Programmable long-period grating in a liquid core optical fiber.

A programmable fiber long-period grating (LPG) is experimentally demonstrated in a liquid core optical fiber with a low insertion loss. The LPG is dynamically formed by a temperature gradient in real time through a micro-heater array. The transmission spectrum of the LPG can be completely reconfigured by digitally changing the grating period, index contrast, length, and design. The phase shift inside the LPG can also be readily defined to enable advanced spectrum shaping. Owing to the high thermo-optic coefficient of the liquid core, it is possible to achieve high coupling efficiencies with driving powers as low as a few tens of milliwatts. The proposed thermo-programmable device provides a potential design solution for dynamic all-fiber optics components.