Abstract
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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> RIU scale. The self-photoheating could be realized by 980 nm pump absorption and non-radiative 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 °C increase of the device in the air, 8 °C in the ethanol, and 4 °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.
Highlights
Optical fiber sensors for the determination of ambient refractive index (RI) have attracted increasing attention due to their capability in mediating bio-chemo molecular reactions [1]–[3]
We demonstrate a microfiber Bragg grating as the reflective refractometer with the function of self-photoheating
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
Summary
Optical fiber sensors for the determination of ambient refractive index (RI) have attracted increasing attention due to their capability in mediating bio-chemo molecular reactions [1]–[3]. Bragg grating in the microfiber (μFBG) adds features of reflective signal operation, compactness, narrow bandwidth signal, and wavelength multiplexing, facilitating the fabrication of miniature fiber detectors and establishment of bio/chemical sensing network [9], [10]. Erbium-ytterbium (Er/Yb) co-doped optical fiber allows the effective pump absorption derived from the high-density clusters of ytterbium ions and a large portion of the non-radiative transition that originates from the erbium ions, providing excellent opportunity in developing the intracore self-heated fiber Bragg grating device [28]. The flame taper method, that is, the current workhorse for the fabrication of microfiber, is inadequate because minimizing fiber core may lead to the dissipation of the active dopants, which would reduce the pump adsorption and rate of photo-thermal conversion [29], [30]. The pump switch test shows that the heater could respond to the on and off instantaneously, enabling the dynamic self-heat governing capability, which may motivate the accelerative biosensing and volatile chemical solution treatment
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