DESC:FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(SEE SECTION 10, RULE 13)

SYSTEM AND METHOD FOR RECORDING LARGER SIZE HOLOGRAPHIC ELEMENTS

BHARAT ELECTRONICS LIMITED

WITH ADDRESS:
OUTER RING ROAD, NAGAVARA, BANGALORE 560045, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
TECHNICAL FIELD
[0001] The present invention relates generally to the technical field of holographic imaging technologies, specifically relating to systems and methods for recording and reproducing holographic elements of larger dimensions or sizes. This encompasses advancements in optical engineering, holography, and data storage techniques to facilitate the creation, manipulation, and storage of holographic images exceeding conventional size limitations.

BACKGROUND
[0002] The field of holography, particularly the printing or recording of Holographic Elements (HEs), has seen considerable interest due to the pivotal role these elements play in the manipulation of light information beams within waveguides, leveraging the Total Internal Reflection (TIR) phenomenon. Despite the growing demand for efficient HEs, current hologram recording configurations fall short in adequately addressing the needs for producing high-quality, large-scale holographic elements suitable for these advanced applications.
[0003] A thorough examination of existing literature reveals a significant focus on techniques aimed primarily at diffracting light information beams. While such methods contribute valuable insights into the general principles of holography, they offer limited utility for specific applications in waveguide technologies where precise control over light manipulation is required. Moreover, the scant research that does address waveguide applications tends to rely on the use of multiple prisms to achieve the desired holographic effects. This approach, while effective to a degree, introduces complexity, increased cost, and potential limitations in scalability and integration within more compact or sophisticated waveguide systems.
[0004] US005182659A, titled “Holographic recording and scanning system and method” describes a recording geometry which results in a recorded pattern on a photosensitive surface, thereby creating hologram on a scanning surface.
[0005] In Vadivelan et.al., Fabrication of a phase transmission holographic optical element in polycarbonate and its characterization is disclosed. This paper describes about the recording of a transmission element from a triangular geometry. Not recorded for waveguide applications.
[0006] In Philip D. Nystrom, et al., High dynamic range two-stage photopolymer materials through enhanced solubility high refractive index writing monomers is disclosed. In this paper, total angle for recording of the photosensitive medium is not zero due to non-application of waveguide.
[0007] In Byoungho Lee et.al., Holography display for see-through augmented reality using mirror-lens holographic optical element is disclosed. This paper does not use prism or any kind of waveguide arrangement.
[0008] In Hui-Ying Wu et al., Holographic optical elements and application is disclosed. This paper explains about recording holographic elements but without the use of prism and that shows smaller angles and HOE formation.
[0009] In Bigler et.al., Holographic waveguide heads-up display for longitudinal image magnification and pupil expansion is disclosed. This paper discussed about the HOE formation with large dimension but with use of dual prism stacked together and photosensitive material stuck with gel in between waveguide and dual prism which is quite cumbersome
[0010] Thus, there exists a notable gap in the current technological landscape for a system and method capable of recording larger-size Holographic Elements that are not only efficient in manipulating light information beams within waveguides but also overcome the limitations posed by existing methodologies, including those dependent on multiple prism configurations.
SUMMARY
[0011] This summary is provided to introduce concepts related to a novel system and method specifically designed for the recording of enlarged holographic elements. This innovative approach addresses and overcomes the limitations inherent in conventional holographic recording techniques, particularly those related to the size constraints of holographic elements and their efficiency in manipulating light information beams within waveguide systems. Through the application of advanced optical engineering principles and leveraging unique materials and configurations, this invention facilitates the production of large-scale holographic elements.
[0012] In an embodiment of the present invention, a method for recording larger size holographic elements (HEs) is disclosed. The method comprises providing a recording setup that includes a laser, a plurality of mirrors, a right-angle customized prism, and a thin waveguide. It further includes generating a laser beam from a laser for recording interference patterns onto the HEs. Further, the method includes directing the laser beam through the plurality of mirrors arranged to split the beam and adjust its path towards the right-angle customized prism. The method further includes passing the adjusted laser beam through the right-angle customized prism to further refine the beam’s angle and alignment in relation to a recording medium. The method further includes guiding the refined laser beam into the thin waveguide configured to uniformly distribute the laser beam across a predetermined area of the recording medium. The method further includes recording one or more interference patterns onto the recording medium by the uniformly distributed laser beam, wherein the interference patterns correspond to a plurality of configurations for the HEs.
[0013] In accordance with one embodiment of the present invention, a system for recording larger size holographic elements (HEs) is disclosed. This system comprising a laser configured to generate a beam for recording interference patterns onto the HEs. A plurality of mirrors configured to receive the laser beam from the laser and direct the beam along a predetermined path. A right-angle customized prism configured to receive the directed laser beam from the plurality of mirrors, the prism being configured to adjust the beam's angle for optimized incidence onto a recording medium. A thin waveguide configured to receive the laser beam from the right-angle customized prism, the waveguide being configured to distribute the laser beam uniformly across the recording medium. A control unit configured to select and implement a plurality of configurations for designing the interference patterns to be recorded onto the HEs by modulating at least one of the laser, the plurality of mirrors, the right-angle customized prism, and the thin waveguide, wherein the system is configured to produce larger-size HEs.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0014] The detailed description is described with reference to the accompanying figures.
[0015] Figure 1 illustrates a system for recording larger size holographic elements (HEs), in accordance with an exemplary embodiment of the present invention.
[0016] Figure 2 illustrates a method for recording larger size holographic elements (HEs), in accordance with an exemplary embodiment of the present invention.
[0017] Figure 3 illustrates recording of HE1/HE2 when its size is very less, in accordance with an exemplary embodiment of the present invention.
[0018] Figure 4 illustrates recording of HE1/HE2 when its size is relatively larger, in accordance with an exemplary embodiment of the present invention.
[0019] Figure 5A illustrates recording of transmissive HE1/HE2, in accordance with an exemplary embodiment of the present invention.
[0020] Figure 5B illustrates recording of reflective HE1/HE2, in accordance with an exemplary embodiment of the present invention.
[0021] Figure 6 illustrates summary of all the three configurations, in accordance with an exemplary embodiment of the present invention.
[0022] Figure 7 illustrates conversion of circular beam to rectangular beam with the aid of beam shapers for recording different shape of Holographic Optical Elements, in accordance with an exemplary embodiment of the present invention.
[0023] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present invention.

