  When light is confined in all three directions and in dimensions of the order
of the light wavelength, full discretization of the photon spectra and
distinctive phenomena occur, the Purcell effect and the inhibition of emission
of atoms being two paradigmatic examples. Diverse solid-state devices that
confine light in all three dimensions have been developed and applied.
Typically the confinement volume, operating wavelength, and quality factor of
these resonators are set by construction, and small variations of these
characteristics with external perturbations are targeted for applications
including light modulation and control. Here we describe full 3D light
trapping, that is set and tuned by laser excitation in an all-optical scheme.
The proposed device is based on a planar distributed Bragg reflector GaAs
semiconductor microcavity operated at room temperature. Lateral confinement is
generated with an attractive effective photonic potential tailored by the
increase in the cavity spacer refractive index, induced by carriers
photoexcited by a focused laser. Strong three dimensional trapping of light is
evidenced by the laser-induced changes on the spectral, spatial, and k-space
distribution of the emission. The dynamics of the laser induced photonic
potential is studied using modulated optical excitation, highlighting the
central role of thermal effects at the origin of the observed phenomena.
