Rare Earth-Doped Microfiber Bragg Grating Refractive Index Sensor With Self-Photothermal Manipulation

We demonstrate a microfiber Bragg grating as the reflective refractometer with the function of self-photoheating. The rare earth-doped fiber provides not only the photosensitivity to the UV modulation but also the effective pump laser absorption and photoheating conversion. The rare earth-doped microfiber Bragg grating, which is cladding-removed by the hydrofluoric acid, can detect the tiny refractive index change with a resolution of 10(-4) RIU scale. The self-photoheating could be realized by 980 nm pump absorption and nonradiative transition process of the ytterbium and erbium ions, which are well-preserved by the core structure after etching. Monitored by the reflective grating signal, the photoheating can manipulate 30 degrees C increase of the device in the air, 8 degrees C in the ethanol, and 4 degrees C in the water. The second time-scale heating/cooling response allows the sensor to act as ad optical switch for engineering temperature. The work may open a new route for accelerative biosensing and pollutant determination and treatment.