Amplifier Limited Information Rates in High-Speed Optical Fiber Communication Systems

Due to the high transmission capacity, optical fiber systems have been extensively applied, as significant components, in the modern telecommunication infrastructure to meet the ever-increasing demand of data traffic. Optical amplifiers have been employed to amplify optical signals and to compensate for the transmission losses. They play a key role in relaying the signals in ultra-wideband optical fiber communication systems. However, the amplified spontaneous emission (ASE) noise will be introduced during such process, and it will degrade the performance of optical fiber systems and will pose constraints on the transmission information rates. The mutual information (MI) and the generalized mutual information (GMI) have been applied and investigated, as figures of merit, to evaluate the information rates in communication systems. The MI measures the highest achievable information rate (bits per symbol) that can be realized in a channel based on ideal symbol- wise encoder and decoder. The GMI, also known as the bit-interleaved coded modulation (BICM) capacity, indicates an upper bound on the number of bits per symbol that can be reliably transmitted through a channel based on the bit-wise decoding. Although the MI and the GMI are equal when the signal-to-noise ratio (SNR) tends to infinity, the MI is strictly higher than the GMI in any practical transmission scenarios. This discrepancy depends on the constellation cardinality and the binary labeling. In this work, we have investigated the impact of ASE noise on the MI and the GMI, and have developed corresponding analyses and estimations across different modulation formats, in linear optical fiber communication systems. Our work aims to explore the limit and requirements on optical amplifiers and to provide a comprehensive insight for the design of next-generation ultra-wideband optical fiber communication systems.