Numerical analysis of long period grating fibre sensor fabrication using thermal processing

Important efforts have been and are made in studying, designing and manufacturing grating structures in single mode optical fibre. These efforts are made in order to develop all-fibre devices which can perform a transformation on the propagation of light beam (e.g. by modulating, amplifying, routing, and coupling optical signals) without extracting it from the fibre for telecommunication and sensing applications. Long Period Grating Fibre Sensors (LPGFS) form a numerous class among such all-fibre optical grating devices, being used in communications and thermal, mechanical strain and ambient refractive index (chemical) sensing. LPGFS are operated by coupling the optical power from the fundamental optical mode guided through the core into co-propagating cladding modes. LPGFS consist of a long-period grating (LPG) with 10-1000 pm spatial wavelength (period) of core refractive index modulation inscribed along the single mode fibre axis over 5-50 mm length. LPG can be manufactured using several thermal processing techniques among which CO2 laser local heating is a well-known and cost effective one. For being efficient these thermal processing techniques applied on optical fibres have to be computer controlled. In order to improve the design and fabrication of LPGFS development of simulation models of the thermal processes produced in optical fibre are absolutely necessary. The aim of this study consists in presenting a synthesis of results obtained into the development of optical fibre thermal processing performed for LPG fabrication.