Current Research


In the past few years, our group's research has been focused on fibre-based photonic technologies and applications. In particular, our group have explored applications of fibre-optic technologies in the emerging field of quantum communication where our research is making vital contributions to bringing quantum technology from scientific possibility to commercial viability.
    At the same time, we have made a significant impact in the traditional field of optical metrology, where our technological innovations in fibre-based interferometers have created new and better methods for dispersion measurements and optical sensing.
    In addition, we have also made contributions to the areas of fiber amplifiers and ultrafast nonlinear photonics.
    The highlights of our research include the first demonstration of experimental decoy-state quantum key distribution system, the first experimental verification of group velocity dispersion inversion in III-V semiconductor nanowires, and the invention of the frequency-shifted interferometry, a technology that has many applications in optical sensing and metrology.

Quantum Cryptography (QC)

Built on quantum physics and information theory, QC offers absolute information security. Our group's research in QC focuses on experimental quantum key distribution (QKD). In collaboration with Prof. Hoi-Kwong Lo, we aim to advance QC from the realm of scientific possibility into the realm of commercial viability, and we have one of world's leading laboratories in QKD.



Ultrafast and Nonlinear Photonics

Optical processes on a timescale of subpicosecond to picosecond are orders of magnitude faster than electronic processes. Therefore, photonic devices based on ultrafast technologies can greatly surpass their electronic counterparts in speed and bandwidth. We aim to develop key devices and enabling tools that will be required not only in future high-speed communication, but also in high-speed computing and signal processing, and even in wireless applications.



Optical Sensing and Metrology

The smallness of the optical wavelength makes light an excellent micro "yardstick" for sensing minute changes in space or in time; The narrowness of the laser makes it an excellent discriminator of atomic fingerprints of gases and liquids. Combining such natural qualities of light with the flexibility, low-loss, and robustness of the optical fiber, we aim to generate new ideas and applications in optical sensing and metrology.



Optical Amplifier Technology

The erbium-doped fiber amplifier (EDFA), regarded as the greatest innovation in optical communication since the invention of the optical fiber, is a key enabler for terabit optical communications. As the EDFA technology is maturing and EDFAs become a commodity, we are exploring niche applications and new erbium-doped materials for the future generation of optical amplifiers.




<<Project: Gaussian Modulated Coherent State QKD over Conventional Fiber Links

Researchers: Bing Qi, Leilei Huang, Yuemeng Chi, Li Qian, Hoi-Kwong Lo
Other contributors: R. Bolen, J. Chan
Collaborators: Hoi-Kwong Lo
Major findings/Achievements:
  • Implemented GMCS-QKD over 5km fiber link with standard telecom components and a home-built, highly sensitive homodyne detector
  • Achieved 0.3bit/pulse secure key rate (under the realistic assumption that Eve cannot change the noise within Bob's system)
  • Performed detailed noise measurement, analysis, and modeling revealing some of the practical limitations of GMCS-QKD.

Publications:

<<Project: Quantum Cloning with Optical Amplifiers

Researchers: Bing Qi, Li Qian
Major findings/Achievements:
  • Conducted a semi-classical analysis on the fidelity of a quantum cloning machine based on broadband amplifiers followed by optimal filters. As the output photon number increases, the differences among the three approaches disappear.
  • Counter-intuitively, for 1-to-2 photon cloning, we demonstrated that the fidelity of this system is no better than a random cloning machine, but better than cloning based on state estimation
  • As input photon number increases, this system asymptotically approaches the quantum limit of an optimal quantum cloning machine.

Publications:

<<Project:QKD Performance Improvement with Dual Detectors

Researchers: Bing Qi, Y. Zhao, X. Ma, H-K Lo, L. Qian
Collaborators: Y. Zhao, X. Ma, H-K Lo
Major findings/Achievements:
  • Proposed the novel implementation of a dual-detector scheme in QKD systems to overcome the tradeoff between speed and detector noise, resulting in a higher secure key rate: The measurement results from the quiet detector can be used to bound eaves-dropper's information, while the measurement results from the fast detector are used to generate secure key
  • Applied this idea to various QKD protocols, including BB84, GMCS, and Decoy-state protocols, and analyzed modeling results to verify the merit of the method.

Publications:

  • Bing Qi,Y. Zhao,X. Ma,H-K Lo, Qian L., "Quantum key distribution with dual detectors", Phys. Rev. A, vol. 75, article no. 052304 (2007)
  • B. Qi, Y. Zhao, X. Ma, H-K Lo, L. Qian, "Dual detectors scheme in practical quantum key distribution systems", CLEO/Europe-IQEC Conference and World of Photonics Congress, Munich, Germany, June 2007
<<Project: QKD based on a Sagnac Interferometer

Researchers: Bing Qi, L. Huang, R. Mong, L. Qian, H-K Lo
Other contributors: N. Sood
Collaborators: H-K Lo
Major findings/Achievements:
  • Proposed stable Sagnac quantum key distribution (QKD) system employing a polarization-insensitive phase modulation scheme based on frequency modulation of light waves using either one or a pair of acousto-optic modulators.
  • Achieved 96% and 99% interference visibility for a 40km and a 10km fiber loop, respectively, at single-photon level. We ran standard BB84 QKD protocol in 40-km Sagnac setup continuously for one hour and the measured quantum bit error rate (QBER) stayed within 2%-5% range.

