Search

We demonstrate an increase in achievable refractive index change of 1.2×10-3 in Gedoped silica in writing waveguides and gratings using pulsed 213 nm light to deposit the same total fluence over multiple writing passes.

We investigate the dynamics of pulsed 213 nm planar Bragg grating writing for a range of powers and fluences. We report the regime for achieving high index contrast, and where damage is likely to occur.

We present the first substantive investigation into the photosensitivity response of planar-doped silica to pulsed 213 nm light. We look at the response over a broad range of fluences and average powers to identify suitable regimes for simultaneous waveguide and Bragg grating writing. Unlike previously reported work, we do not observe any clear evidence of a similar non-linear photosensitivity response in B/Ge doped silica. We discuss laser-induced damage, saturation of photosensitivity, and grating response. This paper presents writing regimes for small spot direct UV writing where the photosensitivity and grating response are optimum, thereby confirming the suitability of the fabrication approach for complex devices.

Flexible and stretchable photonics is a rapidly evolving area, with various materials, design, processing, and device technologies being explored [1] . As with flexible electronics, flexible photonics particularly lends itself to integration upon engineered and natural structures, such as interfacing with the soft, curvilinear, and dynamic surfaces of living organisms. Here we explore a potential new growth opportunity interfacing with engineered structures, namely embedding into advanced composite materials (such as Carbon Fibre Reinforced Polymer and Glass Fibre Reinforced Polymer). The motivation being ultimately new optical functionality and intelligence for engineered structures (e.g. wind turbines, aircraft, civil infrastructure), going beyond what has been developed with embedded optical fibre through realising the full geometric diversity offered by flexible photonics. This work embeds ultra-thin glass [3] , utilising its flexibility in order to be conformal to the shape of composite structures which flex and in parts are non-planar. It is noted that cyclic olefin copolymer planar chips have recently shown feasibility in composite material [2] , whilst these demonstrations use rigid planar optics they do show feasibility for other flexible photonic materials to exploit this application.

We demonstrate for the first time the reconfigurability of optical signals within advanced laminated composite. The approach employs an ultra-thin planar optical circuit, embedded within glass fibre reinforced polymer (GFRP) that switches an optical input though Ohmic heating. This advance highlights new opportunities for optical reconfigurability within advanced composites, enabling data transmission redundancy and a consideration of branching optical fibre architectures.

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 demonstrated two different methods for fabricating a record number of over 40 co-located fiber Bragg gratings: consecutively written superimposed and digitally synthesized superstructure gratings fabricated through small spot direct UV writing. The development of ’AC’ refractive index for superimposed gratings has been analyzed.

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.

We demonstrated the fabrication of a record number of over 40 overlaid fiber Bragg gratings. We compared two different fabrication techniques: consecutively superim- posed and digitally superstructured gratings and analyzed the evolving AC refractive index change.

Waveguide propagation loss is a key parameter for integrated devices, yet characterisation of this parameter can be challenging. This is especially true for more complex integrated devices where it can be difficult to extract the propagation loss using cut-back measurement or Fabry-Perot methods. An ideal technique would perform the measurement in situ, and be able to determine variations in the loss along the waveguide.

We report the first integrated implementation of a polarizer based on the use of 45° tilted gratings in planar waveguides. The waveguides and gratings are fabricated by direct UV writing in a hydrogenated germanium-doped silica-on-silicon chip. We experimentally demonstrate a polarization extinction ratio per unit length of 0.25 dB mm−1 with a modelled wavelength dependence smaller than 0.3 dB for a 20 mm device over the C band from 1530–1570 nm. We also present a novel numerical study and analytical description of the architecture that are in good agreement with each other and the experimental data.

We have demonstrated the inscription of Bragg gratings into five individual cores of a seven core fiber using small spot direct UV writing. With this technique, we defined spectrally multiplexed Bragg gratings consecutively in separate cores as well as spectrally multiplexed gratings at the same longitudinal location in different cores. The effect of bending on the optical spectrum was evaluated to allow the differentiation between cross-exposure and cross-talk, and an alignment process to reduce cross-exposure by 13 dB was found.

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.

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.

Direct UV-written waveguides are fabricated in silica-on-silicon with birefringence of $(4.9 \pm 0.2) \times 10^{-4}$, 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 $\mathrm{GeCl_4}$ and $\mathrm{BCl_3}$ using the flame hydrolysis deposition process. The technology provides a route towards the scalability of silica-on-silicon integrated components for photonic quantum experiments., Comment: 9 pages, 5 figures

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.

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.

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).

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.

