Dual Grating In-Coupler for Thin AR Waveguides
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Solution Overview
Problem
Current optical waveguides in AR/VR glasses face challenges in achieving a wide field of view and efficient light coupling due to the limited angular bandwidth of the glass plate, leading to reduced image quality and increased device size and weight.
Innovation Solution
The use of a double-sided diffraction grating in-coupler with differently oriented gratings on both surfaces of the waveguide, where the first grating diffracts light into the waveguide and the second grating rotates the polarization, allowing for effective light trapping and increased in-coupling efficiency, even in thin waveguides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional single-sided diffraction grating in-coupler is used, then the device structure is simple, but the in-coupling efficiency is limited and the field of view is restricted
Solution Approach 1:
The in-coupler is divided into two separate diffraction gratings positioned on opposite sides of the waveguide. Each grating performs a specific function: the first grating diffracts incident light into the waveguide, while the second grating rotates the polarization of the diffracted light. This segmentation allows each component to be optimized independently, achieving high in-coupling efficiency without requiring a single complex grating structure.
Solution Approach 2:
The solution transitions from a single-sided in-coupler to a dual-sided configuration by adding a second diffraction grating on the opposite side of the waveguide. This dimensional change enables the system to manipulate light in multiple stages - first diffracting light into the waveguide, then rotating its polarization - thereby overcoming the angular bandwidth limitations of conventional single-sided designs and expanding the field of view.
2Length of moving object
If the waveguide thickness is reduced to make the device more compact, then the device size and weight decrease, but the light trapping efficiency deteriorates
Solution Approach 1:
The first diffraction grating performs preliminary action by diffracting incident light into the waveguide at optimized angles before the light propagates through the thin waveguide. This pre-diffraction ensures that light enters the waveguide within the acceptable angular range for total internal reflection, compensating for the reduced interaction length in thin waveguides and maintaining high light trapping efficiency despite the reduced thickness.
Solution Approach 2:
The system changes the polarization parameter of light using the second diffraction grating. By rotating the polarization of diffracted light, the system optimizes the interaction between light and the waveguide boundaries, enhancing light trapping efficiency. This parameter change allows thin waveguides to achieve effective light confinement that would otherwise require much greater thickness.
3Adaptability or versatility
If a wide field of view is achieved through conventional means, then the angular bandwidth increases, but the device size and weight increase
Solution Approach 1:
The patent replaces conventional mechanical or geometric methods for expanding field of view with an optical mechanism based on dual diffraction gratings. The gratings manipulate light through diffraction and polarization rotation, achieving wide angular bandwidth without requiring larger physical components. This substitution of optical mechanisms for mechanical/geometric solutions enables wide field of view in compact, lightweight devices.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the field of view and in-coupling efficiency, reducing the thickness of the waveguide while maintaining high light trapping and image quality, thus enabling more compact and lightweight AR/VR glasses with improved image fidelity.
Implementation Method 1
The in-coupler comprises a first diffraction grating with a first grating vector on the first surface... diffracting the incident light to a non-zero diffractive order with the first diffraction grating
Implementation Method 2
the second diffraction grating is a reflective grating... reflecting the diffracted light with the second diffraction grating
Implementation Method 3
the second diffraction grating rotates the polarization, allowing for effective light trapping
Implementation Method 4
light propagates into the optical waveguide by TIR (for Total Internal Reflection) only over a limited range of internal angles
Data Source
AI summary
In example embodiments, an apparatus includes a waveguide having an in-coupler an out-coupler. The waveguide has a first surface and an opposite second surface, and the waveguide provides at least one optical path from the in-coupler to the out-coupler. The in-coupler comprises a first diffraction grating with a first grating vector on the first surface and a second diffraction grating with a second grating vector on the second surface. At least one of the first and second grating vectors is not oriented along any of the optical paths from the in-coupler to the out-coupler. The second grating may alter the polarization state of in-coupled light and/or change the direction of the in-coupled light to aid in preventing the light from being out-coupled by the first diffraction grating.