This PDF file contains the front matter associated with SPIE Proceedings Volume 8257, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The process of erbium sensitization through silicon nanocrystals (Si-nc) in silicon rich oxide host is analyzed through a model involving five levels of Er energy states. Energy transfer processes from Si-nc to Er, and mechanisms involving deteriorating effects in Er sensitization are studied. It is proposed that Er atoms are excited through quasi-direct processes involving excitonic recombinations in Si-nc. An effective range of 1.3 nm is estimated for erbium sensitization through Si-nc. Effects of multiple excitation of Si-nc during an erbium lifecycle is analyzed. It is shown that, the fraction of Si-nc that is repeatedly excited at every alternate cycle of excitation increases from small fractions to percentage levels for incident flux levels above 10¹⁸/cm²-s. For typical values of Er and Si-nc incorporation, saturating effects in Er luminescence is found to start at flux levels much lower than that for Si-nc excitation. Occurrence of multiple excitation of Si-nc is correlated with the deteriorating effects in Er sensitization at higher flux incidence. Simulated results with our model are in good agreement with reported data of Er luminescence through Si-nc sensitization.

We have developed several rugged materials for multiband applications in the 0.2-12.0 μm wavelength region. These materials include spinel ceramic and barium gallogermanate (BGG) glass which transmit in the UV, visible, SWIR and MWIR wavelength region. They also include MILTRAN^TM and IR glasses which transmit in the SWIR, MWIR and LWIR. These materials have superior mechanical and optical properties compared to the currently used materials on various Navy / DoD systems. Spinel ceramic is comparable to sapphire in its ruggedness but it overcomes the birefringence and poor 4-5 μm transmission of sapphire. Spinel has also been made into large size windows as well as domes for several applications. BGG glass is very useful for systems requiring very large windows with visible - MWIR transmission. High optical quality BGG glass windows in sizes up to 20" in diameter have been made. MILTRAN^TM is > 3 times harder and stronger than ZnS and can provide a rugged window or dome for broadband sensors. IR glass can be easily made in complex shapes. BGG glass and spinel ceramic laminated dome was developed for tri-mode seeker. MILTRAN^TM and IR glasses can be combined to make achromats for multispectral imaging systems.

We report on the study of praseodymium doped ZBLA channel waveguides obtained by ionic exchange. Fluorozirconate glasses synthesis, photolithography process and ionic exchange are studied. Chemical characterizations are performed on waveguides, as well as refractive index profile. Spectroscopic measurement and emission cross section calculation are also reported. These results show the ability of rare earth doped fluoride glasses channel waveguide to serve as active materials for integrated solid state laser sources.

Yb³⁺-doped fiber is one of the most promising hosts for high-power fiber lasers [1]. However, in the late 1990s, photodarkening effect, i.e., the creation of color centers induced by light, was observed and reported [2]. Like in other rare-earth-doped materials, a broad visible and near infrared absorption band appears during laser operation, which strongly lowers the laser efficiency. We have shown how thulium impurities, present at the parts-per-billion weights (ppb) level in the raw doping material, can induce UV emission which in turn creates defects responsible for photodarkening in ytterbium-doped continuous-wave fiber lasers [3]. This new vision is not in contradiction with others but it gives for the first time a possible explanation for UV defect creation by an infrared beam.

In this work we study the influence of the host matrix on the spectroscopic properties of Nd³⁺ ions in 0.8CaSiO₃-0.2Ca₃(PO₄)₂ eutectic glass and glass-ceramics obtained by the laser floating zone technique at different growth rates in the 100-500 mm/h range. Site-selective emission and excitation spectra of the ⁴Ι_9/2→⁴F_5/2,3/2 transitions show the presence of a complex structure which suggests the existence of different crystal field sites for the rare-earth (RE) in these matrices. The spectra of the samples grown at lower rates show more structure and more resolved components. These experimental results suggest that Nd³⁺ ions incorporate in a crystalline phase in these glass-ceramics.

We investigate the cross relaxation parameter of Tm3+ ions in tellurite glasses over a wide range of concentrations: from 0.36 mol% up to 10 mol%. We propose a new measurement approach based on monitoring the steady-state emission spectra. The proposed method is very simple and allows to measure even very highly doped samples. The crossrelaxation parameter shows a linear dependence with respect to dopant concentration over the full investigated interval and the measured slope is 1.81x10-17 cm3 s-1 mol%-1. The linear dependence suggests a dipole-dipole interaction.

