Holographic Display Optical Path Alignment
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Solution Overview
Problem
Holographic colour display systems face issues such as mismatched physical sizes of colour reconstructions, low-quality composite images due to resolution mismatch, and bulky systems requiring large space, making them impractical for applications like near-eye devices.
Innovation Solution
A display system with two or more monochromatic colour channels, each with a Fourier transform lens and optical paths that can be adjusted for precise alignment and compact configuration, using mirrors to redirect light and allow for different optical paths for each colour channel, enabling precise matching and overlap of holographic reconstructions for a full-colour display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If spatially separated colours method is used with single SLM, then system compactness is improved, but image quality deteriorates due to decreased SLM surface area for each monochromatic image
Solution Approach 1:
The patent divides the single SLM surface into three distinct regions, each dedicated to a specific monochromatic colour channel. This segmentation allows each colour to be processed with sufficient resolution while maintaining a compact single-SLM architecture, resolving the contradiction between system compactness and image quality.
Solution Approach 2:
The patent introduces optical path length as an additional dimension for differentiation. By providing different optical path lengths from the SLM to the replay plane for each colour channel, the system achieves wavelength-specific focal adjustments that maintain image quality across all colours while using a single compact SLM.
2Manufacturing precision
If different optical path lengths are provided for each colour channel, then colour reconstruction matching is improved, but system complexity increases
Solution Approach 1:
The patent employs a single SLM that serves multiple functions: it displays holograms for all three colour channels sequentially and acts as the common spatial modulator for the entire system. This multi-functionality reduces overall device complexity while achieving precise colour reconstruction matching through software-controlled sequential operation.
Solution Approach 2:
The system uses frame-sequential colour methodology where the SLM displays holograms for red, green, and blue colours in periodic succession at high speed. This periodic action allows different optical path lengths to be utilized for each colour while maintaining a relatively simple optical configuration, as only one hologram needs to be displayed at a time.
3Volume of moving object
If frame-sequential colour method is used, then system compactness is improved, but brightness deteriorates due to sequential rather than simultaneous laser firing
Solution Approach 1:
The patent adjusts the duration of laser firing for each colour channel to optimize brightness. By carefully controlling the temporal parameters of sequential laser activation and ensuring sufficient integration time for each colour frame, the system maintains adequate brightness while preserving the compactness benefits of the frame-sequential approach.
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 allows for high-quality, compact holographic colour displays with consistent resolution and position of colour reconstructions, addressing the issues of size and quality mismatch and space efficiency, suitable for applications like head-up and head-mounted displays.
Implementation Method 1
a Fourier transform lens arranged to form a holographic reconstruction of the hologram at a replay plane
Implementation Method 2
using mirrors to redirect light and allow for different optical paths for each colour channel
Data Source
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Figure 2B
AI summary
A display system and a method of adjusting a display system are disclosed. A first plurality of pixels (601) is arranged to display a first hologram, receive light (605) of a first wavelength, and output spatially-modulated light (609) according to the first hologram, along a first optical path. A first Fourier transform lens on the first optical path forms a first holographic reconstruction at a replay plane (650). A second plurality of pixels (601) is arranged to display a second hologram, receive light (605) of a second wavelength, and output spatially modulated light (609) according to the second hologram, along a second optical path. A second Fourier transform lens on the second optical path forms a second holographic reconstruction at the replay plane. A first optical element (607b) on the first optical path is arranged to receive the output light from a first part of the first optical path and redirect it along a second part (609b) of the first optical path to the replay plane. A second optical element (617g) on the second optical path is arranged to receive the output light of the second wavelength from a first part of the second optical path and redirect it along a second part (609g) of the second optical path to the replay plane. The length of the first part of the first optical path is not equal to the length of the first part of the second optical path. The first part of the first optical path may be substantially collinear with the first part of the second optical path.