Publications:

Patents:

<<Project: Experimental Decoy-State QKD

Researchers: Y. Zhao, Bing Qi, X. Ma, H-K Lo, L. Qian
Collaborators: Y. Zhao, X. Ma, H-K Lo
Major findings/Achievements:
  • Implemented decoy-state QKD experimentally for the first time.
  • Demonstrated that, by implementing a decoy-state protocol in a QKD system, a secure key generation rate of 165 bit/s, which is 1/4 of the theoretical limit, can be obtained over 15 km of a telecommunication fiber, while with the same experimental parameters, not even a single bit of secure key can be extracted with a non-decoy-state protocol.

Publications:

  • Yi Zhao, Bing Qi, Xiongfeng Ma, Hoi-Kwong Lo, Li Qian, "Experimental Quantum Key Distribution with Decoy States" , Physical Review Letters, v96, no.7, 070502,2006
  • Yi Zhao, B. Qi, X. Ma, H-K Lo, L. Qian, "Decoy state quantum key distribution: theory and practice", APS March Meeting, Denver, US, March 2007
  • Yi Zhao, Bing Qi, Xiongfeng Ma, Hoi-Kwong Lo, and Li Qian,"Experimental Studies on Decoy State Quantum Cryptography", Oral presentation at the Asian Conference on Quantum Information Science 2006 (AQIS'06), Beijing, China, Sept 1-4, 2006
  • Yi Zhao, Bing Qi, Xiongfeng Ma, Hoi-Kwong Lo, Li Qian, "Simulation and Implementation of Decoy State Quantum Key Distribution over 60km Telecom Fiber", IEEE International Symposium on Information Technology Seattle, WA, July 9-14, 2006, pp. 2094-2098
<<Project: Multi-Fiber-Channel All-Optical Signal Processing

Researchers: D. Wu, W. Mohammed, L. Qian, P.W.E. Smith
Other Contributors: D. Chen, Eric Lau, D. Schwartz-Narbonne
Collaborators: P.W.E. Smith, Pradeep Srinivasan, Eric Johnson
Major findings/Achievements:
  • Implemented a multi-fiber-channel all-optical switching device based on a 2D Fresnel lens array and a fiber array.
  • Demonstrated multi-fiber channel ultrafast switching.
  • Demonstrated 40Gb/s multi-fiber channel wavelength conversion
  • Demonstrated simultaneous 1-to-N channel wavelength conversion at 40Gb/s

Publications:

Early Work:

<<Project: Pulse Shaping and Arbitrary RF Waveform Generation in an All-Fiber System

Researchers: Y.Y. Ho, S.A. Neata, A.M.H. Wong, L. Qian, P.W.E. Smith, X. Gu
Collaborators: P.W.E. Smith, X. Gu
Major findings/Achievements:
  • Proposed and implemented a dynamic, all-fiber, ultra low-loss, arbitrary waveform generation system.
  • Demonstrated static arbitrary picosecond pulse shaping using a linearly chirp grating fabricated with an amplitude mask.

Publications:

Invention Disclosures:

  • Y.Y. Ho and L. Qian, "Arbitrary waveform generation via spectral modification and interference in the optical domain using an all-fiber system with Fiber Bragg Gratings", submitted to the University of Toronto, Sept. 2007
<<Project: Fiber Poling and Nonlinear Frequency Generation

Researchers: J. Zhang, C. Sapiano, E. Zhu, L. Qian, J. S. Aitchison
Collaborators: P.G. Kazansky, J. S. Aitchison, MPB Communications, HighQ Labs
Project Status:
  • Obtained periodically poled fiber samples from our collaborator (Kazansky's group) and successfully measured second harmonic generation in the samples
  • Measured linear properties of the twin-hole fiber, including mode field and dispersion.
  • Currently building theoretical model to include both quadratic and 3rd-order nonlinear effects.
  • Currently building fiber poling facility to obtained large 2nd-order nonlinearity by poling a specialty fiber. (80% complete)

Publications:

  • J. W. Zhang, L. Qian, "Dynamics of room temperature DC-induced second-order nonlinearity in poled fiber under an external field",Accepted for oral presentation at the Optical Fiber Communication Conference (OFC 2008)
<<Project: Multi-Point Optical Sensing System based on Frequency-Shifted Interferometry

Researchers: Fei Ye, B. Qi, Y. Liu, L. Qian, H-K. Lo
Collaborators: X. Gu, H-K Lo
Major findings/Achievements:
  • Proposed and demonstrated a novel multi-point optical sensing system based on frequency-shifted interferometry. This scheme uses a simple cw laser and resolves the location as well as the spectral information of the reflections from multiple sensing points along a fiber. It allows spectral overlap of the reflected signals, and does not require coherent detection scheme.
  • Demonstrated interrogation of an 11-grating-sensor array.

