Radio-Over-Fiber Access Network Architecture Based on New Optimized RSOA Devices With Large Modulation Bandwidth and High Linearity

Next-generation wireless communications systems need to have high throughputs to satisfy user demand, to be low-cost, and to have an efficient management as principal features. Using a high-performance, low-cost reflective semiconductor optical amplifier (RSOA) as a colorless remote modulator at the antenna unit, the wavelength-division multiplexing (WDM) technique can be used for supporting distributed antenna systems (DASs). Each antenna unit is connected to the central unit using optical fiber and all links are used to transmit radio signals. Due to a large optical bandwidth, RSOAs are potential candidates for cost effective WDM systems. In this paper, simulations are carried out to determine optimized RSOA devices for wireless technology. New RSOA structures are fabricated and evaluated. The optimized RSOA is electrically driven by a standard Wi-Fi input signal (IEEE 802.11 g) with a 64-quadrature amplitude modulation (QAM) format. A large modulation bandwidth and a high electrooptic gain are demonstrated, which are confirmed by good performance when using orthogonal frequency-division multiplexing techniques. Characteristics such as high linearity and large electrooptic modulation bandwidth of our RSOA are sufficient to ensure an error vector magnitude (EVM) lower than 5% with a dynamic range exceeding 35 dB in a back-to-back configuration (at 0 dBm). Uplink transmission over a 20 km of single-mode fiber is also demonstrated with EVM lower than 5% and a dynamic range exceeding 25 dB (at 5 dBm).