The inventive high density optical packaging header apparatus, in various embodiments thereof, provides configurable, modular, and highly versatile solutions for simultaneously connecting multiple optical fibers/waveguides to optical-fiber-based electronic systems, components, and devices, and is readily usable in a variety of applications involving highly flexible and modular connection of multiple optical fibers/waveguides assembled in a header block configuration to optical-fiber-based system/component backplanes, while providing advantageous active and passive alignment features.