Patent Description:
The invention is defined in claim <NUM> and discloses a spectrometer comprising an inverted image slicer configured to accept input light to the spectrometer; an adjustable interferometer configured to accept light from the inverted image slicer; a sensor configured to sense light from the interferometer; wherein the inverted image slicer causes a linear field of view of the spectrometer to be imaged as a two-dimensional grid on the sensor.

In some embodiments of the spectrometer, the sensor is configured to sense a range of wavelengths, wherein the range of wavelengths includes <NUM> micrometers.

In some embodiments of the spectrometer, the sensor comprises a two-dimensional array of pixels, wherein data from each pixel of the two-dimensional array of pixels can be used to determine a spectrum of light imaged at that pixel with a resolution better than <NUM>-<NUM>.

In some embodiments of the spectrometer, the inverted image slicer converts a field of view with at least one dimension extending across at least <NUM> milliradians to a field of view with each dimension extending across less than <NUM> milliradians.

In some embodiments of the spectrometer, the sensor comprises a two-dimensional array of pixels, wherein each pixel images a field of view between <NUM> and <NUM> milliradians.

According to claim <NUM> the inverted image slicer comprises a first lens to focus input light onto a first plurality of mirrors; the first plurality of mirrors, wherein each of the first plurality of mirrors is tilted at an angle different from each other of the first plurality of mirrors, wherein each of the first plurality of mirrors is configured to direct light from the first lens to a corresponding mirror of a second plurality of mirrors; the second plurality of mirrors, wherein each of the second plurality of mirrors is configured to direct light from the corresponding mirror of the first plurality of mirrors to a corresponding mirror of a third plurality of mirrors; the third plurality of mirrors, wherein each of the third plurality of mirrors is tilted at an angle different from each other of the third plurality of mirrors, wherein each of the third plurality of mirrors is configured to direct light from a corresponding mirror of the second plurality of mirrors to a second lens; and the second lens.

In some embodiments of the spectrometer, each of the second plurality of mirrors is configured to image a surface of the corresponding mirror of the first plurality of mirrors on a surface of the corresponding mirror of the second plurality of mirrors.

In some embodiments of the spectrometer, the interferometer comprises a beam splitter, a first mirror, and a second mirror, wherein each of the first mirror and the second mirror is a corner-cube mirror.

In some embodiments of the spectrometer, the interferometer is in a Michelson configuration.

According to another aspect of the present disclosure, a satellite comprises a spectrometer according to any of the embodiments described above, including any combination of any or all of the features described above.

According to claim <NUM> a method of using a spectrometer is suggested, the method comprising gathering light into an inverted image slicer, the inverted image slicer configured to accept input light to the spectrometer; transmitting light from the inverted image slicer to an adjustable interferometer; and detecting light from the adjustable interferometer at a sensor, wherein the inverted image slicer causes a linear field of view of the spectrometer to be imaged as a two-dimensional grid on the sensor.

In some embodiments, the method may further include analyzing data from the sensor to determine a spectrum of the gathered light.

In some embodiments, the method may further include predicting the weather based on the spectrum of the gathered light.

In some embodiments of the method, the sensor is configured to sense a range of wavelengths, wherein the range of wavelengths includes <NUM> micrometers.

In some embodiments of the method, the sensor comprises a two-dimensional array of pixels, wherein data from each pixel of the two-dimensional array of pixels can be used to determine a spectrum of light imaged at that pixel with a resolution better than <NUM>-<NUM>.

In some embodiments of the method, the inverted image slicer converts a field of view with at least one dimension extending across at least <NUM> milliradians to a field of view with each dimension extending across less than <NUM> milliradians.

In some embodiments of the method, each of the second plurality of mirrors is configured to image a surface of the corresponding mirror of the first plurality of mirrors on a surface of the corresponding mirror of the second plurality of mirrors.

In some embodiments of the method, the interferometer comprises a beam splitter, a first mirror, and a second mirror, wherein each of the first mirror and the second mirror is a corner-cube mirror.

In some embodiments of the method, the spectrometer is on a satellite orbiting Earth.

While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described herein in detail.

