This PDF file contains the front matter associated with SPIE Proceedings Volume 8982 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Holmium-doped fibres provide a power scalable gain-medium capable of operation at wavelengths beyond 2.05 μm. We discuss and review our approach to the power scaling of pulsed and CW laser sources at 2.1 μm using holmium-doped fibres. This paper outlines experiments which demonstrate the wavelength region accessible using holmium-doped silica fibres, as well as a linearly polarised pulsed master-oscillator power amplifier and high average power CW laser and amplifier systems. These devices demonstrate the applicability of holmium fibre lasers to a range of scientific, medical, industrial and defence applications.

Due to their long photon lifetimes, ultra high quality factor (Q) silica microcavities form an ideal platform for microlaser development. Previous work verified that these devices exhibit Raman lasing, because the high Q compensates for the low Raman gain of silica. However, only devices with Q>1E8 are able to achieve microwatt thresholds, limiting the application space. One approach for overcoming this barrier is to increase the inherent Raman gain of the material without degrading the optical performance of the device. To address this challenge, we synthesize a series of titanium (Ti) doped silica sol-gels with different concentrations of Ti, including a null. The refractive indices of the coatings are characterized using spectroscopic ellipsometry and increase linearly with the concentration of Ti from 1.44 to 1.51. We apply the sol-gel as a conformal coating on silica toroidal microcavities and characterize the basic cavity properties (Q) and the lasing behavior, including the lasing threshold and the slope efficiency. All measurements are performed in ambient conditions. Although the cavity Q’s are modest (5E6), comparable lasing thresholds (microwatt) to higher Q silica devices are achieved because of the reduction in mode volume and the increase in Raman gain due to the presence of the Ti. Additionally, the efficiency of the laser increases with increasing Ti concentration.

Fibercore have developed AstroGain^TM fiber optimized for multichannel amplifiers used in optical satellite communications and control. The fiber has been designed to take full advantage of the photo-annealing effect that results from pumping in the 980nm region. The proprietary trivalent structure of the core matrix allows optimum recovery following radiation damage to the fiber, whilst also providing a market leading Erbium Doped Fiber Amplifier (EDFA) efficiency. Direct measurements have been taken of amplifier efficiency in a multichannel assembly, which show an effective photo-annealing recovery of up to 100% of the radiation induced attenuation through excitation of point defects.

We demonstrate a spatially distributed measurement technique to observe temperature changes along a pumped Ybdoped fiber. The technique is based on an array of fiber Bragg gratings acting as temperature sensor line. The Bragg gratings are inscribed directly into the actively doped fiber core using high intensity laser pulses and an interferometric setup. We studied the temperature evolution in differently doped fibers under pumping conditions and find different effects contributing to the observed temperature increase. To avoid an additional heating caused by pump-induced photodarkening, we measure the spatially resolved temperature profile during pumping along a photodarkening-reduced, cerium co-doped fiber.

While there are several methods for creating a blue microlaser, most have very high lasing thresholds and are not integrated on a silicon substrate. The present work demonstrates a blue laser based on the upconversion of thulium in a doped silica sol-gel microtoroid resonant cavity integrated on a silicon wafer. The thulium is pumped at 1060nm, and emission occurs near 780nm and 450nm. The high intensity of the circulating optical field in the microcavity increases the photon interaction pathlength and interaction time with the thulium atoms, enabling sub-mW thresholds at both blue and near-IR lasing emissions.

Semiconductor optical amplifiers (SOAs) are a well-established solution of optical access networks. They could prove an enabling technology for DataCom by offering extended range of active optical functionalities. However, in such costand energy-critical applications, high-integration densities increase the operational temperatures and require powerhungry external cooling. Taking a step further towards improving the cost and energy effectiveness of active optical components, we report on the development of a GaInNAs/GaAs (dilute nitride) SOA operating at 1.3μm that exhibits a gain value of 28 dB and combined with excellent temperature stability owing to the large conduction band offset between GaInNAs quantum well and GaAs barrier. Moreover, the characterization results reveal almost no gain variation around the 1320 nm region for a temperature range from 20° to 50° C. The gain recovery time attained values as short as 100 ps, allowing implementation of various signal processing functionalities at 10 Gb/s. The combined parameters are very attractive for application in photonic integrated circuits requiring uncooled operation and thus minimizing power consumption. Moreover, as a result of the insensitivity to heating issues, a higher number of active elements can be integrated on chip-scale circuitry, allowing for higher integration densities and more complex optical on-chip functions. Such component could prove essential for next generation DataCom networks.

In this paper we present preliminary studies on liquid crystal materials suitable for near-infrared applications. This includes initial analysis of the liquid crystal properties when doped with CuInS₂ quantum dots. We also discuss potential applications of LCs. Passively mode-locked fiber laser is presented in which simple LC-cells are used for intracavity polarization control, which greatly simplifies the configuration of the laser.

We review results on the growth of glassy and crystalline materials inside photonics crystal fibres (PCFs), seeking specific sensing and light confining properties. Initial results refer to the infiltration of silver metaphosphate (AgPO₃) glass inside PCFs, and the subsequent thermal poling of those composite PCFs for attaining plasmon resonance characteristics. Accordingly, the wet chemistry growth and characterization of crystalline ZnO layers inside PCFs is shown also. Finally, the use of laser etching technique for the inscription of relief periodic Bragg gratings on the capillary walls of a solid core, all silica glass PCF that exhibited demarcation temperatures near 1200 °C is presented. Ongoing work refers to the exploitation of the aforementioned PCFs for developing sensing, bio-sensing and actuating optofluidic devices.

