Diffraction grating system

Abstract

The folding system includes a first diffraction grating separated from the second diffraction grating by a wave plate. Both the first diffraction grating and the second diffraction grating have a high diffraction efficiency for the polarization of the first light and a low diffraction efficiency for the polarization of the second light. The incident light passing through the first diffraction grating is rotated by the wave plate. The diffracted light changes from the first polarization to the second polarization and passes through the second diffraction grating with little diffraction. The light passing through the first diffraction grating changes from the second polarization to the first polarization and is diffracted by the second diffraction grating.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit and priority of U.S. Application No. 17 / 861,812, filed on July 11, 2022, which is hereby incorporated by reference in its entirety.

[0002] Diffraction gratings are commonly used as dispersive elements in a wide range of scientific and engineering applications, such as spectroscopy, dense wavelength division multiplexing (DWDM) in telecommunications, and laser pulse compression. In many of these applications, having high levels of dispersion and good diffraction efficiency in both s - polarization (e.g., transverse electric (TE)) and p - polarization (e.g., transverse magnetic (TM)) improves system performance. Further, depending on the application, it may be necessary to keep the difference between the s - polarization diffraction efficiency and the p - polarization diffraction efficiency at a low level, which may be characterized as polarization - dependent loss (PDL). However, high - dispersion diffraction gratings may have high PDL.

Background Art

[0003] When designing a diffraction system, the specifications of a diffraction grating that an optical designer considers include the peak diffraction efficiency and the spectral bandwidth of the diffraction grating. Since a diffraction grating can be a resonant optical structure, the diffraction efficiency may peak at the central wavelength and decrease as the incident light moves away from that wavelength.

Summary of the Invention

[0004] One aspect of the present disclosure is directed to a diffraction grating system including a first diffraction grating having a first diffraction efficiency in a first polarization and a second diffraction efficiency in a second polarization. The first diffraction efficiency is higher than the second diffraction efficiency. The diffraction grating system also includes a second diffraction grating and a polarization rotation medium disposed between the first diffraction grating and the second diffraction grating. The polarization rotation medium is configured to rotate the light passing through the first diffraction grating between the first polarization and the second polarization.

[0005] In some embodiments, the first diffraction grating may be the same as the second diffraction grating.

[0006] In some embodiments, the first diffraction efficiency can be greater than 99%.

[0007] In some embodiments, the system polarization-dependent loss of the system can be less than 1%.

[0008] In some embodiments, the diffraction grating polarization-dependent loss of the first diffraction grating can be greater than 95%.

[0009] In some embodiments, the polarization rotation medium may be connected to the first diffraction grating with an adhesive.

[0010] In some embodiments, the polarization rotation medium may be offset from at least one of the first diffraction grating or the second diffraction grating.

[0011] In some embodiments, the gap between the polarization rotation medium and the first diffraction grating may be filled with a fluid.

[0012] In some embodiments, the first diffraction grating may be formed from a volume phase holographic diffraction grating.

[0013] In some embodiments, the first diffraction grating may include one or more surface relief structures.

[0014] Another aspect of the present disclosure is directed to a method of diffracting light. The method includes passing incident light through a first diffraction grating. The first diffraction grating has a first diffraction efficiency for a first polarization of light and a second diffraction efficiency for a second polarization of light. Passing the incident light through the first diffraction grating includes diffracting a first light segment of the incident light with the first diffraction grating, passing a second light segment of the incident light through the first diffraction grating without diffracting it, rotating the first light segment and the second light segment through a wave plate such that the polarizations of the first light segment and the second light segment change, and passing the first light segment and the second light segment through a second diffraction grating.

[0015] In some embodiments, passing the first light segment through the second diffraction grating may include passing the first light segment through the second diffraction grating with little diffraction of the first light segment.

[0016] In some embodiments, passing the second light segment through the second diffraction grating may include diffracting most of the second light segment with the first diffraction efficiency.

[0017] In some embodiments, the wave plate may be a half-wave plate.

[0018] In some embodiments, the method may further include collecting at least 98% of the incident light at a detector.

[0019] In some embodiments, the first diffraction grating may be the same as the second diffraction grating.

[0020] Another aspect of the present disclosure is directed to a diffraction system including an incident light source and a diffraction grating having a first diffraction efficiency in a first polarization plane and a second diffraction efficiency in a second polarization plane. The first diffraction efficiency is greater than the second diffraction efficiency. The diffraction system also includes a wave plate that rotates the light passing through the diffraction grating, a mirror located on the opposite side of the wave plate from the diffraction grating and reflecting light toward the diffraction grating, and a light detector.

[0021] In some embodiments, the diffraction grating may be asymmetric.

[0022] In some embodiments, the photodetector may be disposed on the same side as the diffraction grating as seen from the waveplate.

[0023] In some embodiments, the waveplate may be a quarter-wave plate.

[0024] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0025] Additional features and advantages will be described in the following description. The features and advantages of the present disclosure can be realized and enjoyed by systems and methods particularly specified in the appended claims. The features of the present disclosure will become more fully apparent from the following description and the appended claims, or can be understood by the practice of the disclosed subject matter described below.

[0026] To describe the manner in which the above and other features of the present disclosure can be obtained, a more specific description will be made with reference to the specific embodiments shown in the accompanying drawings. For better understanding, throughout the various accompanying drawings, like elements are designated by like reference numerals. It is understood that the drawings depict some exemplary embodiments, and the embodiments will be described and explained more specifically and in detail using the accompanying drawings.

Brief Description of the Drawings

[0027]

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DETAILED DESCRIPTION OF THE INVENTION

[0028] This application relates to an apparatus, system, and method for a diffraction grating system having high diffraction efficiency in both p-polarized light (e.g., transverse magnetic (Tm)) and s-polarized light (e.g., transverse electric (Te)). A wave plate may be disposed between two diffraction gratings. When incident light passes through the first diffraction grating, the diffraction grating diffracts s-polarized light with high efficiency and allows p-polarized light to pass through (e.g., diffracts with low efficiency). After the light passes through the first diffraction grating, the wave plate may rotate the polarization of the light. Thus, s-polarized light may be rotated to p-polarized light, and p-polarized light may be rotated to s-polarized light. The second diffraction grating may be the same as the first diffraction grating, and may diffract the rotated s-polarized light with high efficiency and allow the rotated p-polarized light to pass through. In this way, both s-polarized light and p-polarized light may be diffracted with high efficiency.

