Low-Cost Fiber Grating Laser Module Package Employing a Hyperbolic Fiber Microlens

In this study, we demonstrate that it is possible to fabricate a fiber grating external cavity laser (FGECL) module with a low cost while still maintaining a good performance using a low-cost antireflection (AR)-coated (5×10-3) laser and a tapered hyperbolic-end fiber (THEF) microlens. Previously, high-performance FGECL modules have only been available by using a complicated AR-coated (1×10-5) laser process that leads to a high packaging cost. Our FGECL consisted of a HR/AR-coated diode laser, a THEF microlens, and a fiber grating. The results showed that the FGECL module exhibits a side-mode suppression ratio (SMSR) higher than 44 dB, a higher output power of more than 2 mW, and a larger operation current range of over 50 mA. In addition, excellent wavelength stability and a low-penalty directly modulated 2.488 Gbit/s were also obtained for FGECL modules. The THEF microlens demonstrated up to 86% coupling efficiency for a laser with an aspect ratio of 1:1.5. Low-cost FGECL modules with good performance were achieved primarily owing to the THEF microlens having a high coupling efficiency (typically 75%) which enhanced the feedback power from the fiber grating external cavity to the HR/AR-coated laser compared with the currently available hemispherical microlens which has low coupling efficiency (typically 50%). Therefore, the packaged FGECL module is suitable for use in low cost 2.5 Gbit/s lightwave transmission systems.