Organic Nonlinear Optical
Devices and Integrated Optics
Outline
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Directional Coupler
Nonlinear Fabry-Perot Interferometer
Frequency Converter
Optical Limiter
Integrated Optics
Conclusions
Signal Switching I:
Directional Coupler
Directional Coupler
• Interaction length and refractive index
difference of the cores control the splitting
ratio
Fluorine doped polyimide
• Fluorine content controls the refractive index of
polyimide
• Core and cladding layer can be made from the
same polymer---polyimide.
Fabrication
mask
• To make multi-layer patterned structure,
only need: spin coating, photolithography
and RIE
Nonlinear directional coupler
• Refractive index changes with light intensity
• Splitting ratio changes with light intensity
Material requirement
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Low switching power: High n2 , (2)
Fast switching: Low response time
Low propagation loss: Low absorption
High optical damage threshold
High thermal stability
A candidate: DPOP-PPV
• A side chain
substituted PPV
• Loss = 0.4 dB/cm at
920 nm
• n2 = 1.1e-14 cm2/W
• Imax > 16 GW/cm2
• Tg = 163C
Experimental Result
Waveguide 2
Waveguide 1
• Length = 1/3 beat length (0.67 cm)
• Switching at 5.5 GW/cm2
Advantages and applications
Advantages:
• All optical switching
• Bar state splitting: 90/10
• Cross state splitting: 33/67
• Polymer: Easy processing
Applications:
• Beam splitter, Wavelength Add-Drop
Multiplexer, Cross/Bar Switch
Signal Switching II:
Fabry-Perot Interferometer
Nonlinear Fabry-Perot Device
Signal In
Signal Out
Pump
Mirrors:
Reflectivity > 95%
Nonlinear medium
• A wavelength selective device
• Wavelength of the output signal depends on
refractive index of the middle medium
Operation
• Nonlinear middle medium: poly-1,6dicarbazoly 1-2,4-hexadyne (DCHC)
• Signal range: 700 - 900 nm
• Pump range: 637 - 645 nm
• Pump light changes the index of the middle
medium and changes the wavelength
selection at the output.
Experimental Results
Performance
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Pump: 2 GW/cm2 at 641 nm for 0.8 ps
Turn on time: 0.33 ps
Recovery time: 3 ps
Can switch at 333 GHz
All optical switching
Very simple structure, easy processing
Frequency Conversion:
Second Harmonic Generation
Device
A waveguide-type with periodic
structure
Waveguide-type periodic
structure
• Waveguide-type: compact, easy coupling to
fibre/laser
• Periodic alternations of nonlinearities in the
waveguide: enable phase-matching for light
at  and 2.
• Conversion:
2
2
 2
P
 0 L ( P )
Periodic structure
Nonlinear
material
Linear material
Organic crystal + Semiconductor
• Nonlinear material: mNA (organic crystal
grown on the grating)
• Linear material: SiN (grating)
Performance
(2) = 2*d33
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50 nm
mNA: d33 = 20 pm/V
3 m
Period = 7 m
Length = 5 mm
Wavelength = 1.06 m
Conversion efficiency = 0.16% /W/cm2
5 mm
An all-polymer one
• Nonlinear polymer: diazo-dye-substituted
• Linear polymer: UV curable epoxy resin
Fabrication
Serial grafting technique:
Photolithography
RIE
Experimental Results
5 mm
2 um
6 m
• The nonlinear polymer: d33 = 15 pm/V
(after poled at 35 MV/m at 140C)
• Loss = 1.2 dB/cm
• Period = 32 m
• Wavelength = 1550 nm
• Conversion efficiency = 0.5%/W/cm2
Signal Processing:
Optical Limiter
Operation of Optical Limiter
• Low fluence:
Linear
transmittance
• High fluence:
Clamped output
level
Reverse saturable absorption
• Low intensity: Molecule is in low
absorption state. Linear transmittance
• High intensity: Molecule is in photoinduced
absorbing state. The material becomes
highly absorptive.
• Candidate material:
– Metallo-Phthalocyanines
– Fullerenes
Metallo-Phthalocyanines
• Very weak ground state absorption
• Strong excited state absorption
Experimental Results
C60 in toluene
AlClPc in
methanol
InClPc in
toluene
• Length = 1 cm
• Wavelength = 532 nm
• Pulse width = 8 ns
Fullerenes (Bucky balls)
• All-carbon cluster
• Abundance of C=C
gives plenty
delocalizeable
electrons
• C60, C70, C 76, ...
