Multiple Layer Graphene Optical Modulator

Compared to traditional devices with limited bandwidth range, up to 10 nanometers, the Berkeley Lab optical modulator operates at a 1.2 GHz (at 3dB) and at a broad optical bandwidth— from 1.35mm to 1.6mm under ambient conditions. The speed for a single modulator could, theoretically, reach 500 GHz. The device has a 25 square micron footprint, offering the potential for integration.

The Berkeley Lab team demonstrated that graphene can be used as the active media for an optical modulator with a modulation ability of 0.1 dB/micron. In initial demonstrations, drive voltages were added between the silicon waveguide and the graphene, which cannot avoid the carrier-induced optical loss in the waveguide. In another configuration, drive voltages were added between two graphene layers separated by an insulator layer. In this version, no charge accumulates in the waveguide, so the optical loss is low. Double or even more graphene layers can modulate light more efficiently. The operation speed of the device is limited by the carrier mobility of graphene, but not the waveguide materials, meaning much higher modulation speed can be achieved.

Integrated silicon modulators have a relatively large footprint, on the order of millimeters, and are limited by weak plasma dispersion. Germanium and compound semiconductors have the challenge of integration with existing silicon electronics and photonics platforms. High quality-factor optical resonators have been used to increase the modulation strength; however, these devices suffer from intrinsic narrow bandwidth. The Berkeley Lab graphene optical modulator overcomes these limitations to potentially revolutionize digital communications.

• Compact footprint
• Broad operation bandwidth
• Fast modulation speed
• Low insertion loss
• Insensitivity to temperature
• Compatibility with silicon technology

• Optical modulator for digital communication
• Flexible modulator, e.g., graphene or optical fiber
• Biosensor

FOR MORE INFORMATION:

Liu, M., Yin, Xiaobo, Ulin-Avila, E., Geng, B., Zentgraf, T., Ju, L., Wang, F., Zhang, X., “A graphene-based broadband optical modulator,” Nature, Vol. 474, June 2, 2011.

Yang, Sarah, “Graphene Optical Modulators Could Lead to Ultrafast Communications,” UCBerkeley News Center, May 8, 2011. http://newscenter.berkeley.edu/2011/05/08/graphene-optical-modulators-ultrafast-communications/