This PDF file contains the front matter associated with SPIE Proceedings Volume 7212, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Bi-doped silica glass is a new broadband infrared fluorescence material. We drew optical fibers with the Bi doped silica glass for the fiber core and evaluated the fluorescence spectrum. The FWHM of fluorescence spectrum is measured to be 390 nm. When this broad band spectrum is used as an OCT light source, the expected axial resolution is calculated to be 1.9μm, This is comparable to the axial resolution (Δz~1μm) by Ti:Al₂O₃ system. And we also examined the local structure of Bi ion in Bi-doped silica glass. These are analyzed by ESR, EXAFS, XPS, and ²⁷Al-NMR. According to these results, the structural model of Bi luminescent center is proposed that Bi⁵⁺ ion with 6-fold coordination exists close to Al³⁺ ion with 6-fold coordination.

In this paper we present the development process of a glass based on bismuth and aluminum co-doped germanate (GAB) glass. Other workers have demonstrated broadband optical gain in GAB glass. We found the addition of PbO to this glass (GAPB glass) increased the quantum efficiency (QE). Excitation of GAPB glass at 808 nm produced emission peaking at 1230 nm with a width of 260 nm, indicating the glass may be useful as a broadband optical amplifier covering the second telecoms window. The composition of each component of the GAPB glass was optimized for the QE and lifetime of this emission to produce an optimized composition of 87.4GeO₂-6Al₂O₃-6PbO-0.6Bi₂O₃ (% molar) which had a QE of 67%. However, this composition contained many white inclusions which x-ray diffraction measurements indicated were a phase separation. This would make the glass unsuitable for fibre fabrication. We tried a variety of melting condition which did not improve the glass, the melting conditions did however affect the QE and lifetime. The optimum melting conditions were 1250°C for 30 min in a N₂ atmosphere. Next we tried adding various quantities of a variety of glass additives including SiO₂, LiO, ZnO and SrCO₃. All these additives reduced the QE, and all except SiO2 produced a transparent glass in the appropriate quantity. The quantity of these additives which gave a transparent glass and their QE's were LiO: 10% and 6%, ZnO: 10% and 43%, SrCO₃: 5% and 27% respectively. Therefore the optimized composition for QE and transparency is 74.4GeO₂-10ZnO-6Al₂O₃-6PbO-0.6Bi₂O₃.

In this work, we report the optical properties of Tm³⁺, Er³⁺, and Tm³⁺-Er³⁺ codoped tellurite TeO₂-WO₃-PbO glasses for different Er³⁺ and Tm³⁺ concentrations. Judd-Ofelt intensity parameters have been determined to calculate the radiative transition probabilities and radiative lifetimes of excited states of Tm³⁺ and Er³⁺ ions. Luminescence spectra and lifetimes were measured under 793 nm and 800 nm excitations. The infrared emission of Tm³⁺ at 1470 nm is broader by around 30 nm and the stimulated emission cross section twice if compared to fluoride glasses used for S-band amplifiers. Moreover, a broad emission from 1350 to 1600 nm with a full width at half-maximum of ~ 160 nm is obtained by codoping the glass with Tm₂O₃ an Er₂O₃ which suggests these glasses could be promising materials as broadband light sources and broadband amplifiers for wavelength-division-multiplexing (WDM) transmission systems.

The presentation will give the state of the art and the results of the last advances obtained in the growth, the characterization and the implementation of three kinds of rare-earth doped halide laser crystals: Pr³⁺ doped fluorides, Yb³⁺ doped CaF₂ and its isotypes, and Er³⁺ and Pr³⁺ doped chloride and bromide KPb₂Cl₅ and Tl₃PbBr₅.

