HK1243770B - Hybrid image-pupil optical reformatter - Google Patents

Description

Hybrid Image-Pupil Optical Reformatter

Related applications

This application claims priority to U.S. Provisional Application No. 62/105,928, filed January 21, 2015, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to the field of optical reformatters, and more particularly to improved reformatter apparatus and methods for improving the performance of optical systems, such as improving the spectral resolution of a spectrometer.

Background Art

Optical reformatters are typically implemented to receive an input image and light beam and produce a reshaped output image and light beam that is better suited for measurement by an optical system (such as an optical spectrograph or a detector or detector array) or further processing by a light processing system. Specifically, optical reformatters can be used to prepare and configure light from the output of a light source (such as an optical fiber, a fiber bundle, a telescope, an image relay, or a physical aperture such as an input slit) for delivery to an optical spectrograph.

As background, a conventional optical spectrometer includes a small input aperture, typically a slit. This input aperture can alternatively be a circular pinhole, an optical fiber, or other input device; however, for simplicity, the input aperture will be referred to as a slit below. The input light can be a converging or diverging beam projected toward the slit, or it can be some other light source positioned so that a portion of the light passes through the slit. In a typical optical spectrometer, the light passing through the slit is projected onto a lens or mirror that collimates the light to form a beam of generally parallel light rays. In a typical optical spectrometer, a dispersive element (such as a prism, transmission grating, or reflection grating) bends the collimated beam by different amounts depending on the wavelength of the light, thereby producing a spectrally dispersed beam. Often, a camera lens or mirror focuses these spectrally dispersed beams onto an array detector (such as a charge-coupled device (CCD) detector) or some other single-element or multi-element detector at the final focal plane, which can measure the focused spectrum and record the intensity of light at various wavelengths.

In a typical optical spectrograph, a collimating lens (or mirror) and a camera lens (or mirror) act as image relays to produce an image of light passing through a slit on a detector (such as a CCD detector), where the image is laterally shifted depending on the wavelength of the light. The spectral resolution of an optical spectrograph (a quantitative description of its ability to detect and measure narrow spectral features, such as absorption or emission lines) can depend on various characteristics of the spectrograph. Such characteristics can include: a dispersive element, such as a prism, transmission grating, or reflection grating; the focal lengths of the collimating lens (or mirror) and camera lens (or mirror); and the width of the slit along the dispersion axis. For a particular disperser and camera lens, the resolution of the spectrograph can be increased by narrowing the width of the input slit, which results in each image of light passing through the slit (depending on the wavelength of the light) and onto the detector subtending a smaller cross-section of the detector, allowing adjacent spectral elements to be more easily distinguished from each other.

By narrowing the width of the input slit, less light is transmitted through the slit, which can reduce the quality of any measurement due to a reduction in the signal-to-noise ratio. In some applications, such as astronomical spectroscopy, high-speed biomedical spectroscopy, high-resolution spectroscopy, or Raman spectroscopy, this efficiency loss can be a limiting factor in the performance of optical spectrographs. In the field of spectroscopy, it would be advantageous to have a device that increases the amount of light that can be transmitted through the slit by compressing the image of the input beam along the dispersion axis (i.e., horizontally) while generally maintaining the light intensity or flux density, even if the point image is compressed along the dispersion axis at the expense of expansion along the vertical axis (i.e., vertically).

Those skilled in the art will understand that the terms "horizontal," "vertical," and other such terms, such as "above," and "below," used throughout this specification are used to explain various embodiments of the present invention, and such terms are not intended to limit the present invention.

The skilled artisan will also understand that while the term component is often used to refer to a specific item, such as a lens or mirror, and the term element is often used to refer to a group of components that share a common functional purpose, it is also possible to have an element that is composed of a single component or a single component that functions as multiple components. For example, in the case of an optical component with multiple reflective or refractive surfaces, such as a lens with a reflective coating, the lens can function as one element, and the reflective coating can function as a different element. Similarly, a curved mirror can both redirect and change the divergence of a light beam, thereby providing the functions of multiple elements in the same component.

The skilled artisan will also understand that a focused image produced by focusing a collimated light beam can be referred to as a point or point image, and that the light source need not be a focused point image in order to be collimated. Image refers to the spatial distribution of the light field at the focal plane of a lens or mirror where wavefront concavity changes direction, while image space refers to any space in the light field where the wavefront is substantially non-planar. Pupil refers to a transverse cross-section of the light field where the wavefront is substantially planar, and thus pupil-space refers to any location where the wavefront is substantially planar.

An optical reformatter can be used to receive an input beam and/or input image and produce an output beam and/or output image that better matches the input slit of the spectrometer. An optical slicer is a type of optical reformatter in which portions of a beam or image are divided and redirected or repositioned.

