In this paper, the strong influence of alkali halide in chalcogenide glasses is reminded, leading for the first time to highly transparent glasses from the visible range up to 11μm. The behavior of crystallization has been demonstrated to be similar in sulfide and selenide glasses containing gallium as well. The structural evolution of several glass compositions from the Ge-Ga-S or Ge-Ga-Se systems leading to reproducible glass ceramics has been studied by XRD, NMR and thermal analysis. Whatever the composition, gallium plays a fundamental role as nanosized domains appear by phase separation between Ge rich regions and Ga rich regions. The determination of the appropriate crystallization time and temperature has permitted to obtain new passive and active glass-ceramics with a broadened transmittance region thanks to the incorporation of various alkali halides. In the first case, the controllable generation of nanocrystals leads to an increase of the main thermo-mechanical properties. In the second case, the incorporation of rare-earth ions inside the glass ceramics has exacerbated their photoluminescence properties. The possibility to combine the ceramization process with the shaping has also been demonstrated.

Erbium doped optical materials have been widely researched and many applications have been demonstrated. According to the Fermi golden rule, the spontaneous emission rate from excited level |i> to lower level |j> is Γ_ij ∞ |M_ij|² ρ(νij), where M_ij is the matrix element related to the two energy levels, ρ_ij is the optical density and is also known as the photon mode density (PMD). The concept of PMD was put forward by Purcell in 1946, and is a quantity determined by the environment aound the rare earth ions. The radiative performance of a rare earth(RE) doped material is decided not only by the wave function of the energy level that the rare earth ions are located, but also by the environment of the RE ions, i.e., the PMD. In various materials, the state of the host (crystal, glass or glass ceramics), the composition of the host with same state (for examples, the different glasses), the doping of metal into the host, and the surface plasmon portions (SPP) arised from the metal gratings or nanoparticals on the host, will all change the optical density of the materials, Thus the PMD are different. In this paper, we summarized the influence of the PMD on the luminescence of erbium doped materials for above indicated cases. Especially, we reported the difference of the luminescence performance of the erbium doped phosphate glass ceramics and its precursor glass, from which, we can find that even the composition of both glass ceramics and glass are the same, the luminescence performance are quite different due to the different PMD. Another example we illustrate in this paper is to use SPP to change the PMD. When RE doped glass is coated with a thin metal film or islands, SPP mode will be generated under special condition. We summarized the recent progress on the field, and also demonstrated the enhancement of fluorescence in the visible wavelengths and 1.5μm wavelength, from which, we can think that the SPP changes the PMD of the material and the emission rate is modified.

We report the first observation of two-photon pumped random laser action in the ground powder of a silica gel containing rhodamine 6G doped silica nanoparticles. When this solid-state dye system is pumped with 800 nm femtosecond-lasing pulses, random laser-like effects such as spectral narrowing and temporal shortening are observed with a laser-like emission peak centered around 598 nm. A comparison between the emission features, random laser behavior and threshold of random laser action, following one- and two-photon excitations is also performed.

The properties near infrared (NIR) - emitting centers were investigated in Bi-doped Mg.Al-silicate and phosphate glasses. The NIR-emitting optical centers containing a pair of bismuth ions were shown to be formed in a reversible redox chemical reaction. The common electric charge (+5) of bismuth ions in such centers was determined. The NIR-emission saturation measurements have made it possible to calculate the ground-state absorption cross-section (~4.4×~10^-19 cm²) of these centers at 532 nm and their absolute concentration in the glass. It was found that similar emitting centers can also be formed in a colorless and non-luminescent Bi-doped glass by γ-irradiation. This fact allowed deriving some conclusions on an optical center structure.

Multicolor visible light emitting NIR-excited Tm/Ho/Yb-codoped tantalum oxide nanopowders were produced using the sol-gel method. The generation of wide color gamut fluorescence in glass-ceramic with orthorhombic Ta₂O₅ nanocrystals dispersed into amorphous silica-based matrix is observed. The light emission spectroscopic properties of the rare-earth doped SiO₂:Ta₂O₅ nanocomposites as a function of the tantalum content and temperature of annealing is examined. Simultaneously emitted multicolor fluorescence consisting of blue(480 nm), green(540 nm) and red(650 nm) upconversion signals in the SiO₂:Ta₂O₅ system doped with holmium and thulium and sensitized with ytterbium, is demonstrated. It is also demonstrated that the proper choice of the rare-earth content and the NIR excitation power yielded the generation and control of the three primary colors and allows the emission of a balanced white overall luminescence from the glass-ceramic nanopowder samples.

Near infrared wavelength region between 0.8 and 2 μm is an attractive region for biomedical imaging due to the low loss in biomedical objects in the region. Rare-earth doped ceramic phosphors are known to emit efficient fluorescence in the same wavelength region. The authors have developed micro fluorescence bioimaging system for cellular or tissue imaging and macro one for in vivo imaging. This paper will review the materials synthesis for the near infrared fluorescence probes as well as the system development and demonstrative works. Er-doped or Yb/Er-doped ceramic phosphors were synthesized with required particle size. The phosphors were partly modified with polyethylene glycol to give dispersion and controlled interaction with the biological objects. By using the micro imaging system, nematodes, mouse tissue and M1 cells were observed by detecting 1.5 μm emission from Er doped in the ceramic phosphor. in vivo imaging with the same fluorescence scheme was also performed for the digestive organs of live mouse.

Application of white LEDs is extended toward high-output light sources, e.g. for automotive headlights, and better spectral matching with optical filters for LCD backlighting. To meet such new demands, phosphor materials have been investigated with focus on their luminescence spectra, temperature characteristics and reliability. The conventional yellow phosphor based on Y₃Al₅O₁₂:Ce³⁺ has excellent performance as a single phosphor combined with a blue LED. More recently developed nitrido- or oxonitrido-silicates activated with Eu²⁺ are also promising materials showing green to red luminescence depending on a composition and high thermal and chemical stability. And yet, demands for specific application have been made clear and strong. This paper reviews the present status and challenging goals of phosphors in the next stage further to make progress in white LEDs.

