Ioanna Stamataki

Investigation on the Multimode Dynamics of InGaAsP–InP Microring Lasers

A multimode model based on the rate equation approximation is presented in order to simulate the mode dynamics of 1.55-mum InGaAsP-InP microring lasers. A detailed characterization is performed including calculated optical spectra, time traces and relative intensity noise spectra. Different operation regimes are observed, bidirectional multimode with/without alternate oscillations, unidirectional single mode, bidirectional single mode and mode hopping. The boundaries of the above operation regimes are investigated with respect to the current level, bus waveguide reflectivity and ring radius. Varying the current level a transition from multimode to single mode and eventually mode hopping operation is observed. Increasing the bus waveguide reflectivity a transition from unidirectional to bidirectional operation is revealed, while the use of nonequal reflectivities between the two facets, promotes unidirectional operation. Moreover, the ring radius is proved to be a critical parameter for the extent of each operation regime since it directly influences the modal wavelength separation

Widely Tunable All-Active Microring Lasers

A tunable laser based on an InGaAsP-InP microring resonator with multimode interference coupler is demonstrated. Tuning ranges from 18 to 30 nm are achieved and mappings of the tunable operation are experimentally produced and analyzed. The observed tunability is the result of the interaction between counterpropagating ring modes through back-reflection from the device facets

Low-Frequency Relative Intensity Noise due to Nonlinear Mode Competition in InGaAsP–InP Microring Lasers

An enhanced low frequency relative intensity noise due to mode hopping induced from the asymmetric gain suppression in InGaAsP-InP microring lasers, is observed experimentally for the first time. The experimental results are in good agreement to those predicted by a multimode model based on the rate equation approximation accounting for both symmetric and asymmetric nonlinear gain suppression

Chaotic dynamics of semiconductor microring lasers

The complexity and dynamics of chaotic attractors generated in an InGaAsP-InP microring laser are calculated and evaluated by using a multimode rate equation model. Chaos originates from the continuous mutual injections from each mode to the other because of the bus waveguides residual reflectivity at high values of the injection current. The data analysis of the filtered output power reveals high-dimensional chaos, and phase-dependent behavior is demonstrated.

Relative Intensity Noise Performance of Wavelength Converters Based on Four-Wave Mixing in Semiconductor Optical Amplifiers

We present a numerical and experimental study of the relative intensity noise (RIN) induced by the four-wave mixing (FWM) based wavelength conversion process in a semiconductor optical amplifier (SOA). The study is based on the RIN evaluation of the converted signal, under various operating conditions (input power levels and wavelength detuning) and input noise characteristics. A detailed numerical model is employed to simulate the FWM process, taking into account the amplified spontaneous emission (ASE) noise, the wavelength dependent gain, and the interaction of four waves in the SOA (two input waves and two product waves). It is shown that for low noise input signals, the output RIN is determined by the power levels of the pump and signal and the wavelength detuning. Operation under saturation allows reduction of the output RIN levels with respect to the input

Design and Experimental Evaluation of Active-Passive Integrated Microring Lasers: Noise Properties

The phase and intensity noise of microring lasers coupled with passive waveguides are examined through linewidth and relative intensity noise measurements. Laser linewidth down to 500 KHz was measured through the self-homodyne technique and a direct association is established between the linewidth and the two main structural parameters of a microring, the ring radius and coupling efficiency with the bus waveguide. Coupling efficiency is estimated through waveguiding analysis by means of 3-D finite difference in time domain techniques.

Design and Experimental Evaluation of Active-Passive Integrated Microring Lasers: Threshold Current and Spectral Properties

The relation between the structural parameters and the operating characteristics of microring lasers is examined through theoretical estimations, waveguiding simulations, and experimental measurements. The effects of ring radius, waveguide profile, and overall geometry on the coupling efficiency and subsequently on threshold and spectral characteristics are thoroughly investigated. Coupling efficiency is calculated through 3-D finite difference in time domain methods. Fabricated devices consist of active microrings integrated with passive bus waveguides using wafer bonding techniques.

Characterization and evaluation of chabazite- and mordenite-rich tuffs, and their mixtures as soil amendments and slow release fertilizers

ABSTRACT In the present study, zeolite tuffs of diverse chemistry, mineralogy and origin were characterized and tested for their efficiency as slow release fertilizers (SRF) through a series of leaching tests. Mixtures of zeolite tuffs were created and tested as loamy soil additives, in order to evaluate any synergistic effect on their cation exchange capacity (CEC) and SRF properties. The studied materials were a chabazite-rich tuff (SOR), a mordenite-rich tuff (KIM), 3 mixtures of them (SOR/KIM 30/70, 50/50 and 70/30) and a commercial clinoptilolite-rich tuff (BLG). CEC (sodium acetate method) was 95.7 for BLG, 100.9 for KIM and 92.2 cmol kg−1 for SOR, while their mixtures displayed intermediate values. SRF values vary, with the SOR/KIM 30/70 exhibiting the slowest NH4+ release in 29 days (1.7%) compared to the control sample (19%). Zeolites promoted PO4−3 release, while their selectivity for Mg2+ and K+ was clearly affected by their different structure and chemistry. BLG exhibited the strongest selectivity for Mg2+, having the lowest release (39%). The results demonstrate that mixtures of zeolite tuffs could have a potential use in agricultural processes, by improving parameters like: chemistry, mineralogy, CEC and SRF efficiency, and resulting in the production of a competitive and functional soil additive.

Widely Tunable All-Active Micro-Ring Lasers through Phase Shifted Controlled Feedback

Tunable lasers based on InGaAsP/InP microring resonators are demonstrated. Tuning ranges from 18 to 30 nm are achieved by the interaction of phase shifted counterpropagating modes through back-reflection at the chip facets.

Spectral properties of all-active InP-based microring resonator devices

Microring resonators are excellent candidates for very large scale photonic integration due to their compactness, and fabrication simplicity. Moreover a wide range of all-optical signal processing functions can be realized due to the resonance effect. Possible applications include filtering, add/drop of optical beams and power switching, as well as more complex procedures including multiplexing, wavelength conversion, and logic operations. All-active ring components based in InGaAsP/InP are possible candidates for laser sources, lossless filters, wavelength converters, etc. Our work is based on measurement, characterization and proposal of possible exploitation of such devices in a variety of applications. We investigate the spectral characteristics of multi-quantum well InGaAsP(λ=1.55μm)/InP microring structures of various ring diameters and different configurations including racetracks with one or two bus waveguides and MMI couplers. The latter configuration has recently exhibited the possibility to obtain tunable active filters as well as tunable laser sources based on all-active ring-bus-coupler structures. In the case of tunable lasers single mode operation has been achieved by obtaining sufficiently high side mode suppression ratio. The tuning capability is attributed to a coupled cavities effect, resembling the case of multi-section DBR lasers. However, in contrast to the latter, the fabrication of microring resonators is considered an easier task, due to a single step growth procedure, although further investigation must be carried out in order to achieve wide range tunability. Detailed mappings of achievable wavelengths are produced for a wide range of injection current values.