Additionally, it should be appreciated that items included in a list in the form of "at least one A, B, and C" can mean (A); (B); (C): (A and B); (B and C); (A and C); or (A, B, and C). Similarly, items listed in the form of "at least one of A, B, or C" can mean (A); (B); (C): (A and B); (B and C); (A and C); or (A, B, and C).

Referring now to <FIG>, a satellite <NUM> includes a spectrometer <NUM>. The spectrometer <NUM> has a light gatherer <NUM>, an inverted image slicer <NUM>, an interferometer <NUM>, an image sensor <NUM>, and control circuitry <NUM>. In use, the satellite <NUM> is in orbit around the Earth, as shown in <FIG>. The spectrometer <NUM> is configured to monitor a spectrum of the atmosphere of the Earth below the satellite <NUM>. The spectrometer <NUM> may have a relatively wide field of view across the track of the satellite <NUM> and a relatively narrow field of view along the track of the satellite <NUM>. As the satellite <NUM> moves across its track, the wide across-track field of view sweeps out a wide swath of area that is monitored by the spectrometer <NUM>. In the illustrative embodiment, the spectrometer <NUM> may be supported in a housing designed to withstand the extraterrestrial environment (e.g., an aluminum or stainless steel optical bench and cover).

The spectrometer <NUM> uses the inverted image slicer <NUM> to convert a linear field of view of the satellite into a grid, converting a field of view at the light gatherer <NUM> from, e.g., a horizontal field of view of <NUM> milliradians and a vertical field of view of <NUM> milliradians to an effective field of view at the interferometer <NUM> of <NUM> milliradians by <NUM> milliradians. The field of view of the light gatherer <NUM> may be any suitable field of view, such as <NUM> to <NUM>,<NUM> milliradians in the horizontal and/or vertical direction. It should be appreciated that labeling a particular field of view as horizontal and/or vertical is arbitrary and does not limit the orientation of the satellite <NUM>, the spectrometer <NUM>, or any other component. It should further be appreciated that the field of view is not necessarily rectangular. For example, the field of view may be an ellipse, a circle, a square, or any other suitable shape. In the illustrative embodiment, the field of view of the spectrometer <NUM> is defined by one or more apertures, pupils, acceptance angles, etc., of one or more of the components of the light gatherer <NUM>. Additionally or alternatively, the field of view may be defined by another component of the spectrometer, such as the image that is created on the image sensor <NUM>.

In the illustrative embodiment, the light gatherer <NUM> is a lens combined with an aperture to control the light entering the system. In some embodiments, the light gatherer <NUM> may be embodied as one or more mirrors, one or more lenses, one or more additional optics, and/or any combination of the above. By way of example, in some embodiments, the light gatherer <NUM> may comprise scanning or static folding mirrors to redirect a line of sight of spectrometer <NUM>.

The inverted image slicer <NUM> may be any suitable inverted image slicer <NUM> capable of performing the function described herein. One embodiment of the inverted image slicer <NUM> is described in more detail below in regard to <FIG>. However, it should be appreciated that the inverted image slicer <NUM> may be implemented in a different manner. For example, the inverted image slicer <NUM> may be implemented using one or more lenses, prisms, optical fiber bundle, holograms, or other transmissive optics instead of the mirror-based implementation of the embodiments described in <FIG>. Additionally or alternatively, the inverted image slicer <NUM> may be implemented using one or more additional components, such as gratings, deformable mirrors, adaptive optics, etc. It should be appreciated that the inverted image slicer <NUM> operates in a similar manner and with similar structure as an image slicer known in the art but in reverse (i.e., with input and output swapped). In the illustrative embodiment, the inverted image slicer <NUM> rearranges a field of view with a horizontal field of view that is <NUM> times that of the vertical field of view into an effective field of view of approximately equal fields of view in the horizontal and vertical directions by segmenting the field of view into five groups and rearranging them as shown in <FIG>. In some embodiments, the inverted image slicer <NUM> may rearrange a field of view into a different number of groups, such as <NUM>-<NUM> groups.

