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The intensity and timing noise of a 40-GHz quantum dot passively mode-locked laser with noncolliding cavity is numerically investigated and compared with the corresponding performance of the conventional self-colliding cavity. A detailed mapping of the pulse and noise properties versus the bias conditions shows that the devices based on the noncolliding cavities can generate shorter and stronger pulses with lower intensity and timing noise compared with the self-colliding counterparts if the gain to absorber length ratio is optimized.

We present experimental investigations of the intensity noise properties of injection-locked midinfrared emitting quantum cascade lasers. Following the theoretical approach by Simos et al. , the injection locking is realized below and near the threshold of the free running slave laser, resulting in an efficient technique to achieve low-noise operation. We find that below the threshold, the locking characteristics as locking range, shape and bandwidth, are different in comparison with those above threshold. In addition, we also investigate injection locking into longitudinal side modes of the slave laser apart by several longitudinal mode hops, and observe similar characteristics, however, with the potential to achieve higher relative intensity noise suppression. The measurements are confirmed by additional numerical simulations with a new model, which considers the multimode spectrum of the slave laser and the spectral profile of the material gain. Under the actual experimental conditions, a reduction of the relative intensity noise of the slave laser of up to 10 dB (above threshold) and up to 20 dB (below threshold) in comparison to the free running slave laser noise level is achieved.

We propose and experimentally validate a simple displacement sensing technique, which relies on the optical feedback-induced pulling of the repetition rate in a passively mode-locked semiconductor laser. Depending on the setup para- meters, different realizations of the technique permit displace- ment and vibration sensing of the reflecting object. Other physical parameters that modify the optical length of the external cavity could also be measured. The technique is particularly well adapted for fast phenomena and offers a subwavelength theoretical displacement resolution, which is limited only by the RF linewidth of the laser and resolution of the repetition frequency measurement.

We present a numerical analysis that focuses on the temporal pulse properties of a monolithic two-section passively mode locked quantum dot laser subject to optical feedback from a very long external cavity. Pulse duration, shape and intensity noise are studied for the first time to our knowledge versus feedback delay and strength for the case of a passively mode locked semiconductor laser. These temporal characteristics are correlated to the previously observed dependence of repetition rate and timing jitter on cavity parameters in order to highlight the dynamics and complete the corresponding theoretical explanations.

In this paper, we numerically investigate the effect of optical injection locking on the noise properties of mid-infrared quantum cascade lasers. The analysis is carried out by means of a rate equation model, which takes into account the various noise contributions and the injection of the master laser. The obtained results indicate that the locked slave laser may operate under reduced intensity noise levels compared with the free running operation. In addition, optimization of the locking process leads to further suppression of the intensity noise when the slave laser is biased close to the free-running threshold current. The main factors that significantly affect the locking process and the achievable noise levels are the injected optical power and the master-slave frequency detuning.

The structure of an active Erbium-Doped Distributed Bragg Reflector (ED-DBR) and a Fiber Bragg Grating (ED-FBG) is simulated using a rigorous transmission line model and an approximate version of the coupled-mode theory, respectively. The basic calculation steps and assumptions of the proposed simulation models are described and the key parameters that determine the devices’ reflection characteristics are in detail discussed. By applying the proposed transmission line model, numerical results are provided for both spectral reflectivity and transparency response for an active-slab DBR with increased erbium-ion concentration. In addition, using coupled-mode theory for the simulation of the cylindrical geometry of the ED-FBG device, the pump power-dependent reflection and transmission coefficients are obtained and their potential use in active sensor applications are discussed.

In this paper, we present a theoretical study on the optimization of passively mode-locked quantum dot lasers based on an alternative cavity design. In particular, we investigate a geometry in which the saturable absorber is located near the low reflection facet of the chip (output facet). The investigation is carried out by means of a time-domain traveling wave numerical model for quantum-dot active medium for both the gain and absorbing sections. The analysis shows superior performance in terms of pulsewidth and peak power of devices based on the new geometry compared to devices based on the conventional geometry, where the saturable absorber is placed near the high reflectivity facet. The optimization relies on the enhanced bleaching of the saturable absorber when the latter is located near the output facet, which prevents the generation of colliding or self-colliding pulse effects.

