Investigation for Sidewall Roughness Caused Optical Scattering Loss of Silicon-on-Insulator Waveguides with Confocal Laser Scanning Microscopy

Abstract

Sidewall roughness-caused optical loss of waveguides is one of the critical limitations to the proliferation of the silicon photonic integrated circuits in fiber-optic communications and optical interconnects in computers, so it is imperative to investigate the distribution characteristics of sidewall roughness and its impact upon the optical losses. In this article, we investigated the distribution properties of waveguide sidewall roughness (SWR) with the analysis for the three-dimensional (3-D) SWR of dielectric waveguides, and, then the accurate SWR measurements for silicon-on-insulator (SOI) waveguide were carried out with confocal laser scanning microscopy (CLSM). Further, we composed a theoretical/experimental combinative model of the SWR-caused optical propagation loss. Consequently, with the systematic simulations for the characteristics of optical propagation loss of SOI waveguides, the two critical points were found: (i) the sidewall roughness-caused optical loss was synchronously dependent on the correlation length and the waveguide width in addition to the SWR and (ii) the theoretical upper limit of the correlation length was the bottleneck to compressing the roughness-induced optical loss. The simulation results for the optical loss characteristics, including the differences between the TE and TM modes, were in accord with the experimental data published in the literature. The above research outcomes are very sustainable to the selection of coatings before/after the SOI waveguide fabrication.

Revealing the internal luminescence quantum efficiency of perovskite films via accurate quantification of photon recycling

“…Surface scattering effects have been previously discussed for perovskite waveguides, 21,23,71,72 luminescent solar concentrators, 73 and perovskite LEDs (PeLEDs) 33 and are a well-known phenomenon in high-index-contrast microphotonic devices. 20,22 While it is difficult to ascertain the relative contributions of the above-discussed properties to the total magnitude of scattering, we believe that surface roughness plays the major role. 20,22,23 In the following, we introduce the fundamental underlying optical processes in a perovskite film, leading to the previously discussed asymmetric, broadened, and red-shifted PL spectra.…”

“…20,22 While it is difficult to ascertain the relative contributions of the above-discussed properties to the total magnitude of scattering, we believe that surface roughness plays the major role. 20,22,23 In the following, we introduce the fundamental underlying optical processes in a perovskite film, leading to the previously discussed asymmetric, broadened, and red-shifted PL spectra. Note that, for simplicity, we assume a perfect back reflector here and discuss the more general case of a film on glass in Note S5 and Figure S16.…”

“…Here, we reveal that it is key to account for PL that is initially trapped in guided modes, but coupled out before reabsorption upon scattering after some length of travel within the perovskite film. [20][21][22][23] Scattered PL exhibits a red-shifted spectrum given the much stronger reabsorption of high-energy photons. 13,21,[23][24][25] Extending recent findings, 21,23 we show that the measured fractions of directly emitted and scattered PL critically depend on the collection method and film properties.…”

“…2,4,16,17,75 Instead, it describes a small scattering probability every time a photon impinges on a surface, which is strongly suppressed in near-atomically flat III-V semiconductors. 22,23,64 Specifically, since low-energy photons (lT790 nm) are barely reabsorbed in the perovskite given the exponential drop in absorption, they can travel long distances within the film (Figures 2C, S10, and S17) and thus experience numerous total internal reflections before a scattering event that results in outcoupling. 23,33 The magnitude of scattering for a given propagation distance z i is therefore governed by the film thickness (compare Equation 11) and surface roughness.…”

Special Issue: “Optical Thin Films and Structures: Design and Advanced Applications”

“…The large volume fraction of the last one seriously weakened the coating strength and caused a drop in hardness. Shang et al [10] used a theoretical/experimental combinative model for investigation of the waveguide sidewall roughness (SWR) and its impact on the optical propagation losses in silicon-on-insulator waveguides.…”