86-GBaud subcarrier multiplexed 16QAM signal generation using an electrical 90 degree hybrid and IQ mixers

We experimentally demonstrate an aggregate 86-GBaud (over three sub-bands and one polarization) signal generation based on subcarrier multiplexing technique using IQ mixers, an electrical 90 degree hybrid, and diplexers. The electrical hybrid allows transmitter-side digital signal processing to be simplified to pulse shaping and digital pre-emphasis. We verified the configuration by testing the performance of an 86-GBaud Nyquist-shaped 16 quadrature amplitude modulation signal with differential bit encoding. The implementation penalty assuming 7% hard-decision forward error correction is reduced to 2 dB by utilizing a 31-tap decision-directed least mean square based multiple-input multiple-output equalizer for sideband crosstalk mitigation

200-Gb/s Polarization Multiplexed Doubly Differential QPSK Signal Transmission over 80-km SSMF Using Tandem SSB without Optical Amplification

We propose 200-Gb/s polarization multiplexed tandem SSB DDQPSK with intradyne detection for 80-km SSMF transmission. Without optical amplification, dispersion compensation or carrier recovery, the simulated receiver sensitivity for 80-km transmission was below -25.5 dBm (at 7% HDFEC threshold)

Universal Microwave Photonics Approach to Frequency-Coded Quantum Key Distribution

Design principles of universal microwave photonics system (MPS) for quantum key distribution (QKD) with frequency coding are concerned. Its main modulation concept lies in single photon generation on sidebands of optical carrier and determination of photons ground state through its registration and the amplitude value of its carrier frequency as reference channel. So, it is necessary to solve problems of signal-to-carrier ratio of single photon detector (SPD) and aspects of photon number splitting (PNS) attack, nonlinear phase modulation (NPM) between carrier and sidebands in fiber, and finally, spectral selection of carrier in receiver. The technologies, based on the modulation conversion of an optical carrier, are widely used in microwave photonics. Due to the natural symmetry of modulated signals and the highest achievable ratio of the modulation conversions, amplitude-phase modulation with complete or partial suppression of the optical carrier has found a particularly wide application in MPS. The characteristics of advanced MPS for QKD with frequency coding and carrier suppression based on tandem amplitude modulation and phase commutation are presented. New systems can have classical symmetric or non-classical asymmetric structure for QKD based only on spectral selection of carrier and subcarriers without re-modulation

Cost-Effective Spectrally-Efficient Optical Transceiver Architectures for Metropolitan and Regional Links

The work presented herein explores cost-effective optical transceiver architectures for access, metropolitan and regional links. The primary requirement in such links is cost-effectiveness and secondly, spectral efficiency. The bandwidth/data demand is driven by data-intensive Internet applications, such as cloud-based services and video-on-demand, and is rapidly increasing in access and metro links. Therefore, cost-effective optical transceiver architectures offering high information spectral densities (ISDs > 1(b/s)/Hz) need to be implemented over metropolitan distances. Then, a key question for each link length and application is whether coherent- or direct (non-coherent) detection technology offers the best cost and performance trade-off. The performance and complexity limits of both technologies have been studied. Single polarization direct detection transceivers have been reviewed, focusing on their achievable ISDs and reach. It is concluded that subcarrier modulation (SCM) technique combined with single sideband (SSB) and high-order quadrature amplitude modulation (QAM) signaling, enabled by digital signal processing (DSP) based optical transceivers, must be implemented in order to exceed an ISD of 1 (b/s)/Hz in direct-detection links. The complexity can be shifted from the optical to the electrical domain using such transceivers, and hence, the cost can be minimized. In this regard, a detailed performance comparison of two spectrally-efficient direct detection SCM techniques, namely Nyquist-SCM and OFDM, is presented by means of simulations. It is found out that Nyquist-SCM format offers the transmission distances more than double that of OFDM due to its higher resilience to signal-signal beating interference. Following this, dispersion-precompensated SSB 4- and 16-QAM Nyquist-SCM signal formats were experimentally demonstrated using in-phase and quadrature (IQ)-modulators at net optical ISDs of 1.2 and 2 (b/s)/Hz over 800 km and 323 km of standard single-mode fibre (SSMF), respectively. These demonstrations represent record net optical ISDs over such distances among the reported single polarization wavelength division multiplexed (WDM) systems. Furthermore, since the cost-effectiveness is crucial, the optical complexity of Nyquist-SCM transmitters can be significantly reduced by using low-cost modulators and high-linewidth lasers. A comprehensive theoretical study on SSB signal generation using IQ- and dual-drive Mach-Zehnder modulators (DD-MZMs) was carried out to assess their performance for WDM direct detection links. This was followed by an experimental demonstration of WDM transmission over 242 km of SSMF with a net optical ISD of 1.5 (b/s)/Hz, the highest achieved ISD using a DD-MZM-based transmitter. Following the assessment of direct detection technology using various transmitter designs, cost-effective simplified coherent receiver architectures for access and metro networks have been investigated. The optical complexity of the conventional (polarization- and phase-diverse) coherent receiver is significantly simplified, i.e., consisting of a single 3 dB coupler and balanced photodetector, utilizing heterodyne reception and Alamouti polarization-time block coding. Although the achievable net optical ISD is halved compared to a conventional coherent receiver due to Alamouti coding, its receiver sensitivity provides significant gain over a direct detection receiver at M-ary QAM formats where M ≥16

