Bandwidth-tunable micro-ring filter enabled by multi-channel spectrum synthesis

Bandwidth-tunable optical filters are essential for dynamic wavelength-division multiplexing (WDM) systems. To overcome the limitations of conventional single-ring designs in balancing broad free spectral range and wide tuning range, and to suppress in-band ripple in cascaded-ring configurations, we propose a multi-channel micro-ring based spectral synthesis filter. The structure incorporates six micro-ring pairs (twelve rings in total), the input is split by six MRRs and recombined by another six MRRs. Key to the design is a dual-degree-of-freedom tuning mechanism: simultaneous adjustment of resonant wavelength spacing between adjacent and identical channel rings for bandwidth control, complemented by five phase shifts to minimize ripple. To manage the high-dimensional parametric synergetic puzzle with 12 micro-rings and 5 phase shifts, We employ particle swarm optimization (PSO) with the objective of achieving low insertion loss, an in-band ripple of less than 1 dB, and a shape factor greater than 0.25.The result shows can be continuously tuned from 0.27 nm to 3.6 nm (33.75–450 GHz), with in-band ripple 20 dB/nm, and insertion loss below 5 dB (as low as 1.2 dB at 0.4 nm bandwidth). This work demonstrates a high-performance, reconfigurable filtering solution for dynamic optical networks through structural innovation and intelligent optimization.