Optical components can be a lot faster and cheaper if all components can be integrated in a single chip. The devices research group concentrates on integrated optoelectronic devices: making optical components faster, smaller and more energy-efficient.
The short and mid-term research is focussed on improving COBRA’s work on four basic optical components that are the foundation of photonic integration: passive waveguide structures, phase manipulators, amplitude manipulators, and polarization manipulators. Ninety percent of all optical devices can be made using these four elementary components.
The long-term research is focussed on creating ultrasmall and ultrafast components as building blocks. Standardized, these building blocks may be packed together in Very Large-Scale Photonic Integrated Circuits (VLSI). The aim is to make these VLSI components work as digital photonic devices.
Even with a focus on devices, exploring the underlying fundamental physics of light-matter interaction is essential. One main question is, for example, how semiconductors can be effectively integrated in metal nanocavities in such way as to emit light in the spectrum used for optical telecommunications.
Here are some highlights of the Devices group from the last three years.
First, in 2007 COBRA created the smallest electrically pumped laser in the world. The device is a small pillar, just a few hundred nanometers wide, made of In/InGaAs/In, covered with a film of gold atoms. Prior to the successful demonstration of the nanoscale laser, many optical scientists thought that metal-coated resonators would never work as optical lasers, because the losses would be too great. More recently, COBRA demonstrated again how the optical losses in a thin silver film on top of a semiconducting nanoscale pillar could be overcome. In the center of the pillar is a semiconductor-gain region with dimensions of a few tenths of a nanometer. New ways have been found to improve its gain to such a degree that sufficient light is emitted. The pillar is encapsulated in a silver cavity, which is electrically isolated from the semiconductor material by a dielectric layer with a thickness on the order of 10 nm. The devices were made by employing epitaxy, electron-beam lithography, dry etching, and various material deposition techniques.
Furthermore, COBRA researchers reported the creation of a novel tunable laser that may play an important role in future packet-switched optical networks. The laser is based on a novel tuning principle that allows for tuning speeds of 1 ns, 100 times faster than today's commercially available integrated tunable lasers.
Another successful example is the best performing mode-locked ring laser to date, operating in the long wavelength telecommunication window, which has been developed at COBRA. This included the development of compact polarization converters.
In addition, COBRA found new ways of using splitters as generic building blocks in polarization-handling circuits.