Soft Matter Macro and Micro-Photonics workshop

Soft matter-based topological lasers

Yu Wang1, Shiqi Xia1, Irena Drevensek-Olenik2,3 Xinzheng Zhang1,3, Zhigang Chen1 and Jingjun Xu1

1 The MOE Key Laboratory of Weak-Light Nonlinear Photonics, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, 300457, China

2 Faculty of Mathematics and Physics, University of Ljubljana, and Department of Complex Matter, J. Stefan Institute, SI-1000, Ljubljana, Slovenia

3 International Sino-Slovenian Joint Research Center on Liquid Crystal Photonics, Nankai University, Tianjin, 300071, China

Email: zxz@nankai.edu.cn

In recent years, topological photonics has emerged as one of the most attractive frontiers in photonics, with numerous intriguing fundamental phenomena discovered and novel topological photonic devices proposed [1–4]. A rapidly developing branch of topological photonics is topological lasers, which offer a promising route toward stable, efficient lasing robust against structural disorder and imperfections [5–8].

We first design a photonic structure composed of dye-doped polymer ribbons arranged into a Su–Schrieffer–Heeger lattice, which is then infiltrated with a cholesteric liquid crystal (CLC), as shown in Fig. 1. Such polymer-CLC superlattices support a short–short defect at the interface between topologically trivial and nontrivial domains [9]. Using this composite platform, we achieve topological interface-state lasing with circular polarization in the visible wavelength range. The lasing threshold is as low as 0.4 µJ (722 W/mm2). Moreover, we realize wavelength tuning of the lasing emission via the thermo-optic effect of the CLC. The results demonstrate the potential for realizing low-cost, tunable, circularly polarized, compact, and integrated topological photonic devices. They also provide a promising platform for investigating topological physics involving light–matter interactions in soft-matter systems.

We further design and fabricate a one-dimensional soft-matter optical superlattice by stacking polymerized cholesteric liquid crystal films and Mylar films (Fig. 2), demonstrating a structurally flexible, low-threshold, circularly polarized topological vertical-cavity surface-emitting laser [10]. We use a second harmonic output of a Q-switched Nd: YAG laser (SLIII-10, Continuum) with a wavelength of 532 nm, a repetition rate at 10.0 Hz, and a pulse duration of 4.0 ns to excite the sample. Then, we can observe a left-handed circularly polarized topological lasing at 575 nm from this soft-matter-based topological VCSEL with a low threshold at 0.47 μJ (1.5´106 W/cm2), significantly lower than those of the current topological VCSELs. Besides, its slope efficiency reaches 4.0%, and its total lasing conversion efficiency (the ratio of lasing pulse energy to pump pulse energy) reaches 3.8% under the pump energy of 2.0 μJ, which is much higher than that of previous PCLC lasers. We show that this topological laser exhibits excellent single-mode operation under low pump power, with its spatial mode profile closely matching that of the pump laser. Benefiting from its soft-matter architecture, the topological laser can be conformally attached to substrates of various shapes, preserving its desired lasing characteristics and enabling beam steering even after repeated bending. These features render the demonstrated topological laser highly promising for applications in consumer electronics, laser scanning, displays, and wearable photonic devices.

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