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EP-4667891-B1 - NOVEL TECHNIQUES FOR EXAMINATION OF LIGHT OPTICAL ELEMENTS

EP4667891B1EP 4667891 B1EP4667891 B1EP 4667891B1EP-4667891-B1

Inventors

  • RONEN, Eitan

Dates

Publication Date
20260513
Application Date
20230731

Claims (6)

  1. A system for measuring parallelism of facets (101-104) of a lightguide optical element (LOE)(10), the LOE including a light-transmitting substrate having first and second major surfaces (12,13) parallel to each other such that light coupled into the light-transmitting substrate is trapped between the first and second major surfaces by total internal reflection and the facets configured to couple the light out of the substrate, the system comprising: one or more devices (131,132) having formed thereon a first slit and a second slit; a processing unit (100) configured to control at least one of the first slit and the second slit such that the first slit is disposed optically between a projector (20) configured to emit light corresponding to an image and the first major surface, the first slit disposed such that light from the projector travels through the first slit to the first major surface (12) and to a first facet of the facets and such that the second slit is disposed optically between the second major surface and a detector, the second slit disposed as to block light transmitted by the first facet and such that light reflected by the first facet and a second facet, from the facets, travels from the second facet to the second major surface (13) and through the second slit to the detector; and the processing unit configured to deduce the parallelism between the first facet and the second facet based on a shift of the image as detected by the detector relative to light transmitted normal to the first and second major surfaces (12, 13) through a portion of the substrate not including a facet from the facets.
  2. The system of claim 1, the processing unit (100) configured to laterally move (40) the LOE (10) relative to the first and second slits, or viceversa, to measure parallelism of additional facets of the LOE.
  3. The system of claim 1, the processing unit (100) configured to calibrate by capturing at the detector (32) an image emitted by the projector that travels through a portion of the substrate not including a facet.
  4. A method for measuring parallelism of facets (101-104) of a lightguide optical element (LOE)(10), the LOE including a light-transmitting substrate having first and second major surfaces (12,13) parallel to each other such that light coupled into the light-transmitting substrate is trapped between the first and second major surfaces by total internal reflection and the facets configured to couple the light out of the substrate, the method comprising: placing a first slit between a projector (20) configured to emit light corresponding to an image and the first major surface (12), the first slit placed such that light from the projector travels through the first slit to the first major surface and to a first facet of the facets; placing a second slit between a detector and the second major surface (13), the second slit placed to block light transmitted by the first facet and such that light reflected by the first facet and a second facet, from the facets, travels from the second facet to the second major surface (13) and through the second slit to the detector (32); and deducing the parallelism between the first facet and the second facet based on a shift of the image as detected by the detector (32) relative to light transmitted normal to the first and second major surfaces (12,13) through a portion of the substrate not including a facet from the facets.
  5. The method of claim 4, comprising laterally moving (40) the (LOE)(10) relative to the first and second slits, or viceversa, to measure parallelism of additional facets of the LOE.
  6. The method of claim 4, comprising: calibrating by capturing at the detector (32) an image emitted by the projector (20) that travels through a portion of the substrate not including a facet.

Description

FIELD OF THE INVENTION The present disclosure relates to the field of near eye display systems such as head-mounted displays. More specifically, the present disclosure relates to techniques for examining facets of lightguide optical elements (LOE) of near eye display systems. BACKGROUND OF THE INVENTION Consumer demands for improved human-computer interfaces have led to an increased interest in high-quality image head-mounted displays (HMDs) or near-eye displays (NED), commonly known as smart glasses. These devices can provide virtual reality (VR) or augmented reality (AR) experiences, enhancing the way users interact with digital content and their surrounding environment. Consumers are seeking better image quality, immersive experiences, and greater comfort when using HMDs. They expect displays with high resolution, vibrant colors, and minimal distortion to create a realistic and enjoyable viewing experience. A critical component in NED systems is the waveguide, which guides light from a system image projector to the user's eyes. Waveguides function based on total internal reflection along their major surfaces to propagate light and use reflection off facets placed along the waveguides to direct the light to the user's eyes. Achieving optimal waveguide performance requires precise design and manufacturing to prevent imperfections that could degrade the user's visual experience. Assessing the optical performance of a waveguide before integrating it into an NED system can help reduce production costs. Key factors for achieving optimal waveguide performance include ensuring the facets are parallel and have a homogeneous refractive index. Conventionally, testing these characteristics was time-consuming and expensive, which limited the availability and adoption of NED systems. Therefore, there is a demand for innovative techniques to examine waveguides efficiently. SUMMARY OF THE INVENTION The invention as claimed discloses a system for measuring parallelism of facets of a lightguide optical element (LOE) according to appended claim 1 and a corresponding method according to appended claim 4. The present disclosure introduces innovative techniques for measuring LOE optical performance. Previous methods for measuring facet parallelism in LOE used coupling prisms as disclosed in, for example, U.S. Pat. No. 11,226,261 and PCT International App. Pub. No. WO2023/007491 ; Another prior art method for measuring refractive index inhomogeneity is disclosed in US 2021/116367A1. In contrast, the techniques disclosed herein do not require coupling prisms. In one embodiment, the LOE is measured by coupling light into the waveguide through one or more of the major surfaces to reflect off or transmit through one or more of the facets. This eliminates the need for a coupling prism, simplifying the measurement system mechanics and improving testing efficiency. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various example systems, methods, and so on, that illustrate various example embodiments of aspects of the invention. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. One of ordinary skill in the art will appreciate that one element may be designed as multiple elements or that multiple elements may be designed as one element. An element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates an exemplary implementation of a near-eye display device.Fig. 2 illustrates a schematic diagram of an exemplary system for measuring parallelism of partially reflecting facets of an LOE.Fig. 3 illustrates a schematic diagram of an exemplary system for measuring parallelism of partially reflecting facets of an LOE.Fig. 4 illustrates a schematic diagram of an exemplary system for measuring parallelism of partially reflecting facets of an LOE.Fig. 5 illustrates a schematic diagram of an exemplary system for measuring parallelism of partially reflecting facets of an LOE.Fig. 6 illustrates a schematic diagram of an exemplary system for measuring parallelism of partially reflecting facets of an LOE.Fig. 7 illustrates a schematic diagram of an exemplary system for measuring homogeneity of refractive index of facets of an LOE.Fig. 8 illustrates a flow chart of an exemplary process for measuring parallelism of partially reflecting facets of an LOE.Fig. 9 illustrates a flow chart of an exemplary process for measuring homogeneity of refractive index of facets of an LOE. DETAILED DESCRIPTION Certain embodiments, not part of the present invention as defined by the appended claims, provide a light projecting system and an optical system for achieving optical aperture expansion for the purpose of, for example, head-mounted di