Signal to noise and range enhancement of a Brillouin intensity based temperature sensor

K. De Souza; T. P. Newson

doi:10.1364/OPEX.12.002656

Optics Express
Vol. 12,
Issue 12,
pp. 2656-2661
(2004)
•https://doi.org/10.1364/OPEX.12.002656

Signal to noise and range enhancement of a Brillouin intensity based temperature sensor

K. De Souza and T. P. Newson

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K. De Souza and T. P. Newson, "Signal to noise and range enhancement of a Brillouin intensity based temperature sensor," Opt. Express 12, 2656-2661 (2004)

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Abstract

We report on the theory and use of pre-amplification to enhance the measurement range of a spontaneous Brillouin intensity based distributed fiber-optic sensor. One factor that limits temperature resolution is receiver sensitivity, which degrades for long range sensors. Using optical preamplification before photodetection in a 23km sensor improved the signal-to-noise by approximately 17dB using a 20MHz detector. The major source of noise was amplified spontaneous emission beat noise.

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Fig. 1. Plots showing: (a) the unamplified and optically amplified signals and the variation of RMS noise voltages of photodiode noise, transimpedance noise and EDFA noise with receiver bandwidth. (b) Corresponding variation of optical signal-to-noise ratio with and without optical preamplification. An improvement of 17dB is shown for a 20MHz receiver. G=27dB, N=40960 and B_o=47GHz.

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Fig. 2. Schematic experimental set up and preamplifier configuration.

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Fig. 3. (a) Unamplified and (b) 27dB amplified spontaneous Brillouin signal over 23km. Averages=8192.

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Fig. 4. (a) unamplified and (b) 27dB amplified spontaneous Brillouin signal at far end of fibre sensor. Averages=40960.

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Tables (1)

Table 1. Description of various noise sources and their corresponding mean square currents

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{SNR}_{o} [dB] = 10 \log [\frac{V_{SIGNAL} \sqrt{N}}{\sqrt{(Σ V_{n}^{2})}}]

Description	Mean square currents
Photodiode noise consisting of shot noise of the photocurrent and dark current.	$i_{SHOT}^{2} = 2 e (\frac{η e G_{P_{s}}}{h ν} + I_{d}) B_{eq}$
Thermal noise of the feedback resistor	$i_{THERMAL}^{2} = 4 K T \frac{B_{eq}}{R_{f}}$
Thermal noise of the FET channel	$i_{FET}^{2} = 3.7 K T π^{2} \frac{C_{t}^{2} B_{eq}^{3}}{g_{m}}$
Shot noise of the FET gate leakage current	$i_{FET-SHOT}^{2}$ =2e I_g B_eq
ASE-shot noise	$i_{ASE-SHOT}^{2}$ =2 e²η(G L_ase) F B_o B_eq
Signal-ASE beat noise	$i_{SIG - ASE}^{2} = \frac{{2 (e η)}^{2}}{h ν} F_{G^{2} P_{s} B_{eq}}$
ASE-ASE beat noise	$i_{ASE-ASE}^{2}$ =(ηe)² F²(G L_ase)²B_o B_eq
Electrical signal	$i_{SIGNAL}^{2} = {(\frac{η e}{h ν})}^{2} P_{s}^{2} G^{2}$

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