The designs that will shown to be modeled, simulated, fabricated, and analyzed include 4 MZI circuits for the E field of varying \(\Delta L\) branches, 1 MZI in the H field, and 1 experimental lattice FIR filter of multiple staged MZI's. All MZI's designed are as shown below with include a gradient coupler for the test laser input, followed by a Y branch, followed by the two imbalanced wave guides which connect to a 50/50 broadband directional coupler (BDC) splitter followed connected by waveguides to the gradient couplers for reading the outputs. The factors under test discussed below are the waveguide parameters mainly width and their lengths. It was chosen to use BDC instead of just a Y branch on the output to allow for 2 outputs which should be 180 degrees out of phase from each other, often used for switches and similar applications. The layout took care for all E field MZI circuits to keep waveguide bend radius > 5 um while it is noted the H field MZI should meet the requirement of bend radius > 10 um. This may be discussed further below.
The MZI circuits being designed will be characterized at wavelengths centered around 1550 nm with about 100 nm bandwidth, ranging from 1500 to 1600 nm. This matches the future wafer automated testing that will be performed.
The core wave guide component designed is restricted to 220 nm high and chosen width of 500 nm allows ideal single mode propagation for E field or H field greatly suppressing the higher order modes as will be shown.
3.1 Waveguide Properties
Our 500 nm wide, 220 nm high waveguides can be shown to have about index of refraction \(n_{eff} = 3.47\) for Si and \(n_{eff} = 1.44\) for SiO2 as shown in the below Lumerical Mode analysis setups.