The Design and Characterization of an Ultra-Compact Asymmetrical Multimode Interference Splitter on Lithium Niobate Thin Film

Abstract

We propose and demonstrate a high-performance asymmetrical multimode interference splitter on X-cut lithium niobate on insulator (LNOI) with an ultra-compact size of 5.8 μm × (26.4–35.6) μm. A rectangle with a small region is removed from the upper left corner of the multimode interference (MMI) coupler to achieve a variable splitting ratio. Here, we design and characterize MMIs in six different distribution ratios ranging from 50:50 to 95:5 on a 600 nm thick LNOI. Based on the cascade structure, the linear fitting method accurately shows the device loss (~0.1–0.9 dB). Our fabricated devices demonstrate robustness across a 30 nm optical bandwidth (1535–1565 nm). In addition, we numerically simulate the Z-cut LNOI, showing that the structure corresponding to the TM mode can also achieve a good variable splitting ratio.

Broadband Thin-Film Lithium Niobate Electro-Optic Modulator

“…The arrangement of the waveguide pattern ensures that the transmission direction of the optical signal is perpendicular to the Z-axis direction of the LN crystal, so that the maximum second-order electro-optical coefficient can be utilized. We then relied on conventional ICP-RIE etching technology to transfer the pattern to the chromium layer, followed by transfer to the LN via an argon gas mixture flowing through the ICP-RIE process following an optimized etching recipe [25]. The etching rate was set to about 30 nm/min.…”

“…Photonics 2024, 11, x FOR PEER REVIEW 7 of 12 order electro-optical coefficient can be utilized. We then relied on conventional ICP-RIE etching technology to transfer the pattern to the chromium layer, followed by transfer to the LN via an argon gas mixture flowing through the ICP-RIE process following an optimized etching recipe [25]. The etching rate was set to about 30 nm/min.…”

Gradient Probabilistic Algorithm for Compact Lithium Niobate Integrated Photonic Devices

“…This MMI splitter can achieve splitting ratios from 50:50 to 95:5. The device size measures at 5.8 µm × (26.5 ∼ 35.6 µm), with insertion losses ranging from 0.1 dB to 0.9 dB [4].…”