Rapid Tuning Research Articles

Photoacoustic spectroscopy with a widely tunable narrowband fiber-feedback optical parametric oscillator

Trace gas analysis is a key tool for the investigation of man-made environmental pollution as well as for early detection of respiratory diseases. To detect tiny concentrations, sensitive methods such as cavity ring down spectroscopy or plasmonic sensors have been used. Here, we demonstrate the combination of the photoacoustic effect in a classical cell with a novel, rapidly tunable, narrowband fiber-feedback optical parametric oscillator. The high sensitivity of photoacoustic cells and the extremely narrow linewidth as well as the wide and rapid tunability of the fiber-feedback optical parametric oscillator enable a high resolution of the rotational and vibrational bands of molecules in the near-infrared region. Photoacoustic spectra of methane, carbon dioxide, and water at ambient pressure are obtained in a broad spectral range and compared to high-resolution transmission molecular absorption database. In particular, scanning the entire carbon dioxide overtone around 4965 cm−1 at 2000 ppm takes 185 s with a signal-to-noise ratio of 31. This approach enables a wide tunability in the entire near- and mid-infrared spectral region suitable for many environmental and medical applications.

Wavelength tunable single-frequency ring cavity fiber laser utilizing external injection locking signal

The ring cavity fiber laser with saturable absorption fibers is a simple and practical technical way of achieving single-frequency laser output. However, this structure cannot obtain wavelength-tunable laser output. In this work, an external injection locking signal launched by tunable LD is used to optimize the tunability in single-frequency ring cavity fiber lasers. By aligning the external injection signal, tunable laser output ranging from 1544.13 to 1546.51 nm is achieved. The maximum output is 16.5 mW and the linewidth is less than 6.15 kHz. The operation process and the linewidth compression effect of external Injection signals are investigated. The results indicate that there is a correlation between the output signal-to-noise ratio and the output linewidth, and this wavelength-tuning structure has the potential for rapid tuning. This work provides a technical solution for achieving a tunable single-frequency laser in the ring cavity structure.

Development of S-domain experimental correlation thermal control model and rapid enumeration PID tuning method for uncooled Laser chip module

Uncooled semiconductor lasers are sensitive to ambient temperature variation which makes the PID thermal control for the uncooled semiconductor is complicated. In this work, a kind of enumeration PID tuning method based on S-domain experimental correlation thermal control model for the uncooled semiconductor lasers is introduced. Numeric validation and enumeration PID tuning of S-domain experimental correlation model for uncooled semiconductor are conducted. Results shows that the control accuracy prediction result of the S-domain experimental correlation model has a deviation of 3.6% in contrast with CAE simulation result. The PID tunning speed of rapid enumeration S-domain experimental correlation method is 17,000 times that of CAE method.

Ultralow-phase-noise and broadband frequency-hopping coupled optoelectronic oscillator under quiet point operation

Advancements in microwave photonics have yielded novel approaches for generating high-purity microwave sources. Among these, optoelectronic oscillators (OEOs) and coupled optoelectronic oscillators (COEOs) have demonstrated the capability to generate frequency-independent microwaves with exceptionally low phase noise. Nonetheless, the tunability of the oscillators is rather limited due to the necessity for narrowband electronic bandpass filters, presenting challenges in achieving both wide and rapid tuning capabilities. Here, we present a COEO featuring ultralow phase noise, flexible tuning capability, and high robustness. This is achieved through a quiet point (QP)-operated harmonic mode-locked fiber laser, which effectively mitigates optical amplifier noise and supermode competition, thus significantly diminishing the necessity for ultra-narrow electronic filters. Due to the liberated tuning ability, we present an oscillator that can be tuned from 2 GHz to 18 GHz, with phase noise as low as −140 dBc/Hz at 10 kHz under the QP operation. We then illustrate the practical application of the proposed oscillator in generating frequency-hopping signals with consistent spurious modes less than −85 dBc, absolute phase noise below −135 dBc/Hz at 10 kHz, hopping resolution of 1.25 MHz, and fractional frequency stability below 6.1×10−12 at 1 s averaging time when locked to a reference. The presented COEO structure emerges as a compelling solution for agile and low-noise microwave sources in advanced wireless communication and radar systems.

