Optical Isolator Assembly for Multi-Port Switches
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Solution Overview
Problem
Existing multi-port optical switching devices, such as wavelength selective routers, face challenges in preventing spurious output signals without the need for external isolators at each input port, which adds cost and space, and are often polarization-dependent.
Innovation Solution
An internal isolator assembly is integrated within the switching device, comprising linear polarizers and a Faraday rotator, arranged to cover input beam paths but not the output path, ensuring that returned light is blocked by rotating its polarization state orthogonally, thus preventing spurious outputs without external isolators and maintaining polarization independence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external isolators are installed at each input port to prevent spurious outputs, then spurious output signals are blocked, but device complexity and space requirements increase
Solution Approach 1:
The patent combines multiple isolator functions into a single integrated isolator assembly located in the common optical path. Instead of placing separate isolators at each input port, the invention merges their functions into one shared component that uses a single polarization rotation device to isolate all input ports simultaneously, thereby reducing overall device complexity while maintaining spurious output prevention
Solution Approach 2:
The isolator assembly serves multiple functions: it prevents spurious outputs from all input ports, maintains polarization independence across all channels, and reduces the total number of components. The single polarization rotation device universally isolates all input ports rather than requiring port-specific isolation mechanisms
2Reliability
If external isolators are used at each input port, then spurious outputs are prevented, but cost and space requirements increase
Solution Approach 1:
The patent consolidates the spatial footprint of multiple isolators into a single compact isolator assembly. By locating one polarization rotation device in the common optical path rather than distributing isolators across multiple input ports, the invention significantly reduces the total area required while maintaining isolation functionality for all ports
3Reliability
If conventional isolator designs are used, then spurious outputs are blocked, but polarization dependence is introduced
Solution Approach 1:
The patent employs a polarization rotation device that actively changes the polarization state of light passing through it. By rotating the polarization by a specific angle (e.g., 45 degrees), the device creates a polarization state transformation that provides isolation while maintaining polarization independence across all input ports, unlike conventional fixed-polarization isolators
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 effectively prevents spurious outputs from unintended input ports while maintaining efficient transmission to intended output ports, eliminating the need for additional isolators and ensuring polarization independence, thus enhancing the operational efficiency and cost-effectiveness of the switching device.
Implementation Method 1
a 45° polarization rotation device, such as a Faraday rotator, disposed between them
Implementation Method 2
A first example of the switching device has a sequence of two linear polarizers aligned with their preferred polarization axes at 45° to each other
Data Source
AI summary
An isolator assembly, for use internally within a multi-port optical switch, and which operates on a preselected number of input port channels. The assembly incorporates a sequence of a birefringent crystal with a half wave plate on part of its output face acting as a linear polarizer, a 45° Faraday rotator element and a half wave plate aligned at 22.5° to the polarization direction of the light rotated by the Faraday rotator. This arrangement ensures that any light spuriously returned from a reflective beam switching element of the switch is blocked from transmission out of the paths of light which the isolator assembly covers because of the orientation of the light polarization returned to the birefringent crystal. The isolator assembly is arranged such that it does not cover the beam path leading to the output port or ports, such that legitimate output beams are transmitted unhindered.