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

Abstract

1 Abstract-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 m, offset within 0.7 m, and axis orientation accuracy  1º, 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  2º. 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.Index Terms-Passive alignment polarization-maintaining fiber, oriented hyperboloid microlens, fiber optic gyroscope.

An Oriented-Dependence-Microlens Visual Alignment and Packaging for Lasers Coupling to PMFs

“…From the lasers to the ODM, the Fresnel diffraction theory was used for beam propagation through free space. According to the previous literature [4], the coupling efficiency between 980-nm lasers and microlenses was dominated to the minor radius of curvature and was insensitive to the major radius of curvature. Therefore, this study will be focused on the control and fabrication of the minor radius of curvature within 4 -4.8 μm which is close to the ideal shape for precise surface feature alignment.…”

“…The 980 nm high-power lasers typically have far-field divergence angles of 7°(horizontal) × 26°(vertical), with the relative beam waist radius of 3 and 0.8 μm, respectively. The 980 nm laser-to-fiber coupling model was based on the diffraction theory [4]. From the lasers to the ODM, the Fresnel diffraction theory was used for beam propagation through free space.…”

“…Therefore, this study will be focused on the control and fabrication of the minor radius of curvature within 4 -4.8 μm which is close to the ideal shape for precise surface feature alignment. The fiber grinder employed to fabricate the ODM was designed as a three-axis grinding machine and a CCD alignment system [4], as shown in Fig. 1(a).…”

“…1(b). The ODM was fabricated by grinding a cleaved fiber in a single step [4]. The highest and lowest positions of H were controlled to produce two maximum and two minimum grinding pressures while θ was kept constant at 45°.…”

“…Recently, a visually determined position employing oriented-dependence microlens for precise surface feature alignment high-power 980 nm pump lasers coupled to PMFs to achieve high coupling and high polarized extinction ratio (PER) has been demonstrated [4]. Results showed that the fabricated microlenses enabled precisely control and attain the required minor radius, less offset, and axis orientation for achieving both high-average coupling efficiency and highaverage PER from lasers coupling to PMFs.…”