Nonlinear Optics in Silicon Core Fibers
POEM:2012 Nov 20121 Optoelectronics Research Centre, University of Southampton, UK2 Department of Chemistry and Materials Research Institute, Pennsylvania State University, Pennsylvania, USA
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Outline
• Silicon fibers and their fabrication
• Nonlinear propagation equations
• Nonlinear properties of silicon fibers– Absorption (TPA)– Spectral broadening (SPM)– Optical modulation via TPA– Comparison of different core sizes
• Tapered silicon core fibers– Nonlinear pulse shaping
Nonlinear Silicon Photonics- on chip….
• Raman amplifiers/lasers (Claps et al., Opt. Express, v.11, 2003)
• Wavelength conversion: FWM/XPM/THG
• All-optical control: TPA, FCD
• Supercontinuum: SPM
• And much more…
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WOK Publication Data
Breakthroughs in Nonlinear Si Photonics 2011
Y. Okawachi et al., IEEE Photon. J. 4, 601 (2011)
Why Fiberize Silicon?
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• Fibers are the backbone of telecommunications industry
• Silicon waveguides largely used as a nonlinear element
• Incorporation inside the fiber geometry negates some of the coupling issues
• Allow for the construction of cheap/robust devices
• Exploit wide variety of fiber templates for novel designs
• New fiber materials extend applications to medicine, imaging, sensing, and security
Penn State & ORC1
Clemson Univ.2
Virginia Tech.3
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A Brief History of Silicon Fibers
10
8
6
4
2
0
Mar
06
Oct
07
Nov
08
Jan 1
0
Oct
09
Jul 1
0
Jun 1
1
Jan 1
2
dB
/cm
1. P. Sazio et al., Science 311,1583 (2006)2. J. Ballato et al., Opt. Express 16, 18675 (2008)3. B. Scott et al., IEEE Photon. Techn. Lett. 21 1798 (2009)
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A Brief History of Silicon Fibers
10
8
6
4
2
0
Mar
06
Oct
07
Nov
08
Jan 1
0
Oct
09
Jul 1
0
Jun 1
1
Jan 1
2
dB
/cm
1. L. Lagonigro et al., Appl. Phys. Lett. 96, 041105 (2010)2. P. Mehta et al., Opt. Express 18, 16826 (2010)3. P. Mehta et al., CLEO 2012, CTh1C.2
Penn State & ORC1-3
Clemson Univ.
Virginia Tech.
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Chemical Deposition
• High Pressure Chemical Fluid Deposition
• Pressure
– 35MPa
• Precursor
– SiH4+Hydrogen
• Temperature
– low (<400 oC) for a-Si
– high (>500 oC) for p-Si
Silicon Optical Fibers
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1. N. Healy et al., Opt. Express 17, 18076 (2009)
2. N. Healy et al., Opt. Express 19, 10979 (2011)
3. J. R. Sparks et al., JLT 29, 2005 (2011)4. N. Healy et al., Opt. Express 18, 7596
(2010)
1 2
3 4
Hydrogenated Amorphous Silicon
• High nonlinear refractive index
• n~3.6
• Bandgap ~1.7eV
• Transparent from ~800nm-6m
• Hydrogen can passivate dangling bonds for optical low loss
• Lowest loss to date at
– 0.8 dB/cm (1.55m)
– 0.7 dB/cm (2.8m)
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D=5.7m
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Nonlinear Propagation in Silicon
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Nonlinear Propagation in Si Fibers
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Nonlinear Loss
1. P. Mehta et al., Opt. Express 16, 16826 (2010).
Hyperbolic secant input
Self-Phase Modulation
131. P. Mehta et al., Opt. Express16, 16826 (2010)2. A. C. Peacock et al., Opt. Lett. 37, 3351 (2012)
• High power pump induces an absorption dip on weak probe
• One photon from the pump and one photon from the probe
– Total energy must be greater than the bandgap Eg
• Makes use of the imaginary component of the third order nonlinearity Im[(3)] – ultrafast! 1
– All-optical modulation
– Wavelength conversion
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Modulation via TPA
1. D. J. Moss et al., Electron. Lett. 41, 2005
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Modulation via TPA
• Simplified pump-probe equations
• High power pump I1 at 1
• Weak probe A2 at 2
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Modulation via TPA
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• Degenerate pump-probe technique
