Fig. 1. (a) Schematic diagram of the Si3N4-to-aSi:H-to-III-V coupler. (a1)–(a8) Fundamental TE (TE0) modes at different cross-sections along the coupler (SCH, separate-confinement heterostructure; MQWs, multi-quantum wells). Field plots of (b) aSi:H-to-Si3N4 coupling and (c) III-V-to-aSi:H coupling along the cross-section. (d) Coupling loss and TE0 reflection and (e) optical confinement in wells as a function of lateral misalignment for the III-V-to-aSi:H coupler. (f) Coupling loss and (g) optical confinement in wells as a function of BCB thickness under different lateral misalignments for the III-V-to-aSi:H coupler.

Fig. 2. (a) Microscope picture of the proposed tunable laser. (b) Corresponding schematic diagram of the cavity structure (MRR, micro-ring resonator; MMI, multimode interferometer). (c) A zoom-in view of the micro-transfer-printed III-V gain section on aSi:H/Si3N4 waveguides. (d) SEM image of a cross-section of the micro-transfer printed III-V gain element on the aSi:H/Si3N4 waveguide.

Fig. 3. Calculated and measured loaded quality factor (a) and drop port loss (b) as a function of self-power coupling ratio. (c) A microscope picture of the MRR test structure. (d) A measured pass-port spectrum of a 600-nm-gap MRR and its theoretical fitting.

Fig. 4. (a) Schematic structure of MRRs inside the loop mirror. (b) Schematic structure of MRRs followed by a loop mirror. (c) A typical reflection spectrum of a cascade of MRRs followed by a loop mirror [structure in (b)], and the corresponding reflection spectrum of each MRR. Comparison of the reflection spectra (d) and the effective lengths (e) of the structures depicted in (a) and (b) when the same MRRs are employed in both structures. (f) A zoom-in view of the reflection spectra at the resonance peak. (g) Loss penalty as a function of Si3N4 waveguide loss.

Fig. 5. (a) Vernier inner SMSR as a function of Vernier FSR for different radii (delta: radius difference between the two MRRs, which varies with the Vernier FSR). (b) Effective index dispersion of the Si3N4 waveguide. (c) Vernier outer SMSR as a function of resonant wavelengths while tuning the refractive index of one MRR. (d) Corresponding reflection spectra at different resonant wavelengths (upper part: a zoom-in view of resonance peaks).

Fig. 6. (a) Simulated temperature distribution of the waveguide cross-section. (b) Phase shift of fundamental TE mode versus heater power. (c) 2π phase shift power and extra waveguide loss as a function of TOX thickness. (d) Heater temperature under 2π phase shift power as a function of TOX thickness. (e) 2π phase shift power and extra waveguide loss as a function of heater offset. (f) Heater temperature under 2π phase shift power as a function of heater offset.

Fig. 7. (a) Schematic diagram of the micro-heater on the MRR. (b) Simulated temperature distribution on top of the MRR. (c) Microscope picture of a standalone MRR for tuning efficiency measurements. (d) Pass-port transmission spectra under heater tuning. (e) Simulated and measured phase shift and extracted loaded Q-factor as a function of heater power.

Fig. 8. Schematic process flow of (a)–(h) active coupons on III-V-substrate for micro-transfer printing, and (i)–(m) Si3N4/aSi:H circuits and preparation on the target substrate, and (n)–(p) heterogeneous integration and postprocessing.

Fig. 9. (a) Transmission spectrum of the reference waveguide with grating couplers at both sides. (b) LIV curve of III-V on the Si3N4 tunable laser. (c) Laser frequency noise spectrum at 1571.56 nm (inset: zoom-in view of the spectrum from 20 MHz to 40 MHz). (d) Two-dimensional output power tuning map of the laser. (e) Optical spectra under different operation wavelengths. (f) Lorentzian linewidth as a function of wavelength.

Fig. 10. (a) Fiber-coupled output power and laser linewidth as a function of heater power of phase tuning section. (b) Frequency noise spectra under different biases of phase tuning section.

Fig. 11. (a) Fiber-coupled output power as a function of heater power on one MZI arm. (b) Optical spectra at different MZI phases. (c) LI curves at different biases of the heater (inset: zoom-in view of the curves from 60 mA to 90 mA). (d) Threshold current and fiber-coupled slope efficiency as a function of MZI heater power.