Stretching the spectra of Kerr frequency combs with self-adaptive boundary silicon waveguides

Abstract

Dispersion engineering of optical waveguides is among the most important steps in enabling the realization of Kerr optical frequency combs. A recurring problem is the limited bandwidth in which the nonlinear phase matching condition is satisfied, due to the dispersion of the waveguide. This limitation is particularly stringent in high-index-contrast technologies such as silicon-on-insulator. We propose a general approach to stretch the bandwidth of Kerr frequency combs based on subwavelength engineering of single-mode waveguides with self-adaptive boundaries. The wideband flattened dispersion operation comes from the particular property of the waveguide optical mode that automatically self-adapts its spatial profile at different wavelengths to slightly different effective spatial spans determined by its effective index values. This flattened dispersion relies on the squeezing of small normal-dispersion regions between two anomalous spectral zones, which enables it to achieve two Cherenkov radiation points and substantially broaden the comb, achieving a bandwidth between 2.2 and 3.4 μm wavelength. This strategy opens up a design space for trimming the spectra of Kerr frequency combs using high-index-contrast platforms and can provide benefits to various nonlinear applications in which the manipulation of energy spacing and phase matching are pivotal.

Enhancing Si3N4 Waveguide Nonlinearity with Heterogeneous Integration of Few-Layer WS2

“…According to the design of the waveguide structure (details in Methods), the waveguide in this experiment has a minimum of integrated dispersion near to the pump wavelength of 800 nm (Figure a), which makes it an ideal choice for characterizing the pulse broadening through the SPM process. The integrated dispersion can be expressed as , where β k is the k th order dispersion . By controlling the orientation of a half-wave plate, the TE mode of the waveguide is excited (details in the Supporting Information).…”

“…The integrated dispersion can be expressed as , where β k is the k th order dispersion. 31 By controlling the orientation of a half-wave plate, the TE mode of the waveguide is excited (details in the Supporting Information ). The pump pulse spectrum is characterized to have a fwhm of ∼13 nm.…”

“…Using the calculated waveguide dispersion profile, the nonlinear pulse propagation in the waveguides has been modeled with the generalized nonlinear Schrödinger equation in the frequency domain. ,, To better assess the influence of the WS 2 flake to the SiN waveguide, the finite length of the flake has been taken into account. We divide the device into three sections: one heterogeneous section with a WS 2 flake between two pristine SiN waveguides.…”

Silicon electro-optic modulators based on microscopic photonic structures: from principles to advanced modulation formats

“…Note that for a PCW-MZ modulator, the driving voltage will be higher if the device length is shorter (for a given group index), which is similar to a conventional MZ modulator. In addition, strained silicon [88] and the DC Kerr effect [89] have been shown to be beneficial for high-speed modulation, and a PCW-MZ slow-light modulator based on the DC Kerr effect is demonstrated [90]. The experimental results show that the device can achieve 112 Gb s −1 PAM4 modulations.…”

Silicon nitride-based Kerr frequency combs and applications in metrology

“…We usually select inorganic materials to provide a higher laser damage threshold. Furthermore, the flat dispersion regime of the material can be used to achieve anomalous modal dispersion via structural engineering of the waveguide, 41 , 42 increasing the total anomalous dispersion regime of the waveguide. Figure 3 illustrates the dispersion engineering with different parameters.…”