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, e.g., 500 Mb/s for 5-GHz band IEEE 802.11ac. Extending the high data-rate capacity of optical fiber transmission to wireless devices requires greatly increased carrier frequencies. This paper will describe how photonic techniques can enable ultrahigh capacity wireless data distribution and transmission using signals at millimeter-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 μW at 457 GHz, 24 μW at 914 GHz when integrated with resonant antennas and 105 μW at 255 GHz, 30 μW at 408 GHz, 16 μW at 510 GHz and 10 μW at 612 GHz. Record levels of Terahertz figure of merit (P_THz/P_opt ² 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 radio transmission. We have developed self-pulsating 60-GHz range quantum-dash 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 a 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 ~70-110 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, 2³¹ - 1 PRBS, NRZ) outdoor wireless 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 Gb/s (EVM 17.6%) using a 16-QAM OFDM modulation format resulting in a spectral efficiency as high as 3.86 b/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 when using high-gain antennas and higher transmit power levels.

This paper describes the advantages that the introduction of photonic integration technologies can bring to the development of photonic-enabled wireless communications systems operating in the millimeter wave frequency range. We present two approaches for the development of dual wavelength sources for heterodyne-based millimeter wave generation realized using active/passive photonic integration technology. One approach integrates monolithically two distributed feedback semiconductor lasers along with semiconductor optical amplifiers, wavelength combiners, electro-optic modulators and broad bandwidth photodiodes. The other uses a generic photonic integration platform, developing narrow linewidth dual wavelength lasers based on arrayed waveguide gratings. Moreover, data transmission over a wireless link at a carrier wave frequency above 100 GHz is presented, in which the two lasers are free-running, and the modulation is directly applied to the single photonic chip without the requirement of any additional component.

We propose and experimentally demonstrate a photonic multichannel terahertz (THz) wireless system with up to four optical subcarriers and total capacity as high as 100 Gb/s by employing an externally injected gain-switched laser comb source. Highly coherent multiple optical carriers with different spacing are produced using the gain switching technique. Single- and multichannel Terahertz (THz) wireless signals are generated using heterodyne mixing of modulated single or multiple carriers with one unmodulated optical tone spaced by about 200 GHz. The frequency stability and the phase noise of the gain switched comb laser are evaluated against free-running lasers. Wireless transmission is demonstrated for single and three optical subcarriers modulated with 8 or 10 GBd quadrature phase-shift keying (QPSK) (48 or 60 Gb/s, respectively) or for four optical subcarriers modulated with 12.5 GBd QPSK (100 Gb/s). The system performance was evaluated for single- and multicarrier wireless THz transmissions at around 200 GHz, with and without 40 km fiber transmission. The system is also modeled to study the effect of the cross talk between neighboring subcarriers for correlated and decorrelated data. This system reduces digital signal processing requirements due to the high-frequency stability of the gain-switched comb source, increases the overall transmission rate, and relaxes the optoelectronic bandwidth requirements.