Danish researchers have developped a thermo-optic in-line extinction modulators (ILEMs) whose operation is based on the guiding of longrange surface plasmon polaritons (LRSPPs) along metal stripes embedded in polymer and heated by electrical signal currents. Several 1 cm long ILEMs, which utilize 15 nm thin and 8 micron wide gold stripes guiding LRSPPs and comprising 3-6 mm long control electrodes, are investigated at telecom wavelengths. The fabricated ILEMs feature low driving powers (approx. 100 mW) and high extinction ratios (approx. 30 dB) that depend weakly on the wavelength, moderate response times (approx. 0.5 ms) and the total (fiber-to-fiber) insertion loss of approx. 8 dB when using single-mode fibers.

Schematic (a) representation of the LRSPP field distribution near a thin metal film embedded in dielectric along with the orientation of the dominant electric field component and (b) layout of LRSPP-based ILEM along with single-mode fibers used for the LRSPP excitation. Optical microscope images of (c) the end-fire in/out coupling arrangement showing a cleaved single-mode fiber and two gold stripes for guiding LRSPPs and (d) the intensity distribution of fundamental LRSPP mode at the output facet of a stripe guide excited at 1.55 lm.

(a) Total (fiber-to-fiber) transmission of 1 cm long ILEMs having the control electrodes of different length as a function of the applied electrical power per unit electrode length. (b) The temporal responses of the ILEM having a 3-mm long electrode for different levels of the applied electrical power.

Images courtesy of Prof. S. I. Bozhevolnyi, Department of Physics and Nanotechnology, Aalborg University, Denmark.