The plasmonic properties of metallic nanoparticles and macroscopic Au film have been thoroughly investigated for the development of biosensors based on surface plasmon resonance (SPR). Nanoparticle based localized surface plasmon resonance (LSPR) is a technique extremely sensitive to molecular adsorbate, whilst conventional SPR based on the Kretschmann configuration (macroscopic smooth Au film) is especially sensitive to bulk refractive index. SPR currently provides the best RI resolution, a measure typically used for comparison of the potential of plasmonic sensor. A technique that could combine high bulk refractive index resolution and high sensitivity to molecular adsorbate would increase the scope of SPR-based technique by providing lower detection limits. A potential solution may exploit micro-structured Au films. However, the plasmonic properties of micropatterned metallic films are still relatively unknown. We have undertaken the study of the plasmonic properties from Au film with features on the order of 1 to 3 μm. Microtriangle and microhole arrays were fabricated by modified nanosphere lithography, consisting of a polymer microsphere mask deposited in a close-packed hexagonal monolayer, etched by oxygen plasma. Etch time controls the diameter of the microhole and the initial microsphere diameter sets the periodicity. Investigation of the SPR properties in the Kretschmann configuration was undertaken using a SPR with a dove prism and a multi-wavelength scanning angle SPR. The sensitivity of SPR with microhole arrays exhibits an improvement by a factor of 3 in comparison to SPR using a smooth Au film. This is accomplished by tuning the angle to near 73 degrees (with a BK7 glass prism). Moreover, the sensitivity to the immobilization of an antibody was improved by at least a factor of 4 as demonstrated with the kinetics of immobilization for IgY, without employing secondary amplification techniques. No modification to the instrumentation is required and microhole arrays improve resolution of the SPR response.

Waveguides consisting of Au embedded in Cytop with micro-fluidic channels etched into the cladding are used for sensing via the propagation of long-range surface plasmons. Initially, a range of water/glycerol solutions with varying refractive indices were sequentially injected in a waveguide section in order to assess its bulk sensitivity and to find a solution supporting a strong high quality mode. Au waveguide surfaces were then functionalized with antibodies against Gram negative bacteria (Anti-Gneg) by first forming a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (16-MHA) and subsequent conjugation with antibodies through carbodiimide chemistry. E.Coli XL-1 Blue was used as an analyte in static incubations. Wavelength sweeps of 16-MHA covered waveguides were compared against waveguides covered with E-coli. The results indicate that very few bacteria cells are required to obtain a measurable change in output signal.

A simultaneous two wavelength band swept laser source and a fiber-based dual-band common-path swept source optical coherence tomography is reported. Simultaneous 1310/1550 dual-wavelength tuning is performed by using two fiber-ring cavities with corresponding optical semiconductor amplifier as their gain mediums and two narrowband optical filters with a single dual-window polygonal scanner. Measured average output powers of 60 mW and 27 mW have been achieved for 1310 and 1550 nm bands, respectively, while the two wavelengths were swept simultaneously from 1227 nm to 1387 nm for 1310 nm band and from 1519 nm to 1581 nm for 1550 nm band at an A-scan rate of 65 kHz. A broadband 1310/1550 wavelength-division multiplexing is used for coupling two wavelengths into a common-path single-mode GRIN-lensed fiber probe to form a dual-band common-path swept-source optical coherence tomography. Simultaneous OCT imaging at 1310 and 1550 nm is achieved by using a depth ratio correction method. This technique allows potentially for in vivo endoscopic high-speed functional OCT imaging with high quality spectroscopic contrast with low computational costs. On the other hand, the common path configuration is able to reject common mode noise and potentially implement high stability quantitative phase measurements.

Full-field optical coherence tomography (FFOCT) acquires image data in parallel. It has a big advantage in high-speed imaging because 2-dimensional mechanical raster scanning in the sample arm, which is essentially needed in a common fiber-based OCT system, does not exist anymore. Swept-source FFOCT (SSFFOCT) further makes the system free of depth scanning that significantly increases the operation speed. National Instrument's LabVIEW is a powerful tool to fast develop optical-electronic systems which have motion/vision units, signal processing functions and easy-to-generate Graphic User Interface (GUI). In this paper, we describe the design and implementation of Labview program prepared for an SSFFOCT system. Basically, there are four modules of Labview programming in such a system: 1. Wavelength sweeping control; 2. Synchronized image grabbing; 3. SSFFOCT signal processing; 4. 3-dimensional tomogram displaying mode selection. A general graphic user interface is used to input the parameters and monitor all necessary data and curves. The tomographic images can be displayed at any given cutting direction. More details and examples are provided and discussed.

Long-range surface plasmon-polariton (LRSPP) waveguide structures fabricated of gold stripes (5 μm wide and 35 nm thick) embedded in CYTOP were characterized. TM polarized 1310 nm light emerging from a polarisationmaintaining optical fibre was injected into the structures via butt-coupling and the output light was measured so that the loss could be calculated. Cutback measurements were carried out on straight waveguides so as to determine their attenuation as well as the butt-coupling loss per facet. Various other passive elements were also characterized. The results were compared with theoretical expectations and errors are surmised to be caused by fabrication imperfections. Thermo-optic modulation measurements were also carried out on straight waveguides. These elements are of interest for biosensors, where propagation through an aqueous solution (having an index of refraction very close to that of Cytop) is necessary.

Noble metal (Au, Ag, Pd) - PDMS composites show highly enhanced mechanical and optical properties compared with the polymer alone. Among the different methods of synthesis, the in situ "one step" preparation of these composite materials, by immersion of PDMS films into the solution of the metal salt and reduction to elemental metal is a simple and straightforward method. The metal nanoparticles are immobilized and uniformly distributed into the surface layers of the polymer and this structure proved to be suitable for biosensing purposes. Sensing is performed by measuring the position and intensity of the Localized Surface Plasmon Resonance (LSPR) band of silver in the UV-Visible spectrum of the nanocomposite. In this work, the structure and composition of Ag-PDMS nanocomposites are optimized in order to enhance the sensitivity of the sensing platform. A novel method of tuning the morphology of nanocomposite by annealing it for the desired optical property is optimized. The quality of the platform is investigated for sensing polypeptides such as hormones, through an immunoassay, by using the antigen-antibody interaction.

Here, we report that intense ultra-short laser pulses produce a plasma of low energy electrons (LEEs) by the inverse Bremsstrahlung effect and multiphoton ionization process. The phenomena show five striking characteristics. First, the self-focusing of ultra-short laser pulses creates a plasma of LEEs (6.5 eV), which is concentrated in filaments through an avalanche process. Second, kinetically hot 6.5 eV electrons interact with surrounding molecules resulting in reactive radical species. Third, the dose rate reaches an enormous level of ~2.8 × 10¹¹ Gy/s as determined by a cericcerous sulfate dosimetry and this leads to an ultra-high deposition of energy of between 4.6 × 10⁷ to 8.16 × 10⁷ keV/μm. Fourth, filaments of variable length are produced by femtosecond pulses depending on the pulse duration as determined by a tissue-equivalent radiation polymer gel dosimeter and imaged by magnetic resonance imaging (MRI). These results reveal that one of the very interesting novelty of filamentation is the very low entrance dose, similar to proton irradiation. Lastly, filamentary irradiation results in the decomposition of thymidine in the absence and the presence of oxygen similar to the radiolysis of water.

