Gain Suppression Research Articles

SBS Gain Suppression in a Passive Single-Mode Optical Fiber by the Multi-Mode Acoustic Waveguide Design

A novel method of stimulated Brillouin scattering (SBS) gain suppression in passive single-mode optical fibers is proposed and experimentally verified. The effect is achieved due to special propagation conditions created for a number of the core-bounded acoustic modes effectively involved in the SBS, such that its gain becomes approximately evenly distributed over a wide spectral range, thereby proportionally reducing its maximum. To verify and investigate this method in depth, single-mode large-mode-area (LMA) fibers with correspondingly optimized acoustic index profiles are fabricated, experimentally tested, and analyzed. Uneven complex doping of the core with two additives, P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> and F, forms a high-contrast gradient acoustic index profile while maintaining a quasi-uniform optical refractive index profile. With a contrast of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> of more than 6 mol.%, we achieved 8 dB of SBS suppression over conventional uniformly doped LMA fibers. Moreover, it is shown that more than 10 dB of SBS gain suppression can be achieved if the optimal dopant distribution is realized.

A Method of Generating Radiation Nulls Utilizing Inherent Resonance Modes for Dual-Polarized Filtering Dipole Antenna Design

This communication proposes a method of generating radiation nulls for designing wideband dual-polarized filtering dipole antenna with simple structure. The proposed antenna consists of a pair of crossed dipole radiators, a ground plane, and a balun. Different from the previously proposed methods, the filtering performance of the proposed antenna is achieved by fully exciting the out-of-band resonance modes of the balun and radiator. The proposed dual-polarized filtering antenna has a very simple structure without any extra circuit and nearly has no radiation performance degradation. One radiation null and two other ones are generated at the lower and higher edges of the passband to achieve good frequency selectivity, respectively. The proposed antenna has high efficiency of about 90% inside the operating bandwidth of 1.7-2.8 GHz and out-of-band gain suppression of more than 20 dB.

Measurement delay compensated LADRC based current controller design for PMSM drives with a simple parameter tuning method

For permanent magnet synchronous motor drives, the difficulty of parameter tuning of nonlinear active disturbance rejection control (ADRC) current controller is the bottleneck for its application. This paper proposes a measurement delay compensated linear ADRC (LADRC), and a simple tuning method for LADRC’s parameters is presented. Firstly, an ideal model without resistance is acquired, because the current coupling terms, dead-time effects, and motor parameter variations are estimated and canceled out by an linear extended state observer. Secondly, an improved LADRC considering time delay of current measurement is developed. It eliminates unmatched disturbance compensation caused by measurement delay. And frequency responses of current closed-loop gain and disturbance suppression are evaluated. Then, based upon the frequency characteristics of the LADRC controller, a simple tuning method founded on desired frequency bandwidth is presented. It is convenient to be implemented. Finally, experimental results demonstrate that the proposed method is effective.

Effect of asymmetric intermodal gain suppression on dynamics of multimode semiconductor lasers

This paper introduces a theoretical study on the influence of intermodal asymmetric gain suppression (AGS) on dynamics and output of multimode semiconductor lasers. The study includes comprehensive and intensive simulations of the dynamics of 21-oscillating longitudinal modes taking account of the self- and cross-modal gain suppression mechanisms. AGS is varied in terms of a pre-defined parameter, Hc, that combines the linewidth enhancement factor and differential gain as controlling parameters of AGS. We classify laser oscillation into four types, namely, single mode oscillation (SMO), symmetric steady-state multimode oscillation (SSMMO), asymmetric steady-state multimode oscillation (ASMMO) and hopping multimode oscillation (HMMO) depending on the values of Hc and injection current. We allocate the operating regime of each of these classes over a mapping diagram of Hc versus current. SMO is attained when the current increases beyond the threshold and Hc has small values. Jumping of the oscillating mode on the long-wavelength side is noticed by increasing Hc. When Hc increases and violates AGS, HMMO is induced among a number of modes, and asymmetric output spectra are obtained. In this case the mode-hopping frequency ranges between 36 and 392 MHz and the hopping modes are anti-correlated with correlation coefficient exceeding – 0.25.

Adaptive Background Suppression Method Based on Intelligent Optimization for IR Small Target Detection Under Complex Cloud Backgrounds

To improve the detection of dim and small targets in infrared (IR) images containing high-intensity cloud clutter, a novel adaptive background suppression method is proposed. By using three-dimensional cooperative filtering and differential calculation, the different and complex background clutter is suppressed. To obtain the optimal parameters for the background suppression algorithm, an adaptive parameter optimization method is proposed. The adaptive parameter optimization problem is transformed into a multiobjective optimization problem in which the signal-to-clutter ratio gain and background suppression factor, which effectively reflect the background suppression performance, are chosen as the optimization objectives, and the parameters of the proposed background suppression algorithm are considered as the variables. To effectively solve the established multiobjective optimization problem, a particle swarm parameter optimization-based method is utilized. Experimental results indicate that the proposed adaptive background suppression method using these optimal parameters has good performance for IR images in real complex scenes, as well as performance superior to that of other baseline methods.

Cavity-Backed Patch Filtenna for Harmonic Suppression

A co-design consisting of a filtering antenna integrating a cavity-backed patch antenna and a low-pass coaxial filter is proposed for size reduction of the RF front-end. The cavity-backed patch antenna is developed to exhibit a broad impedance bandwidth and a unidirectional radiation pattern. The low-pass coaxial filter is implemented to suppress harmonic resonances and gain in the stop-band of the antenna and is embedded directly inside the antenna cavity to realize a compact small-footprint co-designed filtering antenna structure. Two prototypes of the proposed filtering antennas, which integrate cavity-backed patch antennas with $4^{\textit {th}}$ and $5^{\textit {th}}$ order low-pass coaxial filters and with the overall dimensions of $0.697\lambda _{0} \times 0.585\lambda _{0} \times 0.236\lambda _{0}$ and $0.697\lambda _{0} \times 0.585\lambda _{0} \times 0.320\lambda _{0}$ (where $\lambda _{0}$ is the free space wavelength at 3.15 GHz), respectively, are fabricated and measured. The experimental results show fractional bandwidths of 25% and 23.8% and gain suppression levels exceeding 11 dB and 22 dB in the stop-bands for the filtering antennas with the $4^{\textit {th}}$ and $5^{\textit {th}}$ order filters, respectively. The measured gain is more than 6.5 dBi in the pass-band for both filtering antennas. In addition, excellent agreement is obtained between the simulated and measured results.

Optimization of ASE suppression in high efficiency Tm3+-doped pulsed all-fibered MOPA operating at 1908.12 nm

We proposed and demonstrated high efficiency Tm3+-doped pulsed all-fibered master oscillator power amplifier (MOPA) operating at 1908.12 nm with Amplified Spontaneous Emission (ASE) suppressed by optimizing the pumping power, seed laser power and fiber length. Considering the effect of pulsed seed laser and ASE on amplifier output characteristics, the amplifier gain and ASE suppression ratio under different conditions are simulated. Using an optimized length of 1.0 m large-mode-area (LMA) Tm-doped fiber (TDF) is used as amplifier fiber, the maximum average output power of 14.62 W (slope efficiency of 46.0%) with total amplifier gain of 24.66 dB is obtained when pumping power of 30.5 W and input signal laser power of 1.225 W. Meanwhile, ASE can be effectively suppressed with maximum ASE suppression ratio of 49.85 dB is obtained at the repetition frequency (RF) of 1 MHz and the duty cycle of 80%. Central wavelength of 1908.12 nm with linewidth of 0.65 nm and the beam quality of Mx2 = 1.35 and My2 = 1.51. This is, to the best of our knowledge, the maximum ASE suppression ratio in pulsed Tm3+ doped fiber laser by using acousto-optic (AO) external modulation operating at 1908.12 nm without filter.

