Improved Power Handling Research Articles

Raman suppression in high-power fiber oscillators by femtosecond-written chirped and tilted fiber Bragg gratings

Realizing stimulated Raman scattering (SRS) suppression is a key topic for high-power fiber lasers. Here, we report an effective and simple strategy for SRS suppression using chirped and tilted fiber Bragg gratings (CTFBGs) in high-power fiber oscillators while maintaining the compactness and stability of the system. The CTFBG is inserted on the side of a cavity mirror FBG without cutting the gain fiber. To improve power handling capability, the CTFBG and cavity mirror FBGs are inscribed by femtosecond (fs) lasers. The optimal SRS suppression effect can be realized when the CTFBG is inserted into the resonant cavity and on the side of the output coupler FBG. The SRS threshold is increased by approximately 11% with an SRS suppression ratio of nearly 14 dB. Moreover, the output power of the fiber oscillator is improved to 3.5 kW, which is the maximum power achieved in fiber oscillators with SRS suppression using CTFBGs, to the best of our knowledge. The temperature of the air-cooled CTFBG is 50.2 °C, which has the potential to handle higher power. This work provides new insights for suppressing SRS in fiber oscillators, promoting the application of CTFBGs in high-power lasers.

Reflectarray Feeds Augmented With Size-Reducing GRIN Lenses for Improved Power Handling and Aperture Efficiency

The feed for reflectarrays and transmitarrays is crucial for determining the overall antenna aperture efficiency, gain, and power handling. In the past, several methods, such as altering the horn shape to achieve higher modes, have been employed to modify the feed radiation pattern to improve these key parameters. However, another approach is to use gradient index (GRIN) lenses, which offer unprecedented control over the radiation pattern and can be used to shrink the overall antenna. In this paper, we demonstrate highly effective approaches for optimizing GRIN lenses to achieve different design objectives including high gain radiation with a compact feed as well as improved aperture efficiency and power handling. Additive manufacturing is employed to fabricate the lenses, and measured results agree well with simulations.

Surface-Acoustic-Wave Devices Based on Lithium Niobate and Amorphous Silicon Thin Films on a Silicon Substrate

This work presents an acoustic platform using solidly mounted thin-oriented lithium niobate (LiNbO3) film on silicon (Si). A thin layer of amorphous Si eliminates a conductive layer generated in the thin-film bonding processes and contributes to acoustic energy confinement and thermal frequency stability. The gigahertz operating frequency is achieved by resorting to the guided acoustic wave shear-horizontal wave (SH0) in a 400-nm-thick X-cut LiNbO3 thin film. Due to the elimination of the parasitic surface conduction (PSC) effect, the electromechanical coupling of the guide acoustic wave is maximized in the Si-based heterogeneous wafer. Due to the minimized acoustic impedance mismatch between surface material and substrate, longitudinal and higher order spurious modes are suppressed. Due to the stiff substrate with a small temperature expansion coefficient (TEC), the solidly mounted structure features a reduced temperature coefficient of frequency (TCF) and improved power handling. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22.8%, a high loaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1208 at 1.6 GHz, and a TCF of −36 p/min/K. The compressed filter is demonstrated with a minimum insertion loss (IL) of 0.6 dB, a fractional bandwidth (FBW) of 8%, an out-of-band rejection of 30 dB, a TCF of −38.5 p/min/K at roll-off, and a miniaturized footprint of 0.4 mm2. The performance has shown the strong potential of the LiNbO3–Si platform for front-end applications in 5G.

