The ability to access and modify optical phase with high resolution is opening exciting new opportunities in the optical communications, optical signal processing, and RF photonics arenas. Optical demultiplexing with a resolution better than allows overlay optical communications scenarios compatible with the existing transparent WDM optical networks. We review the use of such high-resolution control of the optical phase of mode-locked laser frequency combs as an enabling technology for a new class of optical-code-division multiplexing (OCDM) systems. A network based on such systems is compatible with and has a comparable spectral efficiency to existing DWDM networks, and can even occupy the unused bandwidth of an existing single-channel DWDM window. Through inverse multiplexing of tributaries we are demonstrating a security-enhanced optical transmission over metropolitan area at that is scalable to and beyond. Such photonic layer “security” (PLS) is offered through phase scrambling using integrated microring resonator phase coders. This OCDM-based PLS is robust against exhaustive and archival attacks and can compliment digital encryption at higher layers if need arises. We review and highlight the advantages of our proposed OCDM-based PLS system. This system exploits optical integration to support new applications where electronic encryption is impractical because of space, weight, power, availability, and cost requirements. Such applications range from a timely security support for the emerging to all-optical multilevel security offered through the compatibility of PLS with the DWDM networks. In the former application we refer to the fact that there is no security solution available for in the next few years as the standards are being written, and in the latter applications, cost-effective solutions applying electronic encryption to multilevel security are challenging, especially for avionic applications.
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