Tunable Optical Filter with Curved Mirror for Side Mode Suppression
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Solution Overview
Problem
Current tunable optical filters require higher voltages to operate and have limited frequency tuning ranges due to structural limitations, which restricts their applications and frequency resolution.
Innovation Solution
The optoelectronic device features a Fabry-Perot etalon with a second mirror having alternating layers of higher and lower refractive indices, designed to reduce the curvature of the mirror, thereby suppressing side modes and increasing the working distance between the device and the fiber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional MEMS-FPI tunable optical filter uses a curved movable mirror, then the device can operate with standard voltage, but the frequency tuning range is limited and side modes are not sufficiently suppressed
Solution Approach 1:
The patent applies the curvature principle by designing the movable mirror with a specific spherical curvature radius (R ≥ 10mm) that optimizes the resonant cavity performance. This curvature configuration suppresses side modes by creating a more uniform standing wave pattern within the cavity, while the alternating high-low refractive index layers further enhance this effect by controlling light propagation paths.
Solution Approach 2:
The movable mirror is constructed as a composite structure with alternating layers of high refractive index material (e.g., TiO2, Ta2O5) and low refractive index material (e.g., SiO2, air gaps). This composite layered structure achieves both high reflectivity for the desired wavelength and suppression of side modes through interference effects, while maintaining mechanical flexibility for voltage-tuned positioning.
2Volume of moving object
If the second mirror has high curvature (small radius of curvature), then the device structure is more compact, but side modes are enhanced and working distance is reduced
Solution Approach 1:
The patent specifies an optimal curvature radius range (R ≥ 10mm) that balances compactness with performance. This curvature value is large enough to suppress side modes by creating a near-planar wavefront, yet small enough to maintain a practical device footprint. The alternating refractive index layers work synergistically with this curvature to further suppress side modes through optical interference.
3Reliability
If the working distance between the device and fiber is increased, then coupling efficiency improves, but the device size increases
Solution Approach 1:
The spherical curvature of the movable mirror (R ≥ 10mm) creates a focused beam profile that maintains high coupling efficiency over increased working distances. The curved surface acts as a built-in lens, collimating and focusing the optical beam to match the fiber's mode field distribution, thereby enabling efficient coupling at larger separations without requiring additional external lenses.
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 allows for lower operating voltages, a wider range of tuned frequencies, and improved side-mode suppression, enhancing the device's performance and versatility in optical filtering applications.
Implementation Method 1
The first and second mirrors define a resonant cavity of a Fabry-Perot etalon configured to filter the optical signal along the optical path
Implementation Method 2
The second mirror has alternating layers stacked with alternating higher and lower refractive indices. Each of the layers has at least one structural parameter, which is configured to reduce the 'curvature' (i.e., increase a radius of curvature) of the second mirror
Implementation Method 3
The first and second electrodes are configured to tune the resonant cavity
Data Source
AI summary
An optoelectronic device, including a tunable optical filter or tunable optical filter with photodiode, uses voltage differentials to filter an optical signal passing along an optical path. A membrane has an electrode and is disposed adjacent a fixed mirror and another. A central portion of the membrane is distanced from the fixed mirror and has an aperture in which a second mirror is disposed. This second mirror translates with the membrane at a freespace gap relative to the fixed mirror when the electrodes are subject to the voltage differentials. In turn, the freespace gap is configured as a Fabry-Perot etalon to pass one or more spectral frequencies of the optical signal along the optical path. The membrane is shaped and reinforced to limit possible bowing. The translatable mirror in the aperture of the membrane is also shaped and reinforced to limit it from possible bowing as well.