Versatile Germanium Photodiodes with 3dB Bandwidths from 110 GHz to 265 GHz

We demonstrate waveguide coupled germanium fin photodiodes for C- and O-band applications. By scaling the germanium (Ge) fin widths record 3dB-bandwidths reaching from 110GHz to 265GHz are achieved. The intrinsic, undoped germanium fins of the photodiodes are sandwiched in between two complementary in situ-doped silicon regions, circumventing ion-implantation into Ge. This reduces the impact of minority carrier diffusion, which is beneficial for the bandwidth [1,2].In silicon photonics, waveguide integrated germanium photodiodes are a key asset. However, until 2020 optoelectrical bandwidth of foundry manufactured germanium photodiodes remained substantially below the 100GHz benchmark, typical values ranging up to approximately 70GHz [3,4,5]. All of these devices rely on ion-implantation into silicon and/or germanium. Discrete devices in InP technology, on the other hand, achieved 170GHz bandwidth and 0.27A/W responsivity already several years ago [6]. Having such performance available in silicon technology has been a major motivation for our work.The most recent germanium fin photodiodes show a 3dB-bandwidths of 240GHz (with internal responsivity of 0.45A/W) and 265GHz (with internal responsivity of 0.3A/W) both at 1550nm wavelength and 1mA photocurrent at 2V reverse bias [2]. These devices have been fabricated in IHP’s BiCMOS pilot line on 200mm silicon-on-insulator (SOI) wafers. These novel photodiodes do not rely on ion-implantation, but instead the undoped germanium is contacted by in situ-doped silicon offshoot, thus minimizing minority carrier diffusion effects. This novel technology approach allowed us to match or even surpass the state-of-the-art of III-V devices. By scaling the width of the germanium region, different combinations of bandwidths and responsivities can be realized. Certainly, broader fins will yield higher responsivities but on the expense of 3dB-bandwidths.In this paper, we present for the first time the responsivity and bandwidth at 1310nm and 1550nm, as well as dark current and capacitance of the high-speed germanium fin photodiodes. Several aspects important for high performance photodiodes will be discussed:(1) Optoelectrical 3dB-bandwidths and responsivities for various germanium fin widths.(2) Improved power handling capability of the photodiode at 1310nm and 1550nm.(3) Temperature dependent electrical behaviour for photodiodes with various germanium fin widths.Figure 1 shows STEM cross-sections (cut perpendicular to the light-incidence direction) of the 70GHz Ge photodiode integrated at IHP EPIC platform (left) and a novel germanium-fin photodiode with 3dB-bandwidth of 265GHz (right). Two major changes, the transition from Ge-stripe to germanium fin and from ion-implantation to in situ-doped silicon offshoot, eventually lead to record 3dB-bandwidths.[1] Lischke, S. et al., "Ge photodiode with −3-dB OE bandwidth of 110 GHz for PIC and ePIC platforms", In Proc. 2020 IEEE International Electron Devices Meeting (IEDM) 7.3.1–7.3.4, 2020.[2] Lischke, S., et al., "Ultra-fast germanium photodiode with 3-dB bandwidth of 265 GHz", Nat. Photon. 15, 925–931, 2021.[3] Chen, H., et al., " −1-V bias 67-GHz bandwidth Si-contacted germanium waveguide p-i-n photodetector for optical links at 56 Gbps and beyond", Opt. Express 24, 4622–4631, 2016.[4] Boeuf, F., et al., "A silicon photonics technology for 400-Gbit/s applications", In Proc. 2019 IEEE International Electron Devices Meeting (IEDM) 33.1.1–33.1.4, 2019.[5] Lischke, S., et al., "High bandwidth, high responsivity waveguide-coupled germanium p-i-n photodiode", Optics express, vol. 23, no. 21, pp. 27213–27220, 2015.[6] Rouvalis, E., et al., "170-GHz uni-traveling carrier photodiodes for InP-based photonic integrated circuits", Opt. Express 20, 20090–20095, 2012. Figure 1

Conical Ground Helical Antenna with Feed-Through Insulator for High-Power Microwave Applications

In this paper, a novel helical antenna for high-power microwave is proposed. The proposed antenna is intended to demonstrate improved power handling capacity without any deterioration in matching characteristics, gain, and axial ratio. The proposed antenna with a long helix structure is investigated in order to achieve high gain and a relatively wide impedance bandwidth. By increasing the distance between the helix and the ground plane, an improved power handling capacity is obtained, and the impedance matching problem caused by the proposed method is addressed with the use of a feed-through insulator. In addition, a conical-shaped ground is used to compensate for the gain reduction by increasing the distance between the helix and the ground plane. As a result, the proposed antenna exhibits a gain exceeding 11 dBi and an axial ratio of less than 2 dB within the frequency range of 0.86–1.09 GHz. In addition, its power handling capacity exceeds 50 MW for a 0.7-ns input pulse length in air conditions.

High-speed and high-power germanium photodetector based on a trapezoidal absorber.