In order to understand the thermal quenching of rare-earth doped phosphors, the clarification of electronic energy structure of excited states is an important step. As an experimental approach, the photoconductivity measurement of the phosphor is one of the effective methods to clarify the direct interaction of the excited electron (hole) and conduction- (valence-) band. In this study, we constructed an automatic measurement system of photoconductivity in inorganic phosphors. The wavelength- and temperature- dependence of the photocurrent in a Eu²⁺: SrAl₂O₄ phosphor was measured by using this system. Excitation wavelength dependence of photocurrent showed a similar profile to the PL-excitation spectrum of Eu²⁺. The result clearly indicates interaction of 5d level of Eu²⁺ with the conduction band. The activation energy of the photocurrent was evaluated from its temperature dependence for each wavelength. It decreased with wavelength from 490nm to 400nm, and became constant (~20 meV) below 400 nm. The ground state of Eu²⁺ (⁸S_7/2) was estimated to be 3.1 eV below the bottom of the conduction band.

The efficiency of energy transfer from Cr to Nd in silicate glasses has been examined in order to develop a gain medium for high-efficiency solar pumped fiber lasers (SPFLs). The internal quantum efficiency (QE) of the emission from the ⁴T₂ state of Cr in Cr-doped glasses and from the ⁴F_3/2 state of Nd in Nd-doped and Nd,Cr codoped glasses was measured using an integrating sphere. For Cr-doped and Nd,Cr codoped glasses, 650 nm excitation was used. For Nd-doped glasses, 808 nm excitation was used. The QE of Cr-doped glass (η_Cr) was 7.5 % for 0.05 mol.% Cr₂O₃, the QE decreased monotonically with increasing Cr₂O₃ content. The QE of the Nd-doped glass (η_Nd) has a maximum of 43% at 0.2 mol.% Nd₂O₃. We suggest that absorption of host glass could lower the QE at the low content side of the maximum. The QE of Nd emission in Nd,Cr codoped glass (η_Nd,Cr) excited at 650 nm, which excites the ⁴A₂→⁴T₂ transition of Cr was 5.7 % for 0.05 mol.% Cr₂O₃ and 0.2 mol.% Nd₂O₃ content. The energy transfer quantum efficiency, η_tr, from Cr to Nd which is defined as the ratio of the η_Cr and the η_Nd,Cr was calculated from the obtained QEs. The largest η_tr was 13.4 % at 0.01 mol.% Cr₂O₃, and decreased with increasing Cr₂O₃ when content of Nd₂O₃ was fixed by 0.2 mol.%. This tendency is quite similar to the QEs of the Cr emission in Cr-doped glasses. Thus an increase in the QE of Cr maybe essential to increase the η_tr.

Up to now, the role of divalent ytterbium ion has been controversially discussed in the literature concerning its influence on the photodarkening of ytterbium doped high power laser fibers. In general, however, the experimental findings are relatively sparse and some discussions are based more on speculations than on examined facts. Here we report on systematical investigations concerning the formation of Yb²⁺ during the fabrication process of preforms and fibers. By Modified Chemical Vapor Deposition, fibers with different codopants (additional to the active ytterbium doping) have been prepared in a well-defined manner, regarding process parameters and glass composition. The comprehensive characterization of the samples involves the ytterbium absorption in the NIR, the UV absorption and UV excited emission. The typical spectral features in the UV and visible range have been analysed and correlated with the presence of Yb²⁺. The amount of formed divalent ytterbium ions shows a strong dependence on the process route and varies remarkably with the kind and concentration of the codopants. Photodarkening tests have been accomplished in order to correlate the power stability with the Yb²⁺ content. Moreover, the formation of Yb²⁺ during the process of UV radiation darkening was investigated.

We show wavelength conversion and wavelength multicasting using four-wave mixing in silicon waveguides, achieving record performance in both bandwidth and bit rates in this CMOS-compatible platform. Non-return-to-zero data at 10- and 40-Gb/s bit rates is wavelength converted across nearly 50 nm, with error-free transmission. Bit-rate transparency of the all-optical process is demonstrated by converting up to 160-Gb/s return-to-zero data. In addition, an eight-way wavelength multicast of 40-Gb/s data is shown using the same silicon waveguide platform, with error-free transmission. The communication performance is evaluated using measured eye diagrams, bit-error rates, and power penalty performance metrics.

Atomic layer deposition (ALD) is a promising method to grow optical materials on waveguide structures. Propagation loss analysis indicates that amorphous TiO₂ and Al₂O₃ films are promising for the waveguide purposes. Instead, polycrystalline ZnO does not work properly as a waveguide by itself, but the waveguiding properties can probably be enhanced by introducing intermediate Al₂O₃ layers. The wide variety of available materials, conformal growth properties and low scattering losses of many ALD films enable their usage in various waveguide applications. Experimental coating of silicon waveguides is discussed.

We present novel 2-dimensional slot waveguide schemes. Such geometries allow high confinement for both quasi-TE and the quasi-TM modes in the lower index slot material. Dependence of quasi-TE and quasi-TM mode properties such as effective index and confinement factors on geometrical and material parameters of different waveguide structures is studied. Optimal structure depends on the targeted functionality. For example, 2-dimensional slot waveguides to achieve non-birefringent structures are presented.

Optoelectronic oscillators are classically based on a feedback fiber loop acting as a delay line for high spectral purity. One of the problems due to long fiber loops is the size and the requirement of temperature control. Going toward integrated solutions requires the introduction of optical resonators with a very high quality factor. A structure based on silicon on insulator material has been designed for application to an oscillator working at 8 GHz. The micro-resonator has a stadium shape with a ridge of 30 nm height, 1 μm width, a millimetric radius and a gap of some microns in agreement with the required free spectral range. A quality factor of 500000 can be achieved leading to an equivalent fiber loop of 2 km.

Designed to overcome the limitations in case of extreme bending conditions, Bend- and Ultra-Bend-Insensitive Fibers (BIFs and UBIFs) appear as ideal solutions for use in FTTH networks and in components, pigtails or patch-cords for ever demanding applications such as military or sensing. Recently, however, questions have been raised concerning the Multi-Path-Interference (MPI) levels in these fibers. Indeed, they are potentially subject to interferences between the fundamental mode and the higher-order mode that is also bend resistant. This MPI is generated because of discrete discontinuities such as staples, bends and splices/connections that occur on distance scales that become comparable to the laser coherent length. In this paper, we will demonstrate the high MPI tolerance of all-solid single-trench-assisted BIFs and UBIFs. We will present the first comprehensive study combining theoretical and experimental points of view to quantify the impact of fusion splices on coherent MPI. To be complete, results for mechanical splices will also be reported. Finally, we will show how the single-trench- assisted concept combined with the versatile PCVD process allows to tightly control the distributions of fibers characteristics. Such controls are needed to massively produce BIFs and to meet the more stringent specifications of the UBIFs.

