T. Palmisano

Design of Rare-Earth-Doped Microspheres

Two original computer codes for the design of rare-earth-doped dielectric microspheres have been ad hoc developed. The former code is based on a finite-difference time-domain algorithm, suitably extended to model the amplification of the whispering-gallery modes propagating into rare-earth-doped microspheres. It takes into account the wavelength dispersion of the microsphere refractive index and the polarization obtained via the density matrix model. The design of an Er3+-doped silica microsphere coupled with a tapered silica fiber is reported. The latter home-made computer code solves the rate equations and the power propagation equations in frequency domain. The results are in excellent agreement.

Optimization of pump absorption in MOF lasers via multi-long-period gratings: design strategies

Different strategies for designing optical couplers, optimized to enhance the pump absorption in the rare-earth-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 N(Yb)=5×10(25) ions/m(3), the slope efficiency S can be increased up to 20%, depending on the fiber length.

Improvement of the pump power coupling in double cladding photonic crystal fiber

An optical coupler constituted by a long-period grating (LPG) written into the single-mode core of a double- cladding photonic crystal fiber (DCPCF) is designed. The LPG allows an optimal power transfer from the inner cladding modes toward the fundamental mode guided in the core. The optical coupler feasibility is numerically demonstrated and its refinement is obtained via a large number of simulations. The calculations highlight that the 25% of the total input power is transferred from the inner cladding modes toward the fundamental mode guided into the core.

Near and medium infrared fiber optic lasers and applications

The demand for efficient optical active devices operating in the near and medium infrared wavelength ranges is originated from different needs. This wavelength band is of strong interest in a number of applications as remote sensing, sensors, optical communication, medical and military technology. The paper is a review on the NIR and MID-IR fiber NIR, also with reference to the host materials and the dopants employed for their construction, and the corresponding applications. An example of MID-IR fiber optic laser design is mentioned.

Design of high gain Er3+-Yb3+-Ce3+ co-doped ZELA fluoride glass waveguide amplifier

This paper reports an accurate design of Er3+-Yb3+-Ce3+ doped ZrF4-ErF3-LaF3-AlF3 (ZELA) fluoride glass channel amplifier operating in the third window of the telecommunication systems. By considering measured spectroscopic and optical parameters, we demonstrate the feasibility of a novel optical waveguide amplifier exhibiting high gain and low noise figure. The electromagnetic investigation has been carried-out by employing a full-vector Finite Element Method (FEM) solver. The mode electromagnetic field, calculated at different wavelengths, constitutes the input data for the home-made numerical code which solves both the power propagation and population rate equations via a Runge-Kutta based iterative algorithm. The dependence of the up-conversion coefficients on erbium concentration are taken into account. In the simulations, the core shape, the waveguide length, the input pump and signal powers, the erbium and the ytterbium concentration are varied with the aim to optimize the amplifier performance. The goal of achieving high gain with a short device length is demonstrated. In particular, the simulation results show that the waveguide amplifier exhibits an optimal internal gain value close to 22.5 dB and a noise figure of 4.1 dB for a waveguide amplifier 5.5 cm long, an erbium concentration of NEr=2.5×1026 ions/m3, ytterbium concentration NYb=2.4×1026 ions/m3, NCe=6×1026 ions/m3, an input pump power Pp=100 mW and an input signal power Ps=1 μW.

Erbium-doped chalcogenide fiber ring laser for mid-IR applications

In recent years, infrared light sources have attracted great attention for their application in remote sensing, sensors, optical communication, medical and military technology, and so on. Innovative erbium-doped microstructured optical fiber ring lasers (EDFRLs) have been proposed in order to increase the performance of the conventional fiber lasers, enabling a number of advantages such as smaller size, higher power, better beam quality. In a previous work, the authors proposed a design of a Fabry Perot laser made of a novel erbium-doped Ga5Ge20Sb10S65 chalcogenide glass, operating in the Mid-IR wavelength range. This work reports the design of a ring laser, made of the same glass, operating at the signal wavelength λs = 4600 nm and at the pump wavelength λp = 806 nm. The design and optimization has been performed in order to improve the laser performance. The numerical computer code, implemented ad-hoc to investigate the fiber ring laser, takes into account the rate equations of the 5-level erbium ion system, the pump and signal power propagation, the energy transfer of the up-conversion and cross-relaxation phenomena, the cavity losses and the coupling losses. The measured amplified spontaneous emission ASE power spectrum has been accurately sampled in 150 wavelength slots from λ1=4200 nm to λ2=4800 nm, to obtain more realistic simulations.

Near and medium infrared optical fiber lasers and emerging applications

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

Modeling of nano- and micro-spheres for sensing applications

The design of both active and passive micro/nano-sphere systems is performed by optimizing their sizes, spatial distribution and the other physical and geometrical parameters. In particular, rare earth doped spherical particles are designed in order to obtain distributed and highly efficient light sources for active sensors. The lasing characteristics of active silica glass microsphere are numerically simulated in the third band of optical fibre communication by means of a home made computer code. Finally, passive and active spherical nanoparticles, covered by a thin metallic shell, surrounded by different dielectric materials and arranged in different lattices are optimized for sensing applications.

Laser sources based on rare earth doped glasses: Recent strategies

Laser sources based on rare earth doped glasses are used in material processing, medical and surgical applications, remote sensing, spectroscopy, generation of ultrafast pulses, and so on. Fiber or planar waveguide laser sources are competitive with respect to other light sources, such as ion-doped crystal and bulk glass lasers, optical parametric oscillators, semiconductor and gas lasers for their high conversion efficiency, excellent beam quality, compactness of optical cavities, good heat dissipation capability. The paper illustrates a few recent strategies followed to obtain laser sources based on rare earth doped glasses, even with reference to the host materials and the dopants employed for their construction, and the corresponding applications. An example of NIR fiber optic laser fabrication is illustrated in detail.

Design of erbium doped microsphere lasers

The lasing characteristics of an erbium doped silica glass microsphere coupled to a tapered fiber are numerically investigated in the third band of the optical fiber communication. In the model, the electromagnetic field profile of the whispering gallery modes (WGMs) traveling in the microsphere is described by means of spherical Bessel functions for the radial dependence and spherical harmonics for the angular dependence, at both pump and signal wavelengths. Moreover, the microsphere laser operation has been simulated by taking into account the rare earth ion emission, via the rate equations, and the coupling with the tapered fiber. A number of simulations have been performed in order to demonstrate the feasibility of the active microspheres to be employed as distributed micro laser sources or to fabricate active microsensors.