Broad Tuning Research Articles

High power, broad tuning quantum cascade laser at λ ∼ 8.9 µm

Many molecules have broad fingerprint absorption spectra in mid-wave infrared range which requires broadly tunable lasers to cover the interested spectrum in one scan. We report a strain-balanced, InAlAs/InGaAs/InP quantum cascade laser structure based on diagonal transition active region with high output power and and wide tuning range at λ ∼ 8.9 µm. The maximum pulsed optical power and the wall-plug efficiency at room temperature are 4 W and 11.7%, respectively. Maximum continuous wave double-facet power is 1.2 W at 25 °C for a 4 mm by 9 µm laser mounted epi-side down on a diamond/copper composite submount. The maximum pulsed and continuous wave external-cavity tuning range are from 7.71 µm to 9.15 µm and from 8 µm to 8.9 µm, respectively. The continuous wave power of the external cavity mode exceeds 200 mW across the entire spectrum.

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.

Neuronal Encoding of Speech Features in the Human Thalamus in Parkinson's Disease and Essential Tremor Patients.

The human thalamus is known, from stimulation studies and functional imaging, to participate in high-level language tasks. The goal of this study is to find whether and how speech features, in particular, vowel phonemes, are encoded in the neuronal activity of the thalamus, and specifically of the left ventralis intermediate nucleus (Vim), during speech production, perception, and imagery. In this cross-sectional study, we intraoperatively recorded single neuron activity in the left Vim of eight neurosurgical patients with Parkinson's disease (PD) (n = 4) or essential tremor (n = 4) undergoing implantation of deep brain stimulation (n = 3) or radiofrequency lesioning (n = 5) while patients articulated the five monophthongal vowel sounds. In this article, we report that single neurons in the left Vim encode individual vowel phonemes mainly during speech production but also during perception and imagery. They mainly use one of two encoding schemes: broad or sharp tuning, with a similar percentage of units each. Sinusoidal tuning has been demonstrated in almost half of the broadly tuned units. Patients with PD had a lower percentage of speech-related units in each aspect of speech (production, perception, and imagery), a significantly lower percentage of broadly tuned units, and significantly lower median firing rates during speech production and perception, but significantly higher rates during imagery, than patients with essential tremor. The results suggest that the left Vim uses mixed encoding schemes for speech features. Our findings explain, at the single neuron level, why deep brain stimulation and radiofrequency lesioning of the left Vim are likely to cause speech side effects. Moreover, they may indicate that speech-related units in the left Vim of patients with PD may be degraded even in the subclinical phase.

Broadly tunable continuous wave 2.3-µm Tm3+:tellurite bulk glass laser.

We report, for the first time to the best of our knowledge, a continuous wave trivalent thulium ion (Tm3+)-doped bulk glass near 2.3 µm. In the experiments, a bulk Tm3+-doped tellurite glass with the stoichiometric composition of 74TeO2-12ZnO-4La2O3-10Na2O (Tm3+:TZLN) was used. Lasing operation was achieved by using an x-fold cavity at the free-running wavelength of 2303 nm. The maximum slope efficiency of 6.2% was obtained with respect to the absorbed pump power with a 1% transmitting output coupler. In this case, as high as 100-mW output power was generated with 2.2 W of absorbed pump power. Continuous, broad tuning was achieved from 2233 nm to 2400 nm. The excitation spectrum of the laser was also investigated and 2.3-µm lasing was obtained by varying the pump wavelength over the 773-809-nm range. The absorption cross section was determined to be 4.4 × 10-21 cm2, based on open-aperture z-scan measurement. By using the laser efficiency data, the emission cross section of the Tm3+:TZLN glass was further determined to be 1.3 × 10-20 cm2 at 2.3 µm.

A Terahertz Broad Compound Tuning Range Extended Interaction Oscillator Operating at Quasi-TM51 Mode

A Terahertz Broad Compound Tuning Range Extended Interaction Oscillator Operating at Quasi-TM₅₁ Mode

Multifocal attention within a single hemifield results in broad tuning of attention across relevant and irrelevant locations.

