Photonic crystal fibre based modal interferometer with four-beam path interference

In recent years, photonic crystal fibre based modal interferometers have been widely investigated. Owing to the nature of Mach-Zenhder-like interference, the sensing range is limited by the sinusoidal spectrum´s period. A splicing approach is proposed and demonstrated to achieve unique four-beam interference so that quadrupled sensing range is obtained without reduction in detection limit, which would be much desired in wide range refractive index, pressure and temperature sensing. As an example, a high-temperature sensor ranging from 28 to 484°C is demonstrated.