Seán Ó Dúill

Dublin City University | DCU

We derive analytical expressions to show that the pulse-to-pulse phase coherence is critical to generate an optical frequency comb with clearly defined comb lines. Our results are verified by supporting numerical simulations. We build upon previous works that only considered the pulse timing jitter; here we consider the effect of the pulse-to-pulse...

We report on the impact that the random group delay ripple of wavelength select switches has on Nyquist pulse shaped signals and on the cascadability of wavelength select switches (WSS) for use as wavelength-based routers within optical communication networks. We show how to simulate the appropriate WSS filter response that accounts for the random...

We report on a potentially deleterious issue regarding the four-wave mixing (FWM)-based processing of dispersion-altered signals. We estimate the baudrate-dependent pump linewidth tolerances by calculating the extra optical signal to noise ratio (OSNR) penalty with respect to the propagation distance. We find that the issue is not important for 10...

We present detailed numerical simulations of the laser dynamics that describe optical frequency comb formation by injection-locking a gain-switched laser. The typical rate equations for semiconductor lasers including stochastic carrier recombination and spontaneous emission suffice to show the injection-locking behavior of gain switched lasers, and...

Modulation cancellation and signal inversion are demonstrated within reflective semiconductor optical amplifiers. The effect is necessary to implement colorless optical network units for network end-users, where downstream signals need to be erased in order to reuse the carrier for upstream transmission. The results presented here indicate that ref...

We present the results of the detected voltage distribution of a quantum random number generator (QRNG) based on a photonic integrated circuit comprising a semiconductor laser, delay interferometer and photodetector. We find that the integrated QRNG system behaves as expected for a QRNG from discrete gain-switched laser sources, especially exhibiti...

We present results of the detected voltage distribution of a quantum random number generator based on the photonic integration of semiconductor laser, delay interferometer and photodetector. We find that the integrated system behaves as expected for random number generation from gain-switched laser sources. The biggest advantage is that only electr...

We experimentally demonstrate 4×75 Gbit/s optically amplified 4-level pulse amplitude modulation (PAM-4) transmission based on an external Mach-Zehnder modulator (MZM) and electro-absorption modulator (EAM) for monolithically integrable intensity modulation and direct detection wavelength division multiplexed passive optical networks (WDM-PONs). Th...

Owing to advances in fabrication technology and device design, semiconductor optical amplifiers (SOAs) are evolving as a promising candidate for future optical coherent communication links. This review article focuses on the fundamentals and broad applications of SOAs, specifically for optical channels with advanced modulation formats, as an integr...

We present comprehensive numerically simulated scans of the spectral evolution of the output from a single-mode semiconductor laser diode undergoing external light injection. The spectral scans are helpful to understand the different regimes of operation as well as the system evolution between each state: i.e., locked state, four-wave mixing, pulsa...

We report on a technique that uses RF quadrature demodulation to measure laser FM-noise based on a delayed self-heterodyne setup. The measurement is self-referencing and the FM-noise can be measured with high precision over a sufficiently long duration that allows us to explore the limits imposed by the delay line in the self-heterodyne setup. We p...

This paper describes the detailed characterization of a novel InP-Si3N4 dual laser module with results revealing relative intensity noise (RIN) as low as −165 dB/Hz and wide wavelength tunability (100 nm). The hybrid coupled laser is deployed in an unamplified 28 GBd 8 level pulse amplitude modulation (PAM) short-reach data center (DC) transmission...

The future evolution of wireless networks, throughout the 5G era and beyond, will require the expansion and augmentation of millimetre-wave systems for both terrestrial and satellite communications. Photonic technologies offer a cost efficient and high bandwidth platform for millimetre-wave carrier generation and distribution, but can introduce hig...

Small-signal techniques are a useful engineering tool to estimate system performance, though small-signal models need to be tested against the large-signal from which they are derived. We show that combined small-signal models for lasers and optical fiber are valid for passive optical networks employing directly modulated semiconductor lasers, prov...

Coherent fiber-optic communication systems are limited by the Kerr-induced nonlinearity. Benchmark optical and digital nonlinearity compensation techniques are typically complex and tackle deterministic-induced nonlinearities. However, these techniques ignore the impact of stochastic nonlinear distortions in the network, such as the interaction of...

