Toward the realization of subsurface volumetric integrated optical systems

Abstract

Next generation mobile devices and computing architectures would benefit from ultra-high bandwidth technologies that efficiently transport and process optical signals. Subsurface fabrication can address this challenge by forming volumetric photonic integrated circuits with a more compact aerial footprint than planar on-chip circuits. These 3D optical systems may utilize densely packed low-loss, freeform optical interconnects for high volume data transfer. In this Perspective, we provide a comparative overview of the two main methods for subsurface fabrication, including our recently developed SCRIBE process, and assess the advantages and future directions of each approach. After analyzing the underlying technologies, we provide a roadmap of important steps to transition from laboratory demonstrations of individual elements to industrial-scale production of subsurface volumetric photonic integrated circuits.

Femtosecond Laser Densification of Hydrogels to Generate Customized Volume Diffractive Gratings

“…The RI can also be enhanced by performing fs laser densification in the presence of dyes, nanoparticles, and metallic ions. Moreover, material properties and pattern designs need to be optimized to increase detection range, sensitivity, and specificity for biosensing applications. − Overall, fs laser densification will pave the way for miniaturized and integrated hydrogel-based photonic systems where multiple photonic elements are embedded within a hydrogel matrix, a capability not achieved by surface structuring methods …”

“…43−46 Overall, fs laser densification will pave the way for miniaturized and integrated hydrogel-based photonic systems where multiple photonic elements are embedded within a hydrogel matrix, a capability not achieved by surface structuring methods. 47…”

Enabling High Precision Gradient Index Control in Subsurface Multiphoton Lithography

“…To enable a direct comparison of previously collected index data, 9 sets of 12 prisms each were measured at each target fluorescence intensity (equivalent to an average laser power). Because we are interested in knowing the reproducibility of fabricating a particular index, 12 rather than the precision to which we know the average index, we choose to plot the standard deviation as the error bars in Figure 6a,b, which shows the variability in measured index of identically fabricated prisms. Plotting it this way does not meaningfully change the comparison, as we are comparing similar sample sizes.…”

“…The galvo is inherently faster due to the smaller distance the mirrors must travel to change the angle of the light, while the high-resolution piezo must move the full scan distance. Writing with the galvo, or another method by which different angles incident on the objective are used to map to different positions in the system (such as light-sheet microprinting), is necessary to fabricate typical micro-optic structures in a reasonable amount of time …”

“…By contrast, constant-index optics fabricated with conventional DLW are not sensitive to moderate variations in exposure dose. Conventional DLW uses exposure doses well above the threshold, a region where the index versus exposure curve is almost flat . Interference-based devices, e.g., prisms, become effectively unusable when written near the threshold because they are sensitive to small index variations .…”