Method of measuring efficiency for optical devices

Abstract

The embodiments disclosed herein relate to a measurement system and method for measuring the 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 to be diffracted into a diffracted beam having a diffraction order. The diffracted beam forms a diffraction pattern. The method includes positioning the optical device in the measurement system and guiding the diffracted beam to the sensor. The sensor is operable to measure the efficiency of the optical device by measuring the diffraction pattern.

Description

[Technical Field]

[0001] The embodiments disclosed herein generally relate to optical devices. More specifically, the embodiments disclosed herein relate to a measurement system and method for measuring the diffraction efficiency of an optical device. [Previous Technology]

[0002] Optical devices, including waveguide combiners and planar optical elements (such as metasurfaces and planar lenses), are used in various sensing applications (e.g., face recognition sensors). The generated light propagates through the optical device until it exits the device with a diffraction pattern. Improving the diffraction efficiency of the optical device and achieving a uniform distribution across the field of view are advantageous. Furthermore, measuring the diffraction order of the diffraction pattern with a large numerical aperture is advantageous. However, simultaneously measuring the efficiency of all diffraction orders is difficult.

[0003] Therefore, what is needed in the art is 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 disposed in the light beam. The light beam includes a diffracted beam. The measurement system further includes a mirror operable to guide the diffracted beam from the objective lens through two or more relay lenses, and a sensor disposed near the two or more relay lenses. The two or more relay lenses guide the diffracted beam having a diffraction pattern to the sensor. The measurement system further includes an illumination source disposed opposite to the light source.

[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 opposite the light source and the illumination source. The measurement system further includes a mirror operable to guide a diffracted light beam having a diffraction pattern to the sensor.

[0006] In yet another embodiment, a method is provided. The method includes positioning an optical device in a measurement system. The method further includes aligning the optical device with a light source by capturing a reference mark on the optical device. The method further includes guiding 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 guiding the diffracted beam through an objective lens, guiding the diffracted beam to a sensor with a mirror and one or more relay lenses, and measuring the diffraction efficiency of the diffraction pattern formed by the diffracted beam with the sensor.

Implementation Method

[0017] Embodiments disclosed herein relate to a measurement system and method for measuring the diffraction efficiency of an optical device.

[0018] FIG1A is a schematic top view of an optical device 100 according to an embodiment. FIG1B is a schematic side view of an optical device 100 according to an embodiment. The optical device 100 can be any optical device operable for use in sensing applications (e.g., a face recognition sensor). For example, the optical device 100 can be a waveguide combiner or a planar optical device, such as a metasurface or a planar lens.

[0019] The optical device 100 includes a plurality of optical device structures 102 disposed on a substrate 104. The optical device structures 102 may be nanostructures having sub-micron dimensions (e.g., nanometer dimensions). Although Figures 1A and 1B depict the optical device structures 102 as having a square or rectangular cross-section, the cross-section 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 twenty-five 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 inclined, wherein at least one sidewall 106 of the plurality of optical device structures 102 is inclined relative to the substrate 104. The optical device 100 includes a reference mark 110 disposed on the substrate 104.

[0020] The substrate 104 can be any substrate used in the art, and can be opaque or transparent depending on the purpose of the substrate 104. The substrate 104 includes any suitable material, as long as the substrate 104 can sufficiently transmit light of a predetermined wavelength or wavelength range and can serve as a sufficient support for a plurality of optical device structures 102. The substrate 104 includes, but is not limited to, amorphous dielectric crystal dielectrics, silicon dioxide (e.g., fused silicon dioxide), magnesium oxide, polymers, silicon (Si), silicon dioxide (SiO2), quartz, silicon carbide (SiC), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), sapphire, or combinations thereof. In some embodiments that can be combined with other embodiments described herein, the substrate 104 includes a transparent material. Suitable examples may include oxides, sulfides, phosphides, tellurides, or combinations thereof. The substrate 104 can be any size or shape, such as, but not limited to, a wafer with a diameter of 150 mm, 200 mm, or 300 mm.

[0021] FIG2 is a schematic top view of a diffraction pattern 200 according to an embodiment. The diffraction pattern 200 is generated when a light beam is diffracted by the optical device 100. The diffraction pattern 200 includes a diffracted beam 201 forming the diffraction pattern 200. The diffracted beam 201 includes one or more diffraction orders n having a highest order N and a negative highest order -N. As shown in FIG2, the highest order N (TN) beam is diffracted, and the negative highest order -N (TN) beam is diffracted. When the light beam is incident on the optical device 100, the light diffracts from the optical device structure 102 in a direction corresponding to the diffraction order n, where n = -2, -1, 0, 1, 2, 3, etc. The zero-order mode (T0) beam is also diffracted. The diffracted beam 201 has no upper limit on the highest order N and the negative highest order -N.

