A Universal Approach to High‐Index‐Contrast Flexible Integrated Photonics

Abstract

stimulation probes, [4][5][6][7] optical communication, [8][9][10][11][12] etc.Polymers have been commonly used to fabricate flexible photonic devices due to their natural flexibility and low-temperature film deposition. [13][14][15] However, a low-refractive-index contrast between the polymer core structures and cladding substrates cannot allow strong optical confinement, which often leads to the large size of the fabricated devices and is not conducive to high-density integration. In comparison with polymers, silicon-based materials, [16] inorganic oxides, [17,18] and chalcogenide glass [19] materials show high refractive index and low absorption loss, enabling a large degree of freedom in obtaining functional optical structures for strong optical confinement on flexible substrates. [20][21][22][23] It is innately advantageous to realize compact, flexible photonic devices using an inorganic-organic hybrid structure consisting of inorganic core material and organic cladding substrate. [24] Nowadays, the manufacturing processes of high-index-contrast (HIC) flexible integrated photonic devices are based on pattern transfer [25][26][27] and monolithic integration. [16,28] Among the many materials used for flexible photonics, silicon-based flexible devices were prepared by transferring nanostructures from a rigid carrier wafer to the flexible substrate via under-cut etching of the sacrificial oxide layer. [26,27] Hydrofluoric acid (HF) is often used during this process, which etches optical films like silicon nitride (SiN), resulting in device degradation. [26] Flexible integrated photonics is an essential technology for emerging applications, including flexible optical interconnects, optogenetic stimulation, and implantable conformal sensing. Here, a novel and universal route for fabricating flexible photonic components with high-refractive-index contrast is reported. Central to such a unique method is the utilization of germanium oxide (GeO) as the sacrificial layer for releasing nanostructures from rigid substrates to flexible substrates. Various high-quality inorganic optical materials can be grown directly on GeO by different thin-film deposition methods due to its resistance to both high temperature and high-power oxygen plasmas. In addition to the absence of restrictions on the material choices and integration processes for flexible photonic structures, the approach uses water as the etchant to remove the sacrificial layer, which has minimal impact on the optical performance of the photonic structures. Using this approach, a strain-insensitive/sensitive microring resonator based on plasma-enhanced chemical vapor deposited silicon nitride and reactive sputtered titanium oxide, respectively, is demonstrated, establishing the strategy as a facile and universal route for the fabrication of high-index-contrast flexible integrated photonic devices with various functionalities.

Economical synthesis of functional aromatic polythioamides from KOH-assisted multicomponent polymerizations of sulfur, aromatic diamines and dialdehydes

“…One major advantage of aromatic polythioamides compared with aliphatic polythioamides is the high light refractivity, owing to the large amount of conjugation system of these sulfur-rich polymers. Polymer materials with high light refractivity above 1.80 are highly desired for optoelectronic devices, [31][32][33][34] only limited examples of organic polymer materials possessing high thin film refractive indices have been reported. While introducing chalcogen atoms into the polymer structure or increasing the content of aromatic structure in the polymer is an effective approach to increase the refractive indices of polymers, [35][36][37][38][39][40][41] the aromatic polythioamides synthesized in this work may be promising polymer materials with high refractive indices.…”