Here, we emphasize the importance of a bottom reflector for achieving unidirectional far-field emission. As a
result, over 80% of photons generated inside the cavity can be collected within a divergence angle of ±30° from
the top. We also discuss interesting analogy in which the nanocavity-bottom reflector coupled system is treated
as a point-like emitter in front of a mirror. Based on such a view point, the observed directivity is explained
by using a comprehensive interference model. Finally, we propose a very practical form of an efficient photonic
crystal nanolaser bonded on a flat metal surface, which may enable current injection and room-temperature
The waveguides and light sources are essential building blocks in optofluidics. Here, we have developed the new
approach to fabricate efficient waveguides and light sources by using two-phase stratified flow of dye containing liquid
and air. The liquid-core/air-cladding (LA) waveguide can overcome some of major drawbacks of the liquid-core/liquid-cladding
(L2) waveguide without losing its unique advantages. Specifically, stronger optical confinement, originated
from the large refractive index contrast between core and cladding, enable us to achieve lower propagation losses and
larger captured fractions (the amount of light to be coupled into the liquid core). In addition, the LA waveguides are free
from diffusional mixing of the core and cladding fluids. The fluorescent LA waveguides can be fabricated by
conventional poly(dimethylsiloxane) (PDMS) based soft lithography, which is compatible with the other parts of
optofluidic devices. Therefore, the fluorescent LA waveguide can be easily integrated with precise alignment as an
internal light source of optofluidic devices.
Biomolecular detection using Localized Surface Plasmon Resonances (LSPR) has been extensively investigated
because these techniques enable label-free detection. The high-density metal nanopatterns with tunable LSPR
characteristics have been used as refractive index sensing because LSPR property is highly sensitive to refractive index
change of surroundings. Meanwhile, Colloidal lithography is a robust method for fabricating regularly ordered
nanostructures in a controlled and reproducible way using spontaneous assembly of colloidal particles. In this study,
nanopatterns on UV-curable polymer were prepared via colloidal lithography. Then, metallic nanograil arrays with high
density were fabricated by sputtering noble metals such as gold and subsequent removal of residual polymers and
colloidal particles. From Finite-Difference Time-Domain Method (FDTD) simulations and reflectance spectra, we found
that multiple dipolar plasmon modes were induced by gold nanograil arrays and each mode was closely related with
structural parameters. LSPR characteristics of gold nanograil arrays could be tuned by varying the fabrication conditions
to obtain optimal structures for LSPR sensing. Sensing behavior of gold nanograil arrays was tested by applying various
solvents with different refractive indices and measuring the variations of LSPR dips. Finally, gold nanograil arrays as
LSPR sensors were integrated in optofluidic devices and used to achieve real-time label-free monitoring of biomolecules.
An etch-less ultraviolet nanoimprint lithography (UV-NIL) process is proposed for patterning a photonic crystal (PC)
structure onto an organic light-emitting diode (OLED) substrate. In a conventional UV-NIL, anisotropic etching is used
to remove the residual layers and to transfer the patterns onto the substrate. The proposed process does not require an
etching process. In the process, a stamp with nano-scale PC patterns is pressed on the dispensed resin and UV light is
then exposed to cure the resin. After tens of seconds, the stamp is separated from the patterned polymer layer on the
substrate. Finally, high-refractive index material is coated onto the layer. The refractive index of the polymer should be
very similar to that of glass. The enhancement of the light extraction was assessed by the three-dimensional (3D) finite
difference time domain (FDTD) method. The OLED was integrated on a nanoimprinted substrate and the electro-luminance
intensity was found to have increased by as much as 50% compared to a conventional device.
We propose and demonstrate a new type of a photonic crystal nanolaser integrated into a microfluidic chip, which
is fabricated by multilayer soft lithography. Experimentally, continuous-wave operation of the lasing action has
been observed owing to efficient water-cooling. Characteristics of wavelength tuning by the fluid are investigated
using both theory and experiment. In addition, we propose that dynamic modulation of far-field radiation
pattern can be achieved by introducing a bottom reflector and by flowing the fluid on it. Especially, by choosing
effective one-wavelength distance between the reflector and the cavity, efficient unidirectional emission can be
We propose efficient unidirectional light emitters, which are enabled by the use of large Purcell effect, defect engineering, and the bottom Bragg reflector. Enhanced spontaneous emission rate enables us to achieve very efficient light sources, in which most of the emitted photons can be funneled into a specific resonant mode of interest. The far-field radiation properties of a photonic crystal resonant mode are modified by tuning the cavity geometry and by placing a reflector below the cavity. As a result, > 80% of the photons generated inside a photonic crystal resonator can be collected from the top, within a small divergence angle of ±30°.
Recent progress toward wavelength-scale photonic crystal lasers is summarized. To realize the ultimate laser, one needs to have a wavelength-scale photonic crystal cavity that is lossless. As a candidate for this ultimate laser, the two-dimensional unit-cell photonic crystal laser compatible with current injection is proposed. Experimental demonstration of the low-threshold two-dimensional photonic crystal lasers in the triangular lattice and the square lattice will be discussed. The very high quality factor in excess of 1,000,000 is theoretically predicted from the wavelength-scale resonator supporting the whispering-gallery-like photonic crystal mode.
Novel square lattice photonic band gap lasers are realized at room temperature from single cell photonic crystal slab micro-cavities fabricated in InGaAsP materials emitting at 1.5 micrometers . This single cell photonic band gap laser operates in the new class of two-dimensional mode to be classified as the smallest possible whispering gallery mode with genuine energy null at the center. The low-loss nondegenerate mode with modal volume of 0.1 ((lambda) /2)3 demonstrates a spectrometer-limited below-threshold quality factor > 2000 and a theoretical quality factor of > 10,000. Threshold incident peak pump power of 0.8 mW is achieved from this whispering-gallery-type laser mode. The other class of photonic crystal lasers is also observed outside the photonic band gap of the square lattice, operating in the mode characteristically one-dimensional.
Recent deployments of digital cameras and fast PCs have led real-time interactive systems to adopt vision-based interfaces. However, 2D vision-based interfaces, due to the lack of 3D information, have inherent weakness in tracking 3D objects in real world. In this paper, we propose a vision-based 3D interface for interactive systems that allows an object tracking on the fly in 3D by exploiting multi-view images. Due to the characteristics of interactive systems, requiring real time processing, the main challenge is a simple and robust estimation of 3D information from the images captured by asynchronous digital cameras. The proposed vision-based 3D tracking consists of three steps: (i) dynamic stereo calibration (ii) simple object segmentation (iii) robust 3D movement tracking. To show its effectiveness of the proposed framework, we applied the proposed 3D interface to an interactive 3D Gumdo simulation. Due to the simplicity and robustness of the proposed framework, it can be applied to various real-time interactive applications.