Abstract
Pulse compression processing based on stimulated Brillouin scattering (SBS) in an optical fiber is theoretically and experimentally demonstrated. Broadband microwave signal is electro-optically modulated onto the pump lightwave that is launched into one end of the fiber. Acoustic wave in the fiber inherits the amplitude and phase information of the pump lightwave and thus the coupling between the acoustic wave and pump lightwave leads to the auto-correlated process of the pump lightwave as well as the modulated microwave signal. Derivation of the SBS coupling equations shows that the short-pulse probe lightwave amplified by the pump lightwave possesses the nature of auto-correlation formula. All-optical pulse compression of the broadband microwave signal is implemented after a subtraction between the detected probe pulse with and without SBS. A proof-of-concept experiment is carried out. The pulse compression of a linear frequency-modulated microwave signal with 1 GHz sweep range at the carrier frequency of 4.3 GHz is successfully realized, which well matches the theoretical analysis.
Highlights
Pulse compression raised up in 1960s is a key signal processing technique to realize better spatial resolution and higher signal-to-noise ratio in the radar field [1]
As a proof-of-concept experimental verification, the pump lightwave is modulated by an linear frequency modulated (LFM) pulse which is generated via a voltage-controlled oscillator (VCO, Mini-circuits ZX955400-S+) and an RF amplifier (Mini-circuits ZX60-542LN-S+)
During the interaction between the pump lightwave and acoustic wave in the stimulated Brillouin scattering (SBS) process, the time delay and amplitude conjugation conditions for matched filtering are automatically satisfied. This is because the acoustic wave inherits the amplitude and phase information of the microwave signal that is modulated onto the pump lightwave
Summary
Pulse compression raised up in 1960s is a key signal processing technique to realize better spatial resolution and higher signal-to-noise ratio in the radar field [1]. The matched filtering process of the microwave signal for modern coherent radar application is always required after the digitization [1, 2]. It leads to a big challenge for analog-to-digital conversion (ADC) that should provide sufficient analogue bandwidth, ultra-high sampling rate, and great sampling resolution ( called the effective number of bits) [7]. The pulse compression is implemented by direct detection of the probe pulse with and without SBS, which is short in time and significantly reduces the difficulty of digital storage and signal processing. The range resolution of compressed LFM signal is 0.88 ns, which is in good agreement with the ideal auto-correlation of the LFM pulse
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