We present a new device platform which defines on-chip chalcogenide waveguide/resonators without directly etching chalcogenide. Using our platform, we have demonstrated chalcogenide ring resonators with record high Q-factor exceeding 1.1x107 which is 10 times larger than previous record on on-chip chalcogenide resonators. A ring cavity is designed and fabricated for Stimulated Brillouin lasing on our platform. Thanks to the high-Q factor, Brillouin lasing with threshold power of 1 mW is demonstrated. This value is more than an order of magnitude improvement than previous world record for on-chip chalcogenide Brillouin lasers. We also developed an efficient and flexible method for resonator waveguide coupling with our device platform. Coupling between a resonator and a waveguide can be varied from under coupled region to over-coupled region.
Electric field enhancement has been actively studied recently and many metallic structures that are
capable of locally enhancing electric field have been reported. The Babinet's principle can be utilized,
especially in the form of Booker's extension, to transform the known electric field enhancing structures
into magnetic field enhancing structures. The authors explain this transformation process and discuss
the regime in which this principle breaks down. Unless the metals used can be well approximated with
a PEC model, the principle's predictions fails to hold true. Authors confirm this aspect using numerical
simulations based on realistic material parameters for actual metals. There is large discrepancy
especially when the structural dimensions are comparable or less than the skin-depth at the wavelength
of interest. An alternative way to achieve magnetic field enhancement is presented and the design of a
connected bow-tie structure is proposed as an example. FDTD simulation results confirm the operation
of the proposed structure.
We propose and demonstrate a metal-dielectric thin film that delivers low reflection and high absorption over the entire
visible spectrum. This thin black film consists of SiO2/Cr/SiO2/Al layers deposited on glass substrate. Measured
reflectance and absorptance of the black film are 0.7% and 99.3%, respectively, when averaged over the range 380-780
nm. The total thickness of the black film is only about 220 nm. This thin black film can be used as a thin absorbing layer
for displays that require both broadband anti-reflection and high contrast characteristics.
We proposed and demonstrated a simple approach for designing and developing blue-excitation-light passing and
phosphor-yellow-emission-light reflecting dielectric multilayer to enhance the forward efficiency of Y3Al5O12:Ce3+
(YAG:Ce) yellow phosphor on top of a blue InGaN LED cup. When inserting a modified quarter-wave films of alternate
high- and low-refractive index dielectric films (TiO2/SiO2) into the interface between a YAG:Ce phosphor layer and a
glass substrate, enhancements of the efficiency and luminous efficacy of the forward white emission become 1.64 and
1.95 times that of a conventional phosphor on top of a blue LED cup with a lower correlated color temperature (<
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
We propose and demonstrate weak-microcavity organic light-emitting diode (OLED) displays that deliver both a high
light-extraction efficiency and wide viewing-angle characteristics. A single pair of low- and high-index layers is
inserted between indium tin oxide (ITO) and a glass substrate. The electroluminescent (EL) efficiencies of discrete red,
green, and blue weak-microcavity OLEDs (WMOLEDs) are enhanced by 56%, 107%, and 26%, respectively with
minimal changes viewing angle and EL spectra characteristics. The color purity is also improved for all three colors.
Moreover, we fabricated full-color 128×160 passive-matrix bottom-emitting WMOLED displays to prove their
manufacturability. This design is realized by simple one-step 20-nm etching of the low-index layer of red/green subpixels.
The EL efficiency of white color in the WMOLED display is 27% higher than that of a conventional OLED
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.
Micro-disk resonators were fabricated using Er doped silicon-rich silicon nitride (SRSN:Er). SRSN:Er thin films are fully CMOS-compatible and show efficient Er3+ luminescence pumped off-resonantly via Si nanoclusters. The high refractive index of SRSN (>2.0 at 1.5 μm) allows freedom in designing compact micro-disk resonators. Micro-disks with two different contents of Er (0.2 at.%, 0.02 at.%) with a diameter of 25 μm were fabricated, and characterized using evanescent coupling using tapered fibers. Whispering gallery modes with Q-factors in excess of 13000 were obtained, and FDTD calculations indicate that much higher values should be possible. Finally, we demonstrate excitation of fundamental whispering gallery mode via off-resonant, top-pumping of the SRSN microdisk.
We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In this generic
configuration, the position of a PhC resonator can be defined (and redefined) repeatedly by simply relocating a curved
microfiber along the linear PhC waveguide. In the proximity of the PhC waveguide in contact with the microfiber, the
cutoff frequency (effective index) of the PhC waveguide becomes smaller (larger) than that of a bare PhC waveguide.
Accordingly, when a curved microfiber is in contact with the PhC waveguide, a linear PhC resonator having Gaussianshaped
potential well is formed. Experimentally we confirm the formation of the reconfigurable resonator by observing
laser operation slightly below three available band edges.
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°.
Lasing dynamics of photonic-crystal single-cell cavity is studied by Lorentz-dispersive Gain FDTD method. From hexapole mode of a photonic-crystal single-cell cavity, the generation of laser modes and the relaxation oscillation are observed.
