  We present Simphony, a free and open-source software toolbox for abstracting
and simulating photonic integrated circuits, implemented in Python. The toolbox
is both fast and easily extensible; plugins can be written to provide
compatibility with existing layout tools, and device libraries can be easily
created without a deep knowledge of programming. We include several examples of
photonic circuit simulations with novel features and demonstrate a speedup of
more than 20x over a leading commercially available software tool.
