Method and system for high magnification photography utilizing a reflective polarizer and a faraday rotator

Abstract

Systems and methods are described herein for enabling small, high magnification cameras or imaging systems to operate in low light {e.g., nighttime} conditions. These systems include the use of reflective polarizers and non-reciprocal elements {Faraday rotators} to allow longer light paths and allow the light to reach the sensor and form an image.

Description

[Technical field]

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 267,100, filed January 24, 2022, which is incorporated by reference herein in its entirety.

[0002] This application generally relates to the field of high magnification photo imaging and imaging technology. More specifically, the present invention relates to a system and method that utilizes a polarizer and a non-reciprocal element or elements (e.g., Faraday rotators) for use in high magnification cameras or imaging devices. This application also relates to imaging devices or cameras built into mobile phones, smartphones, tablets, laptops, drones, or any other mobile devices. [Background technology]

[0003] Digital cameras are widely used in mobile devices, e.g. smartphones. Camera performance is a major differentiator for customers and has a major impact on market share. This drives mobile device manufacturers and component suppliers to strive to improve camera performance.

[0004] One key aspect of a mobile device's camera performance is high magnification (or high zoom) photography. Typically, cameras or imaging devices that achieve high magnification photo capture have long and large lens assemblies (e.g., zoom lenses in DSLR cameras). However, mobile devices are thin and compact and cannot accommodate long lens assemblies. This has traditionally limited their magnification and zoom capabilities. Summary of the Invention [Problem to be solved by the invention]

[0005] This application discloses systems and methods for improving the performance of high-magnification, small-volume (e.g., thin) cameras or imaging systems. Specific embodiments include the use of at least one transmissive non-reciprocal optical element, such as a lens, a reflective polarizer, and a Faraday rotator. Doing so can expand the light path within the camera, which allows for a longer focal length and therefore higher magnification. In some cases, it can do so without significant light loss. This allows, for example, high-magnification, small-volume camera photography / videography in low-light conditions (e.g., at night). It is also beneficial for both long-range smartphone photography / videography, and for close-up "macro" photography / videography (meaning taking high-magnification photos or videos of small, but close-by objects, such as ants on a leaf). [Means for solving the problem]

[0006] One aspect includes methods and systems for improving the performance of high magnification, small volume (e.g., thin) cameras or imaging systems, which include internal reflection and polarization as part of their operation. Such small, but very high magnification cameras are advantageous for smartphones, tablets, drones and other mobile devices, or for use in small, confined spaces, such as discreet locations inside autonomous vehicles. Having internal reflections inside a small camera or imaging system allows for a longer light path, and therefore allows for the use of longer focal lengths, which in turn allows for higher magnification. In particular, the present application discloses the use of polarizers, reflectors and non-reciprocal elements (Faraday rotators) to improve performance, including allowing operation in low light conditions.

[0007] Another aspect includes an imaging system for capturing an image having a substrate having a focal length, a first reflective polarizer adjacent to the substrate, a second reflective polarizer downstream with respect to the substrate, a nonreciprocal optical element between the first reflective polarizer and the second reflective polarizer, and a sensor for forming an image, where the substrate, the first reflective polarizer, the nonreciprocal element, the second reflective polarizer, and the sensor are arranged along an optical path. Light entering the substrate of the imaging system is polarized by the first reflective polarizer, transmitted through the nonreciprocal element where its polarization is rotated, reflected from the second reflective polarizer, returned through the nonreciprocal element where its polarization is further rotated, reflected from the first reflective polarizer, transmitted through the nonreciprocal element a third time where its polarization is rotated, and transmitted through the second reflective polarizer to form an image on the sensor.

[0008] Another embodiment involves a non-reciprocal optical element that is a Faraday rotator.

[0009] Another embodiment includes a Faraday rotator positioned to provide a 45° polarization rotation.

[0010] Another aspect includes a system arranged to change the polarization of light during its passage along the optical path.

[0011] Another aspect includes the substrate being a lens.

[0012] Another embodiment includes a second lens.

[0013] Another embodiment includes one or more additional lenses or substrates having a focal length, the one or more additional lenses or substrates having a spherical or aspherical curved surface.

[0014] Another embodiment includes cornering prisms or turning reflectors.

