Recent advances in additive manufacturing enable redesigning material morphology on nano-, micro-, and meso-scale, for achieving an enhanced functionality on the macro-scale. From non-planar and flexible electronic circuits, through biomechanically realistic surgical models, to shoe soles individualized for the user comfort, multiple scientific and technological areas undergo material-property redesign and enhancement enabled by 3D printing. Fiber-device technology is currently entering such a transformation. In this paper, we review the recent advances in adopting 3D printing for direct digital manufacturing of fiber preforms with complex cross-sectional architectures designed for the desired thermally drawn fiber-device functionality. Subsequently, taking a recursive manufacturing approach, such fibers can serve as a raw material for 3D printing, resulting in macroscopic objects with enhanced functionalities, from optoelectronic to bio-functional, imparted by the fiber-devices properties. Graphic abstract

Fibers are ubiquitous and usually passive. Optoelectronics realized in a fiber could revolutionize multiple application areas, including biosynthetic and wearable electronics, environmental sensing, and energy harvesting. However, the realization of high-performance electronics in a fiber remains a demanding challenge due to the elusiveness of a material processing strategy that would allow the wrapping of devices made in crystalline semiconductors, such as silicon, into a fiber in an ordered, addressable, and scalable manner. Current fiber-sensor fabrication approaches either are non-scalable or limit the choice of semiconductors to the amorphous ones, such as chalcogenide glasses, inferior to silicon in their electronic performance, resulting in limited bandwidth and sensitivity of such sensors when compared to a standard silicon photodiode. Our group substantiates a universal in-fiber manufacturing of logic circuits and sensory systems analogous to very large-scale integration (VLSI), which enabled the emergence of the modern microprocessor. We develop a versatile hybrid-fabrication methodology that assembles in-fiber material architectures typical to integrated microelectronic devices and systems in silica, silicon, and high-temperature metals. This methodology, dubbed "VLSI for Fibers," or "VLSI-Fi," combines 3D printing of preforms, a thermal draw of fibers, and post-draw assembly of fiber-embedded integrated devices by means of material-selective spatially coherent capillary breakup of the fiber cores. We believe that this method will deliver a new class of durable, low cost, pervasive fiber devices, and sensors, enabling integration of fabrics met with human-made objects, such as furniture and apparel, into the Internet of Things (IoT). Furthermore, it will boost innovation in 3D printing, extending the digital manufacturing approach into the nanoelectronics realm.

Additive manufacturing of fiber preforms enables greater flexibility on fiber cross-sectional geometry. We compare the optical properties and geometry preservation of fibers drawn from 3D-printed preforms both annealed and non-annealed before the draw process.

Considering the demand for increasing complexity in optical fiber cross-sections, we present a novel approach for glass perform fabrication based on 3-D printing and show that it can produce glass preforms with non-equilibrium cross-sections.

Multi-material fibers are a promising platform for integrating nanoscale structures into macroscale photonic systems due to their unique aspect ratio: fiber cores can be kilometers long and sub-micrometric in their cross-section simultaneously. We are introducing Very Large-Scale Integration for Fibers (or, in short, VLSI-Fi) – manufacturing of integrated photonic circuits in a fiber analogous to VLSI from the microelectronics realm. VLSI-Fi starts with a thermal draw of the 3D printed preform, defining the cross-sectional geometry of the fiber, followed by the axial patterning of the fiber cores into arrays of integrated devices using a material-selective spatially coherent capillary breakup1,2 . Additional control over the photonic and electronic properties of devices is accomplished through segregation-driven control of doping. The result is a fiber-embedded integrated photonic circuit with user-defined 3D architecture providing the desired functionality. We argue that the capillary breakup of a viscous thread, nonlinear and often chaotic, becomes predictable if the axial symmetry of the thread viscosity is broken. We found that the capillary breakup of semiconducting fiber cores initiated by feeding the fiber through a spot-like liquefaction zone results in deterministic photonic and optoelectronic structures, such as gratings and spherical resonators. As a proof of concept, we demonstrate a selective breakup of a silicon core in fiber with one silicon and one vanadium core into an array of spherical silicon resonators, with a vanadium electrode flanking those resonators for electrical tuning of their resonant frequencies. Such cascaded resonators are a nontrivial example of photonic circuitry implemented in fiber using a non-CMOS approach.