Ting Zhou

Bio: Ting Zhou is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Optical switch & Computer science. The author has an hindex of 13, co-authored 70 publications receiving 562 citations. Previous affiliations of Ting Zhou include Tsinghua University.

Adaptive Postdistortion for Nonlinear LEDs in Visible Light Communications

Abstract: In a visible light communications (VLC) system, the light emitting diode (LED) is the majorsource of nonlinearity. The nonlinear effects in the VLC system are different from the conventionalwireless communications system. The channel separation in the VLC system is significantly largerthan the signal bandwidth, thus the adjacent channel interference (ACI) is not an issue. Predistortiontechnique may not be a cost-efficient approach as it needs additional feedback physical circuits atthe transmitter. In this paper, we propose a post-distortion technique to estimate and compensatefor the LED’s nonlinearity at the receiver. The post-distortion technique only needs some additionalcomputational resources. In addition, the proposed approach significantly improves the error vectormagnitude (EVM) and bit-error-rate (BER) performance of the VLC system. Simulation results validatethe theoretical analysis.Index Terms: VLC, nonlinearity, memory effects, Wiener model, post-distortion, memory polynomialmodel.

General architectures for on-chip optical space and mode switching

Abstract: The optical switches for single-mode operation cannot be directly utilized in optical communication and interconnect systems adopting mode-division multiplexing In this paper, three general architectures for on-chip optical space and mode switching are proposed, which are optimized for optical space switching, optical space switching plus local optical mode switching, and global optical mode switching, respectively A silicon thermo-optic 2×2 four-mode optical switch is demonstrated The minimum and maximum optical link insertion losses are 160 and 209 dB (including ∼6 dB coupling loss), respectively, in the wavelength range of 1525–1565 nm, while the optical signal-to-noise ratios of the optical links are larger than 153 dB The optical power penalty at a bit error rate of 10−9 varies from 10 to 56 dB for 40 Gbps data transmission through different optical links This work provides a systematic solution to on-chip information switching for different physical and mode channels

Inverse-Design and Demonstration of Ultracompact Silicon Meta-Structure Mode Exchange Device

Abstract: Data exchange among different mode channels is indispensable for optical communication system adopting mode-division multiplexing. Traditional mode exchange device is complex in procedure and large in footprint, which makes it not suitable for dense and large-scale photonic integration. Utilizing the degree of freedom of silicon meta-structure, we design an ultracompact and optically broadband mode exchange device between TE0 and TE1 modes by the step-by-step inverse-design method considering the axisymmetric constraint. Simulation result shows that it is robust to a temperature variation of 100 K and a fabrication error of ±20 nm. The fabricated device is 4 × 1.6 μm2 in footprint. The simulated conversion efficiencies are over 73% and 71% for TE0 to TE1 and TE1 to TE0 within the whole C-band, and the experimental results are about 10% lower than the simulation. 40 Gbps OOK and 25 GBaud PAM-4 data transmission through the device are carried out, which shows good signal quality. We envision that the device...

Optical switch compatible with wavelength division multiplexing and mode division multiplexing for photonic networks-on-chip

Abstract: We propose a 2 × 2 multimode optical switch, which is composed of two mode de-multiplexers, n 2 × 2 single-mode optical switches where n is the number of the supported spatial modes, and two mode multiplexers. As a proof of concept, asymmetric directional couplers are employed to construct the mode multiplexers and de-multiplexers, balanced Mach-Zehnder interferometer is utilized to construct the 2 × 2 single-mode optical switches. The fabricated silicon 2 × 2 multimode optical switch has a broad optical bandwidth and can support four spatial modes. The link-crosstalk for all four modes is smaller than −18.8 dB. The inter-mode crosstalk for the same optical link is less than −22.1 dB. 40 Gbps data transmission is performed for all spatial modes and all optical links. The power penalties for the error-free switching (BER<10−9) at 25 Gbps are less than 1.8 dB for all channels at the wavelength of 1550 nm. The power consumption of the device is 117.9 mW in the “cross” state and 116.2 mW in the “bar” state. The switching time is about 21 μs. This work enables large-capacity multimode photonic networks-on-chip.

