Jianjun Yu's research while affiliated with Fudan University and other places

We propose an optical dual-single-sideband (dual-SSB) modulated 16384-quadrature amplitude modulation (QAM) photonic vector millimeter-wave (mm-wave) signal generation scheme based on delta-sigma modulation (DSM). With the aid of the DSM, the severe nonlinear distortion of envelope detection for high-order QAM modulation signals in wireless communication can be effectively resolved. For the validation of our proposed scheme, we experimentally demonstrate the generation of a 40 GHz 16384-QAM orthogonal frequency division multiplexing (OFDM) photonic vector mm-wave signal and transmission over a 25-km standard single-mode fiber (SSMF), and a 1-m wireless link with the bit error ratio (BER) reaches the hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10⁻³.

We propose a digital pulse-code-modulation radio-over-fiber (DP-RoF) scheme and verify it experimentally in a 10-km standard single-mode fiber (SSMF) coherent system. The 20-Gbaud DP-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 112 Gb/s is successfully transmitted in the system with excellent performance. The recovered signal-to-noise ratio (SNR) of wireless signal in DP-RoF scheme is 50.14 dB, which is 26.62, 20.01 and 13.28 dB higher than that of analog radio-over-fiber (A-RoF), digital-analog radio-over-fiber (DA-RoF) and digital radio-over-fiber (D-RoF), respectively. The DP-RoF scheme meets the error vector magnitude (EVM) requirement of 65536 quadrature amplitude modulation (QAM), while A-RoF and DA-RoF schemes cannot reach the EVM threshold of 1024 QAM. With improved SNR, the proposed DP-RoF system is a promising scheme for ultra-high-order QAM transmission in future 6G fronthaul.

In this experiment, we demonstrate a real-time intensity modulation and direct detection (IM/DD) system based on a field programmable gate array (FPGA). For high-speed parallel signal processing, we propose and implement the simplified parallel-constant modulus algorithm (CMA) and decision-directed least mean square (DDLMS) equalizers with low complexity and low latency. Moreover, the bit-class probabilistic shaping (PS) scheme is adopted with very few hardware resources. The digital signal processing (DSP) steps are implemented in the XCVU9P-FLGB2104-2-I Xilinx FPGA with a clock frequency of 230.4 MHz. Based on the experimental results, 4 × 29.4912 Gbit/s PS-pulse amplitude modulation (PAM4) signals can be successfully transmitted over 25 km of standard single-mode fiber (SSMF) while satisfying the hard-decision forward error correction (HD-FEC) threshold at 3.8 × 10⁻³. Compared with the uniformly distributed PAM4 signal, the low-complexity PS scheme can improve the receiver sensitivity by more than 1 dB.

This Letter demonstrates a real-time 100-GbE fiber-wireless seamless integration system operating at the whole W band (75–110 GHz). Based on a pair of commercial digital coherent optical modules, the real-time transparent transmission of 125-Gb/s dual-polarized quadrature phase-shift keying signal has been successfully achieved over two-spans of 20-km fiber and up to 150-m electromagnetic dual-polarized single-input single-output wireless link. To the best of our knowledge, this is the first real-time demonstration of 100-GbE signal transmission over >100-m wireless distance at the millimeter-wave band based on photonics. We believed this real-time and high-speed fiber-wireless seamless integration system with a wireless coverage up to hundreds of meters can significantly accelerate the progress of upcoming 6G.

We have proposed and experimentally implemented a photonics-aided large-capacity long-distance mm-wave bidirectional full-duplex communication system at the W-band based on polarization multiplexing. The same radio frequency (RF) carrier source is shared by both the uplink and the downlink, and a pair of orthomode transducers (OMTs) are used to separate the dual orthogonally polarized channels. To achieve the maximum spectrum efficiency and throughput, 10-Gbaud probabilistically shaped 256-level quadrature-amplitude-modulation (PS-256QAM) signals with 7.07 bit/symbol/Hz are transmitted in Ch. H and Ch. V. The system can support the bidirectional transmission with 103-Gbps data rate over 4600-m RF wireless distance. To the best of our knowledge, based on a photonics-aided bidirectional full-duplex system, this is the first time to realize a record-breaking bit rate–distance product at the W-band, i.e., 103 Gbps × 4.6 km = 473.8 Gbps•km.

We experimentally demonstrate 2-Gbaud 4096-ary quadrature amplitude modulation (4096QAM) signal transmission over 2-m wireless distance at 370 GHz in a photonics-aided terahertz (THz)-wave communication system. By using one-bit quantized delta-sigma modulation (DSM) and photonics-aided technology, we successfully achieve the transmission of high-order QAM signals over THz multiple-input multiple-output (MIMO) links. After 2 m of free space transmission, its bit error rate (BER) is below the 20% soft-decision forward error correction (20% SD-FEC) threshold of 2.4 × 10⁻². To the best of our knowledge, this is the first time to apply DSM technology in a THz MIMO link transmission.

In this letter, we experimentally demonstrate a long-distance, large-capacity and photonics-aided wireless terahertz (THz) transmission system without THz amplifier. Using dielectric lenses and advanced digital signal processing (DSP), we have achieved 124 Gbit/s signal transmission over 54 meters wireless distance and 44 Gbit/s signal transmission over 104 meters wireless distance. For all we know, this is the longest wireless distance that can be achieved by using dielectric lenses without any THz amplifiers.