<title>Auto-aligning and splicing PM fibers of different types with a passive method</title>

Abstract

Many different types of Polarization Maintaining (PM) fibers and Polarizing (PZ) fibers are playing important roles in most of fiber optical gyros and high speed communication networks. A new method for passively aligning and fusionsplicing those fiber types are developed with the help of the lens-effect tracing technique [1,2]. Instead of calculating the correlation directly between the two POL (Polarization Observation by the Lens-effect tracing, see [2]) profiles measured from the two sides of fibers, two simulated POL profiles are generated with a truncated trigonometric Fourier series expansion. The azimuthal position of each fiber and the angular offset between the fibers are then obtained by either an analytic method or an indirect correlation method. With the methods, different types of PM and PZ fibers, such as Bow-tie, PANDA, elliptical core and elliptical jacket, can be automatically aligned and spliced to each other with a mean extinction ratio higher than 30 dB, and mean difference between the actively measured and passively estimated extinction ratio about 1.0 dB.Various types of polarization maintaining (PM) fibers and polarizing (PZ) fibers are developed and produced by different venders with different designs. Even from the same vender, several variations of its PM and PZ fiber designs are normally available for specific requirement: like different wavelengths, cladding diameters, and mode field diameters. Those PM and PZ fibers, as well as those optical components with PM fiber pigtails, are more and more frequently employed in optical fiber sensors, erbium doped fiber amplifiers (EDFA) for dense WDM systems, fiber-optic gyros (FOG), etc., in order to avoid polarization mode dispersion (PMD) in EDFAs and polarization drift error in FOGs. The fast technical development for producing FOGs and EDFAs is progressively transferring prototypes in labs to production lines in industry. Therefore, an automated, passive (no light injection to fiber core), and fiber-type independent PM-fiber splicing method is called for.In previous reports, several approaches were developed in combination with automated fusion splicers, which are equipped with digital imaging systems. However, they are all hardly to meet the entire requirements. For instance, the intensity profile analyzing method using a side-view-image is developed mainly for PANDA fiber (see [3] and [4J) and is fiber-type dependent. The algorithm of the method developed for one fiber type normally does not work for other fiber types. The end-view image processing technique (see [5], [6], and [7]) is also developed. With this technique, the azimuthal offset deviation caused by imperfect cleaving angles during the fusion [8] cannot be checked passively after splicing. Thus, it is impossible to estimate extinction ratio degradation of a splice without active measurement. Another side-view-image method using the direct correlation between the POL (Polarization Observation by the Lens-effect tracing, see [2]) profiles meets the complete requirement if the fi...