Coherent supercontinuum generation in all-normal dispersion Si₃N₄ waveguides

Abstract

Spectral broadening of optical frequency combs with high repetition rate is of significant interest in optical communications, radio-frequency photonics and spectroscopy. Silicon nitride waveguides (Si3N4) in the anomalous dispersion region have shown efficient supercontinuum generation spanning an octave-bandwidth. However, the broadening mechanism in this regime is usually attained with femtosecond pulses in order to maintain the coherence. Supercontinuum generation in the normal dispersion regime is more prone to longer (ps) pulses, but the implementation in normal dispersion silicon nitride waveguides is challenging as it possesses strong requirements in propagation length and losses. Here, we experimentally demonstrate the use of a Si3N4 waveguide to perform coherent spectral broadening using pulses in the picosecond regime with high repetition rate. Moreover, our work explores the formation of optical wave breaking using a higher energy pulse which enables the generation of a coherent octave spanning spectrum. These results offer a new prospect for coherent broadening using long duration pulses and replacing bulky optical components.

Supercontinuum in integrated photonics: generation, applications, challenges, and perspectives

“…However, the broadening for the ANDi SC was limited owing to the large value of GVD at the pump wavelength, such that the fs pump pulse quickly broadened along the propagation direction. In [ 81 ], the authors fabricated an optimized ANDi Si 3 N 4 waveguide, with a low and flat GVD value near 1550 nm ( Figure 10(e) ), based on a subtractive processing method [ 94 ]. Similar to [ 80 ], the cross-section of the waveguide is relatively large resulting in a γ less than 1 m −1 W −1 .…”

“…Panels (c) and (d) adapted from [ 80 ]. Panels (e) and (f) adapted from [ 81 ]. Panels (g) and (h) adapted from [ 82 ].…”

“…The potential of long and low dispersion waveguides was also recently validated for the controlled broadening of GHz pulses. In [ 81 ], the authors relied on a 20 cm long spiral Si 3 N 4 waveguide with low ANDi to coherently broaden a spectrum centered at 1550 nm. A span from 1525 to 1575 nm could be generated from a 0.5 ps pump pulse with a 25 GHz repetition rate, initially generated from simple electro-optic modulation.…”

“… Comparison of selected demonstrations of SCG in integrated platforms (Refs. from top to bottom of the figure: [ 15 , 25 , 28 , 35 , 55 – 60 , 81 , 82 , 129 ]). For each result, the width of the colored band indicates the bandwidth of the generated SC, the color indicates the type of platform, and the coupled peak power.…”

Mitigating waveguide loss in Ge–Sb–Se chalcogenide glass photonics

“…Specifically, lowloss silicon nitride waveguides have reached a remarkably low 0.014 dB cm −1 value, which represents the lowest record among all planar waveguide platforms [6]. The successful demonstration of ultra-low loss in silicon nitride waveguides soon promotes several striking technologies, such as selfinjection-locked turnkey soliton combs [7], highly coherent supercontinuums for tomography [8], and monolithic on-chip amplifiers [9].…”