Recent development in artificial neural network based distributed fiber optic sensors

Distributed fiber optic sensors are promising technique for measuring strain, temperature and vibration over tens of kilometres by utilizing the backscattered Rayleigh, Raman and Brillouin signals. Recently, the use of an artificial neural network (ANN) has been adopted into the distributed fiber sensors for advanced data analytics, fast data processing time, high sensing accuracy and event classification. In this paper, the recent developments of ANN-based distributed fiber sensors and their operating principles are reviewed. Moreover, the performance of ANN is compared with the conventional signal processing algorithms. The future perspective view that can be extended further research development has also been discussed

Integrating radio-over-fiber communication system and BOTDR sensor system

In this paper, we propose and experimentally demonstrate for the first time, the integration of a radio-over-fiber (RoF) communication system and a Brillouin optical time-domain reflectometry (BOTDR) distributed sensor system using a single optical fiber link. In this proof-of-concept integrated system, the communication system is composed of three modulation formats of quadrature phase-shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM) and 64-QAM, which are modulated onto an orthogonal frequency division multiplexing (OFDM) signal. Whereas, the BOTDR sensor system is used for strain and/or temperature monitoring over the fiber distance with a spatial resolution of 5 m using a 25 km single-mode silica fiber. The error vector magnitude (EVM) is analyzed in three modulation formats in the presence of various BOTDR input pump powers. Using QPSK modulation, optimized 18 dBm sensing and 10 dBm data power, the measured EVM values with and without bandpass filter are 3.5% and 14.5%, respectively. The proposed system demonstrates a low temperature measurement error (±0.49 °C at the end of 25 km) and acceptable EVM values, which were within the 3GPP requirements. The proposed integrated system can be effectively applied for practical applications, which significantly reduces the fiber infrastructure cost by effective usage of a single optical fiber lin

High Sensitivity Refractometer Based on Reflective Smf-Small Diameter No Core Fiber Structure

A high sensitivity refractive index sensor based on a single mode-small diameter no core fiber structure is proposed. In this structure, a small diameter no core fiber (SDNCF) used as a sensor probe, was fusion spliced to the end face of a traditional single mode fiber (SMF) and the end face of the SDNCF was coated with a thin film of gold to provide reflective light. The influence of SDNCF diameter and length on the refractive index sensitivity of the sensor has been investigated by both simulations and experiments, where results show that the diameter of SDNCF has significant influence. However, SDNCF length has limited influence on the sensitivity. Experimental results show that a sensitivity of 327 nm/RIU (refractive index unit) has been achieved for refractive indices ranging from 1.33 to 1.38, which agrees well with the simulated results with a sensitivity of 349.5 nm/RIU at refractive indices ranging from 1.33 to 1.38

A simple all-fiber comb filter based on the combined effect of multimode interference and Mach-Zehnder interferometer

A polarization-dependent all-fiber comb filter based on a combination effect of multimode interference and Mach-Zehnder interferometer was proposed and demonstrated. The comb filter was composed with a short section of multimode fiber (MMF) fusion spliced with a conventional single mode fiber on the one side and a short section of a different type of optical fiber on the other side. The second type of optical fiber is spliced to the MMF with a properly designed misalignment. Different types and lengths of fibers were used to investigate the influence of fiber types and lengths on the performance of the comb filter. Experimentally, several comb filters with free spectral range (FSR) values ranging from 0.236 to 1.524 nm were achieved. The extinction ratio of the comb filter can be adjusted from 6 to 11.1 dB by varying polarization states of the input light, while maintaining the FSR unchanged. The proposed comb filter has the potential to be used in optical dense wavelength division multiplexing communication systems

A Simple All-fiber Comb Filter Based on the Combined Effect of Multimode Interference and Mach- Zehnder Interferometer

A polarization-dependent all-fiber comb filter based on a combination effect of multimode interference and Mach-Zehnder interferometer was proposed and demonstrated. The comb filter was composed with a short section of multimode fiber (MMF) fusion spliced with a conventional single mode fiber on the one side and a short section of a different type of optical fiber on the other side. The second type of optical fiber is spliced to the MMF with a properly designed misalignment. Different types and lengths of fibers were used to investigate the influence of fiber types and lengths on the performance of the comb filter. Experimentally, several comb filters with free spectral range (FSR) values ranging from 0.236 to 1.524 nm were achieved. The extinction ratio of the comb filter can be adjusted from 6 to 11.1 dB by varying polarization states of the input light, while maintaining the FSR unchanged. The proposed comb filter has the potential to be used in optical dense wavelength division multiplexing communication systems

