Fig. 1. Structural diagrams. (a) Add-drop MRR; (b) rectangle filter

Fig. 2. Output spectra of rectangle filter

Fig. 3. Design of ultra-small size rectangle filter. (a) 3D diagram; (b) top view and related structural parameters

Fig. 4. Output spectra of add port. (a) Output power varying with l_s; (b) output power varying with w_s

Fig. 5. Output spectra of add port. (a) Output power varying with g₁; (b) output power varying with g₂

Fig. 6. Optimized output spectra of ultra-small size rectangle filter

Fig. 7. Performance variations of filter when g₁ and g₂ have fabrication errors. (a) Ripple coefficient; (b) shape factor; (c) sidelobe suppression ratio; (d) insertion loss

Fig. 8. Performance variations of filter when l_s and w_s have fabrication errors. (a) Ripple coefficient; (b) shape factor; (c) sidelobe suppression ratio; (d) insertion loss

Fig. 9. Improvement of performance of filter by adding heaters. (a) Structural diagram; (b) optimized spectra of filter when g₁ and g₂ have fabrication errors; (c) optimized spectra of filter when l_s and w_s have fabrication errors

Fig. 10. Combination of add port and drop port. (a) Schematic diagram of structure; (b) optimized transmission spectrum