The interferometer <NUM> may be any suitable interferometer <NUM> capable of being used in a Fourier transform spectrometer. One embodiment of the interferometer <NUM> based on a Michelson interferometer is described in more detail below in regard to <FIG>. In some embodiments, a different type of interferometer may be used, such as a Fabry-Perot interferometer, a Mach-Zehnder interferometer, a Sagnac interferometer, a static interferometer, a slit-based interferometer, etc..

In the illustrative embodiment, the image sensor <NUM> is a two-dimensional (2D) array of five by five pixels. Each pixel in the illustrative image sensor <NUM> corresponds to a field of view of approximately <NUM> milliradians. In other embodiments, the image sensor <NUM> may be any suitable array of pixels, such as an array of <NUM> to <NUM>,<NUM> pixels by <NUM> to <NUM>,<NUM> pixels. The field of view per pixel may be any suitable value, such as <NUM> microradians to <NUM> milliradians. The illustrative image sensor <NUM> is sensitive to light, such as infrared light from <NUM>-<NUM> to <NUM>-<NUM> (i.e., about <NUM> micrometers to <NUM> micrometers). In the illustrative embodiment, the spectral resolution for the central pixel is <NUM>-<NUM> at a wavelength of <NUM> microns, and the spectral resolution for the pixel that is the farther off axis (i.e., the cornet pixels) is <NUM>-<NUM> at a wavelength of <NUM> microns. It should be appreciated that the spectral resolution may depend on the interferometer <NUM> discussed in more detail below as well as factors such as the wavelength of the light. The image sensor <NUM> may be sensitive to any suitable range of wavelengths, such as any range covering any part of the UV to far infrared (e.g., <NUM> nanometers to <NUM> micrometers). In some embodiments, the spectrometer <NUM> may include more than one sensor <NUM> that is sensitive to different wavelength ranges. The image sensor <NUM> may be embodied as a charge coupled device (CCD), a complementary metal-oxide semiconductor device (CMOS), a superconducting camera, or any other suitable light sensor. In some embodiments, the image sensor <NUM> may use narrow gap semiconductors, such as indium antimonide, indium arsenide, mercury cadmium telluride, lead sulfide, or lead selenide. In the illustrative embodiment, the image sensor <NUM> is actively or passively cooled, such as by using a heat sink, a peltier cooler, a Stirling engine cryocooler, etc. In some embodiments, the image sensor <NUM> may be on a translation stage.

The control circuitry <NUM> is configured to provide any necessary electrical control, processing, communication, etc., for the satellite <NUM> and/or the spectrometer <NUM>. In the illustrative embodiment, the control circuitry <NUM> receives a signal from the image sensor <NUM>. The control circuitry <NUM> may include a pre-amplifier and an analog-to-digital converter to convert the signal from the image sensor <NUM> to a digital signal. The control circuitry <NUM> may be configured to control and/or monitor the relative displacement of the two paths of the interferometer <NUM>. It should be appreciated that signal from the image sensor <NUM> does not directly indicate the intensity for a given wavelength. Rather, the output from the image sensor <NUM> is in the form of an interferogram or interference pattern. In the illustrative embodiment, the control circuitry <NUM> performs the necessary analysis to transform the interferogram into a spectrum. Additionally or alternatively, the control circuitry <NUM> may transmit the data of the image sensor <NUM> to a ground station, which may perform the analysis to generate a spectrum.

The control circuitry <NUM> may be implemented as any suitable electronic device or set of devices capable of performing the function here. For example, the control circuitry <NUM> may be implemented as an application specific integrated circuit (ASIC), a system-on-a-chip (SoC), a field programmable gate array (FPGA), a processor-based computer, a multiprocessor system, and/or any other suitable electronic circuit. In some embodiments, some or all of the control circuitry <NUM> may be implemented as a processor, memory, and associated components. The processor may be embodied as a single or multi-core processor(s), a single or multi-socket processor, a digital signal processor, a microcontroller, or other processor or processing/controlling circuit. Similarly, the memory may be embodied as any type of volatile or non-volatile memory or data storage capable of performing the functions described herein. In operation, the memory may store various data and software used during operation of the control circuitry <NUM>, such as operating systems, applications, programs, libraries, and drivers. The control circuitry <NUM> may include additional components such as data storage and communication circuitry. The data storage may be embodied as any type of device or devices configured for the short-term or long-term storage of data. For example, the data storage may include any one or more memory devices and circuits, memory cards, hard disk drives, solid-state drives, or other data storage devices. The communication circuitry may be embodied as any type of interface capable of communicating information to and/or from the satellite <NUM>. The communication circuitry may include or be connected to one or more antennas. The communication circuitry may be capable of interfacing with any appropriate cable type, such as an electrical cable or an optical cable. The communication circuitry may be configured to use any one or more communication technology and associated protocols (e.g., Ethernet, Bluetooth®, Wi-Fi®, WiMAX, near field communication (NFC), Omni-Path, etc.). In the illustrative embodiment, conductive sinking is provided to allow the control circuitry <NUM> (and other electronics of the system) to operate in low pressure.

