This PDF file contains the front matter associated with SPIE Proceedings Volume 8621, including the Title Page, Copyright Information, Table of Contents, Introduction and Conference Committee listing.

PbSe quantum dots (QDs) were grown in high-refractive-index low-melting-temperature leadphosphate glass. QDs with various sizes ranging from 2 nm to 5.3 nm were grown by controlling the growth parameters, heat-treatment temperature and time. The corresponding room-temperature exciton absorption was tuned within the infrared region from 0.93 μm to 2.75 μm. Photoluminescence was measured for samples with absorption peaks above 0.95eV. Real time quantum dot growth was demonstrated by monitoring the evolution of exciton absorption with temperature and time duration. As a demonstration of the use of QDs in laser applications, the saturation fluence (F_sat) of one of the QDs was evaluated and found to be ~2.1 μJ/cm2 at 1.2 μm.

Bismuth is a half metal having anisotropic susceptibility and optical constants. Therefore, the crystal axis of bismuth particle can be oriented by magnetic torque under magnetic fields. Recently, bismuth nano-particles, which have spherical, plate-like and rod-like shapes, have been prepared by some chemical methods. Orientation of bismuth nanospheres in a viscous liquid was demonstrated by using in-situ observation system of x-ray diffraction under high magnetic field in this study. The anisotropic susceptibility determined from the orientation behavior was slightly smaller than that of the bulk bismuth crystal. We have successfully introduced oriented-bismuth nano-spheres into the transparent polymethyl metacrylate under high magnetic fields up to 8 T. The composite showed a difference in transmittance depending on the direction of propagation of light being parallel or perpendicular to the applied field, indicating an anisotropic nature of optical constants of the nano-particles. Transmission spectra, which were simulated on the nano-spheres oriented composite by rigorously coupled wave analysis (RCWA), indicated that the nano-sphere has larger anisotropy in optical constants than bulk bismuth.

In the recent twenty five years the technique of imaging atmospheric Cherenkov telescopes for ground-based very high energy gamma-ray astrophysics has emerged and rapidly established itself as a new powerful discipline in science. The next generation large instrument, known under the name Cherenkov Telescope Array, will soon move from the prototyping into the construction phase. Its sensitivity will be an order of magnitude higher than that of the currently leading instruments VERITAS, H.E.S.S. and MAGIC. Currently, the standard light sensors for IACTs are the classical photo multipliers. Since very recently photo multipliers with a peak quantum efficiency of 40% are becoming available. In addition, also the photo electron collection efficiency on the first dynode has been increased to ~95-98%, providing a photon detection efficiency that is almost as high as the quantum efficiency. SiPMs, also known as MPPC, GAPD, Micro-channel APD, are novel semiconductor light sensors that are rapidly maturing. Compared to photo multiplier tubes the currently best SiPM have comparable photon detection efficiency, better amplitude and time resolution, but much worse noise. Their parameters are steadily improving and sometime in the future they may become almost ideal light sensors, substituting classical photo multiplier tubes in many applications. Also in astrophysics they can find wide applications. In this report we will dwell on the potential and advantages of using SiPM for Cherenkov telescopes.

Preparation of high quality facets for low-loss coupling is a significant production issue for integrated photonics, usually requiring time consuming lapping and polishing. Recently, the development of precision dicing saws with diamond impregnated blades has allowed the achievement of optical grade surfaces in optical materials based on dicing alone. In this report we investigate the optimization dicing conditions to achieve optical quality surfaces in a silica-on-silicon planar substrate and show what can be achieved by correct selection of machining parameters.

In this article we present a new approach for implementation of computation algorithms to perform nonlinear signal processing with light on the surface of a photorefractive crystal and Bacteriorhodopsin thin film. Using the developed mathematical models for the photodynamics of these materials, we demonstrate a specific operation mode and a design procedure to obtain nonlinear response which can be used for implementation of high-performance photonic computers.

Nonlinear optical materials are important to extend the spectral coverage of existing lasers, mainly via frequency doubling and with optical parametric oscillators. The quality of the materials and components, e.g. in terms of residual absorption, is pivotal for the performance of the devices. The paper presents high-sensitivity absorption measurements of nonlinear optical materials. They were performed using a photoacoustic spectrometer which combines high sensitivity with broad spectral coverage. This allows one not only to quantify the level of residual absorption but also to assist in the characterization of the materials in terms of optically relevant impurities and imperfections. The spectrometer covers the wavelength range between 407 and 2600 nm using a pulsed optical parametric oscillator as excitation source. Pulse energies up to 100 mJ allow one to record absorption spectra with a sensitivity down to 10 ppm/cm. The paper presents spectra of lithium niobate and lithium triborate crystals which are important for highpower nonlinear optical applications. The results are discussed with respect to material impurities and the suitability of individual samples for frequency conversion.

