HAL Id: hal-01940024
https://hal.archives-ouvertes.fr/hal-01940024
Submitted on 29 Nov 2018
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entic research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diusion de documents
scientiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
Integrated optouidics: A new river of light
Christelle Monat, P. Domachuk, B. Eggleton
To cite this version:
Christelle Monat, P. Domachuk, B. Eggleton. Integrated optouidics: A new river of light. Na-
ture Photonics, Nature Publishing Group, 2007, 1 (2), pp.106-114. �10.1038/nphoton.2006.96�. �hal-
01940024�
1
Integrated Optofluidics: A new river of light
C. Monat*, P. Domachuk and B. J. Eggleton
Centre for Ultrahigh-bandwidth Devices for Optical Systems (CUDOS), School of
Physics, University of Sydney, NSW, 2006, Australia
*Corresponding author: monat@physics.usyd.edu.au
Abstract
The realization of miniaturized optofluidic platforms opens up novel potentialities for the
achievement of devices with enhanced functionality and compactness. Such integrated
systems bring fluid and light together and exploit their micro-scale interaction for a large
variety of applications. The high sensitivity of compact microphotonic devices can
generate effective microfluidic sensors, with integration capabilities. By turning the
technology around, the exploitation of fluid properties holds the promise of highly
flexible, tunable or reconfigurable microphotonic devices. We overview some of the
exciting developments to date.
2
1. Introduction
Optofluidics fundamentally aims at manipulating fluids and light at the microscale and
leveraging their interaction for creating novel and highly versatile systems. Whereas
micro-electromechanical systems (MEMS) and “lab-on-a-chip” communities have made
efforts to incorporate optical devices in their micro(fluidic) systems to improve their
functionality
1,2
, a wide variety of optofluidic devices have been demonstrated recently
3
.
Combining fluids and light has produced all sorts of creative devices, such as adaptive
optical lenses
4,5
or optofluidic microscopy
6
. New opportunities were undeniably opened
up with the recent attempts to synergetically combine both integrated microphotonic
devices and microfluidic systems. The potential applications present a dual aspect. Fluids
can be used to carry substances to be analysed through highly sensitive microphotonic
circuits, in the context of integrated bio-chemical sensing. Conversely, microfluids can be
exploited to control microphotonic devices, making them tunable, reconfigurable, and
adaptive.
Photonics has evolved towards device miniaturization with the ultimate goal to
integrate many optical components onto a compact chip, producing photonic integrated
circuits with low cost and higher degrees of functionality. Planar photonic crystals
7
,
formed from periodic lattices of sub-micrometer air holes inscribed in a slab waveguide,
provide a generic platform to realize photonic integrated circuits
8
. The generation of
microstructured optical fibres with micrometer air voids
9,10
and the capability of tapering
fibres
11
also offer new opportunities to achieve miniaturized optical functions.
Nonetheless, control systems should be developed simultaneously to operate such
3
compact devices. In particular, the generation of advanced integrated photonic systems
depends on our capability to “miniaturize” tunability. Optical tunability relies on the
dynamic modification of the optical properties of a photonic circuit through substantial
and local variations in its refractive index. As the spatial scale is reduced in microscopic
devices, the necessary range of index modulation becomes higher and challenging to
achieve. For instance, a tunability range of Δn~7.5×10
-2
(7.5×10
-5
) is required to fully
modulate the response of a 10 μm (1 cm) long interferometer at 1.5 μm wavelength.
Since the 1990’s, microfluidics has been the subject of concerted research efforts both
in academia and industry, especially for biotechnology. Microfluidics found broad
application in the “lab-on-a-chip” paradigm: the principle of incorporating large-scale
biochemical synthesis and analysis functionalities onto a small chip
12
. Integration offers
significant advantages to these systems including minimized consumption of reagents,
portability, increased automation and reduced costs. Applications have been found in
clinical analysis, drug discovery, small-volume DNA replication and testing
13,14
. The
analytical efficiency and throughput of these devices also make them perfectly suited for
ambient bio-threat detection, where the local environment is continuously and remotely
tested. Integrating monolithic or hybrid optical and optoelectronic devices (light sources,
filters, or photodetectors) into lab-on-a-chips
15-18
is a current field of investigation for
improving the performance and portability of these systems
1,2
.
In addition to the straightforward sensing application of optofluidic systems,
microfluidics can provide what an integrated photonic circuit lacks at the micrometer
scale: a means to tune and reconfigure microphotonic devices. For that, microfluidics
displays some unique properties. Microfluidic laminar flows can efficiently transport
4
various species or nanostructures with desirable optical properties. Those species, that are
otherwise difficult to handle, can be brought into targeted locations of a microphotonic
circuit. Microfluidics also offers a wealth of ways to control microphotonic devices. The
range of index modulation achievable through fluid manipulation is very large and can be
induced locally using microfluidic circuitry. Because fluid is a mobile phase, it can be
used as a changeable part of a photonic device, which becomes reconfigurable. Liquid/
liquid and liquid/ air flexible interfaces themselves can produce highly adaptive
optofluidic devices. Eventually, the specific behaviour of fluids that are confined at the
micro-scale can be exploited in a unique fashion (Textbox 1).
We focus here on the latest developments related to the combination of integrated
optics and microfluidics by highlighting three main ranges of applications. We first
review a new class of optofluidic light sources. Second, we demonstrate how the high
sensitivity of integrated microphotonic devices can generate effective and miniaturized
fluidic sensors. The last range of application relies on the use of microfluids to control,
tune, and reconfigure optical microdevices.
2. Micro-fabrication
Microdevices, such as MEMS, are usually fabricated in silicon or silica, using the well-
established micromachining process of microelectronics. Whereas numerous microfluidic
systems have been built from those techniques and materials, alternative and cheaper
processes, using low cost polymeric materials such as polydimethylsiloxane (PDMS) or
polymethylmethacrylate (PMMA), have been developed more recently. PDMS elastomer
displays attractive properties like elasticity, optical transparency and biocompatible