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 realized^{1, 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, ⁽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.

1. COMDTU, Department of Communications, Optics & Materials, Building 345V, NanoDTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
   
2. CINF, MIC-Department of Micro and Nanotechnology, Building 345E, NanoDTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
   
3. †Present addresses: MIC, Building 345E, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark (K.A.); iNANO and IFA, University of Aarhus, Ny Munkegade, Building 1520, DK-8000 Århus C, Denmark (M.K.)

Correspondence to: Rune S. Jacobsen¹ Correspondence and requests for materials should be addressed to R.S.J. (Email: Rune@com.dtu.dk).