[0022] The diffracted beam 201 generates a plurality of light spots 202 in a 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 with 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 with 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 spots 202. The diffraction efficiency is a measure of how much optical power is diffracted to a specified direction compared to the power incident on the optical device 100. In some embodiments, each light spot 202 has the same size but different light spot intensities.

[0023] FIG3A is a schematic cross-sectional view of the configuration 301A of the measurement system 300 according to an embodiment. The measurement system 300 can be used to measure the diffraction efficiency of the optical device described herein. The measurement system 300 is capable of both real-space imaging (microscope) and k-space (angular space / back focal plane) imaging. Therefore, diffraction efficiency (k-space) and inspection device can be measured 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 one embodiment that can 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 system 300. In another embodiment that can be combined with other embodiments described herein, only optical devices 100 are disposed between the objective lens 304 and the light source 302.

[0024] The light source 302 is configured to guide the light beam 320 to one of the optical devices 100. As shown in FIG3A, the light beam 320 passes through the optical device 100 and is diffracted onto the objective lens 304. The objective lens 304 is disposed between the optical device 100 and the first mirror 306. In some embodiments that may be combined with other embodiments described herein, the light beam 320 is guided to the optical device 100 and the light beam 320 propagates through the optical device 100 before being diffracted onto the objective lens 304. For example, in an embodiment where 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 a diffracted beam 201 and guided 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 between about 20x and about 60x.

[0025] Illumination source 310 is configured to guide white light 322 to second mirror 308. Illumination source 310 is disposed opposite to light source 302. Second mirror 308 may be a dichroic mirror. White light 322 is reflected by second mirror 308 to objective lens 304. Dichroic mirror is a mirror with different reflection or transmission characteristics depending on the wavelength of the incident light. Therefore, diffracted beam 201 can be transmitted through second mirror 308 and guided to tube lens 312. Tube lens 312 guides diffracted beam 201 to produce real image 324. Real image 324 and white light 322 guided to objective lens 304 are used to position optical device 100 in measurement system 300. For example, optical device 100 may be aligned such that the desired portion of optical device 100 to be measured is positioned in measurement system 300. In some embodiments, alignment camera (not shown) captures reference mark 110 on optical device 100. The relative positions of the reference marks 110 on the optical device 100 are known, and the design of the optical device 100 is known. Therefore, a scan map can be created for each optical device 100 to be measured. Thus, the optical device 100 can be positioned to be aligned with the light source 302.

[0026] The diffracted beam 201 is further guided to a first mirror 306. The first mirror 306 may be a beam splitter. The first mirror 306 is disposed between a second mirror 308 and an 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 pass through the first mirror 306 and illuminate 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 has a surface area between approximately 70 mm² and approximately 864 mm². The second relay lens 316 guides the diffracted beam 201 toward the sensor 318. The diffracted beam 201 forms a diffraction pattern 200 on the sensor 318. The sensor 318 may be a 2D LiDAR sensor. The diffraction pattern 200 includes a diffracted beam 201 having one or more diffraction orders n with a highest order N and a negative highest order -N. As shown in Figure 3, the highest order N (TN) beam is diffracted, and the negative highest order -N (TN) beam is diffracted. The zero-order mode (T0) beam is also diffracted.

[0027] FIG3B is a schematic cross-sectional view of the configuration 301B of the measurement system 300. The measurement system 300 can be used to measure the diffraction efficiency of the 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 mounting the sensor 318 directly after the optical device 100. In one embodiment that can 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 system 300. In another embodiment that can be combined with other embodiments described herein, only the optical device 100 is disposed between the objective lens 304 and the light source 302.

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

[0029] FIG4 is a schematic cross-sectional view of a measurement system 400 according to an embodiment. The measurement system 400 can be used to measure 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 one embodiment that can 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 can be combined with other embodiments described herein, only optical devices 100 are disposed between the light source 402 and the sensor 408. The sensor 408 includes a surface area between approximately 70 mm² and approximately 864 mm². The sensor 408 is disposed opposite the light source 402 and the illumination source 406.

[0030] Light source 402 is configured to guide beam 420 to one of the optical devices 100. As shown in FIG4, beam 420 is guided to mirror 404. Mirror 404 reflects beam 420 to pass through optical device 100. Beam 420 is diffracted to sensor 408. In some embodiments that may be combined with other embodiments described herein, beam 420 is guided to optical device 100 and beam 420 propagates through optical device 100 before being diffracted to sensor 408. For example, in an embodiment where optical device 100 is a waveguide, beam 420 may propagate through optical device 100. Beam 420 is diffracted into diffracted beam 201 and guided to sensor 408. Sensor 408 may have a numerical aperture (NA) between about 0.85 and about 1.0. Sensor 408 may be a 20 mm sensor.