[0029] The present disclosure provides advantages related to diffraction and other optical dispersion systems and / or includes a number of practical applications that solve problems related to diffraction and other optical dispersion systems. For example, as described in more detail herein, embodiments according to the present disclosure can enable high diffraction efficiency in multiple polarizations. Depending on the situation, a dispersive element such as a diffraction grating may have different diffraction efficiencies for different polarizations of light. The first diffraction efficiency for the polarization of the first light may be higher than the second diffraction efficiency for the polarization of the second light. A technician may select a dispersive element based on the difference in diffraction efficiency for a given application. However, in this case, the diffraction efficiency of the incident light may deteriorate, and the effectiveness of the application may decrease. By sandwiching a waveplate between two diffraction gratings to rotate the light, high diffraction efficiency may be obtained for each polarization. As a result, a high-efficiency diffraction system tailored to a specific application can be realized.

[0030] According to embodiments of the present disclosure, the polarization rotation medium may be any optical medium that can cause rotation in the polarization of a light beam. For example, the polarization rotation medium may be a waveplate. A quarter-wave plate may rotate the polarization intermediate between s-polarization and p-polarization. A half-wave plate may rotate the polarization from s-polarization to p-polarization.

[0031] According to embodiments of the present disclosure, the dispersive element may be an element that diffracts a light beam. For example, the dispersive element may be a diffraction grating. Although embodiments of the present disclosure may discuss diffraction gratings, it should be understood that the principles discussed herein may be applicable to any other type of dispersive element.

[0032] According to embodiments of the present disclosure, the diffraction grating may use constructive interference and destructive interference to spatially separate polychromatic light into its component wavelengths. One type of diffraction grating is a surface relief diffraction grating. The surface relief diffraction grating may include an optical surface having surface features (such as equally spaced grooves) cut into the optical surface.

[0033] Another type of diffractive grating is the volume phase holographic grating (VPHG). The VPHG may not include surface features. Instead, the VPHG may diffract light using refractive index modulation. The VPHG may have a refractive index modulation profile with a specific shape such as a sine wave, a truncated sine wave, a rectangular wave, etc. In other designs, the VPHG may include a secondary surface relief structure that is not a major factor in the diffraction performance of the VPHG. The VPHG may include regions having a higher refractive index than other regions of the VPHG. For example, the VPHG may include a series of repeating structures known as the Bragg planes that diffract light. The Bragg planes may have a higher refractive index than the regions between the Bragg planes. The VPHG may have a bulk refractive index that is the average of the refractive index of the Bragg planes and the refractive index of the regions between the Bragg planes. The VPHG may have a refractive index modulation that may be the difference between the refractive index of the Bragg planes and the refractive index of the regions between the Bragg planes.

[0034] The orientation of the Bragg planes can affect certain characteristics of the VPHG. For example, the Bragg planes can be oriented such that the VPHG is a symmetric diffractive grating. A symmetric diffractive grating diffracts the central wavelength at a first angle (diffraction angle (AOD)) with respect to the substrate normal that is the same as a second angle (angle of incidence (AOI)) at which the incident light strikes the diffractive grating. Tilting the Bragg planes can result in an asymmetric VPHG. An asymmetric diffractive grating diffracts the central wavelength at a first angle with respect to the substrate normal that is different from the second angle at which the light strikes the diffractive grating.

[0035] In some embodiments, the VPHG may be a transmissive diffraction grating or a transmission diffraction grating. In other designs, the VPHG may be a reflective diffraction grating or a reflection diffraction grating. A transmissive VPHG may enable low PDL, high diffraction efficiency, and high dispersion. The VPHG may not include surface grooves or may not require a surface relief to diffract incident light. Instead, the VPHG may diffract light using refractive index modulation. The VPHG may have a sinusoidal refractive index modulation profile, a truncated sinusoidal refractive index modulation profile, a rectangular refractive index modulation profile, or a refractive index modulation profile of a different shape.

[0036] In some embodiments, the VPHG may include a secondary surface relief structure on the surface of the VPHG. The secondary surface relief structure may not be a major factor in the diffraction performance of the VPHG. The VPHG may use a continuous blazed surface relief diffraction grating. The VPHG may include thin layers (media) of materials that alternately include regions having different refractive indices. Specifically, along the length direction of the VPHG, a region having a high refractive index (which may be a Bragg plane) may be followed by a region having a low refractive index. The VPHG may have a bulk refractive index and a refractive index modulation. Depending on the refractive index modulation of the VPHG, the VPHG may have lower polarization dependence than a surface relief diffraction grating. The VPHG may be manufactured by irradiating a medium (such as photothermally refractable glass) with an interference pattern from an ultraviolet laser.

[0037] When designing an optical spectrometer including a VPHG, the designer may consider several VPHG specifications and operating characteristics, such as the peak diffraction efficiency of the VPHG and the wavelength at which the peak diffraction efficiency occurs in relation to it. The diffraction efficiency may be a measure of power throughput. The diffraction efficiency may be a measure of how much light power is diffracted in one or more specific directions compared to the amount of light power incident on the diffraction element. The diffraction efficiency may compare the light diffracted in any direction to the total incident light. As another method, the diffraction efficiency may compare the incident light diffracted into the first spatial diffraction order to the total incident light.

[0038] In some embodiments, the diffraction efficiency of the VPHG may be measured as the amount of light diffracted by the diffraction element relative to the amount of light incident on the diffraction element. The diffraction efficiency can be measured as a ratio or percentage. The diffraction efficiency may be compared by comparing the total diffracted power to the total incident power. Alternatively, the diffraction efficiency may be compared by comparing the diffracted power at the first order to the total incident power. The diffraction efficiency of the diffraction element may vary based on the wavelength of the incident light. In other words, the diffraction element may have a first diffraction efficiency for a first wavelength, but may have a second different diffraction efficiency for a second wavelength different from the first wavelength. The diffraction efficiency of the diffraction element may vary based on the polarization of the incident light.

[0039] The diffraction element may have a peak diffraction efficiency. The peak diffraction efficiency may be the highest diffraction efficiency of the diffraction element. The peak diffraction efficiency may occur at a specific wavelength. The diffraction efficiency of the diffraction element may be less than the peak diffraction efficiency for all wavelengths other than the specific wavelength. Alternatively, the peak diffraction efficiency may occur when the diffraction efficiency of the diffraction element at a specific wavelength is higher than the diffraction efficiency of the wavelengths adjacent to the specific wavelength. In this case, the diffraction element may have multiple peak diffraction efficiencies.

[0040] The diffraction efficiency of the diffractive element may vary based on the wavelength of the incident light. In other words, the diffraction efficiency of the diffractive element may be a function of wavelength. The peak diffraction efficiency of the diffractive element may refer to the highest diffraction efficiency of the diffractive element for a given wavelength range. The peak diffraction efficiency may occur at a specific wavelength. For example, a VPHG may have a peak diffraction efficiency of 99% at 1545 nm. The diffraction efficiency may depend on the polarization of the incident light. The wavelength at which the peak diffraction efficiency occurs and the value of the peak diffraction efficiency may affect the spectral bandwidth of the VPHG. The overall diffraction efficiency of the diffractive element may be polarization-dependent loss (PDL). The PDL may be the difference between the s-polarization efficiency and the p-polarization efficiency. Depending on the application, a diffractive element with low PDL may be utilized. However, as discussed herein, many high-dispersion diffraction gratings have a high PDL (e.g., a large difference in diffraction efficiency between s-polarization and p-polarization).

