Page 283 - Optofluidics Fundamentals, Devices, and Applications

Optofluidic Dye Lasers 257

either by applying the generated light in integrated optics, or by
using the on-chip, microfluidic laser as an intracavity sensor itself.
Among the major conceptual challenges discussed in the chapter
are (a) the design and performance of high-quality optical resonators,
which can be realized by patterning a thin dielectric film, (b) fre-
quency tuning schemes for the miniaturized laser devices, and (c)
strategies to overcome dye bleaching.
Optofluidic dye lasers represents an active research field and
although optofluidic dye lasers have not yet been developed for true
applications, their size, integration and functionality holds promise
for applications within lab-on-a-chip technology.
From a more fundamental point of view, miniaturized lasers and
optofluidic lasers in particular are interesting since they pose new
challenges and physics not encountered in macroscopic laser realiza-
tions. In particular, low mode-volume high-Q resonators may dra-
matically enhance the feedback and consequently lower the optical
threshold power where gain outbalances cavity losses. So far, Fabry–
Perot, DFB and ring resonators have been applied to realize optofluidic
dye lasers. Photonic crystals offer rich opportunities for further devel-
opment of the field, exploiting band-edge lasing and other types of
dispersion engineering. By pushing laser cavities to yet higher Q fac-
tors, the lasing threshold approaches zero asymptotically. This is
often referred to as zero-threshold lasing. While the quest for zero-
threshold lasing may seem somewhat academic we foresee that low-
threshold lasing will find applications in sensing applications where
a low-power pump source can be used to power a low-threshold laser
cavity employed in an intracavity sensing setup where minute chem-
ical changes will perturb the onset of lasing and/or shift the lasing
wavelength.

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