Wavelength Selective Switch Using Polarization Grating
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Solution Overview
Problem
Current wavelength selective switch (WSS) technologies face challenges such as high costs, complex electronics, low resistance to vibration, and difficulty in expanding to a large number of ports, including Micro Electro Mechanical Systems (MEMS), Liquid Crystal on Silicon (LCOS), Liquid Crystal with a crystal wedge, and Digital Micromirror Devices (DMD).
Innovation Solution
The use of combinations of switchable polarization grating (SPG) and liquid crystal (LC) cells, as well as polymer polarization grating (PPG) and LC cells, to achieve a 1×N wavelength selective switch, which simplifies the optical system, reduces electronic complexity, and enhances reliability and port count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional WSS technologies (MEMS, LCOS, DMD) are used, then wavelength switching functionality is achieved, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical scanning systems (MEMS mirrors, DMD moving parts) with a static holographic grating structure. The wavelength routing is achieved through optical diffraction by the hologram pattern rather than mechanical beam steering, eliminating moving parts and associated electronic control complexity while improving vibration resistance.
Solution Approach 2:
The patent uses a holographic grating that records and reproduces wavelength-specific diffraction patterns. The hologram captures the optical field distribution and recreates it through diffraction, enabling wavelength selective routing without complex electronic control systems. This optical copying approach simplifies the device while maintaining functionality.
2Ease of manufacture
If conventional WSS technologies are used, then wavelength routing is achieved, but manufacturing cost increases
Solution Approach 1:
The patent extracts the wavelength routing function from complex electronic control systems and mechanical components, consolidating it into a single holographic grating element. This extraction eliminates the need for multiple moving parts, drivers, and control electronics, reducing both manufacturing cost and optical system complexity.
Solution Approach 2:
The patent changes the operational parameter from electrical control (voltages, currents) to optical parameter control (wavelength, diffraction angle). The holographic grating routes wavelengths based on their optical properties rather than electrical signals, simplifying the system architecture and reducing manufacturing complexity.
3Adaptability or versatility
If conventional WSS technologies are used, then switching functionality is achieved, but expanding to large port counts becomes difficult
Solution Approach 1:
The holographic grating serves multiple functions simultaneously: it acts as a wavelength separator, a spatial router, and a port selector all in one element. By programming the hologram with appropriate interference patterns, the same device can support different port configurations and scaling scenarios without adding complexity.
Solution Approach 2:
The patent utilizes the angular dimension of diffraction to create multiple output ports. Different wavelengths are diffracted at different angles according to the grating equation, naturally providing spatial separation for multiple ports. This angular multiplexing approach allows port scaling without increasing device complexity.
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 results in a high-performance WSS with simple electronics, high reliability, easy realization of high port counts, and low product costs, overcoming the limitations of existing technologies.
Implementation Method 1
The first photo-alignment layer and the second photo-alignment layer comprising photosensitive polymer that have been physically altered by exposure using two interfering light beams with opposite handedness of circular polarization
Implementation Method 2
A liquid crystal layer is placed between the two photosensitive polymer layers. When a voltage is applied to the liquid crystal layer, the liquid crystal redirects the light beam
Implementation Method 3
diffracting, at the polarization grating, the polarized incident light beam in a determined angle that corresponds to a diffraction order in accordance to the circular polarization of the incident light beam and a hologram pattern direction formed inside the polarization grating
Implementation Method 4
exposure using two interfering light beams with opposite handedness of circular polarization
Data Source
AI summary
Apparatus and method embodiments are provided for implementing a wavelength selective switch (WSS). The embodiments use combinations of switchable polarization grating (SPG) and LC cells and combinations of polymer polarization grating (PPG) and LC cells to achieve 1×N WSS systems. An embodiment optical switch includes a liquid crystal cell and a polymer polarization grating (PPG) cell adjacent to the liquid crystal cell. The PPG includes a glass substrate, a photo-alignment layer overlying the glass substrate and comprising photosensitive polymer that has been physically altered by exposure using two interfering light beams with opposite handedness of circular polarization, and a polymerized liquid crystal layer overlying the photo-alignment layer on an opposite side of the glass substrate, the polymerized liquid crystal layer has been physically altered by illumination using a uniform light beam.