Publications:

Patents:

<<Project: Dispersion Characterization of Short Lengths (mm to cm) of Fibers and Waveguides

Researchers: W.S. Mohammed, M.A Galle, J. Meier, L. Qian
Collaborators: P.W. E. Smith, J.S. Aitchison, M. Mojahedi, A. Jugessur
Major findings/Achievements:
  • Developed a novel single-arm 3-wave spectral interferometer to measure directly the second-order dispersion parameter in short lengths of fiber (< 50 cm), with a measured precision of 0.0001 ps/nm.
  • Developed a technique to measured linear and quadratic dispersion on mm-length fibers, waveguides and nano-wires based on common-path interferometry. Using this method, we experimentally confirmed the sign inversion of the group velocity dispersion of AlGaAs nanowires for the first time.

Publications:

Invention Disclosures:

  • M.A. Galle, W.S. Mohammed, L. Qian, P.W.E. Smith, "Technique for the Measurement of the Propagation Constant and the Dispersion of an Optical Fiber/Waveguide", submitted to U. of Toronto on 12 April 2007.
  • M.A. Galle, W.S. Mohammed, L. Qian, P.W.E. Smith, "Single Arm 3 Wave Interferometer for the Measurement of Dispersion in Fiber of Short Length", submitted to U. of Toronto on 1 May 2007
<<Project: Precision Fiber length and Dispersion Measurements using Frequency-Shifted Interferometry

Researchers: B. Qi, A. Tausz, L. Qian, H-K Lo
Collaborators: H-K Lo
Major findings/Achievements:
  • Proposed and experimentally demonstrated a single-mode fiber length and dispersion measurement system based on a novel frequency-shifted asymmetric Sagnac interferometer.
  • Achieved a dynamic range of length measurement from a few centimeters to 60 km, with a resolution of ~1 part per million for long fibers.

Publications:

Patents:

<<Project: Er-doped Silicon-Compatible Materials

Researchers: H. Alizadeh, W. Shams-Kolahi, R. Tsai, D. Stanley, N. Kherani, L. Qian, S. Zukotynski
Collaborators: H. Alizadeh, W. Shams-Kolahi, D. Stanley, N. Kherani, S. Zukotynski
Project Status:
  • Demonstrated room-temperature photoluminescence (PL) in Er-doped silicon-rich SiO2 on silicon, showing promise for silicon-compatible amplifiers and lasers.
  • Currently investigating Er-doping in amorphous hydrogenated carbon, a material compatible with silicon substrate.

Publications:

  • Hossein Alizadeh, Wahid Shams-Kolahi, Li Qian, Nazir P. Kherani, and Stefan Zukotynski, "Room temperature photoluminescence from erbium-doped silicon rich silicon oxide prepared by evaporation and thermal annealing in air", in preparation
<<Project: Low-cost Gain and Noise Figure Measurements using a Tunable Optical Comb Filter

Researchers: S. Gupta, L. Qian
Major findings/Achievements:
  • Proposed and demonstrated a low-cost technique for broadband gain and noise figure characterization of EDFAs using an amplified-spontaneous-emission source and a wavelength filter with multiple steep slopes.

Publications:

Invention Disclosures:

  • L. Qian, S. Gupta, " Broadband Gain and Noise Figure Measurements of Optical Amplifiers Using Filter Slopes", submitted to U. of Toronto in March 2004
<<Project: Extended L-band Amplifiers

Researchers: L. Qian, S. Gupta, R. Bolen
Collaborators: D. Fortusini, S.D. Benjamin, P.V. Kelkar, V.L. da Silva, G. Qi
Major findings/Achievements:
  • Demonstrated an extended L-band amplifier with gain extending to 1620nm for the first time.
  • Investigated various EDFA configurations and their effect on noise figure and efficiency
  • Investigated and reported large pump-induced gain inhomogeneity in P-Si based Er-doped fiber for the first time

Publications:

<<Project: Modeling of EDFAs with high Er concentration

Researchers: V. Chernyak, L. Qian
Collaborators: V. Chernyak
Major findings/Achievements:
  • Developed a novel analytical model for calculating the gain of high-concetration doped fiber based on an inversion function. The modeling results was validated by experimental measurements for several input power conditions and inversion levels.

Publications: