Efficient Coupling of a Laser Diode to a Upside Down Tapered Microlens Tipped Circular Core Photonic Crystal Fiber using ABCD Matrix Formalism

Abstract

We investigate theoretically the coupling optics involving a laser diode and a series of circular core photonic crystal fibers with different air filling ratio and hole-pitch via upside down tapered microlens of two specific taper lengths on the tip of such fibers in absence of possible transverse and angular misalignments. By employing Gaussian field distributions for both the source and the fiber and also the already derived ABCD matrix for upside down tapered microlens, we formulate analytical expressions for the concerned coupling efficiencies for practically interesting two different light emitting wavelengths of 1.3 μm and 1.5 μm, respectively. Further, it is observed that, for a fit taper length of 70.0 µm of upside down tapered microlens, photonic crystal fiber with air filling ratio of 0.35 and hole-pitch of 5.0 µm comes out to be the most suitable one to couple laser diode emitting light of wavelength . Moreover, the coupling efficiency can reach to 94.63% with simultaneous optimization of taper length and source position of specific lensed fiber. Such analysis which as per our knowledge is the first theoretical investigation, will be extremely important in ongoing investigations for the design of optimum launch optics involving upside down tapered microlens on the tip of photonic crystal fiber.