Packaging high-coupling lasers to polarization maintaining fibers employing visual alignment

An oriented-dependence-microlens (ODM) fabricated by automatic grinding and fusion techniques is proposed. The ODM can be visually surface-feature aligned for high tolerance coupling lasers to polarization-maintaining-fibers (PMFs). The 3-dB coupling efficiency and polarized-extinction-ratio (PER) angular tolerances of the ODM were obtained as high as ± 16°. Furthermore, the 1-dB coupling and PER angular tolerances of the ODM were measured to be ± 2° for the ODM necessary to achieve both high coupling of 80% and high PER of 30-dB. The position accuracy of the grinding machine for the ODM was ± 1°, which was less than the fabricated angular tolerance of ± 2° necessary to achieve high coupling and PER and was much less than ± 16° to achieve 3-dB coupling and PER. This high coupling and high angular tolerance of fabricated ODM indicates that the ODM endface of the fast axis can be easily and visually observed and then surface feature aligned to the axis of the laser polarization direction. The proposed ODM with visually precise surface feature alignment to achieve both high coupling and polarization is beneficial for the application of laser/PMF modules for use in high-precision fiber optic gyroscopes and many high-performance and low-cost lightwave interconnections.

1. Introduction

Polarization-maintaining-fibers (PMFs) are employed in many applications required for preserving polarization properties and are commonly used in fiber optic gyroscopes for the connection between a high-power 980 nm pump lasers coupled to a modulator via PMFs, since the modulator requires polarized light as input source[1]. The PMFs allow preservation and control of the mode polarization state due to the polarization preserving characteristics of the PMFs. Therefore, an accurate alignment between high-power pump lasers and the PMFs to achieve both high coupling and accurate polarization is important to the development of high-performance pump laser modules.