Broadband Coupling Research Articles

Comments on “Two-Section Broadband Couplers With Wide-Range Phase Differences and Power-Dividing Ratios”

Comments on “Two-Section Broadband Couplers With Wide-Range Phase Differences and Power-Dividing Ratios”

Design, fabrication, and low-power rf measurement of an X -band dielectric-loaded accelerating structure

Dielectric-loaded accelerating (DLA) structures are being studied as an alternative to conventional disk-loaded copper structures to produce the high accelerating gradient. This paper presents the design, fabrication and low-power RF measurement of an externally-powered X-band DLA structure with a dielectric constant epsilon_r=16.66 and a loss tangent tan_delta=0.0000343. A dielectric matching section for coupling the RF power from a circular waveguide to an X-band DLA structure consists of a very compact dielectric disk with a width of 2.035 mm and a tilt angle of 60 degree, resulting in a broadband coupling at a low RF field which has the potential to survive in the high-power environment. Based on simulation studies, a prototype of the DLA structure was fabricated. Results from bench measurements and their comparison with design values are presented. The detailed analysis on the fabrication error which may cause the discrepancy between the RF measurements and simulations is also discussed.

2–2.2 GHz Reconfigurable 1 × 4 Filtering Beamforming Network Using Novel Filtering Switch-Coupler and Twisted Rat-Race Coupler

In this article, a reconfigurable 1 <inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 filtering beamforming network using a novel filtering switch coupler and twisted broadband rat-race coupler is proposed. The filtering switch coupler is constructed by four evanescent-mode cavity (EVA) resonators that are connected by varactors. By controlling the capacitance value of varactors, switchable 0&#x00B0;, 90&#x00B0;, &#x2212;90&#x00B0;, or 180&#x00B0; output phase differences at fixed output ports can be obtained. The broadband rat-race coupler is realized by integrating a crossover inside a conventional broadband rat-race coupler. With such a simple technique, the center area of the conventional broadband coupler is fully utilized, resulting in a size reduction; more importantly, the output ports are adjusted to be adjacent to each other, resulting in a convenient position for next-stage connection. By using the proposed filtering switching coupler and twisted broad-band rat-race coupler, a <inline-formula> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> 4 beamforming network is demonstrated. It exhibits more integrated functionalities, including filtering response and reconfigurable center frequencies with a similar amount of circuit components as the conventional Butler matrix network, providing an alternative solution to conventional beamforming networks in recognition radios. Detailed simulation and measurement have been given to demonstrate the techniques.

A Design of Wideband Microstrip-to-Microstrip Vertical Transition for RF Circuits

With the miniaturization of RF circuits, the transmission of signals in different layers becomes important. How to realize the vertical transition structure with wide transmission band and low loss has become the focus of research. In this paper, we proposed a broadband vertical transition structure design based on cavity coupling. This model achieves broadband coupling between the upper and lower microstrips by adding parabolic patches, which improves the model transmission bandwidth. The simulation results show that the optimized model has ultra-wideband transmission characteristic, the 1dB bandwidth is 3.32 GHz-10.42 GHz and the fractional bandwidth is more than 103%. What’ more, the thick ground layer of the model improves the heat dissipation performance. Therefore, this structure is very suitable for high-speed and high-density RF circuits.

Multi‐section broadband couplers with arbitrary phase differences and power‐dividing ratios

Multi-section broadband couplers with arbitrary phase differences and arbitrary power-dividing ratios are presented. By using the even- and odd-mode analysis, the closed-form design equations are derived and then used to determine the circuit parameters of the proposed couplers. Furtherly, the corresponding performance analysis in terms of the bandwidth requirement is provided. Finally, the design procedure of the proposed general couplers is presented. For verification, several couplers with different phase differences and power-dividing ratios are designed, fabricated and measured. The measured results agree well with the simulated results.

Efficient silicon integrated four-mode edge coupler for few-mode fiber coupling

Here, we designed a broadband, low loss, compact, and fabrication-tolerant silicon-based four-mode edge coupler, composed of a 1×3 adiabatic mode-evolution counter-taper splitter and a triple-tip inverse taper. Based on mode conversion and power splitting, the proposed structure can simultaneously realize efficient mode coupling from TE0, TM0, TE1, and TM1 modes of multimode silicon waveguides to linearly polarized (LP), LP01,x , LP01,y , LP11a,x , and LP11a,y , modes in the few-mode fiber. To the best of our knowledge, we proposed the first scheme of four LP modes coupling, which is fully compatible with standard fabrication process. The 3D finite-difference time-domain simulation results show that the on-chip conversion losses of the four modes remain lower than 0.62 dB over the 200 nm wavelength range, and total coupling losses are 4.1 dB, 5.1 dB, 2.1 dB, and 2.9 dB for TE0-to-LP01,x , TM0-to-LP01,y , TE1-to-LP11a,x , and TM1-to-LP11a,y , respectively. Good fabrication tolerance and relaxed critical dimensions make the four-mode edge coupler compatible with standard fabrication process of commercial silicon photonic foundries.

