Jong-Hoi Kim

All-optical switching by counterpropagating operation in cascaded semiconductor optical amplifiers

We propose a simple, compact, integrative, flexible, power-efficient, and all-optical switch. The operation is based on self-induced gain modulation leading to nonlinear transmittance with a threshold level dependent on input powers of the data and control signals counterpropagating in cascaded semiconductor optical amplifiers. We demonstrate numerically the all-optical switch with small-signal modulation, low-power consumption, high-output power, and high-output extinction ratio.

Spectral characteristics of optical pulse amplifications with a holding light in semiconductor optical amplifiers

Abstract This paper analyzes spectral characteristics of optical pulse amplifications with a holding light in semiconductor optical amplifiers and investigates spectral dependence on optical inputs and amplifier parameters. It is shown that spectral broadening decreases almost linearly with the holding light power by 10–20% and moreover the spectral width decreases up to that of the input pulse under the gain reduction of 3 dB. For a linear-chirped input pulse, it is indicated that the spectral shift to lower frequency is general without the holding light but spectral peak can shift to higher frequency by the holding light. For bias current and amplifier length, the peak that the spectral shift is maximized appears since the carrier recovery is faster while the frequency chirp is induced by self-phase modulation.

All-Optical Mach-Zehnder Interferometric Wavelength Converter Monolithically Integrated with Loss-Coupled Distributed Feedback Probe Source

Wavelength conversion is demonstrated for the first time at 10 Gb/s in a Mach-Zehnder interferometric wavelength converter monolithically integrated with a CW probe source of a loss-coupled distributed feedback (DFB) laser diode. The integrated device was fabricated using a buried ridge stripe (BRS) structure with an undoped InP clad layer on the top of a passive waveguide to reduce high propagation loss. Good performance at 10 Gb/s was obtained with an extinction ratio of 7 dB and a power penalty of 2.8 dB at a 10-9 bit error rate.

InGaAsP/InP Laser Diodes Monolithically Integrated with Waveguide-Type Light Deflectors

A ridge waveguide-type InGaAsP/InP laser diodes monolithically integrated with light deflectors (DLDs) were fabricated and light deflection was demonstrated, for the first time. The light deflection was simulated and measured in a fabricated device. The output beam deflection in a fabricated device was controlled by carrier induced refractive index change of the deflector. The maximum beam deflection angle of 3.12° was obtained at an applied current of 15 mA.

Experimental filtering effect on the daylight operation of a free-space quantum key distribution

One of the challenges of implementing free-space quantum key distribution (QKD) systems working in daylight is to remove unwanted background noise photons from sunlight. Elaborate elimination of background photons in the spectral, temporal, and spatial domains is an indispensable requirement to decrease the quantum bit error rate (QBER), which guarantees the security of the systems. However, quantitative effects of different filtering techniques and performance optimization in terms of the secure key rate have not been investigated. In this study, we quantitatively analyze how the performance of the QBER and the key rates changes for different combinations of filtering techniques in a free-space BB84 QKD system in daylight. Moreover, we optimize the conditions of filtering techniques in order to obtain the maximum secure key rate.

Continuous wave operation of an electrically driven spiral microcavity InGaAsP/InP laser diodes

A spiral microcavity InGaAsP/InP laser diode is demonstrated with a threshold current density of ~500 A/cm2 from a tilted directional emission under continuous current-injection condition at room temperature.

Planar waveguide parabolic-shaped collimating lens

The planar waveguide parabolic-shaped collimating lens on the InGaAsP/InP material system was proposed and demonstrated. The laser diode monolithically integrated with planar waveguide lens exhibits beam divergence angle of 0.61/spl deg/ along lateral direction.

Mononolithically integrated external cavity wavelength tunable lasers with a diffraction grating and beam steering controller

We present an external cavity tunable laser based on beam steering and grating-assisted diffraction in a Littrow configuration by monolithically integrating a semiconductor optical amplifier, an etched grating, and a beam steering controller with two current injecting stripes. We have demonstrated the wavelength tuning by steering the beam toward the grating, which is controlled by varying the injection current into the stripe. As a result, the tuning range of 11.9 nm with the side mode suppression ratio from 35 to 45 dB has been achieved.

Monolithic integration of the BRS active waveguide with the undoped upper cladded passive waveguide for the 4x4 SOA gate switch matrix application

A new fabrication process is proposed to integrate low loss undoped-upper-cladded passive waveguides with a buried ridge stripe semiconductor optical amplifiers. A lossless 4x4 semiconductor optical amplifier gate switch matrix was successfully fabricated using this process technology.