Tunable Attenuator Research Articles

A miniaturized tunable optical attenuator with ultrawide bandwidth based on evanescent-field coupling between nanofibers

We propose a novel miniaturized optical attenuator based on the evanescent-field coupling between two nanofibers. Benefiting from a wavelength-dependent waveguiding property of the coupled structure, a tunable attenuation with maximum extinction ratio of ~ 20 dB is demonstrated with an ultrawide optical bandwidth up to 0.7 μm in experiment. The wavelength-depended waveguiding properties of both one single nanofiber and coupled nanofibers are investigated in both theory and simulation. Using an adiabatic coupling structure, an attenuation range from − 0.16 dB to − 18.46 dB is obtained within a spectrum from 1.2 μm to 1.7 μm experimentally. Moreover, the simulated results indicate that, the attenuation only shows a slight change of ~ 0.1 dB with a lateral misalignment of 0.5 μm between the two nanofibers, indicating a high tolerance of this attenuator to the lateral misalignment. Considering the wide bandwidth as well as the ultracompact structure, this attenuator shows high potential in applications such as all-fiber optical sensing and communicating.

Separation of twin beams generated in a Sagnac fiber loop

We theoretically demonstrate the propagating performance of twin beams generated in a Sagnac fiber loop by developing a practical model of optical parametric loop mirror consisting of an optical coupler with adjustable splitting ratio, a nonlinear fiber, a dispersion element, and two tunable attenuators placed at different positions in the loop. Two situations of frequency degenerate and frequency non-degenerate four-waving mixing are considered and various of factors including dispersion conditions, internal losses in the loop, and splitting ratios of the coupler are investigated in detail. When the splitting ratio of the coupler is 1:1 and no loss is in the loop, both the frequency degenerate and non-degenerate twin beams can propagate from different ports completely by introducing proper dispersion, and switching between phase-sensitive and phase-insensitive amplification can be realized by changing the dispersion within the loop. In general, the propagation of signal and idler beams at the two output ports of the fiber loop are influenced by both the splitting ratio of the coupler and the internal loss within the loop. Adjusting the internal loss can partially compensate for the asymmetry of the splitting ratio of the coupler, facilitating spatial separation of the signal and idler beams. Our research is useful for the generation of twin beams using Sagnac fiber loop and the realization of switchable phase-sensitive amplifiers.

Tunable fiber attenuator for electrically wet-driven micromirrors

Herein we report an electronically controlled tunable fiber-optic attenuator that leverages the microfluidic electro-wetting effect, which enables a fine-tuning of the solid-liquid interface wetting angle to control the micro-reflector, thus regulating the lens fiber coupling efficiency. Theoretical calculations indicated an optical attenuation regulation effect of 0–45.0 dB in the voltage range of 0–30.0 V. Experimental results align closely with theoretical calculations, demonstrating an attenuation range of 0.59–43.0 dB within a voltage variation range of 0–25.0 V, with control accuracy of 0.56 dB. Our study unveils the potential for designing fiber-optic attenuators with varying tuning accuracy by precisely adjusting the solid-liquid interface wetting angle.

The Structure Design of a Microstrip Tunable Attenuator Based on Few-Layer Graphene

There are innovative applications for graphene materials in microwave Radio Frequency (RF) due to their unique optoelectronic properties. In this paper, a series of existing tunable microstrip attenuators based on few-layer graphene are compared and studied, and a new microstrip tunable attenuator based on few-layer graphene is proposed on this basis. Firstly, the relationship between the performance of different pair spacing attenuators with 4 pairs of graphene structures is analyzed based on the existing pair spacing studies with 1-3 pairs of structures; after that, the performance characteristics of the existing 1-4 pairs of graphene structures on different substrates are tested and analyzed; finally, a new tunable attenuator structure is proposed based on the above research results. The new attenuator consists of four parts, including a dielectric substrate, a microstrip line, a total of five pairs of graphene flakes on both sides and corresponding metal vias. The resistivity of the graphene flake can be changed by changing the access bias voltage, thus regulating the insertion loss of the attenuator. The experimental results show that the proposed attenuator can operate in the frequency range from 3 GHz to 10 GHz, and the insertion loss can be adjusted from -2 dB to -63 dB, with a high tunable performance of 61 dB.

A tunable and versatile 28 nm FD-SOI crossbar output circuit for low power analog SNN inference with eNVM synapses

In this work we report a study and a co-design methodology of an analog SNN crossbar output circuit designed in a 28 nm FD-SOI technology node that comprises a tunable current attenuator and a leak-integrate and fire neurons that would enable the integration of emerging non-volatile memories (eNVMs) for synaptic arrays based on various technologies including phase change (PCRAM), oxide-based (OxRAM), spin transfer and spin orbit torque magnetic memories (STT, SOT-MRAM). Circuit SPICE simulation results and eNVM experimental data are used to showcase and estimate the neurons fan-in for each type of eNVM considering the technology constraints and design trade-offs that set its limits such as membrane capacitance, supply voltage, leakage, etc.

Integrated optical pattern generation on thin-film lithium niobate with electro-optic modulators and phase-change material cells

Reconfigurable photonic integrated circuits enable high-bandwidth signal shaping with the prospect for scalability and compact footprint. Cointegration of electro-optical tunability with nonvolatile attenuation through functional materials allows for implementing photonic devices that operate on both phase and amplitude. Based on this approach, we propose an integrated photonic design for optical pattern generation deploying a continuous-wave laser and a single electrical function generator. We employ the nonvolatile and reconfigurable phase-change material Ge2Sb2Te5 (GST) as a tunable attenuator for an integrated photonic circuit on the lithium-niobate-on-insulator (LNOI) platform. The GST can be switched between its amorphous and crystalline phases, leading to an optical contrast of ≅18dB. Combining this with integrated electro-optical modulators with a 4 GHz bandwidth in LNOI enables the generation of short optical pulses, based on the principles of inverse discrete Fourier transform.

Optical Microwave Waveforms Generation Based on the Round-Trip Phase of the DFB Laser

In this paper, we theoretically and experimentally analyze the influence of the round-trip phase of distributed feedback (DFB) lasers on the harmonic-phase of photocurrent, caused by the external injection current. The results indicate that the harmonic-phase of photocurrent introduced by the round-trip phase (HPIRP) reduces with the increase of modulation depth at a fixed frequency. Then, based on the HPIRP of the DFB laser, a simple photonic generation method of optical microwave waveforms is proposed and verified. In this scheme, three lasers with different wavelengths are mainly used. By adjusting the tunable optical delay lines and attenuators, the amplitude and phase of the photocurrent of the three branches converted by the photodetector (PD) can be controlled individually. The photocurrent of the superposition of the three branches can be controlled properly to form the target waveform. Dispersive elements and complex microwave photonic filtering are not required. Through experiments, rectangular and triangular waveforms with a repetition frequency of 3.75 GHz are generated.

Extended Method of Lines to Model Cylindrical Graphene-Based Multilayer Structures

In this article, the method of lines (MoL) is extended to analyze 2-D multilayer structures loaded with graphene plates in cylindrical coordinates. Accordingly, the admittance transformation matrices through a 2-D interface are derived taking into account the tensor-form conductivity of the magnetized graphene plate. The transformations determine the admittance matrices on all the planes of the multilayer structure. Furthermore, a technique to obtain the characteristic equation and hence the propagation constant of the structure is proposed by matching the fields at the interfaces loaded with graphene. As a result, the proposed method is able to analyze a generic graphene-loaded multilayer structure in cylindrical coordinates. As a proof of concept, the MoL is exploited to analyze 2-D cylindrical graphene microstrip and stripline transmission lines. The proposed method is validated by comparing the results with COMSOL simulations exhibiting a good agreement. Tuning the chemical potential of the graphene plate has potential applications in tunable microwave attenuators and phase shifters.

Design of a 24×28 gbaud tunable channel attenuator IC for PCB backplane transmission

This paper proposes a tunable 24-channel attenuator integrated circuit (IC) that can simulate the attenuation characteristics of different-length printed circuit board (PCB) backplane channels in the 0–25 GHz frequency range. The attenuation value of −3 dB ∼ -20 dB@14 GHz can be tuned by the IIC interface by steps of 0.5 dB. The fitting error between each attenuation curve and the PCB corresponding backplane attenuation curve is less than ±5%. The input and output characteristic impedance of this attenuator is 50 Ω. This 24-channel attenuator was packaged in a flip-chip ball grid array (FC-BGA) with interchannel crosstalk less than −45 dB. This 24 × 28 Gbaud tunable channel attenuator IC can replace the PCB backplane channel to transmit a non-return-to-zero (NRZ) signal or a 4-level pulse amplitude modulation (PAM4) signal for serializer/deserializer (SerDes) testing. To the best of our knowledge, no similar approach to modeling transmission lines with ICs was found.