[0031] Illumination source 406 is configured to guide white light 410 to beam 420 when 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 can be aligned such that the desired portion of optical device 100 to be measured is positioned within measurement system 400. Reference mark 110 on optical device 100 is used for alignment of optical device 100 within measurement system 300.

[0032] The diffracted beam 201 is guided to the sensor 408. The diffracted beam 201 forms a diffraction pattern 200 on the sensor 408. The sensor 408 may be a 2D LiDAR sensor. The diffraction pattern 200 includes one or more diffraction orders n having a highest order N and a negative highest order -N. As shown in FIG3, the highest order N (TN) beam is diffracted, and the negative highest order -N (TN) beam is diffracted. The zero-order mode (T0) beam is also diffracted.

[0033] The diffracted beam 201 generates a plurality of light spots 202 in a 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 with other light spots 202 to determine the uniformity of the light spot intensity of the diffraction pattern 200. In addition, the light spot intensity of each light spot 202 can be compared with the total light from the light source 402 to determine the 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 with the light spots 202 of other optical devices 100.

[0034] Figure 5 is a flowchart 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 for a numerical aperture close to 1. By controlling the distance between the optical device 100 and the sensor 318, and by giving the sensor 318 a large surface area, the numerical aperture can approach 1. The numerical aperture is achieved using microscope objectives. Furthermore, diffraction orders can be measured in parallel for all diffraction orders to increase yield. For ease of explanation, the method will be described with reference to configuration 301A of the measurement system 300, but it should be understood that configuration 301B can be used in conjunction with the method provided herein.

[0035] In operation 501, the optical device 100 is positioned within the measurement system 300. For example, a portion of the optical device 100 to be measured is positioned within the measurement system 300. A real image 324 and white light 322 are used to position the optical device 100 within the measurement system 300. The optical device 100 is aligned with the light source 302. The optical device 100 is aligned by capturing a reference mark 110 on it. White light 322 illuminates the reference mark 110. Once the reference mark is positioned, the optical device 100 can be positioned aligned with the light source 302 based on the relative position of the reference mark 110. Furthermore, the distance variation between the optical device 100 and the objective lens 304 of the measurement system 300 is measured. In embodiments where the measurement system 300 includes an autofocus system 326, the autofocus system 326 is used to compensate for bending and drooping of the optical device 100. The autofocus system 326 allows the optical device 100 to focus within the measurement system 300.

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

[0037] In operation 503, the diffracted beam 201 forming the diffracted pattern 200 is measured by the sensor 318. The diffracted beam 201 generates a plurality of light spots 202 with the diffracted pattern 200 (as shown in FIG2). The sensor 318 measures the light spot intensity of each light spot 202 (as shown in FIG2).

[0038] In operation 504, the light intensity of each light spot 202 is compared with that of other light spots 202. This comparison allows for determination of the uniformity of the light spot intensity of the diffraction pattern 200. Furthermore, in operation 505, the light intensity of each light spot 202 (as shown in FIG. 2) can be compared with 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 (as shown in FIG. 2) can be compared with the light spots 202 of other optical devices 100.

[0039] Figure 6 is a flowchart 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 for a numerical aperture close to 1. By controlling the distance between the optical device 100 and the sensor 408, and by giving the sensor 408 a large surface area, the numerical aperture can approach 1. Furthermore, diffraction levels can be measured in parallel for all diffraction levels to increase yield.

[0040] In operation 601, the optical device 100 is positioned within the measurement system 400. For example, a portion of the optical device 100 to be measured is positioned within the measurement system 400. White light 410 is used to position the optical device 100 within the measurement system 400. The optical device 100 is aligned with the light source 402. The optical device 100 is aligned by capturing a reference mark 110 on it. Illumination source 406 illuminates the reference mark 110 to be captured. Once the reference mark 110 is positioned, the optical device 100 can be positioned aligned with the light source 402 based on the relative position of the reference mark 110.

[0041] In operation 602, the light beam 420 is guided to the optical device 100. The light beam 420 can be guided to the optical device 100 through the mirror 404. The optical device 100 diffracts the light into a diffracted beam 201. The diffracted beam 201 is guided to the sensor 408.

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

[0043] In operation 604, the intensity of the light spot is compared with that of other light spots 202. This comparison allows for determination of the uniformity of the light spot intensity of the diffraction pattern 200. Furthermore, in operation 605, the light spot intensity of each light spot 202 can be compared with 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 with those of other optical devices 100.