[0015] Another embodiment includes where the non-reciprocity element has two or more elements.

[0016] Another embodiment includes a Faraday rotator having two or more elements.

[0017] Another aspect involves the focal length of the system being matched to the round trip distance of the optical path.

[0018] Another aspect includes one or more of the substrate, reflective polarizer, non-reciprocal optical element being mechanically moved to change the overall focal length of the imaging system.

[0019] Another aspect includes a smart device having the system.

[0020] Another aspect includes a smart device that is a smartphone, a cell phone, a tablet, a laptop, a drone or a mobile device.

[0021] Another aspect includes an optical system for capturing an image, the optical system having a lens having a focal length and a curvature, a first reflective polarizer adjacent to the lens, the first reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal second polarization state, a second reflective polarizer, a Faraday rotator between the first reflective polarizer and the second reflective polarizer, and a sensor for forming an image. The substrate, the first reflective polarizer, the Faraday rotator, the second reflective polarizer, and the sensor are arranged along an optical path. Light entering the optical system is polarized by the first reflective polarizer, passes through a nonreciprocal element, has its polarization rotated, is reflected from the second polarizer, passes back through the nonreciprocal element, has its polarization further rotated, is reflected from the first reflective polarizer, passes through the nonreciprocal element a third time, has its polarization rotated, and passes through the second reflective polarizer to form an image on the sensor.

[0022] Further aspects include cameras having the system, and devices such as telescopes, monoculars, binoculars, cameras, etc. having a system or utilizing the methods disclosed herein.

[0023] Another aspect includes a method for high magnification imaging including the steps of accepting light entering a substrate having a focal length, polarizing the light, rotating the light in one direction, reflecting the light with the rotated polarization, rotating the light in an opposite direction to the first rotation, reflecting the light with the rotated polarization, rotating the light in the same direction as one of the previous steps, and transmitting the light into a sensor to capture an image. [Brief description of the drawings]

[0024] [Figure 1] FIG. 4 shows an example embodiment having a lens or focusing substrate (201), two polarizers (202, 204) with a Faraday rotator (203) therebetween, and a sensor (401), which may enable high magnification and low light photography in a camera or imaging system. [Diagram 2] FIG. 2 illustrates the embodiment of FIG. 1 integrated into an example smartphone. [Diagram 3] FIG. 2 shows an alternative embodiment of FIG. 1 integrated into an example smartphone, also having a steering mirror or cornering prism (200). [Figure 4] FIG. 13 illustrates the advantages of the disclosed embodiments when movement of optical elements is related to changes in focus adjustment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present application will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown, however, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0026] This application discloses compact, low-volume cameras or imaging systems that use polarizing reflectors and at least one non-reciprocal element (such as a Faraday rotator). They allow both high magnification and low illumination operation. A key aspect of this specification is the selection of the properties of the unique and innovative arrangement of polarizers and the non-reciprocal element between them, such as a Faraday rotator. In particular, the properties of the Faraday rotator are selected so that the polarization of the light is adjusted each time it passes through the Faraday rotator and back, in such a way that each reflecting polarizer acts as either a transmitter or a reflector, depending on the exact need. In particular, the Faraday rotator precisely adjusts the polarization to choose the desired transmission or reflection behavior of the polarizer at each stage along the light path. Thus, light can enter the space between the polarizers, which then reflect the light back and forth, again through the action of the Faraday rotator, from where it subsequently exits and reaches the imaging sensor to form an image.

[0027] At the end of this process, the amount of light reaching the sensor is large. Substantially most of the polarized light travels all the way from the entrance to the first polarizer through round-trip reflections to the exit from the second polarizer and reaches the imaging sensor. The round-trip light reflections allow for long optical path lengths in compact cameras, which allows for long focal lengths and therefore high magnification. Since a significant portion of the light can reach the sensor and form an image, it can enable operation in low light, for example at night. Thus, the resulting embodiment can enable a compact camera or imaging system that can achieve both high magnification and low light operation. Such a camera can be suitable for use in smartphones, tablets, drones or other mobile devices.

[0028] In current smartphone camera modules, there is typically one camera (a telephoto camera) responsible for high magnification photography / videography and another camera (e.g., a normal or wide-angle camera) responsible for low light operation, such as nighttime operation. In the presently disclosed method and system, a single camera can handle both high magnification and low light photography / videography. This is desirable for use in smartphones and other mobile devices because it can reduce the size and cost of the camera module while allowing for comparable or higher performance.

