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We demonstrate that the stimulated Brillouin scattering of a 250 mm long distributed feedback Raman fiber laser can self-pulse with repetition rates up to 7 MHz, pulse widths of 25 ns, and peak powers of 1.2 W. While both CW and pulsed lasing are produced from a bespoke grating at 1119 nm this laser design could be constructed at almost any wavelength, as the Raman and Brillouin gain regions are relative to the pump wavelength. The laser has a low lasing threshold for a Raman laser of 0.55 W, a peak slope efficiency of 14 %, and a maximum average output of 0.25 W. An investigation of beating between pure Raman and Raman-pumped Brillouin lasing shows that the outputs of the two processes are highly correlated and thus the Brillouin lasing is essentially single-frequency when CW and near transform limited for pulsed operation. A phenomenological model of the Raman-Brillouin interaction shows that the pulsing behaviour of such a cavity is expected and produces very similar pulsing to that the seen in experimental results.

Vibrational modes of chemical bonds in organic erbium (Er3+) materials play an important role in determining the efficiency of the 1.5 μm Er3+ emission. This work studies the energy coupling of the Er3+ intra-4f transitions and vibrational modes. The results demonstrate that the coupling introduces enormous nonradiative internal relaxation, which condenses the excited erbium population on to the 4I13/2 state. This suggests that vibrational modes can be advantageous for optimizing the branching ratio for the 1.5 μm transition in organic erbium materials. Through control of the quenching effect on to the 4I13/2 state and a reliable determination of intrinsic radiative rates, it is found that the pump power for population inversion can be reduced by an order of magnitude at high erbium concentrations compared to conventional inorganic erbium materials.

Two methods to inscribe co‐located fibre Bragg gratings using the small spot direct UV writing technique are described and compared, namely: superimposed gratings, which are written one over the other at the same spatial location, and superstructured gratings, where a refractive index modulation is digitally designed and all spectral signatures are written in a single step writing process. In this letter, we report a record number of 45 superimposed and 39 superstructured gratings being inscribed with an interference spot of only 14 μm in diameter.

Uniform Fiber Bragg Grating sensors based on Polarization-Maintaining fibers are designed for simultaneous longitudinal strain and temperature measurement of Carbon Fiber Reinforced Polymer laminates. Panda, Bow tie and Pseudo-rectangle optical fiber shape sections are investigated employing three different embedding methods, for each optical fiber. The simulation accurately takes into account that the fibers are embedded in unidirectional Carbon Fiber Reinforced Polymer and covered between two adhesive polyimide films. An exhaustive, accurate and robust investigation of the mechanisms originating Bragg wavelength shift is developed by considering a complete multiphysical model including: the propagation modes and their interaction, the birefringence, the optomechanical and thermal behaviour of both the optical fiber and the embedding composite material. For the first time, the use of polyimide films is proposed to obtain an increase of temperature sensor sensitivity, reducing the stress-transfer, due to thermal expansion, between the composite laminate and the sensing element. The designed Fiber Bragg Grating sensors are compared and their potential application, for simultaneous strain and temperature measurement of Carbon Fiber Reinforced Polymer is discussed.

We propose and investigate theoretically the use of bi-directional propagation of light in silica integrated coupled waveguide structures for linear optical processing of fiber-coupled photons. We show that the class of linear operations that can be implemented in such a system is given by symmetric and unitary matrices. We present how an arbitrary $4\times 4$ coupler of this form can be realized by a linear sequence of more fundamental $2\times 2$ couplers and single-waveguide phase shifters and discuss in detail the implementation in a silica integrated platform utilizing direct UV-written waveguides and long- and short-period grating couplers with tilted gratings for optimized coupling efficiency.

This work proposes a new route to overcome the limits of the thermal poling technique for the creation of second order nonlinearity in conventional silica optical fibers. We prove that it is possible to enhance the nonlinear behavior of periodically poled fibers merging the effects of poling with the nonlinear intrinsic properties of some materials, such as MoS2, which are deposited inside the cladding holes of a twin-hole silica fiber. The optical waves involved in a second harmonic generation process partially overlap inside the thin film of the nonlinear material and exploit its higher third order susceptibility to produce an enhanced SHG., SCOPUS: ar.j, info:eu-repo/semantics/published

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.

