Tunable coupler based on thermally poled twin-core fiber (TCF) with a hole-core-core-hole configuration was proposed in this letter. The thermal poling process therein was investigated based on the 2-D charge dynamics model. Effective χ(2) in the twin-cores pointing toward opposite directions were introduced. By subjecting the poled TCF to modulating voltage, the tunability of coupling ratio between the twin-cores was investigated.
The results indicate that the coupling characteristics of thermally poled twin-cores could be controlled flexibly by modulating voltage, and consequently achieving a stable and highly compacted electrically tunable TCF coupler.