A wireless communication system with a maximum data rate of 100 Gbit s−1 over 20 m is demonstrated using a carrier frequency of 237.5 GHz. The photonic schemes used to generate the signal carrier and local oscillator are described, as is the fast photodetector used as a mixer for data extraction.

Wireless sub-THz communication system with high data rate

In communications, the frequency range 0.1–30 THz is essentially terra incognita. Recently, research has focused on this terahertz gap, because the high carrier frequencies promise unprecedented channel capacities1. Indeed, data rates of 100 Gbit s were predicted2 for 2015. Here, we present, for the first time, a single-input and single-output wireless communication system at 237.5 GHz for transmitting data over 20 m at a data rate of 100 Gbit s. This breakthrough results from combining terahertz photonics and electronics, whereby a narrow-band terahertz carrier is photonically generated by mixing comb lines of a mode-locked laser in a uni-travellingcarrier photodiode. The uni-travelling-carrier photodiode output is then radiated over a beam-focusing antenna. The signal is received by a millimetre-wave monolithic integrated circuit comprising novel terahertz mixers and amplifiers. We believe that this approach provides a path to scale wireless communications to Tbit s rates over distances of >1 km. Data rates in both fibre-optic and wireless communications have been increasing exponentially over recent decades. For the upcoming decade this trend seems to be unbroken, at least as far as fibreoptic communications is concerned. In wireless communications, however, the spectral resources are extremely limited because of the heavy use of today’s conventional frequency range up to 60 GHz. Even with spectrally highly efficient quadrature amplitude modulation (QAM) and the spatial diversity achieved with multipleinput and multiple-output (MIMO) technology, a significant capacity enhancement to multi-gigabit or even terabit wireless transmission requires larger bandwidths, which are only available in the high millimetre-wave and terahertz region. Between 200 and 300 GHz there is a transmission window with low atmospheric losses3. In contrast to free-space optical links, millimetre-wave or terahertz transmission is much less affected by adverse weather conditions like rain and fog4,5. Here, we present for the first time a single-input single-output (SISO) wireless 100 Gbit s link with a carrier frequency of 237.5 GHz. By combining state-of-the-art terahertz photonics and electronics and by utilizing the large frequency range in the terahertz window between 200 and 300 GHz, we realize a wireless 100 Gbit s link with SISO technology, that is, a link with one transmit antenna and one receive antenna. To date, 100 Gbit s wireless links have only been demonstrated at lower carrier frequencies around 100 GHz (refs 6–8) over a wireless distance of 1 m, with a bit error ratio (BER) of 1 × 10. Because of the limited bandwidth, these systems relied on optical polarization multiplexing and spatial MIMO with more than one wireless transmitter and receiver. Here, a 100 Gbit s wireless transmission capacity is achieved without resorting to MIMO technology. We envisage various applications1,9,10 for such a high-capacity wireless link (Fig. 1). If an end-to-end fibre connection is absent and the deployment of a new fibre link is not economical, as might be the case in difficult-to-access terrains and certain rural areas (last mile problem), or if an already existing fibre connection fails, a permanent or ad hoc wireless connection could help. Furthermore, we anticipate indoor applications, such as highspeed wireless data transfers between mobile terminals and desktop computers. Figure 1 presents a schematic of our 100 Gbit s wireless experiment embedded into an application scenario where an obstacle, here a broad river, is bridged by the wireless link. We first discuss the general system concept, and then provide further details. For the transmitter (Tx) we use a terahertz photonics technology set-up (Fig. 1). We generate exceptionally pure and stable terahertz carriers by heterodyning frequency-locked laser lines11. A control unit contains a single mode-locked laser (MLL), selects the appropriate frequency-locked comb lines, and modulates data on the carrier lines. An optical fibre transmits the modulated carriers together with an unmodulated comb line, which acts as a remote local oscillator (LO), to a remote uni-travelling-carrier photodiode (UTC-PD). By photomixing the LO and the modulated carriers, radiofrequency signals are generated. Optical heterodyning has already been used in earlier works to implement multi-gigabit wireless systems in the 60 GHz band12–14, in the W-band (75–110 GHz, refs 6–8,15,16), at 120 GHz (refs 17,18) and at carrier frequencies beyond 200 GHz (refs 19,20). For the electronic in-phase/quadrature (IQ) receiver (Rx), we use a custom-developed, active millimetre-wave monolithic integrated circuit (MMIC) with a radiofrequency bandwidth of 35 GHz (refs 21,22). This is, to the best of our knowledge, the first active broadband IQ mixer at 237.5 GHz. The Rx comprises a low-noise amplifier (LNA) and a subharmonic downconversion IQ mixer, and is realized in a metamorphic high electron mobility transistor (mHEMT) technology (Supplementary Section S5) featuring a gate length of 35 nm and a cutoff frequency of more than 900 GHz (refs 23,24). The complex data are directly downconverted to the baseband and separated into I and Q signals. Previous works6–8 in the W-band have illustrated the importance of a high carrier frequency. However, to date, no direct downconversion to baseband has been used due to a lack of IQ mixers covering the full W-band. For carrier frequencies beyond 110 GHz (refs 17–20), simple on–off keying modulation and envelope

