How to measure the efficiency of an optical device

Abstract

Embodiments of the present disclosure relate to a measurement system and method for measuring the diffraction efficiency of an optical device. In one example, the measurement system includes a light source, a mirror, an illumination source, and a sensor. The light source provides a light beam to the optical device, which is diffracted into a diffracted beam having diffraction orders. The diffracted beam generates a diffraction pattern. The method includes placing the optical device in the measurement system and directing the diffracted beam to a sensor. The sensor is operable to measure the efficiency of the optical device by measuring the diffraction pattern.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE

[0001] Embodiments of the present disclosure relate generally to optical devices, and more particularly to measurement systems and methods for measuring the diffraction efficiency of optical devices. [Background technology]

[0002]

[0002] Optical devices, including waveguide combiners and flat optical devices such as metasurfaces and flat lenses, are used in various sensing applications (e.g., face recognition sensors). Generated light propagates through the optical device until it emerges from the optical device accompanied by a diffraction pattern. It is beneficial to improve the diffraction efficiency of the optical device and obtain a uniform distribution across the field of view of the optical device. Furthermore, it is beneficial to measure the diffraction orders of the diffraction pattern with a large numerical aperture. However, it is difficult to simultaneously measure the efficiency of all diffraction orders.

[0003]

[0003] Therefore, there is a need for a measurement system and method for measuring the diffraction efficiency of an optical device. Summary of the Invention

[0004] In one embodiment, a measurement system is provided. The measurement system includes a light source configured to project a light beam and an objective lens positioned within the light beam. The light beam includes a diffracted beam. The measurement system further includes a mirror operable to direct the diffracted beam from the objective lens through two or more relay lenses, and a sensor positioned adjacent to the two or more relay lenses. The two or more relay lenses direct the diffracted beam having a diffraction pattern to the sensor. The measurement system further includes an illumination source positioned opposite the light source.

[0005]

[0005] In another embodiment, a measurement system is provided. The measurement system includes a light source configured to project a light beam, the light beam including a diffracted beam. The measurement system further includes an illumination source configured to provide white light and a sensor disposed on an opposite side of the light source from the illumination source. The measurement system further includes a mirror operable to direct the diffracted beam having a diffraction pattern to the sensor.

[0006] In yet another embodiment, a method is provided. The method includes placing an optical device in a measurement system. The method further includes aligning the optical device with a light source by capturing fiducial marks on the optical device. The method further includes directing a light beam from the light source to the optical device. The optical device diffracts the light beam into a diffracted beam. The method further includes directing the diffracted beam through an objective lens, directing the diffracted beam to a sensor using mirrors and one or more relay lenses, and measuring a diffraction efficiency of a diffraction pattern produced by the diffracted beam using the sensor.

[0007]

[0007] In order that the above-mentioned features of the present disclosure may be understood in detail, the disclosure briefly summarized above will now be more particularly described with reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings depict only exemplary embodiments and therefore should not be considered as limiting the scope thereof, and that the present disclosure may admit of other equally effective embodiments. [Brief explanation of the drawings]

[0008] [Figure 1A]

[0008] FIG. 1 is a schematic top view of an optical device according to several embodiments. [Figure 1B]

[0009] 1 is a schematic side view of an optical device according to several embodiments. [Figure 2]

[0010] 1A-1C are schematic top views of diffraction patterns according to several embodiments. [Figure 3A]

[0011] 1 is a schematic cross-sectional view of a measurement system configuration according to several embodiments. [Figure 3B]

[0012] 1 is a schematic cross-sectional view of a measurement system configuration according to several embodiments. [Figure 4]

[0013] 1 is a schematic cross-sectional view of a measurement system according to several embodiments. [Figure 5]

[0014] FIG. 1 is a flow diagram of a method for measuring the diffraction efficiency of one or more optical devices using a measurement system according to several embodiments. [Figure 6]

[0015] FIG. 1 is a flow diagram of a method for measuring the diffraction efficiency of one or more optical devices using a measurement system according to several embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0009]

[0016] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements common to the figures. It is believed that elements and features of one embodiment may be beneficially incorporated in multiple other embodiments without further description.

[0010]

[0017] SUMMARY Embodiments of the present disclosure relate to measurement systems and methods for measuring the diffraction efficiency of optical devices.

