Today, the ultrafast laser has become a powerful and robust tool for both science and commercial applications, opening new discoveries in high intensity interaction with materials through to enabling new medical procedures or manufacturing of novel product concepts. One of the most rewarding areas has been the novel means for inducing absorption inside of normally transparent materials. In Prof. Herman’s group, these interactions are studied in the context of strong nonlinear optical effects and the unfolding of remarkably energetic processes that begin in the non-equilibrium domain of thermodynamics. By tuning such processes, our group has sought out the technical benefits in three-dimensional (3D) structuring of optical materials to nano-scale dimensions, aiming to invent new forms of 3D additive and subtractive manufacturing. The research often leads to invention of new processes and product concepts touching the wide areas of photonics, optical communications, optical packaging, fibre optics, data storage, security marking, optical sensing, heads-up display, biosensing, lab-in-a-chip, and lab-in-fibre. The present paper builds on a myriad of additive and subtractive laser techniques that have culminated in transparent glasses to address a significant challenge in packaging of photonics devices. On the level of laser processing, femtosecond laser interactions were exploited for full-scale 3D structuring of the internal dimensions of glass wafers to define optical circuits and to guide etching selectively along laser tracks. Following chemical etching, the optical glass circuits become precisely arranged with alignment slots for enabling a facile assembly and packaging with optical fibers or other optical devices, with the focus here on the silicon photonic chip and multi-core optical fiber. The alignment slots provide exception self-guidance in optical-to-optical interconnections to sub-micron dimensions. The optical interposer presented herein demonstrates the potential for scaling up of laser 3D writing to enable high-density optical packaging, specifically addressing the major bottleneck for efficiently connecting optical fibers to silicon photonic processors as required in telecom and data centers. Moreover, such 3D additive and subtractive processing promises higher scale integration and rapid photonic assembly and packaging of micro-optic components for broader-based applications from integrated biophotonic chips to wearable displays.