Self-interference (SI) influenced the recovery of the signal of interest (SOI) in In Band Full Duplex (IBFD) radio-over-fiber (ROF) links. The multipath effect and nonlinear distortion aggravate the difficulty of the SI signal elimination. A fiber-transmission-assisted digital self-interference cancellation (DSIC) scheme is proposed to solve the problem at a low time complexity. The key to removing the impact of harmful factors is combined with the advantages of photonics architecture and digital filter algorithm. A fiber-transmission-assisted scheme achieves the transmission of reference signals with all the linear and nonlinear features which transform the nonlinear problem into a linear question for DSIC subsequently. In DSIC, a fast transversal recursive least-squares (FTRLS) algorithm realizes a fast-channel estimating process when the SOI is involved. For 10km fiber transmission, exceeding 38 dB and 34 dB cancellation depth over 50 MHz bandwidth in the X band and Ku band are experimentally demonstrated, and 25 Mbaud 16-quadrature amplitude modulation (16-QAM) SOI is successfully recovered after SIC. In addition, FTRLS merely consumed 7N+14 multiplication times at each iteration (filter order N) in the channel estimating process, which saves multiplications amount above 86% than RLS, DNN, Volterra-RLS algorithm, when N is equal to 80.

A photonic-assisted approach for instantaneous frequency measurement (IFM) based on a 1×4 Mach–Zehnder interferometer (MZI) structure is proposed and experimentally demonstrated. In this IFM method, a Mach–Zehnder modulator (MZM) in conjunction with an optical filter play the role of CS-SSB signal generator, mapping the unknown microwave into a tunable optical sideband. Due to the property of the subsequent 1×4 MZI structure, two amplitude comparison function (ACF) that convert the frequency information into optical power ratio can be established. A detailed theoretical analysis illustrates the realization of frequency measurement with a range of full free spectral range (FSR) and optimized estimation error by using these two ACFs. Simulation has been carried out to verify the mechanism, and the discussion about the merits of CS-SSB modulation and the applicable scenarios is also given. A proof-of-concept experiment is performed, in which the microwave frequency measurement from 7.5 to 20 GHz is demonstrated with an estimation error of less than 100 MHz.

A microwave photonic scheme for multi-functional radio over fiber based in-band full duplex communication links to realize deep self-interference cancellation, long range transmission, and efficient signal recovery is proposed. In the proposed scheme, double sideband modulation helps avoid applying electrical couplers or optical filters and is beneficial to improve the frequency conversion efficiency. By virtue of the intermediate frequency signal amplitude regulation mechanism induced by fiber dispersion, the conditions of dispersion induced power fading compensation, amplitude matching, and phase reversion between self-interference and reference signals can be satisfied through joint DC bias tuning. The high precision delay matching in the optical domain is advantageous to the deep self-interference cancellation performance in a wide frequency range compared to its electrical counterparts. Furthermore, the deterioration of signal quality and self-interference cancellation performance caused by fiber dispersion is avoided. Experimental analyses show that a single tone signal in a wide frequency range of 2–20 GHz can be cancelled over 60 dB. A broadband signal with bandwidth of 50 MHz in the C-band, X-band, and K-band can be cancelled over 35 dB. Furthermore, the recovery performance of the signal of interest with different modulation formats and different signal to interference ratios is investigated, showing high quality signal transmission and efficient signal recovery. The capability of dispersion induced power fading compensation is also verified, and the spurious-free dynamic range is measured to be 88.47dB⋅Hz^2/3.

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity and harmonic frequency down-conversion function is proposed based on an integrated, dual-parallel, dual-drive Mach–Zehnder modulator (DP-DMZM). A dual-drive Mach–Zehnder modulator (DMZM) is used as an optical interference canceller, which cancels the self-interference from the impaired signal before fiber transmission to avoid the effect of fiber transmission on the cancellation performance. Another DMZM is used to provide carrier-suppressed, local-oscillation (LO)-modulated, high-order double optical sidebands for harmonic frequency down-conversion to release the strict demand for high-frequency LO sources. By regulating the DC bias of the main modulator, the signal of interest (SOI) can be down-converted to the intermediated frequency (IF) band after photoelectric conversion with improved frequency-conversion efficiency, immunity to the fiber-dispersion-induced power-fading (DIPF) effect, and effective signal recovery. Theoretical analyses and simulation results show that the desired SOI in the X and K bands with a bandwidth of 500 MHz and different modulation formats can be down-converted to the IF frequency. The self-interference noise with the 2 GHz bandwidth is canceled, and successful signal recovery is achieved after a 10 km fiber transmission. The recovery performance of down-converted signals and the self-interference cancellation depth under different interference-to-signal ratios (ISRs) is also investigated. In addition, the compensation performance of DIPF is verified, and a 6 dB improvement in frequency conversion gain is obtained compared with previous work. The proposed scheme is compact, cost-effective, and thus superior in wideband self-interference cancellation, long-range signal transmission, and effective recovery of weak desired signals.

In this paper, a photonic-enabled image rejection mixer (IRM) that features an ultrawideband self-interference cancellation (SIC) function and a compact configuration is proposed. The parameter tuning of SIC is realized in an optical domain, which avoids the use of electrically tuned devices with limited bandwidth and precision, so that high-precision parameter matching can be realized in the optical domain to realize deep and ultrawideband SIC. The key point of image rejection (IR) is to construct a pair of orthogonal local oscillation (LO) signals through DC-bias-induced phase shift. This not only avoids a high-frequency electrical 90-degree hybrid coupler (HC) applied in the traditional Hartley structure, but also compensates the phase deviation in the electrical intermediate frequency (IF) 90-degree HC flexibly, ensuring wideband and deep IR operation. The simulation results show that the proposed IRM can achieve ultrawideband SIC and IR with the simultaneous high-efficiency recovery of useful signals. They also verify that the scheme has good resistance to strong interference, and can cope with the phase imbalance of the IF 90-degree electrical HC, ensuring the good performance of the system, which has a wide application prospect in various in-band full-duplex (IBFD) systems.

A novel photonics-assisted technique for generating reconfigurable frequency hopping (FH) signals is proposed and demonstrated through optical comb filtering (OCF). The arithmetic progression of frequency difference between OCF passbands and optical frequency comb lines is exploited to enable wavelength selection controlled by an intermediate frequency signal, with ultra-wideband FH signals subsequently being generated through optical heterodyning. Comprehensive theoretical and numerical investigations are conducted, demonstrating the successful generation of diverse FH waveforms including 5-, 10-, and 25-level stepped frequency signals, Costas-coded patterns, as well as complex wideband signals such as 30 GHz linear frequency modulated and 24 GHz sinusoidal chirped waveforms. Critical system considerations including laser frequency stability, FH speed, and parameter optimization are examined. Wide tunable bandwidth exceeding 30 GHz, good stability, and inherent compatibility with photonic integration is achieved, showing significant potential for advanced applications in cognitive radio and modern radar systems where high-performance frequency-agile signal generation is required.