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We propose and experimentally demonstrate a power efficient dual-stage optical frequency comb using laser gain switching followed by a dual-drive Mach-Zehnder modulator (DD-MZM). The laser is initially gain switched at ∼ 9.5 GHz and the resultant comb is then expanded using a dual-drive Mach-Zehnder modulator driven at ∼ 19 GHz with signal amplitudes below 1.5 V. The setup generates an optical frequency comb, with 12 lines within 3 dB flatness, in a power efficient manner. Theoretical analysis is presented and verified through simulation and experimental results.

This paper examines and compares the use of orthogonal frequency division multiple access (OFDMA)and generalized frequency division multiple access(GFDMA) multicarrier formats in next-generation passive optical networks (PONs) through experimentation and numerical simulations. It is demonstrated that GFDMA presents a high resilience toward multiple access interference (MAI) compared to OFDMA at the uplink channel of aPON. Moreover, two methods are proposed for achieving synchronization in the uplink channel of PONs, enabling high spectral efficiency. These proposed methods can lead to the elimination of inter-ONU guard bands, and facilitate overlapping inter-ONU subcarriers, while eliminating the effects of MAI. Additionally, the performance of these multi-carrier formats was analyzed in the downlink channel at a data rate of 15.6 Gb/s and a transmission span of 50 km where neglible performance penalty was observed

Due to the growing popularity of optical superchannels and software-defined networking, reconfigurable optical add-drop multiplexer (ROADM) architectures for superchannel switching have recently attracted significant attention. ROADMs based on micro-electro-mechanical system (MEMS) and liquid crystal-on-silicon (LCoS) technologies are predominantly used. Motivated by requirements for low power, high-speed, small area footprint, and compact switching solutions, we propose and demonstrate spatial and wavelength flexible superchannel switching using monolithically integrated silicon photonics (SiP) micro-ring resonators (MRRs). We demonstrate the MRRs’ capabilities and potential to be used as a fundamental building block in ROADMs. Unicast and multicast switching operation of an entire superchannel is demonstrated after transmission over 50 km of standard single mode fiber. The performance of each sub-channel from the 120 Gb∕s QPSK Nyquist superchannel is analyzed, and degradation in error vector magnitude performance was observed for outer sub-channels due to the 3 dB bandwidth of the MRRs, which is comparable with the superchannel bandwidth. However, all sub-channels for all switching cases (unicast, multicast, and bi-directional operation) exhibit performance far below the 7%FEClimit. The switching time of the SiPMRRchip is such that high-capacity superchannel interconnects between users can be set up and reconfigured on the microsecond time scale.

We report on an InP photonic integrated circuit for the generation of an externally injected gain switched optical frequency comb. The device is fully characterized and generates a comb with frequency spacing ranging from 6 to 10 GHz, good noise properties that include relative intensity noise of

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 relationships between the mixing frequencies and the generated frequencies during an FWM process, for various conditions. We also study the variance, relative intensity noise (RIN), and signal-to-noise ratio (SNR) of the generated frequencies as a function of the power, RIN, and SNR of the input signal.

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 cavity round-trip time. This observation allows us to deduce an empirical formula relating the accumulated dispersion of the output pulse to the spectral extent and free-spectral range of the MLL. We find excellent agreement with previously reported dispersion measurements of both quantum-dash and quantum-dot MLLs over a wide range of operating conditions.

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 the wavelength conversion of polarization-multiplexed (PM)-QPSK, PM-16QAM and a Nyquist WDM super-channel modulated with PM-QPSK signals at a baud rate of 12.5 GBaud, with total data rates of 50 Gbps, 100 Gbps and 200 Gbps respectively.

We propose and experimentally demonstrate a long-reach Nyquist ultradense wavelength division multiplexed passive optical network using a tunable optical frequency comb source and a digital coherent receiver. Each of the six comb tones on a 12.5 GHz grid is modulated with a 12 Gbaud Nyquist polarization division multiplexed quadrature phase shift keyed signal which includes a 20% overhead for forward error correction. Unrepeated downlink transmission of 100 km is demonstrated at three different operating wavelengths across the C-band. A worst-case channel sensitivity of −35.3 dBm (59 photons/bit) is achieved at a bit error rate of 1.5 × 10−2, yielding a system loss budget of 35.7 dB.

