Projection Objective Grouping for Telecentric Waveguide Coupling
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Solution Overview
Problem
Existing projection objectives for waveguide displays struggle to effectively expand the projector exit pupil along two dimensions while maintaining a compact size and high telecentricity, particularly for augmented reality applications where the exit pupil must be close to the in-coupling grating and the projected beam highly collimated.
Innovation Solution
A projection objective with a positive-negative-positive lens grouping and specific refractive surface configuration that allows for high telecentricity and collimation, comprising three optical element groups with defined refractive surfaces to achieve a compact design that expands the exit pupil along two dimensions and maintains a collimated beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compact projection objective design is used, then the volume is reduced, but the telecentricity and collimation quality deteriorate
Solution Approach 1:
The projection objective is divided into three distinct optical element groups (first positive group, second negative group, third positive group) with specific refractive surface configurations. This segmentation allows each group to contribute differently to the overall optical function, enabling compact design while maintaining high telecentricity and collimation quality through coordinated action of the grouped elements.
Solution Approach 2:
The patent employs specific parameter relationships between the optical groups, including focal length ratios (0.3 < |f2/f| < 0.7) and refractive surface curvatures (concave first surface of second group, convex second surface of third group). These parameter changes enable the compact objective to achieve the required telecentricity and collimation performance despite reduced volume.
2Area of stationary object
If the exit pupil is expanded along two dimensions, then the eye box is increased, but the optical complexity increases
Solution Approach 1:
The patent expands the exit pupil from one dimension to two dimensions by positioning the aperture stop at a strategic location within the three-group optical structure. The specific arrangement of positive-negative-positive lens groups with defined refractive surfaces enables bidirectional pupil expansion, increasing the eye box area while managing optical complexity through the structured grouping approach.
3Volume of moving object
If the aperture stop is positioned to minimize objective size, then the volume is reduced, but the telecentricity decreases
Solution Approach 1:
The patent applies local quality by positioning the aperture stop at a specific location within the optical system (not at the extreme front or back) and configuring the refractive surfaces of each lens group with specific curvatures (concave/convex arrangements). This localized optimization allows the compact objective to maintain high telecentricity by ensuring chief rays approach the aperture stop at appropriate angles, while the third positive group's convex second surface specifically contributes to restoring telecentricity after the negative group.
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
The solution enables a compact, telecentric projection objective that efficiently couples light into a waveguide, ensuring a collimated and nearly perpendicular chief ray arrival, enhancing light engine efficiency and allowing for a small form factor suitable for augmented reality devices.
Implementation Method 1
an in-coupling grating arranged thereto so as to diffract light hitting the in-coupling grating to the waveguide
Implementation Method 2
the light propagates therein within the total internal reflection limit angle until it is coupled out from the light guide at an out-coupling region
Implementation Method 3
Ray splitting at the out-coupling region can effectively expand the eye box of the system
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 1E
AI summary
The invention concerns a projection objective and a waveguide display. The objective is adapted to project an image from a first plane (20A-20E) to a second plane (10A-10E) and comprises in order from the second plane a first optical element group (G1) having a positive effective focal length, a second optical element group (G2) placed between the first plane and the first optical element group and having a negative effective focal length, and a third optical element group (G3) placed between the first plane and the second optical element group and having a positive effective focal length. Counting from the second plane, the first refractive surface of the second optical element group is concave towards the second plane and the second refractive surface of the third optical element group is convex towards the first plane. The objective suits well for projecting images to diffractive optical displays.