In this paper, we numerically investigate the role of gain and absorber dynamics on the operation of monolithic two-section mode-locked quantum-dot lasers under optical feedback. The analysis is carried out by means of a time-domain traveling wave model for propagation in the gain and absorbing sections. The obtained results indicate that in devices with slow dynamics, pulse duration tends to increase significantly with feedback. On the contrary, devices with fast dynamics exhibit an operation that depends primarily on the external cavity length.

A new method for the analysis and design of fiber Bragg gratings (FBGs) based on the theory of transmission lines has been developed and verified both theoretically and experimentally. The method is an extension of the coupled-mode theory and utilizes the equivalent transmission lines in order to simulate any type of grating, with an easy and direct implementation. The method provides the ability to analyze the optical devices without using full wave approaches, while also facilitating the incorporation of core materials with a complex or non-linear refractive index, non-uniform distributions of the grating&\#x2019;s refractive index, and tilted and phase-shifted gratings. The approach also allows the design of the grating for a given reflection spectra. Numerical results of the method&\#x2019;s application on a randomly varied inscription of the refractive index of a FBG have also been simulated and discussed. Using this method, the characteristics of an erbium-doped (ED)-FBG have been simulated and the predictions verified experimentally.

In this paper, the impact of the simultaneous presence of input and add signals in add/drop filters realized with microring resonators is numerically investigated. It is shown that the notch spectral response of output ports is responsible for the intraband crosstalk appearing on the dropped signals in add/drop operation. The investigation of the filter performance is performed with modulated signals at both the input and the add port. The analysis highlights the strong competition between the levels of induced intraband crosstalk and the wavelength selectivity at high bit rate add/drop operation, even in higher order filters. Multistage add/drop topologies that address the inefficiencies of the single-stage add/drop filters are proposed, and successful operation at 40 Gbps nonreturn to zero and return to zero signals is numerically demonstrated.

Polarization properties of active semiconductor micro-ring structures are studied theoretically emphasizing on the prospects for equalising the structure response for the two polarizations. The evaluation is performed with the help of a scheme for polarization insensitive operation of active MR that, unlike previous approaches, addresses both the waveguide and the heterostructure polarization properties. A self-consistent rate equation model is used to assess the spectral response of the polarization insensitive structures. Based on these findings the inherent spectral limitations for polarization insensitive performance imposed by the highly resonant nature of micro-ring are discussed and compared to that of conventional structures.

The use of InGaAs/GaAs quantum dots (QDs) in vertical cavity semiconductor optical amplifiers (VCSOAs) is proposed and analyzed. The results underline the distinctive differences between practical designs for QD vertical cavity semiconductor lasers and QD-VCSOAs. By means of a QD rate-equation scheme that accounts for both homogeneous and inhomogeneous broadening and the VCSOA cavity characteristics, the effects of material properties are identified. The design routes outlined here ensure the suitability of QD-VCSOAs for high-speed applications (>100 Gb/s) that rely on the fast carrier dynamics.

The spectral and power (I/O) bistable characteristics of active microring (MR) structures are analyzed theoretically. The theoretical formulation is based on the rate equation under the assumption of the z-independent optical power accounting for amplified spontaneous emission. The analysis is performed for MRs in both all-pass and add-drop configurations. The effect of cavity characteristics on the bistable performance are explored. Based on these the merits of the resonant nonlinearity enhancement are discussed and strategies for optimized bistable loops are outlined.

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

The properties of an all-optical AND logic gate based on the four-wave mixing (FWM) effect in an InGaAsP/InP microring resonator side coupled to a bus waveguide are investigated. Using an ultrafast nonlinear process such as FWM, operation at a bit rate of 40 Gb/s is demonstrated for both nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats. The gate operation in terms of microring structural parameters and operating conditions is studied

The properties of an all-optical 2R regenerator based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) are investigated. The regeneration is based on the nonlinear FWM transfer function and a study of the system's static behavior reveals the operating conditions, under which the transfer function approaches most the ideal, step-like discrimination characteristic function. A fiber Bragg grating (FBG) is employed in order to overcome the SOAs speed limitations due to limited carrier dynamics. The simulations with dynamic input data by means of extinction ratio (ER) and Q-factor calculations, showed satisfactory regenerative behavior up to 40 Gb/s.

