Ultra-wideband low radar cross-section metasurface and its application on waveguide slot antenna array

A novel approach devoted to achieving ultra-wideband radar cross section reduction（RCSR） of a waveguide slot antenna array（WGSAA） while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors（AMCs） tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultrawideband RCSR involving in-band and out-of-band is achieved for co-and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-tofabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.

Broadband printed antennas and dual-polarized microstrip and waveguide slot antenna arrays

In order to meet the urgent needs in wireless communications, microwave image synthetic aperture radars （SAR）, and electronic warfare systems, this dissertation studies several types of broadband dual-polarized planar antenna elements and arrays, and proposes a few of novel designs with experimental verification. The main accomplishments reported in the dissertation are as follows.

Effect of Surface Roughness in Micro-nano Scale on Slotted Waveguide Arrays in Ku-band

Modeling of the roughness in micro-nano scale and its influence have not been fully investigated, however the roughness will cause amplitude and phase errors of the radiating slot, and decrease the precision and efficiency of the SWA in Ku-band. Firstly, the roughness is simulated using the electromechanical coupled（EC） model. The relationship between roughness and the antenna＇s radiation properties is obtained. For verification, an antenna proto- type is manufactured and tested, and the simulation method is introduced. According to the prototype, a contrasting experiment dealing with the flatness of the radiating plane is conducted to test the simulation method. The advantage of the EC model is validated by comparisons of the EC model and two classical roughness models （sine wave and fractal function）, which shows that the EC model gives a more accurate description model for roughness, the maxi- mum error is 13%. The existence of roughness strongly broadens the beamwidth and raises the side-lobe level of SWA, which is 1.2 times greater than the ideal antenna. In addition, effect of the EC model＇s evaluation indices is investigated, the most affected scale of the roughness is found, which is 1/10 of the working wavelength. The proposed research provides the instruction for antenna designing and manufacturing.

Extraordinary Optical Confinement in a Silicon Slot Waveguide with Metallic Gratings

We present a silicon slot waveguide with metallic gratings embedded on the silicon surface in the slot region. The dependence of the optical coupling between two silicon wires on the width of the metal gap and the slot size are studied in detail. The results show that the optical field in the slot region with metallic gratings is significantly enhanced compared with the traditional slot waveguide due to the surface plasmon polaritons coupling on metallic gratings. The extraordinary optical confinement is attributed to the low effective dielectric constant of metallic gratings. The effective dielectric constant decreases with the increasing wavelength, and reaches the minimum when the width of the metal gap is about 0.01 times the wavelength.

Hybrid silicon slotted photonic crystal waveguides:how does third order nonlinear performance scale with slow light?

We investigate in this paper the influence of slow light on the balance between the Kerr and two-photon absorption(TPA) processes in silicon slotted hybrid nonlinear waveguides. Three typical silicon photonic waveguide geometries are studied to estimate the influence of the light slow-down factor on the mode field overlap with the silicon region, as well as on the complex effective nonlinear susceptibility. It is found that slotted photonic crystal modes tend to focalize in their hollow core with increasing group index(n_G) values. Considering a hybrid integration of nonlinear polymers in such slotted waveguides, a relative decrease of the TPA process by more factor of 2 is predicted from n_G=10 to n_G=50. As a whole, this work shows that the relative influence of TPA decreases for slotted waveguides operating in the slow light regime, making them a suitable platform for third-order nonlinear optics.

Spontaneous emission rate and optical amplification of Er3+ in double slot waveguide

The spontaneous emission(SE) of Er3+ embedded in a double slot dielectric structure was studied by a quantum-electrodynamical formalism. The study shows that the slot width and the position of Er3+ in slot structure have a significant effect on the SE. The double slot waveguides were fabricated by embedding two low-index Er/Yb silicate material layers into high-index silicon. The radiative efficiency of Er3+ in the double slot waveguides is found to be higher than that of the single slot waveguide, which is consistent with the theory simulation. The 0.67 d B signal enhancement at 1.53 ?m in a 4.6-mm-long slot waveguide was observed pumped by 1476 nm laser. These results show the relevance of our model to study the SE processes in multilayer structures and are important for future realization of silicon-compatible active optical devices.

