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Proceedings Paper • Open Access

Epitaxially grown vertical junction phase shifters for improved modulation efficiency in silicon depletion-type modulators
Author(s): S. Sharif Azadeh; S. Romero-García; F. Merget; A. Moscoso-Mártir; Nils von den Driesch; D. Buca; J. Witzens

Paper Abstract

High-speed silicon modulators based on the plasma effect in reverse-biased p(i)n junction phase shifters have been extensively investigated. The main challenge for such modulators is to maximize their modulation efficiency without compromising high-speed performance and insertion losses. Here, we propose a highly efficient silicon modulator based on a Mach-Zehnder Interferometer in which the doping profile of a vertical pin junction is precisely controlled by means of in-situ doping during silicon epitaxial growth. The precise level of control afforded by this fabrication procedure allows separately optimizing doping concentrations in the immediate vicinity of the junction and in surrounding electrical transport layers at the nanometric scale, enabling high performance levels. Free carrier absorption losses are minimized by implementing high carrier densities only in the waveguide regions where they benefit the most, i.e., in the immediate vicinity of the junction. Since these devices rely entirely on single crystal silicon, performance degradation caused by poor transport and high optical losses in poly- or amorphous silicon (as utilized in similar vertical phase shifter geometries such as semiconductor-insulator-semiconductor capacitive phase shifters) is avoided. Furthermore, unlike conventional plasma effect silicon phase shifters, the bandwidth of the proposed phase shifters is largely independent of the applied reverse voltage and the phase shift versus applied voltage is linearized, making them more suitable for complex modulation formats. The efficiency of the single ended phase shifters is expected to reach a VπL of 0.56 V•cm and absorption losses of α=4.5 dB/mm, a good performance metric for depletion-type modulators. Lumped element Mach-Zehnder Modulators as well as travelling-wave modulators with phase matching based on meandered waveguides have been designed and their RF characteristics simulated and optimized with Ansoft HFSS. First experiments have validated the growth of the epitaxial stack and complete devices are currently being fabricated.

Paper Details

Date Published: 1 May 2015
PDF: 7 pages
Proc. SPIE 9516, Integrated Optics: Physics and Simulations II, 95160T (1 May 2015); doi: 10.1117/12.2178790
Show Author Affiliations
S. Sharif Azadeh, RWTH Aachen Univ. (Germany)
Jülich Aachen Research Alliance (Germany)
S. Romero-García, RWTH Aachen Univ. (Germany)
Jülich Aachen Research Alliance (Germany)
F. Merget, RWTH Aachen Univ. (Germany)
Jülich Aachen Research Alliance (Germany)
A. Moscoso-Mártir, RWTH Aachen Univ. (Germany)
Jülich Aachen Research Alliance (Germany)
Nils von den Driesch, Peter Grünberg Institute 9, Forschungszentrum Jülich (Germany)
Jülich Aachen Research Alliance (Germany)
D. Buca, Peter Grünberg Institute 9, Forschungszentrum Jülich (Germany)
Jülich Aachen Research Alliance (Germany)
J. Witzens, RWTH Aachen Univ. (Germany)
Jülich Aachen Research Alliance (Germany)


Published in SPIE Proceedings Vol. 9516:
Integrated Optics: Physics and Simulations II
Pavel Cheben; Jiří Čtyroký; Iñigo Molina-Fernández, Editor(s)

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