In recent years, the development of photonic crystal fibers has allowed novel opportunities for enhancing optical amplifier characteristics. In this field, accurate numerical modeling is a significant need to predict the device behavior. Conventional approaches perform this task by using methods which could yield solutions characterized by divergent or unstably convergent algorithms. Global optimization methods can be considered as efficient tools to face this problem. In this paper, the application of particle swarm optimization to perform the design and characterization of photonic crystal fiber amplifiers is proposed. The employment of this technique shows different attractive features. In particular, solutions are found quickly and the implementation of the algorithm does not require complicated evolutionary operators. Numerical results show the effectiveness of the approach for both the design and characterization of a fiber amplifier. In fact, if considered as a design tool, the obtained numerical results are in good accordance with respect to the ones yielded by a conventional approach. If considered as a characterization tool, the algorithm performs a forecasting, allowing to determine parameters, such as homogeneous upconversion coefficients, whose computation could present difficulties when it is obtained via direct or indirect measurements.

In this paper, an antenna array is designed in order to transform the thermal energy, provided by the Sun and re-emitted from the Earth, in electricity. The proposed antenna array is constituted by four square spirals of gold printed on a low cost dielectric substrate. A microstrip line, embedded into the substrate, is used to feed the array and to collect the thermal radiation. The dispersive behavior of gold at infrared frequencies has been taken into account through the LorentzeDrude model. Simulations have been conducted in order to investigate the behavior of the antenna array illuminated by a circularly polarized plane wave with an amplitude chosen according to the StefaneBoltzmann radiation law. An output current of about 3.8 mA has been simulated at 28.3 THz, i.e. at the frequency of the Earth emitted radiation. Moreover, these infrared antennas could be coupled with other components to obtain direct rectification of infrared radiation. As a consequence, these structures further optimized could be a promising alternative to the conventional photovoltaic solar cells.

Four different high power ytterbium doped fiber lasers are designed and compared via a home-made computer code. Their effective mode areas and beam qualities are numerically evaluated. A novel aperiodic fiber microstructure, very promising in order to construct high power and single mode lasers, has been identified.

In the fields of electromagnetic interference and electromagnetic compatibility, it is important to measure the strength of the electric field originating from electric devices. Knowledge of the antenna factor of a receiving antenna is necessary. In this paper, we discuss the antenna impedance method as a new calibration method measuring the free-space antenna factor. The experimental measurements are compared with both the standard field method and the data provided by the manufacturer of biconical, log-periodic and horn antennas. A good agreement with the technical regulation ANSI C63.5.

In this review paper some recent advances on optical fiber sensors are reported. In particular, fiber Bragg grating (FBG), long period gratings (LPGs), evanescent field and hollow core optical fiber sensors are mentioned. Examples of recent optical fiber sensors for the measurement of strain, temperature, displacement, air flow, pressure, liquid-level, magnetic field, and the determination of methadone, hydrocarbons, ethanol, and sucrose are briefly described.

Numerical results obtained by the authors via theoretical models, implemented in computer codes developed for designing lasers and optical amplifiers based on rare-earth doped glasses, are illustrated. Different photonic structures are investigated. As an example, by an accurate design of a cascade of multiple long-period gratings (MLPGs) inscribed in the fiber core, the pump absorption enhancement and the laser efficiency increasing are demonstrated. Further results pertaining to multicore fiber (MCF) configuration and rare-earth doped microspheres are reported. Moreover, global search methods, as the genetic algorithms (GA) and the particle swarm optimization ones (PSO), for the complete design and characterization of lasers and amplifiers are recalled.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Microspheres of rare-earth-doped chalcogenide glass coupled to mid-IR amplifiers and lasers of tapered fibers may serve as efficient biomedical sensing devices.

