Seán P. Ó Dúill

Examination of the photoinitiation processes in photopolymer materials

Holographic data storage requires multiple sequential short exposures. However, the complete exposure schedule may not necessarily occur over a short time interval. Therefore, knowledge of the temporally varying absorptive effects of photopolymer materials becomes an important factor. In this paper, the time varying absorptive effects of an acrylamide/polyvinylalcohol photopolymer material are examined. These effects are divided into three main photochemical processes, which following identification, are theoretically and experimentally examined. These processes are (i) photon absorption, (ii) photosensitizer recovery, and (iii) photosensitizer bleaching.

Optoelectronic Oscillator Tunable by an SOA Based Slow Light Element

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 choosing the operating conditions of the slow light element and the oscillator fiber length.

Reflective-SOA Fiber Cavity Laser as Directly Modulated WDM-PON Colorless Transmitter

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 reflective mirror with the latter two positioned at the remote node. In this paper, we introduce a model and perform simulations to elucidate the recently discovered successful operation of this new PON source. The results are in agreement with experiments; the formation of a narrow laser spectrum with a relatively constant output power is seen despite a relatively broad passband window of the waveguide grating router. We further study mode competition and mode partition noise. It is shown that proper chromatic dispersion management can overcome mode partition noise limitations. The quality of the RSOA fiber cavity laser does not degrade when being directly modulated and as a result these highly multimode lasers offer an economic way to transport Gbit/s upstream data over kilometers of fiber in a wavelength division multiplexing-PON.

Efficient modulation cancellation using reflective SOAs

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 reflective semiconductor optical amplifiers possess the perfect high-speed all-optical gain saturation characteristics to completely cancel the downstream modulation at microwatt optical power levels and are thus the prime candidate to be constituents of future optical network units. Theoretical considerations are supported by experiments that show the cancellation of signals with a 6 dB extinction ratio at 2.5 Gbit/s.

Cross talk free multi channel processing of 10 Gbit/s data via four wave mixing in a 1550 nm InAs/InP quantum dash amplifier

We demonstrate multi wavelength processing in a broad band 1550 nm quantum dash optical amplifier. Two 10 Gbit/s signals, spectrally separated by 30 nm are individually wavelength converted via four wave mixing with no cross talk.

On the Role of High-Order Coherent Population Oscillations in Slow and Fast Light Propagation Using Semiconductor Optical Amplifiers

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 modulation indexes of the input field. We highlight the role of the fields that are generated by high-order nonlinearities and compare the results with those of more common small-signal nonlinear models. We find that conventional models suffice only for low powers, small modulation indexes, and moderate amplifier gain levels.

Signal-to-noise ratio of a semiconductor optical-amplifier-based optical phase shifter

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 of the up to a 6 dB reduction in the detected noise, the SNR remains dominated by the decrease in the detected signal power.

Simulations of an OSNR-Limited All-Optical Wavelength Conversion Scheme

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 the signal can be converted without incurring any phase-noise transfer from the pumps. We highlight the capabilities of this scheme by simulating the conversion of 16-QAM signals at 10 GBd and showing that errors due to phase-noise accumulation are eliminated, thus enabling conversion whose only impairment would be the total additive optical noise.

Detailed Investigation of the Pump Phase Noise Tolerance for Wavelength Conversion of 16-QAM Signals Using FWM

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.

Intermodulation distortion in microwave phase shifters based on slow and fast light propagation in semiconductor optical amplifiers.

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 intermodulation product, is clearly evidenced. These two dips occur at different bias currents. Their depths increase as the filtering strength of the red sideband is increased, and they completely vanish in the unfiltered case. Influence on the microwave photonics link is discussed.