Holographic Diffraction Efficiency Monitoring via Periodic Beam Blocking
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Solution Overview
Problem
Existing methods for measuring the diffraction efficiency of volume holographic elements (VHOEs) are either inaccurate or require additional equipment and complex setups, and they fail to account for fluctuations in material or laser power, leading to inconsistencies in achieving the desired diffraction efficiency during fabrication.
Innovation Solution
A method involving the use of a shutter or chopper to periodically block one of the exposing beams during fabrication, allowing real-time measurement of the diffracted beam power, which enables precise control of exposure energy and accounts for local variations in material or laser power, thereby ensuring accurate and efficient monitoring of diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous beam illumination is used during hologram fabrication, then the fabrication process can proceed continuously, but the diffraction efficiency measurement becomes inaccurate due to inability to account for material and laser power fluctuations
Solution Approach 1:
The patent applies periodic action by intermittently blocking the reference beam during hologram fabrication. The beam is blocked in periodic intervals to allow measurement of diffracted beam power, which enables accurate determination of diffraction efficiency. This periodic interruption resolves the contradiction by sacrificing some fabrication continuity to achieve precise real-time measurement of diffraction efficiency, accounting for material and laser power fluctuations.
2Measurement precision
If additional measurement equipment is added to monitor diffraction efficiency, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent applies self-service by using the hologram itself to measure its own diffraction efficiency. The system uses the diffracted beam from the hologram under fabrication to determine the diffraction efficiency, eliminating the need for separate measurement equipment. This resolves the contradiction by achieving accurate real-time measurement without adding external measurement devices or complex setup.
3Productivity
If both reference and object beams are continuously illuminated, then hologram fabrication efficiency is maximized, but real-time monitoring of diffraction efficiency becomes impossible
Solution Approach 1:
The patent resolves this contradiction by periodically blocking the reference beam while keeping the object beam continuous. During the blocked intervals, the diffracted beam power is measured to determine diffraction efficiency. This periodic interruption allows real-time monitoring without completely stopping fabrication, as the object beam remains active and can resume hologram formation immediately when the reference beam is unblocked.
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 allows for real-time, accurate monitoring of diffraction efficiency, reducing material waste and improving the precision of VHOE fabrication, especially in applications requiring precise diffraction efficiency, such as display systems and multiplexed holograms.
Implementation Method 1
directing a reference beam and an object beam toward a holographic material for formation of a diffraction grating
Implementation Method 2
formation of a diffraction grating in the holographic material
Implementation Method 3
measuring a power level of a diffracted beam associated with the reference or the object beam
Data Source
AI summary
Methods, devices and systems are described that enable monitoring the diffraction efficiency of holographic material in real-time while they are being formed. One example method includes directing a reference beam and an object beam toward a holographic material for formation of a diffraction grating and blocking one of the beams for at least a portion of time during which the diffraction grating is being formed. The method further includes, upon blockage of one of the beams, based on power level measurements, determining whether or not a first diffraction efficiency is reached. If the first diffraction efficiency is reached, one of the reference or the object beams is disabled or blocked while the other beam illuminates the holographic material with a particular duty cycle. Further measurements of the diffraction efficiency are made until the final diffraction efficiency is reached.