A detail study was done on the sensitivities of 1-D photonic crystal (PC) and 2-D PC coupled cavity sensors with changing sensing layer parameters of thickness and refractive index (RI). Though both refractive index and thickness are interrelated they have significant individual affects on device response. In 1-D PC shifts in normal transmission peak due to surface change in thickness and RI and in 2-D PC coupled cavity shifts in transmission dip due to surface changes are observed. Here sensitivity analysis in change in thickness and RI on these devices was done for four cases; case 1: change in thickness from 2nm-10nm on PC sensors, case 2: change in thickness from 75nm-175nm on PC sensors, case 3: change in RI in thin film (6nm) on surface and case 4: change in RI in thick film (100nm) on sensors surface. Sensitivities due to change in thickness (S_t) of 1-D PC and 2-D PC coupled cavity were calculated from the slope of the sensitivity curves and found to be (for RI of 1.4) 1.423nm/nm and 2.285nm/nm for case 1 and 0.455nm/nm and 0.801nm/nm for case 2. Sensitivities due to change in RI (S_r) of 1-D PC and 2-D PC coupled cavity were obtained from the transmission peak and dip shifts due to change in RI from 1(air) to 2. Sr for 1-D PC and 2-D PC coupled cavity were found to be 70nm/RIU and 103nm/RIU for case 3 and 143nm/RIU and 213nm/RIU for case 4. The results are based on FDTD simulations.

The rapidly growing popularity of internet-based services has increased the number of end users that are connected to access networks every year. Internet Service Providers (ISPs) have to deal with an increasing density of access networks in urban areas and extended reach of the network in remote locations. Existing public network infrastructure requires new energy efficient and cost effective extension technologies to accommodate new subscribers and to provide the required bandwidth for new services such as High Definition TV or Video on Demand. This paper presents a study of the low power Optical Semiconductor Amplifier (SOA). The most important characteristics of the SOA are presented and compared with other technologies such as Erbium Doped Fiber Amplifier (EDFA). Aspects of the energy consumption are discussed and potential problems related to the SOA implementation are presented.

Fiber Bragg gratings (FBGs) are attractive as reflector elements in fully integrated all-fiber laser systems. Furthermore, FBGs made with femtosecond laser technology allow to reduce splice connections in the fiber, since no special photosensitive fibers are required. Fiber Bragg grating inscription with deep ultraviolet femtosecond laser (267 nm) and two beam interferometry allows to target germanium-free and non-photosensitive fibers while maintaining versatility in the choice of the output wavelength of the fiber laser. This concept offers the potential of gratings with high spatial resolution, great flexibility and good homogeneity and complements the methods of point-by-point inscription at 800 nm or of phase-mask inscription with 400 nm femtosecond laser exposure. We report on the application of the interferometric fiber Bragg grating inscription technology to build a grating-stabilized fiber laser with high beam purity. Output powers up 160 W have been achieved.

Using femtosecond (fs) radiation and multi-photon absorption processes for fiber Bragg grating (FBG) inscription offers the advantage of writing FBGs independent of the chemical fiber composition. Especially for fiber laser applications the fabrication of FBGs integrated in rare earth doped fibers is a favorable option for monolithic fiber lasers. In this paper we report on the growth and stability of femtosecond generated fiber Bragg gratings in different rare earth doped fibers. For this purpose we use two different fs laser wavelengths at 266 nm and 400 nm and a modified Talbot- interferometer setup for the generation of first order Bragg gratings. We study the growth characteristics of FBGs in terms of reflectivity, Bragg wavelength and spectral grating width during the writing with UV and VIS fs radiation. For these experiments fibers drawn in-house at the IPHT are used, which possess varying contents of Ytterbium and/or Cerium with a comparable Phosphor and Aluminum co-doping and a standard geometry (125 μm cladding, 8-10 μm core diameter). We observe different kinds of grating growth processes depending on the inscription wavelength and the specific doping level of the fibers. It is possible to produce high reflective Type I gratings by UV fs exposure and high reflective Type II gratings with higher temperature stability by VIS fs exposure. The transformation from Type I to Type II gratings with a 400 nm inscription wavelength is studied in dependence on the exposure conditions. Our experimental results underline the role of doping for fs material photosensitivity and for FBG inscription process.

We have modeled the soliton propagation in an As₂Se₃ microwire coated with PolyMethyl MethAcrylate (PMMA) with the purpose of optimizing the soliton self-frequency shift (SSFS). We provide the optimal waist diameter and initial soliton energy required to maximize the wavelength shifting from a wavelength of 2.29 um through a 20 cm long microwire. In light of the dynamics of a fundamental soliton, we provide the optimal uniform and nonuniform microwires that maximizes the soliton frequency-shift. Finally, we propose an approach to avoid the dispersive waves emission by which the soliton energy density maintain at the output of the system.

Fiber optical parametric oscillators are laser sources with multiple longitudinal modes arising from their cavity length reaching several tens of meters. To reduce the noise due to multimode beating, the spacing between neighboring modes is increased using a Smith predictor internal control scheme. The Smith predictor utilizes a model of the dynamic behaviour of the system to deal with pure time delay and eliminate the effect of the delay in the overall closed-loop system. Applying the smith predictor, the system can be made to operate in a single-longitudinal mode, removing the excess modes. In this paper a linear model for operation of parametric oscillator is proposed and based on that transfer function of Smith predictor enhanced parametric oscillator is established. Numerical analysis of resulting transfer function will lead us toward single-longitudinal mode operation.

A wideband and frequency-tunable optoelectronic oscillator implemented by employing a two-port optical phase modulator and a phase-shifted fiber Bragg grating without using electrical microwave filters is proposed and experimentally demonstrated. The key device is the phase-shifted fiber Bragg grating, which functions, in conjunction with the phase modulator in the loop, to form a tunable high-Q microwave bandpass filter to perform frequency selection. The central frequency of the microwave photonic filter can be tuned by tuning the wavelength of the incident light wave; therefore, the oscillation frequency can also be continuously tuned. An experiment is performed. The generation of a microwave signal with a frequency that is tunable from 6 to 14 GHz is demonstrated.

This paper presents a new type of broadband impedance transformer loaded with capacitive fins (ITF) suitable for use in the frequency range 10 GHz to 70 GHz. Compared with conventional, unloaded, tapered impedance transformers, these ITF structures extend the impedance matching range and the operating bandwidth for the same amount of on-chip real-estate. We have designed ITFs capable of impedance matching resistive loads from ~ 10 Ω to ~ 229 Ω, on a 650 μm thick GaAs substrate over about a 60 GHz bandwidth. Design examples are used to demonstrate the flexibility of these ITF structures.

A novel approach to interrogating in real time a linearly chirped fiber Bragg grating (LCFBG) sensor based on chirped pulse compression using a Sagnac loop interferometer (SLI) with improved pulse compression performance is proposed and experimentally demonstrated. The proposed system consists of a mode-locked laser (MLL), a SLI incorporating an LCFBG, which makes the SLI have a spectral response with an increasing or decreasing free spectral range (FSR), a dispersive element and a photodetector. The significance of using an SLI incorporating an LCFBG is its capability of providing equal dispersion for two pulses traveling along the clockwise and counter-clockwise paths, which would effectively avoid a non-complete temporal interference, and improves the pulse compression performance. When the fiber sensor is experiencing a strain, the strain information would be conveyed to a wavelength shift caused by the Bragg wavelength change, which is further transferred to the change of the FSR. An ultra-short pulse train generated by the MLL would be spectrum shaped by the SLI, and the shaped spectrum would contain the information of the wavelength change. The demodulation is performed in the time domain by mapping the spectrally shaped waveform to the temporal domain using a dispersion compensating fiber (DCF) as the dispersive element. The generated temporal waveform is then correlated with a special reference waveform, with the location of the correlation peak indicating the wavelength change which reflects the strain or temperature change. A theoretical analysis is carried out, which is validated by an experiment. The experimental results show that the proposed system can provide an interrogation resolution as high as 0.22 με at a speed of 48.6 MHz with a correlation peak to sidelobe ratio of 2.5.

A new approach to cool solids with super-radiance (SR) pulses is presented in comparison with laser cooling based on traditional anti-Stokes fluorescence. Contrary to the anti-Stokes fluorescence, which is in-coherent radiation propagating in all directions around a sample, SR is the coherent, sharply directed spontaneous emission of photons by a system of excited ions. We consider an Yb³⁺ doped ZBLAN sample pumped at the wavelength 1015nm with a rectangular pulsed source. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR permits an increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare earth doped solids with anti-Stokes fluorescence. This scheme overcomes the limitation of using only low phonon energy glasses for laser cooling.