[0041] In some embodiments, the diffraction efficiency characteristics of the VPHG may vary based on the angle of incidence of the incident light. The VPHG may have a peak diffraction efficiency, a wavelength at which the peak diffraction efficiency occurs, and a bandwidth. By adjusting the thickness of the medium and the refractive index modulation of the VPHG, the wavelength at which the peak diffraction efficiency of the VPHG occurs and the bandwidth of the VPHG may change.

[0042] FIG. 1 depicts a schematic of a diffraction system 100 according to at least one embodiment of the present disclosure. A light source 102 may provide incident light 104. The light source 102 may be any type of light source. For example, the light source 102 may be a light source from an optical fiber cable. In some examples, the light source 102 may be a light source from a spectroscopic system. In some examples, the light source 102 may be other types of light sources.

[0043] The incident light 104 may interact with a first dispersive element 106 such as a diffraction grating. The first dispersive element 106 may disperse or separate the incident light 104 into at least two segments (collectively 108). The first light segment 108-1 may be the diffracted portion of the incident light 104. The second light segment 108-2 may be the non-diffracted (or transmitted) portion of the incident light 104.

[0044] In some embodiments, the dispersive element may have a higher diffraction efficiency for a first polarization (such as s-polarization) than for a second polarization (such as p-polarization). Thus, in some embodiments, the first light segment 108-1 may predominantly have the first polarization and the second light segment 108-2 may predominantly have the second polarization. In FIG. 1, the light segment 108 having the first polarization as the main polarization is indicated by a dotted line, and the light segment having the second polarization as the main polarization is indicated by a solid line.

[0045] Thereafter, the light segments 108 may be passed through a waveplate 110. The waveplate 110 may rotate both light segments 108 by 90°, thereby changing the polarization. As a result, a rotated first light segment 108-1-1 and a rotated second light segment 108-2-1 are obtained. As may be understood from the figure, the rotated first light segment 108-1-1 switches the polarization from the first polarization to the second polarization. Similarly, the rotated second light segment 108-2-1 switches the polarization from the second polarization to the first polarization.

[0046] Next, the optical segment 108 may pass through the second dispersive element 112. The second dispersive element 112 may then diffract a rotated second optical segment 108-2-1 having a first polarization (which then becomes a rotated and diffracted second optical segment 108-2-2) with higher efficiency than a rotated first optical segment 108-1-1 having a second polarization (which is diffracted and becomes a rotated and diffracted first optical segment 108-1-2). In this way, most or all of the incident light 104 from the light source 102 may be diffracted. This may enable more efficient and / or higher-quality analysis when the optical segment 108 is received by the detector 114.

[0047] According to an embodiment of the present disclosure, the diffraction system 100 may be used in a spectroscopic system. For example, in high-sensitivity applications such as fusion reactors and power generation systems, atomic emission lines of different isotopes and atoms may be very close. Therefore, if the diffraction efficiency is high, there is a possibility of analyzing more spectroscopic light. Furthermore, the plasma generated during fusion applications may be randomly polarized. Since the polarization of the emitted plasma is not always s-polarized or p-polarized, if high diffraction efficiency is obtained in both s-polarization and p-polarization, the amount of light that is not diffracted may decrease, and the amount of light available for analysis may increase. This can improve the accuracy and / or precision of spectroscopic analysis. Although a specific example of spectroscopy related to fusion has been shown, it should be understood that the principles of the present disclosure may provide similar advantages for spectroscopy in any other industry where spectroscopy is used.

[0048] According to embodiments of the present disclosure, the diffraction system 100 may further be used for signal analysis of a telecommunication system. In some situations, the telecommunication system may determine system efficiency based on the least efficient part of the system. In the case of a diffraction grating that has high diffraction efficiency in one polarization but low diffraction efficiency in a second polarization, it may become a diffraction grating with reduced availability and / or effectiveness in a telecommunication system. The systems and methods described herein may be able to improve the availability of diffraction gratings in a telecommunication system and improve signal analysis and decoding efficiency.

[0049] FIG. 2 shows an exploded view of a diffraction system 200 according to at least one embodiment of the present disclosure. The diffraction system 200 includes a first diffraction grating 206 and a second diffraction grating 212. A waveplate 210 (or multiple waveplates, or any combination of components or materials that rotate or change the polarization of light) may be disposed between the first diffraction grating 206 and the second diffraction grating 212. In the following discussion, the characteristics described with respect to the first diffraction grating 206 may be applied to the second diffraction grating 212. In some embodiments, the first diffraction grating 206 may be the same as the second diffraction grating 212. However, it should be understood that there may be differences in the characteristics discussed herein between the first diffraction grating 206 and the second diffraction grating. For example, the first diffraction grating 206 and the second diffraction grating may differ in symmetry, refractive index modulation, refractive index modulation profile, diffraction efficiency, PDL, thickness, height, spatial frequency, wavelength of peak diffraction efficiency, any other characteristic, and combinations thereof.

[0050] In the illustrated embodiment, the first diffraction grating 206 includes a plurality of Bragg planes 216. The Bragg planes 216 may have a refractive index higher than that of a plurality of low refractive index regions 218 arranged at intervals between the Bragg planes 216. The Bragg planes 216 may enable the diffraction grating 206 to diffract light incident on the first diffraction grating 206. The first diffraction grating may have a bulk refractive index and a refractive index modulation. In the embodiment shown in FIG. 2, the first diffraction grating 206 and the second diffraction grating 212 are VPHGs. In a VPHG, the refractive index modulation may vary, and as a result, a refractive index modulation profile may be obtained (for example, refer to the refractive index modulation profile shown in FIG. 3). The refractive index modulation profile may have a shape such as a sine wave, a truncated sine wave, a rectangular wave, or a different shape. The first diffraction grating 206 and / or the second diffraction grating 212 may further have a bulk refractive index. The bulk refractive index may be an average of the refractive indices of the Bragg planes 216 and the low refractive index regions 218.

[0051] The first diffraction grating 206 and / or the second diffraction grating 212 may have a spatial frequency. The spatial frequency may be a measure of the distance between the Bragg planes 216. The spatial frequency may be a measure of how many sets of high refractive index regions (for example, Bragg planes 216) and low refractive index regions (for example, low refractive index regions 218) are arranged in a 1 millimeter long portion of the first diffraction grating 206 measured along the length direction of the first diffraction grating 206 (typically, represented by the number of lines per millimeter, lpmm, or l / mm). For example, the first diffraction grating 206 may have a spatial frequency of 905 l / mm. This may mean that the first diffraction grating includes 905 Bragg planes 216 and 905 low refractive index regions 218 along a 1 millimeter length of the first diffraction grating 206.