Optical splitters that include transparent prisms and plates to split the input beam can have drawbacks because they can produce reformatted images at slits that are tilted along the optical axis. Furthermore, the beam splitting can occur along the hypotenuse of a 45° prism, which can lead to focus degradation because different segments of the split image are located at different focal positions. The performance of such splitters can also depend on the absorption coefficient and refractive index of the prism material used (both of which are wavelength-dependent). These drawbacks can limit the use of such splitters in broadband optical devices.

There are also other optical splitters that operate entirely in image space, such as Bowen-Walraven splitters or fiber optic point-to-line converters. Some of these image splitters generally do not retain spatial image information and are therefore unable to independently resolve spectral information from different parts of the source image. These reformatters also have challenges in implementing in a commercially viable manner, can be large in size, and can lead to reduced or inefficient implementation in various systems. These splitters often produce multiple copies of the slit image, which results in wasted space on the detector due to gaps between the splits at the final focal plane, which add noise to the signal, thereby reducing the quality of the output data, limiting the number of spectra (or spectral levels) that can be accommodated on the detector, and reducing the efficiency of the detector readout because the spectra are spread over a larger detector area. Optical splitters that use fiber bundles to allow the extended (often circular) image of the input source to be formed into a narrow slit image also result in a degradation of the output f-ratio and overall performance inefficiency. Existing splitter devices are almost uniformly affected by this reduced efficiency and output f-ratio, which is a significant limitation of splitter design and implementation. Furthermore, fiber optic bundles tend to be inefficient for light collection due to the gaps between individual fibers and the space occupied by the individual fiber claddings.

Recently, new pupil reformatter designs and their use to improve the spectral resolution of spectrometers have been disclosed. These segmenter-based reformatters operate entirely in pupil space, segmenting and then anamorphically expanding a collimated beam. This approach is useful when preservation of spatial image information is required, such as with push-broom hyperspectral imaging and multi-fiber inputs, but larger input sources can make pupil beam divergence problematic, and optical system complexity increases with the number of segmentations generated.

The present invention differs from existing reformatter designs in that it operates partially in pupil space and partially in image space. Therefore, throughout this application, it is referred to as a hybrid image-pupil optical reformatter, and embodiments of the present invention may be described as hybrid splitters or hybrid reformatters that operate partially in pupil space and partially in image space. This approach has advantages over conventional optical splitters, including in situations where a larger number of splits is required, because having the reformatter operate partially in pupil space and partially in image space as disclosed in the present invention tends to be characterized by a reciprocating beam path through a collimator that limits beam spread. In embodiments of the present invention, larger splitting factors can be achieved with fewer components, reduced beam divergence losses, and less stringent alignment tolerances, and the number of splits tends to be relatively independent of optical complexity, with the preferred number of splits being roughly equal to the ratio of the input beam width to the output beam width. Embodiments of the present design also tend to handle larger input spot sizes and/or faster input beams (small focal ratios) more easily than conventional optical splitters.

The pupil beam in the present invention tends to become narrower rather than taller, and the pupil segments disclosed in embodiments of the present invention tend to overlap. This is in contrast to most pupil reformatters, where the pupil beam becomes both narrower and taller, and the pupil segments generally do not overlap. Furthermore, many other optical reformatters use "explicit" expansion as part of the reformatting, whereas in some embodiments disclosed herein, the expansion is "implicit."

Summary of the Invention

In one aspect of the present invention, an optical reformatter for generating an output beam is provided, comprising: a collimator that receives input light and generates a first collimated beam; a first optical element that redirects one or more portions of the first collimated beam toward the collimator to generate one or more re-imaged beams, and allows one or more portions of the first collimated beam to pass through the first optical element to form a portion of the output beam; and a second optical element that redirects some or all of the re-imaged beams toward the collimator to generate additional collimated beams, so that multiple portions of the additional collimated beams also form part of the output beam.

In some embodiments of the present invention, one or more portions of the first collimated light beam that form part of the output light beam may be passed through the first optical element without any further redirection. In other embodiments, the input light may be the output of an optical fiber, an image relay, or a physical aperture.

The collimator can be a single lens, a compound lens, a single mirror, or another optical element that collimates a diverging light beam and focuses a collimated light beam. Furthermore, the first collimated light beam and the additional collimated light beam can be substantially collimated or fully collimated. Furthermore, the first optical element and the second optical element can each include one or more mirrors.

In some embodiments, the one or more portions of the first collimated beam that are redirected toward the collimator can be located at the extremities of the first collimated beam. In other embodiments, the one or more portions of the first collimated beam that are redirected toward the collimator can be redirected to be non-parallel to the first collimated beam; or the one or more portions of the first collimated beam that are redirected toward the collimator can be redirected to be non-parallel to each other.

The re-imaging beams can produce a focused image at a location that does not coincide with the input light, and the second optical element can be positioned to redirect the one or more re-imaging beams without blocking the optical path between the input light and the collimator. The second optical element can also be positioned at the location where the re-imaging beams produce the focused image.

