Silicon-tapered waveguide for mode conversion in metal-insulator-metal waveguide-based plasmonic sensor for refractive index sensing

In this study, we have undertaken a comprehensive numerical investigation of a refractive index sensor designed around a metal-insulator-metal (MIM) plasmonic waveguide. Our approach utilizes the finite element method to thoroughly analyze the sensor's performance. The sensor's configuration utilizes a ring resonator design, which has been slightly modified at the coupling segment. This modification enhances the efficiency of light coupling between a bus waveguide and the ring resonator, particularly at the resonance wavelength. This strategic adjustment significantly improves the device's extinction ratio, a critical factor in its functionality. Remarkably, the sensitivity of this sensor is determined to be approximately 1155.71 nm/RIU, while it possesses a figure of merit of 25.9. Furthermore, our study delves into the intricate mechanism governing the injection of light into the nanoscale MIM waveguide. We achieve this through the incorporation of silicon-tapered waveguides, which play a pivotal role in facilitating the transformation of a dielectric mode into a plasmonic mode, and vice versa. Ultimately, the findings of this research hold significant promise for advancing the field of plasmonic sensing systems based on MIM waveguide technology. The insights gained here pave the way for the practical realization and optimization of highly efficient and precise plasmonic sensors.

Numerical scrutiny of a silica-titania-based reverse rib waveguide with vertical and rounded sidewalls

In this work, a modal analysis of reverse rib waveguide (RRW) structures based on a silica-titania platform is carried out. The silica-titania waveguide films can be deposited via the sol-gel method and dip-coating technique. To combine this low-cost deposition technique with the economical fabrication method, we propose to structure the samples via wet-chemical etching. Due to the isotropic nature of wet etching, the waveguide architecture with rounded sidewalls is considered to model the RRW. Additionally, the modal conditions and bending loss are compared with the RRW with vertical sidewalls. It is assumed that this study will be beneficial for comprehending the modal conditions of waveguide structures with perfectly vertical and rounded sidewalls.

Development of a low-cost silica-titania optical platform for integrated photonics applications

This paper investigates a highly attractive platform for an optical waveguide system based on silica-titania material. The paper is organized into two parts. In the first part, an experimental study on the development of an optical waveguide system is conducted via the sol-gel dip-coating method, and the optical characterization of the waveguide system is performed at a visible wavelength. This system is capable of operating from visible to near-IR wavelength ranges. The experimental results prove the dominance of this waveguide platform due to its low-cost, low loss, and easy to develop integrated optics systems. The numerical analysis of a one-dimensional Photonic crystal waveguide optical filter based on the silica-titania platform is considered in the second part of the paper by utilizing the 2D-finite element method (2D-FEM). A Fabry-Perot structure is also analyzed for refractive index sensing applications. We believe that the results presented in this work will be valuable in the realization of low-cost photonic integrated circuits based on the silica-titania platform.

Plasmonic sensor based on metal-insulator-metal waveguide square ring cavity filled with functional material for the detection of CO2 gas

In this work, a straightforward and highly sensitive design of a CO₂ gas sensor is numerically investigated using the finite element method. The sensor is based on a plasmonic metal-insulator-metal (MIM) waveguide side coupled to a square ring cavity filled with polyhexamethylene biguanide (PHMB) functional material. The refractive index of the functional material changes when exposed to the CO₂ and that change is linearly proportional to the concentration of the gas. The sensors based on surface plasmon polariton (SPP) waves are highly sensitive due to the strong interaction of the electromagnetic wave with the matter. By utilizing PHMB polymer in the MIM waveguide plasmonic sensor provides a platform that offers the highest sensitivity of 135.95 pm/ppm which cannot be obtained via optical sensors based on silicon photonics. The sensitivity reported in this work is ∼7 times higher than reported in the previous works. Therefore, we believe that the results presented in this paper are exceedingly beneficial for the realization of the sensors for the detection of toxic gases by employing different functional materials.

327 Rare Synchronous Volvulus of Sigmoid Colon and Caecum, Management of Two Cases

Colonic volvulus accounts for approximately 5% of cases of large bowel obstruction. Sigmoid volvulus is commonest (75%), followed caecal volvulus (15%). Synchronous volvulus of the caecum and sigmoid is rare, with five reported cases in the literature. We report two cases in a London teaching hospital managed within 6 months. Both male patients (aged 72 and 79 years) had presented to the emergency department on multiple occasions (2-5 times in the preceding 1-8 months), with obstructive symptoms including tender abdominal distension and constipation. On all occasions, sigmoid volvulus was diagnosed based on plain abdominal films and flatus tubes were inserted, with initial clinical resolution. On their final presentation, both patients were admitted for definitive surgery. CT scans of the abdomen and pelvis were consistently reported as showing only sigmoid volvulus. Only intra-operatively was the diagnosis of synchronous caecal and sigmoid volvulus appreciated. Complete symptom resolution was achieved with subtotal colectomy and ileostomy formation. The key learning points from these cases are: 1) synchronous large bowel volvulus is a rare and easily missed diagnosis, 2) conservative management is unlikely to be successful, 3) radiological appearances may only suggest one type of large bowel volvulus and 4) definitive diagnosis is made intra-operatively.