[0052] In the embodiment shown in FIG. 2, the incident light 220 may be incident on the first diffraction grating 206 at the incident point. The incident angle 222 may be the angle between the incident light 220 and the normal 224 to the surface of the first diffraction grating 206 at the incident point. The Bragg plane 216 may diffract the incident light 220. The central wavelength of the diffracted light may exit from the first diffraction grating 206 at a diffraction angle 226 with respect to the normal 224 to the surface of the first diffraction grating 206. The Bragg plane 216 may further disperse the light received at the incident angle 222 at a specific dispersion angle.

[0053] As can be seen in the figure, the incident light 220 may include a plurality of different polarizations. For the sake of simplicity of illustration and discussion, and not to limit the disclosure, the illustrated incident light 220 includes s-polarized light 221 and p-polarized light 223.

[0054] The Bragg plane 216 may have an orientation (which may also be called an inclination). In the illustrated embodiment, each of the Bragg planes 216 has the same orientation. The Bragg plane 216 may be oriented such that the diffraction angle 226 is equal to the incident angle 222. When the Bragg plane 216 is oriented such that the diffraction angle 226 is equal to the incident angle 222, the first diffraction grating 206 (or an individual Bragg plane 216) may be referred to as symmetric in this case. In some embodiments, the Bragg plane 216 may not diffract the incident light 220 at a diffraction angle 226 equal to the incident angle 222, in which case it is an asymmetric diffraction grating.

[0055] In some embodiments, the first diffraction grating 206 may include a total diffraction angle. The total diffraction angle may be the sum of the incident angle 222 and the diffraction angle 226. As can be seen in the figure, when the first diffraction grating 206 is symmetric, the total diffraction angle may be determined by doubling the incident angle 222. When the first diffraction grating 206 is asymmetric, the total diffraction angle may be determined by adding the incident angle 222 to the diffraction angle 226.

[0056] The first diffraction grating 206 has a diffraction efficiency. The diffraction efficiency of the first diffraction grating 206 may be a function of wavelength. In other words, the diffraction efficiency of the first diffraction grating may vary according to the wavelength of the incident light 220. In some embodiments, the medium thickness of the first diffraction grating 206 may affect the diffraction efficiency of the first diffraction grating 206.

[0057] Different applications and / or different optical wavelengths may be handled at different total diffraction angles. The diffraction efficiency in a particular application may be determined at least in part based on the total diffraction angle. In some embodiments, the total diffraction angle may change the modulation profile for s-polarized or p-polarized light. For example, increasing the total diffraction angle may decrease the diffraction efficiency of p-polarized light. As a result, even if optimized for high diffraction efficiency for s-polarized light, a diffraction grating may have low diffraction efficiency at any refractive index modulation level that can be used. This may increase the total PDL of individual diffraction gratings. In fact, by changing the spatial frequency and / or film thickness, a wide variety of refractive index modulation curves can be obtained.

[0058] According to embodiments of the present disclosure, the first diffraction grating 206 may have one or more peak diffraction efficiencies. The one or more peak diffraction efficiencies may occur at one or more specific wavelengths. The first diffraction grating 206 may be specifically designed to have one or more characteristics, and as a result, the first diffraction grating 206 may have one or more peak diffraction efficiencies at one or more specific wavelengths. For example, the first diffraction grating 206 may be designed to have a peak diffraction efficiency at 1545 nm. Alternatively, the first diffraction grating 206 may be designed to have a peak diffraction efficiency at 720 nm, or any other wavelength. As described herein, the diffraction efficiency of a particular diffraction grating may be different for s-polarized and p-polarized light.

[0059] The difference in diffraction efficiency between s-polarized light and p-polarized light is polarization-dependent loss (PDL). A low PDL may indicate a diffraction grating or system where the diffraction efficiencies of s-polarized light and p-polarized light are approximately the same. In some cases, the diffraction grating may have high diffraction efficiencies for both s-polarized light and p-polarized light, and the PDL may be low. In some applications of the diffraction grating system of the present disclosure, it may be desirable to have a low PDL so that a technician or other operator can analyze at least samples of both the s-polarized and p-polarized components of the incident light 220. In some embodiments, it may be desirable to have both high diffraction efficiency and low PDL so that a technician can analyze as much of the incident light having both s-polarized and p-polarized components as possible.

[0060] The first diffraction grating 206 may have a bandwidth. The bandwidth of the first diffraction grating 206 may be the range of wavelengths for which the diffraction efficiency of the first diffraction grating 206 is greater than a threshold value. For example, the bandwidth of the first diffraction grating 206 may be the set of wavelengths for which the PDL of the first diffraction grating 206 exceeds 95%. In some embodiments, the bandwidth of the first diffraction grating 206 may depend on the thickness of the medium of the first diffraction grating 206. The first diffraction grating 206 may be designed to have one or more characteristics, such that the first diffraction grating 206 may have a bandwidth that includes a particular set of wavelengths.

[0061] According to an embodiment of the present disclosure, when the incident light 220 is incident on the first diffraction grating 206, the first diffraction grating 206 may separate the light into a first light segment 208-1 and a second light segment 208-2. The first light segment 208-1 may be the diffracted portion of the incident light 220. In other words, the portion of the incident light 220 diffracted by the first diffraction grating 206 may be the first light segment 208-1. In the illustrated embodiment, the first diffraction grating has a high diffraction efficiency with respect to s-polarized light. Based on the high diffraction efficiency of the first diffraction grating 206 for s-polarized light 221, the first light segment 208-1 is mainly composed of s-polarized light 221 between the first diffraction grating 206 and the wave plate 210. In other words, most of the first light segment 208-1 is s-polarized light.

[0062] The second optical segment 208-2 may be the non-diffracted light that has passed through the first diffraction grating 206. In the illustrated embodiment, the first diffraction grating 206 has a low diffraction efficiency for p-polarized light. Based on the diffraction efficiency of the diffraction grating 206 for p-polarized light, the p-polarized light 223 of the incident light 220 may mainly pass through the first diffraction grating 206. Therefore, the second optical segment 208-2 is mainly composed of the p-polarized light 223 between the first diffraction grating 206 and the wave plate 210. In other words, most of the second optical segment 208-2 is p-polarized light.

[0063] After the incident light 220 is at least partially diffracted by the first diffraction grating 206, the separated portions of the incident light (collectively the optical segment 208) may pass through the wave plate 210. The wave plate 210 may rotate the optical segment 208. In some embodiments, the wave plate 210 may be a half-wave plate. In some embodiments, the half-wave plate may rotate the light wave to change the polarity between s-polarized light and p-polarized light.

