Kwangjoon Kim

In situ investigation of degradation in polymeric electroluminescent devices using time-resolved confocal laser scanning microscope

Degradation progress in polymeric electroluminescent devices during device operation was clarified by in situ measurement of photoluminescence image change using time resolved confocal laser scanning microscope. It is found that the degradation stems from two kinds of dark spots, which have the dented circle shape and the dome shape. Dented circle shapes grow during the operation. Dome shapes, where the polymer layers are detached from the indium-tin-oxide electrode, appear suddenly and do not change in size. Comparison of the Auger analysis depth profiles of the dented and the normal sites indicates that the polymer layer at the dented sites disappears. Time-resolved confocal laser scanning microscopy is found to be a powerful technique to analyze the degradation process.

Effect of IQ Mismatch Compensation in an Optical Coherent OFDM Receiver

The performance enhancement using the Gram-Schmidt orthogonalization procedure (GSOP) for compensating transmitter (Tx) and receiver (Rx) in-phase/quadrature (IQ) mismatch in the coherent optical orthogonal frequency-division-multiplexing system is investigated. The analytic result containing frequency offset is presented to describe the different behavior of Tx and Rx IQ mismatch. Bit-error-rate curves measured at back-to-back and 1040-km transmission over single-mode fiber indicate that the GSOP is more efficient to compensate of Rx IQ mismatch than Tx IQ mismatch.

Mode division multiplexed optical transmission enabled by all–fiber mode multiplexer

Mode division multiplexed optical transmission enabled by all-fiber mode multiplexer is investigated. The proposed all-fiber mode multiplexer is composed of consecutive mode selective couplers. It multiplexes or demultiplexes LP01, LP11, LP21, and LP02 modes simultaneously. We demonstrate successful transmission of three spatial modes with 120 Gb/s PDM-QPSK signals over 15 km of four mode fiber by using 6x6 MIMO digital signal processing.

Pulse-amplitude equalization of rational harmonic mode-locked fiber laser using a semiconductor optical amplifier loop mirror

Abstract The authors demonstrate, for the first time to our knowledge, the amplitude equalization of high-repetition-rate pulses generated from a rational harmonic mode-locked fiber laser using a semiconductor optical amplifier loop mirror. Here, the loop mirror acts as an all-optical pulse-amplitude equalizer. Optimized parameters of the loop mirror for pulse-amplitude equalization were determined by a simulation. The pulse-amplitude equalization was successfully demonstrated up to the thirteenth rational harmonic mode-locked pulse train (∼14 GHz).

Impact of Quadrature Imbalance in Optical Coherent QPSK Receiver

In this letter, we present the impact of quadrature imbalance in an optical coherent quadrature phase-shift-keying (QPSK) receiver. Arbitrary conjugate misalignment was realized in all-fiber optical hybrid and two correction algorithms of quadrature imbalance, the ellipse correction method, and the Gram-Schmidt orthogonalization method, were independently applied. Bit-error-rate curves versus optical signal-to-noise ratio (OSNR) were measured for the 20-Gb/s optical QPSK signal. We show that OSNR penalty is reduced from ~6 to 1 dB at ~20deg conjugate misalignment with the help of correction algorithms.

A simple packet-level clock extraction scheme using a terahertz optical asymmetric demultiplexer

The authors experimentally demonstrate simple packet-level clock extraction using a modified terahertz optical asymmetric demultiplexer without wavelength-division-multiplexed couplers in the loop mirror. For a 10-Gb/s optical packet composed of identical pulses, we have obtained more than 10-dB contrast ratio between the packet-level clock pulse and the other pulses.

Transmission of Multiple HD-TV Signals Over a Wired/Wireless Line Millimeter-Wave Link With 60 GHz

For the first time to our knowledge, we demonstrate a transmission of 37 channels a 64 quadratic-amplitude-modulation (QAM)-coded high-definition television (HD-TV) signal over a fiber-optic millimeter-wave link. The 60-GHz upconverter/downconverter is implemented based on a Gunn oscillator and a nonradiative dielectric waveguide. For the remote delivery of 37 channels of HD-TV signal through 20 km of single-mode fiber, we use a laser diode operating at 1554 nm and an electroabsorption modulator. We evaluate the performances of HD-TV by measuring error vector magnitude and confirm transmission qualities by observing video contents coded with moving picture expert group-2 (MPEG-2).

Explanation of stretched exponential growth behavior

We show that the photoinduced defect population growth of an optically thick film may have stretched exponential time dependence if the defect does not decay nor diffuse within the time scale of the experiment. After the formulation of this simple model, low‐temperature photoinduced absorption of polyaniline is described as an example.

Wavelength dependent performance of a wavelength converter based on cross-gain modulation and birefringence of a semiconductor optical amplifier

By exploiting pump-induced birefringence in addition to cross-gain modulation, we have obtained improved extinction ratio and reduced optical power penalties for a wavelength converter using a semiconductor optical amplifier. In the probe beam wavelength range of 1528-1566 nm, while extinction ratios and power penalties of a conventional wavelength converter are found to be 4.5-9.2 dB and -0.5-2.1 dB, those of the proposed converter are 6.6-10 dB and -0.7-1.0 dB, respectively. The proposed converter shows better performance for all wavelengths in the range examined for both extinction ratio and power penalty. Especially, more improvements have been obtained in the longer wavelength.

Mode- and wavelength-division multiplexed transmission using all-fiber mode multiplexer based on mode selective couplers.

We propose all-fiber mode multiplexer composed of two consecutive LP₁₁ mode selective couplers that allows for the multiplexing of LP₀₁ mode and two-fold degenerate LP₁₁ modes. We demonstrate WDM transmission of 32 wavelength channels with 100 GHz spacing, each carrying 3 modes of 120 Gb/s polarization division multiplexed quadrature phase shifted keying (PDM-QPSK) signal, over 560 km of few-mode fiber (FMF). Long distance transmission is achieved by 6×6 multiple-input multiple-output digital signal processing and modal differential group delay compensated link of FMF. The all-fiber mode multiplexer has considerable potential to be used in mode- and wavelength-division multiplexed transmission.