This workpackage is aimed at obtaining new generations of all optical flip-flops with improved performance with respect to the micro-disk based approach (WP2) in terms of size, speed and power consumption. Two paths will be explored: one based on two-dimensional photonic crystal (2DPC) lasers, for which mainly LPN will be responsible, and another based on plasmonic lasers, for which mainly TUE will be responsible. Both of these systems are very exploratory and as such will require intense effort in numerical studies and technological development.
1) Flip-flop based on connected 2D PC lasers
A schematic of the flip-flop is depicted below.
2) Metallic nanocavity lasers
Both the micro-disk and photonic crystal lasers are based on dielectric cavities and their dimensions are thus limited by the wavelength of the light. Metallic cavities can confine the light to volumes with considerably smaller dimensions. Although it is commonly believed that the high losses of the metals are prohibitive for laser operation in small metallic cavities, it has been demonstrated recently that metallic-coated nano-cavities with modal volumes smaller than dielectric cavities can have moderate quality factors and that indeed laser operation is possible. The structure of the demonstrated laser is shown in Figure 9. It consists of an InP/InGaAs/InP pillar with a conventional heterostructure surrounded by a thin insulating silicon nitride layer and then encapsulated in gold. The InGaAs layer forms the laser gain medium, with electrons injected via the top of the pillar and holes via the p-InGaAsP layer and a large area lateral contact.
The initial demonstration of the metallic nano-cavity laser has been at cryogenic temperatures. To be useful in many signal processing applications, operation at room temperature is required. Obtaining room temperature operation of these lasers is a key objective for this proposal. Another objective is the further miniaturization of the laser concept from what has been demonstrated. This miniaturization will require the realization of true Plasmon gap mode metallic waveguide cavities. In such cavities the laser modal and active regions can in principle be shrunk down to the scale of a few tens of nanometers, or less, in two dimensions. Finally the integration of such lasers in a membrane environment needs to be investigated. To make use of such lasers they will have to be efficiently coupled to dielectric waveguides.