[0064] The wave plate 210 may rotate the first optical segment 208-1 having mainly s-polarized light 221 into a rotated first optical segment 208-1-1 having mainly p-polarized light 223. The rotated first optical segment 208-1-1 may then be directed towards the second diffraction grating 212. In the illustrated embodiment, the second diffraction grating 212 has the same characteristics as the first diffraction grating 206. Therefore, the second diffraction grating 212 has a low diffraction efficiency for p-polarized light. Therefore, most of the rotated first optical segment 208-1-1 may pass through the second diffraction grating 212 without being diffracted, and as a result, may become the first detected optical segment 228-1. The first detected optical segment 228-1 may then be directed towards a detector (e.g., the detector 114 in FIG. 1) or other collection device for analysis.

[0065] The wavelength plate 210 may mainly rotate the second optical segment 208-2 having p-polarized light 223 into the rotated second optical segment 208-2-1 mainly having s-polarized light. The rotated second optical segment 208-2-1 may then be directed toward the second diffraction grating 212. As described above, the illustrated second diffraction grating 212 has the same characteristics as the first diffraction grating 206. Therefore, the second diffraction grating has a high diffraction efficiency with respect to s-polarized light. Thus, most of the rotated second optical segment 208-2-1 may be diffracted by the second diffraction grating 212, resulting in the second detected optical segment 228-2. The second detected optical segment 228-2 may then be directed toward a detector or other collection device for analysis. A portion of the non-diffracted light 230 may pass through without being diffracted by both the first diffraction grating 206 and the second diffraction grating 212. Additional diffraction devices and / or collection devices may be used to further analyze the non-diffracted light 230.

[0066] Combining the detected optical segments (collectively 228), may represent most of the original incident light 220. For example, consider an embodiment where the diffraction efficiency for s-polarized light of the first diffraction grating 206 and the second diffraction grating 212 is 99%, the diffraction efficiency for p-polarized light of the first diffraction grating and the second diffraction grating is 1%, the ratio of s-polarized light 221 to p-polarized light 223 in the incident light 220 is 50 / 50, and there are no other efficiency losses in the system. In this case, the first optical segment 208-1 may include 50% of the incident light (e.g., 50% of s-polarized light 221 multiplied by 99% (resulting in 49.5% s-polarized light) + 50% of p-polarized light multiplied by 1% (resulting in 0.5% p-polarized light)). The second optical segment 208-2 may include 50% of the incident light 220 (e.g., the remaining portion of s-polarized light (0.5%) and the remaining portion of p-polarized light (49.5%)).

[0067] When the first optical segment 208-1 passes through the wave plate 210, the polarization is switched, and thereafter, it may become the rotated first optical segment 208-1-1 having 49.5% p-polarized light and 0.5% s-polarized light of the total incident light 220. When the rotated first optical segment 208-1-1 passes through the second diffraction grating 212, the first detected optical segment 228-1 may include 49.005% p-polarized light (for example, obtained by subtracting from 49.5% the product of 49.5% and 1% diffraction efficiency for p-polarized light) and 0.005% s-polarized light (for example, obtained by subtracting from 0.5% the product of 0.5% and 99% diffraction efficiency for s-polarized light) of the total incident light 220. The remaining portion of the rotated first optical segment 208-1-1 may be diffracted and become the diffracted portion 232 including 0.495% s-polarized light and 0.495% p-polarized light, which in this case totals 0.99% of the incident light 220.

[0068] When the second optical segment 208-2 passes through the wave plate 210, the polarization is switched, and there may remain 49.5% s-polarized light (of the total incident light 220) and 0.5% p-polarized light in the rotated second optical segment 208-2-1. When the rotated second optical segment 208-2-1 passes through the second diffraction grating 212, the second detected optical segment 228-2 can include 49.005% s-polarized light (for example, 49.5% multiplied by 99% diffraction efficiency for s-polarized light) and 0.005% p-polarized light (for example, 0.5% multiplied by 1% diffraction efficiency for p-polarized light) of the total incident light 220. The remaining portion of the rotated second optical segment 208-2-1 may be the undiffracted light 230 including 0.495% p-polarized light and 0.495% s-polarized light, which corresponds to a total of 0.99% of the incident light 220.

[0069] As shown in the figure, the first detection light segment 228-1 and the second detection light segment 228-2 account for 98.02% of the total incident light 220. This may be considered as the total light collection ratio of the diffraction system 200. In other words, in the provided example, the total light collection ratio of the diffraction system 200 may be 98.02%. The non-diffracted light 230 and the diffracted portion 232 account for approximately 1.98% of the total incident light 220. This may be considered as the total non-collected light ratio of the diffraction system 200. In other words, in the provided example, the total non-collected light ratio of the diffraction system 200 may be 1.98%. Reducing the total non-collected light ratio of the diffraction system 200 may help to increase the sensitivity and / or effectiveness of the analysis of the detected light segment 228.

[0070] As can be understood, the total non-collected light ratio may be determined based on the diffraction efficiencies of the first diffraction grating 206 and the second diffraction grating 212. In some embodiments, the total non-collected light ratio may be within an upper limit, a lower limit, or a range having an upper limit and a lower limit including 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.75%, 1.0%, 1.5%, 2.0%, 2.5%, 5%, 7.5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 90%, 100%, or any value therebetween. For example, the total non-collected light ratio may be greater than 0.1%. In another example, the total non-collected light ratio may be less than 100%. In yet another example, the total non-collected light ratio may be any value within the range between 0.1% and 100%. In some embodiments, it may be important for the total non-collected light ratio to be less than 2% in order to increase the sensitivity and / or effectiveness of the diffraction system 200.

[0071] Figure 3 is a diagram showing the refractive index modulation profile 334 of a diffraction grating with 1175 l / mm and a total diffraction angle of 130.4°, with the refractive index modulation on the horizontal axis and the diffraction efficiency on the vertical axis. The illustrated refractive index modulation profile 334 includes an s-polarization profile 336 and a p-polarization profile 338.

[0072] As can be seen in the figure, the s - polarization profile 334 includes a plurality of diffraction - efficiency peaks 340 at different refractive - index modulation values. The p - polarization profile 338 does not include peaks. In fact, the maximum diffraction efficiency is about 10%. A conventional diffraction system using this diffraction grating will have a low overall efficiency rating based on the generally low diffraction efficiency of the p - polarization profile 338.

