Spherical distributed Bragg reflector with an omnidirectional stop band in the near-IR spectral range

Spherical distributed Bragg reflectors (SDBR) for near-IR (infrared) applications are fabricated by plasma-enhanced chemical-vapor deposition. The SDBRs consist of alternating quarter-wave layers of amorphous hydrogenated silicon ($a$-Si:H) and amorphous silicon oxide ($a$-SiO$_2$), deposited onto a glass or quartz microsphere that has a diameter of 500 $\mu$m and is doped with erbium ions. The reflection and transmission spectra of a SDBR are measured at different points on its surface. A wide band with high reflectance and low transmittance, i.e., a stop band, is detected. It is demonstrated that, for different radial directions from the center of the microspheres, the stop bands overlap to form an omnidirectional stop band. The influence exerted by the omnidirectional stop band on the spontaneous emission of erbium ions (1.53 $\mu$m) from the quartz microsphere is studied. It is shown that the omnidirectional stop band suppresses the intensity of spontaneous emission by more than an order of magnitude.