When a light beam passes through areas of differing (but static) refractive index, its wavelength changes while its frequency stays the same. If the refractive index of a medium is dynamically changed while the light is within it, however, the frequency of the photons can change. The details of such a “photon energy lifter” have been described by scientists at the University of Trento, CNR-INFM, and CRS BEC-INFM, all in Trento, Italy. Their simulations show that a device that can be fabricated with existing silicon photonic technology can shift the wavelength of a 1550 nm beam by -0.49 nm with a 95% efficiency.
A many-cavity coupled-resonator optical-waveguide filter (CROW) with two external distributed-Bragg-reflector (DBR) mirrors and 27 intercavity-coupling DBR mirrors drastically slows light entering the filter; the refractive index within the filter is quickly changed by introducing optically or electrically injected carriers. The pulse is delayed by 116 ps; the index change happens in 20 ps. Use of an electro-optical material such as lithium niobate could increase the tuning range. Contact Zeno Gaburro at [email protected].