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Rank: Full Professor, Canada Research Chair in Fiber Optics and Photonics (tier I)

Department: Physics

Education: 

  • BSc: Optics, Nankai University
  • MSc: Optics, Nankai University
  • PhD: Optics, Chinese Academy of Science

 

  • HONOURS & DISTINCTIONS

MAJOR RESEARCH PRIZES

Governor General’s Innovation award for invention and development of the “Distributed acoustic sensors" (2021)

Canadian Association of Physicists (CAP) Medal for Outstanding Achievement in Industrial and Applied Physics (2013)

The Federation of Chinese Canadian Professionals Education Foundation Award of Merit (2012) 

Outstanding contribution award from the 4th International Forum on Opto-Electronic Sensor-Based Monitoring in Geo-Engineering (2012)

CAP-National Optics Institute Medal for Outstanding Achievement in Applied Photonics (2010)

Networks Centers of Excellence CHAIRS’ Award Medal (2006)

The Medal was given to five individuals in Canada who had made outstanding contributions in transferring technology to industry.

Premier's Research Excellence Awards, Ontario, Canada (2001)

Alexander von Humboldt Fellowship (1988-1989)

Rao Yutai Optics Award (1988)

FELLOWSHIPS AND DISTINCTIONS

Honorary Doctorate Degree from the University of Lethbridge, 2015

Fellow of the International Society for Optics and Photonics (SPIE) (2012)

Fellow of the Optical Society of America (2011)

Fellow of the Royal Society of Canada (2009)

Royal Society of Canada (2009-2011): the honorary secretary of the Academy of Science, council member of the Royal Society of Canada.

SPIE Women in Optics Calendar (2006)

University of Ottawa Inventor of the Year Award (2003)

Canada Research Chair in Fiber Optics and Photonics (Tier I) (2003-2023)

Intelligent Sensing and Innovative Structures of (ISIS) Canada (2002-2009): Research Management Committee (RMC) 

Canadian Institute for Photonics Innovations (CIPI), (1999-2002): Research Program Committee (RPC) 

NSERC Council member (1998-2001)

Research Topics

My research

 https://www.dropbox.com/s/cjvohyx2i41k31w/Episode%2066_Dr%20Bao.m4v?dl=0

1. Distributed acoustic and impact wave detection

Distributed acoustic and impact wave sensors can measure time-dependent strain at every point along an optical fiber attached to a structure, allowing the recording of information required for non-destructive testing (NDT), and structural health monitoring. An optical fiber is a thin flexible strand of glass through which a laser light signal can travel tens of kilometers with little loss of signal strength.

There is a need to develop a sensor that can detect cracks that were in progress of being formed. This would turn monitoring from reactive detection (finding an existing crack) to proactive prediction - predicting where cracks will be formed and repairing before disaster occurs. The implications would be huge and worth the effort: for example preventing bridges from collapsing and loss of life, and finding potential pipeline leaks before oil spills and preventing environmental and wildlife damage.

Our first demonstration of the wave monitoring using the telecom fiber without interferometer configuration was in 2005 on submarine fiber that was buried underneath the ocean floor to a depth of over 14,000'; this project was the first measurements of tidal waves using buried submarine fiber [1, 2]. The straight optical fiber detected ocean waves - this meant the straight optical fibre could hear sound [1,2].

[1] Z. Zhang, X Bao, Q Yu and L Chen, “Time Evolution of PMDs due to the Tides and Sun Radiation on Submarine Fibers,” Optical Fiber Technology, 13 (1), 62-66 (2007). Available online 2006/08/21

[2] Z Zhang, X Bao, Q Yu and L Chen, “Fast States of Polarization and PMD Drift in Submarine Fibres”, Photonics Technol. Lett., 18(9), 1034-1036 (2006).

