Noise investigation and signal processing in fiber optic gas sensor with wavelength modulation of the DFB laser diode

Noise from optical and electronic components of a fiber optic gas sensor system using wavelength modulation of the DFB laser diode in either transmission or reflection mode were investigated. Our experimental results indicate that reflective type cells give poorer performance due to interference effects from connectors and joints within the fiber system compare to transmissive type cell. Intensity noise from optical coupler, collimator, was measured and its affection to sensing system was discussed. In order to raise the signal to noise ratio (SNR), signal processing methods, such as data average, low pass filter were used and compared. The results would be a useful engineering tool to design high SNR optical gas sensing system.

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