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In this paper, we propose a 3-D chiral metamaterial comprising of a high-K dielectric cube and metallic mesh in the microwave region. Our numerical results show that the metamaterial has dispersionless optical activity and an impedance matching to free space, resulting in broad polarization rotation and low reflectance.

In this paper, a polarization-plane-controllable beam-scanning leaky-wave antenna based on pseudo-traveling-wave resonance is proposed and demonstrated by using nonreciprocal metamaterials. The antenna is composed of a ferrite-microstrip-line-based nonreciprocal composite right/left-handed transmission-line resonator that is terminated with tunable reactive loads for reflectors and a feed line. By changing the externally applied dc magnetic field to the ferrite, beam scanning was achieved at the fixed frequency. In addition, plane of polarization can be rotated independently by changing the phase condition of the reflectors. The numerical and experimental results verified the basic concept.

In this paper, we propose stacked metasurfaces that can convert linearly polarized (LP) wave into circularly polarized (CP) wave. The metasurfaces consist of two layers of periodic subwavelength Jerusalem cross elements and one interlayer of periodic square rings. The anisotropic metasurface elements yield 90° phase difference for two orthogonal linear polarizations upon transmission. The aperture coupling interlayer can provide a flat and close to unity magnitude response to improve the axial ratio (AR). A prototype of this metasurface polarization converter is simulated, fabricated and measured in Ku band. Both simulation and measurement results demonstrate good AR in the operating frequency band. This linear-to-circular polarization converter design can also be used in quasi-optical applications.

In this paper, enhancement of phase-shifting nonreciprocity is proposed by using metamaterial lines with comb-shaped capacitive stubs on the normally magnetized ferrite substrate. The insertion of capacitive stubs enhances the effective permittivity, i.e., effective propagation distance in one propagation direction due to edge-guided mode propagation along the comb-shaped stub edges. The nonreciprocity of the proposed structure was numerically compared with those of other types of metamaterial lines, and transmission characteristics of the prototype circuit were measured and reproduced by the numerical simulations, verifying the enhancement.

A new approach to enhance the phase-shifting nonreciprocity of microstrip-line-based metamaterials with normally magnetized ferrite substrates is proposed, by using a combination of curvature of the lines and asymmetric insertion of stubs. In the analytical approach, the nonreciprocity is approximately formulated by introducing asymmetric surface admittance on the side walls at the strip edges, showing that a linear combination of two factors due to the line curvature and the difference of asymmetric admittances contributes to geometrical asymmetry of the wave-guiding structures. Numerical simulation and measurement results verify predictions from the analytical approach. It is demonstrated that a combination of larger curvature of the metamaterial lines and hybrid insertion of inductive and capacitive stubs on the inner and outer sides, respectively, provides significant enhancement of the nonreciprocity compared to the single side insertion of stubs.

Novel 2-D gray-scale inkjet printed microstrip line (MSL) terminations are presented in this paper. The proposed open-end type MSL termination is constructed of a lossy trace printed on paper and placed on a typical dielectric substrate with background. Optimal design guidelines are also discussed for attaining best absorption band given ink resistivity and termination size. Both fixed width and tapered width lines are presented, experimentally showing high absorption levels over a wide bandwidth. These simple to fabricate structures may find applications in scenarios where low-cost wideband planar terminations are needed.

A multiharmonic absorption circuit utilizing the quasi-multilayered striplines is presented. The circuit consists of a multiharmonic reflection filter, a broadband bandpass filter, and a termination. The novel quasi-multilayered striplines, which consist of alumina substrates stacked using solder balls, provide flexibility in the filter structure and realize low insertion loss at the fundamental frequency. The measured results of the fabricated filter exhibit an insertion loss of less than 0.47 dB at the fundamental operation frequency in C-band, as well as high absorption of the second, third, and fourth harmonics, thus outperforming existing solutions. In addition, the device is compact, with a size of only 0.21 λ 0 × 0.39 λ 0 , where λ 0 is the free space wavelength at C-band.