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

Complex Field Modulation in Direct Detection Systems

Even though fiber optics communication provides a high bandwidth channel to achieve high-speed data transmission, there is still demand for higher spectral efficiency, faster data processing speeds with reduced resource requirements due to ever increasing data and media traffic. Also, lately the demand for online streaming because of remote working has increased significantly. Various multilevel modulation and demodulation techniques are used to improve spectral efficiency. Although spectral efficiency is improved, there are other challenges that arise. Such as requirements for high speed electronics, receiver sensitivity degradation, chromatic dispersion, operational flexibility, effects of nonlinearity impairments etc. Here, we investigate complex bandwidth efficient field modulation and coding techniques to improve spectral efficiency while reducing the digital signal processing (DSP) resources required for implementations using FPGAs or ASICs and compensation for linear and nonlinear impairments that appear in fiber optic communication systems. In this dissertation we investigated and developed solutions for various limitations and impairments in a direct-detection transmission system with complex field modulated optical signal. The solutions that we developed to compensate the fiber optical impairments can be implemented using DSP either at transmitter side or the receiver. By employing DSP based approach to mitigate the optical impairments and limitations we can achieve more flexibility in the optical transceivers while achieving higher spectral efficiency. We proposed and demonstrated digital-analog hybrid subcarrier multiplexing (SCM) technique which can reduce the speed requirement of high-speed digital electronics such as ADC and DAC, while providing wideband capability, high spectral efficiency, operational flexibility and controllable data-rate granularity. Hybrid SCM is a modular approach in which multiple digitally generated subcarriers are aggregated through RF oscillators and IQ mixers for frequency up- and down-conversions. Next, to achieve maximum spectral efficiency with conventional Quadrature Phase Shift Keying (QPSK) we need highly spectral efficient Nyquist filters which require large amount of FPGA resources for digital signal processing (DSP). Hence, we investigated Quadrature Duobinary (QDB) modulation as a solution to reduce the FPGA resources required for DSP while achieving spectral efficiency of 2bits/s/Hz. We compared QDB with QPSK in a digital-analog hybrid subcarrier multiplexing system and we show that with minor changes in transmitter design we can achieve 2bits/s/Hz spectral efficiency, which is same as the Nyquist QPSK with relaxed resource requirements for DSP. We investigated and developed a solution to digitally compensate the nonlinearities introduced by semiconductor optical amplifiers (SOA). In a field modulated direct-detection system, due to square-law detection of the photodiode, leads to an interference called signal-signal beat interference (SSBI). To eliminate SSBI we can use Kramers-Kronig (KK) receiver as we can retrieve the phase information from the direct detected optical signal for the class of signals called as minimum phase signals. However, it is under the assumption that the entire transfer function of our optical transmission system is linear except for photodiode. However, when the system transfer function is non-linear due to SOA nonlinearities when operated in gain saturation region. By using electrical forward propagation method for pre-compensation of nonlinearities caused by SOA we show that we can simultaneously restore the efficiency of KK receiver and as well achieve electronic dispersion post-compensation

Orthogonal frequency division multiplexing for next generation optical networks

Next generation optical networks will be required to provide increased data throughput on a greater number of optical channels and will also have to facilitate network flexibility in order to adapt to dynamic traffic patterns. Furthermore, the potentially wide deployment of optical Access and Metropolitan networks in particular require that these challenges are met in a cost effect manner. This thesis examines the use of Orthogonal Frequency Division Multiplexing (OFDM) as a means of helping to meet these requirements for next generation optical systems with a high market volume. OFDM is a multi–carrier modulation technique which exhibits high spectral efficiency and a tolerance to chromatic dispersion making it an excellent candidate for use in next generation optical networks. The work presented in this thesis shows how the use of OFDM in conjunction with novel laser devices and direct detection can be used to construct cost effective, low footprint optical systems. These systems are capable of providing >10Gb/s per optical channel and are suitable for implementation as optical access networks. Furthermore, OFDM is shown to be a realistic candidate for use in an optical switching environment where external modulation is employed and, as such, can be considered for use in next generation metropolitan networks

Flexible optical and millimeter-wave analog-RoF transmission with a silicon-based integrated dual laser module

A hybrid integrated InP-Si3N4 dual tunable laser module is deployed as a highly flexible source for converged optical/mm-wave fronthaul. Experimental results show the wavelength flexible delivery of 5G signals over analog radio-over-fiber, incorporating wireless transmission at 60 GHz, with received EVMs as low as 5%

Optical heterodyne analog radio-over-fiber link for millimeter-wave wireless systems

Optical heterodyne analog radio-over-fiber (A-RoF) links provide an efficient solution for future millimeter wave (mm-wave) wireless systems. The phase noise of the photo-generated mm-wave carrier limits the performance of such links, especially, for the transmission of low subcarrier baud rate multi-carrier signals. In this work, we present three different techniques for the compensation of the laser frequency offset (FO) and phase noise (PN) in an optical heterodyne A-RoF system. The first approach advocates the use of an analog mm-wave receiver; the second approach uses standard digital signal processing (DSP) algorithms, while in the third approach, the use of a photonic integrated mode locked laser (MLL) with reduced DSP is advocated. The compensation of the FO and PN with these three approaches is demonstrated by successfully transmitting a 1.95 MHz subcarrier spaced orthogonal frequency division multiplexing (OFDM) signal over a 25 km 61 GHz mm-wave optical heterodyne A-RoF link. The advantages and limitations of these approaches are discussed in detail and with regard to recent 5G recommendations, highlighting their potential for deployment in next generation wireless systems

Phase noise robust optical heterodyne system for reduced complexity millimeter-wave analog radio-over-fibre

Strict optical linewidth/coherence requirements for A-RoF systems are overcome through development of an analog optical heterodyne architecture tolerant to phase noise and carrier offset. Successful generation and reception of a 60GHz UF-OFDM signal using two free-running tunable lasers, without digital phase/frequency offset compensation, is demonstrated