Multi-pass Etalon Filter for Spectral Contrast
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Solution Overview
Problem
Existing optical filters using multiple Fabry-Perot etalons face challenges in maintaining high wavelength selectivity and tuning multiple etalons to track a single wavelength change, as increasing mirror reflectivity enhances selectivity but complicates tuning, and tilting or varying optical thicknesses across different planes complicates simultaneous tuning across multiple interactions.
Innovation Solution
A multi-pass optical filter configuration using a first Fabry-Perot etalon and an external reflector that recycles reflected light at a similar angle of incidence but in a perpendicular plane, allowing for enhanced suppression of target wavelengths through double reflection, optimizing tuning rates and maintaining high selectivity by ensuring equal incidence angles in both passes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple separate etalons are combined in series to achieve higher contrast, then the spectral contrast is improved, but the device complexity and tuning difficulty increase
Solution Approach 1:
The patent combines multiple etalon interactions into a single etalon by using an external reflector to create multiple passes. The light reflects back and forth between the etalon and external reflector, achieving multiple etalon interactions without requiring multiple separate etalon devices. This merging approach maintains high spectral contrast while reducing device complexity and tuning difficulty.
Solution Approach 2:
The patent introduces a spatial dimension by tilting the etalon relative to the external reflector. The light path is arranged at an angle, creating a multi-pass configuration where light traverses the etalon multiple times in a folded optical path. This dimensional approach enables multiple interactions within a single etalon while maintaining compact geometry.
2Measurement precision
If multiple separate etalons are tilted relative to each other to avoid secondary etalons, then the wavelength selectivity is improved, but the tuning complexity increases
Solution Approach 1:
The patent merges multiple etalon interactions into a single tilted etalon configuration. By arranging the external reflector at a specific angle to the etalon, the light undergoes multiple passes through the same etalon at the same tilt angle, achieving wavelength selectivity without requiring multiple tilted etalons. This single-etalon multi-pass approach simplifies tuning while maintaining selectivity.
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 configuration achieves enhanced suppression of target wavelengths, maintains high wavelength selectivity, and simplifies tuning by ensuring equal tuning rates across interactions, improving the performance of optical filters in applications like LIDAR and spectroscopy by doubling the reflection contrast and maintaining port-to-port transmission characteristics close to single-pass performance.
Implementation Method 1
Fabry-Perot (FP) etalons are frequency selective devices that are used in a variety of applications to discriminate between different wavelengths of light. An FP etalon is formed by two parallel partially reflective mirrors which are typically closely spaced, and transmit light at a series of wavelengths defined by the separation between the two partial reflectors. Light that doesn't interfere constructively at the output of the FP etalon because the mirror separation is not an even multiple of half-wavelength, is reflected by the FP etalon.
Implementation Method 2
a reflector disposed to receive the first reflected light, and to reflect the first reflected light back toward the first FP etalon as returned light for a second reflection therefrom
Data Source
AI summary
The invention relates to a multi-pass etalon-based optical filter in which input light once reflected from the etalon is returned back to the etalon for a second reflection to enhance etalon contrast. The external mirror may be tilted relative to the etalon so that two planes of incidence are orthogonal. The multi-pass etalon-based optical filter may be used to clean scattered light from an excitation wavelength in Raman and Brillouin spectroscopy.