Abstract
A novel broadband multimode waveguide bend is proposed that supports the propagation of multiple TE modes on a silicon-on-insulator platform. The gradient curvature bend utilizes trapezoidal subwavelength grating (SWG) segments, connected by adiabatically tapered radial strips to achieve efficient mode (de)multiplexing. The inclusion of the radial strips offers an extra degree of design freedom, allowing the realization of a multimode bend with only one single full etch step. The access waveguide has a width of 2.075 μm with an effective radius of 10 μm. Propagation loss for all modes remains below 2.96 dB, and intermodal crosstalk has a maximum of -19 dB across a broad bandwidth of 100 nm, centred at 1550 nm. This work presents an excellent design choice for broadband mode-division multiplexing operations.
Highlights
As the demand for increased signal capacity in optical networks grows, many solutions have been explored to increase the number of possible waveguide channels
Higher order modes suffer from the generation of asymmetric outputs due to the asymmetry of their modal profiles within the multimode waveguide bend (MWB)
We propose a novel design that adopts the trapezoidal subwavelength grating (SWG) segments, connected by adiabatically tapered radial strips
Summary
As the demand for increased signal capacity in optical networks grows, many solutions have been explored to increase the number of possible waveguide channels. To compensate for the radial asymmetry of the bend’s index profile on-chip transformation optics can be applied Attempts at this approach employed a custom grayscale lithography process [6], varying the height of a 500 nm thick silicon layer such that the inner edge was taller than the outer edge. Trapezoidal subwavelength grating (SWG) segments are commonly employed when designing SWG bends, where the inner radius has a larger duty cycle than that of the outer radius [7] It has been used extensively for single-mode bends but has recently found use in multimode bends as well, successfully maintaining the symmetry of modes up to TE2/TM2 at a radius as small as 10 μm [8,9]. The radially bridged SWG design provides a greater degree of freedom in tailoring the index gradient, making it possible to realize the bends with only one single etch step
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