W.H. Chung

The University of Hong Kong, Hong Kong, Hong Kong

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Publications (53)41.37 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a novel and simple temperature-insensitive fiber Bragg grating (FBG) based smart tilt sensor. The sensor design is free from any inherent mechanical joints/frictions with a capability to measure magnitude as well as the direction of the inclination. The first design is with a sensitivity of 0.00282 nm/$^{\circ}$ in a very large dynamic range of ${\pm} 35^{\circ}$. The sensor response is optimized against design parameters and observed to be completely reversible. Since there is a strain discrepancy on individual FBGs of the first design, a modified design is then proposed for optimization. An excellent sensitivity of 0.0395 nm/$^{\circ}$, resolution of 0.013$^{\circ}$ and accuracy of 0.051$^{\circ}$ have been achieved. These features along with the freedom to tune the dynamic range, accuracy of measurement and the sensitivity of the proposed sensor to a desired operation range make the proposed sensor of extreme importance for practical engineering applications.
    Journal of Lightwave Technology 05/2011; 29(11):1714-1720. · 2.56 Impact Factor
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    ABSTRACT: We report the fabrication, characterization and application of extremely short linear-cavity distributed Bragg reflector fibre lasers (DBR-FLs) written in commercial erbium-doped fibres. The DBR-FL has a total length of 7 mm, of which the nominal cavity is 0.4 mm in length, making it the shortest DBR-FL being reported. Two distinct spectral properties are observed: ultra-narrow linewidth and ultra-low polarization beat frequency, which are measured to be 0.22 kHz and 18.9 MHz, respectively. For the former, the FLs find applications in high sensitivity interferometric sensing, optical frequency metrology and coherent optical communications, whereas for the latter, such a low beat frequency is beneficial to the construction of low-cost and simple demodulator electronics for sensor signal demodulation. The relative intensity noise measurement showed that the relaxation oscillation frequency and relative peak are 120 kHz and −75 dB Hz−1, respectively. The FL exhibited low-noise characteristics, with an intensity noise of −107 dB Hz−1 at 1 MHz. We demonstrate the use of these extremely short FLs in the construction of an efficiently pumped and serially multiplexed FL sensor array suitable for practical sensing applications. Two array configurations were tested, namely with individual FLs fabricated in short sections of EDF and connected via passive fibres and with all FLs fabricated along a single EDF.
    Measurement Science and Technology 02/2011; 22(4):045202. · 1.44 Impact Factor
  • A.C.L. Wong, W.H. Chung, H.Y. Tam, C. Lu
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    ABSTRACT: We report the fabrication of extremely short linear-cavity distributed Bragg reflector fiber lasers (DBR-FLs). It has a total length of 7 mm, the shortest FL being reported. The FLs are characterized in details. We constructed a FL sensor array that has great potentials for large-scale, high sensitivity sensing applications.
    Communications and Photonics Conference and Exhibition (ACP), 2010 Asia; 01/2011
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    ABSTRACT: Railway signaling facilitates two main functions, namely, train detection and train control, in order to maintain safe separations among the trains. Track circuits are the most commonly used train detection means with the simple open/close circuit principles; and subsequent adoption of axle counters further allows the detection of trains under adverse track conditions. However, with electrification and power electronics traction drive systems, aggravated by the electromagnetic interference in the vicinity of the signaling system, railway engineers often find unstable or even faulty operations of track circuits and axle counting systems, which inevitably jeopardizes the safe operation of trains. A new means of train detection, which is completely free from electromagnetic interference, is therefore required for the modern railway signaling system. This paper presents a novel optical fiber sensor signaling system. The sensor operation, field setup, axle detection solution set, and test results of an installation in a trial system on a busy suburban railway line are given.
    IEEE Sensors Journal 01/2011; · 1.48 Impact Factor
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    ABSTRACT: An FBG sensing network consisting of over 200 sensors are installed on the Guangzhou New TV Tower for long-term monitoring of strain, temperature and inclination to provide a mean for structural health monitoring of super-tall structures.
    Optical Fiber Communication Conference and Exposition (OFC/NFOEC), 2011 and the National Fiber Optic Engineers Conference; 01/2011
  • A. C. L. Wong, W. H. Chung, H. Y. Tam, C. Lu
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    ABSTRACT: A low-noise, ultra-short linear-cavity distributed feedback fiber laser (DFB-FL) with extremely narrow linewidth is presented. The FL has a total length of 17 mm, which is, to our knowledge, the shortest DFB-FL being reported. It has a measured linewidth of merely 250 Hz without active stabilization. It has a polarization beat frequency of 101 MHz, which is several times lower than that of most FLs. The relaxation oscillation frequency and relative peak are 110 kHz and −76.5 dB/Hz, respectively. The FL exhibited low-noise characteristics, with an intensity noise of −107 dB/Hz at 1 MHz. Due to low dopant concentration of the EDF and low splice loss with ordinary single-mode fibers, the net insertion loss amounts to only 0.45 dB. Such low pump power loss greatly enhances the capability of multiplexing a large number of FL sensors. Thus, these ultra-short DFB-FLs open up new opportunities for the development of compact-sized point sensor array systems for large-scale high sensitivity sensing applications.