Eu³⁺ doped (100-x) SiO₂ - x SnO₂ (x = 8, 16 and 25 mol %) glass-ceramic waveguides were fabricated by sol-gel technique with dip-coating processing at 800 °C. Higher thermal treatments led to the formation and growth of SnO₂ nanocrystals in the matrix, enhancing the ⁵D₀ → ⁷F₂ emission of Eu³⁺. Spectroscopic investigations reveal the evolution of a centro-symmetric local environment around the Eu³⁺ ion. This property of glass-ceramic waveguides can be exploited for obtaining a higher rare-earth concentration in a smaller volume. The glass-ceramic waveguides exhibited low-losses (0.8 ± 0.2 dB/cm at 632.8 nm) and thus are promising for the development of high-gain integrated optical amplifiers.

The europium-doped tin dioxide nanopowders co-doped with Mg²⁺ and Li⁺ ions were synthesized using modified Pechini method. In order to determination of structure and morphology of obtained powders the X-ray diffraction (XRD) measurement were carried out. The photoluminescence of obtained powders were measured. Intensity of emission was compared using blue ZnS:Ag reference peak method. The intensity of emission of samples with different Mg²⁺, Li⁺ concentration and pure Eu³⁺:SnO₂ were compared. After that mixed powders were deposited on ITO-glass slide. The cathodoluminescence of obtained layers were also measured and compared. In the same time, slurries with obtained nanoparticles were carried out. The layers consisted obtained nanopowders were fabricated from prepared slurries using spin-coating method. The electrical properties of obtained layers measured and compared. The influence of co-doping, properties and the potential application of obtained nanopowders will be discussed.obtained layers measured and compared. The influence of co-doping, properties and the potential application of obtained nanopowders will be discussed.

Accuracy at which population inversion in an ytterbium-doped fiber can be determined by modeling is studied. Here inversion refers to the percentage of ions excited to a higher energy level by the various optical fields. Knowledge of rare-earth ion inversion is crucial for determining the photodarkening behavior of a fiber, but can also be used to study the gain and noise properties of amplifiers. Sample fibers are first characterized for their optical and mechanical properties (e.g. absorption and fluorescence spectrum, excited state lifetime, rare-earth concentration and geometrical dimensions). Fiber specific absorption and emission cross-sections are then derived from the measured fiber parameters. Two methods (i.e. McCumber theory and Fuchtbauer-Ladenburg relation) are used to determine the detailed shape and the relative level of absorption to emission at different wavelengths. A full numerical model is used to simulate both core and cladding pumped YDFs. In order to validate the inversion results produced by the simulator a comparison between the measured and simulated ASE spectra is made. Sensitivity of the simulated ASE spectrum on the different parameters is investigated. Uncertainty analysis is made to show the contributions of various measured parameters on the uncertainty of the inversion. The principal contributor of uncertainty on the inversion was found to be the cross-section values.

A review of research into stimulated Brillouin scattering (SBS) phase conjugation and beam cleanup conducted at the Air Force Institute of Technology is presented. CW phase conjugation was demonstrated using SBS in short lengths of multi-mode, step-index fiber. A fidelity of 0.8 was achieved using a 0.06-NA fiber of 40 m length and a 0.13-NA fiber at 15 m length. In modeling and experiment, the fidelity declined as fiber length or numerical aperture increased. A relationship was established empirically between step-index fiber parameters and the phase conjugation fidelity. In addition, increased fidelity was related to an increase in the effective Brillouin gain coefficient in step-index fibers. Beam cleanup was observed in both graded-index and step-index fibers. The Stokes beam generated in long, multimode, graded-index fibers was analyzed using spatial and phase methods and found to be a low-order mode of the fiber instead of a phase conjugate of the pump. SBS in long, graded-index fibers was used to combine multiple beams and to improve the beam quality of a single aberrated beam.

In this work a compact green laser light source is presented based on a single-pass second harmonic generation (SHG) in non-linear material. The green light source consists of a distributed feedback (DFB) laser with a monolithically integrated power amplifier (PA) and a periodically poled lithium niobate (PPLN) crystal with a ridge waveguide. To achieve the smallest size and to reduce the number of parts to be assembled, a direct coupling approach is implemented without using any lens. The waveguide of the laser is bent and the facet of the crystal is tilted and AR-coated in order to reduce undesired reflections and to increase the stability of operation. By varying the injection current of the amplifier the infrared output power of the laser changes proportionally. The wavelength remains stable during current variation and in that way the green optical output power can also be modulated. No additional external modulator is required for the generation of distinct green light levels. At a wavelength of 530 nm, a green optical output power of more than 35 mW is achieved for injection currents of 93 mA and 400 mA through the DFB section and amplifier section respectively.