GeO₂ transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO₂ laser. Different techniques like m-line, micro-Raman spectroscopy, atomic force microscopy, and positronbannihilation spectroscopy were employed to evaluate the effects of CO₂ laser processing on the optical and structuralbproperties of the waveguides. The GeO₂ planar waveguide after 2h of CO₂ laser irradiation exhibits an increase of 0.04 inbthe refractive index, measured at 1542 nm. Moreover, the technique of laser annealing is demonstrated to significantlybreduce propagation loss in GeO₂ planar waveguides due to the reduction of the scattering. Upon irradiation of the surfacebthe roughness decreases from 1.1 to 0.7 nm, as measured by AFM. Attenuation coefficients of 0.7 and 0.5 dB/cm at 1319 and 1542 nm, respectively, were measured after irradiation. Micro-Raman measurements evidence that the system embeds GeO₂ nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 μm thickness.

In this paper we describe an approach to reduce the propagation loss in titanium dioxide strip waveguides. We achieved to reduce losses down to 2.4 dB/cm in 1 μm-wide waveguide at λ=1550 nm.

The utilization of infrared chalcogenide glass (ChG) fibers has long been hampered by the unfavorable mechanical characteristics typical of these glasses. Furthermore, the usual pathways to producing such fibers necessitate large-scale synthesis of high-purity glass, which represents a challenge in an academic environment, and thus presents an obstacle to the transfer of research results from academia to industry. Here we present our recent progress on multimaterial coextrusion technology that allows for high-efficiency disc-to-fiber manufacturing. A one-step extrusion from two glass discs (10-mm-diameter and 3-mm-thick) and a thermoplastic disc results in a robust step-index preform that is thermally drawn in an ambient atmosphere into continuous lengths of fiber with core diameters on the order of tens of micrometers. These results offer an alternative methodology that overcomes many of the traditional obstacles while potentially reducing the production cost.

The potential of a new class of multifunctional photonic circuits is demonstrated by femtosecond laser micro-machining and inscription of micro-optical structures, such as ring and disk resonators, Mach-Zehnder interferometers, and microfluidic devices, in a flexible flat-fibre chip. Additional filling of surface channels with functional materials is employed towards sensing applications. Furthermore, direct write femtosecond-laser inscribed Bragg gratings were written in the Ge-doped core of flat-fibre enabling a number of relevant applications. The flat-fibre platform offers a unique degree of freedom by allowing surface and sub-surface devices to be integrated onto an a single optical chip with the potential for straightforward incorporation into integrated photonic circuits or optofluidic devices.

Ultrathin materials and nano-structuring are becoming essential for the functionalization of optical surfaces. In the talk we will show how ultrathin metals can be exploited to create competitive transparent electrodes. At the same time they can be used to create nanostructured surfaces through mass scalable dewetting and etching techniques. After presenting the techniques, we will focus on the applications made possible by these materials and technologies, including self-cleaning or easy-to-clean display screens, efficient indium-free light emitting diodes and solar cells, antireflective structures for the laser industry and super-wetting surfaces for biology.

This work demonstrates metamaterial (MM) selective thermal emitters for potential use with energy harvesting photodiodes, such as thermophotovoltaic cells. Preliminary structures have been designed, simulated, and fabricated using CST Microwave Studio and microfabrication techniques including electron beam evaporation, atomic layer deposition, and electron beam lithography, respectively. Samples were tested to determine the effect of top layer metal thickness on the absorption of these devices. Preliminary simulation and testing was also performed to design a device for operation at 500°C.

Nanoplasmonic optical interconnects is proposed to mitigate challenges facing electronics integration. It provides fast and miniaturized data channel that overcome the diffraction limit. We present a three dimensional plasmonic coupler that vertically bends the light to multilevel circuit configurations. It exploits light guiding in nanoscale plasmonic slot waveguides (PSWs). A triangularly-shaped plasmonic slot waveguide rotator is introduced to attain such coupling with good efficiency over a wide bandwidth. Using this approach, light propagating in a horizontal direction is easily converted and coupled to propagate in the vertical direction and vice versa. The proposed configuration is further extended to the design of a multilayer power divider/combiner with ultra-compact footprint that guides the light to multiple channels. A detailed study of the triangular rotator is demonstrated with the analysis of multiple configurations. This structure is suitable for efficient coupling and splitting in multilevel nano circuit environment.

Plasmonic lenses are based on complex combinations of nanoscale high aspect ratio slits. We show that their design can be greatly simplified, keeping similar performance while releasing technological constraints. The simplified system, called Huygens lens, consists in a central aperture surrounded by several identical single mode slits in a thin gold layer that does not rely anymore on surface plasmons. The focusing behaviour with respect to the position and number of slits is investigated, and we demonstrate the interest of this design to get compact array of lenses which are able to compensate the angle of incidence of the incoming wave.

Through the application of a bias voltage, metamaterials can dynamically change their response, opening up new technological possibilities. Combining design elements from three common metamaterial patterns, we have created a metamaterial polarizing filter that will transmit all polarization orientations equally when in the static mode. When a bias voltage is applied, the filter will minimize the transmission of x-polarized light in the wavelength band of interest. Progress has been made on creating a sufficiently conductive metamaterial to enable the dynamic mode, as well as on incorporating several filters into a monolithic stack. Fabrication methods and transmission results for the required substrates will be discussed.