Coupling between free space components and slab waveguides is a common requirement for integrated optical devices, and is typically achieved by end-fire or grating coupling. Power splitting and distribution requires additional components. Usually grating couplers are used in combination with MMI/Y-splitters to do this task. In this paper, we present a photonic crystal device which performs both tasks simultaneously and is able to couple light at normal incidence and near normal incidence. Our approach is scalable to large channel counts with little impact on device footprint. We demonstrate in normal incidence coupling with multi-channel splitting for 785 nm light. Photonic crystals are etched into single mode low refractive index SiON film on both SiO2/Si and borosilicate glass substrate. Triangular lattices are shown to provide coupling to 6 beams with equal included angle (60°), while a quasi-crystal lattice with 12-fold rotational symmetry yields coupling to 12 beams with equal included angle (30°). We show how to optimize the lattice constant to achieve efficient phase matching between incident and coupled mode wave vectors, and how to adjust operating wavelength from visible to infrared wavelengths.

Trabajo presentado al XVII Optical Components and Materials, celewbrado en San Francisco, California (USA) del 1 al 6 de febrero de 2020., SnO2-based glass-ceramics activated by rare earth ions have been extensively investigated because of the need to develop reliable fabrication protocols and clarify some interesting optical, structural, and spectroscopic features of the system. There is one important weakness in glass photonics when the rare earth ions are employed as luminescent sources. This is the low absorption cross section of the electronic states of the rare earth ions. A sensitizer is therefore requested. In the last years, we demonstrated that SiO2-SnO2 glass ceramics, presenting a strong absorption cross section in the UV range due to the SnO2 nanocrystal, are effective rare earth ions sensitizers. Another interesting property of the SiO2-SnO2 system is its photorefractivity. The high photorefractivity of sol-gel-derived SnO2-SiO2 glass-ceramic waveguides has been demonstrated in several papers published by our consortium. It has been shown that the UV irradiation induces refractive index change allowing the direct writing of both channel waveguides and Bragg gratings. The results presented in this communication not only demonstrate the viability and outstanding properties of the SiO2- SnO2 glass-ceramics for photonic applications but also put the basis for the fabrication of solid state and integrated lasers. The next steps of the research are the fabrication of the channels and mirrors exploiting the photorefractivity as well as to draw glass ceramic fiber, checking the lasing action and corresponding functional characteristics. Finally, it is worth noting that the dynamic of the energy transfer from the nanocrystals to the rare earth ions is still an exciting open question., This research is performed in the framework of the projects ERANet-LAC “RECOLA” (2017-2019), Centro Fermi MiFo (2017–2020) and NaWaGui (ANR-18-MRS1-0014). WB and MF acknowledge the support of CNR-STM - Short Term Mobility program 2019-2020.

Thermal poling, a technique to create permanently effective second-order susceptibility in silica optical fibers, has recently been improved by the discovery of an "induction poling" technique1 and the adoption of liquid electrodes2, allowing for poling fibers of any length and geometry. Nevertheless, the nonlinearity created via thermal poling is always limited by the ooelig;'(3)of the optical fiber material and by the maximum electric field that can be frozen inside the glass. For these reasons research is ongoing to determine routes for further improving the nonlinear effects due to the thermal poling process. In this work, we propose to enhance the effects of the thermal poling by exploiting the intrinsic nonlinear properties of some 2D materials3, which are deposited inside the cladding holes of a twin-hole silica fiber. The materials we focused on are 2D Transition Metal Chalcogenide (2D TMDC) MoS2 and WS2 and the technique adopted to realize the deposition inside the cladding channels of a twin-hole step index silica fiber consists of a thermal decomposition process4 of the precursor ammonium tetrathiomolybdate (NH4)2MoS4 in 6% H2/Ar flow. The technique has allowed us to uniformly coat the two cladding channels for a length of 25 cm with a film nominally consisting in a bi-layer of the 2D materials. A Raman based analysis has been used to test the morphology of the coating. The fiber deposited with 2D materials was later thermally poled and periodically erased via exposure to UV light to reach the QPM condition at a wavelength of 1550 nm. The effective oœ'(2) of the fiber was measured via SHG for both the deposited and the pristine fiber, showing an enhancement of the nonlinearity in favor of the deposited one. The phenomenon can be explained by the exploitation of a higher oœ'(3) seen by the pump wave due to the presence of the 2D layer deposited inside the cladding holes and opens the possibility of exploiting the higher intrinsic material oœ'(2), in case of a periodic patterning/synthesis of the TMDC., SCOPUS: cp.p, info:eu-repo/semantics/published

