Desirable material properties for all-optical χ (3) nonlinear chips are a high Kerr nonlinearity and low linear and nonlinear losses to enable high four-wave mixing (FWM) efficiency and parametric gain. Many material platforms have been investigated showing the different trade-offs between nonlinearity and losses [2][3][4][5][11][12][13][14][15][16] . In addition to good intrinsic material properties, the ability to perform accurate and high yield processing is desirable in order to integrate additional functionalities on the same chip and also to decrease linear losses. Silicon-on-insulator is the model system for integration 2 . It supports a large index contrast and shallow etch depths, enabling patterning submicron structures with smooth sidewalls. However, due to two-photon absorption (TPA) at telecom wavelengths, 19 . Its bandgap can be tailored in such a way that TPA, which is the main detrimental effect for the FWM process, is mitigated and at the same time, the three-photon absorption is low 10 while a high material nonlinearity is maintained. Over the past two decades, efforts have been made to realize efficient nonlinear processes in AlGaAs waveguides [17][18][19] . However, the fabrication of such waveguides with very high and narrow mesa structures becomes very challenging and prevents advanced designs that go beyond simple straight waveguides. In addition, the low vertical index contrast of such waveguides limits the effective nonlinearity.To enhance light confinement and relax the etching process requirements, we propose an AlGaAs-on-insulator (AlGaAsOI) platform as shown in Fig. 1a. In this layout, a thin AlxGa1-xAs layer on top of a low index insulator layer resides on a semiconductor substrate. Wafer bonding and substrate removal are used to realize the structure. In this letter, the aluminium fraction (x) is 17%, which makes the material bandgap 1.63 eV and the refractive index 3.33. Thanks to the large index contrast (~55%) of this layout, light can be confined in a sub-micron waveguide core. As the nonlinear parameter (γ) is highly dependent on the waveguide effective mode area (Aeff) as expressed 2 by γ=2πn2/λAeff, an ultra-high effective nonlinearity of about 660 W -1 m -1 , which is orders of magnitude higher than that of a typical Si3N4 waveguide 5 , can be obtained for an AlGaAsOI waveguide using a cross-section dimension of 320 nm×630 nm (see Methods). In addition, the waveguide dispersion dominates over material dispersion for subwavelength sized waveguides and therefore the group velocity dispersion (GVD) can be engineered from the normal dispersion of bulk material to anomalous dispersion (Fig. 1b), which is required to achieve parametric gain in nonlinear processes in the under-coupled regime and its transmission is shown in Fig. 2c for the transverse electric (TE) mode. Only one mode family with a free spectral range (FSR) of ~0.82 nm (98 GHz) is observed in the spectrum, which implies that the resonator waveguide with anomalous dispersion can be operated in a single-mode state....

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Abstract:We propose hydrogenated amorphous silicon nanowires as a platform for nonlinear optics in the telecommunication wavelength range. Extraction of the nonlinear parameter of these photonic nanowires reveals a figure of merit larger than 2. It is observed that the nonlinear optical properties of these waveguides degrade with time, but that this degradation can be reversed by annealing the samples. A four wave mixing conversion efficiency of + 12 dB is demonstrated in a 320 Gbit/s serial optical waveform data sampling experiment in a 4 mm long photonic nanowire.

Four‐wave mixing (FWM) is a versatile optical nonlinear parametric process that enables a plethora of signal processing functionalities in optical communication. Realization of efficient and broadband all‐optical signal processing with ultra‐low energy consumption has been elusive for decades. Although tremendous efforts have been put into developing various material platforms, it has remained a challenge to obtain both high efficiency and broadband operation. Here, an aluminum gallium arsenide nonlinear chip with high FWM conversion efficiency per length per pump power and an ultra‐broad bandwidth is presented. Combining an ultra‐high material nonlinearity and strong effective nonlinear enhancement from a high‐index‐contrast waveguide layout, an ultra‐high conversion efficiency of −4 dB is obtained in a 3‐mm‐long nano‐waveguide. Taking advantage of high‐order dispersion, a scheme is presented to realize an ultra‐broad continuous conversion bandwidth covering 1280–2020 nm. A microresonator is also utilized to demonstrate a conversion efficiency enhancement gain of more than 50 dB with respect to a waveguide device, which significantly reduces the power consumption. Moreover, wavelength conversion of an optical serial data signal is performed at a bit rate beyond terabit‐per‐second, showing the capabilities of this III‐V semiconductor material for broadband optical signal processing.