SpectraSwitch said Friday that it has raised $6 million as an extension of its earlier second round of funding. Advanced Technology Ventures and NIF Ventures led the financing. With the $6 million, Santa Rosa, Calif.-based SpectraSwitch has raised $24.1 million in its second round, which initially closed in May last year. SpectraSwitch designs and manufacturers optical switching components and components that change the intensity of fiber-optic light. The company has raised a total of $29 million.