Young Wan Choi

Optical properties of selectively oxidized vertical cavity laser with depleted optical thyristor structure

The authors show that the optical properties of selectively oxidized vertical cavity lasers with a depleted optical thyristor structure have a low threshold current and high sensitivity to input optical light. The oxidized thyristor laser clearly shows a nonlinear s-shaped current-voltage and lasing characteristics. A switching voltage of 5.24V, a holding voltage of 1.50V, and a very low threshold current of 0.65mA are measured, making these devices attractive for optical processing applications.

Optical AND/OR gates based on monolithically integrated vertical cavity laser with depleted optical thyristor structure

Latching optical switches and optical logic gates with AND and OR functionality are demonstrated for the first time by the monolithic integration of a vertical cavity lasers with depleted optical thyristor structure. The thyristors have a low threshold current of 0.65 mA and a high on/off contrast ratio of more than 50 dB. By simply changing a reference switching voltage, this single device operates as two logic functions, optical logic AND and OR. The thyristor laser fabricated by using the oxidation process and has achieved high optical output power efficiency and a high sensitivity to the optical input light.

Multimode-interference-coupled ring resonators based on total-internal-reflection mirrors

We investigate the properties of a multimode-interference (MMI) coupled ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA) in an InGaAsP material system. The TIR mirrors were fabricated by the self-aligned process with a loss of about 1.4 dB per mirror. The resulting free spectral range (FSR) was approximately 0.8 nm (97 GHz) near 1569 nm. The on–off ratio and the full width at half maximum (FWHM) were 8 dB and 0.152 nm, respectively, corresponding to a finesse of 5.2 and a Q factor of 10,322. Hence, such resonators can be directly integrated with other devices making possible the fabrication of compact and highly functional photonic integrated circuits.

AlGaAs/GaAs NpnP Depleted Optical Thyristor Using Bottom Mirror Layers

A novel fully depleted optical thyristor (DOT) using quarter wavelength reflector stacks (QWRS) is proposed. QWRS are employed as bottom mirrors to enhance the emission efficiency as well as optical sensitivity. To analyze their switching characteristics, s-shapes nonlinear current–voltage curves were simulated and the reverse full-depletion voltages (Vnegs) of DOTs were obtained as a function of semiconductor parameters using a finite difference method associated with a current-oriented method. The fabricated DOTs show sufficient nonlinear s-shaped current–voltage (I–V) characteristics, and switching voltage changes with and without bottom mirrors are 1.82 V and 1.52 V, respectively. Compared to a conventional DOT, this device with the bottom mirror shows about 20% and 20–50% enhancement in switching voltage changes and spontaneous emission efficiency, respectively.

Lasing characteristics of InGaAs∕InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor with vertical window

This study demonstrates the lasing characteristics of InGaAs∕InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor using the vertical window. The measured switching voltage and current are 3.36V and 10μA, respectively. The lasing threshold current is 131mA at 25°C. The output peak wavelength is 1570nm at a bias current of 1.22 Ith and there is no input signal. The vertically injected depleted optical thyristor shows very good isolation between input and output signals.

A high-speed tunable filter using a concave fiber mirror

A tunable Fabry-Perot filter using a concave mirror fabricated on the end of a fiber is demonstrated. The concave mirror simplifies angular alignment and reduces vibration sensitivity. A scanning rate of 150 kHz over a FSR of 47 nm with a finesse of 600 was demonstrated.

Lasing characteristics of InGaAs/InGaAsP multiple-quantum-well optical thyristor operating at 1.561 μm

We present a demonstration of a waveguide-type depleted optical thyristor laser diode with InGaAs/InGaAsP multiple-quantum-well structure. The measured switching voltage and current are 4.63 V and 10 μA, respectively. The holding voltage and current are, respectively, 0.59 V and 20 μA. The lasing threshold currents at 25 °C and 10 °C are 111 mA and 72.5 mA, respectively. The lasing wavelength is centered at 1.561 μm at a bias current equal to 1.41 times threshold.

Design and Measurement of Waveguide-Type PnpN Optical Thyristors for Optical Communications

Waveguide-type InGaAs/InP multiple quantum well PnpN depleted optical thyristors operating at 1.55 µm are proposed and fabricated for the first time. In this paper, using the finite difference method (FDM), we calculate the effects of parameters such as doping concentration and the thicknesses of the outer and inner layers of the thyristor to determine the optimized structure in the view of fast and low-power-consuming operation. With these results, the fabricated optical thyristor shows sufficient nonlinear s-shape I–V characteristics with a switching voltage of 4.03 V, a holding voltage of 1.77 V, and spontaneous emission along the waveguide.

Compact Rectangular Ring Resonator with Optimum Multimode Interference

Rectangular microring resonators containing active and passive sections are fabricated and characterized with various multimode-interference (MMI) lengths. The optimum MMI length and width turn out to be 110 and 9 µm, respectively. The material platform and fabrication process used are the same used for other active and passive devices except for a deep etch step. Hence such resonators are easily integrated with other active and passive devices. A free spectral range of approximately 244 GHz is observed with an on–off ratio of 13 dB.

Micro/nano-scale fabrication of integrated polymer optical wire circuit arrays for optical printed circuit board (O-PCB) application

We report on the results of our study on the micro/nano-scale design, fabrication and integration of waveguide arrays for optical printed circuit boards (O-PCBs) and VLSI micro/nano-photonic applications. The O-PCBs are designed to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards or substrates. We have assembled O-PCBs using optical waveguide arrays and circuits made of polymer materials and have examined information handling performances. We also designed power beam splitters and waveguide filters, using nano-scale photonic band-gap crystals, for VLSI photonic integration application. We discuss potential applications of polymer optical waveguide devices and arrays for O-PCB and VLSI micro/nano-photonics for computers, telecommunications, and transportation systems.