Detection schemes, algorithms and device modeling for TDLS

Electrical and Computer Engineering

Speaker: Andreas Hangauer
Monday, January 9, 2012
11:00 AM to 12:00 PM


202 Space Science Building
Rice University
6100 Main St
Houston,Texas,USA


The basic question which provides the frame of the work is what TDLS sensor
properties can be improved when a digital sensor hardware is utilized.
One topic I will present is the analysis of multi-harmonic detection schemes
for wavelength modulation spectroscopy. I will show theroretically and
experimentally that multi-harmonic detection has advantages in terms of
noise over standard second harmonic detection and will outline the method
how to implement the proper data processing and anaysis. In course of this
I will also show general properties of harmonic spectra including an
improved computation method for these including their derivatives. This is
important for spectral least squares curve-fitting using the Voigt or Gauss
absorption line profile because no numerical integration is required. It is
based on spline approximation of the transmission spectrum and an exact
closed form expression for the harmonic spectrum of a spline function.
The second major topic is device modeling with aim of creating computer
simulations of TDLS sensors to improve algorithms and detection schemes in
case this is not possible analytically. The challenge for this is proper
modeling of the laser diode in the lower frequency range (< 100 MHz)
including thermal tuning and nonlinear intensity modulation behavior. This
is not done in literature so far since these effects are negligible for
telecomunication applications. I will present a general theory and
comparison with experimental results for VCSELs of different types and
operating wavelengths. This significantly improves the understanding and
modeling of the tuning behavior of these lasers.

Host: Frank K. Tittel (AL A237, x4833)