The Research on Microwave Drying Characteristics of Polyethylene Terephthalate Materials Based on Frequency and Power Tuning Technology

Polyethylene Terephthalate (PET), renowned for its exceptional physical and chemical properties, finds widespread use in our daily lives. However, conventional PET drying methods are time consuming and energy intensive. Leveraging microwave heating effects, we investigated drying characteristics concerning both microwave parameters and PET permittivity. The PET permittivity variation during heating is related to the microwave reflection at the incident port. Our innovative approach involves frequency and power tuning based on reflection. This method not only significantly improved heating uniformity and reduced temperature covariance (COVT) but also led to a more uniformly distributed temperature profile and a drastic reduction in energy consumption. Integrating precise and rapid frequency tuning, we compared our method’s efficiency with traditional approaches, revealing an impressive time savings of 2 h and an energy consumption limited to approximately less than 3 kWh/kg. Notably, our laboratory system’s logistic models of the Moisture Ratio (MR) related to rotary rates, masses, and powers whose averages of R-square are 0.9972, 0.9982, and 0.9977, respectively, which provide intriguing insights for industrial production forecasts during variable frequency PET drying.

Rapid evolutionary tuning of endospore quantity versus quality trade-off via a phase-variable contingency locus

The UV resistance of bacterial endospores is an important quality supporting their survival in inhospitable environments and therefore constitutes an essential driver of the ecological success of spore-forming bacteria. Nevertheless, the variability and evolvability of this trait are poorly understood. In this study, directed evolution and genetics approaches revealed that the Bacillus cereus pdaA gene (encoding the endospore-specific peptidoglycan-N-acetylmuramic acid deacetylase) serves as a contingency locus in which the expansion and contraction of short tandem repeats can readily compromise (PdaAOFF) or restore (PdaAON) the pdaA open reading frame. Compared with B.cereus populations in the PdaAON state, populations in the PdaAOFF state produced a lower yield of viable endospores but endowed them with vastly increased UV resistance. Moreover, selection pressures based on either quantity (i.e., yield of viable endospores) or quality (i.e., UV resistance of viable endospores) aspects could readily shift populations between PdaAON and PdaAOFF states, respectively. Bioinformatic analysis also revealed that pdaA homologs within the Bacillus and Clostridium genera are often equipped with several short tandem repeat regions, suggesting a wider implementation of the pdaA-mediated phase variability in other sporeformers as well. These results for the first time reveal (1) pdaA as a phase-variable contingency locus in the adaptive evolution of endospore properties and (2) bet-hedging between what appears to be a quantity versus quality trade-off in endospore crops.

CMOS-compatible high-speed endless automatic polarization controller

Automatic polarization controllers find broad applications in various fields, including optical communication, quantum optics, optical sensing, and biomedicine. Currently, the predominant integrated automatic polarization controllers employ either lithium niobate or silicon platforms. Devices based on lithium niobate platforms exhibit excellent performance; however, their fabrication complexity hinders widespread commercial deployment. In contrast, silicon-based integrated automatic polarization controllers benefit from complementary metal–oxide–semiconductor compatibility and reduced fabrication costs. Nevertheless, these silicon automatic polarization controllers suffer from low tracking speeds, peaking at merely 1.256 krad/s. In this study, we demonstrated a silicon high-speed automatic polarization controller, incorporating innovative thermal tuning units combined with a sophisticated control algorithm. The response time of these thermal tuning units has been markedly decreased to 3.2 µs. In addition, we have implemented a novel automatic polarization control algorithm, utilizing gradient descent techniques, on a field-programmable gate array control board. The synergy of the rapid thermal tuning unit and the advanced control algorithm has enabled us to attain an unprecedented polarization control speed of up to 20 krad/s, with this rate being solely limited by the capabilities of our characterization equipment. To our knowledge, this speed is the fastest yet reported for a silicon-based integrated automatic polarization control chip. The proposed device represents a significant breakthrough in the field of silicon-based automatic polarization controllers, paving the way for the future integration of additional polarization management devices. Such an advancement would mark a substantial leap in the realm of integrated photonics, bridging the gap between performance efficiency, cost-effectiveness, and technological integration.