Cross-polarization suppression for patch array antennas via generalized Kerker effects.

The generalized Kerker effect has recently gained an explosive progress in metamaterials, from the scattering management of particle clusters to the reflection and transmission manipulation of metalattices and metasurfaces. Various optical phenomena observed can be explained by the generalized Kerker effect. Due to the same nature of electromagnetic waves, we believe that the generalized Kerker effect can also be used in the microwave field. Inspired by this, in this letter we design a kind of patch array antenna to suppress the cross-polarization by interferences of multipoles. Using different far-field radiation phase symmetries of electromagnetic multipoles for the patch, the cross-polarization can be almost cancelled while the co-polarization be kept. A pair of 8×8 U-slot patch array antennas, working in a wide band (8.8 GHz-10.4 GHz), have been designed, fabricated and measured to verify our proposal. Simulated and measured results both agree well with the theory, showing more than 20 dB gain suppression of the cross-polarization, which indicates the universality of the generalized Kerker effect in electromagnetic waves.

Infrared Small Target Detection via Low-Rank Tensor Completion With Top-Hat Regularization

Infrared small target detection technology is one of the key technologies in the field of computer vision. In recent years, several methods have been proposed for detecting small infrared targets. However, the existing methods are highly sensitive to challenging heterogeneous backgrounds, which are mainly due to: 1) infrared images containing mostly heavy clouds and chaotic sea backgrounds and 2) the inefficiency of utilizing the structural prior knowledge of the target. In this article, we propose a novel approach for infrared small target detection in order to take both the structural prior knowledge of the target and the self-correlation of the background into account. First, we construct a tensor model for the high-dimensional structural characteristics of multiframe infrared images. Second, inspired by the low-rank background and morphological operator, a novel method based on low-rank tensor completion with top-hat regularization is proposed, which integrates low-rank tensor completion and a ring top-hat regularization into our model. Third, a closed solution to the optimization algorithm is given to solve the proposed tensor model. Furthermore, the experimental results from seven real infrared sequences demonstrate the superiority of the proposed small target detection method. Compared with traditional baseline methods, the proposed method can not only achieve an improvement in the signal-to-clutter ratio gain and background suppression factor but also provide a more robust detection model in situations with low false-positive rates.

Inducing tunable single-mode operation of Fabry-Perot semiconductor laser coupled with very-short cavity with selective optical feedback

We report on achieving tuned single mode operation of a multimode semiconductor laser by coupling it to a very-short external cavity with selective feedback. We show that the induced uniform feedback light from the very-short external cavity can induce single-mode oscillation over a broad range of optical feedback. Then by applying selective external to the optimum settings of the single-mode oscillation, we predict tuning of the single-mode output over a wavelength range of ~ 20 nm by detuning the peak wavelength of optical feedback from the central wavelength of the modal gain. The study is based on modeling of the dynamics of multimode semiconductor laser subject to selective optical feedback. The model takes into account mechanisms of both self- and cross-modal gain suppression, and the study is concerned with the very-short external cavity that corresponds to stable continuous-wave (CW) operation.

A 1.0-Mb/s 198-pJ/bit Bluetooth Low-Energy Compatible Single Sideband Backscatter Uplink for the NeuroDisc Brain–Computer Interface

Wireless brain-computer interfaces (BCIs) are highly energy constrained because of the need to minimize battery size and weight, as well as the need to minimize the thermal dissipation into the living tissue. We demonstrate an ultralow-power Bluetooth Low Energy (BLE) v5.0 compatible backscatter communication uplink for the NeuroDisc BCI. This backscatter approach is compatible with completely unmodified BLE devices such as PCs, smartphones, and tablets and has an energy consumption of under 200 pJ/bit, over 50× less than commercially available BLE transmitters. This article is the first to present an analysis and demonstration of single sideband (SSB) BLE backscatter, which increases the available channel power by +3 dB while suppressing out-of-channel emissions. An analytic model of SSB backscatter communication is provided, along with simulations showing how nonidealities in the achieved backscatter constellation impact opposite-sideband suppression. The experimental measurements of in-channel gain and opposite-sideband suppression are provided. Additional experiments demonstrate a range of 6 m using a +20-dBm external carrier source and an unmodified Nordic Semiconductor nRF51DK BLE adapter, while uplinking prerecorded neural data sampled at 500 Hz.