Spectral and kinetic properties of Er,Ce:Y₃Al₅O₁₂ crystals with various concentrations of impurities are investigated under optical excitations at 445, 457, 532, 808 and 980 nm wavelengths. An essential contribution of Ce³⁺ sensitizer ions in the process of population inversion formation between the ⁴I_13/2 and ⁴I_15/2 levels of Er³⁺ ions in YAG matrix is revealed due to the fact that their dipole-allowed interconfigurational f-d transitions have intense absorption UV bands and there are effective channels of optical excitation energy nonradiative transfer to the Er³⁺ ions. As a result, significant increase in the optical excitation efficiency near 445 nm wavelength is achieved which is important precondition for generation realization near 1.5 μm.

There are two switching processes where observe in polymer-dispersed liquid crystals (PDLC) when pulse electric field applied: - Slow switching process with rise time hundreds microseconds; - Fast switching process with nanoseconds rise time. The result of research, design and testing ultra-fast PDLC optical gate is presented. The feasibility of 100 nsec rise time optical gate with 1 square inch crystal clear transmission (better than 1.54 dB) and attenuation in OFF state more than 26 dB (30.4 dB for two serial layers) for non-polarized light has been shown.

A novel simple optical pulse width modulation generator (OPWMG) based on injection-locking property of a single mode FP-LD (SMFP-LD) has been proposed and experimentally verified. The OPWMG consists of a SMFP-LD (which acts as comparator), an optical sinusoidal wave source (analog input), and a continuous optical beam (control signal). The power required for fully injection-locking the SMFP-LD acts as the referent power whereas the combination power of continuous optical beam and analog optical sinusoidal signals work as control signals for changing the duty cycle of the proposed OPWMG. The presence of only continuous optical beam is not sufficient to suppress the dominant mode of SMFP-LD with high ON/OFF contrast ratio; however, the application of additional sinusoidal wave of constant amplitude and frequency, the dominant mode of SMFP-LD can be suppressed for the certain time window. Since, injection-locking power is dependent with the combined power of input injected continuous beam and sinusoidal optical wave, the time window of injection-locking can be varied by changing input beam power which provides different duty cycle of 13% to 68% at the output. Current available schemes for generating PWM signals are in electrical domain, hence, they need to convert electrical signals into optical domain by using expensive O/E converters for application in optical control and signal processing. The proposed OPWMG scheme has several advantages, such as low cost, low power consumption (~0.5 mW) which can be used for various applications where the effect of EMI/EMR is considered as an important factor such as control circuit for high voltage converters in power plant and electrical vehicles.

Optical RAM has emerged as a promising solution for overcoming the “Memory Wall” of electronics, indicating the use of light in RAM architectures as the approach towards enabling ps-regime memory access times. Taking a step further towards exploiting the unique wavelength properties of optical signals, we reveal new architectural perspectives in optical RAM structures by introducing WDM principles in the storage area. To this end, we demonstrate a novel SOAbased multi-wavelength Access Gate for utilization in a 4x4 WDM optical RAM bank architecture. The proposed multiwavelength Access Gate can simultaneously control random access to a 4-bit optical word, exploiting Cross-Gain-Modulation (XGM) to process 8 Bit and Bit channels encoded in 8 different wavelengths. It also suggests simpler optical RAM row architectures, allowing for the effective sharing of one multi-wavelength Access Gate for each row, substituting the eight AGs in the case of conventional optical RAM architectures. The scheme is shown to support 10Gbit/s operation for the incoming 4-bit data streams, with a power consumption of 15mW/Gbit/s. All 8 wavelength channels demonstrate error-free operation with a power penalty lower than 3 dB for all channels, compared to Back-to-Back measurements. The proposed optical RAM architecture reveals that exploiting the WDM capabilities of optical components can lead to RAM bank implementations with smarter column/row encoders/decoders, increased circuit simplicity, reduced number of active elements and associated power consumption. Moreover, exploitation of the wavelength entity can release significant potential towards reconfigurable optical cache mapping schemes when using the wavelength dimension for memory addressing.

The remarkable properties (internal gain larger than 100 and close to unity excess noise factor) of Short Wave Infrared (SWIR) HgCdTe electron-initiated Avalanche Photodiodes (e-APDs) are put to good use to demanding applications, i.e. spectroscopy and LIDAR. Knowing the requirements of both situations, we have designed specific models based on highly sensitive single elements APDs and adapted proximity electronics. On one hand, we use the e-APDs low noise equivalent power (NEP) at 180K (few fW/Hz^1/2). We simultaneously designed a specific Transimpedance Amplifier (TIA) which allows us to take advantage of the low APD NEP. The combination of both elements along with a dedicated cryostat enables direct LIDAR detection at moderate bandwidth (BW = 20 MHz) without the need for long time averaging, which is crucial in far field (≥ 5 km) analysis. One the other hand, we have optimized a low-noise and low-frequency LN₂ cooled prototype operating with an external commercial amplifier. It allows us to observe the photoluminescence of Ge nanostructures in the range 1.5-2.5 μm with a significantly increased SNR along with a reduce pump laser power. The possibility to use these detectors in the photon counting limit will be discussed in light of our recent results. In parallel, we present preliminary time response measurements performed on SWIR APD suggesting that a higher GHz BW could be reached with this type of detector. This is however subjected to optical optimization at the moment.

