Rex H. S. Bannerman

High-birefringence direct UV-written waveguides for use as heralded single-photon sources at telecommunication wavelengths

Direct UV-written waveguides are fabricated in silica-on-silicon with birefringence of (4.9 ± 0.2) × 10-4, much greater than previously reported in this platform. We show that these waveguides are suitable for the generation of heralded single photons at telecommunication wavelengths by spontaneous four-wave mixing. A pulsed pump field at 1060 nm generates pairs of photons in highly detuned, spectrally uncorrelated modes near 1550 nm and 800 nm. Waveguide-to-fiber coupling efficiencies of 78-91 % are achieved for all fields. Waveguide birefringence is controlled through dopant concentration of GeCl4 and BCl3 using the flame hydrolysis deposition process. The technology provides a route towards the scalability of silica-on-silicon integrated components for photonic quantum experiments.

Taking quantum entanglement out of the lab

The Networked Quantum Information Technologies hub (NQIT) is one of the quantum hubs of the UKs agship scheme, bringing together academia, industry and government. The Optical Engineering and Quantum Pho- tonics group at the University of Southamptons Optoelectronics Research Centre have developed an interactive demonstrator of a key device within NQIT to bring quantum photonics technologies to a wider audience. The system was exhibited at the 2017 UK Quantum Showcase in London to an audience of industry and government. It also featured as part of the Quantum City stand at the 2018 Cheltenham science festival, one of the UKs leading annual science events.

Taking large optical quantum states out of the lab: engaging pupils and the public on quantum photonics sciences

Novel research-inspired outreach activities allow scientists and members of the public to engage in a conversation, increasing the public’s understanding and interest in scientific research. This paper reviews outreach and public engagement initiatives undertaken by researchers from the University of Southampton’s Optical Engineering and Quantum Photonics Group during a 5-year research program grant entitled Building Large Optical Quantum States. The activities have been supported by a UK Engineering and Physical Sciences Research Council program grant and institutional, national and international professional organizations. The paper discusses activities and hand-outs that have been developed to increase the visibility and public understanding of integrated-photonics fabrication and testing facilities, including a cleanroom-based process for the design and fabrication of quantum outreach chips. More than 1,000 of these chips have been distributed to children, parents and government officials in public events and the activities have contributed towards the authors’ research group receiving the 2017 South East England Physics Network Highly Commended Award for Best Research Group. This paper also discusses the impact of these activities and lessons learned.

Direct UV-written integrated waveguides using 213nm light (Conference Presentation)

Direct UV writing is a technique capable of fabricating low-loss channel waveguides, couplers and Bragg gratings in planar silica devices by translating an appropriate substrate through a tightly focused UV beam. To date direct UV written waveguides have been primarily formed using 244nm laser light, relying on the photosensitivity provided by doping with germanium and boron. To induce sufficient refractive index change, necessary for wave guiding, the substrates also require hydrogenation prior to UV writing. Not only does this require additional processing but over time the hydrogen present within the silica out-diffuses, which can cause variation of the final written structures. Deep-UV light, with a wavelength of 213 nm, has previously been used to inscribe strong fibre Bragg gratings (FBGs) in hydrogen-free Ge-doped fibres. Here we present the use of a 213 nm UV laser to write planar waveguide devices without the need for hydrogen loading. Flame Hydrolysis Deposition (FHD) was used to deposit core and cladding layers of doped silica onto a thermally oxidised silicon wafer. Individual planar chips were diced from this wafer and a 5th harmonic Q-switched solid state laser operating at 213 nm wavelength was used to inscribe waveguides within the germanium-doped core layer of the chips without prior hydrogen loading. We shall present our latest results of direct deep-UV written waveguides, including; the characterisation of single mode waveguides, detailed fluence and loss measurements, induced refractive index change and the first demonstration of planar Bragg gratings and photonic structures written with 213nm light.