We propose here a liquid level sensor using a long period fiber grating (LPFG) in which direct liquid level measurement is carried out by utilising an LPFG, 100mm in length and a periodicity of 1mm. The LPFG was exposed to liquids with varying levels and the wavelength shift of a selected loss band of the transmission spectra was monitored using a broadband light source and an optical spectrum analyzer. The mechanism of this LPFG sensor is based on the fact that the effective Refractive Index (RI) of a cladding mode is directly dependant on the RI of the surrounding medium, be it air, or in this case water and petrol. As the surrounding RI changes, so does the phase matching condition of the LPFG. The result for the level change of the liquid with a specific RI is both a shift in wavelength and a change in the attenuation level of the selected loss band. For the selected loss band, continuous wavelength shifts of 9.5 nm and 25 nm for 100 mm of water and petrol level change have been observed respectively, with sub-millimetre accuracy.

We demonstrate two types of in-fiber linear polarizers based on PANDA PM fibers with < 0.7 dB insertion loss, > 30 dB extinction ratio, and > 40 dB return loss. The first is a chiral fiber, realized by twisting an etched and tapered PANDA fiber. A form birefringence of 10^-2 is achieved in the noncircular fiber produced by differentially etching the pure silica cladding and the doped silica stress members. The chiral grating scatters one polarization component out of the fiber over a broad band while the orthogonal polarization component propagates freely. The second polarizer is produced in an untwisted tapered PANDA fiber. Polarization selectivity is the result of opposite modal interferometric oscillation of two orthogonal polarization components. Both types of in-fiber polarizer are all-glass, scattering, and non-absorbing devices without back-reflection and are therefore suitable for high-power applications.

High reflectivity fiber Bragg gratings are written with ultrafast infrared radiation in H₂ loaded SMF-28 fiber that retain in excess of 60 percent of their index change at 1000 °C using writing intensities below the damage threshold of the fiber. The reflectivity after annealing (>-15 dB transmission loss at the Bragg resonance) and index modulation (1×10^-3) in these devices is significantly higher than what can be achieved with UV devices such as Type II, Type IIA and chemical composition gratings. In this study the stability of these devices is compared to that of gratings fabricated in unloaded SMF-28 fiber.

In this work, we review recent progress on the realization of chalcogenides Photonic Crystal Fibers (PCFs). We present the fabrication of chalcogenide PCFs with a solid core for three different glass compositions containing a variety of chalcogens. We show that the Stack and Draw technique currently used for silica PCFs can be problematic in the case of chalcogenides glasses. We present correct PCF design enables a significant improvement of final fiber losses. We obtained a lowest attenuation of 3 dB/m at 1.55 μm, of 4.5 dB/m at 3.39 μm and 6 dB/m at 9.3 μm. We also present experimental demonstration of self phase modulation spectral broadening around 1,55 μm. Moreover, we investigate the Brillouin and Raman scattering properties of a GeSbS PCF.

The effect of an ambient index change on the transmission characteristics of versatile D-shaped fibers such as single mode fibers (SMFs) and photonic crystal fibers (PCFs) is investigated, which depend on the coupling strength of the evanescent field. The transmission loss of the D-shaped fibers increases as the ambient index increases because the evanescent field coupling from the core region can be enhanced by the increase of the ambient index. The coupling strength of the evanescent field can be changed by the remaining length of the cladding region in the D-shaped fiber, which can be defined as the distance between the core and the cladding. The transmission loss becomes extremely high when the ambient index is equal to the effective index of the core mode. When the ambient index is higher than that of the effective index of the core mode, the transmission loss decreases because the evanescent field is coupled back into the core region. The sensitivity of the transmission loss to the ambient index change is strongly depending on types, the remaining length of the cladding, and the polished length of fibers such as SMFs and PCFs. The remaining length of the cladding region can be determined by the coupling strength of the evanescent field.