A compact high-power germanium photodetector (Ge PD) is experimentally demonstrated by re-engineering light distribution in the absorber. Compared with a conventional Ge PD, the proposed structure shows a DC saturation photocurrent improved by 28.9% and 3 dB bandwidth as high as 49.5 GHz at 0.1 mA. Under the same photocurrent of 10.5 mA, the proposed Ge PD shows a 3 dB bandwidth of 11.1 GHz, which is almost double the conventional Ge PD (5.6 GHz). The 25 Gb/s eye-diagram measurement verifies the improved power handling capability. The compact size and manufacturing simplicity of this structure will enable new applications for integrated silicon photonics.

Particle Swarm Optimization and Modular Multilevel Converter Communication in Electrical Applications with Machine Learning Algorithm.

As a result of their natural capacity to recover harmonic current and reactive power from alternating current sources, power electronic devices utilized in conjunction with nonlinear loads have the potential to generate significant harmonic problems within the power system when employed in this way. When this occurs, voltage instability occurs, which must be avoided in order to maintain the consistency and dependability of the power system's power flow. With this approach, the series controller has been replaced by a multilevel modular controller in order to improve power handling capability and achieve higher modular levels with minimal distortions. The shunt compensator is the most effective way to achieve an extremely protected energy system as well as righteous steadiness in electric potential difference under a variety of load constraints. The DQ thesis is employed in this proposed converter to separate the harmonic components by establishing reference frame current, which is accomplished by machine learning techniques. As part of the constant mode operation, the PI controller contributes to maintaining the direct current-potential difference, which is given to the PWM generator. Optimization of the values of K p and K i is accomplished by the use of particle swarm optimization (PSO). The construction of this power system simulation model has been made feasible by the use of time-fluctuating characteristics modeling and the MATLAB programming environment. The new (unified power flow controller) UPFC research that has been made available is persuasive in its capacity to reduce distortions and watt-less power components while simultaneously enhancing efficiency and reducing costs.

X-Cut Lithium Niobate-Based Shear Horizontal Resonators for Radio Frequency Applications

This article reports Lithium Niobate (LN) based shear horizontal (SH0) resonators utilizing suspended and solidly mounted structures for radio frequency (RF) applications. The solidly mounted SH0 structure (also termed guided SH0 structure) is advantageous in obtaining reduced temperature coefficient of frequency (TCF), reduced high frequency overtone spurious responses, and improved power handling. The demonstrated solidly mounted guided SH0 resonators exhibit a mechanical Q as high as 1316 around 950 MHz, and electromechanical coupling factor (k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) of around 21.8 % - resulting in a figure of merit (FoM = k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> · Q) of 288.

Development of High Power 220 GHz Frequency Triplers Based on Schottky Diodes

In this paper, the development of two high power 220 GHz frequency triplers is proposed. The GaAs Schottky diodes with six nodes are applied to realize high efficiency 220 GHz tripler, while the application of GaN Schottky diodes with eight nodes is another attempt to improve power handling of the 220 GHz tripler. To reduce thermal effect of high power multipliers, the AlN substrates with high thermal conductivity are applied to provide better heat dissipation at the diode areas. A combination of electrical and thermal model of the Schottky diodes is established while the optimization of 220 GHz triplers are realized with 3D electromagnetic (EM) simulation and harmonic balanced simulation. Good agreement is achieved between the simulated results based on electro-thermal model and measured performances of the triplers. At room temperature, peak efficiency of the tripler based on GaAs Schottky diodes is 17.8%, while the maximum output of the tripler is 38.2 mW with 300 mW input power. As for the 220 GHz GaN Schottky diode tripler, measured results show that the maximum power handling is beyond 400 mW. The peak efficiency and maximum output are 4.7% and 18.4 mW, respectively. The proposed methods of developing high power multipliers can be applied in higher frequency band in the future.

Integrated high-power germanium photodetectors assisted by light field manipulation

We experimentally demonstrate integrated high-power germanium photodetectors (Ge PDs) by means of light field manipulation. Compared to the conventional Ge PD, the proposed structures have more uniform light distributions in the absorption region. A maximum photocurrent of 27.1mA at -3 V bias voltage is experimentally obtained, demonstrating 50% more photocurrent generation under high-power illumination. Bandwidth and modulated signal measurements also verify the improved power handling capability. The proposed high-power Ge PD with compact size and large fabrication tolerance will bring new applications for silicon photonics.

