Effect of Thermal Annealing on Mid-Infrared Transmission in Semiconductor Alloy-Core Glass-Cladded Fibers

Abstract

We report a study investigating the effects of thermal annealing on the optical properties of Si-Ge alloy-core silica-cladded fibers. Low temperature fiber draw was performed with a laboratory-made draw tower at 1760 °C that minimizes impurity diffusion from cladding to the core. As a post-drawing process, Si-Ge core fibers were annealed in a box furnace to alter the core structure. Microstructural and optical properties of fibers were investigated, and transmission losses were measured as 28 dB/cm at 6.1 µm. Numerical studies were performed to analyze the experimental results and to find the optimum structure for low loss semiconductor-core glass-cladded fibers.

Semiconductor core fibres: materials science in a bottle

“…Methods that have been used to perform post-fabrication annealing/recrystallisation of continuous crystalline core fibres include oven thermal annealing 72 , rapid photothermal annealing 73 , laser treatment (at both visible 74 and IR 46 , 47 wavelengths) and diverse heating methods in tapering rigs. The non-standard treatments are illustrated in Fig.…”

“…4 , fibres typically are drawn at temperatures of ~1950 °C, based on the use of silica as the cladding. SiGe based fibres with Ge concentrations from 1 at% 99 to 46 at% 118 have been studied, both as continuous fibre cores 46 , 72 , 75 , 118 , and as source material for particles 48 within the silica cladding. Compositional variations due to the preferential solidification of silicon from the melt are observed in the as-drawn material 75 , 118 , as seen in Fig.…”

“…Variations in the solidification velocity and imposed thermal gradients have been used to form cores with periodic axial 46 , end-cap 122 and radial 120 Ge-rich features, showing the breadth of in-fibre microstructures that can be created in these isomorphic systems. Optical transmission of nominally uniform fibres has not yet been optimised 46 , 72 , but oven annealing of low Ge concentration HPCVD-fabricated fibres was shown to reduce optical losses 123 , and laser-treated molten core fabricated fibres that were subsequently oven annealed were reported to have decreased losses 119 . This suggests that while slow (~100 µm s −1 ) translation speeds give overall compositional uniformity (Fig.…”

Recent progress of semiconductor optoelectronic fibers

“…Compositional variations along the fiber's length is a potential route for the fabricating in-fiber diode-like structure, leading to photodetection and solar cell applications, while the radial graded core structure is particular useful for infrared transmission beyond 4 µm as the Gerich region serves as the preferential guiding medium. Numerical studies suggested a graded-index core structure could have a 100-time lower transmission loss in the mid-IR region and also suppress the strong absorption by the silica cladding [84].…”

CO2 laser annealed SiGe core optical fibers with radial Ge concentration gradients

“…If the speed exceeds a critical value, non-planar growth results. For a radially dominated cooling process, a high transverse scan speed can lead to the formation of a concave crystallization front in a cylindrical geometry [33,34] and the large surface-to-volume ratio of a fiber may be expected to enhance this effect. BSE images in Fig.…”