Design of all-optical temporal dif ferentiator using a Moire fiber grating

Abstract

We design and demonstrate an all-optical temporal differentiator based on a simple Moiré fiber grating operated in reflection. The simulation results prove that a single Moiré fiber grating with only one π-phase shifted point can act as the first-order temporal differentiator and that a Moiré fiber grating incorporating two symmetrical π-phase shifted points can act as the second-order temporal differentiator. A practical Moiré fiber grating is fabricated, thereby proving that such a grating can act as the first-order temporal differentiator. Our results verify the feasibility, flexibility, and accuracy of the proposed method.OCIS Recently, all-optical circuits implemented for all-optical computing and signal processing have attracted significant attention due to the exponential development of photonics technologies. Such devices operated in the optical domain can provide a wider bandwidth and higher operating speed than devices operated in the conventional-electronics-based system. One of the fundamental devices, the temporal differentiator, has been designed and researched by several groups. A temporal differentiator can transform the field complex profile of an optical signal to its differential signal immediately. Aside from applications in the all-optical computing and signal processing fields, a temporal differentiator has a wide variety of applications in other areas, such as pulse characterization [1,2] , femtosecond pulse shaping [3,4] , ultrashort pulse train generation [5] , and high-speed optical communication [6] . Currently, several technologies have been proposed to realize a temporal differentiator theoretically and experimentally. In general, these reported temporal differentiators can be classified into two categories: incoherent and coherent [7] . Incoherent optical differentiators based on cross-gain modulation in a semiconductor optical amplifier have been reported since 2007 [8,9] . The incoherent optical differentiator operates on the optical intensity, instead of the field complex profile, of an initial optical signal. Many methods have been proposed to realize the coherent optical differentiator, including the use of silicon micro ring resonator [10] , long-period fiber grating (LPFG) [11,12] , and optical interferometer [13] . The silicon micro ring resonator can offer an operational bandwidth in the tens of gigahertzs [10] , whereas the experimentally proven differentiator based on LPFG offers operational bandwidth up to many terahertzs. However, the longperiod fiber grating is extremely sensitive to environmental changes [7,14] . In addition integral differentiator (the differentiation order is an integer) and fractional differentiators have been proposed since 2008, including the use of a Mach-Zehnder interferometer [15] , LPFG [16] , and tilted fiber grating [17] . The differentiation order can be continuously adjusted when the tilted fiber grating acts as a fractional differentiator [17] . High-order temporal differentiator can be obtained by concatenating a linearly chirped fiber ...