Novel and intriguing lithographic approaches based on instabilities of liquid polymers and electro-hydro-dynamic at nanoscale have been developed. The unusual fabrication methods were aimed at fabricating 3D polymeric microstructures. A variety of microstructures were fabricated and tested for applications in different fields

We demonstrate a novel atomic layer deposition (ALD) process to make high quality nanocrystalline titanium dioxide (TiO₂) and zinc oxide (ZnO) with intermediate Al₂O₃ layers to limit the crystal size. The waveguide losses of TiO₂/Al₂O₃ nanolaminates measured using the prism coupling method for both 633 nm and 1551 nm wavelengths are as low as 0.2 ± 0.1 dB/mm with the smallest crystal size. We also show that the third-order optical nonlinearity in ZnO/Al₂O₃ nanolaminates can be enhanced by nanoscale engineering of the thin film structure.

Asymmetric contacts or split gate geometries can be used to obtain rectification, electroluminescence (EL) and photocurrent from carbon nanotube field effect transistors. Here, we report devices with both split gates and asymmetric contacts and show that device parameters can be optimised with an appropriate split gate bias, giving the ability to select the rectification direction, modify the reverse bias saturation current and the ideality factor. When operated as a photodiode, the short circuit current and open circuit voltage can be modified by the split gate bias, and the estimated power conversion efficiency was 1×10^-6. When using split gates and symmetric contacts, strong EL peaking at 0.86 eV was observed with a full width at half maximum varying between 64 and 120 meV, depending on the bias configuration. The power and quantum efficiency of the EL was estimated to be around 1×10^-6 and 1×10^-5 respectively.

The active core diameter in silica preforms can be significantly increased by the deposition of ytterbium (Yb) and the most important codopant aluminum (Al) in the gas phase through the high-temperature evaporation of an Yb chelate compound and Al chloride in the Modified Chemical Vapor Deposition (MCVD) process. Here, we report on systematic investigations of the incorporation of Yb and Al into silica by gas phase doping technique. Preforms and fibers were prepared in a wide range of Yb and Al concentrations. The samples were characterized concerning the radial distribution of the refractive index and dopant concentrations, the efficiency of the deposition, and the absorption and emission properties in the NIR region. First laser experiments have demonstrated a slope efficiency of 80%, which is comparable to fibers made by MCVD/ solution doping and powder sinter technology.

The integration of optical components into the digital processing units of satellite subsystems has the potential to remove interconnect bottlenecks inherent to the volume, mass, complexity, reliability and crosstalk issues of copper-based interconnects. Assuming on-board high-bandwidth communications will utilize passive optical fibers as a communication channel, this work investigates the impact of gamma irradiation from a Co-60 source on both passive optical fibers and ytterbium-doped single-mode fibers operated as amplifiers for a 1060-nm light source. Standard optical patch cables were evaluated along with active Yb-doped double-clad fibers. Varied exposure times and signal transmission wavelengths were used to investigate the degradation of the fibers exposed to total doses above 100 krad (Si). The effect on the amplified signal gain was studied for the Yb-doped fibers. The increased attenuation in the fibers across a broad wavelength range in response to multiple levels of gamma radiation exposure along with the effect that the increased attenuation has on the actively pumped Yb-doped fiber amplifier performance, is discussed.

In this paper we report our investigation on the lifetime reduction in ytterbium doped aluminosilicate fibers due to the pump induced photodarkening (PD). We show a linear correlation between equilibrium lifetime reduction and equilibrium losses due to PD and a squared-law dependence between lifetime reduction at equilibrium and dopant concentration (wt%). Finally, we did not observe interplay between PD and quenching effect. The quantitative analysis carried out allows to determine the photodarkening quenching term in the laser rate equations system to properly model laser device.

New Yb³⁺, Er³⁺ and Tm³⁺ triply doped fluoro-phosphate glasses belonging to the system NaPO₃-YF₃-BaF₂-CaF₂ have been prepared by the classical melt-casting technique. Glasses containing up to 10 wt.% of rare-earth ions fluorides have been obtained and characterized by using differential scanning calorimetry (DSC), UV-visible-near-infrared spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and optically homogeneous glass-ceramics have been reproducibly obtained by appropriate heat treatment in view to manage the red, green and blue emissions upon 975 nm laser excitation. According to the applied thermal heat-treatment, a large enhancement of intensity of the up-conversion emission – from 10 to 160 times higher – has been achieved in the glassceramics compared to that of glasses, suggesting incorporation of the rare-earth ions into the crystalline phase. Furthermore, a large range of color rendering has been observed in these materials by controlling the laser excitation power and material crystallization rate. Time-resolved luminescence experiments as well as X-ray diffractometry and scanning electron microscopy techniques have been employed in order to understand and correlate the multicolor emission changes to the crystallization behavior of this material. A progressive phase transformation of the fluorite-type CaF₂-based nanocrystals initially generated was observed along with increasing heat-treatment time, thus modifying the rare earth ions spectroscopic features.

A 30 Gb/s Ge waveguide photodetector was demonstrated and its reliability under elevated temperatures and high stress biases were investigated. For different reverse biases, the slopes of the dark current increment versus stress bias time curves were initiatively found to be the same and made the lifetime extrapolation feasible. The lifetime of the Ge waveguide photodetector under different stress bias was predicted by using a simple extrapolation method. To maintain the ten-year lifetime of the Ge waveguide photodetector, the bias voltage should be kept lower than -3V. For the first time, the degradation mechanism under stress biases was analyzed in detail by the reaction-diffusion model. The experimental results agree well to the theoretical derivation based on reaction-diffusion model.