Although the illustrative spectrometer <NUM> is shown on a satellite <NUM>, it should be appreciated that the spectrometer <NUM> may be used in other embodiments other than a satellite <NUM>. For example, the spectrometer <NUM> may be used under an aircraft, used fixed over a conveyor belt, or used in any instance where a pushbroom interferometer would have a field of view that is too large for the desired spectral resolution.

Referring now to <FIG>, in one embodiment, components of the inverted image slicer <NUM> are shown. A lens <NUM> gathers incoming light. Light from the lens <NUM> reflects off of a pointing mirror <NUM> and is focused to an array of mirrors <NUM> (i.e., mirrors 306A-306E). Each of the illustrative mirrors 306A-306E is concave (to image aperture of lens <NUM> on each mirror of the array <NUM>). In the illustrative embodiment, each of the mirrors 306A-306E is placed approximately one focal length away from the lens <NUM>. Each of the mirrors 306A-306E directs incoming light to one of the array of mirrors <NUM> (i.e., mirrors 308A-308E). In particular, mirror 306A is configured to direct incoming light to mirror 308A, mirror 306B is configured to direct incoming light to mirror 308B, etc. Each mirror 308A-308E refocuses the light and directs it to another array of mirrors <NUM> (i.e., mirrors 310A-310E). In particular, mirror 308A is configured to direct incoming light to mirror 310A, mirror 308B is configured to direct incoming light to mirror 310B, etc. Each of the illustrative mirrors 310A-310E is concave (to image the aperture of the lens <NUM> on the lens <NUM>). In the illustrative embodiment, each of the mirrors 308A-308E is a concave mirror that focuses the light. The focal length and placement of each of the mirrors 308A-308E is such that light that is focused at the surface of the mirrors 306A-306E is also focused at the surface of the mirrors 310A-310E. In particular, in the illustrative embodiment, each of the mirrors 308A-308E is placed two focal lengths away from the corresponding mirrors 306A-306E and 310A-310E. Each of mirrors 310A-310E is configured to reflect the incoming light towards the lens <NUM>. The lens <NUM> is placed approximately one focal length away from the array of mirrors <NUM> to collimate the light. It should be appreciated that any rays that are incoming parallel to the gathering lens <NUM> are also parallel after passing through the lens <NUM>, which is then suitable as an input to the interferometer (see <FIG>). It should further be appreciated that, in the illustrative embodiment, the mirrors 306A-306E, 308A-308E, 310A-310E are configured such that any ray that passes through the center of the lens <NUM> also passes through the center of the lens <NUM>. Additionally or alternatively, in some embodiments, the aperture of the lens <NUM> may be imaged on one or both of the mirrors of the interferometer <NUM>, such that any ray that passes through the center of the lens <NUM> also reflects off of the center of the one or both mirrors of the interferometer <NUM>.

It should be appreciated that a linear field of view of the spectrometer <NUM> is imaged at the array of mirrors <NUM>. The linear field of view of divided into five groups, which are reorganized from a line at the array of mirrors <NUM> into a grid pattern at the array of mirrors <NUM>.

Each of the mirrors and lenses shown in <FIG> may be any suitable mirrors and lenses. For example, the lenses <NUM>, <NUM> may be, e.g., glass, fused silica, silicon, plastic, or any other suitable material. The mirrors <NUM>, 306A-306E, 308A-308E, 310A-310E may be any suitable type of mirror, such as a substrate coated with, e.g., gold, aluminum, silver, copper, an interference coating, etc..

