International Journal of Advances in Engineering & Technology, Sept 2011. ©IJAET ISSN: 2231-1963 388 Vol. 1, Issue 4, pp. 388-394 DESIGN AND MODELING OF TRAVELLING WAVE ELECTRODE ON ELECTROABSORPTION MODULATOR BASED ON ASYMMETRIC INTRA-STEP-BARRIER COUPLED DOUBLE STRAINED QUANTUM WELLS ACTIVE LAYER Kambiz Abedi Department of Electrical Engineering, Faculty of Electrical and Computer Engineering, Shahid Beheshti University, G. C., Evin, Tehran, Iran ABSTRACT In this paper, a travelling wave electroabsorption modulators (TWEAMs) based on asymmetric intra-step- barrier coupled double strained quantum wells (AICD-SQW) active layer is designed and analyzed at 1.55 m for the first time. The AICD-SQW structure has advantages such as very low insertion loss, zero chirp, large Stark shift and high extinction ratio in comparison with the intra-step quantum well (IQW) structure. For this purpose, the influence of the electrode width and ground metal separation on their transmission line microwave properties (microwave index, microwave loss, and characteristic impedance) and modulation bandwidth are analyzed. KEYWORDS: travelling wave electroabsorption modulator, aicd-sqw, microwave properties, modulation bandwidth. I. INTRODUCTION Electroabsorption modulators (EAMs) are advantageous external modulators in high-speed optical communication systems due to low chirp, small size, high modulation efficiency, low driving voltage, high extinction ratio, wide modulation bandwidth and the capability to be integrated with other semiconductor devices. Improving the operation by overcoming the trade-off between bandwidth and device length, EAMs with travelling wave electrodes have been documented to be a good candidate [1-10]. Fig. 1 shows the principle of operation for a travelling-wave electroabsorption modulator. In a travelling-wave electrode configuration, the microwave signal is applied from one end of the optical waveguide and it co-propagates with the optical signal. At the output end of the waveguide, the microwave signal is terminated with a matching load such that there is little reflection from this end. Therefore, in a TW-EAM, the electrode is designed as a transmission line to distribute the capacitance over the entire device length [5]. This can increase the modulation efficiency while maintaining a large bandwidth. The bandwidth and the device length are only limited by the microwave loss at high frequencies, which includes propagation loss and source port reflection loss and the velocity mismatch between the optical signal and the microwave signal. Another limiting factor is the increased optical loss with a longer device, which is related to the optical signal-to-noise ratio of the modulated signal [3]. Due to waveguide dispersion, high frequency components will experience smaller characteristic impedance and hence higher reflection loss when launched from a 50  driver [8-12]. In previous articles, we have proposed an asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQW) structure based on the InGaAlAs material system that has advantages such as large Stark shift, very low insertion loss, zero chirp, high extinction ratio, and higher figures of merit in comparison with the IQW structure [13-17]. In this article, we have designed and analyzed a TWEAM based on asymmetric intra-step-barrier coupled double strained quantum wells at 1.55 m optical wavelength for the first time. Design of TWEAM includes the reduction of electrical losses, velocity mismatch, and impedance mismatch. It