Real-time rail-track monitoring system employing innovative wavelength diversity technique in distributed optical fibre sensors

Brillouin based distributed fibre sensors gained a lot of attention in recent years for structural health monitoring applications, due to their higher sensing range over tens of kilometres and distributed measurement capability of simultaneous strain and temperature. In Brillouin optical time domain reflectometry (BOTDR) system, the signal-to-noise ratio (SNR) determines the sensing performance of the system. However, the SNR is limited by the restricted maximum input pump power, which is limited by the non-negligible nonlinear effects, such as stimulated Brillouin scattering. In this research, a novel wavelength diversity technique is proposed to enhance the SNR, hence improve the strain and temperature measurement accuracies, which is required for accurate rail-track condition monitoring. In addition, this research work presents the following contributions (i) a simple, low-cost passive depolarizer is adopted to reduce the polarization noise; (ii) an inline erbium-doped fibre amplifier (EDFA) is employed at a certain distance to amplify the attenuated pulse in order to improve the sensing range; and (iii) a cost-effective reference Brillouin ring laser is used in BOTDR system to overcome the complexity of the receiver bandwidth reduction. The proposed wavelength diversity BOTDR system combined with a passive depolarizer and Brillouin ring laser is validated over a 50 km sensing fibre with a 5 m spatial resolution. The SNR is improved by 5.1 dB, which corresponds to 180% improvement compared to a conventional BOTDR system. Whereas, the strain and temperature accuracies at a 50 km fibre distance are ±10 με and ±0.45oC, respectively. Furthermore, for the first time, simultaneous integration of long-term evolution (LTE) radio-over-fibre (RoF) data system and BOTDR sensing system using a single optical fibre is proposed and demonstrated. The error vector magnitude (EVM) performance of LTE-RoF data system is analysed for three modulation formats of QPSK, 16-QAM and 64-QAM in the presence of various BOTDR sensing powers

Performance improvement of Brillouin based distributed fiber sensors employing wavelength diversity techniques (Invited Paper)

The sensing performance in Brillouin-based distributed fiber sensors is ultimately depends on the signal-to-noise ratio (SNR) of the received signal. In order to enhance the SNR, thus improve the sensing performance, several wavelength diversity techniques have been proposed. This paper presents the current wavelength diversity techniques employed in both Brillouin optical timedomain reflectometry (BOTDR) and Brillouin optical time-domain analysis (BOTDA) systems. So far, the best SNR improvement in BOTDR system is 4.85 dB with a 25 km sensing fiber, whereas, 4.8 dB in BOTDA system with a 50 km sensing fiber

Future of distributed fiber sensors (invited paper)

Distributed fiber sensors offers an innovative technology for a spatially distributed measurement based on Raleigh, Brillouin and Raman scattering. By analyzing backscattered signal frequency, intensity and phase, one can realize a distributed measurement of strain, temperature and vibration over a tens of kilometers. This paper reviewed the history and current technology development of distributed time-domain fiber sensors in terms of spatial resolution and sensing range while present the standard operating principles. The future prospective view that can be extend further research development has also been discussed

Performance analysis of Brillouin optical time domain reflectometry (BOTDR) employing wavelength diversity and passive depolarizer techniques

We propose and experimentally validate a wavelength diversity technique combined with a passive depolarizer to improve the performance of Brillouin optical time domain reflectometry (BOTDR). This technique enables the maximization of the launch pump power and suppresses the nonlinear effects, the latter of which limits the conventional BOTDR performance. As a result, the signal-to-noise ratio (SNR) increases, thus improving the measurement accuracy for strain and temperature. In addition, considering the complexity and expensive methods required for polarization noise suppression in BOTDR system, a simple, lowcost passive depolarizer is employed to reduce the polarization noise. The experimental results show that the SNR is improved by 4.85 dB, which corresponds to 174% improvement compared to a conventional BOTDR system