Multifocal attention within a single hemifield results in broad tuning of attention across relevant and irrelevant locations.

High power, broad tuning, double-stack quantum cascade laser at λ ∼ 6.9 µm

Broadband double-stack quantum cascade lasers with strain-balanced In0.60Ga0.40As/In0.43Al0.57As and In0.60Ga0.40As/In0.41Al0.59As emitting at a wavelength of 6.9 µm are reported. The double-stack design is achieved by changing the beam flux of the aluminum effusion cell. The maximum continuous-wave power at room temperature (293 K) is 1.07 W. Tuning ranges of 195 and 104 cm−1 in pulsed and continuous-wave modes, respectively, are obtained using an external-cavity measurement system. The continuous-wave power of the external-cavity mode exceeds 110 mW, and is thus suitable for the detection of some functional groups.

Design and Beam Dynamic Studies of an Injector for a Compact THz Coherent Radiation Source

An intense narrow-band terahertz (THz) radiation source has been designed to generate a broad tuning range of radiation frequencies between 0.5 THz and 5.0 THz. The THz radiation is produced when a short-bunch electron beam propagates through an undulator. To achieve high-power peak radiation, the source requires high-brightness electron beams with low beam emittance and short bunch length. A proposed design for the photocathode RF gun used as the electron source is presented. The gun with high mode separation and high Q-factor can be achieved for producing a good beam quality. The beam dynamics of the injector have been preliminarily optimized using the software ASTRA and Elegant, investigating the impact of laser pulse shape on electron beam quality. The results of the beam dynamics studies are comprehensively discussed in this paper.

Electric-Field-Enhanced Electroluminescence Color Tuning of Colloidal Type-II Tetrapods.

Color-tunable electroluminescence (EL) from a single emitting material can be used to develop single-pixel multicolor displays. However, finding materials capable of broad EL color tuning remains challenging. Herein, we report the observation of broad voltage-tunable EL in colloidal type-II InP/ZnS quantum-dot-seeded CdS tetrapod (TP) LEDs. The EL color can be tuned from red to bluish white by varying the red and blue emission intensities from type-II interfaces and arms, respectively. The capacitor device proves that an external electric field can enhance the color tuning in type-II TPs. COMSOL simulations, numerical calculations, and transient absorption measurements are performed to understand the underlying photophysical mechanism. Our results indicate that the reduced hole relaxation rate from the arm to the quantum dot core can enhance the emission from the CdS arms, which is favorable for EL color tuning. This study provides a novel method to realize voltage-tunable EL colors with potential in display and micro-optoelectronic applications.

A tale of two copies: Evolutionary trajectories of moth pheromone receptors

Pheromone communication is an essential component of reproductive isolation in animals. As such, evolution of pheromone signaling can be linked to speciation. For example, the evolution of sex pheromones is thought to have played a major role in the diversification of moths. In the crop pests Spodoptera littoralis and S. litura, the major component of the sex pheromone blend is (Z,E)-9,11-tetradecadienyl acetate, which is lacking in other Spodoptera species. It indicates that a major shift occurred in their common ancestor. It has been shown recently in S. littoralis that this compound is detected with high specificity by an atypical pheromone receptor, named SlitOR5. Here, we studied its evolutionary history through functional characterization of receptors from different Spodoptera species. SlitOR5 orthologs in S. exigua and S. frugiperda exhibited a broad tuning to several pheromone compounds. We evidenced a duplication of OR5 in a common ancestor of S. littoralis and S. litura and found that in these two species, one duplicate is also broadly tuned while the other is specific to (Z,E)-9,11-tetradecadienyl acetate. By using ancestral gene resurrection, we confirmed that this narrow tuning evolved only in one of the two copies issued from the OR5 duplication. Finally, we identified eight amino acid positions in the binding pocket of these receptors whose evolution has been responsible for narrowing the response spectrum to a single ligand. The evolution of OR5 is a clear case of subfunctionalization that could have had a determinant impact in the speciation process in Spodoptera species.

