<title>Bending loss of a single-mode triangular-index fiber with a depressed cladding ring by a vector mode method</title>

Abstract

The design of single-mode fibers for wideband communication networks is of considerable current interest. The triangular-index fiber with a capability of shifting the zero-dispersion wavelength from 1.3 micrometers to 1.55 micrometers has been attracting much attention. In this work, we direct our attention to the bending loss property of the triangular-index fiber with a depressed cladding ring and present some near-optimal designs. The numerical method used to obtain the propagation constants and fields is a vector mode multi-point power series expansion method which has been tested to be very accurate and efficient for calculations with a triangular-index profile. The bending loss results are computed using a vectorial volume current method. Results show that the depressed-ring can be added either to reduce the bending sensitivity of the usual triangular-index dispersion-shifted fiber, or to create a dispersion-flattening effect--which is advantageously combined to the dispersion-shifting feature of the triangular-index core. It is also found that for both of these design cases, the best core and when it is made as deep as possible. In the case where a reduction of bending loss is wanted, a comparison made with the elevated-ring design--known for its very low sensitivity to bending--shows that the depressed-ring design is more sensitive to bending than the elevated-ring design. However it offers a lower dispersion slope. As for the dispersion- flattened design, it is found that in terms of macrobending loss, the triangular-index W-fiber competes well with the step-index W-fiber.