Integrated and Interconnected Array of Light-Emitting Transistors and Transistor Lasers on Silicon for Photonic Logic

A scalable method of integrating III-V epitaxial structures onto silicon and producing a large-area array of interconnected three-terminal photonic devices in the integrated material is demonstrated. This work establishes CMOS-compatible techniques for GaAs-based active photonic material (n-InGaP/p-GaAs/n-GaAs) to be converted into a distribution of epitaxial islands with direct thermal and electrical connection to a silicon host wafer. A temporary epitaxial bonding process orients and etches modified heterojunction bipolar transistor (HBT) material into a gridded mesh of islands (collector-side up) on a silicon-based carrier wafer with device-level alignment. A subsequent epitaxial transfer creates a permanent metal-eutectic bond between the III-V islands and the silicon host wafer that serves as a uniform electrical interconnect between front-end-of-line processed CMOS and the collector terminals of a photonic chip layer. Thermal, electrical, and mechanical characterization of the integrated material is performed to ensure that the interconnect is suitable for fabrication of photonic devices into the larger-area transferred material. A separate epitaxial process for uniting passive waveguide materials to the same host wafer is then similarly performed. The result is a closely-aligned grid where each III-V island is surrounded by passive material islands. The integrated III-V islands (emitter-side up) are then patterned in unison into an array of light-emitting transistors (LET) and edge-emitting transistor lasers (TL) that are designed for efficient optical coupling into waveguides formed in the passive material, functioning together as active and passive devices in a single network. Device processing parameters are inspected and optimized to account for variations in processing on integrated (thin-film) III-V materials as compared to monolithic device processing, as well as to adhere to CMOS-compatible methods and metallization. The resulting array of three-terminal photonic devices are linked by means of a vertical electrical interconnect through the collector contact and a lateral optical interconnect aligned to the carrier-recombination quantum well (QW) in the base region. Optical and electrical testing (DC) is performed on the integrated devices both individually and as an integrated network for electrical and optical output characteristics, while a comparison to fabricated monolithic three-terminal photonic devices is utilized to relate performance of integrated active photonic devices. Initial work on high-speed testing is performed to benchmark the thermal and electrical improvements in integrated photonic devices. Simulation of the device characteristics is further employed to investigate methods to optimize optical output in relation to electrical gain and beta suppression. The techniques and processes established enable a scalable network of photonic devices for novel heterogeneously integrated electronic-photonic circuitry. This heterogeneous integration produces a platform for pairing a photonic chip layer with a CMOS host wafer such that the interconnects for electrical and optical signals allow for photonic logic designs. Figure 1

Infrared Small Target Detection Using Homogeneity-Weighted Local Contrast Measure

Detecting small targets in infrared (IR) image sequences is an important task in IR guidance systems. The clutter of complex backgrounds often submerges small targets, making detection difficult. Achieving high detection and low false alarm rates with complex backgrounds is a primary problem. We propose an IR small target detection method using our new homogeneity-weighted local contrast measure (HWLCM). Inspired by the ability of the human visual system (HVS) to determine saliency characteristics, we implement our method to use the local contrast features of the central and surrounding regions and the weighted homogeneity characteristics of the surrounding regions to enhance the target while suppressing the complex background. Our method divides each image into blocks with a sliding window for which the HWLCM is calculated. The HWLCM enhances the actual target and suppresses interference simultaneously. We apply an adaptive threshold to target region extraction to further refine the results. Our experimental results show that our proposed method is more effective than six comparable methods, especially in terms of the signal-to-clutter gain (SCRG) and background suppression factor (BSF) indicators.

