Laser radiation transfer through the optical rotary joint

Abstract

The transfer of radiation is often required between a fixed high power laser transmitter and a rotating or gimballed optical projection head. This can be achieved using a set of optical fibers, coupled to each other by small optical systems, at which continuous rotation can occur. We term this system an optical rotary joint. The ideal rotary joint should be efficient, compact, simple, and able to operate with large angles between source and receiver fibers. In this use the radiation transfer is between fibers of a diameter that is large compared to the wavelength, and is a problem in geometrical nonimaging energy concentration. The fiber to fiber radiation transfer process has a closer affinity to geometric imaging theory than, say, solar energy concentration, since the ray angles as well as positions are significant to en sure continued fiber transmission. The basic geometrical requirements for efficient transfer are developed, together with some theoretical limitations. The transfer efficiency of some single surface reflective and simple refractive optical systems is explored. A general method of computing the transfer efficiency using ray tracing is described, and a practical design of optical rotary joint is described in detail.