Central Idea
Based on
the idea of intentionally introducing crystal defects, a broad
range of potentially functional designs,such as integrated
micro-cavities, channel drop filters, optical switches, and
low-threshold lasers has been proposed. Connecting such
devices could essentially enable the photonic version of an
integrated electronic circuit. Traditionally, the experimental
realization of such structures is limited to simple
photonic-crystal design variations, such asmissing pores,
pores of different sizes, or pores at different positions, all
of which must be incorporated at the growth stage of the
photonic crystal. An alternative and much more flexible
approach for functionalizing two dimensional photonic crystals
consists of locally filling single pores of the crystal with
liquids. If the refractive index of the filling material is
sufficiently larger than 1, the filled pore behaves the same
as a missing pore, except that the defect can be erased and
overwritten.
The infiltrated liquid can be easily
removed by dipping the photonic crystal in an ultrasonic bath,
opening the way torewritable circuits and reconfigurable
integrated photonic-circuit chips. Moreover, using polymer
composites enables the creation of permanent structures. The
ability to address a single pore also allows creation of local
light sources by filling pores with activematerials, such as
colloidal quantum dots in solution. An example of a rewritable
circuit is provided in the above figure; the photons
created by optically pumping the colloidal quantum dots are
guided through the sample along a waveguide, obtained by
infiltrating adjacent pores in a linear geometry, until they
reach a Y-shaped intersection. Here, depending on the
alignment of the liquid crystals infiltrated in the lower
branch (blue), the photons propagate either in the S-shaped
branch or in both arms. Two point-defect micro-cavities are
placed along the tunable waveguide and can couple with the
light flowing in the waveguide whenever the photon wavelength
matches their resonances. The use of liquids with different
refractive indices allows the design of cavities that couple
light at different wavelengths and thus work as selective
add/drop filters.
Water-based waveguide
Experimental realization of an
S-shaped
waveguide by
filling with water the pore of two dimensional photonic
crystals. 
Nano-fluidric light source
in 2D photonic crystal cavity
The opportunity to insert a light emitting
element in photonic crystal nano cavities is of interest not
only for the applications but also for fundamental
physicsresearch. Here the realization of an active structure
based on
local
infiltration of
liquids in a photonic crystal is reported. In particular,a
re-writable local source in the telecom window (at 1.3
µm)
inside a silicon photonic crystalmicro-cavity is realized. The
solution of colloidal PbS quantum dots is located inside
only one pore of the photonic crystals. The emission
spectrumof the infiltrated source ismappedwith a spatial
resolution of lambda/5 by using a commercial Scanning
Near-Field Optical Microscope. The opportunity of having
simultaneously the information about the topography of the
sample and the optical signal from the local source permits to
localize the signal in well-defined positions around the
cavity, and to access the spatial distribution of the
opticalmodes. The spectral and spatial redistribution of the
emission intensity assures the coupling between the
infiltrated sources and photonic crystal cavity
modes.
Scheme of the setup and
photoluminescence Spectra of the infiltrated
(black) and not-infiltrated (gray) quantum
dots. (The inset (I) reports a SEM image of the
sample).
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