US-12619087-B2 - Method of manufacturing optical element and projection device

US12619087B2US 12619087 B2US12619087 B2US 12619087B2US-12619087-B2

Abstract

A method of manufacturing a holographic element used in a projection device is provided. The projection device has a light source configured to emit light conforming to a non-uniform light intensity distribution function. The method includes: multiplying the non-uniform light intensity distribution function by a diffraction intensity and angle function of a grating to obtain a product function; determining whether the product function is substantially equal to 1 in a predetermined range of angle or wavelength; if the the determination result is yes, determining a pair of incident angles respectively of a reference beam and a signal beam according to the diffraction intensity and angle function; and recording a holographic material with the reference beam and the signal beam respectively at the pair of incident angles, so as to manufacture a holographic element with the grating therein.

Inventors

Qing-Long Deng
Chih-Ying CHEN

Assignees

HTC CORPORATION

Dates

Publication Date: 20260505
Application Date: 20230928

Claims (11)

1 . A method of manufacturing an optical element used in a projection device, the projection device having a light source configured to emit light conforming to a non-uniform light intensity distribution function, the method comprising: multiplying the non-uniform light intensity distribution function by a diffraction intensity and angle function of at least one first grating to obtain a product function; determining whether the product function is substantially equal to 1 in a predetermined range of angle or wavelength such that the light, when compensated by the at least one first grating, conforms to a uniform light intensity distribution function; if the product function is not substantially equal to 1 in the predetermined range of angle or wavelength, adjusting the diffraction intensity and angle function by adjusting at least one of at least one surface period width and at least one slant angle of the at least one first grating; if the product function is substantially equal to 1 in the predetermined range of angle or wavelength, determining at least one pair of incident angles respectively of a reference beam and a signal beam according to the diffraction intensity and angle function; and recording at least one piece of holographic material with the reference beam and the signal beam respectively at the at least one pair of incident angles, so as to manufacture at least one holographic element with the at least one first grating therein.
2 . The method of claim 1 , further comprising: obtaining the diffraction intensity and angle function of the at least one first grating according to Kogelnik's coupled-wave theory.
3 . The method of claim 2 , wherein the obtaining the diffraction intensity and angle function uses parameters comprising a total internal reflection angle, a refractive index modulation of the at least one piece of holographic material, a thickness of the at least one piece of holographic material, at least one grating established wavelength, at least one surface period width, and at least one slant angle of the at least one first grating.
4 . The method of claim 1 , further comprising: iteratively adjusting the diffraction intensity and angle function to approximate the product function to 1 in the predetermined range of angle or wavelength.
5 . The method of claim 1 , further comprising: multiplying the non-uniform light intensity distribution function by another diffraction intensity and angle function of a second grating to obtain another product function; determining whether the another product function is substantially equal to 1 in another predetermined range of angle or wavelength; if the another product function is substantially equal to 1 in the another predetermined range of angle or wavelength, determining another pair of incident angles of the reference beam and the signal beam according to the another diffraction intensity and angle function; and recording the at least one piece of holographic material with the reference beam and the signal beam respectively at the another pair of incident angles, so as to form the second grating in the at least one holographic element.
6 . The method of claim 5 , wherein the at least one first grating and the second grating are configured to diffract light within an identical range of angle and are configured to respectively diffract light within different ranges of wavelength.
7 . The method of claim 5 , wherein the at least one first grating and the second grating are configured to diffract light within an identical range of wavelength and are configured to respectively diffract light within different ranges of angle.
8 . The method of claim 1 , further comprising: obtaining the diffraction intensity and angle function by convolving a plurality of sub-diffraction intensity and angle functions.
9 . The method of claim 8 , wherein a number of the at least one first grating is plural, the first gratings respectively conform to the sub-diffraction intensity and angle functions, a pair number of the at least one pair of incident angles is plural, each of the pairs of incident angles respectively corresponds to the sub-diffraction intensity and angle functions, and the recording comprises recording the at least one piece of holographic material with the reference beam and the signal beam respectively at each of the pairs of incident angles.
