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A WDM/DWDM model for AWGs and Echelle Gratings

Multiple Etch Depth Tapers

Optimise your deep etch to shallow etch transitions

In Echelle and AWG designs there can be some loss due to reflection from the abrupt change in the materials at the interface between the waveguides and the slab in the start coupler. One possible way to avoid this is to use a shallower etch at this interface and thus reduce the contrast. Away from the star coupler a more confined deeper etch is preferred to reduce bend loses in bends. Epipprop provides you with the ability to define any combination of etches in the transition region and model them with its sister product FIMMPROP.

Layout showing tapering with two etch levels

An example of an AWG in SOI with a shallow to deep etch transition.
Using EPIPPROP's connection to FIMMPROP this transition can be rigorously
modelled and used in the simulation of the whole device.

Intensity distribution in the taper

Intensity along the central axis of the taper for the waveguide laid out in EPIPPROP and modelled in FIMMPROP.

This additional step in the etch along the taper will broaden the modes at the start and end of the AWG, improving coupling into the array, and the shallow etch will also reduce the reflection. The result is that more light can be coupled and transferred through the waveguides than would be possible with just a single deep etch. In the case of this device, the addition of the extra etch step improved the insertion loss by around 0.9dB without effecting the channel shape.

You can see the results in the images below: as a result of using a deep etch to shallow etch transition, an improvement of around 0.9 dB can be achieved across all channels compared with a single deep etch process!

Improvement in transmission after introducing the second etch

Transmission spectra for (left) single deep etch process and
(right) the same device with a deep etch to shallow etch transition