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Strained silicon as a new electro-optic material


For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized1,2. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon3. Recently, however, a continuous-wave Raman silicon laser was demonstrated4; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, χ(2) ≈ 15 pm V-1, makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck5 in modern computers by replacing the electronic bus with a much faster optical alternative.

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Figure 1: Applying strain to crystalline silicon.
Figure 2: Diagram of a Mach–Zehnder modulator.
Figure 3: Effect of straining the silicon structure.
Figure 4: Experimental verification of the linear enhancement of with the group index.


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We thank R. Kjær and M. Svalgaard for their contributions. This work was supported in part by the NKT academy, the Danish Research Council for Technology and Production Sciences via the PIPE project, by NEDO via the Industrial Technology Research Area and by CINF via the Danish National Research Foundation. All generic SOI PCWs were fabricated within the framework of the European IST project PICCO and in this connection we especially thank W. Bogaerts and R. Baets.

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Correspondence to Rune S. Jacobsen.

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Jacobsen, R., Andersen, K., Borel, P. et al. Strained silicon as a new electro-optic material. Nature 441, 199–202 (2006).

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