[0029] 1 shows an example embodiment having a lens or focusing substrate (201), a first reflective polarizer (202), a Faraday rotator (203), a second reflective polarizer (204) whose orientation is selected to reflect light polarized along a direction that is +45 degrees relative to the direction of light transmitted by the first reflective polarizer, and an imaging sensor (401). The Faraday rotator is configured to rotate the linear polarization of light passing through it (for one pass, i.e., from 102 to 103) by substantially +45 degrees. It rotates the polarization of linearly polarized light by +45 degrees (i.e., counterclockwise) for light traveling from left to right (rightward arrow in FIG. 1 and labeled "CCW, +45 degrees" above 203), and rotates the polarization of linearly polarized light by -45 degrees (i.e., clockwise) for light traveling from right to left (leftward arrow in FIG. 1 and labeled "CW, -45 degrees" below 203).

[0030] The propagation of light through the example system of FIG. 1 is now described in more detail. Light (101) from an external object or source or scene enters the system through an entrance lens (201). Such incoming light is typically unpolarized (and is therefore labeled as unpolarized light with a "U" in the diagram). This light then enters a first linear reflective polarizer (202). A linear reflective polarizer allows linearly polarized light of one orientation to be transmitted therethrough while the other polarization is reflected. The direction of linearly polarized light transmitted through the first reflective polarizer is labeled as horizontal (labeled "H" for short at 102). The direction reflected away from the first polarizer is labeled as vertical (labeled "V" for short). In typical imaging applications, the input light does not have a preferred polarization orientation, so the orientation of the first polarizer can be chosen arbitrarily. In some cases, however, the input light has a preferred polarization orientation. In such cases, it is disclosed that the orientation of the reflective polarizer can be selected to optimize the desired performance of the system (eg, optimal image quality, contrast, etc.).

[0031] The light (102) then enters the Faraday rotator (203), which may be composed of a material that exhibits the Faraday effect. The Faraday effect is a magneto-optical effect that involves the transmission of light through a material in the presence of a longitudinal static magnetic field. In the Faraday effect, the polarization of the light rotates around the propagation vector of the light ray. The direction of rotation depends on the direction the light propagates through the material. For example, if the light propagates from left to right, the polarization may rotate counterclockwise around the propagation vector. If the light propagates from right to left, in this example, it would rotate clockwise. Such differences in behavior due to the propagation of light in one direction versus the other are a manifestation of the non-reciprocal property of the Faraday effect. The Faraday effect exhibits a broken time-reversal symmetry, which means that the behavior of light may depend on which direction the light passes through the material.

[0032] In FIG. 1, the linear polarization of the light rotates counterclockwise when the light travels from left to right and clockwise when the light travels from right to left. However, it should be understood that this is only an example case and the light may also undergo reverse rotation depending on the selected properties of the Faraday material as well as based on the direction of the applied external magnetic field or the direction of the internal magnetization. In our example case, the properties of the Faraday rotator are selected to rotate the linear polarization by substantially +45 degrees for light propagating from left to right. Thus, when the light (103) exits the Faraday rotator, it has a linear polarization oriented substantially at +45 degrees (hence 103 is labeled +45 degrees).

[0033] FIG. 1 further shows a second reflective polarizer (204). The light 103, linearly polarized at +45 degrees, will reflect and return as light 104. Upon reflection from the second polarizer (204), the direction of the light's propagation vector is reversed, but the direction of the polarizing electric field remains in the same direction. This results in the linearly polarized vector undergoing a near vertical (V) reflection. Hence, the polarization is reversed from a linear polarization at +45 degrees (with respect to 103) to a linear polarization at +135 degrees (with respect to 104) after reflection from the reflective polarizer (204).

[0034] This (104) light with its +135 degree linear polarization then re-enters the Faraday rotator (203). Due to the non-reciprocal nature of the Faraday effect, the Faraday rotator now rotates the light 45 degrees (i.e., -45 degrees) in a clockwise direction, which rotates the polarization from +135 to +90 degrees. Therefore, for light 105, the linear polarization vector is now oriented at +90 degrees (relative to a horizontal "H" polarization), which is therefore a vertically oriented linear polarization (shortened to "V" in 105).

