Si3N4 microring (MR) stands out as a promising platform in the integrated photonics for optical filter, optical delay lines, generation of Kerr frequency comb and optical computing. In this work, we study the optical temporal differentiation in a designed Si3N4 MR array. In order to avoid the limitations of a single MR, which can not reproduce the third peak at the trailing edge when differentiation order is between 1 and 2, a MR array consisting of two add-drop MRs and one all-pass MR is designed. Simulation results show that by reusing the drop port of add-drop MRs, differential orders between 0 to 2 can be obtained from different output ports. Furthermore, we propose an optimization algorithm to select the parameters of MRs. As a result, the differentiation deviations for 4-ps input Gaussian pulse can be minimized when the interior-point method is employed. Calculation results show that the differentiation deviations for orders between 1 and 2 are reduced to around 10%, and for orders between 0 to 1 are reduced to within 33%.
A strip titanium dioxide (TiO2) waveguide is designed for highly coherent mid-infrared (MIR) supercontinuum (SC) generation. For the designed TiO2 waveguide, three zero-dispersion wavelengths (ZDWs) are obtained through adjusting the waveguide structure parameters. The three ZDWs are located at 1.53, 3.96, and 5.43 μm, respectively. The nonlinearity coefficient γ is calculated as 1.12 W − 1 m − 1 at wavelength 3.1 μm. By optimizing the pump pulse parameters, the highly coherent MIR SCs are generated when the hyperbolic secant pump pulse with a duration of 80 fs, peak power of 1 kW, and wavelength of 3.1 μm is launched into the TiO2 waveguide and propagated 4.2-mm in length. The obtained SC covers a wavelength range from 1.71 to 9.90 μm (more than 2.5 octaves). Our research results can find important applications in MIR photonics and spectroscopy, biophotonics, optical precision measurement, etc.
Soliton solutions of the Haus master equation and the transverse wave equation are discussed. These solutions are obtained by converting the eigenvalue problem of a differential operator into an algebraic problem. Compared to free space solutions of the respective equation, the solutions space shrinks to discrete soliton solutions, which often strongly deviate from the well-known bell-shaped free space solutions. We find qualitatively very similar solutions describing two very different physical scenarios. As these solitons show a similar reaction to a limited support in the Fourier domain, we term these characteristic profiles cage solitons.
A spectral economized scheme for optical quantization is proposed by using cascaded unbalanced Mach–Zehnder modulators (UMZMs) to introduce phase differences between two arms. Less spectra are needed in this scheme since the period of sampling pulse can be modulated to be larger. Simulation results show that the effective number of bits (ENOB) reaches 4 when only 2 additional wavelengths and 4 periods are employed, in contrast to the 15 additional wavelengths required by traditional frequency quantization schemes. Larger NOB is predicated when more wavelengths are used in the quantization system. The influence of noise on ENOB is also studied. It is revealed that the timing and intensity jitters do not influence ENOB. Instead, the ultimate ENOB is limited by the largest phase difference introduced by UMZMs. The proposed scheme can be used in both low- and high-resolution optical quantizers, indicating promising spectrum economized applications for future optical circuits.
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