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The general Electro-Optic modulators which employ lumped electrode structures face the limitation that the bandwidth of the device is constrained by the RC constant and a higher operation speed requires a shorter device length, which is also restricted by the RC-lump limitation. There is a significant advantage to employ a traveling-wave configuration of the electrodes type in order to eliminate limitations imposed by a lumped electrode design.  In this section, the modulator employs traveling wave electrode structure is introduced and characterized. To simulate the distribution of the charge carriers, a self-consistent simulation of the charge and electrostatic potential is performed using CHARGE. MODE will then take the carrier density information and calculate the corresponding changes in the real and imaginary parts of the refractive index of the material. These parameters are then exported to INTERCONNECT, including the voltage dependent junction capacitance. INTERCONNECT element library offers the flexibility required for the design and simulation of traveling wave modulators. For more information of the simulation procedure, please see the Traveling Wave Modulator on device level.





In this topic

Literature Review

System Modeling Instruction & Results

Associated files



See also

Getting started: Mach-Zehnder modulator

PIN Mach-Zehnder modulator
Traveling Wave Modulator: device level


[1] Baehr-Jones, Tom, et al. "Ultralow drive voltage silicon traveling-wave modulator." Optics express 20.11 (2012): 12014-12020.

[2] Kim, Inho, Michael RT Tan, and Shih-Yuan Wang. "Analysis of a new microwave low-loss and velocity-matched III-V transmission line for traveling-wave electrooptic modulators." Lightwave Technology, Journal of 8 (1990): 728-738.

[3] Kubota, K. A. T. S. U. T. O. S. H. I., J. U. N. I. C. H. I. Noda, and Osamu Mikami. "Traveling wave optical modulator using a directional coupler LiNbO 3 waveguide." Quantum Electronics, IEEE Journal of 16.7 (1980): 754-760.

[4] Xu, Hao, et al. "Demonstration and Characterization of High-speed Silicon Depletion-mode Mach-Zehnder Modulators." (2014): 1-1.

[5] Lin, S. H., and Shih-Yuan Wang. "High-throughput GaAs PIN electrooptic modulator with a 3-dB bandwidth of 9.6 GHz at 1.3 µm." Applied optics 26.9 (1987): 1696-1700.

[6] Wang, S. Y., and S. H. Lin. "High speed III-V electrooptic waveguide modulators at λ-1.3 μm." Lightwave Technology, Journal of 6.6 (1988): 758-771.

[7] Chiu, Yijen, et al. "High-speed traveling-wave electro-absorption modulators."International Symposium on Optical Science and Technology. International Society for Optics and Photonics, (2001).














In a traveling wave electrode configuration, the reflections at the output end of the waveguide is significantly reduced by terminating the microwave signal with a matching load. Therefore the configuration overcomes the RC constant limitations suffered by lump devices. The device could be made longer and still can achieve the speed requirement as for the lump devices. By carefully controlling the index mismatch and impedance mismatch, the desired modulator can be achieved. Following are two figures of the demonstration of the traveling wave modulators.


TW Modulator waveguide electrodes system modeling (click to enlarge)

TW Modulator waveguide electrodes system modeling (click to enlarge)



TW Modulator system modeling (click to enlarge)

TW Modulator system modeling (click to enlarge)


To evaluate the accuracy of the traveling wave electrode model, we tested several key features of the element according to relevant papers, please see Literature Review for more information.

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