A novel multicore ytterbium doped fiber laser is designed, with the target of maximizing both the effective mode area and the beam quality, by means of a complete home-made computer code. It can be employed to construct high power and Quasi-Gaussian beam lasers. The novel laser configuration exploits a single mode multicore fiber and does not need Talbot cavity or other in-phase mode selection mechanisms. This is an innovative solution, because to the best of our knowledge, for the first time, we have designed a truly single-mode multicore fiber laser. For comparison we have optimized two other laser configurations which are well known in literature, both employing a multimode multicore fiber and a Talbot cavity as a feedback for the in-phase supermode selection. All three multicore fibers, constituted by the same glass, are doped with the same ytterbium ion concentration and pumped with the same input power. Multimodal fiber lasers exhibit lower beam quality, i.e. a higher beam quality factor M2, with respect to the single mode one, even if suitable Talbot cavities are designed, but they are very competitive when a more compact laser cavity is required for the same output power. The novel single mode nineteen core laser exhibits a simulated effective mode area Aeff = 703 lm2 and a beam quality factor M2 = 1.05, showing better characteristics than the other two lasers

A mid-IR amplifier consisting of a tapered chalcogenide fiber coupled to an Er3þ-doped chalcogenide microsphere has been optimized via a particle swarm optimization (PSO) approach. More precisely, a dedicated three-dimensional numerical model, based on the coupled mode theory and solving the rate equations, has been integrated with the PSO procedure. The rate equations have included the main transitions among the erbium energy levels, the amplified spontaneous emission, and the most important secondary transitions pertaining to the ion-ion interactions. The PSO has allowed the optimal choice of the microsphere and fiber radius, taper angle, and fiber-microsphere gap in order to maximize the amplifier gain. The taper angle and the fiber-microsphere gap have been optimized to efficiently inject into the microsphere both the pump and the signal beams and to improve their spatial overlapping with the rare-earth-doped region. The employment of the PSO approach shows different attractive features, especially when many parameters have to be optimized. The numerical results demonstrate the effectiveness of the proposed approach for the design of amplifying systems. The PSO-based optimization approach has allowed the design of a microsphere-based amplifying system more efficient than a similar device designed by using a deterministic optimization method. In fact, the amplifier designed via the PSO exhibits a simulated gain G ¼ 33.7 dB, which is higher than the gain G ¼ 6.9 dB of the amplifier designed via the deterministic method

A mid-IR lasing system based on a tapered fiber coupled to an Er3þ-doped microsphere has been modeled and numerically investigated. In order to design and optimize the device performance, a dedicated 3-D numerical code exploiting the coupled mode theory and the rate equations model has been developed. The main energy level transitions among the Er3þ ions, the most relevant secondary ion–ion interactions, the amplified spontaneous emission, and the fiber-microsphere coupling phenomena have been taken into account. In order to optimize the lasing performance, several parametric simulations have been carried out. The obtained numerical results show that a laser threshold of about 55m Wand an output power of about 17.8 dBm can be obtained by using small microspheres.

A dedicated 3D numerical model based on coupled mode theory and solving the rate equations has been developed to analyse, design and optimize an optical amplifier obtained by using a tapered fiber and a Er3+-doped chalcogenide microsphere. The simulation model takes into account the main transitions among the erbium energy levels, the amplified spontaneous emission and the most important secondary transitions pertaining to the ion-ion interactions. The taper angle of the optical fiber and the fiber-microsphere gap have been designed to efficiently inject into the microsphere both the pump and the signal beams and to improve their spatial overlapping with the rare earth doped region. In order to reduce the computational time, a detailed investigation of the amplifier performance has been carried out by changing the number of sectors in which the doped area is partitioned. The simulation results highlight that this scheme could be useful to develop high efficiency and compact mid-infrared amplifiers. (C)2012 Optical Society of America

We present an approach coupling a limited experimental number of tests with numerical simulations regarding the design of radiation-hardened (RH) rare earth (RE)-doped fiber amplifiers. Radiation tests are done on RE-doped fiber samples in order to measure and assess the values of the principal input parameters requested by the simulation tool based on particle swarm optimization (PSO) approach. The proposed simulation procedure is validated by comparing the calculation results with the measured degradations of two amplifiers made with standard and RH RE-doped optical fibers, respectively. After validation, the numerical code is used to theoretically investigate the influence of some amplifier design parameters on its sensitivity to radiations. Simulations show that the RE-doped fiber length used in the amplifier needs to be adjusted to optimize the amplifier performance over the whole space mission profile rather than to obtain the maximal amplification efficiency before its integration in the harsh environment. By combining this coupled approach with the newly-developed RHRE-doped fibers, fiber-based amplifiers nearly insensitive to space environment may be designed in the future.

