Ph.D. Orals Examination - Mike Wiemer

Michael Wiemer mwiemer at
Wed Mar 7 13:44:11 PST 2007

Ph.D. Oral Examination
*Monolithically Integrated Long Vertical Cavity Surface Emitting Lasers*

Michael W. Wiemer
Department of Electrical Engineering
Advisor: Professor David A. B. Miller

Date: Tuesday, March 13th, 2007
Time: 10:00am (Refreshments at 9:45am )
Location: Packard 101

Electrical interconnect technology in computing and communication
systems is under extreme pressure to improve performance and meet
future demands. Future systems will need aggregate interconnect
bandwidths well into the terahertz range, thereby making electrical
spatial bandwidth density and power targets very difficult to meet.
However, link performance is not the only consideration. In a typical
interconnect system, the number of links rapidly increases as link
distance decreases, making low cost per link also critical. Thus, if
computing system performance is to scale into the future as it has in
the past, a low-cost yet high-performance short distance interconnect
technology must be found.

Under certain conditions, optical interconnect solutions can decrease
link power consumption over their electrical counterparts. In
addition, Optical Wavelength Division Multiplexing (WDM) may increase
the spatial bandwidth density of an interconnect. Due to the bosonic
nature of light, optical waves do not interact with each other. Thus,
in contrast to the electrical paradigm where a different metallic
wire is required for every electrical interconnect signal, a single
optical waveguide can simultaneously carry many data channels, each
on a different optical wavelength. WDM systems therefore require
multiple laser sources, each at a different, well-controlled
wavelength. These two issues (large number of lasers & their strict
wavelength control) increase the cost and complexity of WDM systems
significantly. However, a single mode-locked laser naturally produces
a spectral comb of many optical wavelengths. Such a laser could
potentially replace a multitude of discrete wavelength lasers in
future short distance WDM interconnect systems.

A Fully Integrated Long Vertical Cavity Surface Emitting Laser
(LVCSEL) platform, capable of being mode-locked, is proposed as a
low-cost optical source solution for future WDM interconnects.
Motivated by the concept of mode-locking, we will review our work
developing this laser platform. In particular, we will address the
need for high intracavity optical power/cm 2, which is required for
passive mode-locking at high repetition rates.
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