High common mode rejection ratio InP 90° optical hybrid in ultra-broadband at 60 nm with deep-rigded waveguide based on × 4 MMI coupler

Lu Zi-Qing^{1, 2}, Han Qin^{1, 2, 3, †}, Ye Han^{1, 2}, Wang Shuai^{1, 2}, Xiao Feng^{1, 2}, Xiao Fan^{1, 2}

(a) Measurement instrument and (b) coupling system for testing performance of fabricated 90° hybrid.