Yu and her team based the design of their device on a new type of photonic-crystal fiber (PCF). PCFs include spaces in the glass that run along the entire length of the fiber. When examined in cross-section (see image), these ‘air holes’ have a honeycomb-like arrangement. Reflection of the incoming light at the numerous air–glass interfaces confines the light to the center of the fiber.
In a theoretical modeling study, Yu and co-workers showed that the addition of a metal wire through the center of the fiber improved device efficiency. The incoming light couples to the electrons in the metal wire, and this forms matter–light hybrid particles called surface plasmons, Yu explains.
The researchers simulated the optical confinement of infrared light in a structure with air holes 2 micrometers in diameter. They then divided the light-carrying core of the fiber with a silver wire. Their calculations indicated that the best design has a hole-to-hole distance of 4 micrometers: it enabled a coupling efficiency of nearly 82%.
“The next step is to fabricate the device,” says Yu. “The structure can be easily realized by replacing the center air hole with a metal wire during fiber production, or by pumping molten metal into the center air hole post fabrication.”