One- and two-photon pumped random lasing have been demonstrated in a powder based on a Rhodamine B-doped diureasil hybrid by using a picosecond pump laser emitting either at 532 nm or 1064 nm under controlled experimental conditions. In both cases, we have used the same diffusive medium with identical spatial disorder, the same time-width and temporal profile for the pump pulse, as well as equal pump spot sizes. The corresponding onsets of laser-like emission and slope efficiencies are also investigated.

Numerical results obtained by the authors via theoretical models, implemented in computer codes developed for designing lasers and optical amplifiers based on rare-earth doped glasses, are illustrated. Different photonic structures are investigated. As an example, by an accurate design of a cascade of multiple long-period gratings (MLPGs) inscribed in the fiber core, the pump absorption enhancement and the laser efficiency increasing are demonstrated. Further results pertaining to multicore fiber (MCF) configuration and rare-earth doped microspheres are reported. Moreover, global search methods, as the genetic algorithms (GA) and the particle swarm optimization ones (PSO), for the complete design and characterization of lasers and amplifiers are recalled.

We investigate the spectroscopic and lasing performance of Tm³⁺-Ho³⁺ co-doped tungsten tellurite single mode fiber operating around 2.1 μm with a commercial 800 nm diode laser pump source. The optimum doping concentration of Tm₂O₃ and Ho₂O₃ in Tm³⁺-Ho³⁺ co-doped TeO₂-WO₃-La₂O₃ (TWL) glass is 1 mol% and 0.5 mol%, respectively. The lifetime of Ho³⁺:⁵I₇ level is 3.3 ms in the bulk glass. The maximum stimulated emission cross-section of Ho³⁺ in TWL is 10.0×10^-21cm². The tungsten tellurite single mode fibers are prepared by using rod-in-tube method. The infrared emission spectra are compared with varying fiber lengths. Tm³⁺-Ho³⁺ co-doped fiber shows weak emission at ~1.9 μm very strong emission at ~2.1 μm, which indicates efficient energy transfer from Tm³⁺ to Ho³⁺ in the fiber. The 1.47 μm emission increases with the increment of the fiber length, which means a back energy transfer from Ho³⁺ to Tm³⁺. A 106 mW continuous wave laser emission at ~2.1 μm is demonstrated from a 16 cm length of this fiber, the slope efficiency is 23%, corresponding to a 17% optical to optical efficiency. Lasing has also been achieved in <5 cm length of this fiber, making this material a promising candidate for single frequency ~2.1 μm laser sources.

Optical results concerning the generation of laser and optical gain by using an Er³⁺-doped tellurite micro-structured fiber are reported for the first time. For this purpose a scheme that consist of two 980 nm diode pump lasers (simultaneously in the co-propagating and the counter-propagating directions) and short Er³⁺-doped tellurite micro-structured fibers (fabricated by using the stack-and-draw technique and a soft glass drawing tower) was used. The laser produced here was obtained within the range 1530 to 1565 nm, and the maximum optical gain obtained was higher than 8 dB.

Perfos and the laboratory Glasses and Ceramics Group of University of Rennes 1 have worked together to develop a new fabrication technique for chalcogenide preforms based on the glass-casting process. Various fiber profiles have been designed by the Fresnel Institute and fiber losses have been significantly improved, approaching those of the material losses. Using this technology, we have manufactured an AsSe CPCF exhibiting a nonlinear coefficient γ of 46 000 W^-1km^-1. Self-phase modulation, Raman effect, Brillouin effect, Four-Wave Mixing have been observed leading to the demonstration of various optical functions such four-wave mixing based wavelength conversion at 1.55 μm by FOTON, the demonstration of Raman Shifts and the generation of a mid-IR supercontinuum source by ONERA and the demonstration of a Brillouin fiber laser by FOTON.

We report on fabrication a composite microstructured optical fibre composed of highly nonlinear chalcogenide Ge-Ga- Sb-S glass core and tellurite TeO₂-ZnO-Li₂0-Bi₂O₃ glass clad. We aimed at obtaining more flattened chromatic dispersion for pumping chalcogenide glass based optical fibre by a pulse laser at current telecommunication wavelengths, i.e. λ = 1.35 - 1.7 μm, which is difficult to achieve by using a single material chalcogenide fibers due to their high refractive index (n > 2.1). A fibre design exploiting a composite of two glasses and one ring of the air holes brings similar options for tuning the fibre dispersion such as use of complex multi rings of air-holes approach. A good choice of glasses, allows for fabricating a composite chalcogenide-tellurite optical fibre benefiting from high nonlinearity of chalcogenide core glass but exploiting a tellurite glass technology and fibre drawing. In the paper, we discuss some aspects of CMOF design concerning current chalcogenide and tellurite glass choice. Also, we show the supercontinuum spectra recorded from current chalcogenide-tellurite CMOF pumped with a custom made femtosecond fibre laser at λ = 1.55 μm with the pulse duration of 400 fs.

