All-optical modulator is capable of terahertz speeds

Researchers at the California Institute of Technology (CalTech; Pasadena, CA) have demonstrated intensity modulation of light with light, based on the all-optical Kerr effect in a planar, hybrid silicon-on-insulator/polymer, all-optical device. The group directly measured time-domain intensity modulation at 10 GHz and showed through spectral measurements that intensity modulation at frequencies in excess of 1 THz could be obtained. Integrating the optical polymer through evanescent coupling to the silicon waveguide increased the effective nonlinearity of the waveguide, allowing operation at continuous-wave power levels compatible with telecommunications requirements.

The device was based on a Mach-Zehnder geometry, in which the source waveguide was split into two arms. A gate signal was introduced into one of the arms and induced a phase shift in the source signal via the nonlinear Kerr effect. Intensity modulation was accomplished through interference between the phase-shifted source signal and the optical signal traveling along the reference arm of the Mach-Zehnder interferometer. The interferometer was unbalanced to allow the intrinsic phase shift to be controlled by tuning the source wavelength, an ability that made the Mach-Zehnder easier to characterize. Contact Michael Hochberg at hochberg@caltech.edu.