为了在基于回音壁模式光学微腔的光学频率梳生成中优化微腔的性能和光频梳的质量，对氟化镁晶体微腔的色散调控进行研究。首先，理论仿真研究了MgF₂晶体微腔边缘形状对腔内模场和总色散的影响；接着根据仿真结果实际加工了两种面形的MgF₂晶体微腔，分别为边缘平面型和单边楔形；然后，搭建了微腔性能检测系统和晶体微腔光梳生成系统，实测加工出的MgF₂晶体微腔样品的品质因子（Q值）最高可达1.1×108；最后在加工的两种面形晶体腔中均有效激发了超过200 nm的宽光谱范围的克尔光频梳。实验结果验证了边缘楔形的微腔结构确实能够有效压缩模场并调控总色散，相比于边缘平面型的微腔能够产生更宽光谱范围的光梳。

Glide symmetry, which is one kind of higher symmetry, is introduced in a special type of plasmonic metamaterial, the transmission lines (TLs) of spoof surface plasmon polaritons (SSPPs), in order to control the dispersion characteristics and modal fields of the SSPPs. We show that the glide-symmetric TL presents merged pass bands and mode degeneracy, which lead to broad working bandwidth and extremely low coupling between neighboring TLs. Dual-conductor SSPP TLs with and without glide symmetry are arranged in parallel as two channels with very deep subwavelength separation (e.g., λ₀ / 100 at 5 GHz) for the application of integrated circuits and systems. Mutual coupling between the hybrid channels is analyzed using coupled mode theory and characterized in terms of scattering parameters and near-field distributions. We demonstrate theoretically and experimentally that the hybrid TL array obtains significantly more suppressed crosstalk than the uniform array of two nonglide symmetric TLs. Hence, it is concluded that the glide symmetry can be adopted to flexibly design the propagation of SSPPs and benefit the development of highly compact plasmonic circuits.

Chromatic aberration-free meta-devices (e.g., achromatic meta-devices and abnormal chromatic meta-devices) play an essential role in modern science and technology. However, current efforts suffer the issues of low efficiency, narrow operating band, and limited wavefront manipulation capability. We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties, which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval. The phase dispersion is tuned successfully based on a multiresonant Lorentz model, and high reflection is guaranteed by the presence of the metallic ground. As proof of the concept, two microwave meta-devices are designed, fabricated, and experimentally characterized. An achromatic meta-mirror is proposed within 8 to 12 GHz, and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function. Both meta-mirrors exhibit very high efficiencies (85% to 94% in the frequency band). Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free meta-devices with other functionalities or working at higher frequency.

Dispersion control is crucial in optical systems, and chromatic aberration is an important factor affecting imaging quality in imaging systems. Due to the inherent property of materials, dispersion engineering is complex and needs to trade off other aberration in traditional ways. Although metasurface offers an effective method to overcome these limits and results in well-engineered dispersion, off-axis dispersion control is still a challenging topic. In this paper, we design a single-layer metalens which is capable of focusing at three wavelengths (473 nm, 532 nm, and 632 nm) with different incident angles (0°, -17° and 17°) into the same point. We also demonstrate that this metalens can provide an alternative for the bulky color synthetic prism in a 3-chips digital micromirror device (DMD) laser projection system. Through this approach, various off-axis dispersion controlling optical devices could be realized.