Long period fiber gratings couple core and co-propagating cladding modes to produce dips in the transmission spectrum and have been widely utilized as sensors and filters. We have recently developed a new approach to long period fiber gratings utilizing optical fibers, which are uniformly twisted at elevated temperatures to produce double or single helices. Because these fibers are not manufactured by exposing photosensitive glass to patterned UV illumination, as is the case for traditional fiber Bragg gratings (FBGs) or long period gratings (LPGs), they are more robust in harsh thermal and chemical environments. Double helix fibers are polarization sensitive and are fabricated by twisting fiber preforms with high-index noncircular cores while single helix gratings are polarization insensitive and are created by twisting standard optical fibers with cores that are not perfectly centered. Here, we present a new approach to single-helix chiral long-period gratings (CLPGs). The CLPG is created in a glassforming process in which two optical fibers are twisted together to form a helix in the signal fiber as the fibers pass through a miniature oven. "Dual-twist" CLPGs may be fabricated from any conventional or specialty fiber and provide reproducible spectra that may be tailored to specific applications.

After many years of expectations, Fiber To The Home (FTTH) has finally become a reality with a wide number of projects already running worldwide and growing. Optical fiber is inevitably taking more and more importance in our environment, but for many good reasons, the space we are truly willing or able to allocate to it remains limited. These installation constrainsts have turned into additional requirements that need to be addressed for both active and passive components. If exceptional bending performances obtained without degrading backward compatibilities is a pre-requisite to deployment success,1 other parameters also need to be carefully taken into account when designing the ideal candidate for use in confined environments. Among them, one can cite the bend loss homogeneity over length and bending directions, the resistance to high optical power under bending and the tolerance to modal noise. In this paper, we present the design and performances of a bend insensitive fiber optimized towards more space savings and miniaturization of components. In addition to exceptional bending performances - lower than 0.1 dB/turn over a 5 mm bending radius -, its design guarantees impressive homogeneity levels and enhanced safety margins for high power applications while being still resistant to modal noise. Successfull cleave- and splice-ability results are finally presented, making this fiber ideally suited for use in components, pigtails and patchcords.

We review recent developments for controlling supercontinuum spectral structure generated in photonic crystal fibers. Specifically, we describe two different approaches to generating supercontinuum with improved stability characteristics in the long pulse regime where the use of picosecond or nanosecond pulses is generally associated with large instabilities and decoherence. On the one hand, the use of dispersion-varying fibers results in efficient soliton compression and symmetric dispersive wave generation mechanism leading to near-uniform spectra. On the other hand, applying a modulation on the input pulse allows control of "optical rogue wave" fluctuations with significant stabilization of the long wavelength Raman solitons position.

Herein we report efficient random lasing in two powder samples containing rhodamine 6G (Rh6G) doped SiO₂ nanoparticles which are either directly dispersed within pure silica particles or embedded in a silica gel matrix which is subsequently ground. Basic properties of random lasing such as emission kinetics, emission spectrum, and stimulated emission threshold are investigated in both novel solid-state materials by real-time spectroscopy. The laser-like emission dynamics of the ground powder obtained out of a bulk silica gel containing 2% Rh6G-SiO₂ nanoparticles was accurately described by a light diffusive propagation model. The device behavior is close to a conventional ultrafast Q-switched laser, which is a very interesting feature aimed to further applications.

