Wide class of new fractal light sources [Invited plenary paper]

Pattern emergence in Naturepsilas complex systems is mostly attributed to a classic Turing instability. There, a single length-scale becomes dominant and this defines a simple emergent structure (for example, a striped or hexagonal pattern). We have investigated whether a multi-Turing instability may result in another universal type of pattern: fractals. Fractals possess proportional levels of detail across decades of length-scale, and are thus inherently scale-less. Here, we make the first predictions of spontaneous spatial fractal patterns in nonlinear ring cavities. This will include the first reported spatial optical fractals arising from purely-absorptive nonlinearity. Analyses reveal characteristic (multi-Turing) spectral features for both dispersive and absorptive cavities. Simulations verify and quantify the fractal properties of the spontaneously-patterned light. Our findings greatly widen the scope for potential realization and exploitation of fractal light sources. In Nature-inspired device and system architectures, such sources are likely to play a pivotal role in developments