Cladding Geometry Research Articles

Optimal cavity design for high-radiance, double-clad, Yb3+-doped fiber lasers

An analytical model for optimal cavity determination in Yb3+-doped double clad fiber lasers (YDFL) in free running configuration is presented. The proposed model is based on laser cavity design parameters such as pump and signal wavelengths, emission and absorption cross sections, core diameter and doping concentration. It derives the optimal cavity for maximum conversion efficiency, considering both counter propagating and co-propagating amplified spontaneous emission in the core, along with boundary conditions at the fiber facets. Results show that the model could determine an optical cavity length for Yb3+-doped fibers 10,000ppm doping concentrations, 1–100m fiber length range, core diameters between 1 and 25μm, for different inner cladding geometries. The aim is to perform exact determination of important cavity parameters for designing efficient, diffraction limited, high-radiance optical fiber laser devices with emphasis on optimal cavity length.

Cylindrical thermal concentrator：theory, simulation, and implement

As a kind of ultra-efficient thermal energy harvesting cell, thermal concentrator has recently attracted great attention from researchers. An analytical expression which describes the temperature distribution in the concentrator is deduced from the heat conduction equation and coordinate transformation relations. The expression is validated by numerical experiments based on COMSOL. Influence of the anisotropy due to cladding and device geometry on the performance of the thermal concentrator is analyzed. It is demonstrated that the greater the anisotropy, the better the thermal concentration effect. Besides, increasing the aspect ratio between the cladding and the core radius also gives rise to a better performance. Based on the temperature distribution relations between the core and the background region, we further explore a method to practically realize such a thermal concentrator by using naturally available materials. It is suggested that different levels of thermal concentration can be achieved by arranging alternately two isotropic conductivities along the azimuth direction and tuning their thermal localizations respectively.

High slope efficiency and high refractive index change in direct-written Yb-doped waveguide lasers with depressed claddings

We report the first Yb:ZBLAN and Yb:IOG10 waveguide lasers fabricated by the fs-laser direct-writing technique. Pulses from a Titanium-Sapphire laser oscillator with 5.1 MHz repetition rate were utilized to generate negative refractive index modifications in both glasses. Multiple modifications were aligned in a depressed cladding geometry to create a waveguide. For Yb:ZBLAN we demonstrate high laser slope efficiency of 84% with a maximum output power of 170 mW. By using Yb:IOG10 a laser performance of 25% slope efficiency and 72 mW output power was achieved and we measured a remarkably high refractive index change exceeding Δn = 2.3 × 10(-2).

Beam shaping of laser diode radiation by waveguides with arbitrary cladding geometry written with fs-laser radiation

Waveguides with arbitrary cross sections are written in the volume of Al(2)O(3)-crystals using tightly focused femtosecond laser radiation. Utilizing a scanning system with large numerical aperture, complex cladding geometries are realized with a precision around 0.5 µm and a scanning speed up to 100 mm/s. Individual beam and mode shaping of laser diode radiation is demonstrated by varying the design of the waveguide cladding. The influence of the writing parameters on the waveguide properties are investigated resulting in a numerical aperture of the waveguides in the range of 0.1. This direct laser writing technique enables optical devices which could possibly replace bulky beam shaping setups with an integrated solution.

Directional Bend Sensing With a CO$_{2}$-Laser-Inscribed Long Period Grating in a Photonic Crystal Fiber

In this paper, we present a directional bend sensor based on a long period grating (LPG) formed by introducing periodic grooves along one side of a photonic crystal fiber (PCF) with a focused CO2 laser beam. A bend sensitivity of 2.26 nm/m-1 within a range of - 5 ~ + 5 m-1 is experimentally demonstrated. Numerical simulation suggests that the directional response is the result of asymmetric cladding geometry resulted from collapse and/or deformation of air holes and asymmetric material-index modulation caused by one-sided illumination of the CO2 laser beam. The sensitivity could be further enhanced by increasing the area of the air-silica photonic crystal cladding and optimizing the size of individual air holes. The easy fabrication process and good linear response of the proposed sensor make it a suitable candidate for structural shape sensing in harsh environments.

Parametric Development of Problem Descriptions

This paper addresses the development of parametric models in contemporary architectural practice. A parametric model can be regarded as a representation of a solution space and in order to structure this, a description of the problem is required. Architectural design tasks are typically ill structured, the goals may not be defined and the means unknown. Moving from an incomplete problem description to a functional parametric model is a difficult task. In this paper the aim is to demonstrate that through a combination of knowledge acquisition and capture a parametric model can develop from an incomplete problem description. This demonstration draws on existing strands of design theory which are then used to outline a theoretical framework. This framework is then used to examine a case study of a live project and practical examples of the described theory in action are given. The practical observations are the result of a case study involving the author as a participant and observer working with Populous to develop a cladding geometry solution for Lansdowne Road Stadium in Dublin (now know as the AVIVA STADIUM).

Knowledge Acquisition in Parametric Model Development

This paper addresses the development of parametric models in contemporary architectural practice. A parametric model can be regarded as a representation of a solution space and in order to structure this, a description of the problem is required. Architectural design tasks are typically ill structured, the goals may not be defined and the means unknown. Moving from an incomplete problem description to a functional parametric model is a difficult task. This paper aims to demonstrate that through a combination of knowledge acquisition and capture a parametric model can develop from an incomplete problem description. This demonstration draws on existing strands of design theory which are then used to outline a theoretical framework. This framework is then used to examine a case study of a live project and practical examples of the described theory in action are given. The practical observations are the result of a case study involving the author as a participant and observer working with HOK Sport to develop a cladding geometry solution for Lansdowne Road Stadium in Dublin.