Helical resonator filters with improved multipactor performance exploiting rigorous modelling and the large gap approach

The power handling capability of helical resonator filters is studied by means of the parallel plate model (employed in the European Cooperation for Space Standardisation) and more rigorous modelling techniques (like the one available in the commercial software tool SPARK3D™) as well as through an experimental test campaign. The results indicate that the parallel plate model provides conservative power handling capabilities for this class of filters, while rigorous modelling can better capture the impact of the geometrical features on multipactor evolution. Although the accuracy of the estimated power handling depends on the knowledge of the practical secondary emission yield values, the use of such rigorous modelling tools enables the design of helical resonator filters with improved power handling capability by exploiting the large gap approach, therefore opening opportunities to avoid additional dielectric fillings.

A Rectenna System With Power Combining Topology for Improved Power Handling Capabilities

This article proposes a new rectenna system that is based on a radio frequency (RF) rectifying circuit with enhanced power handling capabilities. The rectenna consists of an antenna that receives the RF signal and a rectifying circuit that converts it into a direct current (dc) output. The rectifier's power handling capability is improved by delaying the breakdown effect of a Schottky diode, resulting in higher maximum dc output power. The power handling capability enhancement is attained by splitting the received RF signal and directing it to feed multiple rectifying branches. The dc outputs from all branches are then combined across an optimized load. This topology results in a single-input single-output rectifier. The designed rectenna is fabricated and tested. The results indicate a 1.9 times increase in input power at which breakdown occurs. The rectenna system is proposed for use in wireless energy transfer applications, where dedicated power is transmitted towards the rectifier. This rectifier can be integrated into nodes of a wireless sensor network, where the enhanced power handling capabilities contribute to enhance the breakdown characteristics.

CMOS-embedded high-power handling RF-MEMS tunable capacitor using quadruple series capacitor and slit with dielectric bridges structure

In this paper, we report on a high-power handling RF-MEMS tunable capacitor that has a quadruple series capacitor (QSC) and a movable electrode using a slit with dielectric bridges (SDB) structure. The QSC structure consists of two fixed metal–insulator–metal (MIM) capacitors and two MEMS capacitor elements connected in series, and enables reduction of the RF voltage to the MEMS capacitors. The SDB structure is able to increase the release voltage without increasing the pull-in voltage. The combination of these structures enables improving power handling capabilities. A capacitor bank using QSC and SDB structures was fabricated by a micromachining process above CMOS control circuits. Measurement results demonstrate the excellent power handling capability up to +44 dBm for cold switching, and up to +35 dBm under hot switching. Moreover, the Q-factor of the capacitor bank is very high that is above 150 at 1 GHz, and the capacitance can be changed from 1.1 to 5.3 pF at a resolution of 4 bits by the internal control circuits thanks to monolithic integration.

A 57GHz overmoded coaxial relativistic backward wave oscillator with high conversion efficiency and pure TM01 mode output

A 57GHz overmoded relativistic backward wave oscillator (RBWO) operating on the quasi-TEM mode with pure TM01 mode output is presented in this paper, by using outer trapezoidal slow wave structure (SWS) with large distance between inner and outer conductors. The large overmoded ratio can be obtained in coaxial devices to improve power handling capacity, while the large distance between inner and outer conductors can guarantee the electron beam transmit effectively. The 8π/9 mode of quasi-TEM synchronously interacts with the electron beam, while the TM01 mode diffracted by the quasi-TEM mode outputs. The existence of TM01 6π/9 mode in SWS can extract energy from the quasi-TEM mode (which has a high value of Qe) thus increasing the power handling capacity. Particle-in-cell simulation shows that generation with high power 560 MW and efficiency 43.5% is obtained under the diode voltage 520 kV and current 2.47 kA. And the microwave has the pure frequency spectrum of 56.8 GHz radiates in the pure TM01 mode (about 98%).

Codesign of &lt;italic&gt;Ka&lt;/italic&gt;-Band Integrated Limiter and Low Noise Amplifier

In this paper, a thorough design procedure for concurrent design of integrated antiparallel Schottky-diode-based limiter and low noise amplifier (LNA) is presented. The optimum number of limiter branches, the size and number of diodes in each branch, width of the transmission line loaded by diode branches, and design considerations for input transistor of the LNA are discussed in detail. To improve power handling of the limiter with a minimum impact on overall noise figure (NF), a novel limiter structure is proposed where transistors are utilized in a limiter topology. A design procedure is also introduced for the transistor-based limiter-LNA. Developed methodologies are employed to design and fabricate a diode-based and transistor-based limiter-LNA in a 0.1-μm AlGaAs/InGaAs pHEMT process. Measurement results show that the diode-based limiter-LNA tolerates up to 2-W continuous wave (CW) input power without failure, while transistor-based limiter-LNA is capable of handling 5-W CW input power. Measured average gain and NF for the diode-based limiter-LNA are 21 and 2.3 dB over 28-38-GHz frequency range, while the transistor-based limiter-LNA achieves an average 18-dB small-signal gain and 2.5-dB NF over the 30-38-GHz bandwidth.