A low‐profile, dual‐band filtering antenna with high selectivity for 5G sub‐6 GHz applications

AbstractA low‐profile patch antenna with dual‐band filtering response is proposed in this letter. By etching a slot at the edge of a rectangle radiating patch, two modified resonate modes are simultaneously excited. More importantly, a natural radiation null is generated between the two operation bands. Additionally, an inverted L‐shaped feedline combined with a stepped‐impedance resonator is introduced, and two radiation nulls are produced outside the two bands. Finally, a dual‐band bandpass filtering response is obtained. Measured results demonstrate that the two operation bands are 3.32‐3.65 GHz and 4.67‐5.15 GHz, which can cover two main bands of 5G sub‐6 GHz applications. Besides, the antenna achieves stable in‐band gains and radiation patterns, and maintains good out‐of‐band gain suppression performances with three radiation nulls. In addition, a low profile of 0.06 λ (at 3.5 GHz) or 0.08 λ (at 4.9 GHz) is also achieved.

White-light cavity with multiple broad bands based on tunable negative dispersion in a multi-level system

We propose a scheme for the generation of a white-light cavity with multiple broad frequency bands by using an incoherent pumped multi-level atomic system. Owing to the destructive quantum interference induced by the coherent coupling fields, multiple negative dispersion regions with a broadband characteristic can be achieved within the transparency windows, which result from resonant gain suppression. By simply adjusting the control fields, the negative material dispersion compensates the normal dispersion of cavity in the transparency regions, so we can obtain a white-light cavity with multiple wide frequency bands. Moreover, the cavity linewidth depends explicitly on the incoherent pumping rate and gas density. When the system interacts with more coherent coupling fields, we anticipate that more bands will be generated in the cavity transmission spectrum. The proposed scheme can find applications in many fields, such as a wide-band optical switch for multiple signals.

Optimization investigation for high-power 1034 nm all-fiber narrowband Yb-doped superfluorescent source

An optimization for all-fiber narrowband Yb-doped superfluorescent source with a central wavelength shorter than 1040 nm is conducted theoretically and then verified experimentally using steady-state rate equations. Theoretical investigation indicates that with the increase in fiber length, signal power presents one peak value, but the ratio of signal power to output power is decreasing monotonously. Moreover, a filter with high extinction ratio and a gain fiber with high absorption coefficient can have gain suppression on a long wavelength. One all-fiber superfluorescent source is built experimentally on the basis of the theoretically optimized parameters. The source achieves an output power of 214.64 W with a central wavelength of 1034.18 nm and signal–noise ratio of 30 dB. The output power of the source can have further power scaling with considerable available pump power.

Dual-Polarized Low-Profile Filtering Patch Antenna Without Extra Circuit

This paper proposes a novel dual-polarized filtering patch antenna without an extra circuit. The proposed antenna shows a quasi-elliptic filtering response with four radiation nulls. One radiation null is achieved with a stacked patch, and three more radiation nulls are introduced by the split ring resonators (SRRs) placed inside the antenna aperture. The SRR can achieve one radiation null, and the shorted SRR (SSRR) can achieve two radiation nulls for its odd and even modes. This filtering antenna is fabricated on two stacked substrates with three metallic layers, which is suitable for integration. As demonstrations, two antennas are designed to meet the applications for the 5G band (4.8-5 GHz) for S11 <; -10 dB with the total profile of 0.06 λL, where λL is the free-space wavelength at the lowest operating frequency. The antenna implemented on FR4 substrate achieves an average gain of 5 dBi, while the antenna fabricated on two substrates, Rogers-4350 and FR4, can improve the realized gain to over 6 dBi. The measured isolation is better than 20 dB within the operating band. The out-of-band gain suppression level is more than 15 dB within the 3.4-3.6 GHz and more than 20 dB for WLAN band.

