Diffractive Optical Element Sawtooth Profile
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Solution Overview
Problem
Conventional diffractive optical elements (DOEs) have efficiency limitations due to power loss in secondary diffracted orders and are constrained by the need for uniform power distribution among primary orders, which restricts their use in combining multiple input beams efficiently.
Innovation Solution
A DOE design with a gradually sloped surface and continuous depth profile allows for higher efficiency by enabling the deposition of low absorption coatings, optimizing the phase retardance to maximize the power in primary diffracted orders while minimizing secondary orders, and using optimization methods like simplex or Gerchberg-Saxton algorithms to determine the etch depth profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional binary DOE splitters with single etch depth are used, then manufacturing is simple, but efficiency is limited to around 80%
Solution Approach 1:
The patent changes the etch depth parameter from a single uniform depth to a continuous gradient of depths across the DOE surface. This creates a sawtooth profile where the etch depth varies continuously, enabling more precise control of the diffracted beam phases and achieving over 90% efficiency by minimizing energy loss to secondary orders.
2Loss of energy
If multi-level etch depths are used to improve efficiency, then efficiency increases to about 90%, but the surface patterns remain discontinuous with steep walls
Solution Approach 1:
The patent replaces the discontinuous stepped profile with a continuous sawtooth profile featuring gradually sloping surfaces. The sawtooth shape provides the necessary phase modulation while maintaining continuous, gentle slopes that allow subsequent coating deposition without performance degradation.
Solution Approach 2:
The patent transitions from discrete multi-level steps to a continuous gradient in the depth dimension, creating a sawtooth profile that varies etch depth continuously across the surface. This dimensional approach enables both high efficiency and coating compatibility.
3Loss of energy
If discontinuous etch profiles with steep walls are used, then efficiency can be improved, but additional coating layers cannot be deposited without degrading performance
Solution Approach 1:
The continuous sawtooth profile with gradual slopes eliminates the steep walls and discontinuities that prevent proper coating adhesion. The gentle, continuous surfaces allow thick reflective coatings (5 μm or more) to conform uniformly to the etched surface, maintaining optical performance while enabling high-power operation.
4Manufacturing precision
If DOE splitters are designed with uniform power distribution among primary orders, then beam uniformity is achieved, but efficiency is limited due to power loss in secondary orders
Solution Approach 1:
The patent changes from uniform etch depth to a continuous gradient of etch depths, creating a sawtooth profile that provides precise phase control. This enables the DOE to achieve over 90% efficiency by minimizing secondary orders while still providing sufficient uniformity for combiner applications where input beams are combined into a single output.
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 design achieves a combining efficiency greater than 90% with a relaxed uniformity requirement for diffracted orders, allowing for higher efficiency in combining multiple input beams into a single output beam, even with unequal power distributions among the input beams.
Implementation Method 1
the pattern is formed such that when an incoming light beam having a wavelength λ is shone onto the top surface of the light-reflective substrate, the incoming light beam will reflect and be split into a plurality of diffracted light beams
Implementation Method 2
the incoming light beam will reflect and be split into a plurality of diffracted light beams
Data Source
AI summary
A transmissive or reflective diffractive optical element, comprising: a substrate having a top surface, the top surface being etched into a pattern, the pattern including a periodic surface pattern of grooves formed such that when an incoming light beam is shone onto the top surface, the incoming light beam will be split into a plurality of diffracted light beams, the plurality of diffracted light beams including a plurality of primary diffracted order beams and a plurality of secondary diffracted order beams, wherein the primary diffracted order beams have a primary aggregate efficiency above ninety percent, wherein the plurality of secondary diffracted order beams have a secondary aggregate efficiency of lower than ten percent, and wherein a maximum power of the primary diffracted order beams and a minimum power of the primary diffracted order beams differ by at least ten percent of an average power of the primary diffracted order beams.