Tunable diode laser frequency modulation spectroscopy through an optical fiber: High-sensitivity detection of water vapor

Abstract

Frequency modulation spectroscopy through a single-mode optical fiber has been demonstrated for monitoring H2O vapor at 7665 cm−1. Using a 2.5 mW distributed feedback laser and 100 m of optical fiber, a minimum detectable absorption of 5×10−7 was achieved. To obtain this sensitivity limit, very large spurious signals and technical noise were suppressed using a dual-channel detection scheme.