Realization of spectral tunable filter based on thermal effect in microfiber structure

• Microfiber Hybrid knot/interferometer structure.
• Spectral filtering based on resonance in the microfiber structure.
• Filter parameters tuning through thermal effect in an electrical wire through the micro-knot.

This paper demonstrates a new approach for tuning the extinction ratio of a complex microfiber structure output using thermal effect. The microfiber filter device comprises of a microfiber Mach–Zehnder interferometer followed a knot structure, where temperature is controlled by a DC current applied to a copper wire placed inside the knot. This enables electrical tuning, where applying electrical current increases the temperature and affects the optical path. The change of temperature facilitates the fine tuning of the resonance output spectrum. From the experiment, it was observed that the extinction ratio of the output comb spectrum can be controlled within 2 dB to 10 dB by varying the current rating from 0 A to 1.22 A.