Wavelength conversion using self-pumped cross-gain modulation in a microring laser vertically coupled to a passive waveguide is presented. Successful conversion at 2.5 Gb/s along with a 100-km transmission is demonstrated. Tunable conversion from almost any wavelength of the gain bandwidth to any of the three supported modes of the laser is shown and the limitations of the method, related to mode switching of the laser, are also briefly discussed.

An all-optical AND logic gate based on the four-wave mixing (FWM) effect in an InGaAsP-InP microring resonator side-coupled to a bus waveguide, is proposed and simulated. Using an ultrafast nonlinear process such as FWM, operation at a bit rate up to 160 Gb/s is demonstrated for the return-to-zero modulation format.

A detailed experimental investigation of the regenerative properties of the four-wave mixing (FWM) for the conventional nonreturn-to-zero data format is reported. A key feature in the proposed scheme, and contrary to the conventional approach, is application of the ON-OFF keying modulation on the pump wave. Measurement of the static transfer functions of the FWM process in a semiconductor optical amplifier shows that certain operating regimes exist, mainly related to the power levels "one" and "zero" of the modulated pump, where a significant improvement of the extinction ratio (ER) can be achieved. This conclusion has been confirmed by dynamic measurements at 2.4 Gb/s, where up to 3-dB improvement in the ER has been observed.

A broadly tunable master-oscillator power-amplifier (MOPA) picosecond optical pulse source is demonstrated, consisting of an external cavity passively mode-locked laser diode with a tapered semiconductor amplifier. By employing chirped quantum-dot structures on both the oscillator's gain chip and amplifier, a wide tunability range between 1187 and 1283 nm is achieved. Under mode-locked operation, the highest output peak power of 4.39 W is achieved from the MOPA, corresponding to a peak power spectral density of 31.4 dBm/nm.

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation.

The switching properties of a resonator consisting of two serially cascaded active microrings (MRs) are reported. The switching is achieved through the variation of the refractive index and the losses of the MRs with current injection, which alters the overall output spectral response. The switch is suitable for optical burst switching systems and metro architectures as it provides fast optical switching in the nanosecond scale with contrast ratio higher than 30 dB for 10-Gb/s intensity modulated signals. The capacity of the switch can be remarkably increased if multiwavelength switching is employed.

In this Letter, a design for a tapered InAs/InGaAs quantum dot semiconductor optical amplifier is proposed and experimentally evaluated. The amplifier's geometry was optimized in order to reduce gain saturation effects and improve gain efficiency and beam quality. The experimental measurements confirm that the proposed amplifier allows for an elevated optical gain in the saturation regime, whereas a five-fold increase in the coupling efficiency to a standard single mode optical fiber is observed, due to the improvement in the beam quality factor M² of the emitted beam.

In this paper, we present the generation of high peak-power picosecond optical pulses in the 1.26 μm spectral band from a repetition-rate-tunable quantum-dot external-cavity passively mode-locked laser (QD-ECMLL), amplified by a tapered quantum-dot semiconductor optical amplifier (QD-SOA). The laser emission wavelength was controlled through a chirped volume Bragg grating which was used as an external cavity output coupler. An average power of 208.2 mW, pulse energy of 321 pJ, and peak power of 30.3 W were achieved. Preliminary nonlinear imaging investigations indicate that this system is promising as a high peak-power pulsed light source for nonlinear bio-imaging applications across the 1.0 μm - 1.3 μm spectral range.

In this paper we present experimental results related to the dynamic switching of the emission wavelength of a passively mode-locked InAs/InGaAs quantum dot laser. The wavelength switching is achieved through application of varying optical feedback, as opposed to varying electrical biasing conditions, whereas the different regimes of operations include pulse operation either from the ground or the excited state and dual mode locking. Furthermore, through the same technique, Q-switching elimination was achieved, allowing stable pulse amplitude, which is a highly desired feature in many applications.

Analysis of a design scheme that relaxes alignment issues is reported. This entails the use of vertically coupled microring resonators (MR). It is shown that an almost flat response of the coupling coefficient to offset values up to 1 µm is feasible by judicious choice of the bus and ring waveguide geometry. The scheme is evaluated using FDTD simulations and its applicability to functional devices is probed via the transfer-matrix method of the transmission characteristics of microring-based filters.