WDM-compatible multimode optical switching system-on-chip

Abstract: The development of optical interconnect techniques greatly expands the communication bandwidth and decreases the power consumption at the same time. It provides a prospective solution for both intra-chip and inter-chip links. Herein reported is an integrated wavelength-division multiplexing (WDM)-compatible multimode optical switching system-on-chip (SoC) for large-capacity optical switching among processors. The interfaces for the input and output of the processor signals are electrical, and the on-chip data transmission and switching process are optical. It includes silicon-based microring optical modulator arrays, mode multiplexers/ de-multiplexers, optical switches, microring wavelength de-multiplexers and germanium-silicon high-speed photodetectors. By introducing external multi-wavelength laser sources, the SoC achieved the function of on-chip WDM and mode-division multiplexing (MDM) hybrid-signal data transmission and switching on a standard silicon photonics platform. As a proof of concept, signals with a 25 Gbps data rate are implemented on each microring modulator of the fabricated SoC. We illustrated 25 x 3 x 2 Gbps on-chip data throughput with two-by-two multimode switching functionality through implementing three wavelength-channels and two mode-channel hybrid-multiplexed signals for each multimode transmission waveguide. The architecture of the SoC is flexible to scale, both for the number of supported processors and the data throughput. The demonstration paves the way to a large-capacity multimode optical switching SoC.

LED Based Indoor Visible Light Communications: State of the Art

Abstract: Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979–2014. VLC is compared with infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation, and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented.

Non-Orthogonal Multiple Access (NOMA) for cellular future radio access

Abstract: Radio access technologies for cellular mobile communications are typically characterized by multiple access schemes, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and OFDMA. In the 4th generation (4G) mobile communication systems such as Long-Term Evolution (LTE) (Au et al., Uplink contention based SCMA for 5G radio access. Globecom Workshops (GC Wkshps), 2014. doi:10.1109/GLOCOMW.2014.7063547) and LTE-Advanced (Baracca et al., IEEE Trans. Commun., 2011. doi:10.1109/TCOMM.2011.121410.090252; Barry et al., Digital Communication, Kluwer, Dordrecht, 2004), standardized by the 3rd Generation Partnership Project (3GPP), orthogonal multiple access based on OFDMA or single carrier (SC)-FDMA is adopted. Orthogonal multiple access was a reasonable choice for achieving good system-level throughput performance with simple single-user detection. However, considering the trend in 5G, achieving significant gains in capacity and system throughput performance is a high priority requirement in view of the recent exponential increase in the volume of mobile traffic. In addition the proposed system should be able to support enhanced delay-sensitive high-volume services such as video streaming and cloud computing. Another high-level target of 5G is reduced cost, higher energy efficiency and robustness against emergencies.

8-Gb/s RGBY LED-Based WDM VLC System Employing High-Order CAP Modulation and Hybrid Post Equalizer

Abstract: In this paper, for the first time, we propose the use of a hybrid post equalizer in a high-order carrierless-amplitude-and-phase-modulation-based visible light communication (VLC) system. The hybrid equalizer consists of a linear equalizer, a Volterra-series-based nonlinear equalizer, and a decision-directed least mean squares equalizer to simultaneously mitigate the linear and nonlinear distortions of the VLC system. A commercially available red-blue-green-yellow light-emitting diode (RBGY LED) is utilized for four-wavelength multiplexing. By the hybrid equalizer, an aggregate data rate of 8 Gb/s is experimentally achieved over a 1-m indoor free-space transmission with the bit error rate (BER) below the 7% forward error correction (FEC) limit of 3.8 × 10 -3 . To the best of our knowledge, this is the highest data rate ever reported in high-speed VLC systems.

A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

Abstract: The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined.