Soft Glass Based Large Mode Area Photonic Bandgap Fibre for Mid-Infrared Applications

Abstract

An all-solid LMA Bragg fibre (mode area exceeding 1100µ m 2 ) is presented for midinfrared applications, based on a new design strategy that induces large differential loss between fundamental and higher order modes for effective single-mode operation. OCIS codes: (060.4005) Microstructured fibres (060.2280) Fibre design and fabrication IntroductionThe mid-infrared (IR) wavelengths (2-25µ m) have recently become increasingly important due to emerging applications in areas such as mid-IR spectroscopy for astronomy, optical coherence tomography, and chemical sensing. This has spawned wide interest in the development of optical fibres that can efficiently guide light and enable high power laser delivery at these wavelengths. Besides the choice of optimum material system, a major challenge in this field is the design of optical fibres that enable efficient distortion-free transmission at high power levels and supplement the design of efficient mid-IR fibre sources. Single-mode large-mode area (LMA) fibres are crucial in this regard because they mitigate the undesirable nonlinear processes (e.g. stimulated Brillouin scattering, stimulated Raman scattering, four-wave mixing) in the fibre that deteriorate their power handling capability. Single-mode LMA fibres based on step index profiles are limited in functionality due to their high bend-loss sensitivity and tight tolerances in fabrication parameters. Thus, more recently, alternative routes have been explored, which have relied on the use of multimode LMA fibres in which effective guidance of the fundamental mode (FM) is achieved by inducing a large differential loss for its higher order modes (HOMs). The necessary differential losses can be engineered through fibre design by a number of means including controlling the inherent modal confinement loss and/or relative bend loss. Techniques that maximize the coupling efficiency into the FM are also critical. Most of these fibre designs are based on microstructured optical fibres (MOFs) that provide unprecedented structural design freedom for controlling their propagation characteristics. In this context, all-solid Bragg fibres are extremely promising as they enable better control over the structural parameters during fibre drawing thereby ensuring good repeatability with minimal transverse deformations and allowing for accurate targeting of the optical characteristics in the final fibre [1,2]. Bragg fibres can also provide considerably lower bending losses as compared to MOFs (with air holes) with the same size of the mode field [3]. The highly nonlinear non-silica based glasses are promising candidates for fabricating the mid-IR fibres owing to their good transparency across the mid-IR wavelength spectrum [4]. Due to their lower toxicity, higher thermal stability, and mature fabrication process, the lead-silicate glasses are attractive for fabrication of fibres and fibrebased devices operating in the wavelength range of 2-5µ m [5]. In this paper, we report a new design strategy to realize a soft glass (lead s...

Co‐Extrusion of Multilayer Glass Fiber‐Optic Preforms: Prediction of Layer Dimensions in the Extrudate

“…Glass/glass or glass/polymer layers formed by co-extrusion have a zone of dimensional stability for desired optical performance. 4,5,9 As presented elsewhere, 10,11 the dimensions of the layers required within a fiber-optic preform, to be subsequently drawn into optical fiber, should be of calculated values, within expected tolerances, to ensure the desired electromagnetic performance is subsequently achieved in the finished fiber after fiber-drawing. Thus, it is important to know the section in the extruded preform [shown as "L" in Fig.…”