About

Dr Chao Wang is currently a Senior Lecturer in the School of Engineering and Digital Arts at University of Kent, where he first joined as a Lecturer in 2013. From 2011 to 2012, he was a NSERC Postdoctoral Fellow in the Photonics LaboratoryUniversity of California, Los Angeles (UCLA), USA. He received his B.Eng degree in Opto-electrical Engineering from Tianjin University, China, in 2002, M.Sc degree in Optics from Nankai University, China, in 2005, and Ph.D degree in Electrical and Computer Engineering from the University of Ottawa, Canada, in 2011. 

Dr Wang's research interests lie in inter-disciplinary areas that study the interaction between photonics and other traditional or state-of-the-art technologies in different fields, such as microwave photonics, optical communications and biophotonics, for widespread industrial, communications, biomedical, and defense applications. His research activities have been well funded by EU Marie-Curie Actions, the Royal Society of UK, the University of Kent, and Natural Sciences and Engineering Research Council (NSERC) of Canada. He has authored more than 80 peer-reviewed journal publications and international conference papers (including five invited papers and three Best Student Paper Awards). For a complete list of his publications, please visit this page. The total citations of his work are over1520 and h-index is 22. His research work has been highlighted in major academic media, such as Nature PhotonicsNature BiotechnologyTime MagazineScientific AmericanOptics & Photonics News and Laser Focus World.

He has received several prestigious international and national awards, including SPIE Scholarship in Optical Science and Engineering (2008), Vanier Canada Graduate Scholarship (2009) , IEEE Photonics Society Graduate Student Fellowship (2009), IEEE Microwave Theory and Techniques Society Graduate Fellowship (2010), Natural Science and Engineering Research Council of Canada (NSERC) Postdoctoral Fellowship (2011), and Marie-Curie Career Integration Grant (2014). He also received the Best Paper Awards from APMP 2009 and MWP 2010.

He is a member of IEEE, the IEEE-PS, the IEEE-MTTS, and OSA, and a Fellow of Higher Education Academy. He also serves as a regular reviewer of many leading photonics journals of OSA, IEEE, Nature, AIP, IET, SPIE, Elsevier and Wiley. He has served as the Co-organizer and Chair of Mini-Symposium on Microwave Photonics in PIERS 2014, and the Symposium Co-chair in CLEO-PR/OECC/PGC 2017, and Technical Programme Sub-committeee co-chair of CLEO-PR 2018. He also served as the Guest Editor of a Special Session on Microwave Photonics in SPIE Optical Engineeringand the Guest Editor of a Specital Issue on Microwave Photonics in MDPI Photonics.

In the School of Engineering and Digital Arts, Dr Wang is the Programme Chair of MSc Advanced Communications Engineering (RF Technology and Telecommunications) and MSc Advanced Communications Engineering (Wireless Systems and Networks).

Research interests

Dr Chao Wang's research interests lie in inter-disciplinary areas that study the interaction between photonics and other traditional or state-of-the-art technologies in different fields, such as microwave photonics, biophotonics and fiber optics, for industrial, communications, biomedical, and defense applications. 

  • Microwave Photonics: photonic generation of microwave arbitrary waveforms, microwave photonic signal processing, radio-over-fiber, optical sensors.
  • Biophotonics: ultrafast high-throughput optical imaging for biomedical applicaitons, optical coherence tomography.
  • Ultrafast Optics: coherent optical pulse shaping, characterization of ultrafast optical pulses, ultrafast optical signal processing.
  • Fiber Optics: fiber lasers and amplifiers, fiber Bragg gratings, fiber-optic sensors and ultrafast interrogation systems, photonic crystal fiber devices.

His research activities have been funded by the EU Marie-Curie Actions, the Royal Society of UK, University of Kent, and the Natural Sciences and Engineering Research Council (NSERC) of Canada. His current funded research projects include:

  • 2016-2017 (PI) The Royal Society Research Grants, "Photonic-enabled big data compression in ultrafast imaging".
  • 2014-2017 (Co-I, with Dr N. Gomes (PI), Prof J. Wang and Dr H. Zhu) EU Horizon 2020 EU-Japan Cooperation Project, "Radio Technologies for 5G using Advanced Photonic Infrastructure for Dense User Environment (RAPID)". 
  • 2014-2018 (PI) EU FP-7 Marie-Curie Career Integration Grant (CIG), "Next generation ULTrafast continuously running Imaging System for biomedical applications (NULTIS)".
  • 2014-2016 (PI) The Royal Society International Exchanges Grant, "Integrated Microwave Photonics Signal Processing for High-speed Optical Imaging".
  • 2014-2017 (PI, with Dr P. Young and Prof J. Stiens) University of Kent - VUB Collaboration Project, "Real-time Photonic Terahertz Coherence Tomography".
  • 2014-2017 (Co-I, with Dr N. Gomes(PI)) University of Kent 50th Anniversary PhD Studentship,  "Optical fibre transport of MIMO/virtual-MIMO radio signals for 5G wireless/mobile systems".
  • 2013-2016 (PI) University of Kent Faculty of Sciences Research Funds.

More information about Dr Wang's research can be found here.

Teaching

Undergraduate modules:

Postgraduate modules:

Foundation Year modules:

Supervision

PhD students supervised as the first supervisor:

PhD students supervised as the second supervisor:

  • AE Aighobahi: Radio over fibre
  • U Habib: Radio over Fibre, Millimetre Wave Communication, 5G Mobile/Communication Networks
  • S Noor: Subcarrier multiplexing radio over fibre

Professional

  • Regular Reviewer of more than 20 international Journals from IEEE, OSA, Nature, AIP, IET, SPIE, Elsevier, and Wiley. 
  • Remote Referee of European Research Council (2016-2017)
  • Grant Reviewer and Panelist of British Council Newton Fund (2014-2017)
  • Member of EPSRC Associate Peer Review College (2016- ) 
  • Guest Editor of SPIE Optical Engineering (2015) and MDPI Photonics (2017).
  • External examiner for PhD viva in Aston, VUB and Monash.  

Publications

Showing 50 of 125 total publications in the Kent Academic Repository. View all publications.