Experimental measurements of light emitted by a novel type of broad-band laser are presented. The laser cavity is realized by placing a Semiconductor Optical Amplifier (SOA) between two Linearly Chirped Fiber Bragg Gratings (LCFBGs). The P-I (power-current) curve of this structure and its spectral distribution of optical power at high currents show similarities with those of continuum lasers. Finally, a simple all-optical mode-locking is realized by injecting a master laser inside the cavity. The efficiency of the mode-locking is shown to be much higher in the bandwidth corresponding to the initial lasing emission.

Multi-wavelength fiber lasers have attracted a lot of interest, recently, because of their potential applications in wavelength-division-multiplexing (WDM) systems, optical fiber sensing, and fiber-optics instruments, due to their numerous advantages such as multiple wavelength operation, low cost, and compatibility with the fiber optic systems. Semiconductor optical amplifier (SOA)-based multi-wavelength fiber lasers exhibit stable operation because of the SOA has the property of primarily inhomogeneous broadening and thus can support simultaneous oscillation of multiple lasing wavelengths. In this letter, we propose and experimentally demonstrate a switchable multi-wavelength fiber laser employing a semiconductor optical amplifier and twin-core photonic crystal fiber (TC-PCF) based in-line interferometer comb filter. The fabricated two cores are not symmetric due to the associated fiber fabrication process such as nonuniform heat gradient in furnace and asymmetric microstructure expansion during the gas pressurization which results in different silica strut thickness and core size. The induced asymmetry between two cores considerably alters the linear power transfer, by seriously reducing it. These nominal twin cores form effective two optical paths and associated effective refractive index difference. The in-fiber comb filter is effectively constructed by splicing a section of TC-PCF between two single mode fibers (SMFs). The proposed laser can be designed to operate in stable multi-wavelength lasing states by adjusting the states of the polarization controller (PC). The lasing modes are switched by varying the state of PC and the change is reversible. In addition, we demonstrate a tunable multi-wavelength fiber laser operation by applying temperature changes to TC-PCF in the multi-channel filter.

We report on the study of adding metal dopants in chalcogenide glasses to enhance the photosensitivity of the fiber core versus cladding compositions, with goal to enable high reflectivity gratings in infrared-transmitting fibers. Results for the optical and thermal properties of these glasses will be presented, as well as for gratings formation in the glasses using various writing wavelengths for the different doped compositions.

Fiber Bragg gratings (FBG) have garnered interest as temperature and strain sensors because they are compact, inexpensive, and can be utilised for distributed and multi-parameter sensing. Ultrafast laser induced FBGs have been shown be especially promising for higher temperature (>500 ºC) applications. In this presentation we will discuss our most recent measurements of ultrafast gratings at elevated temperatures.

High efficiency reflecting volume Bragg gratings (VBGs) recorded in PTR glass plates have shown un-preceded performances that make them very good candidates for narrowband spectral filtering with sub-nanometer spectral widths. However, decreasing the bandwidth to value below 30-50 pm is very challenging as it requires increasing the thickness of the RBG to more than 15-20 mm. To overcome this limitation, we propose a new approach which is a monolithic Fabry-Perot cavity which consists from a reflecting VBG with a multilayer dielectric mirror (MDM) deposited on its surface. A VBG with a grating vector perpendicular to its surface and a MDM produce a Fabry-Perot resonator with a single transmission band inside of the reflection spectrum of the VBG. We present a theoretical description of this new class of filters that allow achieving a single ultra-narrowband resonance associated with several hundred nanometers rejection band. Then we show the methods for designing and fabricating such filter. Finally, we present the steps that we followed in order to fabricate a first prototype for 852 nm and 1062 nm region that demonstrates a 30 pm bandwidth, 90+% transmission at resonance and a good agreement with theoretical simulation.

