Modified Maxwell fish-eye approach for efficient coupler design by graded photonic crystals

Abstract

We present a novel design of two dimensional graded index medium that provides coupling of light with high coupling efficiency between two planar dielectric waveguides of different widths (15.46 μm vs. 2.21 μm). Poor light coupling performance of butt-coupler can be mitigated by implementing tapered coupler at the expense of long coupler section. In order to reduce coupling losses, a new coupling device approach based on graded index (GRIN) concept is proposed. The refractive index distribution is in the form of modified version of the Maxwell fish-eye lens. The inhomogeneous refractive index distribution is approximated by photonic crystals (PCs) such that the positions of each PC rods are appropriately arranged. Strong electric field focusing ability of the designed GRIN PC medium provides relatively high coupling efficiency that is around 90%. Spectral region corresponding to coupling efficiency over 75% has a bandwidth of Δω = 18.56% (284 nm). Finally, we discuss the durability of the proposed coupler against the lateral displacement and angular misalignment of output waveguides.

Comprehensive analysis of two different graded-index photonic-crystal lenses

“…due to altering the lattice spacing, the radii of rods (or holes) and the refractive index of a material. The GRIN PCs have numerous applications when forming mode-order converters [13,14], wavelength demultiplexers [15,16], couplers [17] and lenses [18].…”

Large bandwidth mode order converter by differential waveguides

“…The term mode conversion has different meanings according to the change that the mode undergoes. One of the conversion schemes deals with the manipulation of the optical mode size [4,5]. Another method addresses polarization conversion of waveguide modes, i.e., TE-TM mode conversion [6].…”

Mode transformation using graded photonic crystals with axial asymmetry

“…It is expected that input and output coupling of light is not a formidable task due to easy beam width alteration in GRIN medium. Finally, planar front and back surfaces of the medium provide some misalignment tolerances [33]. This paper is organized as follows: firstly, the mode conversion problem and need of a compact converter device are defined in Section 2.…”