SriRaman Kannan

Thermal stability analysis of UV-induced fiber Bragg gratings

The phenomenon of decay in UV-induced Bragg gratings is examined. Thermal stability of gratings with large and small index changes are studied and compared. The role of stabilization in enhancing the thermal stability of gratings is explained. Approaches to analyzing and predicting grating decay are reviewed and compared.

Thermal stability of optical add/drop gratings for WDM systems

One important application for fiber Bragg gratings is add/drop multiplexing for wavelength-division multiplexing (WDM) systems. This application puts a very stringent requirement on the grating rejection bandwidth and its spectral profile. Standards for these components also require that the grating characteristics be stable for up to 25 years at normal operating temperatures. It has been established that the decay rate of UV-induced refractive index change depends strongly on the temperature that the grating is exposed to. However, a relationship between the decay rate and the temperature found for one type of grating does not necessarily apply to other types of gratings. The fact that different decay rates are reported in different studies for apparently similar gratings indicates that the index decay depends strongly on the fiber material property and the inscribing techniques. This report presents the thermal reliability of add/drop gratings developed for WDM systems.

Thermal reliability of Bragg gratings written in hydrogen-sensitized fibers

Summary form only given. In this work, the thermal reliability of gratings in hydrogen-loaded fibers is studied. It is known that the refractive index modulation in the fiber core is caused by UV-generated defects in the fiber core. It may, hence, be expected that a thermally induced decrease in concentration of the defects that are responsible for the refractive index change would also reduce the UV-induced index modulation, which in turn would decrease the spectral width in strong gratings.

Analysis of recovery in radiation-induced loss in rare-earth-doped fibers through master curve/demarcation energy diagrams

Radiation-induced losses in rare-earth-doped fibers are analyzed in a novel manner. The mastercurve approach is used for analyzing stability of defects induced by radiation. This method can be applied to examine fibers for space applications.

Reliability of long-period gratings

Summary form only given. Ever since their conception in 1996, long-period gratings (LPGs) have come to be used in a wide variety of applications. LPGs involve coupling of core and cladding modes. The importance of thermal stabilization techniques for successful use of Bragg gratings is now well acknowledged. This is even more important in LPGs, because the wavelength at which the coupling from the core to the cladding modes takes place is directly dependent on the UV-induced refractive-index change (/spl Delta/n/sub UV/) and on n/sub core/-n/sub clad/ (/spl Delta/n). A decrease in these can greatly shift the spectra in a LPG. For example, thermal conditions that cause a 2% decrease in n/sub UV/ would have a negligible effect in a add/drop wavelength-division multiplexed (WDM) Bragg grating (/spl Delta//spl lambda/<10 picometers) but a similar decay in the case of a LPG would shift its center wavelength by about 0.5 nm, which is unacceptable for most applications (such as gain equalizers). In this paper, we present a method to analyze and predict LPG decay. Using our analysis method we have arrived at stabilization conditions yielding LPGs with predicted end-of-life (25 years) shifts of <0.02 nm at 40/spl deg/C and <0.12 nm at high aggressive conditions (60/spl deg/C).

Reliability Assessment of Optical Fibers and Fiber Gratings

The topic of reliability of UV-induced fiber gratings is reviewed. Approaches to assess and predict changes in optical properties of fiber gratings due to thermal decay of refractive index modulation are presented and compared. The mastercurve/demarcation energy diagram approach is shown to be a powerful and general method for the purpose. The process of thermal stabilization to obtain gratings with superior stability is delineated. It is shown that the mastercurve approach could be used to analyze other reliability problems such as in predicting hydrogen-induced losses in fibers.