This PDF file contains the front matter associated with SPIE Proceedings Volume 9388, including the Title Page, Copyright information, Table of Contents, Authors, Introduction (if any), and Conference Committee listing.

We present the fundamentals of multi-input multi-output (MIMO) signal processing for mode-division multiplexing (MDM) in multi-mode fiber. We review group delay management techniques that minimize adaptation time and complexity in MIMO signal processing. We describe long-period fiber grating (LPFG) devices for introducing strong mode coupling, which represent a promising practical approach for group delay management. We analyze MIMO equalization complexity, adaptation time and throughput efficiency for MDM systems employing LPFG devices.

The overall spectral efficiency in optical transmission systems needs to be enhanced by employment of advanced modulation, multiplexing, and coding schemes, as well as the advanced detection techniques. In parallel, novel networking concepts with the griddles and elastic bandwidth allocation are needed to increase the network dynamics and flexibility. In this paper we discuss multidimensional modulation, multiplexing, and coding schemes, which are enablers not only of the information capacity increase, but also for the next generation elastic high-speed optical networking and outline possible future directions and application scenario in different networking segments.

Optical multilevel signals for QKD are evaluated in terms of security and key generation rate when they are used with post-selection. Potential receiver architectures are analyzed from a quantum-mechanical point of view and compared regarding these parameters as well as implementation complexity. Based on that, a coherent state QKD system is proposed.

This paper presents a solution for upgrading optical access networks by reusing existing electronics or optical equipment: sliceable transponders using signal spectrum slicing and stitching back method after direct detection. This technique allows transmission of wide bandwidth signals from the service provider (OLT - optical line terminal) to the end user (ONU – optical network unit) over an optical distribution network (ODN) via low bandwidth equipment. We show simulation and experimental results for duobinary signaling of 1 Gbit/s and 10 Gbit/s waveforms. The number of slices is adjusted to match the lowest analog bandwidth of used electrical devices and scale from 2 slices to 10 slices. Results of experimental transmission show error free signal recovery by using post forward error correction with 7% overhead.

We developed a design technique for a photonics-electronics convergence system by using an equivalent circuit of optical devices in an electrical circuit simulator. We used the transfer matrix method to calculate the response of an optical device. This method used physical parameters and dimensions of optical devices as calculation parameters to design a device in the electrical circuit simulator. It also used an intermediate frequency to express the wavelength dependence of optical devices. By using both techniques, we simulated bit error rates and eye diagrams of optical and electrical integrated circuits and calculated influences of device structure change and wavelength shift penalty.

With the continuous increase in Internet traffic, reconfigurable optical add-drop multiplexers (ROADMs) have been widely adopted in the core and metro core networks. Current ROADMs, however, allow only static operation. To realize future dynamic optical-network services, and to minimize any human intervention in network operation, the optical signal add/drop part should have colorless/directionless/contentionless (C/D/C) capabilities. This is possible with matrix switches or a combination of splitter-switches and optical tunable filters. The scale of the matrix switch increases with the square of the number of supported channels, and hence, the matrix-switch-based architecture is not suitable for creating future large-scale ROADMs. In contrast, the numbers of splitter ports, switches, and tunable filters increase linearly with the number of supported channels, and hence the tunable-filter-based architecture will support all future traffic. So far, we have succeeded in fabricating a compact tunable filter that consists of multi-stage cyclic arrayed-waveguide gratings (AWGs) and switches by using planar-lightwave-circuit (PLC) technologies. However, this multistage configuration suffers from large insertion loss and filter narrowing. Moreover, power-consuming temperature control is necessary since it is difficult to make cyclic AWGs athermal. We propose here novel tunable-filter architecture that sandwiches a single-stage non-cyclic athermal AWG having flatter-topped passbands between small-scale switches. With this configuration, the optical tunable filter attains low insertion loss, large passband bandwidths, low power consumption, compactness, and high cost-effectiveness. A prototype is monolithically fabricated with PLC technologies and its excellent performance is experimentally confirmed utilizing 80-channel 30-GBaud dual-polarization quadrature phase-shift-keying (QPSK) signals.

Optical nonlinearities in various materials pose some of the biggest challenges and opportunities in optical communications. Many important functions can be implemented using various forms of photonic nonlinear-interactions. Bit rate tunable all-optical noise mitigation of QPSK data signal and optical channel deaggregtion of QPSK signals are recent applications of nonlinear optical signal processing. In addition, optical tapped-delay-line (TDL) as a key building block in digital signal processing is discussed. Utilizing TDL, optical Nyquist generation of 32-Gbaud QPSK signals, and one/two dimensional optical correlation of 20-Gbaud QPSK signals are performed.

