Test and Measurement of Fibers

Authored by: Liang Dong , Bryce Samson

Fiber Lasers

Print publication date:  September  2016
Online publication date:  September  2016

Print ISBN: 9781498725545
eBook ISBN: 9781315370521
Adobe ISBN:

10.1201/9781315370521-6

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Abstract

Examples of data sheets for two industry standard passive optical fibers are shown in Table 5.1. One of these fibers (1060-XP) is an industry standard fiber widely used in low power (mostly telecommunication) applications. The other is a fiber almost exclusively used for high-power fiber lasers, LMA-GDF-20/400 (standing for large-mode-area, germanium-doped fiber) and available from multiple fiber suppliers (e.g., References 1 and 2). From this table we can identify some of the major differences between fibers optimized for high-power fiber lasers and those associated with more conventional telecom fibers. First one can see that some of the specifications are not actually measured on both sets of fibers. This reflects partly the different standards that have been adopted in the telecom and fiber laser industries and also the difficulty in measuring some values, particularly in the case of the LMA fibers. The 1060-XP fiber is primarily used around the wavelength range 980–1060 nm, and carrying low-power single-mode light at those wavelengths. Indeed the most common application for the 1060-XP fiber is to pigtail to single-mode components such as laser diodes and couplers operating at 980 nm or 1060 nm. However, we can see that the operating wavelength range for the 1060-XP fiber is stated to be 980–1600 nm, spanning the three common telecommunications wavelengths at 980 nm, 1300 nm, and 1550 nm. The fiber is therefore specified to be single mode at 1060 nm by defining a cutoff wavelength specified at <920 nm, guaranteeing that the fiber does not have more than one mode across the entire specified operating wavelength range from 980 to 1600 nm. By comparison, the LMA-GDF-20/400 fiber does not specify a cutoff wavelength and includes an operating wavelength regime, which is arguably rather unclear in this case since it does not refer to the single-mode regime of the fiber. Rather, the LMA-GDF-20/400 fiber specifies a core numerical aperture (NA) and core diameter d, which may be used to calculate a normalized frequency parameter (V value) at the desired operating wavelength λ, using equation 5.1, which can then be used to calculate the cutoff wavelength (a V value of 2.4 corresponds to the cutoff wavelength): 5.1 V=πdλNA

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