Efficient photonics beam forming system incorporating super structure fiber Bragg grating for application in Ku band

Abstract

We propose and demonstrate a photonic true-time delay beamforming system for a 1 × 4 linear phased array antenna, operating in the Ku-band, based on superstructured fiber Bragg gratings (SFBGs) with linearly rising equivalent chirps. The proposed beam-forming network operates at 18 GHz frequency, which is theoretically analyzed and simplified by simulated results. The SFBG has a distinct number of gratings in each beamforming path, which provides a large and progressive phase delay. The advantage of the proposed technique can be found in terms of its wavelength tunable scheme making the system squint-free. The proposed architecture is a true time delay optical beam forming a network, which enables squint-free beam steering of radio frequency (RF) signals. In this study, a technique known as double sideband modulation of multiple wavelengths is utilized to investigate the reflection quality of SFBG at various chirp rates. Taking into account that each segment of FBG consists of 50, 60, 70, and 80 gratings and phase shift section samples of each segment, the overall length of the SFBGs is calculated to be 2 cm, 2.4 cm, 2.8 cm, 3.2 cm, respectively, are used for calculating group delay. An equation in a closed form representing the corresponding dispersion is derived. SFBG group delay response is analyzed theoretically with required simulation to investigate the reflectance characteristics. All simulation work for designing the beam forming system is done on Optisystem version 19 and designing of Super structure fiber Bragg grating Optigrating version 4.2. The optically process wavelengths are detected by high speed dedicated photo-detector (PD) and delay response is investigated through array factor of each antenna. Errors in the fabricated SFBGs' group delay responses are examined also.