We propose and experimentally demonstrate a new chemical molecule sensing scheme using multi-wavelength fiber laser based on inter-core interference in twin-core photonic crystal fiber. In our proposed multi-wavelength fiber laser, two separated cores are integrated in a single photonic crystal fiber and surrounded by air channels. The anti-symmetrical super-modes participate in inter-core interference, which leads to the formation of twin-core photonic crystal fiber-based wavelength-selective comb filter. Most of the evanescent waves are localized in the 13 air channels around the two integrated cores, where light-matter interaction takes in place. The presence of chemical molecules in the air channels of TC-PCF leads to perturbation of the inter-core effective index difference between the two propagating core modes and the associated lasing wavelength shift.

An experimental study of the characteristics of arc-induced long-period fiber gratings inscribed in the longer transition of asymmetric adiabatic tapers is presented. Compared to the inscription in non-tapered fibers, the grating inscription in the linear taper transition resulted in deeper notch bands, whose bandwidth and separation increased with the transition slope. Changes in external refractive index from 1 to 1.606 resulted in variations in the notch bandwidth and spectral position.

Glass ceramic activated by rare earth ions are nanocomposite systems that exhibit specific morphologic, structural and spectroscopic properties allowing to develop interesting new physical concepts, for instance the mechanism related to the transparency, as well as novel photonic devices based on the enhancement of the luminescence. At the state of art the fabrication techniques based on bottom-up and top-down approaches appear to be viable although a specific effort is required to achieve the necessary reliability and reproducibility of the preparation protocols. In particular, the dependence of the final product on the specific parent glass and on the employed synthesis still remain an important task of the research in material science. Glass-ceramic waveguides overcome some of the efficiency problems experienced with conventional waveguides. These two-phase materials are composed of nanocrystals embedded in an amorphous matrix. The respective volume fractions of the crystalline and amorphous phases determine the properties of the glass ceramic. They also represent a valid alternative to widely used glass hosts such as silica as an effective optical medium for light propagation and luminescence enhancement. Looking to application, the enhanced spectroscopic properties typical of glass ceramic in respect to those of the amorphous structures constitute an important point for the development of integrated optics devices, including optical amplifiers, monolithic waveguide laser, novel sensors, coating of spherical microresonators, and up and down converters for solar energy exploitation.

Ce:LYSO (Lu_1.90Y_0.1SiO_5:Ce) single crystals were prepared by the Czochralski technique. We report some effects of the X-ray irradiation on the shape of the emission spectra. For instance a large decrease of the longest wavelength emission (at about 500 nm) is observed with an increase of the light yield after one hour under X-ray irradiation. Electron paramagnetic resonance (EPR) evidences no change in the two cerium site occupancy along with the irradiation time. A mechanism taking into account the evolution of the oxygen vacancies as neighbors of Ce³⁺ ions is proposed.

Under 405 nm diode laser excitation Europium doped Lanthanum fluoride glows bright white and revealed numerous wavelengths in the blue, green and red regions of the electromagnetic spectrum. These lines were emitted from ⁵D_J (J=0, 1, 2 and 3) to ⁷F_J (J=0, 1, 2, 3, 4, 5, and 6) levels. For the same excitation conditions Europium doped Calcium fluoride glows white with abundant blue emission and some yellow light. These materials appear to be promising candidates for solid state white light sources. Emission characteristics are described in detail.

We report on SiO₂-Al₂O₃-La₂O₃ glasses – with and without Yb₂O₃ – suitable for nonlinear and fiber laser applications. We also present successful supercontinuum generation and fiber laser operation around 1060 nm in step-index fibers. We have optimized the glass compositions in terms of thermal and optical requirements for both a high La₂O₃ (24 mol%) and Yb₂O₃(6 mol%) concentration. The aluminum concentration was adjusted to about 21 mol% Al₂O₃ to increase the solubility of lanthanum and ytterbium in the glass beyond possible MCVD based techniques. The glasses have been characterized by dilatometrical methods to find transition temperatures from 860 to 880°C and thermal expansion coefficients between 4.1 and 7.0 × 10^-6 K^-1. Structured step index fibers with a SiO₂-Al₂O₃-La₂O₃ core and silica cladding have been realized showing a fiber loss minimum of about 500 dB/km at 1200 nm wavelength. The chromatic dispersion could be adjusted to shift the zero dispersion wavelength (ZDW) close to the pump wavelength of 1550 nm in a supercontinuum generation setup. First fiber laser experiments show an efficiency of about 41 % with a remarkably reduced photodarkening compared to MCVD based fibers.

