Enhanced Operation Range of Silicon MZI Filters Using a Broadband Bent Directional Coupler

Mach-Zehnder interferometers (MZIs) are essential components that are used in a variety of wavelength division multiplexing (WDM) systems. Wavelength-sensitive straight directional couplers (DCs) are usually used as the beam splitter and combiner in traditional waveguide-based MZIs, which often limit the operational bandwidth and cause additional insertion loss. To overcome these challenges, we present an MZI based on bent DCs achieving <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.7\times $ </tex-math></inline-formula> increase in operational wavelength range, expanding the bandwidth from 36.7 nm in straight DC-based MZIs to at least 100 nm, while maintaining a large extinction ratio (ER) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {\geq 18.4~dB}$ </tex-math></inline-formula>. The proposed MZI is robust across a 300 mm wafer, achieving minimum ER over 100 nm wavelength range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {14.3 }}\sim {\mathrm {18.4~dB}}$ </tex-math></inline-formula> in all the 63 measured dies, significantly outperforming MZIs based on straight DCs, which exhibit minimum ER of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {4.2~ }}\sim {\mathrm {6.1~dB}}$ </tex-math></inline-formula>. Finally, the proposed MZI is theoretically proven to be highly efficient for more complex WDM systems. Transfer matrix method calculations for 16 −channel MZI-based WDM system demonstrate an improvement of the worst-channel isolation from 5.42 dB to 17.18 dB and the average insertion loss from 1.02 dB to 0.30 dB, as compared to the straight DC based counterpart. This underscores the potential of the proposed MZI to enable scalable and high-performance WDM systems.