Soo-Min Kang

Timing-offset-tolerant universal- filtered multicarrier passive optical network for asynchronous multiservices-over-fiber

We propose a universal filtered multicarrier (UFMC) passive optical network for asynchronous multiservices- over-fiber to overcome the limitations of a conventional discrete multitone (DMT). The channel performance in terms of error vector magnitude was compared by adding a timing offset to conventional DMTand UFMC signals. In addition, both signals were adaptively modulated at the most asynchronous timing-offset case. Our experimental results demonstrated improvement in UFMC performance, which was 32% and 32.5% higher in terms of bit rate and spectral efficiency, respectively, compared with conventional DMT in the most asynchronous case.

Universal filtered multi-carrier system for asynchronous uplink transmission in optical access network

In passive optical network (PON), orthogonal frequency division multiplexing (OFDM) has been studied actively due to its advantages such as high spectra efficiency (SE), dynamic resource allocation in time or frequency domain, and dispersion robustness. However, orthogonal frequency division multiple access (OFDMA)-PON requires tight synchronization among multiple access signals. If not, frequency orthogonality could not be maintained. Also its sidelobe causes inter-channel interference (ICI) to adjacent channel. To prevent ICI caused by high sidelobes, guard band (GB) is usually used which degrades SE. Thus, OFDMA-PON is not suitable for asynchronous uplink transmission in optical access network. In this paper, we propose intensity modulation/direct detection (IM/DD) based universal filtered multi-carrier (UFMC) PON for asynchronous multiple access. The UFMC uses subband filtering to subsets of subcarriers. Since it reduces sidelobe of each subband by applying subband filtering, it could achieve better performance compared to OFDM. For the experimental demonstration, different sample delay was applied to subbands to implement asynchronous transmission condition. As a result, time synchronization robustness of UFMC was verified in asynchronous multiple access system.

AMO-FBMC based RoF transmission for efficient wired/wireless converged optical networks

Sinc-shaped side-lobes of OFDM problematic in multi-services integrated optical network were effectively suppressed by employing FBMC. It is experimentally verified that signal performance and spectral efficiency of FBMC becomes better in comparison with OFDM in wired/wireless converged optical transmission.

Multi-band OFDMA based passive optical network with windowing technique for asynchronous multiple access

Multi-band OFDMA PON with windowing technique is proposed for asynchronous multiple access. In the asynchronous multiple access system, frequency orthogonality is not maintained among OFDM bands, and it leads to inter-band interference arisen from OFDM sidelobe. To mitigate this effect, raised cosine window is applied to suppress the sidelobe. The proposed system is experimentally compared with conventional Multi-band OFDMA PON according to different roll-off factor of raised cosine window.

Energy level diagrams of optimized ambipolar organic thin film transistors used pentacene and C60

The interface electronic structure of pentacene and C60 layer was investigated in detail by using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The magnitudes of measured interface dipole were 0.11 eV and 0.07 eV for the C60 deposited on pentacene (C60/pentacene) and the pentacene deposited on C60(pentacene/C60), respectively. The obtained C 1s spectra on pentacene/C60 and C60/pentacene indicate no significant chemical bonds existing at the interface. The offsets of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) at the C60-pentacene interface were 1.29 eV and 0.89 eV for C60/pentacene/Au while it were 1.5 eV and 1.1 eV for pentacene/C60/Au. This resulted in that the HOMO and LUMO offset depend on the deposition order of the organic layers. We fabricated the ambipolar OTFTs used the favorable structure of pentacene and C60, and obtained the field effect mobilities were 0.017 cm2/Vs and 0.007 cm2/Vs for p-channel and n-channel operations.