REMONDER: PhD Dissertation Defense tomorrow

Luigi Scaccabarozzi scaccag at stanford.edu
Tue May 2 10:29:09 PDT 2006


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Department of Applied Physics
University Ph.D. Dissertation Defense

ALGAAS/ALOX-BASED SUBMICRON WAVEGUIDES
AND RESONANT CAVITIES FOR NON-LINEAR OPTICS
Luigi Scaccabarozzi
Research Advisor: Professor J. S. Harris

Wednesday May 3rd, 2006,   10:00 a.m.
(Refreshments served at 9.45)
CIS-X Auditorium, Room 101

ABSTRACT
In fiber optics systems, such as Wavelength Division Multiplexing,
there is an increasing need for fast, compact switches. Currently
employed opto-electro-optical converters are relatively slow and
power demanding.  Non-linear optical devices, such as lithium niobate
(LiNbO3) waveguides, can provide fast, all-optical wavelength
conversion.  However, because they require interaction lengths on the
order of centimeters for high efficiency, they are not suitable for
dense optical integration.  Gallium Arsenide quasi-phasematched (QPM)
waveguides have also been demonstrated, and although the interaction
length is smaller (millimeters), they require a complex fabrication
process.

In this work we present the design, fabrication and characterization
of a tightly confining, (AlGaAs)/aluminum oxide (AlxOy) non-linear
waveguide device.  AlGaAs has a nonlinear coefficient five times
larger than LiNbO3 and a well-established fabrication technology.
Moreover, passive and active devices could potentially be integrated
to realize on-chip photonic circuits.  Because of the high index
contrast of the AlGaAs/AlxOy material system, phasematching can be
achieved by artificial birefringence, greatly simplifying the
fabrication process compared to QPM waveguides.  This technique has
been recently demonstrated. However, the conversion efficiency
remained low, due to poor lateral confinement.

We employed the AlGaAs/AlxOy material system to achieve both
birefringent phasematching and sub-micron confinement.  We developed
a new fabrication process to realize high aspect ratio, extremely
smooth AlGaAs/AlxOy structures, leading to low propagation loss (~2.5
dB/mm) at the fundamental wavelength.  Normalized conversion
efficiency larger than 20000 %/W/cm2, one order of magnitude larger
than previously reported works, was obtained.  Moreover, we showed
that nonlinear effects can be further enhanced using a cavity
embedded in the waveguide, resonant at the fundamental wavelength.
For this purpose, a novel dichroic mirror that is highly reflective
at the fundamental wavelength and has high transmission at the second
harmonic wavelength was designed and fabricated.  Ultra-compact
(100-mm long) cavity devices have been realized and showed large
resonant enhancements compared to plain waveguide devices.

In conclusion, we demonstrated tightly confining, birefringently
phasematched waveguides and resonant cavities with the highest
normalized conversion efficiency ever reported.  In addition, a novel
dichroic mirror was developed, allowing large resonant enhancement of
second harmonic generation.

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