Integrated optical beam-forming network based on silicon arrayed waveguide grating

In this study, an integrated optical beam-forming network (OBFN) with multiple channel optical true time delay lines (OTTDLs) based on silicon-on-insulator (SOI) platform is designed and fabricated. The optical carriers in C-band are with a frequency space of 100 GHz and designed to meet the ITU standard. 1×32 arrayed waveguide grating (AWG) is applied to achieve dense wavelength division multiplexing(DWDM). The OTTDLs are single-mode strip waveguide for TE mode. The nominal delay step between the OTTDLs is 21 ps. To achieve a compact footprint and low loss photonics circuit, spiral routing strategy and Euler bendings are employed. The insertion loss of such waveguide is estimated to be 1.5 dB/cm. A Mach-Zehnder interferometer (MZI) based variable optical attenuator (VOA) array is designed in order to adjust the uniformity of optical power in each OTTDL, which can employ an attenuation of more than 30 dB. Due to the wavelength dependent loss of the grating coupler, AWG, and prapagation loss difference of OTTDLs, the output spectrum shows that the optical power fluctuation is less than ±2 dB before VOA tuning. The group delay is examined by a microwave transmission response measurement in the frequency range of 6∼18 GHz, which is derived from the frequency derivative of the phase. The average delay step of 21.3 ps is achieved, and no significant fluctuation of group delay among such frequency range. It denotes the broadband feature of OBFN, which is promising for application in microwave photonics (MWP) radar and other related scenarios.