Impact of Non-Vertical Sidewalls on Bandgap in Lithium Niobate Photonic Crystals | #Sciencefather

Introduction

The study explores the impact of non-vertical sidewall angles on the band structure of thin-film lithium niobate photonic crystals. Both suspended membranes and lithium niobate on insulator structures are analyzed to highlight fabrication-dependent deviations. By employing the gap-to-midgap ratio as a primary figure-of-merit, the work demonstrates significant performance changes under varying sidewall conditions, thus providing valuable insights into the challenges faced in photonic crystal design.

Impact of sidewall angle

Non-vertical sidewalls, a common occurrence in fabricated photonic crystals, critically affect the optical performance of lithium niobate devices. For suspended structures, the reduction in bandgap is notable, but for lithium niobate on insulator platforms, the effect is even more severe, emphasizing the necessity of precise control over etching processes. This observation underlines the importance of sidewall angle as a decisive factor in achieving optimal photonic band structures.

Suspended lithium niobate photonic crystals

The suspended photonic crystal configuration presents unique opportunities for tailoring optical properties. However, with sidewall angles deviating from verticality, a 34% reduction in the gap-to-midgap ratio is reported at 60°. This reduction implies that suspended structures, although advantageous in some scenarios, demand careful parameter optimization to balance performance and fabrication feasibility.

Lithium niobate on insulator configuration

Lithium niobate on insulator photonic crystals exhibit more substantial performance degradation when sidewall angles are non-vertical. At 70°, a reduction of nearly 73% in the gap-to-midgap ratio is observed, highlighting the pronounced sensitivity of this configuration. These findings stress the need for advanced fabrication methods to maintain the functional potential of LNOI-based photonic devices.

Optimization strategies

To counteract the challenges posed by slanted sidewalls, geometry optimization emerges as a key solution. By systematically adjusting photonic crystal unit cell parameters, it is possible to recover part of the lost performance. The proposed strategies balance theoretical design ideals with real-world fabrication capabilities, ensuring that the developed devices remain both practical and effective.

Design guideline for scalable devices

The insights from this study extend beyond individual devices, providing a design roadmap for large-scale integration of lithium niobate photonic circuits. By explicitly addressing fabrication-induced imperfections, the work guides researchers in developing robust photonic systems suitable for scalable and realistic applications, thus paving the way for advanced integrated photonics platforms.

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