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Silicon Nitride Band Splitter Based on Multimode Bragg Gratings
Jonathan Cauchon1, Jonathan St-Yves1,2, Francois Menard2, Wei Shi1
1Centre dâoptique, photonique et laser (COPL), UniversitĂŠ Laval, QC, Canada
2AEPONYX inc., 33 Prince St. #200A, Montreal, QC, Canada
June 2021
Outline
1. Motivation
The Si3N4 platform, broadband Filters, NG-PON2 transceivers
2. Design
Multimode Bragg grating, adiabatic directional coupler
3. Results
NG-PON2 diplexer and figures of merit
4. Conclusion
Accomplishment & potential improvements
Motivation: The Si3N4 Platform
Pros:
⢠Low-loss waveguides
⢠Wide transparency range (0.4â 2.35 Âľm)
⢠CMOS-compatible
⢠Low index contrast
Cons:
⢠Larger footprint
⢠Low index contrast
[1] Daniel J Blumenthal, Rene Heideman, Douwe Geuzebroek, Arne Leinse, and Chris Roeloffzen. Silicon nitride in silicon photonics. Proceedings of the IEEE, 106(12):2209â2231, 2018.
SiO2 (n = 1.45)
Si3N4 (n = 2.05)
45
0 n
m
Motivation: NG-PON2 Broadband Filters
Next-Generation Passive Optical Network 2
⢠2 Symmetric 4-channel DWDM (Tx & Rx)
⢠2-channel CWDM to diplex Rx from Tx
⢠CWDM filter figures of merit (FOM):
1. Bandwidth
2. Insertion loss
3. Top flatness
4. roll-off sharpness
5. Out-band suppression ratio
DW
DM
DW
DM
CW
DM
Tx
đ1
đ2
đ3
đ4
đ5
đ6
đ7
đ8
Rx
1
23
4
5
Motivation: NG-PON2
Target Application
⢠4 transmission DWDM channels
(195.3 â 195.6 THz)
⢠4 reception DWDM channels
(187.5 â 187.8 THz)
⢠Filter requirements:⢠4-port
⢠Super-channel diplexing
⢠Figures of merit of CWDM filter
Design: Proposed Solution
Drop
Input Thru
Add
Multimode Bragg Gating (MBG)⢠Reflection⢠Wavelength selectivity⢠Mode conversion(Forward TE0 â Backward TE1)
Input Adiabatic Directional Coupler (ADC)
⢠Mode conversion⢠Couple reflection into drop
port
Output ADC⢠Couple through-put power to
thru port⢠Identical to Input ADC for add-
drop operation
Design: Multimode Bragg Grating
7
TE1
X
â
đŚ
đĽTE0
TE0
TE1
Xâ
đĽw
wâŚ
đŹ
đ2
⢠Coupled Mode Theory:
đ đđ =đ
4ŕśľ đđ
â đĽ, đŚ Îâ° đĽ, đŚ đđ đĽ, đŚ đđŚđđĽ
z
x
X
⢠Phase-Matching Condition:
đđľ = 2 Î ŕ´¤đđđđApodization
Design choice: w = 1500 nm, đŹ = 484 nm
600
Design: Adiabatic Directional Coupler (ADC)
Input ADC
Input
DropTE0
TE1
TE0
TE0
MBG TE1
TE0
Thru
Add
TE0
TE0
500 400
70 đm
1500 nm
750800 nm
Output ADC
- 1.25 dB
Results: Figures of Merit
Bandwidth: 12.8 nm (1500 GHz) C-band ChannelsInsertion loss: 2.7 dBExtinction Ratio: 20.4 dBDrop port roll-off: 6.1 dB/nm
2.7
20.4 20.3
3.3
L-band ChannelsInsertion loss: 3.3 dBExtinction Ratio: 20.3 dBThru port roll-off: -5.0 dB/nm
solution: Phase Apodization
(a) (b)
27.0 22.4
5.076.89
22.2
11.7
[2] Cheng, Rui, and Lukas Chrostowski. "Apodization of silicon integrated bragg gratings through periodic phase modulation." IEEE Journal of Selected Topics in Quantum Electronics 26.2 (2019): 1-15.
đ đđ =đ
4ŕśľ đđ
â đĽ, đŚ Îâ° đĽ, đŚ đđ đĽ, đŚ đđŚđđĽ âŚ
No coupling max. coupling⢠Phase apodization avoids coupling-dependent chirp [2]
TE experimental TM experimental
Conclusion
⢠Broadband add-drop filter on Si3N4-SiO2
⢠Suitable for NG-PON2 super-channel diplexing⢠Channel isolation > 20 dB
⢠Insertion loss < 3.5 dB
⢠Future improvements⢠Extinction ratio: Cascade devices
⢠Insertion Loss: Design non-linear ADC
⢠Make polarization-insensitive
Additional: Polarization Insensitivity
⢠Polarization insensitivity can be achieved by counter-balancing waveguide birefringence [3]
⢠All figures from [3]
[3] Tabti, B., Nabki, F., & MĂŠnard, M. (2017, July). Polarization insensitive Bragg gratings in Si3N4 waveguides. In Integrated Photonics Research, Silicon and Nanophotonics (pp. IW2A-5). Optical Society of America.