[0035] Because the first polarizer was selected such that it is oriented such that it substantially reflects vertically polarized light, light (105) will be substantially reflected from the first reflective polarizer. For this reflected 106 light, the linear polarization will again undergo a mostly vertical reflection. However, since the polarization direction is already aligned along the same direction as the reflection axis, it will not undergo any change. 106 will therefore also be vertically polarized (the "V" label on 106).

[0036] This light (106) then re-enters the Faraday rotator (203). In this third pass of the light through the Faraday rotator, the Faraday rotator again rotates the linearly polarized light counterclockwise. Thus, when the light (107) exits the Faraday rotator (203), it now has a linear polarization oriented substantially at +90+45=+135 degrees.

[0037] As noted above, the second reflective polarizer is oriented such that it substantially reflects light polarized at +45 degrees. A reflective polarizer that reflects +45 degree linear polarization will substantially transmit the orthogonal +135 degree linear polarization. The second reflective polarizer (204) will therefore transmit light 107 with its +135 degree linear polarization orientation. Thus, when light 107 strikes the second polarizer (204), it will be substantially transmitted (108) and reach the imaging sensor (401) to form an image.

[0038] Thus, the selected Faraday rotators (203) precisely applied their rotation to the linear polarization such that the light path (102, 103, 104, 105) is reflected once between the two polarizers, but then on its third section (106, 107, 108) exits to the sensor (401). Such a configuration can allow a longer light path in a compact camera, which supports a longer focal length and therefore a higher magnification.

[0039] Furthermore, the transmission and reflection enabled by the two polarizers can be efficient. Due to the polarization rotation applied by the Faraday rotator, when transmission is required (107 to 108), the polarizer (204) will transmit most of its light, and when reflection is required (103 to 104 and 105 to 106), the first polarizer or the second polarizer (202, 204), respectively, will reflect most of its light. Therefore, a significant amount of the (horizontally polarized) light (101) entering the camera can travel along the optical paths (102, 103, 104, 105, 106, 107, 108) and reach the imaging sensor (401). This can enable operation in low light (e.g., at night), since a significant amount of the incoming light reaches the sensor.

[0040] The system can equally well operate if the sign or direction of rotation is reversed. The embodiment remains operable even if the Faraday rotator (203) rotates the linear polarization of the light by substantially -45 degrees (i.e., now it rotates it clockwise instead of counterclockwise), and even if the second polarizer (204) has a reflected polarization direction oriented at a substantially -45 degree angle with respect to the first polarizer (instead of +45 degrees as described above). Also, the entire assembly can be rotated by any arbitrary angle, which corresponds equally to choosing the orientation of what is labeled as horizontal polarization.

[0041] In another embodiment, the system can operate when the size of the Faraday rotation is smaller than 45 degrees. Assuming that the Faraday rotator rotates the linearly polarized light by an angle beta, where beta is, for example, substantially 40 degrees, 35 degrees, 30 degrees, etc., or some other angle less than 45 degrees. In this case, the angle between the transmission polarization orientation of the first reflective polarizer and the reflection polarization orientation of the second reflective polarizer is selected to be beta. The system operates in the same way, but the total amount of light reaching the sensor is reduced (i.e., the efficiency of the imaging system is reduced).

[0042] The Faraday rotator element (203) can be composed of a material that exhibits circular polarization birefringence. It may be composed of, but is not limited to, doped glass, thin films, or other materials with a high Verdet constant (the Verdet constant is an optical property of a material that describes the strength of the Faraday effect in that material). The Faraday effect is a magneto-optical effect that involves the transmission of light through a material in the presence of a longitudinal static magnetic field. Thus, the Faraday rotator may include surrounding magnets, magnetic materials, electrical wiring, or other components that apply an appropriate magnetic field to allow polarization rotation through the width of the Faraday rotator.

