Demonstration of DC current sensing through Microfiber Knot Resonator

A compact current sensor is demonstrated using a Microfiber Knot Resonator (MKR) which is obtained by knotting silica microfiber fabricated from flame brush technique. With the assistance of a copper wire touching the circumference of the ring, resonant wavelength inside the MKR can be tuned by injecting electric current into the copper wire. The wavelength shift is due to the thermally induced optical phase shifts attributable to the heat produced by the flow of the current. It is shown experimentally that the wavelength shift is linearly proportional to square of the amount of current with a tuning slope of 90 pm/A². Compared to the previous work that place the copper in the loop of the MKR, this technique is simple, more sensitive and robust.