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Plasmonics is a promising technology that can find many applications in nanophotonics and biosensing. Local excitation of surface plasmons with high directionality is required for many of these applications. We demonstrate that by controlling the interference of light in a metal slot with the adjustment of the angle of incidence, it is possible to achieve highly directional surface plasmon excitation. Our numerical analysis of the structure showing a strong directionality of excited surface plasmon is confirmed by near field scanning measurements. The proposed structure can be useful for many applications including excitation of plasmonic waveguides, nanolithography, and optical sensing. To illustrate its usefulness, we experimentally demonstrate that it can be used for highly directional excitation of a dielectric loaded plasmonic waveguide. We also propose a simple structure for surface plasmon interference lithography capable of providing high image contrast using this scheme.

We present a proof-of-concept for a double-layered plasmonic biosensor using stimuli-responsive polymers. The relative change of each SPR and P^ peak are decoupled to identify how much each microgel layer reacts to a given stimulus.

The Augmented Low-index Guiding Waveguide can confine the two orthogonal polarization modes in different layers. We present our recent theoretical and experimental results on several polarization manipulation devices enabled by such a platform.

In general, plasmonic waveguides exhibit a tradeoff between propagation loss and mode confinement—the smaller the mode size, the higher the propagation loss. We compare the confinement and loss of three commonly used plasmonic waveguides. We define two distinct figures of merit based on application for which the plasmonic waveguide is designed: 1) applications which require high power density and 2) applications which require high lateral packing density. The first figure of merit is based on the power density and propagation loss, whereas the second depends on the coupling length and the propagation loss. We have identified the relative advantages and limitations of the plasmonic waveguides for these different applications.

We demonstrate a bead based assay which can detect the presence of an analyte in a small sample using a microfluidic cartridge. The fluorescence emitted by the beads and fluorophores bound to the beads is used to detect the presence of C-reactive protein.

Hybrid plasmonic waveguides (HPWGs) have received attention worldwide for many different kinds of applications, including on-chip polarization control, enhanced nonlinear optical effects, and biosensing. The HPWG sensor can achieve detection limit lower than possible with purely plasmonic sensors. It can be also used for obtaining ad- ditional information about complex biological samples. We analyze the effects of various parameters on such a sensor, optimize the sensor design, and predict the optimum per- formance achievable for an HPWG sensor in the Mach-Zehnder configuration. We also compare the performance of the HPWG sensor to those of other plasmonic sensors.

We have experimentally demonstrated a compact polarization beam splitter based on the augmented-low-index-guiding structure in the silicon nitride/silicon-on-insulator platform. The device is only 4.8 microns long. The design of the device is robust and has a good fabrication tolerance.

Using a newly proposed augmented low-index-guiding scheme with silicon nitride/silicon dual-core waveguide, we have designed, fabricated, and characterized a transverse electric (TE) to transverse magnetic (TM) and TM-to-TE compact polarization rotator. The polarization rotation is realized in an asymmetric directional coupler. The measured peak conversion efficiencies for the TE-to-TM and TM-to-TE rotations are approximately 97%. The measured polarization extinction ratio for the TE-to-TM rotation is greater than 20 dB over 50-nm bandwidth, while for the TM-to-TE rotation it is greater than 15 dB over the C-band.

In this paper we present a portable blood analysis system based on a disposable cartridge and hand-held reader. The platform can perform all the sample preparation, detection and waste collection required to complete a clinical test. In order to demonstrate the utility of this approach a CD4 T cell enumeration was carried out. A handheld, point-of-care CD4 T cell system was developed based on this system. In particular we will describe a pneumatic, active pumping method to control the on-chip fluidic actuation. Reagents for the CD4 T cell counting assay were dried on a reagent plug to eliminate the need for cold chain storage when used in the field. A micromixer based on the active fluidic actuation was designed to complete sample staining with fluorescent dyes that was dried on the reagent plugs. A novel image detection and analysis algorithm was developed to detect and track the flight of target particles and cells during each analysis. The handheld, point-of-care CD4 testing system was benchmarked against clinical cytometer. The experimental results demonstrated experimental results were closely matched with the flow cytometry. The same platform can be further expanded into a bead-array detection system where other types of biomolecules such as proteins can be detected using the same detection system.

