Dr. Kefei Liang Profile

Dr. Kefei Liang

at Univ of Oxford

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Proceedings Article | 31 August 2005 Paper

Two-dimensional wavelength routing for transparent optical wireless networking

Haiyan Shi, Kefei Liang, Stephen Sheard, Dominic O'Brien, Grahame Faulkner

Proceedings Volume 5892, 58920Z (2005) https://doi.org/10.1117/12.620016

KEYWORDS: Beam steering, Mirrors, Transmitters, Receivers, Diffraction gratings, Local area networks, Infrared radiation, Diffraction, Beam shaping, Reflectivity

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In this article a novel system architecture that uses a combination of wavelength and spatial diversity for indoor infrared wireless communications is presented. This configuration promises to fully exploit the available bandwidth of optics and demonstrate all-optical networking. Electronic processing is restricted to mobile terminals, with base stations potentially remaining passive, without any conversion between optics and electronics. For the downlink, multiple transmitter beams with different wavelengths are steered from the fiber infrastructure through the base station to mobile terminals located in different positions. An optimum combination of diffractive optics and reflective optics (a diffraction grating and an array of mirrors) can flexibly steer each transmitter beam and enable full control over the required coverage pattern. For the uplink, in the transmitter, another grating and an array of mirrors can direct multiple beams upward from different mobile users toward the base station. System simulation shows that the downlink has the potential to approach 10 Gbit/s, while maintaining wide-area coverage (such as in a room of 3m×4m×4m) with the help of fine optical tracking. System modeling indicates that the uplink is more susceptible to power losses than the downlink, but the utilization of dynamic beam steering in the uplink can suppress power losses to a tolerable level (e.g. below 30dB). An array of 16 mirrors has been designed to implement point-to-point beam steering in a room of 3m×1m×1m. Two-dimensional coverage patterns measured at a distance of 0.5 m and 1.5 m coincide with simulation results. Operation at 1 Gbit/s has been demonstrated successfully for tracking in two dimensions.

Proceedings Article | 20 October 2004 Paper

Transparent optical wireless hubs using wavelength space division multiplexing

Kefei Liang, Haiyan Shi, Steven Sheard, Dominic O’Brien

Proceedings Volume 5550, (2004) https://doi.org/10.1117/12.561597

KEYWORDS: Receivers, Diffraction, Diffraction gratings, Space division multiplexing, Beam steering, Wavelength division multiplexing, Transmitters, Tunable lasers, Data transmission, Optical tracking

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In this paper we describe a novel scheme that uses wavelength space division multiplexing to provide high bit rate communications using indoor line of sight (LOS) optical links. In the approach, a dispersive grating, or more complex diffractive optics, is used for passive beam steering. Light from a ceiling mounted hub is steered to a corresponding Mobile Terminal (MT) within a cell in the coverage area, depending on the wavelength that illuminates the dispersive element. The hubs can be optically transparent, passive and theoretically reciprocal. An identical or similar dispersive component can be used in the transceivers at both ends of the hub uplink and downlink. The hubs have the potential to provide data rates of Gbits/s, terminal mobility as well as low complexity. In order to test the concept a one-dimensional (1D) system has been fabricated. A simple 1^st order plane diffraction grating with a pitch of 1.1 μm is used to provide 1D beam steering. A dispersive angle of approximately 10 degrees over a wavelength range of 30nm in the wavelength division multiplexing (WDM) 'C' band (1530nm - 1560nm) is obtained. Simulation shows that the dispersive angle can be further increased up to 90 degrees using a secondary optical system. Transmission of 1Gb/s data has been demonstrated using this initial configuration. In the paper we discuss these results and further refinement to the system.

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