Electro-optic modulation in bulk silicon using surface plasmon resonance

The authors acknowledge funding from the EPSRC in the UK under the UK Silicon Photonics project.We propose and present simulated results for a new design of an optical modulator based on Surface Plasmon Polariton (SPP) resonance. The modulator is realized on a bulk silicon substrate, thus offering an opportunity for front-end integration with electronic circuits. The device consists of a dielectric waveguide evanescently coupled to a SPP mode at the interface between bulk silicon and metal. By using SPP resonance we achieved an ultra-high spectral sensitivity (∼5000 nm/refractive index unit) with large modulation bandwidth (90 nm). For a refractive index change of 0.02, we achieved 100 nm shift in resonance wavelength and a modulation depth of ∼10 dB.PostprintPeer reviewe

Toolkit for photonic integrated circuits based on inverted rib waveguides

This work was supported by an EPSRC Doctoral Prize and a European Research Council Starting under Grant 337508.We have performed an exploration of inverted rib waveguide platform for use in optical backplanes. This entailed the design, optimization, and characterization of a variety of passive optical components that may serve as a basis for the functions required of an on-chip optical networks. The presented design introduces an inverted-rib template, which consists of a polymer waveguide layer. We have successfully fabricated and demonstrated low-loss waveguides, and also functional passive devices such as directional couplers, multimode interferometers, waveguide bends and crossings, and distributed Bragg reflectors. We also demonstrate a way of coupling active components (e.g., in silicon) to such a photonic integrated circuit.PostprintPeer reviewe

Polarization Rotation and Mode Splitting in Photonic Crystal Line-Defect Waveguides

In a line-defect waveguide of a planer photonic crystal (PhC), we found a new rotational state of polarized light, which exhibits “polarization rotation” on the PhC plane, when a phase mismatch m was added to the air-hole alignment of the waveguide, where mode splitting was simultaneously observed in the dispersion curve. To account for the polarization rotation together with the mode splitting, we propose a two-state model that is constructed from Schrödinger equation obtained from the equation for electromagnetic waves. The proposed two-state model gives an explanation on the relation between the polarization-rotational angle θ and the mismatch m and on its rotational direction (i.e., clockwise or anticlockwise direction) that depends on the mode. Using the two-state model, we also discuss the angular momenta of the polarized light in the PhC waveguide, which are directly related to the Stokes parameters that characterize the polarization rotations

Exceptional point induced quantum phase synchronization and entanglement dynamics in mechanically coupled gain-loss oscillators

The optomechanical cavity (OMC) system has been a paradigm in the manifestation of continuous variable quantum information over the past decade. This paper investigates how quantum phase synchronization relates to bipartite Gaussian entanglement in coupled gain-loss mechanical oscillators, where the gain and loss rates are engineered by driving the cavity with blue and red detuned lasers, respectively. We examine the role of exceptional point in a deterministic way of producing self-sustained oscillations that induce robust quantum correlations among quadrature fluctuations of the oscillators. Particularly, steady phase synchronization dynamics along with the entanglement phenomena are observed in the effective weak coupling regime above a critical driving power. These phenomena are further verified by observing the mechanical squeezing and phase space rotations of the Wigner distributions. Additionally, we discuss how the oscillators frequency mismatches and decoherence due to thermal phonons impact the system dynamics. These findings hold promise for applications in phonon-based quantum communication and information processing.Comment: 10 pages, 9 figure

Highly efficient coupling between a monolithically integrated photonic crystal cavity and a bus waveguide

We experimentally demonstrate a new optical filter design comprising of a photonic crystal cavity and a low index bus waveguide which are monolithically integrated on a silicon-on-insulator (SOI) platform. We have fabricated oxide clad PhC cavities with a silicon nitride waveguide positioned directly above, such that there is an overlap between the evanescent tails of the two modes. We have realised an extinction ratio of 7.5dB for cavities with total Q of 50,000.Postprin

Wavelength-controlled external-cavity laser with a silicon photonic crystal resonant reflector

This work was partially funded by the EPSRC, Scottish Enterprise, and the European Research Council under the Starting Grant 337508.We report the experimental demonstration of an alternative design of external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises a polymer (SU8) bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and sidemode suppression ratio of more than 25 dB.Publisher PD

Efficacy and safety of intravenous and/or oral levonadifloxacin in the management of secondary bacterial pulmonary infections in COVID-19 patients: findings of a retrospective, real-world, multi-center study

Background: Owing to dysregulated immune response, secondary bacterial pulmonary infections involving both gram-positive and gram-negative pathogens are common in COVID-19 patients and are often associated with higher mortality. This is a first ever report on the safety and efficacy of levonadifloxacin in the treatment of secondary bacterial pulmonary infections in patients with COVID-19 pneumonia.Methods: This multi-center, retrospective, post-marketing and real-world study assessed the safety and efficacy of IV and/or oral levonadifloxacin in the treatment of bacterial infections encountered in COVID-19 patients. Data for 154 male/female patients above 18 years of age who received levonadifloxacin (injectable and/or oral) was collected from 44 participating sites. Study outcomes were the clinical and microbial success at the end of therapy. Safety was assessed based on clinical and laboratory adverse events.Results: Among the 154 patients assessed, 121 (78.6%) were males and 142 (92.2%) were hospitalized. Majority of the patients (119) received all-IV therapy while 11 patients were prescribed with IV followed by oral regimen. All-oral therapy was received by 24 patients. The most common co-morbid conditions were diabetes (19.6%) and hypertension (19.2%). Post-treatment with levonadifloxacin, clinical and microbial success rates were 96.8% and 97.0% respectively.Conclusions: Levonadifloxacin showed promising safety and efficacy when used as IV and/or oral therapy for the treatment of secondary bacterial pulmonary infections in COVID-19 patients. Clinically relevant features of levonadifloxacin such as availability of both IV and oral options, broad spectrum coverage and reassuring safety in patients with significant co-morbidities could help simplify the management.Trial registration no. CTRI/2020/09/028152 [Registered on: 30/09/2020]

Photonic crystal waveguides on silicon rich nitride platform

We demonstrate design, fabrication, and characterization of two-dimensional photonic crystal (PhC) waveguides on a suspended silicon rich nitride (SRN) platform for applications at telecom wavelengths. Simulation results suggest that a 210 nm photonic band gap can be achieved in such PhC structures. We also developed a fabrication process to realize suspended PhC waveguides with a transmission bandwidth of 20 nm for a W1 PhC waveguide and over 70 nm for a W0.7 PhC waveguide. Using the Fabry–Pérot oscillations of the transmission spectrum we estimated a group index of over 110 for W1 PhC waveguides. For a W1 waveguide we estimated a propagation loss of 53 dB/cm for a group index of 37 and for a W0.7 waveguide the lowest propagation was 4.6 dB/cm

Low-loss slot waveguides with silicon (111) surfaces realized using anisotropic wet etching

We demonstrate low-loss slot waveguides on silicon-on-insulator (SOI) platform. Waveguides oriented along the (11-2) direction on the Si (110) plane were first fabricated by a standard e-beam lithography and dry etching process. A TMAH based anisotropic wet etching technique was then used to remove any residual side wall roughness. Using this fabrication technique propagation loss as low as 3.7dB/cm was realized in silicon slot waveguide for wavelengths near 1550nm. We also realized low propagation loss of 1dB/cm for silicon strip waveguides