Tapered and linearly chirped fiber Bragg gratings with co-directional and counter-directional resultant chirps

• New tapered and linearly chirped fiber Bragg gratings (TCFBGs) with co-directional and counter-directional chirps are presented.
• Effects of reduction and enhancement of grating chirp in TCFBGs are presented.
• Theoretical analysis and experimental results of presented structures are shown.
• Advantages of TCFBG over the already known tapered FBG with uniform periodicity and their potential applications are indicated.

A method of spectral width tailoring of tapered fiber Bragg gratings is theoretically analyzed and experimentally verified. This concept is based on inscription grating structures in which synthesis of chirps comes from both taper profile and a linearly chirped phase mask used for grating inscription. It is shown that under UV exposure and depending on the orientation of the optical fiber taper relative to the variable-pitch phase mask, tapered and linearly chirped fiber Bragg gratings (TCFBG) with resultant co-directional or counter-directional chirps are achieved. Thus, both effects, those of reduction and enhancement of the grating chirp, as well as their influence on the grating spectral response, are presented. In particular, using the above approach TCFBG with significantly narrowed spectral width are shown. Moreover, fused tapered chirped FBG with relatively large waist diameter are shown having broad spectrum, something that prior to now was not attainable using previously developed techniques.