Interference between independent single photons is perhaps the most fundamental interaction in quantum optics. It has become increasingly important as a tool for optical quantum information science, as one of the rudimentary quantum operations, together with photon detection, for generating entanglement between non-interacting particles. Despite this, demonstrations of large-scale photonic networks involving more than two independent sources of quantum light have been limited due to the difficulty in constructing large arrays of high-quality single photon sources. Here, we solve the key challenge, reporting a novel array of more than eighteen near-identical, low-loss, high-purity, heralded single photon sources achieved using spontaneous four-wave mixing (SFWM) on a silica chip. We verify source quality through a series of heralded Hong-Ou-Mandel experiments, and further report the experimental three-photon extension of the entire Hong-Ou-Mandel interference curves, which map out the interference landscape between three independent single photon sources for the first time., 16 pages including supplementary information

Optical quantum Information Processing makes use of the quantum mechanical properties of single photons to achieve useful information processing functions. This talk will present work carried out at the University of Southampton on the fabrication of optical waveguide device to realize essential functions for all optical quantum information handling. Utilizing silica-on-silicon as a platform and direct UV writing of waveguides, the talk will present results on key elements including single photon sources, waveguide circuits and waveguide sensors.

We demonstrate a high-efficiency, photon-number resolving transition edge sensor, integrated on an optical silica waveguide structure. The detector consists of three individual absorber/sensor devices providing a total system detection efficiency of up to 93% for single photons at a wavelength of 1551.9 nm. This new design enables high fidelity detection of quantum information processes in on-chip platforms. © 2013 The Optical Society.

We shall present a flexible technique for fabricating fiber Bragg gratings for use around 1550nm. The approach uses small-spot UV-writing on a suspended fiber to achieve highly apodised, chirped gratings with a wide tuning range.

We report the first demonstration of an integrated polarizing coupler based on tilted gratings operating in the C-band with a TE-TM extinction ratio in the out-coupled port in excess of 17 dB.

This invited paper covers the development of UV written MEMS cantilevers on silica-on-silicon. The work uses novel fabrication tools including physical micromachining and UV laser direct writing. Each cantilever contains an optical waveguide and by actuating the cantilevers we have demonstrated optical attenuation operation in an array format.

Spin-chain models have been widely studied in terms of quantum information processes, for instance for the faithful transmission of quantum states. Here, we investigate the limitations of mapping this process to an equivalent one through a bosonic chain. In particular, we keep in mind experimental implementations, which the progress in integrated waveguide circuits could make possible in the very near future. We consider the feasibility of exploiting the higher dimensionality of the Hilbert space of the chain elements for the transmission of a larger amount of information, and the effects of unwanted excitations during the process. Finally, we exploit the information-flux method to provide bounds to the transfer fidelity., Comment: 8 pages, 6 figures, RevTeX4

Integrated optics is becoming increasingly important for applications in quantum information processing, quantum sensing and for advanced measurement. Intrinsically stable and low-loss it provides essential routing and coupling for quantum optical experiments offering functions such as interconnects, couplers, phase delays and routing. Silica-on-silicon has particular attractions, and in this work the fabrication approaches and advantages of the technique will be explored. In particular, UV direct writing of waveguides and Bragg gratings proves useful for its rapid-prototyping capability and its ability to provide grating for characterization of components for loss, birefringence and coupling ratio. This review concentrates on the fabrication of planar waveguide devices, and ways in which direct UV writing provides important functionality. Examples of applications of silica-on-silicon waveguides include quantum enhanced interferometry, teleportation, boson sampling as well as hybrid operation for single photon detection with transition edge sensors directly placed onto waveguide devices

Silica provides a low-loss platform for integrated optics. With demonstrations including teleportation and Boson sampling it is important for developing Quantum Information Processing. We report the design, fabrication, testing and realization of complex waveguide circuits.

An optomechanical double cantilever device has been fabricated with applications as a displacement sensor and variable attenuator. The device is based on a silica glass on silicon substrate. A novel fabrication approach using a precision dicing saw is used, which has benefits in terms of cost, fabrication time and energy consumption compared to cleanroom based lithography techniques. The silica cantilevers contain integrated optical waveguides and Bragg gratings fabricated using a Direct UV Writing process. The cantilevers are deflected out of plane by thin film stress effects, providing a suitable geometry for use in sensing. Displacement causes both cantilevers to move simultaneously resulting in variable coupling due to the angular alignment of the waveguide modes. Using a developed ratiometric approach based on fitting to Gaussian apodized Bragg gratings, the measured displacement is completely independent of fluctuations in light source power as well as insensitive to detector noise. The device is optically interrogated at a wavelength band around 1550nm. As a sensor the device has a sensitivity of 0.8 dB/micron and can be accurately modelled using fiber optic coupling misalignment theory. When operating as an attenuator, a suppression ratio of over 20dB can be obtained. If combined with integrated optical components such as X-couplers, multiple double cantilever arrays can be placed on the same chip for distributed sensing. We will report detailed fabrication procedures as well as optical characterization of the device including the performance metrics of the force sensor.

