Hark Yoo

All-optical flip-flop based on the bistability of injection locked Fabry-Perot laser diode

We demonstrate the operation of a novel all-optical flip-flop. The flip-flop consists of a slave Fabry-Perot laser diode (FP-LD) and a specially designed master FP-LD which has a built-in external cavity and operates in single longitudinal mode oscillation. The set and reset pulses were generated by external modulators at 1 Gbit/s. The rising and falling times of the output signal in on-off operation of the flip-flop were about 50 ps. The required powers of both set and reset pulses were less than -9 dBm.

Efficient dynamic bandwidth allocation for FSAN-compliant GPON

We suggest an immediate allocation with colorless grant (IACG) method for dynamic bandwidth allocation of a gigabit passive optical network (GPON) system. The suggested method is based on the GigaPON Access Network (GIANT) media access control (MAC) method. The IACG method can assign the transmission bandwidth regardless of the value of a scheduling counter, whereas the GIANT MAC method can assign the transmission bandwidth only when the scheduling counter has a value of 1. Also, unlike the GIANT MAC method, the IACG method utilizes the unallocated remainder of the transmission bandwidth. At the end of scheduling, the IACG MAC method assigns the unallocated remainder to each optical network unit (ONU) with an equal share. Using computer simulations with the self-similar traffic model, we show that the IACG method dramatically outperforms the GIANT MAC method in mean delay and frame-loss rate.

Dual cyclic power saving technique for XG-PON.

In a passive optical network (PON), energy conservation is an important system design goal to satisfy the global demands for an energy efficient green network. In this paper, we show that a separate period control for the transmitter and receiver of an optical transceiver can result in better power saving performances in PON systems. Then, we propose a power saving mode called the Dual Cyclic Sleep (DCS) mode. We have implemented the DCS mode in an ETRI XG-PON system and conducted experiments to show the power saving efficiency of the proposed DCS mode. The results indicate that the DCS mode provides higher power saving efficiency than the doze and cyclic sleep modes.

Optical Burst Add-Drop Multiplexing Technique for Sub-Wavelength Granularity in Wavelength Multiplexed Ring Networks

We demonstrate optical burst add-drop multiplexing as a practical application of the optical burst switching technology in a wavelength-division-multiplexed ring network. To control optical bursts in the network, a burst identifier (BI) for delivering control information, and a BI processor for handling the BI, were designed. Optical bursts of 10- to 100-mus in length were optically multiplexed or demultiplexed in an intermediate node of the ring network. The demonstration shows that the optical burst add-drop multiplexing technique provides sub-wavelength granularity to a ring network.

Fast management of ONUs based on broadcast control channel for a 10-gigabit-capable passive optical network (XG-PON) system

This paper proposes a broadcast software download (BSD) scheme for a 10-gigabit-capable passive optical network (XG-PON), which dramatically reduces the time required to update a remotely-located user terminals software. The performance of the proposed BSD is examined by numerical analysis and demonstrated by experimental verification on our XG-PON test platforms. The results show that the BSD takes less than 5 minutes to update 45 user-terminal software, while the conventional unicast software download scheme normally takes more than one and half hours.

Investigation of ONU power leveling method for mitigating inter-channel crosstalk in TWDM-PONs

We investigate ONU power leveling methods for mitigating Inter-channel crosstalk of upstream signals in TWDM-PON. 6-dB power dynamic range was archived with maximum 1.4-dB power penalty by adjusting operation current of Tx. The proposed method is thought to be a simple, low-cost solution in comparison with that with a VOA or SOA. Further study is needed for trade-off between crosstalk and eye distortion penalty and how to specify.

ONU transmit power levelling for TWDM-PONs

In this paper, we investigate the required range of ONU transmit power levelling for TWDM-PONs based on the worst case inter-channel crosstalk analysis. To overcome the crosstalk impairment, an OLT-shared architecture of the ONU transmit power levelling and its operation rule is also proposed.

Optimal wavelength provisioning with fuzzy logic control for power saving in TWDM-PONs

This paper proposes an optimal wavelength provisioning algorithm for power saving in time and wavelength division multiplexing passive optical networks (TWDM-PONs). Fuzzy logic control is used to calculate the optimal number of active wavelengths in response to upstream packet arrival rate, and the simulation results shows the proposed algorithm reduce the average number of active wavelengths and consequently reduce the power consumption in TWDM-PONs without severe degradation of the service quality.

Congestion estimation technique in the optical network unit registration process

We present a congestion estimation technique (CET) to estimate the optical network unit (ONU) registration success ratio for the ONU registration process in passive optical networks. An optical line terminal (OLT) estimates the number of collided ONUs via the proposed scheme during the serial number state. The OLT can obtain congestion level among ONUs to be registered such that this information may be exploited to change the size of a quiet window to decrease the collision probability. We verified the efficiency of the proposed method through simulation and experimental results.

All-optical flip-flop using an injection locked Fabry-Perot laser diode

A novel all-optical flip-flop is proposed and demonstrated experimentally. The flip-flop consists of a conventional multi-mode Fabry-Perot laser diode (FP-LD) and a specially designed master FP-LD which has a built-in external cavity and operates in single longitudinal mode oscillation. The triggering pulses were generated by external modulators with non-return-to-zero pulse pattern generators. The rising and falling times of the output signal in on-off operation of the flip-flop were about 50 ps. The required powers of both set and reset pulses were less than -9 dBm.