PP-FIO-07 Reliable Measurement of Macro-Bend Loss of Bend Insensitive Fibers by Two Point Bend Method Manoj Gupta, Anand Pandey, Bikram Jyot, Nagaraju Bezawada, Pramod R Watekar, Archi Bhattacharya and Badri Gomatam Sterlite Technologies Limited, Aurangabad, Maharashtra, India-431136 Author e-mail address: manoj.gupta2@sterlite.com Abstract: We present the measurement results of the macro-bend loss of bend insensitive fibers by two point bend method. Measurement of macro-bend loss by using this technique is more accurate, easier and less time consuming as compared to conventional technique. Keywords: Bend insensitive single mode fiber, Optical networks 1. Introduction Optical fiber is required to reach the user for FTTX applications [1]. It might be installed with smaller bend radius. It is well known that whenever an optical fiber bends, radiation loss occurs because bend pushes the optical field out of core region [2]. Radiation loss mainly depends on wavelength, the curvature radius and length of curved fiber. Conventional G.652D type single mode fiber gives enormous bend loss when operated with smaller bends. So, a new category of fibers has been developed for use in these networks, called bend insensitive fiber (G.657). Main challenge in designing G.657A2 type bend insensitive fibers was to reduce bend loss to less than 0.5 dB/turn for 15 mm diameter at 1550 nm from 8-10 dB for standard single mode fiber [3]. At the same time the fiber should be compatible with the standard single mode fibers in terms of optical parameters like dispersion, mode filed diameter, cut off wavelength etc. Researchers had proposed multiple designs to meet these challenges. Trench based design [4] of bend insensitive fiber, which is most popular, is shown in figure 1. Figure 1. Schematic refractive index profile of bend insensitive fiber. These fibers have improved confinement in core due to the trench in the cladding and show very small bend induced loss at smaller bend radii. However, measurement of macro-bend loss in these fibers at smaller bend radii is challenging as the bend loss shows oscillatory behavior as a function of wavelength and bend radius and depends on fiber layout, temperature conditions [5]. Oscillatory behavior depends on the interference between reflected wave from cladding- coating layer (whispering-gallery mode) and fundamental mode in the core region as shown in figure 2. Figure 2. Schematic showing the origin of macro bend loss due to curvature of fiber and coupling of reflection from cladding-coating interface with fundamental mode. So, investigation of macro-bend loss of bend insensitive fiber is very important, not only for deployments but also for defining the spectral window in which the fiber is operated. There is need for a measurement technique which allows reliable bend loss measurement to be rapidly made and the measurement uncertainties to be characterized. In this paper, we present the macro bend loss measurement results of bend insensitive fibers by two point bend method [6]. 2. Experimental Set up Figure 3 shows the experimental set up for two point bend method. Incident light radiation from a white light source having power spectral density of -55 dBm/nm and power stability of less than 0.02 dB for 15 min is launched into one end of 2 km sample fiber. Fundamental mode Core-cladding interface Cladding-coating interface Radiation loss n core