Monitoring of the laser wavelength in modern fiber-optic communication systems using dual photodetectors

Abstract

© 2016, Springer Science+Business Media New York. Fiber-optic communication systems enable very fast access to large amounts of data for all users of the information and communication systems. Monitoring and control of such fiber-optic systems is of crucial importance for the very large data rate traffic over the internet. DWDM systems have become a standard in order to maximize utilization of existing resources of the fiber-optic systems. These systems use large number of laser light sources with adjacent wavelengths and therefore constant monitoring and control of all lasers in the system is of vital importance. There are different methods for the determination of the lasers wavelength such as optical spectrometers with a monochromator or Fabry-Perot interferometers. In this paper a simple and cost effective solution for laser wavelength monitoring in DWDM L-band with two different photodetectors is presented. Different sensitivities of Ge and InGaAs photodiodes in the L-band were used for implementation of a simple and accurate sensing system for the monochromatic light source wavelength measurement and monitoring. By illuminating simultaneously both photodiodes with the help of the fiber-optic coupler and corresponding signal processing, a wavelength dependent signal was obtained. While the distance between two adjacent channels in DWDM systems is around 0.8 nm, measurement accuracy achieved using proposed method was around ±0.4 nm. Compared to channel spacing in DWDM systems, acquired accuracy is considered sufficient for monitoring of the laser wavelength.