Multiwavelength DFB laser arrays with integrated combiner and optical amplifier for WDM optical networks

In this paper, we describe the design, fabrication and performance of multiwavelength DFB laser arrays with integrated combiner and optical amplifier built for wavelength-division-multiplexed (WDM) optical networks. The goal is to reduce the per-wavelength transmitter cost in both initial procurement and subsequent operation. Using photonic integration, we have addressed and resolved several important issues related to laser arrays such as wavelength accuracy, output power, high-speed modulation and optical packaging. State of the art results have been obtained. By the use of wavelength redundancy and proximity effect, wavelength deviations of ±0.2 nm or less from the designated eight-wavelength comb have been achieved with high yield. Simultaneous operation of ten wavelengths has also been demonstrated. In spite of the inherent splitting loss of 13 dB, high-output powers of about -13 and 0.5 dBm per wavelength have been measured, under simultaneous operation, into a single-mode fiber (SMF) without and with on-chip optical amplification, respectively. The DFB laser has a 3-dB bandwidth of 9 GHz. A 2.5-Gb/s (OC-48) error-free transmission through 120 km conventional SMF has been demonstrated under single channel operation. The electrical crosstalk from neighboring channels cause negligible degradation to the eye diagram and the bit-error-rate (BER) curve at a bit rate of 2.5 Gb/s. The optical crosstalk due to four-wave mixing and cross-gain modulation (XGM) of the semiconductor optical amplifier (SOA) is also characterized. The impact of this integrated laser array on WDM optical networks is assessed in the conclusion