Sun Hyok Chang

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.

Widely tunable single-frequency Er-doped fiber laser with long linear cavity

A widely tunable single-frequency Er-doped fiber laser is demonstrated in a 21-m-long linear cavity incorporating all-fiber acoustooptic frequency shifters and a saturable absorption grating. Stable single-frequency operation is achieved with a sidemode suppression ratio higher than 50 dB and a wavelength tuning range greater than 40 nm.

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.

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.

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).

The physicochemical properties of polyindole / thiol composites

We synthesized the polyindole (PI) and poly(2,5-dimercapto-1,3,4-thiadiazole) (pDMcT) by chemical oxidation method. The polymerization of PI and pDMcT was confirmed by FT-IR. We have measured the electrochemical properties of the unit cell both before and after charge/discharge experiment. It showed the plateau region around 3.0V in discharge curves behavior. The specific discharge capacity value of these compositions was saturated after 10th cycle as ∼75mAh/g. We have tried to explain the reaction in PI/thiol composites with various methods. The intensity of the ESR signal increases after charging and the σ dc of these composites increases by charging. From the results, it could be found that the formation of unpaired electrons at nitrogen site in PI is confirmed in this system.

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.

Dual-carrier DQPSK based 112 Gb/s signal transmission over 480 km of SMF link carrying 10 Gb/s NRZ channels

We propose and demonstrate a cost-effective 112 Gb/s optical transceiver based on dual carrier-DQPSK with direct detection. The performances of DC-DQPSK are evaluated by transmitting 112 Gb/s signal over 480 km of SMF link carrying 10 Gb/s NRZ neighboring channels.

Digital non-data-aided symbol synchronization in optical coherent intradyne reception

Digital symbol synchronization of optical binary phase shift keying signals is experimentally demonstrated. Algorithm of timing error feedback is proposed for coherent intradyne reception. The feedback loop operates stable in the range of symbol rate, 9.7 approximately 10.3 GSymbol/s with 20 GSampling/s at relatively high bit error rate of approximately 2x10(-2).

Suppression of transient phenomena in hybrid Raman/EDF amplifier

Transient phenomena of hybrid Raman/erbium-doped fiber amplifier (EDFA) upon optical channel add-drop are investigated. The transient responses of surviving channels are resulted from the combined dynamics of Raman amplifier and EDFA. It is shown that the suggested method employing fast gain control of EDFA only can effectively suppress the transient variation of output power. The transient-suppressing hybrid Raman/EDFA is proven to be enough for wavelength-division-multiplexing networks including reconfigurable optical add-drop multiplexer and/or transparent optical cross-connect, if the optical switching speed is carefully chosen.