We experimentally demonstrated a TE-pass polarizer based on the hybrid plasmonic waveguide. The TM mode is coupled and attenuated in an asymmetric coupling section. The device has a high extinction ratio and ultra-low insertion loss.

We report on z-scan characterization of the two-photon absorption properties of crystalline potassium niobate at 430 nm. The value of the two-photon absorption coefficient was found to be similar to 4.3 cm/GW. Furthermore, we demonstrate efficient (> 60%) noncritically-phase-matched second harmonic generation at 430 nm with subpicosecond pump pulses.

Semiconductor optical amplifiers (SOAs) are attractive for integrated photonic signal processing, but because their response is so fast, delays in a controller feedback path can jeopardize performance and stability. Using state-space methods, we quantify the constraints imposed on feedback controllers by closed-loop delay. We first derive a complete nonlinear state-space control model of a SOA with an equivalent circuit containing parasitics and dynamic impedance; the analytical state-space model agrees well with a validated photonic-only control model. Using a linearized version of the model we demonstrate that time delay in the feedback path can destabilize the SOA through phase accumulation. We then apply linear system theory to calculate the best-case stable delay margin for a given controller norm, and find a potentially severe inverse relationship between delay margin and controller norm. Finally, guided by the delay-controller relationship we design a hybrid feedforward-feedback controller to illustrate that good transient and steady-state regulation is obtained by carefully balancing the feedforward and feedback components. Our state-space modeling and design methods are general and are easily adapted to the design and analysis of more complex photonic circuits.

Femtosecond laser written waveguides in glass were characterized across the full telecom spectrum to gain insight into waveguide loss mechanisms, and to aid in the design of a low-loss 1300/1550 nm wavelength demultiplexer. A lambda-4 wavelength scaling of propagation loss confirms Rayleigh scattering as a principal loss mechanism. Laser exposure was optimized for generating low-loss directional couplers with high isolation between the 1300 and 1550 nm bands. Dispersive coupling in the straight and curved wavelength regions was balanced with a 1.5-fold difference in 1300 and 1550 nm beat lengths, leading to the first demonstration of 1300/1550 nm demultiplexer written with a laser. A minimum interaction length of 3.2 mm, ~2 dB insertion loss and channel isolations of 16.7 and 18.8 dB are reported.

In this paper, we derive a new analytical state-space model for semiconductor optical amplifier (SOA) dynamics with nonlinear gain compression. We show that a multichannel closed-form state-space model is possible with polynomial gain compression and position-independent carrier density. The compressed model is significantly more accurate than existing noncompressed models as demonstrated by comparison with pump-probe experiments: response magnitude and recovery time are more accurately modeled with explicit gain compression. We then apply the model to design an optical feedback controller that regulates the total optical power at the output of a gain-compressed SOA.

Second-harmonic generation in a quasi-phase matched waveguide produced using a domain-disordered GaAs-AlAs superlattice is modeled including the effects of group velocity mismatch, nonlinear refraction, two-photon absorption, and linear loss. The model predicts our experimentally observed second-harmonic powers within an order of magnitude. Self-phase modulation and two-photon absorption led to reduced conversion efficiencies of up to 33% at input peak powers >50 W. Group velocity mismatch results in a reduction of 23% in conversion efficiency using estimated group velocities calculated from the measured effective refractive index. The modeling also shows that the conversion efficiency peaks at propagation lengths longer than the pulse walk off length and that duty cycle variations induced shifts in the tuning curves. Group velocity mismatch also increased the conversion bandwidth by ~ 30%. Incomplete modulation of chi(2) in disordered regions reduced the output conversion efficiency by up to two orders of magnitude. Grating-assisted phase matching led to a 7% efficiency drop for a Deltan of 0.045 at the second-harmonic and 0.01 at the fundamental. This model serves as a valuable tool to provide insight into the optimization of these devices.