We propose and experimentally demonstrate a lasing-wavelength selective multiwavelength erbium-doped fiber laser based on a phase-shifted fiber Bragg grating incorporating a nonlinear optical circulating loop. In order to stabilize the multiwavelength output at room temperature, a nonlinear optical circulating loop based on a highly nonlinear photonic crystal fiber is employed. The multiwavelength operation can be realized by using a phase-shifted fiber Bragg grating. The number of resonant peaks can be determined by the number of phase-shifted segments. The high quality of the multiwavelength output with a high extinction ratio of ~45 dB and high output flatness of ~0.3 dB is realized. The switching performance to provide lasing-wavelength selectivity can be realized by the nonlinear polarization rotation based on the nonlinear optical loop mirror. The lasing wavelength can be switched individually by controlling the polarization controller and the cavity loss.

Mechanical stress can significantly influence the optical and mechanical properties of fibers. We present results of nondestructive measurements of thermal stress in rare-earth-doped optical fibers, which are related to the doping variations across the fiber cross section and the preparation conditions. The samples are preforms and fibers with a large ytterbium doped core that were prepared by an alternative glass forming process, which is capable to realize bigger ratios of core to cladding diameter than the MCVD-method. To the best of our knowledge, this is the first time measurements of stresses and birefringence were made on such active optical fibers and their preforms. The results are compared to previous results on ytterbium-doped samples fabricated by the MCVD-technology. From the resultant stress profile, we could calculate the stress induced index changes that are relevant for the light propagation in optical fibers, and discuss the reasons for the observed mechanical stress. In addition, we could evaluate the samples regarding their changes in thermal expansion coefficient induced by doping with one or more oxides in several concentrations and different ratios. We confirmed our earlier result that the active doping component ytterbium generates much higher stress than other common dopants like aluminum, phosphorus or boron.

In this paper, we compare two amplifier technologies, an ytterbium-doped fiber, and a semiconductor taper, regarding their suitability to amplify sub-100ps pulses. With both setups, we obtain amplification of the pulse energy by more than 10dB. However, suppression of self-lasing in the pulse intervals is critical, particularly in the case of the semiconductor amplifier which has a very short upper state lifetime. The seed pulses were generated by a gain-switched distributed feedback (DFB) laser at arbitrary repetition rates. They have widths of below 100ps FWHM, pulse energies of over 100pJ and a peak power of over 700mW. This makes them very suitable for optical amplification. With the fiber amplifier, the pulse form remained unchanged, while with the semiconductor amplifier, it broadened slightly. With both amplifiers, pulse peak powers of over 8W were obtained, which represents an amplification by more than 10dB.

Optical interferometry is a well established technique for high resolution displacement measurements. It is commonly used in the semiconductor industry as a sub-system of manufacturing and metrology tools. As the industry progresses, the tools continue to evolve, requiring the concomitant reduction of size and cost in sensors. Existing interferometric systems are bulky and therefore difficult to incorporate in equipment. Efforts are ongoing to miniaturize these systems but with optical components (beam splitters, detectors and lasers) still in the millimeter range, it is difficult to realize ultra compact systems. Thus, it is imperative to focus on development of micron scale components that would provide the necessary high spatial resolution in a compact format. The focus of this paper is on the development of a micron size optical component that combines multiple optical elements and can be integrated with VCSELs at the wafer level to yield a compact, low cost interferometric system. The design and development of this component containing the beam splitter and reference mirror will be presented including the investigation of suitable polymeric materials with desirable optical properties and appropriate fabrication techniques. Preliminary optical measurements of the integrated system will also be demonstrated. This approach has the potential to impact the next generation of micron scale interferometers as precise position/proximity sensors.

We develop a splicing device for photonic crystal fibers (PCFs) based on a double phase conjugate mirror (DPCM) using a novel photorefractive (PR) Sn₂P₂S₆:Sb 1.5% crystal. This PR splicer has many attractive characteristics including modal field compensation and the automatic reconfiguration of the optical path. Utilizing a DPCM as the splicer, our device can adapt to misalignments automatically since the incident beams continuously rewrite an index grating which formed in the crystal. By the implementation of the Sn₂P₂S₆:Sb crystal, the response time for the characteristic of dynamic reconfiguration is improved several-hundred-fold compared with conventional materials, e.g. BaTiO₃. We demonstrate that the high angular tolerance is provided using the DPCM with the Sn₂P₂S₆:Sb crystal. When the misalignment of the incident angle is from -7° to 8°, the increment of coupling loss is less than 0.6dB. This is several-ten-fold compared with the fusion splicing. We reveal the dependence of the coupling loss on the position of the incident beams and also the dependence of the energy flow on the propagation distance for the first time with the two-dimensional finite-difference beampropagation method. Using our numerical simulation tool, we can visually investigate the beam propagation property considering the influence of the fanning effect in the Sn₂P₂S₆ crystals.