Large-core single-mode channel waveguide based on geometrically shaped leaky cladding

We propose a leaky channel waveguide structure for large-mode-area single-mode operation. The proposed structure is characterized by a uniform rectangular core and a specially designed cladding, through which all the confined modes are leaky. Single-mode operation is ensured by choosing the waveguide parameters properly so that the differential leakage loss between the first two modes is sufficiently high. A general power-law cladding geometry profile is considered, which is solved by the effective-index method in conjunction with the transfer-matrix-method to obtain the effective indices and leakage losses of the modes. We show that, with a suitable choice of cladding parameters, the waveguide can demonstrate extended single-mode operation in the wavelength range 750–1600 nm with a core area as large as 100 μm2. Such a large confinement area for mode propagation can effectively suppress nonlinear optical effects. The waveguide is expected to find applications in the design of high-power lasers and amplifiers.

Single-Polarization Single-Mode Photonic Band Gap Fiber

We studied the polarization properties of four photonic band gap fibers with elliptical core and different cladding geometries. To do so we relied on a fully vectorial calculation method, which uses a hybrid edge/nodal finite element approach with perfectly matched layer absorbing boundary conditions. We determined the spectral dependence of the confinement loss for the fundamental modes of orthogonal polarizations. Our results show that, for the four structures studied, the polarization dependent loss is so high that they can be used as fiber-optic polarizers in the full band gap range.

Wide-band optical field concentrator for low-index core propagation

We propose a novel chirped structure consisting of a low index polymer core bounded by modulated multilayer claddings, to realize an optical field concentrator with virtually zero propagation losses in a wide spectral range, independent of wave polarization. In spite of the absence of the total internal reflection mechanism, properly designed multilayer claddings ensure the achievement of unitary transmittance in a wide spectral range, including the widely used wavelengths for optical communications. Several cladding geometries obtained by varying the thicknesses of the cladding layers are reported and discussed.

Fabrication and emission properties of Er 3+/Yb 3+ codoped tellurite glass fiber for broadband optical amplification

Tellurite glass is proposed as a host for broadband erbium-doped fiber amplifiers because of their excellent optical and chemical properties. A new single mode Er 3+/Yb 3+ codoped tellurite fiber with D-shape cladding geometry is fabricated in this work. When pumped at 980 nm, a broad erbium amplified spontaneous emission (ASE) nearly 100 nm in the wavelength range of 1450–1650 nm around 1.53 μm is observed. It was found that the emission spectrum from erbium in tellurite glass fibers is almost twice as broad as the corresponding spectrum in tellurite bulk glass. The changes in ASE with regard to fiber lengths and pumping power were measured and discussed. The output of about 2.3 mW from Er 3+/Yb 3+ codoped tellurite fiber ASE source is obtained under the pump power of 700 mW. The broad 1.53 μm emission of Er 3+ in Er 3+ /Yb 3+ codoped tellurite glass fiber can be used as host material for potential broadband optical amplifier and tunable fiber lasers.

Double-clad Yb3+-doped fiber lasers with virtually non-circular cladding geometry

We report on cladding pumped Yb3+-doped fiber lasers with novel virtual-non-circular cladding geometries. The geometry of the inner-cladding is in fact circular with D-shaped holes, that form virtual-D (one hole), and virtual-square (four holes) structures for the inner-cladding. The laser performance of this structure is assessed at several wavelengths and lengths, showing efficiencies as high as those obtained with other geometries for the inner-cladding.

Efficient operation of double-clad Yb3+-doped fiber lasers with a novel circular cladding geometry.

A highly efficient double-clad Yb3+-doped fiber laser with a novel cladding geometry is described. A round double-clad fiber with a small D-shaped hole for breaking a circular symmetry in a cladding combines the advantages of ease of manufacture and handling round fibers with efficient absorption of pump light. Fiber lasers with a double-D cladding shape and a D-hole cladding are compared. We report what are to our knowledge the highest slope efficiencies of 73% and 69%, respectively, pumping at 915 nm. Output powers in excess of 13 W are demonstrated.

Asymptotic analysis of silicon based Bragg fibers

We developed an asymptotic formalism that fully characterizes the propagation and loss properties of a Bragg fiber with finite cladding layers. The formalism is subsequently applied to miniature air-core Bragg fibers with Silicon-based cladding mirrors. The fiber performance is analyzed as a function of the Bragg cladding geometries, the core radius and the material absorption. The problems of fiber core deformation and other defects in Bragg fibers are also addressed using a finite-difference time-domain analysis and a Gaussian beam approximation, respectively.

Experimental study of pump power absorption along rare-earth-doped double clad optical fibres

We present an experimental study of the influence of the inner cladding geometry on pump power absorption in double clad fibres. The experimental results are analyzed by taking into consideration the spatial intensity distribution of the modes in the inner cladding. Six different geometries and core dopant are investigated. By comparing the pump power absorption evolution along each fibre, we show that using a chaotic inner cladding geometry, a constant absorption coefficient is achieved independently of the launching light condition.