We experimentally demonstrate a record 400G optical wireless integration system simultaneously delivering 2 × 112 Gb/s two-channel polarization-division-multiplexing 16-ary quadrature amplitude modulation (PDM-16QAM) signal at 37.5 GHz wireless carrier and 2 × 108 Gb/s two-channel PDM quadrature phase shift keying (PDM-QPSK) signal at 100 GHz wireless carrier, adopting two millimeter-wave (mm-wave) frequency bands, two orthogonal antenna polarizations, multiple-input multiple-output (MIMO), photonic mm-wave generation and advanced digital signal processing (DSP). In the case of no fiber transmission, the bit error ratios (BERs) for both the 112 Gb/s PDM-16QAM signal after 1.5 m wireless delivery at 37.5 GHz and the 108 Gb/s PDM-QPSK signal after 0.7 m wireless delivery at 100 GHz are below the pre-forward-error-correction (pre-FEC) threshold of 3.8 × 10⁻³. To our knowledge, this is the first demonstration of a 400G optical wireless integration system in mm-wave frequency bands and also a capacity record of wireless delivery.

We experimentally demonstrate a seamlessly integrated fiber-wireless system that delivers a $108\mathrm{Gb}/\mathrm{s}$ signal through 80 km fiber and 1 m wireless transport over free space at 100 GHz adopting polarization-division-multiplexing quadrature-phase-shift-keying (PDM-QPSK) modulation and heterodyning coherent detection. The $X$- and $Y$-polarization components of the optical PDM-QPSK baseband signal are simultaneously upconverted to 100 GHz wireless carrier by optical polarization-diversity heterodyne beating, and then independently transmitted and received by two pairs of transmitter and receiver antennas, which form a $2\times 2$ multiple-input multiple-output wireless link. At the wireless receiver, two-stage downconversion is performed firstly in the analog domain based on balanced mixer and sinusoidal radio frequency signal, and then in the digital domain based on digital signal processing (DSP). Polarization demultiplexing is realized by the constant modulus algorithm in the DSP part at the receiver. The bit-error ratio for the $108\mathrm{Gb}/\mathrm{s}$ PDM-QPSK signal is less than the pre-forward-error-correction threshold of $3.8\times {10}^{-3}$ after both 1 m wireless delivery at 100 GHz and 80 km single-mode fiber-28 transmission. To our knowledge, this is the first demonstration to realize $100\mathrm{Gb}/\mathrm{s}$ signal delivery through both fiber and wireless links at 100 GHz.

We experimentally demonstrate the photonics-aided wireless transmission of 4×4 multiple-input multiple-output (MIMO) probabilistic shaping 64-ary quadrature-amplitude-modulation (PS 64QAM) millimeter-wave signals at D-band (110-170GHz) over 3.1-m distance with a total bit rate of 1.056Tb/s and a bit-error ratio (BER) under 4×10-2. The employment of advanced digital-signal-processing (DSP) techniques, including probabilistic shaping, Nyquist shaping, and look-up-table (LUT) predistortion, significantly improves the transmission capacity and distance as well as the system performance. To the best of our knowledge, this is the first time to realize $\gt1-Tb/s$ millimeter-wave signal wireless delivery.

We summarize several different approaches for the realization of large capacity (>100Gb/s) fiber wireless integration system, including optical polarization-division-multiplexing (PDM) combined with multiple-input multiple-output (MIMO) reception, advanced multi-level modulation, optical multi-carrier modulation, electrical multi-carrier modulation, antenna polarization multiplexing and multi-band multiplexing. These approaches can effectively reduce the signal baud rate as well as the required bandwidth for optical and electrical devices. We also investigate the problems, such as wireless multi-path effect due to different wireless transmission distance, existing in the large capacity fiber wireless integration system. We demonstrate these problems can be effectively solved based on advanced digital-signal-processing (DSP) algorithms including classic constant modulus algorithm (CMA). Moreover, based on the combination of these approaches as well as advanced DSP algorithms, we have successfully demonstrated a 400G fiber wireless integration system, which creates a capacity record of wireless delivery and ushers in a new era of ultra-high bit rate (>400Gb/s) optical wireless integration communications at mm-wave frequencies.

High-speed millimeter-wave (mm-wave) wireless transmission at 40 Gb/s or higher will be required in the near future. Due to bottleneck in electrical devices, mm-wave wireless signal at such high bit rates cannot be generated in an all-electrical method. Photonics-assisted mm-wave generation technology has become an effective solution to handle this problem of bandwidth limitation. Recent efforts with a single modulator to generate optical mm-wave signal largely simplify the architecture of the optical transmitter. Heterodyne detection based on advanced digital signal processing can overcome nonlinear effects in optical and electrical devices, and it also can improve the spectral efficiency and receiver sensitivity. Multidimensional multiplexing techniques can reduce the baud rate of each subchannel, and hence it can realize mm-wave signal long distance transmission. In this tutorial, we will describe these key enabling technologies and principle for the realization of ultrahigh speed, large capacity mm-wave signal transmission. These enabling technologies can effectively improve the transmission capacity and distance, as well as reduce the required bandwidth for optical and electrical devices.

To meet the enhanced-mobile-broadband (eMBB) challenges in 5G, we have systematically explored the potential of the photonics-aided millimeter-wave (mm-wave) communication in terms of the wireless transmission capacity and distance it can accommodate. Enabled by various kinds of advanced multiplexing and digital-signal-processing (DSP) techniques, we have successfully achieved the significant enhancement of the wireless mm-wave signal transmission capacity from 100Gb/s to 400Gb/s, even to 1Tb/s. Since our large-capacity (>100-Gb/s) experimental demonstrations typically have a very short wireless transmission distance of several meters, we have further explored the techniques for the extension of the wireless mm-wave signal transmission distance, and successfully achieved a series of field-trial demonstrations on photonics-aided long-distance (>100-m) wireless mm-wave signal transmission. We have realized the record-breaking product of wireless transmission capacity and distance, i.e., 54Gb/s×2.5km.