Abstract: A novel lumped electro-absorption modulator with a charge layer and an undercut ridge waveguide (DU-EAM) was fabricated and measured. Also, two other kinds of \,EAM with straight ridge waveguides, one with a charge layer (D-EAM) and another with no charge layer (N-EAM), were fabricated and tested to ensure that the design of the DU-EAM would reduce the RC-time constant. The measured capacitance of the D-EAM and the DU-EAM is lower than that of the N-EAM under reverse bias voltage from -1 to -8 V due to the inserted charge layer. The capacitances of the N-EAM, the D-EAM and the DU-EAM are 0.375, 0.225 and 0.325 pF, respectively, at -3 V. In addition, the DU-EAM had a larger extinction ratio (25 dB at -3 V) and higher modulation efficiency (13 dB/V between -1 and -2 V) than two other straight-ridge-waveguide ones (the D-EAM performed 22 dB and 10 dB/V, the N-EAM performed 20 dB and 10 dB/V) due to the 5.2 μm wider active region.

Key words: undercut waveguide