Optically Controlled Time-Delay Beamformer Employing Tunable Chirped Grating and a Sagnac Ring Based Multiwavelength Fiber Laser
Jianlang Yang and Zhaohua Guo
A new photonics true-time-delay system using a novel tunable chirped fiber grating delay line and a novel multi-wavelength erbium-doped fiber ring laser source based on a Sagnac filtering mirror is described. The Sagnac filtering mirror consists of a polarization maintaining directional coupler and two lengths of polarization maintaining fibers. The lasing wavelength and channel number are determined by properly adjusting the polarization controller within the unidirectional ring cavity and are both very stable. The tunable chirped fiber grating, which acts as a continuous time-delay element, is achieved by bending a uniform fiber Bragg grating bonded at a slant onto the lateral surface of a simply supported beam. By adjusting the chirp rate of the fiber grating via the bend strain, this type of tunable chirped fiber grating can achieve very low and adjustable delay times and therefore provides higher angle resolution for scanning microwave beams. The true-time-delay system using the proposed tunable chirped fiber grating delay element and multi-wavelength fiber ring laser has been constructed and demonstrated experimentally.