Fused 3×3 single-mode fiber optic couplers for fiber interferometric sensors and coherent communications

Fused 3×3 single-mode fiber couplers have been fabricated with low excess loss, low uniformity error in splitting ratio, and a high degree of stability with regard to changes in temperature and input polarization. A special alignment system was utilized to tightly control the process parameters and to keep the fiber cores in the fusion region in a perfect equilateral triangle shape before, during, and after drawing the 3×3 coupler. The 3×3 couplers which were manufactured by using the special alignment system have not only good performance characteristics but also excellent resistance to thermal variation, hot humidity, vibration, and shock. The 3×3 couplers meet all the requirements of optical-fiber interferometric sensors and coherent communications with regard to performance characteristics and resistance to severe environment