High optical quality (high-Q) whispering-gallery mode (WGM) microresonators are key enablers for numerous highperformance photonic devices, including ultrasensitive molecular detectors and advanced light sources such as narrowlinewidth lasers and comb generators. For sensing applications, the unique characteristics of such WGM devices appear to be particularly relevant in the mid-IR (MIR) spectral region because of the stronger molecular absorption bands in this spectral region. However, most current WGM-based passive and active devices function in the near-IR (NIR) spectral region. We propose the development of reproducible high-Q WGM microresonators for the MIR by using low phonon energy glasses (such as fluorides, chalcogenides, and tellurides) along with an elegant and reproducible microsphere fabrication technique based on the use of novel state-of-the-art microheaters. In this paper, we first review the current state-of-the-art of WGM MIR microresonators and related optoelectronic devices, and then present recent results of our work on fabrication and characterization of high-Q WGM optical microresonators with several fluoride (ZBLAN, InF₃ and AlF₃) glasses. Intrinsic quality factors in excess of ten million have been measured in the NIR regime in the fluoridebased microspheres fabricated in our lab with the proposed -- highly reliable and reproducible – microheater fabrication method, and similar or better performances are expected from similar microspheres at MIR wavelengths between 2 to 5 microns. We next discuss potential applications of these microresonators, notably for low-threshold and narrowlinewidth MIR lasers and MIR comb applications.

Due to the non-linear effects in whispering gallery mode microresonators, low threshold microlaser development is possible. The lasing threshold is significantly lowered as high circulating optical intensities build up within the resonator, resulting from long photon lifetimes attributed to the ultra-high quality factor. With such characteristics in place, microresonators can operate as lasers even in complex media. We show cascaded Raman microlaser behavior in an undoped silica microsphere in air and HEPES buffer environments. The first emission peak is at around 800nm with a pump source of around 771nm. The lowest obtained threshold of the first emission line is 105μW in air and a higher threshold power of 760μW is required in buffer. Cascaded behavior of up to ten lasing peaks has been observed in air and up to two peaks were seen in buffer.

Many applications in various fields of science and engineering use steered optical beam systems. Currently, many methods utilize mirrors in order to steer the beam. However, this approach is an off-axis solution, which normally increases the total size of the system as well as its error and complexity. Other methods use a “Risely Prisms” based solution, which is on-axis solution, however it poses some difficulties from an engineering standpoint, and therefore isn't widely used. We present here a novel technique for steering a beam on its optical axis with a linear deflection response. We derived the formulation for the profile required of the refractive optical component necessary for preforming the beam steering. The functionality of the device was simulated analytically using Matlab, as well as using a ray-tracing software, Zemax, and showed agreement with the analytical model. An optical element was manufactured based on the proposed design and the device was tested. The results show agreement with our hypothesis. We also present some proposed geometries of the several other devices, all based on the same concept, which can be used for higher performance applications such as two-dimensional scanner, video rate scanner etc.

We review briefly the different applications of polygonal mirror (PM) scanning heads in biomedical imaging, with a focus on Optical Coherence Tomography (OCT). This overview of biomedical optical systems that employ PMs include: (i) TD (Time Domain) OCT setups, where PM may be utilized for generating the modulation function of the system without separate translation stages; (ii) FD (Fourier Domain) OCT delay line systems, with PM arrays; (iii) broadband laser sources scanned in frequency, for SS (Swept Source) OCT, with the PM placed in various optical configurations; (iv) OCM (Optical Coherence Microscopy) system with double PMs; (v) 2D PM plus galvanometer-based scanner (GS) for fast lateral scanning (not only in OCT, but also in confocal microscopy). We discuss SSs, for which the various PMbased setups used are compared, in their evolution - from on-axis to off-axis polygons - and in the race to obtain higher scan speeds to achieve real-time in vivo medical imaging. The parameters, advantages and drawbacks of these different configurations are pointed out. A necessary comparison is also made with the much faster Fabry-Perot (FP) based SSs. Our approach on PM-based broadband laser sources scanned in frequency, based on a simple off-axis polygon configuration, is also presented. Some of its characteristic mathematical functions are inferred and evaluated.

This paper reviews and extends the work done on photodarkening by our project consortium and present our latest results on bleaching and photodarkening mitigation in fiber lasers. We shows the need for a standard set-up to avoid underestimation of photodarkening equilibrium losses and we suggest photodarkening losses scale with the square of Yb doping level. Investigation on visible light emission suggest an interplay of visible light with the Yb excited level. Finally we present an extensive investigation of photobleaching, both as post-irradiation and as simultaneous bleaching. We show evidence photobleaching can effectively mitigate the impact of photodarkening on laser performance when highly-doped Al-silicate fibers are used.

