Photonic Nanolaser with Extreme Optical Field Confinement

Hao Wu, Liu Yang, Peizhen Xu, Jue Gong, Xin Guo, Pan Wang, and Limin Tong

Phys. Rev. Lett. 129, 013902 – Published 28 June 2022

Abstract

We proposed a photonic approach to a lasing mode supported by low-loss oscillation of polarized bound electrons in an active nano-slit-waveguide cavity, which circumvents the confinement-loss trade-off of nanoplasmonics, and offers an optical confinement down to sub-1-nm level with a peak-to-background ratio of $\sim 30 dB$ . Experimentally, the extremely confined lasing field is realized as the dominant peak of a ${TE}_{0}$ -like lasing mode around 720-nm wavelength, in 1-nm-level width slit-waveguide cavities in coupled CdSe nanowire pairs. The measured lasing characteristics agree well with the theoretical calculations. Our results may pave a way towards new regions for nanolasers and light-matter interaction.

Received 1 October 2021
Accepted 23 May 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.013902

Physics Subject Headings (PhySH)

Nanophotonics

Nanowires Semiconductor lasers

Atomic, Molecular & Optical

Authors & Affiliations

Hao Wu¹, Liu Yang ¹, Peizhen Xu¹, Jue Gong¹, Xin Guo^1,2,3,*, Pan Wang^1,2,3, and Limin Tong ^1,4,†

¹Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
²Jiaxing Key Laboratory of Photonic Sensing and Intelligent Imaging, Jiaxing 314000, China
³Intelligent Optics and Photonics Research Center, Jiaxing Institute of Zhejiang University, Jiaxing 314000, China
⁴Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China

^*guoxin@zju.edu.cn
^†phytong@zju.edu.cn

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Issue

Vol. 129, Iss. 1 — 1 July 2022

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Images

Figure 1
CNP for extreme optical field confinement at 720-nm wavelength. (a) Schematic illustration of a CNP-based nanolaser. (b) Calculated cross-sectional electric field intensity of a ${TE}_{0}$ -like mode in a CNP with nanowire diameter $d = 170 nm$ and slit width $w = 1 nm$ . (c),(d) Field intensity distribution along the horizontal ( $x$ axis) direction ( $y = 0$ ) and the vertical ( $y$ axis) direction ( $x = 0$ ) in (b), respectively. Inset: close-up of the field intensity around the slit in (b). For better clarity, a $100 \times$ profile is also plotted as dotted lines in (c). (e) Close-up view of the intensity profiles in (c) and (d).
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Figure 2
Laser modeling of a CdSe CNP cavity at 720-nm wavelength. (a) The first 4 modes ( ${TE}_{0}$ -, ${TM}_{0}$ -, ${TE}_{1}$ -, and ${TM}_{1}$ -like modes) supported in a CNP with $w = 1 nm$ , and their calculated effective refractive indices $n_{eff}$ . (b),(c) Electric field vectors of the ${TE}_{0}$ - and ${TM}_{0}$ -like modes with $d = 170$ and $w = 1 nm$ . The orientation and size of the white arrow indicate the polarization and amplitude of the local field. (d),(e) Threshold gain $g_{th} L$ of the first 4 modes with (d) $w = 1$ and (e) $d = 170 nm$ , respectively.
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Figure 3
Calculated near-field intensity evolution of optical field output from a ${TE}_{0}$ -like mode in a CNP ( $d = 170 nm$ , $w = 1 nm$ ) and a circular aperture (1-nm diameter). (a) Evolution of $| E |^{2}$ of the ${TE}_{0}$ -like mode output from a CNP end face. A series of isophases of $E_{x}$ are plotted for better visualization. (b) Evolution of $| E |^{2} (0, z)$ of the field output from a ${TE}_{0}$ -like mode (blue) and a 1-nm aperture (orange), respectively. (c),(d) $| E |^{2}$ of an optical field with a wave vector of $k_{0}$ output from (c) a CNP end face and (d) a 1-nm aperture. The calculated overall transmissivity $T$ is also presented. For better visualization, the intensity in (d) is amplified by a factor of $10^{13}$ . The input field is 720 nm in wavelength and 1 nW in power.
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Figure 4
Experimental realization of the CdSe CNP nanolaser. (a) Scanning electron microscopy (SEM) image of a CdSe CNP with $d = 166 nm$ , $L = 22.4 μ m$ , and $w = 1 nm$ . (b) SEM image of a flat end face of the CNP. (c) High-resolution transmission electron microscope image of the 1-nm-width slit. Inset: refractive-index profile around the slit. (d) Schematic of the experimental setup for lasing characterization. Multimode fiber (MMF); beam splitter (BS); polarizer (P); notch filter (NF). (e),(f) Optical images of the end face of CNP from CCD1 (e) below and (f) above the lasing threshold, respectively. (g) Optical image of the CNP from CCD2 around the lasing threshold. Dashed lines in (e)–(g) mark the edge of the substrate.
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Figure 5
Lasing characteristics of the CdSe CNPs. (a) Measured photoluminescence spectra obtained from the end face of a CNP ( $d = 158 nm$ ). Inset: measured (blue circle) and calculated (orange line) polarization-dependent intensity of the peak with pump density of $2.2 MW / {cm}^{2}$ . (b) Pump-density-dependent output intensity (blue circle), linewidth (orange square), and degree of second-order coherence $g^{(2)} (0)$ (green cross) of the peak in (a). (c) Distribution of mode with the lowest threshold gain (I: ${TE}_{0}$ -like; II: ${TM}_{0}$ -like; III: ${TE}_{1}$ -like) with varying $d$ and lasing wavelength. Samples investigated with different $d$ , lasing wavelength, and polarization (white triangle: horizontal polarization; black square: vertical polarization) are also marked. The sample employed in (a) and (b) is marked with a red arrow.
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