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Register a new userLow-loss integrated nanophotonic circuits with layered semiconductor materials
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Monolayer transition metal dichalcogenides with direct bandgaps are emerging candidates for microelectronics, nano-photonics, and optoelectronics. Transferred onto photonic integrated circuits (PICs), these semiconductor materials have enabled new classes of light-emitting diodes, modulators and photodetectors, that could be amenable to wafer-scale manufacturing. For integrated photonic devices, the optical losses of the PICs are critical. In contrast to silicon, silicon nitride (Si3N4) has emerged as a low-loss integrated platform with a wide transparency window from ultraviolet to mid-infrared and absence of two-photon absorption at telecommunication bands. Moreover, it is suitable for nonlinear integrated photonics due to its high Kerr nonlinearity and high-power handing capability. These features of Si3N4 are intrinsically beneficial for nanophotonics and optoelectronics applications. Here we report a low-loss integrated platform incorporating monolayer molybdenum ditelluride (1L-MoTe2) with Si3N4 photonic microresonators. We show that, with the 1L-MoTe2, microresonator quality factors exceeding 3 million in the telecommunication O-band to E-band are maintained. We further investigate the change of microresonator dispersion and resonance shift due to the presence of 1L-MoTe2, and extrapolate the optical loss introduced by 1L-MoTe2 in the telecommunication bands, out of the excitonic transition region. Our work presents a key step for low-loss, hybrid PICs with layered semiconductors without using heterogeneous wafer bonding.
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Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth as well as compatibility for embedding into integrated photonic circuits are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around 1.55 um wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser.
Materials with a zero refractive index support electromagnetic modes that exhibit stationary phase profiles. While such materials have been realized across the visible and near-infrared spectral range, radiative and dissipative optical losses have hindered their development. We reduce losses in zero-index, on-chip photonic crystals by introducing high-Q resonances via resonance-trapped and symmetry-protected states. Using these approaches, we experimentally obtain quality factors of 2.6*10^3 and 7.8*10^3 at near-infrared wavelengths, corresponding to an order-of-magnitude reduction in propagation loss over previous designs. Our work presents a viable approach to fabricate zero-index on-chip nanophotonic devices with low-loss.
Optical nonlinearity plays a pivotal role in quantum information processing using photons, from heralded single-photon sources to long-sought quantum repeaters. Despite the availability of strong light-atom interaction, an all-optical nonlinearity is highly desired for more scalable quantum protocols. Here, we realize quantum nanophotonic integrated circuits in thin-film InGaP with a record-high second-order optical nonlinearity of $1.5%$---the ratio of the single-photon trimodal coupling strength ($g/2pi=11.2$ MHz) and cavity-photon loss rate. We demonstrate photon-pair generation via degenerate spontaneous parametric down conversion in the InGaP photonic circuit with an ultrahigh rate exceeding 27.5 MHz per 1 $mu$W pump power and large coincidence-to-accidental ratio up to $1.4times 10^4$. Our work shows InGaP as a potentially transcending platform for quantum nonlinear optics and quantum information applications.
Nonlinear photonics based on integrated circuits has enabled applications such as parametric amplifiers, soliton frequency combs, supercontinua, and non-reciprocal devices. Ultralow optical loss and the capability for dispersion engineering are essential, which necessitate the use of multi-mode waveguides. Despite that rich interaction among different spatial waveguide eigenmodes can give rise to novel nonlinear phenomena, spatial mode interaction is typically undesired as it increases optical loss, perturbs local dispersion profile, and impedes soliton formation. Adiabatic bends, such as Euler bends whose curvature varies linearly with their path length, have been favoured to suppress spatial mode interaction. Adiabatic bends can essentially connect any two waveguide segments with adiabatic mode conversion, thus efficiently avoid mode mixing due to mode mismatch. However, previous works lack quantitative measurement data and analysis to fairly evaluate the adiabaticity, and are not based on photonic integrated circuits with tight optical confinement and optical losses of few dB/m. Here, we adapt, optimize, and implement Euler bends to build compact racetrack microresonators based on ultralow-loss, multi-mode, silicon nitride photonic integrated circuits. The racetrack microresonators feature a small footprint of only 0.21 mm^2 for 19.8 GHz FSR. We quantitatively investigate the suppression of spatial mode interaction in the racetrack microresonators with Euler bends. We show that the optical loss rate (15.5 MHz) is preserved, on par with the mode interaction strength (25 MHz). This results in an unperturbed microresonator dispersion profile. We further demonstrate single soliton of 19.8 GHz repetition rate. The optimized Euler bends and racetrack microresonators can be key building blocks for integrated nonlinear photonic systems, programmable processors and photonic quantum computing.
Diamond integrated photonic devices are promising candidates for emerging applications in nanophotonics and quantum optics. Here we demonstrate active modulation of diamond nanophotonic circuits by exploiting mechanical degrees of freedom in free-standing diamond electro-optomechanical resonators. We obtain high quality factors up to 9600, allowing us to read out the driven nanomechanical response with integrated optical interferometers with high sensitivity. We are able to excite higher order mechanical modes up to 115 MHz and observe the nanomechanical response also under ambient conditions.
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