Thermal Wavelength Stabilization of Fiber Bragg Gratings Using Bi-Metal Structure

Abstract

A stabilized laser is essential for optical fiber communication network. One of the passive technique for stabilization of central wavelength of laser is based on the application of fiber Bragg gratings. Due to the positive coefficient of thermal expansion of optical fiber, the Bragg gratings within the fiber written by excimer laser gives about 0.01nm/oC shift on the central wavelength respect to the ambient temperature which leads serious problem in the communication network. Since both the temperature and tension force are linearly proportional to the central wavelength of fiber Bragg gratings. A feasible approach to derive the wavelength stabilization is to decrease the tension force of fiber Bragg gratings respect to the increase of ambient temperature. In this paper, a bi-metal structure with similarly negative coefficient of thermal expansion is used to decrease the tension force while the environmental temperature increases. Results show that the theory provides a fundamental solution of the physical data of the temperature compensated fixture for near zero shift of central wavelength. The practical compensation of the bimetal structure is non-linear due to the thermal expansion of the arm of the fixture, while the compensation is linear respect to the ambient temperature by neglecting the thermal expansion of the arm. However, this package is feasible for mass production and can be used for athermalization of the fiber Bragg gratings in optical communication system.