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.
The conventional ridge waveguides and grating-couplers in x-cut single-crystal lithium niobate on insulator (LNOI), have been designed, fabricated and characterized. All the device structures patterned on the sample were monolithically defined by one step of the electron-beam lithography process, followed by dry-etching. A low insertion loss (IL) of −6.3 dB/coupler for transverse-electric (TE) polarization inputs at the wavelength of 1543 nm was measured in the fabricated best device with the tapered structures, and exhibited a broad 3-dB optical bandwidth of more than 90 nm. This work may pave the way towards the future research of high-efficiency photonic waveguide components in thin-film LNOI.
The ridge waveguide integrated grating couplers (GCs) in lithium niobate on insulator (LiNbO 3 , LNOI) were designed, fabricated and characterized. Two ends of the gratings structures were connected through the middle photonic rib-waveguide of a sub-micrometric-diameter, which was nanostructured with the geometry of side-wall corrugated subwavelength gratings structure. A high coupling efficiency of -5.1 dB for the best thin film LiNbO 3 (TFLN) grating coupler was measured at the telecommunication wavelength of 1561 nm for quasi-transverse-electric (TE) polarized signals, with a broad 3-dB optical bandwidth of wider than 95 nm. All the devices structure patterns for the integrated LNOI GCs could be simultaneously defined by one step of electron-beam lithography, and then easily fabricated by the dry-etching processes. This compact component exhibited magnificent performance, and might show the potential functionalities for the TFLN-based integrated optical waveguide devices.
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