Because cracks in structures create sound waves, we can use polarization dependence of Brillouin gain to detect time dependent stress induced by structures. It could locate structural cracks by hearing sound to an accuracy of 2 metres from a fibre cable that would normally be over 1km long for frequency up to 300Hz. The measurement was conducted in 2016 on Highway 40,on a newly built (at the time) highway bridge using a new material (FRP: fiber reinforcing polymer).This new material didn't absorb compression/shock well, which meant it is more prone to deformation and hence there is potentially higher risk of the bridge collapsing. There is a need to measure distributed impact wave on the bridge so that there could be real-time early detection of deformations. After the repairs were completed and cars drove over the bridge, our Brillouin gain based distributed impact wave detected very minor deformations in the bridge indicating the sensor was operating with a high degree of precision to detect and locate the deformations. The first concrete deck (highway bridge) test completed in 2007 [3].

[3] X. Bao, W. Li, C. Zhang, M. Eisa, S. El-Gamal, B. Benmokrane, “Monitoring the distributed impact wave on a concrete slab due to the traffic based on polarization dependence on stimulated Brillouin scattering” Smart Mater. Structures 17 (1), 015003-015008 (2007)

In parallel to the effort of the using Brillouin gain for distributed impact and acoustic/vibration wave detection, the work was also conducted using Rayleigh scattering, it was demonstrated with 10m spatial resolution for frequency of upto 100Hz over 800m fiber [4].

[4] Z. Zhang and X. Bao, “Continuous and Damped Vibration Detection Based on Fiber Diversity Detection Sensor by Rayleigh Backscattering” IEEE J-LT, 26(7), 852-838 (2008)

The improved vibration frequency of 5kHz was demonstrated with 10m spatial resolution over 1km fiber length, which is based on polarization OTDR using fast Fourier transfer (FFT)  method [5].

[5] Z. Zhang, X. Bao, “Distributed Optical Fiber Vibration Sensor Based on Spectrum Analysis of Polarization-OTDR System,” Opt. Express, 16(14), 10240-10247 (2008)

The introduction of coherent detection for phase OTDR has further improved the signal to noise ratio of the Rayleigh backscattering signal, so that the sound of a pencil breaking could be detected at 5m spatial resolution for maximum frequency of 1kHz [6].

 [6] Y. Lu, T. Zhu, L. Chen, X. Bao, “Distributed Vibration Sensor Based on Coherent Detection of Phase- OTDR," IEEE JLT, 28 (22), 3243-3249 (2010)

The introduction of wavelet de-noise procedure further improved the signal to noise ratio in distributed acoustic wave detection for defects, reducing instances where the sensor would falsely identify issues and obtain higher confidence level [7].

[7] Z. Qin, L. Chen and X. Bao,” Wavelet denoising method for improving detection performance of distributed vibration sensor,” IEEE PTL, 24(7), 542-544 (2012)

[8] T. Zhu, Q. He, X. Xiao, and X. Bao, “Modulated pulses based distributed vibration sensing with high frequency response and spatial resolution”, Opt. Express, 21 (3), 2953–2963 (2013)

 This paper showed that using modulated pulse-based DAS-enabled MHz detection, we could determine and located sub-mm crack.

[9] Y. Wang, P. Lu, S. Mihailov, L. Chen, X. Bao, “Ultra-low frequency dynamic strain detection with laser frequency drift compensation Based on Random Fiber Grating Array,” Opt. Lett., 46(4), 789-792 (2021)

This paper presents the use of fiber random gratings to compensate laser frequency drift in distributed acoustic sensors, enabling very low frequency (0.01 Hz-10 Hz) detection, which is important to obtain information about crack depth in pipeline application.

 2. Miniature ultrasound (kHz-100MHz) probe based on structured optical fibers

 Ultrasound detection plays a significant role in many applications, such as structural health monitoring and biomedical imaging. Structural health monitoring is required by the industry to identify the initial damage, monitor its subsequent progress, and predict the remaining life of a structure. The importance of ultrasound detection has been increasing in clinical applications. Ultrasonic waves can propagate into organs without losing their coherence, which have great potential for non-invasive imaging.

 2.1 The ultrasound detection based on a dual-core hybrid taper

The 10 kHz to 34 MHz ultrasound detection based on a dual-core As2Se3-PMMA taper is demonstrated, which showed high sensitivities to both shear and longitudinal waves due to the dual-core structure, low Young’s modulus, sub-micrometer dimension of the core, and the high-contrast interference pattern by the even and odd modes.

