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An alignment-free fiber-coupled microsphere resonator for gas sensing applications
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) 50 and polystyrene spheres on cover slide substrate acting as a resonator reservoir. (b) Top and front (horizontal) view of a sphere attached to the fiber tip probe using a 45° mirror as indicated in (d). (c) sphere just attached to the taper. (e) Two spheres of different diameter are coupled to the same taper. The magnification of the individual images can be estimated by the known size of the spheres. The taper diameter is .

Image of FIG. 2.
FIG. 2.

Experimental setup consisting of the optical components for measuring resonance shifts in the microresonator, the enclosures for the taper-coupled microsphere, and the gas mixing and delivery system.

Image of FIG. 3.
FIG. 3.

(a) shows the transmission signals of the Rb gas cell, of the taper-coupled microresonator system (polystyrene sphere of diameter , taper diameter ), and of the plane-plane Fabry–Pérot interferometer measured by photodiodes. (b) shows the position of the resonance (upper curve) as the temperature of the copper enclosing is changed incrementally (lower curve). (c) shows a plot of set temperature vs induced resonance position. A linear fit is used to estimate the coefficient to be for a coupled power of . At this power level the pump does not induce a measurable heating of the sphere. Points scattered off the fitted line indicate the approach toward a steady state temperature after the incremental increase (decrease) in the temperature at the copper heater.

Image of FIG. 4.
FIG. 4.

(a) shows resonance shifts induced by laser heating for volume mixtures of helium and argon as indicated. The indicated pump power is the power in the taper taking coupling and transmission losses into account. The solid lines are fits of the form . The nonlinearity arises from a temperature dependent shift in the absorption spectrum as discussed in Ref. 12 . The temperature scale is calculated based on a shift of 3.8 GHz/K. (b) is proportional to thermal conductivity and is plotted for the different gas mixtures. The solid line corresponds to the measured thermal conductivities at and 1 bar according to Ref. 26 .


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Scitation: An alignment-free fiber-coupled microsphere resonator for gas sensing applications