Glaucoma is a progressive optic neuropathy, characterized by the selective loss of retinal ganglion cells (RGCs). Therefore, monitoring the change of number or morphology of RGC is essential for the early detection as well as investigation of pathophysiology of glaucoma. Since RGC layer is transparent and hyporeflective, the direct optical visualization of RGCs has not been successful so far. Therefore, glaucoma evaluation mostly depends on indirect diagnostic methods such as the evaluation of optic disc morphology or retinal nerve fiber layer thickness measurement by optical coherence tomography.
We have previously demonstrated single photoreceptor cell imaging with differential interference contrast (DIC) microscopy. Herein, we successfully visualized single RGC using DIC microscopy. Since RGC layer is much less reflective than photoreceptor layer, various techniques including the control of light wavelength and bandwidth using a tunable band pass filter were adopted to reduce the chromatic aberration in z-axis for higher and clearer resolution. To verify that the imaged cells were the RGCs, the flat-mounted retina of Sprague-Dawley rat, in which the RGCs were retrogradely labeled with fluorescence, was observed by both fluorescence and DIC microscopies for direct comparison. We have confirmed that the cell images obtained by fluorescence microscopy were perfectly matched with cell images by DIC microscopy.
As conclusion, we have visualized single RGC with DIC microscopy, and confirmed with fluorescence microscopy.
Two-dimensional (2-D) metal nanodot arrays (NDAs) have been attracting significant attention for use in biological and chemical sensing applications. The unique optical properties of the metal NDAs originate from their localized surface plasmon resonance (LSPR). Nanofabrication methods that use nanoporous alumina masks (NAMs) have been widely used to produce metal NDAs. We report a fabrication technique for a 2-D Ag NDA and its utilization as a platform for LSPR-based sensing applications. A well-ordered Ag NDA of ∼70-nm diameter, arranged in a periodic pattern of 105 nm, was fabricated on an indium tin oxide (ITO) glass substrate using an NAM as an evaporation mask. The LSPR of the Ag NDA on the ITO glass was investigated using ultraviolet–visible spectroscopy. The LSPR wavelength shifts caused by the variations in the quantity of methylene blue adsorbed on the Ag NDA were examined. The results of this study suggest that the Ag NDA prepared using NAM can be used as a chemical sensor platform.
The noble metal nanostructure has attracted significant attention because of their potential applications as sensitive sensor platform blocks for biological and chemical sensing. The unique optical property of the metal nanostructure is originated from localized surface plasmon resonance (LSPR). The fabrication of metal nanostructure is a key issue for sensor applications of LSPR. In this paper, fabrication technique of two-dimensional Ag nanodot array on an indium tin oxide (ITO) glass substrate via the nanoporous alumina mask and the utilization as a platform for LSPR chemical sensor was studied. Well-ordered Ag nanodot array with approximately 65 nm diameter in periodic pattern of 105 nm was fabricated using the nanoporous alumina with through-holes as an evaporation mask. The LSPR of Ag nanodot array on ITO glass substrate was investigated by UV-vis spectroscopy. The LSPR wavelength-shifts owing to the concentration variances of Methylene Blue (MB) adsorbed on Ag nanodot arrays were examined for application of chemical sensor.
The current study describes metal ion sensing with double crossover DNAs (DX1 and DX2), artificially designed as a platform of doping. The sample for sensing is prepared by a facile annealing method to grow the DXs lattice on a silicon/silicon oxide. Adding and incubating metal ion solution with the sensor substrate into the micro-tube lead the optical property change. Photoluminescence (PL) is employed for detecting the concentration of metal ion in the specimen. We investigated PL emission for sensor application with the divalent copper. In the range from 400 to 650 nm, the PL features of samples provide significantly different peak positions with excitation and emission detection. Metal ions contribute to modify the optical characteristics of DX with structural and functional change, which results from the intercalation of them into hydrogen bonding positioned at the center of double helix. The PL intensity is decreased gradually after doping copper ion in the DX tile on the substrate.
In this study, we successfully generated the large bandwidth of supercontinuum spectra through hollow fibers filled with DNA. Also, by observing that spectra bandwidth was the widest in the order of the hollow core fiber filled with DNA modified by copper ion, the hollow core fiber with only DNA, and the bulk hollow core fiber, we demonstrated that DNA material modified with copper ions can further enhance the spectral bandwidth of supercontinuum. As a result, we anticipate that the SCG as a broadband light source can be used in analytical methods to demonstrate a wide range of biological and environmental questions.
