Diffractive Optical Elements via In Situ Photolithography
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Solution Overview
Problem
Current techniques for fabricating high-performance grisms, which combine prisms and diffraction gratings, suffer from optical performance inconsistencies and high manufacturing costs due to multi-step processes involving expensive semiconductor-grade steppers and bonding, which introduce mechanical and optical imperfections.
Innovation Solution
A method for in situ fabrication of diffractive optical elements, such as grisms, directly on a prism using photolithographic techniques, eliminating the need for separate wafer bonding and allowing direct deposition of pattern materials on non-parallel surfaces, with relaxed alignment requirements and the use of larger wavelength light sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate wafer bonding is used to combine diffraction grating and prism, then optical component assembly is achieved, but mechanical and optical imperfections are introduced and manufacturing cost increases
Solution Approach 1:
The patent merges the diffraction grating fabrication and prism assembly into a single integrated process. The diffraction grating is written directly onto the prism surface using photolithography, eliminating the separate wafer bonding step. This combining of operations removes the interface between separate components, thereby eliminating mechanical and optical imperfections that would otherwise be introduced during bonding.
Solution Approach 2:
The patent extracts and eliminates the intermediate bonding step from the fabrication process. By removing the separate wafer bonding operation, the process eliminates the source of mechanical stress and optical imperfections that occur at the interface between bonded components, while still achieving the desired integrated grism structure.
2Manufacturing precision
If semiconductor grade steppers are used for grating writing, then precise diffraction grating patterns are achieved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive, precision semiconductor grade steppers with lower-cost photolithography equipment. While the equipment is less expensive, the process achieves sufficient precision for optical applications by using direct photolithographic patterning on the prism surface, eliminating the need for ultra-precise semiconductor manufacturing tools.
Solution Approach 2:
The patent changes the fabrication parameters from semiconductor-grade precision requirements to optical-grade requirements. By adjusting the photolithography process parameters (wavelength, exposure time, photoresist selection) to match optical application needs rather than semiconductor needs, the process achieves adequate precision at lower cost.
3Manufacturing precision
If multiple exposures per wafer are performed, then complete diffraction grating patterns are achieved, but manufacturing time increases
Solution Approach 1:
The patent performs preliminary preparation of the prism surface with photoresist coating and alignment mark formation before the actual grating exposure. This preliminary action enables single-exposure patterning by ensuring proper surface preparation and alignment, eliminating the need for multiple sequential exposures required in the conventional wafer process.
Solution Approach 2:
The patent implements continuous single-exposure patterning instead of discrete multiple exposures. By preparing the surface once and performing a single continuous exposure across the entire prism surface, the process maintains continuous useful action throughout the patterning step, maximizing productivity without sacrificing grating completeness.
4Manufacturing precision
If ultra-flat substrates are used for grating writing, then depth of focus requirements are met, but substrate complexity and cost increase
Solution Approach 1:
Instead of requiring the substrate to be ultra-flat to meet depth of focus requirements, the patent inverts the approach by using the photolithography process itself to create the flat patterned surface. The photoresist coating and development process produces a uniformly flat grating surface even on prisms with normal optical surface quality, eliminating the need for ultra-flat substrate preparation.
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 enhances optical performance consistency and reduces manufacturing costs by up to 85%, enabling the production of high-performance grisms with improved throughput and reduced equipment expenses.
Implementation Method 1
creating a diffractive pattern in the photoresist layer using a light source
Implementation Method 2
a diffractive surface for adapted to spatially dispersing the input optical beam into a dispersed signal
Data Source
AI summary
Described herein are embodiments of a diffractive optical element (23) such as a grism. In one embodiment, the diffractive optical element (23) includes an input surface (31) configured to receive an input optical signal (29), a diffractive surface (33) adapted to spatially disperse the input optical beam (29) into a dispersed signal and an output surface (35) configured to output the dispersed signal from the diffractive optical element. The input surface (31) and the diffractive surface (33) are non-parallel and the diffractive surface (33) is formed in situ by a photolithographic technique.