We demonstrate, for the first time to our knowledge, a SiN-assisted in-plane adiabatic coupler between SiPh and onboard glass waveguides. Our numerical study is founded on an actual graded index glass waveguide developed by Fraunhofer-IZM. The Silicon taper profile and the optimal length are extracted employing the supermode theory and the adiabatic theorem. Fabrication and assembly issues are investigated, resulting to an optimized coupler design that exhibits a theoretical Si-to-glass loss below 0.1dB over the entire C-band. The proposed solution can be realized utilizing standard passive flip-chip assembly equipment and is, therefore, cost-effective, easy to be fabricated, and well-suited for compact packaging.
Large mode area fibers are imperative for scaling up the peak and average power of fiber lasers. Single-mode behavior
and low FM loss are the crucial functionalities for these fibers. While rod-type Photonic Crystal Fibers (PCFs) have
been very successful in offering large mode areas, the typical device length requirement (~1m) and rigid configuration
limits their attractiveness for practical applications. LMA fibers offering a degree of bend tolerance are thus highly
desired. Leakage channel fibers (LCFs) have shown a great potential for offering substantial bend tolerance along with
large mode areas. However, the proposed use of Fluorine-doped rods in the all-solid version limits their practical design space. Here, we propose a novel design concept to attain single-material, large mode area fibers (mode area >~1000μm<sup>2</sup>) with effectively single mode operation coupled with bending characteristics comparable to all-solid LCFs and, at the same time, greater design flexibility and easier splicing relative to rod-type PCFs.
Fibers used for high power delivery are designed to ensure single-mode operation (in order to guarantee good output beam quality), large effective areas (A<sub>eff</sub>) and resistance to bend-induced distortions (in order to avoid non-linear effects). For simple step index fibers, the maximum Aeff of the fundamental mode that can practically be achieved at 1.06μm is ~350μm<sup>2</sup>. All-solid-silica Bragg fibers with large cores were proposed as an alternative solution for high power delivery through their fundamental core mode. These fibers consist of a low-refractive index core surrounded by a multilayer cladding that acts as a Bragg mirror. The loss spectrum of such fibers consists of a concatenation of several transmission windows separated by high-loss peaks. Here, we simultaneously study, for the first time (at our knowledge), the bending impact on Bragg fibers for the three critical properties required for high power delivery: large A<sub>eff</sub>, single-mode propagation and low bend losses for the fundamental mode. Thanks to their specific guiding mechanism, A<sub>eff</sub> as large as ~500μm<sup>2</sup> at 1.06μm can be achieved in Bragg fibers, while maintaining single-mode operation and bend losses lower than 0.1dB/m. Our numerical results are validated by experimental measurements on a PCVD Bragg fiber with a 40μm diameter core.