Quantum Key Distribution (QKD) directly exploits the quantum phenomenon of entanglement to allow the secure sharing of a cryptographic key for information encoding. The current generation of QKD devices typically operate over dedicated and expensive private ‘dark fiber’ networks, where they are limited in transmission range to 200-300km due to the lack of quantum repeaters. This paper is concerned with an alternative approach that can lift this range limit by exploiting QKD over free-space links between satellites. Typically, commercial QKD systems rely on phase encoding of information on single photons, and more recently on continuously variable schemes with more powerful lasers. However, these protocols are not suitable for communications through atmosphere. On the other hand, QKD by polarization-entanglement holds great promise for satellite-based QKD encoded communications links if the entangledphoton source can be packaged in a compact, robust and commercially-viable form. This paper will describe the development and packaging of an entangled-photon source utilizing space-qualified telecoms packaging techniques, resulting in a compact device that targets satellite deployment. The key design choices that impact performance in a space environment will be discussed and the results of device characterization in the laboratory environment will be shared.
A dual modality fibre sensing system for simultaneous monitoring of temperature and acoustic disturbances in power cables is demonstrated. The system combines Raman OTDR (Optical Time-Domain Reflectometry) and Rayleigh phase- OTDR and is based on a single shared laser source. The performance of the system is demonstrated with absolute temperature measurements in heated fibre sections and detection of echoes from disturbance events. To the best of our knowledge, this is the first single-source simultaneous temperature and disturbance sensing in single-mode fibre. Finally, it is demonstrated that localised temperature variations and acoustic disturbances, such as cable strumming and strike, can be detected in an onshore 30 kV power cable.
This paper will present developments in narrow-linewidth semiconductor-disk-laser systems using novel frequencystabilisation schemes for reduced sensitivity to mechanical vibrations, a critical requirement for mobile applications. Narrow-linewidth single-frequency lasers are required for a range of applications including metrology and highresolution spectroscopy. Stabilisation of the laser was achieved using a monolithic fibre-optic ring resonator with free spectral range of 181 MHz and finesse of 52 to act as passive reference cavity for the laser. Such a cavity can operate over a broad wavelength range and is immune to a wide band of vibrational frequency noise due to its monolithic implementation. The frequency noise of the locked system has been measured and compared to typical Fabry-Perotlocked lasers using vibration equipment to simulate harsh environments, and analysed here. Locked linewidths of < 40 kHz have been achieved. These developments offer a portable, narrow-linewidth laser system for harsh environments that can be flexibly designed for a range of applications.
Commercially available supercontinuum sources continue to experience a strong growth in a wide range of industrial and scientific applications. In addition, there is a significant research effort focused on extending the wavelength coverage both towards UV and Mid-IR. Broadband sources covering these wavelength regions have received significant attention from potential users, as there is a wide array of applications for which there are few suitable alternative light sources – if any. Our developments in the field of Mid-IR supercontinuum sources have been based on radical approaches; such as soft glasses and novel pumping schemes, whereas shifting the spectrum further towards the UV has been based on sophisticated microstructure fiber designs. Here we present our latest developments in tailoring the power and spectral coverage of spatially coherent broadband supercontinuum sources.