Fig. 1. (a) Relationship between waveguide width and effective refractive indices of propagating modes in SiN waveguides at a wavelength of 1550 nm. (b) Bending loss at 90° angle with respect to the bend radius. (c) Cross-sectional view of SiN waveguides. (d) SEM image of as-fabricated SiN-MRRs.

Fig. 2. (a) Coupling measurement platform for samples; (b) schematic illustration of femtosecond laser processing setup; (c) ultrathin nanosheets fabricated based on multilayer SiN-MRR configuration.

Fig. 3. (a) Low-magnification TEM image with the corresponding selected-area electron-diffraction pattern; (b) enlarged view of area shown in (a); (c) TEM-EDS elemental mappings and spectra of laser-modified SiN layer; (d) region A in (b) with the corresponding FFT pattern; (e) region B in (b) with the corresponding HRTEM image; (f) TEM-EDS elemental mappings and spectra of as-fabricated SiN waveguides.

Fig. 4. (a) Variation in transmission spectra of 10 SiN-MRRs at different locations on an 8-inch wafer; (b) variations in resonance wavelength of SiN-MRRs subjected to various laser energy, with the corresponding first trimming at a laser energy of 2.1 nJ depicted in the inset; (c) parameters a and t representing the coupling regimes of SiN-MRRs before and after laser modification, along with the corresponding transmission spectra within the C-band; (d) performance variations of SiN-MRRs before and after the second laser modification at a laser energy of 2 nJ.

Fig. 5. (a) Normalized resonance spectra of second-order MRRs after femtosecond laser manipulation; (b) normalized resonance spectra of upper MRR after two iterations of femtosecond laser manipulation. In the inset, 1st-T and 2nd-T refer to first and second trimmings, respectively.

Fig. 6. (a) Comparison of passband characteristics of filters comprising first- and second-order MRRs; (b) simulation results of second-order MRR-based four-channel WDM; (c) schematic representation of second-order MRR filters. (d) SEM image of as-fabricated four-channel WDM; spectra of second-order MRR-based four-channel WDM (e) before and (f) after femtosecond laser tuning.