Mid-infrared quantum optics in silicon
: Light work with long waves

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Integrated quantum photonics promises to fundamentally transform how we sense, transmit and process information. Applications of quantum optics in fields such as remote sensing, communications, and information technology will all be revolutionised, provided that in scaling up, performance is preserved. Silicon quantum photonics has shown complex, repeatable, and miniaturised integrated photonics circuits. These are fabricated with industry standard CMOS compatible techniques, but linear and nonlinear optical loss limit scalability. In this work, we show that translating to the midinfrared yields a technology platform that simultaneously maximises manufacturability and large scale component integration, while reducing nonlinear loss.

Demonstrating a bright source of quantum correlated photons, suppression of the pump laser to the single photon level, efficient detection, and high visibility quantum interference are all essential ingredients for establishing the viability of any quantum
optics platform. This thesis details these necessary steps for experimentally realising the generation and manipulation of photon-pairs in the 2.1 µm band in crystalline silicon

We show integrated passive structures such as waveguides, grating couplers, edge couplers, directional couplers and multi-mode interference couplers. A sources of photonpairs from spontaneous four-wave mixing is realised by combining these components
into reconfigurable waveguide circuits. At a wavelength of 2.07 µm, a waveguided measurement of the nonlinear refraction finds n2 = 15.3 × 10−18 m2/W and the two-photon absorption coefficient α2 = 0.557 cm/GW, showing an improvement over the 1.55 µm telecommunication band. In various silicon waveguide photon-pair sources, we measure a maximum net coincidence rate of 896 Hz, a coincidence-to-accidental ratio of 25.7 and
a net two-photon interference visibility of 99.3 %, demonstrating the first quantum interference in the mid-infrared on a silicon chip
Date of Award12 May 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorKrishna Coimbatore Balram (Supervisor) & Joshua W Silverstone (Supervisor)

Cite this