Extracting the parameters of a laser from the measured results is critical for laser design, modeling and optimization. This work presents a parameter extraction method for quantum well distributed feedback (DFB) lasers based on the one-dimensional traveling wave model (1D TWM). Facet reflectivities, grating coupling coefficient and the other parameters can be extracted by fitting the lasing spectrum, light-current (L-I) curve, intensity modulation (IM) response and large-signal chirp. During the extraction progress, the 1D TWM is simplified to improve the extraction efficiency. The feasibility of this extraction method is verified by extracting parameters from preset simulation results and experimental results, respectively. The 1D TWM can reflect the physical properties of the laser profoundly and the parameter extraction method based on 1D TWM will be a valuable tool for laser design, optimization or processing improvement.

Optically transparent microwave absorbers based on metamaterials demonstrate exceptional microwave absorption performance while maintaining high optical transmittance, showcasing significant potential for applications in modern communication, defense, and architectural fields. Transparency in the visible light spectrum is primarily achieved through material selection and structural optimization. The artificially designed metamaterials based on transparent resistive films can be used to achieve devices with excellent wave absorption characteristics in the microwave frequency band. In this paper, we systematically review the research progress in the domain of optically transparent microwave metamaterial absorbers. We first introduce the implementation principles of optically transparent microwave metamaterial absorbers from the perspectives of transparency and wave absorption, laying the foundation for the in-depth discussions in subsequent sections. Subsequently, we focus on the research progress of optically transparent microwave metamaterial absorbers. In this paper, microwave metamaterial absorbers are classified into three types: passive absorbers, tunable absorbers and adaptive absorbers. Passive and tunable absorbers are further discussed based on their structural classifications. This paper summarizes the current research status and technical bottlenecks of optically transparent microwave absorbers while envisioning their extensive applications in stealth technology, wireless communication, and multifunctional devices. While challenges persist in balancing thickness, bandwidth and transmittance, future advancements in novel material, innovative structural designs, and manufacturing processes are expected to enable the realization of efficient, intelligent, multifunctional absorbers.

Optical nonreciprocity, stemming from the deviation of the Lorentz reciprocity theorem, holds significant interest in the realm of optics and electromagnetics. Here, we propose and experimentally demonstrate broadband nonreciprocal transmission via a low-biased magnetic Kerker-type dimer metasurface. The designed magneto-optical metasurface comprises three layers of metal sandwiched between two gyromagnetic near-zero thickness slabs. The Kerker-type dimers broaden the isolation bandwidth utilizing multiple resonances where the double-stacked metallic disks act as Kerker-type dipoles, enhancing the transmissibility of the metasurface. The multipole decomposition reveals that the magnetic dipole contribution arising from magnetization is the primary cause of the metasurface's nonreciprocal response. Microwave measurement demonstrates that the bandwidth for an isolation ratio exceeding 10 dB is over 3 GHz. The broadband nonreciprocal performance remains relatively stable, exhibiting strong robustness against the bias disturbance. Our findings provide an alternative avenue for enhancing broadband nonreciprocity transmission under a low-biased magnetic field.

The bandwidth of a distributed feedback (DFB) directly modulated laser (DML) is limited by its carrier–photon resonance (CPR) frequency. A viable approach to break the bottleneck is to introduce a photon–photon resonance (PPR), since the PPR can happen at a much higher frequency than the CPR. Among the many structures that can possibly generate the PPR, the dual-sectional push–pull modulated (PPM) DFB is of particular interest for its fabrication cost-effectiveness as no regrowth is required. The PPR in the PPM DFB, however, usually shows a rapid roll-off on both edges, which brings in an indentation on the lower frequency side of the PPR peak and, consequently, cuts off the bandwidth. To compensate for this dip, we introduce a detuned PPR and restart the CPR response by exploiting a time delay between the differential signals applied to the PPM DFB. Our simulation result shows that the broadened PPR peak and the restarted CPR response indeed mitigate the dip and effectively expand the PPM-DFB’s bandwidth to approximately 50 GHz, a value double that of the conventional (single-sectional) DFB DML.

The excitation of a nonradiating anapole in a high-index dielectric nanosphere is an effective pathway for enhancing light absorption. Here, we investigate the effect of localized lossy defects on the nanoparticle based on Mie scattering and multipole expansion theories and find its low sensitivity to absorption loss. The scattering intensity can be switched by tailoring the defect distribution of the nanosphere. For a high-index nanosphere with homogeneous loss distributions, the scattering abilities of all resonant modes reduce rapidly. By introducing loss in the strong field regions of the nanosphere, we achieve independent tuning of other resonant modes without breaking the anapole mode. As the loss increases, the electromagnetic scattering coefficients of the anapole and other resonant modes show opposite trends, along with strongly suppressed corresponding multipole scattering. While regions with strong electric fields are more susceptible to loss, the anapole’s inability to emit or absorb light as a dark mode makes it hard to change. Our findings provide new opportunities for the design of multi-wavelength scattering regulation nanophotonic devices via local loss manipulation on dielectric nanoparticles.

Parameters used to calculate the operating characteristics of distributed feedback (DFB) lasers have to be chosen properly to ensure a perfect match between the calculated and measured results. We propose a multi-objective parameter extraction method based on the deep neural network (DNN), that can not only efficiently and accurately extract the realistic parameters of DFB lasers but also resolve coupling issues among parameters. Two forward DNN models are trained using traveling wave model (TWM) and transfer matrix method (TMM), respectively, to predict the light-current (L-I) characteristics, amplitude modulation (AM) response, and spectrum of DFB lasers. After fabricating and measuring lasers, the extracted parameters are iteratively optimized against the experimentally measured results utilizing the well-performing forward models and differential evolution algorithm. Through Pareto sorting, an optimal parameter set is extracted, which can accurately reproduce all target characteristics (the LI curve, AM response, and spectrum) at the same time. The proposed method greatly reduces the computational complexity and avoids the time-consuming situation of traditional TWM and TMM calculations. Using the extracted parameters, the large-signal modulation is theoretically calculated. And it fits very well with the measured results, which verifies the practicality and reliability of the proposed method.