Protecting a power-laser diode from retroreflections by means of a fiber /spl lambda//4 retarder

A quarter-wave retarder made by a small loop of fiber on the laser pigtail is an effective means to protect the laser from retroreflections. Suppression factors of about 20 dB have been achieved with negligible insertion losses. An example of application is given. A method to measure the isolation is also presented.