[0043] Magnet-free Faraday rotators are also possible. For such Faraday rotators, no external magnets or external magnetic materials are required. Instead, the magnetic field exists within the Faraday material itself. This can be achieved by doping the material with magnetic impurities or with magnetized elements embedded within the material (e.g., magnetized micro- or nanoparticles, wires, or other mechanisms). Alternatively, the material may exhibit magnetization latching and be pre-magnetized. Some examples of Faraday materials include thin-film crystalline organic and inorganic materials that have been developed to act as Faraday rotation materials. There are organic or polymer films with magnetic additives that can act as Faraday materials. There are also other methods known in the art to create Faraday rotation. It is disclosed herein that Faraday rotators can be constructed from any of the above methods, either with or without external magnets or magnetic materials.

[0044] In other embodiments, one, some, or all of the elements in FIG. 1 may be implemented as multiple elements acting together to perform a function. For example, any single lens or focusing substrate may be replaced by a group of lenses or substrates. Furthermore, the Faraday rotator (203) may be composed of, for example, multiple rotators or multiple layers, each of which achieves a portion of the desired rotation. It may or may not include other elements that enable Faraday rotation, such as magnetic elements, specific materials or films that enable Faraday rotation. It may also include tuning elements (e.g., tuning by voltage, magnetic field, or temperature) that allow tuning of the amount of Faraday rotation.

[0045] Figure 2 shows an example type of camera or imaging system that can be used inside a smartphone, tablet, laptop or other mobile device. This is the example system of Figure 1, but now shown in more detail with its elements oriented inside a smartphone. It consists of a lens or focusing substrate (201) adjacent to which a first reflective polarizer (202) whose orientation is selected to transmit horizontally polarized light and therefore reflect vertically polarized light, adjacent to which a Faraday rotator (203) as described above, adjacent to which a second reflective polarizer (204) whose orientation is positioned at -45 degrees with respect to the first reflective polarizer and therefore selected to reflect +45 degrees polarized light and therefore will transmit +135 degrees linearly polarized light, and adjacent to which an imaging sensor (401). These elements are arranged substantially along the optical path of the camera (contiguous with the incoming light ray 101, i.e., the -Z axis in FIG. 2) and their orientation is substantially perpendicular to this axis or optical path (meaning that they are oriented along the XY plane in FIG. 2).

[0046] As can be seen in FIG. 2, an example system can be used in a smartphone to orient the optical axis of the camera (along 101) through the thickness of the smartphone. This configuration can allow up to doubling the available optical path length (and therefore focal length) across the thickness of the smartphone. FIG. 2 shows the case where the optical axis of the camera (along the incoming optical path 101) can be aligned along the thinnest part of the smartphone (along the -Z axis in FIG. 2). The resulting optical path through the camera and the polarization of the light remain the same as described above with respect to FIG. 1.

[0047] A second way the invention can be utilized is in combination with a periscope geometry. The invention illustrated in FIG. 1 may further include a cornering mirror or prism in front of or behind the lens 201, as illustrated in FIG. 3 for the case where a cornering mirror (200) is in front of the lens 201. In this embodiment, the aperture 701 can also be replaced by a lens or lenses, if desired. Such a design, where the embodiment of FIG. 1 is used in a "periscope" configuration, has advantages over existing smartphone periscope camera designs, where the focusing path length available for the light does not exceed the length of the long axis of the camera (along the Y-axis in FIG. 3). This fixes the available focal length of a conventional smartphone periscope camera, and therefore its maximum magnification. In the embodiment shown in FIG. 3, due to the polarizing reflectors (202 and 204) and the Faraday rotator (203), approximately twice the length of the camera's major axis is available for light travel, and therefore for focusing and magnification.

[0048] In the current example embodiment of FIG. 3, light enters the smartphone along the −Z axis (ray 100) through aperture 701 (which may also be a lens or lens group or a focusing substrate or substrates) and is redirected substantially 90 degrees by a turning mirror (200) or an equivalent cornering prism. The lens (201) may remain behind the turning mirror or cornering prism (as shown in FIG. 3), or it may be located in or near aperture 701, before the turning mirror or cornering prism. The light then travels through this embodiment in the same manner as shown and discussed with respect to FIG. 1 (see light paths 101 to 108 in FIG. 1).

[0049] For example, other optical elements can be added to the embodiment to further improve performance, for example, one or more lenses or focusing substrates, spherical or aspherical, may be added before, between, or after the polarizer and Faraday rotator to reduce imaging aberrations.