Focussing of the output beam of optical fibers is required in a variety of applications. We present a laser micro-machining technique for the fabrication of micro-lenses directly on the end face of single-mode silica fibers using a F2-laser processing station. A uniform ablation spot is projected onto the fiber end face and steered along a trajectory of overlapping concentric circles. The lens profile is controlled by the spot size, the number of circles in the trajectory, and the scanning speed. Strong 157 nm absorption by the silica glass facilitates precise structuring without micro-crack formation in both cases. The surface quality of the fiber-lenses is characterized by AFM and SEM and reveals ∼ 100 nm rms roughness with good control of the surface profile. Optical beam profiling indicates the possibility for creating spot sizes of 1/5 the core diameter at the fiber output.

We assess the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) through an experimental comparative study of three amplifiers, one InAs-InGaAsP-InP quantum dot (0-D), one InAs-InAlGaAs-InP quantum dash (1-D), and one InGaAsP-In-GaAsP-InP quantum well (2-D), all of which operate near 1.55-mum wavelengths. The short-lived (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the three devices are characterized via heterodyne pump-probe measurements. The quantum-dot device is found to have the shortest long-lived gain recovery (~80 ps) as well as gain and phase changes indicative of a smaller linewidth enhancement factor, making it the most promising for high-bit-rate applications. The quantum-dot amplifier is also found to have reduced ultrafast transients, due to a lower carrier density in the dots. The quantum-dot gain saturation characteristics and temporal dynamics also provide insight into the nature of the dot energy-level occupancy and the interactions of the dot states with the wetting layer.

We derive nonlinear and linear state-space control models for a multichannel semiconductor optical amplifier. Verified against the governing partial differential equations through simulation, the linear model tracks modulations up to 20% qualitatively well. Linear feedback control is then employed to design two interchannel crosstalk suppressing systems, one using state feedback into the electronic drive current and the other using optical output feedback into an optical control channel; the controller designed with the linear model is seen to work well even with 100% modulations of the nonlinear system. This linear state-space model opens the way for further robust analysis, design and control of integrated active photonic circuits

We propose a new all-dielectric optical antenna structure with the control of its radiation direction by adjusting its geometrical parameters. As a proof, we experimentally demonstrate the dielectric optical antenna radiating in the broadside.

We have proposed and experimentally demonstrated a broadband polarization rotator based on the augmented-low-index-guiding platform which consists of both silicon and silicon nitride layers as the waveguide core. With single etching process and silica cladding, the device is compatible with photonics integrated circuits.

We propose a new scheme, which is easy to implement and can be used to integrate low index nonlinear materials with silicon photonics to achieve high nonlinearly without suffering nonlinear losses.

A compact broadband polarization beam splitter based on the augmented low index guiding scheme is proposed. TM and TE modes are separated in two layers with the TM mode confined in the lower index layer.

We report on the large modulation of the optical properties of a 14:14 monolayer GaAs-AlAs superlattice waveguide following quantum-well intermixing. Low-temperature photoluminescence measurements illustrate a large 169-meV differential blue-shift obtained between the disordering-suppressed and disordering-enhanced materials. Effective index measurements are presented as a function of polarization, for both the as-grown and disordered material for near-bandedge and half-bandedge wavelengths, which is the wavelength range 775-1550 nm. The largest effective refractive index shift observed was 9/spl times/10/sup -2/ which exceeds that previously reported for disordered AlGaAs ternary multilayer structures, and illustrates the potential of the superlattice for the fabrication of etch-free, planar optical components with large index contrast.

International audience; Photoluminescence (PL) and Raman spectroscopy were devised to study bandgap gratings fabricated in a waveguide with a core consisting of GaAs/AlAs short superlattice (SSL) structure using quantum well intermixing (QWI). The spatially resolved PL is carried out on the superlattice layer from the sample surface, as well as from a cleaved facet to the side of the epitaxial layer. The PL from the sample surface showed a modulation in the PL wavelength with shoulders being observed. The root cause of this observation was resolved via PL scans of the cleaved side of the grating. The results were further supplemented via Raman spectroscopy measurements, where Raman spectra were collected at different depths of the SSL through probing the SSL layer cross-section. SSL-related phonon states were clearly observed for the lower part of the SSL layer where intermixing did not take place, while the Raman spectra for the intermixed regions showed regular bulk phonon modes, indicating the SSL layer intermixing.

