Spontaneous Vacuum Fluctuations and the Fundamental Sensitivity Limit of Wavelength-Multiplexed Fiber Bragg Grating Sensor Array Readouts

• Published in: Journal of lightwave technology Vol. 36; no. 9; pp. 1615 - 1619
• Main Author: Hegyi, Alex
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: amplified spontaneous emission; Bandwidth; Bandwidths; fiber Bragg grating; Light sources; Luminous intensity; Multiplexing; Noise; Noise intensity; Noise measurement; Optical amplifiers; Optical fiber sensors; Optical noise; Optical saturation; Photoconductivity; Sensitivity; Sensor arrays; Sensors; Spontaneous emission; Variation; Wavelength shift detection; zero-point fluctuations
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2017.2785178

Multiplexed wavelength shift detectors are increasingly used to read out arrays of fiber Bragg grating (FBG) sensors that are illuminated by amplified spontaneous emission sources. The fundamental sensitivity limit of these systems is due to excess noise from the light source. This limit is evident when optical intensity is high enough to overcome the electronic noise of the measurement system. Here, we derive a formula for the fundamental sensitivity limit and show it is only a function of sensor optical bandwidth. The formula is corroborated by experiment by measuring the wavelength noise of 12 FBG sensors as a function of optical intensity. First, the expected noise vs. intensity is calculated from the formula with known sensor optical bandwidths and shown to agree to the measured results without fit. Then, the formula is fit to the experimental data, with optical bandwidth as a parameter, to extract the optical bandwidth of each FBG from the noise saturation behavior with respect to optical intensity.