RZ-OOK to NRZ-OOK format conversion based on a single fiber Bragg grating

All-optical format conversion is an important interface technology for future optical transparent networks that will include different formats [1,2] .For instance, with the conversion between return-to-zero (RZ) and nonreturn-to-zero (NRZ) formats, the optical communication system will be more robust and more flexible for use in different networks such as optical time division multiplexing and wavelength division multiplexing networks [3,4] .The conversion from RZ to NRZ can be realized using various schemes [5][6][7][8][9][10][11] .Among the reported schemes, the spectrum-tailoring-based converter is allpassive and very attractive compared with time-domain waveform processing based on active operation device.This is mainly owing to the advantages of the former such as the simplicity of the structure and stable performance [5][6][7][8][9][10][11] .Although fiber Bragg grating (FBG) is a versatile optical filter and has been used in some schemes, such as Mach-Zehnder interferometer cascaded narrow-band filter and optical fiber delay interferometer (DI) cascaded narrow-band filter [5][6][7][8]11] , it only plays a supporting role.In Ref. [12], FBG played a critical role.However, the FBG employed in this scheme is a uniform one, wherein the sidelobes of amplitude transfer function seriously affect the performance of format conversion.To reduce the influence of the FBG sidelobes, they have to choose either a weak FBG (the maximum reflectivity of 21%) or a strong FBG with an additional Gaussian optical band-pass filter with narrow bandwidth [12] , which means high insertion loss is inevitable in both cases.In other words, the filtering capability of FBG is not fully RZ-OOK to NRZ-OOK format conversion based on a single fiber Bragg grating