<p>We propose a photonic approach to generate triangular waveforms based on nonlinear polarization rotation (NPR) effect in a highly nonlinear fiber. A continuous wave probe light is polarization rotated by an intensity-modulated control light through the NPR effect. By tuning the cascaded polarization controller, the undesired second-order harmonic is well suppressed after photodetection. A 90-deg hybrid coupler is used to compensate the phase mismatch between the fundamental and third-order harmonic components, so that triangular waveforms are generated successfully. The proposed approach is theoretically analyzed and experimentally verified. Triangular waveforms at repetition rates of 3, 4, and 5 GHz with full-duty cycle are experimentally generated.</p>
In modern radar system, pulse compression technique has been widely used to increase the detection distance and range resolution. To enlarge the pulse compression ratio, the microwave signals are often phase modulated, such as phase-coded or frequency chirped. Conventionally, the phase-modulated microwave signals generated by electrical methods suffer from low microwave carrier frequency, limited bandwidth, low data rate and high transmission loss. Photonic-assisted generation and transmission of phase-modulated signals is a promising candidate to overcome these limitations In this paper, we review our recent works about the photonic generation and transmission of phase-modulated microwave signals, including the simultaneously frequency up-conversion and phase-coding, background-free frequency-doubled phase-coded microwave signal generation, phase-coded microwave pulse generator by optoelectronic oscillation (OEO), as well as transmission of dual-chirped microwave signals with chromatic-dispersion-induced power fading (CDIP) compensation and elimination technology. These works represent the new progresses in photonic approaches to generate and transmit phase-modulated microwave signals, which has great potential in the modern radar system.