By optimising the geometry of asymmetric split-H (ASH) resonators fabricated on zinc selenide, we have produced a total of four distinct plasmonic resonances that could be matched with six molecular vibration wavelengths (for O-H, C-H, C=O, C=C, CºC-H and C-C bonds) which are relevant to the detection of four estrogenic hormones: estrone (E1), 17β-estradiol (E2), estriol (E3) and synthetic estrogen; 17α-ethinyl estradiol (EE2). Specifically, sensitivities of 363 nm/RIU and 636 nm/RIU were achieved from the deposition of E2 on ASH1 (2 μm and 4 μm) and ASH2 (5 μm and 8 μm) respectively. A Fourier transform infrared (FTIR) spectrometer was used to measure the transmittance resonances of the fabricated ASH arrays. The amplitudes of the molecular vibrational resonances were also around 500 times greater when matched with the plasmonic resonances of the ASHs as compared with deposit on on bulk ZnSe substrates. Finally, when mixtures of two hormones were deposited on the nanoantennas, the molar ratio for each of the hormones could also be calculated by using the peak intensities for the different molecular vibration wavelengths. By engineering the spectral response of ASH resonators to match specific estrogenic fingerprints, the work paves the way for the development of metamaterial sensors with better specificity and enhanced functionalities.

We propose a post-fabrication trimming method for the silicon-on-insulator photonic platform based on localised laser annealing of hydrogen silsesquioxane (HSQ) cladding. The technique is fast, does not degrade the device performance, does not require additional fabrication steps, and can therefore be implemented at minimal cost. Here we experimentally demonstrated how the spectrum of a ring resonator can be shifted by over 1 nm by annealing a section of the device as short as 30 µm, corresponding to a change in the effective refractive index of ∼10−2. Modifications of both the HSQ refractive index and its chemical structure as a function of the annealing temperature are also discussed. Trimming of multi-ring resonators indicate that this technique can be effectively used for post-fabrication reconfiguration of complex photonic circuits or to compensate for the fabrication tolerances of a typical CMOS process.

High-order distributed feedback resonators realized in silicon-on-insulator technology for the implementation of high-performance integrated optical filters are reported. This approach combines design simplicity and flexibility in a compact footprint with filter transfer functions featuring a flat-top response, large out-of-band rejection of more than 40 dB, ultra-steep roll-off up to 1000 dB/nm, and unprecedented stopband-to-passband ratios up to 600 for high-index-contrast technology. Active control of the coupled cavities through local micro heaters is employed for optimizing the filter response and passband tuning. Exemplary implementations of a box-like transfer function filter with a bandwidth of 25 GHz and of a narrow linewidth 2 GHz filter realized with 6 th - and 3 rd -order filter designs, respectively, are presented.

We demonstrate optical wavelength conversion in a multi-mode silicon waveguide using four wave mixing Bragg scattering enabled by a dual-pump CW scheme. The original signal and the generated idler pair excite one spatial mode (first, TE mode), while the two pumps excite a different spatial mode (second, TE mode) of the same waveguide. Our approach exploits the differences in the group velocities of the various supported spatial modes to ensure phase matching only for the desired nonlinear process. In this proof-of-principle experiment, any unintended idlers are generated with an extinction ratio up to 12 dB relative to the phase-matched idlers for a pumps-to-signal-idler-pair wavelength detuning of about 70 nm. The scalability of the scheme to achieve larger and multiple signal wavelength detunings from the pump frequencies is also discussed.

In this paper, we report the generation of an ultra-sharp asymmetric resonance spectrum through Fano-like interference. This generation is accomplished by weakly coupling a high-quality factor (Q factor) Fabry-Pérot (FP) cavity and a low-Q factor FP cavity through evanescent waves. The high-Q FP cavity is formed by Sagnac loop mirrors, whilst the low-Q one is built by partially transmitting Sagnac loop reflectors. The working principle has been analytically established and numerically modelled by using temporal coupled-mode-theory (CMT), and verified using a prototype device fabricated on the 340 nm silicon-on-insulator (SOI) platform, patterned by deep ultraviolet (DUV) lithography. Pronounced asymmetric resonances with slopes up to 0.77 dB/pm have been successfully measured, which, to the best of our knowledge, is higher than the results reported in state-of-the-art devices in on-chip integrated Si photonic studies. The established theoretical analysis method can provide excellent design guidelines for devices with Fano-like resonances. The design principle can be applied to ultra-sensitive sensing, ultra-high extinction ratio switching, and more applications.