In this paper, an enhanced bandwidth technique for a backward-wave directional coupler is proposed. The coupler is composed of a conventional microstrip line and a nonreciprocal composite right/left-handed metamaterial line using a normally magnetized ferrite substrate in order to control the dispersion characteristics. In the numerical simulation and measurement results, enhancement of the coupling bandwidth was achieved for the designed and prototype couplers by applying the dc magnetic field to the ferrite substrate.

The Coupled-Mode Patch Antenna (CMPA) realizes reconfigurable patterns on a single patch antenna. The operating bandwidth and scanning angle range, however, limits its application. In this paper, we propose a general co-designing procedure to improve the bandwidth and the in-band scanning angle range of CMPA while maintaining the compact size and simplicity. An E-shape CMPA is demonstrated as an example. The proposed antenna achieves well-matched three-pole response with a fractional bandwidth of 6.2% centering at 2.37 GHz, and in-band scanning angle range of 35° in the measurement. The procedure provides a practical solution to improve the bandwidth and scanning range for any type of CMPA.

An enhancement technique of phase-shifting nonreciprocity in normally magnetized ferrite metamaterial lines is proposed by applying a slow wave structure based on spoof surface plasmon. The nonreciprocity is further enhanced by inserting an appropriate value of capacitance in the corrugated metallic strip. Metamaterial lines with high dispersive characteristics and large nonreciprocity were numerically designed and demonstrated in the experiment.

In this paper, we consider cube-shaped unit cells including high-ε dielectric cubes under magnetic dipole-like resonance placed at the center and metallic mesh wires for negative permittivity to construct three-dimensional quasi-isotropic metamaterials in the microwave region. Basically, such structures suffer from their low wave impedance due to inclusion of high-ε materials. To reduce effective permittivity of the composite structures, we propose to insert additional inductance into the metallic mesh. For the insertion of lumped inductors along the wires, dispersion diagram and the Bloch-impedance are numerically estimated, and converted to effective permittivity and permeability. The numerical simulation results clearly show almost 3-D isotropic propagation characteristics in a specific frequency region and enhancement of the Bloch-impedance close to free space in the left-handed region. The lumped inductors are replaced by meander-line strip patterns for practical configurations. The metallic patterned structures also achieve the enhanced Bloch impedance that is well-matched to free space.

Nonreciprocal metamaterials using normally magnetized ferrite microstrip lines are reviewed, showing derivation of formula for the phase-shifting nonreciprocity based on the eigenmode solution in terms of the effective magnetization in ferrite and asymmetric boundary condition for the wave-guiding structures. Dispersion engineering of the nonreciprocity is also discussed for potential applications to leaky wave antennas with wide steering angles and reduced beam squint.

In this paper, we design and fabricate a unit cell block for 3-D isotropic left-handed metamaterials impedance-matched to free space which is composed of a dielectric cube and metallic mesh. The numerical simulation results show almost 3-D isotropic propagation characteristics in a specific frequency region with low reflection loss at the boundaries. Furthermore, near field profiles along the 1-D aligned array were simulated and measured verifying the backward wave mode propagation without serious field scatterings.

An on-chip Substrate Integrated Waveguide (SIW) antenna operating in Half (HF) mode and One and a Half (OHF) mode is presented. The antenna is implemented in compliance with design rule of Commercial 65 nm CMOS technology. The proposed antenna shows increased bandwidth (compared to resonant antennas) of 20 GHz (0.54 THz – 0.56 THZ). Moreover, antenna shows a measured directivity of 9.4 dBi, leading to a gain of 2.8 dBi, when calculated with simulated efficiency.

Two capacitor loaded planar resonators are introduced in a two-cavity substrate integrated waveguide (SIW) structure to obtain a fourth order filter. The planar resonators each produce a transmission zero by signal interference. Design methodology for a 5 % bandwidth bandpass filter operating at 2.35 GHz is presented in the paper. Two transmission zeroes are placed on either side of the filter passband to obtain a quasi-elliptic response with a mid-band inserion loss of 1.65 dB. Good agreement is obtained between measured and simulated responses of the single-layer printed circuit board (PCB) filter.