The influence of etching slope on cavity Q-factors in two-dimensional (2D) photonic crystal (PhC) slab is studied. Through FDTD simulation, it is confirmed that the Q-factor decreases with etching slope. The main loss comes from the horizontal coupling into propagating TM-modes. We designed three-lattice-long modified linear cavities having high Q-factors. However, the measured Q-factor was about 250. This small Q-factor is attributed to the non-vertical (13°) side wall.
We fabricated the standing metallic nano-stripe array structure on the thin ITO layer with a very narrow width and a relative high height of the stripe by using the electron-beam lithography and Ar ion milling process. The polarization properties were investigated as the period and the incident angle are varied. In transmission spectra of the TE polarization, the resonance with Fano-like resonance was observed. In case of TM polarization, there's no resonance near normal incidence because the electric field is perpendicular to the very thin metallic grating.
Using the finite-difference time-domain calculations, we study whispering-gallery-like modes in photonic crystal air-bridge slab hexagonal defect cavities as good candidates for high quality-factor (Q) and small mode-volume (V) resonant modes. In the hexapole mode of a modified single-defect cavity, structural parameters are optimized to obtain very large Qs of even higher than 2 x 106 with small effective V of the order of cubic wavelength in material, the record value of theoretical Q/V. In addition, the H2-cavity whispering-gallery mode (WGM) is investigated and the defect geometry is modified to increase the Q of the WGM. By symmetrically distributing 12 nearest neighbor holes around the defect and controlling size of holes, it is possible to drastically increase the Q of >105 while preserving effective mode volume of the order of the cubic wavelength in material. We expect the WGMs in photonic crystal cavities are quite promising for low-loss photonic integrated circuit elements and high-efficiency quantum optical devices.
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.
Recent progress toward wavelength-scale photonic crystal lasers is summarized. Lasing characteristics of two possible configurations of the unit-cell photonic crystal laser that has a central node through which current could be supplied. The very high quality factor in excess of 100,000 is theoretically expected from a square lattice unit-cell photonic crystal resonator. Applications of photonic crystals to other forms of active devices are also briefly discussed.
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.
We report thermally- and mechanically-dependable 2D photonic band-gap lasers operating at room temperature. Our thin slab photonic band-gap laser structure is sandwiched between air and a drilled aluminum oxide layer provided by fusion techniques. In this thin slab structure, the optical confinement of photons is achieved by 2D triangular photonic lattice in horizontal plane and total internal reflection in vertical direction. Pulsed lasing action is observed at 1.54 micrometers by 10-mW optical pumping with duty cycle up to 10%.
We introduce an adaptive equalization technique that compensates for the channel nonlinearities causing asymmetric eye-patterns of RF signals in a digital versatile disk (DVD) system. Based on the observation that a DVD channel can be modeled as a cascade of modulation transfer function (MTF) and a zero-memory nonlinearity (ZNL), an adaptive maximum likelihhood sequence estimation (MLSE) receiver that estimates the nonlinearities and incorporates them in its metric calculation is developed. Computer simulation results demonstrate that the proposed receiver can outperform conventional MLSE when signal asymmetry is present.
Thermal behavior of all-MBE surface-emitting lasers is studied for the temperature range of 80 - 310 K. Minimum threshold current observed around 200 K indicates a slight mismatch between gain maximum and Fabry-Perot resonance for the deep-red superlattice surface- emitting laser. The barrier heights for holes between hetero-interfaces of Al0.3Ga0.7As-Al0.65Ga0.35As and AlAs-Al0.65Ga0.35As are measured to be 77 meV for the deep-red surface-emitting laser.
A DPCM system employing a median predictor, which is called the predictive median-DPCM (PM-DPCM), is proposed. An interesting property that in PM-DPCM transmission noise is often isolated and not propagated over the reconstructed signals is observed and analyzed deterministically as well as statistically. In order to examine the performance characteristics of the PM-DPCM, it is applied to real image signals. The experimental results indicate that the PM-DPCM outperforms the standard DPCM when transmission errors occur, and the former performs like the latter under noise-free conditions.
We report batch-processed, totally planar, vertical-cavity top surface emitting GaAs/AlGaAs laser devices and arrays. Different size devices are studied experimentally. We measure continuous-wave threshold currents down to 1.7 mA and output powers > 3.7 mW at room temperature. We also discuss interesting characteristics such as differential quantum efficiencies exceeding unity and multi-transverse mode behavior. An array having 64 X 1 individually-accessed elements is characterized and shown to have uniform room-temperature continuous-wave operating characteristics in threshold current approximately equals 2.1 +/- 0.1 mA, wavelength approximately equals 849.4 +/- 0.8 nm, and output power approximately equals 0.5 +/- 0.1 mW.
In this paper, based on the fact that the output of a weighted median (WM) filter is always one of the samples in the input window, rank and sample selection probabilities are defined. The former is the probability that a certain ranked sample will appear as the output and latter is the probability that the output equals one of the time-indexed samples. Using the rank selection probabilities, it is shown here that the output distribution of the WM filter of size N with independent identically distributed (i.i.d.) inputs is a weighted sum of the distributions of the ith, i-1, 2, ... , N order statistics. The weights are given by the rank selection probabilities. The sample selection probabilities are the coefficients of the finite impulse response (FIR) filter whose output, of all linear filters, is closest to that of the WM filter. Several statistical properties of WM filters using selection probabilities are then derived. A method to compute the selection probabilities from the weights of the WM filter is also given.