Nonlinear properties of laser-processed polycrystalline silicon waveguides for integrated photonics

Abstract

We report nonlinear optical characterization of cm-long polycrystalline silicon (poly-Si) waveguides at telecom wavelengths. Laser post-processing of lithographically-patterned amorphous silicon deposited on silica-on-silicon substrates provides low-loss poly-Si waveguides with surface-tension-shaped boundaries. Achieving optical losses as low as 4 dB cm-1 enabled us to demonstrate effects of self-phase modulation (SPM) and two-photon absorption (TPA). Analysis of the spectral broadening and nonlinear losses with numerical modeling reveals the best fit values of the Kerr coefficient n2=4.5×10−18 m W-1 and TPA coefficient βTPA=9.0×10−12 m2 W-1, which are within the range reported for crystalline silicon. On-chip low-loss poly-Si paves the way for flexible integration of nonlinear components in multi-layered photonic systems.

Nonlinear Characterization of Laser Processed Polysilicon Waveguides for Integrated Photonics

“…In summary, we have produced low temperature deposited poly-Si waveguides suitable for multi-layer integration with photonic or electronic systems. To the best of our knowledge, we report the lowest recorded loss in such a material, which has enabled the first demonstration of nonlinear transmission, opening a route for additional functionality in multi-layer architectures [6].…”

Laser Thermal Processing of Group IV Semiconductors for Integrated Photonic Systems

“…[120] Although optical losses less than c-f ) Reproduced under the terms of the CC-BY license. [114,116] Copyright 2020 and 2019, The Authors, published by The Optical Society. g) Laser annealing of a patterned a-Ge stripe after encapsulation by a silica capping layer.…”

“…Along a similar vein, our group has recently demonstrated both laser crystallization and reflowing of prepatterned a‐Si optical waveguides on silica‐on‐silicon substrates. [ 114 ] In contrast to ELA, where typically an entire amorphous thin film is processed, [ 115 ] we made use of a CW visible laser to individually process the patterned a‐Si waveguides. Scanning of the focused laser beam along the waveguides offered a key advantage in that the laser‐induced heating is highly localized to the patterned waveguide, reducing the power required to melt the smaller material volume and lowering the thermal budget.…”

“…For optical isolation of the waveguides, local buried oxide layers have been used under poly‐Si waveguides crystallized using heat treatments. Capitalizing on our recent work, [ 114 ] we expect that laser annealing of patterned and glass‐encapsulated a‐Si waveguides can provide better results in terms of crystallinity, enabling optical losses close to those of c‐Si waveguides. In contrast, modification of the material properties via nonlinear multiphoton effects using ultrafast lasers presents an etch‐free maskless approach for the fabrication of optical waveguides with optical losses as low as 2.2 dB cm −1 within bulk Si.…”

“…e) Simulated and f ) experimental TE mode profiles of a poly-Si waveguide with a surface-tension-induced parabolic cross-section. (c-f) Reproduced under the terms of the CC-BY license [114,116]. Copyright 2020 and 2019, The Authors, published by The Optical Society.…”