We demonstrate a compact, robust, and stable terahertz source based on a novel two section digital distributed feedback laser diode and plasmonic photomixer. Terahertz wave generation is achieved through difference frequency generation by pumping the plasmonic photomixer with two output optical beams of the two section digital distributed feedback laser diode. The laser is designed to offer an adjustable terahertz frequency difference between the emitted wavelengths by varying the applied currents to the laser sections. The plasmonic photomixer is comprised of an ultrafast photoconductor with plasmonic contact electrodes integrated with a logarithmic spiral antenna. We demonstrate terahertz wave generation with 0.15-3 THz frequency tunability, 2 MHz linewidth, and less than 5 MHz frequency stability over 1 minute, at useful power levels for practical imaging and sensing applications.

The authors present the performance and noise properties of a software reconfigurable, FSR and wavelength tunable gain switched optical frequency comb source. This source, based on the external injection of a temperature tuned Fabry-Pérot laser diode, offers quasi-continuous wavelength tunability over the C-band (30nm) and FSR tunability ranging from 6 to 14GHz. The results achieved demonstrate the excellent spectral quality of the comb tones (RIN ~-130dB/Hz and low phase noise of 300kHz) and its outstanding stability (with fluctuations of the individual comb tones of less than 0.5dB in power and 5pm in wavelength, characterized over 24hours) highlighting its suitability for employment in next generation flexible optical transmission networks.

Dynamic optical networking with rapid wavelength reconfiguration is a promising capability to support the heterogeneous, bursty traffic rapidly growing in metro-area networks. A major obstacle to realizing dynamicity in the optical layer is the channel power excursions that occur due to continuously changing input conditions into gain controlled optical amplifiers. Here we present a technique of distributing an optical signal across multiple wavelengths chosen to reduce or cancel the power dynamics so that excursion-free switching can be achieved in an optically amplified transparent network. The use of variable wavelength dwell times for excursion-free switching using arbitrary wavelength pairs is presented. Spectral efficiency lost in utilizing multiple wavelengths is recovered through time-division multiplexing two signals distributed over the same wavelengths.

This paper explores experimentally the impairments in performance that are generated when multiple single-sideband (SSB) subcarrier multiplexing (SCM) signals are closely allocated in frequency to establish a spectrally efficient wavelength division multiplexing (WDM) link. The performance of cost-effective SSB WDM/ SCM implementations, without optical filters in the transmitter, presents a strong dependency on the imperfect sideband suppression ratio that can be directly achieved with the electro-optical modulator. A direct detected broadband multichannel SCM link composed of a state-of-the-art optical IQ modulator and five quadrature phase-shift keyed (QPSK) subcarriers per optical channel is presented, showing that a suppression ratio of 20 dB obtained directly with the modulator produced a penalty of 2 dB in overall performance, due to interference between adjacent optical channels.

We use the physics of four-wave mixing to study the decorrelation of two optical frequencies as they propagate through different fiber delays. The phase noise relationship between the four-wave mixing components is used to quantify and measure the correlation between the two optical frequencies using the correlation coefficient. We show the difference in the evolution of decorrelation between frequencydependent and frequency-independent components of phase noise. � 2014 Optical Society of America.

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 modulation (16-QAM) using degenerate and nondegenerate FWM in a semiconductor optical amplifier. We pay particular attention to the phase noise transfer from the pump(s) to the converted signal. The class of laser that can be used as the pump source to implement the scheme is highlighted by the calculations of the required pump laser linewidths to achieve specific system bit error rate performance at the forward error correction threshold. Our results are consistent with theories of phase noise transfer between the pump and converted signals.

We present experimentally and analytically the phase noise characterization of an externally injected gain switched comb source. The results reveal the residual high frequency FM noise in the comb lines, which stays unnoticed in the optical linewidth value but leads to an increased phase-error variance. The potential impact of the residual phase noise is investigated in a 10.7 GBaud optical DQPSK system where a 2 dB power penalty is recorded at BER of 10(-9). In a 10.7 GBaud digital coherent QPSK system no penalty is observed but with 5 GBaud 16-QAM format a 3 dBpenalty exists at the FEC limit of 4.4e-3.

