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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 for mobile communication. However, limited spectrum availability at microwave frequencies results in per-user transmission rates 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.

The design, experimental evaluation and performance of a Traveling-Wave Uni-Traveling Carrier photodiode for Terahertz generation are described and its advantages in terms of frequency response are demonstrated. The device delivered 148 microW at 457 GHz, 24 microW at 914 GHz when integrated with resonant antennas and 105 microW at 255 GHz, 30 microW at 408 GHz, 16 microW at 510 GHz and 10 microW at 612 GHz. Record levels of Terahertz figure of merit (PTHz/Popt2 in W(-1)) were achieved ranging from 1 W(-1) at 110 GHz to 0.0024 W(-1) at 914 GHz.

We report on advanced millimeter-wave (mm-wave) photonic components for broadband wireless transmission. We have developed self-pulsating 60 GHz range quantumdash Fabry-Perot mode-locked laser diodes (MLLD) for passive, i.e. unlocked, photonic mm-wave generation with comparably low phase noise level of-76 dBc/Hz @ 100 kHz offset from 58.8 GHz carrier. We further report on high-frequency 1.55 µm waveguide photodiodes (PD) with partially p-doped absorber for broadband operation (f 3dB~7 0-110 GHz) and peak output power levels up to +4.5 dBm @ 110 GHz as well as wideband antenna integrated photomixers for operation within 30-300 GHz and peak output power levels of-11 dBm @ 100 GHz and 6 mA photocurrent. We further present compact 60 GHz wireless transmitter and receiver modules for wireless transmission of uncompressed 1080p (2.97 Gb/s) HDTV signals utilizing the developed MLLD and mm-wave PD. Error-free (BER=10-9 , 2 31-1 PRBS, NRZ) outdoor transmission of 3 Gb/s over 25 m is demonstrated as well as wireless transmission of uncompressed HDTV signals in the 60 GHz band. Finally, an advanced 60 GHz photonic wireless system offering record data throughputs and spectral efficiencies is presented. For the first time, we demonstrate photonic wireless transmission of data throughputs up to 27.04 Gbit/s (EVM 17.6 %) using a 16-QAM OFDM modulation format resulting in a spectral efficiency as high as 3.86 bit/s/Hz. Wireless experiments were carried out within the regulated 57-64 GHz band in a lab environment with a maximum transmit power of-1 dBm and 23 dBi gain antennas for a wireless span of 2.5 m. This span can be extended to some 100 m span when using highgain antennas and higher transmit power levels.

We demonstrate that the integrated sub-wavelength aperture probe designed for THz near-field scanning probe microscopy can be used to map surface plasmon waves at THz frequencies. Observed near-field images of metallic patterns reveal surface plasmon waves superimposed over THz transmission images. We discuss the coupling mechanism for the surface waves and arrive to an important conclusion that the detected surface wave images represent the spatial derivative of the surface plasmon electric field. The relationship between the electric field and the measured signal is confirmed experimentally by mapping surface waves in bow-tie antennas. This study explains previously observed effects in THz near-field microscopy and provides a framework for analysis of near-field images.

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An Optical Phase Lock Loop (OPLL) is a feedback control system that allows the phase stabilization of a laser to a reference laser with absolute but adjustable frequency offset. Such phase and frequency locked optical oscillators are of great interest for sensing, spectroscopy, and optical communication applications, where coherent detection offers advantages of higher sensitivity and spectral efficiency than can be achieved with direct detection. As explained in this paper, the fundamental difficulty in realising an OPLL is related to the limitations on loop bandwidth and propagation delay as a function of laser linewidth. In particular, the relatively wide linewidth of semiconductor lasers requires short delay, which can only be achieved through shortening of the feedback path, which is greatly facilitated through photonic integration. This paper reviews the advances in the development of semiconductor laser-based OPLLs and describes how improvements in performance have been enabled by improvements in photonic integration technology. We also describe the first OPLL created using foundry fabricated photonic integrated circuits and off-the-shelf electronic components. Stable locking has been achieved for offset frequencies between 4 and 12 GHz with a heterodyne phase noise below -100 dBc/Hz at 10 kHz offset. This is the highest performance yet reported for a monolithically integrated OPLL and demonstrates the attractiveness of the foundry fabrication approach.Index Terms-Optical phase locked loops, photonic integrated circuits, semiconductor laser, microwave photonics.