Article

  • Bandyopadhyay, S., Shao, L., Chao, W., Yan, Z., Hong, F., Wang, G., Jiang, J., Shum, P., Hong, X. and Wang, W. (2020). Highly efficient free-space fiber coupler with 45° tilted fiber grating to access remotely placed optical fiber sensors. Optics Express [Online] 28:16569. Available at: https://doi.org/10.1364/OE.392170.
    In this work, a 45° tilted fiber grating (TFG) is used as a waveguide coupler for the development of a portable interrogation system to access remotely placed optical fiber sensors. The TFG is directly connected to a remote fiber sensor and serves as a highly efficient light coupler between the portable interrogation unit and the sensor. Variation of strain and temperatures are measured with a standard fiber Bragg grating (FBG) sensor, which serves as a remotely placed optical sensor. A light beam from the interrogation unit is coupled into the TFG by a system of lenses, mirrors and optical collimator and acted as the input of the FBG. Reflected light from the FBG sensor is coupled back to the interrogation unit via the same TFG. The TFG is being used as a receiver and transmitter of light and constituent the key part of the system to connect “light source to the optical sensor” and “optical sensor to detector.” A successful demonstration of the developed system for strain and temperature sensing applications have been presented and discussed. Signal to noise ratio of the reflected light from the sensors was greater than ∼ 40 dB.
  • Bandyopadhyay, S., Shao, L., Smietana, M., Wang, C., Hu, J., Wang, G., Hu, W., Gu, G. and Yang, Y. (2020). Employing Higher Order Cladding Modes of Fiber Bragg Grating for Analysis of Refractive Index Change in Volume and at the Surface. IEEE Photonics Journal [Online] 12:1-13. Available at: https://doi.org/10.1109/JPHOT.2019.2963125.
    In this work, a detailed study on volume and surface refractive index (RI) sensitivity of cladding modes for a fiber Bragg grating (FBG) based sensor is presented. Surface RI sensitivity of the cladding mode of FBGs has been illustrated and quantified with the concept of add-layer sensitivity for the first time to the best of our knowledge. A detailed investigation of mode transition of higher-order cladding modes has been revisited and important characteristics of the cladding modes are observed which could open a new designing path of fabrication and innovative way of the use of this family of optical fiber grating-based sensors. The effect of “mode transition” of higher-order cladding modes, higher operating wavelength for respective cladding mode and “mode stretching” effects are combined together to achieve higher volume and surface RI sensitivity of cladding mode of FBG. It has been shown numerically that with proper designing, sub-nanometer (∼0.04 nm) attachment of target analyte could be recognized by cladding mode of FBG which is quite promising for application in optical fiber grating bio-sensors. This critical designing method of FBG based surface refractometer would be very helpful in case of the fabrication of highly sensitive sensors for distinct biochemical applications.
  • Yang, L., Zhu, Q., Wang, C., Chen, H., Li, J. and Xie, H. (2020). Temporal and spatial resolutions of optical time stretch imaging with dispersive grating pair. Physics Letters A [Online] 384:126083. Available at: https://doi.org/10.1016/j.physleta.2019.126083.
    Optical time stretch imaging (OTSI), providing the capability of capturing the dynamics of fast single-shot or random events, overcomes the fundamental trade-off between imaging speed and sensitivity in ultrafast imaging regions. Lying at the heart of the OTSI is dispersive Fourier transformation, being capable of using large chromatic dispersion to map the spectrum of a broadband ultrashort optical pulse into a stretched time-domain waveform. Dispersive grating pair (DGP) is a unique solution to generate large chromatic dispersion for dispersive Fourier transformation at the wavebands, in which dispersion compensation fibers commonly suffer from high dispersion-to-loss ratio. Here we characterize the performances of DGP-based OTSI modality and analyze the crucial parameters that strongly impact on the temporal as well as spatial resolutions, and further discuss its merits and challenges. Our results demonstrate DGP-based OTSI, allowing creation of high resolution images, is an effective modality compared to fiber-based OTSI.
  • Song, X., Zhang, H., Li, D., Jin, Q., Jia, D., Liu, T. and Wang, C. (2020). Liquid Lens with Large Focal Length Tunability Fabricated in a Polyvinyl Chloride/Dibutyl Phthalate Gel Tube. Langmuir [Online] 36:1430-1436. Available at: https://doi.org/10.1021/acs.langmuir.9b03585.
    Usually, an adaptive liquid lens only has a positive focal length, which severely limits its application in imaging and other fields. Therefore, a liquid lens consisting of polyvinyl chloride/dibutyl phthalate (PVC/DBP) gel, glycerol solution, and a glass substrate is proposed to extend the dynamic focal length range. A spherical tube is formed by the PVC/DBP gel under the effect of hydrostatic and surface tensions, which is used to restrict the glycerol solution. The PVC/DBP gel does not deform under the effect of an electric field, so the tangent line at the three-phase junction changes with the change of contact angle, which leads to an enlargement of the dynamic focal length range. At different voltage values, the proposed lens can be configured to work in three different schemes, namely, converging light, nondeflecting light, and diverging light. Here, the proposed lens has high imaging quality; the resolution is better than 114 lp/mm. A lens with a reconfigurable focal length holds great promise in diverse applications such as fluorescence detection, beam shaping, and adaptive optics.
  • Bandyopadhyay, S., Shao, L., Wang, C., Liu, S., Wu, Q., Gu, G., Hu, J., Liu, Y., Chen, X., Song, Z., Song, X., Bao, Q. and Smietana, M. (2019). Study on optimization of nano-coatings for ultra-sensitive biosensors based on long-period fiber grating. Sensing and Bio-Sensing Research [Online] 27. Available at: https://dx.doi.org/10.1016/j.sbsr.2019.100320.
    Bio-chemical sensors are expected to offer high sensitivity and specificity towards the detection of an analyte. It has been found that optical sensors based on long period fiber gratings (LPFGs) meet most of these requirements, particularly when coated with thin and high-refractive index overlays with proper bio-functionalization. In this paper, the influence of properties of the overlay material on the sensitivity of LPFG sensors to bio-analytes is analyzed. It has been observed that the sensitivity of a particular cladding mode of LPFG can be changed drastically with the adhesion of few tens of ‘nm’ of bio-layers to the surface of LPFG. “Volume refractive index sensitivity” and “add-layer sensitivity” of a particular cladding mode, dynamic range, and limit of detection of the sensors have been investigated in the context of overlay materials, bio-functionalization steps, and surrounding buffer medium. The selection criteria of the thin-film deposition technique are discussed with the aim of designing highly sensitive sensors for biological and chemical applications. Concept of optimum overlay thickness has been redefined and an effective case-specific design methodology is proposed.
  • Shao, L., Liu, S., Bandyopadhyay, S., Yu, F., Xu, W., Wang, C., Li, H., Vai, M., Du, L. and Zhang, J. (2019). Data-Driven Distributed Optical Vibration Sensors: A Review. IEEE Sensors Journal [Online] 20:6224-6239. Available at: https://doi.org/10.1109/JSEN.2019.2939486.
    Distributed optical vibration sensors (DOVS) have attracted much attention recently since it can be used to monitor mechanical vibrations or acoustic waves with long reach and high sensitivity. Phase-sensitive optical time domain reflectometry (Φ-OTDR) is one of the most commonly used DOVS schemes. For Φ-OTDR, the whole length of fiber under test (FUT) works as the sensing instrument and continuously generates sensing data during measurement. Researchers have made great efforts to try to extract external intrusions from the redundant data. High signal-to-noise ratio (SNR) is necessary in order to accurately locate and identify external intrusions in Φ-OTDR systems. Improvement in SNR is normally limited by the properties of light source, photodetector and FUT. But this limitation can also be overcome by post-processing of the received optical signals. In this context, detailed methodologies of SNR enhancement post-processing algorithms in Φ-OTDR systems have been described in this paper. Furthermore, after successfully locating the external vibrations, it is also important to identify the types of source of the vibrations. Pattern classification is a powerful tool in recognizing the intrusion types from the vibration signals in practical applications. Recent reports of Φ-OTDR systems employed with pattern classification algorithms are subsequently reviewed and discussed. This thorough review will provide a design pathway for improving the performance of Φ-OTDR while maintaining the cost of the system as no additional hardware is required.
