The formation and manipulation of ultrashort pulses on chip would be of great interest to ultrafast optics and integrated photonics. One of the important issues is dispersion-assisted nonlinear interactions of broadband frequency components. In this paper, we show for the first time that a bilayer waveguide for quasi-TE mode produces a quite flat and saddleshaped dispersion profile. Different from previously reported TE-mode waveguides with flattened dispersion, the proposed waveguide exhibits a greatly simplified structure with no need for a high-aspect-ratio slot and has quite small group delay difference in a wide spectral range with four zero-dispersion wavelengths (ZDWs). For the first time we study supercontinuum generation in hybrid dispersion regime, in which the broadened spectrum covers a bandwidth with all ZDWs. It is found that one can obtain greatly improved spectral flatness in supercontinuum generation, with a power variation as small as 3 dB over a bandwidth of <500 nm. Moreover, the proposed waveguides are particularly suitable for low-distortion pulse propagation over a long distance, which is important for on-chip ultrashort pulse delivery.
Dispersion engineering in integrated waveguides and microresonators has been intensely studied in recent years. The main focus is to achieve desirable adjustment of dispersion value, slope, bandwidth and flatness, which is important for broadband nonlinear applications. Dispersion has been viewed as a control knob to leverage the parameter space provided by high-index-contrast on-chip devices, enabling strong interactions of far apart frequency components over an octavespanning bandwidth. Here, we review recent advances in dispersion engineering in integrated waveguides and microresonators based on various material platforms, with an emphasis on their applications in mid-infrared (IR) photonics.
Photonic integrated circuits suffer from a thermal drift of device performance, which is a key obstacle to the development of commercial optoelectronic products. Temperature-insensitive integrated waveguides and resonators have been demonstrated at a single wavelength, using materials with a negative TOC, which are not suitable for WDM devices and wideband nonlinear devices. Here, we propose two waveguides to realize the generation of broadband athermal features. For one of them, the temperature-insensitivity over a bandwidth of 780 nm (1280 to 2060 nm) with an ultra-small effective-TOC within is ±1×10-6/K. Uniquely, the waveguide has small anomalous dispersion (from 66 to 329 ps/nm/km) over the same band and is suitable for frequency comb generation without being affected by intra-cavity thermal dynamics. We also show another waveguide design with an effective-TOC variation of ±1×10-6/K over a bandwidth of 1060 nm, from 1220 to 2280 nm. The obtained dispersion varies from -232 to -502 ps/nm/km over the same band, which can be used in nonlinear devices.
In this work, we show the possibility of combining grating couplers and mode converters, both with a high efficiency. The proposed devices are very compact with no extra fabrication efforts required. We have shown that the LP01, LP11a, LP11b and LP21b modes in an optical fiber can be successfully excited directly from the proposed grating couplers, which have the fundamental mode as an input from an integrated waveguide. It is shown the overall efficiency could be as high as 50%.
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