Focusing in milliseconds without translational mechanics involved is possible with electrically tunable lenses. Fast shape-changing lenses enable fast imaging systems which can focus at distances from infinity to a few centimeters with a high optical quality. Furthermore, rapid laser processing in three dimensions is realized without mechanical translation of the focusing lens or the sample. With tunable lenses the entire optics can be made compact, robust and abrasion-free. Different configurations are discussed, how to integrate the tunable lens in the optical path. For machine vision applications, the achievable optical quality depends on the chosen combination of the tunable lens with a fixed focal length lens and a camera. It is recommended to use a fixed focus lens with a short distance between the stop position and the front of the lens. Furthermore, important points are presented how to achieve optimal performance in laser processing applications such as orientation and position of the tunable lens and the diameter of the beam incident on the lens. Additionally, different approaches will be discussed for monitoring the focal length of the tunable lens. The focal length of the tunable lens is sensitive to temperature changes, as the lens material is a fluid. However, in contrast to conventional lenses, the focal length of the tunable lens can be corrected electrically. For that purpose, the tunable lens exhibits an integrated temperature sensor for temperature compensation. Also optical feedback solutions will be presented for applications requiring highest precision and tracking of the absolute focal length value.

The properties of multiple reflections from narrow bandwidth reflection Bragg gratings are presented. The use of multiple reflections serves to increase the suppression ratio of the out-of-band spectral content such that contributions of grating sidelobes can be mitigated. The result is a device which retains spectral and angular selectivity in a single high efficiency diffraction order but reshapes spectral/angular response to achieve higher signal to noise ratios (SNR). The material for recording these high suppression devices is photo-thermo-refractive (PTR) glass. PTR is a highly homogeneous photosensitive glass with features such as low losses and high laser damage threshold. It has recently been used with good success to record permanent volume Bragg gratings with high efficiency and narrow band selectivity for use in laser cavities. Multiple reflections from the grating surface are achieved using several different arrangements. The multiple pass grating reflections are demonstrated and compared to the performance of a single reflection from a volume Bragg grating.

The fabrication of Avalanche Photodiodes (APDs) in CMOS processes can be exploited in several application domains, including telecommunications, time-resolved optical detection and scintillation detection. CMOS integration allows the realization of systems with a high degree of parallelization which are competitive with hybrid solutions in terms of cost and complexity. In this work, we present a linear-mode APD fabricated in a 0.15μm process, and report its gain and noise characterization. The experimental observations can be accurately predicted using Hayat dead-space noise model. Device simulations based on dead-space model are then used to discuss the current status and the perspectives for the integration of high-performance low-noise devices in standard CMOS processes.

This work summarizes how plasmonic phenomena can enhance the fluorescence of lanthanides (Ln³⁺) coupled to metallic nanoparticles (MNP). Lanthanide-ions emission lines, based on 4f-4f transitions, are weak due to Laporte selection rules for optical transitions. This effect results in low absorption cross sections for excitation and long lifetimes for emission processes. We propose to use metallic nanoparticles in order to determine how plasmonic nanoparticles can enhance absorption and emission of two emblematic lanthanides ions used for bio-labeling and energy conversion, i.e., Eu³⁺ and Er³⁺. This work quantifies the average enhancement factor (AEF) is expected for different geometries of nanoparticle structures and compares it to previous studies. Then, we theoretically and numerically investigate metal-enhanced fluorescence of plasmonic core–shell nanoparticles doped with lanthanides ions. The shape and size of the particles are engineered to maximize the average enhancement factor of the overall doped shell. We show with theoretical considerations and numerical studies that the highest enhancement (11 in the visible and 7 in the near-infrared) is achieved by tuning either the dipolar or the quadrupolar particle resonance to the rare-earth ion’s excitation wavelength. Additionally, the calculated AEFs are compared to experimental data reported in the literature, obtained under similar conditions (plasmon-mediated enhancement) or when a metal–Ln³⁺ energy-transfer mechanism is involved.

Doping of amorphous chalcogenide films of rather dissimilar bonding type and resistivity, namely, Ga-La-S, GeTe, and Ge-Sb-Te by means of ion implantation of bismuth is considered. To characterize defects induced by ionbeam implantation space-charge-limited conduction and capacitance-voltage characteristics of amorphous chalcogenide/silicon heterojunctions are investigated. It is shown that ion implantation introduces substantial defect densities in the films and their interfaces with silicon. This comes along with a gradual decrease in the resistivity and the thermopower coefficient. It is shown that conductivity in GeTe and Ge-Sb-Te films is consistent with the two-type carrier conduction model. It is anticipated that ion implantation renders electrons to become less localized than holes leading to electron conductivity in certain cases as, for example, in GeTe.

