Optimized 2×2 3dB multi-mode interference coupler
An optimized SOI 2×2 multimode interference (MMI) coupler is designed by use of the particle swarm optimization (PSO) algorithm. Finite Difference Time Domain (FDTD) simulation shows that, within a footprint of 9.4×1.6 μm 2 , <0.1 dB power unbalance and <1 degree phase error are achieved across the entire C-band. The excess loss of the device is <0.2 dB.
1. A multi-mode interference (MMI) coupler, comprising:
a multi-mode interference (MMI) region including: a length L MMI between a first end and a second end; a central distance L MMI /2; and a plurality of segments having widths, at least five of said segment widths from the first end to the second end being different one from the other;
a plurality of first ports at the first end of the MMI region; and
a plurality of second ports at the second end of the MMI region;
wherein the second and fourth segment widths from the first end are greater than the third and fifth widths from the first end.
2. The MMI coupler according to claim 1 , wherein said segment widths vary in a symmetric pattern relative to the central distance L MMI /2 along said length.
3. The MMI coupler according to claim 1 , wherein said segment widths are at equally spaced locations along the length.
4. The MMI coupler according to claim 1 , wherein the plurality of first ports comprises two ports; and wherein the plurality of second ports comprises two ports.
5. The MMI coupler according to claim 4 , wherein said widths range from 1.439 μm to 1.6 μm.
6. The MMI coupler according to claim 4 , wherein the MMI region and the plurality of first and second ports are within a footprint of 9.4×1.6 μm 2 .
7. The MMI coupler according to claim 1 , wherein each of said ports is connected to said MMI region by a taper connector.
8. The MMI coupler according to claim 7 , wherein at least one taper connector is connected to an edge of the MMI region to smoothly transform input/output mode profiles.