Long-period fiber gratings have been used for refractive index measurements under different conditions. Normally, this kind of sensor is based on measuring resonance wavelength shift with respect to different refractive index environments. As high order mode long period fiber gratings are attracting more attention, a new methodology based on intensity measurement of turning points is introduced, which involves simple experiment setup and straightforward demodulation process compared with wavelength shift based method. By using CO₂ laser point by point irradiation method, high order mode gratings working at turning point can be easily fabricated. This type of grating has a very high sensitive response to surrounding refractive index, which can be used in chemical, medical and bio applications. In this paper, high sensitive refractive index sensor is demonstrated based on high order mode using intensity measurement. Phase match curve and couple mode theory are combined to analyze the intensity response to refractive index change at turning point of LPFG. This sensor is also demonstrated as an effective refractive index based glucose sensor with a range from 0 to 40 mM concentration of glucose solution, which can fulfill the medical requirement.

A full fluidic lens system consisting of multi-layers of PDMS membranes, which each builds single convex/concave lens, whose lens aperture is ~4mm, was fabricated. It was operated with magnetic attraction/repulsion induced by voicecoil coiled in between magnets adhesively bonded to each PDMS membrane. It has shown a smooth and fast controllability of the focal-length control versus the applied voltage and quite good image of the target at the distance from 10 mm to 5 m. To verify zooming function of lens, images captured by digital camera was attached, and it also shows good image magnification.

Surface plasmon resonance (SPR) sensors exploit optical coupling to surface plasmons, light waves bound to a metal surface. In the most common configuration, a SPR sensor is used with an external light source, optical components to polarize incident light and guide light to and from a metal surface, a coupling device to convert free-space light into surface plasmons and back into free-space light, and a light detector. The light source, the optical components, and the light detector are external to the SPR device, and the coupling structure is often integrated directly with the surface-plasmon-sustaining metal surface. The requirement of several external components restricts the miniaturization of SPR devices and prohibits low-cost implementation. To address these limitations, we design, fabricate, and test a new SPR device chip that is fibre-addressable, does not require a discrete coupling structure, and integrates light delivery, light polarization control, surface plasmon coupling onto a thin, flexible substrate. Our SPR chip is constructed from a thin gold layer deposited on top of a clear plastic sheet, which is then optically connected from the bottom surface onto a plastic linear polarizer sheet. Two cleaved fibres, one to input light and the other to collect reflected light, are then optically attached to SPR device. We experimentally characterize the SPR device and find good agreement between our measurements and a theoretical model based on transfer matrix formalism.

Flux of electromagnetic radiation is attenuated on propagation through a metal grid disposed on a substrate. The magnitude of extinction is a combination of the total scattering and surface plasmon absorption, which is predicted by the Mie theory adapted to the case at hand. Experimental measurements over a wide wavelength range conducted using a metal grid on a sapphire window support the calculations. Further analyzed is the electric field generated in the wire mesh, treated by the Drude-Lorentz theory. While the analysis and data show that the attenuation across a window covered by a wire mesh is consists of a combination of the Fresnel and Mie losses, a considerable plasmon field is generated in the wire.

We describe a general numerical method for calculating short-pulse laser propagation in rare-earth-doped materials, which are very important as gain materials for solid-state lasers, fiber lasers and optical amplifiers. The split-step, finite difference method simultaneously calculates changes in the laser pulse as it propagates through the material and calculates the dynamic populations of the rare-earth energy levels at any position within the material and for times during and after the laser pulse has passed through the material. Many traditional theoretical and numerical analyses of laser pulse propagation involve approximations and assumptions that limit their applicability to a narrow range of problems. Our numerical method, however, is more comprehensive and includes the processes of single- and multi-photon absorption, excited state absorption (ESA), energy transfer, upconversion, stimulated emission, cross relaxation, radiative relaxation and non-radiative relaxation. In the models, the rare-earth dopants can have an arbitrary number of energy levels. We are able to calculate the electron population density of every electronic level as a function of, for example, pulse energy, dopant concentration and sample thickness. We compare our theoretical results to published experimental results for rare-earth ions such as Er³⁺, Yb³⁺, Tm³⁺ and Ho³⁺.

Silica-on-silicon planar lightwave circuit (PLC) technology is well established and provides a low loss and stable photonic device platform. However, limitations in size and integration of active components remain. Engineering of the layer structure in silica PLCs to achieve high-index contrast, compact device architectures and monolithically integrated optical nonlinearities is described. Modeling of properties of doped-silica layers provides a design strategy for optimization of waveguide loss and birefringence. Optical nonlinearities in poled silica layers have been demonstrated, and recent work to incorporate these into functional device structures and exploit them for high speed modulation is reported.

