Abstract
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.
Highlights
Transformation optics (TO) provides a systematic method to manipulate light propagation by exploiting spatial mappings and distributions of constituent materials.[1,2] Based on the property that Maxwell’s equations are invariant under coordinate transformations, TO represents a powerful new design tool in controlling the trajectory of light and creating novel devices, such as invisibility cloaks,[3] field concentrators[4] and perfect ‘black hole’ absorbers.[5]
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
We introduce the concept of a new type of photonic integrated circuit, as shown in Figure 1, which consists of QCTO elements that can perform a variety of functions, such as light collimation, bending and coupling
Summary
Transformation optics (TO) provides a systematic method to manipulate light propagation by exploiting spatial mappings and distributions of constituent materials.[1,2] Based on the property that Maxwell’s equations are invariant under coordinate transformations, TO represents a powerful new design tool in controlling the trajectory of light and creating novel devices, such as invisibility cloaks,[3] field concentrators[4] and perfect ‘black hole’ absorbers.[5] The important class of embedded coordinate transformations[6] stands out by allowing discontinuities along transformation media boundaries This unique property has facilitated the development of some of the more practical, but remarkable TO devices, including reflectionless beam bends and splitters,[7] polarization rotators[8] and various flat lenses.[9,10,11] Despite the many innovative applications, materials designed using TO are generally complex, exhibiting significant anisotropy and spatial dependence.[12,13] Recent progress on metamaterials promises a pathway for constructing TO devices; the associated absorption loss and limited bandwidth remain as major challenges for their practical application. Nearly-isotropic gradient index (GRIN) materials with broad bandwidth and low losses can be employed, leading to functional QCTO devices, such as carpet cloaks and transformed Luneburg lenses in both the microwave and optical wavelength regimes.[14,15,16,17,18,19,20,21,22,23]
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