Microwave waveforms, such as square waveforms, sawtooth waveforms and triangle waveforms are widely used in radar communication, electronic measurement and medical imaging and so on. Using photonic microwave technology to generate arbitrary microwave waveforms has been a research hotspot.
In this paper, a photonic microwave waveform generation scheme based on dual-wavelength time domain synthesis is proposed and experimentally demonstrated. Used in this scheme mainly are two lasers, two single-drive Mach-Zehnder modulators, a wavelength division multiplexer and a tunable optical delay line. The two Mach-Zehnder modulators are respectively biased at different operating points. When two beams with different wavelengths are superimposed in the time domain, different microwave waveform outputs can be generated. Therefore, by adjusting the bias voltage and modulation depth of the modulator, the phase and amplitude of the modulated optical signal can be controlled, and finally the photonic microwave waveform is generated.
At first, the generation mechanism of square waveform, sawtooth waveform and triangle waveform are analyzed, and the comparisons among ideal square waveform, sawtooth waveform, triangle waveform and their third-order waveforms are made through the simulation analysis. It is verified that third-order waveforms become close to the ideal waveforms. Since the proposed scheme produces higher-order components, and the waveforms of the first three orders are the same as the ideal waveforms, so the scheme has good waveform generation capability. And then square waveform, sawtooth waveform and triangle waveform with a repetition rate of 2.5 GHz are successfully generated experimentally. Thus, experimental results are well consistent with the theoretical analyses. In addition, the system also has good tunable characteristics. By changing the modulation frequency of the modulator, the frequency tuning of the output photonic microwave waveforms can be realized, and square waveform, sawtooth waveform and triangular waveform with a repetition rate of 5 GHz are also experimentally achieved. The repetition rate of the generated microwave waveform is mainly limited by the bandwidth of modulator and electrophotonic detector, so the devices with higher bandwidth can be used to generate arbitrary waveform with a higher repetition rate. Therefore, the scheme has good application prospects.
DownLoad:
