CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to US Provisional Application 62/870,364 filed My 3, 2019, the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

This disclosure generally relates to an apparatus and method for recording a hologram for an object derived from electromagnetic radiation received from the object, and more particularly to the processing of the recorded hologram and reconstruction of super-resolved image data describing the object.

BACKGROUND

Conventional imaging forms images of objects, wherein the image contains intelligible data only about a single plane of the object. Holographic imaging methods record intelligible data about multiple planes of an object in single two-dimensional image recording but require complex illumination methods and carefully controlled imaging conditions. To overcome this, FINCH (Fresnel Incoherent Correlation Holography) creates holograms from the received light from an object, without requiring the light to be coherent, and without placing other constraints on the imaging environment. However, FINCH may require wavelength calibration of optical components used for shifting the phase of the recorded light patterns, as well as recordings of multiple phase-shifted light patterns (phase factors).

SUMMARY OF EXAMPLE EMBODIMENTS

A method of performing FINCH holography that avoided wavelength calibration for phase shifting and could record multiple phase factors in a single exposure would provide great advantages over previous FINCH holographic technology.

Accordingly, one object of the present disclosure is to provide an apparatus in which light received from the object is transformed into a plurality of co-linear co-propagating beams, each of which carries information about the object and each of which has a unique spherical phase curvature (focal length). The plurality of beams is caused to interfere in multiple phase factors without requiring wavelength calibration for the control of the phase factor. Subsequently, the multiple interference pattern phase factors are recorded sequentially and then processed to form the hologram of the object and an image of the object derived from the hologram.

Another object of the present disclosure is an apparatus in which light received from the object is transformed into a plurality of colinear copropagating beams, each of which carries information about the object and each of which has a unique spherical phase curvature (focal length). The plurality of beams is caused to interfere in multiple phase factors without requiring wavelength calibration for the control of the phase factor. The multiple phase factors of the interference are recorded in a single image capture. Subsequently, the interference patterns thus recorded are processed to form the hologram of the object and an image of the object derived from said hologram.

Another object of the present disclosure is an apparatus that produces two geometrically separated interference recordings from light received from an object. Each interference recording contains data sufficient to produce the hologram of the object. The concurrently recorded interference recordings are processed together to increase the signal-to-noise ratio of the hologram.

Another object of the present disclosure is a calibration-free apparatus to create super resolution images of an object or scene in a single exposure, the apparatus comprising an optical assembly to receive light from an object, transform said light into a pair of differentially focused beams with orthogonal circular polarizations, and cause a recording of the interference of the two beams at an image recording plane; wherein the transformation of the light is accomplished by the application of a birefringent lens, and wherein the conversion to circularly polarized light beams is accomplished by a broadband quarter-wave plate, and wherein the interference is created by directing the beam pair to an image detector in which every pixel is registered to a micro-polarizer array containing multiple sets of polarizer elements with predefined linear polarization orientations, wherein the interference recording is further processed computationally to recover the object hologram and super-resolved image.

One skilled in the art will realize that the above objects of the disclosure are discussed in terms of light but that the concepts therein apply to electromagnetic radiation of any other wavelength as well. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic depicting the formation of FINCH holograms of a point in a sample object.

Figure 2 is a schematic depicting the formation of two differentially focused beams from a single beam received by a birefringent lens.

Figure 3 recordings of FINCH holograms of a laser beam.

Figure 4a illustrates an example embodiment using birefringent lenses and a quarter-wave plate to create differentially focused circularly polarized beams from received light, and a single polarizing element to bring the two beams to interfere.

Figure 4b illustrates an example embodiment using birefringent lenses and a quarter-wave plate to create differentially focused circularly polarized beams from received light, and an array of polarizing elements to cause interference of the beams.

Figure 5a illustrates recordings of a FINCH holograms of a laser beam performed by a device of the type of embodiment in Fig. 4a.

Figure 5b illustrates phase images and respective histograms of microscopic beads imaged with a prior-art embodiment of FINCH and with a FINCH device of the type of embodiment in Figure

4b

Figure 6 illustrates an example embodiment with two identical optical trains of the type of the embodiment in Fig. 4b, each receiving a single linear polarization from a linear polarizer operating on the received light from the object.

