Simplified Modal-Cancellation Approach for Substrate-Integrated-Waveguide Narrow-Band Filter Design

Current substrate-integrated-waveguide (SIW) filter design methodologies can be extremely computational and time-inefficient when a narrow-band filter is required. A new approach to designing compact, highly selective narrow-band filters based on smartly positioned obstacles is thus presented here. The proposed modal-cancellation approach is achieved by translating or eliminating undesired modes within the frequency of interest. This is performed by introducing smartly located obstacles in the maxima and nulls of the modes of interest. This approach is different from the traditional inverter technique, where a periodic number of inductive irises are coupled in a ladder configuration to implement the desired response of an nth-order filter, and significantly reduces the complexity of the resulting filter structure. Indeed, the proposed method may be used to design different filters for several frequency bands and various applications. The methodology was experimentally verified through fabricated prototypes.

Reflection Enhancement and Giant Lateral Shift in Defective Photonic Crystals with Graphene

This study investigates the reflectance of the defective mode (DM) and the lateral shift of reflected beam in defective photonic crystals incorporated with single-layer graphene by the transfer matrix method (TMM). Graphene, treated as an equivalent dielectric with a thickness of 0.34 nm, was embedded in the center of a defect layer. The reflectance of the DM was greatly enhanced as the intraband transition of electrons was converted to an interband transition in graphene. The reflectance of the DM could be further enhanced by increasing the Bragg periodic number. Furthermore, a large lateral shift of the reflected beam could also be induced around the DM. This study may find great applications in highly sensitive sensors.

The absorbing properties of one-dimensional plasma photonic crystals

Using the transfer matrix method, absorbing properties of electromagnetic waves in one-dimensional plasma photonic crystals are proposed. Compared with the absorption of bulk plasma, more absorbing bands have been found in one-dimensional plasma photonic crystals, and the first absorbing band appears below the plasma frequency. These absorbing bands can be controlled by varying structure parameters, plasma parameters and the incident angle. Results show that the periodic number and collision frequency only control the absorbing magnitude. Plasma frequency, plasma thickness and incident angle affect both the absorbing magnitude and locations. Increasing the dielectric constant of the dielectric makes more absorbing bands appear. These features of one-dimensional plasma photonic crystals would have potential applications in tunable millimetre absorbers.

Forbidden Band Broadening of Photonic Crystal for Wide Waveband Infrared Stealth

In order to achieve 1~14μm infrared stealth, the forbidden band of photonic crystal (PC) must be broaden. In this paper, we systematically studied several parameters affect the forbidden bandwidth of PC, such as refractive index ratio, thickness and periodic number of two medium layers. Numeric calculation results show that the forbidden bandwidth increases with the refractive index ratio of two medium layers, and it no longer increases when the refractive index ratio is greater than six; the forbidden bandwidth comes largest when the optical thickness of two medium layers is equal to one quarter of center wavelength respectively; and the periodic number has little influence on the bandwidth. Based on these, we chose PbTe and MgF2 to design a compound PC by four photonic crystals whose center wavelengths are at 10.6μm, 4.8μm, 2.5μm and 1.06μm respectively, and obtained nearly 100% reflectance in 1~18μm waveband, which would well meet the demand of the all-infrared waveband stealth.