Design and fabrication of a high-performance binary blazed grating coupler for perfectly perpendicular coupling

Abstract

A high-performance binary blazed grating coupler (BBGC) on a silicon-on-insulator (SOI) platform for perfectly vertical coupling has been proposed. The period and the etching depth of the grating and the fill factors of the sub-gratings are simulated optimally with manufacturable feature sizes, and the coupling efficiency (CE) is as high as −1.78 dB at 1550 nm with a broad 3-dB bandwidth of around 100 nm. Then, a BBGC with the CE of −3.69 dB at 1550.5 nm and a 3-dB bandwidth of about 70 nm was experimentally demonstrated. Moreover, a large process tolerance of about 20 nm on the narrower sub-grating width was proved, achieving the insertion loss lower than −4.64 dB at 1550 nm. The realization of the BBGC on a SOI platform is simple, repeatable, and compatible with standard complementary metal-oxide semiconductor (CMOS) technology.

Miniaturized Bloch Surface Wave Platform on a Multicore Fiber

“…We then localize the cores in the previous engraved frame, by injecting the light of a visible laser (Thorlabs S1FC635) and imaging the end facet of the fiber with an inverse microscope. The spatial coordinates of the cores are then used to engrave the blazed gratings , in the right place. Blazed gratings are fabricated in a raster multipass FIB milling, which ensures an accurate control of the blaze angle and minimum material redeposition.…”

High‐performance binary blazed grating coupler with a mixed structure of germanium and zinc selenide

“…Ultimately, according to the form‐birefringence theory 25 and localized effective refractive index theory of binary grating, 12 the filling factor $${f}_{i}$$ can be obtained using the following formulas: $$${n}_{\mathrm{eff}}=\frac{{h}_{i}}{{H}_{3}}{n}_{{Ge}}+\frac{{H}_{3}-{h}_{i}}{{H}_{3}}{n}_{c},\unicode{x02007}(i=1,2),$$$ $$${h}_{i}=\frac{1}{2}\left[\frac{{H}_{1}}{2}i+\frac{{H}_{1}}{2}(i-1)\right],\unicode{x02007}(i=1,2),$$$ $$${n}_{\mathrm{eff}}=\sqrt{{f}_{i}{n}_{i}^{2}+(1|-|{f}_{i}){n}_{c}^{2}},\unicode{x02007}(i=1,2),$$$where $${n}_{i}$$ represents the refractive index of the grating ridge in the BBGC, and $${n}_{\mathrm{eff}}$$ denotes the effective index of the mode inside the grating. In this work, $${n}_{1}$$ and $${n}_{2}$$ are equal to $${n}_{{ZnSe}}$$…”

“…Ultimately, according to the form-birefringence theory 25 and localized effective refractive index theory of binary grating, 12 the filling factor f i can be obtained using the following formulas:…”

“…Thus, grating couplers are the most practical choice in LWIR with high alignment tolerance 10 and flexible position 11 . Perfectly vertical couplers are more attractive by allowing denser grating‐array integration, eliminating the dependence of angle, and providing fewer difficulties of the alignment 12 . Because the completely symmetrical incident angle, the grating coupler structures must be asymmetrical to break coupling symmetry.…”

“…11 Perfectly vertical couplers are more attractive by allowing denser grating-array integration, eliminating the dependence of angle, and providing fewer difficulties of the alignment. 12 Because the completely symmetrical incident angle, the grating coupler structures must be asymmetrical to break coupling symmetry. Many research achievements have been made on asymmetric grating coupler structures, mainly including slanted gratings couplers.…”