In other embodiments, one or more portions of the additional collimated beams can be redirected by the first optical element toward the collimator to produce additional re-imaged beams, and the additional re-imaged beams can be redirected by the second optical element toward the collimator to produce further additional collimated beams, such that one or more portions of the further additional collimated beams also pass through the first optical element to form a portion of the output beam. In still other embodiments, such redirection of the additional collimated beams and the additional re-imaged beams can be iterative and repetitive in nature.

In some embodiments, substantially all of the light energy received from the input light can be included in the output light beam. Furthermore, the first collimated light beam and the portions of the additional collimated light beams forming the output light beam can substantially overlap and propagate in substantially the same direction. The output light beam can also be dimensionally narrower than the first collimated light beam.

The optical reformatter may further include an additional optical element for redirecting the output beam after passing through the first optical element. Alternatively or additionally, the optical reformatter may further include a focusing element for focusing the output beam onto the input of the spectrometer. In some embodiments, the focusing element may be a rod lens, a cylindrical lens, a cylindrical mirror, or one or more cylindrical or annular lenses or mirrors.

In another aspect of the present invention, the optical reformatter may also include: an optical element for expanding the output light beam along a first dimension to produce an expanded light beam; a dispersive element for spectrally dispersing the expanded light beam along the first dimension to produce a spectrally dispersed light beam; a focusing element for focusing the spectrally dispersed light beam to produce a focused spectrum; and a detector for receiving and measuring the focused spectrum.

In another aspect of the present invention, a method for generating an output beam is provided, comprising: collimating input light through a collimator to produce a first collimated beam; redirecting one or more portions of the first collimated beam back through the collimator to produce one or more re-imaged beams; redirecting some or all of the re-imaged beams through the collimator to produce additional collimated beams; and forming an output beam from multiple portions of the first collimated beam that have not been redirected back through the collimator and the additional collimated beams.

In some embodiments, portions of the additional collimated light beams may also be redirected back through the collimator to produce additional re-imaged light beams, and some or all of the additional re-imaged light beams may be redirected through the collimator to produce further collimated light beams, such that the output light beam may include portions of the further additional collimated light beams. In other embodiments, the redirection is iterative.

The redirected light beams and beam portions can be redirected to produce an output light beam formed by substantially overlapping light beams and beam portions that propagate in substantially the same direction and have substantially all of the light energy in the input light. The redirected light beams and beam portions can also be redirected to produce an output light beam that is narrower than the first collimated light beam in a first dimension. In some embodiments, the method can further include focusing the output light beam onto an input of a spectrometer. In some embodiments, the output light beam can be expanded along a first dimension to produce an expanded light beam; the expanded light beam can be spectrally dispersed along the first dimension to produce a spectrally dispersed light beam; the spectrally dispersed light beam can be focused to produce a focused spectrum, and the focused spectrum can be measured.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the embodiments of the systems and methods described herein, and to more clearly show how they may be practiced, reference will be made, by way of example, to the accompanying drawings, in which:

FIG1A shows an isometric view of one embodiment of a hybrid image-pupil optical reformatter.

1B shows an isometric view of an embodiment of the hybrid image-pupil optical reformatter of FIG. 1A when used with or as part of an optical spectrometer.

2 illustrates the splitting and redirection of a collimated light beam in one embodiment of a hybrid image-pupil optical reformatter, shown as a cross-section of the reformatter at the pupil mirror.

3 illustrates the shapes of pupil beams and focused images that may exist at various points in the operation of an embodiment of a hybrid image-pupil optical reformatter such as that shown in FIGs. 1A and IB.

DETAILED DESCRIPTION

It should be understood that many specific details have been provided in order to provide a thorough understanding of the exemplary embodiments described herein. However, one of ordinary skill in the art will understand that the embodiments described herein can be practiced without these specific details. In other cases, well-known methods, procedures, and components have not been described in detail so as not to obscure the embodiments described herein. Furthermore, this description should not be considered in any way to limit the scope of the embodiments described herein, but rather to merely describe how the various embodiments described herein may be implemented.

In the following description and drawings, references to "top," "bottom," "left," "right," "horizontal," "vertical," and the like are used for convenience and clarity only. They are in no way meant to limit the possible orientations of the various optical components and structures, but are used to describe and illustrate the relative orientations of certain elements in the designs disclosed in this application. The term "collimated" as used in this application shall include both fully aligned and substantially aligned.

In the following description and drawings, optical elements (such as mirrors and lenses) are used to illustrate the present invention. The same results can be achieved using different optical elements or by using a design that replaces reflection with transmission or reflection with reflection to achieve the desired effect on the light signal.

