Jianjun Yu

Bio: Jianjun Yu is an academic researcher from Fudan University. The author has contributed to research in topics: Transmission (telecommunications) & Wavelength-division multiplexing. The author has an hindex of 57, co-authored 746 publications receiving 14528 citations. Previous affiliations of Jianjun Yu include Georgia Institute of Technology & ZTE.

Optical millimeter-wave generation or up-conversion using external modulators

Abstract: We have experimentally compared the performances of optical millimeter-wave generation or up-conversion using external modulators based on different modulation schemes. The generated or up-converted optical millimeter wave using the optical carrier suppression (OCS) modulation scheme shows the highest receiver sensitivity, highest spectral efficiency, and smallest power penalty over long-distance delivery. Moreover, the OCS modulation scheme has a simple configuration and low-frequency bandwidth requirement for both electrical and optical components. Employing an OCS modulation scheme, 16-channel dense wavelength-division multiplexing signals at 2.5-Gb/s per channel have been up-converted to a 40-GHz carrier simultaneously.

Key Enabling Technologies for Optical–Wireless Networks: Optical Millimeter-Wave Generation, Wavelength Reuse, and Architecture

Abstract: The integration of optical and wireless systems is considered to be one of the most promising solutions for increasing the existing capacity and mobility as well as decreasing the costs in next-generation optical access networks. In this paper, several key enabling technologies for hybrid optical-wireless access networks are described, including optical millimeter-wave (mm-wave) generation, upconversion, and transmission in a downlink direction, and full-duplex operation based on wavelength reuse by using a centralized light source in an uplink direction. By employing these enabling technologies, we design and experimentally demonstrate an optical-wireless testbed that is simultaneously delivering wired and wireless services in the integrated optical-wireless and wavelength-division-multiplexing passive-optical-network access networks. The actual applications consisting of 270-Mb/s uncompressed standard-definition TV signal and 2.5-Gb/s data channels for downstream are successfully transmitted over a 25-km fiber and a 10.2-m indoor wireless link with less than a 1.5-dB power penalty. The results show that this integrated system is a practical solution to deliver superbroadband information services to both stationary and mobile users.

Demonstration of 575-Mb/s downlink and 225-Mb/s uplink bi-directional SCM-WDM visible light communication using RGB LED and phosphor-based LED

Abstract: We propose and experimentally demonstrate a novel full-duplex bi-directional subcarrier multiplexing (SCM)-wavelength division multiplexing (WDM) visible light communication (VLC) system based on commercially available red-green-blue (RGB) light emitting diode (LED) and phosphor-based LED (P-LED) with 575-Mb/s downstream and 225-Mb/s upstream transmission, employing various modulation orders of quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM). For the downlink, red and green colors/wavelengths are assigned to carry useful information, while blue chip is just kept lighting to maintain the white color illumination, and for the uplink, the low-cost P-LED is implemented. In this demonstration, pre-equalization and post-equalization are also adopted to compensate the severe frequency response of LEDs. Using this scheme, 4-user downlink and 1-user uplink transmission can be achieved. Furthermore, it can support more users by adjusting the bandwidth of each sub-channel. Bit error rates (BERs) of all links are below pre-forward-error-correction (pre-FEC) threshold of 3.8x 10−3 after 66-cm free-space delivery. The results show that this scheme has great potential in the practical VLC system.

Key Technologies of WDM-PON for Future Converged Optical Broadband Access Networks [Invited]

Abstract: The wavelength-division-multiplexed passive optical network (WDM-PON) is considered to be the next evolutionary solution for a simplified and future-proofed access system that can accommodate exponential traffic growth and bandwidth-hungry new applications. WDM-PON mitigates the complicated time-sharing and power budget issues in time-division-multiplexed PON (TDM-PON) by providing virtual point-to-point optical connectivity to multiple end users through a dedicated pair of wavelengths. There are a few hurdles to overcome before WDM-PON sees widespread deployment. Several key enabling technologies for converged WDM-PON systems are demonstrated, including the techniques for longer reach, higher data rate, and higher spectral efficiency. The cost-efficient architectures are designed for single-source systems and resilient protection for traffic restoration. We also develop the integrated schemes with radio-over-fiber (RoF)-based optical-wireless access systems to serve both fixed and mobile users in the converged optical platform.