DETAILED DESCRIPTION
[0024] The various embodiments of the present disclosure describe about a novel system and method specifically designed for the recording of enlarged holographic elements. This innovative approach addresses and overcomes the limitations inherent in conventional holographic recording techniques, particularly those related to the size constraints of holographic elements and their efficiency in manipulating light information beams within waveguide systems. Through the application of advanced optical engineering principles and leveraging unique materials and configurations, this invention facilitates the production of large-scale holographic elements. These elements are characterized by their enhanced capability to efficiently manipulate light information beams, making them ideally suited for a broad spectrum of applications in the field of holography and beyond. The disclosed system and method improves the functionality of holographic elements and aims to streamline the production process, thereby offering a practical solution to the existing challenges faced by industries reliant on holographic technologies.
[0025] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0026] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
[0027] Furthermore, connections between components and/or modules within the figures are not intended to be limited to direct connections. Rather, these components and modules may be modified, re-formatted or otherwise changed by intermediary components and modules.
[0028] The appearances of the phrase “in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
[0029] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0030] In an embodiment of the present invention, a method for recording larger size holographic elements (HEs) is disclosed. The method comprises providing a recording setup that includes a laser, a plurality of mirrors, a right-angle customized prism, and a thin waveguide. Further, plurality of lenses for beam expansions also exists (not shown). Further, the method includes generating a laser beam from a laser for recording interference patterns onto the HEs. Further, the method includes directing the laser beam through the plurality of mirrors arranged to split the beam and adjust its path towards the right-angle customized prism. The method further includes passing the adjusted laser beam through the right-angle customized prism to further refine the beam’s angle and alignment in relation to a recording medium. The method further includes guiding the refined laser beam into the thin waveguide configured to uniformly distribute the laser beam across a predetermined area of the recording medium. The method further includes recording one or more interference patterns onto the recording medium by the uniformly distributed laser beam, wherein the interference patterns correspond to a plurality of configurations for the HEs.
[0031] In accordance with one embodiment of the present invention, a system for recording larger size holographic elements (HEs) is disclosed. This system comprising a laser configured to generate a beam for recording interference patterns onto the HEs. A plurality of mirrors configured to receive the laser beam from the laser and direct the beam along a predetermined path. A right-angle customized prism configured to receive the directed laser beam from the plurality of mirrors, the prism being configured to adjust the beam's angle for optimized incidence onto a recording medium. A thin waveguide configured to receive the laser beam from the right-angle customized prism, the waveguide being configured to distribute the laser beam uniformly across the recording medium. A control unit configured to select and implement a plurality of configurations for designing the interference patterns to be recorded onto the HEs by modulating at least one of the laser, the plurality of mirrors, the right-angle customized prism, and the thin waveguide, wherein the system is configured to produce larger-size HEs.
[0032] In another embodiment of the present invention, the method further comprises selecting the plurality of configurations for the HEs to produce larger size holographic elements and arranging the two produced larger size holographic elements in a manner that provides an expanded field of view.
[0033] In another embodiment of the present invention, the method further comprises reducing the size of the thin waveguide to half its original size prior to guiding the refined laser beam into the recording medium.
[0034] In another embodiment of the present invention, the right-angle customized prism is the sole prism used in the recording setup to achieve Total Internal Reflection, TIR, of the laser beam.
[0035] In another embodiment of the present invention, the recording of the interference patterns onto both transmission type and reflection type holographic elements.
[0036] In another embodiment of the present invention, the recording medium is selected from the group that includes Silver halide, Dichromated Gelatin, Photopolymers, and the like.
[0037] In another embodiment of the present invention, the method further comprises modifying shape of the circular Gaussian laser beam to a rectangular shape or any other predetermined shape by using customized beam shapers placed along the paths of an object beam (O) and a reference beam (R).