Referring now to <FIG>, a path of one set of rays <NUM> through the inverted image slicer <NUM> are shown. The rays <NUM> correspond to three rays coming from the same direction (i.e., coming from the same point). The rays <NUM> include a left ray 314A, a principal ray 314B, and a right ray 314C. They rays <NUM> are all focused to the same point on the mirror 306B and directed to mirror 308B. Mirror 308B refocuses the rays <NUM> and directs them to mirror 310B. Mirror 310B then redirects the rays <NUM> towards the lens <NUM>. It should be appreciated that mirror 310B directs the principal ray 314B through the center of the lens <NUM>. It should further be appreciated that the rays <NUM> are spaced out in the horizontal direction when passing through lens <NUM> and are also spaced out in the horizontal direction when passing through lens <NUM>. Of course, in use, additional rays parallel to the rays <NUM> may be included that are spaced out in the vertical direction as well.

Referring now to <FIG>, a path of one set of rays <NUM> through the inverted image slicer <NUM> are shown. The rays <NUM> correspond to the principal rays passing through the center of lens <NUM> (and lens <NUM>) for each of several points on the linear field of view of the satellite <NUM>. In particular, rays <NUM> include ray 402A corresponding to the center ray of the first slice of the inverted image slicer <NUM>, ray 402B corresponding to the center ray of the second slice of the inverted image slicer <NUM>, etc. Each of the rays 402A-402E is focused onto the corresponding mirror 306A-306E. Each mirror 306A-306E directs the corresponding ray 402A-402E to corresponding mirror 308A-308E. Each mirror 308A-308E directs corresponding ray 402A-402E to corresponding mirror 310A-310E. Each mirror 310A-310E directs corresponding ray 402A-402E to the center of the lens <NUM>. It should be appreciated that rays 402A-402E are initially spread out in different directions along the vertical plane when passing through lens <NUM> but are reorganized by the inverted image slicer <NUM> to be spread out in different directions along the horizontal plane when passing through lens <NUM>.

Referring now to <FIG>, a path of one set of rays <NUM> through the inverted image slicer <NUM> are shown. The rays <NUM> correspond to the principal rays passing through the center of lens <NUM> (and lens <NUM>) for each of several points on the linear field of view of the satellite <NUM> of a single slice of the inverted image slicer <NUM>. In particular, rays <NUM> include ray 502A corresponding to the principal ray of the lowermost point imaged on mirror 306B, ray 502B corresponding to the principal ray of the center point imaged on mirror 306B, and ray 502C corresponding to the principal ray of the uppermost point imaged on mirror 306B. Mirror 306B directs the rays 502A-502C to mirror 308B. Mirror 308B directs the rays 502A-502C to the mirror 310B. Mirror 310B directs each of the rays 502A-502C to the center of the lens <NUM>. It should be appreciated that rays 502A-502C are initially spread out in different directions along the vertical plane when passing through lens <NUM> and are still spread out in different directions along the vertical plane when passing through lens <NUM>.

Referring now to <FIG>, one embodiment of the interferometer <NUM> is shown. The interferometer includes a beam splitter <NUM>, a mirror <NUM>, a mirror <NUM>, and an actuator <NUM>. A lens <NUM> is also shown, which creates an image on the image sensor <NUM>. The interferometer accepts light from the lens <NUM> of the inverted image slicer <NUM> (see <FIG>). The light is split into two paths at the beam splitter <NUM>. The two paths are reflected by mirrors <NUM>, <NUM> and recombined at the beam splitter <NUM>, where the two paths interfere with each other. One of the interfered paths is focused by the lens <NUM> onto the sensor <NUM>. The other interfered path is not used.

