Generation of multiphoton quantum states on silicon

Multiphoton quantum states play a critical role in emerging quantum technologies and greatly improve our fundamental understanding of the quantum world.Integrated photonics is well recognized as an attractive technology offering great promise for the generation of photonic quantum states with high-brightness,tunability,stability,and scalability.Herein,we demonstrate the generation of multiphoton quantum states using a single-silicon nanophotonic waveguide.The detected four-photon rate reaches 0.34 Hz even with a low-pump power of 600μW.This multiphoton quantum state is also qualified with multiphoton quantum interference,as well as quantum state tomography.For the generated four-photon states,the quantum interference visibilities are greater than 95%,and the fidelity is 0.78±0.02.Furthermore,such a multiphoton quantum source is fully compatible with the on-chip processes of quantum manipulation,as well as quantum detection,which is helpful for the realization of large-scale quantum photonic integrated circuits(QPICs)and shows great potential for research in the area of multiphoton quantum science.

Ultra-compact lithium niobate microcavity electro-optic modulator beyond 110 GHz

A lithium-niobate-on-insulator(LNOI)electro-optic(EO)modulator based on a 2×2 FP-cavity was designed and realized with an ultra-compact footprint and an ultra-high bandwidth.A comprehensive analysis on the present LNOI FP-cavity modulator was conducted to reveal the dependence of modulation bandwidth and modulation effi-ciency on the cavity Q-factor and the operation wavelength detuning to the resonance.In particular,the 2×2 FP cavity was designed to achieve an optimal Q factor by reducing the reflectivity of reflectors and the cavity length,thus reducing the photon lifetime in the cavity.An ultra-short effective cavity length of only∼50μm was achieved for the designed LNOI FP-cavity modulator,with itsfootprint being as compact as∼4×500μm 2.It was demonstrated theoretically that the modulation bandwidth could be improved significantly to be over 200 GHz by utilizing the peaking enhancement effect.The fabricated device exhibited an excess loss of∼1 dB and an extinction ratio of∼20 dB in experiments,while the measured 3-dB bandwidth was higher than 110 GHz(beyond the maximal range of the facilities in experiments).Up till now,to our best knowledge,this has been the first LNOI microcavity modulator with a bandwidth higher than 110 GHz.Finally,high-quality eye-diagrams of 100 Gbps on-off keying(OOK)and 140 Gbps 4-pulse amplitude modulation(PAM4)signals were demonstrated experimentally,and the energy consumption for the OOK signals was as low as 4.5 fJ/bit.

Ten-channel mode-division-multiplexed silicon photonic integrated circuit with sharp bends

A multimode silicon photonic integrated circuit(PIC) comprising a pair of on-chip mode(de)multiplexers with 10-mode channels and a multimode bus waveguide with sharp bends is demonstrated to enable multi-channel on-chip transmissions. The core width of the multimode bus waveguide is chosen such that it can support 10 guided modes, of which there are four transverse-magnetic polarization modes and six transverse-electric polarization modes. This multimode bus waveguide comprises sharp bends based on modified Euler curves. Experimental results demonstrate that the present silicon PIC enables the 10-channel on-chip transmission with a low inter-mode crosstalk of approximately-20 dB over a broad bandwidth of 1520–1610 nm even when the bending radius of the S-bend is as small as 40 μm. Compared with a silicon PIC using a conventional arc-bend with the same bending radius, our proposed PIC demonstrates a significant improvement.

Hybrid silicon nonlinear photonics [Invited]

Nonlinear silicon photonics has shown an ability to generate, manipulate, and detect optical signals on an ultracompact chip at a potential low cost. There are still barriers hindering its development due to essential material limitations. In this review, hybrid structures with some specific materials developed for nonlinear silicon photonics are discussed. The combination of silicon and the nonlinear materials takes advantage of both materials, which shows great potential to improve the performance and expand the applications for nonlinear silicon photonics.