Interferometry was first developed in the radio regime to overcome the low angular resolution of single telescopes. For decades the radioband remained the only one in which this technique could be employed, because it was - due to the long wavelength of radio waves - the only band in which such observations could be technically mastered. Only recently, since the late 1990ies, interferometry is feasible in the near-infrared and lately also the optical waveband.
Due to the difference in wavelengths between radio and optical waves, baselines (i.e. separations between telescopes) of a few hundred meters give optical interferometers the ability to resolve similar details on the sky as radio VLBI with maximum baselines of thousands of kilometers.
Fringes, i.e. interference patterns, have to my knowledge so far been observed with the following optical/NIR observatories:
- Very Large Telescope Interferometry (VLTI)
- Sydney University Stellar Interferometer (SUSI)
- Center for High Angular Resolution Astronomy
external link) interferometer
Optical/IR interferometer with 6 1-m telescopes and a maximum baseline of 330 m on Mount Hopkins, AZ, USA
- Harvard Smithsonian Center for Astrophysics' Infrared
Optical Telescope Array
external link) Michelson interferometer
Optical/IR interferometer with 3 45-cm collectors and a maximum baseline of 38 m on Mount Hopkins, AZ, USA
I am quite sure that others will follow soon - by the time this page is written, it might already be outdated...
An introduction to interferometry is available here.