We simulate the pulse compression around 1550 nm using one stage highly anomalous dispersive photonic crystal fibers, including silica-core photonic crystal fiber with a dispersion value of 600 ps/nm/km and air-core photonic bandgap fiber with a dispersion value of 100 ps/nm/km. A 1.64ps pulse with peak power of 500kW is compressed down to 0.136 ps with a compression factor of 12 by 4.3 m photonic bandgap fiber. Experimental results show that a 1.64 ps pulse is compressed down to 0.357 ps with a compression factor of 4.6 by 1.7 m photonic crystal fiber.

We present successful results of high mid-IR laser power transmission as well as MIL-SPEC environmental testing (thermal cycling and vibration testing) of ruggedized, IR-transmitting chalcogenide glass fiber cables. The cables tested included chalcogenide fiber cables with endfaces imprinted with anti-reflective “moth eye” surfaces, whereby the reflection loss is reduced from about 17% per end to less than 3%. The cables with these moth eye surfaces also show excellent laser damage resistance.

The elastic stability (buckling) condition for a short dual-coated optical-fiber experiencing mechanical and/or thermally induced compression is established based on the developed analytical (mathematical) predictive model. The problem is reduced to a situation when a cantilever beam of finite length is supported by a continuous elastic foundation and is subjected to a compressive force applied to the beam’s free end. Easy-to-use practical guidelines and a simple diagram are suggested for choosing the adequate length of the fiber and/or its flexural rigidity and/or the characteristics of the coating materials, so that the fiber remains elastically stable. The developed model can be used also in the design and reliability evaluations of composites, including nano-composites, and in flexible (large area) photonics when high-modulus and lowexpansion fibers are embedded into a high-modulus-and-low-expansion matrix and experience axial compression at low temperature conditions.

Supercontinuum (SC) generation from a highly nonlinear tellurite microstructured fiber with multi-ring holes was demonstrated by pumping with a 2 μm high power mode-locked fiber laser. The chromatic dispersion of the fiber was measured with a homemade white-light spectral interferometer on a wide wavelength range and matched very well with the theoretical calculation. The zero dispersion wavelength (ZDW) of the fiber was measured to be 1358 nm and calculated to be 1390 nm. Although the pumped wavelength was far away from ZDW, with flat dispersion profile of the fiber on the anomalous dispersion, the SC could be expanded from 650 nm to 2850 nm with launched pulse energy of several hundred picojoules. Simulations of SC generation were performed and showed fair agreement with the experimental results.

In this paper, Soliton self-frequency shift (SSFS) in ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is investigated based on Raman gain coefficients and generalized nonlinear SchrÖdinger equation. We have measured the Raman gain coefficient spectrum of a fluoride ZBLAN glass. The Raman response function and Raman fraction of ZBLAN fibers are obtained from the actual Raman gain spectrum. The enhanced SSFS in the ZBLAN fiber under investigation as compared to the silica fiber is mainly due to the combination of nonlinear coefficient and Raman response function enhancement. Therefore, ZBLAN fiber is promising materials for SSFS.

We demonstrate the square-pulse operation in a ring cavity with a 207 m single-mode tellurite fiber. The high nonlinearity and birefringence of the tellurite fiber play the key role during the square-pulse formation. The CW operation is obtained when pump power exceeds 80 mW. When the pump power is increased to 140 mW, the single pulse operation with the repetition rate of 689 kHz corresponding to the cavity fundamental frequency is initiated from the ASE noise by the nonlinear polarization rotation (NPR) process. Keeping the pump power at 140 mW and rotating one of the paddles of the polarization controller (PC) toward one direction in a small scale, the pulse number in one packet increases monotonically from 1 to 11. This process continues until the stable square pulse is formed at last. The stable square pulse has the FWHM of 118 ns and the repetition rate of 689 kHz. It is formed by the nonlinear polarization switching. In our cavity, the tellurite fiber is long enough to make the laser operate in the multibeat-length regime, which could lower the threshold for nonlinear polarization switching and clamp the peak power at a low level. This is advantageous for increasing the pulse width because the pulse duration is determined by the intra-cavity energy and the clamped peak power. When the linear phase delay bias in the cavity is set close to the polarization switching point, the third-order harmonic pulses and multiple packets are also observed under different pump levels.

We present an all-solid tellurite-phosphate photonic bandgap fiber (PBGF) with high-index rods in the cladding. The low-index background material is phosphate glass (PZNK) and the high-index rods are made of tellurite glass (TZLB). The all-solid tellurite-phosphate PBGF has three bandgaps and the first one is wide in frequency. It is easier to draw than the silicon PBGF due to the phosphate glass has lower fiber-drawing temperature. It can be widely used in the photoelectron field, compact nonlinear devices and devices which work in the mid-infrared range, such as wavelength filter, phase-locked high-power lasers, fiber sensors in the mid-infrared for gases detecting, etc.