Diamond-Like Carbon (DLC) coatings using Plasma Enhanced Chemical Vapor Deposition (PECVD) tend to cause high amount of compressive stress in coated film. This is predominant when coating is applied to germanium windows with high aspect ratios (approximately 40) for applications with wavelengths in the region of 8-12 microns. In this paper, we show that process parameters may be varied in order to control the effect of the coating stress on surface flatness. We investigate the before and after effects of coating on surface figure. It is also found that there is a trade-off among various process parameters in order to achieve high coating durability with low stress in the finished coated film. Finally, we report that, with the appropriate process controls, we have achieved successful production of large germanium windows using DLC coating with surface flatness of less than 8 fringes at 633 nm over window diameters of as large as 270 mm.

An integrated photoconductive (PC) element is introduced as a new optoelectronic device in free-space optical (FSO) wireless applications. The device is a fundamental extension of the standard PC switch, as it has the capabilities for both local optoelectronic signal reception and active directional angle of arrival (AOA) sensing. This second capability is brought about through the use of a three-phase differential technique through three triangular PC switches arranged in a corner-cube architecture. Each PC switch is comprised of 50/150 nm Cr/Au electrodes, patterned on either side of a 200- micron GaAs PC gap, and is biased with the superposition of common DC and AC three-phase (120° phase-shifted) bias voltages. The DC bias forms a summed signal photocurrent on the central vertex output electrode and facilitates data reception; the AC three-phase bias facilitates link reliability for diversity reception in optical wireless communication systems. Complete theoretical and experimental angular characteristics of this device are presented in this work.

All-optical two bit digital comparator using single mode Fabry-Perot laser diodes (SMFP-LDs) is proposed and demonstrated with 10 Gbps PRBS signal of 2³¹-1. Digital comparators are one of the important components for decision making circuits, threshold detection, which are used in optical signal processing and optical computing. The basic principle of the comparator is based on injection locking, multi-input injection locking and combinational input injection locking (CMIL) to realize the greater than, less than, and equal to function of the basic comparator circuit. These principles are used to realize the different optical logic gates which are combined together to demonstrate optical comparator with the minimum number of components, making the configuration cheaper and simpler. The proposed method draws less current and hence power effective too. Output waveform diagram and output eye diagram for all three cases of comparator are presented to verify all functions of all-optical comparator.

The concept of fractal, such as Cantor set, has been combined with the Fresnel zone plates (ZPs) to improve its imaging capability and introduce additional freedom for optimizing. In this letter, Fibonacci zone plates (FiZPs), which is generated by means of Fibonacci fractals, was proposed. The FiZPs can be constructed by the generating rules of the Fibonacci sequences similar with the Cantor set zone plate published. Numerical simulation based on Fresnel diffraction is performed to verify the on-axis intensity distribution of the FiZPs. According to the simulated results, the FiZPs can focus the incident beam as conventional zone plates as well but with fractal on-axis intensity profile. The theoretical results are also verified by the experiment by means of phase-only spatial light modulator (pSLM). Furthermore, the spiral Fibonacci zone plate (sFiZPs) was designed by overlapping the spiral phase on the FiZPs. Both numerical simulations and experiments are performed and the results are coincident well with each other.

In this paper, we theoretically investigated the generation of quantum-correlated photon pair through spontaneous four-wave mixing in tellurite microstructured optical fiber. We evaluated the performance of photon pair generation in tellurite fibers based on Raman gain coefficient spectra. It was shown that the TBSN16P6W tellurite fiber provided a low Raman noise on correlation photon generation over a wide pumpidler detuning range. We can choose proper tellurite composition to obtain a low Raman gain window over a wide range for correlated photon pair generation.

Gallium lanthanum oxysulfide (GLSO) is a promising host material for observing strong upconversion emission from trivalent rare-earth ions such as erbium (Er³⁺). Its attractive properties include high rare-earth solubility due to the lanthanum content of the glass former, a high refractive index (n = 2.2 at 550nm) for high radiative efficiency, and a low maximum phonon energy of approximately 425cm ^-1. Photonic crystals meanwhile can provide controlled light extraction, and may be capable of suppressing unwanted IR emission from lower lying metastable states. Here, we describe the fabrication of photonic crystals in annealed films of Er³⁺-doped GLSO deposited by RF sputtering. The most intense visible upconversion emission is observed in films annealed at 550°C, close to the bulk glass transition temperature. Hexagonal lattice photonic crystals are subsequently milled into the films using a focused ion beam (FIB). The milling parameters are optimized to produce the most vertical sidewall profile.

