Influence of Aberrations on Modal Decomposition for LMA Fiber Laser Systems

Understanding the mode components is of great importance to manipulate the optical modes and to improve the optical system performance. However, various forms of aberrations, stemming from misalignment and imperfect optical components and system design, degrade the performance of the modal decomposition (MD) system. Here we analyze the influence of various Zernike aberrations on MD performance in large-mode-area fiber laser systems. Using computer-generated optical correlation filter together with angular multiplexing technique, we can simultaneously measure multi-modal contents. Among the common aberrations, we find that the MD results are least sensitive to vertical astigmatism aberration. However, the vertical coma aberration and horizontal coma aberration have a large impact on MD results under the same aberration strength, which show a rather large change in modal weight and intermodal phase. Our analysis is useful to construct a precise MD system applicable for high-power optical fiber modal analysis and mode control.

A Triangle Hybrid Plasmonic Waveguide with Long Propagation Length for Ultradeep Subwavelength Confinement

Facing the problems of ohmic loss and short propagation length, the application of plasmonic waveguides is limited. Here, a triangle hybrid plasmonic waveguide is introduced, where a cylinder silicon waveguide is separated from the triangle prism silver waveguide by a nanoscale silica gap. The process of constant optimization of waveguide structure is completed and simulation results indicate that the propagation length could reach a length of 510 μm, and the normalized mode area could reach 0.03 along with a high figure of merit 3150. This implies that longer propagation length could be simultaneously achieved along with relatively ultra-deep subwavelength mode confinement due to the hybridization between metallic plasmon polarization mode and silicon waveguide mode, compared with previous study. By an analysis of fabrication errors, it is confirmed that this waveguide is fairly stable over a wide error range. Additionally, the excellent performance of this is further proved by the comparison with other hybrid plasmonic waveguides. Our work is significant to manipulate light waves at sub-wavelength dimensions and enlarge the application fields, such as light detection and photoelectric sensors, which also benefit the improvement of the integration of optical devices.

Impact of Mode-Area Dispersion on Nonlinear Pulse Propagation in Gas-Filled Anti-Resonant Hollow-Core Fiber

We numerically investigate the effect of mode-area dispersion in a tubular-type anti-resonant hollow-core fiber by using a modified generalized nonlinear Schrödinger equation that takes into account the wavelength-dependent mode area in its nonlinear term. The pulse evolution dynamics with and without the effect of mode-area dispersion are compared and analyzed. We show that strong dispersion of the mode area in the proximity of the cladding wall thickness-induced resonances has a significant impact on the soliton pulse propagation, resulting in considerable changes in the conversion efficiencies in nonlinear frequency mixing processes. The differences become more prominent when the pump has higher energy and is nearer to a resonance. Hence, the mode-area dispersion must be accounted for when modeling such a case.

The influence of axial offset of fusion splicing on a large mode area fiber based oscillator

Fiber oscillators have the potential for achieving high power, high beam quality lasers with simple and compact structure, of which the fusion splicing point is an important aspect to the laser output characteristics. A model taking into account the axial offset of the splicing point and spatial mode competition has been proposed to analyze the mode interaction of a large mode area fiber based oscillator. The calculated results show that the axial offset of the output side fusion point has the main influence on the laser output beam quality, but the axial offset would not obviously reduce the optical efficiency, especially when the value is smaller than 2 μm. The influence of cavity parameters on the laser output characteristics under the existence of splicing point with axial offset has also been discussed. This model can provide a method for analyzing the mode dynamic that may be helpful for understanding the mode interactions in fiber oscillators.

Characteristics of Collimators Based on the Large-Mode-Area CMCF for Coupling Laser Beam

A new collimator based on a homemade concentric multilayer-core fiber (CMCF) is proposed and experimentally demonstrated. This collimator was fabricated using a tail fiber with large mode area and single-mode operation. By exploiting the optical transmission matrix, the propagation characteristic and coupling mechanism of this CMCF-based collimator was introduced meticulously. The coupling losses of the laser beam using this collimator in the off-axis, angular, and axial deviations were analyzed separately. In order to determine the relationship between the geometric redundancy of this collimator and the effective mode field area of the tail fiber, the corresponding mathematical model was established. Through model calculation and experiment measurement, the coupling properties of the collimator were improved effectively. Compared with the common SMF-based collimator, the declination redundancy of the CMCF-based one improved by 20%, which could make the coupling of the optical fiber collimator easier. Therefore, this collimator has potential application value in the laser diode coupling unit and high-speed optical communication system.

NONLINEAR PROPERTIES OF STRUCTURAL HETEROGENEOUS PHOTONIC CRYSTAL FIBERS WITH As2Se3 SUBSTRATE

We examine the possibility of improving the nonlinear properties of photonic crystal fibers (PCFs) with As2Se3 substrates by creating a difference in the diameters of the air holes of the rings around the core. With the new design, all-normal dispersion properties, small effective mode area, high nonlinear coefficient, and low confinement loss were achieved in the long-wavelength range of 2.0–7.0 µm. The highest nonlinear coefficient is 4414.918 W-1.km-1 at 4.5 µm for the lattice constant (Ʌ) of 3.0 µm and the filling factor (d/Ʌ) of 0.85, while the lowest loss is 1.823´10-21 dB/cm with Ʌ = 3.5 µm and d/Ʌ = 0.8. Based on the numerical simulation results, the characteristics of two optimal structures have been analyzed in detail to guide the application in supercontinuum generation.