[0038] In another embodiment of the present invention, the arrangement of refractive elements is done to pass light from one end to another for laser light magnification. Further, the multiple arm adjustment to reach minimum angle of reflected light to waveguide is done in order to maximize available space inside waveguide for image magnification. The design depicts novelty in recording of HE at particular angle to record maximum size HE. Novelty is also in utilizing single prism to manipulate light for TIR for one arm and direct hit of light from another arm onto HE front/back face. The design also caters to creation of focused and diverging beam for multiple focal length, hence the HE also works as convex or diverging lens. The essential feature is also in putting rectangular beam shapers to get square images on the waveguides.
[0039] In another embodiment of the present invention, Holographic Elements (HEs) plays an important role in achieving the in-coupling and out-coupling of the imagery. HE is an optical element providing a system of thin film optics employed by using holographic imaging techniques or principles. HE can be designed and recorded to perform different functions of a conventional refractive optical element such as lens, filter, beam splitter, diffraction grating etc.
[0040] To make it cost effective and efficient, conventional interferometry setups or configurations are not good enough to reach bigger HE recording. Therefore, this work is a piece of idea to change certain arrangements in the triangle configuration to make the HE recording area bigger. Recording of HE depends on various factors such as Bragg angle, interference of two coherent beams, coherence length of the laser. All this has been addressed by Kogelnik theory.
[0041] Kogelnik theory needs to be followed for understanding of the object and reference location, construction wavelength, reconstruction procedure, calculation of diffraction efficiency. The formation of grating pattern on a film (HE) is mainly based on the theory proposed by Kogelnik named as Kogelnik’s Coupled Wave Theory. Based on the theory, HEs can be constructed in a volume phase material which can be a photographic film/ dichromated gelatin.
[0042] Figure 1 illustrates a system for recording larger size holographic elements (HEs), in accordance with an exemplary embodiment of the present invention. This system comprising a laser configured to generate a beam for recording interference patterns onto the HEs. A plurality of mirrors configured to receive the laser beam from the laser and direct the beam along a predetermined path. A right-angle customized prism configured to receive the directed laser beam from the plurality of mirrors, the prism being configured to adjust the beam's angle for optimized incidence onto a recording medium. A thin waveguide configured to receive the laser beam from the right-angle customized prism, the waveguide being configured to distribute the laser beam uniformly across the recording medium. A control unit configured to select and implement a plurality of configurations for designing the interference patterns to be recorded onto the HEs by modulating at least one of the laser, the plurality of mirrors, the right-angle customized prism, and the thin waveguide, wherein the system is configured to produce larger-size HEs. The system further comprises customized beam shapers placed along the paths of an object beam (O) and a reference beam (R), configured to modify the shape of the circular Gaussian laser beam to a rectangular shape or any other predetermined shape.
[0043] Figure 2 illustrates a method for recording larger size holographic elements (HEs), in accordance with an exemplary embodiment of the present invention. The method comprises providing a recording setup that includes a laser, a plurality of mirrors, a right-angle customized prism, and a thin waveguide. The method further includes generating a laser beam from a laser for recording interference patterns onto the HEs. Further, the method includes directing the laser beam through the plurality of mirrors arranged to split the beam and adjust its path towards the right-angle customized prism. The method further includes passing the adjusted laser beam through the right-angle customized prism to further refine the beam’s angle and alignment in relation to a recording medium. The method further includes guiding the refined laser beam into the thin waveguide configured to uniformly distribute the laser beam across a predetermined area of the recording medium. The method further includes recording one or more interference patterns onto the recording medium by the uniformly distributed laser beam, wherein the interference patterns correspond to a plurality of configurations for the HEs.
[0044] Figure 3 illustrates recording of HE1/HE2 when its size is very less, in accordance with an exemplary embodiment of the present invention. This figure represents recording of HE1/HE2 when its size is very less and angle between normal to P’s hypotenuse and O arm beam may or may not be zero which is a classic case of normal interferometry configurations. The architecture of the recording of photosensitive medium (P) is as given herewith. The laser emit coherent light beam with coherence length greater than the overall path length of the configuration, which gets splitted by polarizing beam splitter (BS). The splitted beam gets processed, expanded and forwarded to mirror (M1). The mirror reflects the light towards right angle prism (P) which then transfers the light to inside of the waveguide (W). Further, the splitted beam towards W may be called R (Reference) whereas beam towards M1 may be called as O (Object).
[0045] Hereafter, the Object beam, Reference beam, Mirror 1, Mirror 2, Mirror 3, Mirror 4, Right angle prism, Waveguide, Beam splitter and Holographic Element 1&2 will be referred as O, R, M1, M2, M3, M4, P, W, BS, HE1 and HE2 respectively. One of the features of the present disclosure here is to record the interference pattern with single prism by manipulating O with the aid of P, and using R directly on HE1 and HE2. This looks very promising but only for larger angles that is for:

