An Erbium-Doped Whispering-Gallery-Mode Microlaser for Sensing

An erbium-doped whisper gallery mode microlaser is presented, which consists of an erbium-doped microsphere placed in an optical fiber open microcavity. The erbium-doped microsphere is obtained from melting the etched erbium-doped fiber tip by electrode discharge of a fusion splicer, and the open microcavity is fabricated by using femtosecond laser micromachining together with fusion splicing technique. The microcavity is positioned in a place just touching the fiber core, thus the light propagating in the fiber core is coupled into the erbium-doped microsphere through the evanescent field. The whispering-gallery-mode light field established in the microsphere interacts with the erbium ions, and ends up with laser operation. The quality factor value of the device is 6089 and the laser threshold is 0.033 mW. When the pump power changes continuously within the range from 0.39 mW to 0.72 mW, the lasing wavelength shifts from 1564.59 nm to 1565.6 nm, respectively. Such a WGM microlaser is low cost, robust and stable in operation and can be used for temperature and refractive index (RI) sensing. The sensitivity of the microlaser to temperature and RI is 33.3 pm/°C and 26 nm/RIU, respectively, higher than that achieved by pure WGM resonator, 8.3 pm/°C and 19.42 nm/RIU, respectively. More significantly, the detection limit of RI sensing for WGM microlaser is ~4.87 × 10
^-5
RIU, lower than ~2.71 × 10
^-4
, achieved the WGM resonator.