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Applied Physics Express

High coincidence-to-accidental ratio continuous-wave photon-pair generation in a grating-coupled silicon strip waveguide

Kai Guo, Erik Nicolai Christensen, Jesper B. Christensen, Jacob G. Koefoed, Davide Bacco, Yunhong Ding, Haiyan Ou, Karsten K. Rottwitt

Published May 25, 2017• 43 citations
Publisher

Abstract

We demonstrate a very high coincidence-to-accidental ratio of 673 using continuous-wave photon-pair generation in a silicon strip waveguide through spontaneous four-wave mixing. This result is obtained by employing on-chip photonic-crystal-based grating couplers for both low-loss fiber-to-chip coupling and on-chip suppression of generated spontaneous Raman scattering noise. We measure a minimum heralded second-order correlation of , demonstrating that our source operates in the single-photon regime with low noise.

DOI
10.7567/apex.10.062801

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We demonstrate a very high coincidence-to-accidental ratio of 673 using continuous-wave photon-pair generation in a silicon strip waveguide through spontaneous four-wave mixing. This result is obtained by employing on-chip photonic-crystal-based grating couplers for both low-loss fiber-to-chip coupling and on-chip suppression of generated spontaneous Raman scattering noise. We measure a minimum heralded second-order correlation of , demonstrating that our source operates in the single-photon regime with low noise.
We observed high-purity correlated and entangled photon pairs generated through spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW). Employing a nano-scale silicon waveguide with a low loss mode size converter, we obtained a high coincidence to accidental coincidence ratio (CAR) of around 200 that was larger than that of cooled dispersion shifted fiber (DSF) by a factor 3.2, and observed the two-photon interference fringe of time-bin entangled photons with > 95% visibility without subtracting the accidental coincidences.
We report a comprehensive characterization of photon-pair generation by spontaneous four-wave mixing in a partially deuterated amorphous silicon (a-Si:D) waveguide for C-band heralded single-photon generation. In a 3.3-mm-long strip waveguide pumped with a continuous-wave laser at telecom wavelengths, we measure an on-chip pair-generation rate of 3.1 × 10 6 pairs/s, a maximum coincidence-to-accidental ratio of 66, and a heralded second-order correlation g H (2) (0)=0.058±0.002, with these values obtained at different pump powers. We also demonstrate, to the best of our knowledge, the first observation of time-energy entanglement from an amorphous silicon waveguide, with a Franson interference visibility of 77±5%. The power scaling of the singles and accidental coincidences indicates a significant noise contribution that currently limits the source performance. Our results identify a-Si:D as a promising nonlinear platform for bright, integrated photon-pair sources and future hybrid quantum photonic circuits.
Integrated silicon photonics has played an important role in advancing the applications of quantum information and quantum science. However, it is challenging to integrate all components with state-of-the-art performance using only a homogeneous platform. Here, by combining high nonlinearity and low losses in a heterogeneous silicon platform, we efficiently generate high-quality photon pairs through spontaneous four-wave mixing in a hydrogenated amorphous silicon waveguide and route them off-chip through a low-loss silicon nitride waveguide. A record high coincidence-to-accidental ratio value of 1632.6 (±260.4) is achieved in this heterogeneous design with a photon pair generation rate of 1.94 MHz. We also showcase a wide range of multichannel photon sources with a coincidence-to-accidental ratio consistently around 200. Lastly, we measure heralded single-photons with the lowest g H (2) (0) of 0.1085 ± 0.0014. Our results demonstrate the heterogeneous silicon platform as an ideal platform for the efficient generation of photon pairs and off-chip routing with low losses. It also paves the way for a future hybrid photonic integrated circuit by collecting distinct features from different materials.
We fabricate silicon waveguide spirals and a ring resonator to generate photon pairs based on a spontaneous four-wave mixing. The coincidence-to-accidental-ratio (CAR) of photon pairs from the silicon waveguides is measured up to 400 after a noise-filtering by using the combination of bandpass filters and pump-rejection filters. The CAR is enhanced up to 700 by adding on-chip pump-rejection MZIs. We observe the CAR of the photon pairs from a silicon spiral is highly depending on the wavelength detuning from the pump wavelength. We discuss the noise sources related to the degradation of the CAR based on our experimental results.