Referring to FIG1A , one embodiment of a hybrid image-pupil optical reformatter is shown. For reference, the hybrid image-pupil optical reformatter is depicted as part of a dispersive spectrometer system in FIG1B . The system of FIG1B can be entirely contained within a single physical housing, or can be split between several physical housings with appropriate optical couplings. The orientations in FIG1A and FIG1B are described herein as "horizontal," where the orientation is generally parallel to the dispersion axis of the disperser, and "vertical," where the orientation is generally perpendicular to the dispersion axis of the disperser, although skilled artisans will appreciate that the system can be configured in other orientations.

1A , light source 110 a generates light beam 112, which is shown as a diverging light beam that is collimated into a first substantially collimated light beam 114 by collimating element 113. Light source 110 a can be the output of an optical fiber, a multi-fiber bundle, an image relay, a physical aperture, or some other source. Several types of optical elements can be used to form collimating element 113, including, for example, singlets, doublets, compound lenses, single or compound mirrors, or other optical elements that collimate a diverging light beam (as well as other optical elements that focus a collimated light beam based on the principle of optical reciprocity).

In the embodiment shown, the collimated light beam 114 reaches an optical element 115, which is shown to include a pair of mirrors 115a and 115b that redirect portions of the light beam 114 by reflection. In other embodiments, the optical element 115 may include other optical components that redirect portions of the light beam 114. Because these mirrors operate on a collimated pupil beam, they are also referred to as pupil mirrors. They can be configured to have straight edges that impinge on the beam profile and can be, for example, two vertical D-shaped mirrors, although those skilled in the art will appreciate that other optical elements and optical element configurations can be used. In the depicted embodiment, mirrors 115a and 115b are planar and separated by a small gap so that a portion of the collimated light beam 114 passes between the gap to form a portion of the collimated output light beam 116. Those skilled in the art will appreciate that the term "passes" or "passes" can refer to moving through, moving through, moving through, or other similar motions. A portion of the light beam 114 reflects from mirror 115a and is redirected toward the collimating element 113. When the collimated light beam passes back through the collimating element 113, the collimating element 113 converts the redirected collimated light beam into a re-imaged light beam that converges and reaches a focus near (i.e., not coinciding with) image 110a. This focus can be located on the optical element 111, which is shown as including a pair of mirrors, but can include other optical components for redirecting the light beam. This refocused image tends to be the same size as the input source 110a and tends to have a lower light intensity. In the illustrated embodiment, the mirror 115a is vertically tilted (i.e., tilted with the vertical axis about the horizontal axis) so that the reflected light beam portion is not parallel to the light beam 114. This change in angle of the reflected light beam portion passing through the collimator causes the refocused point image 110b to be vertically displaced from the image 110a, landing on the plane mirror 111a located above the image 110a. Similarly, another portion of light beam 114 reflects from mirror 115b, passes back through optical element 113, and reaches a focal point near image 110a. However, mirror 115b is tilted so that the reflected and refocused point image 110c is vertically displaced from image 110a in the opposite direction of image 110b, landing on a plane mirror 111b located below image 110a. Mirrors 111 may also be referred to as image mirrors because they tend to operate on focused images. These image mirrors can, for example, be two horizontal D-shaped mirrors, though those skilled in the art will appreciate that other optical elements and configurations can be used. In some embodiments, one of the image mirrors can be located in the source image focal plane directly above the source image, while the other image mirror can be located in the source image focal plane directly below the source image, so that the source image enters the splitter by passing between the image mirrors. In other embodiments, the mirror or mirrors can be one-way mirrors placed in front of the input source, allowing light from the input source to enter while still reflecting the re-imaged light beam.

Images 110b and 110c are reflected from their respective mirrors back toward optical element 113, where they are re-collimated into an additional collimated beam that is similar and generally coincident with, but slightly tilted and laterally offset from, beam 114. In the illustrated embodiment, mirror 111a is tilted horizontally such that the redirected, re-imaged beam is directed toward collimator 113 at a different horizontal angle than diverging beam 112, such that the resulting additional collimated beam is offset toward the center of optical element 115 relative to the portion of the redirected collimated beam generated by mirror 115b. Similarly, mirror 111b is tilted horizontally such that the additional collimated beam generated from the redirected, re-imaged beam is offset toward the center of optical element 115 relative to the portion of the redirected collimated beam generated by mirror 115a. These additional collimated beams encounter mirrors 115a and 115b, and a portion of each additional collimated beam passes through the gap between the pupil mirrors and is added to the output beam 116, while the other portion is reflected back through optical element 113 to form point images 110d and 110e on mirrors 111a and 111b. Depending on the spacing and angular tilt of mirrors 115a, 115b, 111a, and 1111b, the number of multiple reflections and multiple point images 110 can be two, three, four, five, or any greater number, and the number of point images, multiple reflections, and beam portions passing between the pupil mirrors can be equal or unequal. In other embodiments, optical elements 115 and 111 can each comprise a single mirror, and there can be only a single reflection from each optical element and only a single additional point image generated. In some embodiments, and preferably for some embodiments, the remaining beam portion at the final reflection passes entirely through mirrors 115a and 115b without any portion being reflected. In alternative embodiments, there may be reflections that cause optical element 115 to reflect all of the light and not allow any of the light to form part of output beam 116 until it is later reflected back. Furthermore, in alternative embodiments, optical element 111 may redirect only some of the re-imaged beam or portions of the re-imaged beam, rather than the entire re-imaged beam, as shown.

