Abstract
The design of an all-solid, soft glass-based, large mode area Bragg fiber for effective single mode operation with mode effective area exceeding 1100 µm(2) across the wavelength range of 2-4 μm is reported. The design adopts a new strategy to induce large differential loss between the fundamental and higher order modes for effective single-mode operation within few tens of centimetres length of an otherwise multimode fiber. In addition to having the potential for the targeted application in high power laser delivery systems; complemented by a zero dispersion wavelength at 2.04 µm and rapidly developing mid-IR optical sources, the proposed fiber should also be attractive for generation of high power, single mode and less divergent supercontinuum light over this mid-IR window.
Highlights
IntroductionApplications such as gas sensing for security and environmental monitoring, spectroscopy for pollution monitoring, industrial process control and astronomy have become increasingly important in recent years [1,2,3]
Applications such as gas sensing for security and environmental monitoring, spectroscopy for pollution monitoring, industrial process control and astronomy have become increasingly important in recent years [1,2,3]. Much progress in these areas relies on the development of lasers and laser delivery systems that can efficiently emit and transmit light at mid-infrared (2-20 μm) wavelengths. This has generated widespread interest in developing optical fibers that can enable efficient distortion-free transmission of optical signals at high power levels in the mid-IR to complement the design of efficient mid-IR optical sources such as high power Thulium/ Holmium doped fiber lasers and quantum cascade lasers operating at room temperatures [4,5,6,7,8,9,10]
More recently, alternative routes have been explored that rely on the use of multimode large-mode area (LMA) fibers in which effective single-mode guidance of the fundamental mode (FM) is achieved by inducing a large differential loss to its higher order modes (HOMs) [12,13]
Summary
Applications such as gas sensing for security and environmental monitoring, spectroscopy for pollution monitoring, industrial process control and astronomy have become increasingly important in recent years [1,2,3] Much progress in these areas relies on the development of lasers and laser delivery systems that can efficiently emit and transmit light at mid-infrared (mid-IR) (2-20 μm) wavelengths. We report a new design route to engineer the bandgap of a soft-glass based all-solid LMA Bragg fiber to achieve effective single-mode operation in the mid-IR wavelength region beyond 2 μm Operating at these wavelengths necessitates the use of glasses other than silica (lead-silicate glasses in the case of this paper) that exhibit good transparency at these wavelengths [21] while having low toxicity, higher thermal stability and a mature fabrication process [22]. The fiber is essentially multimoded at these wavelengths, we show that effective single-mode guidance can be established within few tens of centimetres of the fiber length, making it an attractive platform for high power (CW or short pulse) delivery as well as for generation of clean supercontinuum at relatively high powers [23,24,25,26] in the mid-IR
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