Direct all-optical programmability and circuit composition

Establish which forms of direct programming of linear-optical circuits by incoming optical light can be achieved using near-term classical optical platforms, thereby enabling optical composition of functions such as $f_2\circ f_1(x)$ without electro-optical conversion.

Background

The paper notes that composing single-variable functions, such as $f_2\circ f_1(x)$, would be useful, but the output of the presented optical circuit is itself optical and normally must be converted into an electrical signal before it can program subsequent linear-optical elements. This electro-optical conversion reintroduces the bottleneck that the architecture is intended to avoid.

The authors therefore leave unresolved whether near-term classical photonic platforms can support optical circuits that are programmable directly by incoming optical light. A solution would enable generalized all-optical computation and practical chaining of optical nonlinear-function modules.