Coupling characteristics of laser diode to multimode fiber using separate lens methods

This paper presents the characteristics of an InGaAsP laser diode to a multimode fiber coupling using four separate lens methods. The maximum coupling efficiencies and misalignment tolerances of optical circuit components are clarified for the specific methods: (1) using a relatively large spherical lens, (2) applying a hemispherical-ended GRIN rod lens, (3) using a combination of a relatively large spherical lens and a GRIN rod lens, and (4) employing a combination of two relatively large spherical lenses. The measured results are compared with those for a butt joint and tapered hemispherical-ended fiber methods. The coupling methods utilizing relatively large lenses are shown to have several features advantageous in the fabrication of practical laser diode modules.