We demonstrate passively mode-locked and Q-switched operation in the same fiber laser cavity with normal dispersion. The passively mode-locked pulse works in the stretched-pulse mode-locking mechanism, and the spectrum has smooth and broad rectangular shape. The 3 dB bandwidth of the spectrum increases with the pump power increasing, and it is also changed by the polarization state in the cavity. The obtained maximum 3 dB bandwidth for the pulse is 35.8 nm. The output pulse width is 2.31 ps with high chirp and is dechirped to 210 fs by a standard single-mode fiber, which can be further dechirped to about 110 fs according to the transform-limited time-bandwidth product by compensating the third-order dispersion. The repetition rate of the single pulse operation is 38.3 MHz. With increasing the pump power further, multiple pulses appear and finally six pulses are observed. When the pump power exceeds 180 mW, the mode-locked operation can be switched to the passively Q-switched operation by the polarization state variation. The repetition rate of the Q-switched pulse increases from 162.9 to 348.9 kHz corresponding to the pump powers from 180 mW to 643 mW, and the pulse width decreases from 1122 to 382 ns simultaneously. The Q-switched pulse can be tunable in the spectral range of 8.45 nm from 1558.50 to 1566.95 nm. The operation between the passively mode-locking and the Q-switching can be switched by adjusting the polarization controllers in the cavity.

With the development of more powerful lasers for applications, optical limiters and blockers are required for providing human eye and optical sensors protection. In some scenarios, laser radiation may seriously interrupt the signal, from transient saturation and can lead to permanent damage. We present a variety of non-linear, solid-state dynamic filter solutions protecting from dazzling and damage in a passive way. Our filters either limit or block the transmission, only if the power exceeds a certain threshold as opposed to spectral filters that block a certain wavelength permanently. We propose a dynamic protection for cameras, sensors and the human eye from laser threats.

Highly nonlinear tellurite holey fiber can be transparent from visible to 5 μm. Its nonlinearity can be higher than highly nonlinear silica fiber by more than one order of magnitude. However, the dispersion of tellurite holey fiber is difficult to tailor because of the difficulties in fabrication. Tellurite glass shows a low viscosity at the fiber drawing temperature. Moreover the viscosity decreases sharply with increasing temperature. Tellurite holey fiber with a complex microstructure could be subject to heavy deformation during fabrication process. So far most tellurite highly nonlinear holey fibers just have a simple structure which results in an unflattened dispersion. It cancels the advantage of high nonlinearity greatly in practical applications. In this work we try to develop a dispersion flattened tellurite composite holey fiber (TCHF). The holey structure of the TCHF is composed of only one ring of holes, so the heavy deformation, which probably occurs for tellurite complex microstructured fiber during the fabrication process, can be avoided. Since the holey structure is simple, to improve the flexibility in tailoring dispersion, we use two kinds of tellurite glasses which have different refractive-indices to design and fabricate the TCHF. The holes are formed by two tellurite glasses. The fiber can be fabricated by a simple rod-in-tube method. By using this structure the dispersion is engineered to be the most flattened for the highly nonlinear soft glass fiber within 1.5-1.6 μm. More than one octave supercontinuum generation, mainly broadened by self phase modulation, is demonstrated by using the fabricated TCHF.

An approximated technique to optimize the gain profile of multi-pump broadband hybrid amplifiers (EDFA+Raman) under residual pump recycling is applied to a WDM system. The optimization has been focused on the global gain and its ripple factor for the hybrid amplifier. The EDFA spectral gain profile is the one to be compensated by the Raman amplification. The results of gain, ripple and noise figure for 8, 16, 32, 64 and 128 WDM input channels, with - 20 dBm each, are presented. The increase in the level of input power reduces the overall gain of the amplifier, but the profile remains unchanged. The performance of this configuration presented better results that means high gain, lower ripple, and higher bandwidth than those found in the literature.

Numerical simulation of Nd-doped fluoride and tellurite fiber lasers pumped directly by sunlight have been performed. Calculations have been done for double clad fibers to achieve both efficient coupling sunlight with a fiber and spatial power condensation. The pumping source was assumed to be initially AM1.5 sunlight and was focused onto a fiber end. The both ends of the fiber were assumed to be transparent for at the pump wavelength and highly reflective at laser wavelength. It was assumed that the launched sunlight propagate in one longitudinal direction in the inner but the laser light propagate in both longitudinal directions in the core. Propagation equations were solved under boundary conditions determined by the reflectivity of the fiber ends by a boundary value problem solver in MATLAB. The calculated sunlight concentration ratio at lasing threshold was about 300 suns for solar pumped fiber lasers with optimized structure. This sunlight concentration can be achieved by conventional optics such as lenses and ellipsoidal mirrors. The slope efficiency was about 0.78 % for a fluoride fiber and 1.32 % for a tellurite fiber. These efficiencies are can be improved by farther optimization of fiber parameters and pumping scheme. Solar pumped fiber lasers will be able to provide alternative means to utilize solar power.

