Spatial Filter for Proton Exchange Polarizer Crosstalk
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Solution Overview
Problem
Proton exchange polarizers used in fiber-optic gyros suffer from reduced extinction ratios due to crosstalk caused by unguided TM mode light, which is reflected from the substrate's sides and bottom, leading to unwanted light pickup, especially in longer devices.
Innovation Solution
An integrated spatial filter is positioned at the primary and secondary reflection points within or on the sides of the optically transmissive substrate to block the propagation of unguided TM mode light, using methods like saw cutting, etching, or laser-machining to create barriers that prevent light coupling back into the output fiber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the polarizer length is increased to improve polarization performance, then the extinction ratio deteriorates due to increased TM mode light reflection and coupling
Solution Approach 1:
The patent extracts and removes the harmful reflected TM mode light from the optical path by positioning spatial filters at reflection points within the substrate. This extraction principle directly addresses the contradiction by removing the harmful factor (reflected light causing crosstalk) that deteriorates the extinction ratio, allowing longer polarizer lengths to be used without sacrificing polarization performance.
Solution Approach 2:
The patent introduces spatial filters as intermediary elements positioned at strategic locations within the substrate to intercept and block reflected TM mode light. These intermediaries prevent the harmful light from coupling back into the output fiber, thereby maintaining high extinction ratios even in longer devices where reflection paths are more numerous.
2Object-affected harmful factors
If spatial filters are added to block reflected light, then the extinction ratio improves, but the device complexity increases
Solution Approach 1:
The patent merges the spatial filter functionality directly into the substrate structure by positioning filters at internal reflection points. This integration combines multiple functions (polarization filtering and reflection blocking) into a single component, improving the extinction ratio without proportionally increasing device complexity as would separate external filters.
Solution Approach 2:
The patent applies spatial filters only at specific local positions within the substrate where reflection points are located, rather than uniformly throughout the entire device. This localized application provides the necessary light blocking function to improve extinction ratio while minimizing the addition of complex structural elements.
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
The spatial filter significantly improves the extinction ratio by effectively blocking unwanted TM mode light reflections, enhancing the performance of proton exchange polarizers by reducing crosstalk and maintaining high extinction ratios across varying device lengths.
Implementation Method 1
The spatial filter acts to block the propagation of the unguided TM light
Implementation Method 2
The sides of the substrate couple the unguided TM mode light to the output fiber
Data Source
AI summary
Methods and devices for polarizing light in a proton exchange polarizer where cross-coupling of unwanted modes of light is reduced with an integrated spatial filter. An optically transmissive substrate such as a substrate created from LiNbO3 or LiTaO3 has side surfaces, which reflect unguided TM mode light. The light originates from an input fiber. The input fiber is connected to the substrate at one end and an output fiber is connected to receive guided TE mode light at the opposite end. The spatial filter is positioned at the primary reflection position of the light with respect to the sides of the polarizer. To improve extinction further, the spatial filter can also be located at secondary reflection points in another alternate embodiment.