  • Qin, H., He, Q., Xing, Z., Guo, X., Yan, Z., Sun, Q., Wang, C., Zhou, K., Liu, D. and Zhang, L. (2019). In-fiber single-polarization diffraction grating based on radiant tilted fiber grating. Optics Letters [Online] 44:4407-4410. Available at: https://doi.org/10.1364/OL.44.004407.
    In this letter, we proposed an in-fiber single polarization diffraction grating based on a radiant tilted fiber grating (TFG), in which the s-polarization light could be diffracted from the fiber core to free space with the wavelength-dependent diffraction angle. For the first time, we have presented the theoretical model of angular dispersion of radiant TFG by employing Fourier optics analysis method. The angular dispersion of radiant TFG has been numerically characterized in terms of tilt angle, period and wavelength. In the experiment, we have measured the diffraction angles and angular dispersion of the radiant TFGs with tilt angles of 41°, 45° and 47° UVinscribed into single mode fiber, where the experimental results matched well with the simulation results. The simulation and experimental results have indicated that the diffraction light of radiant TFGs has a linear polarization state with over 0.99 degree of polarization at the tilt angle range from 41° to 47°.
  • Yang, L., Chen, M., Zhu, Q., Yang, T., Wang, C. and Xie, H. (2019). Development of a small-diameter and high-resolution industrial endoscopy with CMOS image sensor. Sensors and Actuators A: Physical [Online] 296:17-23. Available at: https://doi.org/10.1016/j.sna.2019.04.026.
    In the industrial field, an endoscope is typically employed for the observation and inspection of internal defect and corrosion of an engine and chemical plant. Current industrial optical endoscopes normally use CMOS sensor which offers best performance as an image pickup device. Here we report experimental demonstration of an industrial endoscope modality consisting of a 5 mm diameter rigid tube and 1280 × 960 pixels CMOS camera, which enables accurate diagnosis of small-scale industrial components with hollow shape. As a proof of concept, we successfully perform arc-surface imaging at a resolution of 57 lp/mm and ± 30^o field of view. Finally, potentially applying the wavefront coding method to extend the depth of field of endoscopic system is comprehensively discussed.
  • Liu, T., Zhang, H., Liu, B., Zhang, X., Liu, H. and Wang, C. (2019). Highly compact vector bending sensor with microfiber-assisted Mach-Zehnder interferometer. IEEE Sensors Journal [Online]. Available at: https://doi.org/10.1109/JSEN.2019.2892897.
    A low-cost and highly compact fiber-optic component is proposed and experimentally demonstrated for vector bending sensing. A segment of microfiber tapered from standard single-mode fibers (SMFs) is spliced between two SMFs with pre-designed lateral offset to construct a sandwich type Mach-Zehnder interferometer of 243.32 ?m in length. Sensing performances of the proposed vector bending sensor is theoretically analyzed in detail. As the applied curvature increases from 0.3873 m-1 to 3.0 m-1, the transmission spectra of the proposed sensor show distinct linear wavelength shift sensitivities for different directions, the maximum of which is up to 3.419 nm/m-1. Besides, temperature test indicates that the proposed sensor possesses a low temperature cross sensitivity of 33.71 pm/°C, which ensures its applicability for practical uses in temperaturefluctuated environment. Hence, our proposed vector bending sensor possesses such desirable merits as high sensitivity, compact size, low thermal crosstalk, low cost and orientation-dependent spectral response.
  • Xie, N., Zhang, H., Liu, B., Liu, H., Liu, T. and Wang, C. (2018). In-line microfiber-assisted Mach-Zehnder interferometer for microfluidic highly sensitive measurement of salinity. IEEE Sensors Journal [Online]. Available at: https://doi.org/10.1109/JSEN.2018.2869273.
    We present a microfluidic U-shaped micro-cavity sensor by splicing a segment of microfiber of a few hundred micrometers in length tapered from a single-mode fiber (SMF) between two SMFs with predesigned lateral offset for highly sensitive salinity measurement. The proposed sensing probe serves as an in-line microfiber-assisted Mach-Zehnder interferometer (MAMZI) with an ultra-high refractive index sensitivity of 104 nm/RIU. Three Mach-Zehnder interferometer structures with different cavity lengths of 351.82 ?m, 242.56 ?m and 181.31 ?m are fabricated, by which microfluidic sensing systems are established for in-line measurement of sodium chloride (NaCl) solution. Experimental results indicate that the detection limit of NaCl solution is as low as 4×10-3 wt% and the response time is less than 15 s, which would make the MAMZI-based microfluidic measuring system play an important role in label-free biological and chemical detection applications.
  • Yang, C., Zhang, H., Liu, B., Liu, H., Wang, C. and Lin, S. (2018). Electrically tuned whispering gallery modes microresonator based on microstructured optical fibers infiltrated with dual-frequency liquid crystals. Nanophotonics [Online] 7:1333-1340. Available at: https://doi.org/10.1515/nanoph-2018-0042.
    An electrically tunable whispering gallery mode (WGM) microresonator based on an HF-etched microstructured optical fiber (MOF) infiltrated with dual-frequency liquid crystals (DFLCs) is proposed and experimentally demonstrated for the investigation of the crossover frequency and Freedericksz transition of DFLCs. Experimental results indicate that for applied electric field with operation frequency below the crossover frequency, WGM resonance wavelength decreases with the increment of applied electric field strength. On the contrary, for applied electric field with operation frequency beyond the crossover frequency, WGM resonance dips show red shift as the applied electric field intensity increases. The proposed electrically tunable microcavity integrated with DFLCs is anticipated to find potential applications in optical filtering, all-optical switching, and electrically manipulated bi-directional micro-optics devices.
  • Xing, J., Wang, C., Chi, H., Yu, X., Zheng, S., Jin, X. and Zhang, X. (2018). Modulation fading in temporal Talbot effect. IEEE Photonics Technology Letters [Online] 30:1376-1379. Available at: https://doi.org/10.1109/LPT.2018.2848634.
    Temporal Talbot phenomenon is the time-domain counterpart of the well-known spatial Talbot phenomenon, which can be used to compress/expand input pulses or multiply the pulse repetition rate. It is of great interest to study the temporal Talbot effect with modulation due to its potential applications in information transmission, in which the envelope of the input pulse sequence is modulated by a signal. In this letter, we report the modulation fading phenomenon in the temporal Talbot effect, i. e. the phenomenon that the modulation depth degrades with the increase of the order of the Talbot effect, for the first time to our knowledge. Distinct from the attenuation caused by the fiber loss, the modulation fading relates to the pulse width, the repetition period of the pulse sequence, and the frequency of the modulating signal as well as the order of the Talbot effect. A fully analytical expression of the modulation transfer function is presented to explain this phenomenon. Potential application of the modulation fading in temporal cloaking is discussed.
  • Yang, C., Zhang, H., Liu, B., Liu, H., Wang, C. and Lin, S. (2018). Tuning of polarization-dependent whispering gallery modes in grapefruit microstructured optical fibers infiltrated with negative dielectric anisotropy liquid crystals. Journal of Lightwave Technology [Online]. Available at: https://doi.org/10.1109/JLT.2018.2845104.
    An electrically tunable whispering gallery mode (WGM) microresonator based on microstructured optical fibers (MOFs) infiltrated with negative dielectric anisotropy liquid crystals (LCs) is proposed and experimentally demonstrated. Experimental results indicate that the second radial order mode of the MOF microresonator has stronger electric field response than the first radial order mode and the resonance dip for TE polarization mode is more sensitive to the applied electric field intensity in comparison with the TM polarization mode resonance dip. The Freedericksz transition threshold of the proposed MOF microresonator is experimentally found to be about 2.0 V/um. The electrically tunable microresonator integrated with negative dielectric anisotropy LCs is anticipated to find potential applications in optical filtering, all-optical switching, and electrically controlled micro-optics devices.
