  We theoretically demonstrate a fiber-integrated single photon source of
unprecedented efficiency. This fiber single photon source is achieved by
coupling optically a single quantum emitter to a monomode optical fiber with a
new concept of ultra-broadband optical antenna. Such an optical antenna concept
is the result of the transposition to optical frequencies of the well-known
low-frequency horn antenna The optical horn antenna is here shown to be capable
of directing the radiation from the emitter toward the optical fiber and
efficiently phase-matching the photon emission with the fiber mode. Numerical
results show that an optical horn antenna can funnel up to 85% of the radiation
from a dipolar source within an emission cone semi-angle as small as 7 degrees
(antenna directivity of 300). It is also shown that 50% of the emitted power
from the dipolar source can be collected and coupled to an SMF-28 fiber mode
over spectral ranges larger than 1000 nm, with a maximum energy transfer
reaching 70 %. This approach is highly promising in the engineering of
all-fiber "on-demand" single photon sources for telecommunication, quantum
optics and sensing.
