DISCRETE ELECTROABSORPTION MODULATORS WITH ENHANCED MODULATION DEPTH

In this paper, we present an investigation into factors that limited t he median modulation depth of a batch of packaged discrete waveguide E A modulators to 23 dB at a wavelength of 1.55 mu m. Results from detai led measurements of the DC absorption and photocurrent spectra are use d to show how stray parasitic light can perturb the absorption charact eristic and reduce the modulation depth of these high-speed multiple-q uantum-well modulators. A novel ridged deeply etched buried heterostru cture EA modulator design is presented in which stray light is removed from the immediate vicinity of the guided mode. The key structural di fference between these and the previous devices is that they employ a much thicker Fe-doped InP current blocking layer that was grown by atm ospheric pressure MOVPE using PCl3 for planarization. Detailed measure ments of the DC absorption spectra of a packaged ridged deeply etched buried heterostructure device confirm that stray light causes only a m inor perturbation on its absorption characteristics. Consequently the new batch of EA modulator modules have a higher median modulation dept h of 40 dB, as well as lower fiber-to-fiber insertion losses and picos econd pulse generation capabilities that are very similar to the previ ous devices which were used in 40 Gb/s optically time division multipl exed experiments.