Tunable mode converter using electromagnet-induced long-period grating in two-mode fiber

• The fiber mode converter that is variable in conversion efficiency and wavelength.
• Electrically-controlling the mode conversion between the LP01 and LP11 core modes in a two-mode fiber.
• Conversion efficiency is tuned by the voltage applied to the electromagnet under the fiber.
• Phase-matching wavelength is tuned by expanding the nonmagnetic spring on the fiber.

We present an in-fiber mode converter that changes the propagation ratio of two core modes. A dynamic long-period grating is constructed in a two-mode fiber by the combination of an electromagnet with a nonmagnetic spring coiled around a stiff iron rod. The fundamental mode is converted to the LP11 mode according to the voltage applied on the electromagnet. The mode-conversion wavelength can be tuned by stretching the coil spring. Compared to the coupling result with leaky cladding modes, the mode-conversion bandwidth expands from 5 nm to 90 nm and the drive voltage decreases almost by half.