Basic Waveguide Properties - Lumerical · Basic waveguide properties MODE list provides basic...
Transcript of Basic Waveguide Properties - Lumerical · Basic waveguide properties MODE list provides basic...
Lumerical Solutions, Inc.
Basic Waveguide Properties
1. Basic waveguide properties Propagation constant, loss
TE vs TM
2. Waveguide cut off condition
3. Understanding dispersion
4. Evaluating loss
Learning Objectives
MODE Solutions introductory video:
https://www.lumerical.com/support/courses/mode_introductory_webinar_video.html
Getting started examples:
http://docs.lumerical.com/en/mode/getting_started.html
Pre-lesson preparation
BASIC WAVEGUIDE PROPERTIES
Basic waveguide properties
Open waveguide.lms
SOI strip waveguide
500nm x 220nm
Click
Brings up solver window
Wavelength = 1.55um
Click “Calculate modes”
Basic waveguide properties
MODE list provides basic waveguide properties
neff, loss, TE fraction
Mode profiles
Basic waveguide properties
Plot the different field components for the fundamental TE and TM mode.
How many modes does this waveguide support?
How do we know if a mode is bound?
Questions
Basic waveguide properties
BASIC WAVEGUIDE PROPERTIES
Waveguide cutoff conditions
In waveguide.lms, go to the “Optimizations and Sweeps”
Open the edit window for “waveguide_width”
• sweep will track neff of each mode as a function of the waveguide width
Click “run sweep”
Go to the “Result View” window, select all results and “Visualize”
Waveguide cutoff conditions
run sweepedit sweep
Open and run waveguide.lsf in the “Script File Editor” window to plot the sweep results in normalized units
Waveguide cutoff conditions
At what waveguide width does each mode cutoff?
When does the waveguide become single mode?
If we want the waveguide to operate with a single TE mode, what waveguide width should we use?
Questions
Waveguide cutoff conditions
Instead of running the parameter sweep, run waveguide2.lsf in the script file edtor
This script will track each mode
individually (instead of only tracking
the largest effective indices)
Notice mode crossing at 0.65um
Look at the polarization for the modes right before and after the mode crossing. Verify that the mode with the 2nd highest neff changes from TE to TM
Additional exercise
Waveguide cutoff conditions
BASIC WAVEGUIDE PROPERTIES
Understanding dispersion
Refractive index of material is dependent on wavelength
Open waveguide.lms, click on in the tool bar
Click on “Fit and plot” to see
material dispersion for silicon
Squares show actual Palik data
Line shows what is actually
used in simulation
Material dispersion
Understanding dispersion
Calculate modes in Eigenmode solver
Go to “Frequency analysis” tab
Select mode(s) to track
Ex. fundamental TE
Set wavelength range
Click “frequency sweep”
Understanding dispersion
plot results
Modal dispersion: neff()
Includes both material and
waveguide dispersion
Modal Group velocity: vg = d/d
Group velocity dispersion: D = d(1/vg)/d
Understanding dispersion
Understanding dispersion
Additional exercise
Remove the effect of material dispersion by changing the waveguide material from silicon to dielectric
Re-run the frequency sweep. Does the material dispersion of silicon have a strong effect on the overall modal dispersion?
Change the waveguide width, re-run the frequency sweep and observe how the dispersion is affected
BASIC WAVEGUIDE PROPERTIES
Evaluating loss
Open waveguide.lms, click on in the tool bar
Change wavelength range to go from 0.2um to 1um
Click on “Fit and plot” to see material dispersion for silicon Im(index) > 0 indicates material loss
Silicon highly lossy at wavelengths < 0.5um
Loss ~ 0 for wavelengths > 1um
Material loss
Evaluating loss
Open waveguide_bend.lms, calculate modes Record loss for the fundamental TE and TM mode
Right-click on each and select “add selected modes to global deck”
Select “bent waveguide”, set bend radius to 5um and re-calculate
Compare radiative loss between the straight and bent waveguide
Radiative loss for bent waveguides
Evaluating loss
Straight waveguide Bent waveguide
TE ~0 dB/cm* ~0 dB/cm*
TM ~0 dB/cm 2778 dB/cm
* ~0 since imag(neff) ~ 10e-6 ~ numerical error
Go to the “Overlap analysis” tab
Select the fundamental TE mode in the mode list
Select “global_mode1” in the DECK
Click “Calculate”• Power coupling gives the amount of power that can couple from one mode
to another (ie. coupling efficiency)
Repeat for the fundamental TM mode and “global_mode2”
Mode-mismatch loss for bent waveguides
Evaluating loss
TE power coupling TM power coupling
0.999 0.800
TE:
TM:
Mode-mismatch loss for bent waveguides
Evaluating loss
Calculate total loss in a 90 degree bend
Radiative loss
Overlap loss
Total loss for a 90 degree bend:
𝑙𝑜𝑠𝑠 𝑓𝑟𝑜𝑚 2 𝑖𝑛𝑡𝑒𝑟𝑓𝑎𝑐𝑒 + 𝑙𝑜𝑠𝑠 𝑓𝑟𝑜𝑚 90 𝑑𝑒𝑔𝑟𝑒𝑒 𝑏𝑒𝑛𝑑
= −2 × 10 log 𝑐𝑜𝑢𝑝𝑙𝑖𝑛𝑔 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 + 𝑟𝑎𝑑𝑖𝑢𝑠 ×𝜋
2× 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑣𝑒 𝑙𝑜𝑠𝑠
TE = 0.0087 dB + 0 dB = 0.0087 dB
TM = 1.938 dB + 2.182 dB = 4.12 dB
Total loss for bent waveguides
Evaluating loss
In this lesson plan, we covered:
1. Basic waveguide properties • Propagation constant, loss
• TE vs TM
2. Waveguide cut off condition
3. Understanding dispersion
4. Evaluating loss
Summary
We would like to thank Professor Lukas Chrostowski from the University of British Columbia (Vancouver, Canada) for contributing to the contents of this module
http://www.ece.ubc.ca/faculty/lukas-chrostowski
Acknowledgement