[0050] For example, a cornering mirror or cornering prism can be added just before or just after the first lens or focusing substrate, so that the optical path is essentially bent by 90 degrees. This can allow the imaging system to operate along the length of the mobile device (rather than its width), thereby further increasing the available length of the optical path.

[0051] In all of the above embodiments, a single lens or focusing substrate can be replaced by a group of lenses or focusing substrates, or additional lenses can be added before or between the other elements. An aperture, such as aperture 701 in FIG. 3, may also be replaced by a lens or lenses. Or vice versa, a first lens, for example lens 201 in the figure, can be replaced by an aperture, and the required lens can be placed after the aperture.

[0052] It is disclosed that the elements and their surfaces may be curved instead of being flat. Alternatively, curved optical surfaces may be placed in front of or behind the disclosed elements. In particular, mirrors or mirror surfaces may be curved, either spherically or aspherically. If such components are available, one, some or all of the polarizers or the Faraday rotator may be curved or shaped instead of remaining flat. In general, one, some or many elements may be curved or have curved surfaces or have curved optical elements in front of or behind them.

[0053] It is disclosed that some of the optical elements in the embodiments may be moved over time, e.g. translated or tilted, or for some element types, their shape may be adapted over time. Such movements or changes in shape are commonly used to change focus and / or correct video jitter in cameras and imaging systems, and it is disclosed that the same can be used in the systems disclosed herein. There are many ways to affect such movements, including piezoelectric, electrostatic, magnetic, motor-actuated rack-and-pinion, MEMS (micro-electromechanical systems) actuators, or other types of actuation. The inclusion of such movements is disclosed with respect to our embodiments.

[0054] Figure 4 shows another embodiment aspect for improved performance. If the polarizer 204 is moved to the right by an amount ΔX, the change in optical path length is twice that amount, or 2ΔX. This is illustrated in Figure 4. For a polarizer movement ΔX (labeled 4), the light from the lens (201) to the sensor (401) traverses the distance the mirror is displaced more than once. The light traverses it in the forward direction (added optical path 113) and then traverses it again in the return direction (added optical path 114).

[0055] As shown, there is no third magnification of ΔX. For the third pass of light, i.e., 107, 108, the added distance +ΔX from 204 to 214 to the right is offset by the shortened distance -ΔX from 214 to 401. This allows the distance along 106, 107, 108 from 202 to 401 to remain the same even if 204 is moved. However, it is disclosed that if the polarizer (204) and the sensor (410) are moved together as a unit by ΔX, the distance from 202 to 401 also increases by +ΔX. Hence, there is now a 3ΔX benefit in terms of the ΔX movement of the unit. The 2ΔX benefit shown in FIG. 4 and the +ΔX distance added from 204 to a 401.

[0056] The above advantages of double or triple movement are advantageous for small camera applications, including cameras in smartphones or other mobile devices. In such cameras, the amount of space available for element movement is limited. Thus, it is highly desirable to obtain a larger optical path change, and therefore a larger focus change, from the same amount of element movement. Although the above advantages are presented in the context of the embodiment of FIG. 1, the same is true for other embodiments herein.

[0057] In Figures 1-4, there is free space shown between components. However, this is done primarily for purposes of clarity of illustration so that the reader can easily see all of the components of the invention. It is noted that this free space can be maintained, or the components may be moved as close together as desired or as close as permitted by manufacturing or other requirements, and doing so is anticipated and disclosed.

[0058] The disclosed embodiments are selected to allow operation in low light in addition to high magnification. Low light is achieved by inventively selecting a design that delivers a significant portion of light to the sensor, e.g., nearly all light of one type of polarization. It is noted that delivering a significant amount of light to the sensor allows for a better signal-to-noise ratio. If more light reaches the sensor, the signal from the object or scene will be higher compared to the dark noise level of the imaging sensor (dark noise is the amount of noise of the sensor when no light reaches the sensor). By maintaining the amount of light reaching the sensor at a high level, the signal-to-noise ratio is increased, which in turn allows the camera to operate well with less light, i.e. at lower light levels.

[0059] For all of the embodiments, it is disclosed that there are different names and / or different versions of the components that may be used, and that the present disclosure contemplates and includes such uses. Specifically, the polarizing elements may include, but are not limited to, thin film polarizers, micro wire grid polarizers, corrugated plates, liquid crystal rotators, Fresnel rhomboids, and similar devices. One or more of the polarizers may be tunable polarizers, such as liquid crystal polarizers, whose polarization orientation may be changed by applying a voltage.

