Stable wavelength tunable fiber ring laser for true-time delay system

Abstract

In this paper, we propose and experimentally demonstrate a novel wavelength tunable fiber ring laser source for a photonic beamforming system to control phased-array antenna. In this fabrication, a Sagnac loop composed of a polarization-maintaining (PM) coupler and a piece of high-birefringence (Hi-Bi) PM fiber is acted as a comb filter to make the frequency spacing equal. The wavelength of the output signal is controlled by the tunable filter outside the Sagnac loop. The intensities of the output signals with different wavelengths increased or decreased at the same frequency spacing are equal. A five-channel true-time delay system consisting of this tunable fiber source and five grating delay lines for discrete beamsteering has been demonstrated. In the experiment, the output signals of the tunable fiber ring with the equal frequency spacing have the same intensity of about 5.9 dBm and the same high signal to noise ratio (SNR) of 40 dB. If the tunable filter in this laser is replaced by a micro-electro-mechanical systems (MEMS) tunable filter, the speed of switching wavelength will increase rapidly.