Surface-enhanced Raman scattering (SERS) has attracted considerable attention for chemical and biological agent detection through
the amplification of electromagnetic fields from localized surface plasmon resonance on a metal nanostructure. The fabrication of
metal nanostructure is the key issue for applications of SERS substrate. Particularly, well-ordered noble metal nanodot array can be
reproducibly fabricated using anodic aluminum oxide layer with uniform channels of nanometer dimensions. In this study, we report
the fabrication of Ag nanodot array on indium-tin-oxide (ITO) glass via the nanoporous alumina mask with through-holes and the
utilizing the array as a substrate for SERS application. Ag nanodot array with 55 nm diameter was fabricated in periodic pattern with
separation distance of 105 nm as a replica of the alumina mask. Optical property of Methylene Blue adsorption on Ag nanodot array
was examined by Raman spectroscopy. These results suggest that Ag nanodot array might be useful as a SERS platform for the future
application in sensitive detection of chemical materials.
We present polarization-sensitive full-field optical coherence tomography (PS-FF-OCT), which is based on a bi-stable polarization switch (BSPS) device. The proposed PS-FF-OCT is a Linnik type interferometer, and allows getting both the birefringence-induced phase retardation and the intensity images of specimens with high resolutions using a pair of micro objectives and a BSPS device. Two orthogonal polarization states are formed with a regular time interval by the BSPS device that changes the polarization direction of light in a short time by switching its optic axes. Therefore, both the horizontally polarized light signal and the vertically polarized light signal from the sample can be detected with a single CCD camera. For getting a phase retardation image in real-time, the BSPS device is phase-locked with the CCD camera. The proposed method makes easy implementation of the PS- FF-OCT system without the needs of complex alignment process of using two identical CCD cameras. The experimental results confirm the feasibility of the system.
By using only two input signals of A and B, an all-optical half adder that utilizes a cross gain modulation in
semiconductor optical amplifiers is demonstrated at 10 Gbps. The half adder utilizes two logic functions of SUM
and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. The extinction
ratios of SUM and CARRY are approximately 6.1 dB. No additional input beam such as clock signal or
continuous wave light, which is required in many other all-optical logic gates, is used in this design concept.
Latching optical switches and optical logic gates with AND or OR, plus the INVERT functionality are demonstrated for
the first time by the monolithic integration of a single and differential typed vertical cavity lasers with depleted optical
thyristor (VCL-DOT) structure with a low threshold current of 0.65 mA, a high on/off contrast ratio of more than 50 dB,
a high slope efficiency of 0.38 mW/mA, and high sensitivity to input optical light. By simply changing a reference
switching voltage, this single-typed device operates as two logic functions, optical logic AND and OR. The differential-typed
VCL-DOTs operate also as all logic gates, AND/NAND, OR/NOR, and INVERT function by simple change of a
reference input light power. The thyristor laser fabricated by using the oxidation process shows a high optical output
power efficiency and a high sensitivity to the optical input light.
Using the cross-gain modulation (XGM) characteristics of semiconductor optical amplifiers (SOAs), multi-functional
all-optical logic gates including XOR, AND, and OR gates are successfully demonstrated at 10 Gbps by using VPI
component makerTM simulation tool. Multi-quantum well (MQW) SOA is used for the simulation of all-optical logic
system. Our suggested system is composed of four MQW SOAs, SOA-1 and SOA-2 for XOR logic operation and SOA-
3 and SOA-4 for AND logic operation. By the addition of two output signals XOR and AND, all-optical OR logic can
be obtained.
KEYWORDS: Logic, Semiconductor optical amplifiers, Modulation, Logic devices, Clocks, Electrons, Signal processing, Optical signal processing, Signal generators, Computing systems
By using cross gain modulation in semiconductor optical amplifiers, basic logics for all-optical computing
and signal processing are successfully demonstrated at 10Gbps. These functions will bring up the increased
speed and capacity of telecommunication systems, basic or complex optical computing, and many other optical
signal processing systems.
The wafer bonding of III-V semiconductor materials with garnet thin films has become of increasing technological importance in integration of optical components. The wafer bonding between InP wafer and GGG was demonstrated by using O2 plasma surface activation. The same process was applied to the bonding process of InP/Ce:YIG, which is indispensable for the fabrication of an integrated optical waveguide isolator.
Requirements for suitable communication systems with large capacity and high speed processing of information are rapidly on increase. Fiber-optic communication systems are presented for these requirements today. Modulation is one of the most important part in these system. Although many optical modulators already has been existed, for more high speed and performance we are interested in design of traveling-wave type electro-optic modulator which can be used for wide-band applications. Quantum dots(QDs) have long been expected to improve the performance of optical devices. Since their density of states due to the three-dimensional (3-D) carrier confinement behave as delta function, thus, QDs have the characteristics such as enhanced differential gain, suppressed thermal distribution of carriers, and a nearly zero alpha parameter at the peak gain. In this paper, we fabricated electro optic modulator using InAs/InGaAs columnar QD. The height of one QD is 4 nm and 10 periods of QDs are stacked including InGaAs capping layer. The peak wavelength of photoluminescence is 1260 nm at room temperature. The electrode of QD modulator is designed as Traveling-wave Mach-Zehnder type for high speed operation. And the microwave characteristics are simulated to design Traveling-wave QD modulator using Finite Difference-Time Domain method. Using simulation results, we fabricated Traveling-wave type quantum dot electro-optic modulator with varying the length of modulation region.
