Athermally packaged fiber Bragg grating for sensor and DWDM applications using liquid carbon

Abstract

Highly stable central wavelength with temperature variations is crucial for Dense Wavelength Division Multiplexing (DWDM) multiplexers/demultiplexers, filters, laser sources, sensors, and any equipment that uses fiber Bragg grating (FBG) filters. The wavelength stability prevents channel drift and interference with other channels and thus enables the increase of DWDM channels inside a single fiber. It also ensures the accuracy of the measured values in relation to the reference FBG of the sensors. Stable FBG wavelength is traditionally achieved by athermal packaging which is a complex process involving preloading or bonding under elevated temperatures to compensate for any wavelength shifts caused by temperature variations. Since FBGs are sensitive to both temperature and strain, temperature-induced shifts in the central wavelength can be compensated by athermal packaging. This packaging minimizes axial strain on the FBG as temperature increases, thereby canceling the temperature effect using strain-induced wavelength changes. In this article, we propose and experimentally validate a simple and straightforward athermal packaging solution for FBG to counteract the changes in the central wavelength due to temperature variations. The proposed FBG package involves coating the FBG with two layers of Liquid Carbon material, which possesses a negative thermal expansion (NTE) coefficient of at room temperature. The results demonstrate that the central wavelength is maintained within a narrow range of 0.06 nm over a wide temperature span, from 24 to 96 °C. These findings significantly advance FBG packaging by providing a simpler and more efficient method to achieve central wavelength stability. The practical applications of this research are vast, potentially improving the performance and reliability of DWDM systems and other optical devices that rely on FBG filters. This advancement could lead to more robust and higher-capacity optical communication networks.