A method of constructing an electronic circuit assembly comprises forming a circuit board having first and second sets of circuit layers and an internal optically transmissive layer, sandwiched between the first and second sets of circuit layers. Holes are formed through the first set of circuit layers...http://www.google.se/patents/US5408568?utm_source=gb-gplus-sharePatent US5408568 - Electronic circuit board with internal optically transmissive layer forming optical bus
