In-fiber beam splitters for construction of in-line Michelson interferometers

We demonstrate optical fiber in-line Michelson interferometers based on two in-fiber beam splitters crossing the core of a single-mode fiber, fabricated by a femtosecond laser. The in-fiber beam splitter reflects part of the incident light to the air-cladding interface before being reflected back while passing the rest to travel along the fiber core. The two in-fiber beam splitters, air-cladding interfaces, and the cutting fiber end face together form a combined three in-line Michelson interferometers. This Michelson interferometer device is robust in mechanical strength, easy in fabrication, compact in size, and low in cost.