Broadband polarization rotator and optical switch
AssigneeMeta Platform Technologies, LLC
InventorsGary D. Sharp, David Coleman
Life of this patent
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Abstract
A reflective polarization rotator based on a twisted nematic (TN) liquid crystal (LC) configuration may be optimized for achromatic performance in both bright and dark states by compensating wavelength dependence of polarization transformation by the TN LC layer. At linear achromatic input polarization, the compensation aims to provide a circular achromatic polarization at the reflector, which guarantees the achromaticity of the 90 degrees polarization rotation on double pass. The compensation takes care to preserve linear polarization at the reflector when the LC device is driven to a vertical LC director configuration. Such an approach ensures that the performance of the polarization rotator is achromatic in both driven and undriven states of the LC device.
Claims20
A passive compensation structure (PCS) for a liquid crystal (LC) layer switchable between an undriven state corresponding to a twisted LC director configuration and a driven state corresponding to a substantially vertical LC director configuration, wherein the LC layer is configured to rotate, when the LC layer is in the undriven state, an achromatic polarization state of a light beam orthogonally upon completion of a double pass of the light beam through the LC layer, the PCS comprising:
- a stack of fixed-retardation layers configured to rotate, when the LC layer is in the undriven state, the achromatic polarization state of the light beam orthogonally upon completion of a double pass of the light beam through the PCS such that the achromatic polarization state of the light beam received by the PCS and the achromatic polarization state of the light beam exiting the PCS are orthogonal to one another.
A polarization rotator comprising:
- a reflective liquid crystal (LC) device comprising an LC layer that is coupled to a reflector and switchable between an undriven state corresponding to a twisted LC director configuration and a driven state corresponding to a substantially vertical LC director configuration, wherein the reflective LC device is configured to rotate, when the LC layer is in the undriven state, an achromatic polarization state of a light beam orthogonally upon completion of a double pass of the light beam through the reflective LC device;
- and
- a passive compensation structure (PCS) disposed upstream of the reflective LC device and comprising a stack of fixed-retardation layers, wherein the PCS is configured to rotate, when the LC layer is in the undriven state, the achromatic polarization state of the light beam orthogonally upon completion of a double pass of the light beam through the PCS such that the achromatic polarization state of the light beam received by the polarization rotator and the achromatic polarization state of the light beam exiting the polarization rotator are orthogonal to one another.
An optical switch comprising:
- a frontlight illuminator for providing a light beam;
- a polarization rotator downstream of the frontlight illuminator, for receiving and redirecting the light beam to propagate back through the frontlight illuminator;
- and
- a polarizer downstream of the polarization rotator for transmitting or blocking the light beam depending on an achromatic polarization state of the light beam;
- the polarization rotator comprising:
- a reflective liquid crystal (LC) device comprising an LC layer that is coupled to a reflector and switchable between an undriven state corresponding to a twisted LC director configuration and a driven state corresponding to a substantially vertical LC director configuration, wherein the reflective LC device is configured to rotate, when the LC layer is in the undriven state, the achromatic polarization state of the light beam orthogonally upon completion of a double pass of the light beam through the reflective LC device;
- and
- a passive compensation structure (PCS) disposed upstream of the reflective LC device and comprising a stack of fixed-retardation layers, wherein the PCS is configured to rotate, when the LC layer is in the undriven state, the achromatic polarization state of the light beam orthogonally upon completion of a double pass of the light beam through the PCS such that the achromatic polarization state of the light beam received by the polarization rotator and the achromatic polarization state of the light beam exiting the polarization rotator are orthogonal to one another.
Dependencies are inferred from the claim text.