25 August 2008 Simulation of multimode interference couplers with deep rib structure and tunable power splitting ratio
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The multimode interference (MMI) couplers, which operate at 1.55 microns in deep rib InGaAsP/ InP waveguide with large lateral confinement and tunable power splitting ratios, are of high interest in integrated optics. The gold contacts are applied on the top of waveguides where tuning is desired and the plasma effect will lead to negative refractive index change. The three-dimensional (3D) finite difference beam propagation method (FD-BPM) is used to model the tunable MMI couplers. The length of a 2×2 overlap-MMI is determined by FD-BPM, so the longitudinal position of tuning spots is obtained. The position of gold contacts with two types, the edge-pads or center-pad, are also determined. In our design, the length of MMI is 180 microns. If the width of pads is 50 micros and the refractive index is tuned from 0 to -0.027, the power ratio is tuned from50:50 to maximums 88.5:11.4. For deep rib structure, the effective index (EI) method can not be used to simplify the 3D waveguide to plane waveguide because its lower precision, and then the direct 3D FD-BPM simulation is necessary for the design of 3D MMI couplers.
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ChaoJun Yan, Xiang Liu, Binghua Jiang, Junli Wan, "Simulation of multimode interference couplers with deep rib structure and tunable power splitting ratio", Proc. SPIE 7056, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications II, 70561E (25 August 2008); doi: 10.1117/12.794908; https://doi.org/10.1117/12.794908

Brain-machine interfaces


Refractive index

3D modeling

Beam propagation method

Planar waveguides


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