Frequency-resolved optical gating for the complete reconstruction of attosecond bursts (FROG-CRAB) is a well-known technique for the complete temporal characterization of ultrashort extreme ultraviolet (XUV) pulses, with durations down to a few tens of attoseconds. Recently, this technique was extended to few-femtosecond XUV pulses, produced by high-order harmonic generation (HHG) in gases, thanks to the implementation of a robust iterative algorithm the extended ptychographic iterative engine (ePIE). We demonstrate, by using numerical simulations, that the ptychographic reconstruction technique is characterized by an excellent degree of convergence and robustness. We analyse the effects on pulse reconstruction of various experimental imperfections, namely, the jitter of the relative temporal delay between the XUV pulse and a suitably delayed infrared (IR) pulse and the noise of the measured FROG-CRAB spectrograms. We also show that the ePIE approach is particularly suitable for the reconstruction of incomplete FROG-CRAB spectrograms (i.e., spectrograms with a reduced number of measured time delays) and of spectrograms acquired with a reduced spectral resolution, particularly when relatively high-intensity IR pulses are employed.It is common understanding that multilayered dielectric metamaterials, in the regime of deeply subwavelength layers, are accurately described by simple effective-medium models based on mixing formulas that do not depend on the spatial arrangement. In the wake of recent studies that have shown counterintuitive examples of periodic and aperiodic (orderly or random) scenarios in which this premise breaks down, we study here the effects of deterministic disorder. With specific reference to a model based on Golay-Rudin-Shapiro sequences, we illustrate certain peculiar boundary effects that can occur in finite-size dielectric multilayers, leading to anomalous light-transport properties that are in stark contrast with the predictions from conventional effective-medium theory. Via parametric and comparative studies, we elucidate the underlying physical mechanisms, also highlighting similarities and differences with respect to previously studied geometries. Our outcomes may inspire potential applications to optical sensing, switching and lasing.In microscopy, proper modeling of the image formation has a substantial effect on the precision and accuracy in localization experiments and facilitates the correction of aberrations in adaptive optics experiments. The observed images are subject to polarization effects, refractive index variations, and system specific constraints. Previously reported techniques have addressed these challenges by using complicated calibration samples, computationally heavy numerical algorithms, and various mathematical simplifications. In this work, we present a phase retrieval approach based on an analytical derivation of the vectorial diffraction model. Our method produces an accurate estimate of the system’s phase information, without any prior knowledge about the aberrations, in under a minute.A holographic and deep learning-based method is presented for three-dimensional laser damage location. The axial damage position is obtained by numerically focusing the diffraction ring into the conjugate position. A neural network Diffraction-Net is proposed to distinguish the diffraction ring from different surfaces and positions and obtain the lateral position. Diffraction-Net, which is completely trained by simulative data, can distinguish the diffraction rings with an overlap rate greater than 61% which is the best of results reported. In experiments, the proposed method first achieves the damage pointing on each surface of cascade slabs using diffraction rings, and the smallest inspect damage size is 8µm. A high precision result with the lateral positioning error less than 38.5µm and axial positioning error less than 2.85mm illustrates the practicability for locating the damage sites at online damage inspection.Alkali-free borosilicate glasses are one of the most used dielectric platforms for ultrafast laser inscribed integrated photonics. Femtosecond laser written waveguides in commercial Corning Eagle 2000, Corning Eagle XG and Schott AF32 glasses were analyzed. They were studied in depth to disclose the dynamics of waveguide formation. We believe that the findings presented in this paper will help bridge one of the major and important gaps in understanding the ultrafast light-matter interaction with alkali-free boroaluminosilicate glass. It was found that the waveguides are formed mainly due to structural and elemental reorganization upon laser inscription. Aluminum along with alkaline earth metals were found to be responsible for the densification and silicon being the exchanging element to form a rarefied zone. Strong affinity towards alkaline earth elements to form the densified zone for waveguides written with high feed rate (>200 mm/min) were identified and explained. Finally we propose a plausible solution to form positive refractive index change waveguides in different glasses based on current and previous reports.Wavelength-division multiplexed optical communication systems used in 5G networks require tunable wavelength filters with narrow bandwidth for 100 GHz channel spacing, wide wavelength range to cover 16 channels, and a side mode suppression ratio (SMSR) exceeding 30 dB. To fabricate wavelength filters satisfying these specifications, tunable Bragg grating filters based on polymeric optical waveguides are proposed. The combination of mode-sorting waveguide and tilted Bragg grating enables the extraction of Bragg reflected signals to another path, without using an external circulator. Moreover, the double reflection by the two-stage cascaded structure produces narrower reflection bandwidth, improved SMSR characteristics, and reduced adjacent-channel crosstalk through the suppression of undesired mode coupling. The proposed device exhibits a 20 dB bandwidth of 1.0 nm and SMSR of 35 dB, over the entire wavelength-tuning range.We propose and experimentally demonstrate an accurate modulation-format-indepen-dent and cascaded filtering effect (CFE) insensitive in-band optical signal-to-noise ratio (OSNR) monitoring technique enabled by Gaussian process regression (GPR) utilizing a widely tunable optical bandpass filter (OBPF) and optical power measurements. SB202190 mw By adjusting the center frequency of a widely tunable OBPF and measuring the corresponding output optical power as the input features of GPR, the proposed OSNR monitoring technique is experimentally proven to be transparent to modulation formats and robust to CFE, chromatic dispersion (CD), polarization mode dispersion (PMD), and nonlinear effect (NLE). Experimental results for 9-channel 32Gbaud PDM-16QAM signals with 50GHz channel spacing demonstrate OSNR monitoring with the root mean squared error (RMSE) of 0.429 dB and the mean absolute error (MAE) of 0.294 dB, in the OSNR range of -1∼30 dB. Even better, our proposed technique has the potential to be employed for link monitoring at the intermediation nodes and can eliminate the necessity to know the transmission information.