A terahertz tunable attenuator based on hybrid metal–graphene structure on spoof surface plasmon polaritons waveguide

A novel type of tunable attenuator on spoof surface plasmon polaritons (SSPP) waveguide based on hybrid metal–graphene structure for terahertz applications is proposed in this paper. Two structures are analyzed and designed, where the first is composed of a graphene sheet at only one cell of the SSPP waveguide and the second at all cells. By varying the graphene chemical potential via a biased voltage, the surface conductivity of graphene can be adjusted. Therefore, the attenuation can also be adjusted. Moreover, an equivalent circuit model is proposed to facilitate the designs of the proposed attenuator and offer the general understanding of the attenuation mechanism. Numerical simulation results with the CST simulator and WCIP method have a good agreement with the theoretical results. The simulated results show that the attenuator can obtain adjustment range from 6.02 to 14.32 dB for the first structure and from 1.58 to 30.93 dB for the second, as the chemical potential rises from 0 to 0.5 eV.

MEMS-based metamaterial grating waveguide for tunable optical attenuator and modulator applications

We present a metamaterial grating waveguide (MGW) for tunable optical attenuator and modulator applications in the infrared (IR) wavelength range, which is composed of sixty periodically one-dimensional gold (Au) nanograting structures on silicon (Si) nanograting waveguide. The first thirty Au nanograting structures along the opposite propagation direction of the guided wave are divided equally into three groups. By elevating the first group (G1) of Au nanograting structures from the Si waveguide surface, the transmission intensity of MGW decreases from 1.0 to 0.3 at the wavelength of 1.278 μm. While elevating the second (G2) and third (G3) groups of Au nanograting structures from the Si waveguide surface, the transmission intensities can be attenuated from 1.0 to 0.3 and 1.0 to 0.4, respectively. For the elevation of G3, the transmission intensity at a specific wavelength can be switched between 0 and 0.8. Furthermore, MGW shows a linear blue-shifting relationship of resonant wavelengths and incident angles between 8° and 20° with a correction coefficient of 0.9991. The resonances of MGW also exhibit blue-shifting characteristics by increasing the environmental refraction index. This proposed design of MGW provides a useful approach for variable optical attenuating, optical switching, wavelength tuning, and sensing applications in the IR spectrum range.

A Novel S-Band High Power Tunable Attenuator With a Magnetron for RF Conditioning of Linac

An S-band high-power tunable attenuator (HPTA) is proposed to adjust the output power of a 2.5 MW magnetron to the range of 40–2400 kW, which is equal to 0.17–17.78 dB attenuation. Additionally, the attenuation control accuracy is better than 0.9 dB/mm. The output power of the magnetron tube is changed by its current, which leads to the output frequency. Thus, the magnetron tube is not suitable for applications that require RF signals with a constant frequency and variable power. By using the proposed HPTA, which is connected to the output port of the magnetron, a signal with a constant frequency and variable power can be produced. In this new setup, the magnetron current is set to a maximum value, and then, the desired output power is realized by adjusting the attenuation of HPTA. This idea prevents the magnetron variation frequency while changing the output power. It should be noted that this system is low cost and lightweight when compared with other technologies, such as Klystron and traveling wave tubes (TWT) for RF conditioning of the linear accelerator.

Stretchable and Dynamically Tunable Attenuator Based on Graphene

In this article, a flexible, stretchable, and dynamically tunable attenuator based on coplanar waveguide (CPW) and graphene is proposed. Soft silicone elastomer and serpentine metal structure are used to realize the flexible, stretchable, and biocompatible characteristics of the CPW. A graphene sandwich structure (GSS) is placed on the upper surface of the CPW to dissipate the electromagnetic wave, achieving the dynamically adjustable characteristics of the stretchable attenuator. When the surface impedance of the GSS is tuned by applying a proper bias voltage, the simulated and measured results reveal that the attenuation tuning range is dynamically tuned from 4–11 dB with a low reflection below −10 dB. In addition, the fabricated attenuator is simultaneously optimized to work at conditions of the normal state, 180° bending and 130% stretching, with acceptable changes between insertion loss and return loss up to 6 GHz. The attenuator covers the medical frequency band of 2.4–2.483 GHz and the 5th generation (5G) communication frequency band of 3.5–3.8 GHz, which demonstrates that the attenuator has potential applications in stretchable electronic systems.

Calibration of Ultrasonic Flaw Detectors in Accordance with ISO 22232-1:2020

This paper presents the ultrasonic flaw detectors calibration system at Standards and Calibration Laboratory (SCL) developed in accordance with the Group 2 tests of ISO 22232-1:2020. The calibration system contains a delay-pulse generator, a function generator, an amplifier, an oscilloscope and a set of tunable attenuators. The measurement setup, model and uncertainty components for each tests are presented. The difference in test parameters from the preceding international standard EN 12668-1:2010 are also reviewed and compared.

Calibration of Loop Antennas in Accordance with CISPR 16-1-6:2014+AMD1:2017 at SCL

This paper presents the ultrasonic flaw detectors calibration system at Standards and Calibration Laboratory (SCL) developed in accordance with the Group 2 tests of ISO 22232-1:2020. The calibration system contains a delay-pulse generator, a function generator, an amplifier, an oscilloscope and a set of tunable attenuators. The measurement setup, model and uncertainty components for each tests are presented. The difference in test parameters from the preceding international standard EN 12668-1:2010 are also reviewed and compared.

