Tunable Optical Filter Using Cascaded Diffraction and MEMS Mirror
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Solution Overview
Problem
Existing tunable optical filters in optical communication networks are bulky, slow, prone to wear-out, and have varying optical characteristics across their tuning range, with high costs, large sizes, and high power consumption, making them unsuitable for dynamic reconfiguration of wavelength selection in modern DWDM systems.
Innovation Solution
The use of cascaded optical diffraction gratings combined with a microfabricated MEMS mirror as a tuning element, allowing light to be diffracted and reflected multiple times for precise wavelength selection, resulting in a compact, fast, and reliable tunable optical filter with consistent optical characteristics across the tuning range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a motor is used to rotate or tilt the thin-film optical filter, then the wavelength selection function is achieved, but the device becomes bulky, slow, and prone to wear-out
Solution Approach 1:
The patent replaces the motor-driven mechanical rotation/tilting system with a prism-based optical system. The prism rotates to change the angle of incidence of light on the thin-film filter, substituting direct mechanical actuation of the filter with mechanical actuation of the prism. This reduces wear on the filter itself and simplifies the mechanical coupling mechanism.
Solution Approach 2:
The patent introduces a prism as an intermediary element between the light source and the thin-film filter. The prism mediates the wavelength selection by controlling the angle at which light strikes the filter, allowing wavelength tuning without directly mechanically moving the fragile thin-film filter component.
2Adaptability or versatility
If the thin-film optical filter is tilted to select different wavelengths, then wavelength tuning is achieved, but the passband width varies and optical characteristics become non-uniform
Solution Approach 1:
The patent changes the parameter being varied from the tilt angle of the thin-film filter to the angle of incidence controlled by the rotating prism. By maintaining the thin-film filter at a fixed optimal angle while varying the incident light angle through prism rotation, the system achieves wavelength tuning while preserving uniform optical characteristics and consistent passband width across the tuning range.
3Adaptability or versatility
If a linearly-variable thin-film filter is moved laterally by a stepping motor, then wavelength selection is achieved, but the device becomes bulky and the filter fabrication becomes difficult
Solution Approach 1:
Instead of moving the linearly-variable thin-film filter laterally to achieve wavelength selection, the patent inverts the approach by using a fixed thin-film filter with a rotating prism to vary the angle of incidence. This eliminates the need for complex lateral positioning mechanisms and simplifies the filter fabrication process, as standard thin-film filters can be used without requiring precise lateral alignment mechanisms.
4Adaptability or versatility
If an etalon cavity length is changed to tune the wavelength, then wavelength selection is achieved, but the device becomes expensive and thermally unstable
Solution Approach 1:
The patent replaces the thermally-controlled or mechanically-precise etalon cavity length adjustment mechanism with a prism-based angular incidence system. The wavelength tuning is achieved by rotating the prism to change the angle at which light enters the thin-film filter, eliminating the need for precise thermal control or expensive piezoelectric actuators required for etalon-based systems, thereby improving thermal stability and reducing cost.
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 provides a compact, cost-effective, and high-reliability tunable optical filter with a wide tuning range and high adjacent channel isolation, overcoming the limitations of existing filters by using cascaded gratings and a reflective MEMS mirror to achieve low insertion loss and consistent optical performance.
Implementation Method 1
an optical diffraction element to disperse light of a first wavelength into a plurality of wavelength components at a first set of angles
Implementation Method 2
a mirror to reflect light from the optical diffraction element back towards the optical diffraction element such that light is diffracted by the optical diffraction element a second time
Implementation Method 3
light is diffracted by the optical diffraction element a second time, with a second set of angles, than when diffracted by the optical diffraction element the first time
Data Source
AI summary
At least one diffraction element is used to diffract light of multiple wavelengths into different wavelength components. Instead of moving the diffraction element as in certain prior filters, light from the at least one element is reflected back towards the at least one element so that light is diffracted at least twice by the at least one element. The reflection is such that at least one selected wavelength component of said wavelength components will pass from an input port to an output port or to another device.