Diamond NV Centers Based Quantum Sensor Using a VCO Integrated With Filtering Antenna

This paper presents a diamond nitrogen-vacancy (NV) center based magnetic field sensor using a voltage-controlled oscillator (VCO) integrated with a filtering antenna. In existing NV-based quantum sensing systems, microwave source and delivery units are implemented by a set of bulky and costly instruments. This limits its practical applications as well as portability. Here, a VCO integrated with the filtering antenna is designed, providing a more uniform, efficient, broadband and lower phase noise microwave field coupling to the NV centers. As a result, the sensitivity and the dynamic range have been improved over the conventional scheme using separate microwave components, such as antennas, transmission lines, and resonators. Moreover, in this work, the optic filter, and photodetector are also integrated using the hybrid microwave integrated circuits (HMIC) technique for the first time. This significantly increases the integration level and reduces the cost of the NV-based magnetometers. The experimental results indicate that our VCO integrated filtering antenna achieves a sensitivity of 8.52 &#x03BC;T/Hz^1/2 and a dynamic range up to 32.73 dB, which are both greatly improved compared to the VCO with a single resonator. This validates the effectiveness of the approach.

Towards Integrated Single Photon Avalanche Detectors for Visible Light (Invited)

Integrated avalanche photodetectors (APDs) are essential and ubiquitous devices in quantum photonics applications. While free-space APDs are a mature technology, the development of integrated APDs for visible light is still in its infancy. In this invited talk, we review our work on integrated photodetectors – the Germanium photodetector for O band, and the first integrated silicon (Si) APD for visible light. A unique feature of the integrated Si APD system for visible light is the end-fire coupling between the silicon nitride (SiN) waveguide and the Si APD in the same layer. This allows for broadband and high-efficiency coupling of light from the SiN waveguide to the Si APD for light detection, without the drawbacks of conventional interlayer coupling. Our work on integrated Si APDs based on Geiger-mode and our progress towards achieving single photon detection for visible light is discussed in the talk.

A Systematic Design of a Compact Wideband Hybrid Directional Coupler Based on Printed RGW Technology

Printed ridge gap waveguide (PRGW) is considered among the state of art guiding technologies due to its low signal distortion and low loss at Millimeter Wave (mmWave) spectrum, which motivates the research community to use this guiding structure as a host technology for various passive microwave and mmWave components. One of the most important passive components used in antenna beam-switching networks is the quadrature hybrid directional coupler providing signal power division with 90° phase shift. A featured design of a broadband and compact PRGW hybrid coupler is propose in this paper. A novel design methodology, based on mode analysis, is introduced to design the objective coupler. The proposed design is suitable for mmWave applications with small electrical dimensions ( $1.2\,\,\lambda _{o} \times 1.2\,\,\lambda _{o}$ ), low loss, and wide bandwidth. The proposed hybrid coupler is fabricated on Roger/RT 6002 substrate material of thickness 0.762 mm. The measured results highlight that the coupler can provide a good return loss with a bandwidth of 26.5% at 30 GHz and isolation beyond 15 dB. The measured phase difference between the coupler output ports is equal $90^\circ \pm ~5^\circ $ through the interested operating bandwidth. A clear agreement between the simulated and the measured results over the assigned operating bandwidth has been illustrated.

Two-Section Broadband Couplers With Wide-Range Phase Differences and Power-Dividing Ratios

A two-section broadband coupler with wide-range phase differences and power-dividing ratios is proposed. Closed-form design equations for the proposed couplers are derived. For verification, two couplers I and II operating at 2 GHz with phase difference of 45° and power-dividing ratio of 1, and phase difference of 60° and power-dividing ratio of 2, respectively, are fabricated and measured. For the coupler I (II), the measured 15-dB return loss and isolation bandwidth is 38.0% (51.5%). The measured bandwidths of the amplitude imbalance <; 1 dB and the phase imbalance <; 5° of the coupler I (II) are 29.5% (35.5%) and 29.0% (43.0%) with 15-dB return loss and isolation, respectively.

