Sang-Yuep Kim

DSP-based optical access approaches for enhancing NG-PON2 systems

Motivated by recent progress in next-generation PON2, or NG-PON2, standardization, this article reviews digital signal processing technologies to further enhance NG-PON2 systems by realizing flexible and cost-effective optical access network deployments. First, flexible speed upgrades by DSP-enabled advanced modulation and multiplexing approaches are described, followed by a consideration of cost-performance trade-offs. Next, reach extension using DSP-based digital coherent reception and impairment compensation is overviewed. Finally, as a future goal, access network virtualization with reconfigurable optical line terminals and optical network units is discussed.

Electronic post-compensation for nonlinear phase noise in a 1000-km 20-Gbit/s optical QPSK transmission system using the homodyne receiver with digital signal processing

Abstract: We demonstrate electronic post-compensation for nonlinear phase noise in a 1000-km 20-Gbit/s optical QPSK transmission system. Optimized phase shift proportional to intensity noise is given to the homodyne-detected electric field, leading to effective phase-noise reduction.

VCSEL-based coherent detection of 10-Gbit/s QPSK signals using digital phase noise cancellation for future optical access systems

We propose a VCSEL-based QPSK coherent system to be implemented for future access systems, using digital phase noise cancellation to achieve a coherent detection of 10-Gbit/s QPSK signals with a laser linewidth of 300 MHz.

10-Gbit/s next-generation coherent QPSK-PON with reduced bandwidth requirements employing linear digital equalization with adaptive algorithm

We experimentally demonstrate a 10-Gbit/s coherent QPSK-PON with a reduced bandwidth. Using a linear feed-forward equalizer with an adaptive algorithm, the bandwidth requirement is reduced down to 2.5 GHz with an approximate 0.5-dB power penalty.

1,000-km transmission of 20-Gbit/s QPSK-NRZ co-polarized DWDM signals with spectral efficiency of 1 bit/s/Hz using coherent detection

We demonstrate co-polarized 20-Gbit/s DWDM NRZ-QPSK transmission over 1074 km using a phasephase-diversity optical homodyne receiver. The spectral efficiency is as high as 1.05 bit/s/Hz, which is limited by cross-phase modulation between DWDM channels.

Frequency Response Equalization of Optical Transceivers Enabling OEO-Based Extender in OFDM-PON Systems

We investigate the feasibility of using a 1R optical-electrical-optical-based extender in orthogonal frequency-division multiplexing passive optical network (OFDM-PON) systems; our key advance is an equalization algorithm composed of a fractionally spaced equalizer and self-phase error correction in conjunction with a one-tap equalizer. The proposed algorithm maximizes the available system bandwidth, which would otherwise suffer the unavoidable limitations created by the cascaded components used in the actual transceivers of OFDM-PON systems.

Parallelization of cipher algorithm on CPU/GPU for real-time software-defined access network

Network Function Virtualization (NFV) and Software Defined Network (SDN) are attracting attention with the goal being enhanced networks efficiency. To enhance flexibility and to meet user requests and conditions, software implementation of communications equipment is pursued as our approach. It becomes possible to implement various optical line terminal (OLT) functions on the common hardware by realizing the functions as software. The proposed approach prevents kinds of systems from increasing and simplifies maintenance. Throughput on lower-performance software comparing with dedicated circuits is a problem. This paper focuses on a cipher algorithm for the access network as typical of the more demanding OLT functions and proposes parallel implementation on CPU/GPU resources that offers real-time processing. This paper targets the CTR and GCM which are utilized on PON systems. For software implementation, this paper proposes a data-parallelization-based algorithm architecture. Evaluation results gathered from a many-core CPU simulator and GPU show that throughput is sufficient for the 5.37-Gbps CTR-AES128 process and the 914 Mbps GCM-AES128 process. The proposed parallel algorithm on a GPU is 141 times faster than serial processing. It is also found that the cipher circuit of 1-Gbps-class PON systems utilizing CTR-AES128 can be replaced with GPU.

Constellation design for next-generation hierarchically-modulated PON systems

In this paper, we study the performance of star quadrature amplitude modulation (QAM) signals with various constellations for hierarchically-modulated PON systems that overlay an over 20-Gbps PSK signal on a 10-Gbps on-off keying (OOK) signal; previous work examined only the performance of an 8-star QAM signal. A star QAM signal consists of a PSK signal with lower amplitude (inner-PSK signal) and a PSK signal with higher amplitude (outer-PSK signal). We propose to decrease the modulation level of the inner-PSK signal and increase that of the outer-PSK signal with the goal of improving the bit error rate performance in some conditions. Simulations indicate the minimum required received power for the various constellations examined: it is shown that effective design depends on the extinction ratio. For example, 10-star QAM improves the minimum required received power by 3 dB compared to 8-star QAM when the extinction ratio is 12 dB.

Rectangular short pulse generation by using strong unchirped fiber Bragg grating

We demonstrate rectangular optical pulse generation from short input pulses by using a highly reflective unchirped fiber Bragg grating (FBG) with a simple structure. ~18-ps rectangular pulses are generated successfully from ~3-ps input optical pulses.

Real-Time Demonstration of PHY Processing on CPU for Programmable Optical Access Systems

Virtualization of optical access systems is being pursued to speedup service deployment and reduce CAPEX/OPEX. Several passive optical network (PON) specifications have been standardized and the applicability of virtualization to access networks is being considered. We have proposed a programmable optical line terminal (OLT) that performs OLT functions by software processing on general-purpose hardware.Unfortunately, general-purpose hardware struggles to achieve the 10-Gbps throughput demanded of access systems. Our work solves this problem by introducing software implementation techniques for PHY processing, a key component of computation complexity. This paper proposes a 2-stage parallel pipeline based on data-parallelism, and details its implementation with the use of look up table (LUT) for the Galois-field multiplier for implementing the standard OLT functions of forward error correction (FEC) and encryption. We implement our proposals on a general-purpose server with optical transmitter. Evaluation results show that proposals drastically accelerate algorithm performance and attain the throughputs of 10 Gbps with RS(255,239), 5.1 Gbps with RS(255,223), 2.5 Gbps with CTR-AES-128 and 1.2 Gbps with GCM-AES-128.