Optical transport networks have been affected by the following problems: (i) limited bandwidth of information infrastructure, (ii) high power consumption, (iii) heterogeneity of network segments, and (iv) security issues. As a solution to the first three problems, the multidimensional signaling has been proposed recently by author. In multidimensional signaling, for the conveyance information over spatial domain multiplexing (SDM) based fibers (few-mode fibers, few-core fibers, few-modefew-core fibers), all available degrees of freedoms, be optical or electrical, have been employed. In electrical domain discrete-time basis functions (such as Slepian sequences) have been employed. In optical domain, both polarization states and spatial modes have been employed. Additionally, the orthogonal division multiplexing (ODM) has been employed in optical domain to enable beyond 1 Pb/s serial optical transport over single-mode fibers. With SDM, the serial optical transport over SDM fibers exceeding 10 Pb/s is achievable. Concepts of statistical physics and information theory have been used in energy-efficient multidimensional signal constellation design. To solve for the security issues problem, the use of FBGs with impulse responses derived from mutually orthogonal Slepian sequences has been advocated.