The laser performances of silica microspheres functionalized by neodymium doped gadolinium oxide nanocrystals
are investigated. First, we have developed a new method to identify and selectively excite small mode volume
WGMs using a tapered fiber coupler. The electromagnetic-field distribution ofWGMs is mapped by the excitation
efficiency, providing a measurement of the near field intensity. Moreover a method to characterize the ultra-low
threshold microlaser is presented here, which relies on the use of the thermal bistability effect: the thermal drift
of the resonance line which slows down the power scanning help us to detect the onset of laser effect on the
emitted light. Finally, a single mode lasing at 1088.2 nm with threshold as low as 65 nW is achieved, for a
quality factor at lasing wavelength of 1.4 × 108.
We report on light emission from high-Q neodymium-implanted silica microtoroids. Following the description
of the fabrication process of microtoroids, neodymium light emission is analysed. This emission is coupled to
various cavity modes. Using evanescent wave coupling we achieve selective detection of Whispering Gallery
Modes of a microtoroid.
In the past few years, many studies have been carried out to use the ability of light to transport information into silicon-based integrated photonic circuits. The realization of an efficient silicon-based light source is therefore necessary but however challenging. Lasing cannot be easily achieved from silicon emission because of its indirect bandgap. Therefore, one solution proposed is to use other efficient emitters, like rare earth, into silicon or Silicon On Insulator based microcavities. Silica microdisk has been demonstrated to support high-Q whispering-gallery modes, and can be upgraded to ultra-high-Q toroidal microcavities by a CO2 laser melting process. Microdisk high Q-factor balances the low gain generally obtained from the active medium. Thus, those microcavities may be good candidates
for silicon-based laser. In this paper, the fabrication and room
temperature operation of silica microdisk associated with Er-doped silicon rich oxide is presented. Er atoms are excited at the 351 nm wavelength via the silicon clusters, giving to the material a high photonic capture section, and therefore a good photoluminescence efficiency. We demonstrate efficient coupling of erbium atoms to high-Q whispering-gallery modes. The photoluminescence spectrum is then theoretically treated. The WGM resonances are thus identified. We also discuss the contribution of the spot excitation and the weak coupling to the higher radial order modes. Finally, the polarization dependence of the observed modes is investigated, and the experimental results are compared to our analytical model of disk-shape cavities. Those results give us to think that an integrated laser should be soon achieved.
We report an experiment where InAs/GaAs self-organized Quantum Dots (QD) are coupled to the evanescent field of very-high-Q Whispering Gallery Modes (WGM) in a silica microsphere. The high
performance of these microcavity and nanoemitters allowed to achieve very low threshold (200 μm) laser operation at room temperature, involving a few thousands of QD. We show that such a low threshold relies heavily on WGM deconfinement and reconstruction in the micromesa etched in GaAs sample. Next, we present some prospects on further experiments involving various semiconductor nanostructures coupled to microspheres or to silica microtoroids integrated on a Si chip (as recently introduced by K.J.~Vahala and coworkers at Caltech).
Silica microspheres behave as efficient optical microresonators when small-volume whispering-gallery modes (WGMs) are used. We have realized a cryogenic set-up to work with microspheres immersed in a superfluid helium bath. Quality factors up to 109 have been obtained at 2 K. In this environment, we have been able to observe a dispersive bistable behavior of the WGM resonances, due to the weak intrinsic Kerr optical nonlinearity of silica, with a threshold power of 10 (mu) W only. This result opens the way to the realization of thresholdless microlaser, based on a rare-earth doped silica microsphere and to other Cavity-QED projects with microspheres at low temperatures.