Packaging a fiber Bragg grating with metal coating for an athermal design

This paper presents an athermal package to compensate for temperature deviation of a fiber Bragg grating (FBG) with a metal coating. The metal coating is electroless plated onto the optical fiber to function as a thermal compensator. From the cross section of a thermal compensator used for FBG athermal package, an optical fiber and a metal coating appear. Therefore, in theory, the two-phase constant model is applied in designing the metal coating thickness associated with the effective thermal expansion coefficient and the effective Young's modulus in the composite thermal compensator. As a result, the total variation of Bragg wavelength over the temperature ranging from 30 to 80°C is around 0.05 nm in a new package based upon the concept of a bimaterial device. To the authors' knowledge, the configuration proposed in this paper is probably the simplest bimaterial package design there is.