Mode and polarization-division multiplexing technologies (MDM and PDM)can offer considerable parallelism for optical multiplexing biosensors, complex optical neural networks, and high-capacity optical interconnects, while requiring only a single-wavelength laser source. Thanks to the mature fabrication processes of silicon nitride and superior material properties of lithium niobate, the silicon nitride loaded lithium niobate on insulator (LNOI) platform allows the integration of high-speed optical modulators and optical (de)multiplexing devices to achieve high-capacity and low-cost photonic integrated circuits suitable for data communication applications. In this contribution, MDM and PDM are investigated in a silicon nitride loaded LNOI (X-cut) platform. As a proof of concept, an asymmetrical directional coupler-based mode ( de)multiplexer (MMUX) and polarization splitter-rotator (PSR) are designed, fabricated, and experimentally demonstrated. The measured insertion losses are lower than 1.46 and 1.49 dB, while the inter-modal crosstalk is lower than −13.03 and −17.75 dB for the MMUX and PSR, respectively, for a wavelength range of 1525-1565 nm. A 40 Gbps data transmission experiment demonstrates the data transmission capabilities of the fabricated devices. The measured eye diagrams are clear and wide-open, and the bit error rate measurements show reasonable power penalties, indicating good device performance.

Electro-optic (EO) modulators, which convert signals from the electrical to optical domain plays a key role in modern optical communication systems. Lithium niobate on insulator (LNOI) technology has emerged as a competitive solution to realize high-performance integrated EO modulators. In this Letter, we design and experimentally demonstrate a Mach–Zehnder interferometer-based modulator on a silicon nitride loaded LNOI platform, which not only takes full advantage of the excellent EO effect of L i N b O 3 , but also avoids the direct etching of L i N b O 3 thin film. The measured half-wave voltage length product of the fabricated modulator is 2.24 V·cm, and the extinction ratio is ∼ 20 d B . Moreover, the 3 dB EO bandwidth is ∼ 30 G H z , while the modulated data rate for on–off key signals can reach up to 80 Gbps.

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(De)Multiplexing Technologies In article number 2100529, Yonghui Tian, Arnan Mitchell, Yikai Su, and co‐workers experimentally demonstrated mode and polarization‐division multiplexing on a thin‐film lithium niobate on insulator (LNOI) platform. By introducing silicon nitride as a loading material atop the LNOI photonics chip, the devices can be integrated with high‐speed electro‐optic modulators to achieve high‐capacity and low‐cost photonic integrated circuits suitable for data communication applications, while avoiding the direct etching of lithium niobate.

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.

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Integrated silicon nitride (SiN) waveguides with anomalous dispersion have the potential to bring practical nonlinear optics to mainstream photonic integrated circuits. However, high-stress and high-processing temperatures remain an obstacle to mass adoption. We report low-stress, high-confinement, dispersion-engineered SiN waveguides utilizing low temperature grown reactive sputtered thin-films. We demonstrate a microring resonator with an intrinsic quality factor of 6.6 × 105, which enabled us to generate a native free spectral range spaced frequency comb with an estimated on-chip pump power of 850 mW. Importantly, the peak processing temperature is 400 °C making this approach fully back-end compatible for hybrid integration with preprocessed CMOS substrates and temperature sensitive photonic platforms such as lithium niobate on insulator.

Subwavelength Gratings In article number 2200130, Yonghui Tian and colleagues experimentally demonstrate compact subwavelength grating (SWG) waveguides on a LNOI platform for on‐chip mode and polarization manipulation. To overcome the limitation of direct etching waveguide fabrication, a silicon nitride thin film was deposited onto the surface of LNOI chip, where the SWGs were formed using CMOS‐compatible etching processes developed by microelectronics industry.