We describe the application of inorganic organic hybrid materials (ORMOCERs) as optical fiber coatings for use in Fiber Bragg Grating sensors and high power transmission fibers. The materials are UV curable, enable a single layer thickness of about 50 μm and show high a high peak temperature stability >300 °C. Regarding the fiber protection the coatings have been investigated using tensile strength measurements before and after temperature load. Best coatings maintain the high tensile strength of 68 N (125 μm fiber) with a Weibull parameter of 182 after a temperature cycling up to 300 °C. For the first time a low refractive index ORMOCER will be presented showing a numerical aperture of 0.47 at a wavelength of 1000 nm on a pure silica fiber. This corresponds to a refractive index of 1.37. The fiber possesses a fiber loss of 18 dB/km at a wavelength of 1000 nm. The fibers have been coated using a gravity as well as pressure technology. The latter possesses extremely minimized die equipment and is therefore well applicable for small coating amounts. The so called dead volume within the coating die is about 1 ml. The overall dead volume is only influenced by the supply pipe and can be reduced down to 5 ml.

In this paper, the capacity and quality of a shape memory alloy device is demonstrated for installation and connection of 125-μm to 1000-μm optical fibres. The new mechanical splice has the particularity of using a very simple tool for aligning and holding the cladding of fibres itself without the need of glue. Optimend main characteristics are its small dimensions (few millimetres), reusability, glueless, ruggedness, low temperature variation, heat dissipation and ease of use. These properties are very suitable for many optical fibre applications where both quick and reliable connections are desirable.

We propose a new method to induce low loss tunable birefringent phase shifts in fiber Bragg gratings (FBG) by applying mechanical stresses at precise locations along the FBG. A specially designed shape memory alloy (SMA) ferrule is used to transfer mechanical stress to the optical fiber. A piezoelectric actuator control the amount of stress delivered to the fiber by the SMA ferrule, thus allowing a precise and dynamic tuning of the amplitude of the phase shift induced in the FBG. A distributed feedback (DFB) fiber laser based on this phase modulator is also introduced.

Novel bottle microresonators fabricated from standard telecommunications optical fiber were recently shown to support helical whispering gallery modes (WGMs) extending along the bottle length between the bottle necks. Intensity maxima were observed around the turning points on both sides close to the bottle necks where the WGMs are effectively reflected. Selective excitation on one side of the bottle microresonator leads to strong power localization at a symmetrically located turning point for the WGMs and can potentially be exploited to form effective add-drop filters. Channel dropping characteristics have been studied experimentally for the first time in this novel type of microresonator. A tapered optical fiber (drawn down to 2-3 microns in diameter with effective index of approximately 1.2) was placed on one side of the bottle to excite the bottle WGMs. A similar tapered fiber placed symmetrically on the other side of the bottle acted as a probe to extract the excited modes. We have successfully extracted power from all the resonance wavelengths using the probe placed at appropriate positions along the bottle, leading to the potential to construct efficient all fiber add-drop filters.

We propose a novel design of optical router or switch based on the multimode interference phenomenon in waveguide with parabolic index profile. A stair case index approximation of this index profile is utilized to facilitate the fabrication process. The fabrication of this profile is feasible through the current technology using multiple etching. A new design methodology is also proposed to ensure that the response of the stair case MMI (SCMMI) imitates the response of the parabolic MMI. In this methodology, a two-stage optimization procedure is exploited to obtain the optimal design. Gradient-based optimizers are utilized in these two stages exploiting the wide angle BPM. The required response gradient is efficiently obtained using the adjoint variable method. The proposed design has the ability to rout or switch any wavelength over a wide bandwidth.

Chalcogenide glasses are known for their large transparency in the mid infrared and their high refractive index (>2). They present also a high non linear refractive index (n₂), 100 to 1000 times larger than for silica. An original way to obtain single-mode fibers is to design photonic crystal fibers (PCFs). Until now, chalcogenide PCFs are realized using the stack and draw process. However this technique induces defects, like bubbles, at the capillaries interfaces, causing significant scattering losses. Until now, the best transmission obtained was 3dB/m at 1.55μm. The poor PCF transmission reduces significantly their application potential. So, we present a new efficient method to realize low-loss chalcogenide PCFs. This original method by molding permits to reduce the optical losses down to 1dB/m at 1.55μm and less than 0.5dB/m between 3 and 5μm for an As-Se PCF. Furthermore, this molding method can be used for different compositions. Single mode fibers were realized. Moreover, very small core fibers were realized with this method, obtaining a non linear coefficient of 15 000W^-1km^-1 with an As-Se PCF. We also observed self phase modulation at 1.55μm on a fiber with a 2.3μm² mode area.

We report on the fabrication and characterization of metallo-dielectric colloidal structures (MDCS) based on the realization of inverse silica opals and following attachment of gold nanoparticles on the silica network of the inverse structure. In particular we present the protocols developed for the realization of both inverse silica opals and gold nanoparticles together with the procedure used for the immobilization of the metallic nanoparticles on the silica network. Contact angle measurements evidenced a modification in term of wettability of the surface after gold immobilization process. Optical measurements showed that MDCS have unique optical properties that combine the localized surface plasmon resonance of single Au nanoparticles with the photonic band gap features of colloidal crystal structure. Preliminary results on MDCS used as SERS substrate evidenced an increase of the Raman signal in respect to others metallic structures used as comparison.

This work presents long period grating (LPG) devices based on a silica-on-silicon planar waveguide platform. All-silica and hybrid polymer/silica device architectures are demonstrated for potential applications in wavelength filtering, power distribution, and various types of sensors. The grating structure was realized through a periodic corrugation on a thermally oxidized silicon layer that also serves as the waveguide lower cladding. For the hybrid architecture, waveguide ridges were photo-patterned in a layer of low-loss fluorinated poly(arylether ketone), and covered with a similar polymer cladding having lower refractive index. For all-silica LPGs, GeO₂-doped silica waveguides were fabricated over the grating by PECVD and reactive ion etching, and embedded in a layer of borophosphosilicate glass (BPSG) with a refractive-index matched to that of the lower cladding material. In these structures, the corrugated silica layer allows a stable grating structure, while the fluorinated polymer or silica waveguides offer low propagation loss and versatile processability. Strong rejection bands have been observed in the C+L wavelength region, in good agreement with theoretical calculations. Based on these designs, an array of waveguides incorporating long period gratings has also been fabricated. Distribution of light at the resonance wavelength across all channels, from a single input, has been demonstrated. These results are promising for power distribution in photonic network applications or on-chip sensors. The sensitivities of the fabricated LPGs to temperature and to the refractive index of the surrounding medium have been investigated and are discussed.

