Phone-sized whispering-gallery microresonator sensing system

Abstract

Abstract:We develop a compact whispering-gallery-mode (WGM) sensing system by integrating multiple components, including a tunable laser, a temperature controller, a function generator, an oscilloscope, a photodiode detector, and a testing computer, into a phone-sized embedded system. We demonstrate a thermal sensing experiment by using this portable system. Such a system successfully eliminates bulky measurement equipment required for characterizing optical resonators and will open up new avenues for practical sensing applications by using ultra-high Q WGM resonators. References and links1. K. J. Vahala, "Optical microcavities," Nature 424(6950), 839-846 (2003). Xiong, "Robust spot-packaged microsphere-taper coupling structure for in-line optical sensors," IEEE Photon.

High-Q silk fibroin whispering gallery microresonator

“…The resulting device has a thermal response with a measured sensitivity of -1.17 nm/K (circle points in Fig. 4), which is about 8 times what was previously reported in WGM thermal sensor [21][22][23][24].…”

“…Furthermore, we have demonstrated thermal sensing based on silk fibroin microtoroid with the sensitivity as high as 1.17 nm/K, which is about 8 times higher than the previous WGM resonator based thermal sensors [21][22][23][24]. The high sensitivity of the silk resonator based thermal sensor originates from the large thermal expansion coefficient [25], which is three order of magnitude larger than that of silica.…”

A scatterer-assisted whispering-gallery-mode microprobe

“…Note that the overall coupling efficiency includes both the input and the output coupling processes, which are two reversible processes and thus should have the same coupling efficiency. Therefore, the coupling efficiency of the proposed coupling method is the square root of the overall coupling efficiency, i.e., 16.8%. The high scattering-based coupling efficiency is attributed to both Purcell effect and the proposed two-step focusing technique.…”

“…Whispering gallery mode (WGM) microresonators have attracted increasing attentions in the last two decades in the fields of microlaser [1][2][3][4][5], optomechanics [6][7][8], bio/chemical/thermal sensing [9][10][11][12][13][14][15][16][17], nonlinear optics [18][19][20][21][22][23], etc., due to their intense ligh confinements originating from ultrahigh quality (Q) factors and small mode volumes. It is critical to effectively couple light into and out of the microresonator for the aforementioned experiments and applications.…”

“…Specifically, a nanotip mounted on a 3-axis nano-stage is utilized as a light scatterer, so we could adjust its position on the resonator in the experiments. A graded-index (GRIN) lens coupled with a single mode fiber is used to focus the laser beam in 1,550 nm wavelength band onto the nanotip, which then scatters the focused laser into WGMs with a coupling efficiency as high as 16.8%. Particularly, the reflection signal is also collected by the same lens and fiber, which makes the whole coupling system a fiber based WGM microprobe, which will become a compact platform for sensing/imaging applications.…”