  Iron-chalcogenide superconductor Fe$_{1.03}$Se$_{0.5}$Te$_{0.5}$ has been
investigated under high pressure using synchrotron based x-ray diffraction and
mid-infrared reflectance measurements at room temperature. Pressure dependence
of the superconducting transition temperature (T$_c$) of the same sample has
been determined by temperature-dependent resistance measurements up to 10 GPa.
Although the high pressure orthorhombic phase ($\textit{Pbnm}$) starts emerging
at 4 GPa, structural transition becomes clearly observable above 10 GPa. A
strong correlation is observed between the Fe(Se,Te)$_{4}$ tetrahedral
deformation in the tetragonal phase ($\textit{P4/nmm}$) and the sharp rise of
T$_c$ up to $\sim$4 GPa, above which T$_c$ is found to be almost pressure
independent at least up to 10 GPa. A subtle structural modification of the
tetragonal phase is noticed above 10 GPa, suggesting a structural transition
with possible Fe$^{2+}$ spin-state transition. The evolution with pressure of
the optical conductivity shows that the Drude term increases systematically
with pressure up to 5.4 GPa, indicating the evolution of the tetragonal phase
towards a conventional metallic state. At further higher pressures the Drude
term reduces drastically implying a poor metallic character of the high
pressure orthorhombic phase. Our results suggest that occurrence of large onset
T$_c$ above 4 GPa is due to a systematic increase of high pressure orthorhombic
phase fraction.
