Improved Bend Loss Formula Verified for Optical Fiber by Simulation and Experiment

Abstract

Abstract-This paper presents an improved curvature loss formula for optical waveguides, which is shown to accurately predict the bend loss of both single-mode and multimode fibers. The formula expands upon a previous formula derived by Marcuse, greatly improving its accuracy for the case of multimode fiber. Also presented are the results of bent fiber simulations using the beam propagation method (BPM), and experimental measurements of bend loss. Agreement among simulation, formula and measurement support the validity of both theoretical methods. BPM simulations showed that the lowest order modes of the bent fiber were reduced to their linearly polarized constituents prior to the onset of significant bend loss. This implies that certain LP mode orientations should propagate with much lower loss than previously expected, and should impact the mode stripping ability of bent large mode area fibers, as employed in fiber lasers and amplifiers.Index Terms-Dielectric waveguides, laser amplifiers, optical fiber amplifiers, optical fiber lasers, optical waveguide theory, waveguide bends.

Use of a Bent Single SMS Fiber Structure for Simultaneous Measurement of Displacement and Temperature Sensing

“…Figure 3(a) shows that the field distribution in the MMF section for a straight SMS is symmetric, relative to the propagation direction (the z direction in the figure). However for the bent SMS structure, while the field distribution is symmetric up to the bend point (at z = 20 mm in figure 3 (b)), beyond this point since the bent fiber portion has effectively an asymmetric refractive index distribution [12], the modes excited in the bent fiber portion are also asymmetrically distributed. As a consequence in the remaining straight section of the MMF, the field distribution is also asymmetrical, in particular at the reimaging point where the SMF is attached.…”

“…The equivalent refractive index distribution used in our simulation for the bent fiber portion is Eq. (4) in [12].…”

Mode degeneration in bent photonic crystal fiber study by using the finite element method

“…Subsequently, the straight waveguide with a transformed index profile can be analysed by a number of modal solution techniques, such as the eigenmode expansion [23], the methods of lines [24], the FDM [26], the variational method [28], the matrix method [29], the WKB analysis [30], and the FEM [32,33]. The FEM has also been employed by using cylindrical co-ordinate with E field [35] and the equivalent anisotropic refractive index approaches [36]. The beam propagation approach [37,38] has been used successfully, but this approach makes the problem 3-dimensional with additional computational costs.…”

Thermal Effects in Optical Fibres

“…The additional attenuation of waveguides subject to tight bending is a well know phenomenon, studied in 1976 by Marcuse (Marcuse, 1976). Marcuse associated the additional losses in bent waveguides with the optical signal radiated to the cladding region, this model was later improved by other authors (Harris et al, 1986;Valiente et al, 1989;Schermer et al, 2007). Besides the new attenuation limits imposed by the bending, other constrain was observed.…”