Single mode lasing and spectral narrowing in photonic crystal line-defect cavities via spatially selected Bloch modes

TL;DR

The paper tackles multi-mode lasing in slow-light photonic-crystal line-defect cavities by introducing a spatially selective Bloch-mode pumping scheme that leverages optical interference to target a specific Bloch mode. A theoretical framework combining Bloch-mode distributions, slow-varying envelopes, and traveling-wave rate equations is developed, incorporating slow-light effects and Purcell-enhanced emission. Numerical simulations for a LN-based cavity show that interference pumping can achieve single-mode lasing with SMSR exceeding 30 dB, reduced thresholds, and narrowed linewidths with lower intensity noise, by aligning the interference fringe pattern with the Bloch-mode envelope. This Bloch-mode selection offers a practical, scalable approach for on-chip PhC laser mode control, with potential impact on dense photonic integration and nanophotonic device design.

Abstract

The demand for high-efficiency and miniaturized on-chip light sources drives continuous innovation in photonic crystal (PhC) microcavity lasers. The presence of slow-light effects in PhC microcavities leads to the mode competition between Bloch modes resulting in multi-mode lasing, which obstructs the dense integration of PhC lasers. Here, we theoretically verify a technical scheme for the single-mode lasing of PhC line-defect-cavity lasers by spatially pumping a certain Bloch mode via optical interference.We demonstrate the capability to select a specific longitudinal mode to lase with a side mode suppression ratio (SMSR) exceeding 30 dB. The interaction between optical interference fringes and the vacuum electromagnetic field inside the PhC cavity improves the linewidth and noise characteristics of lasers. This scheme of Bloch mode selection provides a novel and viable tool for the manipulation of PhC microcavity lasers.

Figures (7)

• Figure 1: The propagation of forward and backward Bloch waves in a PhC microcavity and the reflection at both ends of the periodic structure.
• Figure 2: Schematic for optical interference pumping and the mode selection in a PhC cavity. a. Interference pumping on an $L20$ PhC cavity. b. The field energy distributions of the first three Bloch modes in the $L20$ cavity obtained via finite element method.
• Figure 3: The distribution of carrier density and optical gain along the longitudinal direction under the various types of spatial pumping. a. Carrier density and gain distribution under uniform pumping. b. Carrier density and gain distribution under the interference pumping with three interference maxima. c. Carrier density and gain distribution under the interference pumping with two interference maxima. d. Carrier density and gain distribution under the interference pumping with one interference maximum.
• Figure 4: $LN$ cavity's lasing performance under uniform optical pumping. a. Light-light curves for three Bloch modes. b. Lasing spectra for the three Bloch modes.
• Figure 5: Mode selection performance. a. Light-light curves of the three Bloch modes under two-node interference pumping. b. Spectra under optical interference pumping. The number of envelop maxima for spatial pumping are 1 (POS, blue lines), 2 (Cen, green lines), and 3 (Neg, red lines), respectively.