    Laser Physics 01/2011; 21(1):163-168. · 2.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a novel and simple temperature-insensitive fiber Bragg grating (FBG) based smart tilt sensor. The sensor design is free from any inherent mechanical joints/frictions with a capability to measure magnitude as well as the direction of the inclination. The first design is with a sensitivity of 0.00282 nm/° in a very large dynamic range of ± 35°. The sensor response is optimized against design parameters and observed to be completely reversible. Since there is a strain discrepancy on individual FBGs of the first design, a modified design is then proposed for optimization. An excellent sensitivity of 0.0395 nm/° , resolution of 0.013° and accuracy of 0.051° have been achieved. These features along with the freedom to tune the dynamic range, accuracy of measurement and the sensitivity of the proposed sensor to a desired operation range make the proposed sensor of extreme importance for practical engineering applications.
    Journal of Lightwave Technology 01/2011; 29:1714-1720. · 2.56 Impact Factor
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    ABSTRACT: A type of fiber laser, called tilted Bragg reflector fiber laser (TBR-FL), is proposed and its application in simultaneous sensing of surrounding refractive index (SRI) and temperature is demonstrated. This FL is formed by a pair of wavelength and tilt-angle matched tilted fiber Bragg gratings (TFBGs) that acted both as a resonant cavity and sensing element. A unique spectral feature of the TBR-FL is the presence of grating tilt-induced cladding modes spectrum that does not appear in other type of FL, which provides an extra sensing mechanism. By employing a simple experimental setup with the discrete wavelet transform as the demodulation technique, simultaneously sensing of SRI and temperature are achieved by measuring and analyzing the wavelet coefficients shifts of the laser output and averaged cladding modes.
    Optics Express 01/2011; 19(2):409-14. · 3.55 Impact Factor
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    ABSTRACT: We report the fabrication of extremely short linear-cavity distributed Bragg reflector fiber lasers (DBR-FLs). It has a total length of 7 mm, with the nominal cavity of only 0.4 mm. The FL has a linewidth and polarization beat frequency of 220 Hz and 18.9 MHz, respectively. The relaxation oscillation frequency and its relative peak are 120 kHz and -75dB/Hz, respectively. The FL exhibited low-noise characteristics, with an intensity noise of -107 dB/Hz at 1 MHz. We constructed a FL sensor array that has great potentials for large-scale, high sensitivity sensing applications.
    Proc SPIE 12/2010;
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    ABSTRACT: We propose and demonstrate using a single composite structure distributed Bragg reflector fiber laser (DBR-FL) for simultaneous sensing of refractive index (RI) and temperature. The FL structure consists of a pair of uniform fiber Bragg gratings (FBGs) forming the laser cavity. A variable cavity attenuator made by a blazed FBG (BFBG) is written inside the cavity, which varies the optical loss upon changes in the surrounding RI. Simultaneous sensing is realized from the fact that the output power only varies with the surrounding RI, whereas the lasing wavelength with the temperature. The sensitivity of RI measurement of the proposed FL improved by several times in comparison with the passive BFBG sensor.
    IEEE Photonics Technology Letters 11/2010; · 2.04 Impact Factor
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    ABSTRACT: Eight channel 100 Gbit/s CSRZ-DQPSK system with automatic bias control and clock and data recovery module is demonstrated. 1520 km transmission with standard single mode fibre and EDFA amplification is achieved with 1.9 dB OSNR penalty.
    OptoElectronics and Communications Conference, 2009. OECC 2009. 14th; 08/2009
  • H.Y. Fu, H.L. Liu, W.H. Chung, H.Y. Tam
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    ABSTRACT: A novel fiber Bragg grating (FBG) sensor configuration using three broadband light sources of different wavelength bands for the interrogation of FBG sensors distributed over 75 km of fiber is proposed and demonstrated. Rayleigh backscattering was reduced and a 60-dB effective dynamic range was demonstrated.
    IEEE Sensors Journal 10/2008; · 1.48 Impact Factor
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    ABSTRACT: In this paper, we report the gain-switching operation in Yb3+-doped DFB fiber laser. Our DFB fiber laser operates with single longitudinal mode and single polarization state under cw pump, however, the DFB fiber laser will operate with gain-switching mode if it is pump by pulse of certain duration. Detail experimental results are given in the paper. We believe this king of pulse source is useful in optical sensor.
    Optoelectronic Devices and Integration Ii. 01/2008; 6838:83808-83808.
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    ABSTRACT: Transmission of eight channel 100Gbit/s CS-RZ DQPSK signals up to 1500km SSMF was demonstrated. This transmission system only used EDFA and did not adopt coherent detection and polarization multiplexing. The span spacing in this system varies from 80km to 100km to simulate the practical optical network. Keywords: Transmission system, modulation format