Tailored laser sources for UV/blue wavelengths are in ever-increasing demand due to the advancing fields of quantum ion-trapping, metrology and computation. In particular, compact sources are required for the field deployment of quantum technologies. In recent work, we demonstrated the ability to fabricate ridge waveguides in Periodically Poled Lithium Niobate (PPLN) for Rb atom trapping based on 1560 nm Second Harmonic Generation (SHG) and mode matched to standard telecommunications optical fibre [1]. Here, we present our advancement of this work toward UV generation at 369 nm for Yb+ Doppler cooling, with an emphasis on manufacturing scalability.Our first example is a zinc-indiffused PPLN ridge waveguide for conversion of ~780 nm to 390 nm light. Electric field poling was used to achieve periodic gratings in 5% MgO-doped lithium niobate with a width of 200 μm and a phase-matching period of 2.2 μm through the entire 500 μm thickness of the crystal. Metallic zinc was deposited and indiffused to create a planar waveguide in the MgO:PPLN crystal, followed by ridge and facet definition via ultra-precision ductile dicing.Fig. 1. (a) SHG spectra generated from a 5.6 μm wide PPLN ridge waveguide with an overlaid model of a theoretical sinc2 with the corresponding Fabry-Perot interference fringes. (b) Pump mode profile, demonstrating single-mode operation. (c) Photograph of the device and the input/output coupling optics for characterisation. (d) Colour photograph of prism separated fundamental and second harmonic output.Fig. 1(a) shows a SHG spectra from a 5.6 μm wide diced ridge waveguide. Detailed spectra in low power operation is taken using lock-in amplification. As the sample is non-AR coated, the associated Fabry-Perot interference fringes for a 14 mm cavity can modelled to explain the SHG spectrum, also shown in Fig. 1(a).Fig. 1(b), the corresponding pump 2nd moment MFD is calculated as 4.7 x 6.1 μm in the x and y axes, respectively.Fig. 1(c) shows the device and the characterisation optics for simple input coupling using a 15 mm focal length aspheric lens from a collimated, fibre coupled source; the 390nm signal can be seen in Fig. 1(d). A conversion efficiency of ~10 %/W/cm2 has been attained with a 14 mm-long waveguide. This device offers a higher efficiency than typical UV-transmissive, nonlinear crystals in low-power operation, such as LBO, which typically require cavity enhancement for application [2]. This approach provides a simpler fabrication process to other ridge-style PPLN waveguides achieved through thinning, resin bonding and dicing to 1.5 μm depth ridge waveguides [3].We will present the optimisation of parameters for both periodic poling and waveguide fabrication. Current results on device efficiency, spectra and advancements to longer devices will also be presented. The effects of ridge width variation to understand distortion from the expected sinc2 SHG spectra will also be discussed to further understand the fabrication limitations in these indiffused, ridge waveguides.References:1. L. G. , S. A. Berry, R. H. Bannerman, A. C. Gray, J. W. Field, C. Holmes, J. C. Gates, P. G. R. Smith and C. B. E. Gawith, “Developing PPLN Waveguides for Quantum Rubidium Atom Traps in Space” Nonlinear Photonics Optical Society of America, (pp. NpTh1C-6). (2018).2. M. Pizzocaro, D. Calonico, P. C. Pastor, J. Catani, G. A. Costanzo, F. Levi, and L. Lorini. "Efficient frequency doubling at 399nm" Applied optics, 53, 3388-3392 (2014).3. K. Mizuuchi, T. Sugita, K. Yamamoto, T. Kawaguchi, T. Yoshino, and M. Imaeda "Efficient 340-nm light generation by a ridge-type waveguide in a first-order periodically poled MgO:LiNbO3" Optics letters 28, 1344-1346 (2003).

