Research On First-order Optical Temporal Differentiator Based On Double-clad And Twin-core Fiber

Optical signal processing,which could overcome the "electronic bottleneck",is one of key technologies to achieve all-optical network.It enables fast signal processing directly in optical domain.Optical signal processing technology has been widely applied.As one of the most important devices in optical signal processing,the optical temporal nth-order differentiator provides the nth-order derivative of the optical signal.In this thesis,the double-clad and twin-core fiber is proposed.And the mode field matrix,the eigenvalue equations,the propagation properties and the dispersion of the double-clad and twin-core fiber are discussed.An optical temporal first-order differentiator based on the double-clad and twin-core fiber is proposed.Several characteristics of the proposed differentiator,including the 3dB bandwidth,error factor and energy efficiency,have been investigated in details.The main research achievements are summarized as follows:(1)The optical signal processing,as one of key technologies to realize the all-optical network,has been reviewed.Current optical temporal differentiators are introduced and compared.(2)A double-clad and twin-core fiber is proposed.The propagation properties of the twin-core fiber under the complete coupling and incomplete coupling conditions are analysed.The mode field matrix and the eigenvalue equations of the double-clad and twin-core fiber are obtained under complete coupling condition.The propagation properties and the dispersion of the double-clad and twin-core fiber under the complete coupling condition are discussed.The results show that,the dispersion values roughly linearly vary with wavelength.The propagation constant reduces with increasing the input wavelength,inner-cladding radius and refractive index difference.While the propagation constant increases as the core radius increases.Moreover,compared to the conventional twin-core fiber,the double-clad and twin-core fiber offers higher propagation constant.The conclusion obtained in this paper provides an important theoretical basis for the proposed design of the first-order optical temporal differentiation based on double-clad and twin core fiber.(3)An optical temporal first-order differentiator based on double-clad and twin-core fiber is proposed.The 3dB bandwidth,error factor and energy efficiency of the optical temporal first-order differentiator is analyzed.And the capability of the optical temporal first-order differentiator for the derivative of the Gaussian pulse signal is verified.The results present that the tunability of central frequency of differentiator can be realized by choosing appropriate fiber length,as the central frequency reduces as fiber length increases.The 3dB bandwidth of the proposed differentiator reduces with increasing the inner-cladding radius and refraction index difference.The maximum 3dB bandwidth of the differentiator is 1.775THz,and is higher than the maximum 3dB bandwidth of the first-order optical temporal differentiator based on the twin-core fiber.Furthermore,when the input Gaussian pulse's attenuation factor is 0.5ps,the minimum error factor is 0.00997.