Penetration rate of water in sapphire and silica optical fibers at elevated temperature and pressure

Photonic Microresonators Created by Slow Optical Cooking

“…Previous work has shown that microresonators with similar CW variation can be created at much higher temperatures by local annealing with a CO 2 laser during several seconds. , Here, the resonator introduced was created over significantly longer time and much lower temperature. We suggest that the physical mechanism of the slow cooking phenomenon can be explained by complex processes at the silica–water interface reviewed above, for example, hydration and hydrolysis, − crack formation, , and silica dissolution. − In addition, momentum transfer between WGMs and water and the temperature gradient evident from Figure b and eq can induce the flow of water inside the MCF . Water flow replenishes fresh water at the silica–water interface, allowing the continuous reactions of hydrolysis and hydration …”

“…Developed experimental methods to investigate the silica–water interactions include vibrational spectroscopy, ,,− ,, calorimetry, , STM, AFM, , TEM, optical fiber transmission of light, inelastic deformation of optical fibers, − and others. These methods have demonstrated hydration and hydrolysis, − structural and stress relaxation, ,− crack formation, , volume expansion, deep water diffusion, and silica dissolution. − Due to the inertness of the silica–water interaction, temporal variations caused by processes near the silica–water interface have been required to last over days and sometimes years to be measurable. ,,,− ,,,,,− Previous work accelerated these processes by using high temperature and pressure ,− or by increasing the surface area of the reaction using silica microparticles , or porous silica. , The insight into the physics and chemistry of these processes at environmental temperatures and pressures, which are most important for applications, requires the development of approaches enabling exceptional temporal and spatial resolution of alterations near the silica–water interface.…”

“…Developed experimental methods to investigate the silica− water interactions include vibrational spectroscopy, 5,7,[14][15][16][17][18][19]35,36 calorimetry, 20,21 STM, 22 AFM, 24,30 TEM, 25 optical fiber transmission of light, 26 inelastic deformation of optical fibers, 27−29 and others. These methods have demonstrated hydration and hydrolysis, 14−25 structural and stress relaxation, 14,27−29 crack formation, 30,31 volume expansion, 4 deep water diffusion, 26 and silica dissolution. 32−37 Due to the inertness of the silica−water interaction, temporal variations caused by processes near the silica−water interface have been required to last over days and sometimes years to be measurable.…”

An alternative method to develop fibre grating temperature sensors using the fibre loop ringdown scheme

“…The chemical degradation of the FBG may result from penetration of environmental molecules into the optical fibre and/or diffusion of chemical compounds from the optical fibre to the testing environment when the FBG is exposed to the high temperature atmospheric testing environment (the ceramic tube of the oven in this work). For instance, water vapour may penetrate into optical fibres at an escalated temperature [27], and fibre chemical constituents such as germanium dopant may diffuse out of the fibre when the temperature is above 1000 • C [28]. The change of chemical compositions of the fibre affects directly the thermal expansion coefficient of the FBG; thus the reading of the measured ringdown time is affected.…”

Graphene-Material Based Nanocomposite-Coated Optical Fibres: A Multi-Functional Optical Fibre for Improved Distributed Sensing Performance in Harsh Environment

“…When the fibre-optic sensor is to be installed in harsh settings, it is common to use polyimide-coated optical fibres, for their durability at high temperatures and in other challenging environments. Polyimide coatings provide excellent long-term protection to fibres up to 300˚C in air for long period of time in harsh environment applications (shorter term to 350˚C) [1][2][3]. Yet, there are many use-cases where long-term, higher temperature monitoring of processes and assets using distributed fibre-optic sensing techniques would be beneficial [4][5][6][7].…”