We have recently developed and experimentally demonstrated the technology of tilted Bragg gratings in integrated optical waveguides to achieve polarisation selective coupling between parallel waveguides. Here I will review our ideas, designs and simulations for novel devices based on this platform. Multimode devices, tailored phase matching, and methods for significantly improved coupling efficiencies will be discussed that will be of interest for applications in quantum information processing and multimode optical telecommunication.

We propose and experimentally demonstrate wideband and continuously tunable fractional-order photonic Hilbert transformers (FrHT). These are realized by a single apodized planar Bragg grating within a high-birefringence planar substrate. The fractional order of the FrHT is continuously tuned and precisely controlled by changing the polarization state of the input light. The experimental characterization demonstrates an operating bandwidth up to 120 GHz with amplitude ripples below 3 dB. The optical phase shift response is directly measured to verify the proposed tuning property, demonstrating transform orders of around 1, 0.7, and 0.5. This approach is simple, stable, and compact compared to other existing methods and has great potential in the fields of ultrafast all-optical signal processing.

The high intensity and continuous nature of small-spot direct UV writing makes characterisation of gratings types difficult by conventional approaches. Investigating the thermal response of gratings up to 850 °C allows elucidation of grating type.

We investigate theoretically devices based on arrays of parallel planar waveguides inscribed with tilted Bragg gratings. We demonstrate polarization-dependent N by N+1 linear couplers. Deterministic switching can be achieved by coherent control of input beams with optimized apodization of the gratings.

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.

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

We propose and experimentally demonstrate an integrated photonic Hilbert transformer (PHT) with substantial time bandwidth product (TBP). Due to the current substrate material and fabrication technique, PHT devices find it challenging to achieve ultrawide operative bandwidth while maintaining the minimum bandwidth level presented as the narrow central notch in frequency response. This implies that the TBP value is restricted. Here, we investigate the synthesized refractive index profile in compact Bragg grating design for theoretical simulation and the linearity-enhanced direct UV grating writing fabrication for experimental implementation. The fabricated device could process microwave photonic signals as Hilbert transformation between 50 GHz and 3 THz, with the TBP above 60, which is the largest experimental data to the best of our knowledge. This technique allows the PHT with improved spectral performance to be suitable for analog all-optical signal processing.

Flat optical fibre technology is a glass-based substrate technology that has emerged recently, it offers a flexible and potentially very long, distributed sensing medium, whilst also having increased lateral and vertical dimensions; this allows for the development of optical integrated circuits with the enhanced functionality promised by optical chips. In this work we report on recent developments to highlight the incorporation of integrated structures on the surface and in the bulk volume of flat fibres using femtosecond laser inscription. This fusion of two innovative technologies, and in particular the flexibility afforded by femtosecond laser inscription and micromachining, has led to the realisation of microfluidic channels, ring resonators, resonator disc, Mach-Zehnder and complex microfluidic designs in the surface of the optical chip, whereas Bragg grating waveguides have been recorded in the bulk volume of the optical chips. The flat-fibre platform offers a unique degree of freedom by allowing surface and sub-surface devices to be integrated onto a single optical chip with the potential for straightforward incorporation into integrated photonic circuits or opto-fluidic devices.

This paper reports for the first time a planarised optical fiber composite formed using Flame Hydrolysis Deposition (FHD). As a way of format demonstration a Micro-Opto-Electro-Mechanical (MOEMS) hot wire anemometer is formed using micro-fabrication processing. The planarised device is rigidly secured to a silicon wafer using optical quality doped silica that has been deposited using flame hydrolysis and consolidated at high temperature. The resulting structure can withstand temperatures exceeding 580K and is sensitive enough to resolve free and forced convection interactions at low fluid velocity.