Several growths of Si nanodots on Si and GaAs substrates were conducted by pulsed laser deposition (PLD) using a KrF laser of 248nm, 15ns, 12Hz and a Ti-sapphire laser of 800nm, 130fs, 1kHz at 1x10^-5mbar vacuum. The laser fluencies on a Si target were varied from 3 to 32J/cm² for the nanosecond (ns) PLD growths and 1-2.75J/cm² for the femtosecond (fs) PLD. Wide range of nanodots from 20nm to a few micron size droplets were observed from both the ns and fs PLD. Auger electron spectroscopy of the nanodots was conducted and which indicated that the nanodots were without contamination. A technique using a mask consisting of an array of small holes was used to obtain high density nanodots with uniform size. The array of 100nm diameter holes was created by E-beam lithography. With this technique we have achieved 100nm Si dots with 300nm spacing between them, with few defects. We have observed that laser fluences closer to the ablation threshold work better for deposition using the EBL mask. In summary, we have demonstrated the growth of 100nm Si nanodots in an array with very few defects using the EBL masking technique.

The mechanical response of biological molecules at the microscopic level contributes significantly to their function. Optical tweezers are instruments that enable scientists to study mechanical properties at microscopic levels. They are based on a highly focused laser beam that creates a trap for microscopic objects such as dielectric spheres, viruses, bacteria, living cells and organelles, and then manipulates them by applying forces in the picoNewton range (a range that is biologically relevant). In this work, mechanical properties of single collagen molecules are studied using optical tweezers. We discuss the challenges of stretching single collagen proteins, whose length is much less than the size of the microspheres used as manipulation handles, and show how instrumental design and biochemistry can be used to overcome these challenges.

Focusing a high intensity laser pulse, onto a thin foil target generates a plasma and energetic proton and ion beams from the target rear and front sides, propagating along the target normal. Such laser produced collimated and energetic protons beams are of high interest because of the wide range of applications: ion based fast ignitor schemes, probing of electromagnetic fields in plasma, isotopes production or hadron therapy. The 100 TW class laser system at the Advanced Laser Light Source facility, is used with an intensity close to 10¹⁹ W/cm², to study protons acceleration with femtosecond laser pulses, ultra thin foil target and high contrast laser pulse ratio. To characterize the plasma expansion, we monitor it with an imaging technique using a femtosecond laser probe. In this configuration we were able to reach a proton critical energy of 12 MeV and to work with target foil thickness as small as 15 nm.

Several new designes of different type fiber Bragg grating(FBG) sensors, including long range strain sensor, pressure sensor, and displacement sensor, have been introduced. A new concept of sliced fiber Bragg grating as free space optical element has been presented. Some new waveguide Bragg grating writing technologies have been introduced.

Periodically poled lithium niobate (PPLN) waveguide based green lasers have attracted much attention in the past years due to their excellent properties, such as high efficiency and small size. The potential application fields include laser display, bio-instrumentation, undersea communication and so on. In this paper, recent progresses on the development of PPLN waveguide based green lasers are introduced and reviewed.

In this paper, we discuss the recent achievements in realizing plasmonic networks, which are compatible with silicon photonics platform. Obtaining good coupling between plasmonic gap and silicon waveguides is necessary for these networks to be practical. We report our experimental realization of novel wide band, and non-resonant coupling scheme between plasmonic gap and silicon waveguides.

Optical waveguide crossings based on silica-on-silicon technology are investigated. The effect of crossing angle (θ) on light transmitted at through and cross-port on a sequence of waveguide crossings with angle varying from 7 to 28° is modeled and experimentally validated. Results demonstrate that structures with small footprint (θ≈9°) can achieve low crosstalk of -32 dB with high throughput, insensitivity to wavelength of operation, low polarization dependent loss of 0.6 dB, and low sensitivity to fabrication tolerances. As a result, waveguide crossings with small crossing angle present an attractive approach to reducing the overall component footprint without compromising the performance.

The optimization of a 2×2 silica-on-silicon Mach-Zehnder interferometer (MZI) thermo-optic switch is presented. The device consists of 2 multimode interference (MMI) couplers as splitter and combiner with metal heater strips for phase control. The switching characteristics of the devices have been examined in detail as a function of several parameters. The electrical power consumption of the switch has been reduced by a factor of 2 by etching trenches alongside the waveguide heaters located on the arms of the MZI, and the polarization dependent loss has been controlled and reduced through adjustment of top cladding properties. The effect on the response time of the switch of these design changes has been investigated. Detailed characterization of the devices will be presented, and trade-offs in optimization discussed. Incorporation of these device elements into increasingly complex components for new applications in optical signal processing will be demonstrated.

A pressure or touch sensor is proposed by using a tapered optical fiber and polydimethylsiloxane (PDMS) curved films. Under pressure, the light in the tapered optical fiber is partially leaked into the films by the evanescent field properties. The optical attenuation of the tapered optical fiber is directly related to the pressure change and sensitive to the profile of the film. By monitoring the change of the transmitted optical power of the tapered optical fiber, the change of pressure is measured.

In this paper, we review recent progress towards efficient and versatile waveguides and transmission lines for terahertz applications. Terahertz waveguides are compared in terms of loss and coupling efficiency. Different loss mechanisms and fundamental limits are treated. We also propose a slot-line structure suitable for terahertz frequencies.

The top cladding layer in planar lightwave circuits (PLC) is more than an optical buffer. By variously doping, adjusting the thickness of, etching patterns in and annealing the cladding layers in waveguide devices, a wide range of sensors and photonic devices can be realized. The material properties of the cladding determine, for instance, the modal birefringence of the waveguides; knowledge and control of these properties can be harnessed to produce polarization-independent components. The fabrication of thermo-optically controlled switches and interferometers for tunable filtering and optical signal processing is possible through the creation of micro heaters on top of the cladding. The optimization of such components can benefit from engineering of the cladding, ranging from better planarization and thickness control, to selective etching to better confine the heat distribution and provide stress relief. In addition, the thermal properties of a given device can be radically enhanced by using a polymer layer as top cladding, which yields an order of magnitude increase in the temperature sensitivity, an invaluable enhancement that can be harnessed for phase-tunable waveguides or sensor structures. Long period gratings (LPGs) can be etched in the lower cladding to provide filtering, signal processing, or sensor functions. In a borophosphosilicate cladding, typically used in silica-on-silicon PLCs, control of the reflow properties through composition can be exploited to manufacture fillable microchannels that are monolithically integrated with solid-core devices, enabling a unique platform for sensing, signal processing, or nonlinear optics.

A simple structure is proposed to generate slow and fast light simultaneously in a double-waveguide coupled disk resonator (DCDR) launched with dual contra-propagating inputs. The interaction between the intra-cavity backscattering and the losses out of cavity are investigated for the disk resonator while random surface defects (backscatters) are intentionally introduced in the cavity to produce the backscattering. The theoretical investigation done in this work shows that by adjusting the amplitude and/or phase difference between the dual inputs the interaction between the cavity modes and backscatters can be controlled thus the transmission and dispersion of the output lights of the system can be manipulated. This scheme is attractive for slow and fast light tuning applications especially when active tuning elements such as a p-i-n diode or a heater is absent in the cavity.

A silicon-based athermal double-ring resonator biosensor with a vertically coupled configuration is developed. We present an optimal design of the sensor structure by specifying the radii of the reference and the sensing rings, the vertical coupling offset, d, between the two rings and the bus waveguide, and the lateral offset, l, between the edges of the rings and the bus waveguide. By using Lumerical software package, we demonstrate that the optimal vertical and lateral offsets are d=325 nm and l=-80 nm, respectively. One major challenge faced by ring based biosensors is their temperature dependent characteristics. In this study, the sensing ring is exposed to the biomaterial under test, while the reference ring provides a temperature-insensitive reference to the sensing measurements. By assuming the biomaterial medium has small variations in temperature, we conclude that the proposed biosensor device offers temperature insensitive measurement, where the temperature effects are fully corrected by the reference ring response. The double-ring sensors are proposed to be fabricated with the local oxidation of silicon process, without the need for advanced lithography methods such as e-beam or deep UV lithography. In addition, the vertically coupled double-ring configuration allows precise control of the critical coupling separation between the rings and the bus waveguide. The proposed silicon double-ring biosensor can be used for highly sensitive and stable sensing for both biomedical and environmental applications.

