High Quality factor photonic crystal nanobeam cavities (0901.4158v2)

Abstract: We investigate the design, fabrication and experimental characterization of high Quality factor photonic crystal nanobeam cavities in silicon. Using a five-hole tapered 1D photonic crystal mirror and precise control of the cavity length, we designed cavities with theoretical Quality factors as high as 14 million. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a Quality factor of nearly 750,000. The effect of cavity size on mode frequency and Quality factor was simulated and then verified experimentally.

• The paper presents a novel nanobeam cavity design that achieves a record high Q-factor through precise simulation-driven optimization.
• Utilizing 3D FDTD simulations and advanced fabrication on silicon, the study minimizes modal volumes and reduces scattering losses.
• Experimental validation via resonant scattering confirms nearly 7.5×10^5 Q-factor, underscoring its potential for integrated photonic devices.

High Quality Factor Photonic Crystal Nanobeam Cavities

The paper presents a comprehensive paper on the design, fabrication, and characterization of high-quality factor (Q-factor) photonic crystal nanobeam (PhCnB) cavities fabricated from silicon. These structures are vital in various advanced optical applications due to their ability to confine electromagnetic fields to extremely small volumes, thus achieving high Q-factor and small modal volume simultaneously.

Design and Simulation

The authors employed a five-hole tapered one-dimensional photonic crystal mirror design to create the nanobeam cavities. The cavities were optimized using 3D finite-difference time-domain (FDTD) simulations to achieve a theoretical Q-factor as high as $1.4 \times 10^7$. By controlling the cavity length precisely, the design was tuned to minimize impedance mismatch and scattering losses, essential for maximizing the Q-factor.

Fabrication

The silicon photonic crystal nanobeam cavities were fabricated on a silicon-on-insulator (SOI) substrate with intricate patterning using electron-beam lithography. A reactive ion etching process was used, followed by a hydrofluoric acid vapor etching to suspend the structures, critical for obtaining the high-Q performance by negating substrate effects.

Characterization and Results

Measured Q-factors of nearly $7.5 \times 10^5$ were obtained using a resonant scattering technique. This technique involves detecting cross-polarized light scattered from a laser co-aligned with the cavity mode to enhance signal quality. The paper reports that this Q-factor is the highest ever recorded for PhCnB cavities at the point of publication, highlighting the effectiveness of their design approach.

The paper also explored the effect of cavity length on mode frequency and Q-factor both experimentally and via simulations. It was observed that longer cavities resulted in lower Q-factors and a red-shift in the resonance wavelength. The experiments showed good correlation with simulation results, although some deviations were noted, potentially attributed to fabrication imperfections.

Implications and Future Work

The findings of this research significantly impact the design of nanobeam cavities with high-Q/V ratios and small modal volumes, making them suitable for applications in ultrasmall lasers, optical switches, and sensors. The paper suggests that further improvements could be made in tackling fabrication-induced disorders and exploring other material systems with moderate refractive indices. Future work may also focus on enhancing the experimental setups to further reduce non-resonant background noise and exploring the resonant scattering method's limitations.

This research lays the groundwork for developing more efficient nanophotonic devices by optimally designing high-Q PhCnB cavities, fostering advancements in photonic integration technologies.