Quantum teleportation is a fundamental concept in quantum physics which now finds important applications at the heart of quantum technology including quantum relays, quantum repeaters and linear optics quantum computing (LOQC). Photonic implementations have largely focussed on achieving long distance teleportation due to its suitability for decoherence-free communication. Teleportation also plays a vital role in the scalability of photonic quantum computing, for which large linear optical networks will likely require an integrated architecture. Here we report the first demonstration of quantum teleportation in which all key parts - entanglement preparation, Bell-state analysis and quantum state tomography - are performed on a reconfigurable integrated photonic chip. We also show that a novel element-wise characterisation method is critical to mitigate component errors, a key technique which will become increasingly important as integrated circuits reach higher complexities necessary for quantum enhanced operation., Originally submitted version - refer to online journal for accepted manuscript; Nature Photonics (2014)

Ductile regime dicing has been used to machine a variety of optical materials to produce waveguides for lasers, multimode interference devices and non-linear devices. However, few papers discuss the properties of the machining, either qualitatively or quantitatively. In this work ductile regime dicing of germanium, Yttrium Aluminum Garnet (YAG), lithium niobate and silicon for photonic applications are reported. Machining parameters are discussed, surface micrographs shown, and surface roughnesses are calculated for each sidewall machined. The sidewall average surface roughnesses (Sa) were measured to be 2.1 nm for germanium, 3.5 nm for YAG, 7.9 nm for lithium niobate and 8.6 nm for silicon.

The potential of a new class of multifunctional photonic circuits is demonstrated by femtosecond laser micro-machining and inscription of micro-optical structures, such as ring and disk resonators, Mach-Zehnder interferometers, and microfluidic devices, in a flexible flat-fibre chip. Additional filling of surface channels with functional materials is employed towards sensing applications. Furthermore, direct write femtosecond-laser inscribed Bragg gratings were written in the Ge-doped core of flat-fibre enabling a number of relevant applications. The flat-fibre platform offers a unique degree of freedom by allowing surface and sub-surface devices to be integrated onto an a single optical chip with the potential for straightforward incorporation into integrated photonic circuits or optofluidic devices.

We have demonstrated that a planar integrated optical Bragg grating sensor chip, fabricated using a direct UV-writing approach, can perform as an all-optically accessed relative humidity sensor. Using a simple mesoporous silica thin film enabled operation across the range 0–100%RH, however a thickness decrease of 25% caused by hydrolytic degradation of the silica thin film resulted in a permanent decrease in sensitivity after 1–2 weeks use. Grafting the thin-film with aluminium oxide is shown here to prevent hydrolytic degradation with long-term sensitivity maintained. Aluminium oxide grafting offers the additional benefit of enhanced sensitivity, up to 3.5 times that of the silica analogue; the sensitivity of the aluminium oxide modified thin film device = 0.69 ± 0.05%RH/pm, in the range 0–60%RH within a gas flow system, whilst the sensitivity of the silica thin film sensor device = 2.47 ± 0.18%RH/pm. Long-term measurements, in static ambient lab conditions, were in excellent agreement with a commercial humidity sensor and also indicated that the thermal compensation afforded by the on-chip reference gratings was sufficient to prevent any drift in calibration. As with all humidity sensors, contamination of the sensor occurred. But for the aluminium oxide device, this was easily removed by rinsing with common organic solvents and the sensitivity was repeatedly and reproducibly restored. The device is accessed using optical fibre technology and is intrinsically safe in flammable environments.

Increasing the complexity of quantum photonic devices is essential for many optical information processing applications to reach a regime beyond what can be classically simulated, and integrated photonics has emerged as a leading platform for achieving this. Here, we demonstrate three-photon quantum operation of an integrated device containing three coupled interferometers, eight spatial modes and many classical and nonclassical interferences. This represents a critical advance over previous complexities and the first on-chip nonclassical interference with more than two photonic inputs. We introduce a new scheme to verify quantum behaviour, using classically characterised device elements and hierarchies of photon correlation functions. We accurately predict the device's quantum behaviour and show operation inconsistent with both classical and bi-separable quantum models. Such methods for verifying multiphoton quantum behaviour are vital for achieving increased circuit complexity. Our experiment paves the way for the next generation of integrated photonic quantum simulation and computing devices., 7 pages, 4 figures

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.

