Precisely tunable multi-wavelength fiber laser source for phased array antenna

Abstract

Photonic true-time delay (TTD) beamforming has been considered as a promising technique for future wide-band phased array antenna systems. A TTD beamforming system based on a linear chirped fiber grating (LCFG) requires a tunable multi-wavelength laser source, in which the wavelengths are tuned simultaneously with equally increased or decreased wavelength spacing. We present a novel approach of a TTD laser source employing a DQPSK modulator and a highly nonlinear fiber (HNLF). The wavelength tuning is achieved by tuning the frequency of the radio frequency signal generator that drives the DQPSK modulator. Up to 41 lasing wavelengths with 0.08 nm spacing, 29 lasing wavelengths with 0.06 nm spacing and 31 lasing wavelengths with 0.12 nm spacing in 3 dB bandwidth were obtained. In theory, the multi-wavelengths can be simultaneously tuned from 10 MHz to 20 GHz in our experiments based on the fact that the frequency range of the RF signal source is from 10 MHz to 20 GHz and the bandwidth of DQPSK modulator is up to 22 GHz. The tuning precision of the RF signal generator is up to 1Hz and phase noise is about -104dBc/Hz. Therefore, the wavelengths can be tuned precisely and stably.