[0011]

[0018] 1A is a schematic top view of an optical device 100 according to several embodiments. FIG. 1B is a schematic side view of the optical device 100 according to several embodiments. The optical device 100 may be any optical device operable to be utilized in sensing applications (e.g., a face identification sensor). For example, the optical device 100 may be a waveguide combiner or a flat optical device such as a metasurface or a flat lens.

[0012]

[0019] The optical device 100 includes a plurality of optical device structures 102 disposed on a substrate 104. The plurality of optical device structures 102 may be nanostructures having submicron dimensions, e.g., nano-sized dimensions. Although FIGS. 1A and 1B depict the optical device structures 102 as having square or rectangular cross-sections, the cross-sections of the optical device structures 102 may have other shapes, including, but not limited to, circular, triangular, elliptical, regular polygonal, irregular polygonal, and / or irregularly shaped cross-sections. Although only 25 optical device structures 102 are shown on the substrate 104, any number of optical device structures 102 may be disposed on the substrate 104. In some embodiments, the optical device structures 102 may be angled. That is, at least one sidewall 106 of the plurality of optical device structures 102 may be angled relative to the substrate 104. The optical device 100 includes a fiducial mark 110 disposed on the substrate 104.

[0013]

[0020] The substrate 104 can be any used in the art and can be either opaque or transparent depending on the application of the substrate 104. The substrate 104 comprises any suitable material, provided that the substrate 104 can adequately transmit light of a predetermined wavelength or range of wavelengths and can serve as a suitable support for the optical device structures 102. The substrate 104 can include, but is not limited to, an amorphous dielectric, a crystalline dielectric, silica (e.g., fused silica), magnesium oxide, a polymer, silicon (Si), silicon dioxide (SiO), quartz, silicon carbide (SiC), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), sapphire, or a combination thereof. In some embodiments, which can be combined with other embodiments described herein, the substrate 104 comprises a transparent material. Suitable examples can include oxides, sulfides, phosphides, tellurides, or a combination thereof. The substrate 104 can be of any size or shape, including, but not limited to, a 150 mm, 200 mm, or 300 mm diameter wafer.

[0014]

[0021] 2 is a schematic top view of a diffraction pattern 200 according to several embodiments. The diffraction pattern 200 is produced when a beam of light is diffracted by the optical device 100. The diffraction pattern 200 includes a diffracted beam 201 that produces the diffraction pattern 200. The diffracted beam 201 includes one or more diffraction orders n, with the highest order N and the negative of the highest order −N. As shown in FIG. 2, the highest order N(T N ) beam is diffracted into the most negative order −N(T -N ) beam is diffracted. When a ray of light is incident on the optical device 100, the light is diffracted from the optical device structure 102 in a direction corresponding to the diffraction order n (n=-2, -1, 0, 1, 2, 3, etc.). A zero-mode (T0) beam is also diffracted. The diffracted beam 201 does not have an upper limit between the highest order N and the most negative order −N.

[0015]

[0022] The diffracted beam 201 generates a plurality of light spots 202 within the diffraction pattern 200. Each of the plurality of light spots 202 has a light spot intensity. The light spot intensity of each light spot 202 can be compared to the other light spots 202 to determine the uniformity of the light spot intensity of the diffraction pattern 200. Furthermore, the light spot intensity of each light spot 202 can be compared to the total light emitted from the light source to determine the diffraction efficiency of the diffraction order n of the diffracted beam 201. The light spot intensity is the total power of the light spot 202. The diffraction efficiency is the amount of optical power diffracted in a specified direction compared to the power incident on the optical device 100. In some embodiments, each of the light spots 202 has the same size but a different light spot intensity.

