Hyeon Yeong Choi

BER-adaptive flexible-format transmitter for elastic optical networks

We propose a new optical transmitter which is capable of changing flexibly the modulation format of the optical signal. By using this transmitter, we can handle and assign various modulation formats: binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-ary quadrature amplitude modulation (8QAM), and 16QAM. The proposed transmitter is based on a combination of a dual-drive Mach-Zehnder modulator (DD-MZM) and a dual-parallel MZM (DP-MZM) with electrical binary drive signals. DD-MZM is a key element to produce the 8QAM and 16QAM formats where each arm of DD-MZM is driven by independent binary data. This is because we can modulate the amplitude and phase of the optical signal by using a frequency chirp of the modulator when we adjust properly the amplitudes of the electrical drive signals. In addition, we show an algorithm by which the proposed transmitter can intelligently select the modulation format in accordance with the signal quality.

Demonstration of a dynamic transparent optical network employing flexible transmitters/receivers controlled by an OpenFlow-stateless PCE integrated control plane [invited]

OpenFlow, which allows operators to control the network using software running on a network operating system within an external controller, has recently been proposed and experimentally validated as a promising intelligent control plane technique. To mitigate the potential scalability issue of an OpenFlow-based centralized control plane and to leverage the mature, well-defined, and feature-complete path computation element (PCE) communication protocol, the complex path computation function required in optical networks can be formally decoupled from the OpenFlow controller so the controller can off-load the task to one or more dedicated PCEs. In addition to the control plane intelligence, future optical networks also feature data plane intelligence such as the introduction of flexible transmitters and receivers, which can dynamically change the modulation format and transmission rate of the optical signal without hardware modifications. In this paper, for the first time, we successfully demonstrate a dynamic transparent wavelength-switched optical network employing flexible transmitters and receivers controlled by an OpenFlow-stateless PCE integrated control plane. Our designed flexible transmitter is implemented by a cas-cadeof adual-drive Mach-Zehnder modulator (MZM) and a dual-parallel MZM. By adjusting the electrical binary drive signals, the flexible transmitter is able toflexibly switch the symbol rate and the modulation format, including binary phase shift keying, quadrature phase shift keying, 8-ary quadrature amplitude modulation (8QAM), and 16QAM. The flexible receiver is able to automatically detect different modulation formats and symbol rates and measure the bit-error rate. All the network elements, including optical switching nodes and flexible transmitters and receivers, are extended with OpenFlow interfaces, which can be intelligently controlled by the OpenFlow-stateless PCE integrated control plane with significant protocol extensions. On an actual network testbed with real hardware, we successfully validate dynamic and seamless interworking operations between the OpenFlow controller, a stateless PCE, and all the data plane hardware. The overall feasibility and efficiency of the proposed solutions are verified, and dynamic end-to-end path provisioning and lightpath restoration in such a new network scenario are quantitatively evaluated. We also tested the scalability of the proposed control plane; the experiment results indicated that dynamic path provisioning and restoration can be achieved within hundreds of milliseconds by using the proposed approach, and the overall architecture scales well with a batch of requests.

Demonstration of BER-Adaptive WSON Employing Flexible Transmitter/Receiver With an Extended OpenFlow-Based Control Plane

A bit-error rate (BER)-adaptive wavelength-switched optical network (WSON) employing the multiformat and multirate transmitter/receiver is experimentally demonstrated. The flexible transmitter is capable of generating binary phase-shift-keying, quadrature phase-shift-keying, eight-ary quadrature amplitude modulation, 8QAM, and 16QAM, as well as changing the symbol rate. On the other hand, the flexible receiver based on a coherent detection scheme is utilized not only to detect the optical signal with any modulation format/rate, but also to send the BER information to an OpenFlow controller via extended OpenFlow protocols. Since the measured BER is a reliable barometer of the optical path conditions, an extended OpenFlow-based control plane with the OpenFlow controller intelligently determines and assigns either appropriate modulation format/rate or a backup path in WSON in accordance with BER information.

Optical performance monitoring of QPSK data channels by use of neural networks trained with parameters derived from asynchronous constellation diagrams

We demonstrate a technique for performance monitoring of quadrature phase-shift keying data channels by simultaneously identifying optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) using neural networks trained with parameters derived from asynchronous constellation diagrams. A correlation coefficient of 0.987 is reported for a set of testing data from a 40 Gbps return-to-zero, quadrature phase-shift keying (RZ-QPSK) system. The root-mean-square (RMS) errors are 0.77 dB for OSNR, 18.71 ps/nm for CD, and 1.17 ps for DGD.

Modulation-format-free bias control technique for MZ modulator based on differential phasor monitor

We propose a novel bias control technique based on the differential phasor monitor for the LiNbO3 modulator. For demonstrations, the proposed bias control technique was used for 20-Gb/s QPSK and 43-Gb/s 16-QAM signals.

Generation and detection of 240-Gb/s PDM-64QAM using optical binary synthesizing approach and phase-folded decision-directed equalization

We present new generation and detection methods for high symbol-rate 64-ary quadrature amplitude modulation (64QAM). The 64QAM signal is created by tandem in-phase/quadrature (I/Q) modulators driven by electrical binary signals. The first I/Q modulator, which has four drive arms (i.e. a dual-drive I/Q modulator), yields 16QAM with an offset at the 1st quadrant of the complex plane. Subsequently, the second modulator switches this 16QAM signal over four quadrants via the typical quadrature phase-shift-keying (QPSK) modulation scheme, hence the desired 64QAM is generated. To mitigate the impacts of transmitter imperfections, we also propose a phase-folded decision-directed (PF-DD) linear equalizer at the receiver. Using these new techniques, we experimentally demonstrate the 120- and 240-Gb/s polarization-division-multiplexed (PDM) return-to-zero (RZ) 64QAM systems. The required optical signal-to-noise ratio (OSNR) for a bit-error rate (BER) of 2.4x10(-2) is measured at 20.2 or 23 dB, respectively, which is ~3.5 dB off the theoretical limit.

Filtering tolerance of 108-Gb/s PolMux quadrature duobinary signal on 25-GHz grid

We demonstrate the error-free transmission of 108-Gb/s PolMux quadrature duobinary signal in a 25-GHz spaced WDM system and investigate its tolerance to narrow optical filtering.

Improved polarization-nulling technique for monitoring OSNR in WDM network

We propose a simple method to improve the polarization-nulling technique by using a tunable optical filter. The results show that the proposed technique can monitor OSNR accurately even when the signal is significantly depolarized due to the nonlinear birefringence

A new multi-purpose optical transmitter for higher-order QAM generation

We present a versatile optical transmitter composed of tandem I/Q modulators driven by electrical binary signals. This transmitter is able to simply generate higher-order QAM formats (from BPSK up to 64QAM) without hardware modification.

Adjustment-free DxPSK receiver based on single delay interferometer using 120-degree optical hybrid

We report an adjustment-free DxPSK receiver based on a single delay-interferometer using a 3times3 optical coupler. We experimentally demonstrate wavelength- and polarization-independent detection of DQPSK and D8PSK signals with near quantum-limited sensitivities.