BEAM: Design and Characterization of a 10-Gb/s Broadband Electroabsorption Modulator

The market for data modulators at 10 Gb/s is currently dominated by Mach-Zehnder phase modulators fabricated in LiNbO3 (LN). However they are relatively expensive to manufacture and large compared to semiconductor devices. InP based electroabsorption modulators (EAMs), are more compact; however they have a limited bandwidth (5-8 nm) over which chirp is in the correct range to allow >80 km reach. This paper reports the broadband electroabsorption modulator (BEAM) concept in which reach performance in line with LN modulators can be achieved using integrated InP components. The BEAM consists of a series of EAMs, each one tuned to give the correct chirp over a certain wavelength range. The bandwidth of the BEAM can be extended to cover the C-band (1535nm-1565nm). In addition, a semiconductor optical amplifier (SOA) is serially integrated in order to recover the total insertion loss. Details of the design, fabrication and testing of prototype BEAM chips operating at 10 Gb/s are reported. Quantum well intermixing technology is employed to realize the multiple bandgaps required for the prototype chips which are fabricated on semi-insulating InP substrates. Highlights of the operational characteristics of the BEAM chips include extinction ratios of up to 12 dB at 10 Gb/s and SOA gains of 20 dB