Open AccessElimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line
Author(s) -
Arup Lal Chakraborty,
Keith Ruxton,
Walter Johnstone,
Michael Lengden,
Kevin L. Duffin
Publication year - 2009
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.17.009602
Subject(s) - optics , materials science , attenuator (electronics) , laser , tunable diode laser absorption spectroscopy , amplitude modulation , optical modulation amplitude , modulation (music) , optical fiber , laser diode , intensity modulation , phase modulation , fiber laser , wavelength , optical attenuator , distributed feedback laser , fiber optic sensor , frequency modulation , optoelectronics , physics , attenuation , optical amplifier , phase noise , bandwidth (computing) , telecommunications , computer science , acoustics
A new fiber-optic technique to eliminate residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy is presented. The modulated laser output is split to pass in parallel through the gas measurement cell and an optical fiber delay line, with the modulation frequency / delay chosen to introduce a relative phase shift of pi between them. The two signals are balanced using a variable attenuator and recombined through a fiber coupler. In the absence of gas, the direct laser intensity modulation cancels, thereby eliminating the high background. The presence of gas induces a concentration-dependent imbalance at the coupler's output from which the absolute absorption profile is directly recovered with high accuracy using 1f detection.