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In this paper, the first demonstration of simultaneous UV written Bragg gratings and waveguides in germanium and boron‐doped planar silica is presented using a 5th harmonic solid‐state nanosecond laser operating at 213 nm wavelength. The fabrication of high‐quality gratings by using a high peak power density, yielding sufficient uniformity and without any surface damage is demonstrated. The photosensitivity of the doped silica layer is investigated by measuring the local effective refractive index of the optical modes. The written gratings are used to measure grating refractive index modulation, grating detuning bandwidth and the waveguide propagation loss with a minimum value of 0.28 ± 0.07 dB cm−1. This paper shows that this new generation of pulsed UV lasers is a promising alternative for conventional longer wavelength CW laser sources used in small spot direct grating writing in doped silica.

In this paper we present the first example of waveguides fabricated by UV writing in non-hydrogen loaded Ge-doped planar silica with 213 nm light. Single mode waveguides were fabricated and the numerical apertures and mode field diameters were measured for a range of writing fluences. A peak index change of 5.3 x 10 −3 was inferred for the waveguide written with 70 kJ cm −2. The refractive index change is sufficient to match the index structure of standard optical fiber. Uniformity of the written structures was measured and a propagation loss of 0.39 ± 0.03 dB cm −1 was determined through cutback measurements.

We report the first demonstration of integrated waveguides and Bragg gratings direct UV written into planar silica using a fifth harmonic 213 nm laser without hydrogen loading. We observe 0.44 ±0.26 dB cm − 1 propagation loss.

Consolidation of flame hydrolysis deposited silica soot with a 9.3 μm CO2 laser has been demonstrated. A range of laser parameters were investigated and the surface roughness of the resulting silica layers were characterised with a stylus profiler and white light interferometer. The surface roughness parameters were Ra = 68.9 nm, Rq = 83.8 nm perpendicular to the trajectory of the translated laser beam for a speed of 300 mm s-1 and an average laser power of 42.5 W, and Ra = 29.5 nm, Rq = 36.18 nm along the trajectory of the translated laser beam for a speed of 250 mm s-1 and an average laser power of 35.8 W.

Micromechanical devices are typically fabricated in expensive cleanrooms using techniques that are not conducive towards rapid and varied prototyping. This is typically because photolithography remains the main method for patterning of layers and should a small change be desired in the design, a new mask would have to be made, which is both a costly and slow process. This work reports a laser based approach for micromechanical diaphragm fabrication. The technique uses rapid thermal heating and subsequent quenching to a pattern a hard thermal oxide layer on a silicon substrate. This method used a computer controlled 9.3 micrometre wavelength CO 2 laser beam to spot mark areas that were subsequently wet etched. This approach was found to be extremely repeatable and gave good consistency. It does not require cleanroom processing and is significantly more cost and time effective. Diaphragm feature size was observed to have a variability of

We demonstrate thermal classification of sequentially written fiber Bragg gratings. This Letter presents a process to determine the type of fiber Bragg grating written in SMF28 and GF4A by introducing the gratings to thermal treatment. This technique can be applied to several approaches based on sequential writing, including the small spot direct ultraviolet writing technique. Four different types of gratings have been identified, which are dependent on the fiber type and fluence used during the writing process.

The Networked Quantum Information Technologies hub (NQIT) is one of the quantum hubs of the UK's agship scheme, bringing together academia, industry and government. The Optical Engineering and Quantum Pho- tonics group at the University of Southampton's 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 UK's leading annual science events.

The temperature dependent polarity inversion in double-metal (DM) terahertz (THz) emitters was investigated. DM emitters utilising different metal pairings and single edge metal emitters were cooled in a helium flow cryostat and their THz emission was measured over a range of temperatures. Most emitters, including those with insulating layers between the metal and semiconductor, exhibit a flip in polarity of their THz emission between 50 and 100 K. This shows the inversion is a trait intrinsic to the semiconductor and not influenced by the metallic contact on the surface.

Integrated Optical Fiber is a new optical platform that planarizes optical fiber through Flame Hydrolysis Deposition. It demonstrates robustness when exposed to harsh environments; features low propagation loss; and planar integration advantages. In this work we summarize the latest developments made and the future trajectory for the technology in quantum technology and harsh environment sensing.

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.

Integrated Optical Fibre (IOF) allows for robust planar integration and seamless monolithic coupling. Fabrication is achieved through an adapted Flame Hydrolysis Deposition (FHD) technique, which forms a ruggedized glass alloy between the fibre and planar substrate. It has been previously demonstrated as a low linewidth external cavity lasers diode and a hot-wire anemometer, inherently suitable for harsh environments. This work looks at implementing the platform for harsh environment refractometry, in particular monitoring hydrocarbon fuels in the C14 to C20 range (e.g. Jet A1 and diesel). The platform uses SMF-28 fibre and direct UV written Bragg gratings to infer refractive index and thus the quality of the fuel. A challenge arises as the refractive index of these fuels are typically greater than the refractive index of the waveguide. Therefore, the guided mode operation of FBG refractometers is unsuitable. This work uniquely reports leaky mode operation and a regression analysis, inferring propagation loss through changes in amplitude of successive gratings. In effect, the proposed methodology utilises the imaginary part of the effective index as opposed to the real part, typically used by such sensors. Initial results have shown a 350 (dB/cm)/riu sensitivity is achievable above a refractive index of 1.45. This was measured for a SMF-28 fibre wet etched to 30 µm and planarized. Considering a 0.01 dB/cm propagation loss resolution, refractive index changes of the order 10-5 can be approached. Work will be presented on the fabrication of an IOF platform for refractometers as well as metrics for survivability in harsh environments.

