Design and construction of a fiber bundle connector using microlenses

A prototype of a multiway fibre bundle connector for astronomical applications is described. The connector provides for connection and disconnection in the fiber trains that feed an astronomical spectrograph. It also provides the more important function of converting the focal ratio from f/2 to f/5 because f/2 is too fast either for good transmission of light along a substantial length of fiber or for the input to typical astronomical spectrographs. The fiber bundle connector consists of 100 coupling fibers. It works over the full 0.9- to 1.8-mm wavelength range, and the chromatic aberration is well corrected in the design. The design principle and the construction of the connector are discussed. The measured coupling efficiency is up to 88%. The coupling efficiency is compared with a theoretical estimate, and good agreement is achieved. Possible further improvement is discussed.