Cascaded Optical Fiber Sensor for Simultaneous Measurement of Ultraviolet Irradiance and Temperature

A new cascaded optical fiber sensor, which can measure Ultraviolet irradiance and Temperature simultaneously was designed and verified by experiment, which consists of an extrinsic Fabry-Perot interferometer (EFPI) with benzocyclobutene (BCB) and a few-mode fiber Mach Zehnder interferometer (MZI). By performing a Fourier transform and applying a frequency domain bandpass filter, the polymer-EFPI and few-mode fiber MZI spectra were separated from superimposed spectra of cascaded structure. The sensing characteristics of temperature and ultraviolet (UV) irradiance were tested and analyzed in detailed, respectively. By constructing a sensitivity matrix, the difference in sensitivity between MZI and EFPI can be used to make simultaneous measurements of temperature and UV irradiance. The UV irradiance and temperature sensitivities are 0.0039 nm/(mW/cm2) and 0.2021 nm/°C, respectively. In addition, the cascaded structure is insensitive to the change of ambient refractive index (RI), which can effectively avoid the cross-interference of RI. The new optical fiber sensor is more stable, requires a simpler manufacturing process and can be produced at lower cost when compared to existing sensors. The new optical fiber sensor can also be applied to multi-parameter applications, reducing the complexity of the deployed system.