Integrated Subwavelength Gratings on a Lithium Niobate on Insulator Platform for Mode and Polarization Manipulation

Abstract

Lithium niobate on insulator (LNOI) has emerged as a promising platform for photonic integrated circuits, with a fast‐growing toolbox of components. This paper proposes, designs, and experimentally demonstrates compact subwavelength grating (SWG) waveguides on an LNOI platform for on‐chip mode and polarization manipulation. To overcome the limitation of waveguide fabrication, the SWGs are designed and formed on a silicon nitride thin film deposited onto the surface of LNOI chip. As proof‐of‐concept devices, the SWG‐based spatial mode filters (including a TE1‐mode‐pass filter and a TE2‐mode‐pass filter) and a TM‐pass polarizer are fabricated successfully on the same chip, with the device lengths of only ≈50 μm. The measured insertion losses for the devices are lower than 3.1 dB, with high extinction ratio larger than 30 dB, at a wavelength of 1550 nm. The proposed and demonstrated SWGs can serve as important building blocks in a series of mode and polarization handling devices for LNOI integrated photonics.

Multimode Waveguide Bends in Lithium Niobate on Insulator

“…[10] As a common optical loading material on the LNOI platform, Si 3 N 4 has a similar but slightly lower refractive index and similar transparency window to LN, and more importantly, it can be deposited and pat-terned by the mature fabrication processes that have been developed in CMOS foundries. This platform uses the mature Si 3 N 4 fabrication process while the waveguide design results in most of the optical field being confined in the LN layer, [10,[27][28][29] taking full advantage of LN's attractive properties. Figure 1a shows a schematic diagram of the 90°multimode waveguide bend formed by a circular curved waveguide with two similar curved air grooves.…”

Demonstration of a High‐Performance 3 dB Power Splitter in Silicon Nitride Loaded Lithium Niobate on Insulator

“…Thus, such Si 3 N 4 -loaded LNOI waveguides can retain the excellent material characteristics of LN, while avoiding the direct etching of LN and simplifying the fabrication processes. [19,29,46] Here, our proposed 3 dB power splitter based on the tapered SWG-assisted Y-branch can effectively split power with lower loss and less imbalance in an ultra-wide bandwidth, in which the tapered SWG plays both functions of adiabatic taper and SWG simultaneously. Thus, it can effectively increase the evanescent coupling and reduce radiation loss at the Y-junction to improve the performance of the proposed device.…”

High-Speed Optical Mode Switch in Lithium Niobate on Insulator

“…In this contribution, we design, fabricate, and experimentally demonstrate an optical mode switch that uses a three-waveguide-coupling structure based on a silicon nitride-loaded lithium niobate on insulator (Si 3 N 4 -LNOI) waveguide platform. , To achieve high-speed operation, we adopt traveling wave electrodes for the RF signal, which is phase-matched to the group index of the optical wave in the waveguides. This enabled us to demonstrate an ultrafast switching time of below 28 ps, for an optical mode switch that exhibited an insertion loss of 4.3 dB and an extinction ratio (ER) of 17.1 dB, at a wavelength of 1550 nm.…”