Hwan Seok Chung

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.

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).

Experimental demonstrations of next generation cost-effective mobile fronthaul with IFoF technique

We described next generation mobile fronthaul based on IFoF technique and theoretically estimated its system performances. Based on our analysis, we also experimentally demonstrated mobile fronthaul with 12 IF carriers on a single 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.

Design of RoF based mobile fronthaul link with multi-IF carrier for LTE/LTE-A signal transmission

We report a design of RoF based mobile fronthaul link considering quality of optical link and LTE/LTE-A signal simultaneously. The requirement of CNR in analog link supporting LTE/LTE-A services is presented, and effects of analog link quality on LTE/LTE-A signal is investigated. The EVM measurement after transmission of LTE-A signal with various numbers of intermediate frequency over 20 km SMF link is also presented.

Performance comparison between Manchester and inverse-RZ coding in a wavelength re-modulated WDM-PON

We compare the performance of wavelength re-modulated WDM-PON implemented by Manchester or IRZ coded downstream and NRZ re-modulated upstream, and investigate effects of bit-rate difference between downstream and upstream on the two coding schemes.

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).