A full-duplex radio-over-fiber system based on optical carrier suppression and reuse

Abstract: We have experimentally demonstrated a full-duplex radio-over-fiber system using a single light source at central station (CS). Optical carrier suppression modulation scheme was employed to generate 40-GHz optical millimeter wave and up-convert the baseband signal simultaneously at CS for downlink transmission while the same optical carrier was reused at base station for uplink connection. The bidirectional full-duplex 2.5-Gb/s data was successfully transmitted over 40-km standard single-mode fiber (SMF-28) for both upstream and downstream channels with less than 2-dB power penalty. This system shows simple cost-efficient configuration and good performance over long-distance delivery

Terabit free-space data transmission employing orbital angular momentum multiplexing

Abstract: Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

Capacity Limits of Optical Fiber Networks

Abstract: We describe a method to estimate the capacity limit of fiber-optic communication systems (or ?fiber channels?) based on information theory. This paper is divided into two parts. Part 1 reviews fundamental concepts of digital communications and information theory. We treat digitization and modulation followed by information theory for channels both without and with memory. We provide explicit relationships between the commonly used signal-to-noise ratio and the optical signal-to-noise ratio. We further evaluate the performance of modulation constellations such as quadrature-amplitude modulation, combinations of amplitude-shift keying and phase-shift keying, exotic constellations, and concentric rings for an additive white Gaussian noise channel using coherent detection. Part 2 is devoted specifically to the "fiber channel.'' We review the physical phenomena present in transmission over optical fiber networks, including sources of noise, the need for optical filtering in optically-routed networks, and, most critically, the presence of fiber Kerr nonlinearity. We describe various transmission scenarios and impairment mitigation techniques, and define a fiber channel deemed to be the most relevant for communication over optically-routed networks. We proceed to evaluate a capacity limit estimate for this fiber channel using ring constellations. Several scenarios are considered, including uniform and optimized ring constellations, different fiber dispersion maps, and varying transmission distances. We further present evidences that point to the physical origin of the fiber capacity limitations and provide a comparison of recent record experiments with our capacity limit estimation.

Survey on Free Space Optical Communication: A Communication Theory Perspective

Abstract: Optical wireless communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, infrared (IR), and ultraviolet (UV) bands. In this survey, we focus on outdoor terrestrial OWC links which operate in near IR band. These are widely referred to as free space optical (FSO) communication in the literature. FSO systems are used for high rate communication between two fixed points over distances up to several kilometers. In comparison to radio-frequency (RF) counterparts, FSO links have a very high optical bandwidth available, allowing much higher data rates. They are appealing for a wide range of applications such as metropolitan area network (MAN) extension, local area network (LAN)-to-LAN connectivity, fiber back-up, backhaul for wireless cellular networks, disaster recovery, high definition TV and medical image/video transmission, wireless video surveillance/monitoring, and quantum key distribution among others. Despite the major advantages of FSO technology and variety of its application areas, its widespread use has been hampered by its rather disappointing link reliability particularly in long ranges due to atmospheric turbulence-induced fading and sensitivity to weather conditions. In the last five years or so, there has been a surge of interest in FSO research to address these major technical challenges. Several innovative physical layer concepts, originally introduced in the context of RF systems, such as multiple-input multiple-output communication, cooperative diversity, and adaptive transmission have been recently explored for the design of next generation FSO systems. In this paper, we present an up-to-date survey on FSO communication systems. The first part describes FSO channel models and transmitter/receiver structures. In the second part, we provide details on information theoretical limits of FSO channels and algorithmic-level system design research activities to approach these limits. Specific topics include advances in modulation, channel coding, spatial/cooperative diversity techniques, adaptive transmission, and hybrid RF/FSO systems.

Microwave Photonics

Abstract: Broadband and low loss capability of photonics has led to an ever-increasing interest in its use for the generation, processing, control and distribution of microwave and millimeter-wave signals for applications such as broadband wireless access networks, sensor networks, radar, satellite communitarians, instrumentation and warfare systems. In this tutorial, techniques developed in the last few years in microwave photonics are reviewed with an emphasis on the systems architectures for photonic generation and processing of microwave signals, photonic true-time delay beamforming, radio-over-fiber systems, and photonic analog-to-digital conversion. Challenges in system implementation for practical applications and new areas of research in microwave photonics are also discussed.

Advances in terahertz communications accelerated by photonics

Abstract: This Review covers the state-of-the-art technologies on photonics-based terahertz communications, which are compared with competing technologies based on electronics and free-space optical communications. Future prospects and challenges are also discussed. Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.