We report the synthesis of polystyrene (PS) nanospheres through emulsion polymerization and fabrication of three dimensional PS photonic crystals (PhCs) with good crystalline quality using vertical deposition method. The reflection and transmission spectral characteristics of the PhCs fabricated from the pure and dye doped PS nanospheres are compared.

Slot waveguides are designed for silicon-based nonlinear optics. The critical processes in manufacturing such waveguides are lithography, etching and slot filling. Their effects on the properties of the waveguides are studied.

The high-index contrast between the silicon core and silica cladding enable low cost chip-scale demonstration of all-optical nonlinear functional devices at relatively low pump powers due to strong optical confinement the in silicon waveguides. So far, broad ranges of applications from Raman lasers to wavelength converters have been presented. This presentation will highlight the recent developments on ultrafast pulse shaping and pulse characterization techniques utilizing the strong nonlinear effects in silicon. In particular, pulse compression due to two photon absorption and dual wavelength lasing and ultrafast pulse characterization based on XPM FROG measurement will be highlighted.

The importance of polarization manipulation is increased as optical fiber systems evolve to higher data rates. Photonic integrated circuits should be insensitive to the state of polarization of the light emanating from fibers if they are to be used as detectors, add-drop mutiplexers or cross connects. Either all the integrated components have to be polarization independent or only one polarization direction should be used. For either method, a compact polarization converter is useful. A model is developed for the mode propagation in the waveguide of the slanted side polarization converter based on double hetero structures. The model is extended to include polarization dependent absorption and mismatch. Polarization converters on different double heterostructures (with and without quantum wells) have been designed and are realized by contact optical lithography. The performance of the realized converters is well described with the model.

We develop a tunable optical wavelength filter with PR (photorefractive) materials applied the external field for achieving higher sensitivity and efficiency. In the past, the diffraction efficiency of the PR tunable filters with transmission gratings has been much lower than other conventional wavelength filters, such as the array wavelength gratings filter, the thin film filter, and the fiber Bragg gratings filter. By applying the external field to PR materials, we can obtain the refractive index modulation depth of 13 times larger than that without applied field, specifically in lithium niobate with the acceptor density of ~10²² [1/m³] and the voltage of 10 [kV/cm]. Our PR tunable filter provides reconfigurable wavelength routing of the signal beam since the various diffraction gratings can be immediately induced and multiplexed by changing incident conditions of two coherent writing beams viewpoint in comparing experimental results to numerical simulations, and can be rewritten dynamically through the PR effect. These advantages allow us to achieve more flexible optical net work based on the wavelength division multiplexing technique. In this work, we calculate the relationship between the diffraction efficiency and the magnitude of the applied external field by solving coupled wave equations in the case of lithium niobate, respectively.

We discuss possible applications of (III,Mn)V ferromagnetic semiconductors as novel magneto-optical devices for optoelectronics. These materials systems possess several distinguishing characteristics that make them attractive candidates for such applications. Processing technology for III-V compound semiconductors is very well established and can be employed for these materials. Illumination with light can induce much stronger changes in their electronic, magnetic, and optoelectronic properties than in ferromagnetic metals. Furthermore, electric-field-tunable magnetization, by utilizing the strong spin-orbit coupling in these materials, may lead to entirely new functionalities unachievable with conventional magneto-optical materials. We present some CW magneto-optical Kerr effect spectroscopy results for (III,Mn)V samples and discuss their potential for magneto-optical device applications.