 [2.1] S. Gao, C. Baker, W. Cai, L. Chen, and X. Bao , (2019). 10 kHz-34 MHz ultrasound detection based on a dual-core hybrid taper. APL Photonics 4, 110805. https://doi.org/10.1063/1.5093987

 2.2 Ultrasound sensor based on an in-fiber dual-cavity Fabry–Perot interferometer

The ultra-compact fiber-based multi-mode dual-cavity Fabry–Perot interferometer (DCFPI) ultrasound sensors are proposed by splicing three sections of cleaved standard single-mode fibers with the fiber off-core cross section in the middle. The broadband frequency responses, ranging from 5 kHz to 45.4 MHz, are demonstrated. Device size: <500 micro-meters in length, dimeter: 130 micro-meters.

[2.2] H. Fan, L. Zhang, S. Gao, L. Chen, & X. Bao. (2019). Ultrasound sensing based on an in-fiber dual-cavity Fabry--Perot interferometer. Optics Letters, 44(15), 3606-3609. https://doi.org/10.1364/OL.44.003606

 2.3. Chalcogenide microfiber-assisted silica microfiber for ultrasound detection

An ultra-compact ultrasound sensor with a chalcogenide (ChG) microfiber and a silica microfiber is fabricated. It can detect the ultrasound wave from 18kHz to 31 MHz with high SNR of >12dB. Probe dimension: 20 micro-meters in diameter, length: 5-6mm.

[2.3] H. Fan, L. Chen, & X. Bao. (2020). Chalcogenide microfiber-assisted silica microfiber for ultrasound detection. Optics Letters, 45(5), 1128-1131. https://doi.org/10.1364/OL.383238    

2.4 Ultra-compact twisted silica taper for 20 kHz to 94 MHz ultrasound sensing

With the taper waist length of 5 mm, waist diameter of 5 micro-meters, a broadband ultrasound frequency of 20 kHz to 94.4 MHz can be detected, verifying the high sensitivity of the compact twisted silica taper.

[2.4] H. Fan, W. Ma, L. Chen, & X. Bao. (2020). Ultra-compact twisted silica taper for 4 kHz to 94 MHz ultrasound sensing. Opt Lett. 45(14), 3889-3892 (2020): https://doi.org/10.1364/OL.397213

 2.5 Tapered assisted dual micro-bubble-device for ultrasound sensor

A compact hybrid structure of silica taper-assisted dual micro-bubbles is proposed and fabricated for broadband ultrasound sensing. A broad bandwidth acoustic signal response from 3 kHz to 23.5 MHz is detected with the miniature ultrasound probe. Dimension: length: 2-5mm. Diameter: <100 micro-meter.

[2.5] W. Ma, H. Fan, L. Chen, and X. Bao, (2020). Taper assisted dual micro-bubble-device for ultrasound sensor. IEEE PTL, 32(18), 1219-1222 (2020) Digital Object Identifier: 10.1109/LPT.2020.3018034

 3. Current projects on fiber technology:  

•Multi-parameter sensing: temperature, refractive index, vibration, ultrasound, displacement, pressure and humidity

•Ultrasound probe and generator

•Nano-fiber device for quantum sensing

•Surface acoustic wave device

•Temperature in-sensitive devices and sensors

3. Fiber lasers and applications

Low phase and frequency noise sub-kHz bandwidth lasers development

•Multi-wavelength lasers

•Kerr effect for small signal amplification

•True random number generator and physical layer secret key generation

•Statistics properties of random laser

•Quantum noise limited laser development

•Laser sensors for ultra-sensitive sensing

•Optical signal processing

4. Current Distributed fiber sensors

  • Fibre nerve system to pick up high stress, hot spots, “hear” and locate  the internal cracks via ultrasound detection.
  • Structural health monitoring (SHM)
  • Distributed NDT detection for vibraion, acoustci wave, impact wave, temperature and strain sensing at the accuracy of nano-strain (nanometer change over a meter)