We present the details and characteristics of graded index multimode mode interference (GIMMI) and its applications in optical communication components. This structure has unique features that allow for less sensitive wavelength dependant than the step Index case. This feature allows for wideband applications. In this paper, we present the applications of this structure to design wideband ultrafast integrated optical switch and integrated wideband polarization splitter. The graded index effect is produced using stair case index profile that mimics the parabolic index profile. The MMI with parabolic index profile has the analytical expression for the imaging length which provides simple design equations for the whole structure. The accuracy of this model is verified using 3D full vectorial beam propagation method.

The emergence of nanotechnology now enables the controlled fabrication of nanometer scale structures capable of steering and confining light waves over small distances. To realize complex nanoscale light guiding structures, it will be necessary to develop methods to guide light around tight bends and corners with high efficiency. Achieving high efficiency waveguide bends, however, is generally difficult because of radiation losses at the bend. To achieve tight waveguide bends several approaches have been put forward including the use of dielectric photonic crystals and resonators. One recent and promising method to limit the amount of loss over a bend is to restrict the path of light by encasing a bend in an opaque medium, such as metal. Such a bend can be conceptualized by joining the two metal-dielectric- metal (MDM) waveguides such that their dielectric cores are connected to each other at 90° as shown in Fig. 1. When the thickness of the dielectric cores is subwavelength, only the lowest order surface plasmon polariton (SPP) mode is sustained by the bend. Further, when the metal walls are constructed from a low-loss metal such as Ag, the SPP mode can propagate over the bend.

The extended depth of field of axicons is an advantage for imaging applications but comes with a degradation of image quality. Image processing is proposed to solve this problem. In the present work, three types of refractive axicons are examined for imaging applications: a linear axicon, a logarithmic axicon and a Fresnel axicon. Each one has its own advantages: a linear axicon is simple, the Fresnel axicon is compact and has a potential low cost of production and the logarithmic axicon generates nearly constant longitudinal intensity distribution which might ensure a more uniform image quality along the focal length. Preliminary experimental measurements of the Point Spread Function (PSF) for each one of these axicons were performed and are used to design digital filters to de-noise the images.

Silicon-on-insulator (SOI) photonic integrated circuits have recently become a research topic of great interest due to their compact confinements and compatibility with the modern micro-electronics. As the dominant issues of the integration density of planar lightwave circuits on a single SOI chip, low-loss SOI curved waveguides and corner turning mirror (CTM) structures are attracting attention. This work aims at the performance comparison between the SOI curved waveguides and CTM structures. For this goal we have designed both SOI curved waveguides and SOI CTM structures and then fabricated them. The performance of these two devices, such as the propagation loss and polarization dependent loss, is measured and compared.

Electroluminescent devices based on light emission from Tb-doped SiO₂ incorporated in a MOS capacitor structure have been formed on SOI substrates. It is shown that with appropriate choice of Si film and buried oxide thickness the SOI substrate can serve as a quarter-wave high-low-high index back reflector. Analysis predicts this back reflector can boost total light output integrated over the Tb emission spectrum by approximately 35% compared to a bulk substrate control device. Experimental devices using 100 nm thick PECVD SiO₂ emitting layers doped with 1% Tb were fabricated on substrates with nominal 32 and 108 nm Si film thickness (corresponding to approximately λ/4 and 3λ/4 at the Tb emission peak). The Si films were doped to 10¹⁹ - 10²⁰ cm^-3 by As implantation. Uniform bright green electroluminescence was obtained from 250 μm square devices, demonstrating that current crowding is not an issue even with such a thin Si film. The comparison of output spectra for thick and thin Si films demonstrates that optical absorption in the heavily doped Si film does not seriously degrade the light output of the devices.

Photonic crystals (PhCs) have recently been the focus for the developing micro- and nano-optical sensors, due to its capability to control and manipulate light on planar devices. This paper presents a novel design of micro-optical pressure sensor based on 2-dimensional PhC slab suspended on Si substrate. A line defect was introduced to the PhC slab to guide and reflect light with frequency in the photonic bandgap in the plane of the slab. The structure, with certain surface treatment, can be used in miro-scale pressure catheters in heart ablation surgeries and other biomedical applications. The working principle of the device is to modify light reflection in the PhC line defect waveguide by moving a substrate vertically in the evanescent field of the PhC waveguide. Evanescent field coupling is the critical step that affects light transmission and reflection. High resolution electron-beam lithography and isotropic wet etching have been used to realize the device on the top layer of a Si-On-Insulator (SOI) wafer. The PhC slab is released by isotropic wet etch of the berried oxide layer. The output reflection spectrum of the device under different pressure conditions is simulated using 3-dimensional finite difference time domain (FDTD) method. The result showed that when the PhC slab is close enough to the substrate (less than 400 nm), the reflected light intensity decreases sharply when the substrate moves towards the PhC slab. Mechanical response of the sensor is also studied.

In this work, the diffractive capability of nano-scale gratings fabricated on transparent substrates is investigated. Nano-hole arrays of 9 to 20 mm² with 450 nm, 550 nm and 650 nm periodicities were milled on 5 nm-thick chromium coated sheet of polyethylene terephthalate (PET) substrates using a focused ion beam (FIB) to create periodicity-dependent diffraction patterns. Based on the method with which the diffraction pattern was measured a new technology is proposed in which the optical signals are used to encode information.

In this work the dependency of the transmitted spectrum through arrays of nano-holes on the angle of incident light was investigated. The arrays of nano-holes fabricated on thin aluminum (Al) layer which was deposited on a quartz substrate were used to observe how change of the angle of incident light could change the peak of transmitted spectrum. Through far-field spectroscopy it was shown that the transmitted spectrum is detectable at the distances beyond 20 cm.

Silicon photonic microring resonators can be fabricated with the conventional CMOS technology. But there is one fundamental problem with this new technology that must be solved: wavelength non-uniformity. In this paper, a new approach to solve this problem is presented. It intends to show that a device problem can sometimes be tackled with an architectural technique.

Digital Backward Propagation (DBP) algorithm for mitigating fiber dispersion and non-linearities based on modified non-iterative symmetric split-step Fourier method (M-SSFM) is implemented and numerically evaluated. The algorithm is modified by shifting the calculation point of non-linear operator (r) together with the optimization of dispersion (D) and non-linear coefficient (γ) to get the optimum system performance. DBP is evaluated for 10x10Gbit/s wavelength division multiplexed (WDM) system (a total transmission capacity of 100Gbit/s) with RZ-DQPSK encoded signals over a transmission length of 1600km standard single mode fiber (SMF) with no in-line optical dispersion compensation. Furthermore, we quantify the impact of optical add-drop multiplexers (OADMs) in the transmission link. Modification of DBP parameters and bandwidth of optical filters associated with OADMs give significant improvement in the system performance.

Silicon nanocrystals (Si-nc) embedded in silica exhibit intense visible photoluminescence (PL) at room temperature. However, under continuous wavelength (CW) laser excitation at 405 nm, the Si-nc PL intensity decreases with time, approximately with two decay constants. The fast decay component is unchanged by repetitive laser exposures, it is related to the local sample heating induced by the laser. The slower time constant corresponds to a permanent decrease of the PL emission. This photodeterioration strongly affects the precision of optical gain measurements using VSL (Variable Stripe Length) or P&P (Pump and Probe) techniques, hindering the development of Si-nc technology for photonics applications. In this context, a procedure that would restore the PL intensity of Si-nc samples or minimize this deterioration is highly desirable. UVC light (254 nm) irradiation of samples followed by an annealing at different temperatures for 1 h under nitrogen flux increases the PL emission of Si-nc embedded in silica that have been previously exposed to a CW laser pumping. Although this procedure does not prevent the decrease of the PL intensity associated with the increase of sample temperature under CW pumping (the fast decay component), it contributes significantly to reduce the permanent deterioration of the PL intensity. This procedure can also be applied to non-irradiated samples. The PL emission collected from treated samples was studied as a function of laser irradiation time, and compared to that of non-treated samples. The resistance to degradation of light-emitting silicon nanocrystals can be increased by UVC irradiation followed by annealing at an optimal temperature of 400 °C under nitrogen environment. Following this treatment, a reliable optical gain measurement can be performed once the local heating has been stabilized (the fast decay component).

