Photon Netw Commun DOI 10.1007/s11107-016-0683-7 ORIGINAL PAPER Multi-mode interference-based photonic crystal logic gates with simple structure and improved contrast ratio Enaul haq Shaik 1 · Nakkeeran Rangaswamy 1 Received: 28 September 2016 / Accepted: 24 December 2016 © Springer Science+Business Media New York 2017 Abstract We present a MMI-based photonic crystal all- optical logic gate structure for logic functions such as XNOR, XOR, OR and NAND with square-type lattice of Si rods in air host. Phase-based logic inputs produce intensity-based logic outputs with high contrast ratio. The calculated ON to OFF contrast ratio for the logic functions XNOR/XOR and OR/NAND is 40.41 and 37.40 dB, respectively. Fur- ther, it is improved by 11.53 and 12.46% for XNOR/XOR and OR/NAND logic functions, respectively, by reducing the back reﬂection with the introduction of absorbing waveg- uides. The structure in both the forms has a fast response period that is less than or equal to 0.131 ps. The size of the structure is quite compact with dimension 6.4