Antireflective coatings (ARC) are a necessary element of solar cells and infrared (IR) optical applications. Current state-of-the-art coatings consist of materials such as TiO2 and Si3N4 deposited on silicon via chemical vapor deposition (CVD). This method of coating is undesirable due to the costly, tedious, and time intensive nature of the process. Herein, we have developed a novel antireflective coating (ARC) that is facile in nature. Through the implementation of high sulfur content polymers, with ultrahigh refractive index, and near to mid infrared (IR) transparency, we have been able to demonstrate high-quality films via spin/dip coating. This polymer was produced via inverse vulcanization of elemental sulfur, a byproduct of petroleum refining, and the organic monomer 1,3-diisopropenylbenzene (DIB) to yield poly(sulfur-r-(1,3-diisopropenylbenzene)) (poly(s-r-DIB)). The reaction product (poly(s-r-DIB)) was taken up into solution and deposited directly onto a silicon substrate. To verify the performance of a quarter wave antireflection coating, the spectra of the coated silicon wafer was taken. In this we found we could create a high performance, single layer, antireflection coating. Due to the unique nature of the polymer (poly(s-r-DIB)) used in this system we were able to fine tune the thickness of the coating, and therefore the target wavelength in which desired performance could be observed. Further investigation of the system is underway, as the polymer’s index can be tuned to fit a variety of substrates, making this system ideal for a multitude of antireflective applications.
For the first time, a high sulfur content polymer has been photo-bleached to yield an optical waveguide suitable for mid-wave infrared (MWIR) photonics. The polymer was synthesized by inverse vulcanization of elemental sulfur with the organic monomer 1,3-diisopropenylbenzene (DIB) to produce the polymeric material poly(sulfur-r-(1,3-diisopropenylbenze)) (poly(s-r-DIB)). This glassy, red polymer is available in bulk/solution form and affords easy processability. This novel polymer is extremely low cost, displays high refractive index (1.8), and is transparent at most short-wave infrared (SWIR) and MWIR wavelengths. These attributes make it highly desirable and a more suitable substitute to commercially available alternatives, such as chalcogenide glasses, which can be toxic, expensive and difficult to process. In this work, we demonstrate that photo-bleaching of the polymer occurs when exposed to intense UV light, inducing a change in the refractive index. The index can thereby also be tuned by changing the exposure parameters and the ambient atmospheric conditions. This phenomenon was used to fabricate optical waveguides suitable for SWIR and MWIR wavelengths. Optical characterization of the waveguides was performed to measure the propagation losses of the material. The low cost of the material and the facile nature of the fabrication and processing enables high reproducibility making this system desirable for a multitude of photonic applications such as on-chip spectroscopy and frequency combs.
Bragg mirrors are 1D photonic crystals made of a periodic stack of high and low refractive thin film materials that reflect only a small bandwidth of the spectrum. Such high-reflective devices are commercially available in the visible spectrum at relatively low costs. Functional Bragg mirrors for IR applications are greatly desired, but there exist challenges due to the limited availability of inexpensive, high refractive index, and transparent IR materials. Here, we present the design of high reflectivity Bragg mirrors working in the near and mid-IR range. Our mirror designs use the refractive index values of novel ultrahigh refractive index IR materials known as chalcogenide hybrid inorganic/organic polymers (CHIPs). CHIPs are synthetized from an inverse vulcanization process for elemental sulfur and selenium as reported by the Pyun group [1]. We integrate the optical properties of these materials and those of different low refractive index materials to generate various Bragg mirror designs. The extinction coefficients derived from absorption plots are also taken into account to increase accuracy. The theoretical values for reflectivity, physical thickness, and optical bandwidth are reported, as well as preliminary experimental results. We also present changes in reflectivity and bandwidth due to layer thickness variability. These IR Bragg mirrors have applications in devices and industries which require the use of specific wavelengths in the near and mid-IR range, such as beam-splitters, filters, anti-reflection coatings, etc.
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