The beam splitter <NUM> may be embodied as any suitable component for splitting the incoming light into two or more paths. The beam splitter <NUM> may be embodied as a cube beam splitter, a plate beam splitter, a pellicle beam splitter, a polarizing beam splitter, a non-polarizing beam splitter, etc. The beam splitter <NUM> may be made of any suitable material, such as glass, fused silica, silicon, plastic, or any other suitable material. Each of the mirrors and lenses shown in <FIG> may be any suitable mirrors and lenses. For example, the lens <NUM> may be, e.g., glass, fused silica, silicon, plastic, or any other suitable material. The mirrors <NUM>, <NUM> may be any suitable type of mirror, such as a substrate coated with, e.g., gold, aluminum, silver, copper, an interference coating, etc. In the illustrative embodiment, each of the mirrors <NUM>, <NUM> is embodied as a corner-cube reflector. It should be appreciated that, in such an embodiment, the interferometer <NUM> may be less sensitive to rotations from the mirrors <NUM>, <NUM>. Additionally or alternatively, in some embodiments, one or both of the mirrors <NUM>, <NUM> may be planar mirrors.

It should be appreciated that the resolution of the interferometer <NUM> may depend on the angle of the incoming light. In particular, light that is nearly on-axis may have a better spectral resolution, and light that is farther off-axis may have a worse spectral resolution. As a result, the transformation of the light at the gathering lens <NUM> from a wide, linear field of view to a grid field of view may improve the average resolution of the interferometer <NUM>.

The actuator <NUM> is configured to move the mirror <NUM> along the principal axis of the light. The mirror <NUM> may be mounted on a translation stage (not shown) that interfaces with the actuator <NUM>. The actuator <NUM> may be able to move any suitable distance, such as <NUM>-<NUM> millimeters close to or farther away from the beam splitter <NUM> relative to a balanced configuration. It should be appreciated that, in the illustrative embodiment, the optical path difference is twice the offset of the mirror <NUM> relative to a balanced configuration. In other embodiments, the optical path difference may be four or more times the offset of the mirror <NUM> relative to a balanced configuration. In the illustrative embodiment, the actuator <NUM> oscillates back and forth over an optical path difference of ± <NUM>. In some embodiments, the actuator <NUM> may oscillate over a different optical path length, such as any suitable distance from several micrometers to several meters. The actuator may oscillate over any suitable period of time, such as <NUM> milliseconds to <NUM> hours. It should be appreciated that, in the illustrative embodiments, the center of the oscillation of the actuator <NUM> may be offset from the balanced configuration. For example, the actuator <NUM> may be offset by, e.g., <NUM>-<NUM>,<NUM> times the center wavelength of the light being detected. It should be appreciated that a higher offset can correspond to a higher resolution with a corresponding loss of spectral range.

Claim 1:
A spectrometer (<NUM>) comprising:
an inverted image slicer (<NUM>) configured to accept input light to the spectrometer (<NUM>);
an adjustable interferometer (<NUM>) configured to accept light from the inverted image slicer (<NUM>), wherein the adjustable interferometer is capable of being used in a Fourier transform spectrometer;
a sensor (<NUM>) configured to sense light from the adjustable interferometer (<NUM>);
wherein the inverted image slicer (<NUM>) causes a linear field of view (<NUM>) of the spectrometer (<NUM>) to be imaged as a two-dimensional grid on the sensor (<NUM>),
wherein the inverted image slicer (<NUM>) comprises:
a first lens (<NUM>) to focus input light onto a first plurality of mirrors (306A-306E);
the first plurality of mirrors (306A-306E), wherein each of the first plurality of mirrors (306A-306E) is tilted at an angle different from each other of the first plurality of mirrors (306A-306E), wherein each of the first plurality of mirrors (306A-306E) is configured to direct light from the first lens (<NUM>) to a corresponding mirror of a second plurality of mirrors (308A-308E);
the second plurality of mirrors (308A-308E), wherein each of the second plurality of mirrors (308A-308E) is configured to direct light from the corresponding mirror of the first plurality of mirrors (306A-306E) to a corresponding mirror of a third plurality of mirrors (310A-310E);
the third plurality of mirrors (310A-310E), wherein each of the third plurality of mirrors (310A-310E) is tilted at an angle different from each other of the third plurality of mirrors (310A-310E), wherein each of the third plurality of mirrors (310A-310E) is configured to direct light from a corresponding mirror of the second plurality of mirrors (308A-308E) to a second lens (<NUM>); and
the second lens (<NUM>).