Fig. 1. Schematic of on-chip flat-top filter

Fig. 2. Simulated spectra of flat-top filter under differentt2. (a) Output spectra of out1 port under differentt2; (b) spectra of the two output ports when t2=0.23; (c) enlarged view of the spectrum of out1 port

Fig. 3. Top view and related structure parameters of on-chip flat-top filter

Fig. 4. Simulated spectra of flat-top filter under different g. (a) Output spectra of out1 port under different g; (b) spectra of the two output ports when g=0.25 μm; (c) enlarged view of the spectrum of out1 port

Fig. 5. Metallographic micrograph of proposed flat-top filter. (a) Whole filter; (b) symmetrical 2×2 MMI; (c) all-pass RMRR

Fig. 6. Experimental spectra of flat-top filter when there is no temperature change. (a) Spectra of the two output ports; (b) enlarged view of the spectrum of out1 port

Fig. 7. Relationship between voltage and temperature

Fig. 8. Output spectra of flat-top filter when heating temperature changes. (a) 0-6.31 ℃; (b) 6.31-18.53 ℃; (c) 18.53-36.81 ℃; (d) 36.81-54.49 ℃