We present results from the development of a fiber-coupled Acousto-Optic modulator (Fiber-Q®) operating at near-UV and blue wavelengths. A conventional TeO2 based Bragg diffraction design is introduced for short wavelengths optical input. Pure silica core single mode fibers (both Polarisation Maintaining (PM) and non-PM) are used as coupling fibers for their transmission at these wavelengths, and to avoid the possibility of photo darkening. The end of the fibers are fused with silica end-caps, lowering the power density on their fiber-air interfaces to achieve a higher power handling. The Fiber-Q® can be optimized for multiple wavelengths (including 397nm or 422nm) and can accept power levels of up to 100mW. A hermetically sealed package is selected to provide a clean in-package environment thus protecting the optics from damage caused by external contamination. In this presentation we report details of the design, and test results of a fiber-coupled Acousto-Optic modulator that demonstrates the performance required for use in ion-trap quantum information processing applications.

In this paper the first demonstration of a planar silica-on-silicon chip pressure sensor based on monitoring ratiometric Bragg grating amplitude loss across a diaphragm is made. The device resolution was found to be 0.46 kPa.

Integrated optical fiber is a planarized format, enabling ruggedized integrated functionality for silica optical fiber. This work is the first demonstration showing the platform's operation at temperatures exceeding 1000°C.

Illuminated by ultrashort optical pulses, large area multiplex terahertz semiconductor emitters that work on photo-Dember currents and Schottky potentials radiate a directional electromagnetic terahertz pulse which is controlled by the angular spectrum of the incident optical beam. Using the lens that focuses the incident near infra-red pulse, we have demonstrated THz emission focusing in free space and characterized a Gouy phase shift.

We present a method for tailoring emission field profiles through engineering of double-metal (DM) emitters. A device with a circular DM pattern is characterized and shown to emit a radial electric field profile, ideal for coupling to coaxial waveguides.

Integrated Optical Fibre (lOF) is a low-loss photonic platform that directly integrates optical fibre to a planar substrate. The platform possess advantages associated with optical fibre including low propagation loss, whilst at the same time enabling planar functionality associated with integrated optics. IOF fabrication is achieved through a modified Flame Hydrolysis Deposition (FHD) technique that forms a robust glass alloy between the fibre and substrate. The binding medium is of optical quality and mechanically robust, illustrated in fig 1 (a). Although non-trivial seamless on/off-chip coupling has also been demonstrated, which could further act to minimise coupling losses typically associated with integrated optics.

Integrated Optical Fibre (IOF) is a passive optical platform that directly integrates optical fibre to a planar substrate, illustrated in Fig 1(a). It possess advantages associated with optical fibre such a low propagation loss, whilst enabling planar functionality commonplace with integrated optics. Planarization is uniquely achieved through a modified Flame Hydrolysis Deposition (FHD) technique that forms a robust glass alloy between the fibre and substrate. The binding medium is of optical quality and resistant against common solvents, chemicals and elevated temperatures of up to 1000oC. Furthermore as fibre can be brought seamlessly on-off chip there is no need for glues or cumbersome coupling arrangements, which are typically a point of mechanical weakness when monitoring harsh environments.

Flame Hydrolysis Deposition (FHD) is a traditional route to deposit layers of doped silica onto the surface of a substrate for planar lightwave circuits. To form a uniform layer of fused glass the deposited soot must be consolidated, typically within a furnace at temperatures between 1200 °C and 1400 °C. This thermal processing is not localised as the temperature of the entire wafer is raised. This could be an issue for thermally sensitive, metallic or active photonic structures. This also limits the materials used for the substrate and requires the silica glass to have sufficient dopants to permit consolidation. CO 2 lasers have previously been used for smoothing and polishing of silica [1, 2] and were performed with CO 2 lasers operating with a wavelength of 10.6 μm. Silica however has a large absorption peak between 9 to 9.5 μm [4]. This paper demonstrates that using a CO 2 laser operating at 9.3 μm allows for highly localised heating and consolidation of FHD silica soot on a silicon wafer, this greatly reduces processing time and relaxes the constraints on dopants and substrate used in FHD, and to knowledge of the authors is the first example of FHD consolidation with a 9.3 μm laser.