[0046] Figure 4 illustrates recording of HE1/HE2 when its size is relatively larger like in case of automotive Head Up Displays, in accordance with an exemplary embodiment of the present invention. This figure represents recording of HE1/HE2 when its size is relatively larger and angle between normal to P’s hypotenuse and O arm beam is in range of zero to half of right angle. In this figure, a lesser angle is obtained than in figure 1 using similar elements except with a change of architecture in O and addition of two more M2 and M3. With this, minimum angle which can be efficiently recorded on a photosensitive medium is:

[0047] Keeping the gap between BS and M1 less.
[0048] Figure 5A illustrates recording of transmissive HE1/HE2, in accordance with an exemplary embodiment of the present invention. This figure represents recording of transmissive HE1/HE2 when its size is much bigger for applications where larger FOV is required in lesser depth of W. In this figure, interference pattern is recorded on HE1/HE2 at zero degree by tilting O arm by same amount which was restricted in claim related to figure 2. Here again the O is passing P with almost half of right angle with the longest arm of the P’s normal whereas in claims related to figure one and two are zero degree and between zero to one fourth of right angle with the P’s normal respectively. This is transmissive method to record larger size HOE.
[0049] Figure 5B illustrates recording of reflective HE1/HE2, in accordance with an exemplary embodiment of the present invention. This figure represents recording of reflective HE1/HE2 when its size is much bigger for applications where larger FOV is required in lesser depth of W. With this concept, larger size Holographic Optical Elements are recorded by making the beam to fall parallel to the waveguide, hence zero projection. The object beam falls onto the prism at zero incidences and utilizing full aperture of the prism on base side to pass through and interact with the reference beam falling just at the place where interference will take place. This allows us to record larger size HOE’s. This is a reflective method to record larger size HOE.
[0050] Figure 6 illustrates summary of all the three configurations, in accordance with an exemplary embodiment of the present invention. This figure represents summary of all the three configurations wherein first one shows basic triangular configuration where the recorder HE1 is very small in size and angle between P’s normal and O arm beam is zero, second one shows relatively bigger HE1/HE2 and also angle between O arm beam and P’s normal is in range of zero to one fourth of right angle. Third one is for zero-degree projection and angle between P’s normal and O arm beam may be half of the right angle, fourth is similar to third one except the configuration is changed to cater reflective nature of the HE1/HE2. In this, the summary of all the three configurations is disclosed and a reflective kind of HE1/HE2, where also zero projection is possible to achieve.
[0051] Recording of holographic optical elements in volume phase materials allows for achieving maximum diffraction efficiency in one order (nearly 100%). The approach requires two beams labeled as the probe beam and the signal beam both denoted by their K-vectors: kp & ks. Illumination of the film by these beams leads to modulation either in the absorption coefficient or refractive index. The interference pattern formed by the group onto the film creates a grating pattern specified by the grating vector (K) oriented perpendicular to the Bragg planes. For realization of maximum diffraction efficiency in HE, the three vectors should follow a criterion of Bragg matching as mentioned:

