Researchers in Japan claim to have developed the first continuous-wave (cw) nanolaser to operate at room temperature. What's more, they believe that their nanolaser is the smallest to date and uses only a microwatt of power - one of the smallest operating powers ever achieved. (Optics Express 15 7506)
"Our laser is so small and its power consumption is so low that one can integrate many devices for many channels without severely increasing the total power consumption. It can be used as an optical switch and wavelength converter," Toshihiko Baba, a researcher from Yokohama National University, told optics.org. "Such a photonic chip will soon be really important for photonic routers and silicon photonics."
Measuring just 20 x 20 x 100 microns, the nanolaser has a high Q factor of 20,000 and an effective lasing threshold of just 1.2 µW. The nanolaser's small size and cw emission make it suitable for applications ranging from a functional light source in integrated photonic chips or a fast single photon source in quantum cryptographic communication systems to a sensor head of biological and environmental material.
Finding a way to efficiently heat sink such a small device has limited the development of cw room temperature nanolasers in the past.
The key to achieving cw operation was to lower the operating power from 100 mW to a few microwatts. "We employed a high Q and small modal volume of the point shift nanocavity and used a fine fabrication process. These two improvements greatly reduced the operating power which resulted in cw operation," explained Baba.
"The main problem for room temperature operation is the large nonradiative relaxation of excited electrons, which reduces the internal efficiency of light generation from electrons," he continued. "It is particularly severe for photonic crystal lasers because the holey structure combined with heating, accelerates the nonradiative loss of electrons."
The team believes its method of manufacturing the device helps to reduce these losses. "We think using hydrogen iodide gas and additional chemical etching are effective for re-covering the etching damage of the emitting layer and terminating the electronic states at the sidewalls of holes, which results in an internal efficiency of 50 - 100 %," explained Baba.
The group is not confining its photonic crystal research to nanolasers. "We are studying methods of stopping optical signals in waveguides and the superlensing effect that has been demonstrated for the first time at light wave frequencies," concluded Baba. "We are dreaming of developing an integrated photonic chip using these technologies."