  • Zhang, X., Liu, B., Zhang, H., Wu, J., Song, B. and Wang, C. (2018). A magnetic field sensor based on a dual S-tapered multimode fiber interferometer. Measurement Science & Technology [Online] 29. Available at: https://doi.org/10.1088/1361-6501/aac00e.
    A multimode interferometer (MMI) for the measurement of a magnetic field based on concatenated S-tapered fibers is proposed and experimentally demonstrated. Spectrally interrogated magnetic field sensing is achieved by integrating the proposed MMI with magnetic fluids. The magnetic sensitivity of the MMI reaches 0.011 dB Oe?1. Owing to its desirable advantages such as compactness, low cost, fast response and flexible structure, the proposed MMI is anticipated to find potential applications in in situ measurements of the magnetic field.
  • Wu, W., Liu, X. and Wang, C. (2018). Quantum speed-up capacity in different types of quantum channels for two-qubit open systems. Chinese Physics B [Online] 27:60302. Available at: http://dx.doi.org/10.1088/1674-1056/27/6/060302.
    A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the “quantum speed-up capacity” which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment:selecting an appropriate coefficient of an initial state or changing the memory degree of environments.
  • Wang, G., Habib, U., Yan, Z., Gomes, N., Sui, Q., Wang, J., Zhang, L. and Wang, C. (2018). Highly efficient optical beam steering using an in-fiber diffraction grating for full duplex indoor optical wireless communication. Journal of Lightwave Technology [Online] 36:4618-4625. Available at: https://doi.org/10.1109/JLT.2018.2832200.
    Diffraction gratings have been widely used in wavelength-controlled non-mechanical laser beam steering for high data-rate indoor optical wireless communications (OWC). Existing free-space diffraction gratings suffer from inherent difficulties of limited diffraction efficiency, bulky configuration, high cost and significant coupling loss with optical fiber links. In this work, a new optical approach for highly efficient, compact and fiber compatible laser beam steering using an in-fiber diffraction grating is proposed and experimentally demonstrated for the first time to our best knowledge. In-fiber diffraction is made possible based on a 45° tilted fiber grating (TFG), where wavelength dependent lateral scattering is obtained due to the strongly tilted grating structure. Improved diffraction efficiency of 93.5% has been achieved. In addition, the 45° TFG works perfectly for both light emission and reception, enabling full-duplex optical wireless transmission. Utility of the 45° TFG in all-fiber laser beam steering for multi-user full duplex optical wireless communications has been verified in experiments. 1.4 m free-space full-duplex wireless transmission has been demonstrated with data rate up to 12 Gb/s per beam using 2.4 GHz bandwidth OFDM signals.
  • Zhao, W., Wang, C., Chen, H., Chen, M. and Yang, S. (2018). High-speed cell recognition algorithm for ultra-fast flow cytometer imaging system. Journal of Biomedical Optics [Online] 23. Available at: https://doi.org/10.1117/1.JBO.23.4.046001.
    An optical time-stretch flow imaging system enables high-throughput examination of cells/particles with unprecedented high speed and resolution. A significant amount of raw image data is produced. A high-speed cell recognition algorithm is, therefore, highly demanded to analyze large amounts of data efficiently. A high-speed cell recognition algorithm consisting of two-stage cascaded detection and Gaussian mixture model (GMM) classification is proposed. The first stage of detection extracts cell regions. The second stage integrates distance transform and the watershed algorithm to separate clustered cells. Finally, the cells detected are classified by GMM. We compared the performance of our algorithm with support vector machine. Results show that our algorithm increases the running speed by over 150% without sacrificing the recognition accuracy. This algorithm provides a promising solution for high-throughput and automated cell imaging and classification in the ultrafast flow cytometer imaging platform.
  • He, H., Shao, L., Wang, C., Luo, B., Zou, X., Zhang, X., Pan, W. and Yan, L. (2018). Arbitrary spectral synthesis and waveform generation with HiBi fiber loop mirrors. IEEE Photonics Technology Letters [Online] 30:943-946. Available at: https://doi.org/10.1109/LPT.2018.2818326.
    An arbitrary spectral synthesis scheme with parallel-connecting high-birefringence fiber loop mirrors (HiBi-FLMs) based on Fourier synthesis theory has been proposed and demonstrated. Three typical spectra of triangle, rectangle and sawtooth shape have been synthesized by implementing only four HiBi-FLMs. The experimental results are in good agreement with theoretical simulations with a goodness of fit of 0.9565. Furthermore, higher precise optical spectrum with narrower bandwidth can be obtained by adopting longer polarization- maintaining fiber and more sections of HiBi-FLMs. Besides, a typical application of arbitrary waveform generation has been implemented. By incorporating with frequency-to- time mapping, triangle- and sawtooth-shaped electrical pulses with repetition rate of 1 GHz and pulse width of ~860 ps have been generated
  • Wang, G., Yan, Z., Yang, L., Zhang, L. and Wang, C. (2018). Improved resolution optical time stretch imaging based on high efficiency in-fiber diffraction. Scientific Reports [Online] 8:600. Available at: https://www.nature.com/articles/s41598-017-18920-8.
    Most overlooked challenges in ultrafast optical time stretch imaging (OTSI) are sacrificed spatial resolution and higher optical loss. These challenges are originated from optical diffraction devices used in OTSI, which encode image into spectra of ultrashort optical pulses. Conventional free-space di?raction gratings, as widely used in existing OTSI systems, suffer from several inherent drawbacks: limited diffraction efficiency in a non-Littrow configuration due to inherent zeroth-order reflection, high coupling loss between free-space gratings and optical fibers, bulky footprint, and more importantly, sacrificed imaging resolution due to non-full-aperture illumination for individual wavelengths. Here we report resolution-improved and diffraction-efficient OTSI using in-fiber diffraction for the first time to our knowledge. The key to overcome the existing challenges is a 45° tilted fiber grating (TFG), which serves as a compact in-fiber diffraction device offering improved diffraction efficiency (up to 97%), inherent compatibility with optical fibers, and improved imaging resolution owning to almost full-aperture illumination for all illumination wavelengths. 50 million frames per second imaging of fast moving object at 46 m/s with improved imaging resolution has been demonstrated. This conceptually new in-fiber diffraction design opens the way towards cost-effective, compact and high-resolution OTSI systems for image-based high-throughput detection and measurement.
  • Xie, H., Jiang, M., Wang, Y., Pang, X., Wang, C., Su, Y. and Yang, L. (2017). Aspheric optical surface profiling based on laser scanning and auto-collimation. Review of Scientific Instruments [Online] 88. Available at: https://dx.doi.org/10.1063/1.4995685.
    Nowadays the utilization of aspheric lens has become more and more popular, enabling highly increased degree of freedom for optical design and simultaneously improving the performance of optical system. Hence this also entails a stringent requirement for fast and accurate measuring the shape of these aspheric components. In this paper, the instrument is greatly developed to satisfy the growing need to test axially symmetric aspheric surface, which is implemented by converting the pose of reflective mirror in optical path to the coordinate of reflection point on the surface when laser rapidly scans . At each movement position managed by grating-rule sensor, the rotating angle of reflective mirror is defined using position sensitive detector based on the laser auto-collimating and beam center-fitting principle. Testing a convex and a concave surfaces with highly reproducible results, including coefficient of determination better than 0.999 and RMSE less than =10, validates the feasibility of this method. In comparison to the conventional computer-generated hologram tester or interferometer, the present instrument—essentially builds on the pure geometrical optics technology—is a powerful tool to measure the aspheric surface quickly and accurately with simple structure and algorithm.
