<title>Novel gain tilt monitoring method for DWDM submarine cable systems</title>

Abstract

ABSTRACT We propose a novel monitoring method of gain tilt for DWDM (Dense Wavelength Division Multiplexing) submarine cable systems with simple configuration. This method can be applied to DWDM systems on in-service condition without any special devices and dedicated wavelengths. The relation between the measurement sensitivity and pre-emphasis is studied, and we can distinguish more than 4dB gain tilt variation in 25nm transmission bandwidth. Keywords: Erbium-doped fiber amplifier (EDFA), Gain tilt, Gain equalizer, Pre-emphasis, Dense wavelength division multiplexing (DWDM), Submarine cable system 1. INTRODUCTION In recent years, with the rapid increase of demand for international communication, transmission capacity of submarine cable systems has been increasing explosively. Dense wavelength division multiplexing (DWDM) technology is expected to be a simple method to increase the transmission capacity of the submarine cable system. The large capacity DWDM transmission system requires wide bandwidth of erbium-doped fiber amplifiers (EDFAs) [1]. The gain flatness of the concatenated EDFAs is very important characteristics since the transmission performance depends on the gain flatness of the system [2-5]. However, the gain profile of the EDFA chain might be degraded by the fluctuation of the system parameters such as fiber loss [6]. There have been many reports on the gain tilt compensation devices [6-25] and the gain tilt monitoring methods [2,6]. Conventional measurement methods of the gain tilt require optical band-pass filters and dedicated wavelengths. However, as these monitoring methods need many optical components, they will require a large space and high cost. In this paper, we propose a novel gain tilt monitoring method with the very simple configuration consisting of an optical coupler, a photodiode (PD) in the gain equalization unit and pre-emphasis adjustment at the transmitter. The gain tilt variation of the DWDM submarine cable system can be continuously measured by the proposed method.