Arshad Chowdhury

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

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.

Design and implementation of ultra-low latency optical label switching for packet-switched WDM networks

An ultra-low latency, high throughput Internet protocol (IP) over wavelength division multiplexing (WDM) packet switching technology for next-generation Internet (NGI) applications has been designed and demonstrated. This method overcomes limitations of conventional optical packet switching, which require buffering of packets and synchronization of bits, and optical burst switching methods that require estimation of delays at each node and for each path. An optical label switching technique was developed to realize flexible bandwidth-on-demand packet transport on a reconfigurable WDM network. The aim was to design a network with simplified protocol stacks, scalability, and data transparency. This network will enable the NGI users to send their data applications at gigabit/second access speed with low and predictable latency (<1 /spl mu/sec per switch node), with a system capacity of beyond multi-Tb/s. Packet forwarding utilizes WDM optical headers that are carried in-band on the same wavelength and modulated out-of-band in the frequency domain.

Cost-Effective Optical Millimeter Technologies and Field Demonstrations for Very High Throughput Wireless-Over-Fiber Access Systems

The broadband penetration and continuing growth of Internet traffic among residential and business customers are driving the migration of todays end users network access from cable to optical fiber and superbroadband wireless systems The integration of optical and wireless systems operating at much higher carrier frequencies in the millimeter-wave (mm-wave) range 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 very high throughput wireless-over-fiber networks are reviewed, including photonic mm-wave generation based on external modulation or nonlinear effects, spectrum-efficient multicarrier orthogonal frequency-division multiplexing and single-carrier multilevel signal modulation. We also demonstrated some applications in wireless-over-fiber trials using these enabling techniques. The results show that the integrated systems are practical solutions to offer very high throughput wireless to end users in optically enabled wireless access networks.

Simultaneous Generation of Independent Wired and Wireless Services Using a Single Modulator in Millimeter-Wave-Band Radio-Over-Fiber Systems

We experimentally demonstrated a novel radio-over-fiber scheme to simultaneously obtain independent wired and wireless signals by using only a single intensity modulator. The optical 40- or 60-GHz millimeter-wave (mm-wave) carriers are generated by means of subcarrier-multiplexing techniques to carry 2.5-Gb/s wireless signals while 10-Gb/s wired signals are imposed on the original optical carrier via regular intensity modulation. The signals with dual services are successfully transmitted over 20-km single-mode fiber (SMF-28) with less than 1.5-dB power penalty.

Advanced System Technologies and Field Demonstration for In-Building Optical-Wireless Network With Integrated Broadband Services

This work describes a concept of a hierarchical radio-over-fiber (RoF) network architecture that provides both intra- and inter-network connectivity for end user wireline and wireless terminals with high-bandwidth, in-building access applications. An intelligent gateway router (IGR) is proposed as a unified platform to accommodate multi-gigabit, millimeter-wave services at 60-GHz band as well as being backward compatible with all current wireless access technologies such as WiFi and WiMAX. In addition, we further present an advanced multi-band optical carrier generation technique that can simultaneously deliver independent 60-GHz mm-wave, 2.4-GHz WiFi, and 5.8-GHz WiMAX signals efficiently carried over the same wavelength, and is suitable for the proposed IGR. Finally, we report, for the first time to our knowledge, a campus-wide field trial demonstration of RoF system transmitting uncompressed 270-Mbps standard definition (SD) and 1.485-Gbps high definition (HD) real-time video contents carried by 2.4-GHz radio and 60-GHz millimeter wave signals, respectively, between two on-campus research buildings distanced over 2.5-km standard single mode fiber (SMF-28) through the Georgia Institute of Technologys (GT) fiber network.

Multiband Signal Generation and Dispersion-Tolerant Transmission Based on Photonic Frequency Tripling Technology for 60-GHz Radio-Over-Fiber Systems

We designed and experimentally demonstrated an efficient photonic frequency-tripling technology for 60-GHz radio-over-fiber systems to simultaneously realize millimeter-wave (mm-wave), microwave, and baseband signal generation. The technique utilizes vestigial sideband filtering in combination with optical carrier suppression to generate novel alternate subcarrier modulation for high tolerance of fiber dispersion. Experimental verification of the proposed scheme is presented with generation and error-free transmission of 2.1-Gb/s data on the 63-GHz mm-wave and 21-GHz microwave carriers over 50-km single-mode fiber (SMF-28) without dispersion compensation. The power penalty for both signals is less than 1.0 dB.

Enabling Technologies for Next-Generation Optical Packet-Switching Networks

The optical packet-switching network is considered to be one of the most promising solutions for end-to-end delivery of high-bitrate data, video, and voice signals across optical networks of the future. Optical label switching (OLS) technology incurs simpler extraction and processing of the labels so that the optical packets can be routed with low latency to the destinations. We have developed several key enabling technologies for integrated optical networks, including optical label generation, label swapping, optical buffering, clock recovery, and wavelength conversion. We have designed and experimentally demonstrated these enabling techniques that can provide efficient broadband services in future optical networks

Super-Broadband Optical Wireless Access Technologies

Network enabling technologies and architectures design for delivering super-broadband wireless services at >1 Gb/s over optical access networks are reviewed. Cost-efficient optical mm-wave generation and transmission technology, optical OFDM, and hierarchical architecture for high-mobility access are discussed.

Multiband 60-GHz Wireless Over Fiber Access System With High Dispersion Tolerance Using Frequency Tripling Technique

A new optical millimeter-wave generation scheme to triple the beating frequency based on subcarrier multiplexing in combination with single sideband technique is proposed, capable of high tolerance of fiber chromatic dispersion. The proposed scheme can be applied to two types of multiband 60-GHz wireless over fiber access systems: one with widely separated bands including millimeter-wave, microwave and baseband and the other one with multiple 60-GHz sub-bands. Experimental verification of the proposed system with widely separated bands is presented with the generation and error-free transmission of 2.1-Gb/s data on the 63-GHz mm-wave and 21-GHz microwave carriers over 50-km single-mode fiber (SMF-28) without dispersion compensation. The power penalties caused by 50-km fiber transmission for both signals are both less than 1.0 dB at BER of 10-9 Meanwhile, simultaneous generation and transmission of multiple services at 60-GHz sub-bands are also introduced. The experimental results demonstrate the successful delivery of the 1-Gbps data carried by 60-GHz millimeter-wave both over 50-km SMF-28 and wireless distance of 6-m without any dispersion compensation. The optical receiver sensitivity of the transmission with two sub-bands degrades by 2 dB compared with the single band 60-GHz signal, and the power penalty from 50-km SMF-28 transmission is 0.8 dB at BER of 10-9. From the theoretical analysis and experimental demonstrations of the two multiband systems, it is concluded that the proposed millimeter-wave generation scheme indeed increase the transmission distance for the system with 60-GHz signal, which normally having SMF transmission distance of few tens of kilometers, by utilizing optical and electrical components with low-bandwidth requirements.

Multi-service multi-carrier broadband MIMO distributed antenna systems for in-building optical wireless access

A novel broad spectrum band-shifting technique is experimentally demonstrated to simultaneously transmit broadband (500 MHz to 3 GHz) multi-service, multi-carrier MIMO signals for in-building radio-over-fiber based wireless distributed antenna systems. The proposed scheme uses fewer local oscillators and does not require any service-specific narrowband band pass filters, thus upgrading of existing non-MIMO services to MIMO services or adding new MIMO services would be easier and cost-effective.