The article puts the lack of development down to technology but it's arguably the lack of applications that came first. We've developed solutions for most of the spectrum (anything below cosmic gamma rays) because we needed to and the tech followed. As we find applications it will follow.<p>Also, not to be pedantic but about the terminology, the spectrum below the terahertz range is generally called radio (with optical or light for above it) not 'electronic', while the technology for producing frequencies above it is called photonics (with electronics for below it), not 'optics'.