Multiband LFM waveform generation and band-selection using stimulated Brillouin scattering.

Modern radar systems are designed to simultaneously serve multiple applications such as ranging, surveillance, imaging, or warfare, which necessitates operation at multiple carrier frequencies. Linear frequency modulated (LFM) signals are inherently capable of pulse compression leading to enhanced range resolution and good signal-to-noise ratios; therefore, they are widely employed in various radar applications. In this paper, a photonic-based generation scheme for carrier frequency multiplication of LFM waveforms up to a factor of four through a single dual-drive Mach-Zehnder modulator is proposed and experimentally demonstrated. The technique is employed to produce multiband LFM having wide-bandwidth chirps (500 MHz, 1 GHz) as well as narrow bandwidth chirps (10, 20 MHz) that are compatible with the intrinsic linewidth of stimulated Brillouin scattering (SBS). The frequency bands of the narrow bandwidth chirps are further selected through a frequency-agile Brillouin RF filter. The generated tupled chirped waveforms are at continuous multiples of the RF carrier frequency at 2, 4, 6, and 8 GHz, respectively, with the first three multiples having 10 MHz and the fourth multiple having 20 MHz chirp bandwidth. This scheme is also experimentally verified for generating different tupled products and respective filtering through SBS at multiples of 4 GHz up to 16 GHz, thereby verifying the system's agility and flexibility.

Energy-efficient bandwidth enhancement of Brillouin microwave photonic bandpass filters.

Stimulated Brillouin scattering has been widely utilized to realize frequency-agile narrowband and wideband microwave photonic bandpass filters by primarily utilizing its gain response. However, most demonstrated wideband Brillouin-based filters are limited in operation due to the high-power requirements for bandwidth tailoring. We propose a novel approach to realize wideband reconfigurable, Brillouin-based microwave photonic bandpass filters employing RF interferometry and advanced phase engineering. Demonstrated filters exhibit >20 dB selectivity and >700 MHz bandwidth using only 8 dB peak SBS gain (of intrinsic linewidth 30 MHz), and total optical pump power of only ∼14 dBm. We also demonstrate frequency tunability up to 22 GHz. The filter passband has a very flat and highly linear phase response, thus exhibiting zero group delay which we have experimentally verified by propagating an RF pulse at 10.25 GHz. Furthermore, the filter does not suffer from added Brillouin noise in the passband, which is a major advance compared to conventional Brillouin-based microwave photonic sub-systems. This paper presents simulations, mathematical analysis, and experimental results of the proposed filter. The proposed filter demonstrates a pathway toward power-efficient Brillouin-based microwave photonic filters, utilizing SBS responses, in combination with phase manipulation for advanced filtering operations.