Compact Polarization Beam Splitter for Free-Space Light Coupling
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Solution Overview
Problem
The challenge lies in the difficulty of coupling light into a single-mode waveguide for compact light receiver and emitter structures, particularly in mobile free-space communications, which limits the large-scale commercial utilization of quantum cryptography and other applications like ellipsometry and polarization imaging.
Innovation Solution
A compact optical structure using a stack of miniature beam splitter cubes and wave plates is employed to divide input light into multiple polarized outputs, allowing simultaneous measurement of polarization components, thereby enhancing robustness against intensity noise and enabling instantaneous depolarization calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a single-mode waveguide is used for compact light receiver structure, then device compactness is improved, but coupling difficulty increases
Solution Approach 1:
The optical receiver is divided into multiple functional modules: a multi-mode waveguide input stage, polarization beam splitters, wave plates, and single-mode waveguide detection stages. This segmentation allows the system to benefit from both multi-mode coupling ease and single-mode detection precision, resolving the contradiction between compactness and coupling difficulty.
Solution Approach 2:
A multi-mode waveguide acts as an intermediary between the free-space optical input and the single-mode waveguide detectors. This intermediary stage facilitates easy coupling from free-space while enabling subsequent single-mode operation, thus resolving the coupling difficulty without sacrificing compactness.
2Device complexity
If sequential measurement of polarization components is used, then device complexity is reduced, but measurement time increases
Solution Approach 1:
The measurement system transitions from sequential temporal measurement to parallel spatial measurement by using multiple polarization beam splitters arranged in different orientations. This allows all polarization components to be measured simultaneously in space rather than sequentially in time, resolving the contradiction between device complexity and measurement time.
Solution Approach 2:
The optical receiver is designed with multiple polarization beam splitters and wave plates that can simultaneously measure multiple polarization components (horizontal, vertical, diagonal, circular). This multi-functional design enables parallel measurement of all polarization states, eliminating the time loss associated with sequential measurement while maintaining manageable device complexity through modular architecture.
3Volume of moving object
If integrated photonic platform is used, then device compactness is improved, but coupling flexibility decreases
Solution Approach 1:
The optical receiver incorporates adjustable wave plates and rotatable polarization beam splitters that can be dynamically reconfigured to adapt to different input polarization states and coupling conditions. This dynamic adjustability provides coupling flexibility while maintaining the compact integrated photonic platform structure, resolving the contradiction between compactness and flexibility.
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 solution provides a robust and compact light receiver and emitter structure capable of instantaneous depolarization measurement, suitable for secure communication and polarization imaging, with applications in quantum key distribution and ellipsometry, and can be constructed from off-the-shelf components for wide field of view and cost-effective implementation.
Implementation Method 1
A first polarization beam splitter divides the first part of the light input into a first polarized part and a second polarized part
Implementation Method 2
polarization of light in the second part is altered at least once
Data Source
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AI summary
A light input is divided into a plurality of light outputs by a structure comprising a first beam splitter configured to divide the light Input into a first part and a second part, a first polarization beam splitter configured to provide from the first part a first polarized part and a second polarized part, wherein the first polarized part is for providing a first output and the second polarized part for providing a second output, at least one polarization altering device configured to alter the polarization of light in the second part, and at least one second polarization beam splitter configured to receive light altered by respective at least one polarization altering device and provide therefrom at least one third polarized part for providing at least one third output, A light output can be generated based on similar principles in reverse.