Four wave mixing and supercontinuum from tellurite photonic crystal fibers have been widely researched. Their efficiencies depend largely on fiber nonlinearity and chromatic dispersion. We have shown that the composite microstructured optical fibers (CMOFs) can have high flexibility on chromatic dispersion control when refractive index difference between core and cladding becomes larger. Cladding materials with much lower refractive index than tellurite glass are required. We report here a novel tellurite core-phosphate cladding CMOF. Phosphate glasses which thermal expansion coefficient, viscosity, glass transition temperature, deformation and crystallization temperature are close to those of tellurite 78TeO₂ - 5ZnO - 12Li₂O - 5Bi₂O₃ (mol%) (TZLB) glass are systematically investigated. The phosphate glass we developed has high transparency and a broad transmission region up to 3 μm as well as a notably low refractive index. Using the phosphate glass doped with mixed alkali oxides obtained in this work, the refractive index difference between core and cladding becomes as high as 0.5 which is sufficiently high to control the chromatic dispersion with high freedom. Our work shows that tellurite-phosphate CMOFs are promising candidates as highly nonlinear fibers with freely controlled chromatic dispersion for nonlinear applications.

Invisible grid-pattern structure light has often been used for being shined on objects for contour reconstruction based on the distortion of grid pattern, for vehicle collision prevention etc. However, the structure light can be easily disturbed by surrounding nature light even if infra-red (IR) light source is used because natural light contains quite an amount of IR spectrum. In this paper, it is proposed that the structure light is provided from a highly coherent laser source, so that the structure light pattern reflected from the target object will contain not only the distorted irradiance distribution of grid pattern, but also laser speckle associated with it. The laser speckle pattern depends on the surface roughness of the target object, which provides extra information for extracting the distorted grid pattern from the background irradiance of surrounding natural light. The laser speckle pattern therefore helps to improve the immunity for surrounding light disturbance, and hence the robustness and reliability of contour reconstruction system. A binary surface relief phase-type diffractive optical element(DOE) has been proposed for generating desired pattern directly at far field when working together with laser light source. The design process is based on iterative Fourier transform algorithm(IFTA) in scalar diffraction theory.

Secure proof of sterilization processes on packaging materials is an important issue in many economic sectors. In this context, electron beam sterilization is a highly effective low temperature technique. However, verifying the application of a sufficient electron dose is still difficult - especially on products with complex geometry. Here we report on an optical, hence fast and contactless approach which gives reliable evidence of a successful e-beam treatment. The technique is based on placing a suitable marker material (rare-earth based particles) inside or as a coating on the packaging material. By electron irradiation these particles change their optical properties and thus indicate the successful application of the electron beam.

In previous works it was demonstrated that the electrical resistivity of Polypyrrole (PPY) changes when exposed to different organic solvents which allowed the development of applications in gas sensors [1,2]. Also, is well known that optical gas sensors have several advantages over conventional electronic ones like high sensitivity, reduced signal-to-noise ratio, and compatibility with combustible gases. The optical properties of polymer materials have became of great importance in modern optical design of polymer based optical sensors and devices. Thin polymer films appear in an ample spectrum of applications such as photonics, data storage, communications and sensor devices [3]. In this work an optical sensor for the detection of water vapor using Polypyrrole (PPY) as active material is proposed. As a first step in studying polypyrrole for this application, the refractive index of this material was measured after the films were exposed to water vapor, and the results showed a variation of the refractive indices of the polymer in the wavelength of 632.8 nm. Finally, an optical device was fabricated using integrated optics technology over silicon, which uses polypyrrole as active layer for sensing. The results of the characterization of this optical device showed that for relative humidity concentrations above a specific value (~70%) the optical power at the output of the device decays to insignificant values, which allows for the device to be used as an optical switch.

This paper reports a long-period fiber gratings(LPFG) fabricated on a double-clad fiber (DCF) by the CO₂ laser point-by-point technique. The LPFG is tested by measuring temperature and refractive index (RI) of different liquids. The results show that the LPFG inscribed on the DCF has no measurable sensitivity to external RI but has a high sensitivity for temperature. The measured temperature sensitivity is ~0.11 nm/^oC, about 10 times higher than that of conventional FBGs. Such LPFGs can be used as a modulator in fiber lasers or temperature/strain sensors in applications where the surrounding RI is prone to variation, such as simultaneous measurement of the temperature and RI of chemical reactions.

