Model-based spectral shaping technique for WSSs with insertion loss and ripple penalties consideration

The bandwidth narrowing effect introduced by cascaded wavelength-selective switches (WSSs) has emerged as a critical factor limiting communication system performance, particularly in future systems employing higher baud rates and advanced modulation formats. As a widely adopted solution, spectral shaping through the attenuation control of WSSs enhances channel bandwidth. However, determining the optimal attenuation profile across channel slices remains challenging due to the optical intensity overlap between neighboring slices and the absence of a suitable physical model for the spectral shaping process. Furthermore, the relationship between bandwidth enhancement and the corresponding insertion loss (IL) and ripple penalties during WSS spectral shaping has not been systematically investigated. To address these issues, what we believe to be a novel WSS filtering model is proposed and integrated into a gradient descent algorithm to iteratively determine the optimal attenuation profile under given constraints on IL and ripple penalties. In addition, we have quantified the trade-off relationship among bandwidth enhancement, IL penalty, and ripple penalty during the spectral shaping process through simulations and experiments. These results show close agreement, identifying a generally practical and advantageous strategy that trades off 0.5 dB of IL and 0.3 dB of ripple for bandwidth enhancement. Furthermore, under this set of constraints, experimental results validate that our approach achieves a mean enhancement of 1.9 GHz and 0.76 GHz in 0.5-dB and 3-dB bandwidths, respectively. These findings contribute to optimizing spectral shaping in WSSs and provide valuable guidance for practical system design.