Figure 7 illustrates a pixelated imaging sensor, divided into sampled regions for both polarization of received light and wavelength of received light.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Inventors of the subject matter in this disclosure include an inventor of the Fresnel Incoherent Correlation Holography (FINCH) techniques and systems that are described in, for example, US Patent # 8,179,578 filed July 18, 2006. The inventors of FINCH also published several papers describing the FINCH system and technique. See, for example, Joseph Rosen and Gary Brooker,“Digital spatially incoherent Fresnel holography”, Optics Letters, Vol. 32, No. 8, April 15, 2007. The contents of US Patent # 8, 179,578 and the publication“Digital spatially incoherent Fresnel holography” noted above are each incorporated by reference in their respective entireties. However, a brief description of FINCH is provided below for convenience.

FINCH is a single beam interferometric method that can create an interference pattern (also referred to as a hologram or a recorded hologram or a raw hologram) from visible light or any kind of electromagnetic radiation, either incoherent or coherent. In order to obtain a complex-valued 3D image representation of a scene captured by the FINCH technique (also referred to as a complex hologram), a plurality of holograms must be recorded. This plurality of recorded holograms or interference patterns must include at least two“phase shifted” holograms, each with a unique phase factor. The plurality of holograms is typically obtained in a serial manner or in a parallel manner by a variety of beam-splitting techniques.

Figure 1 illustrates a generalized FINCH imaging system. An object (also referred to as sample) 101 emits or reflects light toward the FINCH optical system 102, which receives the light through a lens or other aperture and produces (from any single received beam of light) two co-propagating beams (e.g. 103, 104) with distinct phase curvatures. The two co-propagating beams are directed to a recording device in a manner that allow them to produce an interference pattern 105, which is then recorded by an image recording device (not shown) and stored 106 for subsequent calculated reconstruction of the image 107 computed in a computing device 108.. As noted above, multiple phase-shifted interference patterns (raw holograms) are recorded and stored for use in creating a complex hologram and calculated reconstructed images. The method of formation of the complex hologram and the reconstruction process are described in detail in references 1-5, 7-9 and are thus saved from detailed reiteration here. Briefly, the recorded holograms with different phase factors are super-imposed on each other in a computing device by the following operation:

H _F = åp= H _n (x, y) [exp (iifln-i) - exp( ± W _n+1 )]; (equation 1) wherein HF is the complex hologram, H _n are the raw or recorded holograms (interference patterns), and n the index of the phase shift of a given raw hologram, with / phase shifted images, and q _h _-, , for n= 1, and q _h+1 = Q ₁ , for n=n _max. The complex hologram is then reconstructed into a 2D image s representing a single in-focus plane by one of a number of different computational operations. One common method is Fresnel Propagation, exemplified in the following equation: (equation 2)

wherein the asterisk represents a 2D convolution operation, z _rec is the desired distance of the in focus plane at which the hologram is to be reconstructed, and the exponential term is a propagation function for optical propagation by a distance of Other image reconstruction methods may be applied, including angular spectrum reconstruction, image inversion, compressive sensing and deep learning computations, amongst others. The reconstructed image is then displayed on a computer monitor or other suitable display device Note that equation 2 or another reconstruction operation may be repeated many times for any different irec as desired to create a three-dimensional collection of images.

One of the unique aspects of FINCH is that, unlike interferometric techniques which require a“test beam” (also referred to as sample beam or signal beam) and a“reference beam” to be interfered with each other, FINCH uses two test beams to be interfered with one another.

FIG. 32 in the above noted US Patent # 8, 179,578 illustrates a typical conventional non-FINCH holographic system. In said FIG. 32, 9012 is the reference beam and 9010 is the test or sample beam.

In interferometry, the test beam is the light that returns from the sample (also referred to as object) being measured. In many interferometers, all the information about the sample being investigated is included in the test beam. The reference beam, in contrast, is a well-characterized beam that is either brought directly from the source (for example a single mode laser beam) or which returns from a well-characterized standard reference. The reference beam carries no information about the sample.

