Complementary and Asymmetric Tapered Bent Mid-Infrared Waveguide Arrays for Subwavelength-Pitch Integration and Crosstalk Minimization

Abstract

This paper delivers the first report of a mid-infrared (MIR) waveguide array design that employs complementary and asymmetric tapered Euler-shaped bends. These provide greater fabrication flexibility to achieve subwavelength-pitch integration while reducing crosstalk to below 30 dB across the 3.1 to 3.6 micron wavelength range. Unlike previous designs, which maintained constant waveguide widths, the Euler waveguide bends are characterized by asymmetric and complementary tapered waveguide widths. This approach significantly reduces crosstalk to below 30 dB for both the first and second neighboring waveguides across a 500 nm wavelength range, enhancing the efficiency of optical phased arrays (OPA) with a large field of view, optimizing light propagation and minimizing crosstalk. The waveguide array is fabricated on a silicon-on-insulator platform, with a 2-micron buried oxide layer and a 500 nm-thick silicon layer. The design is highly tolerant to fabrication variations, maintaining consistent performance even with width variations. The spectral responses, simulated using the 3D finite-difference time-domain method, demonstrate negligible coupling and low insertion loss across the wavelength range. This work offers a robust and CMOS-compatible solution for MIR integrated photonic circuits.

Figures (4)

• Figure 1: : Schematic illustration of the proposed waveguide array: (a) 3D view, (b) cross-sectional view, (c) enlarged view of the output section of the waveguide array, (d) 200µm long waveguide array with bend radius of 12µm and $30^o$ bend angle, (e) enlarged view of neighboring waveguides indicating complementary widths, (f) enlarged view of the middle section, (g) array with $12^o$ bend angle, (h) array with $30^o$ bend angle.
• Figure 2: The coupling coefficient variation factor as a function of bend angle and radius for the 3.55µm wavelength and center-to-center spacing of 1.775µm, (a) first neighboring waveguide, (b) second neighboring waveguide
• Figure 3: (a) top view illustrates the propagation of light at 3.55µm wavelength, showing the electric field intensity of the TE mode entering from the middle channel of a 10-channel waveguide array, indicating negligible light coupling to the neighboring waveguides. (b) SEM images of the waveguide arrays fabricated using electron beam lithography
• Figure 4: (a) The simulated spectral transmissions for a 10-channel waveguide array are shown, with dashed lines indicating the insertion loss, and dotted and solid lines representing the crosstalk in the first and second neighboring channels on both sides of the input waveguide, respectively. (b) Enlarged view of the insertion loss.