[0044] In summary, this document describes a measurement system and method for measuring the efficiency of an optical device. In one example, the measurement system 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 to be diffracted into a diffracted beam having diffraction orders. The diffracted beam forms a diffraction pattern. The method includes positioning the optical device in the measurement system and guiding the diffracted beam to the sensor. The sensor is operable to measure the efficiency of the optical device by measuring the diffraction pattern. Furthermore, the uniformity of the diffraction pattern can be measured by the sensor. The embodiments described herein allow for numerical apertures close to 1. The sensor is operable to simultaneously measure the efficiency of the diffraction orders, thereby improving output. The measurement system can be easily integrated into a production line to reduce diffraction efficiency and uniformity.

[0045] Although the foregoing content is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be designed without departing from the basic scope of the present disclosure, and the scope thereof is determined by the appended claims. [Simplified Explanation of the Diagram]

[0007] Therefore, the methods with the above-described features of this disclosure can be understood in detail. A more specific description of this disclosure is briefly summarized above, and reference can be made to embodiments, some of which are depicted in the accompanying drawings. However, it should be noted that the accompanying drawings only show exemplary embodiments and therefore should not be considered as limiting the scope, as this disclosure may acknowledge other equivalent embodiments.

[0008] FIG1A is a schematic top view of an optical device according to an embodiment.

[0009] FIG1B is a schematic side view of an optical device according to an embodiment.

[0010] FIG2 is a schematic top view of a diffraction pattern according to an embodiment.

[0011] FIG3A is a schematic cross-sectional view of the configuration of the measurement system according to an embodiment.

[0012] FIG3B is a schematic cross-sectional view of the configuration of the measurement system according to an embodiment.

[0013] FIG4 is a schematic cross-sectional view of the measurement system according to an embodiment.

[0014] Figure 5 is a flowchart of a method for measuring the diffraction efficiency of one or more optical devices using a measurement system according to an embodiment.

[0015] Figure 6 is a flowchart of a method for measuring the diffraction efficiency of one or more optical devices using a measurement system according to an embodiment.

[0016] For ease of understanding, the same element symbols have been used to denote common elements in the figures where possible. It is conceivable that elements and features of one embodiment may be advantageously incorporated into other embodiments without further description. [Biomaterial Storage]

[0047] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. A measurement system, comprising: A light source configured to project a light beam; an objective lens disposed within the light beam, wherein the light beam is diffracted into a diffracted beam by an optical device and guided to the objective lens; a first mirror operable to guide the diffracted beams from the objective lens through two or more relay lenses; a sensor disposed near the two or more relay lenses, wherein the two or more relay lenses guide the diffracted beams having a diffraction pattern to the sensor; an illumination source disposed opposite to the light source and configured to provide white light; a second mirror operable to guide the white light from the illumination source to the objective lens; and a tubular lens configured to guide the diffracted beams to form a real image of the optical device, wherein the first mirror is disposed between the second mirror and the objective lens, and wherein the diffracted beams are guided to the tubular lens through the second mirror.

2. The measurement system as described in claim 1, further comprising an autofocus system.

3. The measurement system as claimed in claim 2, wherein the autofocus system includes an autofocus module and a third lens.

4. The measurement system as claimed in claim 1, wherein the optical device is configured to be disposed between the light source and the objective lens, wherein 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 as described in claim 1, wherein the first mirror and the second mirror are dichroic mirrors.

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

0.

7. The measurement system as claimed in claim 1, wherein the diffracted beams generate a plurality of light spots with the diffraction pattern, wherein the sensor is operable to measure the intensity of a light spot for each light spot.

8. A method for measuring diffraction efficiency, the method comprising the steps of: positioning an optical device in a measurement system; aligning the optical device with a light source by capturing a reference mark on the optical device; guiding a light beam from the light source to the optical device, the optical device diffracting the light beam into a diffracted beam; guiding the diffracted beam through an objective lens; guiding the diffracted beam to a sensor using a first mirror and one or more relay lenses; and measuring a diffraction efficiency of a diffraction pattern formed by the diffracted beams using the sensor, wherein 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 formed by the diffracted beams, wherein the white light provided by the illumination source is guided to the objective lens by a second mirror, wherein the first mirror is disposed between the second mirror and the objective lens, and wherein the diffracted beam is guided through the second mirror to a tube lens, thereby forming the real image by the tube lens.

9. The method as described in claim 8, wherein the diffracted beams generate a plurality of light spots with the diffraction pattern, wherein the sensor is operable to measure the intensity of a light spot for each light spot.

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

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

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

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