Silicon and silicon nitride photonic circuits for spectroscopic sensing on-a-chip [Invited]

There is a rapidly growing demand to use silicon and silicon nitride（Si3N4） integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS technology,complex miniaturized circuits can be easily realized on a large scale and at a low cost covering visible to mid-IR wavelengths. In this paper we present our recent work on the development of silicon and Si3N4-based photonic integrated circuits for various spectroscopic sensing applications. We report our findings on waveguide-based absorption, and Raman and surface enhanced Raman spectroscopy. Finally we report on-chip spectrometers and on-chip broadband light sources covering very near-IR to mid-IR wavelengths to realize fully integrated spectroscopic systems on a chip.

Widely tunable,heterogeneously integrated quantum-dot O-band lasers on silicon

Heterogeneously integrated lasers in the O-band are a key component in realizring low-power optical interconnects for data centers and high-performance computing.Quantum-dot-based materials have been particularly appealing for light generation due to their ultralow lasing thresholds,small linewidth enhancement factor,and low sensitivity to reflections.Here,we present widely tunable quantum-dot lasers heterogencously integrated on silicon-on-insulator substrate.The tuning mechanism is based on Vernier dual-ring geometry,and a 47nm tuning range with 52 dB side-mode suppression ratio is observed.These parameters show an increase to 52nm and 58 dB,respectively,when an additional wavelength filter in the form of a Mach-Zehnder interferometer is added to the cavity.The Lorentzian linewidth of the lasers is measured as low as 5.3 kHz.

Integrated dispersion compensated mode-locked quantum dot laser

Quantum dot lasers are excellent on-chip light sources,offering high defect tolerance,low threshold,low temperature variation,and high feedback insensitivity.Yet a monolithic integration technique combining epitaxial quantum dot lasers with passive waveguides has not been demonstrated and is needed for complex photonic integrated circuits.We present here,for the first time to our knowledge,a monolithc offset quantum dot integration platform that permits formation of a laser cavity utilizing both the robust quantum dot active region and the versatility of passive GaAs waveguide structures.This platform is substrate agnostic and therefore compatible with the quantum dot lasers directly grown on Si.As an illustration of the potential of this platform,we designed and fabricated a 20 GHz mode-locked laser with a dispersion-engineered on-chip waveguide mirror.Due to the dispersion compensation effect of the waveguide mirror,the pulse width of the mode-locked laser is reduced by a factor of 2.8.