We propose adiabatic elimination (AE) to suppress the cross-talk in ultra-dense optical waveguides with sub-wavelength spacing. AE in atomic system is caused by a strong coupling nearby levels and a large detuning between them. Analogous to a three-level atomic system, in a set of three AE waveguides the outer waveguides function as an effective two-mode system like ground- and excited- states and the middle waveguide is same as dark state. While decomposition of three level system to two plus one has been reported previously, thanks to the “critical-point” three waveguides could be fully decomposed into three separate waveguides. Here we calculated the power profile using combination of three-dimensional (3D) finite difference time domain (FDTD) and 3D eigen-mode expansion method. At the input waveguide, initial amplitude of super-eigen-modes are obtained with 3D FDTD and the optical power in the three arms is then simulated with the overlap integral of the propagating super-eigen-modes with the fundamental transverse-electric (TE) of the isolated three waveguides. In the conventional coupled waveguides, sufficient inversion length at the telecommunication wavelength (1530 nm to 1565 nm) requires lambda spacing. Thanks to the critical point in our proposed waveguide, ultra-dense packaging with spacing as low as lambda/6, inversion length of several millimeters and cross-talk as low as 1 dB is obtained. Our preliminary experimental results are in good-agreement with the design. This concept can be extended to numerous number of optical waveguides. This AE waveguides will pave the way to ultra-dense multiplexing system as well as optical short-reach interconnects.
Iman Zand, Hamed Dalir, Elham Heidari, Fazard Mokhtari-Koushyar, Volker Sorger, and Ray T. Chen, " Ultra-dense ultra-high speed optical waveguides with sub-wavelength spacing (Conference Presentation)," Proc. SPIE 10526, Physics and Simulation of Optoelectronic Devices XXVI, 1052618 (Presented at SPIE OPTO: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291070.5751404167001.
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