Thus, the collimated light beam 116 can also include a plurality of substantially similar and spatially overlapping light beams or beam portions, each corresponding to one of the point images 110, and those light beams and beam portions together forming the output beam of the optical reformatter. Each of the beam portions forming the output beam can have a tall and narrow profile, similar in height to the first collimated light beam and narrower in width, and each having a slightly different vertical tilt. The vertical tilt tends to produce a slight vertical divergence in the output beam. In some embodiments, and preferably for some embodiments, the reformatter output beam 116 includes substantially all of the light intensity (light energy) contained in the input light, with only a small amount lost due to the reflection efficiency or transmission efficiency of optical components in the reformatter. In some embodiments, an additional optical element can redirect the output beam 116 to change the layout of the optical system or to more conveniently or efficiently couple with downstream optical elements.

FIG2 further illustrates the splitting and redirection of the collimated beam and additional beam portions in one embodiment of a hybrid image-pupil reformatter, as shown at the pupil mirrors. FIG2a shows a first collimated beam 203 received by pupil mirrors 201 and 202, corresponding to mirrors 115a and 115b in FIG1 . FIG2b shows that after the middle portion has passed through the gap between the pupil mirrors to form part of the output beam, the left portion (204) and the right portion (205) of the beam are redirected back to the collimator (not shown). FIG2c shows an additional collimated beam 206 produced by beam portion 204 after beam portion 204 has been re-imaged, redirected by a corresponding image mirror (not shown), and realigned by a collimator (not shown). Note that in the embodiment shown, beam 206 has been flipped and offset toward the middle of pupil mirrors 201 and 202, and offset downward relative to beam 204. A portion of beam 206 will pass through the gap between the pupil mirrors to also form a portion of the output beam, while another portion of beam 206 will be reflected by mirror 202. Similarly, FIG2 d shows an additional collimated beam 207 produced by beam 205 after beam 205 has been re-imaged, redirected by corresponding image mirrors (not shown), and realigned by a collimator (not shown). A portion of beam 207 will pass between pupil mirrors 201 and 202 to join the output beam, while another portion of beam 207 will be reflected by mirror 201. FIG2 e shows beam 208, with a portion of beam 206 reflected by the pupil mirrors, while the remainder of beam 206 passes through the gap between the pupil mirrors. Finally, FIG2 f shows beam 209 produced by beam portion 208 after beam portion 208 has been re-imaged and redirected by image mirrors (not shown) and realigned by a collimator (not shown). This process can continue until all the light has been deflected into the gap between the mirrors and passed through to form a portion of the output beam. It can be seen that in one embodiment, which is preferred for some applications, the number of iterations will be equal to the width of the first collimated beam divided by the separation distance of the pupil mirrors.

Returning to FIG. 1B , an exemplary embodiment is shown in which an optional image relay with one or more curved lenses or mirrors is used to re-image a light source (such as a fiber output) onto the light source focal plane 110a of the reformatter. This can be advantageous when using a fiber-feedback source because, through the image relay, the fiber cladding or jacket or ferrule will not tend to interfere with the image mirror, and the focal ratio within the splitter section can be modified from that exiting the fiber, for example, by lowering the focal ratio to reduce aberrations in the collimating lens. In the image relay of FIG. 1B , an input aperture 101 emits a diverging light beam 102 having a broadband spectral profile. Those skilled in the art will appreciate that input aperture 101 can be implemented, for example, using an optical fiber, a pinhole, or a light source, although other input sources are also suitable. Diverging light beam 102 is refocused by optical element 103, which is depicted as a singlet lens in the embodiment of FIG. 1B . Optical element 103 can be implemented using a variety of optical elements, such as an achromatic doublet, a compound lens, a single concave mirror, or a compound mirror system. Optical element 103 focuses the light beam into a converging light beam 104 that forms an image 110 a of the input aperture 101 .

FIG1B also illustrates how the output of the reformatter can be directed toward the input of a spectrometer, or how the reformatter can be incorporated directly into the spectrometer. A skilled artisan will appreciate that there are a variety of ways to send the reformatter output beam to the dispersive spectrometer section of the system. In the illustrated embodiment, the collimated reformatter output beam 116 is passed through a focusing element 117, which can be a rod lens, a cylindrical lens, a cylindrical mirror, or any other optical element that will tend to focus a portion of the beam along a horizontal axis rather than along a vertical axis. In the illustrated embodiment, the light in the beam portion thus tends to focus into a tall, narrow, slit-like image at an intermediate focal plane 118 (relative to the input aperture 101, which may already have a circular appearance). A physical slit or light baffle can be placed at the focal plane 118 to limit light passing through, block scattered light, make the slit image narrower (at the expense of reduced light intensity), or all horizontally focused light can be allowed to pass through this focal plane. The spectrometer can also be positioned so that its input aperture is at the focal plane 118.