For example, if it was desired to see what shape (e.g. how flat) a newly made mirror is, it is possible to use an interferometer to compare it to a mirror that is known to be perfectly flat. The new mirror (e.g. the sample) is placed in one leg of an interferometer, and the perfect mirror in another leg of the interferometer (e.g. the reference leg). A light source is then directed through the interferometer to create interference between the light that returns from each leg. Since there is precise knowledge of what the beam from the reference leg should look like, the interference pattern that is actually obtained contains information about any differences in the shape of the test mirror. Any deviations from a perfect interference pattern can only be attributed to the new mirror, and it is possible to calculate what the test mirror shape must be.

The use of two test beams, as in FINCH, is better than the use of a test beam and a reference beam at least because: both test beams carry information about the sample, and therefore their interference enables super-resolution of up to twice the standard resolution of the single test beam case and single reference beam case; and with two test beams, all of the light from the sample and no non-informative reference light is used to form the interference with maximum interference efficiency, resulting in the maximum possible signal and minimum possible background.

Some inventors of the subject matter described in this application subsequently improved upon the original FINCH technique described in US Patent # 8,179,578, leading to, in one particular improved implementation, using one or more birefringent lenses in association with FINCH in order to achieve super resolution in the obtained holographic images. US patent #10,228,655 (which claims priority to US Provisional Application 61/886,064 filed on Oct 3,

2013) describes FINCH using a liquid crystal lens (which is also birefringent). The use of a birefringent crystal lens in FINCH was described in a provisional application that was filed May 1, 2014, which claimed priority to US. Patents 10,289,070, 10,423,123, and 10,591,870. This novel use of a birefringent lens in FINCH was also described in Nisan Siegel, Vladimir Lupashin, Brian Storrie and Gary Brooker,“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers”, Nature Photonics, 14 November 2016. The contents of US patents 10,228,655, 10,289,070, 10,423,123, and 10,591,870 and US patent application 20170185036, and“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers” are each incorporated by reference in their respective entireties.

In the current state of the art FINCH using birefringent lenses (e.g. see Figure 2), the two co-propagating beams 103, 104 are produced by polarizing the incoming light 201 at an input polarizer 202 before it reaches the FINCH birefringent lens assembly 203 so that the light is polarized and +45° and -45° relative to the ordinary and extraordinary refractive indices of the birefringent optics. The birefringent lens assembly 203 includes at least one birefringent lens as well as any other optics necessary to transform the beam, including chromatic correction lenses, standard converging or diverging lenses, birefringent compensating optics, and any other optics necessary to achieve the interference of the beams as well as a final image that is free of aberrations. The birefringent optic thus separates the incoming beam into two outgoing beams, polarized along the ordinary and extraordinary refractive indices, each with its own phase curvature that is a function of the incoming phase curvature and the birefringent lens curvature and respective refractive index. Subsequent to the birefringent lens assembly 203, the overall phase of one of the beams is changed by a dynamic and variable phase-shifting optic 204 before both beams are passed through an output polarizer 205 that projects parts of both beams along a common axis to permit mutual interference at the interference recording plane 206. Sequential images with differing phase shifts (created by the dynamic phase-shifting optic) are recorded and used to calculate images free from the effects of bias and twin image noise that are

characteristics of on-axis holograms. Generally, the phase shifting optic used is a variable waveplate that delays light of either the ordinary or extraordinary polarization before it reaches the output polarizer. An example hologram of a laser beam taken with such a system is shown in Figure 3, displaying three“raw” phase shifted holograms 301, 302, 303 as well as the recovered amplitude 304 and phase 305 of the complex hologram.

The present inventors realized that the already improved super resolution provided by birefringent lens-equipped FINCH can be further enhanced by acquiring at least a required minimum number of“phase shifted” holograms simultaneously, instead of serially as in the previous implementations. It should be noted that, although embodiments are described in relation to birefringent lens-equipped FINCH, certain other improvements by one or both of the present inventors introducing the use of polarization to the originally proposed FINCH, such as, for example, STM (spatial light modulator) or GRIN (gradient refractive index) lens equipped FINCH, may also be further enhanced by acquiring at least a required minimum number of “phase shifted” holograms simultaneously.