The use of machine learning techniques to characterize lasers with low output power is reviewed. Optimized phase tracking algorithms that can produce accurate noise spectra are discussed, and a method for inferring the amplitude noise spectrum and rate equation model of the laser under test is presented.

We discuss about digital signal processing approaches that can enable coherent links based on semiconductor lasers. A state-of-the art analysis on different carrier-phase recovery (CPR) techniques is presented. We show that these techniques are based on the assumption of lorentzian linewidth, which does not hold for monolithically integrated semiconductor lasers. We investigate the impact of such lineshape on both 3 and 20 dB linewidth and experimentally conduct a systematic study for 56-GBaud DP-QPSK and 28-GBaud DP-16QAM systems using a decision directed phase look loop algorithm. We show how carrier induced frequency noise has no impact on linewidth but a significant impact on system performance; which rises the question on whether 3-dB linewidth should be used as performance estimator for semiconductor lasers.

We successfully demonstrate 20-Gb/s quadrature phase-shift keying (QPSK) signal transmission. The transmission was carried out over endlessly single-mode holey fiber in the waveband of 1276.02–1304.26 nm, whose bandwidth of 5.09- THz is broader than the traditional C-band. A wavelength-tunable quantum dot (QD) laser with broad wavelength tunability helps realize bandwidth availability. A single InAs/InGaAs QD optical gainchip was grown using a sandwiched sub-nanometer separator technique in the wavelength of 1.3-μm band. Using this gain chip, the QD light source has good wavelength stability, compactness and wavelength tunablility. The measured transmission results show bit error rates within a forward error correction limit of 2×10^–3 using intradyne coherent detection with offline digital signal processing. In this study, it is expected that abundant frequency resources such as the O-band are coherently enhanced by the use of a large number of wavelength channels by effectively using the QD- laser.

Optical performance monitoring (OPM) is considered as an important tool in order to operate and manage dynamic, flexible, and thus complex photonic networks. In this paper, firstly we review recent studies on OPM and discuss its possible applications, such as failure diagnosis of transmitter, receiver, and other transport equipment, optimization of system reach design, and so on. We then present two different types of in-band OSNR monitor, consisting of an optical bandpass filter, a photo-detector, and a signal processer. Since the proposed monitor might be realized by the same hardware implementation as an optical channel monitor (OCM), this is potentially integrated with an OCM in a low-cost fashion. We also explain a BER monitor, which is realized by the same hardware configuration as the above in-band OSNR monitor. The BER in the method is estimated by monitoring OSNR including nonlinear noise as noise source and taking the imperfection of Tx, Rx, and other equipment into account. Finally we develop FPGA-based optical performance monitor prototype and experimentally demonstrate successful monitoring performance.

The joint optimization of coding and modulation formats would provide significant receiver sensitivity improvement due to the increased Hamming distance of codes. By applying Arimoto-Blahut algorithm to maximize mutual information, optimized coded-modulation has been found out together with optimized bit-mapping rule. Simulated channel capacity shows that optimized coded modulation could outperform its counterparts, such as regular qaudrature-amplitude modulation, by around 0.3dB up to about 0.9 coding rate. The improvement is found to be larger in higher modulation formats. Optimal coded-8QAM modulation has been further verified in experiment, where 40Tb/s over 6787km is demonstrated by transmitting 200G per wavelength thanks to the better receiver sensitivity of optimal coded modulation.

Discrete multi-tone (DMT) technology is an attractive modulation technique for short reach optical transmission system. One of the main factors that limit system performance is fiber dispersion, which is strongly influenced by the chirp characteristics of transmitters. We investigated the fiber dispersion impairment in a 400GbE (4 × 116.1-Gb/s) DMT system on LAN-WDM grid for reach enhancement up to 40 km through experiments and numerical simulations.

In this paper, we review our recent research progresses on real-time orthogonal frequency division multiplexing (OFDM) transmission and reception. We successfully realized the transmission and reception of real-time 100Gbps dual optical carrier 16-ary quadrature amplitude modulation (16QAM)-OFDM with direct detection for ultra-short fiber transmission. And we also successfully demonstrated the transmission and reception of real-time 100Gbps single-band coherent optical dual polarization (DP)-16QAM-OFDM signal for the first time with coherent detection. The measured bit error ratio (BER) for 100Gbps single-band coherent optical DP-16QAM-OFDM signal is less than 3.8×10^-3 after 200-km standard single mode fiber (SSMF) without electrical dispersion compensation (EDC).

