As a proof of the concept, an experiment is performed in which the magnitude and phase responses of a narrow-band fiber ring resonator (FRR) and a hydrogen cyanide (HCN) gas chamber are measured with the proposed OVA. The measurement results show that a measurement range as broad as 418 GHz and a frequency resolution as high as 0.5 MHz are achieved with a measurement time as short as 400 µs. The key advantages of the proposed OVA include a largely extended measurement range, high measurement speed and high resolution.Analytical expression of the Airy transform of an arbitrary Hermite-Gaussian beam is derived. The optical field in the x-direction of the Airy transform of Hermite-Gaussian beams with transverse mode number m is the sum of the zero-order derivative to mth-order derivative of the Airy function with different weight coefficients. The analytical expressions of the centre of gravity and the beam spot size of an arbitrary Hermite-Gaussian beam passing through an Airy transform optical system are also presented, which are very concise. Because the Airy transform of a Hermite-Gaussian beam has the same evolution law in the two transverse directions, only the effects of the control parameter α and the transverse mode number m on the normalized intensity distribution, the centre of gravity, and the beam spot size in the x-direction are theoretically investigated, respectively. The Airy transform of Hermite-Gaussian beams is also realized in the experiment. The influence of the control parameters on the normalized intensity distribution, the centre of gravity, and the beam spot size is experimentally investigated, respectively. The experimental results are consistent with the theoretical simulation results. When Hermite-Gaussian beams pass through an Airy transform optical system, the number of lobes may change, and the importance of lobes with the same status in the input plane may become different. By using the Airy transform of Hermite-Gaussian beams, the practical applications of Hermite-Gaussian beams can be extended.An improved fiber amplifier model for simulating thermal mode instability (TMI) in high-power fiber amplifiers is developed. The model is applied to reveal new physics regarding the thermal physics that is critical to the TMI process, which are not the glass volume or the cooling method, but rather the transit path length of the quantum-defect-defined thermal peak in the fiber amplifier. The new physics and model analysis are applied to create a set of design rules to guide the development of new fiber types specifically for intrinsically mitigating TMI. These rules and the improved model are applied to three new fiber concepts for mitigating TMI in high-power fiber amplifiers. All three fiber types are shown to substantially increase the TMI threshold, up to a factor of 2 in some cases. In addition, all three new fiber classes offer ways to simultaneously increase the core diameter and the TMI threshold.The dual modulation of a directly modulated laser (DML) and an electro-absorption modulator (EAM) is known to be an effective way to generate an optical single sideband (SSB) signal in highly compact and cost-effective fashions.  https://www.selleckchem.com/products/ki696.html  Two theoretical models were developed for this dual modulation scheme under the assumptions of negligible intensity modulation of DML and/or zero chirp of EAM. In this paper, we develop a generalized model of dual modulation scheme without those assumptions. We show theoretically that the previous models can be unified as special cases of our generalized model. We evaluate the validity of our model using numerical simulations and experiments. The results show that our model estimates the modulation conditions for optical SSB generation accurately over wide ranges of modulation frequency and EAM's chirp. We also show experimentally that we can achieve an optical sideband suppression ratio higher than 40 dB by using our generalized model. This is >25 dB higher than the ratios obtained from the previous models.Micro-milling has been proved to be the most effective method to mitigate the growth of laser-induced surface damage on potassium dihydrogen phosphate (KDP) crystals used in high power laser systems. However, the secondary peak of downstream light field modulation caused by Gaussian mitigation pits on the rear KDP surface would cause potential risk to damage downstream optics. In order to explore the effect of the mitigation pits on the secondary peak, we numerically calculated the downstream light field modulations caused by Gaussian mitigation pits on the rear KDP surface based on the angular spectrum diffraction theory. The results suggest that the secondary peaks are dependent on the parameters of the width, depth, depth error and title error. Among them, the tilt error and depth have greater influence on the mitigation effect. To reduce the laser damage risk caused by the secondary peak, the depth of the pre-designed mitigated contour should be optimized according to the actual operating conditions. The tilt error and depth error are proposed to be controlled within 1' and 2 μm, respectively, during the micro-milling. Also, the experiments verified the calculation results of downstream modulations and the effects of these parameters on the secondary peak. This work can not only provide available models for evaluating the laser damage risk of secondary peak caused by mitigation pits on the KDP surface but also contribute to the development of optimal micro-milling parameters for laser damage mitigation as well as the installation strategy of optical components employed in the high power laser systems.We propose a novel design architecture to realize scalable selective mode filter based on the asymmetric directional coupler structure. In this structure, any arbitrary high-order mode can pass, whereas other unwanted modes are blocked. Furthermore, multiple optical modes can be blocked by only adjusting the structural parameters. As a proof of concept, we experimentally demonstrated a three-mode device and the scalability of the proposed structure is demonstrated by another design of four-mode filter. The proposed architecture offers scalability and high-design flexibility, and it has excellent potential to be used in advanced mode division multiplexing optical networks.