In this paper we present two different techniques for photonic generation of millimeter and THz waves. Each of them tackles the phase noise problem associated with optical sources in a different way. The first one relays on the heterodyne down-conversion of two phase noise correlated optical tones. The correlation is achieved by generation of an optical frequency comb. To select one of the optical lines we use an optical phase lock loop, which besides enabling a frequency offset between output and input, can provide optical gain and is highly selective. The second one relays on the envelope detection of a single sideband-with carrier signal. In this approach the photonic remote antenna unit is implemented as monolithically integrated photonic chip.
A comparative study of two different Photonic Integrated Circuits (PICs) structures for continuous-wave generation of millimeter-wave (MMW) signals is presented, each using a different approach. One approach is optical heterodyning, using an integrated dual-wavelength laser source based on Arrayed Waveguide Grating. The other is based on ModeLocked Laser Diodes (MLLDs). A novel building block -Multimode Interference Reflectors (MIRs) – is used to integrate on-chip both structures, without need of cleaved facets to define the laser cavity. This fact enables us to locate any of these structures at any location within the photonic chip. As will be shown, the MLLD structure provides a simple source for low frequencies. Higher frequencies are easier to achieve by optical heterodyne. Both types of structures have been fabricated on a generic foundry in a commercial MPW PIC technology.
Optical fibre transmission has enabled greatly increased transmission rates, with 10 Gb/s common in local area networks. End users find wireless access highly convenient, however limited spectrum availability at microwave frequencies results in per-user transmission rates which are limited to much lower values, 500 Mb/s for 5 GHz band IEEE 802.11ac, for example. Extending the high data-rate capacity of optical fibre transmission to wireless devices, requires greatly increased carrier frequencies. This paper will describe how photonic techniques can enable ultra-high capacity wireless data distribution and transmission using signals at millimetre-wave and TeraHertz (THz) frequencies.