We generate multiple optical carriers with ultra-low phase noise, over a useable bandwidth of 160 GHz, from an externally injected gain-switched comb source with exceptional low linewidth below 10 Hz. We show successful transmission of 17 demultiplexed channels using 64-quadrature amplitude modulation signals at 5 GBaud.

We experimentally demonstrate, for the first time, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm to improve the receiver performance of wavelength converting 40-Gb/s 16-quadrature amplitude modulation (16-QAM) and 30-Gb/s 64-QAM using four-wave mixing in semiconductor optical amplifier (SOA). Two novel modified...

A multi-section laser PIC for use as a directly modulated transmitter is demonstrated. The unique architecture of the chip, employing a master-slave configuration, delivers chirp reduction and enables error-free transmission of 10 Gb/s on-off keyed signal over 37 km of single-mode fiber.

We experimentally demonstrate, for the first time, blind nonlinearity compensation using the Density-Based Spatial-Clustering of Applications with Noise (DBSCAN) algorithm for a 40-Gb/s 16-quadrature amplitude modulated being transmitted at 50 km of standard single-mode fiber. At high launched optical powers, DBSCAN offers up to 0.83- and 8.84-dB e...

An active injection-locked demultiplexer for optical combs with flexible channel spacing is demonstrated. Relationships between the injected power and frequency detuning of a 6.25GHz comb and the output comb suppression and phase noise are characterized

Tunable lasers are necessary devices for modern-day telecommunications and sensing systems. Tunable lasers based on altering the refractive index of the tuning sections of distributed Bragg reflectors (DBR) by varying the injected electrical current show significantly more instantaneous random changes in the instantaneous lasing frequency (or exces...

Nonlinearities in SOA-based wavelength conversion are experimentally tackled using post-blind-compensation based on machine learning clustering for coherent 16/64-QAM signals. We show that K-means outperforms fuzzy-logic since it tackles more effectively non-circularly- symmetric Gaussian noise and nonlinearity.

In this work, we experimentally demonstrate wavelength conversion of a 5 GBaud 64-QAM signal in an SOA-based single pump configuration that incorporates machine learning (ML) based digital signal processing (DSP) to improve the tolerance to nonlinear distortion induced from wavelength conversion. The ML is placed at the receiver-side of the system...

We provide numerical verification of a feed-forward, heterodyne-based phase noise reduction scheme using single-sideband modulation that obviates the need for optical filtering at the output. The main benefit of a feed-forward heterodyne linewidth reduction scheme is the simultaneous reduction of the linewidth of all modes of a mode-locked laser (M...

The millimeter-wave (mm-wave) frequency band has emerged as a means to overcome current radio frequency spectral limitations and represents an interesting solution to fulfil the bandwidth and networking requirements of fifth generation (5G) mobile communications and beyond. Photonic generation of these frequencies holds advantages over electronic m...

We demonstrate an all-optical wavelength conversion system based on four-wave mixing (FWM) in semiconductor optical amplifiers for quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM) signals using tunable dual-correlated pumps provided by the combination of a quantum dash passively mode-locked laser (QD-PMLL) and a...

We present a scheme of frequency-degenerate mid-span spectral inversion (MSSI) for nonlinearity compensation in fiber-optic transmission systems. The spectral inversion is obtained by using counter-propagating dual pump four-wave mixing in a semiconductor optical amplifier (SOA). Frequency-degeneracy between signal and conjugate is achieved by keep...

We present results of our optical frequency comb technology based on gain-switching a semiconductor laser. These optical frequency comb sources are entirely opto-electronic in nature, lightweight, small form factor, rigid and robust. We present the optical comb spectra and the corresponding pulsating output with 20 ps pulses, with repetition rates...

We report sub-harmonic injection locking of a 40 GHz passively mode-locked quantum-dash ( Q -dash) laser through spectral enrichment in a nonlinear semiconductor optical amplifier. The proposed scheme is demonstrated for injection locking of the Q -dash passively mode-locked laser using data modulated with non-return-to-zero line-coding at 10 G sym...

Optical spectra of signals at the output of semiconductor optical amplifiers (SOA) provide useful insight into amplifier nonlinearities. In this work, we determine the parameters of an analytical SOA model with a pump-probe experiment by evaluating the measured spectra of the pump and probe pulses at the SOA output. The analytical lumped SOA model...

