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Rank: Full Professor

Department: Physics

Recent Research Awards

2024  Canadian Association of Physicists (CAP) Medal for Lifetime Achievement in Physics: https://services.cap.ca/medal/publicity/press.php?year=2024&num=1&medal_...

2023 Joseph Fraunhofer Award/Robert M. Burley Prize Recipient: https://www.optica.org/en-us/2023fraunhoferburleywinner/

2021 Governor General’s Innovation award for invention and development of the “Distributed acoustic sensors": https://innovation.gg.ca/winner/dr-xiaoyi-bao/

 

The Canadian Association of Physicists (CAP) Fellow (2024)

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)

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)

Research Projects

Nano-fibers, Structured fibers,  Microelectromechanical systems (MEMS), and Waveguide devices for sensors, low noise laser and nonlinear signal processing, 

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) and acoutsic 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, off-core fiber coupled microsphere 

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

2.6 Surface acoutsic wave detection by the nanofiber interferomter  

Ultrasound and acoustic sensors have been widely used in medical imaging, structural health monitoring (SHM) and non-destructive testing (NDT) in civil/mechanical structures. Detection of high frequency acoustic wave (tens of MHz to 1 GHz) enables high spatial resolution imaging, the acoustic wave can be generated by surface acoustic waves-electromechanical systems (MEMS) with high signal-to noise-ratio (SNR) are difficult, as the conversion from mechanical wave to electrical signal is low due to the larger dimension of the electrical device compared to the spatial period of the acoustic wave. This difficulty can be overcome by coupling acoustic/mechanical to optical wave within one SAW wavelength in a few micrometers via optomechanical interaction. The sensing signal is measured in optical domain at high sampling rate, instead of electrical domain as micro-wave. Novel micro-structured optical fiber from conventional SiO2 to As2Se3 tapered fiber have brought major advancements in high frequency and high sensitivity detection by SAW generation and detection. This tutorial paper discusses basic principles of sound waves, acoustic waves and ultrasound, the photo-acoustic effect, the effect of electrical-strain and vice-versa. The acoustic generation by PZT, mechanical wave via a pencil break, laser ultrasound generation, and the SAW can be detected by micro-structured fibers and telecom fibers from kHz to 1 GHz are demonstrated with SNR of greater than 40 dB at ∼100 MHz and greater than 20 dB at ∼1 GHz. This sensing technology opens a new on chip sensing platform that combines electrical, mechanical and optical components on one chip for acoustic-optical sensing and imaging probe with high spatial resolution.
https://doi.org/10.1109/JLT.2024.3472488

Optical acoustic interaction in subwavelength acoustic and optical nanofiber interferometer excited by surface acoustic waves

DOI: https://doi.org/

2.7 Microcrack grating based LPG for high frequency ultrasound (tens to hundreds of MHz) detection 

High-frequency (> 50 MHz) ultrasound sensing requires the detection of subtle, rapid perturbations, often a small fraction of the acoustic wavelength, which can be much smaller than the optical wavelength. This leads to the associated phase shift due to ultrasound modulation to being too small to be detected using a telecom fiber-based interferometer. Structured fiber-based sensors can overcome these challenges by detecting locally induced deformations in the fiber structure inside the core. We propose a novel approach using CO2- written long-period fiber gratings (LPFGs), where randomly distributed micro-deformities act as amplitude gratings, eliminating the need for phase detection. Unlike commonly used UV light inscribed LPFGs, where the inscription pitch is uniform in the fiber between the periods, the wavelength of the CO2 laser falls in the absorption band of SiO2. This causes thermal stress-induced deformations in the fiber, leading to the formation of randomly spaced Fabry-Perot (FP) cavities in the micrometer range, as demonstrated by the spatial frequency spectrum (inverse fast Fourier transform (IFFT)). The higher-order modes in CO2-written LPFGs and tilted LPFGs enhance the sensitivity to high-frequency ultrasound waves. This sensitivity arises from the broadband frequency resonance condition MHz-GHz in randomly spaced deformation-formed FP cavities. By analyzing the transmission and spatial frequency spectra of CO2- and UV-written LPFGs, where the latter fails to respond to ultrasound signals beyond 10MHz, we establish a framework for practical high-sensitivity ultrasound sensing.

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=10965887

 

3. Fiber lasers and nonlinear fibers

•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

•Random optical parametric oscillator and applications for distributed fiber sensors

•Laser sensors for ultra-sensitive sensing

•Optical signal processing

4. Distributed fiber sensors and applications

  • 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 vibration, acoustic wave, impact wave, temperature and strain sensing at the accuracy of nano-strain (nanometer change over a meter) 
  • Measuring nonlinear optical effects in optical fibers