Equilibrium mode distribution

About: Equilibrium mode distribution is a research topic. Over the lifetime, 928 publications have been published within this topic receiving 14939 citations.

Length dependence of effective cutoff wavelength in single-mode fibers

Abstract: Transmission characteristics of single-mode fiber operated in the two-mode (LP 01 and LP 11 ) propagation region is investigated experimentally and theoretically. The effective cutoff wavelength of the LP 11 mode λ ce is commonly used to assure practically the single-mode operation of the LP 01 mode above λ ce up to certain fiber length. The experimental λ ce decreases linearly in a logarithmic scale of fiber length as increasing fiber length, and eventually becomes constant after a few kilometers' propagation. Theoretical λ ce is obtained from a coupled power equation by taking into account the mode coupling as well as the losses of the two modes. To calculate λ ce , the losses of the two modes are individually measured by a new measurement technique. It is clarified from the theory that the nonlinear property of the length dependence of λ ce in the logarithmic scale is due to a relatively small mode coupling between the LP 01 and LP 11 modes.

Higher-order mode fiber enables high energy chirped-pulse amplification

Abstract: Energy scaling of femtosecond fiber lasers has been constrained by nonlinear impairments and optical fiber damage. Reducing the optical irradiance inside the fiber by increasing mode size lowers these effects. Using an erbium-doped higher-order mode fiber with 6000 µm2 effective area and output fundamental mode re-conversion, we show a breakthrough in pulse energy from a monolithic fiber chirped pulse amplification system using higher-order mode propagation generating 300 µJ pulses with duration 600 MW at 1.55 µm. The erbium-doped HOM fiber has both a record large effective mode area and excellent mode stability, even when coiled to reasonable diameter. This demonstration proves efficacy of a new path for high energy monolithic fiber-optic femtosecond laser systems.

Mode conversion in planar dielectric separating waveguides

Abstract: Separating optical waveguides are expected to become important in integrated optics. They occur whenever a branching waveguide is used (Fig. 1a) or whenever two parallel waveguides in close proximity are separated (Fig. 1b). These situations will arise in virtually all applications of electrooptic switches and waveguide couplers that depend on evanescent coupling. Using quasi-normal modes and a step transition model we have studied theoretically the mode conversion behavior of separating planar dielectric waveguides as a function of taper slope and mode synchronism, which is adjusted by branch asymmetry. When the taper slope is large in a near symmetric structure, considerable mode conversion will occur and the structure will act as a power divider (Fig. 2b). Incident power concentrated in the upper and lower parts of the structure will end up in the upper and lower arms of the branch, respectively. This behavior is usually required for conventional evanescent couplers. However, in a more asymmetric structure with smaller taper slope, mode conversion is negligible and the structure will act as a mode splitter (Fig. 2a). Mode power is then transferred to one arm of the branch or the other. The transition boundary between a power divider and mode splitter (Fig. 3) is conveniently described approximately by: equation Here Δβ is the difference in mode propagation constant for large waveguide separation, θ is the taper slope, and γ is the decay constant of the field in the separating region. This result will allow quantitative design of mode splitters or power dividers, as desired, and should aid in the design of separating waveguides with minimum radiation losses.

Mode conversion and radiation losses in a step-index optical fibre due to bending

Abstract: Wave propagation in a step-index optical fibre with a curved section is treated theoretically. Mode conversion and radiation take place. The mode coupling coefficients which depend on the polarization of the incident mode are calculated. Radiation losses at the transition between a straight and a curved fibre section and total losses including the continuous radiation loss due to a uniform bend are evaluated. Comparisons are also made between singly and doubly clad fibres. It is shown that the doubly clad fibre can tolerate a sharper bend.

An investigation of the mode characteristics of SOI submicron rib waveguides using the film mode matching method

Abstract: The mode characteristics of SOI (silicon-on-insulator) submicron rib waveguides are very different from those of micrometer-sized ones. Using the full-vector film mode matching method, we propose a simple criterion to determine whether a waveguide mode is guided or not. The single-mode condition for deep-etched waveguides is obtained using this criterion. We also obtain the inherent TM mode leakage and sharp cancelation effects due to TE–TM mode coupling in shallow-etched rib waveguides from numerical simulations, which agree well with the analytical results based on total internal reflection and interference theories.