We theoretically analyze the phase noise transfer issue between the pump and the wavelength-converted idler for a nondegenerate four-wave mixing (FWM) scheme, as well as study the vector theory in nonlinear semiconductor optical amplifiers (SOAs), in order to design a polarization-insensitive wavelength conversion system employing dual co-polarized...

We report on the frequency noise reduction performance of a feed-forward technique. The Letter is based on frequency noise measurements that allow the spectral response of the feed-forward phase noise correction to be determined. The main limitation to the noise compensation is attributed to the local oscillator flicker noise and the noise added by...

This article appears in the special issue on ""Applications of Semiconductor Optical Amplifiers". Multi-section semiconductor optical amplifiers (SOA) have been shown to have superior noise and linearity performance compared with single section SOAs. We show how to create a simplified numerical model for multi-section SOAs that is suitable for opti...

We give the analytical expressions for the transfer of amplitude noise from the mixing frequencies to the generated frequencies during a nondegenerate and partially degenerate four-wave mixing (FWM) process and verify them by comparing with the numerical simulation results. We use these analytical expressions to study the amplitude noise relationsh...

Optical sources for the forthcoming terabit/s era of optical communications and networking will require multiple frequency-locked carriers, each with low phase noise, in order to minimize the spectral occupancy of the overall channel bandwidth. One method to construct a highly reconfigurable version of such a source is to use an optical frequency c...

The optical outputs of single-section quantum-dash and quantum-dot mode-locked lasers (MLLs) are well known to exhibit strong group velocity dispersion. Based on careful measurements of the spectral phase of the pulses from these MLLs, we confirm that the difference in group delay between the modes at either end of the MLL spectrum equals the cavit...

We study and experimentally validate the vector theory of four-wave mixing (FWM) in semiconductor optical amplifiers (SOA). We use the vector theory of FWM to design a polarization insensitive all-optical wavelength converter, suitable for advanced modulation formats, using non-degenerate FWM in SOAs and parallelly polarized pumps. We demonstrate t...

We show through simulations how polarization demultiplexing of dual-polarization, intensity modulated signals of arbitrary format can be performed by only using the information in Stokes space. The technique would be applicable for short-range communications within data centers.

In this work, the performance of all-optical wavelength conversion (WC) of Nyquist-WDM superchannels is investigated for future implementation in optical networks. We consider advanced modulation formats of DQPSK and 16-QAM for the subchannel modulation format achieving raw bit rates of 448 and 896 Gbit/s respectively. We demonstrate through simula...

We present results of all-optical wavelength conversion of a 1.008 Tb/s 6×28 Gbaud Nyquist-WDM superchannel based on 64-QAM using four-wave mixing in a semiconductor optical amplifier. We employ the phase noise tolerant dual-correlated pumping scheme to eliminate phase noise transfer from the pumps to the converted 64-QAM superchannel and thus achi...

We demonstrate, through experimental results and supporting numerical simulations, the optimum conditions to generate an optical comb via gain switching of a single mode DFB semiconductor laser. The DFB laser is biased appropriately and gain-switched with a large amplitude sinusoidal current, modulating the gain that is sufficient to turn the laser...

We recently presented results pertaining to the impact of nonlinear phase noise on the wavelength conversion of quadrature phase shift signals using four-wave mixing.1 We provide a qualitative description of the resulting FM-noise spectral density in the high pump OSNR regime.

Nyquist-WDM superchannel technology, which involves the combination of several lower data rate optical wavelength carriers (sub-channels), is a suitable technique to increase the spectral efficiency of WDM systems, and satisfy the growing demand for bandwidth in future networks. These superchannels will need to be routed through the optical network...

We perform injection-locking of a passively mode-locked Fabry-Perot quantum dash laser at 40 GHz using 10 Gbps PRBS data in NRZ-OOK format after spectral enrichment and thus demonstrate all-optical clock recovery through sub-harmonic injection-locking.

We generate random numerical waveforms that mimic laser phase noise incorporating laser-resonance enhanced phase noise. The phase noise waveforms are employed in system simulators to estimate the resulting bit error rate penalties for differential quadrature phase shift keying signals. The results show that baudrate dependence of the bit error rate...

The impact of nonlinear phase noise on all-optical wavelength conversion using four-wave mixing and dual-correlated pumps is studied. It is shown that there are optical signal-to-noise ratio requirements on the dual-correlated pumps for penalty-free all-optical wavelength conversion. We also show that the nonlinear phase noise generated in the nonl...