Developing PPLN Waveguides for Quantum Rubidium Atom Traps in Space

We demonstrate single mode zinc-indiffused MgO:PPLN ridge waveguides with insertion losses of <1.3 dB (2 cm device length), developed towards rubidium atom traps. We will report on fabrication, modal engineering, loss, and second harmonic generation.

Enhanced temperature sensitivity of thermally regenerated direct ultraviolet written gratings in germanium doped core fiber

The use of thermally regenerated gratings for monitoring harsh environments is becoming increasingly attractive due to their thermal resilience and high precision. They are a unique type of Bragg grating created through annealing UV-laser written Fiber Bragg Gratings (FBGs) at high temperatures (above 600°C) and they have been demonstrated to operate at temperatures over 1000 °C in oxygen free environments [1]. In this work we report two new observations. Firstly, a second phase thermal regeneration process at temperatures above 650 °C and secondly an enhanced thermal response for these second phase regenerated gratings of over 140%. Uniquely, fabrication of the gratings was made through a small spot Direct Ultraviolet Writing (DUW) process. This utilizes a high precision four-axis stage system and a frequency double argon-ion continuous wave 244 nm laser that is split and recombined at a focus to form a ∼7 μm diameter interferometric spot [2]. A series of 46 different FBGs, from 1400 to 1620 nm, were written into a single non-hydrogen loaded double clad germanium doped 4 μm core fiber (Nufern GF4A). Gratings in the series were written with fluences ranging from 0.05 kJ/cm2 up to 90 kJ/cm2.

High-birefringence direct-UV-written silica waveguides for heralded single-photon sources at telecom wavelengths

The reliable generation of high-quality single photons has long been a goal of research in photonic quantum information. Direct-UV-written (DUW) silica-on-silicon waveguides provide a reproducible, uniform, low-loss, and fiber-compatible platform for the integration of spontaneous four-wave mixing-based heralded single-photon sources [1]. To overcome limitations caused by Rayleigh scattering, which induces loss, and for compatibility with telecommunications equipment, it is desirable to move to the C-band. Waveguides with birefringence greater than 4.5×10−4 are required in this wavelength of operation [2]. We report the development of a high-birefringence silica-on-silicon integrated platform for heralded single-photon sources at telecom wavelengths.

A reconfigurable modular system for on-chip quantum optics

Quantum optics experiments are increasingly taking an integrated format for the benefits of phase stability and scalability. Silica has proved an advantageous material for this work due to its low propagation loss and high-efficiency coupling to optical fibre, and a number of key on-chip experiments have already been carried out with up to four photons using this material [1]. Fabrication imperfections create a number of difficulties in moving to more complex setups since the classical performance of the network must be characterised before an analysis of its quantum properties can be carried out, and this process becomes greatly more challenging as the circuit complexity grows.

Insertion loss characterisation for UV written Bragg gratings in fiber and planar waveguides

Integrated optical systems offer high component density in a compact, stable and robust platform. However, there are many situations in which it is useful to transition from an integrated waveguide to an optical fiber, such as long distance transmission. The loss associated with coupling between the two platforms can be critical in applications such as quantum information processing (QIP).

Direct UV written integrated planar waveguides fabricated with 213nm light

Direct UV written planar waveguides in silica have been explored for over two decades [1]. The technique is capable of fabricating low-loss channel waveguides, couplers and Bragg gratings by translating an appropriate substrate through a focused UV beam. To date direct UV written waveguides have been primarily formed by using 244nm laser light, relying on the photosensitivity provided by germanium doping, and also typically boron. To induce sufficient refractive index change necessary to form waveguides the substrates also require hydrogen and deuterium loading prior to UV writing [2]. Not only does this require additional processing but over time the hydrogen present within the silica depletes, which can cause variation of the final written structures. Deep UV light at 213 nm has previously been used to inscribe strong fibre Bragg gratings (FBGs) in hydrogen-free Ge-doped fibres [3]. Here we present the first use of a 213 nm UV laser to write planar waveguide devices without the need for hydrogen loading.