BEAM: design and characterization of a 10-Gb/s broadband electroabsorption modulator

Abstract

The market for data modulators at 10 Gb/s is currently dominated by Mach-Zehnder phase modulators fabricated in LiNbO 3 (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 semiinsulating 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.