Broadband Coupler Manipulation Through Particle Swarm Optimization for Arrayed Waveguide Grating Based Optical Coherence Tomography

The state-of-the-art optical coherence technology (OCT) has its limitation, such as bulky and quite expensive. Miniaturization and integration of the OCT system are promising to get a compact, less costly, and more stable device. In this paper, we report the influence of optical power splitting on the sensitivity and axial resolution in spectral-domain OCT (SD-OCT) on silicon chip using tandem Mach-Zehnder directional coupler (MZDC) based broadband coupler through particle swarm optimization (PSO). A less-flat wavelength response from a broadband coupler in an interferometer for SD-OCT on-chip will decrease the sensing sensitivity. The arrayed waveguide grating (AWG) as a spectrometer in SD-OCT typically suffers from the axial resolution degradation due to the non-flat free spectrum range (FSR). To avoid the higher optical loss from the large FSR, the PSO manipulation in MZDC is then proposed to demonstrate U-shaped wavelength compensation on the non-flat AWG spectrum. With the broadband coupler configuration, a SD-OCT on-chip can maintain the sensitivity and axial resolution performance.

Ultra-broadband microstrip directional couplers

Conventional broadband couplers use multi-sectioning techniques and consist of multiple coupled lines. In this study, in contrast to traditional methods, one pair of coupled lines is used to design multi-octave broadband couplers. In the proposed microstrip couplers, the coupled lines are weakly coupled and are of one-eighth wavelength at the highest operating frequency. The weakly coupled lines exhibit a linear coupling response with a slope of 6 dB/octave. To compensate the coupling response, one-pole low-pass networks with a slope of −6 dB/octave are cascaded with the microstrip coupled lines. To validate the design concept, two broadband microstrip couplers for the frequency range of 30–500 MHz and 1–3 GHz have been designed and fabricated. The couplers exhibit a coupling of 52 and 39 dB, respectively. The broadband couplers provide a ripple of 0.5 dB in the coupling response. The proposed weakly coupled couplers are adequate for high-power measurements. The weak coupling permits lumped-element surface mount devices to be used as the compensating network. The multi-octave couplers are realised in small areas.

Final design and on-sky testing of the iLocater SX acquisition camera: broad-band single-mode fibre coupling

ABSTRACT Enabling efficient injection of light into single-mode fibres (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fibre injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broad-band SMF coupling in excess of 35 per cent (absolute) in the near-infrared (0.97–1.31 ${\mu {\rm m}}$) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality.

Compact and low-loss 90-deg optical hybrid based on silicon-on-insulator 2 × 2 multimode interference couplers

We design an ultracompact, broadband, and low-loss 90-deg optical hybrid coupler using a silicon-on-insulator (SOI) material platform for coherent receivers in optical communication systems. The proposed hybrid coupler uses a cascaded topology that includes five 2 × 2 multimode interference (MMI) couplers in three different fundamental kinds. The working principle of the suggested 90-deg optical hybrid is based on theoretical analysis on the MMI effect and the transfer matrix relations. The optimization of geometrical parameters and the optical characteristics are employing through the numerical simulation method. The investigated 90-deg optical hybrid coupler can be integrated on a microscale footprint as much as 6 μm × 172 μm. Furthermore, our hybrid coupler expresses lots of advantages of optical performances, with an insertion loss lower than 2.6 dB, a common-mode rejection ratio better than −25 dB, and phase error smaller than 5 deg in 90-nm wavelength-bandwidth in the third telecom window. In addition, the designed device, based on the SOI platform, is endowed with large geometrical tolerances possessing width, height, and multimode tolerances corresponding to ±20, ±10, and ±10 nm in the 1-dB variation limit of transmission, respectively. Such advantages of good performances thus make the proposed hybrid device playing the role of a promising potential candidate for widely varying applications of silicon photonics, such as coherent optical receivers, optical interconnects, and high-bitrate optical phase modulators.

Spatially Broadband Coupled-Surface Plasmon Wave Assisted Transmission Effect in Azo-Dye-Doped Liquid Crystal Cell

Active tuning on a plasmonic structure is discussed in this report. We examined the transient transmission effects of an azo-dye-doped liquid crystal cell on a metallic surface grating. The transition between isotropic and nematic phases in liquid crystal generated micro-domains was shown to induce the dynamic scattering of light from a He-Ne laser, thereby allowing transmission through a non-transparent aluminum film overlaying a dielectric grating. Various grating pitches were tested in terms of transmission effects. The patterned gratings include stripe ones and circular forms. Our results indicate that surface plasmon polariton waves are involved in the transmission process. We also demonstrated how momentum diagrams of gratings and Surface Plasmon Polariton (SPP) modes combined with Mie scattering effects could explain the broadband coupling phenomenon. This noteworthy transition process could be applied to the development of spatially broadband surface plasmon polariton coupling devices.