Some techniques have been proposed by others for achieving multiplexed recording of phase shifted interference patterns in a single image capture (also referred to as“single shot” or “single exposure”) by using a different polarization scheme in the raw hologram formation. Examples are: Nobukawa T, Muroi T, Katano Y, Kinoshita N, Ishii N,“Single-shot phase- shifting incoherent digital holography with multiplexed checkerboard phase gratings”, Optics Letters 43 (S) 1698 (2018); Choi K, Yim J, Min S-W,“Achromatic phase shifting self- interference incoherent digital holography using linear polarizer and geometric phase lens”, Optics Express 26(13) 16212 (2018); Awatsuji Y, Fujii A, Kubota T, Matoba O,“Parallel three- step phase-shifting digital holography”, Applied Optics 45(13) 2995-3002 (2006); Millerd J, Brock N, Hayes J, North-Morris M, Novak M, Wyant J,“Pixelated phase-mask dynamic interferometer”, Proceedings of SPIE Vol 5531 Issue 520 p 304-314 (2004); U S. Patent 8,351,048; US patent 6,304,330; US patent 7,230,717; US patent 7,777,895. Many of these single shot techniques, however, have drawbacks in that they often require image registration that is difficult to achieve, or difficult optical geometries, all of which reduce image resolution. Moreover, many of these single shot systems proposed previously require a test beam and a reference beam.

FINCH is a form of self-interference interferometry in which the interference is created from two copies of the beam coming from the sample, i e. two test beams. FINCH, while an interferometer with orthogonally polarized beams, does not have a reference beam as is the case in some conventional holography. As noted above, FINCH requires two test (sample) beams that interfere with one another. This is a substantial difference that changes what information can be obtained from the interferometer. Significantly, it is the fact of having two test beams that allows FINCH to achieve high spatial super-resolution that classical imaging methods and other holography methods do not, and from conventional non-FINCH interferometer methods with test and reference beams.

In the case of FINCH, each copy of the beam has all the object information in it. Thus, the interference pattern obtained in FINCH can be thought of (colloquially) as "amplifying" the sample information.

In contrast to FINCH which“amplifies” the sample information, some conventional techniques use a reference beam that is weaker than the test beam, and thus cannot achieve maximum efficiency in the obtained interference. In some cases, the reference beam created is weaker than the test beam by as much as 99: 1 and therefore an efficiency loss of converting light from the sample into interference is observed.

In some instances a point diffraction (“PDF) optic is used to produce a reference beam from a filtered copy of the test beam from the sample, this technique used to create the reference beam erases all the sample information, and thus cannot "amplify" the sample information as in FINCH. The reference beam in U.S. Patent 8,351,048, US patent 6,304,330, US patent 7,230,717, and US patent 7,777,895, is truly a reference beam in that it has no sample information. Moreover, in contrast, for FINCH the ratio of the two beam intensities is 50:50, and thus the maximum efficiency in converting light into interference is obtained.

The present inventors discovered that a modification of the polarization scheme typically used to create the test FINCH beams could be used to create higher quality holograms than those that are produced by our other techniques described in US patents 10,228,655, 10,289,070, 10,423,123, and 10,591,870 and patent application 20170185036, and“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers”. The improved quality may at least in part be the result of the absence of incorrect calibration and stability of the phase shifter at any wavelength or bandwidth and the fact that more sample information creates the hologram.

Further, when a FINCH system is adapted with a polarization scheme as noted above, it also permits single shot recording, and it is then possible to advantageously apply the system to imaging that particularly benefits from single shot recording, including for example, chemiluminescent or bioluminescent imaging, or any low light system in which long exposures might exacerbate the problems inherent in sequential recording as listed above, i.e. the sample must not change during the recording of the interference patterns necessary to reconstruct the scene.

