TeV scale superstring and extra dimensions

Utilizing the idea of extra large dimensions, it has been suggested that the gauge and gravity couplings unification can happen at a scale as low as 1 TeV. In this paper, we explore this phenomenological possibility within string theory. In particular, we discuss how the proton decay bound can be satisfied in type I string theory. The string picture also suggests different scenarios of gauge and gravitational couplings unification. The various scenarios are explicitly illustrated with a specific 4-dimensional N=1 supersymmetric chiral type I string model with Pati-Salam-like gauge symmetry and 3 fermion families. We point out certain features that should be generic in other type I strings.