[0016]

[0023] FIG. 3A is a schematic cross-sectional view of a configuration 301A of a measurement system 300 according to several embodiments. The measurement system 300 may be used in the methods for measuring the diffraction efficiency of an optical device described herein. The measurement system 300 enables both real-space imaging (microscopy) and k-space (angle-space / back-focal-plane) imaging. Therefore, diffraction efficiency (k-space) measurements and device inspection can be performed simultaneously. The measurement system 300 includes a light source 302, an objective lens 304, a first mirror 306, a second mirror 308, an illumination source 310, a tube lens 312, a first relay lens 314, a second relay lens 316, and a sensor 318. The measurement system 300 images the diffraction pattern 200 at the back-focal-plane of the objective lens. The back-focal-plane is located between the objective lens 304 and the first mirror 306. The back-focal-plane is relayed to the sensor 318 through the first relay lens 314 and the second relay lens 316. One or more optical devices 100 are disposed between the objective lens 304 and the light source 302. In an embodiment that may be combined with other embodiments described herein, multiple optical devices 100 may be disposed between the objective lens 304 and the light source 302. For example, multiple optical devices 100 may be disposed on a translation stage to be measured by the measurement apparatus 300. In another embodiment that may be combined with other embodiments described herein, only optical device 100 is disposed between the objective lens 304 and the light source 302.

[0017]

[0024] The light source 302 is configured to direct a light beam 320 to one of the optical devices 100. As shown in FIG. 3A , the light beam 320 passes through the optical device 100 and is diffracted into the objective lens 304. The objective lens 304 is disposed between the optical device 100 and the first mirror 306. In some embodiments, which may be combined with other embodiments described herein, the light beam 320 is directed to the optical device 100, where the light beam 320 propagates through the optical device 100 before being diffracted into the objective lens 304. For example, in some embodiments in which the optical device 100 is a waveguide, the light beam 320 may propagate through the optical device 100. The light beam 320 is diffracted into the diffracted beam 201 and directed to the objective lens 304. The objective lens 304 may have a numerical aperture (NA) between about 0.5 and about 1.0. The objective lens 304 may have a magnification power between about 20x and about 60x.

[0018]

[0025] The illumination source 310 is configured to direct white light 322 to the second mirror 308. The illumination source 310 is disposed opposite the light source 302. The second mirror 308 may be a dichroic mirror. The white light 322 is reflected by the second mirror 308 to the objective lens 304. A dichroic mirror is a mirror whose reflection or transmission characteristics vary depending on the wavelength of the incident light. Thus, the diffracted beam 201 may be directed to the tube lens 312 by transmitting through the second mirror 308. The tube lens 312 directs the diffracted beam 201 to generate a real image 324. The real image 324 and the white light 322 directed to the objective lens 304 are used to position the optical device 100 in the measurement system 300. For example, the optical device 100 may be aligned so that a desired portion of the optical device 100 to be measured is positioned in the measurement system 300. In some embodiments, an alignment camera (not shown) captures fiducial marks 110 on optical device 100. The relative positions of fiducial marks 110 on optical device 100 are known, and the design of optical device 100 is also known. Thus, a scan map can be constructed for each optical device 100 to be measured. Thus, optical device 100 can be positioned to align with light source 302.

[0019]

[0026] The diffracted beam 201 is further directed to a first mirror 306. The first mirror 306 may be a dichroic mirror. The first mirror 306 is disposed between a second mirror 308 and the objective lens 304. The first mirror 306 reflects the diffracted beam 201 from the objective lens 304 to a first relay lens 314 and a second relay lens 316. The diffracted beam 201 may also be transmitted through the first mirror 306 to the second mirror 308. The first relay lens 314 is disposed between the first mirror 306 and the second relay lens 316. The second relay lens 316 is disposed between the first relay lens 314 and a sensor 318. The sensor 318 is approximately 70 mm 2 and approximately 864 mm 2The second relay lens 316 directs the diffracted beam 201 to a sensor 318. The diffracted beam 201 produces a diffraction pattern 200 on the sensor 318. The sensor 318 may be a 2D LIDAR sensor. The diffraction pattern 200 includes the diffracted beam 201 having one or more diffraction orders n, with the highest order N and the negative of the highest order −N. As shown in FIG. 3, the highest order N(T N ) beam is diffracted into the most negative order −N(T -N ) beam is diffracted. The zeroth mode (T0) beam is also diffracted.