In this paper, the feasibility of Substrate Integrated Waveguide (SIW) couplers, fabricated using single-layer TACONIC RF-35 dielectric substrate is investigated. The couplers have been produced employing a standard PCB process. The choice of the TACONIC RF-35 substrate as alternative to other conventional materials is motivated by its lower cost and high dielectric constant, allowing the reduction of the device size. The coupler requirements are 90-degree phase shift between the output and the coupled ports and frequency bandwidth from about 10.5 GHz to 12.5 GHz. The design and optimization of the couplers have been performed by using the software CST Microwave Studio°c . Eight di®erent coupler con¯gurations have been designed and compared. The better three couplers have been fabricated and characterized. The proposed SIW directional couplers could be integrated within more complex planar circuits or utilized as stand-alone devices, because of their compact size. They exhibit good performance and could be employed in communication applications as broadcast signal distribution and as key elements for the construction of other microwave devices and systems.

In this paper, the optimization of the design of rare earth-doped cladding-pumped fiber amplifiers is investigated to improve their performance with respect to the constraints associated with space missions. This work is carried out by means of a computer code based on particle swarm optimization (PSO) and rate equation model. We consider a fiber that is radiation tolerant at the space dose levels, and we characterize the radiation response of the amplifier based on it. By simulations, we study how the design of the radiation-tolerant double-cladding Er3+/Yb3+-codoped fiber amplifiers (EYDFAs) can improve the global system response in space. The rate equations model includes the first and secondary energy transfer between Yb3+ and Er3+, the amplified spontaneous emission and the most relevant upconversion and cross relaxation mechanism among the Er3+ ions. The obtained results highlight that the developed PSO algorithm is an efficient and reliable tool to perform the recovering of the most relevant spectroscopic parameters and the optimum design of this kind of devices. These results demonstrated that the performance of high power optical amplifiers can be optimized through such a coupled approach, opening the way for the design of radiation-hardened devices for the most challenging future space missions.

Different strategies for designing optical couplers, optimized to enhance the pump absorption in the rareearth- doped core of microstructured fiber lasers, are illustrated. Three kinds/configurations of optical couplers have been designed and compared as examples of the different design strategies which can be followed. Their effectiveness to enhance the performance of an ytterbium-doped, double cladding, microstructured optical fiber laser has been accurately simulated. They consist of a suitable cascade of multiple long-period gratings (MLPGs) inscribed in the fiber core region. The characteristics of the MLPG couplers have been simulated via a homemade computer code based on both rate equations and an extended coupled mode theory. The proposed MLPG couplers seem particularly useful in the case of low rare-earth concentration but, even for a middle-high ytterbium concentration, as NYb 5 × 1025 ions∕m3, the slope efficiency S can be increased up to 20%, depending on the fiber length.

In this Letter, a method for recovering homogeneous upconversion coefficients (HUCs) in Er3þ-doped glasses and erbium-activated devices is illustrated. It is based on a particle swarm optimization (PSO) approach. The HUCs are calculated on the basis of known values of optical gain evaluated in different pumping conditions. The obtained numerical results proof that the proposed technique provides solutions that are very close to the expected values. Therefore the method constitutes a tool for the design and optimization of efficient rare-earth doped lasers and optical amplifiers. This approach can be considered a feasible and valid alternative method in the field of material science and optical engineering for determining HUCs and avoiding the employment of expensive equipment for the measurement of ion–ion interaction parameters.

The design and characterization of a single-layer wideband substrate integrated waveguide 3-dB standalone directional coupler are described. The device exhibits a bandwidth of 2 GHz, ranging from 10.7 to 12.7 GHz, and both return loss and isolation better than 15 dB. The coupler has been built using a TACONIC RF-35 A2 substrate. A very good agreement between simulations and experimental results is obtained