  The emission cascade of a single quantum dot is a promising source of
entangled photons. A prerequisite for this source is the use of a symmetric dot
analogous to an atom in a vacuum, but the simultaneous achievement of
structural symmetry and emission in a telecom band poses a challenge. Here we
report the growth and characterization of highly symmetric InAs/InAlAs quantum
dots self-assembled on C3v symmetric InP(111)A. The broad emission spectra
cover the O (1.3 micron-m), C (1.55 micron-m), and L (1.6 micron-m) telecom
bands. The distribution of the fine-structure splittings is considerably
smaller than those reported in previous works on dots at similar wavelengths.
The presence of dots with degenerate exciton lines is further confirmed by the
optical orientation technique. Thus, our dot systems are expected to serve as
efficient entangled photon emitters for long-distance fiber-based quantum key
distribution.