In this paper, a novel slow-wave transmission line structure substrate integrated waveguide (SIW) is proposed and investigated. The slow-wave effect is achieved by the enhanced capacitance between the signal trace grid and periodic grounded patches on the same top layer. Such slow-wave effect can provide more than 40% size reduction in lateral dimension compared with the conventional SIW with the same cutoff frequency. At the same time, the longitudinal dimension can also be reduced by more than 40%. To demonstrate its applications, two-pole bandpass filters (BPF) built from conventional SIW and proposed slow-wave SIW (SW-SIW) are compared through simulations and experiments. The BPF implemented with SW-SIW reduces the size by 58.8%. Its measured unloaded quality factor $(Q_{u})$ is up to 120.2.

A chip capacitor loaded dual-band microstrip patch filtering antenna with closely spaced bands is presented. It is shown that an additional resonance can be created in the frequency response of a microstrip patch antenna by etching a slit on its signal plane and loading it with chip capacitors. The frequency of the new resonance can be controlled through the chip capacitor. For dual-band design, the new resonance frequency (2.46 GHz) is placed close to the patch antenna resonance frequency (2.4 GHz) to obtain a frequency ratio of 1.025. The realized gain in the upper and lower bands is 7.7 dBi and 7.1 dBi leading to estimated efficiencies of 81.5% and 73% respectively. The patch antenna is implemented on a single layer printed circuit board (PCB), occupying an area of 0.54 λ g × 0.48 λ g .

Blazed gratings have so far been made tunable by mechanically changing the grating geometry, such as its periodicity. In this work, a low-profile planar blazed metasurface grating is demonstrated which is electronically tunable, with no moving or mechanically changing parts. The reflective metasurface is comprised of planar patch resonators with a cutting slot loaded with a surface mount varactor in each unit cell. Coupling of the incident wave to the resonant surface provides a high efficiency back reflection or blazing. We show that by changing the DC bias, we are able to control the blazing frequency and the reflection angle of the operation. This tuning has been confirmed by simulations and measurements for the Transverse Magnetic polarized incident wave within the X band.

Terahertz quantum-cascade vertical external cavity surface emitting laser (VECSELs) are made possible through the development of amplifying reflectarray metasurfaces. The metasurface is made up of sub-wavelength arrays of antenna coupled sub-cavities loaded with quantum-cascade active material. The QC-VECSEL approach allows scaling of laser power while maintaining a high quality, near diffraction limited beam - something which has been a long standing challenge for THz quantum-cascade lasers with sub-wavelength metallic waveguides. The latest results of cavity and metasurface engineering are presented, including the demonstration of a focusing reflectarray metasurface that enables a "flat-optics" hemispherical VECSEL cavity, with improved geometric stability and a Gaussian profile beam with beam quality parameter of M2=1.3.

In this paper, a pair of tunable reactive elements for reflectors with impedances having a relation of complex conjugate is proposed based on nonreciprocal composite right/left handed transmission lines using a ferrite rod embedded substrate. These reflectors are inserted at both ends of a zeroth-order resonator. Numerical simulation results clearly show that the field profile on the zeroth-order resonator is continuously tunable by changing the applied DC magnetic field to the ferrite rods.

A terahertz quantum-cascade vertical-external-cavity surface-emitting laser (VECSEL) is demonstrated using an active focusing metasurface. This enables a hemispherical cavity with flat optics, which exhibits an excellent beam pattern and higher stability than a plano-plano cavity.

We report a terahertz metasurface quantum-cascade VECSEL laser without moving parts that can electronically switch between near-orthogonal linearly polarized output. It exhibits excellent beam pattern, single-mode operation, and power up to 93 mW at 77 K.

