1. FWM IN SILICON NANOWIRE & MULTICORE FIBER COUPLING
Kéven Bédard
Benoît Filion
Université Laval

2. Four-Wave Mixing
Wavelength conversion technique : modulation format transparency.
A strong pump at ω0 and a weaker signal at ω1 = ω0 – Ω are injected at the input of the nonlinear medium.
A new optical field is generated at ω2 = ω0 + Ω through the third-order polarization term : 𝑃 𝑡 ∝ 𝜒 1 𝐸 𝑡 + 𝜒 2 𝐸2 𝑡 + 𝜒 3 𝐸3 𝑡 +… Ω
NL Medium
Pump
Signal
Idler ω1 ω2 ω0

3. FWM in Silicon Nanowires
The high index contrast of SOI waveguides allows for a tight confinement inside the waveguide.
SOI waveguides exhibit larger third-order nonlinearity than that of an optical fiber.
The dispersion of the SOI waveguides is mostly governed by its shape and dimensions : dispersion can be engineered to get a large conversion bandwidth.

4. Design Challenges Conversion efficiency (CE) FWM conversion bandwidth
→ CE = Idler output / Signal input
→ Must be as high as possible over a wide wavelength conversion range
→ The efficiency is tightly related to the effective mode area of the waveguide.
FWM conversion bandwidth
→ Phase-matching condition : dispersion engineering
→ Single mode or multimode waveguide?
Polarization diversity ?

5. Dispersion Engineering
𝜅 z =Δβ 𝜔 0 , 𝜔 1 , 𝜔 2 +2γ𝑃 𝑝 𝑒 (− 𝛼+ 𝛼 𝑓𝑐𝑎 𝑧)
The phase mismatched is dependent on the linear loss (𝛼) and the free carrier absorption induced loss ( 𝛼 𝑓𝑐𝑎 ).
Single mode operation in a multimode waveguide?
Waveguide Dispersion
Phase-Mismatch Condition
Input Powers
Conversion Efficiency
Conversion Bandwidth
linear phase-mismatch
non-linear phase-mismatch
The conversion efficiency and bandwidth are dominated by the phase-mismatched condition, which is determined by the dispersion of the SOI waveguide and the input pump powers.

6. FWM conversion Bandwidth
Etched Waveguide
700nm x 220nm
Pump at 1550nm

7. Polarization Diversity ?
Figure from Lukas presentation!!!

8. Multicore fiber coupling
Figures from: Silicon Photonics Core-, Wavelength-, and Polarization-Diversity Receiver, C. R. Doerr and T. F. Taunay, IEEE Photonics Technology Letters, Vol. 23, No. 9, May 1, 2011

9. Vertical grating coupler
Figures from: Fabrication-Tolerant Waveguide Chirped Grating Coupler for Coupling to a Perfectly Vertical Optical Fiber, Xia Chen, Chao Li, and Hon Ki Tsang, IEEE Photonics Technology Letters, Vol. 20, No. 23, December 1, 2008

10. Thank you!