We present the design and fabrication of 1-to-N multimode interference (MMI) splitters, suitable for use in integrated optical fluorescence array sensing, with particular applications in lab-on-a-chip (micro-TAS) technologies. Electron beam irradiation of germanium-doped flame hydrolysis deposited silica was used to define the MMI waveguide regions. The splitters were integrated with microfluidic channels to form direct-excitation fluorescence sensor chips for use at visible wavelengths. Characterization of the waveguides shows that predictable splitting ratios can be achieved. Two devices are presented: a 1/spl times/2 splitter integrated with one analytical chamber and a 1/spl times/4 array device for multipoint excitation. A photomultiplier tube was used to assess the analytical performance of the chip, in response to standard aliquots of fluorophore (31 nM to 1.25 /spl mu/M).

The structural changes responsible for the refractive index variations induced in Ge-doped flame-hydrolysis deposited (FHD) silica by electron-beam irradiation have been studied using confocal micro-Raman spectroscopy. Two structural mechanisms, an increase in the concentration of 4- and 3-membered rings in the silica structure and a reduction of the oxygen bridging bond angle between silica tetrahedra have been observed. The formation of small membered rings occurs along the penetration depth of the electrons in the layer, decreasing with depth. The reduction of the angle between silica tetrahedra only occurs on the surface of the material. The results are consistent with previous measurements of the compaction of the material and will determine the shape of the refractive index profile of the waveguides fabricated using this technique.

This article presents results of device fabrication using UV processing of materials and integrated optic components produced by flame hydrolysis deposition and hybrid sol-gel technology. Photosensitive materials were employed in the fabrication of channel waveguides and channel photo-imprinted waveguides incorporating Bragg gratings through single and double-step exposure.

We measured the self-phase modulation spectra at the output of deep-etched AlGaAs waveguides. The light source was an OPO laser system providing 250 fs long pulses, at wavelengths around 1520 nm, with a peak power as high as 1 kW. FROG measurements of the OPO pulses reveal their asymmetric shape. The multi-peak spectra, observed at the waveguide output, show a dramatic asymmetry and a power shift towards short wavelengths. The interplay between the Kerr non-linearity, dispersion and self-steepening amplifies the initial slight asymmetry of the injected spectrum. Experimental results compare favourably with the numerical solution of the generalized non-linear Schrodinger equation.

Electron beam irradiation of silica is a very flexible technique for the fabrication and trimming of optical circuits for the telecommunications and biosensing areas. In this paper, we review the effects induced by electron beam irradiation of germanium-doped, flame-hydrolysis deposited (FHD) silica. The structural modifications were studied with Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The compaction of the material was characterized by profilometry and the refractive index variation and index distribution of channel waveguides were characterized using the m-line technique and microreflectivity, respectively. Finally, some optical devices were fabricated using this technique with application in optical fluorescence sensing. The technique appears as a very interesting way of fabrication low-loss optical waveguides in silica.

The optical properties of germanium-doped silica layers deposited by flame-hydrolysis have been investigated by analyzing the effective refractive indices of the modes using an inverse-WKB (Wentzel–Kramers–Brillouin) approach followed by an optimization algorithm. The shape obtained for the refractive index profile is consistent with the compositional and density characterization, performed by X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity, respectively. We believe that the origin of the non-uniformity was the high-temperatures to which the as-deposited soot is subjected in order to obtain fully consolidated, high-optical quality films.

Genetic algorithms have been demonstrated to be a robust method for the calculation of the refractive-index profile of annealed germanium-doped flame-hydrolysis deposited (FHD) silica layers using measurements of the effective refractive indexes of the different modes of propagation. A nonuniform refractive-index profile in depth was obtained, which agrees well with the germanium concentration and density profiles measured for the films.