The stability of an electro-optic modulator has been significantly improved by implementing an original temperature control system. In particular, the evolution of the modulator characteristics can be followed through its nonlinear behavior by detecting the second harmonic of a low-frequency modulation signal; the evolution can be investigated with a higher accuracy by measuring also the phase-shift of this harmonic signal. Two digital boards have been developed with PSOC microcontrollers. The first one is associated with a small power amplifier for the temperature control; the second board is used to analyze the behavior of the electro-optic modulator. By thermal control of the modulator it is possible to reduce significantly the drift of its optical bias point.

We report low frequency Stokes and anti-Stokes Raman spectra resolving frequency shifts down to 15 cm^-1 using a standard commercial Raman spectrometer with ultra-narrow band notch filters. The ultra-narrow band notch filters were fabricated holographically in a glass material with optical densities ranging from 4 to 6 per notch filter at the standard Raman laser lines of 488 nm, 532 nm, 633 nm and 785 nm. The notch filters have greater than 80% transmission at 15cm^-1 away from the laser line. This simple notch filter-based system provides high performance low frequency Raman spectroscopy as a low cost alternative to bulky and expensive triple spectrometer Raman systems.

We describe a unique new, high-contrast, laser-grade polarizer which also acts a high-performance bandpass filter for the desired, transmitted polarization. This thin-film based polarizer combines a polarization contrast ratio greater than 1,000,000-to-1 (extinction ratio < 10^-6) with a bandpass filter with transmission > 93%, very steep edges, and high out-of- band blocking, all in a single, high-layer-count optical coating. Compared to other polarizer technologies, it offers superior optical quality, high angle-of-incidence tolerance, and large clear apertures, making it suitable for high-performance imaging applications. And this filter exhibits excellent environmental reliability and high laser damage threshold (> 1 J/cm²). These new polarizing bandpass filters are excellent laser source clean-up filters to eliminate the undesired polarization at the laser line and light noise away from the laser wavelength, as well as detection filters to pass a laser wavelength range and block background noise. They are ideal for a wide variety of laboratory laser applications, especially those involving holographic and interferometric systems, as well as laser materials processing, polarization diversity detection in communications and rangefinding, and fluorescence polarization and second-harmonic-generation imaging.

This method reduces the data path from the counter to the pixel register of the analog-to-digital converter (ADC) from as many as 10 bits to a single bit. The reduction in data path width is accomplished by using a coded serial data stream similar to a pseudo random number (PRN) generator. The resulting encoded pixel data is then decoded into a standard hexadecimal format before storage. The high-speed serial pixel ADC concept is based on the single-slope integrating pixel ADC architecture. Previous work has described a massively parallel pixel readout of a similar architecture. The serial ADC connection is similar to the state-of-the art method with the exception that the pixel ADC register is a shift register and the data path is a single bit. A state-of-the-art individual-pixel ADC uses a single-slope charge integration converter architecture with integral registers and "one-hot" counters. This implies that parallel data bits are routed among the counter and the individual on-chip pixel ADC registers. The data path bit-width to the pixel is therefore equivalent to the pixel ADC bit resolution.

A structure for backside illuminated ultrahigh-speed charge coupled devices (CCDs) designed to improve the light sensitivity was investigated. The structure's shooting speed of 1 million frames/second was made possible by directly connecting CCD memories, which record video images, to the photodiodes of individual pixels. The simultaneous parallel recording operation of all pixels results in the highest possible frame rate. Because back-side illumination enables a fill factor of 100% and a quantum efficiency of 60%, sensitivity ten or more times that of front-side illumination can be achieved. Applying backside illumination to ultrahigh-speed CCDs can thus solve the problem of a lack of incident light. An n- epitaxial layer/p- epitaxial layer/p+ substrate structure was created to collect electrons generated at the back side traveling to the collection gate. When a photon reaches the deep position near the CCD memory in the p-well, an electron generated by photoelectric conversion directly mixes into the CCD memory. This mixing creates noise, making it necessary to reduce the reach of the incident light. Setting the thickness of a double epitaxial layer to 30 μm, however, will inhibit the generation of this noise. A potential profile for the n-/p-/p+ structure was calculated using a three-dimensional semiconductor device simulator. The transit time from electron generation to arrival at the collection gate was also calculated. The concentrations of the n- and p- epitaxial layers were optimized to minimize transit time, which was ultimately 1.5 ns. This value is adaptive to a frame rate of 100 million frames/second. Charge transfer simulation of a part of the pixel was conducted to confirm the smooth transfer of electrons without their staying too long in one place.

A modified uni-traveling-carrier photodiode-based V-band optoelectronic mixer is demonstrated which can up-convert intermediate-frequency (IF) signals with both the 59.5 GHz local oscillator (LO) and the IF signals in optical form. By properly choosing the ratio between the injected optical LO and IF signals, a high up-converted signal power of -13.1 dBm was obtained at 30 mA of photocurrent and 1.6 V reverse bias without any cooling operation. When a thermal electric cooler is used, up-converted signal power as high as -4.7 dBm was obtained at 70 mA of photocurrent and 3.5 V reverse bias.

We electrically and optically tested both single pixels and complete arrays of Silicon Photomultipliers, from 5×5 to 64x64, fabricated by STMicroelectronics. Single cell devices operation was studied as a function of the temperature from -25°C to 65°C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage. Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the optical power. We determined the single pixel gain by using both the time resolved dark count signal and the current under controlled illumination. Typical gain values above 1×10⁵ and above were obtained for operation times of 10 ns, while higher gains are obtained for longer integration times and lower photon flux.