1. P. Mehta et al., Opt. Express, vol. 19, 19081 (2011).
1717
Modulation via TPA• Non-degenerate pump-probe technique
• Highly Nonlinear Fibre (HNLF)
• Bandwidth Variable TuneableFilter (BVF)
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Modulation via TPA• Non-degenerate pump-probe technique
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Cross-Absorption Modulation• Extinction: ~ 3 dB
• Pulse width ~ 1 ps
~87ns Pump
Probe
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Cross-Phase Modulation
1. R. Dekker et al., Opt. Express 14, 8336, 20062. E. Tien et al., Appl. Phys. Lett. 95, 051101, 20093. H. Hsieh et al., Opt. Express 18, 9613, 2010
See next presentation: IF5B.4
• Real part of the third order nonlinearity Re[(3)]
• High power pump induces a phase shift on a weak probe due to intensity dependent refractive index change
– Optical switching1
– Gating2
– Regeneration3
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Towards smaller core fibers- Nonlinear Absorption
• 1.7µm core diameter
• Aeff = 1.24m2
• L = 6mm
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Towards smaller core fibers -Self-Phase Modulation
• 1.7µm core diameter
• Aeff = 1.24m2
• L = 6mm
• Combine large nonlinearity with reduced for low power high-speed devices
Core Size Comparison
• Core sizes: 1.7m (green), 5.7m (red)
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• Nonlinear parameter:
Tapered Silicon Core Fibers
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• BIT communications fusion splicer
• Arc current in the range: 8-15 mA
• Duration: 5.5 s – heat silicon above melting point 1410oC
• Pull distance selected for desired ratio
Tailor Waveguide Parameters
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• Decreasing dispersion is formally equivalent to dispersion and gain
– Pulse shaping
• Applications of tapered fibers
– Short pulse generation
– Phase matched four-wave mixing
– Supercontinuum generation
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Dispersion and Nonlinearity Tailoring
=1.55m
NormalAnomalous
• High core/cladding index contrast allows for tailoring of the waveguide dispersion
• Normal dispersion regime₋ decreasing dispersion₋ increasing nonlinearity₋ parabolic pulses?
• Anomalous dispersion regime₋ decreasing dispersion₋ decreasing nonlinearity₋ soliton solutions?
Normal Dispersion - Parabolic Pulse Shaping
Silicon Taper ₋L = 2mm₋Din = 2.5m₋Dout = 1m
Input Pulse₋Gaussian₋Tin = 200fs₋P0 = 200W
271. A. Peacock , N. Healy, “Parabolic pulse generation in tapered silicon fibers,” Opt. Lett., vol. 35, 1780 (2010).
• Self-similar solutions for high power pulse propagation– strict linear chirp
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Anomalous Dispersion- Soliton Propagation
Silicon Taper ₋L = 10mm₋Din = 640nm₋Dout = 850nm
Input Pulse₋N = 1₋Tin = 170fs₋P0 = 1W
1. A. Peacock “Soliton propagation in tapered silicon core fibers,” Opt. Lett., vol. 35, 3697, 2010.
• Compensate for loss induced broadening of fundamental soliton
Conclusions
• Demonstrated the smallest core silicon fibers
– losses comparable with on-chip technologies
• First nonlinear characterization of silicon fibers
– demonstrate device functionality
• Moving towards nanoscale waveguides
– low power operation and faster device speeds
• Exploit fiber geometry for novel nonlinear functionality
– tapered fibers29
Thank [email protected]
Acknowledgments
• EPSRC (EP/G051755/1 and EP/J004863/1)
• Royal Academy of Engineering
• NSF (DMR-1107894 and DMR-0820404)
