THE EFFECTS OF EXTREMELY-SHORT EXTERNAL CAVITY OPTICAL
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Date
2011-02-16
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Abstract
Telecommunications is a growing and intensely competitive global
multi-trillion dollar industry that specializes in the transmission
of information all over the world. The data for every television
show, website, and telephone conversation travels through one of the
industry s many information networks. One of the most common methods
of transmission is using fiber optic networks, in which a laser is
modulated to send light signals into an optical fiber. The
importance of vertical-cavity surface-emitting lasers (VCSELs) to
the telecommunications industry is growing rapidly. VCSELs are more
cost-efficient to mass-produce and they have better fiber coupling
efficiencies as compared to the edge-emitting semiconducting lasers
that are the current industry standard.
VCSELs were developed with the hope that they would not be subject
to some of the main failings of edge-emitting lasers, such as
sensitivity to optical feedback. This occurs when some of the
emitted light from a laser is accidentally reflected off other
optical components in a system, like the end of an optical fiber,
back into the laser. The space between the aperture of the laser and
the reflective surface is defined as an external cavity.
Extremely-short external-cavity (ESEC) optical feedback is feedback
that occurs from a surface within a few microns of the VCSEL
aperture.
In an unmodulated VCSEL, ESEC feedback has been shown to produce
periodic variation in the VCSEL's threshold current, output power
[1], polarization switching current and polarization switching
current hysteresis width [2], with respect to variation in the
external cavity length. The experimental setup for this experiment
mimics the operational setup of a modulated fiber coupled VCSEL as
it would be used for data transmission. This presentation will
examine those same laser characteristics under the effects of ESEC
optical feedback on VCSELs modulated up to 10 GHz.
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Keywords
VCSEL, ESEC feedback, vertical-cavity surface-emitting laser, Extremely-short external-cavity optical feedback