The authors present a direct UV writing approach to fabricate fiber Bragg gratings (FBGs) and gratings in photolithographic waveguides. The technique uses two coherent UV beams, which are focused to a small spot (~7µm diameter) at the point at which they overlap. The resulting interference pattern at the foci consists of fringes which are used to define several grating planes per exposure, giving greater design flexibility and a significantly larger accessible spectral range compared to traditional approaches. The typical index contrast during grating fabrication is observed to be 4.7x10-3, at writing speeds of 8 mm/min.

Terahertz bandwidth photonic Hilbert transformers are proposed and experimentally demonstrated. The integrated device is fabricated via a direct UV grating writing technique in a silica-on-silicon platform. The photonic Hilbert transformer operates at bandwidths of up to 2 THz (~16 nm) in the telecom band, a 10-fold greater bandwidth than any previously reported experimental approaches. Achieving this performance requires detailed knowledge of the system transfer function of the direct UV grating writing technique; this allows improved linearity and yields terahertz bandwidth Bragg gratings with improved spectral quality. By incorporating a flat-top reflector and Hilbert grating with a waveguide coupler, an ultrawideband all-optical single-sideband filter is demonstrated.

A direct UV grating writing technique based on phase-controlled interferometry is proposed and demonstrated in a silica-on-silicon platform, with a wider wavelength detuning range than any previously reported UV writing technology. Electro-optic phase modulation of one beam in the interferometer is used to manipulate the fringe pattern and thus control the parameters of the Bragg gratings and waveguides. Various grating structures with refractive index apodization, phase shifts and index contrasts of up to 0.8×10-3 have been demonstrated. The method offers significant time/energy efficiency as well as simplified optical layout and fabrication process. We have shown Bragg gratings can be made from 1200 nm to 1900 nm exclusively under software control and the maximum peak grating reflectivity only decreases by 3dB over a 250 nm (~32THz) bandwidth.

Direct UV Grating Writing (DGW) is effective route for fabricating high quality Bragg gratings, similar to fiber Bragg gratings, in a planar geometry. We will present a phase modulation controlled DGW method using an Electro-Optical Modulator for planar Bragg grating fabrication that offers improved performance. This new approach not only provides much greater modulation depths for stronger and shorter Bragg gratings but also offers greater fabrication speed and a higher fidelity of control than previous amplitude modulation methods [1].

Summary form only given. Microbeams integrated with optical components have found applications in telecoms and sensing applications[1][2]. We present fabrication, characterisation and modelling of silica microbeams containing an integration optical waveguide and Bragg reflectors. These optical elements, fabricated using direct UV writing process, have applications in telecoms and sensing[3]. Thermal tuning of the integral Bragg gratings is enhanced and the energy requirements greatly reduced by a factor of 50.The ability to tune a Bragg grating's reflected wavelength provides a route to numerous potential applications such as tunable add/drop multiplexers. While this has already been achieved in fibre optics there are situations where the planar format has advantages in terms of compactness and integration. Of the possible tuning mechanisms, temperature tuning is most common, yielding wide tuning ranges as well as uniform spectral response. Temperature tuning can however suffer from power inefficiency and poor time response due to the large thermal mass of the device. Locating the optical elements in a microbeam is an elegant way to provide localised tuning to a small thermal mass, thereby increasing energy efficiency and reducing crosstalk with other components on the device. Silica microbeams have been fabricated using a series of microfabrication techniques including micro-milling, KOH etching of silicon and evaporative metal deposition. The resultant devices are geometrically uniform and surprisingly robust although only 100μm wide.The devices characterized show that the observed Bragg peak shift is close to linear with the applied electrical power. The data in figure 1 shows a tuning of almost 0.5 nm with 12 mW of heating power. Another potentially useful property of microbeams is elastic buckling[4]. Buckling either occurs following fabrication due to the stresses caused by the silica deposition process or can be induced by other forms of actuation such as thermal stress. Utilizing buckling in thermal tuning could allow tuning between bi-stable states with no requirement for continuous energy supply. We shall present our findings including the fabrication and characterization of microbeam devices and applications of a tunable Bragg grating.

