Polarisation-Insensitive Optical Beam Steering via Segmented Liquid Crystal
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Solution Overview
Problem
Optical beam steering devices face challenges in achieving polarisation insensitivity and reduced insertion loss, particularly in telecoms communication systems where light with varying polarisation states requires efficient routing without disturbance.
Innovation Solution
The use of a splitter to split optical beams into mutually orthogonal polarisations, with separate liquid crystal device regions aligned to each polarisation state, allowing for polarisation insensitive phase modulation through nematic liquid crystal materials and controlled director orientations, either within a single LCOS device or separate devices, and the implementation of a wide aperture optical circulator to manage light transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single liquid crystal device with uniform director orientation is used, then the device structure is simple, but polarisation insensitivity cannot be achieved and insertion loss increases
Solution Approach 1:
The liquid crystal device is segmented into multiple regions with different director orientations. Specifically, the device includes a first region with a first director orientation and a second region with a second director orientation that is non-parallel to the first. This segmentation allows different polarisation states to experience matched phase modulation in their respective regions, achieving polarisation insensitivity while maintaining a relatively compact device structure.
Solution Approach 2:
Different regions of the liquid crystal device are assigned different local properties (director orientations) tailored to specific polarisation states. The first region has its director oriented to optimally modulate one polarisation state, while the second region has its director oriented for another polarisation state. This local quality approach ensures that each region performs its specific function efficiently, resulting in overall polarisation insensitivity.
2Loss of energy
If binary phase levels are used in LCOS devices, then the device is polarisation insensitive, but higher diffraction orders cause power loss and crosstalk
Solution Approach 1:
The invention changes the phase modulation parameter from binary (0 and π only) to multi-level phase modulation. By enabling continuous or multi-level phase control in the liquid crystal device, the system can implement blazed grating profiles that concentrate diffracted energy into the first order, thereby reducing power loss in higher orders while maintaining polarisation insensitivity through the multi-region director orientation 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 approach ensures polarisation insensitivity and reduced insertion loss by ensuring both polarisation states experience the same refractive index profile, enhancing the efficiency of optical beam steering in applications like optical add drop multiplexers (OADM) and visual displays.
Implementation Method 1
When an electric field is applied to such a device, the director changes its orientation in the plane of the device
Implementation Method 2
The liquid crystalline molecules in a material exhibiting a nematic or ferroelectric LC phase are typically rod shaped. The direction of preferred orientation of such LC molecules in the neighbourhood of any point can be represented by n
Implementation Method 3
a splitter arranged to split an optical beam into at least a first part having a first polarisation and a second part having a second polarisation, said first and second polarisations being substantially mutually orthogonal
Implementation Method 4
Such a binary phase array produces diffraction peaks in the device output plane that include both the first order (routing) peak and unwanted higher and symmetric orders
Data Source
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AI summary
The invention relates to optical beam steering. There is described an optical beam steering apparatus, comprising: a splitter arranged to split an optical beam into at least a first part having a first polarization and a second part having a second polarization, said first and second polarizations being substantially mutually orthogonal; a first liquid crystal device region arranged to receive said first part and to have director orientation substantially aligned to said first polarization; and a second liquid crystal device region arranged to receive said second part and to have director orientation substantially aligned to said second polarization.