by the at least one array detector.

13. The hyperspectral imaging device of claim 12, wherein, The spectral encoder comprises a first spectral encoder portion configured to spectrally encode the first sheared light field and a second spectral encoder portion configured to spectrally encode the second sheared light field.

14. The hyperspectral imaging device of claim 13, wherein, The first spectral encoder portion is disposed on the first discrete imaging path and the second spectral encoder portion is disposed on the second discrete imaging path.

15. The hyperspectral imaging device of claim 12, wherein, The spectral encoder is a transmissive encoder.

16. The hyperspectral imaging apparatus of claim 1, further comprising a focusing element between the entrance element and the encoder.

17. The hyperspectral imaging device of claim 16, wherein, The focusing element is arranged to image the scene onto the encoder.

18. The hyperspectral imaging apparatus of claim 1, wherein, The at least one dispersive element comprises at least one concave grating.

19. The hyperspectral imaging apparatus of claim 1, wherein, At least one of the dispersive elements is formed by a combination of a focusing element and a planar grating.

20. The hyperspectral imaging device of claim 18, wherein, The at least one dispersive element is arranged to image the sheared light fields onto the at least one detector, respectively.

21. The hyperspectral imaging apparatus of claim 1, wherein, The encoder and the at least one dispersive element are integrated into a single component.

22. The hyperspectral imaging device of claim 21, wherein, The single component integrating the encoder and the at least one dispersive element comprises an encoding pattern disposed on a diffractive grating.

23. The hyperspectral imaging apparatus of claim 1, wherein, The processor is arranged to determine the datacube by solving a minimization problem.

24. The hyperspectral imaging device of claim 23, wherein, The minimization problem comprises a regularization term that promotes sparsity.

25. The hyperspectral imaging device of claim 23, wherein, The processor is arranged to solve a minimization problem of the form: where S1 is the signal detected by the first array detector, S2 is the signal detected by the second array detector, k1 and k2 are weighting factors, o1 and o2 are measurement operators depending on the encoder and the first and second dispersive elements, φ(I) is a regularization term that promotes sparsity, a is a regularization parameter, and ||.|| denotes the l-norm 2 , I = I(x, y, l) being the datacube.

26. The hyperspectral imaging apparatus of claim 4, wherein, The processor is arranged to solve a minimization problem of the form: where S1 is the signal detected by the first array detector, S2 is the signal detected by the second array detector, S3 is the signal detected by the third array detector, k1, k2 and k3 are weighting factors, o1, o2 and o3 are measurement operators depending on the encoder, the first and second dispersive elements and the beam splitter, φ(I) is a regularization term that promotes sparsity, a is a regularization parameter, and ||.|| denotes the norm l 2 , I = I(x, y, l) being the datacube.

27. A method of hyperspectral image acquisition, comprising: receiving a light field from a scene; transforming the light field to provide a first encoded light field and a second encoded light field having different spatial patterns; applying spectral shearing to the first and second encoded light fields, respectively, to provide first and second sheared light fields; detecting the first and second sheared light fields and a third un-sheared light field, respectively, to provide detection data; and processing the detection data to determine a datacube corresponding to a hyperspectral image of the scene.

28. The method of claim 27, wherein, The first and second sheared light fields have different magnitudes and / or different spatial directions.

29. The method of claim 27, further comprising determining the datacube by solving a minimization problem.

30. The method of claim 29, wherein, The minimization problem comprises a regularization term that promotes sparsity.

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