Continuing with the description of a hybrid image-pupil optical splitter used as part of a dispersive spectrometer as shown in FIG. 1B , upon passing through focal plane 118, the plurality of beam portions form beam 120, which tends to appear as a diverging beam, e.g., f/5 vertically and f/5 horizontally. This diverging beam is collimated by optical element 121 to produce collimated beam 122, which has been expanded in the dispersive direction relative to output beam 116. The expansion can also be implemented using expander elements (e.g., convex and concave lenses, or convex and concave mirrors) that diverge and recollimate the beams, in place of components 117 and 121, causing the beams to converge through the focal point to form a substantially recollimated diverging beam. This expansion of the pupil beam helps narrow the refocused image produced by that beam. The expanded collimated beam 122 is reflected from a flat folding mirror 123 onto a dispersive element 124, which can be a diffraction grating, a prism, a grism, or any other spectrally dispersive element. Disperser 124 produces a spectrally dispersed beam 125 comprising a plurality of monochromatic collimated beams, where the horizontal angle of each beam depends on its wavelength. A focusing element 126 (comprising, for example, a simple or compound lens, a simple or compound mirror, or a combination thereof) focuses these dispersed beams onto a focal plane detector 127 on a detector system 128, which can be a CCD device, a CMOS device, an InGaAs sensor, a linear photodiode array, photographic film, a single-pixel photodiode, a photomultiplier tube, or any other light-detecting instrument. The measured intensity of each sensor element in detector system 128 provides a measure of the spectral distribution of the original beam passed through aperture 101. The optical sequence from focal plane 118 to detector system 128 is similar to many other dispersive spectrometer designs; however, unlike other dispersive spectrometer designs, the beam reformatting method implemented by the hybrid image-pupil optical splitter through elements 101 to 117 causes the input source 101 to reformat a tall, narrow image at focal plane 118 to provide higher spectral resolution without losing light at the narrow slit.

The skilled person will appreciate that in some cases it may be advantageous to utilize a dispersive spectrometer with additional optical reformatting, a dispersive spectrometer with additional beam expansion and/or compression along one or more axes, or some other dispersive spectrometer design.

FIG3 illustrates the shapes of pupil beams and focused images at multiple points that may exist in the embodiments of FIG1A and FIG1B . A first collimated pupil beam 114 is shown as a circular beam having a relatively uniform intensity. A reformatted output beam 116 is shown having a width corresponding to the gap between mirrors 115a and 115b, and superimposed beam portions contributed by the first collimated beam and the additional collimated beam. The delivery of the additional collimated beams is combined through the overlapping D-shaped portions of optical element 115 so that some portions of the output beam have greater light intensity than other portions. An expanded output beam 122 is also shown. FIG3 also shows the input source image 110a, the replicated sources 110a-e at the focus of collimating element 113 (which is also the source image focal plane and position of mirror 111), and the refocused camera image at the focal plane of the camera image (127). Note that the intensity of the replicated source decreases with each pass between the first and second optical elements because additional beam portions pass through optical element 115 to form part of the output beam at each pass and less light is reflected back.

In some embodiments, there may be different numbers of pupil mirrors (e.g., one or three instead of a pair), different numbers of image mirrors, or even unequal numbers of pupil and image mirrors. Some embodiments may also include only a single pupil splitting mirror and a single image mirror, which tends to provide only two splits. In such an alternative, light will tend to pass around the image mirror rather than through the gaps between the mirrors. Furthermore, in other embodiments, the design can be configured so that not all portions of all reflected pupil beams are later reflected back to the pupil by the image mirror.

In cases where the beam is redirected only once between the pupil mirror and the image mirror, the design can tend to be described as a first-pass design. As the number of passes increases (i.e., the number of iterations increases), and as the portion of the collimated beam that passes through the image mirror to form part of the output beam on each pass decreases, the narrowing of the output beam relative to the first collimated beam can be greater, which can be advantageous, for example, by enabling the output beam to be expanded a greater multiple without becoming larger than the first collimated beam. In some systems, the number of iterative passes can be quite large. However, as the number of passes increases, the light intensity will decrease due to reflection losses and transmission losses. A compromise between these two factors will determine the most appropriate number of passes for a given implementation.

