In recent years, we have presented results on the development of erasable gratings in silicon to facilitate wafer scale testing of photonics circuits via ion implantation of germanium. Similar technology can be employed to develop a range of optical devices that are reported in this paper. Ion implantation into silicon causes radiation damage resulting in a refractive index increase, and can therefore form the basis of multiple optical devices. We demonstrate the principle of a series of devices for wafers scale testing and have also implemented the ion implantation based refractive index change in integrated photonics devices for device trimming.
A crucial component of any large scale manufacturing line is the development of autonomous testing at the wafer scale. This work offers a solution through the fabrication of grating couplers in the silicon-on-insulator platform via ion implantation. The grating is subsequently erased after testing using laser annealing without affecting the optical performance of the photonic circuit. Experimental results show the possibility for the realisation of low loss, compact solutions which may revolutionise photonic wafer-scale testing. The process is CMOS compatible and can be implemented in other platforms to realise more complex systems such as multilayer photonics or programmable optical circuits.
Since their inception, metamaterial fishnet structures have frequently been used to exhibit a negative refractive index. Their shape and structure make it possible to independently produce both a negative permeability (μ) and a negative permittivity (ε). Fishnets that display this characteristic can be referred to as a double negative metamaterial. Although other techniques have been demonstrated, fishnets are commonly fabricated using electron-beam lithography (EBL) or focused ion-beam (FIB) milling. In this paper we demonstrate the fabrication of fishnets using nano-imprint lithography (NIL). Advantages associated with NIL include a shorter fabrication time, a larger feasible pattern area and reduced costs. In addition to these advantages, the quality of the fabricated structures is excellent. We imprint a stamp directly into a metal-dielectric-metal stack which creates the fishnet and, as an artifact of the technique, a periodic array of nanopillars. Two different designs of the fishnet and nanopillar structure have been fabricated and optical measurements have been taken from both. In addition to the experimental measurements the structures have also been extensively simulated, suggesting a negative refractive index with a real part as large in magnitude as five can be achieved.
We report on the fabrication and characterisation of fishnet structures of various dimensions on a polymer layer. The fabrication process causes metal-dielectric-metal rectangular pillars to be compressed to the bottom of fishnet structures. The metamaterial structures are fabricated using nanoimprint lithography, allowing large areas to be patterned quickly and good reproducibility through multiple use of the nanoimprint stamp. A tri-layer comprising of silver (Ag) and magnesium fluoride (MgF<sub>2</sub>) was deposited on a thick polymer layer, in this instance PMMA, before being directly imprinted by a stamp. When the metal-dielectric layered pillars are imprinted to a sufficient depth in the PMMA below the fishnet, distinct resonance peaks can be measured at both visible and near-infrared frequencies. The precise wavelength of the resonant peak at near-infrared and its Q-factor can be changed by altering the physical dimensions and number of metal and dielectric layers of the fishnet respectively. The response viewed at visible frequencies is due to the pillars that sit in the PMMA, below the fishnet. Silver and magnesium fluoride layers that comprise the suppressed pillars are crushed during the imprinting process but still allow for light to be transmitted. Despite imprinting directly into multiple metal and dielectric layers, high quality structures are observed with a minimum feature size as low as 200 nm. Resonance peaks are measured experimentally in reflectance using an FTIR spectrometer with a calcium fluoride (CaF<sub>2</sub>) beam-splitter and a visible wavelength range spectrometer with a silicon (Si) detector.
We present the most recent results of EU funded project P3SENS
(FP7-ICT-2009.3.8) aimed at the development of a
low-cost and medium sensitivity polymer based photonic biosensor for point of care applications in proteomics. The
fabrication of the polymer photonic chip (biosensor) using thermal nanoimprint lithography (NIL) is described. This
technique offers the potential for very large production at reduced cost. However several technical challenges arise due
to the properties of the used materials. We believe that, once the NIL technique has been optimised to the specific
materials, it could be even transferred to a kind of roll-to-roll production for manufacturing a very large number of
photonic devices at reduced cost.
We report on the fabrication of 70 nm wide, high resolution rectangular U-shaped split ring resonators (SRRs) using
nanoimprint lithography (NIL). The fabrication method for the nanoimprint stamp does not require dry etching. The
stamp is used to pattern SRRs in a thin PMMA layer followed by metal deposition and lift-off. Nanoimprinting in this
way allows high resolution patterns with a minimum feature size of 20 nm. This fabrication technique yields a much
higher throughput than conventional e-beam lithography and each stamp can be used numerous times to imprint patterns.
