Alfalight Inc., a Madison, Wisc., manufacturer of diode lasers, announced that it has named Sanetronic Co. Ltd. as its distributor in China. Sanetronic, based in Kowloon, Hong Kong, is an international distributor of electronic components with offices throughout China.    . . .    NanoOpto Corp. was chosen as one of the Top Picks for 2005 Early Stage companies at the NSTI Nanotech Ventures Conference, held this month in Anaheim, Calif. NanoOpto, of Somerset, N.J., is applying nanofabrication technology to the design and manufacture of nano-optic devices for optical components and systems.