Particle swarm optimization-assisted approach for the extraction of VCSEL model parameters.

We propose a direct particle swarm optimization (PSO) method for extracting the parameters of a physical model describing the behavior of vertical-cavity surface-emitting lasers (VCSELs), starting from the light-current (L-I) characteristics and the small signal modulation (S21) responses, at different currents and temperatures. With an optimal choice of hyperparameters of the algorithm, the method is able to predict parameters that accurately reproduce the behavior of the device. Its prediction capabilities are compared to those of two commonly used nonlinear optimizers (Interior Point and Levenberg-Marquardt), to benchmark its performances.

Design and performance assessment of modular multi-band photonic-integrated WSS.

Today, optical transport and data center networks extensively utilize photonic integrated systems due to their large bandwidth and a high degree of reconfigurability. In addition to these properties, photonic integrated-based systems can deliver an overall low fabrication cost, a small footprint, and low power consumption. In this perspective, we present a modular photonic integrated multi-band wavelength selective switch (WSS) capable of managing a wide spectrum, covering the three S+C+L bands, and potentially scalable to larger numbers of output fibers and routed channels. We propose a complete description of the device starting from the physical level, commenting on the device's internal structure and design-related issues. Then, we move to the transmission level, providing a complete abstraction of the proposed WSS in the context of software-defined optical networks by providing a deterministic model to evaluate the routing controls, thermal spectral tunability, and the quality of transmission degradation. Finally, a transmission scenario operating on 400ZR standards and a network case study are also demonstrated to evaluate the performance of the proposed WSS in a single or multistage cascade setup.

Optimized management of ultra-wideband photonics switching systems assisted by machine learning.

Recent years have seen an unprecedented growth of data traffic driven by a continuous increase of connected devices and new applications. This trend will tend to saturate transparent optical networks that are the backbone of the whole telecommunication infrastructure. To improve the capacity of already deployed network infrastructures and maximize operators CAPEX returns, band-division multiplexing (BDM) has emerged as a promising solution to expand the fiber bandwidth beyond the existing C-band. Along with this, the demand for flexible and dynamically reconfigurable functionalities in each network layer is increasing. In this regard, optical networking is fast evolving towards the applications of the software-defined networking (SDN) paradigm down to the physical layer. The implementation of optical SDN requires the full abstraction and virtualization of each network element in order to enable complete control by a centralized network controller. To pursue this objective, photonics transmission components and their transmission functionalities must be abstracted to allow the definition of the control states and a real-time quality-of-transmission (QoT) evaluation of transparent lightpaths (LP). In this work, we propose an SDN based model of a photonic switching fabric that allows determining the control state and evaluating QoT degradation. Our investigations present a wideband optical switch design based on photonic integrated circuits (PICs), where QoT degradation is abstracted using a structure-agnostic approach based on machine learning (ML). The ML engine training and testing datasets are generated synthetically by software simulation of the photonic switch architecture. Results show the potential of the proposed technique to predict QoT impairments with high accuracy, and we envision its application in a real-time control plane.

Wide and tunable spectral asymmetry between narrow and wide facet outputs in a tapered quantum-dot superluminescent diode.

A wide spectral asymmetry between the front and rear facets of a tapered chirped quantum dot multi-section superluminescent diode is reported. The spectral asymmetry between the two facet outputs was found to be tunable and highly dependent on the bias asymmetry between the two contact sections, with a spectral mismatch of up to 14 nm. Numerical simulations confirmed a relationship between this spectral asymmetry and the non-uniform filling of the quantum dots' confined states when different current densities are applied to the device electrodes. The results from this investigation open up an additional degree of freedom for multi-section superluminescent diodes, which could pave the way for optical bandwidth engineering via multiplexing the spectral output from both facets, using only a single device.

Double-pass amplification of picosecond pulses with a tapered semiconductor amplifier.

Double-pass amplification of picosecond pulses is demonstrated and compared with single-pass amplification. This was achieved using a two-section tapered semiconductor optical amplifier with a chirped quantum-dot active region and a mode-locked laser diode as a seed. Across the range of biasing conditions common to both configurations, an enhancement in signal gain of up to 7 dB and output power by a factor of 4.1 was seen in the double-pass amplifier, compared to the single-pass. Only marginal increases in pulse duration were observed in the double-pass regime compared to the single-pass amplifier, meaning that enhancements in output power were well translated into peak power. Furthermore, the two-section contact layout of the SOA allowed the pulse duration to be optimised for a given fixed output power, giving additional flexibility to the amplifier. These results demonstrate the suitability of this simple and versatile technique, which could become the new standard in amplification of ultrashort pulses.

Threshold behavior of optical frequency comb self-generation in an InAs/InGaAs quantum dot laser.

We report on a significant reduction of both the radio-frequency beat note line width at 40.7 GHz and the integrated relative intensity noise of a 1 mm long edge-emitting monolithic Fabry-Perot InAs/InGaAs quantum dot semiconductor laser emitting from the ground state at 1250 nm by injection current control. For increasing injection currents, first an unlocked multi-mode behavior is observed and then, at a certain current above lasing threshold, self-locking of the longitudinal modes due to the internal non-linear effects occurs yielding a beat line width of 20 kHz (-3 dB) in contrast to tens of megahertz for lower injection currents. These results are confirmed by simulations.