Switching of lasing direction in reconfigurable chiral photonic crystals

In recent years, the development of lasers using photonic crystals as resonant cavities has emerged and continued to grow. These photonic crystal lasers offer the advantages of reduced threshold levels and compact dimensions. Chiral liquid crystals (CLCs) are self-assembled one-dimensional photonic crystals that enable a wide range of photonic crystal lasers to exhibit broad wavelength tuning capabilities. Our research exploits the uniform standing helix (USH) and uniform lying helix (ULH) states of CLCs as resonant cavities; therefore, the direction of laser emission of CLC lasers can be changed by switching between USH and ULH states. Both USH and ULH lasers in CLCs also exhibit wavelength tuning. The USH laser induces a blue shift in the laser wavelength by dielectric heating, while the ULH laser achieves a redshift of the laser wavelength by applying a vertical electric field to lengthen the helical pitch. Such a reconfigurable chiral photonic crystal laser based on the CLCs provides bidirectional switching of the laser direction while maintaining the ability to tune the wavelength, so it has the potential for use in photonic applications.

Twist-tunable polaritonic nanoresonators in a van der Waals crystal

Optical nanoresonators are key building blocks in various nanotechnological applications (e.g., spectroscopy) due to their ability to effectively confine light at the nanoscale. Recently, nanoresonators based on phonon polaritons (PhPs)—light coupled to lattice vibrations—in polar crystals (e.g., SiC, or h-BN) have attracted much attention due to their strong field confinement, high quality factors, and their potential to enhance the photonic density of states at mid-infrared (mid-IR) frequencies, where numerous molecular vibrations reside. Here, we introduce a new class of mid-IR nanoresonators that not only exhibit the extraordinary properties previously reported, but also incorporate a new degree of freedom: twist tuning, i.e., the possibility of controlling their spectral response by simply rotating the constituent material. To achieve this result, we place a pristine slab of the van der Waals (vdW) α-MoO3 crystal, which supports in-plane hyperbolic PhPs, on an array of metallic ribbons. This sample design based on electromagnetic engineering, not only allows the definition of α-MoO3 nanoresonators with low losses (quality factors, Q, up to 200), but also enables a broad spectral tuning of the polaritonic resonances (up to 32 cm−1, i.e., up to ~6 times their full width at half maximum, FWHM ~5 cm−1) by a simple in-plane rotation of the same slab (from 0 to 45°). These results open the door to the development of tunable and low-loss IR nanotechnologies, fundamental requirements for their implementation in molecular sensing, emission or photodetection applications.

Octa-band reconfigurable monopole antenna frequency diversity 5G wireless

<span lang="EN-US">An octa-band frequency-reconfigurable antenna (28×14×1.5 mm<sup>3</sup>) with a broad tuning range is shown. Antenna mode1 (4.31 GHz) works in one single-band mode and two dual-band in modes 2 and 3 (i.e., 3.91 and 5.9 GHz) as well as one tri-band in mode 4 (i.e., 3.09, 5.65, and 7.92 GHz) based on the switching situation of the antenna. Changing capacitance for frequency reconfigurability is accomplished with the use of lumped components. The antenna’s observed tuning spans from 3.09 GHz to 7.92 GHz. for all the resonant bands, the suggested antenna has a voltage standing waves ratio (VSWR)<1.45 except for one band with a VSWR<1.85. From 70.57% to 97.93%, the suggested structure’s radiation efficiency may be calculated. For a better understanding proposed antenna’s far field and scattering characteristics, we used CST Microwave Studio 2021. We may conclude that our suggested antenna is suitable for today’s wireless applications, which need multiband and multimode small antennas. Using a small stainless-steel wire as a switch, a prototype of the antenna design is built and tested to verify the simulation findings. The suggested reconfigurable antenna’s strong concordance between simulated and measured findings.</span>

