Ideal, constant-loss nanophotonic mode converter using a Lagrangian approach

Abstract

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Mode-evolution-based silicon-on-insulator 3 dB coupler using fast quasiadiabatic dynamics

“…There have been numerous approaches to optimize the design of adiabatic mode-evolution-based devices in integrated optics. For adiabatic tapers, one approach is based on the equalization of taper loss along each propagation step [16][17][18]. A similar approach is to limit the fraction of power scattered into the unwanted mode below a constant value [19].…”

A general design approach for inverted tapers

“…A general design approach has been proposed by Horth et al and a constant-loss framework taper was presented. [8] Firstly, it was theoretically demonstrated that an inverted taper with constant loss as a function of position along the taper would be most efficient. Then, like multistage tapers, Horth divided the taper into small steps and designed every step with the same propagation loss.…”

“…The basic design principle of inverted tapers is to calculate a taper profile which can keep a constant loss at any point of the taper. [8] Essentially, the spot-size conversion loss is mainly from effective mode area (EMA) changing along the taper, which means that the rapid EMA changing results in a large spot-size conversion loss. Motivated by this idea, an equation between EMA and the position within the taper, which make the constant-loss condition satisfied, is firstly derived.…”

“…It is numerically demonstrated that the designed inverted taper can reach a much shorter size and a lower loss compared with linear and parabolic inverted tapers. For an inverted-taper SSC with a given length, a clear design guideline is demonstrated in [8]: the taper should have a constant instantaneous loss at any point of the inverted taper. A normal inverted taper profile is illustrated in Figure . 1.…”

“…Assuming that the waveguide tapers slowly enough that the EMA changing is small during the extracted cell and the reflection can be ignored. Here, the EMA is defined as: [8] ( )…”