Cesium iodide (CsI) and sodium iodide (NaI) are good scintillators due to their high luminescence efficiency. These alkali halides can be excited by ultra-violet or by ionizing radiation. In this study, CsI and its Na-doped films about 8 μm thick were deposited by thermal evaporation boat without heating substrates at high deposition rates of 30, 50, 70, 90, and 110 nm/sec, respectively. The as-deposited films were sequentially deposited a silicon dioxide film to protect from deliquesce. And, the films were also post-annealed in vacuum at 150, 200, 250, and 300 °C, respectively. We calculated the packing densities of the samples according to the measurements of Fourier transform infrared spectroscopy (FTIR) and observed the luminescence properties by photoluminescence (PL) system. The surfaces and cross sections of the films were investigated by scanning electron microscope (SEM). From the above measurements we can find the optimal deposition rate of 90 nm/sec and post-annealing temperature of 250 °C in vacuum for the asdeposited cesium iodide and its sodium-doped films.

The photodarkening resistivity of ytterbium doped alumosilicate fibers can be remarkably improved by cerium codoping. Here we report on systematical investigations of the influence of cerium on an optimized fiber design. Fibers with different ytterbium, aluminium and cerium contents have been prepared both under reducing and oxydizing conditions and characterized concerning refractive index, absorption and emission from UV to NIR. Typical spectral features in the UV and visible range have been analysed with respect to the ratio of Ce³⁺ / Ce⁴⁺. Photodarkening tests have been accomplished in order to correlate the power stability with the Ce content and valency state.

Recently, the high power fiber laser has attracted much attention and the laser power combiner is one of the key components for power scaling in the high power laser system. Up to now, several methods have been exploited to develop the combiner and among them the tapered fusion bundling method becomes one of the most popular and reliable technology. In the conventional tapered fusion bundling method, the input fibers were bundled with the honeycomb configuration then fused tapered and spliced to the output fiber. In the method, however, the fiber ports configuration was constrained to certain values such as 3×1, 7×1, 19×1, and 35×1 to satisfy the compactness and reliability in the bundling procedure. In this study, we suggest a novel double bundling method to make combiners with the large flexibility in the fiber port configuration. In making the (14-18)×1 combiners, seven input fibers in the honeycomb stacking configuration was fused bundled and a single layer of secondary 7-11 fibers were stacked outside of the bundle and subsequently tapered and spliced to a output fiber. As a result, (14-18)×1 laser power combiners were made using 105/125 μm input fibers (0.15 NA) and a 200/220 μm output fiber (0.46 NA). In the bundling procedures a LPG torch was used and process parameters such as the gas flow and the tapering length/speed/frequency were optimized. The power transmission efficiency of the combiner was larger than 93% in all ports at the handling power of 100 W.

The paper presents some of our advances in the study and development of optical choppers. The modulation functions we have studied for classical choppers are pointed out – for top-hat (constant intensity) light beam distributions. The eclipse choppers that, to the best of our knowledge we have introduced are also presented. We thus point out the differences between the profiles of light (laser) impulses produced by the classical devices (with rotating wheels with windows with linear edges) and the novel eclipse choppers – under patent (with windows with circular edges that produce for the circular-shaped section of the laser beam in the plane of the wheel a planetary eclipse-like effect – from which the name we have proposed for this type of device). The most convenient (from the technological and from the cost point of view) solution, with wheels with circular holes is also obtained. The advantages and the drawbacks of the various devices are discussed. Both a theoretical and an experimental approach are considered. The latter is done on a chopper module we have constructed, with prototype chopper wheels we have designed and manufactured. Throughout the study, top-hat laser beams are considered, as they are most used in laser manufacturing applications. The perspective of conducting the study on other light beams distributions (e.g., Gaussian) is also pointed out.

In this study, cw and pulsed 1532 laser excitation of the ⁴I_13/2 band of Er³⁺ was explored in the low phonon-energy hosts KPb₂Cl₅and KPb₂Br₅. Crystal growth along with upconversion and eye-safe emission (~ 1550 nm) studies were conducted on both samplesunder 140 mW of cw laser excitation. Excitation spectra and emission decay transients of the infrared (⁴I_9/2 →⁴I_15/2) and green upconversion (²H_11/2 + ⁴S_3/2 →⁴I_15/2) revealed that energy transfer upconversion (ETU) is the origin of the infrared and the green upconversion under 1532 nm excitation. Spectral emission measurements indicate that the infrared upconversion is dominant relative to the green upconversion in both Er: KPb₂Cl₅and Er: KPb₂Br₅ crystals.

Thermal-Lens (TL) for fluorescence quantum efficiency (η) characterizations in a new phosphate glass matrix doped with Nd³⁺ were performed. η studies were accomplish in function of Nd³⁺ concentrations (0.5-3 x 10²⁰ ions/cm³). In addition, fluorescence quenching was studied by measuring the concentration dependence of the fluorescence lifetime. The results obtained by TL and fluorescence lifetime techniques are in good agreement, and corroborate with the theory for an energy transfer process involving a pair of ions, in which the main process occurring is cross-relaxation (CR).

