Optimizing Brillouin Optical Time-Domain Analyzers Based on Gain Spectrum Engineering

Summary

A protocol for Brillouin optical time-domain analyzers based on gain spectrum engineering is presented. Enhancements in the sensing performance, including sensing range and measurand resolution are achieved and the excess Brillouin intensity noise is studied. The protocol introduces a new way to enhance distributed Brillouin sensing performance.

Abstract

Demonstrated is a unique method for sensing performance enhancement in Brillouin optical time-domain analyzers (BOTDA). A Brillouin gain spectrum (BGS) is superimposed with two symmetric Brillouin loss spectra (BLS). This leads to a complex engineered spectrum shape that is more resistant to the sensing system noise. Instead of only one pump and probe interaction as in the conventional BOTDA setup, three optical probe waves are exploited, with one probe located in the BGS and the other two symmetrically in the BLS. Due to the resistance and insensitivity of the engineered spectrum shape to the noise, the sensing performance is enhanced by 60% and the measurand resolution is doubled.

Introduction

Distributed fiber sensing (DFS) is a unique mechanism that employs a whole fiber as a sensing medium. It has attracted a lot of interest due to the low fiber loss; small size; and the ability to be easily embedded in various structures, such as dams, bridges, and buildings, to perform environment surveillance as an artificial nerve system. In comparison to applying numerous traditional point sensors, such as fiber Bragg gratings (FBG), it provides a more efficient and cost-effective solution in a wide range of large-scale sensing tasks, such as infrastructure and structural health monitoring¹.

Current distributed sen....

Protocol

1. Selecting optimized parameters for the spectrum engineering via simulation

1. Model the engineered BGS g_SBS(ν,z) with the equations^28,29
   
   as implemented by, for example, the supplemental MATLAB script.
   NOTE: Here, G(ν) is the complex gain coefficient, calculated in the script as G_complex within the SBS_g function for the conventional BGS or SBS_gl function for the engineered BGS; <....

Results

Figure 3 shows the simulation results. Points with η < 1 in Figure 3A indicate a smaller frequency error (higher measurand resolution) with the engineered BGS. The lower the value was, the bigger the advantage. The minimum ratio was at m = 1, indicating that a multiprobe instead of multipump scheme can be carried out (see Discussion). Figure 3B

Discussion

The most critical step during the experiment is the equalization of the three probe powers so that m = 1 and symmetry between the two Brillouin loss spectra is achieved. Besides the separate power check using the power meter at Cir port 2, as presented in steps 4.9 and 4.10, the power equalization can be more precisely checked in the digitizer. By setting the RF 1 frequency to ~11 GHz (the fiber BFS) and switching off EDFA 3, the conventional trace with the peak gain can be recorded in the digitizer (trace I). T.......

Materials

Name	Company	Catalog Number	Comments
Current controller for laser diode	ILX Lightwave	LDX3220
Digitizer	Acqiris SA	U5309A-1039
Erbium doped fiber amplifier 1	Photop	PTEDFA-A-PA-C-SCH-15
Erbium doped fiber amplifier 2	LiComm	OFA-TCH
Erbium doped fiber amplifier 3	Calmar Optcom	AMP-ST30
Erbium doped fiber amplifier 4	Photop	PTEDFA-A-PA-C-SCH-15
Fiber Bragg grating 1	Advanced Optics Solutions	T-FBG
Fiber Bragg grating 2	Advanced Optics Solutions	T-FBG
Fiber under test	ofs
Isolator	General Photonics	S-15-NTSS
Laser diode	3SP Group	A1905 LMI
Mach-Zehnder modulator 1	Avanex	IM10
Mach-Zehnder modulator 2	Avanex	IM10
Mach-Zehnder modulator 3	Avanex	IM10
Nanosecond driving board for semiconductor optical amplifier	Highland Technology	T160-9 (28A160-9C)
Optical coupler 10:90	Newport		Benchtop coupler/WDM
Optical coupler 50:50	Newport		Benchtop coupler/WDM
Optical spectrum analyzer	Hewlett Packard	86145A
Optical switch 1	JDSU	SN12-1075NC
Photodiode	Thorlabs	D400FC
Polarization scrambler	General Photonics	PSY-101
Pulase generator	Hewlett Packard	8082A
Radio function generator 1	Anritsu	MG3692C
Radio function generator 2	Agilent Technology	E8257D
Radio function generator 3	HTM	T2100
Semiconductor optical amplifier	Thorlabs	SOA1013SXS
Temperature controller for laser diode	ILX Lightwave	LDT5948
Temperature controller for semiconductor optical amplifier	Tektronix	TED200
Variable optical attenuator	JDSU	mVOA-A1	With optical switch function