Energy consumption of the telecommunication networks contributes to a large portion of the greenhouse gas (GHG) emissions due to the global electricity consumption. Furthermore, backbone networks dominate the energy consumption of the telecommunication networks by high peak data rates. In this paper, we enhance our previously proposed energy-efficient availability design scheme for IP over WDM (IP/WDM) networks, i.e., Power-Aware Reliable Design (PARD).1 Here, PARD-QoP is proposed which incorporates Quality of Protection (QoP) with power-aware reliable IP/WDM Network design. According to the QoP concept, each connection demand specifies a working bandwidth capacity requirement and a minimum backup capacity requirement. We evaluate the performance of PARD-QoP under the 14-node NSFNET topology for six QoP classes that are uniformly distributed among the connection requests and for various demand sizes. The simulation results show that PARD-QoP enhances its predecessor PARD by 7%-12% in terms of Capital Expenditure (CAPEX), denoting the number of wavelength channels, and by 4%-8% in terms of Operational Expenditure (OPEX), denoting the energy consumption. Moreover, PARD-QoP is shown to differentiate the demands in three availability classes as 99.9%, 99.99% and 99.999% with respect to the backup bandwidth requirements.

Practical applications to both ground-based and satellite exploitations have demonstrated that acousto-optical spectrum analyzers of radio-signals represent really reliable signal-processing technique for the millimeter radio-astronomy. These spectrometers provide sufficiently high efficiency of operation together with the frequency resolution needed for astronomic observations. The basic component of similar spectrometer is the acousto-optical cell, whose operation is based on its ability to shape large amount of independent dynamic diffractive gratings. Each of them reproduces the amplitude, frequency, and phase of only one spectral component from the signal under analysis. A multi-pixel CCD linear array detects the obtained responses in Fourier plane of the integrating lens. The main peculiarity of this prototype lies in exploiting a large-aperture tellurium-dioxide crystalline acousto-optical cell, oriented almost along the [001]- and [110]-axes. This cell allows a two-phonon light scattering providing the improved frequency resolution in comparison with conventional one-phonon regime. This fact determines technical requirements to the framing sub-systems and performances of the prototype as a whole. Due to rather high anisotropy of tellurium dioxide, the efficiency of both one- and two-phonon light scattering depends essentially on the ellipticity of the incident light polarization, so that high-efficient operation needs the eigen-state elliptic polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. Currently, an advanced prototype has used a green laser beam at 532 nm with central acoustic frequency about 52 MHz. The first trial experiments in a two-phonon light scattering regime have shown frequency resolution of about 30 KHz.

Optical disc drives are inexpensive, readily available, and use highly sophisticated optoelectronic components which can be adapted for sensing. One limitation of using compact discs (CDs) and optical disk drives for sensing of analytes placed on a CD is the fluctuations in the voltage signal from the disk drive generated while reading the data on the CD. In this study, we develop a simple, low-cost strategy for sensing and identification using CDs and optical disk drives that spectrally separates contributions to the voltage signal caused by an analyte intentionally placed onto the CD and that caused by the underlying data on the CD. Analytes are printed onto a CD surface with fixed spatial periodicity. As the laser beam in an optical disk drive scans over the section of the CD containing the analyte pattern, the intensity of the laser beam incident onto the photodiode integrated into the disk drive is modulated at a frequency dependent on the spatial periodicity of the analyte pattern and the speed of the optical disk drive motor. Fourier transformation of the voltage signal from the optical disk drive yields peaks in the frequency spectrum with amplitudes and locations that enable analyte sensing and identification, respectively. We study the influence of analyte area coverage, pattern periodicity, and CD rotational frequency on the peaks in the frequency spectrum associated with the patterned analyte. We apply this technique to discriminate differently-coloured analytes, perform trigger-free detection of multiple analytes distributed on a single CD, and detect at least two different, overlapped analyte patterns on a single CD. The extension of this technique for sensing and identification of colorimetric chemical reagents is discussed. Future work will focus on adapting this technique to perform measurements at multiple wavelengths and streamlining the data collection and processing.

An optical material encountered during ongoing field collection activities displays tenebrescence, fluorescence and photo-refractive properties. The material is an uncommon variety of sodalite called hackmanite. It is part of the tectosilicate family, a type of silca-based polymer structure, which was discovered to accommodate two separate dopant sites within close proximity to each for fast carrier mobility. The dopants serve to either create vacancies or donors of electrons within the material, thus providing the carriers to be manipulated. Variations of these materials can be found in either an isometric (hackmanite) or asymmetric (marialite) forms providing for application in the development of nonlinear optical devices, i.e. frequency mixers or harmonic sum or difference generation. Also discovered were results that indicated a lack of sulphur being present, contrary to previous publications.

We review the need for coherent optical communication systems and briefly describe the receiver frontend they require. The key element of the receiver is an optical 90° hybrid, which combines the received signal with the local oscillator laser with the adequate amplitude and phase relations. Silicon technology offers several advantages for the realization of such devices: compactness and CMOS compatibility, among others. However, the realization of high-performance hybrids is hampered by the high index contrast of this technology. We show that using multimode interference couplers with fully etched access waveguides and a shallowly etched multimode region, ultra-compact, high performance 90° hybrids can be realized. We experimentally demonstrate a device with a phase error below 5° and a common mode rejection ratio better than -20dBe in a ~50nm bandwidth.

After more than thirty years after Arthur Ashkin's pioneering experiments the optical trapping is a widely established technique of the modern science. Its applications cover wide range of physics, chemistry and biology. In many of these applications the irregular, inhomogeneous or ensembles of many particles are exposed to the light fields where such particles could be stably confined. In this paper we will present results of several numerical methods that describe optical forces acting on particles placed in the non-diffracting Bessel Beam.

We propose using slow light structures to greatly enhance the spectral performance of on-chip spectrometers. We design a calzone photonic crystal line-defect waveguide which can have large group index over a certain wavelength range. An arrayed waveguide gratings (AWGs) is studied as an example, and the performance of such a slow-light AWG is analyzed numerically.

Passive alignment of photonic components is an assembly method compatible with a high production volume. Its precision performance relies completely on the dimensional accuracies of geometrical alignment features. A tolerance analysis plays a key role in designing and optimizing these passive alignment features. The objective of this paper is to develop a systematic approach for conducting such tolerance analysis, starting with a conceptual package design, setting up the tolerance chain, describing it mathematically and converting the misalignment to a coupling loss probability distribution expressed in dB. The method has successfully been applied to a case study where an indium phosphide (InP) chip is aligned with a TriPleX¹ (SiO₂ cladding with Si₃N₄ core) interposer via a silicon optical bench (SiOB).

Two-frame interferometric method with blind phase shift of a reference wave for smooth surfaces retrieval is considered. The ability of this method to reconstruct a macrorelief of diffusing surfaces with a given roughness is studied. Computer simulations have testified the ability of reliable low-noise reconstruction of the diffusing surface macrorelief with standard deviation of the roughness heights up to λ/10 by using the developed interferogram processing algorithm. The simulations have shown that the proposed correlation approach, which is used to determine the reference wave blind phase shift, is more suitable for a diffusing surface than for a smooth one and the increase of surface roughness leads to a quadruple decrease of this error in comparison with that for the smooth surface. Experimental verification of the interferometric method performance to retrieve real diffusing surface macroreliefs with given roughness has been done by using the experimental setup based on a Twyman-Green interferometer and roughness comparison specimen. The obtained experimental results virtually have coincided with the computer simulation results that prove the performance of the considered method to retrieve not only smooth, but also diffusing surfaces.