We report on the systematic, broadband characterization of the third-order nonlinearities of the commonly used reference materials: sapphire, the lead-silica glass SF-59 and pure carbon disulfide CS/sub 2/. Using the z-scan technique with /spl sim/1-ps pulses experimental data on the nonlinear refraction and two-photon absorption were obtained in the 550-1600 nm wavelength range. Theoretical treatment of spectra and scaling of the measured nonlinearities in sapphire and SF-59 glass is given using a simple Kramers-Kro/spl uml/nig transformation-based model. Compact empirical relations are suggested.

When a defect associated with a weak linear excitation or incoherent pump inside a resonant photonic crystal is created, dynamics of light propagation in a gap soliton regime undergo a considerable modification. We show that dynamic control of such a defect can be used to convert coherently a propagating optical pulse into a stationary excitation trapped inside the photonic crystal. This can also impose changes onto a pulse interaction with each other, thus facilitating possible applications in optical switching, signal processing, and quantum computing.

We analyze the structure of the optical field emerging from a superposition of two soliton-like pulses with different frequencies and arbitrary phase-shift between them, and show that the optical output contains either symmetric or antisymmetric two-soliton states. Furthermore, we study numerically the dynamics of these emerging two-soliton states under the influence of perturbative effects that are important for optical communications systems: frequency-sliding filters, third-order dispersion, and intrapulse Raman scattering.

We present results of the characterization of the nonlinear refractive index of the laser crystal Yb:KGd(WO4)2 using a z-scan technique over the 800–1600 nm wavelength range. Based on our experimental and theoretical results we conclude that Yb:KGW crystal is a good candidate for efficient Kerr-lens mode locking.

Because of the increasing use of e-beam lithography in telecom optical applications, e-beam induced refractive index change (RIC) has been further investigated in this paper in Ge-doped silica in comparison with pure silica. We investigated modified chemical vapor deposition (MCVD) Ge-doped SiO2 glasses containing 0, 5, 13 and 25 wt% of Ge. Contrary to ultraviolet (UV) photosensitivity for which Ge doping has a positive effect; here, the densification is diminished and even an expansion process appears for larger Ge content. Comparing RIC, directly measured and deduced from topography change, we conclude that specific volume change is the main contribution to RIC. UV and e-beam induced densification are by different mechanisms.

In this paper, the effects of irradiation of Ge-doped FHD silica with 2 MeV Ar+ ions were optically characterized using an m-line technique based on grating couplers. An increase of refractive index as high as 1.2 × 10−2 was obtained, larger than the values normally reported for UV or electron-beam irradiation of the same material (typically of ≈10−3). Thermal annealing has been carried out and an activation energy of 0.36 eV for the recovery of the refractive index has been estimated, suggesting that a bond rearrangement mechanism could be responsible for the change in refractive index.

Blue energy upconversion emission in Tm/sup 3+/-doped SiO/sub 2/-P/sub 2/O/sub 5/ channel waveguides off-resonance pumped by infrared radiation is reported. The waveguide samples were excited by a single continuous-wave laser source at 1.064 /spl mu/m. Two distinct blue emission signals around 450 and 480 nm, in addition to red at 660 nm and near-infrared at 800-nm less intense emissions were observed. The upconversion excitation mechanism was assigned to stepwise multiphoton absorption processes followed by nonradiative multiphonon-assisted relaxation processes. Infrared-to-blue conversion efficiencies with respect to the absorbed pump power of /spl sim/6.0/spl times/10/sup -7/ for this off-resonance pumping scheme was measured. The dependence of the infrared-to-blue upconversion mechanism upon the excitation power and thulium content is also examined.

Channel waveguides incorporating photo-imprinted Bragg gratings were produced in germano-borosilicate glass layers fabricated by flame hydrolysis deposition, through single- and double-step exposure direct writing processes with UV laser irradiation. To our knowledge, this is the first time that UV exposure has been used to simultaneously realize both waveguiding and spectral selectivity functions.

