1. Simulations Based on Paper
Nanophotonics, 2014
Review
Simulation with different waveguide geometry
Simulation with different junction location
Simulation of interleaved junction modulator
Conclusion

2. Carrier Depletion Based Modulator
<Carrier depletion modulator>
<Refractive index vs Carrier concentration>
Plasma dispersion effect -Change in carrier concentration change in refractive index, absorption coefficient change in phase & intensity
∆𝑛=−[8.8× 10 −22 ∆ 𝑁 𝑒 +8.5× 10 −18 ∆ 𝑁 ℎ ]
∆𝛼=6× 10 −18 ∆ 𝑁 𝑒 +4× 10 −18 ∆ 𝑁 ℎ ]
<Loss vs Carrier concentration>
Ref. “Electrooptical Effects in Silicon”, Soref and Bennett, IEEE J. of Quantum Electronics, 1987

3. Categories Of Modulators
Three types of modulator -Vertical junction -Horizontal junction -Interleaved junction
<Vertical Junction>
<Horizontal Junction>
<Interleaved Junction>

4. Waveguide Geometry(Height)
500 nm
500 nm
220 nm
450 nm
90 nm
<220nm Height>
<450nm Height>
Different height of waveguide -Rib waveguide -Doping: p(1× ), n(2× ) -Same waveguide width(500nm) -1cm length

5. Simulation Results
500 nm
500 nm
220 nm
90 nm
450 nm
<220nm Height>
<450nm Height>
Smaller effective index changes for larger height -Effective index without bias is larger  Smaller effective index changes
Smaller loss for larger height -Large confinement factor  Smaller loss

6. Transmission Curves
<220nm Height>
<450nm Height>
Smaller effective index changes for larger height Larger efficiency
Smaller loss for larger height Smaller insertion loss

7. Position of PN Junction
Offset of junction location -P-type has larger refractive index change (Soref & Bennett equation) -Large portion of P-type Increased efficiency
<Cross section of modulator>

8. Junction Location
500 nm
500 nm
100 nm
<Junction located on middle of waveguide>
<Junction located with offset from middle>
Different junction location -Rib waveguide -Doping: p(1× ), n(2× ) -Same waveguide width(500nm) -1cm length

9. Simulation Results
500 nm
500 nm
100 nm
<No offset>
<100nm offset>
Larger effective index changes with offset -P doping has larger effect on effective index changes  Larger effective index change
Smaller loss with offset -N doping has larger effect on loss(doping concentration)  Smaller loss

10. Transmission Curve
<No offset>
<100nm offset>
Larger effective index changes with offset Smaller efficiency
Smaller loss with offset Smaller insertion loss

11. Interleaved Type Modulator
Density of depletion increase -Period of p,n region should be small -Increase in capacitance Lower BW, more power -Tolerant to alignment errors
MZM -44-Gbps, 1.7V.cm efficiency 1dB/mm loss is reported
<Interleaved Junction>
<MZM with interleaved junction>

12. Simulation Setup & Results
<Interleaved junction>
Ref. “A 25Gbps silicon microring modulator based on an interleaved junction”, J. C. Rosenberg, et al., Optics Express, 2012
-Rib waveguide(220nm height) -Doping: p(2× ), n(2× ) -Junction period: 560nm -Field profile in one period  Extract phase information  Calculate Vπ
<Simulation Result>

13. Conclusion
Waveguide Geometry Larger height has small loss, but larger efficiency
Junction Location Large portion of p-doping has small loss & small efficiency
Interleaved Junction Small efficiency achieved