We report tuning of a terahertz quantum-cascade vertical-external-cavity surface-emitting-laser (VECSEL) using piezoelectric actuators and an intra-cryostat cavity. Continuous tuning over 260 GHz at a center frequency of approximately 3.3 THz is demonstrated

The implementation and application of single-layer fully-planar extended-composite right-/left-handed transmission lines (E-CRLH TLs) in substrate-integrated waveguide (SIW) technology are presented. The multiband CRLH behavior of these artificial lines is explained by considering the lumped element equivalent circuit model. The potential of these lines for dual-band and quad-band applications is demonstrated by designing and fabricating a quad-band Y-junction power divider and two dual-band band-pass filters. The main relevant advantage of SIW-based E-CRLH TLs over other E-CRLH lines is fabrication simplicity, since only a single metal layer must be etched and lumped elements are avoided. The fabricated prototypes exhibit very reasonable performance. It is remarkable that for dual-band band-pass filters, standard Chebyshev responses can be obtained to a very good approximation.

A low-profile flat resonant metasurface grating for achieving strong blazing and auto-collimation at microwaves is experimentally demonstrated. The design utilizes a planar approach for blazed gratings, but is different in its fundamental operation compared to phase-modulated blazed metasurface gratings. It operates similar to 3D perfectly blazed resonant cavity gratings, but realized with a planar strip resonator of lowest order resonance in each unit-cell. The structure is capable of achieving strong blazing (i.e. low specular reflection and high m = −1 diffraction). Simulations and Measurements confirm strong auto-collimation blazing in the Transverse Magnetic polarization at microwave frequencies.

We have demonstrated THz quantum-cascade metasurface vertical external cavity surface emitting lasers (VECSELs) using a variety of metasurfaces. The dependence of the laser spectrum on the metasurface design parameters is analyzed via simulation and experiment.

Chiral structures are composed of periodically arranged asymmetric particles. The asymmetry of chiral particles results in extraordinary properties like negative refraction index, giant optical activity and circular dichroism. Consequently, they have applications in super lens and various polarization controllers. There are two types of chiral structures, namely planar and 3D structures. The planar ones usually have three- or fourfold rotational symmetry, which limits the polarization tuning capability. On the other hand, the 3D prototypes are difficult to fabricate and measure. Here, we propose a highly tunable sub-wavelength 3D chiral structure. It can be conveniently manufactured on the single-layer double-side printed circuit board. Based on the proposed idea, a sample converting a linearly polarized wave to a circularly polarized one is demonstrated both theoretically and experimentally. The conversion efficiency is measured to be 60%.

A pseudo-traveling-wave resonator with magnetically tunable phase gradient of field distribution is investigated, and a new type of beam-steering antenna based on the resonator is experimentally demonstrated for the first time. It is a short-ended transmission-line resonator and is composed of a nonreciprocal phase-shift composite right/left-handed transmission line using a polycrystalline yttrium-iron-garnet rod. The resonator operates as zeroth-order resonator if there is no dc magnetic field, and the radiation beam directs to broadside. By increasing an externally applied dc magnetic field normal to the substrate, the effective dc magnetization in the ferrite increases under the unsaturated regime. The phase gradient of the field distribution along the resonator is then continuously increased. As a result, the radiation beam direction changes obliquely with respect to broadside. Continuous backfire-to-endfire beam steering with more than 40° was achieved with almost constant gain of 5 dBi. In addition, numerical simulation results show considerably high radiation efficiency of 85%-95%, and the measured beam angle and gain were found almost constant within the relative bandwidth of 2%.

Composite right/left-handed (CRLH) substrate integrated waveguide (SIW) and half mode substrate integrated waveguide (HMSIW) leaky-wave structures for antenna applications are proposed and investigated. Their propagation properties and radiation characteristics are studied extensively. Their backfire-to-endfire beam-steering capabilities through frequency scanning are demonstrated and discussed. These metamaterial radiating structures are realized by etching interdigital slots on the waveguide surface and the ground. The slot behaves as a series capacitor as well as a radiator leading to a CRLH leaky-wave application. Four antennas are fabricated, measured, and analyzed, including two balanced CRLH SIW designs characterized by single-side or double-side radiation, and two unbalanced HMSIW designs characterized by different boundary conditions. Antenna parameters such as return loss, radiation patterns, gain, and efficiency are all provided. Measured results are consistent with the simulation. All these proposed antennas possess the advantages of low profile, low cost, and low weight, while they are also showing their own unique features, like high directivity, quasi-omnidirectional radiation, miniaturized size, continuous beam-steering capabilities covering both the backward and forward quadrants, etc., providing much design flexibility for the real applications.