  • Xie, H., Ren, D., Wang, C., Mao, C. and Yang, L. (2017). Design of high-efficiency diffractive optical elements towards ultrafast mid-infrared time-stretched imaging and spectroscopy. Journal of Modern Optics [Online]:1-7. Available at: http://dx.doi.org/10.1080/09500340.2017.1386332.
  • Xie, H., Mao, C., Ren, Y., Zhu, J., Wang, C. and Yang, L. (2017). Design of an omnidirectional single-point photodetector for large-scale spatial coordinate measurement. Optical Engineering [Online] 56:104105. Available at: http://dx.doi.org/10.1117/1.OE.56.10.104105.
    In high precision and large-scale coordinate measurement, one commonly used approach to determine the coordinate of a target point is to utilize the spatial trigonometric relationships between multiple laser transmitting stations and the target point. A light receiving device at target point is the key element in large-scale coordinate measurement systems. To ensure high-resolution and highly-sensitive spatial coordinate measurement, a high-performance and miniaturized omnidirectional single-point photodetector (OSPD) is highly desired. Here we report one design of OSPD using aspheric lens, which achieves enhanced reception angle of -5 to 45 degree in vertical and 360 degree in horizontal. As the heart of our OSPD, the aspheric lens is designed in geometric model and optimized by LightTools Software, which enables reflecting wide-angle incident light beam into the single-point photodiode. The performance of home-made OSPD is characterized with working distances from 1 m to 13 m and further analyzed utilizing established geometric model. The experimental and analytic results verify that our new device is highly suitable for large-scale coordinate metrology. The developed device also holds great potential in various applications such as omnidirectional vision sensor, indoor global positioning system, optical wireless communication systems.
  • Mididoddi, C., Bai, F., Wang, G., Liu, J., Gibson, S. and Wang, C. (2017). High throughput photonic time stretch optical coherence tomography with data compression. IEEE Photonics Journal [Online] 9. Available at: https://dx.doi.org/10.1109/JPHOT.2017.2716179.
    Photonic time stretch enables real time high throughput optical coherence tomography (OCT), but with massive data volume being a real challenge. In this paper, data compression in high throughput optical time stretch OCT has been explored and experimentally demonstrated. This is made possible by exploiting spectral sparsity of encoded optical pulse spectrum using compressive sensing (CS) approach. Both randomization and integration have been implemented in the optical domain avoiding an electronic bottleneck. A data compression ratio of 66% has been achieved in high throughput OCT measurements with 1.51 MHz axial scan rate using greatly reduced data sampling rate of 50 MS/s. Potential to improve compression ratio has been exploited. In addition, using a dual pulse integration method, capability of improving frequency measurement resolution in the proposed system has been demonstrated. A number of optimization algorithms for the reconstruction of the frequency-domain OCT signals have been compared in terms of reconstruction accuracy and efficiency. Our results show that the L1 Magic implementation of the primal-dual interior point method offers the best compromise between accuracy and reconstruction time of the time-stretch OCT signal tested.
  • Liu, X., Wu, W. and Wang, C. (2017). Modified quantum-speed-limit bounds for open quantum dynamics in quantum channels. Physical Review A: Atomic, Molecular and Optical Physics [Online] 95:52118. Available at: http://dx.doi.org/10.1103/PhysRevA.95.052118.
    The minimal evolution time between two distinguishable states is of fundamental interest in quantum physics. Very recently Mirkin et al. argue that some most common quantum-speed-limit (QSL) bounds which depend on the actual evolution time do not cleave to the essence of the QSL theory as they grow indefinitely but the final state is reached at a finite time in a damped Jaynes-Cummings (JC) model. In this paper, we thoroughly study this puzzling phenomenon. We find the inconsistent estimates will happen if and only if the limit of resolution of a calculation program is achieved, through which we propose that the nature of the inconsistency is not a violation to the essence of the QSL theory but an illusion caused by the finite precision in numerical simulations. We also present a generic method to overcome the inconsistent estimates and confirm its effectiveness in both amplitude-damping and phase-damping channels. Additionally, we show special cases which may restrict the QSL bound defined by “quantumness”.
  • Han, X., Huo, B., Shao, Y., Wang, C. and Zhao, M. (2017). RF self-interference cancellation using phase modulation and optical sideband filtering. IEEE Photonics Technology Letters [Online] 29:917-920. Available at: http://dx.doi.org/10.1109/LPT.2017.2693690.
    A novel optical approach to implement RF self-interference cancellation for full-duplex communication using phase modulation and optical sideband filtering is proposed and demonstrated experimentally. Based on the inherent out-of-phase property between the left and right sidebands of phase-modulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. RF self-interference cancellation for single frequency and microwave with various bandwidth of 1MHz, 5MHz and 10 MHz is experimentally demonstrated to verify the proposed technique.
  • Mididoddi, C. and Wang, C. (2017). Adaptive non-uniform photonic time stretch for blind RF signal detection with compressed time-bandwidth product. Optics Communications [Online] 396:221-227. Available at: http://dx.doi.org/10.1016/j.optcom.2017.03.052.
    Photonic time stretch significantly extends the effective bandwidth of existing analog-to-digital convertors by slowing down the input high-speed RF signals. Non-uniform photonic time stretch further enables time bandwidth product reduction in RF signal detection by selectively stretching high-frequency features more. However, it requires the prior knowledge of spectral-temporal distribution of the input RF signal and has to reconfigure the time stretch filter for different RF input signals. Here we propose for the first time an adaptive non-uniform photonic time stretch method based on microwave photonics pre-stretching that achieves blind detection of high-speed RF signals with reduced time bandwidth product. Non-uniform photonic time stretch using both quadratic and cubic group delay response has been demonstrated and time bandwidth product compression ratios of 72% and 56% have been achieved respectively.
  • Ahmad, E., Wang, C., Feng, D., Yan, Z. and Zhang, L. (2016). High temporal and spatial resolution distributed fiber Bragg grating sensors using time-stretch frequency-domain reflectometry. Journal of Lightwave Technology [Online] 35:3289-3295. Available at: http://dx.doi.org/10.1109/JLT.2016.2605401.
    A novel interrogation technique for fully distributed linearly chirped fiber Bragg grating (LCFBG) strain sensors with simultaneous high temporal and spatial resolution based on optical time-stretch frequency-domain reflectometry (OTS-FDR) is proposed and experimentally demonstrated. LCFBGs is a promising candidate for fully distributed sensors thanks to its longer grating length and broader reflection bandwidth compared to normal uniform FBGs. In the proposed system, two identical LCFBGs are employed in a Michelson interferometer setup with one grating serving as the reference grating whereas the other serving as the sensing element. Broadband spectral interferogram is formed and the strain information is encoded into the wavelength-dependent free spectral range (FSR). Ultrafast interrogation is achieved based on dispersion-induced time stretch such that the target spectral interferogram is mapped to a temporal interference waveform that can be captured in real-time using a single-pixel photodector. The distributed strain along the sensing grating can be reconstructed from the instantaneous RF frequency of the captured waveform. High-spatial resolution is also obtained due to high-speed data acquisition. In a proof-of-concept experiment, ultrafast real-time interrogation of fully-distributed grating sensors with various strain distributions is experimentally demonstrated. An ultrarapid measurement speed of 50 MHz with a high spatial resolution of 31.5 µm over a gauge length of 25 mm and a strain resolution of 9.1 µ? have been achieved.

