Light travels in a zero-index medium without accumulating a spatial phase, resulting in perfect spatial coherence. Such coherence brings several potential applications, including arbitrarily shaped waveguides, phase-mismatch-free nonlinear propagation, large-area single-mode lasers, and extended superradiance. A promising platform to achieve these applications is an integrated Dirac-cone material that features an impedance-matched zero index. Although an integrated Dirac-cone material eliminates ohmic losses via its purely dielectric structure, it still entails out-of-plane radiation loss, limiting its applications to a small scale. We design an ultra-low-loss integrated Dirac cone material by achieving destructive interference above and below the material. The material consists of a square array of low-aspect-ratio silicon pillars embedded in silicon dioxide, featuring easy fabrication using a standard planar process. This design paves the way for leveraging the perfect spatial coherence of large-area zero-index materials in linear, nonlinear, and quantum optics.
Infrared (IR) wire grid polarizer is the core device of polarization imaging system with exceptional properties. However, the fabrication of high-quality devices with large area and good uniformity remains challenging. Herein, a new high aspect ratio structure is designed and fabricated, which makes the polarizer have high transverse magnetic (TM) transmittance and extinction ratio in a wide wavelength band. This study also presents some innovations to traditional fabrication processes. These improvements make it easier to fabricate polarizers with good performance as well as large areas. In a very wide wave band (3-15 μm), the extinction ratio is over 32.33 dB. The average TM transmittance of the wire grid layer is 80%, and of the polarizer is 56.57%, which is almost the highest on silicon substrate without antireflection (AR) coating. Meanwhile, the diameter with good uniformity is larger than 30 mm. This method is highly reproducible and can be mass-produced. The polarizer can cover atmospheric IR windows in both 3-5 and 7-12 μm simultaneously, which is suitable in IR imaging systems for remote sensing and astronomy observation.
A fabrication method for large-area gratings with uniform duty without using a spatial beam modulator is introduced in this study. The inhomogeneity of gratings caused by flaws of the lens and stray light was solved by controlling exposure time within an appropriate range and selecting a suitable beam expansion aperture in the optical path. A model for representing this process was established by analyzing the effects of exposure and development time length, and experimental results exhibited good agreement with the simulation results. Finally, a grating with a period of 550 nm, a uniform duty cycle, and a diameter larger than 30 mm was achieved using a Mach–Zehnder interferometer optical path without a spatial beam modulator. The uniformity of this grating was observed via atomic force microscopy, and the results were highly desirable.
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