Fiber-optic dual-cylindrical wave sensor for measurement of wall velocity gradient in a fluid flow

A Young's fringe pattern created by two light waves emanating from a pair of slits has been used as the basis of a fiber-optic device for measuring the velocity gradients of flows near solid surfaces. This device is a variant of a dual-beam laser Doppler velocimeter, specialized to direct measurements of wall velocitygradients. A compact version of the device is described in which a fiber-polishing technique is employedfor fabrication of a two-point optical source consisting of two fiber cores separated by 18 µm. The light from this source is collimated and focused on two slits that are prepared through electron-beam lithography and that are 1 µm wide and 10 µm apart. Preliminary testing of the compact probe has been successful.