[0073] The diffraction grating may be adjusted to one or more refractive - index modulations. According to an embodiment of the present disclosure, the diffraction system may be designed using a diffraction grating adjusted to the diffraction - efficiency peak 340. To reduce the overall un - collected light fraction of the diffraction system, the diffraction grating may be selected to have a high PDL individually. Two diffraction gratings with individually high PDLs separated by a half - wave plate can result in a diffraction system with a low overall un - collected light fraction. As described above with respect to FIG. 2, this may be because, due to the diffraction grating having a low diffraction efficiency for p - polarization, a large amount of p - polarization may pass through the diffraction grating. In the first diffraction grating, as a result, a large amount of p - polarization may pass through the wave plate and the second diffraction grating, be rotated by the wave plate, and be diffracted by the second diffraction grating. In the second diffraction grating, a large portion of the rotated light segment may pass through the second diffraction grating. Thus, when the individual PDLs in the diffraction grating of the diffraction system are high, the overall un - collected fraction of the diffraction system may be low.

[0074] In the embodiment shown in FIG. 3, the diffraction system may be designed using two identical diffraction gratings adjusted to the first (e.g., the left - most, having the lowest refractive - index modulation) diffraction - efficiency peak 340. As can be seen in the figure, the difference 342 between the peak 340 and the p - polarization profile 338 may be a position where the PDL of the diffraction grating can be maximized. Two diffraction gratings adjusted to this particular peak 340 may have a low overall un - collected light fraction.

[0075] FIG. 4 shows a diffraction efficiency curve 444 of a diffraction system over a wavelength bandwidth, with diffraction efficiency on the vertical axis and wavelength on the horizontal axis, according to at least one embodiment of the present disclosure. The diffraction efficiency curve 444 includes an s-polarization efficiency profile 446 and a p-polarization efficiency profile 448. As can be seen in the figure, there is little difference in efficiency between the s-polarization efficiency profile 446 and the p-polarization efficiency profile 448.

[0076] This may be due to the structure of the diffraction system. The first diffraction grating may diffract s-polarization with high efficiency and p-polarization with low efficiency. When the light passing through the first diffraction grating is rotated by a wave plate, the initially diffracted s-polarization is rotated to p-polarization and passes through the second diffraction grating. The p-polarization efficiency profile 448 may represent the s-polarization diffracted by the first diffraction grating, rotated to p-polarization, and passed through the second diffraction grating. Thus, before rotation, the p-polarization efficiency profile is substantially diffracted with the diffraction efficiency of the s-polarization from the first diffraction grating.

[0077] The s-polarization efficiency profile 446 may represent the p-polarization diffracted by the second diffraction grating after passing through the first diffraction grating and being rotated to s-polarization. Thus, the s-polarization efficiency profile 446 represents the portion of the incident light that passes through the first diffraction grating without being initially diffracted and is finally diffracted by the second diffraction grating. In this way, both the p-polarization efficiency profile 448 and the s-polarization efficiency profile 446 can be the light diffracted while being oriented in s-polarization.

[0078] The comparison of the s-polarization efficiency profile 446 and the p-polarization efficiency profile 448 can provide an indication of the overall PDL of the system. Specifically, the gap between the s-polarization efficiency profile 446 and the p-polarization efficiency profile 448 can be the PDL of the diffraction system. When the first diffraction grating and the second diffraction grating are identical, the diffraction efficiencies for both s-polarized and p-polarized light are the same, and the PDL of the system is very low (e.g., less than 1%). In some embodiments, the PDL of the system can be an upper limit, a lower limit, or a range having an upper limit and a lower limit that includes any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.75%, 1.0%, 1.5%, 2.0%, 2.5%, 5%, 7.5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a value therebetween. For example, the PDL of the system can be greater than 0.1%. In another example, the PDL of the system can be less than 50%. In yet another example, the PDL of the system can be any value within the range between 0.1% and 50%. In some embodiments, it can be important for the PDL of the system to be less than 1% in order to reduce the sensitivity of the system to polarization changes. In some embodiments, the PDL can be quantified in dB.

[0079] FIG. 5 depicts an assembled diffraction system 500 according to at least one embodiment of the present disclosure. The diffraction system 500 includes a first diffraction grating 506 and a second diffraction grating 512 separated by a waveplate 510. In the illustrated embodiment, the waveplate 510 is in contact with the first diffraction grating 506 and the second diffraction grating 512.

[0080] In some embodiments, the waveplate 510 may be connected to the first diffraction grating 506 and / or the second diffraction grating 512 with an adhesive. In some embodiments, the adhesive may be an optically transparent adhesive (e.g., an adhesive with very low diffraction, diffusion, scattering, reflection, or other light-scattering or light-altering properties). In some embodiments, the adhesive may have known diffraction or other light-altering properties. When designing the diffraction system 500 and when determining the diffraction characteristics of the diffraction system 500, the characteristics of the adhesive may be taken into account. In some embodiments, the adhesive may serve as a refractive index matching medium between the diffraction grating and the waveplate. In some embodiments, a refractive index matching or other fluid that can perform other functions such as cooling the diffraction grating-waveplate-diffraction grating system may be used.

[0081] In some embodiments, the waveplate 510 may be connected to the first diffraction grating 506 and / or the second diffraction grating 512 by a mechanical connection. For example, screws, bolts, latches, clamps, or other mechanical fasteners may connect the waveplate 510 to the first diffraction grating 506 and / or the second diffraction grating 512. In some embodiments, the mechanical fasteners may connect the first diffraction grating 506, the waveplate 510, and the second diffraction grating 512 at a location outside the transparent aperture of the diffraction system 500. For example, the incident light directed towards the diffraction system 500 (e.g., the incident light 220 in FIG. 2) may contact or act on the diffraction system inside the capture region. Fasteners or other obstacles located outside the capture region will not interfere with or otherwise change the path of the captured light. The mechanical fasteners can connect the first diffraction grating 506, the waveplate 510, and / or the second diffraction grating 512 without an adhesive, thereby reducing or eliminating optical disturbances caused by the adhesive. In some embodiments, the mechanical fasteners may be used in combination with an adhesive.

[0082] In the embodiment shown in FIG. 5, the first diffraction grating 506 is identical to the second diffraction grating 512. For example, the Bragg surface 516 of the first diffraction grating 506 may have the same size, shape, thickness, width, depth, structure, refractive index modulation, orientation, other sides of the Bragg surface 516, and combinations thereof as the Bragg surface 516 of the second diffraction grating 512. Similarly, the low refractive index region 518 of the first diffraction grating 506 may have the same size, shape, thickness, width, depth, structure, refractive index modulation, orientation, other sides of the low refractive index region 518, and combinations thereof as the low refractive index region 518 of the second diffraction grating 512.