[0020]

[0027] 3B is a schematic cross-sectional view of a configuration 301B of a measurement system 300. The measurement system 300 may be used in the method for measuring the diffraction efficiency of an optical device described herein. The measurement system 300 includes a light source 302, an objective lens 304, a first mirror 306, a second mirror 308, an illumination source 310, a tube lens 312, a first relay lens 314, a second relay lens 316, and a sensor 318. One or more optical devices 100 are disposed between the objective lens 304 and the light source 302. The diffraction efficiency is obtained by attaching the sensor 318 directly after the optical device 100. In an embodiment that may be combined with other embodiments described herein, multiple optical devices 100 may be disposed between the objective lens 304 and the light source 302. For example, multiple optical devices 100 may be disposed on a translation stage to be measured by the measurement apparatus 300. In another embodiment, which may be combined with other embodiments described herein, only the optical device 100 is positioned between the objective lens 304 and the light source 302 .

[0021]

[0028] Configuration 301B is utilized to control the gap between one or more optical devices 100 and objective lens 304. Configuration 301B includes measurement system 300, as described with reference to FIG. 3A , and autofocus system 326. Autofocus system 326 includes autofocus module 328 and third mirror 330. Autofocus system 326 compensates for sagging or warping of substrate 104. As the distance between objective lens 304 and optical device 100 changes due to sagging or warping, autofocus system 326 compensates for the changing distance.

[0022]

[0029] 4 is a schematic cross-sectional view of a measurement system 400 according to several embodiments. The measurement system 400 may be used in the methods for measuring the diffraction efficiency of an optical device described herein. The measurement system 400 includes a light source 402, a mirror 404, an illumination source 406, and a sensor 408. One or more optical devices 100 are disposed between the light source 402 and the sensor 408. In an embodiment that may be combined with other embodiments described herein, multiple optical devices 100 may be disposed between the light source 402 and the sensor 408. For example, multiple optical devices 100 may be disposed on a translation stage to be measured by the measurement system 400. In another embodiment that may be combined with other embodiments described herein, only the optical device 100 is disposed between the light source 402 and the sensor 408. The sensor 408 is located approximately 70 mm apart. 2 and approximately 864 mm 2 The sensor 408 is positioned opposite the light source 402 and the illumination source 406.

[0023]

[0030] The light source 402 is configured to direct a light beam 420 to one of the optical devices 100. As shown in FIG. 4 , the light beam 420 is directed to a mirror 404. The mirror 404 reflects the light beam 420 through the optical device 100. The light beam 420 is diffracted to the sensor 408. In some embodiments, which may be combined with other embodiments described herein, the light beam 420 is directed to the optical device 100, where the light beam 420 propagates through the optical device 100 before being diffracted to the sensor 408. For example, in embodiments in which the optical device 100 is a waveguide, the light beam 420 may propagate through the optical device 100. The light beam 420 is diffracted into a diffracted beam 201 and directed to the sensor 408. The sensor 408 may have a numerical aperture (NA) between about 0.85 and about 1.0. The sensor 408 may be a 20 mm sensor.

[0024]

[0031] Illumination source 406 is configured to direct white light 410 into light beam 420 when light beam 420 contacts optical device 100. White light 410 is used to position optical device 100 within measurement system 400. For example, optical device 100 may be aligned such that a desired portion of optical device 100 to be measured is positioned within measurement system 400. Fiducial marks 110 on optical device 100 are used to align optical device 100 within measurement system 300.

[0025]

[0032] The diffracted beam 201 is directed to a sensor 408. The diffracted beam 201 produces a diffraction pattern 200 on the sensor 408. The sensor 408 may be a 2D LIDAR sensor. The diffraction pattern 200 includes the diffracted beam 201 having one or more diffraction orders n, with the highest order N and the negative of the highest order −N. As shown in FIG. 3, the highest order N(T N ) beam is diffracted into the most negative order −N(T -N ) beam is diffracted. The zeroth mode (T0) beam is also diffracted.

[0026]

[0033] The diffracted beam 201 generates a plurality of light spots 202 in the diffraction pattern 200. The sensor 408 is operable to measure the light spot intensity of each light spot 202. The light spot intensity can be compared to other light spots 202 to determine the uniformity of the light spot intensities in the diffraction pattern 200. Furthermore, the light spot intensity of each light spot 202 can be compared to the total light emitted from the light source 402 to determine the diffraction efficiency of the diffraction order n of the diffracted beam 201. In some embodiments, the uniformity and intensity of the light spots 202 can be compared to light spots 202 of other optical devices 100.