Metal-semiconductor-metal (MSM) polysilicon photodetectors which are compatible with all standard complementary metal-oxide-semiconductor (CMOS) processes and which were made in a commercial 0.35 ìm process have demonstrated DC responsivities up to 1.3 A/W at 690 nm. An effective absorption coefficient of 0.63 dB/ìm was found from a comparison of responsivities of 5- and 10-μm long detectors. For a constant bias voltage, responsivity varies as the inverse square of the contact spacing, with responsivity continuing to increase for the smallest available contact spacing devices. Responsivities corresponding to quantum efficiencies over 200% were observed, implying a gain mechanism. For AC performance, electrical pulse full-width at half-maximum (FWHM) as low as 0.81 ns and 10% - 90% rise times as low as 0.39 ns have been measured in response to ~0.65 ns FWHM optical input pulses. The ability to modulate the source laser diode limits the measured pulse performance of the detectors. Observed DC and pulse results are well explained by an analytic expression which incorporates the effects of bulk and contact recombination. Possible means of improving the detector speed are proposed.2

Miniaturized field-deployable spectrometers used for the rapid analysis of chemical and biological substances require high-sensitivity photo detectors. For example, in a Raman spectroscopy system, the receiver must be capable of high-gain, low-noise detection performance due to the intrinsically weak signals produced by the Raman effects of most substances. We are developing a novel, high-gain hetero-junction phototransistor (HPT) detector which employs two nano-structures simultaneously to achieve 100 times higher sensitivity than InGaAs avalanche photodiodes, the most sensitive commercially available photo-detector in the near infrared (NIR) wavelength range, under their normal operation conditions. Integrated into a detector array, this technology has application for Laser-Induced Breakdown Spectroscopy (LIBS), pollution monitoring, pharmaceutical manufacturing by reaction monitoring, chemical & biological transportation safety, and bio-chemical analysis in planetary exploration.

Back-thinning of a CCD image sensor is a very well established process for achieving high quantum efficiency and the majority of high-specification space and science applications have used such back-thinned devices for many years. CMOS sensors offer advantages over CCDs for a number of these applications and, in principle, it should be possible to back-thin CMOS devices and obtain the same performance as the CCD. This has now been demonstrated by e2v and results from two recent programmes to back-thin CMOS sensors show excellent quantum efficiency values.

Image intensifiers (I2) have many advantages as detectors. They offer single photon sensitivity in an imaging format, they're light in weight and analog I2 systems can operate for hours on a single AA battery. Their light output is such as to exploit the peak in color sensitivity of the human eye. Until recent developments in CMOS sensors, they also were one of the highest resolution sensors available. The closest all solid state solution, the Texas Instruments Impactron chip, comes in a 1 megapixel format. Depending on the level of integration, an Impactron based system can consume 20 to 40 watts in a system configuration. In further investing in I2 technology, L-3 EOS determined that increasing I2 resolution merited a high priority. Increased I2 resolution offers the system user two desirable options: 1) increased detection and identification ranges while maintaining field-of-view (FOV) or 2) increasing FOV while maintaining the original system resolution. One of the areas where an investment in resolution is being made is in the microchannel plate (MCP). Incorporation of a 2 micron MCP into an image tube has the potential of increasing the system resolution of currently fielded systems. Both inverting and non-inverting configurations are being evaluated. Inverting tubes are being characterized in night vision goggle (NVG) and sights. The non-inverting 2 micron tube is being characterized for high resolution I2CMOS camera applications. Preliminary measurements show an increase in the MTF over a standard 5 micron pore size, 6 micron pitch plate. Current results will be presented.

Recently developed glass-clad crystalline semiconductor core optical fibers potentially offer a series of advantages over present optical fiber materials including greatly enhanced Raman cross-sections and extended infrared transparency. Indeed, the low-cost high-through-put fiberization of crystalline materials could permit a step-jump in performance critical for use in high energy laser, infrared counter-measure, communication, and sensor systems. Further, the high degree of crystallinity is of considerable scientific value since optical fiber fabrication is a highly non-equilibrium process and so achieving high degrees of crystallinity is very counter-intuitive and offers new insight into crystal growth mechanisms. This talk will review progress in glass-clad fibers possessing cores of highly crystalline silicon and germanium including anomalies in Si and Ge that may benefit fiber fabrication as well as paths forward to optimization of fiber design and performance.

This paper presents detailed numerical and experimental study of SPM in semiconductor optical amplifiers (SOAs) with ultrafast gain-recovery times. These SOAs have a range of gain-recovery speed which is a function of drive current. At increased drive current, the amount of internal ASE in the SOA increases, which causes the small signal gain to saturate and reduces the gain-recovery time. Understanding pulse amplification in these SOAs is important for optimizing the performance of SOA-based optical regenerators and wavelength converters. Our study addresses the full range of gain-recovery times in commercial SOAs extending from less than 10 ps to >100 ps.

High-temperature stability of lasing wavelength of GaAsSb/GaAs quantum well (QW) lasers grown by metal-organic vapor phase epitaxy will be demonstrated. According to the best of our knowledge, this is the first trial of using triethylgallium (TEGa) as the precursor to grow QW at low temperature (525°C). The lasing wavelength ranges from 1117 to 1144 nm and varies with temperature (dλ/dT) from 0.24 to 0.287 nm/K. These values are lower than other previously reported results. The QW grown at high temperature (600 °C) by using trimethylgallium (TMGa) is also examined. The lasing wavelength is 1125.6 nm at room temperature and dλ/dT is 0.36 nm/K, which is higher than those lasers grown at lower temperature.

Er doped III-nitride semiconductors are a major field of research aiming to achieve photonic devices with multiple functionalities in photonic integrated circuits (PICs), which are not possible with either Er doped silica glasses or narrow band gap semiconductors like InGaAsP. Emitters and optical amplifiers based on Er doped GaN/InGaN operating at 1.54 μm are expected to be electrically pumped, integratable, temperature insensitive and have high signal gain with low noise. These properties are very attractive for next generation optical network systems where multiple amplification steps are required. We will discuss here the metal organic chemical vapor deposition (MOCVD) growth of Er doped GaN/InGaN epilayers. Further, we report on the fabrication of chip size current injected 1.54 μm emitters and optical amplifiers by heterogeneously integrating MOCVD grown Er doped GaN/InGaN with 365 nm nitride light-emitting diodes. The emitted intensity at 1.54 μm varied almost linearly with input forward current. The feasibility of electrically pumped optical amplifiers for PICs with the advantages of both semiconductor optical amplifiers and Er-doped fiber amplifiers will also be discussed.

Laser cavities emitting in the near and medium infrared wavelength range, made of rare earth doped optical fibers and suitable pairs of integrated mirrors, are used in a large number of applications. Nowadays, the efficient employment of near and medium infrared laser beams is largely widespread in the field of m*aterial processing, surgery, directed energy, remote sensing, spectroscopy, imaging, and so on. In a lot of cases, the high conversion efficiency, the excellent beam quality, the compactness and, the good heat dissipation capability make fiber lasers competitive and attractive with respect to other light sources, such as ion-doped crystal and bulk glass lasers, optical parametric oscillators, semiconductor and gas lasers. The paper aims to recall and/or briefly illustrate a few among the numerous strategies recently followed by research laboratories and industries to obtain laser sources based on rare earth doped optical fibres. A recall on the host materials and the dopants employed for their construction, and the corresponding applications is given, too. Moreover, an example of near infrared (NIR) fiber optic laser development, by employing available on market components is illustrated by underlining the possibility to easily obtain high beam quality.

