Source: http://aoot.osa.org/ome/abstract.cfm?uri=ome-9-3-1333
Timestamp: 2019-04-21 20:44:13+00:00

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Ge core fibers fixed on a SiO2 rod were annealed by a 360° axially symmetric distribution CO2 laser of the different power, respectively. The residual stress distribution, crystalline properties, and optical loss of the Ge cores were investigated. The non-uniform distribution of Raman frequencies at the Ge core cross-section were found after the fiber was annealed, which means that CO2 laser irradiation is one of the key factors determining the uniformity of the Ge core annealed by a CO2 laser. The bonding state between the Ge core and SiO2 cladding was analyzed according to the Raman mapping. Compared with the Si core fiber, there are fewer covalence bonds between the core and the SiO2 cladding in the Ge core fiber. For the Ge core fiber annealed at relatively high CO2 laser power, the tensile stresses transformed to compressive stresses in some areas of the Ge core cross-section, and the splitting of (111) plane X-ray diffraction peak appeared in the X-ray diffraction spectrum. The optical loss measured using a quantum cascade laser with the wavelength range from 4.7 μm to 4.9 μm shows the lowest optical loss of 2.05 dB/cm has been achieved in all samples.
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Fig. 1 (a) The schematic diagram of the fiber annealing apparatus, (b) the schematic diagram of the laser irradiating on rod, the arrow refers to the 3D illustration of bronze mirrors, (c) photographs of various parts of the bronze mirrors, (d) optical paths of CO2 laser in a cross-sectional diagram, (e) the fiber attached longitudinally to the side of the quartz rod, both ends of the fiber are fixed with heat-resistant tape.
Fig. 2 The measured values of the annealing laser powers.
Fig. 3 The diagram of the laser distribution.
Fig. 4 The estimated laser powers irradiated on the Ge core fiber.
Fig. 5 (a) The schematic diagrams of the fiber optical loss measurement, (b) the detail of the device for placing fiber in the measurement, (c) the spectrum of the light source (from spec sheet of THORLABS QF4800CM1).
Fig. 6 (a) Raman spectrum of a point at Ge core cross-sections of as-drawn fiber, the arrow indicates the fitted peak position and fitted FWHM data. The inserted graph is an unfitted spectrum. (b) Raman frequency maps of the as-drawn Ge core fiber, (c) Raman frequency maps of the fiber annealed at the laser power of 10%, (d) Raman frequency maps of the fiber annealed at the laser power of 15%, (e) Raman frequency maps of the fiber annealed at the laser power of 20%, (f) Raman frequency maps of the fiber annealed at the laser power of 25%.
Fig. 7 The box diagram of the Raman frequency distribution.
Fig. 8 Raman spectra of 3 different positions of Ge core side. (a) The schematic diagram of the Raman measurement performed on the side of Ge core, (b) Raman spectra taken from position 1, (c) Raman spectra taken from position 2, (d) Raman spectra taken from position 3.
Fig. 9 Raman FWHM value maps of the Ge core fibers annealed at the different power of laser, (a) as-drawn, (b) annealed at the laser power of 10%, (c) annealed at the laser power of 15%, (d) annealed at the laser power of 20%, (e) annealed at the laser power of 25%.
Fig. 10 The box diagram of the Raman FWHM value distribution.
Fig. 11 XRD spectra of the Ge core fibers.
Fig. 12 The cross-section image and the elemental analysis of the Ge core fiber annealed at the laser power of 20%.
Fig. 13 Optical losses of Ge core fibers.

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