Coupling efficiency of a laser diode to a single-mode fiber via a microlens on the fiber tip

A conical microlens on the tip of a fiber for improving the coupling efficiency (CE) of a laser diode and a single-mode fiber in butterfly packaging was experimentally fabricated via the grinding and polishing method and theoretically designed using the beam propagation method. The CE, varying with working distance, was explored under all kinds of optical coupling system parameters, such as incident wavelength, laser beam waist radius, numerical aperture of the fiber, refractive index, and diameter of the microlens. The optimal working distance for the maximal CE was located at approximately 15 μm, proving that the conical-tip coupling was a tight packaging type. Therefore, the CE trends under misalignment and tolerance adjustments could be explained by the spherical aberration theory and light-gathering ability of the microlens. The results are useful in optimum launch optics for designing and fabricating microlens tips on coupled packaging of optoelectronic devices.