This paper reviews the demonstrations of photonic Hilbert transformers (PHTs), describing their progress and recent developments. The physical operating principles of PHTs including fractional Hilbert transformers are discussed, together with device applications in all-optical signal processing. Versatile approaches to realize PHTs are discussed, e.g., discrete free space optics, fiber-based schemes and integrated planar geometry. The numerical designs and experimental performances of these PHTs are analyzed in terms of spectral quality, operating bandwidth, system integration, and mechanical and thermal stability. Recent developments of the monolithically integrated photonic Hilbert transform (HT) devices include directional couplers and planar Bragg gratings which allow all-optical single-sideband (SSB) suppression and sideband switching.Erratum: The author of Ref. [1] Frederick W K should be King F W.

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.

Integrated quantum optics provides great promise for enabling photonic experiments to reach new regimes of complexity. Chip-based fabrication enables sophisticated networks involving multiple interfering pathways in a compact and stable physical architecture. In a recent work [1] we demonstrated an advance in the complexity of these integrated devices by showing the first quantum interference of three separate input photons. Such complexity allows the demonstration of three qubit protocols never before realised on-chip. Here, we report the first results showing quantum teleportation on an integrated photonic circuit. Quantum teleportation provides the mechanism for quantum relay schemes and is an important constituent in linear optical quantum computing. Whilst demonstrations to date have relied upon complex and fragile bulk optical systems, being able to teleport quantum states on a compact and stable integrated architecture will be a critical step towards scalable realisations of these schemes. © 2013 IEEE.

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.

While universal quantum computers ideally solve problems such as factoring integers exponentially more efficiently than classical machines, the formidable challenges in building such devices motivate the demonstration of simpler, problem-specific algorithms that still promise a quantum speedup. We construct a quantum boson sampling machine (QBSM) to sample the output distribution resulting from the nonclassical interference of photons in an integrated photonic circuit, a problem thought to be exponentially hard to solve classically. Unlike universal quantum computation, boson sampling merely requires indistinguishable photons, linear state evolution, and detectors. We benchmark our QBSM with three and four photons and analyze sources of sampling inaccuracy. Our studies pave the way to larger devices that could offer the first definitive quantum-enhanced computation., Main text: 5 pages, 4 figures. Supp Info: 6 pages

Tilted Bragg grating refractometers are ideal devices for sensing applications. They work by diffracting light from a confined core mode into a series of well-defined cladding modes that are sensitive to the refractive index of an adjacent fluid. Using the Cauchy integral method, we find the modes of a ridge waveguide refractometer. To gain good agreement with the experiment, the method requires us to take into account the dispersion and the 2-D geometry of the waveguide. The resulting modes are then used to predict the coupling dips in the reflection spectrum. Comparison with experimental measurements verifies the ability of this method to accurately determine the mode structure in the waveguide and, with minimal calibration, the refractive index of the adjacent fluid with error less than 2 ×10-4.

We present a planar-integrated optical surface plasmon refractometer. The fabricated device operates by grating-matched coupling between a core waveguide mode and a set of hybrid plasmon-dielectric modes of a much wider integrated structure. The constructed device incorporates a 50-nm-thin gold layer that separates a tilted planar-waveguide Bragg grating and a liquid analyte. It is demonstrated that polarization-dependent plasmon anomalies occur in the transmission spectra of the device, which are understood using a numerical Cauchy integral mode solving approach. Sensitivities in this planar-integrated device are comparable with existing fiber-based plasmonic sensors but with the advantages of planar integration and microfluidic adaptation.

Integration is currently the only feasible route toward scalable photonic quantum processing devices that are sufficiently complex to be genuinely useful in computing, metrology, and simulation. Embedded on-chip detection will be critical to such devices. We demonstrate an integrated photon-number-resolving detector, operating in the telecom band at 1550 nm, employing an evanescently coupled design that allows it to be placed at arbitrary locations within a planar circuit. Up to five photons are resolved in the guided optical mode via absorption from the evanescent field into a tungsten transition-edge sensor. The detection efficiency is 7.2 +/- 0.5%. The polarization sensitivity of the detector is also demonstrated. Detailed modeling of device designs shows a clear and feasible route to reaching high detection efficiencies.