Combination of magnetically-resonant dielectric resonators and TE cut-off waveguide structures provides unbalanced or balanced composite right/left handed transmission lines. This idea has been expanded into 1-D, 2-D, and 3-D composite structures, and can be applied to potential microwave and millimeter wave circuits and antennas in the same manner as conventional composite right/left handed transmission lines.

Miniaturized waveguide slot antennas using negative order resonance are proposed and developed in this paper. The design of these novel resonant-type antennas is based on the study of a composite right/left-handed (CRLH) substrate integrated waveguide (SIW) starting from the dispersion diagram and the equivalent circuit. These proposed CRLH resonators are realized by etching the interdigital slot on the surface of the SIW. The slot acts as a series capacitor as well as a radiator leading to a CRLH antenna application. Two types of slot antennas, which are open-ended and short-ended, respectively, are proposed and discussed. The short-ended antenna, which represents a quasi-quarter-wavelength resonator, is characterized by a cavity-backed slot antenna thus providing a high gain. On the other hand, the open-ended antenna exhibits a small size owing to a quasi-half-wavelength operation in the left-handed (LH) region. Four antennas with one or two unit cells are fabricated and measured. Compared with the existing CRLH patch antennas and waveguide slot antennas, our antennas show advantages in terms of simplicity, low-profile, high efficiency, easy fabrication and integration with other circuits.

A novel low-temperature co-fired ceramic (LTCC) resonator is proposed based on the hybrid resonant circuits. The resonator exhibits a very compact size and is also able to introduce a transmission zero in the filter design. A super compact bandpass filter with high performance was designed at the center frequency of 2.45 GHz and fabricated using the proposed LTCC hybrid resonator. This filter has a very compact size of 0.9 mm 0.688 mm 0.652 mm and exhibits a low insertion loss of less than 1.2 dB in the passband. Moreover, the transmission zero that is located at 4.5 GHz efficiently suppresses the spurious responses. In order to improve the stopband suppression even more, the revised resonator is used for the second filter design. Besides occupying an even smaller volume of 0.76 mm 0.748 mm0.67 mm, the second filter exhibits a wide stopband suppression higher than 35 dB from 3.4 to 8 GHz. In addition to the super compact size and wide stopband suppression, insertion losses of less than 2.5 dB were achieved in the passband. A transmission zero at 5.8 GHz was also achieved.

Leaky wave radiation from evanescent-mode left-handed (LH) transmission lines is investigated that are composed of a cut-off parallel plate waveguide loaded with a one-dimensional (1-D) array of the disc type dielectric resonators. The apertures are placed on side walls of the parallel plate waveguide. First of all, the dispersion diagram is numerically obtained with the complex eigenmode solutions. The simulated and measured backward wave radiation characteristics validate the backward wave propagation along the 1-D waveguides. Based on the concept, the backfire leaky wave antenna was designed and demonstrated with the 15-cell structure. The beam scanning with the operational frequency was achieved by more than 30 degrees.

Simple configuration of a unit cell block including dielectric cube at the center covered with a host medium and metallic wire mesh is proposed to realize the 3-D isotropic CRLH metamaterials. The block can be flexibly stacked to construct an arbitrary shape of 3-D isotropic CRLH metamaterials with a discrete step. Influence of air gaps between adjacent blocks on the dispersion curves is also investigated. A small triangular prism is designed and fabricated to demonstrate a frequency-selective beam scanning with an angle ranging from positive to negative values. The experiment for TM mode propagation in the designed metamaterial lens clearly shows negative to positive refractive indices.

