Jiangnan Xiao

An independent dual-single-sideband (IDSSB) signal carries distinct data on its two optical sidebands, and conventional IDSSB receivers require two sideband-separation optical bandpass filters (OBPFs) and two photodetectors (PDs). We propose a simplified IDSSB direct-detection optical orthogonal frequency-division multiplexing (OFDM) scheme using one in-phase/quadrature (IQ) modulator and one PD together with a single noniterative digital signal processing (DSP) chain that recovers two independent left- and right-sideband quadrature phase shift keying (QPSK) OFDM streams from the synthesized 16-ary quadrature amplitude modulation (16-QAM) OFDM signal formed after photodetection. Simulations demonstrate 2 × 5.23-Gb/s transmission over 10-km standard single-mode fiber (SSMF), with the bit error rates (BERs) of both sideband signals below 3.8 × 10 ⁻³ . The optimum carrier-to-signal power ratio (CSPR) is found to be 2 dB. Compared with a conventional dual-OBPF/dual-PD receiver operating on the same transmitted waveform, the proposed receiver incurs an approximately 0.7-dB sensitivity penalty.

This paper presents the implementation of a photonics-assisted V-band 1   ×   3 single-input multiple-output (SIMO) millimeter-wave wireless transmission system, achieving a transmission distance of 1.2   km. The system utilizes a dual-laser beating technique to generate a high-purity millimeter-wave carrier and incorporates offline digital signal processing (DSP) algorithms—including down-conversion, resampling, combination of Constant Modulus Algorithm (CMA) equalization and a Fractionally Spaced Equalizer (FSE), block phase search (BPS), and maximal ratio combining (MRC)—to achieve signal fusion and performance optimization among multiple receiving branches. Experimental results demonstrate that after maximal ratio combining, the signal’s signal-to-noise ratio (SNR) is improved by approximately 5 dB, and the bit error rate (BER) is reduced by an order of magnitude, with the constellation diagram showing significant convergence, thereby enabling stable transmission without the use of forward error correction (FEC). To the best of our knowledge, this is the first experimental demonstration of high-gain performance achieved using these techniques in a V-band 1   ×   3 SIMO millimeter-wave system.

This paper proposes a scheme for the transmission and generation of independent triple-sideband (TSB) terahertz (THz) signals based on delta-sigma modulation (DSM) technology. The method converts multi-sideband high-order quadrature amplitude modulation (QAM) signals into a low-order quadrature phase shift keying (QPSK) signal, enabling the transmission of independent TSB 256/512QAM signals. Compared to directly transmitting high-order QAM signals over the standard single-mode fiber (SSMF), the signal after the DSM modulator reduces the average energy and enhances the system’s noise resistance. The system achieves an improvement in optical signal-to-noise ratio (OSNR) gain of at least 2.5 dB. The receiver sensitivity gain for back-to-back (BTB) transmission and 60 km SSMF transmission is at least 1.5 dB and 2 dB higher, respectively. Additionally, at the receiver end, the original signal can be restored by simply eliminating out-of-band quantization noise through low-pass filtering, without the need for an additional digital-to-analog converter (DAC), which contributes to cost reduction. Simulation results demonstrate the successful transmission and detection of independent TSB 256/512QAM signals over SSMF at 320 GHz frequency, achieving a maximum transmission distance of 60 km. The bit error rate (BER) remains below the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10⁻³, confirming the feasibility and effectiveness of the proposed scheme.

To further meet the large capacity, high spectrum efficiency (SE), reduce the signal-signal beat interference (SSBI) of the independent dual single sideband (ISB) system and the complexity of the receiver, we propose an iterative signal-signal beat interference counteraction (ISSBIC) algorithm to suppress SSBI. The 16-Gbps left sideband and the 16-Gbps right sideband signals in the ISB system are quadrature phase-shift keying (QPSK) modulated. After standard single-mode fiber (SSMF) transmission, the LSB and RSB signals are synthesized to a 16-quadrature amplitude modulation (QAM) signal after conversion through the photodetector (PD) square law. The simulation results show that the ISSBIC with just 2 iterations is superior to Kramers–Kronig (KK) receiver in processing the system error bit. In the meantime, the ISSBIC requires a sampling rate of 20GSa/s, whereas KK requires 40GSa/s. Moreover, the proposed ISSBIC algorithm has a simpler complexity. According to the simulation results, the suggested ISSBIC receiver can lower the ADC requirements and system costs, which opens up a wide range of applications in multiplex and higher SE transmission systems.

This paper proposes a method for synthesizing a multiple sideband superposed 32QAM (MSBS-32QAM) signal from a QPSK and an 8QAM using a dual drive Mach-Zehnder modulator (DD-MZM) via intensity modulation/direct detection (IM/DD). This technique doubles the electrical spectral efficiency (SE) compared to DD-MZM-based single sideband (SSB) modulation because the two sidebands carry different data. Such ability to carry two different sidebands doubles the SE compared to the typical double sideband (DSB) modulation while realizing the recovery of complex DSB signal via IM/DD. Digital signal processing (DSP) is used to separate and demodulate the QPSK and 8QAM signal from the MSBS-32QAM signal, saving the optical filters/polarizers/interleaves used in the twin-SSB scheme, thus reducing receiver complexity and cost.

