LCOS Diffractive Optical Element Reflectivity
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Solution Overview
Problem
Conventional LCOS devices suffer from diffractive optical losses due to their pixilated electrode structure and polarization dependence, with previous solutions like multilayer dielectric coatings and metallic subwavelength structures either failing to effectively suppress losses or adding absorption losses.
Innovation Solution
A spatial light modulator with a liquid crystal material and a pair of electrodes, incorporating a diffractive optical element formed of silicon and silicon dioxide, which acts as both a reflector and alignment layer, reducing diffractive and absorption losses by using non-metallic materials and optimizing refractive index contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a multilayer dielectric coating is used to suppress pixel structure, then diffractive optical losses are reduced, but voltage drop increases and fringing field losses increase
Solution Approach 1:
The patent extracts the reflective function from the multilayer dielectric coating and relocates it to the silicon substrate beneath the liquid crystal layer. This eliminates the need for multiple overcoat layers, thereby removing the source of voltage drop and fringing field losses while maintaining the suppression of diffractive optical losses through the modified pixel structure.
Solution Approach 2:
The patent moves the reflective function from the optical dimension (multilayer dielectric coating) to the structural dimension (silicon substrate with modified pixel geometry). By changing the dimension in which the reflective function is implemented, the patent avoids the electrical side effects of thick dielectric coatings.
2Adaptability or versatility
If a metallic subwavelength structure is used to achieve polarization independence, then polarization dependence is reduced, but absorption losses increase
Solution Approach 1:
The patent replaces the metallic subwavelength structure with a silicon-based pixel structure that achieves polarization independence through geometric modification rather than material properties. This approach uses the existing silicon substrate and liquid crystal materials instead of introducing additional metal layers, thereby eliminating absorption losses while maintaining adaptability to different polarization states.
Solution Approach 2:
The patent uses a composite approach by combining the silicon substrate with the liquid crystal layer in a modified pixel structure that achieves both polarization independence and low absorption losses. The interaction between the silicon pixel structure and liquid crystal molecules creates the desired optical response without requiring metallic components.
3Loss of energy
If multilayer dielectric coating is applied to suppress pixel structure, then reflectivity is improved, but manufacturing complexity increases due to stress and flatness control
Solution Approach 1:
The patent extracts the reflective function from the complex multilayer dielectric coating structure and places it in the simplified silicon substrate. This eliminates the manufacturing challenges associated with depositing and stress-managing multiple dielectric layers while maintaining the optical performance needed to suppress diffractive losses.
Solution Approach 2:
Instead of adding layers on top of the LCOS to achieve reflection, the patent inverts the approach by utilizing the silicon substrate beneath the liquid crystal layer as the reflective element. This inversion simplifies the manufacturing process by eliminating the need for complex overcoat deposition and stress management.
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 achieves high reflectivity exceeding 99% over a wide bandwidth with reduced optical losses, maintaining polarization independence and avoiding the need for additional metal layers, thus enhancing the performance of LCOS devices.
Implementation Method 1
the diffractive optical element includes a first array of diffracting formations formed of a first material having a first refractive index and extending in a second dimension substantially perpendicular to the first dimension, the formations being at least partially surrounded by a second material formed of a lower refractive index
Implementation Method 2
a first diffractive optical element disposed between the electrodes for at least partially reflecting the incident optical signal
Implementation Method 3
a liquid crystal material; a pair of electrodes for supplying an electric potential across said liquid crystal material to drive liquid crystals in a predetermined configuration
Data Source
AI summary
Described herein is a spatial light modulator (15) for modulating the phase, retardation or polarization state of an incident optical signal propagating in a first dimension. The optical phase modulator (15) includes a liquid crystal material (17) and a pair of electrodes (19 and 21) for supplying an electric potential across the liquid crystal material (17) to drive liquid crystals in a predetermined configuration. Modulator (15) also includes a diffractive optical element (29) disposed adjacent a first electrode (19). Element (29) includes a first array of diffractive elements (31) formed of a first material having a first refractive index and extending in a second dimension substantially perpendicular to the first dimension. Elements (31) are at least partially surrounded by a second material (33) formed of a lower refractive index.