The use of hydrogen (H₂) as a clean energy source is gaining significant global interest. Hydrogen gas can be combustible in air at concentrations starting at 4%, so a low cost, compact and reliable leak detector for hydrogen gas integratable into systems is desired. A Long Range Surface Plasmon Polariton (LRSPP) membrane waveguide structure is discussed as a hydrogen sensor. Palladium on a silicon dioxide free-standing membrane is proposed as the waveguide structure. Palladium absorbs hydrogen thereby inducing a detectable change in its permittivity. The design of straight waveguide and Mach-Zehnder Interferometer (MZI) architectures are discussed. Finite element method (FEM) simulations are conducted to choose appropriate designs to maximize sensor sensitivity.

Discrete Dipole Approximation (DDA) is a computational technique to simulate the optical properties of nanostructures of different shapes, sizes, and compositions. The influence of the target size on the optical response of 5 nm-diameter nanoparticles arranged in a monolayer hexagonal array is investigated by using DDA at various incident angles of the incident light on the target considered for silver (Ag), gold (Au) and copper (Cu) nanoparticles. In our study, the target size is controlled by the number of the spherical nanoparticles used to generate the two dimensional arrays. The interparticle distance is kept constant in all the simulations. The anisotropic response of noble-metal nanoparticles is generally characterized by the excitation of the high-energy (transverse) surface plasmon (SP) mode and the low-energy (longitudinal) SP mode. Results of the simulations for the three chosen metals show an exponential dependency of the absorption efficiency of the SP modes with respect to the target size. As the target size is increased, the energy of Ag-longitudinal SP mode is red-shifted and it displays an exponential decay while the band position of the transverse mode is blue-shifted. They however overlap when the smallest target size is considered. Although, the optical response of Au and Cu nanoparticle arrays shows the same dependency on the target size as observed in the case of Ag, the positions of their respective longitudinal and transverse modes are very close, making these almost indistinguishable. The dependency of the absorption efficiency of SP modes on the incident angle is fitted linearly for Cu, Au and longitudinal- Ag modes to the target size, while the transverse-Ag mode shows an exponential fitting. No change in the Ag-SP band position is observed when the incident angle is changed, but the SP bands for both Au and Cu exhibit exponential variation behavior.

The optical aspects of plasmon coupling occurring through the near-field interactions among metallic spherical nanoparticles assembled in close proximity to each other in two-dimensional and three-dimensional arrays have been examined using the discrete dipole approximation (DDA). Calculations were performed for nano-sized close-packed spheres of silver, gold or copper, hexagonally arranged in a planar monolayer target and extended gradually to three-dimensional multilayer targets with a fastened interparticle spacing. Those targets were simulated under the incident ppolarized light with an energy range of 1.5 - 4.5 eV by executing an open-source code of the DDA. The optical response of three-dimensional targets was revealed in the absorption spectra calculated at various angles of the polarized incident light, showing a blue shift of the plasmon resonance (PR) peak for both gold and copper targets. The splitting of the surface plasmon resonance (SPR) observed in the response of the two-dimensional silver system eventually disappeared into one well-defined resonance peak as the system grew in the third dimension. Moreover, to shed light on the nature of the plasmon coupling among close-packed nanospheres of different metals, we simulated a target composed of mono-sized nanospheres of the three metals placed spatially in three consecutive layers. A combined optical behaviour was thus observed through the absorption spectrum, where the plasmon peaks attributed to the silver, gold and copper interacting nanospheres emerged at the original energy values as if it was applied in isolated planar hexagonal arrays.

The quality of the spectrometer affects the sensitivity fall-off, axial resolution, and depth scan range, therefore overall performance of the spectral domain optical coherence tomography (SD-OCT) imaging. Chromatic aberration, optical resolution, and detector array resolution are the key design consideration for high-quality OCT spectrometer. Traditionally refractive optics spectrometer is used in SD-OCT. In the present work, the optical design of the reflective optics spectrometer and of the refractive optics spectrometers is reported for high-speed line field optical coherence tomography imaging. The performance of the spectrometers was compared by using the ZEMAX optical design software. The ZEMAX optical modeling analysis shows that the reflective optics spectrometer provides better performance by comparison with the refractive optics spectrometer.

The Characterization of the material optical properties with terahertz time domain spectroscopy is usually formulated as an optimization problem with an objective function representing the deviation of the theoretical scattering parameters from the measured ones. Both the magnitude and phase of the scattering parameters are utilized. For samples of unknown thickness, false estimation of the thickness limits the accuracy of the results. We propose an accurate optimization technique that predicts the actual thickness by solving only one optimization problem. Our technique is also efficient compared to other techniques that solve N expensive optimization problems. Dispersive dielectric models are embedded for accurate parameter extraction of a sample with unknown thickness. For doped semiconductors we utilize the surface Plasmon Polariton behavior for accurately estimating the doping level of semiconductor sample of unknown characteristics. By estimating the frequency at which the negative permittivity exists, we can accurately estimate the doping level of the semiconductor. Our technique has been demonstrated to be efficient and accurate through a number of examples.

In this paper, athermal subwavelength grating (SWG) waveguides are investigated. Both numerical simulations and experimental results show that a temperature independent behaviour can be achieved by combining two materials with opposite thermo-optic coefficients within the waveguide. SU-8 polymer with a negative thermo-optic coefficient (dn/dT = -1.1x10^-4 K^-1) is used in our silicon SWG waveguides to compensate for silicon's positive thermo-optic coefficient of 1.9x10^-4 K^-1. The grating duty ratio required to achieve an athermal behavior is reported to vary as a function of the operating wavelength and the waveguide dimensions. For example, for athermal waveguides of 260 nm in height, duty ratios of 61.3% and 83.3% were calculated for TE and TM polarized light respectively for a 450 nm wide waveguide, compared to ratios of 79% and 90% for a 350 nm wide waveguide. It is also reported that with increasing width, and increasing height, a smaller grating duty ratio is necessary to achieve an athermal behaviour. A smaller fraction of silicon would hence be needed to compensate for the polymer's negative thermo-optic effect in the waveguide core. Subwavelength sidewall grating (SWSG) waveguides are also proposed here as alternatives to high duty ratio SWG waveguides that are required for guiding TM polarized light. Assuming a duty ratio of 50%, the width of the narrow segments for temperature-independent behavior is found by numerical simulations to be 125 nm and 143 nm for TE and TM polarized light, respectively.

2-D slab photonic crystal multiple line defect waveguides have been designed for optical power splitting application which has numerous applications in photonic integrated circuit. The operation of the device is based on multimode interference effects and self-imaging phenomenon. The proposed structure consists of multiple photonic crystal line defect waveguides which are formed in the Γ-K direction by removing several entire rows of air-holes. The adjacent photonic crystal waveguides are separated by a row of air-holes. In this scheme a 1×3 power splitter is designed which involves three photonic crystal line defect waveguides multimode region, five photonic crystal line defect waveguides multimode region and one separation region. The entire structure is verified by 3-D finite difference time domain method. The transmitted power achieved at each output channel i.e. CH1, CH2 and CH3 are about 26.3%, 26.8% and 26.3% respectively. The total transmitted output power of 1×3 power splitter is 79.4% at target wavelength of 1.55μm.

We consider rather specific type of a multi-phonon light scattering in both isotropic and anisotropic media. The analysis performed shows that under some conditions it may be possible to expect realizing various multi-phonon processes of light scattering in a regime, which is very close to practically used Bragg scattering case. Preliminary experiment on a four-phonon Bragg anomalous light scattering has been realized in a tellurium dioxide crystal.