Wireless sub-THz communication system with high data rate enabled by RF photonics and active MMIC technology

The increasing demand for wireless video-based interactive and multimedia data services explains why 60-GHz millimeter-wave wireless system is a promising candidate to provide multi-gigabit-per-second wireless services. While attempting to generate and transmit 60 GHz signals in a wireless system cost effectively and increase the spectral efficiency to facilitate multi-gigabit-per-second services, this work reviews three radio-over-fiber (RoF) systems based on optical frequency multiplication (up to 6 times) to reduce the bandwidth requirement of optical transmitters. Additionally, orthogonal frequency division multiplexing (OFDM) signals with multi-level modulation formats (16 QAM) are utilized to achieve an ultrahigh data rate of 28 Gbps within the 7-GHz license-free band and compensate for an uneven frequency response of 60-GHz RoF systems. Negligible power penalty following 25-km standard single mode fiber (SSMF) transmission is observed, capable of significantly extending the service range to various applications within a building or campus.

https://ir.nctu.edu.tw:443/bitstream/11536/32296/1/000290153200007.pdf

Ultra-High Data-Rate 60 GHz Radio-Over-Fiber Systems Employing Optical Frequency Multiplication and OFDM Formats

Radio-over-fiber (ROF)-based mobile fronthaul network supporting the baseband unit and simple remote radio head is a promising network architecture for future wireless networks. In this paper, we propose and demonstrate a silicon photonics (SiPh)-based remote radio frontend (RRF) for the mm-wave ROF systems. The proposed SiPh-based RRF consisted of an integrated Mach-Zehnder modulator and a micro-ring modulator, producing a single-sideband 40 GHz millimeter-wave orthogonal-frequency-division-multiplexing ROF signal, which is robust against fiber chromatic dispersion in the mobile fronthaul transmission. The RRF is fabricated using SiPh platform and could be potentially low cost. High split-ratios can be potentially achieved. Data rate of 7.813 Gbit/s per wavelength channel is achieved in the experiment. Numerical analysis is also performed; there are good matches of the simulation and experimental results.

/pdf/integrated-silicon-photonics-remote-radio-frontend-rrf-for-567e3bbyzi.pdf

Integrated Silicon Photonics Remote Radio Frontend (RRF) for Single-Sideband (SSB) Millimeter-Wave Radio-Over-Fiber (ROF) Systems

We propose and demonstrate a novel approach to generate millimeter-wave (MMW) ultra-wideband (UWB) signal via frequency up-conversion using fiber optical parametric amplifier (OPA). The baseband UWB signal is amplified by a high-repetition-rate pulsed pump and generates many sidebands separated by the modulation frequency of the pump. By selecting two or three of the sidebands and beating in the photodetector, we can obtain an up-converted signal in the MMW band. In our experiment, we have successfully demonstrated UWB signal up-conversion from 3 to ~ 19 GHz with 18-dB optical gain using fiber OPA.

/pdf/millimeter-wave-uwb-signal-generation-via-frequency-up-1mlqwlj3h4.pdf

Millimeter-Wave UWB Signal Generation Via Frequency Up-Conversion Using Fiber Optical Parametric Amplifier

This study proposed and experimentally demonstrated a cost-efficient scheme that can deliver 60 GHz millimeter-wave (mm-wave) multi-gigabit wireless services over 125 km long-reach passive optical networks (PONs) without any dispersion compensation. By introducing a remote local exchange (LE) stage with robust signal regeneration and all-optical upconversion functionalities, the proposed long-reach optical-wireless access network can easily accommodate over 128 users with 2.5 Gb/s shared bandwidth as well as shifting the capital expenditure of multiple hybrid optical network units (ONUs) toward single LE headend. Experimental verification shows that the power penalties for wireless and wired services are 1.8 dB and 0.4 dB at 10-9 BER after 125 km optical fiber transmission.

Multiband negative refraction in one-dimensional photonic crystals

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Multiband negative refraction in one-dimensional photonic crystals