Tuning Range Research Articles

High-power and ultra-wide-tunable fiber-type external-cavity diode lasers

High-power and wide-tunable fiber-type external-cavity diode lasers (FTECDLs) are of pivotal importance across various scientific and practical applications, such as polarization lidar, communication, sensing, and spectroscopy. As the output power and tuning characteristics are currently much lower than the saturation power and bandwidth of semiconductor gain media, further improvements conventionally require additional gain media in parallel and external amplifiers, resulting in lower energy efficiency and complex configurations. This study implemented energy manipulation in FTECDLs with a single gain medium, overcoming the mutual restriction between low damage threshold and laser output power. This approach makes it possible to completely exploit the intrinsic performance of the semiconductor gain medium. We demonstrated various FTECDL designs, achieving a maximum tuning range of 226.8 nm, maximum output power of 160 mW, and maximum optical signal-to-noise ratio of 86.3 dB with different configurations. These results are the highest levels ever achieved for E, S, C, L, and U bands. Additionally, the achieved polarization extinction ratio of nearly 38 dB has not been previously reported. Our work provides significant guidance for the design of traveling wave ring cavity (TWRC) lasers, including free-space light semiconductor and solid-state lasers with a TWRC.

Compact frequency‐reconfigurable circular patch antenna with varactor diode: Design, tuning, and compactness optimization

AbstractIn this study, a frequency‐reconfigurable circular patch antenna with a varactor diode has been presented. The proposed antenna has been designed and investigated in four steps: circular patch antenna (Antenna 1), antenna with double slots (Antenna 2), antenna with quad slots (Antenna 3), and antenna with varactor diode (Antenna 4). The proposed antenna has been made compact with rectangular slots and a hyperabrupt junction tuning varactor diode (SMV1249‐079LF). The proposed antenna has been designed and produced in 32 × 32 × 0.64 mm3 dimensions, approximately 80% minimized compared to a microstrip circular patch antenna operating at 850 MHZ resonance frequency. This frequency‐reconfigurable antenna can perform between the range of 0.85–1.3 GHz frequency with 0–3 V DC voltage tuning of the varactor diode. So, using with the varactor diode, the proposed antenna has obtained a 53% tuning range between 0.85 and 1.3 GHz frequencies. This study offers a different antenna design, compactness, and high tuning ratio compared to previous studies. This frequency reconfigurable antenna can be preferred with its wideband structure in different communications areas and wireless energy transfer systems.

Directly modulated FMCW tunable laser with highly linear frequency chirp and narrow linewidth

Frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR) is a promising technology for long-range, high-accuracy, stray-light-immune distance and velocimetry sensing. To achieve this, a precisely chirped and highly coherent laser source is required. In this work, we propose to generate a highly linear frequency chirp by utilizing an intracavity phase modulator with high linearity and demonstrate a proof-of-concept fully integrated monolithic FMCW laser source based on an InP generic platform. By electrically modulating the intracavity phase modulator at a repetition rate of 100 kHz, a 1.85 GHz chirp range with root mean square (RMS) frequency nonlinearity down to 1.8 MHz is achieved without the need of external feedback loop or predistortion. Meanwhile, the laser shows a 51 nm tuning range with a linewidth down to 16 kHz. By taking advantage of the high-speed electro-optical effects, fast frequency modulation with repetition rate of up to 1 MHz is realized with a frequency chirp range of ∼1.65 GHz and RMS frequency nonlinearity of ∼12 MHz. We demonstrate its feasibility for LiDAR through in-fiber ranging at a distance of 50 m, where a 51 cm resolution is directly achieved.

Broadband and widely tunable second harmonic generation in suspended thin-film LiNbO3 rib waveguides

Our study demonstrates second harmonic generation (SHG) in a high confinement LiNbO3 rib waveguide through type-I birefringence phase matching of fundamental modes. The combination of micro-waveguide dispersion and material birefringence reveals unique SHG characteristics that complement the performance of standard LiNbO3 on insulator (LNOI) components. Dual-pump wavelength phase matching in the near-infrared and mid-infrared regions is shown in a given waveguide. These two wavelengths can be positioned in the 1.1–3.5 μm range or converge near 1.5 μm by adjusting the core waveguide size or through temperature tuning. A 25 °C temperature change enables a broad pump tunability band of 300 nm, ranging from 1350 to 1650 nm, with a conversion efficiency exceeding 40 %/W/cm2 within a single waveguide. A temperature tuning range of up to 900 nm is foreseen by tailoring the waveguide core size. In addition, a broadband response of 150 nm within the telecom window is demonstrated experimentally. The nonlinear waveguide, etched in a thin film membrane, is combined with titanium-indiffused waveguides to form a monolithic LiNbO3 component. This configuration provides low coupling losses of 0.8 dB and single-mode operation. It paves the way for a new generation of versatile and cost-effective frequency conversion components with wide-band spectral responses suitable for optical communications, environmental sensing, and quantum information processing.