This paper provides an overview of the experimental work performed in our research group on the synthesis, spectroscopic investigation, and laser characterization of chromium-doped zinc selenide (Cr²⁺:ZnSe). By using diffusion doping, 40 polycrystalline Cr²⁺:ZnSe samples with ion concentration in the range of 0.8 × 10¹⁸ to 66 × 10¹⁸ions/cm³ were prepared. From the absorption data, temperature-dependent diffusion coefficient of chromium and losses at the lasing wavelength were measured. In luminescence measurements, the concentration dependence of the fluorescence lifetime and fluorescence quantum efficiency was determined. During continuous-wave operation, the optimum concentration for lasing was determined to be 8.5 × 10¹⁸ ions/cm³ at an incident pump power of 2.1 W for 1800-nm pumping. During gain switched operation, intra-cavity pumping with a 1570-nm optical parametric oscillator resulted in continuous tuning between 1880 and 3100 nm. By employing dispersion compensation with a MgF² prism pair, Kerr-lens mode-locked operation was also demonstrated at 2420 nm, resulting in the generation of 95-fs pulses with an average output power of 40 mW and spectral bandwidth of 69 nm. The time-bandwidth product of the pulses was further measured to be 0.335 close to the expected value of 0.315 for sech² pulses.

Cladding-pumped fiber Raman devices are becoming an attractive laser source solution thanks to their potential for power-scaling at arbitrary wavelength and good beam quality output through the beam clean-up of multimode beams. To date, demonstrations have been limited to devices with relatively small inner claddings and small cores because of the intensity required to reach the stimulated Raman scattering threshold. However, the small inner cladding dimension constrains to use relatively high-brightness pump sources. Furthermore, the core dimension also restricts the power scalability because of the smaller damage threshold in smaller core. Here, for the first time, we demonstrate a pulsed cladding-pumped fiber Raman amplifier based on a large mode area fiber with a 20 μm diameter, 0.06 NA, core and a 50 μm diameter, 0.2 NA, inner cladding. With these fiber dimensions, we show that it is possible to efficiently convert the pump into the 1st Stokes without undesired higher-order Raman scattering, provided that the fiber length is matched to the pump power. Using a 1064 nm, pulsed pump source we obtained a 2.15 kW output peak power for 2.8 kW of launched pump peak power in a single pass amplifier configuration. The M² parameter of the output beam at 1st Stokes is measured to be 1.69.

We study experimentally the characteristics of optical rogue waves in supercontinuum generation in the femtosecond regime. Specifically, we show that the intensity histograms obtained from spectrally filtering the supercontinuum exhibit the L-shaped characteristics typical of extreme-value phenomena on the long wavelength. Furthermore, the form of the histogram on the long wavelength edge varies from L-shaped to quasi-Gaussian as wavelengths closer to the pump are included in the filtered measurements. Finally, we show that coupling between the red-shifting solitons on the long wavelength side and dispersive waves on the short wavelength side through cross-phase modulation leads to similar L-shaped statistics when using a low-pass filter on the blue side of the supercontinuum spectrum.

We have successfully made terrace-microspheres for laser emission: micrometer size spherical cavity laser having terrace shaped pumping light entrance. "Terrace-microsphere" is a high refractive index glass sphere (n_D=1.93) of 30μm in diameter with terrace portion of organic-inorganic materials. The glass sphere is in BaO-SiO₂-TiO₂ glass system and contain a few ppm of Nd³⁺. Organic-inorganic hybrid materials of refractive index n_D=1.45 were prepared by sol-gel technique using 3-methacryloxypropyltrimethoxysilane and tetramethoxysilane as starting materials. To make terrace portion, a pico-liter of sol droplet was supplied with a micro-capillary into the boundary between a glass sphere and a Teflon sheet. The sol-derived part attached to a sphere showed the flat portion like a terrace structure. The terrace-microspheres were pumped with a tunable CW Ti:sapphire laser (λ=700nm-850nm) for choosing the suitable pumping wavelengths to WGMs. Pumping the terrace portion at around 800nm wavelength, strong resonances due to WGMs were demonstrated. The resonances originated from Raman scattering and Nd³⁺ fluorescence were observed at 840-880nm and 880-940nm wavelength region respectively. Consequently, we can show the potential application for a multi-wavelength laser (about 100 lines) at the extended wavelength range (840-940nm) in the near-infrared. Stimulated Raman emission of WGMs was performed with threshold of 4mW.

The process of holographic recording based on a direct formation of periodic surface relief in As_xSe_1-x (0 ≤ x ≤ 0.5) and As₂S₃ layers was investigated by in situ AFM depth profiling and compared with data on diffraction efficiency η of the similar relief holographic gratings, measured in a reflection mode. It is established, that the time (exposure) dependence of η has at least two components, which are connected with different components of the surface deformation Δd and relief formation up to the giant, Δd/d >10% changes in the best As_0.2Se_0.8 or As₂S₃ compositions. Correlation is found between light and e-beam induced surface deformations during recording in similar compositions. Applications for prototyping phase-modulated optoelectronic elements are considered.

Recently proposed modern technique of a precise spectrum analysis within an algorithm of the collinear wave heterodyning implies a two-stage integrated processing, namely, the wave heterodyning of a signal in a square-law nonlinear medium and then the optical processing in the same cell. Technical advantage of this approach is in providing a direct processing of ultra-high-frequency radio-wave signals with essentially improved frequency resolution. This algorithm can be realized on a basis of various physical principles, and we consider an opportunity of involving the potentials of modern acousto-optics for these purposes. From this viewpoint, one needs a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The technique under consideration imposes specific requirements on the cell's material, namely, a high optical quality of large-size crystalline boules, high-efficient acousto-optical and acoustic interactions, and low group velocity of acoustic waves together with square-low dispersive acoustic losses. We focus our attention on the solid solutions of thallium chalcogenides and take the TlBr-TlI (thallium bromine - thallium iodine) solution, which forms KRS-5 cubic-symmetry crystals with the mass-ratio 58% of TlBr to 42% of TlI. Analysis shows that the acousto-optical cell made of a KRS-5 crystal oriented along the [111] -axis and the corresponding longitudinal elastic mode for producing the dynamic diffractive grating in that crystal can be exploited. With the acoustic velocity of about 1.92 mm/μs and attenuation of approximately 10 dB/(cm GHz²), similar cell is capable to provide an optical aperture of 50 mm and one of the highest figures of acousto-optical merit in solid states in the visible range. Such a cell is rather desirable for applications to direct parallel multi-channel optical spectrum analysis with substantially improved frequency resolution.