Real-time channel selection in multi-mode multiplexing optical interconnection implemented by hybrid algorithm and material system

Multi-mode multiplexing optical interconnection (MMOI) has been widely used as a new technology that can significantly expand communication bandwidth. However, the constant-on state of each channel in the existing MMOI systems leads to serious interference for receivers when extracting and processing information, necessitating introducing real-time selective-on function for each channel in MMOI systems. To achieve this goal, combining several practical requirements, we propose a real-time selective mode switch based on phase-change materials, which can individually tune the passing/blocking of different modes in the bus waveguide. We utilize our proposed particle swarm optimization algorithm with embedded neural network surrogate models (NN-in-PSO) to design this mode switch. The proposed NN-in-PSO significantly reduces the optimization cost, enabling multi-dimensional simultaneous optimization. The resulting mode switch offers several advantages, including ultra-compactness, rapid tuning, nonvolatility, and large extinction ratio. Then, we demonstrate the real-time channel selection function by integrating the mode switch into the MMOI system. Finally, we prove the fabricating robustness of the proposed mode switch, which paves the way for its large-scale application.

A Temperature Control Method of Lysozyme Fermentation Based on LRWOA-LSTM-PID

In order to overcome the difficulty of parameter tuning caused by the large lag and time-varying nonlinearity of the tank for lysozyme fermentation, a temperature control method based on LRWOA-LSTM-PID is proposed in this paper. Firstly, according to the intrinsic mechanism of the fermenter, a temperature mechanism model based on a dynamic equation is designed, which can better reflect the temperature changes in the fermenter. Secondly, a Proportional Integral Derivative (PID) parameter tuning method based on a Long-Short Term Memory Network (LSTM) is proposed, which takes advantage of the ability of LSTM to learn time sequence information and obtains the variation trend between error sequences under continuous time sampling, thereby adjusting network weights more reasonably and accelerating PID parameter tuning. Finally, a Whale Optimization Algorithm (WOA) based on the Lévy flight and random walk strategy (LRWOA) is proposed for the initialization of LSTM parameters; this algorithm has excellent optimization capabilities and overcomes the problem of LSTM falling into local optimal solutions prematurely during parameter randomization. The results show that the method proposed in this paper can achieve rapid tuning of PID parameters, thereby improving the convergence speed of the system and reducing system overshoot.

Transparent Structures with a Fast De‐Stiffening Functionality

The majority of natural organisms interact with their environments with a degree of mechanical adaptability that allows them to carry out a variety of tasks and adapt to changing circumstances. Human‐made structures, however, lack this versatility and are normally designed to fulfill a certain load‐carrying requirement. This causes limitations in performance, efficiency, and safety. The aim of this article is to present rapid de‐stiffening in the response of conventional structures, without compromising the load‐bearing capacity. This has been achieved by developing an active interface using an interconnected nanostructured metallic network. A very fast heating rate with an average of ≈45 °C s−1 under 4.8 V excitation while retaining transparency of 67% is demonstrated. The embedded metallic network in a thermoplastic matrix has been deployed as an active interface, in a conventional transparent multilayered structure. Upon activation, it provides a rapid (i.e., 2 s after activation) mechanical de‐stiffening capability. The results from finite element modeling have been found to be in good agreements with those from experiments. The rapid reversible stiffness tuning demonstrated here can be implemented in variety of multilayered structures with a wide range of applications in robotics, morphing and deployable structures, active damping, and active impact safety systems.

Ultra-broadband non-collinear optical parametric oscillators: A reliable source of rapidly tunable femtosecond laser pulses

Non-collinear phase matching in optical parametric oscillators enables unique possibilities ranging from ultra-broadband rapid spectral tuning to intrinsic advantages in power scaling. This work is an overview of this concept adapted to different wavelength ranges.

Narrow–linewidth tunable laser source for long-wavelength optical coherence tomography at 1700 nm

We present a widely tunable laser source with narrowed linewidths at the level of 0.4 – 1.1 nm. The laser source incorporates a comb-profile fiber (CPF) which allows for spectral compression of the tunable optical pulses to the linewidths below 1 nm. The spectral compression factor is as high as 37.2 and is the highest obtained for this wavelength range. With the use of an electro-optic modulator (EOM), the laser system ensures rapid tuning up to 10 GHz. Together with the wide spectral range of 1600-1900 nm, and compressed spectral width, the source meets the requirements of the optical coherence tomography (OCT).

