Abstract
We propose a silicon-on-insulator (SOI) polarization diversity scheme in the mid-infrared wavelength range. In consideration of absorption loss in silicon dioxide (SiO2), the polarization splitter-rotator (PSR) is designed and optimized with silicon nitride (SiN) upper-cladding and SiO2 lower-cladding. This asymmetry allows the PSR, which consists of mode-conversion tapers and subsequent mode-sorting asymmetric Y-junctions, to be fabricated with a simple one-step etching process. Simulation shows that our PSR has good performance with low mode conversion loss (< 0.25 dB) and low crosstalk (< -18 dB) in a very large wavelength range from 4.0 μm to 4.4 μm. The PSR also exhibits large fabrication tolerance with respect to the size deviations in waveguide width, height and refractive index of the upper-cladding. Additionally, PSR devices based on Y-junctions with SiO2 upper-cladding, and SiN upper- and lower-claddings are designed for potential applications at shorter and longer wavelengths, respectively. These PSR devices could facilitate the development of silicon photonic devices in the mid-infrared.
Highlights
Silicon (Si) photonics, which takes full advantage of the well-established complementary metal oxide semiconductor (CMOS) processing, offers compact device footprint, high level of integration and low manufacturing cost [1, 2]
While the initial applications have been in optical communications at near infrared, within the recent five years, the scope of Si photonics has expanded to the mid-infrared wavelength range (> 2 μm), with an interest to explore various sensing applications on a “lab-on-a-chip” platform [3,4,5,6]
To achieve polarization diversity for Si photonics at mid-infrared, we propose a siliconon-insulator (SOI) polarization splitter and rotator (PSR) consisting of assisted mode conversion tapers and subsequent mode-sorting asymmetric Y-junction, which potentially has broadband properties according to our previous investigations [19]
Summary
Silicon (Si) photonics, which takes full advantage of the well-established complementary metal oxide semiconductor (CMOS) processing, offers compact device footprint, high level of integration and low manufacturing cost [1, 2]. Polarization diversity schemes in the mid-infrared, to the best of our knowledge, have not been investigated yet. To achieve polarization diversity for Si photonics at mid-infrared, we propose a siliconon-insulator (SOI) polarization splitter and rotator (PSR) consisting of assisted mode conversion tapers and subsequent mode-sorting asymmetric Y-junction, which potentially has broadband properties according to our previous investigations [19]. An important difference at mid-infrared is that silicon dioxide (SiO2) may have strong absorption making them unsuitable as a cladding material. We adopt SiN here as the upper-cladding for the PSR device to potentially reduce the absorption loss at > 4.0 μm wavelength [31,32,33]. We investigate SiO2 as upper-cladding for PSR devices operating at shorter wavelength (~3.3 μm) and SiN as both upper- and lower-cladding for longer wavelength (~6.9 μm)
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