By using gain nonlinearity characteristics of semiconductor optical amplifier, an all-optical binary half adder at 10 Gbps is demonstrated. The half adder operates in single mechanism, which is XGM. The half adder utilizes two logic functions of SUM and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. In the XOR (A NOT B + NOT A B) gate, Boolean A NOT B is obtained by using signal A as a probe beam and signal B as a pump beam in SOA-1. Also, Boolean NOT A B is obtained by using signal B as a probe beam and signal A as a pump beam in SOA-2. By adding two outputs from SOA-1 and SOA-2, Boolean A NOT B + NOT A B (logic XOR) can be obtained. In the AND (AB ) gate, Boolean NOT B is firstly obtained by using signal B as a pump beam and clock signal as a probe beam in SOA-3. By passing signal A as a probe beam and NOT B as a pump beam through SOA-4, Boolean AB is acquired. By achieving this experiment, we also explored the possibilities for the enhanced complex logic operation and higher chances for multiple logic integration.
An all-optical full adder using semiconductor optical amplifiers has been demonstrated at 10 Gbps for the first time. The full adder consisted of XOR and NOR gates only utilizes the mechanism of cross-gain modulation. The full adder utilize two logic functions of SUM and CARRY, which can be demonstrated by using two XOR gates and four NOR gates, respectively. By passing signal A as probe signal and signal B as pump signal into SOA-1, Boolean A NOT B can be obtained. Also, by changing the role of signals A and B for SOA-2, Boolean NOT A B can be acquired. Addition of Boolean A NOT B and NOT A B results in NOT A B + A NOT B , which is Boolean expression of logic XOR. By passing this XOR signal and signal C into the second XOR gate with the same principle, SUM signal of the full adder can be obtained. The Boolean expression of SUM can be expressed as A # B # C . With the first three NOR gates, Boolean NOT(A+B), NOT(B+C), and NOT(C+A) can be obtained. With the addition of these outputs, Boolean NOT(A+B) + NOT(B+C) + NOT(C+A) can be formed. By injecting these outputs through the last NOR gate with clock signal, CARRY signal of the full adder can be realized. The Boolean expression of CARRY can be expressed as AB +BC +CA. The extinction ratio is about 6.1dB.
We present the first demonstration of the vertical-injection depleted optical thyristor-laser diode (VIDOT-LD) with InGaAs/InGaAsP multiple quantum well structure. The VIDOT-LD using the vertical-injection structure shows very good isolation between input and output signal. For the faster switching speed and the lower power consumption, we optimized the structure of a fully depleted optical thyristor (DOT) by the depletion of charge at the lower negative voltage. The measured switching voltage and current are 3.36 V and 10 μA respectively. The holding voltage and current are respectively 1.37 V and 100 μA. The lasing threshold current is 131 mA at 25°C. The output peak wavelength is 1570 nm at a bias current of 1.22 Ith and there is no input signal.
For the faster switching speed and the lower power consumption, we optimized the structure of a fully depleted optical thyristor (DOT) by the depletion of charge at the lower negative voltage. The fabricated optical thyristor shows sufficient nonlinear s-shape I-V characteristics with the switching voltage of 2.85 V and the complete depletion voltage of -8.73 V. In this paper, using a finite difference method (FDM), we calculate the effects of parameters such as doping concentration and thickness of each layer to determine the optimized structure in the view of the fast and low-power-consuming operation.
We present mushroom-type TWEAM, which has improved velocity mismatch, with optimized impedance match compared to conventional modulators by reducing the distance between signal and ground metal line. In this paper, the layer structure of mushroom-type TW MQW EAM is designed for the operation of 1.55 um and optical index of active layer is designed to be 3.6. Also, we simulate an 1.55 um InGaAs/InGaAsP traveling-wave multiple quantum well electro- absorption modulator using 3D Finite Difference Time Domain method. Also, we investigate microwave characteristics in detail.
An InGaAsP/InP variable power splitter utilizing the multimode interference (MMI) and the linear electro-optic (LEO) effect is designed and analyzed. The splitter consists of two MMI waveguides and phase-shifting waveguide section between them. The input MMI waveguide acts as a 3-dB splitter for the TE input signal. In the phase-shifting waveguides, the relative phase of split input signals is changed by using the LEO effect. The output MMI waveguide combines the phase-modulated signals at output ports. Depending on the amount of phase change induced by reverse bias voltages of 0 approximately 2.5 V, the splitting ratio varies from 100(DOT)0 to 50:50 continuously.
We present on the experimental results of the NpnP optoelectronic switching device with a significant optical sensitivity. This structure consists of a novel fully depleted optical thyristor (DOT) with a bottom mirror layers. We measure the emission efficiency for various sizes and injected currents. This device shows 20 percent and 45 percent enhancement in switching voltage change and spontaneous emission efficiency, respectively, which is very important for the sensitivity and the low power consumption of DOT.
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