Insights into the pressure-dependent physical properties of cubic Ca3MF3 (M = As and Sb): First-principles calculations

Here, first-principles calculations have been employed to make a comparative study on structural, mechanical, electronic, and optical properties of new Ca3MF3 (M = As and Sb) photovoltaic compounds under pressure. The findings disclose that these two systems possess a direct band gap, showcasing a large tunable range under pressure, effectively encompassing the visible light spectrum. Adjusting various levels of hydrostatic pressure has effectively tuned both the band alignment and the effective masses of electrons and holes. Both compounds were initially identified as brittle materials at 0 GPa pressure; however, as the pressure increases, they transform, becoming highly anisotropic and ductile. Due to the material's mechanical robustness and enhanced ductility, as evidenced by its stress-induced mechanical properties, the Ca3MF3 (M = As and Sb) material shows potential for use in solar energy applications. Furthermore, as the influence of external pressure increases, the absorption edge seems to move slightly towards lower energy region. Optical properties show that the materials studied might be used from several optoelectronic devices in the visible and ultraviolet range area. Our findings show that pressure considerably influences the physicochemical properties of Ca3MF3 (M = As and Sb) compounds, which is a promising feature that can be useful for optoelectronic and photonic applications, for instance, light-emitting diodes, photodetectors, and solar cells.

Flexible and Large‐Scale Liquid Metal Frequency‐Selective Surfaces: Enhanced Tuning through Mechanical Reconfiguration

The tuning capability is crucial for broadening the application possibilities of frequency‐selective surfaces (FSSs). Flexible and stretchable FSSs have attracted widespread research interest due to their ability for adhering to curved surfaces conformally and reconfiguring electromagnetic (EM) wave transmission performance mechanically. However, conventional metal FSSs lack sufficient flexibility and deformability due to material constraints, resulting in diminished durability and limited EM tuning range. In this article, a design approach for flexible liquid metal FSS (LMFSS), which can conform to curved structures and achieve a wide range of EM wave tuning via mechanical stretching without structural damage, is presented. The fabrication of LMFSS is simplified using silicone elastomer curing and liquid metal inkjet printing, avoiding the complexities of traditional microchannel techniques. In the experimental results, it is demonstrated that the designed LMFSS achieves a tuning range of up to 16% under biaxial stretch strains not more than 25%. The tuning mechanism is explored through mechanical–EM simulations and equivalent circuit analyses. Additionally, the tuning phenomenon observed in another flexible LMFSS in this study underscores the portability of the design approach and tuning mechanism. In this research, a promising direction for tunable flexible LMFSS applications is offered.

Broadly tunable continuous-wave Tm,Ho:SrF2 and Tm,Ho:BaF2 lasers

We report on the first, to our knowledge, room-temperature continuous-wave laser operation of Tm3+,Ho3+-codoped barium and strontium fluoride crystals at ∼2.1 µm. The 3 at.% Tm, 0.5 at.% Ho:BaF2 laser generated 160 mW at 2073 nm with a slope efficiency of 31.0% and a laser threshold of 43 mW. The continuous wavelength tuning of this laser from 2010 to 2090 nm (tuning range, 80 nm) was demonstrated. The spectroscopic properties of Tm,Ho:SrF2 and Tm,Ho:BaF2 crystals were also determined, showing enhanced Tm3+ → Ho3+ energy transfer in rare-earth clusters. For Ho3+ ions in BaF2, the stimulated-emission cross section is 0.40 × 10−20 cm2 at 2044 nm, and the thermal equilibrium luminescence lifetime is as long as 14.1 ms.

