Subwavelength Grating Metamaterial Multimode Bend for Silicon Waveguides

In this paper, a novel multimode waveguide implemented on a silicon-on-insulator (SOI) platform that supports several transverse (TE)/transverse magnetic (TM) modes across a broad range of wavelengths is experimentally demonstrated. The fully etched metamaterial design combines a gradient curvature bend with trapezoidal subwavelength grating segments and tapered concentric bridging strips. The simulations showed successful propagation of up to nine modes (5 TE and 4 TM) on the 340 nm SOI platform, with excess losses below 2.4 dB, and intermodal cross-talk of less than -15.7 dB. Experimentally, a compact multimode bend with a radius of 10 mu m on a 220 nm SOI platform is demonstrated that successfully supports four TE modes, with average signal-to-cross-talk extinction ratio levels of 14.4 dB or better, across a wavelength band of 1500-1600 nm. This versatile multimode waveguide bend can be employed as a fundamental building block for densely integrated photonic circuits and mode multiplexing systems.