Fourier optics with linearly tapered waveguides: light trapping and focusing

An optical pulse asymptotically reaching zero group velocity in tapered waveguides can ultimately stop at a certain position in the taper accompanied by a strong spatial compression. This phenomenon can be also observed in spatio-temporal systems where the pulse velocity asymptotically reaches the velocity of a tapered front. The first system is well known from tapered plasmonic waveguides where adiabatic nano-focusing of light is observed. Its counterpart in the spatio-temporal system is the optical push broom effect where a nonlinear front collects and compresses the signal. Here, we use the slowly-varying envelope approximation to describe such systems. We demonstrate an analytical solution for the linear taper and the piecewise linear dispersion and show that the solution in this case resembles that of an optical lens in paraxial approximation. In particular, the spatial distribution of the focused light represents the Fourier transform of the signal at the input

The Effect of Annotation Quality on Wear Semantic Segmentation by CNN

In this work, we investigate the impact of annotation quality and domain expertise on the performance of Convolutional Neural Networks (CNNs) for semantic segmentation of wear on titanium nitride (TiN) and titanium carbonitride (TiCN) coated end mills. Using an innovative measurement system and customized CNN architecture, we found that domain expertise significantly affects model performance. Annotator 1 achieved maximum mIoU scores of 0.8153 for abnormal wear and 0.7120 for normal wear on TiN datasets, whereas Annotator 3 with the lowest expertise achieved significantly lower scores. Sensitivity to annotation inconsistencies and model hyperparameters were examined, revealing that models for TiCN datasets showed a higher coefficient of variation (CV) of 16.32% compared to 8.6% for TiN due to the subtle wear characteristics, highlighting the need for optimized annotation policies and high-quality images to improve wear segmentation

A distributed architecture of parallel buck-boost converters and cascaded control of DC microgrids-real time implementation

To enhance the stability and reliability of the system, the converters’ parallel operation can be cascaded to address the constraints posed by the substantial integration of renewable resources. Buck-boost DC-DC converters are often controlled via a cascaded control approach to allow parallel operation. The converter’s output current and its voltage will be controlled by nested loop control. This study proposes adaptive droop control parameters that are updated and verified online using the principal current sharing loops to minimize the fluctuation in load current sharing. When the converters in the microgrid are paralleled, load sharing will be accomplished using the droop control approach in addition to nested proportional-integral-based voltage and current control loops. To restore the correct voltage across the DC microgrid, an outer addition voltage secondary loop will be used, rectifying any voltage disparities caused by the droop management strategy. Several common load resistances and input voltage variations are used to test the suggested method. Using a linearized model, this work assesses the stability and performance of the proposed method. It then confirms the findings with an adequate model created in MATLAB/SIMULINK, Real-Time Simulation Fundamentals, and hardware-based experiments

Self-mode-locked vertical-external-cavity surface-emitting laser

Ultrashort laser pulses from vertical-external-cavity surface-emitting lasers (VECSELs) have been receiving much attention in the semiconductor laser community since the first demonstration of sub-ps-pulsed devices more than a decade ago. Originally relying on semiconductor saturable-absorber mirrors for pulse formation, mode-locked operation has not only become accessible by using a variety of saturable absorbers, but also by using a saturable-absorber-free technique referred to as self-mode-locking (SML). Here, we highlight achievements in the field of SML-VECSELs with quantum-well and quantum-dot gain chips, and study the influence of a few VECSEL parameters on the assumed nonlinear lensing behavior in the system

Self-mode-locked quantum-dot vertical-external-cavity surface-emitting laser

We present the first self-mode-locked optically pumped quantum-dot semiconductor disk laser. Our mode-locked device emits sub-picosecond pulses at a wavelength of 1040 nm and features a record peak power of 460 W at a repetition rate of 1.5 GHz. In this work, we also investigate the temperature dependence of the pulse duration as well as the time-bandwidth product for stable mode locking. © 2014 Optical Society of America

Watt-class CMOS-compatible power amplifier

Power amplifier is becoming a critical component for integrated photonics as the integrated devices try to carve out a niche in the world of real-world applications of photonics. That is because the signal generated from an integrated device severely lacks in power which is due mainly to the small size which, although gives size and weight advantage, limits the energy storage capacity of an integrated device due to the small volume, causing it to rely on its bench-top counterpart for signal amplification downstream. Therefore, an integrated high-power signal booster can play a major role by replacing these large solid-state and fiber-based benchtop systems. For decades, large mode area (LMA) technology has played a disruptive role by increasing the signal power and energy by orders of magnitude in the fiber-based lasers and amplifiers. Thanks to the capability of LMA fiber to support significantly larger optical modes the energy storage and handling capability has significantly increased. Such an LMA device on an integrated platform can play an important role for high power applications. In this work, we demonstrate LMA waveguide based CMOS compatible watt-class power amplifier with an on-chip output power reaching ~ 1W within a footprint of ~4mm2.The power achieved is comparable and even surpasses many fiber-based amplifiers. We believe this work opens up opportunities for integrated photonics to find real world application on-par with its benchtop counterpart

Watt-class silicon photonics-based optical high-power amplifier

High-power amplifiers are critical components in optical systems spanning from long-range optical sensing and optical communication systems to micromachining and medical surgery. Today, integrated photonics with its promise of large reductions in size, weight and cost cannot be used in these applications, owing to the lack of on-chip high-power amplifiers. Integrated devices severely lack in output power owing to their small size, which limits their energy storage capacity. For the past two decades, large mode area (LMA) technology has played a disruptive role in fibre amplifiers, enabling a dramatic increase of output power and energy by orders of magnitude. Owing to the ability of LMA fibres to support significantly larger optical modes, the energy storage and power handling capabilities of LMA fibres have significantly increased. Therefore, an LMA device on an integrated platform can play a similar role in power and energy scaling of integrated devices. In this work, we demonstrate LMA waveguide-based watt-class high-power amplifiers in silicon photonics with an on-chip output power exceeding ~1 W within a footprint of only ~4.4 mm2. The power achieved is comparable and even surpasses that of many fibre-based amplifiers. We believe that this work has the potential to radically change the integrated photonics application landscape, allowing power levels previously unimaginable from an integrated device to replace much of today’s benchtop systems. Moreover, mass producibility, reduced size, weight and cost will enable yet unforeseen applications of laser technology

Recent advances in the field of vertical-external-cavity surface-emitting lasers

Vertical-external-cavity surface-emitting lasers (VECSELs) have proved to be versatile lasers which allow for various emission schemes which on the one hand include remarkably high-power multi-mode or single-frequency continuouswave operation, and on the other hand two-color as well as mode-locked emission. Particularly, the combination of semiconductor gain medium and external cavity provides a unique access to high-brightness output, a high beam quality and wavelength flexibility. Moreover, the exploitation of intra-cavity frequency conversion further extends the achievable radiation wavelength, spanning a spectral range from the UV to the THz. In this work, recent advances in the field of VECSELs are summarized and the demonstration of self-mode-locking (SML) VECSELs with sub-ps pulses is highlighted. Thereby, we present studies which were not only performed for a quantum-well-based VECSEL, but also for a quantum-dot VECSEL