Integrated photonic systems based on transformation optics enabled gradient index devices

Integrated photonics is expected to play an increasingly important role in optical communications, imaging, computing and sensing with the promise for significant reduction in the cost and weight of these systems. Future advancement of this technology is critically dependent on an ability to develop compact and reliable optical components and facilitate their integration on a common substrate. Here we reveal, with the utility of the emerging transformation optics technique, that functional components composed of planar gradient index materials can be designed and readily integrated into photonic circuits. The unprecedented design flexibility of transformation optics allows for the creation of a number of novel devices, such as a light source collimator, waveguide adapters and a waveguide crossing, which have broad applications in integrated photonic chips and are compatible with current fabrication technology. Using the finite-difference time-domain method, we perform full-wave numerical simulations to demonstrate their superior optical performance and efficient integration with other components in an on-chip photonic system. These components only require spatially-varying dielectric materials with no magnetic properties, facilitating low-loss, broadband operation in an integrated photonic environment. Using transformation optics, researchers have built miniature gradient-index components for collimating, coupling and splitting light beams. Transformation optics is a popular theoretical approach for designing novel metamaterial-based photonic devices such as invisibility cloaks and perfect light absorbers. Qi Wu, Jeremiah Turpin and Douglas Werner from The Pennsylvania State University in the USA have now used transformation optics to design miniature gradient-index components. The small size and all-dielectric nature of these components means that they can be easily implemented by standard nanofabrication techniques such as silicon-on-insulator patterning, and are well-suited for integration with planar on-chip photonic systems. The researchers suggest that the approach could also yield nanoscale circuitry for controlling surface plasmons in applications such as optical communications, computing and sensing.