A K-Band High Power and High Isolation Stacked-FET Single Pole Double Throw MMIC Switch Using Resonating Capacitor

A K-band monolithic microwave integrated circuit (MMIC) transmit and receive (T/R) single pole double throw (SPDT) switch with low insertion loss, high isolation and ultra-high output power is demonstrated using 0.15- $\mu\text{m}$ Gallium Arsenide (GaAs) technology. A shunt field effect transistor (FET) configuration is used to provide low insertion loss and high isolation while the stacked-FET is employed to improve power handling capability. The novel GaAs switch exhibits a minimum measured insertion loss of 1.4 dB and less than 2.5 dB from 22 GHz to 26 GHz as well as 44 dB isolation. The measured input 1-dB power compression point $({P}_{1\, \mathrm{dB}})$ exceeds 4 W.

DC–X‐band high‐power SOI CMOS T/R switch

A high-power single-pole double-throw transmit/receive (T/R) switch in a silicon-on-insulation (SOI) CMOS process is presented. The T/R switch is based on the series–shunt configuration, and the high performance is achieved by utilising SOI characteristics such as floating body transistors and SOI trench (TQ trench). To improve power handling capability, ten thick gate oxide transistors are stacked in transmitter (TX) shunt and receiver (RX) series paths with the source and drain of transistors biased. The measured insertion losses of TX and RX modes are <0.5 and <0.9 dB, respectively. The measured isolations of TX and RX modes are >30 and >23 dB up to 12 GHz. The measured input 1 dB compression point is 34 dBm.

High isolation wideband CMOS T/R switch with leakage cancellation technique for software-defined radio transceiver

0.1---3 GHz high isolation wideband CMOS Transmit/Receiver (T/R) switch is presented for software-defined radio (SDR) transceiver. The independent bias technique is proposed to keep the transistors in ideal ON/OFF mode to improve power handling capacity. The leakage cancellation technique with two matched paths is introduced to cancel the leakage from TX port to RX port. The proposed T/R switch has been implemented in 65 nm CMOS. The measured results show that the differential T/R switch achieves 23dBm 1-dB compression point (P1dB) and features 50---70 dB isolation.

High energy supercontinuum sources using tapered photonic crystal fibers for multispectral photoacoustic microscopy.

We demonstrate a record bandwidth high energy supercontinuum source suitable for multispectral photoacoustic microscopy. The source has more than 150 nJ/10 nm bandwidth over a spectral range of 500 to 1600 nm. This performance is achieved using a carefully designed fiber taper with large-core input for improved power handling and small-core output that provides the desired spectral range of the supercontinuum source.

Electrodeposited Nanolaminated CoNiFe Cores for Ultracompact DC–DC Power Conversion

Laminated metallic alloy cores (i.e., alternating layers of thin film metallic alloy and insulating material) of appropriate lamination thickness enable suppression of eddy current losses at high frequencies. Magnetic cores comprised of many such laminations yield substantial overall magnetic volume, thereby enabling high-power operation. Previously, we reported nanolaminated permalloy (Ni80Fe20) cores based on a sequential electrodeposition technique, demonstrating negligible eddy current losses at peak flux densities up to 0.5 T and operating at megahertz frequencies. This paper demonstrates improved performance of nanolaminated cores comprising tens to hundreds of layers of 300–500-nm-thick CoNiFe films that exhibit superior magnetic properties (e.g., higher saturation flux density and lower coercivity) than permalloy. Nanolaminated CoNiFe cores can be operated up to a peak flux density of 0.9 T, demonstrating improved power handling capacity and exhibiting 30% reduced volumetric core loss, attributed to lowered hysteresis losses compared to the nanolaminated permalloy core of the same geometry. Operating these cores in a buck dc–dc power converter at a switching frequency of 1 MHz, the nanolaminated CoNiFe cores achieved a conversion efficiency exceeding 90% at output power levels up to 7 W, compared to an achieved permalloy core conversion efficiency below 86% at 6 W.