Laser-Scribed Graphene (LSG) Fabrication Method for Microwave Circuit Applications

In this letter, a laser-scribed graphene (LSG) fabrication method is used to create graphene to be used in a microwave application, for example, a voltage-tunable microstrip attenuator. Graphene used in microwave circuits, such as tunable attenuators, usually focuses on using exfoliated graphene, deposited graphene nanoplatelets, or microwave irradiation. It will be demonstrated that the fabrication of LSG from graphene oxide on standard double-sided FR-4 copper-clad substrate can be used as a voltage-controlled resistor that results in a tunable microstrip attenuator across the microwave frequencies from 50 MHz to 5.5 GHz.

An all-fiber optical attenuator based on adjustable coupling angle of microfiber

A tunable all-fiber optical attenuator (AOA) based on microfiber with adjustable coupling angle is reported and demonstrated. The AOA is fabricated of a microfiber probe coupled to a tapered fiber on the waist region through van der Waals and electrostatic forces. The attenuation can be tuned by adjusting the coupling angle of the two microfibers. When the coupling is fabricated of angles adjust from 80o to 10o, the optical attenuation can be tuned in a large range from 5.7 dB to 40.1 dB with low insertion loss. The simulation and experimental show that the coupling length can be changed by increasing the coupling angle, which results in decreasing the attenuation of AOA. The attenuation of AOA is decreased linearly by increasing the coupling angle. It provides a feasible approach to achieve attenuators with miniature volume, low cost, and multiple functions in optical communication and fiber lasers.

A Tunable Graphene Filtering Attenuator Based on Effective Spoof Surface Plasmon Polariton Waveguide

In this article, to reduce the operating frequency and the size of the spoof surface plasmon polariton (SSPP) attenuator and introduce the filtering function into the graphene attenuator, we propose a tunable graphene filtering attenuator, namely the graphene-based effective SSPP (ESSPP) attenuator. It consists of an ESSPP waveguide and a graphene sandwich structure (GSS). The effect of GSS on the attenuation and dimensions of the ESSPP waveguide on the passband are analyzed in detail, and the closed form of the attenuation is proposed. Finally, five prototypes of the graphene filtering attenuator are fabricated and measured. The experimental results show that not only the attenuation of this attenuator can be tuned but also that the upper and lower cutoff frequencies can be adjusted independently, which means that this filtering attenuator demonstrates expected filtering and attenuation performance.

Dynamically Tunable Filtering Attenuator Based on Graphene Integrated Microstrip Resonators

In this article, a novel class of dynamically tunable filtering attenuators with high selectivity and continuously tunable attenuation is proposed through the comprehensive design of graphene sandwiched structure (GSS), microstrip line, and half-mode substrate integrated waveguide (HMSIW). The GSSs are loaded on microstrip resonators to reduce the resonance intensity, which results in a valid attenuation in the passband. A co-design method of GSS, microstrip resonator, and HMSIW coupling structure based on the equivalent circuit model is proposed to minimize the impact of graphene on the selectivity of filtering attenuator. A transmission zero located on the upper band is also introduced to enhance the selectivity. By varying the bias voltage on GSSs, a controllable attenuation from 1.7 to 8.4 dB can be obtained over the operating bandwidth centering at 1.72 GHz while preserving good selectivity. It is worth mentioning that the out-of-band suppression of the proposed filtering attenuator is also reduced from 40 to 50 dB. Another tunable filtering attenuator based on microstrip short-ended resonators is also designed to verify the method. Finally, a prototype is fabricated and measured and the measured results are in good agreement with the simulation results.

Tunable attenuator based on hybrid graphene-black phosphorus microstrip line for terahertz applications

This paper presents a novel type of tunable attenuator based on hybrid graphene-black phosphorus microstrip line for terahertz applications. Two configurations are studied, the first is composed of a metal microstrip line and one or two graphene sheets, and in the second a BP sheet is placed under the graphene. A transverse equivalent network is proposed to offer the general understanding of the attenuation mechanism. The simulated result shows a strong agreement between the WCIP method and CST simulator, which confirms the accuracy of the algorithm developed by the WCIP method for the graphene, BP and hybrid area. The results suggest that the attenuator with two graphene sheets gives a wider tunable attenuation range when compared with the attenuator with one graphene sheet at only one side. Furthermore, by putting the graphene on the BP, the attenuation tuning range has been enhanced, where it increases from 2.10–23.96 dB to 3.85–31.69 dB.