10 . The method of claim 8 , further comprising: if the product function is not substantially equal to 1 in the predetermined range of angle or wavelength, adjusting the diffraction intensity and angle function by convolving the sub-diffraction intensity and angle functions with another sub-diffraction intensity and angle function; determining whether the adjusted product function is substantially equal to 1 in the predetermined range of angle or wavelength; if the adjusted product function is substantially equal to 1 in the predetermined range of angle or wavelength, determining a plurality of pairs of incident angles of the reference beam and the signal beam respectively according to the sub-diffraction intensity and angle functions and the another sub-diffraction intensity and angle function; and recording the at least one piece of holographic material with the reference beam and the signal beam respectively at each of the pairs of incident angles, wherein a number of the at least one first grating is plural, and the first gratings respectively correspond to the sub-diffraction intensity and angle functions and the another sub-diffraction intensity and angle function.
11 . The method of claim 1 , wherein a number of the at least one piece of holographic material, a number of the at least one holographic element, and a number of the at least one first grating are plural, and the recording respectively forms two of the first gratings in two of the holographic elements.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to U.S. Provisional Application Ser. No. 63/378,512, filed on Oct. 5, 2022, which is herein incorporated by reference. BACKGROUND Technical Field The present disclosure relates to a method of manufacturing an optical element and a projection device. Description of Related Art Various types of computing, entertainment, and/or mobile devices can be implemented with a transparent or semi-transparent display through which a user of a device can view the surrounding environment. Such devices, which can be referred to as see-through, mixed reality display device systems, or as augmented reality (AR) systems, enable a user to see through the transparent or semi-transparent display of a device to view the surrounding environment, and also see images of virtual objects (e.g., text, graphics, video, etc.) that are generated for display to appear as a part of, and/or overlaid upon, the surrounding environment. These devices, which can be implemented as head-mounted display (HMD) glasses or other wearable display devices, but are not limited thereto, often utilize optical waveguides to replicate an image to a location where a user of a device can view the image as a virtual image in an augmented reality environment. As this is still an emerging technology, there are certain challenges associated with utilizing waveguides to display images of virtual objects to a user. Nowadays, many conventional waveguides with diffraction gratings attached thereon have been used. Each of the waveguides and the diffraction gratings attached thereon are used for transmitting a single color. As such, a conventional projection device for providing projected images to an eye of a user usually requires a plurality of waveguides to transmit three primary colors, which is not conducive to the reduction of weight and thickness of the projection device. In addition, when transmitting a monochromatic or full-color exit pupil image, the diffraction efficiency at different angles will be caused by different wavelengths and different incident angles, so the problem of uneven image brightness is prone to occur. To this end, additional optical compensation components need to be added to solve the problem, making the overall optical system more complex and increasing in size. Accordingly, it is an important issue for the industry to provide a method of manufacturing an optical element and a projection device capable of solving the aforementioned problems. SUMMARY An aspect of the disclosure is to provide a method of manufacturing an optical element and a projection device that can efficiently solve the aforementioned problems. According to an embodiment of the disclosure, a method of manufacturing an optical element used in a projection device. The projection device has a light source configured to emit light conforming to a non-uniform light intensity distribution function. The method includes: multiplying the non-uniform light intensity distribution function by a diffraction intensity and angle function of at least one grating to obtain a product function; determining whether the product function is substantially equal to 1 in a predetermined range of angle or wavelength; if the product function is substantially equal to 1 in the predetermined range of angle or wavelength, determining at least one pair of incident angles respectively of a reference beam and a signal beam according to the diffraction intensity and angle function; and recording at least one piece of holographic material with the reference beam and the signal beam respectively at the at least one pair of incident angles, so as to manufacture at least one holographic element with the at least one grating therein. In an embodiment of the disclosure, the method further includes: obtaining the diffraction intensity and angle function of the at least one grating according to Kogelnik's coupled-wave theory. In an embodiment of the disclosure, the obtaining the diffraction intensity and angle function uses parameters including a total internal reflection angle, a refractive index modulation of the at least one piece of holographic material, a thickness of the at least one piece of holographic material, at least one grating established wavelength, at least one surface period width, and at least one slant angle of grating. In an embodiment of the disclosure, the method further includes: adjusting the diffraction intensity and angle function by adjusting at least one of the at least one surface period width and the at least one slant angle of grating if the product function is not substantially equal to 1 in the predetermined range of angle or wavelength. In an embodiment of the disclosure, the method further includes: iteratively adjusting the diffraction intensity and angle function to approximate the product function to 1 in the predetermined range of angle or wavelength. In an embodiment of the disclosure, the method fur