    Proc SPIE 01/2008;
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    ABSTRACT: In this paper, we report the gain-switching operation in Yb3+-doped DFB fiber laser. Our DFB fiber laser operates with single longitudinal mode and single polarization state under cw pump, however, the DFB fiber laser will operate with gain-switching mode if it is pump by pulse of certain duration. Detail experimental results are given in the paper. We believe this king of pulse source is useful in optical sensor.
    Proc SPIE 01/2007;
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    ABSTRACT: The demand for high quality rail services in the twenty-first century has put an ever increasing demand on all rail operators. In order to meet the expectation of their patrons, the maintenance regime of railway systems has to be tightened up, the track conditions have to be well looked after, the rolling stock must be designed to withstand heavy duty. In short, in an ideal world where resources are unlimited, one needs to implement a very rigorous inspection regime in order to take care of the modern needs of a railway system. If cost were not an issue, the maintenance engineers could inspect the train body by the most up-to-date techniques such as ultra-sound examination, X-ray inspection, magnetic particle inspection, etc. on a regular basis. However it is inconceivable to have such a perfect maintenance regime in any commercial railway. Likewise, it is impossible to have a perfect rolling stock which can weather all the heavy duties experienced in a modern railway. Hence it is essential that some condition monitoring schemes are devised to pick up potential defects which could manifest into safety hazards. This paper introduces an innovative condition monitoring system for track profile and, together with an instrumented car to carry out surveillance of the track, will provide a comprehensive railway condition monitoring system which is free from the usual difficulty of electromagnetic compatibility issues in a typical railway environment
    Railway Condition Monitoring, 2006. The Institution of Engineering and Technology International Conference on; 12/2006
  • H. L. Liu, W. H. Chung, H. Y. Fu, H. Y. Tam
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    ABSTRACT: A novel FBG sensor configuration is proposed and demonstrated by using different broadband light sources for the interrogation of FBG over 75 km of fiber. A 60 dB effective dynamic range was demonstrated.
    10/2006;
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    ABSTRACT: We have demonstrated all-optical on-off switching at 10 Gbit/s using four-wave mixing in only 1.9 m of bismuth-based highly nonlinear fiber. The all-optical on-off switch has a fast response time and high ON/OFF switching ratio.
    Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference. CLEO/QELS 2006. Conference on; 06/2006
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    ABSTRACT: The rapid expansion of the optical fiber telecommunication industry due to the explosion of the Internet has substantially driven down the cost of optical components, making fiber optic sensors more economically viable. In addition, the rapid development of fiber-optic sensors, particularly the fiber Bragg grating (FBG) sensors offers many advantages and capability that could not be achieved otherwise. In the past few years, fiber Bragg grating sensors have attracted a lot of interest and they are being used in numerous applications. This paper describes the FBG sensors developed for structural health monitoring, and were installed on Hong Kong’s landmark Tsing Ma bridge (TMB), which is the world longest (1377 m) suspension bridge that carried both railway and regular road traffic. Forty FBG sensors divided into three arrays were installed on the hanger cable, rocker bearing and truss girders of the TMB. The objectives of the study are to investigate the feasibility of using the developed FBG sensors for structural health monitoring, via monitoring the strain of different parts of the TMB under both the railway and highway loads as well as comparing the FBG sensors’ performance with the conventional structural health monitoring system — Wind and Structural Health Monitoring System (WASHMS) that has been operating at TMB since the bridge’s commissioning in May 1997. The experimental observations in this project show that the results using FBG sensors were in excellent agreement with those acquired by WASHMS.
    Engineering Structures. 04/2006; 28(5):648–659.
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    ABSTRACT: A low beat-noise highly polarized tunable fiber ring laser is proposed and experimentally demonstrated by using a Fabry-Pe´rot laser diode (FP-LD), which acts as a high-pass filter to suppress both the beat noise and TM-polarized light. The wavelength of the fiber ring lasers can be tuned from 1536.82 to 1570.72 nm in 1.12-nm steps and its maximum output power is about +3 dBm. The degree of polarization and extinction ratio of the laser output are about 99% and 60 dB, respectively. The beat-noise with and without the FP-LD was reduced dramatically by 50 dB.
    IEEE Photonics Technology Letters 02/2006; · 2.04 Impact Factor

Publication Stats

199 Citations
41.37 Total Impact Points

Institutions

  • 2001–2011
    • The University of Hong Kong
      • Department of Electrical and Electronic Engineering
      Hong Kong, Hong Kong
  • 2009–2010
    • City University of Hong Kong
      • Department of Electronic Engineering
      Kowloon, Hong Kong
  • 2000–2008
    • The Hong Kong Polytechnic University
      • • Department of Electrical Engineering
      • • Department of Electronic and Information Engineering
      Hong Kong, Hong Kong