Deok Ha Woo

All-optical XOR gate using semiconductor optical amplifiers without additional input beam

The novel design of an all-optical XOR gate by using cross-gain modulation of semiconductor optical amplifiers has been suggested and demonstrated successfully at 10 Gb/s. Boolean AB~ and A~B of the two input signals A and B have been obtained and combined to achieve the all-optical XOR gate. No additional input beam such as a clock signal or continuous wave light is used in this new design, which is required in other all-optical XOR gates.

All-optical half adder using semiconductor optical amplifier based devices

An all-optical half adder using semiconductor optical amplifier based devices is suggested and demonstrated at 10 Gbit/s. Boolean AB and AB out of two semiconductor optical amplifiers have been obtained and combined to achieve an all-optical XOR gate, which is logic SUM. Also, an all-optical XPM wavelength converter has been utilized to obtain an all-optical AND gate, which is logic CARRY. Logic SUM and CARRY are simultaneously realized. No additional input beam such as clock signal or continuous wave light other than input signals A and B is used in this new design, which is required in many other all-optical logic gates.

All-optical half adder using cross gain modulation in semiconductor optical amplifiers

By using the gain nonlinearity characteristics of semiconductor optical amplifier, an all-optical binary half adder at 10 Gbps is demonstrated. The half adder operates in a single mechanism, which is cross gain modulation. The half adder utilizes two logic functions of SUM and CARRY, which can be demonstrated by using XOR and AND gates, respectively. The extinction ratios of both XOR and AND gates are about 6.1 dB. By achieving this experiment, we also explored the possibilities for the enhanced complex logic operation and higher chances for multiple logic integration.

All-optical AND gate using cross-gain modulation in semiconductor optical amplifiers

By using the cross-gain modulation of semiconductor optical amplifiers (SOAs), a novel all-optical AND gate has been successfully demonstrated at 10 Gb/s. Firstly, Boolean \overlineB was obtained using the first SOA with signal B and clock injection. Then, the all-optical AND gate is achieved by simultaneously injecting signal A and signal \overlineB out of the first SOA.

Broad-band all-optical flip-flop based on optical bistability in an integrated SOA/DFB-SOA

We have demonstrated a broad-band all-optical flip-flop for wavelength-division-multiplexing system based on optical bistability in a semiconductor optical amplifier (SOA)/distributed feedback (DFB)-SOA with wide gain bandwidth for both SOA and DFB-SOA regions. Input signal with two different wavelength selections of 1530.45 and 1578.12 nm and the repetition ration of about 6 ns is injected into the SOA/DFB-SOA.

Nondestructive propagation loss and facet reflectance measurements of GaAs/AlGaAs strip‐loaded waveguides

A modified Fabry–Perot resonance technique using a single cavity was proposed to obtain the propagation loss of the optical waveguide. The propagation loss as well as the facet reflectance were measured without sequential cleavage for a GaAs/AlGaAs strip‐loaded waveguide based on the contrast ratios of the reflected and transmitted interference patterns.

Realization of all-optical XOR, NOR, and NAND gates in single format by using semiconductor optical amplifiers

By using the cross gain modulation (XGM) characteristics of semiconductor optical amplifiers (SOAs), multi-functional all-optical logic gates including XOR, NOR, and NAND gates are successfully demonstrated at 10 Gbps in single format. Numerical simulation is also performed by using the transmission-line laser model (TLLM), which is confirmed by using three SOAs experimentally. These combined all-optical multi-functional logic gates will provide more complex and complicated all-optical logic operations.

Dependence of the light-current characteristics of 1.55-μm broad-area lasers on different p-doping profiles

We have investigated the dependence of the light-current characteristics of broad-area lasers with different p-doping profiles for a two-step separate-confinement heterostructure (SCH) 1.55-/spl mu/m InGaAs-InP laser. A sizable increase of the optical output power is observed in a structure with delta doping at the heterointerfaces and moderate doping in the thick SCH layer. It is also shown that the characteristic temperature (T/sub 0/) of the structure with delta doping at the heterointerfaces and moderate doping at the thick SCH layer is almost constant as the measurement temperature is increased. Such an improvement in device performance is attributed to a reduction of carrier leakage to the SCH layer.

Enhanced Light Extraction from Nanoporous Surfaces of InGaN/GaN-Based Light Emitting Diodes

The authors fabricated anodic alumina by a two-step anodization process for samples of an Al foil template and an Al deposited film in order to form nanopores on the p-GaN surfaces of InGaN/GaN multi-quantum-well (MQW) light-emitting diodes (LEDs). The GaN nanopores formed by nanopatterning with the alumina template in an inductively coupled plasma dry etching process shows enhanced light extraction at a wavelength of 450 nm. The nanoporous alumina anodized from the deposited Al layer has a channel to allow the flow of electrolytes into the GaN surface and results in the surface etching effect showing light enhancement at 474 nm. The significant enhancement of light extraction has been correlated with the nanoscaled roughness of a randomly distributed and nanoporous p-GaN surface.

Ag nanodot array as a platform for surface-enhanced Raman scattering

Well-ordered Ag nanodot array on indium-tin-oxide (ITO) glass is adopted as a sensor platform based on surface-enhanced Raman scattering (SERS). SERS has attracted extensive attention in the development of sensitive chemical or biological sensors due to its property of the amplification of electromagnetic fields on a metal nanostructure. The key issue for the applications of SERS is to secure the fabrication technique of a noble metal nanostructured surface. For an SERS-active surface with stability and reproducibility, a Ag nanodot array is fabricated on the ITO glass using a nanoporous alumina mask with uniform through holes. The signal intensity of SERS from methylene blue (MB) adsorbed on the Ag nanodot array showed much stronger scattering than the one from the Ag film of 50-nm thick. The SERS intensity on the Ag nanodot array is consistently enhanced by increased concentration of MB. These results confirm that the Ag nanodot array on ITO glass can be utilized as a stable platform for the sensitive detection of chemical materials based on SERS.