Virtually imaged phased arrays (VIPA) offer high dispersion compared to conventional gratings and have been proposed as buildings blocks for several photonic devices, including wavelength multipliers, chromatic dispersion compensators, waveformgenerators and pulse shapers. We introduce an elastomer-based tunable VIPA, providing an additional degree of freedom for these devices. In particular, we investigate its capability to implement reconfigurable optical interconnects. In a wavelength demultiplexing setup it allows for both compensation of misalignment as well as reconfiguration of a source wavelength to a target channel. It consists of an elastomer layer sandwiched between two structured silver coatings on a glass substrate forming the resonator cavity. Using Joule heating of the top silver layer a thermal expansion and a thermo-optic effect of the elastomer cavity is induced allowing for tuning the effective optical resonator cavity. We report a tuning span of one free angular range by a temperature increase of less than 10K induced by a power change in the low mW regime. Both resonance quality and tunability of the device are investigated.

Silicon photomultipliers with high photon detection efficiency in the 350 to 800 nm range and low dark count rate are currently being developed in a variety of geometry, microcell size and area in order to address the needs of the analytical, life science, medical imaging community as well as for various scientific and technological applications. This SiPM development platform is based on previous knowledge of low dark count avalanche photodiode operated in Geiger-mode found in the Excelitas single photon counting module. Low dark counts and low temperature sensitivity are especially important when tiling up SiPMs to form larger area detectors such as block detectors typically used in positron emission tomography. The latest developments include; 1. Optical trenches to suppress crosstalk which allowed to increase the operating voltage range from 5 to 10 V above breakdown, 2. Tailored parasitic capacitance to obtain single photon timing resolution close to 200 ps FWHM and 3. Improved PDE at shorter wavelengths by optimizing the entrance window. A corrected energy resolution of 12.0 % was typically obtained at 511 keV which, alongside the good timing resolution, makes this SiPM a perfect candidate for time-of-flight PET and other application requiring a timing resolution better than 200 ps.

The compositional dependences of glass formation, thermal properties and optical properties are investigated for TeO₂-ZnO-Na₂O-P₂O₅ system for hybrid microstructured optical fibers. The refractive indexes at 1.55 μm and glass transition temperature vary in a wide range from 1.513 to 2.036 and from 265°C to 376°C by controlling of the TeO₂/P₂O₅ and ZnO/Na₂O content, respectively. These properties endow tellurite-phosphate glasses with large freedom in the hybrid microstructured optical fiber design. The structures of glasses are investigated by Raman spectra to understand the structural dependence on composition. Using the present glasses, some microstructured optical hybrid fibers with particular dispersion profiles are designed and demonstrated.

Two different shaped ZnO nanorods were grown on ZnO buffered Al₂O₃ substrate by laser interference lithography and hydrothermal method. The light waveguide within ZnO nano rod and photonic crystal effects in arrayed ZnO nanorods was calculated by 3D-finite dimension time domain(3D-FDTD) programs. The ZnO photonic crystal effect and number of modes of ZnO nanorod was governed by arrangement and shape of ZnO nanorod, respectively.

Quantum efficiencies of Er³⁺-doped silicate, phosphate, tellurite and fluoride glasses have been examined under simulated sunlight excitation. The quantum efficiency of the whole emission bands was obtained as about 75 % for fluoride glass and about 2 % for silicate glass. The maximum quantum efficiency of the emission band at 1530 nm was about 35 % for fluoride glass and about 17 % for silicate glass. The product of the stimulated emission cross-section and the emission lifetime σ_stτ_f was about 46×10^-24 cm² sec for fluoride glass and about 54×10^-24 cm for silicate glass. These values are about 2–4 times larger than that of Nd-doped glasses.

Silicon avalanche photodiodes (APDs) fabricated through a deep diffusion process underwent a modified surface treatment in an attempt to improve their response in the ultraviolet region of the optical spectrum. After adjusting the doping profile in the near-surface region of the detectors, APDs were fabricated and tested at several wavelengths from ultraviolet to the near-infrared. At the target wavelength of 355 nm, the detector bandwidth was increased by a factor of 20 over devices fabricated without the modified surface treatment. Modest improvements in the internal quantum efficiency were also measured. Most importantly, the modified detectors maintained the high gain and low noise performance specifications that are hallmarks of traditional deep diffusion APDs.

Metallic nanostructures upon resonant excitation can enhance the local electric field, which could be increased, if these nanostructures are embedded in a gain medium. In this sense, we propose a gain medium as a candidate for the development of nanowaveguide amplifier based on Er³⁺-doped tellurite glass with embedded silver nanoparticles (NPs). Those glasses are characteristic for their amplifying response in the telecommunication window, and when we embedded metallic NPs modified the crystalline potential surrounding to the Er³⁺ ions, due to an electric coupling between NP (received/emitter) and Er³⁺ ion (emitter) enhancement luminescence intensity from the ⁴I_13/2→⁴I_15/2 transition radiative of the Er³⁺ ions. Besides, the presence these NPs changes the refraction index these glass modifying the complex parameter β(n_eff) increasing the polarizability of the samples f(Ɛ_d). Therefore, a gain medium – Er³⁺ ions (amplification function in the telecommunication band) with silver NPs (luminescence enhancement) – can increment the propagation length of light into nanowaveguide.

