Inverse design and demonstration of a compact and broadband on-chip wavelength demultiplexer

LETTERS

PUBLISHED ONLINE: 11 MAY 2015 | http://dx.doi.org/10.1038/nphoton.2015.69

Web End =DOI: 10.1038/NPHOTON.2015.69

Inverse design and demonstration of a compact and broadband on-chip wavelength demultiplexer

Alexander Y. Piggott, Jesse Lu, Konstantinos G. Lagoudakis, Jan Petykiewicz, Thomas M. Babinec and Jelena Vukovi*

Integrated photonic devices are poised to play a key role in a wide variety of applications, ranging from optical interconnects1 and sensors2 to quantum computing3. However, only a small library of semi-analytically designed devices is currently known4. Here, we demonstrate the use of an inverse design method that explores the full design space of fabricable devices and allows us to design devices with previously unattainable functionality, higher performance and robustness, and smaller footprints than conventional devices5. We have designed a silicon wavelength demultiplexer that splits 1,300 nm and 1,550 nm light from an input waveguide into two output waveguides, and fabricated and characterized several devices. The devices display low insertion loss (2 dB), low crosstalk (<11 dB) and wide bandwidths (>100 nm). The device footprint is 2.8 2.8 m2, making this the smallest dielectric wavelength splitter.

Electronic hardware description languages such as Verilog and VHDL are widely used in industry to design digital and analogue circuits6,7. The automation of large-scale circuit design has enabled the development of modern integrated circuits that can contain billions of transistors. Photonic devices, however, are effectively designed by hand. The designer selects an overall structure based on analytic theory and intuition, and then ne-tunes the structure using brute-force parameter sweep simulations. Due to the undirected nature of this process, only a few degrees of freedom (two to six) are available to the designer. The eld of integrated photonics would be revolutionized if the design of optical devices could be automated to the same extent as circuit design.

We have previously developed an algorithm that can automatically design arbitrary linear optical devices5. Our method allows the user to design by specication, whereby the user simply speci-es the desired functionality of the device, and the algorithm nds a structure that meets these requirements. In particular, our algorithm searches the full design space of fabricable devices with arbitrary topologies. These complex, aperiodic structures can provide previously unattainable functionality, or higher performance and smaller footprints than traditional devices, due to the greatly expanded design...