Numerical method for designing ultrashort and efficient adiabatic mode converters

Abstract

This paper proposes a fully numerical method for designing adiabatic mode converters (NM-AMCs). The proposed method can help compute efficient adiabatic guided-wave shapes for mode converters using a nonuniform section division technique. Such a scheme reduces the memory requirement and computational time for the design of adiabatic devices. Furthermore, the adiabatic mode converter comprises a ridge waveguide, which is difficult to design using analytical methods. This complex case of an adiabatic mode converter is used to demonstrate how the proposed method can readily generate a guided-wave shape that gives the same mode-connection power transfer with a far shorter length compared with a linear-shape converter. The efficiency of the device designed using this NM-AMC is significantly better than that of linear-shape converters; this designed adiabatic mode converter can enable a broad operating bandwidth. Moreover, the efficiency of the adiabatic mode converter that was designed using the NM-AMC method considerably exceeds that obtained using an analytical method proposed for a strip waveguide.

Numerical Method for the Design of Compact Adiabatic Devices with Multiple Parameter Variations

“…Refs. [12,13] are for the design of one structural parameter variation, Although this work focuses on the connection between the strongly guiding waveguide and the weakly guiding waveguide, the proposed numerical method is also applicable to the connection of other more complex waveguides. In such a case, the design procedure followed herein can be adopted: sectioning the 3D geometry and following the method to acquire the final shape.…”

“…Finally, for Sect-3, the initial width of 2.85 µm is joined to the final width of 2.85 µm for the top silicon taper, and the initial width of 4 µm is joined to the final width of 7 µm for the middle silicon taper; each has a length of L 3 . Subsequently, we acquire the mode-connection power transfer efficiency (MCTE) [13] curve with TE 0 mode at the input and output as a function of the length L, as shown in Figure 5. The MCTE is calculated using the "length scan" function in Lumerical EME simulator.…”

“…The MCTE is calculated using the "length scan" function in Lumerical EME simulator. Third, we choose a value for the MCTE along the initial slope of the MCTE curve and determine the length for each section that corresponds to the desired mode-connection power loss fraction (MCLF) [13] value. Here, MCLF = 1 − MCTE, and we take MCLF = 0.0002 as an example.…”

“…The figure shows the NAMSP case enables the same power transfer with a far shorter length than that of the linear-shape case. For example, at 99.9% power transfer, the required total length for the NAMSP case is 49 μm, whereas the linear-shape case requires Third, we choose a value for the MCTE along the initial slope of the MCTE curve and determine the length for each section that corresponds to the desired mode-connection power loss fraction (MCLF) [13] value. Here, MCLF = 1 − MCTE, and we take MCLF = 0.0002 as an example.…”

“…In cases where the geometry is more complicated, such as those that involve the variation or optimization of multiple structural parameters, it is difficult for such methods to solve the problem. Our previous study [12,13] proposed numerical design methods for the design of adiabatic devices, but the design of the adiabatic devices targeted by that study all involved only one structural parameter variation. As shown in Figure 2, if only the width of the top silicon taper waveguide varies, this presents a design problem with "single structural parameter variation".…”