Tilted Bragg grating refractometers have been subject to continuous interest in recent years [1]. They operate by diffracting a well-confined core mode into a discrete set of cladding [2] or plasmonic modes [3], whose properties are dependent upon an external refractive index. Traditionally these components have been fabricated in an optical fibre platform. However, recent work from the authors has demonstrated this concept in an optical planar platform [2-5]. The key advantages of these tilted planar Bragg gratings (TPBGs) include compact multiparameter sensing, signal multiplexing and the potential to seamlessly integrate operation with microfluidics. In addition, there is an increased level of design flexibility that continues to be explored; including waveguide-to-waveguide assisted coupling [5], controllability of cladding thickness, multi-waveguide arrangements and asymmetric waveguide positioning.

Summary form only given. Grating stabilized diode lasers exist in many different configurations, typically using bulk and fiber Bragg gratings. In the last couple of years grating stabilized lasers based on a semiconductor gain chips coupled to integrated or planar lightwave circuits containing Bragg gratings have been demonstrated and developed. These devices not only exhibit excellent optical properties such as ultra-low RIN and phase noise, but also compact size and greater opportunities for mass production. We shall present our latest developments of silica planar Bragg grating stabilized diode lasers, and in particular the generation of tunable narrow linewidth sources for gas sensing.

Direct UV Grating Writing (DGW) is an attractive technique for simultaneously fabricating integrated Bragg grating devices in a silica-on-silicon platform, yielding losses as low as 0.03dB/cm. Previously, an Acousto-Optical Modulator has been used for writing planar Bragg gratings; in this new work we demonstrate a new phase modulation fabrication technique that offers improved performance. We report a novel phase control DGW method using an Electro-Optical Modulator for planar Bragg grating fabrication. We phase modulate one laser beam in a focusing interferometer as a photosensitive silica-on-silicon sample is translated under the spot to give a moving fringe pattern that allows high quality Bragg gratings and waveguides to be fabricated in a single step. This new approach has allowed us to achieve a 1mm long uniform Bragg grating with ~70% reflectivity and a 1.4nm 3dB bandwidth; while a 3mm long grating has 100% top flat reflectivity and a 1.22nm 3dB reflection bandwidth - refractive index changes of up to 0.001 can be achieved. Since there is neither laser power reduction nor writing speed variation, the method offers significantly faster writing speeds. The simplified optical layout offers greater laser power on sample and furthermore the design coding is simplified. By applying Gaussian apodisation to the grating design we can achieve sidelobe suppression of >15dB. Using grating detuning and this new phase control method we have shown that Bragg gratings can be written from 1200nm to 1900nm on a single chip under software control and with less than 3dB variation across a 250nm bandwidth high chemical stability, which makes these materials very interesting for active photonics applications. In particular, Yb3+-doped RTP exhibits a broad fluorescence spectrum that has been exploited to demonstrate ultrafast operation, with pulses as short as 155 fs being generated [1]. Recently, planar waveguiding has been demonstrated in an (Yb3+, Nb5+):RTP film grown by liquid phase epitaxy [2], opening the possibility of planar integrated devices based on this highly functional material.

The first monolithically integrated all-optical single-sideband filter based on photonic Hilbert transform and planar Bragg gratings is proposed and experimentally demonstrated. Single-sideband suppression of 12 dB at 6 GHz and sideband switching are achieved via thermal tuning. An X-coupler, photonic Hilbert transformer, flat top reflector and a micro heater are incorporated in a single silicon-on-silica substrate. The device can be thermally tuned by the micro heater on top of the channel waveguide. The device is fabricated using a combination of direct UV grating writing technology and photolithography.

Summary form only given. The recent trend towards integration of quantum optics experiments has produced a demand for on-chip single photon detectors with high quantum efficiencies. In previous work we demonstrated integrated photon number resolving detectors for use at telecommunications wavelengths [1], here we outline developments of this design which have enabled improvements in the quantum efficiency, permitting an on-chip detection efficiency of 92% to be obtained in the device of Fig. 1.

The presentation will give an overview of the fabrication process of direct UV written planar Bragg grating sensors and the various geometries and applications investigated over the last several years.

Direct UV writing is a planar fabrication process capable of simultaneously defining waveguides and Bragg gratings. The technique is fully computer controlled and uniquely uses a small focused spot ~7 μm in diameter for direct writing exposure. This work investigates its use to achieve phase trimming and Bragg grating definition in silica-on-silicon lithographic waveguides. It is observed that birefringence control using direct UV writing can be made independent of exposure fluence with this technique through tailoring substrate stress. The result is demonstrated experimentally and supported theoretically using finite element analysis.

A dual cantilever device has been demonstrated which can operate as a force sensor or variable attenuator. The device is fabricated using physical micromachining techniques that do not require cleanroom class facilities. The response of the device to mechanical actuation is measured, and shown to be well described by conventional fiber optic angular misalignment theory. The device has the potential to be utilized within integrated optical components for sensors or attenuators. An array of devices was fabricated with potential for parallel operation.