Some practical aspects of creating an acousto-optical processor oriented to the calculation of triple auto- and cross-correlations of low-power short optical pulses in time domain are under preliminary consideration. In so doing, the shapes of both the triple auto-correlations and the bispectra inherent in the most commonly used pulses are mathematically expressed and numerically illustrated, and the needed general schematic arrangement for a triple correlation acousto-optical processor is designed and briefly discussed. Then, in a view of exploiting the one-channel wide-aperture acousto-optical cells within operating similar processor, the performances of lead-molybdate crystalline cells are tentatively estimated.

A new device, optical cross add drop multiplexer (OXADM), is proposed and analyzed. It uses the combination concept of optical add drop multiplexer (OADM) and optical cross connect (OXC). It enables a wavelength switch while implementing add and drop functions simultaneously. So, it expands the applications in fiber to the home (FTTH) and optical core networks. A very high isolation crosstalk level (~ 60 dB) is achieved. Also, a bidirectional OXADM and N×N OXADM are proposed. Finally, a multistage OXADM is presented making some sort of wavelength buffering. To make these devices operate more efficient, tunable fiber Bragg gratings (TFBGs) switches are used to control the operation mechanism.

A proposed new design of optical cross add drop multiplexer (OXADM) is presented. It reduces the number of required circulators and total insertion losses compared with other circulator and FBG based designs. This enhances the isolation and crosstalk levels. In the new design, the homodyne crosstalk is eliminated in the drop signal. Also, the homodyne crosstalk in the output signal is reduced by more than 30 dB.

In this paper, a fully integrated flow sensor is designed and simulated. The sensor involves three PDMS layers, monolithic integration of microfluidic channels and detection unit. The middle thin layer includes the PDMS microcantilever and the microchannels network. The thin layer is sandwiched between the bottom and top PDMS layers to provide microfluidic environment and to release the cantilever for deflecting. The pressure difference on the cantilever causes the cantilever deflection. The optical fibers are embedded in the optical channels to send the light to the gold deposited cantilever tip and to detect the reflected light. Finite element analysis is done using COMSOL Multiphysics 3.5. Fluid structure interaction is done on the cantilever to find the cantilever defection in response to fluid flow in the microchannels. Optical power loss due to cantilever deflection is simulated by two integrated optical fibers. The numerical results confirm the feasibility of detecting the PDMS cantilever deflection in the range of regular microfluidic fluid flows.

Ingots containing cm-sized monocrystals of CuInSe₂ have been grown in quartz ampoules by a vertical-Bridgman method. Included also in the ampoules were varying quantities of elemental Na, as well as excess Se above stoichiometry. Deposits were seen within the ampoules after growth, including a white deposit formed through a reaction of the Na with the quartz, and a reddish-brown deposit mostly containing Na and Se. Thermoelectric power measurements indicate that stoichiometric material grown with no excess Se and no Na is p-type. With the addition of Na above a critical amount to the ampoule, the resulting ingots were always n-type. This p to n conductivity type change is inhibited when excess Se is also present, and more Na is required for the change to occur. The critical amount of Na was found to be approximately twice the atomic amount of excess Se. XRD indicated that the chalcopyrite structure of the material was maintained with additions of up to 3 at. % Na, even as the material was changed from p- to n-type, and no sodium was detected in the bulk. It is suggested that a reaction between the Na and the Se occurs, resulting in the formation of Na₂Se. The Se used in this reaction is therefore unable to be a part of the CuInSe₂ lattice, thereby increasing the number of donor-like Se vacancies, rendering it n-type. In this model, the addition of excess Se replaces those Se atoms which react with the Na, so that the material remains p-type.

In previous Bridgman growth of CuInSe₂ ingots, weighted amounts of high purity materials are introduced together into quartz ampoules. During the initial heating, vigorous reaction occurs mainly between In and Se leading to a sudden increase in the temperature and hence the vapor pressure. Explosion often occurs when the total amount of materials exceeds 10 grams even with quartz ampoules with a wall thickness greater than 1 mm. Although the explosion can be avoided by having very slow initial heating rate, the total materials are still limited to 30 g or less for each growth run. Due to the limited materials, the dimensions of ingots grown in the previous experiments have been limited. In the present work, we have developed a method to control the reaction between Se and In in the initial heating stage and hence to reduce the rate of heat release in the exothermic reaction. Using this improved method, the limit on the material amounts can be increased. Crystalline ingots with a total weight of 300 g and diameter 3 cm have been grown.

A 260 nm layer of organic bulk heterojunction blend of the polymer poly (3-hexylthiophene) (P3HT) and the fullerene [6,6]-phenyl C₆₁-butyric (PCBM) was spin-coated in between aluminum and gold electrodes respectively on top of a laser inscribed azo polymer surface relief diffraction grating. Angle dependent surface plasmons (SP) with a large band gap were observed in the normalized photocurrent by the P3HT-PCBM layer as a function of wavelength. The highest increase in photocurrent was found to be 272% at a wavelength of 618 nm for a grating depth of 50 nm. The SP-induced photocurrents were also investigated as a function of the grating depth and spacing.

The effect of using an anodic layer with low density (~ 6x10⁸ cm^-2) of gold nanorods (GNR) in organic bulk heterojunction poly(3-hexylthiophene) (P3HT) and phenyl-C₆₁-butyric acid methyl ester (PCBM) solar cells was studied. GNRs were deposited using several techniques, which produced various densities of GNRs on the anode layer. The anodic layers were characterized microscopically and spectroscopically. The power conversion efficiency and the short-circuit current for experimental devices incorporating GNR anodic layer showed an enhancement of up to 18% as compared to the control device. The results suggest that the electric field in the P3HT:PCBM active layer was increased by the localized surface plasmon resonances in GNRs. The increase in the electric field enhanced the photo-generation of excitons in the active layer near the plasmon peak, which improved the short-circuit current and the overall power conversion efficiency. Interestingly, photovoltaic devices with a low density of GNRs in the anodic layer showed an increase in the power conversion efficiency that was superior to that of devices with a higher density of GNRs in the anodic layer. This suggests that although the anodic layer with a higher density of GNRs absorbed more light, part of this light was confined in the anodic layer itself, and prevented from reaching the active layer of the bulk heterojunction device. In such cases, the power conversion efficiency was even found to be decreased with respect to the value for the control device.

The electrical carrier transport of a tandem cell structure was evaluated by investigating the band alignment of and carrier transport through a tunnel junction. The modeling structure of a tandem cell consists of a III-V (or II-VI) top cell layer, a Si bottom cell layer and tunnel junction layers in-between which connect the top and the bottom cells. The values of energy bandgap and electron affinity of each layer were varied to investigate their effect on the energy barrier height at the interface between Si and compound semiconductors of interest. The contour plots of barrier heights for majority and minority carriers at the hetero-interface are used as a starting point to define the successful regions for electrical carrier transport through the tunnel junctions.

Bilayers of metal contacts were deposited on p-type monocrystalline copper indium diselenide (CuInSe₂) and the resistance between two contacts were measured to find low resistance metal contacts on crystalline CuInSe₂. The first metal layer was Ni, Pt, Se, or Te and the second metal layer was Au, Ag, Al or Cu. It was observed that the resistance reduced when the surface of crystalline CuInSe₂ were etched before metal deposition with a solution containing H₂SO₄(1 %, w/w) and CrO₃ (1 %, w/w). It was confirmed that the resistance increases after heat-treatments at high temperature. The stability of the metal contacts in room air was estimated from the resistance measured for a period of over 20 days.

Laser bending of ductile materials is a promising manufacturing method for industry because it is contact free, and without spring-back effect. Although laser bending of metals (stainless steel, titanium, aluminum) has been explored since the early 1980's, laser bending of brittle materials such as silicon, borosilicate glass, and ceramics, is a relatively new field of research. Deformed silicon structures find application in microchips (clip chips, MEMS), and silicon cantilevers for atomic force microscopes. In the field of photovoltaics, silicon laser bending allows for novel cell architectures. The subject of this paper is the experimental investigations of laser bending of silicon combined with simulation techniques to model the temperature field.