In the present invention, collimated pupil beam tends to be split into individual sub-beams, such as traditional optical splitters, which tend to have no effect on the refocused point, but the tilt of those splitting mirrors tends to make the refocused point image vertically offset, so "stacking" is done in image space rather than in pupil space. Like this, different collimated segmentations are all superimposed on top of each other in pupil space rather than being stacked vertically. Each collimated segmentation will tend to have different vertical angles, and the whole bundle of split beams will tend to have a vertical divergence greater than any single beam. In practice, this vertical divergence is similar to the horizontal divergence that shows after the input is passed through the slit, so that the optical equipment in downstream can be circular or square rather than highly rectangular. The tall and thin pupil composed of the superimposed segmentation can then be focused horizontally to form a virtual slit image in the middle, which, if necessary, can be passed through a physical slit (to reduce scattered light leakage) and then transferred to the dispersion spectrometer back end. The horizontal focusing can be achieved using a cylindrical lens to produce a virtual slit image in which the original image points are "blurred" together to form a single beam of light. The skilled person will appreciate that the focusing can also be achieved in other ways, such as using a spherical lens, although such a spherical lens may require an unrealistic focal ratio to implement.

The reformatted pupil beam of the present invention can also be directed to the input of a dispersive spectrometer specifically designed to handle this type of input without undergoing horizontal focusing. There may also be applications where the reformatted output of the present invention (collimated or focused) can be used as input to other optical devices in addition to being used solely as input to a dispersive spectrometer.

It will be appreciated by those skilled in the art that in some embodiments, certain optical elements depicted in FIG1 may be replaced with alternative elements that provide similar functionality via different methods or that combine the functionality of two or more original elements. For example, a lens-based transmissive re-imager (103) may be replaced with a catadioptric system or a total reflection re-imaging system. Also for example, the collimator (113) may be implemented with an off-axis parabolic mirror rather than a lens. Also for example, the pupil mirrors (115a and 115b) may be replaced with a single mirror having a slit or hole cut into it. Also for example, the collimator (113) and pupil mirrors (115a and 115b) may be combined into a single element consisting of a transmissive lens having a surface that is fabricated with different angles and partially coated with a reflective coating to act as a mirror or mirrors.

Although the present invention can be used together with any device that tends to use light as input as previously described, one embodiment of the use of the optical splitter described herein can be in the field of spectroscopy. A general spectrometer is a device that disperses light so that the light intensity value as a function of wavelength can be recorded on a detector. For readings requiring higher spectral resolution, a narrower slit tends to need to be directly related to the spectral resolution, and a generally narrow slit will provide a reduction in the light intensity received at the detector or sensor focal plane of a general spectrometer device. Compared to a slit without an optical splitter, positioning the optical splitter in front of the input of a general spectrometer device (possibly in combination with some form of implicit beam expansion or explicit beam expansion) tends to produce an input of the general spectrometer device slit with a light intensity value increased by a multiple of the splitting factor on the area of the slit, thereby tending to provide increased spectral resolution without sacrificing light signal intensity.

Interference spectroscopy is a branch of spectroscopy; its defining characteristic is that the dispersive element used is not a grating or prism. Instead, dispersion is achieved in other ways, such as by Fourier transforming the pattern generated by the two interfering beams. This divider not only increases the brightness of the output but also allows for significant improvements in the contrast of the interference fringes and the signal-to-noise ratio.

Another subset of interferometric spectroscopy related to medical imaging is optical coherence tomography (OCT), which uses an interferometer to produce images. A segmenter will improve the throughput and fringe contrast of an OCT device; as a result, a segmenter can improve the depth penetration possible with an OCT system, speed up imaging time, and increase the value of the captured images. An optical segmenter can be included at the input of an OCT device.

Optical splitters can be used in a subset of OCT known as Fourier domain OCT (FD-OCT), and more specifically in a specific implementation of FD-OCT known as spectral domain OCT (SD-OCT). SD-OCT instruments are interferometric spectrometers with a dispersive spectrometer for recording signals. An optical splitter can be included at the input of the dispersive spectrometer, just before the dispersive beam element in the collimated beam path.

Another application of the splitter is in the field of micro-spectroscopy, particularly in relation to Raman spectroscopy. Current Raman spectrometers have been implemented as being miniaturized to handheld scale. Because the splitter can be used to increase the throughput of any system using light as an input source, a miniaturized embodiment of the splitter can be used in conjunction with a miniaturized spectrometer (e.g., a Raman spectrometer) to increase spectral resolution, increase output signal intensity, and reduce scan time. An optical splitter can be included at the input of a Raman spectroscopy device.

The invention has been described with reference to specific embodiments. However, it will be apparent to those skilled in the art that many variations and modifications can be made without departing from the scope of the invention as described herein.