Ultrashort inverted tapered silicon ridge-to-slot waveguide coupler at 1.55 µm and 3.392 µm wavelength

Herein, a compact and efficient inverted tapered ridge-to-slot waveguide coupler design based on the silicon-on-insulator platform is presented. The proposed device consists of three segments such as ridge waveguide, inverted taper segment, and slot waveguide. The coupling segment resembles a V shape, which provides good mode-matching between the ridge and slot waveguide. Two significant aspects of the proposed coupler design are discussed. In the first part of the paper, the coupler design optimized at 1.55 µm is suggested for optical interconnect. The propagation loss and coupling efficiency of 1.69 dB/µm and 91% are obtained for the 100 nm long tapered segment introduced between the ridge waveguide and slot waveguide, respectively. This propagation loss of the device includes the loss suffered by the ridge waveguide, tapered segment, and slot waveguide. Our proposed device design can be used in integrated optical platforms, where the efficient coupling of light to slot waveguides is required. Whereas, in the second part, the coupler design is optimized at the mid-infrared of 3.392 µm for an evanescent field absorption methane gas sensor. Slot waveguide offers excessive light-matter interaction due to its strong mode confinement in the low index material. The evanescent field ratio of ∼0.73 is obtained for the optimized waveguide geometry. As a result, 3 dB decay in the transmitted power can be obtained at 60% of gas concentration present in the ambient medium.

A HER2 selective theranostic agent for surgical resection guidance and photodynamic therapy

In many cancers early intervention involves surgical resection of small localised tumour masses. Inadequate resection leads to recurrence whereas overzealous treatment can lead to organ damage. This work describes production of a HER2 targeting antibody Fab fragment dual conjugated to achieve both real time near-infrared fluorescent imaging and photodynamic therapy. The use of fluorescence emission from a NIR-dye could be used to guide resection of tumour bulk, for example during endoscopic diagnosis for oesophago-gastric adenocarcinoma, this would then be followed by activation of the photodynamic therapeutic agent to destroy untreated localised areas of cancer infiltration and tumour infiltrated lymph nodes. This theranostic agent was prepared from the Fab fragment of trastuzumab initially by functional disulfide re-bridging and site-specific click reaction of a NIR-dye. This was followed by further reaction with a novel pre-activated form of the photosensitiser chlorin e6 with the exposed fragments' lysine residues. Specific binding of the theranostic agent was observed in vitro with a HER2 positive cell line and cellular near-infrared fluorescence was observed with flow cytometry. Specific photo-activity of the conjugates when exposed to laser light was observed with HER2 positive but not HER2 negative cell lines in vitro, this selectivity was not seen with the unconjugated drug. This theranostic agent demonstrates that two different photo-active functions can be coupled to the same antibody fragment with little interference to their independent activities.

Improvement over time in outcomes for patients undergoing endoscopic therapy for Barrett's oesophagus-related neoplasia: 6-year experience from the first 500 patients treated in the UK patient registry

BACKGROUND

Barrett's oesophagus (BE) is a pre-malignant condition leading to oesophageal adenocarcinoma (OAC). Treatment of neoplasia at an early stage is desirable. Combined endoscopic mucosal resection (EMR) followed by radiofrequency ablation (RFA) is an alternative to surgery for patients with BE-related neoplasia.

METHODS

We examined prospective data from the UK registry of patients undergoing RFA/EMR for BE-related neoplasia from 2008 to 2013. Before RFA, visible lesions were removed by EMR. Thereafter, patients had RFA 3-monthly until all BE was ablated or cancer developed (endpoints). End of treatment biopsies were recommended at around 12 months from first RFA treatment or when endpoints were reached. Outcomes for clearance of dysplasia (CR-D) and BE (CR-IM) at end of treatment were assessed over two time periods (2008-2010 and 2011-2013). Durability of successful treatment and progression to OAC were also evaluated.

RESULTS

508 patients have completed treatment. CR-D and CR-IM improved significantly between the former and later time periods, from 77% and 56% to 92% and 83%, respectively (p<0.0001). EMR for visible lesions prior to RFA increased from 48% to 60% (p=0.013). Rescue EMR after RFA decreased from 13% to 2% (p<0.0001). Progression to OAC at 12 months is not significantly different (3.6% vs 2.1%, p=0.51).

CONCLUSIONS

Clinical outcomes for BE neoplasia have improved significantly over the past 6 years with improved lesion recognition and aggressive resection of visible lesions before RFA. Despite advances in technique, the rate of cancer progression remains 2-4% at 1 year in these high-risk patients.

TRIAL REGISTRATION NUMBER

ISRCTN93069556.