This paper proposes a novel, to the best of our knowledge, independent triplet-single-sideband (triplet-SSB) transmission system scheme aimed at increasing channel capacity and improving spectrum efficiency. The conventional independent multiband transmission systems are limited by their complexity and high computational requirements, which hinder the improvement of spectrum efficiency and channel capacity. To address these challenges, this scheme uses three independent signals, modulated by an in-phase/quadrature (I/Q) modulator, and transmits them over a 5-km standard single-mode fiber (SSMF). At the receiver end, a single photodiode (PD) is used for signal reception, and the signals are separated using digital signal processing (DSP) algorithms. Through simulation and verification, the feasibility and reliability of the system are demonstrated, with the bit error rates (BERs) of all three signals below the hard decision forward error correction (HD-FEC) threshold value of 3.8 × 10⁻³. This independent triplet-SSB transmission system scheme effectively improves spectrum efficiency and channel capacity, providing a valuable solution for meeting the growing demands of data transmission.

We propose and verify a direct detection (DD) system based on a single photodiode (PD) receiving the independent quadruple-single-sideband (quadruple-SSB) signal. At the transmitter side, an I/Q modulator is utilized to modulate the independent quadruple-SSB signal, the signal is received via one PD without optical bandpass filters (OBPFs). Then, the independent quadruple-SSB signal is separated into four sideband signals by subsequent digital signal processing (DSP). In the scheme of back-to-back (BTB), 1-km and 5-km standard single-mode fiber (SSMF) transmission, the four sideband signals are extensively studied and analyzed. The simulation results show that the bit error rate (BER) of 1Gbaud, 2Gbaud and 4Gbaud independent quadruple-SSB signal can reach the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10⁻³ when the received optical power (ROP) is −21, −20 and −17.2 dBm in 5-km SSMF transmission. Meanwhile, as the frequency interval gets wider, the crosstalk in the sideband signal reception can be mitigated and the BER decreases. This scheme for the first time demonstrates that the independent quadruple-SSB signal can further expand the system transmission capacity and enhance the spectrum efficiency. Our simplified independent quadruple-SSB signal direct detection system has a simple structure and high spectral efficiency, which will have a promising future in high-speed optical communication.

To meet the ultra-bandwidth high-capacity communication, improve spectral efficiency and reduce the complexity of system structure, we have proposed the independent triple-sideband signal transmission system based on photonics-aided terahertz-wave (THz-wave). In this paper, we demonstrate up to 16-Gbaud independent triple-sideband 16-ary quadrature amplitude modulation (16QAM) signal transmission over 20 km standard single mode fiber (SSMF) at 0.3 THz. At the transmitter, independent triple-sideband 16QAM signals are modulated by an in-phase/quadrature (I/Q) modulator. Carrying independent triple-sideband signals optical carrier coupled with another laser to generate independent triple-sideband terahertz optical signals with a carrier frequency interval of 0.3THz. While at the receiver side, enabled by a photodetector (PD) conversion, we successfully obtain independent triple-sideband terahertz signals with a frequency of 0.3THz. Then we employ a local oscillator (LO) to drive mixer to generate intermediate frequency (IF) signal, and only one ADC is used to sample independent triple-sideband signals, digital signal processing (DSP) is finally performed to obtain independent triple-sideband signals. In this scheme, independent triple-sideband 16QAM signals is delivered over 20 km SSMF under the bit error ratio (BER) of 7% hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10⁻³. Our simulation results show that the independent triple-sideband signal can further improve THz system transmission capacity and spectral efficiency. Our simplified independent triple-sideband THz system has a simple structure, high spectral efficiency, and reduced bandwidth requirements for DAC and ADC, which is a promising solution for future high-speed optical communications.

Optical twin-single sideband (Twin-SSB) modulation, due to the left sideband (LSB) and right sideband (RSB) signal carrying individual data, has become an attractive technique in fiber transmission because it satisfies the demand of the explosive increase in data traffic. This paper focuses on reducing the complexity of Twin-SSB system and further enhancing the spectral efficiency by proposing a polarization division multiplexing (PDM) Twin-SSB modulation scheme. LSB and RSB signals are extracted using de-mapping algorithm instead of optical bandpass filters (OBPFs) to reduce system complexity. To further improve spectral efficiency, PDM is employed to meet the polarization multiplexing transmission and achieve a higher transmission capacity. Based on the PDM Twin-SSB system, the LSB is 3-arr phase-shift-keying (3PSK) modulated, while RSB is quadrature phase-shift keying (QPSK) modulated. We simulated that the bit error ratio (BER) performance of LSB and RSB of X-polarization (X-Pol) and Y-polarization (Y-Pol) at 8-Gbaud, 10-Gbaud, 12-Gbaud, 14-Gbaud, and 16-Gbaud in the case of back-to-back (BTB) and 2 km standard single-mode fiber (SSMF) transmission. The simulation results verify the effectiveness and practical feasibility of the proposed PDM Twin-SSB scheme for future short-distance transmission owing to low cost, simplified structure, low algorithm complexity, and high data transmission capacity.