An embodiment of the current invention is illustrated in Figure 4a. In Figure 4a, the incoming object light 201 is linearly polarized at an input polarizer 202 and passed through the birefringent lens optics 203 such as, for example, in US patents 10,228,655, 10,289,070, 10,423,123, and 10,591,870 and patent application 20170185036, and“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers”, producing two differentially focused beams with orthogonal linear polarizations. Then, distinctly, a quarter- wave plate 401 is placed in the beam path, with its slow axis aligned ±45 degrees to the ordinary and extraordinary axes of the birefringent lens. This has the effect of turning the linearly polarized light from the birefringent lens into circularly polarized light, one beam with right handed circular polarization and one with left-handed circular polarization. In some

embodiments, this waveplate may be a broadband waveplate that applies the same quarter wave phase shift to every incoming wavelength over its range and does not need to be calibrated. The two circularly polarized beams may be brought to interfere by passing them through a linear polarizer 205. The angle of the polarizer transmission axis with respect to the waveplate slow axis controls the phase of the interference between the two beams (note that for some embodiments the exact angle of polarization needs to be known for each degree of polarization, but the angle of polarization shift can be less precise and compensated for in software by an iterative software routine to obtain the best image of a test pattern). Multiple phase shifted holograms may then be recorded sequentially, by rotating the polarization axis of an output polarizer 205 placed in a plane between the quarter-wave plate and the interference detection plane 206.

Another embodiment of the present invention is illustrated in Figure 4b. In Figure 4b, the incoming object light 201 is linearly polarized at an input polarizer 202 and passed through the birefringent lens optics 203 such as, for example, in US patents 10,228,655, 10,289,070, 10,423,123, and 10,591,870 and patent application 20170185036, and“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers” . Then, distinctly, a quarter-wave plate 401 is placed in the beam path, with its slow axis aligned ±45 degrees to the ordinary and extraordinary axes of the birefringent lens. This has the effect of turning the linearly polarized light from the birefringent lens into circularly polarized light, one beam with right-handed circular polarization and one with left-handed circular polarization. In some embodiments, this waveplate may be a broadband waveplate that applies the same quarter- wave phase shift to every' incoming wavelength over its range and does not need to be calibrated. The two circularly polarized beams may be brought to interfere by passing them through an array 402 of differentially aligned micropolarizers of varying polarization orientations 403, 404, 405, 406 overlaying the image sensor at interference detection plane 206 wherein each micropolarizer is of the size of one of the detector pixels and is registered to a specific detector pixel. The angles of the polarizer transmission axes of the micropolarizers with respect to the waveplate slow axis controls the phase of the interference between the two beams recorded at the detector pixel registered to each micropolarizer. Multiple phase shifted holograms may then be recorded simultaneously. For example, in one embodiment, the micropolarizer array may contain micropolarizers with transmission axis orientation of 0°, 90°, 180°, and 270° (or -90°) with respect to the quarter wave plate, resulting in the collection of multiple phase shifted raw holograms with relative phase shifts of 0, p/2, p, and 3p/2 radians (or 0°, 90°, 180°, and 270°). The micropolarizers may be of any convenient set of axis orientations to produce multiple holograms with any desired set of relative phase shifts. Following the recording of the raw holograms, the different phase shifted holograms may be separated from each other in the computing device. This results in a set of holograms, each of which has a quantity of blank pixels equal to (device pixel count )*(n-l)/n, where n is the number of phase shifts used. These pixels may reassigned with values calculated by nearest neighbor or other interpolation methods, to maintain the sampling interval of the imaging device. A recentering operation of single-pixel sifting the interpolated data may optionally be performed in order to improve the overlap of the raw holograms. Alternatively, the blank pixels may be removed and the sampling interval of the image data increased by a factor appropriate to the number of phase shifts recorded. For example, if four phase shifted raw holograms were recorded on a sensor of the type described in the current embodiment of 2048x2048 pixels of 5 micron pitch, each raw hologram would have (2048*2048)*(4-l)/4 = 3,145,728 blank pixels. These pixels could be filled with interpolated data, or simply be removed, with a concomitant reassignment of the sampling pitch to 10 microns.

