The integration of high-speed optical communication and distributed sensing could bring intelligent functionalities to ubiquitous optical fibre networks, such as urban structure imaging, ocean seismic detection, and safety monitoring of underground embedded pipelines. This work demonstrates a scheme of integrated sensing and communication in an optical fibre (ISAC-OF) using the same wavelength channel for simultaneous data transmission and distributed vibration sensing. The scheme not only extends the intelligent functionality for optical fibre communication system, but also improves its transmission performance. A periodic linear frequency modulation (LFM) light is generated to act as the optical carrier and sensing probe in PAM4 signal transmission and phase-sensitive optical time-domain reflectometry (Φ-OTDR), respectively. After a 24.5 km fibre transmission, the forward PAM4 signal and the carrier-correspondence Rayleigh backscattering signal are detected and demodulated. Experimental results show that the integrated solution achieves better transmission performance (~1.3 dB improvement) and a larger launching power (7 dB enhancement) at a 56 Gbit/s bit rate compared to a conventional PAM4 signal transmission. Meanwhile, a 4 m spatial resolution, 4.32-nε/ $$\sqrt {Hz}$$H z strain resolution, and over 21 kHz frequency response for the vibration sensing are obtained. The proposed solution offers a new path to further explore the potential of existing or future fibre-optic networks by the convergence of data transmission and status sensing. In addition, such a scheme of using shared spectrum in communication and distributed optical fibre sensing may be used to measure non-linear parameters in coherent optical communications, offering possible benefits for data transmission.

Increasing the system capacity and spectral efficiency (SE) per unit bandwidth is one of the ultimate goals for data network designers, especially when using technologies compatible with current embedded fiber infrastructures. Among these, the polarization-division-multiplexing (PDM) scheme, which supports two independent data channels on a single wavelength with orthogonal polarization states, has become a standard one in most state-of-art telecommunication systems. Currently, however, only two polarization states (that is, PDM) can be used, setting a barrier for further SE improvement. Assisted by coherent detection and digital signal processing, we propose and experimentally demonstrate a scheme for pseudo-PDM of four states (PPDM-4) by manipulation of four linearly polarized data channels with the same wavelength. Without any modification of the fiber link, we successfully transmit a 100-Gb s⁻¹ PPDM-4 differential-phase-shift-keying signal over a 150-km single-mode fiber link. Such a method is expected to open new possibilities to fully explore the use of polarization freedom for capacity and SE improvement over existing fiber systems.

An all-fiber approach to generate triangular-shaped pulses based on frequency-to-time conversion is proposed and demonstrated. Two filter modules that have sinusoidal spectral responses are cascaded to create a triangular-shaped optical spectrum. Through the frequency-to-time conversion in a dispersive fiber, periodic triangular pulses with the same shape as the optical spectrum are obtained. The repetition rate and pulse width of the generated signals can be tuned by adjusting the modulation rate and the dispersion value, respectively.

A plasmonic splitter based on slot cavity is proposed and numerically investigated using finite-difference-time-domain (FDTD) methods. The structure consists of the input waveguide, a slot cavity and output waveguides. By varying positions of output waveguides, frequency splitter and power splitter can be achieved in the proposed structure. Flexible output power ratio is feasible through further adjusting the coupling distance and the refractive index of output waveguides.

We propose and numerically demonstrate a scheme of coherent optical chaos communication using semiconductor lasers for secure transmission of optical quadrature amplitude modulation (QAM) signals. In this scheme, a laser intensity chaos and its delayed duplicate are used to amplitude-quadrature modulate a continuous-wave light to generate a chaotic carrier. High-quality chaotic carrier synchronization between the transmitter and receiver is guaranteed by laser intensity chaos synchronization, avoiding laser phase fluctuation. Decryption is implemented by a 90 deg optical hybrid using the synchronous chaotic carrier as local light. Secure transmission of an optical 40 Gb/s 16QAM signal is demonstrated by using a laser intensity chaos with a bandwidth of 11.7 GHz. The system performances are evaluated by analyzing a bit error ratio with different masking coefficients, signal rates, synchronization coefficients, parameter mismatches, and dispersion compensation. It is believed that this scheme can pave a way for high-speed optical chaos communication.

Nowadays, the microwave photonics (MWP) concept has been evolved from laboratory tests to practical applications, and related techniques have been widely deployed in many fields including such as wireless communications, medicine, sensing, radars, electronic warfare, and space explorations. In this paper, we concentrate on the featured applications of MWP in the high-speed railways (HSRs), an emerging field and massive market, and an overview about our recent work is presented. The radio-over-fiber based wireless communications in high-mobility scenarios, photonic-assisted electromagnetic interference detection along HSR lines, and fiber sensing for safety protection of railways are investigated systematically in our group. Experiments are then performed to verify the basic functionalities of the three MWP-enabled systems mentioned above. In particular, field trials have been successfully implemented along two in-service HSR lines located in Southwest China, i.e., the Chengdu–Chongqing and the Chengdu–Mianyang–Leshan HSR lines. With these results and achievements, we can expect more MWP-enabled striking applications in the HSR field in near future.