Misalignment studies in laser diode to hemispherical microlens tipped circular core photonic crystal fiber excitation

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 hemispherical microlens of allowable aperture on the tip of such fiber in absence and presence 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 hemispherical 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 radius of curvature of 6.0 µm of hemispherical microlens, photonic crystal fiber with air filling ratio of 0.45 and hole-pitch of 4.5 µm comes out to be the most suitable one to couple laser diode emitting light of wavelength . Moreover, the coupling efficiency can reach to 86.88% with simultaneous optimization of radius of curvature and working distance 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 hemispherical microlens on the tip of photonic crystal fiber. Moreover, the results are extremely useful for assessing deeply the sensitivity of such coupler with reference to above kind of misalignments.