Reflective Electroabsorption Modulators for Beyond 25 Gb/s Colorless Transmissions

We present a complete characterization of reflective electroabsorption modulators (EAMs) monolithically integrated with semiconductor optical amplifiers (SOAs), components that are capable of operating beyond 50 Gb/s in the C band. The devices are based on GaInAsP multiple quantum wells on an InP substrate, leveraging semi-insulating buried heterostructure waveguide definition and butt-joint integration technologies. Different device configurations, based on 80-µm and 150-µm long EAMs, are fabricated and characterized in both static and dynamic modes. The frequency response of the 80-µm EAM is still flat at 26.5 GHz (setup upper limit) whereas the 150-µm EAM exhibits a 3-dB cutoff bandwidth of 23 GHz. A zero-chirp is achieved for EAM reverse bias voltages between -1.2 V and -1.5 V, depending on the operating wavelength. The frequency chirp induced by the shorter EAM under large-signal modulation is almost half that of the longer EAM, with their respective peak values being +1.5/-2 GHz and +3.2/-3.7 GHz (rising/falling edges) at 1545 nm and -1.3 V for a voltage swing of 2.6 V. We obtained high dynamic extinction ratios of ~14.5 dB and ~8 dB from the longer and the shorter EAMs, respectively, while operating them at 25 Gb/s using non-return-to-zero coding. Finally, we achieved 10 km and 16 km colorless transmissions in the C-band (between 1530 nm and 1545 nm) over a standard single-mode fiber without equalization using the 150-µm and the 80-µm EAMs, respectively, with 3 dB and 2.5 dB dispersion penalties at a bit error rate of 10-3.