Polarization-independent in-line optical isolator with lens-free configuration

A fiber-embedded polarization-independent optical isolator that consists of an isolator chip, and thermally expanded core (TEC) fibers, and that has no lens elements was developed. The chip was made of birefringent crystal plates, rutile polarization-splitters, a quartz half-wave plate, and a Faraday rotation garnet, with the chip embedded into a TEC fiber. By utilizing the proper orientation flat formed on the edge of each plate, alignment of these plates was simplified. Measured backward and forward losses at a wavelength of 1.55 μm are >40 dB and ~2.5 dB, respectively, which agree with predicted values. It is also shown that the characteristics would be dramatically improved by utilizing new polarization splitters instead of rutile plates. Experimental results support the promise of constructing fiber-integrated isolators which then enable the mass-production of inline isolators