Propagation Characteristics of Ethanol Doped Photonic Crystal Fiber

Six PCFs structure with different geometrical shape of holes in the cladding region and with different wafer have been investigated. Three structures A, B and C have silica as wafer where as other structure D, E and F have lead silicate as wafer. Structures consists of holes in the cladding region with circular and elliptical geometry. Four structures are partly filled with ethanol and other two structures have all holes filled with air. Two structures reports anomalous dispersion behaviour. Besides other structures reports zero dispersion. Almost all structures reports high birefringence along with low confinement loss. One structure shows highest nonlinearity compared to others. Besides these other propagation characteristics have also been studied. KeywordPhotonic crystal fiber, birefringence, dispersion, effective mode area.

confinement loss. These losses can be reduced by increasing the contrast of refractive index between core and cladding region. Researchers have made efforts to minimize such losses [18]. Endlessly single mode propagation offered by PCF makes them much preferable for transmission over conventional optical fiber in optical communication system [19].
Six PCFs structure with different geometrical shape of holes in the cladding region have been investigated. Structures A, B and C have silica as wafer where as structure D, E and F have lead silicate as wafer. Structures consists of holes in the cladding region with circular and elliptical geometry. Two structures have all holes filled with air. Other structures have ethanol filled in either circular or elliptical holes. Intention is to study the propagation characteristics of light in structures with different materials as wafer and also with different geometry. Out of the investigated six structures, two structures reports anomalous dispersion behaviour. Besides other structures reports zero dispersion. Almost all structures reports high birefringence along with low confinement loss.
II. THEORY AND DESIGN We have simulated three structures with lead silicate as wafer and three structures have silica as wafer. Lead silicate has refractive index 1.80 and silica has 1.45. Structure A have all the holes filled with air. Structures B have circular holes filled with air and elliptical holes filled with ethanol. Structure C has circular holes filled with ethanol and elliptical holes filled with air. Similar to Structure A, B and C, structure D, E and F have same dimension except wafer with lead silicate instead of silica. Intention is to study and compare the behaviour of light in process of different material with that of air. Also the effect of variation in geometry of holes in the cladding region is investigated. Transverse section of the designed PCFs has been shown in Fig. 1 (a). Designed consists of seven ring of holes in the cladding region. Structure is chosen such that it has exterior three rings with holes of circular dimension. Inner most four rings have holes with elliptical geometry. Both elliptical and circular geometry have equal area. The birefringence of the fiber is often measured as the difference of two polarization modes propagation in the fiber [20].
Birefringence can also be obtained from the beat length. Asymmetric core and effective index contrast between orthogonal polarized modes are two important parameter considered to reactive birefringence of a fiber. Asymmetrical core can be achieved by varying the diameter of holes near core. The same can be achieved by altering the shape of the holes or a defect in the centre of the core can be introduced in this regard. Material dispersion and waveguide dispersion together contributes to chromatic dispersion. It can be controlled by varying diameter of holes facing core in the cladding region, and by varying number of holes in the cladding region. Moreover dimension of holes in the cladding region also effects dispersion. It can be calculated as [21] Where  represents wavelength and ( ) e eff R n is real part of effective refractive index.
Lower effective mode area results high non-linearity. Area occupied by the fundamental mode inside the fiber is termed as effective mode area and is obtained by [22] 2 2 4 ( , ) Effective mode area of a fiber is inversely proportional to its Non-linearity. It can be determined by using [22]: Increase in the number of holes filled with air results the mode to be more confined inside the core. It results reduction in leakage loss. However as the modes spread out of the core with increase in wavelength, it also results increase in loss [22] Where  is the hole pitch,  is the wavelength in vacuum, the core n is the refractive index of core which is Silica and eff n is the effective refractive index.

III. SIMULATION AND RESULTS
All A full vector module of Opti-FDTD software have been used for simulation. TBC (transparent boundary condition) surround the core-cladding region and it has been consider to report optimized result. Wafer is made of silica with refractive index 1.45 and Lead silicate with refractive index 1.80. Structure F having lead silicate filled holes with elliptical geometry reports the highest birefringence in comparison to rest all strutures. Structure A reports birefringence of the order 10 -3 , where as other structures reports birefringence of the order 10 -2 . Structure A, C, D and E reports zero dispersion at first and second optical windows. Moreover structure A and E shows ultra flattened dispersion. However structure C reports negative dispersion in the visible range. Even at a wavelength of 1.2 µm, obtained dispersion by structure C is nearly -170ps/nm-Km. On the other hand, Structure B and F shows anomalous behaviour. Dispersion observed by both structures is below 20 ps/nm-km.  Structure A, C, D and E reports very low loss. Loss for these sstructures is of the order 10 -6 . Structure B and F reports comparatively higher loss.  Effective mode area obtained for Structure F is the highest than other structures. However other structures also have high effective mode areas. Structure A has the lowest effective mode area. Thus Structure offers comparatively less non-linearity than structure A.  IV.CONCLUSION Thus, six PCFs structure with different geometrical shape of holes in the cladding region have been investigated. Structures A, B and C have silica as wafer where as structure D, E and F have lead silicate as wafer. Structures consists of holes in the cladding region with circular and elliptical geometry. Two structures have all holes filled with air. Other structures have ethanol filled once in circular and next in elliptical holes. Intention is to study the propagation characteristics of light in structures with different materials as wafer and with holes of different geometry. Two structures reports anomalous dispersion behaviour. Besides other structures reports zero dispersion. Almost all structures reports high birefringence along with low confinement loss. Hence all the structure is considered to be good for optical communication, optical devices, optical sensor and other linear as well non-linear application.