High-power quantum-dot superluminescent tapered diode under CW operation.

A high-power quantum-dot superluminescent diode is demonstrated under continuous-wave operation, with an output power of 137.5 mW and a corresponding spectral bandwidth of 21 nm. This represents not only the highest output power, but also a record-high power spectral density of 6.5 mW/nm for a CW-operated superluminescent diode in the 1.1 - 1.3 µm spectral region, marking more than a 6-fold increase with respect to the state of the art. The two-section contact layout of the reported device introduces additional degrees of freedom, which enable a wide tunability of the bandwidth and power depending on the desired application. A maximum bandwidth of 79 nm was recorded, with an output power of 1.4 mW. The high-power continuous-wave operation of this device would be particularly relevant for continuous, high-speed, high-sensitivity spectroscopy, imaging and sensing applications, as well as in optical communications.

Self-pulsing in single section ring lasers based on quantum dot materials: theory and simulations.

We studied theoretically coherent phenomena in the multimode dynamics of single section semiconductor ring lasers with quantum dots (QDs) active region. In the unidirectional ring configuration our simulations show the occurrence of self-mode-locking in the system leading to ultra-short pulses (sub-picoseconds) with a terahertz repetition rate. As confirmed by the linear stability analysis (LSA) of the traveling wave (TW) solutions this phenomenon is triggered by an analogous of the Risken-Nummedal-Graham-Haken (RNGH) instability affecting the multimode dynamics of two-level lasers.

Self-generation of optical frequency comb in single section quantum dot Fabry-Perot lasers: a theoretical study.

Optical Frequency Comb (OFC) generated by semiconductor lasers are currently widely used in the extremely timely field of high capacity optical interconnects and high precision spectroscopy. In the last decade, several experimental evidences of spontaneous OFC generation have been reported in single section Quantum Dot (QD) lasers. Here we provide a physical understanding of these self-organization phenomena by simulating the multi-mode dynamics of a single section Fabry-Perot (FP) QD laser using a Time-Domain Traveling-Wave (TDTW) model that properly accounts for coherent radiation-matter interaction in the semiconductor active medium and includes the carrier grating generated by the optical standing wave pattern in the laser cavity. We show that the latter is the fundamental physical effect at the origin of the multi-mode spectrum appearing just above threshold. A self-mode-locking regime associated with the emission of OFC is achieved for higher bias currents and ascribed to nonlinear phase sensitive effects as Four Wave Mixing (FWM). Our results explain in detail the behaviour observed experimentally by different research groups and in different QD and Quantum Dash (QDash) devices.

Optimal sampling frequency in recording of resistance training exercises.

The purpose of this study was to analyse the raw lifting speed collected during four different resistance training exercises to assess the optimal sampling frequency. Eight physically active participants performed sets of Squat Jumps, Countermovement Jumps, Squats and Bench Presses at a maximal lifting speed. A linear encoder was used to measure the instantaneous speed at a 200 Hz sampling rate. Subsequently, the power spectrum of the signal was computed by evaluating its Discrete Fourier Transform. The sampling frequency needed to reconstruct the signals with an error of less than 0.1% was f99.9 = 11.615 ± 2.680 Hz for the exercise exhibiting the largest bandwidth, with the absolute highest individual value being 17.467 Hz. There was no difference between sets in any of the exercises. Using the closest integer sampling frequency value (25 Hz) yielded a reconstruction of the signal up to 99.975 ± 0.025% of its total in the worst case. In conclusion, a sampling rate of 25 Hz or above is more than adequate to record raw speed data and compute power during resistance training exercises, even under the most extreme circumstances during explosive exercises. Higher sampling frequencies provide no increase in the recording precision and may instead have adverse effects on the overall data quality.

Picosecond pulse amplification up to a peak power of 42 W by a quantum-dot tapered optical amplifier and a mode-locked laser emitting at 1.26 µm.

We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 µm without pulse compression, external cavity, gain- or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5 W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps.

Coherence function control of Quantum Dot Superluminescent Light Emitting Diodes by frequency selective optical feedback.

Low coherent light interferometry requires broad bandwidth light sources to achieve high axial resolution. Here, Superluminescent Light Emitting Diodes (SLDs) utilizing Quantum Dot (QD) gain materials are promising devices as they unify large spectral bandwidths with sufficient power at desired emission wavelengths. However, frequently a dip occurs in the optical spectrum that translates into high side lobes in the coherence function thereby reducing axial resolution and image quality. We apply the experimental technique of frequency selective feedback to shape the optical spectrum of the QD-SLD, hence optimizing the coherence properties. For well-selected feedback parameters, a strong reduction of the parasitic side lobes by a factor of 3.5 was achieved accompanied by a power increase of 40% and an improvement of 10% in the coherence length. The experimental results are in excellent agreement with simulations that even indicate potential for further optimizations.