Toroidal Ferrite Transformers With Conformal Laser Direct Structured Windings

Many applications in communications and power electronics demand inductive components that operate at high frequency or a broad range of frequencies. For applications requiring miniature devices with large inductance values, most often the components are manufactured imprecisely in the traditional method where magnetic cores are wound with a fine gauge wire. To achieve the best high-frequency performance, there is a desire to use a practical manufacturing method that removes the imprecision of wire winding. In this article, a unique 3-D laser exposure system is used to direct-write conformal winding patterns on the surface of MnZn ferrite toroids. The toroidal helix windings were fabricated by both an additive laser direct structuring (LDS) process and a subtractive laser-written mask-and-etch process. Both methods were performed on both enamel-coated ferrites and bare ferrites. The performance and equivalent circuit model parameters of the transformers were measured up to 1.5 GHz and will be presented. The transformers fabricated on the enamel-coated cores were found to have comparable or better inductances and broadband coupling than wire-wound transformers of matching construction.

Mirror-Based Broadband Silicon-Photonics Vertical I/O With Coupling Efficiency Enhancement for Standard Single-Mode Fiber

The broadband vertical optical coupling of silicon (Si) photonics poses significant challenges regarding the use of wavelength division multiplexing (WDM). The grating coupler, a type of vertical optical coupling device, strongly depends on the wavelength. As an alternative, we developed another vertical optical coupling device using a 45° curved micro-mirror. To experimentally demonstrate the broadband vertical optical coupling, the curved micro-mirror was designed based on a measured optical beam output from a Si inverse taper waveguide and integrated on a Si photonic chip to experimentally demonstrate the broadband vertical optical coupling. Without using the use of additional lenses, the Si waveguides were coupled with standard single-mode fiber (SMF) by applying fabricated mirrors. Owing to its lens function, the coupling efficiency was enhanced by 1.4 and 3.4 dB for TE and TM polarization. Over the entire O-band, low-wavelength dependent losses of 1 dB were also obtained. Misalignment tolerances were evaluated and 1-dB tolerances of approximately plus or minus 2 micrometers were obtained. By optimizing the design of the Si inverse taper waveguide, a low-polarization dependent loss of 0.3 dB on average was also obtained for the O-band. The average loss was 3.3 dB. Compared with grating couplers, a broadband and low polarization-dependent Si-photonics vertical coupling was demonstrated using an integrated curved mirror.

High-efficiency couplers for graphene surface plasmon polaritons in the mid-infrared region

We numerically demonstrate a novel, to the best of our knowledge, variety of high-efficiency couplers for mid-infrared graphene surface plasmon polaritons (SPPs). The proposed couplers are composed of a dual-parabolic-tapered transition to compress and couple the SPPs of a GaAs slab waveguide into the graphene layer. The dispersion relation, field distributions, transmittance, and coupling efficiency of the couplers are systematically analyzed. It is found that broadband coupling transmission with a transmittance around 0.3 is achieved for the coupler without a silver substrate. To further reduce radiation and enhance the transmittance, a silver substrate is introduced in the proposed coupler design, which achieves a transmittance over 0.5 ranging from 1960 to 2320 c m − 1 with a peak transmittance of 0.75. Furthermore, both couplers with and without a silver substrate achieve a similar coupling efficiency of more than 48% in the whole wavelength range of 1900 − 2400 c m − 1 and a coupling efficiency peak of over 80% around 2120 c m − 1 . This Letter may provide an efficient excitation method for graphene SPPs, which is of great importance for the development of various graphene plasmonic devices.

Generalized Symmetrical 3 dB Power Dividers With Complex Termination Impedances

The paper introduces a class of two-way, 3 dB narrowband power dividers (combiners), closed on complex termination impedances, that generalizes a number of topologies presented during past years as extensions of the traditional Wilkinson design. Adopting even-odd mode analysis, we demonstrate that, under very broad assumptions, any axially symmetric reactive 3-port can be designed to operate as a 3 dB two-way power divider, by connecting a properly designed isolation impedance across two symmetrically but arbitrarily located additional ports. We show that this isolation element can be evaluated by a single input impedance or admittance CAD simulation or measurement; moreover, an explicit expression is given for the isolation impedance. The theory is shown to lead to the same design as for already presented generalizations of the Wilkinson divider; further validation is provided through both simulated and experimental case studies, and an application of the theory to the design of broadband or multi-band couplers is suggested.

Wideband Two-Section Branch-Line Coupler Using Microstrip Technique

This paper introduces a compact quadrature hybrid coupler for wideband applications. Using the conventional technique of cascading two sections in a quadrature hybrid we designed a broadband coupler at a central frequency of 1.8 GHz. To improve the performance of this coupler and to reduce its size we used the artificial transmission line concept, microstrip line loaded with shunt open ended stubs, and meandering lines. A size reduction of about 31% was achieved compared to the conventional one. The proposed design has a relative bandwidth of 33.3 %, and return loss and isolation loss are both better than 18 dB on the entire band. The proposed coupler has been simulated using the CST Studio suite, fabricated, and measured. A good agreement has been obtained between the simulated and measured results.