Silicon-on-Insulator devices are particularly sensitive to fabrication errors. As an example, a deviation in waveguide height or width of as little as 1nm translates directly to a 1nm offset in the transfer function of any interferometric devices (such as a ring resonator) constructed using the said waveguide. Therefore, even as fabrication tolerance continues to improve, post-fabrication treatment is often the only way of ensuring device uniformity for particularly demanding applications. This work proposes a novel approach for post fabrication trimming of SOI devices based on localised laser annealing of HSQ cladding layer. HSQ is a versatile material often used in fabrication of SOI devices as both the mask material for electron-beam lithography resist and as a cladding or planarization layer due to its similarity to conventional silica. However, unlike silica, the refractive index of HSQ can be changed significantly (up to ΔnHSQ = 3.26*10-2) by thermal processing. We utilise this property for trimming by cladding a conventional SOI waveguide optimised for TE propagation (height h=220 nm, width=500nm) with a layer of HSQ and then permanently changing the refractive index of the cladding via laser annealing. This approach allows us to select individual devices and only apply the change where necessary. As a demonstrator, we trim a resonance of a racetrack resonator by 1.3nm. The technique has proven to be robust with no parameter drift observed 7 days after trimming and no thermal cross-talk to neighbouring devices. Furthermore, unlike its predecessors, it is based on a standard fabrication process and does not require expensive specialised equipment.

One approach that has been demonstrated as viable in biomedical sensing is the use of fluorescent labelling, e.g. for carrying out competition immunoassays to identify the possible presence of specific analyte molecules in suitably prepared fluid samples. Many bio-materials exhibit a finite level of fluorescence that could possibly be exploited in sensing, but is also potentially problematic when it forms an undesired background, thereby limiting sensitivity. But the alternative approach of label-free biomedical sensing seems likely to be favoured in future applications. A 'standard' approach to label-free sensing exploits the detection of changes in the (complex) refractive index that occur when bio-material is added to the local environment of a designed resonant structure, thereby changing its resonance frequency. Designed tuning of reflection, transmission and absorption resonances can be used to help identify specific molecules, through selection of the known bond resonances of the molecules of interest. Since it is typically possible to organise resonant structures in arrays that consist of thousands of individual resonant 'atoms', thereby forming a metasurface, it has become possible to select and quantify various characteristic molecular bond resonances simultaneously - and to identify possible molecular compositions in composite bio-material.

Silicon photonics tunable passband optical filters with flat-top feature, large out-of-band rejection in excess of 40 dB, ultra-fast roll-off up to 1,000 dB/nm, and unprecedented passband-to-stopband ratio for high-index-contrast technology have been fabricated and characterized. The integrated filters are based on high-order distributedfeedback resonators implemented with cascaded phase-shifted Bragg gratings in silicon strip waveguides. Local micro-heaters are used for finely controlling the phases of the individual cavities of the coupled resonators and for providing additional tuning mechanism. Two different coupled-cavity resonators with passband widths of 25 GHz and 2 GHz, realized with 6thand 5thorder filter designs, respectively, are exemplarily reported.

The field of silicon photonics has expanded rapidly over the past several decades. This has led to a degree of standardisation in the commercial device fabrication foundries that are available for universities and fabless companies alike. Whilst this is advantageous in terms of yield, repeatability etc., it is not conducive for researchers to develop new and novel devices for future systems. CORNERSTONE offers researchers a flexible device prototyping capability that can support photonics research around the world. The CORNERSTONE project (Capability for OptoelectRoNics, mEtamateRialS, nanoTechnOlogy, aNd sEnsing) is a UK Engineering and Physical Sciences Research Council (EPSRC) funded project between 3 UK universities: University of Southampton, University of Glasgow and University of Surrey. The project is based on deep-ultraviolet (DUV) photolithography equipment, installed at the University of Southampton, centred around a 248 nm Scanner, the first of its kind in a UK university. Utilising these facilities, CORNERSTONE will offer a multi-project wafer (MPW) service on several silicon-on-insulator (SOI) platforms (220 nm, 340 nm & 500 nm) for both passive and active silicon photonic devices. This talk will give an overview of the CORNERSTONE project, present some of its early data, and summarise future MPW offerings.

A new approach for broad and efficient tuning of the narrow resonant transmission window in integrated phase-shifted Bragg gratings realized in silicon waveguides, suitable for the photonic processing of microwave signals, is proposed and demonstrated. The method exploits local micro-heaters (MHs) for the tuning of the resonant cavity formed by the insertion of a phase-shift section within a uniform Bragg grating structure. Two different MHs geometries have been investigated. Wide tuning ranges of the passband filter with a narrow linewidth of ~30 pm up to 7 nm, only limited by the BG stopband region width, for maximum MH absorbed power of ~11 mW are observed.

Multi-cavity integrated passband optical filters using phase-shifted Bragg gratings incorporating micro-heaters for fine phase-shifts control are realized in silicon-on-insulator technology. Experiments report flat-top moderate-loss sharp passband windows with 40dB contrast-ratio, and up to 250 dB/nm roll-off for 3rd-order filter designs.

We report the first demonstration of inter-modal wavelength conversion in a silicon waveguide using a telecom-compatible dual-pump CW scheme. Phase-matched inter-modal four-wave-mixing is achieved locating the pumps in the C-band and the signal in the L-band, and vice versa.