[0052] Note that magnitude of kp & ks should be same for fulfilling the condition of Bragg matched interference. In ideal conditions, any deviation leads to decrease in diffraction efficiency of the output beam. This deviation can be in terms of angle or wavelength from Bragg matching condition as described below:

[0053] Figure 7 illustrates conversion of circular beam to rectangular beam with the aid of beam shapers for recording different shape of Holographic Optical Elements, in accordance with an exemplary embodiment of the present invention. This figure represents shaping of circular gaussian beam into rectangular shape beam using customized shapers kept in path of O and R arm. Shapers kept in O may be different from shaper in R arm.
[0054] Basically, with zero projection of O arm onto P gives bigger HE1/HE2 as shown in Figure 4 , Figure 5A, Figure 5B and Figure 6, as compared to Figure 3 which is conventional recording interferometry and a well-known concept for pattern formation onto the HE. Though other arrangements such as Bow-tie, Michelson etc. are available but the efficiency achieved with those configurations are very less. One expert in art must not confuse the zero-degree projection with the angle between O arm beam and normal to P’s hypotenuse.
[0055] In one of the exemplary implementation, moving platform, flying or land based requires projection systems to be as small as possible. The current projection systems are very bulky due to bulk optics utilization for larger FOV coverage and Head Motion Box requirements. Therefore, a new design based on holographic element which reduces overall volume size and cost by one third of the conventional systems available in the market.
[0056] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:We Claim :
1. A method for recording larger size holographic elements (HEs), said method comprising:
providing a recording setup that includes a laser, a plurality of mirrors, a right-angle customized prism, and a thin waveguide;
generating a laser beam from a laser for recording interference patterns onto the HEs;
directing the laser beam through the plurality of mirrors arranged to split the beam and adjust its path towards the right-angle customized prism;
passing the adjusted laser beam through the right-angle customized prism to further refine the beam’s angle and alignment in relation to a recording medium;
guiding the refined laser beam into the thin waveguide configured to uniformly distribute the laser beam across a predetermined area of the recording medium; and
recording one or more interference patterns onto the recording medium by the uniformly distributed laser beam, wherein the interference patterns correspond to a plurality of configurations for the HEs.