Thermal Effects on Modal Properties of Dual-Core Yb-Doped Fibers

The impact of thermo-optic refractive-index changes arising from the core heat load in a dual-core fiber amplifier is studied through finite-element-based numerical simulations. Trends in coupling lengths, effective area, core overlaps of fundamental and higher-order supermodes, effects of asymmetric heat loads, and thermo-optic mode coupling parameters are quantified. It is concluded that the coupling between cores is only moderately altered by the overall heat load, but can be strongly sensitive to asymmetric loads. The influence of the core coupling strength is demonstrated to be very important on the supermode effective area, besides the shrinking due to thermal effects. While the thermo-optic index perturbations can lead to guidance of higher-order supermodes, it seems realistic to maintain single-mode operation through gain suppression of the higher-order modes. On the other hand, thermo-optic couplings between fundamental supermodes are found to be quite strong.

Dual-Band Shared-Aperture UHF/UWB RFID Reader Antenna of Circular Polarization

A dual-port, dual-band, and circularly polarized (CP) radio frequency identification reader antenna is designed to operate at both ultrahigh frequency (UHF) and lower ultra-wideband (UWB) bands for indoor positioning systems. In conjunction with a properly selected quadruple feed network, a shared aperture using the concept of hybrid mode is utilized for broadening the antenna bandwidth. The concept is demonstrated to achieve a high gain, wideband, and CP operation within a low profile. The measured overlapping 3-dB axis ratio (AR) bandwidth and 10-dB impedance bandwidth for the UHF band ranges from 0.918 to 0.926 GHz with a minimum in-band antenna gain of 9 dBic. The measured overlapping 3-dB AR bandwidth and 10-dB impedance bandwidth covers from 3 to 5.2 GHz with a minimum in-band gain of 9 dBic in the lower UWB band (i.e., 3.1–4.8 GHz). The gain suppression near the two wireless local area network bands (i.e., 2.45 and 5.8 GHz) is more than 20 dB. The isolation between two ports is larger than 25 dB over the UHF and lower UWB bands, respectively.

Bariatric Arterial Embolization: Effect of Microsphere Size on the Suppression of Fundal Ghrelin Expression and Weight Change in a Swine Model.

Purpose To determine whether microsphere size effects ghrelin expression and weight gain after selective bariatric arterial embolization (BAE) in swine. Materials and Methods BAE was performed in 10 swine by using smaller (100-300 μm; n = 5) or larger (300-500 μm; n = 5) calibrated microspheres into gastric arteries. Nine control pigs underwent a sham procedure. Weight and fasting plasma ghrelin levels were measured at baseline and weekly for 16 weeks. Ghrelin-expressing cells (GECs) in the stomach were assessed by using immunohistochemical staining and analyzed by using the Wilcoxon rank-sum test. Results In pigs treated with smaller microspheres, mean weight gain at 16 weeks (106.9% ± 15.0) was less than in control pigs (131.9% ± 11.6) (P < .001). Mean GEC density was lower in the gastric fundus (14.8 ± 6.3 vs 25.0 ± 6.9, P < .001) and body (27.5 ± 12.3 vs 37.9 ± 11.8, P = .004) but was not significantly different in the gastric antrum (28.2 ± 16.3 vs 24.3 ± 11.6, P = .84) and duodenum (9.2 ± 3.8 vs 8.7 ± 2.9, P = .66) versus in control pigs. BAE with larger microspheres failed to suppress weight gain or GECs in any stomach part compared with results in control swine. Plasma ghrelin levels were similar between BAE pigs and control pigs, regardless of microsphere size. Week 1 endoscopic evaluation for gastric ulcers revealed none in control pigs, five ulcers in five pigs embolized by using smaller microspheres, and three ulcers in five pigs embolized by using larger microspheres. Conclusion In bariatric arterial embolization, smaller microspheres rather than larger microspheres showed greater weight gain suppression and fundal ghrelin expression with more gastric ulceration in a swine model. © RSNA, 2018.