Fractional Talbot Lithography for Predesigned Large-Area Liquid-Crystal Alignment

To address the increasing demands for cost-effective, large-area, and precisely patterned alignment of liquid crystals, a fractional Talbot lithography alignment technique was proposed. A light intensity distribution with a double spatial frequency of a photomask could be achieved based on the fractional Talbot effect, which not only enhanced the resolution of lithography but also slashed system costs with remarkable efficiency. To verify the feasibility of the alignment method, we prepared a one-dimensional polymer grating as an alignment layer. A uniform alignment over a large area was achieved thanks to the perfect periodicity and groove depth of several hundred nanometers. The anchoring energy of the alignment layer was 1.82 × 10−4 J/m2, measured using the twist balance method, which surpassed that of conventional rubbing alignment. Furthermore, to demonstrate its ability for non-uniform alignment, we prepared polymer concentric rings as an alignment layer, resulting in a liquid-crystal q-plate with q = 1 and α0 = π/2. This device, with a wide tuning range (phase retardation of ~6π @ 633 nm for 0 to 5 V), was used to generate special optical fields. The results demonstrate that this approach allows for the uniform large-area orientation of liquid-crystal molecules with superior anchoring energy and customizable patterned alignment, which has extensive application value in liquid-crystal displays, generating special optical fields and intricate liquid-crystal topological defects over a large area.

Efficient and widely tunable mid-infrared sources using GaAs and AlGaAs integrated platforms for second-order frequency conversion

Integrated coherent mid-infrared (mid-IR) sources are crucial for spectroscopy and quantum frequency conversion (QFC) to facilitate scalable fiber-based application of single photons. Direct mid-IR emission with broad tunability poses fundamental challenges from the gain media and mirror components. This paper presents a characterization of a second-order nonlinear platform. It showcases a mid-IR parametric coherent source with a continuous tuning range exceeding 230 nm centered around 2425 nm, achieved through difference-frequency generation (DFG). The nonlinear coefficient d14 of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) on insulator is experimentally determined via second-harmonic generation (SHG) in waveguides of various lengths, and the tolerance of the process is investigated. These materials are explored for their high conversion efficiency, utilizing monolithic epitaxial quantum dots and integrated waveguides for QFC. The results demonstrate efficient and tunable mid-IR emission suitable for compact, scalable quantum emitters, with applications in environmental and health monitoring.

56 Gbps externally modulated widely tunable lasers with SOA boosters heterogeneously integrated on silicon

We demonstrate externally modulated widely tunable lasers co-integrated with semiconductor optical amplifiers (SOAs) heterogeneously integrated on silicon. The widely tunable laser enables continuous single-mode operation over a tuning range of approximately 40 nm, with a side-mode suppression ratio (SMSR) of at least 50 dB and an average waveguide-coupled optical power of 5 mW. The integrated electro-absorption modulator (EAM) exhibits an extinction ratio (ER) of 16 dB when reversed biased at -2 V. The bit-error-rate (BER) measurements conducted across the available optical bandwidth (15 nm) showcase error-free transmission at 32 Gbps using non-return-to-zero (NRZ) signals for the majority of wavelengths in a back-to-back (B2B) configuration. Additionally, transmission measurements over distances of up to 10 km through a standard single-mode fiber (SSMF) have been successfully demonstrated. Dynamic extinction ratio (DER) values exceeding 4.5 dB are achieved for all wavelengths. Open-eye diagrams were measured up to 56 Gbps. These results demonstrate that this compact mono-epitaxial externally modulated tunable laser with integrated optical amplification can be a cost-effective transmitter solution for dense wavelength division multiplexing (DWDM) metropolitan and access networks.

A compact and tunable active inductor-based bandpass filter with high quality factor for Wireless LAN applications

A fully-differential compact and tunable second-order bandpass filter (BPF) with high quality factor using a novel active inductor (AI) has been proposed for 3.6 GHz WLAN applications. The proposed AI employs a differential amplifier as a feedforward transconductor and a common-source (CS) transistor as a feedback transconductor in a symmetrical configuration. The combination of a cascode scheme and a resistor in the feedback path enhances the quality factor of the AI, thereby increasing the mid-band gain of the BPF. In order to achieve independent tuning of both the center frequency and mid-band gain of the BPF, a varactor capacitor is utilized. The proposed second-order BPF is designed with a center frequency and a bandwidth of 3.675 GHz and 10 MHz, respectively. Post-layout simulation, process corner, and temperature sweep analysis results are conducted with 65 nm CMOS technology at 1.2 V supply voltage. The proposed filter has a tuning range of 3.655–3.695 GHz and attains a mid-band gain of 67.5 dB, a noise figure of 14.5 dB, and a 1-db compression point of −12.39 dBm. Additionally, the BPF consumes a DC power of 1.22 mW and occupies an active area of only 8.85 μm × 10.3 μm.

Effects of Salt Concentration on a Magnetic Nanoparticle-Based Aggregation Assay with a Tunable Dynamic Range.