Experimental Results
• Solvent used plays an important role
Linear + Nonlinear:
Integrated Optics
Advantages of polymer
• Low loss: 0.1 dB/cm at 1550 nm
• Controllable nonlinearities by doping/poling
• Low cost: only need spin-coating,
photolithography and RIE
• Mechanical properties: rugged, flexible
• Precise control of refractive index:
conveniently done by doping
• Convenient thickness control: spin-coating
Example 1: All polymer
waveguide and MZ
• All polymer 3-D structures
• Achieve multi-level interconnections
Material
• UV15LV: low loss polymer as waveguide
• Polyurethane with tricyano chromophores:
Active polymer with electro-optic
coefficient = r33= 12 pm/V
• Waveguide loss = 0.5 dB/cm
Phase modulator
• Upper level: EO modulator
• Lower level: waveguide
Example 2: Optical Transceiver
Characteristics
• Integrate polymer waveguide into
semiconductor system
• Use polymer for waveguide and splitter
• Easy fabrication of polymer Y-branch
structure
Example 3: Laser array and beam
combiner
Laser array
Polymer beam
combiner
Material
Polymer
waveguide
The polymers are spin-coated on the laser-array-existing
semiconductor substrate
Features and applications
• Loss < 1 dB/cm
• Good polymer adhesion to the substrate
• Applications:
– Wavelength multiplexer/demultiplexer
– MW-O-CDMA transmitter
Conclusions
Polymers are good for:
• waveguide structure: low loss
• EO or nonlinear operation: high and
controllable nonlinearities
• Multi-level structure (3D): result of easy
processing
Hybrid semiconductor/polymer structures or
all polymer structures give rise to ample
opportunities
Reference 1
• Polymer Directional Coupler
– J. Kobayashi et al., “Directional Couplers Using Fluorinated Polyimide
Waveguides,” Journal of Lightwave Technology, Vol.16, No. 4, pp. 610613, 1998.
– T. Gabler et al., “Application of the polyconjugated main chain polymer
DPOP-PPV for ultrafast all-optical switching in a nonlinear directional
coupler,” Journal of Chemical Physics, Vol. 245, pp. 507-516, 1999.
• Polymer Fabry-Perot Device
– M. Bakarezos et al., “Ultrafast nonlinear refraction in an integrated FabryPerot etalon containing polydiacetylene,” Proc. CLEO ‘99, CWF12, pp.
258, 1999.
Reference 2
• Polymer waveguide second harmonic generation devices
– T. Suhara et al., “Optical Second-Harmonic Generation by Quasi-Phase
Matching in Channel Waveguide Structure Using Organic Molecular
Crystal,” IEEE Photonic Technology Letters, Vol. 5, No. 8, pp. 934-936,
1993.
– Y. Shuto et al., “Quasi-Phase Matched Second-Harmonic Generation in
Diazo-Dye-Substitued Polymer Channel Waveguides,” IEEE Journal of
Quantum Electronics, Vol. 33, No. 3 pp. 349-357, 1997.
• Optical limiter
– Y. Sun et al., “Organic and inorganic optical limiting materials. From
fullerenes to nanoparticles,” International Reviews in Physical Chemistry,
Vol. 18, No. 1, pp. 43-90, 1999.
• Integrated Optics
– S. M. Garner et al., “Three-Dimensional Integrated Optics Using
Polymers,” IEEE Journal of Quantum Electronics, Vol. 35, No. 8 pp.
1146-1155, 1999.
– N. Bouadma et al., “Monolithic Integration of a Laser Diode with a
Polymer-Based Waveguide for Photonic Integrated Circuits,” 1994.
– T. Ido et al., “A simple low-cost polymer PLC platform for hybrid
integrated transceiver modules,” 2000
Appendix A
Semiconductor NLDC
• Based on MQW SC laser
• Operate at the transparency point
Properties
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Good nonlinearity
Fast response
Lower switching power
Complicated structure (e.g. MQW)
Need current injection (120 mA)
Loss = 25 dB/cm at 879 nm
Other SC structures
[Villenevue, 1992]
• no current injection is required
• still need MQW
• splitting ratio and switching power are
comparable to the nonlinear polymer ones.
• Semiconductor Directional coupler
– S. G. Lee et al., “Subpicosecond switching in a current injected
GaAs/AlGaAs multiple-quantum-well nonlinear directional coupler,”
Applied Physics Letters,Vol. 64, pp. 454-456, 1994.
– A. Villeneuve et al., “Ultrafast all-optical switching in semiconductor
nonlinear directional couplers at half the band gap,” Applied Physics
Letters, Vol. 61, pp. 147-149, 1992.
Appendix B
Carrier generation through
nonlinear optical process
• Direct bandgap material:
– 2PA
– intensity dependent: effective for ultrashort
pulse (ps to sub-ps)
• Indirect bandgap material:
– linear indirect absorption
– fluence dependent: good for ps to 100s ns
Experimental Results
Si
GaAs
• Pulse width = 25 ps, wavelength = 1060 nm