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A novel structure consisting of an idler-free microwave photonic mixer integrated with a widely tunable and highly selective microwave photonic filter is presented, which is comprised of a spectrum-sliced broadband optical source, a dual-parallel Mach–Zehnder modulator (DPMZM), and a spatial light amplitude and phase processor (SLAPP). By adjusting the optical phase shift in the DPMZM, the dispersion-induced mixing power fading can be eliminated. By applying a phase processor with the SLAPP, the distortion of the mixing filter brought upon by third-order dispersion is also compensated. Experiments are performed and show that the up/down-conversion signal has a clean spectrum and the mixing filter can be tuned from 12 to 20 GHz without any change to the passband shape. The out-of-band suppression ratio of the mixing filter is more than 40 dB, and the 3 dB bandwidth is 140 MHz.

A system for generating radio frequency signals with orbital angular momentum (OAM) is proposed and certificated for the first time, which employs an array of multiple optical-true-time-delay elements and circular antennas array (CAAs). A constructive Fourier series theory about CAAs collectively forming an OAM radio beam is demonstrated. An optical spectrum processor offers the four lines high-resolution time delay by adding a series of linear optical phase shifts. The OAM radio beam with topological charge L=1 is produced and measured successfully.

We present a novel optical arbitrary waveform generation approach based on pair-by-pair pulse shaping. Based on the heterodyne between a pair of optical frequency combs with different repetition rates, the repetition rate of the generated signals can be flexibly tuned from MHz to GHz without changing the setup. The restriction of the spectral resolution of the optical spectrum processor is overcome by the pair-by-pair approach while the spectral resolution of the system can be improved to MHz by dual-comb heterodyne. Hyperfine control of a higher resolution spectrum at MHz is achieved, which benefits the generation of the ultrawideband signals.

We propose a novel structure of a photonic RF phase shifter based on the vector-sum principle. The optical signal with quadrature double-sideband modulation passes through a dual-output Mach–Zehnder interferometer (MZI), and the two outputs are differentially detected. Two phase-quadrature RF terms are generated, and their amplitudes can be controlled in a triangularly complementary way by changing the phase of the MZI. A full tuning range of 0°–360° at 14 GHz is demonstrated experimentally accompanied by nearly constant RF amplitude. The validity of using our scheme in all-optical RF phase modulation is also verified.

A technique for monitoring both the pulse carving misalignment and pi phase shift in a return-to-zero (RZ) differential phase-shift keying (DPSK) system based on a phase modulator is proposed and demonstrated. By monitoring the mean-power variation of a hybrid local oscillation lightwave with the modulated signal lightwave without any deliberated control, the technique can provide the information on pulse carving misalignment and phase modulation index simultaneously, as the power variation reflects the asymmetric distribution of RZ-DPSK in a signal constellation diagram. It is characterized as transparent to signal bit rate, central wavelength, and absolute power level. Both the simulation and experiment results show that more than +/- 15% bit duration misalignment and +/- 5% phase shift deviated from pi can be detected.

A new optical-frequency comb-based microwave photonic harmonic down-convertor with tunable and reconfigurable filtering is proposed and experimentally demonstrated. The coherent evenly spaced optical carriers offer harmonic down-conversion for ultrahigh radio frequency signals with low-frequency local oscillator, and construct a tunable and reconfigurable bandpass filter for the intermediate-frequency (IF) signal combined with dispersion. This implementation features high conversion efficiency. Experimental results show the filtered output IF signal has a clean spectrum with high quality. Measured conversion loss is 8.3 dB without extra electrical amplification.

True time-delay line with a high resolution and wide range is proposed and demonstrated. Tunable lasers and dispersion fibers are employed to control the time delay coarsely. An optical spectrum processor is utilized to realize high-resolution time-delay control by adding a quadratic optical phase shift, which compensates the group velocity dispersion of the fiber simultaneously. A coarse tuning range of 1717 ps is realized by changing the wavelength of the optical carrier, and a high resolution of 0.67 ps is achieved by translating the symmetry axis of the quadratic phase shift.

The M² factor could be decomposed as amplitude term and phase term. A method to improve the beam quality of laser beams is proposed. In our method, the amplitude and phase of a laser beam are both compensated in order to improve the beam quality completely. In experiment, a laser amplifier is set to modulate the amplitude to Gaussian type, and a deformable mirror is used to compensate the phase aberration. The laser beam is well compensated by our method; the beam quality factor of the laser is improved from 1.7 to 1.1.

A phase adjustment technique employing optical spectrum processing is proposed to suppress the dispersion induced phase noise (PN) in optically generated millimeter-wave (MMW) and fiber transmission. A phase shift between the two beating optical tones in an optical MMW link is introduced by an optical spectrum processor (OSP) to compensate the phase mismatch between them, which results from fiber dispersion and deteriorates the PN of optically generated MMW signals. A MMW PN amelioration of 12.63 dB at 10 kHz offset and 11.23 dB at 100 kHz offset is achieved in a 40 GHz, 25 km optical MMW link thanks to this OSP.