Magnetic nanoparticles (MNPs) can be functionalized with antibodies to give them an affinity for a biomarker of interest. Functionalized MNPs (fMNPs) cluster in the presence of a multivalent target, causing a change in their magnetization. Target concentration can be proportional to the 3rd harmonic phase of the fMNP magnetization signal. fMNP clustering can also be induced with salt. Generally, salt can alter the stability of charge stabilized fMNPs causing a change in magnetization that is not proportional to the target concentration. We have developed a model system consisting of biotinylated MNPs (biotin-MNPs) that target streptavidin to study the effects of salt concentration on fMNP-based biosensing in simulated in vivo conditions. We have found that biotin-MNP streptavidin targeting was independent of salt concentration for 0.005x to 1.00x phosphate buffered saline (PBS) solutions. Additionally, we show that our biosensor's measurable concentration range (dynamic range) can be tuned with biotin density. Our results can be leveraged to design an in vivo nanoparticle (NP)-based biosensor with enhanced efficacy in the event of varying salt concentrations.

High power widely tunable frequency-doubled 490 nm blue semiconductor disk laser

This paper presents a high power widely tunable frequency-doubled semiconductor disk laser emitting at 490 nm wavelength. The laser utilizes a specially designed gain chip with widened gain spectrum at the center wavelength of 980 nm, along with an anti-resonant microcavity, to extend the tuning range of the wavelength. A type-I phase-matched 5 mm length LBO crystal is used as the nonlinear crystal, and a fused quartz birefringent filter (BRF) is introduced to polarize the fundamental emission and narrow the linewidth of the laser. When the thickness of the used BRF is 1 mm, 50.7 nm tuning range of the 980 nm infrared laser is performed. A maximum output power of 5.36 W of the frequency-doubled 490 nm blue laser is achieved, and the optical-to-optical conversion efficiency from absorbed pump power to the blue light is about 15.3%. Meanwhile, a record tuning range of 21.5 nm of the blue laser is realized. The measured M2 factors of the blue laser are 1.00 in the x-direction and 1.04 in the y-direction, respectively.

Flexural wave compression behaviors of programmable graded piezoelectric meta-beams

Active electromechanical metamaterials have drawn significant attention due to their remarkable tunability and adaptability in vibration and wave control. Exploiting the electromechanical coupling effect via controlled biased fields enables precise manipulation of the structural vibrations and wave transmissions. In this research, we have developed a programmable graded piezoelectric meta-beam that successfully imitates the wave compression behavior of an acoustic black hole without modifying the structural geometries. The effective parameters of the meta-beam are reshaped into a gradient distribution by tuning the electrical impedances of the digital shunting circuits. With such graded effective parameters, it becomes feasible to tailor the local wavenumber distribution of the meta-beam and hence achieve the desired wave compression. Numerical results validated our proposed paradigm of the programmable black hole in both straight and curved beams. In contrast to the straight beam, curvature of the curved beam reduces the tunable range of the local wavenumber. A comprehensive parametric study was conducted to investigate the influences of the gradient profile, electric damping, and curvature on the wave control function. For a given desired frequency, programmable control of wave compression location and amplified output of electrical signals are achieved.

Reconstructing Magnetic Hysteresis Behavior with Flux Model and Identifying Parameters for Dual-Coil MR Actuator

Magnetorheological (MR) actuators represent an important class of semi-active devices that have received extensive investigation and deployment in the field of vibration reduction systems. Their notable features include a significant reduction in energy consumption, along with an impressive tunable range of continuously controllable damping forces. The force output of these devices is a complex function that involves two hysteretic mechanisms: magnetic and mechanical (i.e. hydraulic). While the total hysteresis mechanism of these devices has been the subject of considerable study, comparatively little attention has been paid to their magnetic hysteretic behavior. In this study, the authors examine the behavior of the dual coil MR actuator’s control circuit and attempt to extract the magnetic flux information from the laboratory measurements of electrical signals applied to it. The study is further enhanced by the incorporation of the Bouc-Wen (B-W) hysteretic unit, which serves to replicate the flux-current (or magnetic) hysteretic relationship. The B-W model's parameters are identified through the use of a hybrid algorithm, namely the particle swarm optimization and fmincon hybrid optimizing strategy. It incorporates the advantages of both algorithms, resulting in an average improvement of 0.38% in standard deviation compared to fmincon, across 1A to 5A, when comparing the experimental and simulation data. This strategy is employed to fit the model predictions to the flux data, derived from the reconstructed flux and current in time histories. The findings of the study demonstrate that the B-W model is an effective tool for predicting the variation in magnetic flux in response to an exciting current. The results can be implemented for prototyping or validating a model-based controller for MR actuator systems.

