Variable Wavelength Filter With Beam Expansion Prism
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Solution Overview
Problem
Conventional tunable filters face a trade-off between increasing vibration and impact resistance and narrowing the filter linewidth, as the size of the MEMS mirror needs to be large to receive a large beam diameter for narrow linewidth, compromising resistance to vibrations and impacts.
Innovation Solution
A tunable filter configuration with a variable-angle mirror positioned before a transmissive diffraction grating, allowing for a larger beam diameter on the grating while using a smaller MEMS mirror, and optionally including beam-diameter-adjusting prisms and a half-wave plate to enhance resistance and reduce wavelength dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the MEMS mirror is made large to receive a large beam diameter for narrow linewidth, then the filter linewidth is narrowed, but the vibration and impact resistance deteriorates
Solution Approach 1:
The patent divides the beam expansion function from the MEMS mirror to a separate optical component (beam expanding prism or cylinder lens). This segmentation allows the MEMS mirror to remain small for high reliability while the beam is expanded downstream to achieve narrow linewidth through large beam diameter interaction with the diffraction grating.
Solution Approach 2:
The patent introduces an intermediary optical component (beam expanding prism or cylinder lens) between the MEMS mirror and the diffraction grating. This intermediary expands the beam diameter after reflection from the small MEMS mirror, enabling narrow linewidth without requiring a large MEMS mirror.
2Reliability
If the MEMS mirror is made small to increase resonance frequency for high vibration resistance, then the vibration resistance is improved, but the beam diameter it can receive is reduced, widening the filter linewidth
Solution Approach 1:
The patent separates the functions of wavelength tuning (MEMS mirror) and beam diameter control (beam expanding optical component). This allows the MEMS mirror to be small for high vibration resistance while the beam expanding component ensures sufficient beam diameter for narrow linewidth.
Solution Approach 2:
The patent uses a beam expanding prism or cylinder lens to expand the beam diameter in a specific dimension after reflection from the MEMS mirror. This dimensional expansion occurs downstream, allowing the MEMS mirror to remain small while the beam diameter at the diffraction grating is sufficiently large.
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 solution enables increased vibration and impact resistance while maintaining a narrow filter linewidth, allowing for stable operation under various conditions without the need for a large MEMS mirror, thus achieving both performance metrics effectively.
Implementation Method 1
The first mirror has a first reflective surface disposed to reflect input light from the optical input/output unit
Implementation Method 2
The transmissive diffraction grating is disposed on a propagation path of the input light reflected by the first mirror
Implementation Method 3
The second mirror has a second reflective surface disposed to reflect transmitted diffracted light from the transmissive diffraction grating
Data Source
AI summary
A tunable filter includes: an optical input/output unit; a first mirror having a first reflective surface disposed to reflect input light from the optical input/output unit; a transmissive diffraction grating disposed on a propagation path of the input light reflected by the first mirror; and a second mirror having a second reflective surface disposed to reflect transmitted diffracted light from the transmissive diffraction grating corresponding to the input light. The first reflective surface is a variable-angle reflective surface. The second reflective surface has a fixed orientation relative to the transmissive diffraction grating.