We propose a system that can perform microwave bandpass filtering and phase shifting simultaneously without redundant optical-electrical and electrical-optical conversions. The principle is based on polarization-dependant phase modulation of a broadband optical source and the variable optical carrier time shift method. A single-bandpass microwave photonic filter with a central frequency of 10.8 GHz, a 3-dB bandwidth of 670 MHz, and a 360° phase tuning range is experimentally demonstrated. The capability of our configuration to implement wideband phase shifters is also verified.

A novel 2N bit bipolar photonic digital-to-analog converter (PDAC) scenario based on the optical differential quadrature phase shift keying (ODQPSK) modulation coupled with differential detection is proposed. Compared with other proposed schemes, this bipolar PDAC has a greater dynamic range and a larger noise margin with good scalabilities both in speed and resolution. We demonstrate a 4 bit PDAC in a proof-of-principle experiment at a sampling rate of 2.5 GS/s.

A method of all-optical microwave mixing and bandpass filtering is proposed to achieve idler-free RF frequency conversion based on cascaded phase modulation of a broadband optical source. The variable optical carrier time-shift method is employed to selectively generate the desired RF mixing components and highly suppress the other idler frequencies. An experimental system that can perform idler-free fundamental and harmonic RF upconversions is demonstrated, and the conversion efficiency is investigated both theoretically and experimentally.

A postcompensation technique for nonlinearity of a Mach-Zehnder modulator in a radio-over-fiber (ROF) system is proposed and experimentally demonstrated based on second-order optical sideband processing and optical carrier band attenuation. The phase of the second-order optical sideband is shifted to suppress the third-order intermodulation distortion (IMD3) in a direct detection ROF link. The optical carrier band is attenuated to make two kinds of origins of IMD3 have equal intensity and cancel each other out. A spurious-free dynamic range of 124.8 dB·Hz(2/3) is achieved, which is about 25 dB more than that without compensation.

A Mach-Zehnder structure with modulation in one arm and dispersive time delay in the other is proposed to implement highly flexible single-bandpass chirped microwave photonic filters based on broadband optical sources. Both the amplitude response and the time delay slope can be fully reconfigured via control of the optical spectra and dispersion. The passband can also be widely tuned without changing the shape. A chirped filter with a bandwidth of ∼4 GHz, a delay slope of ∼-0.6 ns/GHz, and a tunability up to 40 GHz is demonstrated experimentally.

We propose what we believe to be a novel method to generate optical millimeter-wave signals with frequency quadrupling using two cascaded Mach-Zehnder modulators (MZMs). Both theoretical analysis and experimental demonstration are presented. By symmetrically biasing the MZMs, without any optical filters or electrical devices, a high-quality millimeter wave at 40 GHz with an optical harmonic distortion suppression ratio of more than 25 dB is obtained. Furthermore, it is also proved to be valid that the proposed scheme is insensitive to the MZM bias drift, which demonstrates a relatively higher stability.

By employing the self-modulation birefringence difference in a semiconductor optical amplifier (SOA), an improved method is proposed to generate a complete optical single-sideband (OSSB) signal. Over 30 dB sideband suppression ratios (SSRs) of lower OSSB signals are obtained over a 12 dB input power range and a 36 nm wavelength span, with a maximum of over 35 dB. Upper OSSB signals with an SSR of over 15 dB are observed using a SOA for what is believed to be the first time. This method is effective even for the carrier-suppressed signal. The theory for OSSB generation in an SOA is extended and verified by experiment.

A means to achieve all-optical broadband demodulation of subcarrier back into digital data in an upstream link of a millimeter-wave radio over fiber (RoF) system is proposed and demonstrated experimentally. In the central station, the subcarrier from the base station of RoF system can be demodulated in the optical domain directly, without any millimeter-wave electronic device. Using this approach, the rf power degradation can be avoided even when the base stations in systems employ the conventional simple double-sideband modulation. Therefore, an inexpensive and simple configuration of the uplink for broadband signal receiving can be realized.

An optical modulator that provides broadband phase modulation of microwave subcarriers directly in the photonic domain has been proposed. This modulator, which involves no millimeter-wave device, can provide a dispersion-tolerant output signal with arbitrary phase shift. Therefore it has wide applications in high-frequency radio over fiber systems employing complex constellation modulation. Simulations and a proof-of-concept experiment demonstrate the feasibility of the modulator.

We propose a novel implementation of true-time delay (TTD) using air-guiding photonic bandgap fibers (PBGFs) and a broadband light source. The air-guiding PBGFs are experimentally studied and used in the TTD module for the first time, to the best of our knowledge. The proposed approach shows the advantages of simple architecture, compact size, larger dispersion, low-temperature sensitivity, and high immunity to nonlinear effects in our experiments. The PBGFs were spliced with single-mode fibers with a 2 dB loss, and the characteristics of the PBGFs were measured. The PBGF-TTD with a continuously tunable time delays from 0 to 500 ps was demonstrated using the amplified spontaneous emission light of an erbium-doped filter amplifier as a broadband light source.