Miniaturized field-deployable spectrometers used for 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: a 3-30 nm passivation layer that enables micron-sized devices, large-scale integration and low-cost products; and a 50-65 nm amplification layer that offers high sensitivity with 1,000x amplification and zero avalanche access noise. We report preliminary tests on single pixels, validating the design target of >1,000 Ampere/Watt responsivity at the near infrared wavelength of 1550nm, which is 100 times more sensitive than InGaAs avalanche photodiodes, the most sensitive commercially available photo-detector in this 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.

High-energy physics experiments sometimes require exceptionally large areas of photo detection. In many of these cases, low noise and fast response make a photoelectric tube such as a photomultiplier the detector of choice. Hexagonal photomultipliers have been made for a number of years to meet these requirements. This paper describes the design and development of hexagonal image tubes to fulfill the need for improved spatial resolution combined with the ability to closely pack detectors over a large working area.

Time of flight laser range finding, scanning video imaging and deep space communications are three applications requiring very low noise optical receivers in order to achieve detection of fast and weak optical signal. Avalanche photodiode is the detector of choice for its high quantum efficiency, compact size and reduced electronics complexity. Optimal operating condition in terms of gain and temperature is the key to maximize the signal to noise ratio. This paper describes the model and the measured performance of a hybrid optical receiver using a TE cooled Silicon Avalanche Photodiode. Receiver performance in terms of responsivity and NEP will be presented as a function of temperature, signal power and APD Gain. A NEP of only 5fW/sqrt(Hz) has been obtained with a bandwidth of 200MHz in linear mode at a wavelength of 1060nm.

Epitaxial growth of p-type GaN-based UV photocathode by RF plasma assisted molecular beam epitaxy (MBE) on sapphire, fused silica, and alumina substrates was investigated. The electrical measurements indicted the growth of highly p-type GaN films as thin as 0.1 μm on c-plane sapphire with a thin AlN nucleation layer. Polycrystalline p-type GaN was obtained for growth on fused silica and alumina. Negative electron affinity (NEA) photocathodes were fabricated by cesium activation of the p-type GaN films in vacuum. Quantum efficiency for UV detection on different substrates was then characterized. To study the integration of UV photocathodes with MCPs, direct deposition of p-type GaN films on glass MCPs were done at low growth temperatures by MBE. The detection efficiency of polycrystalline p- GaN photocathodes in reflection mode was much less than the high quality p-type GaN films on sapphire, however, it was comparable to the detection efficiency of the latter measured in the semitransparent mode. This indicates the potential for fabrication of improved photocathodes with higher gain and better spatial and temporal resolutions.

The spectroscopic properties of Tb³⁺-doped borosilicate glasses are investigated to assess their potential as gain media in the 0.54 μm band. Analysis of the concentration and temperature dependences of the optical transitions from the ⁵D₄ level of Tb³⁺ is carried out. The emission lifetime of the ⁵D₄ level at 300 K is found to be 2.61 ± 0.03 ms, and almost invariant for Tb³⁺ concentrations less than 15 wt% (1.68×1021 ions/cm³). Judd-Ofelt analysis is used to calculate the emission transition probabilities from the ⁵D₄ level and the emission cross section at 300 K for the ⁵D₄ → ⁷F₅ transition was 8.1 × 10^-22 cm² at 541 nm. Temperature dependent non-radiative relaxation of the ⁵D₄ level is observed in samples with 5 and 20 wt% Tb³⁺. The quenching process of the ⁵D₄ level in the temperature range of 50 ~ 373 K is thought to be caused by a two-photon one-site resonant process, whereas it is dominated by a two-site non-resonant process at temperatures below 40 K. Our results indicate that Tb³⁺-doped borosilicate glass is a promising candidate for optical gain media in the green (0.54 μm) band

