Lossless linear wave propagation is symmetric in time, a principle which can be used to create time reversed waves. Such waves are special “pre-scattered” spatiotemporal fields, which propagate through a complex medium as if observing a scattering process in reverse, entering the medium as a complicated spatiotemporal field and arriving after propagation as a desired target field, such as a spatiotemporal focus. Time reversed waves have previously been demonstrated for relatively low frequency phenomena such as acoustics, water waves and microwaves. Many attempts have been made to extend these techniques into optics. However, the much higher frequencies of optics make for very different requirements. A fully time reversed wave is a volumetric field with arbitrary amplitude, phase and polarisation at every point in space and time. The creation of such fields has not previously been possible in optics. We demonstrate time reversed optical waves with a device capable of independently controlling all of light’s classical degrees of freedom simultaneously. Such a class of ultrafast wavefront shaper is capable of generating a sequence of arbitrary 2D spatial/polarisation wavefronts at a bandwidth limited rate of 4.4 THz. This ability to manipulate the full field of an optical beam could be used to control both linear and nonlinear optical phenomena.

We present a new technique allowing the fabrication of large modal count photonic lanterns for space-division multiplexing applications. We demonstrate mode-selective photonic lanterns supporting 10 and 15 spatial channels by using graded-index fibres and microstructured templates. These templates are a versatile approach to position the graded-index fibres in the required geometry for efficient mode sampling and conversion. Thus, providing an effective scalable method for large number of spatial modes in a repeatable manner. Further, we demonstrate the efficiency and functionality of our photonic lanterns for optical communications. Our results show low insertion and mode dependent losses, as well as enhanced mode selectivity when spliced to few mode transmission fibres. These photonic lantern mode multiplexers are an enabling technology for future ultra-high capacity optical transmission systems.

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