Chang-Hun Kim

Optical pulse division multiplexing-based OBI reduction for single wavelength uplink multiple access in IM/DD OFDMA-PON.

Orthogonal frequency division multiple access-based passive optical network (OFDMA-PON) is considered as a strong candidate for next-generation optical access network. In intensity modulation/direct detection system, OFDMA-PON downlink transmission is relatively stable, but critical issues exist in uplink multiple access. Because of different optical paths, optical beat interference (OBI) and timing offset effect are generated, which seriously disturb signal detection. We propose optical pulse division multiplexing-based OBI reduction. By considering both the spectrum broadening effect and the time domain near orthogonality, OBI could be reduced. We demonstrate that the spectral efficiency can be improved from 0.37 to 3.8 bit/s/Hz in 1-GHz signal bandwidth.

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.

All-Optical Virtual Private Network in OFDM-PON Using Microwave Photonic Filter

We propose and demonstrate a novel all-optical virtual private network (VPN) using a microwave photonic filter, which enables inter-communications among optical network units in a passive optical network system. In our scheme, an optical coupler based recirculating delay line is used at optical line terminal as an optical subsystem to implement a microwave photonic-bandpass filter (MP-BPF). The periodic passbands of an MP-BPF are used to transmit VPN signal, whereas stopbands are used for conventional upstream transmission. The proposed system has two critical issues, optical phase-induced intensity noise in the MP-BPF and Rayleigh back-scattering interference by a single-fiber loop back link. To overcome the issues, an RF clipping tone based spectrum-broadening technique is applied to uplink transmitter. The proposed all-optical VPN system is tolerant to wavelength of VPN optical carrier, and enables multi-VPN data transmission using multi-passbands of MP-BPF.

All-optical virtual private network based on microwave photonic bandpass filter in OFDM-PON system

We propose all optical virtual private network (VPN) using microwave photonic filter for the first time in orthogonal frequency-division multiple based passive optical network (OFDM-PON). In our scheme, optical resonator is used at optical line terminal (OLT) as a subsystem to design photonic bandpass filter (P-BPF). This filter has free spectral range (FSR) corresponding to resonator length. Using this property, VPN data modulated on passbands of P-BPF could be extracted among upstream data at OLT, and transmitted to optical network units (ONUs) without electrical processes. To overcome coherent interference problem in the resonator, spectrum broadening technique using clipping RF tone is applied. The proposed system enables dynamic bandwidth allocation between VPN and conventional upstream by adjusting tunable delay line in the resonator. Also it supports VPN communication regardless of optical wavelength.

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.

All-optical virtual private network system in OFDM based long-reach PON using RSOA re-modulation technique

We propose an all-optical virtual private network (VPN) system in an orthogonal frequency division multiplexing (OFDM) based long reach PON (LR-PON). In the optical access network field, technologies based on fundamental upstream (U/S) and downstream (D/S) have been actively researched to accommodate explosion of data capacity. However, data transmission among the end users which is arisen from cloud computing, file-sharing and interactive game takes a large weight inside of internet traffic. Moreover, this traffic is predicted to increase more if Internet of Things (IoT) services are activated. In a conventional PON, VPN data is transmitted through ONU-OLT-ONU via U/S and D/S carriers. It leads to waste of bandwidth and energy due to O-E-O conversion in the OLT and round-trip propagation between OLT and remote node (RN). Also, it causes inevitable load to the OLT for electrical buffer, scheduling and routing. The network inefficiency becomes more critical in a LR-PON which has been researched as an effort to reduce CAPEX and OPEX through metro-access consolidation. In the proposed system, the VPN data is separated from conventional U/S and re-modulated on the D/S carrier by using RSOA in the ONUs to avoid bandwidth consumption of U/S and D/S unlike in previously reported system. Moreover, the transmitted VPN data is re-directed to the ONUs by wavelength selective reflector device in the RN without passing through the OLT. Experimental demonstration for the VPN communication system in an OFDM based LR-PON has been verified.

Optical beating interference reduction for multi carrier based converged optical access network

We proposed a pulse shaping enhanced optical pulse division multiplexing (e-OPDM) to effectively reduce optical beating interference (OBI) in a multi carrier based optical access network. A potential to accommodate a large number of uplink multiple access was verified by using the proposed technique. Performance improvement was experimentally demonstrated by EVM of uplink signal according to optical pulse delay.

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.