We present the first ever inter-modal silicon photonic wavelength converter operated with a telecom-compatible dual-pump CW scheme. We achieve phase-matched inter-modal four-wave-mixing, allowing for wavelength conversion with a pumps-to-signal wavelength detuning of 70 nm.

Silicon on Insulator (SOI) is a well-established photonic platform that is of interest to photonic integrated circuits (PICs) due to its compatibility with existing fabrication processes used in the manufacture of electronic integrated circuits. Although SOI offers a high refractive index contrast that enables strong optical confinement of the propagating optical mode in the silicon layer, the performance of the photonic circuit components (such as, for example, ring resonators) is significantly dependant on fabrication tolerance. This can result in ring resonances that substantially deviate from the designed ones. It is therefore advantageous to be able to trim or tune such components post-processing, so as to adjust a resonance to the desired wavelength.Metallic heaters placed in close proximity to waveguides have been shown to introduce tunability by inducing a thermal phase velocity mismatch between coupled modes [1]. However, this increases the device power consumption, functions only when the heaters are powered and requires additional fabrication processing involving metals. An alternative and potentially preferential method involves thermally curing a cladding layer on top of the silicon circuit components as a means to permanently change the effective index of the optical mode. It has been demonstrated that thermally curing hydrogen silseqsuioxane (HSQ), a spin-on dielectric commonly used as a negative tone electron-beam resist, increases the porosity of the material and, consequentially, permanently decreases the refractive index. The change in the HSQ refractive index can be controlled by varying both the temperature and the time that curing is performed [2]. Utilising the HSQ layer on top of SOI optical circuits, we can demonstrate tunability of the resonant response. Fig. 1. shows the shift in measured resonance of a SOI racetrack resonator with bus-waveguide cured on a hotplate at 250 ̊ C at 1 minute increments.In conclusion, we present a simple technique that allows spatially selective trimming of silicon photonic chips through laser irradiation of the HSQ upper cladding. Because HSQ is a silica-like material widely used as an upper cladding in silicon photonic processing, the devices can be built on well-established designs and exhibit long-term stability.

Detection and identification of biomedically significant molecules is an important application in infra-red (IR) spectroscopy. This presentation will consider some of the significant features of the different alternative building-block elements that can be used in array metasurfaces for enhanced detection sensitivity. The presentation will also address techniques and issues associated with the deposition and localisation of biological and organic chemical molecular material for detection and measurement using IR spectroscopy.

Split ring resonator (SRR) based metamaterials have frequently been demonstrated for use as optical sensors of organic materials. This is made possible by matching the wavelength of the SRR plasmonic resonance with a molecular resonance of a specific analyte, which is usually placed on top of the metal structure. However, systematic studies of SRRs that identify the regions that exhibit a high electric field strength are commonly performed using simulations. In this paper we demonstrate that areas of high electric field strength, termed “hot-spots,” can be found by localizing a small quantity of organic analyte at various positions on or near the structure. Furthermore, the sensitivity of the SRR to the localized analyte can be quantified to determine, experimentally, suitable regions for optical sensing.

In this paper we report on a very sensitive biosensor based on gold asymmetric nanoantennas that are capable of enhancing the molecular resonances of C-H bonds. The nanoantennas are arranged as arrays of asymmetric-split H-shape (ASH) structures, tuned to produce plasmonic resonances with reflectance double peaks within the mid-infrared vibrational resonances of C-H bonds for the assay of deposited films of the molecule 17β-estradiol (E2), used as an analyte. Measurements and numerical simulations of the reflectance spectra have enabled an estimated enhancement factor on the order of 105 to be obtained for a thin film of E2 on the ASH array. A high sensitivity value of 2335 nm/RIU was achieved, together with a figure of merit of approximately 8. Our experimental results were corroborated using numerical simulations for the C-H stretch vibrational resonances from the analyte, superimposed on the plasmonic resonances of the ASH nanoantennas.

In this paper, both simulated and experimental measurements on arrays of asymmetric split-ring resonators (A-SRRs) with varying diameters are reported. Their responses appear in the mid-infrared (IR) spectral region and match well with the vibrational resonances of many organic molecules. Such structures can be used to detect protein molecules in their native biological environments. The use of a zinc selenide (ZnSe) substrate facilitates measurement of transmission spectra at wavelengths in the mid-IR.

Metamaterial structures fabricated using nanoimprint lithography, allow large areas to be patterned quickly through multiple use of a nanoimprint stamp. The fabrication process produces fishnet structures of various dimensions on a polymer layer with metal-dielectric-metal compressed rectangular pillars. Simulations show negative refractive index and good figures of merit. However both of these figures could be increased by removal from the underlying polymer structure. We also report on the use of asymmetric spilt ring resonators used to detect small quantities of hormone estradiol by tuning the plasmonic resonances near the molecular resonance of the C-H stretch at nominally 3.31 microns.