[0060] The imaging sensor may be a time-integrating sensor, a CCD (charge-coupled device) sensor, a CMOS (complementary metal-oxide semiconductor) sensor, an avalanche photodiode array, an electron multiplier array, a nanoparticle or nanomaterial based sensor, a grayscale or color sensor, any type of sensor used in a smartphone or mobile device camera, or any other type of sensor.

[0061] It is understood that the various stated numbers are not exact values ​​and may have variations. For example, a polarization rotation of plus or minus 45 degrees may have variations. In particular, the amount of rotation does not need to be exactly 45 degrees, both because of the optical properties of light (light at different angles of incidence or different wavelengths of light will experience different phase shifts) and for engineering or manufacturing reasons (Faraday rotator thickness, material variations, and other manufacturing variations) that will also result in variations in the amount of rotation. The current disclosure covers such variations away from the "ideal" 45 degrees of polarization rotation, both for unavoidable reasons (as described above) or for reasons that are intended if a system designer wishes to vary the phase to accommodate system constraints. Other similar cases are likewise covered and are understood to be examples or approximations.

[0062] It is understood that any number also includes its logically opposite sign. For example, one skilled in the art will recognize that the system disclosed herein will function equally well if +45 degrees is replaced by -45 degrees, so long as the embodiment correlation between polarization and Faraday rotation remains self-consistent. Similarly, with respect to polarization in general, a change in sign, or through the addition of an overall positive or negative phase, will not change the operation of the system. Such substitutions are understood to be expected and are covered by the present disclosure.

[0063] For example, with reference to Figures 1-4, the embodiment can equally well operate if the polarizers and other components are selected such that each horizontally polarized light (labeled "H" in the figures) is replaced by a vertically polarized light ("V"), and vice versa. For example, in Figure 1, the polarizer 202 can be oriented such that 102 is linearly polarized vertically ("V" instead of "H"), and then the return path 105 is polarized horizontally ("H"). It is still the case that the light exiting the polarizer (202) and the light returning to the polarizer (202) still differ by 90 degrees, and thus the overall path of light and system operation remains as shown in Figure 1 (except that all "H"s are replaced by "V"s and vice versa, and the +45 degrees and +135 degrees are adjusted appropriately). In this sense, changing the orientation of the polarizer (202) by 90 degrees would leave the system operational and is anticipated and disclosed.

[0064] Changing the orientation of the first reflective polarizer (202) by any other angle other than 90 degrees will leave the system equally operable as long as the orientation of the second reflective polarizer (204) is similarly adjusted. Such changes are understood to be additive to the overall orientation angle and can be selected as desired (e.g., to align the polarization at the sensor with one axis that is convenient for the design of the system, or if the incoming light is polarized to optimize the performance of the system with respect to the polarization of the incoming light). Such changes to the system are understood and disclosed with respect to the embodiment of FIG. 1 as well as with respect to all other embodiments disclosed in this invention.

[0065] A phase-shifted combination of linear polarization states will produce what is called a circular polarization state. Circular polarization can be left-handed (rotates counterclockwise as the beam propagates) or right-handed (rotates clockwise). It is disclosed that left-handed and right-handed polarization states are orthogonal and therefore can also be used as a polarization state in the disclosed invention in the same way that horizontal and vertical linear polarizations are used. There are also elliptical polarization states that are neither perfectly linear nor perfectly circular, but are combinations. Elliptical polarization states are also contemplated in the current invention and may also be used. It is known that the Poincaré sphere can be used to represent polarization states and that any polarization (linear, circular or elliptical) can be represented on this sphere. It is disclosed that linear and circular polarization are just specific special cases and more generally the disclosed invention herein can use polarizations that are anywhere on the Poincaré sphere and that occupy, for example, substantially orthogonal to each other or points that are not directly adjacent on the Poincaré sphere.

