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Liquid Crystal Electrically Tunes Photonic Crystal Laser

Photonics Spectra
Aug 2004
In the July 19 issue of Applied Physics Letters, scientists at California Institute of Technology and the Jet Propulsion Laboratory, both in Pasadena, Calif., presented the results of their experiments with the electrical tuning of a photonic crystal laser infiltrated with liquid crystal. The ability to electrically tune such emitters may enable the study of various optical phenomena as well as functional applications.

The photonic crystal structure in the work comprised a triangular lattice of holes defined in InGaAsP quantum-well material with electron-beam lithography and dry etching. The structure was infil-trated with a commercial nematic liquid crystal from Merck KGaA of Darmstadt, Germany, and sandwiched between plates of indium tin oxide. An 830-nm laser diode served as an optical pump source.

The application of a voltage to the photonic crystal reoriented the liquid crystal, changing the effective refractive index of the laser cavity. The researchers observed a maximum shifting of 1.2 nm in the emission wavelength with the application of 20 V, but they suggest that the tuning range may be increased to more than 20 nm.


GLOSSARY
liquid crystal
A type of material that possesses less geometrical regularity or order than normal solid crystals, and whose order varies in response to alterations in temperature and other quantities. Liquid crystals are characterized by phase varieties, including cholesteric, nematic and smectic. The optical properties of liquid crystals are familiar from their use in displays, known as LCDs.
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