We present simulation results of the nonlinear dynamics of externally-injected, gain-switched laser comb sources. We implement a fully-stochastic laser model and highlight the trade-off between the number of comb lines and the noise properties of the comb.

We present highly accurate and easy to implement, improved lumped semiconductor optical amplifier (SOA) models for both single-pass and reflective semiconductor optical amplifiers (RSOA). The key feature of the model is the inclusion of the internal losses and we show that a few subdivisions are required to achieve an accuracy of 0.12 dB. For the c...

Reflective semiconductor optical amplifier (RSOA) fiber cavity lasers are attractive colorless, self-seeded, self-tuning, and directly modulatable sources for passive optical networks (PONs). They comprise of an RSOA in the optical network unit as the active element, a distribution fiber as the laser cavity, a waveguide grating router, and a common...

We report on the use of a SOA for simultaneous amplification of multicarrier, 10×12.5 Gb/s, DWDM-SSB-OFDM downstream signals finding negligible penalty at FEC limit compared to EDFAs. The scheme allows for a 128 passive split and transmission over 50 km.

WDM PONs offering point-to-point connectivity, independence of multiple access protocol to share the medium are good candidates for supporting the new fronthaul fibre network requirements. The necessity to allow inventory and maintenance cost reduction will favour WDM PON solutions based on colourless transceivers. We present the proposal of a netw...

The use of a semiconductor optical amplifier to increase the power budget of a high-bit rate OFDM-PON is demonstrated through simulations and experiments. Optimal operating conditions are identified and the back-to-back performance is evaluated.

(Invited Paper) We present simulation results of a wavelength conversion scheme that adds no additional phase-noise to the converted signal. The scheme uses an optical comb generator as the pump source in a wavelength converter based on nondegenerate four-wave mixing. The comb source ensures that no phase noise is transferred from the pumps to the...

All-optical wavelength conversion (WC) of advanced modulation formats could have a significant role in the next generation of high-capacity optical networks. Four-wave mixing (FWM) occurring within a semiconductor optical amplifier is one of the most advantageous methods to implement all-optical WC. We demonstrate the WC of 16-quadrature amplitude...

We show through simulations and with supporting experimental results that the performance of four-wave mixing based wavelength conversion of DQPSK signals is severely limited by resonance enhanced phase noise on the pump source.

We employ simple analytical models to construct the entire frequency-modulation (FM)-noise spectrum of tunable semiconductor lasers. Many contributions to the laser FM noise can be clearly identified from the FM-noise spectrum, such as standard Weiner FM noise incorporating laser relaxation oscillation, excess FM noise due to thermal fluctuations,...

We employ simple analytical models to construct the entire frequency-modulation (FM)-noise spectrum of tunable semiconductor lasers. Many contributions to the laser FM noise can be clearly identified from the FM-noise spectrum, such as standard Weiner FM noise incorporating laser relaxation oscillation, excess FM noise due to thermal fluctuations,...

We present simulations of a scheme to perform wavelength conversion of signals that eliminates phase-noise transfer from the pump to the converted signal. Nondegenerate four-wave mixing in a semiconductor optical amplifier is used to convert the signal to a new wavelength, and if an optical comb generator is used as the multiple-pump source, then t...

Optical fibers are the technological innovation that has revolutionized the way we communicate. The development of optical fiber technology started from the earliest studies and pioneering experiments on total internal reflection and passed through several technological advancements, ending with the achievement of modern optical fiber devices and s...

We show how trellis coding can be employed to improve the performance of phase modulated optical transmission systems in the presence of strong phase noise.

This paper describes the technical aspects of optical access solutions for mobile fronthaul application. The mobile context and main constraints of fronthaul signals are presented. The need for a demarcation point between the Mobile operator and the Fiber provider is introduced. The optical solution to achieve such a network is discussed. A WDM net...

This paper describes the technical aspects of optical access solutions for mobile fronthaul application. The mobile context and main constraints of fronthaul signals are presented. The need for a demarcation point between the Mobile operator and the Fiber provider is introduced. The optical solution to achieve such a network is discussed. A WDM net...

Future high capacity wavelength division multiplexed (WDM) optical networks will rely on transmitting signals with information encoded on both the amplitude and phase of multiple optical carriers. To optimise the efficiency of these networks, they are likely to employ some level of wavelength switching [1], and a key function required by wavelength...