Over the past half-decade, the fundamental physical properties of left-handed(LH) metamaterials (MMs) have been established both theoretically and experimentally,and several novel MM-based microwave applications with unique characteristics have already been proposed. This paper provides a recall of the main properties of MMs and an overview of their demonstrated applications and concepts. Moreover,it suggests numerous potential future applications and points out important challenges to meet to design MMs for the next generation of microwave and optical devices.

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is, in essence, a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift keying transmission link and successful recovery of the baseband data is demonstrated.

An isolation technology for radio frequency (rf) applications based on unoxidized porous Si (PS) is demonstrated. This study examines all the important issues pertinent to incorporating PS with Si very-large-scale integration (VLSI) technology, where PS is used as a semi-insulating material. Specifically, the issues on rf isolation performance of PS as a function of porosity [from coplanar waveguide (CPW) line measurements] and PS thickness (from on-chip inductors) and the stress generated from incorporating PS regions by anodization are discussed in detail. CPW line measurements show that the relative dielectric constant of PS films decreases from 9 to 3 with increasing porosity from 24% to 78%. PS is a very low loss material with loss tangent

A high-efficiency and compact AlGaN/GaN heterojunction field-effect transistor (HFET) power amplifier integrated with a microstrip antenna at 7.25 GHz is presented for RF front-end circuit applications. A microstrip circular sector antenna is employed as both a radiator and frequency-dependent output load. Higher order harmonics from the HFET in nonlinear operation are reactively terminated because of the harmonic termination characteristic of the antenna. Based on the optimum load impedance measured by a load-pull measurement setup, the AlGaN/GaN HFET power amplifier has been designed and fabricated at 7.25 GHz using the active integrated antenna concept. In this design approach, the measured antenna impedance is directly transformed to the optimum load impedance for maximum efficiency. The power amplifier with 1-mm gate periphery shows 42% peak power-added efficiency and 30.3-dBm saturated output power with a linear gain of 8 dB, which is in reasonably good agreement with measured discrete HFET load-pull data. Due to the antenna's characteristics, better than 30-dB harmonic suppression has been achieved at both the second and third harmonic frequencies in both the E- and H-planes. To the authors' best knowledge, this is the first demonstration of a high-frequency AlGaN/GaN HFET power amplifier integrated with an antenna.

We have developed an optical pickup with a two-wavelength laser diode unit which can read all the compact disc (CD) and digital versatile disc (DVD) family, including DVD rewritable discs (DVD-RAMs). To enable DVD-RAMs to be read, it is necessary to increase the light power efficiency of the optical system and to reduce the so-called track-crossing noise. This paper discusses several approaches to designing an optical system using a monolithic two-wavelength laser diode, and describes our experimental results and compatible reading of DVD read-only discs (DVD-ROMs), DVD-RAMs, and CDs using an optical pickup with a two-wavelength laser diode unit.

Dielectric materials are continuing to play a very important role in the microwave communication systems. These materials are key in realization of low-loss temperature-stable resonators and filters for satellite and broadcasting equipment, and in many other microwave devices. High dielectric-constant materials are critical to the miniaturization of wireless systems, both for the terminals and base-stations, as well as for handsets. In this paper, a sequential evolution of the dielectric materials applications in microwave devices will be reviewed. This includes dielectric waveguides, low-loss temperature-stable ceramic materials, dielectric resonators, and filters. The recent advances in the multilayer circuit modules, dielectric antennas, and ferroelectrics are also described.

A distributed balanced photodetector with high saturation photocurrent and excellent linearity has been experimentally demonstrated. The maximum linear direct current (DC) photocurrent of 33 mA per branch is equivalent to 66 mA in single-ended photodetectors. A setup for investigating the alternating current (AC) linearity of the receiver is proposed and experimentally demonstrated. The receiver exhibits high AC linearity, even under high power operation. The bandwidth of the receiver remains unchanged when the effective do photocurrent is varied from 1 mA to 21 mA. The distribution of photocurrents was also measured. Device length for optimum radiofrequency performance is calculated and implemented in the design. A correlation between the dark current of the photodiodes and their failure mechanism has been established. Analyzing the failure mechanism, junction diodes are found to be more suitable for high power applications.