Since polarizers isolate a single polarization component of incident light uniformly, regardless of precise wavelength over a broad wavelength band of light, the combination of the broadband quarter wave plate and interference formation by polarizer rotation as in the embodiment described in Fig. 4a results in a FINCH system with truly achromatic, calibration- free phase shifting and therefore with optimized phase recording of the interference patterns. Use of the embodiment described in Fig. 4b for simultaneous single shot recording addresses further aspects that affect the quality of recorded FINCH holograms, by eliminating considerations of long exposure time, photodamage of photosensitive objects, and sample motion between sequential exposures. In summation, it is an all optical system, free of any electronic or mechanical adjustments during image recording, that is capable of producing holograms in a single exposure with precise and reproducible phase shifts.

Sample data from the example embodiment shown in Fig 4a, with sequential interference pattern acquisition, is shown in Figure 5a, displaying four“raw” phase shifted holograms 501, 502, 503, 504 of a laser beam used as a model source object simulating an infinitesimal object point as well as the recovered amplitude 505 and phase 506 of the complex hologram. Example illustrative results of the performance of the polarization-based phase shifting FES1CH holographic method is shown in Figure 5b. A sample of 100 nm diameter beads (sub resolution by standard optical methods) was imaged using a FINCH microscope system with birefringent lenses as the interferometric hologram-forming element, of a type similar to that reported in the above noted Siegel et al“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers”. Two strategies for obtaining multiple phase-shifted holograms (interference patterns) were employed: the strategy of the present invention, with a quarter-wave plate and a micro-polarizer grid-masked camera for single shot acquisition as in Fig. 4b; and the general strategy of sequential phase shifted recordings using a variable waveplate of the conventional techniques (calibrated for a single wavelength) to shift the interference phase. The resulting complex phases of the polarization method according to embodiments were compared with the conventional variable waveplate method are shown in 507 and 508 respectively. Also shown are the image histograms of the phase values in 509 according to embodiments and the conventional phase values in 510. The phase patterns in 507 (embodiments of the present invention) appear quite spherical to the eye, with fewer aberrations than seen in 508, the conventional techniques. Additionally, the histograms of the complex hologram phases show excellent performance of the embodiments of the present invention. In the ideal case, the histogram of a complex hologram phase shown on a 0-65,535 scale should be centered (the mean pixel value should be) at approximately 32,767, with an equal distribution on the positive and negative slopes. Histogram 509 from an embodiment of the present invention is centered at -37,600, much closer to the ideal than histogram 510 from the techniques of US patents 10,228,655, 10,289,070, 10,423,123, and 10,591,870 and patent application

20170185036, and“High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers”, which is centered at -42,350. Since the raw holograms that were recorded with the embodiment of the present invention produced a complex hologram phase that was a better match to the expected phase value histogram, it is clear that the embodiment has solved the problems it was designed for; the applied phase shifts were improved in calibration accuracy and fidelity to the desired values.

In another embodiment shown in FIG. 6, the input polarizer mentioned in the preceding embodiment is a polarizing beam splitter 601, which receives the input light 201. Each of the two linearly orthogonally polarized beams 602, 603 from this polarizing beamsplitter is then directed toward one of two identical FINCH systems 604, 605 of the general type in the preceding embodiment (though lacking discrete input polarizer as that function is shared for both 604, 605 by 601), allowing a greater efficiency of light collection. Each of the FINCH systems 604, 605 contains birefringent lens optics 203, broadband quarter-wave plate 401, and micro-polarizer grid camera 402, and forms co-propagating linearly orthogonally polarized beams 103, 104 that reach an interference plane 206.