[0027]

[0034] FIG. 5 is a flow diagram of a method 500 for measuring the diffraction efficiency of one or more optical devices 100 using a measurement system 300. The measurement system 300 described herein allows a numerical aperture close to 1 to be achieved. By controlling the distance between the optical device 100 and the sensor 318 and having a large surface area of ​​the sensor 318, a numerical aperture close to 1 can be achieved. The numerical aperture is achieved by utilizing a microscope objective. Furthermore, to improve throughput, diffraction orders may be measured in parallel for all diffraction orders. For ease of explanation, the method will be described with reference to configuration 301A of the measurement system 300, although it should be understood that configuration 301B may also be used in conjunction with the methods provided herein.

[0028]

[0035] In operation 501, the optical device 100 is placed in the measurement system 300. For example, the portion of the optical device 100 to be measured is placed in the measurement system 300. The optical device 100 is placed in the measurement system 300 using a real image 324 and white light 322. The optical device 100 is aligned with the light source 302. The optical device 100 is aligned by capturing a fiducial mark 110 on the optical device 100. The white light 322 illuminates the fiducial mark 110. Once the fiducial mark is in place, the optical device 100 can be positioned to align with the light source 302 based on the relative position of the fiducial mark 110. Additionally, a change in the distance between the optical device 100 and the objective lens 304 of the measurement system 300 is measured. In some embodiments where the measurement system 300 includes an autofocus system 326, the autofocus system 326 is utilized to compensate for warping or sagging of the optical device 100. The autofocus system 326 allows the optical device 100 to be brought into focus in the measurement system 300 .

[0029]

[0036] In operation 502, a light beam 320 is directed to the optical device 100. The optical device 100 diffracts the light into a diffracted beam 201. The diffracted beam 201 is directed to the objective lens 304. The diffracted beam 201 is then directed to the sensor 318 by the first mirror 306, the first relay lens 314, and the second relay lens 316.

[0030]

[0037] In operation 503, the diffracted beam 201 that generates the diffraction pattern 200 is measured by the sensor 318. The diffracted beam 201 generates a plurality of light spots 202 (shown in FIG. 2) within the diffraction pattern 200. The sensor 318 measures the light spot intensity of each light spot 202 (shown in FIG. 2).

[0031]

[0038] In operation 504, the light spot intensity of each light spot 202 is compared to the other light spots 202. This comparison can determine the uniformity of the light spot intensities of the diffraction pattern 200. Furthermore, in operation 505, the light spot intensity of each light spot 202 (shown in FIG. 2 ) can be compared to the total light from the light source 302 to determine the diffraction efficiency of the diffraction order n of the diffracted beam 201. In some embodiments, the uniformity and intensity of the light spots 202 (shown in FIG. 2 ) can be compared to the light spots 202 of other optical devices 100.

[0032]

[0039] 6 is a flow diagram of a method 600 for measuring the diffraction efficiency of one or more optical devices 100 using a measurement system 400. The measurement system 400 described herein allows a numerical aperture close to 1 to be achieved. By controlling the distance between the optical device 100 and the sensor 408 and having a large surface area of ​​the sensor 408, the numerical aperture can be made to approach 1. Furthermore, to improve throughput, diffraction orders may be measured in parallel for all diffraction orders.

[0033]

[0040] In operation 601, optical device 100 is placed in measurement system 400. For example, a portion of optical device 100 to be measured is placed in measurement system 400. White light 410 is utilized to place optical device 100 in measurement system 400. Optical device 100 is aligned with light source 402. Optical device 100 is aligned by capturing fiducial marks 110 on optical device 100. White light 406 illuminates the captured fiducial marks 110. Once fiducial marks 110 are positioned, optical device 100 can be positioned to align with light source 402 based on the relative position of fiducial marks 110.

[0034]

[0041] In operation 602, light beam 420 is directed to optical device 100. Light beam 420 may be directed to optical device 100 by mirror 404. Optical device 100 diffracts the light into diffracted beam 201. Diffracted beam 201 is directed to sensor 408.

[0035]

[0042] In operation 603, the diffracted beam 201 that generates the diffraction pattern 200 is measured by the sensor 408. The diffracted beam 201 generates a plurality of light spots 202 within the diffraction pattern 200. The sensor 408 measures the light spot intensity of each light spot 202.

