15 September 2010( Wednesday) 2.30pm to 3.30pm
Venue:Room B212 (B Block), Swinburne University of Technology
Speaker : Associate Professor Manas K Haldar
IET Malaysia is proud to bring you a trial series of 1-hour research seminars, in partnership with Swinburne University of Technology Sarawak Campus (SUTS), to be held at SUTS Campus in Kuching, Sarawak.
The inaugural seminar in the series will be given by Associate Professor Manas K Haldar on quantum cascade lasers.
SYNOPSIS :
Quantum Cascade Lasers (QCLs) have been of great interest for a variety of reasons. They can be used for detection of toxic chemicals and gases by mid infrared spectroscopy. Their narrow line widths make them attractive in coherent applications. For optical communications, they offer a wide range of wavelengths not available from common inter band semiconductor lasers.
Direct intensity modulation refers to intensity modulation of light by varying the drive current of the laser as opposed to indirect modulation which uses modulators external to the laser. The direct intensity modulation characteristics of QCLs are different from those of inter band lasers in several ways. This implies that the model for inter band lasers is not applicable to QCLs.
A set of three rate equations were used by the speaker to analyze direct intensity modulation characteristics. An equivalent circuit obtained from this model but taking into account the non-radiative transition from the highest to the lowest level was presented this year.
A more accurate set of four rate equations was presented by MIT researchers. Keeping this in view, it is shown that three rate equations are adequate, but some parameters have to be changed. Accordingly, the equivalent circuit is modified to conform to the revised rate equations. Future work involves using frequency/wavelength modulation spectroscopy to detect trace gases and functional groups and studying injection locking and chaotic behavior.