High efficiency DBR assisted grating chirp generators for silicon nitride fiber-chip coupling

Abstract

Silicon Nitride (SiN) is emerging as a promising material for a variety of integrated photonic applications. Given its low index contrast however, a key challenge remains to design efficient couplers for the numerous platforms in SiN photonics portfolio. Using a combination of bottom reflector and a chirp generating algorithm, we propose and demonstrate high efficiency, grating couplers on two distinct SiN platforms. For a partially etched grating on 500 nm thick SiN, a calculated peak efficiency of −0.5 dB/coupler is predicted, while for a fully etched grating on 400 nm thick SiN, an efficiency of −0.4 dB/coupler is predicted. Experimentally measured coupling efficiencies are observed to be −1.17 and −1.24 dB/coupler for the partial and fully etched grating couplers respectively in the C-L band region. Furthermore, through numerical simulations, it is shown that the chirping algorithm can be implemented in eight additional combinations comprising SiN film thickness between 300–700 nm as well as alternate claddings, to achieve a per coupler loss between −0.33 to −0.65 dB.

Optical meta-waveguides for integrated photonics and beyond

“…For instance, the substrate light leakage during guided wave and free-space light couplings via metasurfacedecorated waveguides will reduce conversion efficiency. This issue could be solved by using waveguide-integrated distributed Bragg reflector substrate, layered structures, and topologically protected structures 474,475 • Limited bandwidth, phase only modulations (multifunctionality).…”

Advances in Silicon Quantum Photonics

“…Efficient grating couplers have historically been a challenge due to power leakage in the substrate [58], [78], [79]. Further reducing the loss requires directed emission from the grating, which has been demonstrated with distributed Bragg reflectors [80] and metal layers underneath the grating (Fig. 1b) [67], [81], [82], [56], achieving down to 0.5 dB loss.…”

Highly efficient dual-level grating couplers for silicon nitride photonics

“…Several approaches were reported to increase the directionality and, hence, the coupling efficiency (CE) for lower Si N waveguide thicknesses. One of the most common approaches makes use of metal reflectors 15 or Distributed Bragg Reflectors (DBRs) 16 – 18 to recover the light scattered towards the substrate. A reflectivity higher than 92% was numerically demonstrated using a bottom Si grating reflector, with a resulting simulated CE of − 0.88 dB for an apodized 400 nm-thick Si N GC 19 .…”

“…A reflectivity higher than 92% was numerically demonstrated using a bottom Si grating reflector, with a resulting simulated CE of − 0.88 dB for an apodized 400 nm-thick Si N GC 19 . CE values greater than 90% (− 0.45 dB) were numerically simulated by combining a bottom DBR and a chirp generator algorithm 18 , with an experimentally measured CE of − 1.17 dB at 1571 nm for an air-cladding, partially etched GC on a 500 nm thick Si N platform. Another way to increase directionality is to employ a double-etched grating design.…”

“…Several approaches were reported to increase the directionality and, hence, the coupling efficiency (CE) for lower Si 3 N 4 waveguide thicknesses. One of the most common approaches makes use of metal reflectors 15 or Distributed Bragg Reflectors (DBRs) [16][17][18] to recover the light scattered towards…”