Microwave photonic filter with rapid tunability and arbitrary reconfigurability

Microwave photonic filter with rapid tunability and arbitrary reconfigurability

Mars2020 Entry Shock Layer Thermochemical Kinetics Examined by Megahertz-Rate Laser Absorption Spectroscopy

A mid-infrared laser absorption diagnostic was deployed to examine the evolution of thermophysical properties across a simulated Mars2020 shock layer in the Electric Arc Shock Tube (EAST) facility at NASA Ames. Rapid laser tuning techniques using bias-tee circuitry enabled quantitative temperature and number density measurements of CO2 and CO with microsecond resolution over a shock velocity range of 1.30–3.75 km/s. Two interband cascade lasers were utilized at 4.17 and 4.19 μm to resolve rovibrational CO2 lines spanning across J′′=58 to J′′=140 in the asymmetric stretch fundamental bands. In test cases with enough energy to dissociate CO2, a quantum cascade laser scanned multiple transitions of the CO fundamental bands near 4.98 μm. The results are compared to the Data Parallel Line Relaxation (DPLR) code and Lagrange shock tube analysis (LASTA) simulations of the shock layer. A numerical simulation of the compressible boundary layer is used to account for measurement sensitivities to this flow feature in the EAST facility. Temperature and species transients are compared to multiple chemical kinetic models. The laser absorption data presented in this work can be used to refine the models used to simulate the aerothermal environment encountered during Mars entry.

Resonator-Loaded Waveguide Notch Filters with Broad Tuning Range and Additive-Manufacturing-Based Operating Frequency Adjustment Procedure

This article presents a new class of ring-resonator-loaded waveguide notch filters with a broad tuning range, low cost, and improved performance. The proposed approach employs a complementary asymmetric split-ring resonator coupled to a microstrip transmission line and excited in a rectangular waveguide. An equivalent circuit model is proposed to explain the working principle of the proposed notch filter. The adjustment of the operating frequency is based on the additive manufacturing of a metallic copper patch allocated on the microstrip transmission line, which enables extensive tuning capabilities and consistent performance with minimum variations across the tuning window. For demonstration purposes, a filter employing a WR-28 waveguide and photolithography-manufactured resonator is prototyped and experimentally validated. The measured results indicate a broad 8 GHz tuning range with a consistent insertion loss, ranging from 23.4 to 31.4 GHz. An inverse regression model is constructed using measurement data obtained for tuning patches of various sizes, which allows for determining the relationships between the operating frequency and the copper patch size. The resulting calibration curve enables rapid filter tuning to the required frequency by inserting metallic patches of the model-predicted size.

Fully Integrated Point-of-Care Platform for the Self-Monitoring of Phenylalanine in Finger-Prick Blood.

Development of point-of-care platforms combining reliability and ease of use is a challenge for the evolution of sensing in healthcare technologies. Here, we report the development and testing of a fully integrated enzymatic colorimetric assay for the sensing of phenylalanine in blood samples from phenylketonuria patients. The platform works with a customized mobile app for data acquisition and visualization and comprises an electronic system and a disposable sensor. The sensing approach is based on specific enzymatic phenylalanine recognition, and the optical transduction method is based on in situ gold nanostructure formation. The phenylketonuria (PKU) smart sensor platform is conceived to perform self-monitoring on phenylalanine levels and real-time therapy tuning, thanks to the direct connection with clinicians. Validation of the technologies with a population of patients affected by PKU, together with the concurrent validation of the platform through centralized laboratories, has confirmed the good analytical performances in terms of sensitivity and specificity, robustness, and utility for phenylalanine sensing. The self-monitoring of phenylalanine for the daily identification of abnormal health conditions could facilitate rapid therapy tuning, improving the wellness of PKU patients.

The variable domain from dynamin-related protein 1 promotes liquid-liquid phase separation that enhances its interaction with cardiolipin-containing membranes.