[0066] It is further disclosed that there are many known ways to actually accomplish some of the elements listed as components in the disclosed embodiments. For example, the lenses or focusing substrates can be made from glass or plastic or other materials. They can be made using conventional grinding and polishing, single point diamond turning, casting, 3D printing or lithographically defined methods. In addition, the lenses or focusing substrates can also be made through the use of holography, diffractive optical elements, milling, two-dimensional and three-dimensional photonic crystals, microstructured metals and dielectrics, and metalenses using gradient index materials. Polarizers can be made from a variety of materials such as polymeric materials with oriented polymer chains like Polaroid® polarizers, liquid crystal materials, glass, oriented stretched metal nanoparticles embedded in crystals or polymers, Fresnel reflections from dielectric surfaces, birefringent crystal materials, thin films and microscale wire grid materials, or other materials.

[0067] The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention.

Claims

1. 1. An imaging system for capturing an image, comprising: a substrate having a focal length; a first reflective polarizer adjacent to the substrate; a second reflective polarizer downstream relative to the substrate; a non-reciprocal optical element between the first reflective polarizer and the second reflective polarizer; a sensor for forming the image, wherein the substrate, the first reflective polarizer, the non-reciprocity element, the second reflective polarizer, and the sensor are arranged along an optical path; whereby light entering the substrate of the imaging system is polarized by the first reflective polarizer, passes through the nonreciprocal element rotating its polarization, reflects off the second reflective polarizer, passes back through the nonreciprocal element further rotating its polarization, reflects off the first reflective polarizer, passes through the nonreciprocal element a third time rotating its polarization, and passes through the second reflective polarizer to form an image on the sensor.

2. The system of claim 1 , wherein the non-reciprocal optical element is a Faraday rotator.

3. The system of claim 2 , wherein the Faraday rotator is positioned to provide a polarization rotation of 45°.

4. The system of claim 1 , arranged to change the polarization of light during passage along an optical path.

5. The system of claim 1 , wherein the substrate is a lens.

6. The system of claim 1 further comprising a second lens.

7. The system of claim 1 , further comprising one or more additional lenses or substrates having a focal length, the one or more additional lenses or substrates having a spherical or aspherical curved surface.

8. The system of claim 1 further comprising a cornering prism or turning reflector.

9. The system of claim 1 , wherein the non-reciprocity element comprises two or more elements.

10. The system of claim 2 , wherein the Faraday rotator has two or more elements.

11. The system of claim 1 , wherein the focal length of the system corresponds to a round trip distance of the optical path.

12. The system of claim 1 , wherein one or more of the substrate, the reflective polarizer, and the non-reciprocal optical element are mechanically moved to change an overall focal length of the imaging system.

13. A smart device comprising the system of claim 1.

14. 14. The smart device of claim 13, which is a smartphone, a mobile phone, a tablet, a laptop, a drone or a mobile device.

15. A camera comprising the system of claim 1.

16. 1. An optical system for capturing an image, comprising: a lens having a focal length and a curvature; a first reflective polarizer adjacent to the lens, the first reflective polarizer substantially transmitting light having a first polarization state and substantially reflecting light having an orthogonal second polarization state; A second reflective polarizer; and a Faraday rotator between the first reflective polarizer and the second reflective polarizer; a sensor for forming the image, wherein the substrate, the first reflective polarizer, the Faraday rotator, the second reflective polarizer, and the sensor are arranged along an optical path; whereby light entering the optical system is polarized by the first reflective polarizer, passes through the nonreciprocal element rotating its polarization, reflects off the second polarizer, passes back through the nonreciprocal element further rotating its polarization, reflects off the first reflective polarizer, passes through the nonreciprocal element a third time rotating its polarization, and passes through the second reflective polarizer to form an image on the sensor.

17. A camera comprising the system of claim 16.

18. 20. An apparatus comprising the system of claim 17.

19. 20. The device of claim 18, comprising one of a telescope, a monocular, binoculars, and a camera.

20. The system of claim 10 , wherein the lens, the first reflective polarizer, the second reflective polarizer, and the Faraday rotator are substantially along the optical path and parallel.

21. a. receiving light incident on a substrate having a focal length; b. polarizing the light; c. rotating the light in one direction; d. reflecting the light having a rotated polarization; e. rotating the light in an opposite direction to the first rotation; f. reflecting the light having the rotated polarization; g. rotating the light in the same direction as in step c; h. transmitting said light into a sensor to capture an image.

Images