2. The method as claimed in claim 1, further comprises:
selecting the plurality of configurations for the HEs to produce larger size holographic elements, and
arranging the two produced larger size holographic elements in a manner that provides an expanded field of view.

3. The method as claimed in claim 1, further comprises reducing the size of the thin waveguide to half its original size prior to guiding the refined laser beam into the recording medium.

4. The method as claimed in claim 1, wherein the right-angle customized prism is the sole prism used in the recording setup to achieve Total Internal Reflection, TIR, of the laser beam.

5. The method as claimed in any one of claims 1-4, wherein the recording of the interference patterns onto both transmission type and reflection type holographic elements.

6. The method as claimed in any one of claims 1-5, wherein the recording medium is selected from the group that includes Silver halide, Dichromated Gelatin, Photopolymers, and the like.

7. The method as claimed in claim 1, further comprises modifying shape of the circular Gaussian laser beam to a rectangular shape or any other predetermined shape by using customized beam shapers placed along the paths of an object beam (O) and a reference beam (R).

8. A system for recording larger size holographic elements (HEs), said system comprising:
a laser configured to generate a beam for recording interference patterns onto the HEs;
a plurality of mirrors configured to receive the laser beam from the laser and direct the beam along a predetermined path;
a right-angle customized prism configured to receive the directed laser beam from the plurality of mirrors, the prism being configured to adjust the beam's angle for optimized incidence onto a recording medium;
a thin waveguide configured to receive the laser beam from the right-angle customized prism, the waveguide being configured to distribute the laser beam uniformly across the recording medium; and
a control unit configured to select and implement a plurality of configurations for designing the interference patterns to be recorded onto the HEs by modulating at least one of the laser, the plurality of mirrors, the right-angle customized prism, and the thin waveguide, wherein the system is configured to produce larger-size HEs.

9. The system as claimed in claim 8, wherein the control unit is further configured to:
select the plurality of configurations for the HEs to produce larger size holographic elements, and
arrange the two produced larger size holographic elements in a manner that provides an expanded field of view.

10. The system as claimed in claim 8, wherein the thin waveguide is further configured to have its size reduced to half of its original size to facilitate the refined guiding of the laser beam into the recording medium.

11. The system as claimed in claim 8, wherein the right-angle customized prism is the sole prism used in the recording setup, configured to achieve Total Internal Reflection, TIR, of the laser beam.

12. The system as claimed in any one of claims 8-11, further configured to record interference patterns onto both transmission type and reflection type holographic elements.

13. The system as claimed in any one of claims 8-12, wherein the recording medium is selected from the group that includes Silver halide, Dichromated Gelatin, Photopolymers, and the like.

14. The system as claimed in claim 8, further comprises customized beam shapers placed along the paths of an object beam (O) and a reference beam (R), configured to modify the shape of the circular Gaussian laser beam to a rectangular shape or any other predetermined shape.

Dated this 31st day of March, 2023

For BHARAT ELECTRONICS LIMITED
(By their Agent)

D. MANOJ KUMAR (IN/PA-2110)
KRISHNA & SAURASTRI ASSOCIATES LLP