Real photonic waveguides: guiding light through imperfections

Abstract

Real photonic waveguides are affected by structural imperfections due to fabrication tolerances that cause scattering phenomena when the light propagates through. These effects result in extrinsic propagation losses associated with the excitation of radiation and backscattering modes. In this work, we present a comprehensive review on the extrinsic loss mechanisms occurring in optical waveguides, identifying the main origins of scattering loss and pointing out the relationships between the loss and the geometrical and physical parameters of the waveguides. Theoretical models and experimental results, supported by statistical analysis, are presented for two widespread classes of waveguides: waveguides based on total internal reflection (TIR) affected by surface roughness, and disordered photonic crystal slab waveguides (PhCWs). In both structures extrinsic losses are strongly related to the waveguide group index, but the mode shape and its interaction with waveguide imperfections must also be considered to accurately model the scattering loss process. It is shown that as long as the group index of PhCWs is relatively low (ng\<30), many analogies exist in the radiation and backscattering loss mechanisms with TIR waveguides; conversely, in the high ng regime, multiple scattering and localization effects arise in PhCWs that dramatically modify the waveguide behavior. The presented results enable the development of reliable circuit models of photonic waveguides, which can be used for a realistic performance evaluation of optical circuits

Expanding the Silicon Photonics Portfolio With Silicon Nitride Photonic Integrated Circuits

“…These reflections can be caused by an abrupt index variation in the design of the device or due to surface roughness on the waveguides. In [67], it has been shown that LPCVD based SiN waveguides have 5 to 15 dB weaker distributed reflections due to the surface roughness of the waveguides as compared to SOI waveguides. Fig.…”

Disorder effects in subwavelength grating metamaterial waveguides

“…1(b)], also called jitter, inherent to any fabrication process, on the performance of SWG waveguide structures. While the effects of fabrication imperfections in conventional channel waveguides and photonic crystal slab waveguides have been extensively studied in the past (see e.g [23]. for a comprehensive review on this topic), the effect of the jitter on the performance of periodic SWG waveguides has not yet been reported.…”

Stochastic simulation and robust design optimization of integrated photonic filters

“…This situation is common during real circuit fabrications because the exact uncertainties of the fabrication processes are difficult to predict and may change with time. Of course, if the statistics of fabrication variations are precisely known, then we can always solve (9) to get the optimized design under that fabrication variations as done in Section 4.2.…”

“…On the contrary, stochastic uncertainties related to fabrication variations, such as waveguide geometry deviation, gap opening issues, material composition fluctuations, and surface roughness, are unavoidable in production processes [5][6][7][8][9]. It is well known that such uncertainties can have a dramatic impact on the functionality of fabricated circuits [4,[10][11][12][13][14][15].…”