[0083] However, in some embodiments, the first diffraction grating may be different from the second diffraction grating. For example, FIG. 6 shows a diffraction system 600 in which the first diffraction grating 606 separated from the second diffraction grating by the wave plate 610 is different from the second diffraction grating 612. In the illustrated embodiment, the spatial frequency of the first diffraction grating 606 is different from that of the second diffraction grating 612 (in FIG. 6, it is illustrated by offsetting the Bragg surface 616 and the low refractive index region 618 between the first diffraction grating 606 and the second diffraction grating 612). As a result, the optical path of the light diffracted from the second diffraction grating 612 may change.

[0084] It should be understood that other characteristics of the first diffraction grating 606 may be different from those of the second diffraction grating 612. For example, size, shape, thickness, width, depth, structure, refractive index modulation, orientation, spatial frequency, other sides of the Bragg surface 616, and combinations thereof may be different between the first diffraction grating 606 and the second diffraction grating 612. In some examples, the size, shape, thickness, width, depth, structure, refractive index, spatial frequency, and other sides of the low refractive index region 618 may be different between the first diffraction grating 606 and the second diffraction grating 612.

[0085] By having different characteristics between the first diffraction grating 606 and the second diffraction grating 612, it may be possible to differently modify the optical segments in the second diffraction grating 612. Thereby, a technician or other operator can adjust the design of the diffraction system 600 to suit a specific application. In some embodiments, due to the different characteristics of the first diffraction grating 606 and the second diffraction grating 612, this diffraction system 600 can be used in different applications, such as a dual-resolution spectrometer or other applications, where it may analyze two different optical segments generated from the same incident light.

[0086] FIG. 7 depicts a diffraction system 700 in accordance with at least one embodiment of the present disclosure, where a first diffraction grating 706 and a second diffraction grating 712 are separated or offset from a waveplate 710 by a gap 750. As can be seen in the figure, the first diffraction grating 706 and the second diffraction grating 712 may not be directly connected to the waveplate 710. In some embodiments, the waveplate 710 may be rotated to change the diffraction efficiency of the system. In some embodiments, the gap 750 may be an air gap. The gap 750 may be filled with a gaseous medium such as atmospheric air, or a regulated mixture of nitrogen, oxygen, helium, any other gas, and combinations thereof.

[0087] In some embodiments, the diffraction system 700 may be housed in a housing. The housing may be a pressurized housing. The pressurized housing may be pressure-adjusted to a specific pressure, such as a pressure lower than atmospheric pressure. In some embodiments, no material may be disposed in the gap 750. For example, the gap 750 may contain a vacuum.

[0088] In some embodiments, the gap 750 may be filled with a fluid. For example, the gap 750 may be filled with an optically transparent fluid. In some embodiments, the entire diffraction system 700 may be immersed in a fluid. In some embodiments, the fluid may contain liquid crystals.

[0089] FIG. 8 depicts a diffraction system 800 in accordance with at least one embodiment of the present disclosure, in which a waveplate 810 is connected to a first diffraction grating 806 and separated or offset from a second diffraction grating 812 by a gap 850. Thereby, a technician or other operator can further control the path of the optical segment that has passed through the first diffraction grating 806. As can be seen from the comparison from FIG. 5 to FIG. 8, the diffraction system according to the present disclosure can have any structure or any combination of structures in order to achieve any desired characteristics.

[0090] FIG. 9 depicts a diffraction system 952 including a single diffraction grating 953 in accordance with at least one embodiment of the present disclosure. Incident light 920 including both s-polarized light 921 and p-polarized light 923 may be directed toward the diffraction grating 953. As discussed herein, the diffraction grating 953 may have a high diffraction efficiency for s-polarized light 921 and a low diffraction efficiency for p-polarized light 923. When the incident light 920 passes through the diffraction grating 953, the diffraction grating 953 may diffract a first segment 908-1 of the incident light 920 that mainly has s-polarized light 921. The second segment 908-2 mainly has p-polarized light and may pass through the diffraction grating 953 without being diffracted.

[0091] The optical segments (collectively 908) may pass through a waveplate 954, contact a mirror 956, and be reflected back to the waveplate 954. In some embodiments, the mirror 956 may be disposed on the opposite side of the diffraction grating 953 across the waveplate 954 that reflects light back to the diffraction grating 953. In the illustrated embodiment, the waveplate 954 may be a quarter-wave plate. Since the optical segment 908 passes through the quarter-wave waveplate 954 twice, the quarter-wave waveplate 954 acts as a half-wave plate and can change the polarity of the optical segment 908 between s-polarized light 921 and p-polarized light 923.

[0092] In this way, after the first optical segment 908-1 passes through the waveplate 954, is reflected by the mirror 956, and passes through the waveplate 954 again, the first optical segment 908-1 may be the rotated first optical segment 908-1-1 having p-polarization 923. Therefore, the rotated first optical segment 908-1-1 may pass through the diffraction grating 953 with a low diffraction efficiency.

[0093] After the second optical segment 908-2 passes through the waveplate 954, is reflected by the mirror 956, and passes through the waveplate 954 again, the second optical segment 908-2 may be the rotated second optical segment 908-2-1 mainly having s-polarization 921. When the rotated second optical segment 908-2-1 passes through the diffraction grating, the rotated second optical segment 908-2-1 may be diffracted with a high diffraction efficiency.

[0094] Therefore, as can be seen in the figure, the diffraction system 952 shown in FIG. 9 may produce the collected light 928 that is reflected toward the light source of the incident light 920. In some embodiments, the collected light 928 may be reflected to the light source. In some embodiments, the mirror 956 may be tilted so as to move the collected light 928 away from the light source, or may be oriented in other directions so as to move the collected light 928 away from the light source.

[0095] With the diffraction system 952, a technician or other operator can use a photodetector to collect light on the same side as the light source of the incident light 920. In other words, the photodetector may be disposed on the same side as the incident light source. In some embodiments, the mirror 956 may be less expensive than the second diffraction grating, thereby potentially reducing the cost of the diffraction system 952. Further, the mirror 956 may be smaller than the second diffraction grating, thereby enabling the overall size of the diffraction system 952 to be reduced.

[0096] FIG. 10 depicts a method 1000 for optical diffraction according to at least one embodiment of the present disclosure. Method 1000 includes passing incident light through a first diffraction grating (1002). The first diffraction grating diffracts a first portion of the incident light and passes the first diffraction grating without diffracting a second portion of the incident light. The first diffraction grating has a first diffraction efficiency for a first polarization and a second diffraction efficiency for a second polarization. The first diffraction efficiency may be higher than the second diffraction efficiency, and the diffraction efficiency may be represented by PDL.

[0097] In some embodiments, the PDL of the diffraction grating may be an upper limit value, a lower limit value, or a range having an upper limit value and a lower limit value including any of the values of 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, or a value therebetween. For example, the PDL of the diffraction grating may be greater than 20%. In another example, the PDL of the diffraction grating may be less than 99.9%. In yet another example, the PDL of the diffraction grating may be any value within a range between 20% and 99.9%. In some embodiments, it may be important for the PDL of the diffraction grating to be greater than 99% in order to increase the accuracy and / or precision of a sensor or other device to which the diffraction is connected.

