In conventional all-dielectric one-dimensional photonic crystals (1DPCs), photonic gaps will shift toward short wavelengths (blueshift) as the incident angle increases for both transverse magnetic (TM) and transverse electric (TE) polarizations. We theoretically and experimentally achieve redshift gaps in 1DPCs composed of alternative hyperbolic metamaterials (HMMs) and dielectrics for TM polarization based on the anomalous wavevector dispersion of HMMs. The HMM is mimicked by layered titanium dioxide and silver with a subwavelength unit cell. However, the gaps remain to be blue-shifted for TE polarization. Therefore, the edges of such gaps can be utilized for high-efficiency wide-angle polarization selection. We achieve efficient polarization selection for incident angles ranging from 50° to 80° at the wavelength of 365 nm.

Photonic gaps are the core of photonic crystals in the manipulation of light. However, in conventional photonic crystals composed of two types of dielectrics, the photonic gaps strongly depend on the angle of incidence, which limits their applications. In this Letter, we present the experimental demonstration of angle-independent gaps in the visible wavelength range in one-dimensional photonic crystals composed of layered hyperbolic metamaterials (HMMs) and dielectrics. HMMs with anomalous wave-vector dispersion can tune the propagating phase of light to an unprecedented extent that usual dielectrics cannot attain. The HMM is mimicked by the layered titanium dioxide and silver with a subwavelength unit cell. Based on the phase-variation compensation effect between the HMM and the dielectric, an angle-independent gap is experimentally realized, which agrees well with the simulated one. This angle-independent gap is very useful in the design of photonic devices such as omnidirectional reflectors with fixed bandwidth or all-angle filters.

We theoretically and experimentally investigate the wide-angle perfect absorptance in a photonic heterostructure composed of a metal film and a truncated photonic crystal (PC) with layered hyperbolic metamaterials (HMMs) in the near ultraviolet and visible regions. The wide-angle perfect optical absorption depends on the dispersionless Tamm plasmon polarition (TPP) under TM polarization, which originates from reflection phase compensation condition between the metal and the truncated PC with HMMs. Our experimental results show nearly perfect absorptance over 0.91 in an angle range of 0-45 degree, which facilitates the design of perfect optical absorbers working in a wide angle range.

Most solar radio telescopes operate below ∼18 GHz and cannot realize a complete frequency coverage of the microwave spectrum, especially in the optically thin regime during solar bursts, which can provide unique information about the magnetic field in the burst area in the solar corona. Therefore, the development of high-frequency microwave observation equipment is demanded by the solar radio community. In this paper, we present a microwave spectrum observation system operating at 35–40 GHz. In this system, the solar radio signal is acquired by an 80 cm Cassegrain circularly polarized antenna, which is then downconverted and channelized by a 35–40 GHz analog front end. The processed signal is finally sent to the digital receiver to generate the microwave dynamic spectrum, which is transmitted by gigabit Ethernet transmission to a host computer. The system performance has been tested and obtained as follows: a noise figure of ∼300 K, system linearity of >0.9999, time resolution of about 134 ms (default), and frequency resolution of 153 kHz. We further conduct calibration for this system and find that the observed Sun–Moon ratio is about 43.1–53.3 @ 35.25 GHz during the new Moon, and is quite close to the theoretical value. The coefficient of variation of the system is ∼0.61% in a 9 hr test. The system has been designed, developed, and tested for over 1 yr in Chashan Solar Observatory and is expected to play an important role in the microwave burst study in the 25th solar cycle.

We theoretically and experimentally investigate the angle-dependent omnidirectional photonic bandgap (PBG) in one-dimensional photonic crystals (PCs) comprising hyperbolic metamaterials (HMMs) for TM polarization, which is different from blue-shifted PBG in conventional all-dielectric photonic crystals. The frequency range of PBG increases when the incident angles increase, owing to the red-shift and blue-shift of the long-wavelength and short-wavelength band edges, respectively. The red-shifted band edge originates from the phase-variation compensation mechanism between the HMMs and dielectric material. The experimental values are in good agreement with the simulation results. These nanostructures are ideal for fabricating photonic devices such as omnidirectional reflectors.