Fig. 1. (a) Schematic image of the hybrid tunable laser. Left top: top-view image of the RSOA array. Left bottom: well-packaged RSOA with current and TEC control. (b) Schematic diagram showing the resonant Vernier effect of the two ring resonators and the RSOA gain spectrum. (c), (d) Cross-sectional fundamental transverse electric (TE) mode for RSOA and Si rib waveguide, respectively. (e), (f) Top-view scanning electron microscopy (SEM) images of the taper and ring coupler. (g) Standard fabrication process of the passive chip.

Fig. 2. (a) Setup schematic for the characterization of MRRs. (b) Left: modulation depth of the ring resonator. Right: the waveform response with different frequency. (c) The fine scan for Q-factor calculation. (d) Top: the spectrum of center mode and side mode. Bottom: side peak resonances of two rings with 5% κ design. (e) The transmission of two ring shifts when heating Ring1 with 20 mW. (f) Resonance shift as a function of the heater power.

Fig. 3. (a) Transmission of MRRs during coarse tuning. Inset: coarse tuning map. (b) Transmission of MRRs during fine tuning. Inset: fine tuning map.

Fig. 4. Laser characterization results. (a) Hybrid laser measurement setup with TEC and current control. (b) Setup image. (c) Single-mode lasing with 40-dB SMSR at 2.02 μm. (d) L-I-V curve with 92-mA threshold current. (e) Tuning characteristic. (f) The 25-nm tuning range.

Table 1. Literature Overview of the State-of-the-Art Mid-infrared Lasers^a