A New Scheme of Oriented Hyperboloid Microlens for Passive Alignment Lasers to Polarization Maintaining Fibers

A new scheme of oriented-hyperboloid microlens (OHM) with passive alignment to achieve high polarized extinction ratio (PER) is proposed and demonstrated high efficiency coupling of high-power 980 nm pump lasers to polarization maintaining fibers (PMFs). Using an automatic grinding machine and a charge-coupled-device to precisely control and attain the required minor radius of curvature 4-4.8 μm, offset within 0.7 μm, and axis orientation accuracy ±1°, the OHM exhibited a high-average PER of 31.7 dB, and a high-average coupling efficiency of 83.4%. For a 30 dB PER, the angular misalignment tolerance of the OHM was measured to be ±2°. The unique advantage of the proposed OHM is passive alignment to achieve high PER by only aligning the OHM endface of the fast axis parallel to the axis of laser polarization. This newly developed OHM with unique passive alignment to achieve high polarization is beneficial for the applications of laser/PMF modules where mode polarization and high coupling efficiency are required for use in high precision fiber optic gyroscopes as well as many low-cost and high-performance lightwave interconnection applications.