CN-116107094-B - Integrated beam steering system

CN116107094BCN 116107094 BCN116107094 BCN 116107094BCN-116107094-B

Abstract

Embodiments of the present disclosure relate to integrated beam steering systems. The integrated beam steering system is configured in three stages to provide beam steering for image light from an imager (e.g., a laser, light emitting diode, or other light source) to a downstream element in the display system, such as an Exit Pupil Expander (EPE) in a mixed reality computing device. The first stage includes a multi-stage cascaded array of optical switches configurable to spatially route image light across a first dimension of a two-dimensional (2D) field of view (FOV) of a display system. The second waveguide stage conveys the image light along the preformed waveguide to a collimator in a third stage configured to collimate the image light along a first dimension (e.g., horizontal) of the FOV. The waveguide and collimation stages can be implemented using lightweight photonic crystal nanostructures.

Inventors

J O Miller
ZANG KAI
W. O. Davis
M. Evtekal

Assignees

微软技术许可有限责任公司

Dates

Publication Date: 20260512
Application Date: 20190327
Priority Date: 20180411

Claims (6)

1. An integrated beam steering system, comprising: An optical routing system; an optical waveguide structure coupled to an output of the optical routing system, and An optical collimator configured to receive image light from the optical waveguide structure, Wherein the optical routing system comprises: at least one optical switch configured to provide an optical input for an optical signal to the optical routing system; a first plurality of optical switches configured to provide a plurality of optical outputs from the optical routing system; A second plurality of optical switches arranged in a multi-level binary tree cascade array between the input optical switches and the output optical switches, the outputs of the optical switches being coupled to the inputs of the optical switches at each successive level in the array in the multi-level binary tree cascade array, Wherein each of the optical switches in the optical routing system comprises a Mach-Zehnder interferometer located between two directional optical couplers, and each switch is configured with two paths through the Mach-Zehnder interferometer and the directional optical couplers, Wherein each optical switch comprises a power supply configured to apply a voltage to a path in the Mach-Zehnder interferometer, whereby the applied voltage imparts a phase change to light propagating in the path, Wherein the optical routing system is controllable by operation of the power supply to switch the input optical signal to the optical routing system to any one of the optical outputs from the optical routing system, and Wherein the optical waveguide structure comprises: a photonic crystal nanostructure comprising a plurality of nanoelements arranged at least in part in a lattice configuration and having one or more input surfaces and a concave output surface, the parameters of the nanoelements being selected to produce a photonic bandgap for a predetermined range of wavelengths without propagation modes; A plurality of waveguides disposed in the nanostructure, wherein each waveguide includes a negative space formed by a lack of nanoelements along a path in the lattice to generate a propagation band within the photonic band gap; A plurality of inputs to the respective plurality of waveguides, the inputs being disposed on the one or more input surfaces of the nanostructure, and A plurality of outputs from the respective plurality of waveguides, wherein one or more of the waveguides includes a waveguide path having a curved portion, and each of the waveguide paths is located in the nanostructure such that each of the outputs is configured to be orthogonal to the concave output surface.
2. The integrated beam steering system of claim 1, wherein each optical switch comprises a2 x2 optical switch, the 2 x2 optical switch comprising two input ports and two output ports.
3. The integrated beam steering system of claim 1, wherein the directional optical coupler is a 3dB coupler.
4. The integrated beam steering system of claim 1, further comprising a controller disposed in the optical routing system, the controller configured to transmit control signals to the power supply.
5. The integrated beam steering system of claim 4, wherein the controller is operated so that the optical routing system is implemented as a switching fabric.
6. The integrated beam steering system of claim 1, wherein one or more of the optical switches are operated as a variable attenuator.

Description

Integrated beam steering system Description of the divisional application The application is a divisional application of Chinese application patent application with international application date of 2019, 3 month and 27 days, entering China national stage at 10 month and 10 days in 2020, national application number of 201980025167.4 and named as 'integrated beam steering system'. Background Mixed reality computing devices, such as wearable Head Mounted Display (HMD) systems and mobile devices (e.g., smartphones, tablet computers, etc.), may be configured to display information to a user regarding virtual and/or real objects, which are virtual and/or real objects in a field of view of the user and/or in a field of view of a camera of the device. For example, the HMD device may be configured to display a virtual environment mixed with real world objects or a real world environment mixed with virtual objects using a see-through display system. Also, the mobile device may display such information using the camera viewfinder window. Disclosure of Invention An integrated beam steering system is configured in three stages to provide beam steering for image light from an imager (e.g., laser, light emitting diode, or other light source) to a downstream element in a display system, such as an Exit Pupil Expander (EPE) in a mixed reality computing device. The first stage includes a multi-stage cascaded array of optical switches configurable to spatially route image light across a first dimension of a two-dimensional (2D) field of view (FOV) of a display system. The second waveguide stage conveys the image light along the preformed waveguide to a collimator in a third stage configured to collimate the image light along a first dimension (e.g., horizontal) of the FOV. The waveguide and collimation stages can be implemented using lightweight photonic crystal nanostructures. In various illustrative embodiments, each optical switch in the array is configured to use a Mach-Zehnder interferometer between a pair of 3dB optical couplers to form a 2X 2 switch having two inputs and two outputs. The voltage from an external source applied to the arms of the mach-zehnder interferometer causes a phase change in the light propagating in the arms so that light from one input can be split into two outputs in any proportion. For a cascaded array of N optical switches arranged in a binary tree, an input beam from the imager may be routed to any one of 2 N output ports in response to an appropriate control signal. The optical switches in the array may also be used as variable optical attenuators to provide additional dynamic range and control the output illumination amplitude from the beam steering system. For the waveguide structure in the second stage, parameters including diameter and pitch (pitch) associated with elements in the photonic crystal nanostructure (e.g., cylindrical rods (rod) arranged in a lattice) are selected to produce a photonic bandgap effect. The layout of the elements is manipulated in the nanostructure (e.g., by removing rows of rods in the lattice) to create a propagation band within the band gap, thereby providing a preformed waveguide for image light within a predetermined wavelength range. The preformed waveguide propagates light along a curved path with low bending losses and cross-talk. The curved path enables the waveguide output to be configured along a curve to maximize the FOV of the in-coupled light in the downstream components of the display system. The elements in the photonic crystal nanostructure of the waveguide structure that interfaces with the optical switch array can be configured with various taper geometries to provide impedance matching to minimize coupling losses between stages. The collimator in the third stage comprises lattice-configured elements within the photonic crystal nanostructure that vary in diameter to simulate the characteristics of a luneberg (Luneburg) lens having a graded refractive index. The image light output from the waveguide is directly coupled at a plurality of points along the perimeter of the collimator and mapped to a plane wave. The collimator may have a semicircular shape to accommodate the curved waveguide and present a concave surface with respect to the in-coupling diffraction element located at the waveguide. The collimator may further operate with a cylindrical lens configured to provide optical collimation for a second dimension (e.g., perpendicular) of the FOV. When utilizing 2D raster scan technology in a display system, the integrated beam steering system may be configured to support fast or horizontal scanning. Thus, the beam steering system may be operably coupled with a slow, or vertical scanning component, such as a microelectromechanical system (MEMS) scanner. The integrated beam steering system may also be configured as a stack of photonic crystal plates, where each plate handles image light of a particular wavelength. For example, three panels m