Dynamins are an essential superfamily of mechanoenzymes that remodel membranes and often contain a "variable domain" important for regulation. For the mitochondrial fission dynamin, dynamin-related protein 1, a regulatory role for the variable domain (VD) is demonstrated by gain- and loss-of-function mutations, yet the basis for this is unclear. Here, the isolated VD is shown to be intrinsically disordered and undergo a cooperative transition in the stabilizing osmolyte trimethylamine N-oxide. However, the osmolyte-induced state is not folded and surprisingly appears as a condensed state. Other co-solutes including known molecular crowder Ficoll PM 70, also induce a condensed state. Fluorescence recovery after photobleaching experiments reveal this state to be liquid-like indicating the VD undergoes a liquid-liquid phase separation under crowding conditions. These crowding conditions also enhance binding to cardiolipin, a mitochondrial lipid, which appears to promote phase separation. Since dynamin-related protein 1 is found assembled into discrete punctate structures on the mitochondrial surface, the inference from the present work is that these structures might arise from a condensed state involving the VD that may enable rapid tuning of mechanoenzyme assembly necessary for fission.

Multi-Phase Focused PID Adaptive Tuning with Reinforcement Learning

The Proportional-Integral-Derivative (PID) controller, a fundamental element in industrial control systems, plays a pivotal role in regulating an extensive array of controlled objects. Accurate and rapid adaptive tuning of PID controllers holds significant practical value in fields such as mechatronics, robotics, and automatic control. The three parameters of the PID controller exert a substantial influence on control performance, rendering the tuning of these parameters an area of significant interest within related research fields. Numerous tuning techniques are widely employed to optimize its functionality. Nonetheless, their adaptability and control stability may be constrained in situations where prior knowledge is inadequate. In this paper, a multi-phase focused PID adaptive tuning method is introduced, leveraging the deep deterministic policy gradient (DDPG) algorithm to automatically establish reference values for PID tuning. This method constrains agent actions in multiple phases based on the reward thresholds, allowing the output PID parameters to focus within the stable region, which provides enhanced adaptability and maintains the stability of the PID controller even with limited prior knowledge. To counteract the potential issue of a vanishing gradient following action constraints, a residual structure is incorporated into the actor network. The results of experiments conducted on both first-order and second-order systems demonstrate that the proposed method can reduce the tracking error of a PID controller by 16–30% compared with the baseline methods without a loss in stability.

Enhancing Focusing and Defocusing Capabilities with a Dynamically Reconfigurable Metalens Utilizing Sb2Se3 Phase-Change Material.

Metalenses are emerging as an alternative to digital micromirror devices (DMDs), with the advantages of compactness and flexibility. The exploration of metalenses has ignited enthusiasm among optical engineers, positioning them as the forthcoming frontier in technology. In this paper, we advocate for the implementation of the phase-change material, Sb2Se3, capable of providing swift, reversible, non-volatile focusing and defocusing within the 1550 nm telecom spectrum. The lens, equipped with a robust ITO microheater, offers unparalleled functionality and constitutes a significant step toward dynamic metalenses that can be integrated with beamforming applications. After a meticulously conducted microfabrication process, we showcase a device capable of rapid tuning (0.1 MHz level) for metalens focusing and defocusing at C band communication, achieved by alternating the PCM state between the amorphous and crystalline states. The findings from the experiment show that the device has a high contrast ratio for switching of 28.7 dB.

Widely tunable room-temperature green-pumped continuous-wave optical parametric oscillator from the red to mid-infrared

We report, to the best of our knowledge, the first realization of a room-temperature green-pumped continuous-wave (cw) optical parametric oscillator (OPO), providing wide and rapid tunability directly from the red to mid-infrared. The OPO, based on fanout MgO:sPPLT crystal and pumped at 532 nm, can provide a total signal and idler wavelength tuning range over 2554 nm, from 638 to 3192 nm. By deploying finite output coupling of the resonant wave at room temperature, also for the first time, to the best of our knowledge, we achieve enhanced output power and extraction efficiency, with the OPO delivering 4.6 W of total output power with pump depletion of 75% and total external efficiency as high as 50%. We believe 638 nm is the shortest signal wavelength generated from a cw green-pumped OPO in any fanout-grating nonlinear material to date. The passive power and frequency stability, linewidth, spatial beam profile, and beam pointing stability of the output-coupled signal, which are crucial for many applications, have been studied.