Spot-Size Converter Based on Long-Period Grating

Abstract

We propose a spot-size converter (SSC) by exploiting the high-efficiency mode conversion capability that a long-period grating (LPG) possesses. Our proof-of-concept LPG-based SSC, fabricated with optical polymer material on silicon nitride (Si 3 N 4 ) platform, has a length of ∼700 µm, can improve the coupling efficiency between the LP x 01 mode of an ultra-high numerical aperture fiber and the E x 11 mode of the Si 3 N 4 waveguide from ∼24% to ∼33% at 1548 nm wavelength, corresponding to 1.4-dB reduction in insertion loss. Therein, the LPG achieves a maximum mode conversion efficiency of 90% between the two E x 11 modes of the polymer cladding and the Si 3 N 4 core. Our proposed SSC provides a new path to achieve low-loss fiber-to-chip coupling.

An Ultrabroadband and Cost-Effective Edge Coupler for Efficient Thin Film Lithium Niobate Photonics

“…We determine the size of the CWG by calculating the mode overlap between the lensed fiber and the CWG with different sizes. The overlap can be expressed as [43]:…”

“…Vertical couplers, mostly grating couplers [31][32][33][34][35][36][37][38], intrinsically suffer from limited efficiency, limited bandwidth, and polarization sensitivity due to their operational principle. As for edge couplers [39][40][41][42][43][44][45][46][47], taper waveguide structures are usually used in the design and preferred in practical applications, especially in areas with high requirements for both coupling efficiency and bandwidth, such as upconversion single-photon detectors.…”