PCF can be analyzed by effective-refractive-index method, multipole method, local mode expansion method, finite element method (FEM), finite difference time domain (FDTD) method, and so on.
Let us consider the fundamental configuration of single defect core/triangular lattice clad. Based on the core-clad system, typical structural parameters of PCF are explained below. Provided the air hole pitch, Λ, the air hole diameter, d, as shown in Fig., the core diameter, D, and the porosity, F, are expressed by the following equations.
The porosity, F , is the rate of air to highly-refractive medium. The ratio of air hole diameter to to the pitch, d/Λ, is often used as a standardization parameter of structure, since d/Λ is relevant to effective refractive index of the clad.The ratio of pitch to the wavelength, Λ/λ, represents the standardization frequency. By appropriately tuning these parameters, we design various types of optical fibers, featured by wideband SM operation, high nonlinearity, polarization maintaining, or low bending loss, superior to a typical one. In PCF, the refractive index difference between core and clad, the effective refractive index, can be tuned relatively freely and largely compared with a typical optical fiber.
In manufacturing PCF, general methods such as modified chemical vapor deposition (MCVD) method and vapor-phase axial deposition (VAD) method are not available, since PCF has air holes. Stack-and-Draw (capillary) technique and drilling technique are often used. Refer to the citation for more details.
Fig. Cross-section structure of photonics crystal fiber