Excited State Intramolecular Proton Transfer Dynamics of Derivatives of the Green Fluorescent Protein Chromophore

Excited state intramolecular proton transfer (ESIPT) dynamics of the o-hydroxy analogs of the green fluorescent protein (GFP) chromophore have been investigated by time-resolved spectroscopies and theoretical calculations. These molecules comprise an excellent system to investigate the effect of electronic properties on the energetics and dynamics of ESIPT and to realize applications in photonics. Time-resolved fluorescence with high enough resolution was employed to record the dynamics and the nuclear wave packets in the excited product state exclusively in conjunction with quantum chemical methods. The ESIPT are ultrafast occurring in 30 fs for the compounds employed in this work. Although the ESIPT rates are not affected by the electronic properties of the substituents suggesting barrierless reaction, the energetics, their structures, subsequent dynamics following ESIPT, and possibly the product species are distinct. The results attest that fine tuning of the electronic properties of the compounds may modify the molecular dynamics of ESIPT and subsequent structural relaxation to achieve brighter emitters with broad tuning capabilities.

Wavelength-Tunable and OAM-Switchable Ultrafast Fiber Laser Enabled by Intracavity Polarization Control

Ultrafast laser that directly emits vortex beam has broad application prospects in many research fields and applications, such as telecommunication, bio-sampling and quantum information science. In this article, we demonstrate a wavelength-tunable and OAM-switchable ultrafast fiber laser enabled by intracavity polarization controlling elements. The mode-locked laser can emit vortex beam outputs with a topological charge of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = +1 or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = -1 and the center wavelength can be continuously tuned from 1015nm to 1038nm. The obtained output pulse has a pulse energy of 3.3nJ and a compressed pulse duration of 87fs. Compared with previous results, this laser can emit OAM-switchable output with a shorter pulse duration and a broad wavelength tuning range. The concept of adding polarization control elements to a mode-locked fiber laser can be further expanded to build laser with more sophisticated and customizable outputs.

Electro-mechanical tuning of high-Q bulk acoustic phonon modes at cryogenic temperatures

We investigate the electromechanical properties of quartz bulk acoustic wave resonators at extreme cryogenic temperatures. By applying a DC bias voltage, we demonstrate broad frequency tuning of high-Q phonon modes in a quartz bulk acoustic wave cavity at cryogenic temperatures of 4 K and 20 mK. More than 100 line-widths of tuning of the resonance peak without any degradation in loaded quality factor, which are as high as 1.73×109, is seen for high order overtone modes. For all modes and temperatures, the observed coefficient of frequency tuning is ≈ 3.5 mHz/V per overtone number n corresponding to a maximum of 255.5 mHz/V for the n = 73 overtone mode. No degradation in the quality factor is observed for any value of an applied biasing field.

Versatile tuning of Kerr soliton microcombs in crystalline microresonators

Microresonator-based optical frequency combs emitted from high-quality-factor microresonators, also known as microcombs, have opened up new horizons to areas of optical frequency comb technology including frequency metrology, precision sensing, and optical communication. To extend the capability of microcombs for such applications, large and reliable tunability is of critical importance. Here, we show broad spectral tuning of Kerr soliton microcombs in a thermally controlled crystalline microresonator with pump-detuning stabilization. The fundamental elements composing frequency combs, namely the center frequency, repetition frequency, and carrier-envelope offset frequency, are spectrally tuned by up to −48.8 GHz, −5.85 MHz, and −386 MHz, respectively, leveraging thermal effects in ultrahigh-Q crystalline magnesium fluoride resonators. We further demonstrate a 3.4-fold enhancement of soliton comb power resulting from thermal expansion with a temperature change of only 28 K by employing quantitative analyses of the fiber-to-resonator coupling efficiency.