A compact, reliable and safe hydrogen sensor is required for the existing and emerging applications of hydrogen including aerospace and fuel cells. An optical sensor is an attractive option for hydrogen sensing because of its compactness, immunity from electromagnetic interference, and inherent safety. In this work we present the results of experimental demonstrations of a Pd-based hydrogen sensor and a ring resonator based temperature sensor on a siliconon- insulator (SOI) platform. The hydrogen sensor consists of a ridge waveguide with a very thin coating of palladium. The sensor response time is less than 10 seconds for 4% hydrogen concentration, and the sensor response was repeatable under hundreds of cycles of exposure to hydrogen. The response of the hydrogen sensor is affected by variation of temperature, and this effect must be considered in a real life application of the hydrogen sensor. To overcome this limitation we design and experimentally demonstrate a temperature sensor on SOI using a ring resonator, which shows good sensitivity over a wide range of temperature. The hydrogen sensor and the temperature sensor can be integrated on the same chip to implement a sensor capable of reliably measuring hydrogen concentration under varying temperature.

Efficient and thermally enhanced frequency upconversion of cw infrared radiation at 1.064 μm into blue (480 nm), red (660 nm) and near-infrared (800 nm) light in integrated Tm 3+ /Yb 3+ -codoped phosphosilicate silica-on-silicon buried waveguides is reported. Thermally induced frequency upconversion enhancement is observed for the first time in Tm 3+ /Yb 3+ -codoped systems excited off-resonance at 1.064 μm. A times seven thermally induced upconversion efficiency enhancement was obtained when the waveguide's temperature was varied in the 20–120°C range. The thermal effect is believed to be associated with a temperature dependent effective absorption cross-section for the Yb 3+ -sensitizer, which depends upon the phonon occupation number in the host matrix.

We show that two regimes of diffraction exist in arrays of waveguides, depending upon the input conditions. At higher powers, normal diffraction leads to self-focusing and to the formation of bright solitons through the nonlinear Kerr effect. By slightly changing the input conditions, light experiences anomalous diffraction and is nonlinearly defocused. For the first time, self-focusing and self-defocusing have been achieved for the same medium, structure, and wavelength.

It is envisaged that photonic networking will play a significant role in improving performance and reliability in both civil and military avionics systems. Of all the available photonic multiplexing technologies, wavelength-division multiplexing (WDM) has been the primary focus of attention within mainstream telecommunications offering increased throughput at a reasonable cost, with scope for enhanced routing flexibility, connectivity and network survivability. A direct mapping of techniques and devices from the maturing telecommunications sector is, however, not possible because of the stringent requirements of systems operating in the hostile aerospace environment. This paper gives an outline of these requirements and discusses, in detail, the design and development of a multi-gigabit, broadband optical WDM network architecture, specifically for use on aerospace platforms. The paper will also discuss a key element in the system, the arrayed-waveguide grating (AWG) wavelength multiplexing component, which has been designed to allow operation over the full military temperature specification without environmental conditioning.

A photonic wire Bragg grating structure, integrated with fluidic channels and reservoirs for fluid sensing based on refractive index changes, has been designed using 3-D Finite Domain Time Difference (FDTD) method and fabricated using electron beam lithography and reactive ion etching on an Silicon-on-Insulator (SOI) material. A scheme is developed where a Polydimethylsiloxane (PDMS) microfluidic chip is integrated with the SOI photonic chip via a reversible active sealing method. The highest sensitivity (@Dn/@[email protected]) of the device is estimated to be 5.5x10^-^3 nm^-^1 and the volume of the sensing region is approximately [email protected]^3. This device could be a potential candidate for lab-on-a-chip devices for bio-sensing applications.

The optical Kerr effect was measured by observing self-phase modulation in GaAs-AlGaAs superlattice-core waveguides modified by ion-implantation quantum-well intermixing. The band-gap energy was shifted by 68 nm for an implantation dose of 0.5times1013 cm-2 and annealing temperature of 775degC. The Kerr effect was suppressed by up to 71% in the transverse-electric polarization after intermixing. A reduced polarization dependence of the self-phase modulation was observed after intermixing.

We experimentally demonstrate the occurrence of optical Bloch oscillations in a waveguide array with linearly growing effective index of the individual guides. We monitored the output profiles for varying propagation lengths and observed a periodic transverse motion of the field and a complete recovery of the initial excitation. The action of the focusing nonlinearity leads to a loss of recovery, symmetry breaking, and power-induced beam spreading.