Practical Application of Fiber Components manufactured by Bonacom in Hybrid Fiber-Optic Distributed Simultaeous Vibration,Temperature & Strain Sensing     

 

Distributed sensing systems can transform an optical fiber cable into an array of sensors,allowing users to detect and monitor multiple physical parameters such as temperature, vibration and strain with fine spatial and temporal resolution over a long distance. 

 

Rayleigh scattering-based phase optical time domain reflectometry (OTDR) for vibration and Raman/Brillouin scattering-based OTDR for temperature and strain measurements have been developed over the past two decades.The key challenge has been to find a methodology that would enable the physical parameters to be determined at any point along the sensing fiber with high sensitivity and spatial resolution, yet within acceptable frequency range for dynamic vibration, and temperature detection.

There are many applications, especially in geophysical and mining engineering where simultaneous measurements of vibration and temperature are essential. 

Recent developments of B-OTDR and φ-OTDR-Based hybrid vibration, temperature and strain measurements is analyzed based on operation principles and performance shown in Fig.7

Figure 7. Experiment setup of the distributed simultaneous temperature,vibration and strain sensing system. AOM:Acousto-optic Modulator, EDFA: Erbium-Doped Fiber Amplifier, BPF: Band-pass Filter, PZT:Piezoelectric Transducer, AWG: Arbitrary waveform generator, BL: Brillouin Laser, PS: Polarization Scrambler, OS: Optical Switch, PD: Photo-detector, DAQ: Data Acquisition.

 

Bonacom's band pass filter(BPF,BNBPF-31,Bonacom Technology Co.,LTD,Shenzhen,China),1x2 optical switch(OS,BNSW-31),1x2 optical coupler(OC,BNFUC-1-31),1x2 optical circulator(CIR,BNCIR-31-S) have been widely used in distributed simultaneous temperature,vibration and strain sensing system.

 

The Brillouin frequency shift is measured using Brillouin optical time-domain analysis (BOTDA) with differential pulse-width pair technique, while the spectrum shift of the Rayleigh backscatter is measured using optical frequency-domain reflectometry (OFDR) shown in Fig.8 . These shifts are the functions of both temperature and strain, and can be used as two independent parameters for the discrimination of temperature and strain.

 Figure 8. Experiment Setup. OFDR: optical frequency-domain reflectometry; TLS: tunable laser source; DAQ: data acquisition; EOM: electro-optic modulator; OC: optical coupler; PC: polarization controller; PD: photodetector; PBS: polarization beam splitter; WDM: wavelength division multiplexer; FUT: fiber under test. Bottom inset shows the sensing fiber section, where a 0.5 m long fiber could be applied axial strain by attaching the fiber on the translation stage, and a 0.7 m section is placed in the oven for varying temperature; the two sections are separated by about 1.5 m.

 

The OFDR configuration consists of a tunable laser source (TLS; Agilent 81980A) operating around 1,550 nm with a continuous sweep mode. Since the polarization state of the scattered signal is arbitrary, we adopt the polarization diversity detection technique. When the laser is tuned, the interference signals obtained from the combination of the Rayleigh scattering signal and the local laser beam is split by a Bonacom’s polarization beam splitter (PBS,BNPBS-31-2,Bonacom Technology Co.,LTD,Shenzhen,China); The two systems are combined together with a Bonacom’s 1,310/1,550 nm wavelength division multiplexer 1 (WDM1,BNWDM-3155-1). Bonacom’s WDM2( BNWDM-3155-1) is used to couple the TLS beam out of the fiber loop after it passes through the FUT; otherwise, the Rayleigh backscatter data might be corrupted by the reflection of the BOTDA components such as the attenuator(BNAT-31,Bonacom Technology) and the isolator(BNIS-31-S,Bonacom Technology). 

 

Figure 9 shows the another practical application for simultaneous temperature and strain measurements sensing system utilizing Bonacom’s polarization maintaining fiber components. Broadband light was passed through an Bonacom’s polarization maintaining isolator(PMIS, BNPMIS-31-S) to the ASE to remove any back-reflection influence. The light was then divided into two orthogonal linearly polarized components by a Bonacom’s polarization beam splitter (PBS, BNPBS-31-1). A polarization maintaining fiber circulator(PMCIR,BNPMCIR-31-S,Bonacom Technology) was used to pick up one of the linearly polarized components, while the other component was terminated.The state-of-polarization of the circulated polarized light was adjusted by a polarization controller.To keep the selected polarization in the polarization controller, the PM-FMF-FBG was spliced with a PM-SMF without any core offset. 

Fig. 9. Diagram of measurement setup showing the tunable laser source(TLS), a polarization controller(PC) is used to ensure that the reference power is split equally at the Polarization Beam Splitter(PBS) between the S and P modes. The sensing fiber is a segment of Fibercore HB1250P PM fiber. A translation stage is used to apply strain to a segment of fiber with another segment is heated.

 

Fiber-optic sensing technology has revolutionized distributed multi-parameter measurements across many sectors with its novel applications. The oil and gas industry has emerged as one of the key players in advancing the distributed sensing technology for energy exploration, monitoring reservoir integrity, and production optimization. Recent development in hybrid systems, capable of simultaneous measurements of vibration and temperature, is a game-changer, considering performance improvement and low cost in comparison to single parameter measurement systems.

 

Bonacom manufactures various passive fiber components(polarization maintaining/non-PM) for Hybrid Fiber-Optic Distributed Simultaeous Vibration, Temper-ature & Strain Sensing systems application, e.g.: in-line polarizer(ILP), polarization beam splitter(PBS), optical isolator(PM/non-PM), isolator polarization beam splitter hybrid(IPBS), optical circulator(PM/non-PM), fiber coupler(filter/fused based- PM/ non-PM), PM FWDM, polarization maintaining variable optical attentor(PM VOA) with broadband working wavelength at 1310nm,1550nm.

We also offer custom optical modules and subsystems by integrating multiple broadband components such as isolator coupler FWDM PBS hybrid. These components are ideal choices for developing expanding global all-fiber-based sensing systems. Contact Bonacom Technology to discuss your requirements.