Book section

  • Jing, N., Mididoddi, C. and Wang, C. (2020). Compressive Sensing Detection of RF Signals by All-Optically Generated Binary Random Patterns. In: 2019 IEEE 2nd British and Irish Conference on Optics and Photonics (BICOP). IEEE. Available at: https://dx.doi.org/10.1109/BICOP48819.2019.9059595.
    High-speed random bit sequences are crucially important in temporal compressive sensing applications. In this work, we propose a new all-optical binary random patterns generation method for compressive sensing, completely eliminating the use of high-speed electronic circuits. This approach uses photonic time stretched optical pulses as the optical carrier. Spectrum slicing using a tunable ring resonator produces a train of uniformly spaced optical pulses (bits) due to spectrum-to-time mapping in photonic time stretch. Two cascaded dispersive devices with particularly designed nonlinear dispersion profiles are employed to introduce random time delays among optical pulses, leading to a quasi-random binary sequence. The random sampling pulse sequence can be updated by changing the free-spectral range of the ring resonator. The proposed method is verified by numerical simulations. The photonic generated random pulse sequences are used in compressive sensing detection of high-frequency RF signals. In a proof-of-concept demonstration, one-tone and multi-tone microwave signals are successfully reconstructed from four-time compressed measurement data.
  • Mididoddi, C., Wang, G., Liu, X. and Wang, C. (2019). Real-Time User Localisation in Beam Steered NIR Optical Wireless Communications. In: 2019 IEEE MTT-S International Wireless Symposium (IWS). New York, USA: IEEE. Available at: http://dx.doi.org/10.1109/IEEE-IWS.2019.8804053.
    Near infrared (NIR) optical wireless communication provides a promising solution for point-to-point indoor high speed wireless data link. To cover a large area and several multiple users, wavelength-encoded laser beam steering has been demonstrated in previous research work. One remaining challenge in beam steered optical wireless system is real-time user localization. In this paper, ultrafast complete user localization at update rate of 10 MHz based on instantaneous optical wavelength detection and chirped pulse correlation has been demonstrated. Both angular position and absolute distance of each user have been accurately detected.
  • Han, X., Su, X., Wang, S., Wang, H., Shao, Y., Wang, C. and Zhao, M. (2018). Photonic enabled RF self-interference cancellation for full-duplex communication. In: Real-Time Photonic Measurements, Data Management, and Processing III. Bellingham, Washington: SPIE. Available at: https://doi.org/10.1117/12.2503944.
    Photonic enabled RF self-interference cancellation for full-duplex communication by using phase modulation and optical sideband filtering is proposed. Based on the inherent out-of-phase property between the left and right sidebands of phasemodulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. The operational principle of the proposed scheme is theoretically analyzed and the feasibility is experimentally demonstrated. The optical sideband filtering for the phase modulated signals is measured and the RF self-interference cancellation at different carrier frequencies is studied. The results show a good performance of the proposed photonic scheme for RF self-interference cancellation. The full-duplex communication based on the photonic enabled RF self-interference cancellation is also investigated.
  • Mididoddi, C. and Wang, C. (2018). Photonic compressive sensing enabled data efficient time stretch optical coherence tomography. In: Podoleanu, A. G. and Bang, O. eds. 2nd Canterbury Conference on OCT With Emphasis on Broadband Optical Sources. SPIE. Available at: https://doi.org/10.1117/12.2283035.
    Photonic time stretch (PTS) has enabled real time spectral domain optical coherence tomography (OCT). However, this method generates a torrent of massive data at GHz stream rate, which requires capturing as per Nyquist principle. If the OCT interferogram signal is sparse in Fourier domain, which is always true for samples with limited number of layers, it can be captured at lower (sub-Nyquist) acquisition rate as per compressive sensing method. In this work we report a data compressed PTS-OCT system based on photonic compressive sensing with 66% compression with low acquisition rate of 50MHz and measurement speed of 1.51MHz per depth profile. A new method has also been proposed to improve the system with all-optical random pattern generation, which completely avoids electronic bottleneck in traditional binary pseudorandom binary sequence (PRBS) generators.
  • Mididoddi, C., Wang, G., Sun, L. and Wang, C. (2017). Photonic time-stretch optical coherence tomography with data compression and improved resolution. In: 2017 Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR). IEEE. Available at: http://dx.doi.org/10.1109/CLEOPR.2017.8118840.
    In this paper, we investigate the reconstruction of non-harmonic tones in data-compressed PTS-OCT based on multiple pulse integration. To the best of our knowledge, this is the first time that frequency reconstruction resolution less than the pulse repetition rate has been demonstrated in PTS-OCT through all-optical compressive sensing, leading to improved depth resolution in OCT measurement.
  • Wang, G., Habib, U., Wang, C., Gomes, N., Yan, Z. and Zhang, L. (2017). Wavelength-controlled beam steering for optical wireless transmission using an in-fiber diffraction grating. In: CLEO: Science and Innovations Part of CLEO: 2017. Washington, DC, USA: Optical Society of America. Available at: http://dx.doi.org/10.1364/CLEO_SI.2017.SF1L.5.
    Passive beam steering for optical wireless transmission based on wavelength tuning using a novel in-fiber diffraction grating featuring compactness, high diffraction efficiency and inherent fiber-compatibility, is proposed and experimentally demonstrated for the first time.
  • Feng, D., Ahmad, E. and Wang, C. (2016). Ultrafast and High Resolution Crack Detection Using Fully Distributed Chirped Fiber Bragg Grating Sensors. In: Asia-Pacific Optical Sensors Conference, APOS 2016. Optical Society of America. Available at: http://dx.doi.org/10.1364/APOS.2016.W4A.47.
    We demonstrate for the first time that photonic time-stretch frequency domain reflectometry (PTS-FDR) enables ultrafast and high spatial-resolution crack detection using fully distributed chirped fiber Bragg grating strain sensors.
  • Habib, U., Aighobahi, A., Wang, C. and Gomes, N. (2016). Radio over fiber transport of mm-wave 2×2 MIMO for spatial diversity and multiplexing. In: 2016 IEEE International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: http://dx.doi.org/10.1109/MWP.2016.7791280.
    DWDM-RoF transport and photonic generation of millimeter-wave MIMO signals has been demonstrated. Generation and modulation of independent data streams over different wavelengths provides allocation flexibility and centralization. EVM results show that this low-cost technique provides antenna diversity/multiplexing gain for STBC-Alamouti and Zero-Forcing algorithms based OFDM-MIMO.
  • Wang, G. and Wang, C. (2016). Diffraction Limited Optical Time-Stretch Microscopy Using an In-Fibre Diffraction Grating. In: Frontiers in Optics, FiO 2016. Optical Society of America. Available at: http://dx.doi.org/10.1364/FIO.2016.FF2A.5.
    Ultrafast optical time-stretch imaging using a 45° tilted fiber grating as an in-fibre diffraction device is proposed and experimentally demonstrated for the first time featuring high efficiency, complete fiber-compatibility and diffraction-limited lateral resolution.