Oxygen sensing is required for the understanding of many chemical processes across a diverse set of fields including medicine, environmental science and chemical synthesis. Oxygen sensing can be achieved through the use of electronic sensors. However, there are limitations associated with electronic sensors including susceptibility to electromagnetic interference and presenting a spark risk in flammable environments. Optical fiber and integrated optical chemical sensors overcome these limitations of electrical based sensing methods.

High demand on structural health monitoring has encouraged the development of smart structure geometries to be more effective and competitive [1]. One of the technologies that has been integrated into these structures is the fiber Bragg grating (FBG) [2]. The FBG is a mature technology that has seen many applications, particularly the field of sensing where it has many advantages such as immunity to electromagnetic field, long lifetime, high sensitivity, lightweight and low loss. There are several types of optically based physical sensors. Most of which are fabricated in a standard dimension silica optical fiber which due to its cylindrical structure are unable to independently measure twist. Here we demonstrate a bending and twist sensor fabricated in a flat-fiber substrate. A Y-splitter and a series of Bragg gratings along the 50 mm length provides a differential signal providing distinction between bend and twist within the sample.

Multi-mode photonic lightwave circuits (PLCs) provide new avenues for extending the performance of single mode systems. As an example, they can potentially provide increased bandwidth by multiplexing information into different waveguide modes[1]. For practical applications of multi-mode PLCs to be developed, a measurement technique is required to investigate detailed mode profiles and propagation constants in complex circuits. Photon scanning tunnelling microscopy (PSTM) provides a means of experimentally tracking the femtosecond inter-modal delays observed in PLCs with the ability to discriminate modes by their spatial profiles inside the waveguide.

Photonic Hilbert transformers (PHT) offer potential for a wide range of applications in telecommunication, information processing and signal analysis [1]. They provide operational bandwidths and speeds far beyond current electronic technologies. PHTs have been realized in discrete free space components and recently in fiber using multi-tapped sampled fiber Bragg gratings (FBGs), and single phase-shifted FBGs with appropriate apodisation profile [2]. Recently we have presented preliminary spectra from a fabricated PHT device in a planar waveguide [3]. This device employs a single pi phase shift and an apodised grating profile. In this work we use the freedom of the planar format to fabricate a single-side-band suppression (SSBS) module combining regular and phase shifted gratings on a single chip.

A photoactive material has been synthesised in which azobenzene units are attached to a methyl methacrylate/2-hydroxyethyl methacrylate co-polymer and shows repeated photoresponsive switching upon irradiation at 365 nm and 254 nm with long term thermal stability. In combination with a direct UV-written silica-on-silicon Bragg grating, this has been used to fabricate a prototype optical device which undergoes reversible refractive index changes at telecom wavelengths. The 63 GHz tuning response demonstrated by this device has potential applicability for reconfigurable dispersion compensation for use in optical networks.

In this work the theoretical design and experimental realisation of a photonic Hilbert transformer is investigated. Planar Bragg gratings are proposed as a route to realise photonic Hilbert transformers in terms of a finite bandwidth and temporal impulse response. With proper grating apodisation and π-phase shift, the Bragg grating will display the spectral features expected from a Hilbert transformer. The unique features of Direct UV grating writing technology are used to fabricate the proposed device in silica-on-silicon

Integrated planar lightwave circuits (PLCs) provide a promising route to small-scale quantum optical networks [1]. Recent work on quantum logic gates using silica-based PLCs has highlighted the opportunities afforded by the ability to coherently manipulate degrees of freedom at the level of single photons [2]. Increasingly complex waveguide networks are required for linear optics quantum computing (LOQC), a route towards small scale quantum information processing [3]. This approach uses quantum interference between photons and measurements with feedforward to implement the nonlinear interactions between photons that are required for information processing. A major issue in developing such circuits is the internal loss and the coupling efficiency of input photon from optical fibers.