[0098] The method further includes rotating the first portion of the light and the second portion of the light using a waveplate (1004). Thereby, the polarization of the first portion of the light and the second portion of the light may change. Next, the first portion of the rotated light may be passed through a second diffraction grating (1006). Also, the second portion of the rotated light may be passed through the second diffraction grating as well (1008).

[0099] In some embodiments, when the first diffraction efficiency is significantly greater than the second diffraction efficiency (e.g., when the PDL of the diffraction grating is high), the first portion of the rotated light (diffracted by the first diffraction grating) may pass through the second diffraction grating with little diffraction (e.g., most of the second portion of the rotated light may be diffracted by the second diffraction efficiency). Most of the second portion of the rotated light (which passed through the first diffraction grating without being diffracted) may be diffracted by the second diffraction grating with the first diffraction efficiency.

[0100] In this way, most of the incident light may be diffracted with high efficiency by a very low total system PDL. Thereby, higher system efficiency and / or sensitivity can be achieved.

[0101] The terms "comprising", "including", and "having" are intended to be inclusive terms, meaning that additional elements other than the recited elements may exist. Additionally, it should be understood that when referring to "one embodiment" or "an embodiment" of the present disclosure, it is not intended to exclude the existence of additional embodiments that include the recited features. For example, any element or feature described in connection with one embodiment herein can be combined with any element or feature of any other embodiment described herein, if compatible.

[0102] The numerical values, percentages, ratios, or other values described herein are intended to be included in the embodiments of the present disclosure and, as understood by those skilled in the art, include that value, as well as other values that are "about" or "approximately" the recited value. Accordingly, the recited values should be interpreted broadly enough to include values that are at least close enough to the recited values to perform the desired function or achieve the desired result. The recited values include at least the variations expected in a suitable manufacturing or production process and may include values within 5%, 1%, 0.1%, or 0.01% of the recited value.

[0103] Those skilled in the art will understand that, in view of the present disclosure, equivalent configurations do not depart from the concept and scope of the present disclosure, and various changes, substitutions, and modifications can be made to the embodiments disclosed herein without departing from the concept and scope of the present disclosure. Equivalent configurations including functional "means-plus-function" expressions are intended to include structures described herein as performing the specified functions, including both structural equivalents that operate in the same way and equivalent structures that provide the same function. It is the clear intention of the applicant not to apply "means-plus-function" or other functional claims to claims other than those in which the phrase "means for" appears with the associated function. Each addition, deletion, and modification to the embodiments included in the meaning and scope of the claims should be encompassed by the claims.

[0104] As used herein, the terms "about," "approximately," and "substantially" represent an amount close to the recited amount that performs the desired function or achieves the desired result. For example, the terms "about," "approximately," and "substantially" may refer to an amount within less than 5%, less than 1%, less than 0.1%, or less than 0.01% of the recited amount. Further, it should be understood that any direction or reference frame in the foregoing description is merely a relative direction or movement. For example, the expressions "up," "down," "above," and "below" merely describe the relative position and movement of the relevant elements.

[0105] The described embodiments should be considered illustrative rather than restrictive, and the present disclosure may be embodied in other forms than those specifically described herein. Accordingly, the scope of the present disclosure is indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and equivalent scope of the claims are embraced within that scope.

Claims

1. A diffraction grating system comprising: a first diffraction grating having a first diffraction efficiency for a first polarization and a second diffraction efficiency for a second polarization, wherein the first diffraction efficiency is higher than the second diffraction efficiency; a first diffraction grating a second diffraction grating; a polarization rotation medium disposed between the first diffraction grating and the second diffraction grating, the polarization rotation medium being configured to rotate light passing through the first diffraction grating between the first polarization and the second polarization; A diffraction grating system comprising:

2. The system according to claim 1, wherein the first diffraction grating is the same as the second diffraction grating.

3. The system according to claim 1, wherein the first diffraction efficiency is greater than 99%.

4. The system according to claim 1, wherein the system polarization-dependent loss of the system is less than 1%.

5. The system according to claim 1, wherein the diffraction grating polarization-dependent loss of the first diffraction grating is greater than 95%.

6. The system according to claim 1, wherein the polarization rotation medium is connected to the first diffraction grating with an adhesive.

7. The system according to claim 1, wherein the polarization rotation medium is offset from at least one of the first diffraction grating or the second diffraction grating.

8. The system according to claim 7, wherein the gap between the polarization rotation medium and the first diffraction grating is filled with a fluid.

9. The system according to claim 1, wherein the first diffraction grating is formed from a volume phase holographic diffraction grating.

10. The system according to claim 1, wherein the first diffraction grating includes one or more surface relief structures.

11. A method of diffracting light, comprising: passing incident light through a first diffraction grating, the first diffraction grating having a first diffraction efficiency for a first polarization of light and a second diffraction efficiency for a second polarization of light, the step of passing the incident light through the first diffraction grating comprising: diffracting a first light segment of the incident light with the first diffraction grating; passing a second light segment of the incident light through the first diffraction grating without diffracting the second light segment; rotating the first light segment and the second light segment through a wave plate such that the polarizations of the first light segment and the second light segment change; passing the first light segment and the second light segment through a second diffraction grating; A method of diffracting light, comprising:

12. The method according to claim 11, wherein passing the first optical segment through the second diffraction grating includes passing the first optical segment through the second diffraction grating with little diffraction of the first optical segment.

13. The method according to claim 11, wherein passing the second optical segment through the second diffraction grating includes diffracting most of the second optical segment with the first diffraction efficiency.

14. The method according to claim 11, wherein the wave plate is a half-wave plate.

15. The method according to claim 11, further comprising collecting at least 98% of the incident light at a detector.

16. The method according to claim 11, wherein the first diffraction grating is the same as the second diffraction grating.

17. A diffraction system, comprising: An incident light source; A diffraction grating having a first diffraction efficiency in a first polarization plane and a second diffraction efficiency in a second polarization plane, wherein the first diffraction efficiency is greater than the second diffraction efficiency; A wave plate for rotating the light passing through the diffraction grating; A mirror located on the opposite side of the diffraction grating across the wave plate and reflecting light toward the diffraction grating; A photodetector; A diffraction system

18. The diffraction system according to claim 17, wherein the diffraction grating is asymmetric.

19. The diffraction system according to claim 17, wherein the photodetector is arranged on the same side as the diffraction grating when viewed from the wave plate.

20. The diffraction system according to claim 17, wherein the wave plate is a quarter-wave plate.

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