Cross-Connected Ring Resonator Filter for Tunable Laser SMSR
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Solution Overview
Problem
Current widely tunable lasers lack a sufficiently high extinction ratio over a wide wavelength range, which limits their Side-Mode Suppression Ratio (SMSR) and performance stability during wavelength tuning.
Innovation Solution
A reflecting filter with a cross-connected ring resonator configuration and codirectional couplers is used to filter and reflect optical signals, ensuring high extinction ratio and improved SMSR by tuning the ring resonators to equal predetermined wavelengths, and integrating the gain section and filter monolithically on a silicon substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ring resonators are used to filter optical signals, then the laser can achieve wavelength tuning capability, but the extinction ratio is insufficient over a wide wavelength range, limiting SMSR performance
Solution Approach 1:
The single ring resonator is segmented into multiple ring resonators (first ring resonator, second ring resonator, etc.) that operate at different predetermined wavelengths. Each ring resonator handles a specific wavelength band, and their combined filtering effect achieves high extinction ratio across the entire wide wavelength range, resolving the contradiction between narrowband high extinction ratio and wideband tuning capability
Solution Approach 2:
The invention transitions from a single-dimensional wavelength filtering approach to a multi-dimensional approach by introducing multiple ring resonators with different resonance wavelengths. This creates a hierarchical filtering structure where each ring resonator operates in its own wavelength dimension, collectively providing high extinction ratio across the full wavelength spectrum
2Reliability
If a single ring resonator is used for wavelength selection, then the device complexity is low, but the SMSR and performance stability over wide wavelength range are insufficient
Solution Approach 1:
The filtering function is segmented across multiple ring resonators, each optimized for specific wavelength ranges. This segmentation allows each resonator to maintain simple structure while the collective system achieves high reliability and stability across the full tuning range, as each segment contributes to overall performance without requiring any single component to be overly complex
Solution Approach 2:
The multiple ring resonators are designed to work together as a unified filtering system, where each resonator performs the same basic filtering function but at different wavelengths. This multi-functionality approach allows the system to maintain consistent performance characteristics across the entire wavelength range while using identical or similar resonator structures, balancing complexity and reliability
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 enhances the SMSR of widely tunable lasers by suppressing undesirable resonances over a wide wavelength range, improving performance stability and achieving high extinction ratios.
Implementation Method 1
a first and second ring resonator adapted to filter optical signals at the predetermined wavelength λ
Implementation Method 2
the first codirectional coupler is adapted to receive the incoming optical signal and to split it in a first main signal and a second main signal
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention relates to a reflecting filter (100), for widely tunable laser, adapted to filter and reflect an incoming optical signal (IS) so as to select a predetermined wavelength λ, the reflecting filter (100), comprising: - a bidirectional port (1); - an output (2); - a first, a second and a third codirectional couplers (CDC1, CDC2, CDC3); and - a first and second ring resonator (RR1, RR2) adapted to filter optical signals at the predetermined wavelength λ; wherein a incoming signal (IS) is filtered at predetermined wavelength λ by the ring resonators (RR1, RR2) and reflected, the ring resonators (RR1, RR2) being cross-connected so to achieve a better suppression of undesirable resonances over a wide wavelength range. Consequently a widely wavelength tunable laser comprising such a reflecting filter (100) will have a better side-mode suppression ratio - SMSR.