This study aims to expand the body of knowledge about the optical properties of battery cathode materials. Although some studies have been conducted on the optical properties of Lithium Iron Phosphate (LiFePO₄), to the authors’ knowledge, this is the first study of its kind on electrodes extracted from commercially available LiFePO₄ batteries. The use of Vis/NIR and FTIR spectroscopy provides for a methodology to study the optical properties of LiFePO₄ and may allow for the characterization of other properties such as particle size and the proportions of _LiFePO4 versus FePO₄ material. Knowledge of these properties is important for the development of a mechanism to measure the state-of charge (SOC) in lithium ion batteries. These properties are also important in a host of other applications including battery modeling and materials characterization. Cylindrical LiFePO₄ batteries (from A123 Systems Inc.) were acquired from the commercial market and charged to 10 different states between 30% and 80% of their nominal capacity using a constant-current, constant-voltage (CCCV) cycling method. Visual inspection of the extracted electrodes shows that the LiFePO_4/C-cathodes display subtle changes in color (shades of grey) with respect to SOC. Vis/NIR measurements support the visual observation of uniform intensity variations versus SOC. FTIR measurements show an absorbance signature that varies with SOC and is distinct from results found in the literature for similar LiFePO₄-based material systems, supporting the uniqueness of the absorbance fingerprint.

ZnGa₂O₄ (ZGO) is a normal spinel. When doped with Cr³⁺ ions, ZGO:Cr becomes a high brightness persistent luminescence material with an emission spectrum perfectly matching the transparency window of living tissues. It allows in vivo mouse imaging with a better signal to background ratio than classical fluorescent NIR probes. The most interesting characteristic of ZGO:Cr lies in the fact that its LLP can be excited with red light, well below its band gap energy and in the transparency window of living tissues. A mechanism based on the trapping of carriers localized around a special type of Cr³⁺ ions namely Cr_N2 can explain this singularity. The antisite defects of the structure are the main responsible traps in the persistent luminescence mechanism. When located around Cr³⁺ ions, they allow, via Cr³⁺ absorption, the storage of not only UV light but also all visible light from the excitation source.

Photoluminescence (PL) and excitation spectra of Bi melt-doped oxide and chalcogenide glasses are very similar, indicating the same Bi center is present. When implanted with Bi, chalcogenide, phosphate and silica glasses, and BaF₂ crystals, all display characteristically different PL spectra to when Bi is incorporated by melt-doping. This indicates that ion implantation is able to generate Bi centers which are not present in samples whose dopants are introduced during melting. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi²⁺ and Bi clusters.

When metal layers like Ag or Cu deposited on the amorphous chalcogenide films such as As₂S₃, As₂Se₃, GeS₂, and GeSe₂, are illuminated by light, the metal elements diffuse abnormally into the amorphous chalcogenide layer. This abnormal diffusion of metal was found by Kostyshin in Russia in 1965 and called photodoping. The large modulation of refractive index is realized by the doping of large amount of Ag atoms into the amorphous network of chalcogenide film which gives the possibility for various photonic device applications. In this study, the quantitative characterization of photodoping phenomena was carried out for amorphous GeS₂ films using Ag as a doping metal element to obtain the basic information to the photonic device fabrication. Quantum efficiency to reach the saturation of the doping was derived using the laser diodes with different wavelengths which cause a photodoping phenomenon. As for the wavelength dependence of the photodoping, it was suggested that the quantum efficiency was enhanced for the irradiated photon energy near the optical gap energy (ca. 3.3eV) of a-GeS₂ and showed the tendency similar to the absorption spectrum of the amorphous GeS₂ film. Photodoping rate was studied for various irradiated power densities of a He-Cd laser (441.5 nm) and the photodoping rate was proportional to the number of incident photons at low intensity. For the intensity over 10mW/cm², the enhancement of photodoping rate was observed due to some extra effects like a thermal effect.

Photonic crystal fibers (PCF), sometimes also referred to as microstructured fibers (MSF), have been a subject of extensive research for over a decade. This is mainly due to the fact that by changing the geometry and distribution of the air holes the fiber properties can be significantly modified and tailored to specific applications. In this paper we present the results of a numerical analysis of the influence of the air-hole distribution on the sensitivity of the propagated modes’ effective refractive index to externally applied longitudinal strain. We propose an optimal strain sensitive fiber design, with a number of fibers drawn and experimentally evaluated to confirm the theoretical results. Furthermore as the direct measurement of the effective refractive index change may be complex and challenging in field environment, we propose to use fiber Bragg gratings (FBG) in our sensing set-up. As the Bragg wavelength is a function of the effective refractive index, the external strain changes can be monitored through the Bragg wavelength shift with a simple optical spectrometer. Moreover, since the PCF is also optimized for low-loss splicing with standard single mode fiber, our novel sensor head can be used with standard off-the-shelf components in complex multiplexed sensing arrays, with the measured signal transmitted to and from the sensor head by standard telecom fibers, which significantly reduces costs.

The new photodiodes with cut-off wavelengths at 3640 nm, 4600 nm and 5150 nm have been recently developed in a high-tech company LED Microsensor NT (St.Petersburg, Russia) in cooperation with Aalto University (Espoo, Finland). Photodiode (PD) heterostructures InAsSb/InAsSbP were grown by MOVPE on InAs substrates. For the PDs with a cutoff wavelength at 3640 nm at room temperature the responsivity at 3300 nm reached 1.46 A/W and, detectivity was 1.56*10¹⁰ cm.Hz^1/2/W. For the PDs with a cut-off 4600 nm the same parameters were: 1.91 A/W and 6.7*10⁹ cm.Hz^1/2/W respectively (lambda=4100 nm). For the third type of PDs with a cut-off at 5150 nm responsivity was 0.29 A/W, detectivity was 4.2*10⁸ cm.Hz^1/2/W (lambda=5000 nm). Creation of photodiodes for the spectral range 2500-5200 nm with acceptable efficiency in photovoltaic operation mode (with no reverse bias) and using them in a pair with spectrally matched LEDs driven by very short current pulses allows developing optical cells with very low power consumption (less than 1 mW). Small size of the LED and PD dies (0.4-0.8 mm) and low heating makes it possible to design very thin optical cells (less than 2 mm) for measuring CH4, CO2, CO, H2O and other substances [1]. Mounting of a few LED dies that emit at different wavelengths in such a small cell allows measuring different chemical substances simultaneously. Direct coating of optical filters on the LED or PD surface during post-growth process allows improving selectivity and sensitivity of the sensor. Super low power consumption of the diode-based optical cells makes them promising candidates for the wireless mesh sensor networks for various gas monitoring purposes as well as for HVAC systems. Combination of the low power consumption and thin size of the cells opens possibility to embed them in mobile devices.

