We report on a sensitive methane gas detection system using waveguide-based single-photon upconversion from 1651 nm to 798 nm wavelength for efficient detection. Single-photon light detection and ranging (LIDAR) techniques offer a route to high-sensitivity direct detection, which is important for environmental monitoring in industrial settings. We report on waveguide fabrication, testing, and overall system development using a fibre-pigtailed waveguide package. We achieve an internal upconversion efficiency of 86%. By combining this system with an active imaging module, we demonstrate methane gas sensing in an outdoor environment. We show this approach is a practical route to enhance the sensitivity of cost-effective environmental monitoring systems.

The realization of quantum networks requires the development of robust, low-size, weight, and power (SWaP) systems suitable for operation under harsh environments in remote and mobile nodes such as satellites. We present a source of polarization-entangled photon-pairs in a folded linear displacement interferometer based on spontaneous parametric down conversion using a Type-0 periodically poled potassium titanyl phosphate crystal. Featuring a compact and stable double-pass geometry using a corner-cube retroreflector, the source has a detected pair rate of 2.5 M pairs/s/mW with a Bell state fidelity of 94.1% ± 2.1%. The qualities and demonstrated performance of the source make it suitable for deployment in entanglement-based quantum networks.

Characterization of a single photon detector without direct measurement of input photon flux is presented. With calibration of optical power with laser attenuation, the detector is characterized without changing configuration for input photon flux measurement.

We have developed a novel millimetre-sized monolithic fibre-coupled rubidium saturated absorption spectroscopy laser reference suitable for quantum sensing applications. It is based on our novel MEMs vapour cell technology and bonding of optical elements to create a monolithic spectroscopy module. Our unit reproduces the signal visibility of a 70 mm long cell and is compatible with standard packaging techniques. The unit has no free-space elements that would otherwise be subject to vibration. Our reference uniquely combines the qualities of robustness, miniaturisation and signal strength providing an optimal solution for mobile quantum sensing platforms including space and aerospace.

We demonstrate a source of polarization-entangled photons based on periodically poled lithium niobate waveguides that produces pairs of entangled photons at a rate of 1.25 gigahertz and a CHSH entanglement parameter of 2.73.

We present efficient single-photon upconversion detection from SWIR using a precision-machining waveguide fabrication process that offers high power handling and good mode coupling. We demonstrate an internal photon upconversion efficiency of 69%.

Free-space optical links are important for "last-mile" connectivity of future classical and quantum networks, in locations where it is impractical or too costly to run optical fibre. In this presentation, we will discuss the challenges such links present, and strategies for overcoming these. Results of a building-to-building test of such a link over approximately 150 m will be presented.

Silicon nitride (Si3N4) is an excellent material platform for visible wavelength photonic integrated circuits, in particular, as a host for the heterogeneous/hybrid integration of complementary materials. In this work, we characterise the performance of the Si3N4 from LIGENTEC as a base for hybrid integration.

Here, we report on the development of a diode-pumped single-frequency transition-metal-doped crystalline lasers designed in a miniature Fabry-Perot-type resonator by utilizing a narrow-bandwidth volume Bragg grating output coupler. Namely, single-longitudinal-mode operation was achieved from Ti:sapphire and Alexandrite lasers with a maximum output power of 570 mW and 275 mW near 813 nm and 780 nm, respectively. The mode-hop-free laser frequency tunability of up to 30 GHz was achieved by the cavity temperature and length variation with the Ti:sapphire system. The laser linewidth was measured to be in the 180 kHz range when locked to an external reference cavity transmission peak.

In this Letter, we report on the development of an ultra-compact single-frequency Ti:sapphire laser under direct diode pumping. Single-longitudinal-mode operation is realized from a miniature plane-parallel resonator using a volume Bragg grating as an output coupler. InGaN laser diodes operating at around 470 nm and 490 nm with a combined power of 6.7 W are used as an optical pump. A maximum output power of 700 mW is generated during single-frequency operation at 813.4 nm. A laser linewidth of 2.4 MHz is measured during free-running operation, which is reduced to about 180 kHz when the laser is locked to an external reference cavity.

We report a nonlinear optical upconversion 3D imaging system for infrared radiation enabled by zinc indiffused MgO:PPLN waveguides. While raster-scanning a scene with an 1800 nm pulsed-laser source, we record time-of-flight information, thus probing the 3D structure of various objects in the scene of interest. Through upconversion, the 3D information is transferred from 1800 nm to 795 nm, a wavelength accessible to single-photon avalanche diode (SPAD).

We report on GaN lasers with extremely narrow linewidth (~1MHz) at ‘magic wavelengths’ for cold-atom quantum sensors and optical atomic clocks, using extended cavity GaN laser diodes and DFB GaN laser diodes.

The stand-off, range-resolved detection of hydrogen production rates is a valuable mechanism for the long-term condition monitoring of packages containing intermediate-level nuclear materials. To exploit this effect we have developed a long-range optical sensor system which uses Raman detection of hydrogen. Our need for operation over extended ranges (up to 100m) results in very low Raman signals. We therefore use time-correlated (with respect to the outgoing excitation laser pulse) and spectrally-resolved single-photon detection to ascertain molecular species, position and concentration as revealed by photon energy, arrival time and number, respectively.

We have optimised the design and fabrication of low-loss type-I femtosecond-laser-written waveguides in PPLN that are single-transverse mode at 780 nm and 1560 nm and mode-matched to single-mode fibres. Spontaneous parametric downconversion (SPDC) has been demonstrated at 1560 nm when pumped with a 780 nm DFB laser and has been characterised with measurement of the second-order cross-correlation g(2) using superconducting nanowire detectors. This novel approach to waveguide fabrication in PPLN offers routes to high levels of integration and high generation rates which is important for many quantum-information applications.