Conference or workshop item

  • Su, X., Fu, S., Wang, S., Yang, X., Wang, P., Wang, C., Wu, Z., Gu, Y., Zhao, M., Han, X., Jalali, B., Li, M. and Asghari, M. (2019). Performance analysis of photonic RF self-interference cancellation for full-duplex communication. In: SPIE/COS Photonics Asia. SPIE. Available at: https://doi.org/10.1117/12.2538562.
    A photonic RF self-interference cancellation (SIC) scheme for full-duplex communication is proposed and demonstrated experimentally. It is based on phase modulation to convert the RF signal into optical domain. The interference cancellation performance of the photonic RF SIC system under different delay deviation (Δτ) and amplitude deviation (Δα) is analyzed. The cancellation depth of 34.5 dB is measured for 10 GHz signal with bandwidth of 50MHz. According to experimental results, the interference cancellation performance affected by the time delay deviation, the amplitude deviation and the phase response is investigated. The results give a direction for the improvement of system performance.
  • Xiao, D., Han, T., Shao, L. and Wang, C. (2019). Nonuniform Microwave Photonic Delay-Line Filter For Optical Sensor Network Interrogation. In: 2019 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: https://dx.doi.org/10.1109/MWP.2019.8892068%E2%80%8B.
    We propose a new design of nonuniform spaced microwave photonic delay-line filter based generic optical fiber sensors interrogation platform. Both the amplitude and phase response of the microwave filter are used to demodulate optical sensors. Therefore, a large sensor network with different types of optical sensors can be interrogated simultaneously. The concept of this new microwave photonics enabled interrogation approach is presented and verified by simulations where four different types of optical sensors are simultaneously interrogated via inverse Fourier transform of filter frequency response.
  • Su, X., Wang, S., Wang, H., Shao, Y., Wang, C., Wang, P., Wu, Z., Gu, Y., Zhao, M. and Han, X. (2019). RF Characterization of Self-Interference Cancellation Using Phase Modulation and Optical SideBand Filtering. In: 2019 PhotonIcs & Electromagnetics Research Symposium. IEEE, pp. 4305-4310. Available at: https://doi.org/10.1109/PIERS-Spring46901.2019.9017352.
    Full-Duplex scheme transmitting and receiving signals simultaneously in the same frequency band can significantly improve the throughput and the spectrum efficiency, and is considered as a candidate technology for the fifth generation (5G) wireless communication. However, the high power transmitted signal will interfere with the in-band weak received signal, which is called as RF self-interference. It cannot be simply removed by a notch filter or a narrow bandpass filter because the same frequency band is used for both transmitter and receiver. An optical approach to implement RF self-interference cancellation is proposed. Based on the inherent out-of-phase property between the left and right sidebands of phase-modulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. The cancellation depth of the system was measured for different frequencies and bandwidths. The cancellation performance affected by the time delay deviation, the amplitude deviation and phase response is analyzed according to experimental results. It gives the direction for the improvement of system performance. Finally, the full-duplex communication by using the optical SIC approach was also investigated. Signal of interest is recovered and the constellation diagram was also shown.
  • Mididoddi, C., Wang, G., Habib, U., Zhang, H. and Wang, C. (2018). Ultrafast User Localization and Beam Steering in Optical Wireless Communication Using an In-Fibre Diffraction Grating. In: 2018 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: https://doi.org/10.1109/MWP.2018.8552858.
    Wavelength-controlled laser beam steering has been successfully demonstrated for indoor optical wireless communications (OWC). Here we demonstrate ultrafast user localization (50 million scans per second) in OWC based on real-time wavelength monitoring. A separate time stretched pulsed laser source is introduced to implement ultrafast optical wavelength (hence optical beam) scanning. A dispersion unbalanced Mach-Zehnder interferometric configuration creates chirped encoding in stretch optical pulses. The reflected optical wavelength from a remote user carrying the location information of the user is detected by real-time instantaneous microwave frequency detection. This new approach facilitates simultaneous ultrafast user localization and data transmission at communication C-band. A proof-of-concept experiment is carried out to verify the proposed approach.
  • Liu, X., Mididoddi, C., Tan, Z., Wang, G., Shao, L. and Wang, C. (2018). Tunable Multimode Optical Delay Line for Single-Wavelength Microwave Photonic Transversal Filter. In: 2018 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: https://doi.org/10.1109/MWP.2018.8552882.
    Most existing microwave photonic transversal filters are implemented in the incoherent regime using multiple optical carrier wavelengths to avoid optical interference. The system therefore becomes complicated and expensive. In this work, we present a novel single-wavelength microwave photonics transversal filter design in the coherent regime using a single multimode fibre. Filter taps are generated from spatial modes excited by multiple narrow optical beams with different incident angles. Therefore, optical interference is eliminated due to space demultiplexing. Time delays between filter taps are obtained due to large modal dispersion and can be simply tuned using spatial slots. In a proof-of-concept experiment, a modal dispersion enabled optical delay line module for a two-tap microwave photonic transversal filter has been demonstrated with avoided optical interference.
  • Liu, S., Mididoddi, C., Zhou, H., Li, B., Xu, W. and Wang, C. (2018). Single-Shot Sub-Nyquist RF Signal Reconstruction Based on Deep Learning Network. In: 2018 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: https://doi.org/10.1109/MWP.2018.8552894.
    Real-time detection of high-frequency RF signals requires sophisticated hardware with large bandwidth and high sampling rates. Existing microwave photonic methods have enabled sub-Nyquist sampling for bandwidth-efficient RF signal detection but fall short in single-shot reconstruction. Here we report a novel single-shot sub-Nyquist RF signal detection method based on a trained deep neural network. In a proof-of-concept demonstration, our system successfully reconstructs high frequency multi-toned RF signals from 5x down-sampled singleshot measurements by utilizing a deep convolutional neural network. The presented approach is a powerful digital accelerator to existing hardware detectors to significantly enhance the detection capability.
  • Mididoddi, C., Feng, D. and Wang, C. (2018). Optical Phase Shifting Fourier Transform Scanning for Bandwidth-Efficient Blind RF Spectrum Sensing. In: European Conference on Optical Communication (ECOC). IEEE. Available at: https://doi.org/10.1109/ECOC.2018.8535189​.
    Avoiding high-speed electronics, optical time-stretch Fourier transform scanning for RF spectrum sensing is presented. Broadband RF frequency scanning is achieved by using a phase shifting Mach-Zehnder interferometer. GHz RF signals have been detected with only 50 MS/s sampling rate.
  • Wang, C., Wang, G. and Mididoddi, C. (2018). In-Fibre Diffraction Grating for Beam Steering Indoor Optical Wireless Communication. In: British and Irish Conference on Optics and Photonics (BICOP). IEEE. Available at: https://doi.org/10.1109/BICOP.2018.8658291​.
    In-fibre diffraction based on 45° tilted fibre grating enables high-efficiency wavelength-controlled laser beam steering for indoor optical wireless communication with unique features of low-loss and seamless integration with existing fibre-to-home networks. In addition, ultrafast user localization (50 million scans per second) based on real-time wavelength monitoring is demonstrated.
  • Mididoddi, C., Ahmad, E. and Wang, C. (2017). All-optical random sequence generation for compressive sensing detection of RF signals. In: International Topical Meeting on Microwave Photonics (MWP), 2017. IEEE, pp. 1-4. Available at: https://doi.org/10.1109/MWP.2017.8168639.
    Photonic compressive sensing is a promising data compression method and has been successfully applied in high-speed RF signal detection with greatly reduced requirement for receiver bandwidth. A key challenge is due to the electronic bottleneck in high-speed random sequence generation and mixing. In this work, we propose and experimentally demonstrated for the first time all-optical random sequence generation and mixing for compressive sensing detection of RF signals. The technique is based on photonic time stretch involving cascaded Mach-Zehnder Interferometers (MZIs) for spectral domain random mixing. In a proof-of-concept experiment, successful detection of 1 GHz RF signal with 25% compression ratio using only 50 MHz detection bandwidth has been demonstrated?
  • Wang, G., Habib, U., Yan, Z., Gomes, N., Zhang, L. and Wang, C. (2017). In-fibre diffraction grating based beam steering for full duplex optical wireless communication. In: International Topical Meeting on Microwave Photonics (MWP), 2017. Available at: https://doi.org/10.1109/MWP.2017.8168644.
    A novel approach to achieve wavelength controlled optical beam steering using a 45° tilted fiber grating (TFG) for full-duplex indoor optical wireless transmission is proposed and experimentally demonstrated for the first time. The 45° TFG functions as an in-fiber passive diffraction device for wavelength steered light emission and reception, which enables full-duplex optical wireless transmission. The unique advantages of using an in-fiber TFG device for beam steering include high diffraction efficiency, low cost, compactness and inherent compatibility with existing fiber links. In a proof-of-concept experiment, free-space full-duplex transmission over 1.4 m with data rate of 9.6 Gb/s per beam has been demonstrated using 2.4 GHz bandwidth signals.
  • Qin, H., Yan, Z., Sun, Q., Wang, G., Wang, C., Liu, D. and Zhang, L. (2017). Theoretical analysis of diffraction grating based on 45°-tilted fiber gratings. In: 2017 Opto-Electronics and Communications Conference (OECC). Available at: https://doi.org/10.1109/OECC.2017.8114931.
  • Mididoddi, C., Ahmad, E. and Wang, C. (2017). Data-efficient high-throughput fiber Bragg grating sensors using photonic time-stretch compressive sensing. In: European Conferences on Laser and Opto-Electronics. Available at: https://doi.org/10.1109/CLEOE-EQEC.2017.8086896.
    In this paper, we demonstrate the first application of photonic compressive sensing technique in a data-efficient interrogation system for high-throughput distributed FBG sensors. In particular, reconstruction of a wide bandwidth chirped temporal waveform has been achieved using compressive sensing with optical integration. This enables data-compressed high-throughput interrogation of FBG sensors for dynamic non-uniform strain sensing
  • Ahmad, E., Feng, D. and Wang, C. (2017). Analysis on spatial and temporal resolution in photonic time stretch frequency domain reflectometry based fully distributed fiber Bragg grating sensors. In: The 15th International Conference on Optical Communications and Networks (ICOCN 2016). Available at: http://ieeexplore.ieee.org/document/7875829/.
    We propose and experimentally demonstrate fully distributed strain sensing along the length of a linearly chirped fibre Bragg grating with simultaneously high spatial and temporal resolution based on photonic time stretch frequency domain reflectometry (PTS-FDR). The distributed strain information is reconstructed from the instantaneous RF frequency of a temporal interference waveform via short-time Fourier transform analysis. The utility of the proposed method is characterized by analysing the spatial and temporal resolution obtained. An ultrafast strain measurement at a speed of 50 MHz with a high spatial resolution of 31.5 µm over a gauge length of 25 mm and a strain resolution of 9.1 µ? have been achieved.