Mode-locked Vertical External-Cavity Surface-Emitting Lasers (ML-VECSELs) have seen advances in pulse energy and peak power thanks to improved power handling techniques and structure designs. The significant increase in gain and intra-cavity power, coupled with the VECSEL’s accessible external-cavity, has made the addition of intra-cavity elements for frequency conversion possible even for lossy conversion mechanisms. In this paper, we report a gold-patterned Semiconductor Saturable Absorbing Mirror (SESAM) that functions both as a slow saturable absorber in a ML-VECSEL and as an intracavity strip line Photo-Conductive Antenna (PCA) for THz emission. Here we describe the design of the strip emitter, THz-Time Domain Spectroscopy (TDS) performed with a ML-Yb fibre laser and the mode-locked characterisation of a ML-VECSEL built with the patterned SESAM.

In this paper we model the carrier dynamics and resulting THz emission from lateral diffusion currents within a semiconductor device which has been partially masked by a metallic mask. We present a numerical 1D model and a 1D Monte Carlo simulation which both demonstrate that regardless of the excitation laser spot shape we do not expect to see measurable THz emission in the direction of the optical pump propagation from lateral diffusion currents. Experimentally such devices do produce strong THz emission. We analytically investigate the role of the metal mask and we found that it suppresses the emission of dipoles that are in a region that is less than a wavelength away from the interface. The results from the numerical model are also included in a finite element analysis model of the geometry which predicts THz emission if and only if the metal mask is present.

We present the first demonstration of integrated waveguides in planar silica devices fabricated using direct UV writing with 213 nm laser light. Waveguides were produced with different writing fluences and the NA and MFD of each were measured. Single mode waveguides were achieved at fluence values one tenth that typically required when operating with a 244 nm laser, allowing for more rapid fabrication. A maximum in-plane index change of 2.4 x10-3 for a writing fluence of 5 kJ cm-2 was estimated from NA measurements. Finally cutback measurements were performed and a propagation loss of 0.42 ± 0.07 dB/cm was directly measured, though losses as low as 0.2 ± 0.03 dB/cm are indicated through calculations.

Multiplexed gallium–arsenide (GaAs)-based terahertz (THz) emitters fabricated with periodic double-metal structures are demonstrated and the effect of different metals on the THz output is investigated. THz emission originates from the lateral photo-Dember effect and from the different Schottky barrier heights of the chosen metal pair. The metal combinations used were Au–Al, Au–Pb and Cu–Cr. The emitters were characterised according to temperature and the highest peak-to-peak THz emission was achieved with the Cu–Cr metal pairing at 150 K.

We demonstrate a simulation of lateral photo-Dember THz emitters in 2D using the drift diffusion equation coupled to a finite differences time domain (FDTD) model with far-field algorithm. We show that the dynamics of the system are more dependent on the currents travelling perpendicular to the semiconductor surface, as opposed to just the lateral currents as previously thought.

We demonstrate multiplexed terahertz emitters that exhibits 2 THz bandwidth that do not require an external bias. The emitters operate under uniform illumination eliminating the need for a micro-lens array and are fabricated with periodic Au and Pb structures on GaAs. Terahertz emission originates from the lateral photo-Dember effect and from the different Schottky barrier heights of the chosen metal pair. We characterize the emitters and determine that most terahertz emission at 300 K is due to band-bending due to the Schottky barrier of the metal., 4 pages, 6 figures

We characterise THz output of lateral photo-Dember (LPD) emitters based on semi-insulating (SI), unannealed and annealed low temperature grown (LTG) GaAs. Saturation of THz pulse power with optical fluence is observed, with unannealed LTG GaAs showing highest saturation fluence at 1.1 ± 0.1 mJ cm-2. SI-GaAs LPD emitters show a flip in signal polarity with optical fluence that is attributed to THz emission from the metal-semiconductor contact. Variation in optical polarisation affects THz pulse power that is attributed to a local optical excitation near the metal contact.

Pulsed broadband terahertz emission can be observed from lateral diffusion currents near the surface of a partially metallic masked semiconductor after ultrafast photoexcitation. We present a theoretical mechanism for the emission based on diffusion and dipole suppression under the metal mask with supporting experimental and theoretical evidence.

In lateral photo-Dember emitters pulses of coherent terahertz radiation can be generated by ultrafast above bandgap laser illumination of the surface of a partially metallic masked semiconductor. We investigate the role of the metallic mask and how the emission depends on spot size and fluence.

We characterise a set of Lateral Photo Dember (LPD) terahertz emitters fabricated on annealed low temperature grown (LTG) GaAs, unannealed LTG-GaAs and SI-GaAs substrates. Our results show that unannealed LTG-GaAs is the most efficient LPD emitter of this set due to a higher saturation fluence.

Pulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.

We demonstrate a terahertz multiple emitter design based on the lateral photo-Dember effect and illuminated with a cylindrical micro-lens array. The multiple emitter produces an average of 5.2 times the output power of a single lateral photo-Dember emitter and is capable of reaching bandwidth comparable to that of a single commercial photoconductive antenna.