Phase sensitivities of temperature, longitudinal strain or pressure, are very important fiber features in sensing and telecommunication applications. The most common ways to modify such sensitivities are to change the material properties (by adjusting the core doping level) or employ microstructured fibers (which properties strongly depend on the cross-section geometry). We decided to investigate strain sensitivity influenced by effective mode field area and mode field diameter as clear consequence of fiber cross-section geometry. In this paper we present the results of a three dimensional numerical analysis of the correlation between the fiber mode field diameter and its longitudinal strain sensitivity. Both conventional and microstructured (commercially available and custom designed) fibers are investigated. Furthermore we compare the theoretical results with experimental data. To measure fiber sensitivity we developed a dedicated all-fiber Mach-Zehnder interferometer which enables the measurement of strain induced phase changes in various fiber types (including conventional and microstructured fibers). As a conclusion of our work we present relationship between strain sensitivity and MFD .

The authors propose an alternative method for high resolution optical microscopy - Evanescent Field Scanning Optical Microscopy (EFSOM) which eliminates implementation of the scanning tip compare to classical NSOM technique. The approach involves scanning a sample in the evanescent-field of a prism generated using total internal reflection (TIR) and recording the reflected power as a function of position. The reflection pattern of the wave is collected and processed, using comparative differentiation. The extracted information is processed further to eliminate any distortions. The system is not limited by diffraction and resolution primarily depends on the characteristics of the photo-detector and scanning velocity. Implementation of thin silver layer and coupling of incident radiation into Surface Plasmons Polaritons (SPP) improves system sensitivity and reduces photo detector dynamic range requirements.

Glasses embedded with Dysprosium and Samarium were made by the melt quenching technique. Dy³⁺ -doped glasses exhibited bright white luminescence under 10 mW of 405 nm diode laser excitation. Color rending index of the glass was improved by adding Sm³⁺ as a co-dopant to the glass. Spectroscopic results of the glasses are discussed.

A dual-wavelength tunable fiber laser is demonstrated using two polymer waveguide Bragg gratings (PWBGs) as a wavelength tunable filter. The wavelength tuning in the laser could be achieved by changing the applied electrical power to the PWBG. The interval of dual wavelength can be tuned by 18.9 nm for the maximum applied electrical power of 100 mW. The corresponding frequency range is 2.375 THz. The variation of the lasing wavelength is linearly proportional to the applied electrical power. The side mode suppression ratio of the dual wavelength laser has more than 35 dB.

In high end optical designs the quality of the optical system not only depends on the chosen optical glasses but also on the available refractive index and Abbe number tolerances. The primary optical design is based on datasheet values of the refractive index and Abbe number. In general the optical position of the delivered glass will deviate from the catalog values by given tolerances due to production tolerances. Therefore in many cases the final optical design needs to be modified based on real glass data. Tighter refractive index and Abbe number tolerances can greatly reduce this additional amount of work. The refractive index and Abbe number of an optical glass is a function of the chemical composition and the annealing process. Tight refractive index tolerances require not only a close control and high reliability of the melting and fine annealing process but also best possible material data. These data rely on high accuracy measurement and accurate control during mass production. Modern melting and annealing procedure do not only enable tight index tolerances but also a high homogeneity of the optical properties. Recently SCHOTT was able to introduce the tightest available refractive index and Abbe number tolerance available in the market: step 0.5 meaning a refractive index tolerance of +/- 0.0001 and an Abbe number tolerance of +/- 0.1%. This presentation describes how the refractive index depends on the glass composition and annealing process and describes the requirements to get to this tightest refractive index and Abbe number tolerance.

Lithium-niobate-on-insulator (LNOI) is a new material platform for integrated optics allowing for small bending radii, high intensities and superior electro-optical and nonlinear properties. Ridge waveguides of different width are fabricated on pure and Er-doped LNOI substrates using diamond-blade dicing, resulting in smooth side walls with lower roughness when compared to dry etching techniques. Propagation losses for polarized modes are measured by the Fabry-Perot method using a fiber coupling setup and a tunable laser at 1.5 μm. Loss values as low as ~1.4dBcm^-1 were obtained for quasi-TM (qTM) modes, while losses for qTE modes are slightly higher. Characterization of Er:LNOI ridges is performed using Raman and fluorescence spectroscopy. Spectral scans are obtained using a scanning confocal microscope and a 488nm laser. Besides line broadening that may be attributed to internal strain in the bonded layer and implantation induced defects, analysis of Raman spectra shows no significant difference between waveguide and bulk material. However, Er emission of ²H_11/2 and ⁴S_3/2 to ⁴I_15/2 contains small spatial differences across the layer thickness when compared to Er-doped bulk samples. While Raman intensity has a linear relationship with pump power, the intensity of the Er emission starts saturating already at pump levels of a few mW. To investigate fluorescence of the ⁴I_13/2–⁴I_15/2 transition inside the diced ridges, a fiber-coupled laser with wavelength 980nm is used for pumping. The emission is broadened and maxima are shifted to longer wavelengths, which may be attributed to defects induced by implantation, strain induced by the bonded LN-SiO₂ interface, and re-absorption of fluorescence light.

