Detailed numerical analysis for dispersion properties and losses has been carried out for a new type of Photonic crystal fiber where the air-holes are arranged in a circular pattern with a silica matrix called as Circular Photonic Crystal Fiber (C-PCF). The dependence of different PCF geometrical parameters namely different circular spacings, air-hole diameter and numbers of air-hole rings are carried out in detail towards practical applications. Our numerical analysis establishes that total dispersion is strongly affected by the interplay between material dispersion and waveguide dispersion. For smaller air-filing fraction, adding extra air-hole rings does not change dispersion much whereas for higher air-filling fraction, the dispersion nature changes significantly. With proper adjustment of the parameters ultra-flattened dispersion could be achieved; though the application can be limited by higher losses. However, the ultra-flat dispersion fibers can be used for practical high power applications like supercontinuum generation (SCG) by reducing the loss at the pumping wavelength by increasing the no of air-hole rings. Broadband smooth SCG can also be achieved with low loss oscillating near-zero dispersion fiber with higher no of air-hole rings. The detail study shows that for realistic dispersion engineering we need to be careful for both loss and dispersion. 1. Introduction Photonic crystal fibers (PCFs) or microstructured optical fibers (MOFs) [1, 2] are special types of optical fiber where air holes are arranged in a periodic nature in the cladding. These types of fibers possess some novel guiding properties, related to the geometric characteristics of the air holes in their cross-section and have been successfully exploited in different applications [1, 2]. Most of the air holes in the PCFs cladding have been arranged either in a periodic triangular or periodic square orientation. The modal properties, in particular, and the dispersion properties of the above types of PCFs can be altered by varying the hole-to-hole spacing ( ) and the air hole diameter ( ) with air-filling fraction being [3, 4]. Both types of PCFs with a silica background can be successfully implemented to compensate the positive dispersion parameter and dispersion slope of the existing inline fibers [3, 4]. These fibers can be engineered for designing ultraflattened near-zero dispersion [5–7] or can be engineered to have ultranegative dispersion values near the communication wavelength [8–10]. Recently, there have been new types of cross-sectional geometry where air holes are
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