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A novel method, to the best of our knowledge, of frequency upconversion with frequency quadrupling is presented and experimentally demonstrated. The scheme is based on an integrated polarization-division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) and an intensity modulator (IM). Polarization-multiplexed second-order sidebands are obtained by properly adjusting the bias voltage of the PDM-DPMZM. By adjusting the polarization controller, the +2-order sideband is aligned with the IM's slow axis to be modulated by the intermediate frequency (IF) signal, and the -2-order sideband is aligned with the IM's fast axis with a much lower modulation efficiency. An upconverted signal with frequency quadrupling is generated at the photodetector. The experiment result shows that the working bandwidth range is 6-40 GHz, the spur suppression ratio of the upconverted signals is 37.5 dB, and the conversion efficiency is -32 dB. 100 MSym/s quadrature phase shift keying (QPSK) or a 16QAM signal at 26 GHz is generated using a 6 GHz local oscillator signal and transmitted through 25 km SMF.

A novel microwave waveform generator based on a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator is proposed and experimentally demonstrated in this paper. The X-QPSK modulator is modulated by a local oscillator signal. For XI Mach-Zehnder modulator (MZM), odd sidebands are eliminated; for XQ-MZM, even sidebands are eliminated, while the Y-QPSK modulator is not modulated. Triangular or square waveforms can be generated by biasing the X-QPSK and adjusting the polarization controller properly. 3 GHz and 6 GHz triangular and square waveforms are successfully generated by experiment. The scheme does not need a high modulation index (m=1.25 in this paper). In addition, it features low cost and a simple structure without a filter or phase shifter.

The zero-lag correlation properties of intensity chaos in ring networks consisting of three semiconductor lasers mutually coupled with heterogeneous time delays are numerically investigated. The role of heterogeneous coupling delays with specific ratios on the zero-lag chaotic intensity correlation is revealed, and the effects of coupling rate, frequency detuning, and time delay heterogeneity are also considered. Furthermore, by introducing imaginary nodes to map the heterogeneous ring network to equivalent the homogeneous (EHM) ring network with identical delay, the relationship between such zero-lag correlation properties of intensity chaos and the greatest common divisor (GCD) of the EHM ring network loop length is revealed. It is shown that, when the coupling rate is sufficiently large, two types of zero-lag synchrony patterns, zero-lag global synchrony and zero-lag cluster synchrony, can be found in the same ring network, depending on the GCD of the delay loops composing the network. That is to say, by carefully adjusting the coupling delays ratio one can deliberately switch between two different zero-lag synchrony patterns in the same laser ring network, which may be interesting for the field of chaos synchronization. High-quality synchronization can be obtained in wide range of coupling rate, and is robust to small frequency detuning and slight mismatched internal laser parameters. The dependence of zero-lag synchronization of intensity chaos may provide useful guidelines for designing multi-user chaos optical communication among ring networks.

Photonic generation of microwave waveforms is currently an interesting topic due to the advantages of large bandwidth and immunity to electromagnetic interference. In this paper, a photonic microwave waveform generator with tunable waveforms and repetition rates is proposed and experimentally demonstrated. A continuous-wave (CW) light is phase modulated by a local oscillator (LO) signal to generate optical sidebands. By locating the phase modulator (PM) in a Sagnac loop, we can control the intensity and phase of the carrier of the phase modulated signal. Then a compact tunable dispersion compensation module is used to introduce phase shifts to the optical sidebands. Thanks to the flexible controlling of the optical signal, the generation of microwave waveforms with tunable shapes and repetition rates can be realized. In the demonstration experiment, full-duty-cycle triangular and square waveforms with repetition rates of 5 and 10 GHz (bandwidths of 15 and 30 GHz) are successfully generated, respectively. The bandwidths are expected to be improved to above 120 GHz if larger-bandwidth measurement instruments are used. In addition to the flexible tunability, the proposed scheme also features the advantages of easy implementation and free from bias drift.