Showing papers on "Equilibrium mode distribution published in 2023"
TL;DR: In this article , a numerical model of the core-pumped Raman effect in few-mode fibers has been proposed, which provides an accurate tool to reveal the underlying physical mechanism of SRS-induced mode distortion.
Abstract: By employing the mode decomposition method to study the relative mode evolution characteristics during the stimulated Raman scattering (SRS) process, a numerical model of the core-pumped Raman effect in few-mode fibers has been proposed, which provides an accurate tool to reveal the underlying physical mechanism of SRS-induced mode distortion. Mode distortion induced by the SRS effect in large-mode area passive fibers has been investigated numerically. It reveals that the few-mode SRS effect can result in an irreversible power transfer from the signal fundamental mode (FM) to signal high order modes (HOMs), which is a static phenomenon, different from the SRS-induced transverse mode instability. To the best of our knowledge, it is the first time that the numerical results coincide with the experimental phenomenon. Simulation results also illustrate that the inter-mode wave-mixing effect among the signal FM and signal HOMs plays a key role in the signal power transfer. With the help of the numerical model, mitigation strategy by designing and using the Raman-gain-tailored fiber has also been proposed, which shows a clear advantage in suppressing SRS-induced mode distortion.
3 citations
TL;DR: In this article , the spatial and temporal characteristics of a degenerate four-wave converter in a multimode waveguide with resonant nonlinearity in a scheme with counter-pumping waves were analyzed using the time response function and the point spread function.
Abstract: Spatial and temporal characteristics of a degenerate four-wave converter in a multimode waveguide with resonant nonlinearity in a scheme with counter-pumping waves are analyzed using the time response function and the point spread function. For single-mode pump waves with equal mode numbers, the dependences of the time response width on the waveguide length, the intensity of the first pump waves, and the mode number in the mode expansion of the object wave amplitude are obtained for the four-wave converter. The greatest contribution to the object wave amplitude is shown to be from the waveguide mode whose number coincides with the mode number of single-mode pump waves. For the stationary model, taking into account the spatial structure of the Gaussian pump wave leads to a monotonous decrease with a decrease in the pump beam width, followed by a constant value of the PSF module width. With single-mode pump waves with equal mode numbers, An increase in the mode number of the pump waves leads to a redistribution of energy concentrated in the side maxima of the point signal image and improvement in the quality of the wavefront reversal for a model with single-mode pump waves with equal mode numbers.
1 citations
TL;DR: In this paper , a coupled local mode theory is introduced to calculate the mode evolution process in a tapered double-clad fiber, and the expression of mode coupling coefficient is derived.
Abstract: Mode characteristics of a tapered double clad fiber should be analyzed based on three-layer waveguide model, so it is more complicated than that of a single clad fiber. In this paper, a method based on coupled local mode theory is introduced to calculate the mode evolution process in a tapered double clad fiber. Mode field characteristics of double clad fiber are calculated analytically with weak guidance approximation, and the expression of mode coupling coefficient is derived. Based on this, the local mode characteristics and mode coupling characteristics in a tapered double clad fiber are analyzed. The mode evolution characteristics of tapered double clad fibers with different parameters are simulated. As an example, the structure optimization process of a tapered double clad fiber is introduced. High efficiency coupling with a six-mode single clad fiber is realized, and the theoretical transmission loss is less than 0.3 dB.
TL;DR: In this article , a bend-resistant stress-type large-mode-area fiber with segmented cladding is proposed, in which a high refractive index stress rod is introduced at the core, to improve the loss ratio between the least high-order mode (HOM) and fundamental mode loss, and to reduce the fundamental modes loss effectively.
Abstract: We propose a novel bend-resistant stress-type large-mode-area fiber with segmented cladding, to the best of our knowledge, in which a high refractive index stress rod is introduced at the core, to improve the loss ratio between the least high-order mode (HOM) and fundamental mode loss, and to reduce the fundamental mode loss effectively. The mode loss and effective mode field area with or without heat load, and mode field evolution between the straight and bending transition are investigated, by utilizing the finite element method and the coupled-mode theory. The results show that the effective mode field area and the loss of the fundamental mode can reach up to 1050.1 µm2 and 0.0055d B⋅m -1, respectively, and the loss ratio between the least loss HOM and fundamental mode loss is greater than 210. The coupling efficient of the fundamental mode in the straight-bending transition reaches 0.85 at a wavelength of 1.064 µm and a bending radius of 24 cm. In addition, the fiber is insensitive to the bending direction and has excellent single-mode performance in any bending direction; the fiber maintains single-mode operation under heat load from 0 to 8 W/m. This fiber has potential application in compact fiber lasers and amplifiers.
TL;DR: In this article , a bidirectional metasurface mode converter is proposed to convert the transverse electric (TE) or transverse magnetic (TM) modes to the fundamental mode (LP01) with orthogonal polarization, and vice versa.
Abstract: Mode conversion is crucial for coupling a light source to a desired waveguide. While traditional mode converters such as fiber Bragg gratings and long-period fiber gratings exhibit high transmission and conversion efficiency, the mode conversion of two orthogonal polarizations remains challenging. Here, we present a bidirectional metasurface mode converter that can convert the transverse electric (TE)01 or transverse magnetic (TM)01 mode to the fundamental mode (LP01) with orthogonal polarization, and vice versa. The mode converter is located on a facet of a few-mode fiber and connected to a single mode fiber. Through simulations, we find that 99.9% of the TM01 or TE01 mode is converted into the x- or y-polarized LP01 mode, and that 99.96% of the x- or y-polarized LP01 mode is converted to the TM01 or TE01 mode. Furthermore, we expect a high transmission of over 84.5% for all mode conversions, up to 88.7% for TE01 to y-polarized LP01 conversion.