Microwave photonics, which brings together the worlds of radiofrequency engineering and optoelectronics, has attracted great interest from both the research community and the commercial sector over the past 30 years and is set to have a bright future. The technology makes it possible to have functions in microwave systems that are complex or even not directly possible in the radiofrequency domain and also creates new opportunities for telecommunication networks. Here we introduce the technology to the photonics community and summarize recent research and important applications.

Microwave photonics combines two worlds

A general derivation of the optical modulation process in a dual-drive Mach-Zehnder modulator (DD-MZM) is introduced. The expressions include all harmonics and are entirely general in terms of bias point. Chromatic dispersion is also included allowing the prediction of a number of important phenomena in photonic signal transmission. Examples of special cases of these general equations are then presented. Similar expressions are introduced for harmonic optical up-conversion through a photonic mixer based on a DD-MZM covering any bias point or phase shift between DD-MZM drives.

General expressions for IM/DD dispersive analog optical links with external modulation or optical up-conversion in a Mach-Zehnder electrooptical modulator

We present the first demonstration of a millimeter-wave (mm-wave) broadband fiber-wireless system which incorporates baseband data transmission in both the downstream (622 Mb/s) and upstream (155 Mb/s) directions. The local oscillator (LO) required at the remote antenna base station for up- and downconversion to/from the mm-wave radio frequency (RF) is delivered remotely via a modulation scheme that is tolerant to the effects of fiber chromatic dispersion on the detected LO carrier power. The technique employs a single dual electrode modulator located at the central office (CO) and the data and an RF signal at a frequency equal to half the LO frequency, are applied simultaneously to the device. The modulation scheme was optimized as a function of the modulator operating conditions. Simultaneous bidirectional radio transmission in the mm-wave fiber-wireless network was implemented using specially designed mm-wave diplexers located at the base station (BS) and customer unit, and a single Ka-band printed antenna array at the BS operating simultaneously in transmit and receive mode. Error-free data transmission was demonstrated for both down(34.8 GHz) and uplinks (37.5 GHz) after 20 km of single-mode optical fiber and a bit error rate (BER) of 10/sup -6/ was achieved after the inclusion of a 2-m radio link.

Millimeter-wave broad-band fiber-wireless system incorporating baseband data transmission over fiber and remote LO delivery

In this paper, a novel modulation scheme that allows broad-band optical data transmission at both baseband and millimeter-wave RF carriers at twice the local-oscillator frequency is investigated. The dispersion-induced carrier suppression may be overcome by properly setting the optical transmitter parameters. Three different configurations for the modulation scheme are modeled and simulation and experimental results are provided. The key parameters of these configurations are optimized in order to achieve the best performance in broad-band heterogeneous millimeter-wave wireless and wireline access networks.

Simultaneous baseband and RF optical modulation scheme for feeding wireless and wireline heterogeneous access networks

When the electrode separation is long or the applied voltage is low, the tree cannot directly grow to the plane electrode, and extinction of partial discharge (PD) with the re-growth of new channels can be observed after a long time. Before PD extinction, the light emission of the PD changes from the whole tree structure to only the region near the needle tip, and the PD pattern also changes from wing-like to turtle-like. These phenomena are considered to be related to the increase of channel conductivity by PDs. Assuming the channel conductivity is higher in the region at tree tips or in the tree channels than near the needle tip, the simulation results coincide with the experimental results.

Model for partial discharges associated with treeing breakdown: III. PD extinction and re-growth of tree

A full-duplex, optical feeder network for wireless access operating at 39 GHz is presented. The system transports 155 Mbit/s of data and three video channels downstream, and 51.8 Mbit/s upstream over 40 km of standard singlemode fibre. The 39 GHz carrier signal was generated using a novel tripling technique which enables low frequency electronics and optical components to be implemented in the central office. The architecture also incorporates simple, low cost remote base-stations with no millimetre-wave upconverting mixers required. To further minimise cost, an LED was used as the optical source for upstream transmission.

K. Wu

Papers

Full-duplex broadband millimetre-wave optical transport system for fibre-wireless access