Publications
Anatomy of an transparent optical circulator
An optical circulator is a multi-port, nonreciprocal device that routes light from one specific port to another. Optical circulators have at least 3 or 4 ports, up to 6 port possible (JDS Uniphase, Huihong Fiber) Circulators do not disregard backward propagating light, but direct it to another port. Optical circulators are commonly found in bi-directional transmission systems, WDM networks, fiber amplifiers, and optical time domain reflectometers (OTDRs). 3-Port optical circulators are commonly used in PDV systems. 1550 nm laser light is launched into Port 1 and will exit out of Port 2 to the target. Doppler-shifted light off the moving surface is reflected back into Port 2 and exits out of Port 3. Surprisingly, a circulator requires a large number of parts to operate efficiently. Transparent circulators offer higher isolation than those of the reflective style using PBSs. A lower PMD is obtained using birefringent crystals rather than PBSs due to the similar path lengths between e and o rays. Many various circulator designs exist, but all achieve the same non-reciprocal results.