Hybrid fiber-wireless networks incorporating WDM technology for fixed wireless access operating in the sub-millimeter-wave and millimeter-wave (mm-wave) frequency regions are being actively pursued to provide untethered connectivity for ultrahigh bandwidth communications. The architecture of such radio networks requires a large number of antenna base-stations with high throughput to be deployed to maximize the geographical coverage with the main switching and routing functionalities located in a centralized location. The transportation of mm-wave wireless signals within the hybrid network is subject to several impairments including low opto-electronic conversion efficiency, fiber chromatic dispersion and also degradation due to nonlinearities along the link. One of the major technical challenges in implementing such networks lies in the mitigation of these various optical impairments that the wireless signals experience within the hybrid network. In this paper, we present an overview of different techniques to optically transport mm-wave wireless signals and to overcome impairments associated with the transport of the wireless signals. We also review the different designs of subsystems for integrating fiber-wireless technology onto existing optical infrastructure.

Fiber-Wireless Networks and Subsystem Technologies

Driven primarily by cloud service and data-center applications, short-reach optical communication has become a key market segment and growing research area in recent years. Short-reach systems are characterized by direct detection-based receiver configurations and other low-cost and small form factor components that induce transmission impairments unforeseen in their coherent counterparts. Innovative signaling and digital signal processing (DSP) play a pivotal role in enabling these components to realize their ultimate potentials and meet data rate requirements in cost-effective manners. This paper presents an overview of recent DSP developments for short-reach communications systems and discusses future trends.

Digital Signal Processing for Short-Reach Optical Communications: A Review of Current Technologies and Future Trends

Erbium-doped fiber devices have been extraordinarily successful due to their broad optical gain around 1.5–1.6 μm. Er-doped fiber amplifiers enable efficient, stable amplification of high-speed, wavelength-division-multiplexed signals, thus continue to dominate as part of the backbone of longhaul telecommunications networks. At the same time, Er-doped fiber lasers see many applications in telecommunications as well as in biomedical and sensing environments. Over the last 20 years significant efforts have been made to bring these advantages to the chip level. Device integration decreases the overall size and cost and potentially allows for the combination of many functions on a single tiny chip. Besides technological issues connected to the shorter device lengths and correspondingly higher Er concentrations required for high gain, the choice of appropriate host material as well as many design issues come into play in such devices. In this contribution the important developments in the field of Er-doped integrated waveguide amplifiers and lasers are reviewed and current and future potential applications are explored. The vision of integrating such Er-doped gain devices with other, passive materials platforms, such as silicon photonics, is discussed.

Erbium-doped integrated waveguide amplifiers and lasers

Polarization management is very important for photonic integrated circuits (PICs) and their applications. Due to geometrical anisotropy and fabrication inaccuracies, the characteristics of the guided transverse-electrical (TE) and transverse-magnetic (TM) modes are generally different. Polarization-dependent dispersion and polarization-dependent loss are such manifestations in PICs. These issues become more severe in high index contrast structures such as nanophotonic waveguides made of silicon-on-insulator (SOI), which has been regarded as a good platform for optical interconnects because of the compatibility with CMOS processing. Recently, polarization division multiplexing (PDM) with coherent detection using silicon photonics has also attracted much attention. This trend further highlights the importance of polarization management in silicon PICs. The authors review their work on polarization management for silicon PICs using the polarization independence and polarization diversity methods. Polarization issues and solutions in PICs made of SOI nanowires and ridge waveguides are discussed.

Polarization management for silicon photonic integrated circuits

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.

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

http://ieeexplore.ieee.org/iel7/6637129/6647462/06647717.pdf

11×5×10Gb/s WDM-CAP-PON based on optical single-side band multi-level multi-band carrier-less amplitude and phase modulation with direct detection

By combining two different system technologies of optical polarization division multiplexing and wireless multiple-input, multiple-output spatial multiplexing, we have successfully demonstrated 2-Gb/s or 5-Gb/s wireless signal transmission over a 60-GHz wireless channel with a doubled spectral efficiency.

A novel radio-over-fiber system using the xy-MIMO wireless technique for enhanced radio spectral efficiency

Development of system technology for effective networking infrastructure for next generation e-health applications is addressed. An integrated optical wireless access architecture based on radio-over-fiber technology is proposed in order to provide super broadband, ultra low-latency connectivity among various telemedicine modalities to facilitate real-time and near real-time communication for remote health care services.

Radio over fiber technology for next-generation e-health in converged optical and wireless access network

125 km long-reach, 60 GHz optical-wireless access network using remote signal regeneration and upconversion technique without dispersion compensation is first demonstrated to accommodate over 128 users at 2.5 Gb/s.

Long-reach, 60-GHz Mm-wave optical-wireless access network using remote signal regeneration and upconversion

A centrally-managed, colorless, bi-directional wavelength division multiplexed passive optical network (WDM-PON) architecture. The WDM-PON architecture is self-survivable, and can protect network failures in, for example, distribution/feeder fiber, remote node and laser failure. The WDM-PON architecture requires only N-wavelength channels for N optical network units.

Hung-Chang Chien

Papers

11×5×10Gb/s WDM-CAP-PON based on optical single-side band multi-level multi-band carrier-less amplitude and phase modulation with direct detection

A novel radio-over-fiber system using the xy-MIMO wireless technique for enhanced radio spectral efficiency

Radio over fiber technology for next-generation e-health in converged optical and wireless access network

Long-reach, 60-GHz Mm-wave optical-wireless access network using remote signal regeneration and upconversion

Centrally Managed, Self-Survivable Wavelength Division Multiplexed Passive Optical Network