Waveguide-Based Projector for Compact Head-Mounted Displays
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Solution Overview
Problem
There is a need for compact and lightweight projector designs for head-mounted displays that can provide a wide field of view and efficient image projection, as bulky devices are uncomfortable for users and limit the integration of advanced display technologies in mobile devices.
Innovation Solution
The use of a single-mode or few-mode slab waveguide as a platform for a 1D projector, which confines light in one dimension and allows expansion in two others, combined with a spatial modulator and collimation waveguide layers to achieve a compact and thin form factor while maintaining a large field of view, using elements like refractive, reflective, and diffractive optical components for focusing and defocusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If conventional bulky projector designs are used, then image projection capability is achieved, but device size and weight increase making it uncomfortable for head-mounted display
Solution Approach 1:
The patent replaces conventional mechanical optical systems with a waveguide-based optical system. The waveguide uses total internal reflection and evanescent wave coupling to guide and manipulate light, eliminating the need for bulky mechanical lenses, mirrors, and optical benches. This substitution of mechanical optical components with waveguide physics enables drastic miniaturization while maintaining projection functionality.
Solution Approach 2:
The patent transitions from three-dimensional optical paths to two-dimensional waveguide plane propagation. By confining light to propagate within the thin waveguide plane and using evanescent fields for coupling, the system achieves compact form factor suitable for head-mounted displays while maintaining wide field of view through angular multiplexing in the waveguide plane.
2Volume of moving object
If compact projector design is implemented, then device size is reduced, but field of view may be limited
Solution Approach 1:
The patent implements dynamic field of view control through electrically tunable liquid crystal elements within the waveguide. These elements can dynamically adjust the coupling angles and regions, enabling the field of view to be expanded or contracted as needed while maintaining the compact waveguide form factor. This dynamic adaptability resolves the trade-off between size and field of view.
Solution Approach 2:
The waveguide structure serves multiple functions simultaneously: it acts as both the optical guiding medium and the field of view control mechanism. The same waveguide that provides compact form factor also enables wide field of view through its planar geometry and angular multiplexing capability, eliminating the need for separate FOV control components.
3Volume of moving object
If waveguide-based compact projector is used, then form factor is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent employs precise control of waveguide thickness and refractive index parameters to optimize both compactness and manufacturability. By carefully selecting the waveguide thickness (typically hundreds of micrometers) and refractive index contrast, the system achieves compact form factor while using established semiconductor fabrication techniques for mass production, thereby managing manufacturing complexity.
Solution Approach 2:
The patent uses composite waveguide structures combining different materials with complementary properties. For example, polymer waveguides provide flexibility and ease of fabrication, while glass waveguides offer optical precision. The integration of liquid crystal materials with the waveguide substrate enables tunable functionality. These composite approaches balance manufacturing ease with performance requirements.
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 approach enables the creation of a compact projector that can project images with a large field of view and eyebox, maintaining a thin and lightweight form, suitable for integration into mobile devices, while allowing for complex optics fabrication and efficient light management.
Implementation Method 1
a single-mode or few-mode slab waveguide as a platform for a 1D projector, which confines light in one dimension and allows expansion in two others
Implementation Method 2
A collimation waveguide layer is optically coupled to the spatial modulator for receiving and collimating light of the light points to obtain a fan of collimated light beams
Implementation Method 3
The slab waveguide portion may include a curved reflector for collimating the light beam in a plane of the slab waveguide portion
Implementation Method 4
The waveguide structure may include an evanescent out-coupler for out-coupling the fan of collimated light beams from the waveguide structure
Data Source
AI summary
A projector includes an illumination waveguide layer, a collimation waveguide layer, and a spatial modulator. The illumination waveguide layer expands a light beam which is coupled to the spatial modulator. The spatial modulator modulates the expanded light beam to provide a line of light points of controllable brightness. The collimation waveguide collimates light of the light points to obtain a fan of collimated light beams. Each collimated light beam of the fan has an angle corresponding to a coordinate of the corresponding light point of the line. A tiltable reflector may be placed at the exit pupil to scan the fan of light beams in a plane non-parallel to the plane of the fan, thus providing a 2D image in angular domain. An array of Mach-Zehnder interferometers may be used in place of the illumination waveguide layer and the spatial modulator to provide the line of light points.