1. Field of the Invention
The present invention relates to a photonic crystal fiber (PCF) preform and a photonic crystal fiber manufactured using the same.
2. Description of the Related Art
A photonic crystal fiber (PCF) is a special kind of optic fiber. A general single-mode optical fiber is made up of a core material which consists of glass and germanium or phosphorus. On the other hand, the photonic crystal fiber is made up of a single, solid and substantially transparent material 1, such as silica glass, and periodically spaced air holes 2 running along the fiber, as shown in FIG. 1. Difference in dielectric constant between the silica glass material 1 and the periodically spaced air holes 2 forms a photonic band gap, which serves to prevent movement of a ray in a specific direction as in an electronic band gap of a semiconductor. In other words, the ray passes through the photonic band gap only when the ray satisfies conditions under which it may pass through.
The photonic crystal fiber has many important technical properties. For example, the photonic crystal fiber may support a single mode over a wide range of wavelengths, and may provide a large mode region. Consequently, the photonic crystal fiber is capable of transmitting high optical power and providing large phase dispersion in a telecommunication wavelength of 1.55 μm. Furthermore, the photonic crystal fiber is increasingly used as a device for controlling nonlinearity or polarization. It is expected based on recent reports on these functions of photonic crystal fiber, that photonic crystal fiber will be widely applied to optical communication and optical-related industries in the near future.
A photonic crystal fiber must originate from a photonic crystal fiber perform, which is drawn into a photonic crystal fiber having an efficiently long length and retaining its
Generally, the photonic crystal fiber preform may have structures schematically shown in FIGS. 2a and 2b. 
The photonic crystal fiber preform of FIG. 2a is made up of a circular silica glass rod 10 and a plurality of circular air holes 11 longitudinally formed through the circular silica glass rod 10 in a photonic lattice structure. Index of refraction of the photonic crystal fiber preform with the above-stated construction is distributed as illustrated in FIG. 2b. 
The conventional photonic lattice structures, however, limit photonic crystal fiber preform design. Furthermore, the air holes may be deformed when being drawn into desired photonic crystal fibers. The photonic crystal fibers are, as a result, not manufactured according to the originally intended design. Also, the material constituting a core of the photonic crystal fiber is limited as to its properties.