Analog and digital transmission using high-power fiber amplifiers

Abstract

Fiber optic based CATV distribution systems may need very high powers prior to distribution. High optical powers can be obtained using a cladding pumped fiber amplifier. The performance of an analog transmission system using a high power cladding pumped fiber amplifier has been investigated. Analog signals from a 120-channel CATV signal generator was used to directly modulate 1550 nm distributed feed back laser. The output was amplified to ~1W using a cladding pumped fiber amplifier. The carrier to noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) of the composite analog signals were measured before and after amplification. No significant change in CNR, CSO and CTB signals were observed which suggests that the amplifier does not introduce any additional non-linearity. Similar experiment was also carried out using a hybrid digital/analog system where the carrier at 223.25 MHz was modulated at 2Mb/s using the BPSK modulation format. Bit error rate (BER) of &lt;10<SUP>-9</SUP> was obtained for a modulation depth of 2.8% of the BPSK modulated channel. No significant changes in CNR, CSO and CTB were observed for this mixed mode transmission after amplification.