Waveguide structures and methods

Abstract

A waveguide structure has a base having a base height (h) above a substrate and a rectangular waveguide having a waveguide height (H) above the substrate and a waveguide width (W) between opposing sides of the waveguide.

Description

BACKGROUND AND SUMMARY [0001] Embodiments herein generally relate to waveguides that are used to direct and control light. Light has two polarizations, and can propagate in a media (such as a silicon waveguide) at two different speeds for the two polarizations. For a rib / ridge waveguide, the two polarized modes are generally referred to as the transverse electric (TE) and transverse magnetic (TM) modes. The two modes may see the same media differently, as the effective refractive index for the two polarizations may differ. The difference in the effective refractive index could be the result of the symmetry of the media, or, in the case of silicon waveguides, the result of different boundary conditions for the two polarizations. The difference in the refractive index of the two polarizations can cause various adverse effects for an optical communication system and if this difference is not properly compensated for, it will cause adverse effects such as polarization mode dispersion th...

AI Technical Summary

Benefits of technology

[0003] In optical communications using wavelength division multiplexing (WDM), each wavelength channel typically uses a narrow band of wavelengths, and the separation between the channels is in the order of 1 nm. With increasing use of broadband, the channel separation could even get smaller. For λ0=1550 nm, and, nte≈3.42, as typically used, a small difference in nte and ntm could result in significant performance deterioration of the system through channel cross talk. Many compensation methods have been proposed. These include the insertion of a half-wave plate in the middle of the waveguide array, dispersion matching with adjacent diffraction orders, special layer structures, insertion of a waveguide section that compensates for the polarization difference in the phase array, adding a polarization splitter at the input of the arrayed waveguide (AWG), and making a prism-shaped region at the star coupler (combiner) of the demultiplexer. While all these methods reduce or eliminate the polarization dependence, they all add significant complexity to the AWG fabrication, and for many proposed methods, they incur considerable insertion loss.

Problems solved by technology

The difference in the refractive index of the two polarizations can cause various adverse effects for an optical communication system and if this difference is not properly compensated for, it will cause adverse effects such as polarization mode dispersion that causes bit rate errors.

Such a shift will increase the crosstalk between adjacent communication channels and limit bandwidth.

For λ0=1550 nm, and, nte≈3.42, as typically used, a small difference in nte and ntm could result in significant performance deterioration of the system through channel cross talk.

While all these methods reduce or eliminate the polarization dependence, they all add significant complexity to the AWG fabrication, and for many proposed methods, they incur considerable insertion loss.

Using a trial and error method to vary waveguide dimensions in order to obtain near zero TE-TM shift is costly both in terms of time and resource, as each waveguide with different dimension h and H requires different etching depth or wafer thickness.

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