The authors report on a strongly filtered direct detected non-return-to-zero differential quadrature phase shift keying (NRZ-DQPSK) system, based on a multicarrier transmitter with a tunable free spectral range. Transmission of a 7×21.4 Gb/s multichannel NRZ-DQPSK signal over a dispersion compensated optical link (legacy optical infrastructure) on a 15 GHz grid is investigated experimentally and by simulations. Further improvement of the spectral efficiency is demonstrated by simulating the same 7 × 21.4 Gb/s system on a 12.5 GHz grid. Finally, the scalability of the proposed system is investigated by simulating the transmissionof a Tb superchannel, composed of a 10-carrier polarization division multiplexed NRZ-DQPSK operating at 28 GBaud on 33 GHz channel spacing, over 320 km standard single-mode fiber.

We investigate novel pilot-aided transmission of high-order quadrature amplitude modulation (QAM) modulation formats for optical packet-switched networks. The proposed modulation scheme employs a pilot tone operating at the baud rate for noncoherent reception that is highly immune to laser phase noise. The results show that the system performance equivalent to static operation is achieved 5 ns after wavelength switching of a sampled grating distributed Bragg reflector (SG-DBR) tunable laser.

The application of orthogonal frequency-division multiplexing (OFDM) in an optical burst-switched system employing a single fast switching sample grating-distributed Bragg reflector (SG-DBR) laser isdemonstrated experimentally. The effect of filter profiles compatible with 50, 25, and 12.5 GHz wavelength-division multiplexing grids on the system is investigated with system performance examined in terms of error vector magnitude per subcarrier for OFDM burst data beginning at various times after a switching event. Additionally the placement of the OFDM training sequence within the data burst and its effect on the system is investigated.

We investigate the effects of different phase noise processes of SGDBR laser on coherent systems. The SGDBR device operated well with QPSK modulation at 5 Gbaud, while the performance of 16-QAM was significantly degraded due to excess noise. The white FM noise mainly defines the ultimate performance of coherent reception, but the low frequency excess noise can potentially degrade the performance of systems that employ 16-QAM format at 5 Gbaud.

Scalability in terms of both capacity and energy are gaining increasing focus as potential bottlenecks for future optical communication networks. Traffic growth is outpacing the rate of network efficiency improvements as well as the rate of optical system capacity improvement. Laboratory results are rapidly approaching the fiber transmission spectral efficiency limits. The energy efficiency benefits derived from Moore's law scaling are slowing. Research is under way today to address these challenges, covering the full range of technologies from devices to systems and networks. While many problems can be tackled by working independently within these areas, often important innovation comes from solutions that cut across such topical boundaries. Understanding device performance impacts and likewise network requirements can be essential to unlocking the critical ideas that lead to progress.

Lasers with narrow-linewidth emission are a key component for higher-order modulation formats. We report on discrete-mode laser diodes designed for narrow-linewidth emission and demonstrate linewidths less than 80 kHz. Using these devices in quadrature phase shift keying and 16-quadrature amplitude modulation transmission setups, similar performance to that of an external cavity laser is demonstrated.

We propose a novel coherent self-heterodyne receiver structure based on phase modulation detection that potentially simplifies the front-end of a coherent optical receiver. The scheme has been demonstrated via simulations and experimentally for a 10 Gb/s DQPSK transmission system.

Photonic ultra-wideband (UWB) pulses are generated by direct current modulation of a semiconductor optical amplifier (SOA) section of an SOA-integrated sampled grating distributed Bragg reflector (SGDBR) laser. Modulation responses of the SOA section of the laser are first simulated with a microwave equivalent circuit model. Simulated results show a resonance behavior indicating the possibility to generate UWB signals with complex shapes in the time domain. The UWB pulse generation is then experimentally demonstrated for different selected wavelength channels with an SOA-integrated SGDBR laser.

We demonstrate and compare the generation and distribution of pulse position modulation (PPM) ultrawideband (UWB) signals, based on two different techniques using a gain-switched laser (GSL). One uses a GSL followed by two external modulators, while the second technique employs two laser diodes gain switched (GS) using a combined signal from a pattern generator and an RF signal generator. Bit-error-rate (BER) measurements and eye diagrams for UWB signals have been measured experimentally by using the different GS transmitter configurations and various fiber transmission distances. The simulation of both systems also has been carried out to verify our obtained results, which show the suitability of employing gain switching in a UWB over fiber (UWBoF) system to develop a reliable, simple, and low-cost technique for distributing the impulse-radio UWB (IR-UWB) pulses to the receiver destination.

Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ) Differential Phase Shift Keyed (DPSK) systems require cheap and optimal transmitters for widespread implementation. The authors report on a gain switched Discrete Mode (DM) laser that can be employed as a cost efficient transmitter in a 10.7 Gb/s RZ DPSK system and compare its performance to that of a gain switched Distributed Feed-Back (DFB) laser. Experimental results show that the gain switched DM laser readily provides error free performance and a receiver sensitivity of -33.1 dBm in the 10.7 Gbit/s RZ DPSK system. The standard DFB laser on the other hand displays an error floor at 10(-1) in the same RZ DPSK system. The difference in performance, between the two types of gain switched transmitters, is analysed by investigating their linewidths. We also demonstrate, for the first time, the generation of a highly coherent gain switched pulse train which displays a spectral comb of approximately 13 sidebands spaced by the 10.7 GHz modulation frequency. The filtered side-bands are then employed as narrow linewidth Continuous Wave (CW) sources in a 10.7 Gb/s NRZ DPSK system.

A III-V semiconductor photonic crystal (PhC) waveguide is integrated into a semiconductor optical amplifier (SOA); this has the potential to reshape pulses that are distorted and chirped on propagation through the SOA. The PhC waveguide is modeled using the three-dimensional (3D) finite difference time domain (FDTD) method initially for the ideal case of infinite depth holes, and this shows a ministop band close to 1600 nm. The PhC waveguide is then fabricated into a commercial SOA using focused ion beam etching. The optical power measured at the output of the PhC-SOA waveguide shows evidence of a ministop band but with a small stopband depth. More realistic 3D FDTD modeling including effects of finite hole depth and vertical layer structure is then shown to give much better agreement with measured results. Finally predictions are made for the performance of a membrane structure.

What we believe to be a novel system for the distribution of high-definition video streams in a residential environment is demonstrated. The system utilizes impulse radio ultrawideband (IR-UWB) technology integrated with a fiber-based distribution network. The pulses are directly generated in the optical domain, and the receiver is implemented with a carrier recovery system for the demodulation. The system was built and tested to demonstrate error-free operation of the distribution network and the receiver. Spectrum shaping by varying the pulse position within the bit slot to optimize system performance is also examined.

PUBLISHED, In this paper, the polarization response of a GaAs based twophoton absorption microcavity photodetector has been studied. The deviation in the dependence of the detector response from that of bulk GaAs is shown to be due to the birefringence of the cavity. A theoretical model based on the convolution of the cavity birefringence and the polarization dependence of two-photon absorption in GaAs is described and shown to match the measured polarization dependence of the microcavity detector very well., The authors would like to thank Dan Kilper of Bell Laboratories, Crawford Hill, for helpful discussions. This work was supported by SFI under its CSET Centre for Telecommunication Value Driven Research (CTVR), Grant 03/CE3/I404 and by an SFI frontiers grant RFP/2006/ENE012

The optimization of a wavelength tunable RZ transmitter, consisting of an electro-absorption modulator and a SG DBR tunable laser, is carried out using a linear spectrogram based characterization and leads to 1500 km transmission at 42.7 Gb/s independent of the operating wavelength. We demonstrate that, to ensure optimum and consistent transmission performance over a portion of the C-band, the RF drive and bias conditions of the EAM must be varied at each wavelength. The sign and magnitude of the pulse chirp (characterized using the linear spectrographic technique) is therefore tailored to suit the dispersion map of the transmission link. Results achieved show that by optimizing the drive and DC bias applied to the EAM, consistent transmission performance can be achieved over a wide wavelength range. Failure to optimize the EAM drive conditions at each wavelength can lead to serious degradation in system performance.

Optical autocorrelation of ultrashort pulses using two photon absorption (TPA) in commercial semiconductor devices provides a convenient, sensitive, and inexpensive alternative to standard techniques using nonlinear crystals. A summary of readily available commercial devices suitable for TPA autocorrelation of picosecond and femtosecond pulses in the near-IR from 0.7–3 μm is presented.

The technique of frequency-resolved optical gating is used to characterize the intensity and the phase of picosecond pulses after propagation through 700 m of fiber at close to the zero-dispersion wavelength. Using the frequency-resolved optical gating technique, we directly measure the severe temporal distortion resulting from the interplay between self-phase modulation and higher-order dispersion in this regime. The measured intensity and phase of the pulses after propagation are found to be in good agreement with the predictions of numerical simulations with the nonlinear Schrödinger equation.