Claims (25)

1. An optical remodeling device for generating an output beam, comprising: A collimator that receives input light and generates a first collimated beam; First optical element, the first optical element (i) redirecting one or more portions of the first collimated beam to be non-parallel to the first collimated beam and received by the collimator, the collimator generating one or more re-imaging beams; and (ii) Allowing one or more portions of the first collimated beam to bypass the first optical element to form a portion of the output beam; A second optical element, which redirects one or more portions of the re-imaging beam to be received by the collimator, which generates an additional collimated beam; One or more portions of the additional collimated beam also form a portion of the output beam. 2. The optical reshaping device according to claim 1, wherein the input light is the output of one or more optical fibers, an image relay, or a physical aperture. 3. The optical recalibrator according to any one of claims 1 to 2, wherein the collimator is a single lens, a compound lens, a single mirror, or another optical element that collimates the diverging beam and focuses the collimated beam. 4. The optical recalibrator according to claim 1 or 2, wherein the first collimated beam and the additional collimated beam are substantially collimated or fully collimated. 5. The optical resetting device according to claim 1 or 2, wherein each of the first optical element and the second optical element comprises one or more mirrors. 6. The optical recalibrator according to claim 1 or 2, wherein one or more portions of the first collimated beam that are reoriented to be received by the collimator are located at the end of the first collimated beam. 7. The optical recalibrator according to claim 1 or 2, wherein one or more portions of the first collimated beam that are recalibrated to be received by the collimator are recalibrated to be non-parallel to each other. 8. The optical reshaping device according to claim 1 or 2, wherein the re-imaging beam produces a focused image at a location that does not coincide with the input light, and the second optical element is positioned to reorient one or more portions of the re-imaging beam without obstructing the optical path between the input light and the collimator. 9. The optical reshaping device of claim 8, wherein the second optical element is positioned at the location where the re-imaging beam produces the focused image. 10. The optical recalibrator according to claim 1 or 2, wherein one or more portions of the additional collimated beam are reoriented by the first optical element to be received by the collimator, which generates an additional re-imaging beam; and one or more portions of the additional re-imaging beam are reoriented by the second optical element to be received by the collimator, which generates further additional collimated beams. In this process, one or more portions of the additional collimated beams also bypass the first optical element to form a portion of the output beam. 11. The optical reorientation device of claim 10, wherein the reorientation of the additional collimating beam and the additional re-imaging beam is iterative. 12. The optical reshaping apparatus according to claim 1 or 2, wherein substantially all the optical energy received from the input light is contained in the output beam. 13. The optical recalibrator according to claim 1 or 2, wherein the first collimated beam and a plurality of portions of the additional collimated beam forming the output beam substantially overlap and propagate in substantially the same direction. 14. The optical recalibrator according to claim 1 or 2, wherein the output beam is narrower than the first collimated beam in a first dimension. 15. The optical reorientation apparatus of claim 1 or 2, further comprising an additional optical element for reorienting the output beam after it has passed around the first optical element. 16. The optical resetting apparatus of claim 1 or 2, further comprising a focusing element for focusing the output beam onto the input of the spectrometer. 17. The optical refocusing device according to claim 16, wherein the focusing element is a rod lens, a cylindrical lens, a cylindrical mirror, or one or more cylindrical or annular lenses or mirrors. 18. A spectrometer, comprising: Optical remodeling device according to any one of claims 1 to 17; An optical element for extending the output beam along a first dimension to produce an extended beam; A dispersive element is used to spectrally disperse the extended beam along the first dimension to produce a spectrally dispersed beam; A focusing element for focusing the spectral dispersive beam to produce a focused spectrum; and A detector for receiving and measuring the focused spectrum. 19. A method for generating an output beam, comprising: The collimator collimates the input light received by the collimator, and the collimator generates a first collimated beam; One or more portions of the first collimated beam are redirected to be non-parallel to the first collimated beam and received by the collimator, which generates one or more re-imaging beams. To redirect some or all of the re-imaging beam so that it is received by the collimator, which generates an additional collimated beam; and The output beam is formed by one or more portions of the first collimated beam that have not been redirected and have not been received by the collimator, and the additional collimated beam. 20. The method of claim 19, wherein one or more portions of the additional collimating beam are also redirected to be received by the collimator, the collimator generating an additional re-imaging beam, and some or all of the additional re-imaging beam are redirected to be received by the collimator, the collimator generating other additional collimating beams. The output beam includes one or more portions of the other additional collimated beams. 21. The method of claim 20, wherein the redirection is iterative. 22. The method according to any one of claims 19 to 21, wherein the reoriented beam and beam portions are reoriented to produce an output beam formed by substantially overlapping beams and beam portions that propagate in substantially the same direction and have substantially all of the optical energy in the input light. 23. The method according to any one of claims 19 to 21, wherein the reoriented beam and beam portion are reoriented to produce an output beam that is narrower in a first dimension than the first collimated beam. 24. The method according to any one of claims 19 to 21, further comprising focusing the output beam onto the input of the spectrometer. 25. The method according to any one of claims 19 to 21, further comprising: The output beam is extended along the first dimension to produce an extended beam; The extended beam is spectrally dispersed along the first dimension to produce a spectrally dispersed beam; To focus a spectral dispersive beam of light to produce a focused spectrum, and Measure the focused spectrum.