Bandgap tunability achievable using metamorphic epitaxy enables maximization of photodetector performance at target wavelengths. However, an increase in threading dislocation density (TDD), which is inherent for the growth of relaxed, lattice-mismatched layers, could offset this advantage and severely limit detector performance. In this regard, we are investigating the performance of In_xGa_1-xAs and In_zGa_1-zP p-i-n photodetectors as a function of TDD, by utilizing a number of different InxGa1-xAs buffer designs. In particular, internally lattice-matched metamorphic In_0.20Ga_0.80As and In_0.68Ga_0.32P individual p-i-n detectors are studied to optimize the buffer design and performance of optically-aligned In_0.68Ga_0.32P/In_0.20Ga_0.80As visible/near-infrared dual-photodetectors. Reverse-bias dark current density of In_0.68Ga_0.32P detectors were found to be extremely sensitive to TDD compared to that observed for In_0.20Ga_0.80As detectors. Nearidentical spectral response curves were obtained for both detectors as a function of TDD due to the relative insensitivity of the p-i-n detector structure to the minority carrier lifetime. A comprehensive comparison between the different graded buffer designs, TDD achieved and photodetector characteristics are presented.

Conventional core/clad optical fibers composed of all-solid silica material were fabricated using the "stack and draw" technique. The optical fiber consists of Ge-doped silica glass in the core and un-doped silica glass in the clad. The optical attenuation and the chromatic dispersion spectra of these optical fibers, with their external diameters of 212, 176, 150 and 125 μm, were characterized by using a PK2500 and a PK2800 instrument respectively. The attenuation of these optical fibers, at 1550 nm, was approximately 5 dB/km and the zero-dispersion-wavelength range from 1350 to 1370 nm. On the other hand, bend loss spectra of these fibers were characterized by using small bend diameter rods (bend diameters from 2.5 to 10 mm). The bend loss spectra show that these all-solid optical fibers are almost insensitive to bend effect. In addition we explore the nonlinear properties of these fibers to investigate the potential for supercontinuum generation.

EO/IR Nanosensors are being developed for a variety of Defense and Commercial Systems Applications. These include UV, Visible, NIR, MWIR and LWIR Nanotechnology based Sensors. The conventional SWIR Sensors use InGaAs based IR Focal Plane Array (FPA) that operate in 1.0-1.8 micron region. Similarly, MWIR Sensors use InSb or HgCdTe based FPA that is sensitive in 3-5 micron region. More recently, there is effort underway to evaluate low cost SiGe visible and near infrared band that covers from 0.4 to 1.6 micron and beyond to 1.8 microns. One of the critical technologies that will enhance the EO/IR sensor performance is the development of high quality nanostructure based antireflection coating. In this paper, we will discuss our modeling approach and experimental results for using oblique angle nanowires growth technique for extending the application for UV, Visible and NIR sensors and their utility for longer wavelength application. The AR coating is designed by using a genetic algorithm and fabricated by using oblique angle deposition. The AR coating is designed for the wavelength range of 250 nm to 2500 nm and 0° to 40° angle of incidence. These nanostructure AR coatings have shown to enhance the optical transmission in the band of interest and minimize the reflection loss to less than 3 percent substantial improvement from the thin film AR coatings technology.

Optical chemical sensors are the only ones, which are truly gas specific and reliable. But up to now wide application of portable gas sensors is limited by imperfections of currently used heating infrared sources. Recently qualitative technological break-through in growing of narrow band-gap heterostructures was achieved. Full line high effective LEDs for the spectral range 1600-5000 nm and spectral matched photodiodes were developed. For developing of LEDs and PDs we use lattice-matched heterostructures with GaInAsSb quaternary solid solutions in the active layer. It becomes possible to create gas sensors that meet all demands of the mass market: compactness; low electrical power consumption; high selectivity; high sensitivity; long life-time without additional calibration and low cost in mass production. Average optical power up to 3.5 mW and peak power up to 170 mW was achieved for 1600-2400 nm LEDs. Optical power of 3000-5000 nm LEDs is still quite low but absorption of CO₂ and CH₄ in this spectral range is very strong, so creation of simple designs of high sensitive gas sensors is possible. Small sizes of LED chips gives us possibility to design multicomponent LED matrices. This fact provides additional advantages over the thermal infrared sources.