A 25% Tuning Range 7.5–9.4 GHz Oscillator With 194 FoM T and 400 kHz 1/f₃ Corner in 40nm CMOS Technology

An 8-GHz VCO with class-F23 operation was realized in a 40 nm CMOS technology without ultra-thick metals. The class-F23 operation was enabled in a transformer-based LC tank to allow multiple impedance peaks in the common mode (CM) and the differential mode (DM) excitation. With the additional resonance at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2^{nd}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^{rd}$ </tex-math></inline-formula> harmonic frequency, the circuit noise to phase-noise conversion and 1/f noise up-conversion are reduced significantly. In a 40 nm CMOS technology without ultra-thick metal, a patterned shielding structure was proposed to improve the inductor quality factor. A combined varactor and capacitor array is proposed to provide accurate matching for a desired resonance frequency ratio, reducing AM-FM conversion and it achieves a broad tuning range. With the proposed transformer-based LC bank and class-F23 operation, the oscillator achieves a phase noise of −150.8 dBc/Hz at 10 MHz offset from a 1.85 GHz carrier after an on-chip /4 divider, and the measured 1/f3 flicker noise corner is around 400 kHz. The oscillator core covers a 7.5–9.4 GHz frequency range for a 25% tuning range.

A Plasma-Switch Impedance Tuner With Microsecond Reconfiguration

With many frequency bands previously allocated solely for radar now being reallocated for sharing, radar transmitters must be frequency-agile, able to quickly change operating frequency while maintaining detection range. This article details the design of a 2–4-GHz reconfigurable impedance tuner using 35-W plasma switches. The tuner consists of switched shunt capacitor and inductor branches loading a series microstrip line. For many RF matching applications, a reconfigurable impedance tuner must have a broad tuning bandwidth, real-time switching speeds, high power handling, low loss, and broad Smith chart coverage. The implementation of the tuner using semiconductor plasma switches illuminated by laser diodes is described. The tuner is demonstrated in measurements using a custom search algorithm, adjusting and optimizing the tuner settings to provide maximum output power in approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$300~\mu \text{s}$ </tex-math></inline-formula> upon changes in operating frequency or antenna impedance. This tuner provides superior reconfiguration times over other high-power tuners in the literature. The tuner possesses losses as low as 0.77 dB and at least 30% Smith chart coverage over the entire tunable bandwidth. With a 26.7- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> switching speed, the impedance tuner is also demonstrated to handle 20 W of power at all frequencies and states with over 40 W of power for greater than half of the octave bandwidth and power handling measured as high as 70 W. The combination of fast reconfiguration and high power handling in an impedance tuner can enable cognitive radar systems to adapt to a congested and dynamic environment in real time.

Engineering giant excitonic coupling in bioinspired, covalently bridged BODIPY dyads.

Strong excitonic coupling in photosynthetic systems is believed to enable efficient light absorption and quantitative charge separation, motivating the development of artificial multi-chromophore arrays with equally strong or even stronger excitonic coupling. However, large excitonic coupling strengths have typically been accompanied by fast non-radiative recombination, limiting the potential of the arrays for solar energy conversion as well as other applications such as fluorescent labeling. Here, we report giant excitonic coupling leading to broad optical absorption in bioinspired BODIPY dyads that have high photostability, excited-state lifetimes at the nanosecond scale, and fluorescence quantum yields of nearly 50%. Through the synthesis, spectroscopic characterization, and computational modeling of a series of dyads with different linking moieties, we show that the strongest coupling is obtained with diethynylmaleimide linkers, for which the coupling occurs through space between BODIPY units with small separations and slipped co-facial orientations. Other linkers allow for broad tuning of both the relative through-bond and through-space coupling contributions and the overall strength of interpigment coupling, with a tradeoff observed in general between the strength of the two coupling mechanisms. These findings open the door to the synthesis of molecular systems that function effectively as light-harvesting antennas and as electron donors or acceptors for solar energy conversion.