The main features of arranging the polarization control in optical scheme of a 1000-channel acousto-optical spectrometer for the needs of radio-astronomy are analyzed. To realize a high-resolution spectrum analysis rather specific acousto-optical cell has to be exploited. For this cell a tellurium dioxide single-crystal oriented along the [001]- and [110]-axes has been chosen. Due to an extremely high anisotropy of this crystal, the efficiency of light scattering depends essentially on the ellipticity of the incident light polarization and increases when the state of polarization reaches the eigen-state of elliptic polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. This is why we analyze some peculiarities of designing the beam-shaping scheme, which includes tunable light polarizers and a multi-prism beam expander and has to provide the needed pre-assigned states of light polarization on the inputting aperture of acousto-optical cell.

The quantum efficiencies of the emission from the ⁴F_3/2(R) level of Nd doped in tellurite glass were measured with an integrating sphere using natural sunlight(η_ns), simulated sunlight (η_ns), and 808 nm laser light (η₈₀₈), respectively. The radiative quantum efficiency (η_r) was estimated from the fluorescence lifetime (τ_f) and the radiative lifetime calculated by Judd-Ofelt analysis (τ_r). η_r was almost 100 % for χ ≤ 0.5 mol.%. η₈₀₈ was 86 % for χ=0.05 mol.% and decreased monotonically with increasing in χ. η_ns had a peak at χ=0.5 mol.% and the maximum was 33 %. It is thought absorption of the excitation light by the host glass limits the quantum efficiency of the tellurite glass under sunlight excitation. Therefore, it is important to reduce absorption of the tellurite glass host in order to realize efficient solar-pumped tellurite fiber lasers.

We propose a chalcogenide (As₂S₃) core tellurite cladding microstructured fiber with flattened normal dispersion for ultraflat supercontinuum (SC) generation. To realize flattened normal dispersion, the structure parameters are optimized such as the chalcogenide core diameter, the air hole diameter and the distance between the centers of the two neighboring air holes. The ultraflat normal dispersion curve is obtained and the pulse propagation is investigated using a nonlinear Schrödinger equation. It is shown that an ultraflat SC spectrum with deviations less than 4 dB over an octave (from 1400 nm to 3000 nm) can be achieved by the illumination of a pulsed light with a pulse width of 200 fs, central wavelength of 2000 nm and peak power of 1000 W.

We present the design, dispersion calculations and tailoring, and simulation of the parametric gain in the composite tellurite-fluorophosphate glass fiber. The fiber has the tellurite core subsequently surrounded by fluorophosphate and tellurite claddings. Thermal properties of the tellurite and fluorophosphate glasses match, depicting the feasibility of the fabrication of the fiber under controlled environment. The composite fiber introduced here has the advantage of easy handling over the fiber tapers or the air cladding tellurite nanofibers. With our analysis we observe that the fluorophosphate and the tellurite cladding thickness along-with the fiber core diameter, have control on the dispersion and the parametric gain. The wavelength band, over which the dispersion is anomalous, increases with increasing tellurite core diameter. For longer wavelengths, increasing the fluorophosphate cladding thickness causes increase in the anomalous dispersion bandwidth and further flattening of the dispersion curve. The slope of the dispersion curve near the zero dispersion wavelength (ZDWL) is greatly reduced for thicker outer tellurite ring claddings. It is possible to design zero flattened dispersion fiber or the fiber providing two ZDWLs in the communication band, which can generate broadband parametric amplification. The gain obtained has strong bandwidth dependence on the dispersion slope. We study the effects of the fiber length, pump power, and pump detuning from the ZDWL, on the parametric amplification. With multiple pumping with proper selection of the pump wavelengths, the parametric amplification process can generate ultra flat, broadband amplifiers as the dispersion provided by the composite fiber is anomalous over a wide bandwidth.

The samples of Er³⁺/Yb³⁺ co-doped phosphate glasses with different Er³⁺ doped concentrations were prepared by high-temperature melting method. By calculating the electronic polarizabilities and optical basicity of the samples, we find, with the increasing of Er³⁺ ions concentration, the polarizability and optical basicity of oxide ions become large, which indicates that the covalence of the glasses becomes small. Based on Judd-Ofelt (J-O) theory, the J-O intensity parameters Ω_λ (λ=2,4,6), spontaneous radiative lifetime, and fluorescence branching ratio were calculated. With the increasing of Er³⁺ concentration, the Ω₂ values are decrease gradually, which also proves that the covalence of the glasses becomes small. The ratios of Ω₄/Ω₆ are within the range of 7.51-9.84, which are larger. Thereby, our glasses are suitable laser materials. We also studied the upconversion (UC) emission of the samples. The strong 657 nm red emission, 546 nm and 523 nm green emissions were observed under 975 nm laser diode (LD) excitation. The UC emission intensities depend on the ratio of Er³⁺/Yb³⁺. When the ratio is 0.125, the emissions are strongest. The emission cross sections of UC emissions were analyzed using McCumber theory and Füchtbauer Ladenburg (FL) method. The emission cross section of UC red emission is larger (about 0.5×10^-20cm²),which proves our samples are better red light materials.

This paper proposes an optically tunable focal intensity microlens array (MLA) by using a focusing unit with birefringent liquid crystalline polymer (LCP) and a tuning unit with photoalignment for controlling the polarization state of the incident light. Due to the different refractive indices of LCP, it acts as a positive or negative microlens with respect to the polarization state. The resultant tunable focal intensity MLA shows the fast optical switching time without voltage and the multi-stable characteristics.

A one-dimensional periodic sub-wavelength structure (SWS) was fabricated on a glass plate by a glass-imprinting method. Thermal and optical properties of lithium bismuth gallium borate glasses were investigated for the development of glass suitable for the glass-imprinting method. It was found that refractive index and absorption edge energy showed additivity for glass composition and that the substitution of fluorine atoms for oxygen atoms reduced deformation temperature and increase transparency near uv region. The glass had a refractive index higher than 1.80 at 587 nm, internal transmittance higher than 80% (3 mm in thickness) at 400 nm, and deformation temperature lower than 470°C was obtained. A one-dimensional SWS with a period of 300 nm on an SiC mold was transferred to the glass surface by the glass-imprinting method, which showed the phase retardation due to form birefringence.

