# Silicon Ribbon-Based Dual-Beam Optical Phased Array with Low Crosstalk and Large FoV
## 4 Summary and Discussion  
We propose an OPA structure built on an SOI chip using a waveguide array with varying line widths below the half-wavelength spacing. An SR grating array is then implemented between the chirped FBG emitting arrays for crosstalk reduction. Finally, the OPA with bi-directional emitters demonstrates a large FoV and low crosstalk. The FDTD is used to simulate a 32-channel OPA by adding an SR grating array between grating antennas at a distance of 600 nm. The mutual phase effect is diminished and effectively increases the OPA FoV in the \(\Phi\) direction to 95 degrees. The crosstalk reduction also reduces the side lobe of the spot by about 10 dB and makes the beam more focused, increasing the overall beam intensity by 6 dB. This study also demonstrates various fishbone grating line widths to form linear optical-power radiation to cause the effective length of the grating antenna to approximate the physical size. The FWHM in the theta vertical direction can be reduced and reaches about 0.24 degrees. The OPA can be directed to two input grating antennas for two spots in the \(\theta\) direction for this symmetric grating design. Then, by adjusting the input wavelength from 1510 nm to 1600 nm, the FoV in the \(\theta\) direction can achieve 30 degrees. In the future, the chirped FBG built with SR grating in the wavelengths from 1450 nm to 1600 nm can be designed to improve the steering angle further and increase the antenna channel number to reduce the FWHM in the \(\Phi\) direction more effectively. The advantages of the single beam system are its simple construction and ease of operation in phase control. Its disadvantages are its small FoV. On the other hand, the benefit of the dual-beam system is its large FoV, which is almost two times larger than a single beam. Its disadvantages are the complicated phase control and an additional optical switch, which will steer the dual beams in sequence for free interference. The dual vertical beams pass through the antenna array of a bi-directional fishbone grating, and the zero-degree top light steers to \(\pm\theta\) angles, respectively, for emitting. Since there is no crossing steer angle, an optical switch will be implemented to allow steering for only one side angle beam for reflection distinguishment and free interference. The contributions are as follows: conceptualization, S.-H.H. and C.-C.C. ; methodology, H.-Y.C. ; software, H.-Y.C. ; validation, W.H. and H.L. ; formal analysis, H.-Y.C. ; investigation, W.H. and H.L. ; resources, S.-H.H. ; data curation, W.H. ; writing--original draft preparation, H.-Y.C. and S.-H.H. ; writing--review and editing, S.-H.H. ; visualization, C.-C.C. ; supervision, S.-H.H. ; project administration, S.-H.H. ; funding acquisition, S.-H.H. and C.-C.C. All authors have read and agreed to the published version of the manuscript. This research was supported by the Ministry of Science and Technology, grant number 108-2218-E-011-009, the joint research program from National Taiwan University of Science and Technology/Taipei Medical University (TMU-NTUST-108-10), and the chip fabrication service from Taiwan Semiconductor Research Institute (TSRI). Not applicable.