The technique measures the optical absorption of haemoglobin, and relies on the absorption spectrum of haemoglobin varying with its oxygenation status.

Based on the infrared spectrum absorption characterization of methane gas, the long optical distance differential absorption method for methane detection is studied.

Based on the characteristic of spectrum absorption of acetylene, an optical fiber detection system for methane gas is presented, which has reference channel and is for on line and real time detection.