We present a tunable transmissive grating beam splitter for multiple laser line separation based on acousto-optic interaction in tellurium dioxide. Acousto-optic devices are well known for light modulation, frequency shifting, filtration or deflection. For a deflector, the incident light beam is monochromatic and the angular deviation is proportional to the ultrasonic frequency excursion. For a tunable filter, the selected wavelength is determined by the ultrasonic frequency. Several wavelengths may be simultaneously diffracted using several associated ultrasonic frequencies and all the diffracted beams have the same angular deviation. Unlike the classical operating modes of acousto-optic devices, we consider the simultaneous diffraction of several optical wavelengths by a single ultrasonic frequency. The device is based on Bragg anisotropic interaction in the specific “Tangent Phase Matching” configuration. The acousto-optic interaction takes place with a single ultrasonic frequency and the diffraction efficiency remains high over a wide optical spectral range. The different diffracted beams are then angularly well separated, due to the slow velocity of the ultrasonic wave propagating in tellurium dioxide. The optical bandwidth is directly related to the operating ultrasonic frequency. Numerical calculations were carried out to determine the main parameters of the device: operating ultrasonic frequency, optical bandwidth, tunability range, crystalline cut and transducer length. A practical device has been designed for visible spectrum. Experimental results will be presented as for example a spectral bandwidth from 450 nm to 550 nm with a RF carrier frequency f = 125 MHz.

Superluminal propagation at negative group velocity was demonstrated in a highly nonlinear fiber embedded in a Brillouin laser ring cavity. A maximum advancement of 369 ns and strong Stokes lasing power of 482 mW were achieved when the cavity was pumped with a 1 MHz sinusoidal wave modulated signal at power level of 1 W. The frequency dependence of fast light in this fiber ring cavity was examined with modulation frequencies of 1 kHz to 15 MHz. a maximum fractional advancement of 0.54 was achieved at 10 kHz and a maximum negative group index of - 9480 was demonstrated at 1 kHz.

Alternative materials to silica glass are necessary for supercontinuum (SC) generation at longer wavelengths in the midinfrared (MIR) region. The alternative materials should possess the properties of wide transmission window and high nonlinearity, simultaneously. Chalcogenide glass is the suitable candidate due to its excellent properties of transmission and nonlinearity in MIR region. In this paper, we demonstrate the SC generation in a suspended-core As₂S₃ chalcogenide microstructured optical fiber (MOF). The variation of SC is investigated by changing the fiber length, pump peak power and pump wavelength. In the case of long fibers (20 and 40 cm), the SC ranges are discontinuous and stop at the wavelengths shorter than 3500 nm, due to fiber absorption. In the case of short fiber as 2.4 cm, the SC range is continuous and can extend to the wavelengths longer than 4 μm. The process of SC broadening is observed when the pump peak power increases from 0.24 to 1.32 kW at 2500 nm in the 2.4 cm long fiber. The variation of SC range with the pump wavelength changing from 2200 to 2600 nm is studied. The selected wavelengths correspond to the dispersion of As₂S₃ MOF from the normal to anomalous region. The SC generation is simulated by the generalized nonlinear Schrödinger equation. The simulation includes the SC difference between 1.3 and 2.4 cm long fiber at 2500 nm pumping and the variation of SC with pump peak power in 2.4 cm long fiber. The simulation agrees well with the experiment.

Fiber-optical parametric amplification (FOPA) has been intensively studied and exploited for various interesting applications such as wavelength conversion, wavelength division multiplexing, optical signal processing and so on. However, its efficiency is governed by the fiber nonlinearity and chromatic dispersion. By employing tellurite glass we propose novel highly nonlinear tellurite hybrid microstructured optical fibers (HMOFs) which have nonlinearity of 6642 W^-1km^-1 and near-zero flattened dispersion profiles from 1.3 to 2.3 μm with four zero dispersion wavelengths for FOPA applications. The linear phase-mismatch, optical signal gain and gain bandwidth are precisely calculated by using a full propagation constant which includes the contribution of all high-order dispersion parameters. In contrast with silica fibers, the signal gain is shown to be generated in the wavelength regions where Δβ<-4ΥP and the parametric gain coefficient g is imaginary. It is shown that the proposed tellurite HMOFs with short fiber length L<90 cm have the gain bandwidth as broad as 760 nm when it is pumped at 1550 nm. The increase in pump power from 1 to 4 W not only increases the signal gain but also broadens the FOPA gain bandwidth. At 1700-nm pump wavelength, the signal gain larger than 14 dB is obtained over a very broad gain bandwidth of 1200 nm (from 1290 to 2490 nm). To our best knowledge, it is the first time that highly nonlinear tellurite HMOFs are demonstrated as attractive candidates for high performance of FOPA.

