Silicon Photonics

Abstract

Integrated nano-electronic circuits in silicon represent the most striking combination of scientific breakthroughs, technological sophistication and the economics of scale. In recent years, nano-photonic circuits for the manipulation of light in the same material platform follow a similar trend. The main force that drives the advance of integrated photonic circuits is short-reach optical communication among processors and memory elements at the data center. While optical communication was initially developed as a long-haul solution, it is required nowadays at the rack, board and even chip levels. The need for close integration between optical communication functions and electronic logic and memory is calling for silicon photonics. This exciting field of research and development is growing rapidly. Furthermore, silicon photonics is not restricted to data communications only: concepts and building blocks are directly applicable to other major fields of interest such as sensors and laser radars.

The main part of the course focuses on the physical principles and basic building blocks that are underlying the processing of light in silicon-photonic integrated circuits. These include guiding of light in various types of waveguides, splitting and combining of waveforms in couplers, spectral filtering in Mach-Zehnder interferometers and ring resonators, modulation through free-carrier effects, linear and nonlinear losses, all-optical amplification through Raman scattering, and introduction of opto-mechanical effects in suspended structures. Integration with additional material platforms such as germanium and indium-phosphide towards the realization of light sources, electrically-pumped amplifiers and short-wave infra-red detectors is addressed as well. Examples of cutting-edge device applications are presented and analyzed. Lastly, a brief introduction to main fabrication steps is given at the end of the course.

Glossary

1: Introduction: Motivation for silicon photonics. Silicon as an optical medium. Absorption spectrum of silicon. The silicon-on-insulator material platform
2,3: Guiding of light in silicon photonics: Analytic solutions for symmetric and asymmetric 1D slab waveguides. TE vs. TM modes. The cut-off conditions. Multi-mode vs. Single-mode waveguides. Modal, chromatic and polarization-mode dispersion. Approximate solutions for 2D waveguides. Ridge vs. rib geometries. Propagation losses due to bending and roughness
4,5: Couplers in silicon photonics: Directional couplers. The calculation of coupling coefficient. Transfer matrices. Multi-mode interference couplers. Example: vertical grating couplers for input/output interfaces
6,7: Filters: The analogy between digital and optical filters. Zeros and poles Finite and infinite impulse response filters. The Mach-Zehnder interferometer. The ring resonator. Cascading multiple stages. Arrayed waveguide gratings. Methods for post-fabrication trimming. Example: 8-channel wavelength-division multiplexing
8,9: Nonlinear propagation effects: The nonlinear refractive index. Two-photon absorption and associated limitations. Stimulated Raman scattering. Opto-mechanical interactions. Example: Raman laser in silicon
10: Electro-optic modulators: Absence of Pockels effect in silicon. Free-carrier effects, changes in index and absorption. P-N junctions across silicon waveguides. Mach-Zehnder and resonator-based modulators. Plasmonic modulators. Example: a modulator device
11: Heterogeneous materials integration: Indirect bandgap of silicon. Lack of efficient stimulated emission. Bonding of indium-phosphide-based active layers. Hybrid devices. Germanium-based photo-diodes. Example: a hybrid silicon-indium-phosphide laser diode.
12: Introduction to fabrication of devices. Optical lithography. Electron-beam lithography. Reactive ion etching. Deposition of metals. Implantation of ions.
13: Introduction to test and measurement setups. Measurement of transfer function. Transfer of data.

Learning Outcomes

1) Understanding the opportunities and challenges of silicon photonics.
2) Analysis, simulation and design of waveguide, couplers and filters in silicon photonics.
3) Understanding the physical mechanism being used in active photonic devices over silicon, difficulties, solution paths and limitations.
4) Knowledge of the state of the art in silicon photonics
5) Basic acquaintance with fabrication, test and measurement.

Bibliography

1) A. Yariv and P. Yeh, Photonics, 6th Edition, Oxford University Press, 2007.
2) Silicon Photonics, Editors: L. Pavesi and D. J. Lockwood. Springer, 2004.
3) Silicon Photonics: the state of the art. Editor: G. T. Reed. Wiley, 2008.

External Evaluator

1) Prof. Uriel Levy, Hebrew Univ. of Jerusalem, Israel.
2) Prof. Jacob Scheuer, Tel-Aviv Univ, Israel.
3) Prof. Thomas Schneider, Technical Univ. of Braunschweig, Germany.

Responsible Academic

Prof.Prof. Avi Zadok Avi Zadok

Awarded ECTS

5