For applications in optical communications, chip-scale solid-state LIDAR, and quantum information, ultra-low threshold and compact lasers are highly desirable components in photonic integrated circuits. By embedding gain materials into optical cavities with a high quality (Q) factor and/or small mode volume (V-mode), the general strategy for creating such lasers is to effectively trap light and enhance light-matter interaction.
Planar photonic crystal has been used to achieve low-threshold lasing by introducing photonic bound states in the continuum (BICs) modes or defect-type PhC modes. For lasing activity, the detailed imperfection type PhC lasers, while showing minuscule V-mode and hence a super low limit, by and by endure flimsiness, making responsiveness the primary problem.
In this regard, one of the most promising alternative architectures is BIC lasers with topological robustness. However, in PhC slabs or gratings with a high Q-factor, radiative BIC (quasi-BIC) modes are frequently realized by requiring extended lateral periodic structures to reduce in-plane light leakage, which naturally limits their footprint to hundreds of unit cells. Additionally, BICs can only confine light in a vertical direction, making further reduction of their threshold challenging.
An exploration bunch including Ying Yu and Siyuan Yu from Sun Yat-sen College presents the acknowledgment of CW-worked BIC lasers with low limits and little V-modes by joining O-band InAs/GaAs epitaxial QD gain material with scaled-down BIC depressions. Profiting from the three-layered repression of both light and transporters given by the scaled-down BIC cavity and the QD, the super-low limit of under 20 W and the small size of 2.52.5 m2 are accomplished. The study has been published in the Light journal: Science and Applications.
Fig. 2a shows the radiation spectrum at room temperature under various pump powers. The inset depicts the measured L-L curve of the laser at 303 K, indicating a threshold of 17 W. The typical measured lasing wavelengths of M11 mode in cavities of different sizes and periods agree well with theoretical resonant wavelengths. The blue line represents the exponential fit to the experimental data (black dots), revealing the characteristic temperature T0 of 93.9 K. The wavelengths are extremely predictable, and the tuning range is nearly 80 nm. Credit: Hancheng Zhong, Ying Yu, Ziyang Zheng, Zhengqing Ding, Xuebo Zhao, Jiawei Yang, Yuming Wei, Yingxin Chen, Siyuan Yu.
Unique in relation to the customary BIC, small-scale BIC limits light in the upward heading, yet in addition traps light in the cross-over bearing by the photonic bandgap of the horizontal heterostructure. As a result, it makes it possible to reduce the size of the structure because it does not require long-range periodicity. The little BIC structure comprises two arrangements of photonic gems with various periods, An and B, as displayed in Fig. 1a. Hole A fills in as a thunderous microcavity for lasers.
Since it is a limited photonic gem, its mode exists as the discrete state Mpq in k-space (where p and q are positive numbers, like M11). Light can be laterally trapped by designing the state Mpq of A to be precisely in the bandgap of B. As depicted in Fig. Above the light cone, the resonant states 1b, M11, and M12/M21 are in the continuum. By fine-tuning the hole radius and region A’s lattice constant, the discrete state could be designed to converge with accidental BIC modes in k-space, further improving vertical light confinement. The Q element of the favored lasing mode could likewise be additionally moved along.
Tentatively, the specialists initially manufacture a little BIC structure on the InAs/GaAs QD dynamic layer with micromachining and then move the dynamic film to the glass substrate. To ensure the mirror-flip symmetry of the PhC slab, an ultraviolet-curing adhesive was used to cover the membrane’s surface with a layer of glass. By plan, consistent wave, single mode lasing is accomplished with the pit size down to 55 unit-cells (2.52.5 m2 with a mode volume of 1.16(/n)3).
As depicted in Fig. 2a, the device has a single-mode lasing threshold of 17 W (0.074 kW cm2), which is extremely low. A further temperature subordinate laser execution test demonstrates the way that the most extreme working temperature can arrive at 343 K (70 °C), and the trademark temperature is fitted as 93.9 K, as displayed in Fig. 2b. The mini-BIC lasers have also been tuned across a wavelength range of 80 nm by carefully engineering structural parameters (Fig. 2c).
By constructing a miniaturized BIC cavity within an epitaxial QD gain membrane, the researchers demonstrate a structure that enables the effective trapping of both light and carriers in all three dimensions. They effectively accomplish productive, high-ghastly-quality, unequivocally frequency-designed small lasers in the 1,310 nm O-band frequency range. The little BIC lasers, created by the film moving method, can be deftly carried out on various substrates like silicon or LiNbO3.
The mini-BIC lasers are a potential light source for future PICs aimed at high-capacity optical communications, sensing, and quantum information due to their advantages of a small footprint, ultralow threshold, and adaptability for integration, specifically wavelength engineering.
More information: Hancheng Zhong et al, Ultra-low threshold continuous-wave quantum dot mini-BIC lasers, Light: Science & Applications (2023). DOI: 10.1038/s41377-023-01130-5