The present inventors have observed that a system in which FINCH is enhanced with one of the embodiments of Fig. 4a or 4b may often improve the recorded hologram quality and/or performance of current FINCH systems. For example, current FINCH systems require a high level of precision in a real-world system such as a microscope that must be sensitive to multiple wavelengths of light. In such cases, the variable waveplate of conventional methods of phase shifting may require precise calibration for each wavelength. Furthermore, in systems in which the sample light is broadband, this calibration can only be fully corrected for a single wavelength, leaving the other wavelengths in the band open to be shifted by an imprecise amount. This may cause degradation in the raw holograms that form, as incorrect phase shift of any part of the raw hologram results in incorrect calculation of the phase and intensity of the object and therefore reduced image quality in the calculated image. Additionally, even in the absence of calibration error, multiple colors (wavelength bands) of holograms cannot be recorded with accurate phase shift by conventional methods, as only one wavelength band can match the calibration of a variable waveplate at one time. The embodiments of the present invention allows multiple colors or wavelength bands to pass through an identical optical train, each color being phase shifted accurately, with color filters or a Bayer pattern camera then sufficient to record multiple color holograms

Moreover, the single shot embodiments of the enhanced FINCH may improve upon the current FINCH systems by, for example, reducing the length of illumination of potentially delicate samples, by allowing for increased time resolution, reducing possibility of object or background changes between sequential hologram recording, particularly in the case of living or moving objects, eliminating the need for calibration of phase shifting devices for multiple wavelengths. Moreover, the single shot embodiments of the invention may, in the case of broadband light, reduce or eliminate the impact of the inability of some serial hologram acquisition techniques to perfectly shift the phase only for a single wavelength of the light, while other wavelengths experience more or less than the desired phase shift.

In another embodiment of the invention, the input polarizer mentioned in the first embodiment is a polarizing beam splitter. Each beam from this polarizing beamsplitter is then directed toward one of two identical FINCH systems of the general type in the preceding embodiment, allowing a greater efficiency of light collection. The interference patterns collected at the termini of the identical FINCH systems are then correlated with each other in a coincidence imaging image recording, to enhance the signal to noise ratio in the image recording.

Alternatively, in another embodiment of the invention, the input polarizer mentioned in the first embodiment is a polarizing beam splitter. Each beam from this polarizing beamsplitter is then directed toward one of two almost identical FINCH systems of the general type in the preceding embodiment, each for example detecting a different bandwidth or wavelength of light by a variety of means.

When the interference patterns are recorded in the single shot method listed above, it is significant that for n micropolarizer orientations, each phase shifted interference pattern only contains approximately 1 In of the pixels it would contain if all the micropolarizers were of a single orientation. The multiple phase shifted interference patterns, then, are actually sparse representations of the full interference patterns. The significance of this is that in addition to the other benefits of single shot recording, the sparse data sets representing the interference patterns may optionally be analyzed using compressive sensing approaches, which are powerful computational approaches that perform best on sparse data sets. Compressive sensing approaches have been applied to holographic imaging reconstruction before but have not been successful at reconstructing complicated objects. The sparsity of the multiplexed interference recordings, as well as the fact that they are from different phase“viewpoints”, enable the application of compressive sensing approaches to the image reconstruction in ways that are not available to sequentially recorded phase shifted interference patterns.

Accordingly, in another embodiment, the incoming object light is linearly polarized at an input polarizer and passed through the birefringent lens optics. Then the light is passed through a broadband quarter-wave plate that has its slow axis aligned ±45 degrees to the ordinary and extraordinary axes of the birefringent lens. Multiple phase shifted interference patterns are then simultaneously collected as sparse representations of full interference patterns in a single shot, by using a detector with an array of differentially aligned micropolarizers with at least two polarization orientations overlaid on its pixels. These phase shifted interference patterns are each then reconstructed into the full interference patterns using standard or compressive sensing computational approaches. The full interference patterns are then used to construct the complex hologram and reconstructed images.

In another embodiment, the incoming object light is linearly polarized at an input polarizer and passed through the birefringent lens optics. Then the light is passed through a broadband quarter-wave plate with that has its slow axis aligned ±45 degrees to the ordinary and extraordinary axes of the birefringent lens. Multiple phase shifted interference patterns are then simultaneously collected as sparse representations of full interference patterns in a single shot, by using a detector with an array of differentially aligned micropolarizers with at least two polarization orientations overlaid on its pixels. These phase-shifted interference patterns are then reconstructed directly into images (without intermediately being made into complex holograms) using joint iterative computational approaches including compressive sensing and forward convolutional approaches.