Thesis

  • Aighobahi, A. (2017). Performance of MIMO Schemes in Radio-over-Fibre-Based Distributed Antenna System.
    The research presented in this thesis has focused on the use of MIMO wireless communications in a RoF-based DAS to improve wireless coverage and capacity performance in an indoor environment. The aim is to analyse the practical issues that cause throughput to deteriorate when commercial MIMO APs are used in a RoF-DAS, and also to verify that improved performance - lower error rates and higher capacities - can be achieved by a large physical separation between the RAUs when specific multi-antenna scheme algorithms are used.

    The performance of an IEEE 802.11n MIMO-supported AP and IEEE 802.11g spatial-diversity-supported AP are investigated in a RoF-DAS when different fibre lengths are connecting the AP in the central unit to the RAUs, and when the RAUs are widely separated. The analysis indicates that for MIMO, the throughput drops rapidly due to severe ISI caused by differential delay when the fibre-length difference exceeds a certain distance, while for spatial diversity high throughputs can be maintained even at large fibre-length difference. Further, it was observed that largely separated RAU may lead to power imbalances and the throughput drops in specific wireless user's positions when the received power imbalance was above 12-15dB for MIMO-supported AP, while for spatial-diversity-supported AP the power imbalance does not affect the throughput.

    The majority of previous works on RoF-DAS for improving MIMO systems were based on commercial products and the specific algorithms used within these products are unknown. An investigation was carried out at microwave frequency with SIMO algorithms in RoF-DAS uplink, MISO and MIMO algorithms in RoF-DAS downlink, and compared with the performance of a SISO system. This investigation was later extended to millimetre-wave frequency where larger bands of frequency are available enabling the possibility of wider bandwidth and higher data rates. The result shows significantly reduced error rate and modestly increased capacity for a wireless 1x2 SIMO uplink using MRC algorithm and 2x1 MISO downlink using Alamouti STBC algorithm. Also, error rate was reduced for a wireless 2x2 MIMO downlink using the zero-forcing algorithm while, most importantly, greatly increased capacity was achieved through the spatial multiplexing gain.
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