An optical approach to generating chirped microwave signal using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response is proposed and demonstrated. In this scheme, a narrow band Gaussian pulse is used as the original signal. In order to eliminate the need for a wideband original microwave chirped-free signal, a mixer and a radio frequency signal are used to up-convert the spectrum of the original signal and the dispersion curve is tuned to minimize the attenuation caused by the fiber dispersion. Then the required frequency response can be reconstructed by a nonuniformly spaced PMDLF. Since the majority of the power of the original signal can bypass the filter, the power of the generated chirped microwave signal will be increased. A reconstruction example of a desired frequency response with a central frequency of 10 GHz is provided, and the generation of the corresponding chirped microwave signal is demonstrated by numerical simulations.
Realization of a wideband tunable optoelectronic oscillator based on a chirped Mach–Zehnder modulator (MZM) and a chirped fiber Bragg grating is proposed and demonstrated. By simply adjusting the direct-current bias of the chirped MZM, the frequency of the oscillating signal is tuned. A theoretical model is established, then verified by an experiment. A high-purity microwave signal with a tunable frequency from 5.8 to 11.8 GHz is generated. The single-sideband phase noise of the generated signal is −112.6 dBc/Hz at a frequency offset of 10 kHz.
A wideband tunable filter with a complex coefficient is proposed and demonstrated. The output of a polarization modulator is filtered by the optical bandpass filter, an optical single sideband modulation will be generated. When it passes through a polarization controller and a polarizer, a complex coefficient will be achieved by tuning the angle of the polarization controller before the polarizer, and the real coefficients are controlled by the optical power of the lasers. As the real coefficients and complex coefficient can be tuned, a two-taps incoherent photonic microwave filter with a tunable range over the entire full free spectral range is realized by adjusting the polarization angle from −90 deg to 90 deg while the shape of filter remains unchanged.
A novel method to measure the fiber length based on optoelectronic oscillator is firstly proposed in the experiment, showing that an optoelectronic oscillator can be used for measuring the fiber length by detecting the space of the oscillation frequency. The shorter the fiber is, the more precisely it can be measured.
An all-optical realization of a two-tap complex-coefficient microwave photonic filter, working under incoherent mode, is proposed and demonstrated. The complex coefficient is realized by simply adjusting the bias voltage applied to the dual-electrode Mach–Zehnder modulator. The real coefficient is controlled by adjusting the power of the two taps. As a result, the frequency response of the filter can be continuously tuned, over a full free spectral range, without changing the shape of the filter.