Alternatively, the potential reduction in spatial resolution by multiplexing the phase recordings can be overcome by reducing the size and increasing the number of multiplexed pixels. In this way the resultant complex hologram pixels can be the same size as non-phase multiplexed methods.

The use of patterned micropolarizer masks is not limited to monochrome image recording, shown in FIG.7. Color cameras have a plurality of color-selective pixels arranged in patterns such for example as the Bayer pattern; each single color pixel (RGB for example) in the color image is composed of a group of color sensitive pixels 701 (one R, one B, two G, for example). It is therefore possible to align a micropolarizer mask so that each micropolarizer 702 is registered to a group 701 of individual camera pixels that represents a single color pixel in the final image, resulting in 703 a color pixel that accepts only one polarization and therefore only one phase factor of the interference in embodiments of the present invention. See Figure 7 for an exemplary illustration of this, including 704 an array of color pixels under an array of micropolarizers. This Bayer pattern implementation of FINCH works quite well since FINCH only requires 3 phase shifted holograms for the precise elimination of bias and the twin image to create a 3D representation of the subject. Figure 7 shows 4 different polarization orientations, however the polarizers could be arranged with only three orientations.

Accordingly, in another embodiment, the incoming broadband object light is linearly polarized at an input polarizer and passed through the birefringent lens optics. Then the light is passed through a broadband quarter-wave plate with that has its slow axis aligned ±45 degrees to the ordinary and extraordinary axes of the birefringent lens. Multiple phase shifted multi-color interference patterns are then simultaneously collected in a single shot, by using a detector with an array of differentially aligned micropolarizers with at least two polarization orientations overlaid on an array of multi-color recording pixels.

It may be desired to record multiple colors of holograms in a single exposure without using a bayer-pattemed or similar color image sensor. An effective method to accomplish this goal is to fdter the light that has passed the quarter waveplate of the previous embodiment in a sequence of color filters such as dichroic mirrors, and direct the filtered colors of the light to different monochrome image sensors.

Accordingly, in another embodiment, the incoming broadband object light is linearly polarized at an input polarizer and passed through the birefringent lens optics. Then the light is passed through a broadband quarter-wave plate with that has its slow axis aligned ±45 degrees to the ordinary and extraordinary axes of the birefringent lens. The light is then passed through a plurality of color filters and directed to a corresponding plurality of monochrome image detectors arranged in any convenient arrangement, including by subdividing a single

monochrome image sensor into discrete non-overlapping regions. Multiple colors of phase shifted interference patterns are then collected simultaneously, one color on each of the plurality of monochrome image detectors.

The present inventors having practiced in and in one case having originally invented FINCH, propose the above improvements to the FINCH system generally and in particular to the birefringent lens equipped FINCH system. These proposed improvements improve upon and in many instances simplify the FINCH systems proposed previously. It should be noted, however, that although the embodiments of the present invention are discussed in relation to FINCH, the techniques may be applicable to other self-interference interferometric methods including but not limited to those practiced in other types of holography. Moreover, while embodiments of the present invention are discussed in relation to visible light for simplicity, one skilled in the art will recognize that the teachings herein are applicable to all types of electromagnetic radiation.

The following references are incorporated by reference in their respective entireties

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One or more computers may control and/or associated with the imaging device described herein. For example, the computer 108 shown in FIG. 1 may run one or more processes to collect recorded interference patterns and generate holograms and/or reconstructed images as described in this application. It will be understood that a computer (a“computing device,”“computer system,” or“computing system”) such as 108 includes one or more of the following: one or more processors; one or more memory devices; one or more network interface devices; one or more display interfaces; and one or more user input adapters. Additionally, the computing device may be connected to or includes a display device. As will explained below, these elements are hardware devices (for example, electronic circuits or combinations of circuits) that are configured to perform various different functions for the computing device. Whenever it is described in this document that a software module or software process performs any action, the action is in actuality performed by underlying hardware elements according to the instructions that comprise the software module.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.