We propose a small and fast ellipsometer with a basic layout similar to that of conventional ellipsometers using photo-elastic modulators (PEM) oscillating with 50 kHz. A conventional PEM is rather large, ~10×20×100mm, since it consists of one piece of glass and an actuator. Both parts are carefully adjusted to the desired frequency and then glued together. We replace such a standard modulator by a 127 kHz Single Crystal Photo-Elastic Modulator (SCPEM), a LiTaO₃-crystal with a size of 20.6×7.5×5mm. The polarization of light that travels through this crystal is strongly modulated. The modulated light is reflected from the sample, passes a polarizer and hits a detector. Its signal is split into the dc-value and the amplitudes of the 1st and 2nd harmonic of the modulation frequency. These values lead via simple formulas to the ellipsometric parameters. Usually a Lock-In-Amplifier is used here, whereas we propose an automated digital processing based on a fast analog to digital converter controlled by a highly flexible Field Programmable Gate Array (FPGA). This and the extremely compact and efficient polarization modulation allow fast ellipsometric measurements as needed in high volume manufacturing of optics.

Polarization devices developed for fiber optic systems are pigtailed. These pigtails, built with standard single-mode optical fiber (~1 m long) modify the input and output characteristics of the signal's polarization state. Even though this contribution is negligible when the fibers are kept straight, it increases when they are wound up to form compact systems. In this work, we used Mueller calculus and experimental results to analyze the polarization performance of helically wound single-mode fibers. These results have been used to propose the cascaded helical structures we have built. Using linear and circular input polarization states and the Poincaré sphere it is shown that to control the total birefringence the relative orientation of the symmetry axes of these helices must be varied. The experimental results obtained for the birefringence of these structures demonstrates that it is possible to minimize their birefringence contribution within a limited spectral bandwidth.

Aluminum Nitride (AlN) is a wide band gap III-V semiconductor material often used for optical applications due to its transparency and high refractive index. We have produced and characterized AlN thin films by reactive r.f. magnetron sputtering in different Ar-N₂ atmospheres in order to verify the best gaseous concentration to be utilized as anti-resonant layer in ARROW waveguides. The corresponding films were characterized by Fourier transform infrared spectroscopy (FTIR), Rutherford backscattering spectroscopy (RBS), Ellipsometry and visible optical absorption. The AlN properties did not varied significantly between the films deposited with 20 and 70 sccm of N₂, most of the variations occurred for films deposited with 18 sccm of N₂ or below. The film deposited with 20 sccm was selected to be used as the first ARROW layer in the fabricated waveguides. Two routines were used to design the waveguides parameters, the transfer matrix method (TMM) and the semi-vectorial non-uniform finite difference method (NU-FDM). Attenuation as low as 3.5dB/cm was obtained for a 7 μm wide waveguide.

The development of new optical systems requires the design of novel components that fulfill the market constraints. In particular, low loss, high optical rejection and low cost narrowband filters can play an important role for the introduction of the Wavelength Division Multiplexing (WDM) technology in the local network. So, a novel fiber filter is proposed in this article, with a special combined apodized Linearly Chirped Fiber Bragg Grating (LCFBG) which presents the preferable flat-top and steep-edge characteristics. In the design, we use a continuum cavity condition which is obtained when the effective round-trip phase of oscillated wavelength band is kept identical over the whole Bragg wavelength range. And the transmission spectra are calculated by the reconstruction of the matrixes with the continuum oscillation condition. Therefore, our works show that the ideal square shaped filter is obtained with a lower chirp value relatively together with symmetric reflectivity on both mirrors. The coupling coefficient of the FBG is adjusted to get the same reflectivity values and then to get a transmission filter close to unity. We have then introduced an apodization function of the filter to get a flatter transfer function. Various apodizations schemes have been tested. In this paper, we design and analyze a type of continuum fiber filter with the cavity formed between mirror and apodized LCFBG as reflectors. We calculate firstly the reflectivity, the transmissivity and the group time delay of LCFBG modeled by a simple and practical Transfer Matrix Method (TMM), and then the cavity is reconstructed by TMM, the length of the oscillated cavity is calculated by the continuum oscillation condition, so the output of transmission from the side of LCFBG is continuous in the corresponded reflected bandwidth of LCFBG. We obtain the results and discuss some characteristics of this type of continuum fiber filter.

We performed extensive spectroscopy of tellurite glasses doped with high concentration of Tm ions for laser emission at around 2 micron wavelength. The aim of the work is to develop a glass suitable for single-frequency fiber laser. In fact such a kind of laser require the use of short cavity length and therefore high gain per unit length medium. Tellurite glasses allows high-doping concentration and are therefore an excellent candidate. In these paper we review our recent results. In particular we address the optical and thermo-mechanical properties of several tellurite glasses (75mol%Te02.20mol%ZnO. 5mol%Na2O) with Tm³⁺ doping up to 111,564 ppm.

In this paper we investigate the infrared-to-visible upconversion luminescence in bulk crystals and nanocolloid filled photonic crystal fiber with ytterbium and erbium co-doped NaYF4 upconversion phosphor. The phosphor was prepared by using simple co-precipitation synthetic method. The initially prepared phosphor has very weak upconversion fluorescence. The fluorescence significantly increased after the phosphor was annealed at a temperature of 400°C. Nanocolloids of this phosphor were obtained using water and methanol as solvents and they were utilized as laser filling medium in photonic crystal fibers. Under 980nm laser excitation very strong upconversion signals were obtained at 408 nm, 539 nm and 655 nm. Efficiency and decay life time study of the upconverted emissions was conducted to understand the upconversion mechanisms. The reported nanocolloids are good candidates for fluorescent biosensing applications and also as a new laser filling medium in fiber lasers.

X-ray imaging requires unique optical detector system configuration for optimization of image quality, resolution, and contrast ratio. A system is described whereby x-ray photons from multiple anode sources create a series of repetitive images on fast-decay scintillator screens, from which an intensified image is transferred to a fast phosphor on a GEN II image intensifier and collected as a cineradiographic video with high speed digital imagery. The work addresses scintillator material formulation, flash x-ray implementation, image intensification, and high speed video processing and display. Novel determination of optimal scintillator absorption, x-ray energy and dose relationships, contrast ratio determination, and test results are presented.