  The theoretical studies of optical properties of Ga$_{1-x}$In$_x$As
self-assembled quantum-wires (QWR's) made of short-period superlattices with
strain-induced lateral ordering are presented. Valence-band anisotropy, band
mixing, and effects due to local strain distribution at the atomistic level are
all taken into account. Using realistic material parameters which are
experimentally feasible, we perform simulations of the absorption spectra for
both inter-subband and inter-band transitions (including the excitonic effect)
of this material.It is shown that the self-assembled QWR's have favorable
optical properties for application in infra-red detection with normal
incidence. The wavelength of detection ranges from 10 $\mu m$ to 20 $\mu m$
with the length of QWR period varying from 140\AA to 300\AA.