Dynamic control of a laser’s output polarization state is desirable for applications in polarization sensitive imaging, spectroscopy, and ellipsometry. Using external elements to control the polarization state is a common approach. Less common and more challenging is directly switching the polarization state of a laser, which, however, has the potential to provide high switching speeds, compactness, and power efficiency. Here, we demonstrate a new approach to achieve direct and electrically controlled polarization switching of a semiconductor laser. This is enabled by integrating a polarization-sensitive metasurface with a semiconductor gain medium to selectively amplify a cavity mode with the designed polarization state, therefore leading to an output in the designed polarization. Here, the demonstration is for a terahertz quantum-cascade laser, which exhibits electrically controlled switching between two linear polarizations separated by 80°, while maintaining an excellent beam with a narrow divergence of ∼3°×3° and a single-mode operation fixed at ∼3.4 THz, combined with a peak power as high as 93 mW at a temperature of 77 K. The polarization-sensitive metasurface is composed of two interleaved arrays of surface-emitting antennas, all of which are loaded with quantum-cascade gain materials. Each array is designed to resonantly interact with one specific polarization; when electrical bias is selectively applied to the gain material in one array, selective amplification of one polarization occurs. The amplifying metasurface is used along with an output coupler reflector to build a vertical-external-cavity surface-emitting laser whose output polarization state can be switched solely electrically. This work demonstrates the potential of exploiting amplifying polarization-sensitive metasurfaces to create lasers with desirable polarization states—a concept which is applicable beyond the terahertz and can potentially be applied to shorter wavelengths.

This paper presents a memory of the author's interaction with Professor Arthur A. Oliner in regard to hidden phenomena of leakage from certain dielectric waveguide structures. These phenomena are very mild so that they can be revealed only by his insight backed by a rigorous analysis and physical understanding of guided waves. He found mistakes in the author's work but it is not fatal. However, this is a significant lesson to the author.

The slotted waveguide antenna stiffened structure (SWASS) utilizes conventional hat-stiffeners or blade stiffeners in aircraft sandwich structures as microwave waveguides. Slotted waveguide antenna arrays may therefore be integrated into the structure by machining slots through the outer skin. However, the primary mechanical load applied to the structure governs the orientation of these slotted waveguides and so dictates the antenna scan plane. This work extends the SWASS concept by demonstrating a means to achieve electronic phase shifting along the waveguide axis for the purpose of beam steering. This is accomplished by incorporating a varactor loaded coaxial composite right/left-handed transmission line into the SWASS for approximate matched tuning of the dispersion diagram about the design frequency.

We report on the first demonstration of velocity-matched distributed photodetectors and balanced photodetectors with p-i-n photodetectors. Record-high linear dc photocurrent of 45 mA has been achieved without suffering from thermal damage, thanks to the superior power handling capability of p-i-n photodiodes. A novel fiber alignment technique has been developed to achieve high linear photocurrent. More than 37 dB of common-mode-rejection ratio and 45-dB suppression of laser relative intensity noise over a broad frequency range have been achieved using the distributed balanced photodetectors in an RF fiber-optic link. The frequency response is flat from 1 to 35 GHz.

Several novel periodic structures for coplanar waveguides are presented. The proposed structures exhibit low insertion loss in the passband, simple fabrication, and slow-wave characteristics. These structures are applied to realize miniature low-pass filters one-tenth the size of conventional filters, with spurious-free response and deep attenuation levels using only three cells.

A novel velocity-matched distributed balanced photodetector with a 50-/spl Omega/ coplanar waveguide output transmission line has been experimentally demonstrated in the InP/InGaAs material system. Distributed absorption and velocity matching are employed to increase the saturation photocurrent. A common-mode rejection ratio greater than 27 dB has been achieved. The radio-frequency (RF) link experiment conducted at 4.16 GHz shows that the relative intensity noise of the laser has been suppressed by more than 24 dB and shot-noise limited performance has been achieved. Significant improvement of signal-to-noise ratio has been observed over a wide range of frequencies and phase mismatch of input RF signals.