Deterministic design of wavelength scale, ultra-high Q photonic crystal nanobeam cavities (1108.2675v1)

Abstract: Photonic crystal nanobeam cavities are versatile platforms of interest for optical communications, optomechanics, optofluidics, cavity QED, etc. In a previous work \cite{quan10}, we proposed a deterministic method to achieve ultrahigh \emph{Q} cavities. This follow-up work provides systematic analysis and verifications of the deterministic design recipe and further extends the discussion to air-mode cavities. We demonstrate designs of dielectric-mode and air-mode cavities with $Q>10^9$, as well as cavities with both high-\emph{Q} ($>10^7$) and high on-resonance transmissions ($T>95%$).

• The paper presents a deterministic method that replaces trial-and-error with systematic design principles to achieve Q-factors exceeding 10^9 in nanobeam cavities.
• It demonstrates effective tuning for both dielectric- and air-mode cavities by employing tapered hole sizes and adjusted waveguide widths to create Gaussian mirror profiles.
• The design yields impressive on-resonance transmissions of up to 97%, offering significant implications for integrated photonic circuits and quantum photonic technologies.

Deterministic Design of Ultra-High Q Photonic Crystal Nanobeam Cavities

The paper by Qimin Quan and Marko Loncar focuses on a novel deterministic design method for creating wavelength-scale photonic crystal (PhC) nanobeam cavities with ultra-high quality factors (Q). This research builds upon previous methodologies to provide a more systematic approach to designing both dielectric-mode and air-mode cavities, demonstrating Q-factors exceeding $10^9$ and achieving high on-resonance transmissions of over 95%.

The deterministic design method introduced by Quan and Loncar addresses the limitation of traditional trial-and-error procedures commonly used in the optimization of PhC cavities. The proposed approach relies on a set of principles for achieving high-Q cavities: zero cavity length, constant periodicity, and a Gaussian field attenuation facilitated by linear increases in mirror strength. Numerical simulations and finite-difference time-domain (FDTD) analysis are employed to verify the validity of these principles and confirm the capabilities of the deterministic design.

The research systematically explores dielectric- and air-mode cavities. Dielectric-mode cavities are characterized by optical energy concentrated in high-index regions, whereas air-mode cavities focus energy in low-index areas. The team shows that by tapering the hole sizes in dielectric-mode cavities and adjusting the waveguide widths in air-mode cavities, they successfully create Gaussian mirror profiles that maintain ultra-high Q-values.

For dielectric-mode cavities, the paper reports a remarkable radiation-limited Q-factor of $5.0 \times 10^9$ and also explores higher order modes within the cavity, offering insights into the detailed mode behavior. Notably, they achieve a significant Q-factor of $1.3 \times 10^7$ with an on-resonance transmission of 97%, demonstrating the design's effectiveness in waveguide-coupled setups.

Similarly, air-mode cavities achieve a Q-factor of up to $1.4 \times 10^9$. This is accompanied by an impressive mode volume, although larger than its dielectric counterpart, retaining its effectiveness for applications requiring confinement in low-index regions. The adaptability of the design in achieving high Q-factors with effective waveguide coupling is highlighted with a Q-factor of $3.0 \times 10^6$ and a 96% transmission in air-mode cavities.

The implications of this paper are significant for both theoretical investigation and practical implementation. The deterministic method simplifies the design process, allowing for rapid and reliable creation of high-Q cavities suited for versatile uses, including enhancement of light-matter interactions, optomechanics, and quantum photonic technologies. The approach's universality suggests potential applicability to other photonic crystal structures beyond nanobeam cavities, including 2D line-defect photonic crystals.

Looking forward, this research lays substantial groundwork for expanding the utility and efficiency of integrated photonic circuits, contributing to advancements in optical communications and novel opto-electronic applications. The paper's deterministic methodology can catalyze further developments in designing customizable optical systems with precise control over light confinement and manipulation.