High crystalline quality erbium-doped zirconium oxide films were deposited on Si(100) by electron beam evaporation in high vacuum. Characteristics of light emission in the telecommunication window from erbium oxide crystal zirconium oxide films were investigated before and after furnace annealing in oxygen atmosphere. The luminescence intensity of the erbium-doped thin film after annealing at 900 °C was 18 times higher than those before thermal annealing. Also, it was observed a decrease in the intensity of luminescence and the ⁴I_13/2 lifetime with the increase of the erbium concentration, which was analyzed via energy transfer - quenching. The structure environment of the erbium ion in the thin film before and after annealing has been studied by X-ray diffraction. The surface morphology of the films as a function of the annealing temperature and atmosphere showed a significant change.

To realize the online, rapid distinguishing of different petrol in transportation pipelines, a method based on fiber-optic surface plasmon resonance (FO-SPR) sensor is proposed. The calculation and simulation of FO-SPR end-reflection structure were carried out through fiber theoretical model and SPR principle. The impact of different parameters on sensor performance was analyzed. According to the optimized structure parameters, the FO-SPR sensor was manufactured. A wavelength modulation optical measurement system with FO-SPR sensor was established. Sample petrol of 90#, 93# and 97# and their mixture were measured. Different types of petrol were distinguished through the changes of the resonance wavelength. The experiment results showed that the measurement method could distinguish different petrol and had a good degree of distinction and repeatability. It lays the foundation for the identification of mixed product oil in transportation pipelines.

Though soft glass such as tellurite or chalcogenide glass is transparent in the range of 3-6 μm, fiber made of it is difficult to generate supercontinuum (SC) to that range because of the high loss, the wavelength limit of pump source, and the challenges in light-coupling. To circumvent these problems, we developed SC light source by using tellurite bulk glass through filamentation. For this scheme, the optical path length in the glass is very short due to the adopted high pump power, so the negative influence of material loss is reduced greatly. The light-coupling is straightforward, and the coupling efficiency is high. The bulk glass for SC generation is cheap, and can be fabricated easily. We adopted a pump wavelength of 1600 nm which is comparatively long. Such a long pump wavelength ensures a large energy ratio of the glass’s bandgap to the incident photon, so the disadvantage of small bandgap of tellurite glass is reduced, and the twophoton absorption is avoided as well. We have shown that under suitable pump condition, the SC generation by filamentation can cover from visible to 6 μm. It is the broadest SC generation by tellurite (including glass and fiber). For the suitable pump condition, the glass was free of optical breakdown. If the interface reflections were deducted, the SC conversion efficiency was 87%. The SC conversion efficiency was stable. To the best of our knowledge, this is the first report on filamentation in tellurite glass which has a comparatively small bandgap.

We present the modified scalar coupled mode analysis for an array of N diffused channel waveguides. The study simulates the lateral evanescent field coupling in the Graded Index Multi-Waveguide System. In a two-step procedure, the propagation characteristics of individual waveguides are obtained first by the completely analytical, closed form expressions obtained from the variational method. Consequent upon obtaining the individual waveguide characteristics, the complete scalar coupled mode theory has been developed that includes the non-orthogonality of the individual waveguide modes for strongly coupled waveguides. The coupled mode equations are solved to obtain the supermodes corresponding to the coupled waveguides configuration. Further to this, power exchange in the graded index Multi- Waveguide systems has been studied. Complete power transfer between the outside guides of the symmetric three waveguide graded index coupler is reported when the condition of equispaced effective indices is met.

Thermal conductivity values of laser material Yb³⁺:CaGdAlO₄ (CALGO) with various doping rate in Yb³⁺ were measured experimentally and compared to predictive values obtained by modelling. The observed variation of the thermal conductivity with the Yb³⁺ content could be explained by changing the ratio of site substitution Gd³⁺/Ca²⁺ by Yb³⁺. The influence of velocity sound and interionic distance values on thermal conductivity was also studied. Finally, laser results obtained with a 2%Yb:CALGO thin-disk were presented, strengthening the potential of Yb:CALGO for high power laser and ultra-short pulses generation.

The optical properties of zinc (hydr)oxide and the composites of zinc (hydr)oxide with 2% and 5% graphite oxide were investigated by three spectroscopic techniques: absorption, fluorescence and photocurrent techniques. The obtained energy gaps (from 2.85 eV to 2.95 eV) of the composites were smaller than that for zinc oxide (~3.2 eV) and zinc (hydr)oxide (~3.00 eV). The band gap narrowing of the composite materials is due to presence of defects, less confinement, and larger particles. The bonds between zinc (hydr)oxide lattice and the carbon of graphene phase also contribute to this phenomenon.