Transistors aren't the only way to perform computations; it's been known for decades that many classes of problems are amenable to analog computation with optics.  The simplest example of this is a lens, which can be used to perform a Fourier transform.

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  Doing computations with free space optics is challenging, because the effort to align these systems scales nonlinearly with the number of elements.  And making such systems reconfigurable is incredibly challenging.  By contrast, bringing the large-scale integration of silicon photonics to bear on these problems may be a path to building useful optical computers.  Dr. Hochberg has been collaborating with Professor Dirk Englund's group to make this a reality.   This effort has spawned two startup companies:

Lightmatter, founded by Dr. Nicholas Harris, and

Lightelligence, founded by Dr. Yichen Shen.