Expanding software defined networking (SDN) to transport networks requires new strategies to deal with the large number of flows that future core networks will have to face. New south-bound protocols within SDN have been proposed to benefit from having control plane detached from the data plane offering a cost- and energy-efficient forwarding engine. This paper presents an overview of a new approach named KeyFlow to simultaneously reduce latency, jitter, and power consumption in core network nodes. Results on an emulation platform indicate that round trip time (RTT) can be reduced above 50% compared to the reference protocol OpenFlow, specially when flow tables are densely populated. Jitter reduction has been demonstrated experimentally on a NetFPGA-based platform, and 57.3% power consumption reduction has been achieved.

The future optical transport networks will be affected by limited bandwidth of information infrastructure, high power consumption, and heterogeneity of network segments. As a solution to all these problems, the multidimensional signaling has been proposed recently. In this invited paper, we follow a different strategy. Instead of conventional binary and 2^mary signaling (m≥1) we propose to use the nonbinary p^m-ary signaling, where p is a prime larger than 2. With p^m-ary signaling we can improve the spectral of conventional 2^m-ary schemes by log₂p times for the same bandwidth occupancy. At the same time the energy efficiency of pm-ary signaling scheme is much better than that of 2^m-ary signaling scheme based on binary representation of data. We further study the energy-efficient coded modulation for p^m-ary signaling. The energy-efficient signal constellation design for pm-ary signaling is discussed as well. We will demonstrate that with the proposed p^m-ary signaling in combination with energy-efficient signal constellation design, spectral-multiplexing, and polarization-division multiplexing, we can achieve beyond 1 Pb/s serial optical transport without a need for introduction of spatial-division multiplexing.

We demonstrate an optical–electrical hybrid equalizer, which comprises an optical domain equalizer fabricated using optical filter banks and an electrical filter in a digital domain by a digital signal processing, to experimentally demodulate degraded 40-Gbaud quadrature phase-shift keying (QPSK) signal. The optical signal-to-noise ratio (OSNR) required for a BER of 1 × 10^-3 is improved to 7 dB without an optical equalizer (OEQ) under the back-to-back condition. The fluctuation in the OEQ strength between 0–6 dB will not affect signal quality significantly. The signal degradation caused by the frequency response of devices was minimized using by the hybrid equalizer.

We propose a novel optical path routing mechanism that combines coarse-granularity optical multicast with fine-granularity add/drop and block. We implement the proposal in an optical cross-connect node with broadcast-and-select functionality that offers high cost-effectiveness since no addition equipment from conventional ROADMs is needed. The proposed method, called branching, enhances the routing capabilities over the original grouped routing networks by enabling wavelength paths to be established through different GRE pipes. We also present a novel path/GRE routing and wavelength/GRE index assignment algorithm that supports the new routing function. Numerical experiments using real network topologies verify the improved routing performance and the superior efficiency of the proposed control algorithm over original GRE-based networks.

Forward error correction is as one of the key technologies enabling the next-generation high-speed fiber optical communications. Quasi-cyclic (QC) low-density parity-check (LDPC) codes have been considered as one of the promising candidates due to their large coding gain performance and low implementation complexity. In this paper, we present our designed QC-LDPC code with girth 10 and 25% overhead based on pairwise balanced design. By FPGAbased emulation, we demonstrate that the 5-bit soft-decision LDPC decoder can achieve 11.8dB net coding gain with no error floor at BER of 10^-15 avoiding using any outer code or post-processing method. We believe that the proposed single QC-LDPC code is a promising solution for 400Gb/s optical communication systems and beyond.

Device-level reduction of dark current is critical for improving the Signal to Noise ratio and dynamic range of system using III-V based optical components. We report on low-noise, back-illuminated p-i-n photodetector and its arrays with high spectral response for optical communication and also optical interconnects applications at 1.3 μm and 1.55 μm wavelengths. The photodetector is based on planar structure fabricated from InP having a latticematched InGaAs-absorber layer, and it is designed specifically for high sensitivity and low dark current (nA) at room temperature by minimizing leakage current. Electrical and optical performance of both individual diodes and small-pixel array test structures will be presented in this paper.

This paper is dealing with problems and possibilities of RFoG (Radio Frequency over Glass) technology deployment into the new generation optical access networks. Passive optical networks (PON) offer, except high bit rate, also a very wide range of applicability for various traffic data services. These services can be combined with different transmission technologies. The one of the most important needs upon these networks is also their backward compatibility with older analog technologies. The experimental part is devoted to broadcasting of RFoG through the designed PON networks and experimental measurements, using objective methods. The conclusion of this article is focused on the evaluation of individual measurements and considering of the feasibility of RFoG technology deployment in practical utilization.