Nonlinear hybrid plasmonic slot waveguide for second-harmonic generation

A nonlinear hybrid plasmonic slot waveguide composed of periodically poled lithium niobate(PPLN) and two separated silver films is investigated. The e?ective refractive index, propagation length, and energy confinement of the hybrid anti-symmetric mode in this waveguide are calculated using the structure parameters at the fundamental wavelength of λ = 1550 nm and its second harmonic(SH) λ = 775 nm. Through the above indices, coupling e?ciency(maximum SH conversion e?ciency during propagation) and peak position(propagation location of the conversion e?ciency) of SH generation are analyzed. Finally, higher conversion e?ciency can be achieved at a shorter propagation distance by changing the waveguide into a tapered structure.

Integrated fluorescence excitation,collection,and filtering on a GaN waveguide chip

Fluorescence detection is widely used in biology and medicine,while the realization of on-chip fluorescence detection is vital for the portable and point-of-care test(POCT)application.In this Letter,we propose an efficient fluorescence excitation and collection system using an integrated GaN chip consisting of a slot waveguide and a one-dimensional photonic crystal(1D PC)waveguide.The slot waveguide is used to confine the excitation light for intense light–sample interaction,and the one-trip collection efficiency at the end of slot waveguide is up to 14.65%.More interestingly,due to the introduction of the 1D PC waveguide,the fluorescence signal is directly filtered out,and the excitation light is reflected to the slot waveguide for multiple excitations.Its transmittances for the designed exciting wavelength of 520 nm and the fluorescent wavelength of 612 nm are 0.2%and 85.4%,respectively.Finally,based on numerical analysis,the total fluorescence collection efficiency in our system amounts to 15.93%.It is the first time,to our knowledge,that the concept of an all-in-one-chip fluorescence detection system has been proposed,which paves the way for on-chip fluorescence excitation and collection,and may find potential applications of miniaturized and portable devices for biomedical fluorescence detection.

Large group-index bandwidth product empty core slow light photonic crystal waveguides for hybrid silicon photonics

This paper investigates the slow light propaga- tion in silicon on insulator wide slot photonic crystal waveguides （PCWs）. Two design schemes are presented, relying on the dispersion engineering of hole lattice and slot, respectively. Mode patterns and band diagrams are calculated by 3D-plane wave expansion method. Then, coupling and slow light propagations are modeled using finite difference time domain method in a full Mach- Zehnder interferometer （MZI）. Results show high amplitudes interference fringes and high coupling efficiencies. Fabrication and measurement of devices lead to slow light propagation with group indices above 50, while multiple scattering and localized modes near the band edge also observed. This study provides insights for losses in hollow core slot high group index waveguides.

Highly efficient tunable optical filter based on liquid crystal micro-ring resonator with large free spectral range

A highly efficient tunable optical filter of liquid crystal （LC） optical micro-r/rig resonator （MRR） was proposed. The 4-pro-radius ring consists of a silicon-on- insulator （SOI） asymmetric bent slot waveguide with a LC cladding. The geometry of the slot waveguide resulted in the strong electro-optic effect of the LC, and therefore induced an increase in effective refractive index by 0.0720 for the quasi-TE mode light in the slot-waveguide. The ultra-wide tuning range （56.0 nm） and large free spectral range （FSR） （-28.0nm） of the optical filters enabled wavelength reconfigurable multiplexing devices with a drive voltage of only 5 V. The influences of parameters, such as the slot width, total width of Si rails and slot shift on the device＇s performance, were analyzed and the optimal design was given. Moreover, the influence of fabrication tolerances and the loss of device were both investigated. Compared with state-of-the-art tunable MRRs, the proposed electrically tunable micro-ring resonator owns the excellent features of wider tuning ranges, larger FSRs and ultralow voltages.