Inorganic (mostly silicon based) solar cells are important devices that are used to solve the world energy and environmental needs. Now days, organic solar cells are attracting considerable attention in the field of photovoltaic cells because of their low cost and processing flexibility. Often conjugated polymers are used in the construction of the organic solar cells. We study the conjugated polymers' charge transport using computational approach that involves the use of the density functional theory (DFT), semiempirical (ZINDO), and Monte Carlo (MC) theoretical methods in order to determine their transfer integrals, reorganization energies, transfer rates (with the use of Marcus-Hush equation) and mobilities. We employ the experimentally determined three dimensional (3D) structure of poly(9,9'-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) to estimate the electron mobility in a similar co-alternating polymer consisting of carbazole and benzothiadiazole units (C8BT). In agreement with our previous work, we found that including an orientational disorder in the crystal reduces the electron mobility in C8BT. We hope that the proposed computational approach can be used to predict charge mobility in organic materials that are used in solar cells.

Energy conversion efficiency of crystalline silicon (c-Si) solar cells manufactured on thin substrates is strongly influenced by the recombination losses of photo-generated charge carriers at the surface and in its proximity. Intrinsic hydrogenated amorphous silicon (i-a-Si:H) deposited using DC saddle-field plasma enhanced chemical vapour deposition (PECVD) at a low temperature of ~200°C reduces recombination losses of photo-generated carriers through passivation of defects at the surface. This study reports on high quality surface passivation achieved using a dual layer approach wherein a 70nm amorphous silicon nitride (SiN_x) capping layer is deposited on a less than 10nm thin i-a-Si:H layer. While the a-Si:H layer is effective in passivating the interface recombination sites, SiN_x is deemed to incorporate field-effect passivation, thus providing a minority carrier mirror. Additionally, SiN_x layer acts as an anti-reflection coating with a low absorption coefficient in the optical frequency range of interest. The SiN_x deposition conditions, known to strongly influence the passivating quality of the dual layer structure, were systematically investigated using the response surface methodology (RSM). The optimal deposition parameters obtained from the RSM study were experimentally verified to yield the lowest surface recombination velocity of 3.5 cm/s on 1-2 Ω-cm n-type FZ c-Si using a PECVD a-Si:H/SiN_x bi-layer passivation stack.

Highly ordered, visible light driven TiO2 nanowire arrays doped with Fe photocatalysts were grown on the surface of functionalized graphene sheets (FGSs) using a sol-gel method with titanium isopropoxide (TIP) monomer, acetic acid (HAc) as the polycondensation agent and iron chloride in the green solvent, supercritical carbon dioxide (scCO₂). The morphology of the synthesized materials was studied by SEM and TEM, which showed uniform formation of Fe doped TiO₂ nanofibers on the surface of graphene sheets, which acted as a template for nanowire growth through surface -COOH functionalities. Increasing Fe content in the nanowires did not change the morphology significantly. Optical properties of the synthesized composites were examined by UV spectroscopy which showed a significant reduction in band gap with increasing Fe content, i.e. 2.25 eV at 0.6% Fe. The enhancement of the optical properties of synthesized materials was confirmed by photocurrent measurement. The optimum sample containing 0.6% Fe doped TiO₂ on the graphene sheets increased the power conversation efficiency by 6-fold in comparison to TiO₂ alone.

Solar cell efficiency decreases as its temperature increases. Therefore, it is necessary to design a thermally optimal solar cell carrier that will maintain a minimal solar cell temperature. To achieve this optimal solar cell carrier design, a finite-element analysis model of the solar cell on carrier was developed. This numerical model was experimentally calibrated against a known design, in which the average solar cell temperature was determined by examining the shift in the open circuit voltage. This allowed us to explore the relationship between the carrier geometry and the average solar cell temperature. That is, the solar cell carrier is characterized by two independent thermal resistances: the uniform flow thermal resistance, and the thermal spreading resistance. As the copper thickness was increased, the uniform flow resistance acted to raise the cell temperature while the spreading thermal resistance decreased the cell temperature. Therefore, when the carrier geometry minimized the thermal resistances, it was found that the minimum solar cell temperature was achieved at a copper thickness between 1.5 and 3 mm depending on the surface area of the carrier. This optimized carrier design reduced the average solar cell temperature by 16 °C, which corresponds to an increase of 0.8% in cell efficiency at 1666 suns as compared to the original design used to experimentally calibrate the numerical model.

Zinc oxide is a wide band gap semiconductor with a large exciton binding energy (60meV). As a result the nanostructures of this material have many potential applications in electronic and optoelectronic devices. In this work, the growth and optical properties of ZnO nanowires have been studied. The nanowires (NW) of ZnO were synthesized using low pressure chemical vapour deposition method (LPCVD) under different chamber pressures. The growth was carried out on (100) Si wafers pre-coated by gold particles as a catalyst. The morphology of the synthesized NWs and their optical properties like transparency and reflection were studied. The NW arrays have high optical transmittance compared to ZnO thin films prepared by sputtering. The photoluminescence of the NWs were also measured and compared with that of ZnO thin films. The two types of NW structures obtained have potential applications in photovoltaic devices as optical and electrical components.

When refractive optical systems are used to concentrate light onto high efficiency solar cells chromatic aberration creates irradiance distributions over the cells which are neither spatially nor spectrally uniform. Multijunction solar cells are the photovoltaic device with the highest conversion efficiency. However, their efficiency under a concentration system can be significantly lower than the measured efficiency under uniform irradiance and reference conditions. In this paper the irradiance distribution created by a Fresnel lens is studied by ray-tracing simulations and it is characterized using a CCD camera and adequate filters. The effects of the non uniform irradiance distribution on the solar cell performance are analyzed by measuring the IV curve of an elementary unit of the system when illuminated by a solar simulator. IV curves for different lens to cell distances are measured and compared to allow a better understanding of the system.

An on-sun Concentrating Photovoltaic (CPV) test site with a multiplexed current-voltage measurement capability has been installed at the University of Ottawa. Herein, we present details of the instrumentation, which is designed to provide in-situ I-V measurements of individual solar cells within a functioning, series connected, string. A 4-wire multiplexing system enables current-voltage measurements of individual cells. Where other multi-cell test systems have left cells at open-circuit or connected to a fixed resistor when not selected by the multiplexer, in this system each test cell operates within a string of cells controlled by a maximum power point tracker. This allows us to maintain the test cells at realistic operating conditions for all irradiance conditions. Using the current-voltage data, a range of parameters of interest can be monitored over time, including the solar cell temperature, photovoltaic efficiency and optical efficiency. This information is correlated with time-synchronized spectrometer and pyrheliometer data, allowing automated collection of performance data from several strings of optic/solar cell assemblies. The test site includes two 20m², dual-axis, ring mounted solar trackers and is being used to test new CPV systems which incorporate novel lightguiding optics designed and manufactured by Morgan Solar Inc.

This paper focuses on modeling and evaluation of semi-transparent photovoltaic technologies integrated into a coolingdominated office building façade by employing the concept of three-section façade. An energy simulation model is developed, using building simulation software, to investigate the effect of semi-transparent photovoltaic transmittance on the energy performance of an office in a typical office building in Montreal. The analysis is performed for five major façade orientations and two façade configurations. Using semi-transparent photovoltaic integrated into the office façade, electricity savings of up to 53.1% can be achieved compared to a typical office equipped with double glazing with Argon filling and a low emissivity coating, and lighting controlled based on occupancy and daylight levels.e.c

We propose a high efficiency coupling scheme of surface plasmon polaritons (SPP) in a metal-dielectric slit structure. The design includes a narrrow silver-slit structure, which is immersed in a dielectric with refractive index 1.5. We map the dependence of SPP coupling efficiency on the dielectric layer thickness (d). By varying d the dispersion behavior of the SPP mode is tuned enabling minimized wavevector mismatch between the light exiting the slit and the SPP mode. A dielectric layer of thickness in the range 50 nm < d < 150 nm yields coupling efficiencies of approximately 80%, representing a nearly four-fold enhancement relative to the coupling efficiency without a dielectric layer.