Byoung Whi Kim

Bidirectional WDM-PON based on gain-saturated reflective semiconductor optical amplifiers

We propose a bidirectional wavelength-division-multiplexed passive optical network by employing gain-saturated reflective semiconductor optical amplifiers (RSOAs) for wavelength-independent optical network terminals. The fabricated RSOA module has the input saturation power less than -13 dBm and its saturated gain higher than 13 dB within the C-band for arbitrary polarization states. The upstream signals are generated by remodulating the downstream signals whose modulation amplitude is squeezed through gain-saturated RSOAs. We present experimental results on bidirectional transmission with 1.25 Gb/s for upstream and 2.5 Gb/s for downstream data rates over 20-km transmission distance.

Long-reach optical access networks: A survey of research challenges, demonstrations, and bandwidth assignment mechanisms

Long-Reach optical access is a promising proposal for future access networks. This technology can enable broadband access for a large number of customers in the access/metro area, while decreasing capital and operational expenditures for the network operator. First, the paper reviews the evolutionary path of access networks and shows the drivers from technology and business perspectives for high bandwidth and low cost. A variety of research challenges in this field is reviewed, from optical components in the physical layer to the control and management issues in the upper layers. We discuss the requisites for optical sources, optical amplifiers, and optical receivers when used in networks with high transmission rate (10 Gbps) and large power attenuation (due to large split, transmission over 100 km and beyond, and propagation), and the key topological structures that allow to guarantee physical protection (tree-and-branch, ring-and-spur). Then, some relevant demonstrations of Long-Reach Optical Access Networks developed worldwide by different research institutes are presented. Finally, Dynamic Bandwidth Allocation (DBA) algorithms that allow to mitigate the effect of the increased control-plane delay in an extended-reach network are investigated.

Remodulation schemes with reflective SOA for colorless DWDM PON

Feature Issue on Passive Optical Network Architectures and TechnologiesThis article presents remodulation schemes with reflective semiconductor optical amplifiers (RSOAs), which have recently been developed for application to the wavelength-division-multiplexed passive optical network (WDM-PON). The remodulation schemes have a common feature that the optical signal modulated with downstream data is reused to carry the upstream data through the RSOA in the subscriber-side equipment by a series of processes such as being flattened out, reflected at the rear facet of the RSOA, and then remodulated with upstream data. The major advantage of remodulation schemes is the possibility of realizing the simplest WDM-PON optical link structure, which is directly reflected in cost-effectiveness of the network both in equipment and maintenance. Three schemes are presented; the simplest one is to use the RSOA gain saturation, the second uses the effect of frequency detuning on the extinction ratio of optical signal, and the third uses RSOA gain control by dynamically varying the current injection. Feasibilities of those schemes are discussed in the view of commercial application to WDM-PON.

Tunable external cavity laser based on polymer waveguide platform for WDM access network

We developed a wide-range wavelength tunable external cavity lasers based on a polymer waveguide platform for use in wavelength-division-multiplexing (WDM) access networks as a low-cost light source. The lasing wavelength is tuned over 13 nm by thermally changing the reflection spectrum of the polymer waveguide Bragg grating with a heater. With the sidemode suppression ratio higher than 30 dB, it can support 16 WDM channels spaced by 100 GHz. The directly modulated 1.25-Gb/s data streams were successfully transmitted over the single-mode optical fiber link of 20 km.

Radio-over-fiber system using fiber-grating-based optical CDMA with modified PN codes

In this work, we propose the fiber Bragg grating (FBG)-based optical code-division multiple-access (CDMA) with the modified pseudorandom noise (PN) codes for the radio-over-fiber (ROF) systems, and we numerically analyze the characteristics of the proposed system. By the proposed FBG-based optical CDMA with the modified PN codes and spectrally uniform intensity light sources, it is possible to construct interference-free optical CDMA for ROF systems.

RSOA-Based Wavelength-Reuse Gigabit WDM-PON

This article presents the RSOA-based re-modulation schemes for practical application to the WDM-PON link. Emphasis is put on the three methods for reducing the residual downstream signal in the upstream transmission; the simplest one is to use the RSOA gain-saturation property, the second uses selective filtering of the adiabatic-chirped DFB-LD output spectrum, and the last uses a dynamic RSOA gain control by varying its driving current according to the incident binary signal. The reflection sensitivity in the proposed re-modulation link is also qualitatively presented in the cases of using two different types of seed light: coherent light from DFB-LD array and spectrum-sliced incoherent ASE light. We show experimental results of an error-free bidirectional gigabit transmission over 20 km at -30 dB reflection with the spectrum-sliced ASE seed light.

Over 26-nm Wavelength Tunable External Cavity Laser Based on Polymer Waveguide Platforms for WDM Access Networks

We demonstrated a widely tunable hybrid-integrated external cavity laser on a polymer-based waveguide platform. The lasing wavelength was tuned over 26 nm by locally heating the surface-relief-type polymer waveguide Bragg grating fabricated by using the phase mask. The phase-control heater section was inserted between the laser diode and the Bragg grating for the fine wavelength tuning and the stable single-mode lasing. In the 100-GHz-spaced wavelength-division-multiplexing systems, the 1.25-Gb/s directly modulated data streams at each tuned 32 channel were successfully transmitted

A new family of 2-D wavelength-time spreading code for optical code-division multiple-access system with balanced detection

We propose a new family of 2¿D wavelength-hopping/ time-spreading code for optical code-division multiple-access systems with balanced detection, and we numerically analyze the characteristics of the proposed system. By using the proposed decoding scheme, the undesired interference is efficiently eliminated. The proposed scheme has the enhanced performance and allows for a large number of simultaneous users compared with the 3-D and other balanced codes for differential detection.

Optical Transceiver employing an RSOA with Feed-Forward Current Injection

We propose an optical transceiver employing an RSOA of which gain is controlled by feedforward current. With a low injection power below the gain saturation, the improved remodulation is clearly demonstrated at 1.25- Gb/s data rate.

A bidirectional RSOA based WDM-PON utilizing a SCM signal for down-link and a baseband signal for up-link

We propose and demonstrate a bidirectional WDM-PON utilizing a SCM technique for down-link and a baseband technique for up-link with a RSOA for re-modulation. The BER performances of our scheme were shown to be as good as those in the case of continuous wave (CW) light injected RSOA.