Wavelength division multiplexed passive optical networks (WDM PON) offer a promising solution for a variety of applications in Next Generation Access Network (NGAN). Up to now WDM PON technology has been unsatisfactorily obtained by either costly tuneable transmitters or by exploiting external seeding sources. The key to enabling cost-effective WDM...

Modulation cancellation and signal inversion are demonstrated within reflective semiconductor optical amplifiers (RSOAs). The effect is useful to implement colorless ONUs where downstream signals need to be erased in order to reuse the carrier for the upstream.

We present a scheme to extend the frequency operation of phase shifters based on slow light in semiconductor optical amplifiers. We show that phase-shifting can be performed on microwave signals at frequencies approaching 100 GHz.

In this talk we show how slow and fast light effects arising from the nonlinear gain and refractive index dynamics within semiconductor optical amplifiers can be used to control the phase shift of microwave frequency signals. Theoretical predictions with experimental conformation will be shown as to how continuous phase shifting can be achieved and...

We report on measurements of phase shifting using cross gain modulation in a quantum dash semiconductor optical amplifier

We present an experimental and numerical investigation of the influence of filtering the red-shifted modulation on the linearity of a microwave-photonics link with a CPO-based phase shifter. Different behavior versus SOA bias current are evidenced.

We show theoretically and validate experimentally the effect of filtering on the nonlinear behavior of slow and fast light links based on coherent population oscillations in semiconductor optical amplifiers. The existence of a dip in the power-versus-current characteristics for the fundamental frequency, as well as for the third-order intermodulati...

We highlight the importance of the delay arising from optical filters in slow-light-based microwave phase shifting systems. We calculate the filter delay numerically from the measured amplitude response by using the well-known Kramers-Kronig relations. The complex filter transmission response is then incorporated within a numerical model with which...

We present an analytical model to calculate the signal to noise ratio of a slow light based microwave phase shifter that uses semiconductor optical amplifiers. The model includes dynamic noise effects and is confirmed experimentally.

In this paper, we present detailed modeling and experiments of the noise properties of a single-stage microwave phase-shifting element based on slow light propagation in a semiconductor optical amplifier. A wideband large-signal model is used to calculate the performance dependencies on gain, input power, and modulation frequency for the case where...

We present a continuously tunable optoelectronic oscillator with an intra cavity slow light element based on coherent population oscillations in a semiconductor optical amplifier. The performance of the oscillator is characterized in terms of its frequency tuning range and phase noise. These two characteristics can be traded for each other by choos...

We present numerical calculations of the impact that optical nonlinearities have on orthogonal transmission formats that facilitate all-optical switching in wavelength division multiplexed networks (WDM), such as Frequency Shift Keying with Intensity Modulation (FSK/IM). The main nonlinearity under consideration is the Kerr effect in optical fibers...

We report an experimental characterization of additive noise from a single-stage phase shifter based on slow and fast light propagation in a bulk semiconductor optical amplifier. We examine the influence of redshifted sideband suppression and optical input, power on the signal-to-noise ratio (SNR) of the detected signal. We conclude that in spite o...

We investigate the modulation index dependence of the phase shift experienced by a sinusoidal microwave signal carried by an optical carrier and propagating through a semiconductor optical amplifier. We show that for large modulation depths, simple small-signal nonlinear models fail to predict the measured phase shift and we present a large-signal...

In this paper, we present a numerical investigation of the phase shift experienced by the detected envelope of a sinusoidally modulated optical carrier propagating in a nonlinear semiconductor optical amplifier. The model we employed accounts for high-order coherent population oscillations. As such, it allows for large gain levels and arbitrary mod...

A full model for the phase of detected sinusoidal signals with large modulation indices after propagation through a semiconductor optical amplifier is presented with a comparison to a small signal model and an experimental confirmation.

We describe the use of a semiconductor optical amplifier as an intra cavity, continuous phase tuning element in an optoelectronic oscillator. A tuning range larger than 3 MHz is demonstrated in a 10 GHz oscillator.

We describe the use of a semiconductor optical amplifier as an intra cavity, continuous phase tuning element in an optoelectronic oscillator. A tuning range larger than 3 MHz is demonstrated in a 10 GHz oscillator.