Photonic generation of a tunable multi-band linearly frequency-modulated waveform

A photonic-assisted tunable multi-band linearly frequency-modulated (LFM) waveform generator based on optical heterodyne detection is proposed and experimentally demonstrated. The multi-band LFM waveform is generated from a photodetector (PD), where a broadband LFM optical pulse and a multi-wavelength optical signal with the same magnitude at different wavelengths are heterodyne-detected. The LFM optical pulse is generated from a three-electrode distributed Bragg reflector laser diode (DBR-LD). The multi-wavelength optical signal is produced through a Mach-Zehnder modulator (MZM), in which a light wave from an optical fiber laser (OFL) is nonlinearly intensity-modulated by a radio frequency (RF) signal. By tuning the wavelength of the LFM optical pulse lower than that of the multiwavelength optical signal, a multi-band LFM waveform is generated at the PD. The center frequency of the generated LFM waveform can be adjusted by manipulating the wavelength of the OFL. The versatility in the bandwidth and temporal duration of the LFM waveform is attained through the precise tuning of the LFM optical pulse. The tuning of the center frequency difference between frequency bands is performed by altering the frequency of the RF signal. Experimental results have corroborated the realization of a tunable multi-band LFM waveform generator. The bandwidth and temporal duration of each band and the center frequency difference between frequency bands have tuning ranges from 0.7 to 6.7 GHz, 1 to 50 mu s, and 2 to 6.7 GHz, respectively. The demonstration shows new avenues to implement high-performance multi-band LFM waveform generators for applications in multi-functional modern radar systems.