  The modern information networks are built on hybrid systems working at
disparate optical wavelengths. Coherent interconnects for converting photons
between different wavelengths are highly desired. Although coherent
interconnects have conventionally been realized with nonlinear optical effects,
those systems require demanding experimental conditions such as phase matching
and/or cavity enhancement, which not only bring difficulties in experimental
implementation but also set a narrow operating bandwidth (typically in MHz to
GHz range as determined by the cavity linewidth). Here, we propose and
experimentally demonstrate coherent information transfer between two
orthogonally propagating light beams of disparate wavelengths in a fiber-based
optomechanical system, which does not require any sort of phase matching or
cavity enhancement of the pump beam. The coherent process is demonstrated by
phenomena of optomechanically induced transparency and absorption. Our scheme
not only significantly simplifies the experimental implementation of coherent
wavelength conversion, but also extends the operating bandwidth to that of an
optical fiber (tens of THz), which will enable a broad range of
coherent-optics-based applications such as optical sensing, spectroscopy, and
communication.
