Effect of Length and Apodization on Fiber Bragg Grating Characteristics

Fiber gratings have a growing impact on the fiber optic communication industry. The simulation result of the reflectance of the uniform and apodized fiber bragg grating (FBG) are presented. Various apodization technique is useful to reduce secondary lobes or side lobs of reflection spectrum of fibre bragg grating. The effect of FBG length and apodization profile are presented Fiber Bragg Gratings (FBGs) are most commonly used as wave- length selective reflector. Fiber Bragg gratings are spectral fil- ters based on the principle of Bragg reflection. They typically reflect light over a narrow wavelength range and transmit all other wavelengths. When light propagates by periodically alternating regions of higher and lower refractive index, it is partially reflected at each interface between those regions. If the pitch of the rating is properly designed, then all partial reflections add up in phase and can grow to nearly 100%, for a specific wavelength even if the individual reflections are very small. The condition for high reflection is known as Bragg condition. For all other wavelengths the out of phase reflec- tions end up cancelling each other, resulting in high transmis- sion. Fiber grating can be classified into two types. First one is Bragg Grating and another is Transmission Grating. Bragg grating favors coupling between travelling in opposite directions. They are also called reflection gratings or short-period gratings. On the other hand, in transmission grat- ings, coupling occurs between modes travelling in the same direction. Transmission gratings are also referred to as long period gratings. The reflected wavelength is mainly determined by the period of the grating. Most common applications of fiber gratings in fiber optic communications are as add-drop filters in WDM systems, gain flatteners and pump stabilizers for EDFA's, wavelength selective reflectors for Raman amplifiers, Dispersion compensa- tors for long-haul systems, encoder for CDMA systems.