Mechanical strength is one of the biggest limitations of practical application for tellurite fiber. In this study, we design and fabricate a single mode tellurite composite fiber to overcome the flaw. The fiber has a double cladding structure with tellurite core and inner cladding, the outer cladding, which is made of non-tellurite glass, possesses of appropriate softening temperature and coefficient of thermal expansion, well matched the novelty tellurite glass. The propagation loss of the fiber is less than 0.02 dB/cm @1310 nm. We also investigate the laser property of the fiber by using a homemade watt-class 1590 nm fiber laser. 2 micron fiber laser is demonstrated with a 2 cm length of the fiber.

Bi-alkali antimonide photocathode is an essential component in fast timing response photomultipliers. Real-time in-situ grazing incidence x-ray diffraction and post-growth x-ray reflectivity measurement were performed to study the photocathode deposition process on glass substrate. Grazing incidence x-ray diffraction patterns show the formation of Sb crystalline, dissolution of crystalline phase Sb by the application of K vapor and reformation of refined crystal textures. XRR result exhibits that the film thickness increases ~ 4.5 times after K diffusion and almost have no change after Cs diffusion. Further investigation is expected to understand the photocathode growth process and provide guidelines for photocathode development.

A novel highly nonlinear three-core chalcogenide-tellurite fiber is proposed and fabricated in the paper. Each core with high index is made of chalcogenide glass (Ge₁₅Ga₃Sb₁₃S₆₉). The background with low index is made of TeO₂–ZnO–Li₂O–Bi₂O₃ (TZLB) glass. Each core of this fiber can be considered as a single core. And it can be used for the high power transmission. The effective modal refractive index and the chromatic dispersion are calculated with the light beam coupled in one core of the fiber, respectively. Supercontinuum generation from 1400 nm to 3536 nm in this fiber is investigated under the pump of a 2200 nm femtosecond fiber laser.

Towards achieving a functional RAM organization that reaps the advantages offered by optical technology, a complete set of optical peripheral modules, namely the Row (RD) and Column Decoder (CD) units, is required. In this perspective, we demonstrate an all-passive 2×4 optical RAM RD with row access operation and subsequent all-passive column decoding to control the access of WDM-formatted words in optical RAM rows. The 2×4 RD exploits a WDM-formatted 2-bit-long memory WordLine address along with its complementary value, all of them encoded on four different wavelengths and broadcasted to all RAM rows. The RD relies on an all-passive wavelength-selective filtering matrix (λ-matrix) that ensures a logical ‘0’ output only at the selected RAM row. Subsequently, the RD output of each row drives the respective SOA-MZI-based Row Access Gate (AG) to grant/block the entry of the incoming data words to the whole memory row. In case of a selected row, the data word exits the row AG and enters the respective CD that relies on an allpassive wavelength-selective Arrayed Waveguide Grating (AWG) for decoding the word bits into their individual columns. Both RD and CD procedures are carried out without requiring any active devices, assuming that the memory address and data word bits as well as their inverted values will be available in their optical form by the CPU interface. Proof-of-concept experimental verification exploiting cascaded pairs of AWGs as the λ-matrix is demonstrated at 10Gb/s, providing error-free operation with a peak power penalty lower than 0.2dB for all optical word channels.

Spectroscopic properties of the 2 μm infrared (IR) emission (⁵I₇ → ⁵I₈) from trivalent holmium (Ho³⁺) doped potassium lead bromide (KPb₂Br₅) are presented. The investigated Ho³⁺ doped KPb₂Br₅ (KPB) material was synthesized through purification of starting materials including multi-pass zone-refinement, bromination, and subsequently grown using horizontal Bridgman technique. The bromination process was critical for removing oxidic impurities and enhancing the quality of the crystal. Judd-Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were calculated and compared with results reported for Ho³⁺ doped KPb₂Cl₅ (KPC). Under resonant pumping (~1.907 μm), Ho: KPB showed a broad IR emission centered at ~2 μm with an exponential decay time of 7.1 ms at room temperature. The nearly temperature independent emission lifetime is consistent with a negligibly small non-radiative decay rate for the ⁵I₇ excited state of Ho³⁺, as predicted by the multiphonon energy gap law. The optical absorption, emission and gain cross-sections of Ho: KPB were determined for the 2 μm transition. The Ho: KPB crystal was also evaluated as a potential solid-state material for laser cooling applications.

A novel acousto-optic modulation mechanism will be addressed in this paper. Focused Gaussian beam passing through acousto-optic media experiences different refractive index regions arising from acoustic waves generated by ultrasonic source. In this way according to the snell’s law of refraction the beam propagation path will be altered when these periodic traveling waves reach the incoming radiation where a typical p-n junction photodiode located inside the rising or falling lobe of the undiffracted Gaussian beam senses these small lateral deflections. Due to small variations of the refractive index the magnitude of deflection will be up to tens of micron outside the modulator. Hence, sharp intensity gradient is required for detecting such small beam movements by appropriate lens configuration to focus the Gaussian profile on the detector junction area. In the other words intensity profile of zero order beam oscillates proportional to the time dependent amplitude of the acoustic waves versus previous methods that intensity of diffracted beam changes with applied ultrasonic intensity. The extracted signal properties depend on the beam collimation, quality of beam profile and depth of focus inside the modulator. The first experimental approach was proceeded using a collimated 532 nm diode laser source (TEM00), distilled water as interaction media and 10 MHz transducer as ultrasonic generator where a cylindrical glass column with input-output flat windows was used for liquid support. The present method has advantages over common acoustooptical techniques as low cost, simplicity of operation, direct modulation of the signal and minimum alignment requirement.