Abstract
We design and experimentally verify a topology optimized low-loss and broadband two-mode (de-)multiplexer, which is (de-)multiplexing the fundamental and the first-order transverse-electric modes in a silicon photonic wire. The device has a footprint of 2.6 µm x 4.22 µm and exhibits a loss <1.2 dB in a 100 nm bandwidth measured around 1570 nm. The measured cross talk is <-12 dB and the extinction ratio is >14 dB in the C-band. Furthermore, we demonstrate that the design method can be expanded to include more modes, in this case including also the second order transverse-electric mode, while maintaining functionality.
Highlights
The increasing capacity demand for optical fiber communication networks has led to the investigation of space division multiplexing (SDM) as a possible solution to the predicted capacity crunch of the internet
The device has a footprint of 2.6 μm x 4.22 μm and exhibits a loss
We demonstrate that the design method can be expanded to include more modes, in this case including the second order transverse-electric mode, while maintaining functionality
Summary
The increasing capacity demand for optical fiber communication networks has led to the investigation of space division multiplexing (SDM) as a possible solution to the predicted capacity crunch of the internet. The design objective is to de-multiplex the two pulses to the separate output waveguides while keeping the amplitudes and widths of the input pulses This is achieved by estimating the arrival time of the two pulses and optimizing for having a strong signal in the corresponding output waveguide and minimizing the intensity in the opposite waveguide. The gradient calculations are performed extremely efficiently using the so-called adjoint approach, cf [13] This means that, independent on the number of design variables, analytical gradients can be computed at the cost of one extra backward FDTD time integration per objective function. Upon extraction to the design software a simple threshold filtering is taking place converting any greyscale pixel to be either black or white
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