Research roundup

21 Dec 2005

A look at the innovations reported this month including a promising candidate for an electrically-pumped silicon laser.

Silicon photonics

An all-silicon electrically-driven resonant-cavity LED based on a slotted waveguide could be a promising candidate for an electrically-pumped silicon laser, according to its designers. The device, simulated by Carlos Angulo Barrios from Universidad politécnica de Valencia in Spain and Michal Lipson from Cornell University in the US, consists of a micro-ring resonator formed on a Si/SiO₂ slot-waveguide with an electroluminescent material in the slot region. "The geometry of the slotted waveguide defines a MOS diode for the electrical excitation of the active material," say the authors. "Simulations indicate that the micro-resonator could exhibit a quality factor of 6700 and emit light at 1.54 microns with a bias current of only 0.75 nA," conclude the authors. (Optics Express 13 10092)

Optical coatings

Researchers at Japan's Tokyo Institute of Technology and Tokai University have come up with a way of producing a waterproof coating for optical elements used with high-power lasers. The simple method involves spin-coating silicone oil onto the surface of the optical part and then irradiating it with a xenon excimer lamp. This photo-oxidises the silicone oil leaving a thin film of amorphous glass. The researchers have tested their approach on a plastic lens, a mirror and a nonlinear crystal and say the components can now be immersed in water and survive high-power lasing. "This technique has enabled an optical thin film to transmit ultraviolet rays of wavelengths below 200 nm and to exhibit homogeneity, high density, resistance to environmental effects and corrosion by water," say the authors. (Optics Letters 30 3416)

Frequency combs

Three researchers in Germany are using frequency combs to make high-precision measurements of the refractive index of air. Standard methods give an accuracy of around 5 x 10^-8 but the team believes that using a Ti:sapphire laser frequency comb as the light source in a Michelson interferometer has the potential to give an accuracy of 10^-9. The broad bandwidth of the comb also means that the refractive index of air can be characterized at different wavelengths simultaneously. "The accuracy of our experiment reaches a level of 1.3 x 10^-7," say the team. "By changing the laser repetition rate we can achieve a better resolution and accuracy." (Optics Letters 30 3314)