2 nonlinear optics - harvard university
TRANSCRIPT
http://mazur.harvard.edu
Coupling padsWe can optimize for insertion losses by fabri-cating low index polymer coupling pads (top). Using an adiabatic taper, we can in-crease our waveguide input coupling e�-ciency by 30% by implementing a coupling pad (bottom).
Waveguide width (nm)
Pow
er c
oupl
ing
300 400 500 600
1
0.8
0.6
0.4
0.2
0
with coupling padwithout coupling pad
TiO2
SiO2
coupling padLaser
Dispersion engineeringNonlinear e�ects cause ultrafast pulses to broaden, disperse and thus attenuate. By tuning the wave-guide geometry, we obtain anoma-lous group velocity dispersion which directly counters these ef-fects and produces optical solitons.
100 200 300 400 500 600 700 800500
0
500
1000
1500
Waveguide width [nm]
2[fs2 /m
m]
Film thickness
1000 nm900 nm800 nm700 nm600 nm500 nm
Input7 pJ
28 pJ46 pJ
wavelength (nm)
norm
aliz
ed p
ower
(dB)
740 780 820 860
10
0
–10
–20
–301450 1500 1550 1600 1650 1700
Input60 pJ
120 pJ231 pJ
wavelength (nm)
A short pulse in a nonlinear waveguide generates new wave-lengths. Here, we show spectral broadening at both 800 nm (left), 1550 nm (middle), and green-light from 1550 nm pulses (right).
Nonlinear properties
input 1550 nm generated
green light
Smooth features are important to achieve low propagation losses in photonic waveguides. We achieve the most consistent etch by using chromium as an etch mask compared to aluminum oxide (left). We also obtain smoother features by using ZEP as a resist in-stead of PMMA (right).
Fabrication materials
500 nm 1 μm
PMMA ZEPAl2O3 Cr
etch mask comparison e-beam resist comparison
Fabrication steps
SiO2
silicon wafer
begin with silicon wafer with thermal oxide film
deposit thin TiO2 film using reactive sputtering
spin on e-beam resist layer
deposit thin metal film using electron beam evaporation
immerse resist in developer to remove exposed regions
write pattern into resist using electron beam lithography
lift-off metal film by dissolving resist
etch through TiO2 film using reactive ion etching
remove remaining metal leaving TiO2 waveguides
TiO2
400 nmλ = 633 nm
300 μm
Once fabricated, TiO2 photonic waveguides have trapezoidal cross sections (left) and are capable of guiding visible light (right).
WaveguidesOverviewTiO2 is a widely transparent, highly nonlinear novel photonic ma-terial that has potential applications in all-optical switching and other nonlinear processes. In order to best exploit it’s large nonlin-earity, we have optimized our fabrication process and have simu-lated design parameters that aid in producing and maintaining large pulse intensities within integrated photonic structures.
EricMazur
OradReshef
ChristopherEvans
JonBradley
SarahGriesse-Nascimento
Harvard University, Cambridge, MAMassachusetts Institute of Technology, Cambridge, MA
Maximizing intensity in TiO2 waveguides fornonlinear optics