Inverse-designed ultra-compact star-crossings based on PhC-like subwavelength structures

Inverse-designed star-crossings with 8 and 10 ports are proposed, with ultra-short coupling lengths of 5.28μm and 5.4μm respectively. Their measured ILs are less than 1.6dB and 2.4dB respectively over 60nm bandwidth centered 1550nm wavelength.