Hydrophobic iron oxide nanoparticles: Controlled synthesis and phase transfer via flash nanoprecipitation

Iron oxide nanoparticles (IONPs) synthesized via thermal decomposition find diverse applications in biomedicine owing to precise control of their physico-chemical properties. However, use in such applications requires phase transfer from organic solvent to water, which remains a bottleneck.Through the thermal decomposition of iron oleate (FeOl), we systematically investigate the impact of synthesis conditions such as oleic acid (OA) amount, temperature increase rate, dwell time, and solvent on the size, magnetic saturation, and crystallinity of IONPs. Solvent choice significantly influences these properties, manipulating which, synthesis of monodisperse IONPs within a tunable size range (10-30 nm) and magnetic properties (75 to 42 Am2Kg-1) is obtained.To enable phase transfer of IONPs, we employ flash nanoprecipitation (FNP) for the first time as a method for scalable and precise size control, demonstrating its potential over conventional methods. Poly(lactic-co-glycolic acid) (PLGA)-coated IONPs with hydrodynamic diameter (Hd) in the range of 250 nm, high colloidal stability and high IONPs loadings up to 43% were obtained, such physicochemical properties being tuned exclusively by the size and hydrophobicity of starting IONPs. They showed no discernible cytotoxicity in human dermal fibroblasts, highlighting the applicability of FNP as a novel method for the functionalization of hydrophobic IONPs for biomedicine.

Electrowetting lens based on a conical aluminum cavity

A tunable liquid lens based on the electrowetting-on-dielectric effect is demonstrated using a machined aluminum substrate. A metallic substrate eliminates the need for deposited electrodes inside the droplet cavity and simplifies the fabrication procedures required to produce an electrowetting optic. Sloped sidewalls at 45° produce a large optical tuning range, with back focal length tuning from [−134, −18.5 mm] and [+11.3, +134 mm]. An input-shaped overdriven actuation voltage yields a response time of 149 ms. The aluminum substrate is machined using standard processes that allow the device geometry to be customized. A complete lens package is sealed with fluoroelastomer O-rings, enabling applications beyond the laboratory environment.

A Novel 571.78 MHz–11.07 GHz Tuning Range Differential Ring Oscillator Application in a PLL Frequency Synthesizer with 895 ns Lock Time

A Novel 571.78 MHz–11.07 GHz Tuning Range Differential Ring Oscillator Application in a PLL Frequency Synthesizer with 895 ns Lock Time

300-nm-thick, ultralow-loss silicon nitride photonic integrated circuits by 8-in. foundry production

Silicon nitride (Si3N4) photonic integrated circuits are rapidly developing in recent decades. The low loss of Si3N4 attracts significant attention and facilitates a wide range of applications in integrated photonics. In this work, we demonstrate the foundry fabrication of a 300-nm-thick 8-in. wafer-scale Si3N4 platform, with a microresonator intrinsic quality factor of up to 15×106, corresponding to an ultralow loss of 2.2 dB/m. Leveraging this platform, we develop a mature process design kit, achieving a single-mode waveguide propagation loss of less than 5 dB/m, an edge coupler loss of 1.3 dB, and an insertion loss of 0.07 dB for multimode interference couplers. Utilizing the processed Si3N4 chip, we realize a hybrid integrated tunable external cavity laser with a tuning range from 1534 to 1602 nm, a record-high side-mode suppression ratio of up to 76 dB, an optical power of 26 mW, and an intrinsic linewidth of down to 314 Hz. Our work lays a solid foundation for the further development of applications, including nonlinear optics, quantum optics, optical communications, and ranging.

Compact widely tunable laser integrated on an indium phosphide membrane platform

We present the design, fabrication, and characterization results of a compact, widely tunable laser realized on an indium phosphide membrane-on-silicon (IMOS) platform. The laser features a compact Mach–Zehnder interferometric structure as the wavelength-selective intracavity filter with a footprint of 0.13 mm2. The filter design is optimized to ensure narrow filter transmission and high side-mode-to-main-mode-ratio, enabling single-mode operation for the laser. The high optical confinement on the IMOS platform can support tight waveguide bends. Leveraging this, the laser achieves a short cavity length, further enhancing the single-mode operation. Measurement results indicate a threshold current of 29 mA and a maximum on-chip output power of approximately 3.6 dBm and wall plug efficiency of 1.8%. The side-mode suppression ratio ranges from 30 to 44 dB, with a tuning range spanning 40 nm, from 1555 to 1595 nm. A complete tuning lookup table is generated via an automated setup incorporating a stochastic search algorithm.