[0036]

[0043] In operation 604, the light spot intensity is compared to other light spots 202. This comparison can determine the uniformity of the light spot intensities of the diffraction pattern 200. Furthermore, in operation 605, the light spot intensity of each light spot 202 can be compared to the total light from the light source 402 to determine the diffraction efficiency of the diffraction order n of the diffracted beam 201. In some embodiments, the uniformity and intensity of the light spots 202 can be compared to light spots 202 of other optical devices 100.

[0037]

[0044] In summary, a measurement system and method for measuring the efficiency of an optical device are described herein. The measurement system, in one example, includes at least a light source, a mirror, an illumination source, and a sensor. The light source provides a light beam to the optical device, which is diffracted into a diffracted beam having diffraction orders. The diffracted beam generates a diffraction pattern. The method includes placing the optical device in a measurement system and directing the diffracted beam to a sensor. The sensor is operable to measure the efficiency of the optical device by measuring the diffraction pattern. Additionally, the uniformity of the diffraction pattern may be measured by the sensor. Several embodiments described herein enable numerical apertures close to 1 to be achieved. The sensor is operable to simultaneously measure the efficiency of multiple diffraction orders, thus improving throughput. The measurement system can be easily integrated into a production line to measure diffraction efficiency and uniformity.

[0038]

[0045] While the forgoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, which scope is determined by the following claims.

Claims

1. a light source configured to project a light beam; an objective lens disposed within the light beam, the light beam being diffracted by an optical device into a diffracted beam and directed to the objective lens; a first mirror operable to direct the diffracted beam from the objective lens through two or more relay lenses; a sensor disposed adjacent to the two or more relay lenses, the two or more relay lenses directing the diffracted beams having a diffraction pattern to the sensor; an illumination source disposed opposite the light source and configured to provide white light; a second mirror operable to direct the white light from the illumination source to the objective lens; and a tube lens configured to direct the diffracted beam to generate a real image of the optical device; the first mirror is disposed between the second mirror and the objective lens; The diffracted beam is directed to the tube lens by transmitting through the second mirror.

2. The measurement system of claim 1 further comprising an autofocus system.

3. The measurement system of claim 2 , wherein the autofocus system includes an autofocus module and a third mirror.

4. 2. The measurement system of claim 1, wherein the optical device is configured to be disposed between the light source and the objective lens, the light beam is operable to propagate through the optical device, and the light beam is operable to be diffracted by the optical device.

5. The measurement system of claim 1 , wherein the first mirror and the second mirror are dichroic mirrors.

6. The measurement system of claim 1 , wherein the objective lens has a numerical aperture (NA) between 0.5 and 1.

0.

7. The measurement system of claim 1 , wherein the diffracted beam produces a plurality of light spots in the diffraction pattern, and the sensor is operable to measure a light spot intensity of each light spot.

8. Positioning the optical device within the measurement system; aligning the optical device with a light source by capturing fiducial marks on the optical device; directing a light beam from the light source to the optical device, the optical device diffracting the light beam into a diffracted beam; directing said diffracted beam through an objective lens; directing the diffracted beam to a sensor using a first mirror and one or more relay lenses; and measuring, with the sensor, the diffraction efficiency of a diffraction pattern produced by the diffracted beam; positioning the optical device includes positioning the optical device in the measurement system using white light provided by an illumination source and a real image of the optical device created by the diffracted beam; the white light provided by the illumination source is directed to the objective lens by a second mirror; the first mirror is disposed between the second mirror and the objective lens; The diffracted beam is directed to a tube lens by transmitting through the second mirror, thereby generating the real image by the tube lens.

9. The method of claim 8 , wherein the diffracted beam produces a plurality of light spots in the diffraction pattern, and the sensor is operable to measure a light spot intensity of each light spot.

10. The method of claim 8 , wherein a plurality of the optical devices are arranged on a translation stage for measurement by the measurement system.

11. The method of claim 8 , further comprising focusing the optical device in the measurement system using an autofocus system.

12. The method of claim 8 , wherein measuring the diffraction efficiency comprises comparing a light spot intensity of each diffracted beam to total light from the light source to determine the diffraction efficiency of the optical device.

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