Reflectance measurements of fabricated aluminium SRRs on silicon substrates show a so-called an LC resonance peak in
the visible spectrum under transverse electric polarisation. Fabricating the SRRs by NIL rather than electron beam
lithography allows them to be scaled to smaller dimensions without any significant loss in resolution, partly because
pattern expansion caused by backscattered electrons and the proximity effect are not present with NIL. This in turn helps
to shift the magnetic response to short wavelengths while still retaining a distinct LC peak.
Planar devices that can be categorised as having a nanophotonic dimension constitute an increasingly important area of
photonics research. Device structures that come under the headings of photonic crystals, photonic wires and
metamaterials are all of interest - and devices based on combinations of these conceptual approaches may also play an
important role. Planar micro-/nano-photonic devices seem likely to be exploited across a wide spectrum of applications
in optoelectronics and photonics. This spectrum includes the domains of display devices, biomedical sensing and sensing
more generally, advanced fibre-optical communications systems - and even communications down to the local area
network (LAN) level. This article will review both device concepts and the applications possibilities of the various
In this paper we discuss theoretical modelling methods for the design of photonic crystal and photonic quasi-crystal
(PQC) LEDs - and apply them to the analysis of the extraction enhancement performance and shaping of the emitted
beam profile of PQC-LED structures. In particular we investigate the effect of the pitch of the PQC patterning, and
consider the physical mechanisms giving rise to performance improvements. In addition, we examine the relative
contributions to performance improvements from effective index reduction effects that alter the conditions for total
internal reflection at the device air interface, and from photonic crystal scattering effects that give rise to radically
improved extraction performance. Comparisons are made with the performance of recently fabricated devices.
The response of metallic split ring resonators (SRRs) scales linearly with their dimensions. At higher frequencies, metals
do not behave like perfect conductors but display properties characterized by the Drude model. In this paper we compare
the responses of nano-sized gold-based SRRs at near infra-red wavelengths. Deposition of gold SRRs onto dielectric
substrates typically involves the use of an additional adhesion layer. We have employed the commonly used metal
titanium (Ti) to provide an adhesive layer for sticking gold SRRs to silicon substrates - and have investigated the effect
of this adhesion layer on the overall response of these gold SRRs. Both experimental and theoretical results show that
even a two nm thick titanium adhesion layer can shift the overall SRR response by 20 nm.
Metamaterials based on single-layer metallic Split Ring Resonators (SRR) and Wires have been
demonstrated to have a resonant response in the near infra-red wavelength range. The use of
semiconductor substrates gives the potential for control of the resonant properties of split-ring
resonator (SRR) structures by means of active changes in the carrier concentration obtained using
either electrical injection or photo-excitation. We examine the influence of extended wires that are
either parallel or perpendicular to the gap of the SRRs and report on an equivalent circuit model that
provides an accurate method of determining the polarisation dependent resonant response for
incident light perpendicular to the surface. Good agreement is obtained for the substantial shift
observed in the position of the resonances when the planar metalisation is changed from gold to
We report a novel method for modeling the resonant frequency response of infra-red light, in the range of 2 to 10
microns, reflected from metallic spilt ring resonators (SRRs) fabricated on a silicon substrate. The calculated positions of
the TM and TE peaks are determined from the plasma frequency associated with the filling fraction of the metal array
and the equivalent LC circuit defined by the SRR elements. The capacitance of the equivalent circuit is calculated using
conformal mapping techniques to determine the co-planar capacitance associated with both the individual and the
neighbouring elements. The inductance of the equivalent circuit is based on the self-inductance of the individual
elements and the mutual inductance of the neighboring elements.
The results obtained from the method are in good agreement with experimental results and simulation results obtained
from a commercial FDTD simulation software package. The method allows the frequency response of a SRR to be
readily calculated without complex computational methods and enables new designs to be optimised for a particular
frequency response by tuning the LC circuit.
Gold Split Ring Resonators (SRRs) were fabricated on silicon substrates by electron beam lithography and lift-off, with overall dimensions of approximately 200 nm. Reflectance spectra from the SRRs are similar to those published elsewhere. New devices are proposed based on the additional functionality afforded by the use of a silicon substrate.
We describe a simple technique for the selective area modification of the bandgap in planar 3-D photonic crystals (PhC). The PhCs are grown by controlled drying of monosized polystyrene spheres. Uniaxial pressure of 41 MPa can produce a shift in the bandgap of ~90 nm from 230 nm spheres. An unexpected broadening of the bandgap is attributed to the change in topology associated with large necks formed between spheres at pressures greater than 10 MPa.