Ytterbium-doped high-power fiber lasers with high beam quality are promising devices for a variety of applications. Extreme power load and complicated fiber structures make great demands on material properties and preparation technology. Recently, with the further increase of output power, the problem of photodarkening has been identified as a critical issue for fiber laser devices. Detailed knowledge of optical properties of materials and fibers are needed for the successful development of laser fibers, aimed at increasing efficiency and power. It is well known that the properties of silica based rare earth doped fibers can be influenced and remarkably improved by the incorporation of further dopants. Here, the influence of combined aluminium-phosphorus codoping on the optical properties of Yb doped laser fibers was investigated. Preforms and fibers were prepared by MCVD and solution doping both with phosphorus and aluminium excess. The samples were characterized concerning the radial distribution of refractive index and dopant concentrations and the absorption and emission properties in the UV/VIS/NIR region. The observed spectral effects and active properties (laser efficiency, photodarkening) were correlated with changes in the fiber composition. It could be shown, that the combined doping leads to effects which deviate from a simple additivity and which can be beneficially utilized for the improvement of the laser fiber performance.

The terbium-doped yttrium aluminum garnet nanoparticles were synthesized by the modified Pechini method. In order to determination of the structure and the morphology of obtained nanocrystallites the XRD and TEM analysis were carried out. Next, to the ITO nanocrystallites-based slurries Tb:YAG nanoparticles were added. On the base of prepared colloidal suspension the layers were fabricated by the spin-coating method. The resistivity, an optical transmission and the luminescent properties of obtained layers were registered and compared. The influence of fabrication conditions on optical and electrical properties of obtained layers and their potential application will be discussed in this work.

The europium-doped tin dioxide nanopowders were synthesized using modified Pechini method. The samples with different Eu³⁺ concentration were sintered at different temperatures. In order to determination of structure and morphology of obtained powders X-ray diffraction (XRD) measurement and transmission electron microscopy (TEM) investigation were carried out. Photoluminescence of obtained powders were measured. Intensity of emission was compared using (blue ZnS:Ag) reference peak method. After that mixed powders were deposited on ITO-glass slide. The cathodoluminescence of obtained layers was also measured and compared. The properties and the potential application of obtained nanopowders will be discussed.

Nanometer sized crystals has attracted a lot of attention in the recent years because of the size dependent optical and electrical properties. Rare-earth ions in insulating hosts find use in a variety of applications, including phosphors for fluorescence lighting displays, monitors, lasers, fiber optic communication, biolabeling, bioimaging and solar-energy converters. Nanocrystals of trivalent holmium ion doped zirconium oxide crystals have been synthesized by using simple synthetic method. Spectroscopic studies of these nanocrystals have been conducted using visible and infrared laser excitation. Size distribution of the nanoparticles will also be discussed using atomic force microscope.

Nanocolloids of compounds containing fluorescent rare earth ions have recently attracted significant attention as agents for biolabeling, bioimaging, bio- and chemical sensing, and other applications. Erbium oxide nanocolloids have been prepared for the first time in water and gammabutyrolactone. Optical dynamic scatterometry and atomic force microscopy determined an average size (average mean height) of erbium oxide nanoparticles to be 10-11 nm. Prominent optical absorption peaks of the nanocolloids at 442.5 nm, 450.0 nm, 487.2 nm (strong), 492.0 nm, 523.0 nm (strong), 541.6 nm, 548.6 nm, 652.6 nm, and 665.7 nm (strong) can be attributed to erbium ions hosted within nanoparticles. Laser fluorescence spectroscopy of the nanocolloids was conducted using excitations with the lines of argon-ion laser (514 nm, 488 nm, 476 nm, and 458 nm) and 980-nm semiconductor laser. Strong green emission at 571 nm is more likely from transition between ⁴S_3/2 and ⁴I_15/2 levels and relatively weak red emissions from transition between ⁴I_9/2 and ⁴I_15/2 level of erbium was observed at excitation with visible laser radiation 488 nm and 476 nm. The reported nanocolloids thus showed to be good candidates for fluorescent biosensing applications and also as a new lasing filling medium in fiber lasers.