Maximum Tuning Range Research Articles

Tunable polarization beam splitter based on optofluidic ring resonator.

An efficient polarization beam splitter (PBS) based on an optofluidic ring resonator (OFRR) is proposed and experimentally demonstrated. The PBS relies on the large effective refractive index difference between transverse-electric (TE) and transverse-magnetic (TM) polarization states, since the silica-microcapillary-based OFRR possesses a slab-like geometry configuration in the cross section through which the circulating light travels. To the best of our knowledge, this is the first OFRR-based PBS. In our work, the maximum polarization splitting ratio of up to 30 dB is achieved. Besides, water and ethanol are pumped into the core of the silica microcapillary respectively, and the maximum wavelength tuning range of 7.02 nm is realized when ethanol flows through the core, verifing the tuning principle of the PBS effectively. With such a good performance and simple scheme, this OFRR-based PBS is promising for applications such as tunable optical filters, demultiplexers, and routers.

Fast continuous tuning of terahertz quantum-cascade lasers by rear-facet illumination

GaAs-based terahertz quantum-cascade lasers (QCLs) are continuously tuned in their emission frequency by illuminating the rear facet with a near-infrared, high-power diode laser. For QCLs emitting around 3.1 THz, the maximum tuning range amounts to 2.8 GHz for continuous-wave operation at a heat sink temperature of 55 K, while in pulsed mode 9.1 and 8.0 GHz are achieved at 35 and 55 K, respectively.

Study of two contact-less tuning principles for small monolithic radiofrequency MRI coils and development of an automated system based on piezoelectric motor

The Multi-turn Transmission Line Resonator (MTLR) design allows for developing very small and highly sensitive radiofrequency (RF) coils for magnetic resonance imaging. However the monolithic feature and the small size of the developed coils, imposes to employ dedicated contact-free tuning techniques. In this work, we investigated two contact-free tuning principles for small monolithic RF coils: a dielectric tuning principle based on the interception of the electric field lines by a dielectric layer, and an inductive tuning principle based on the interception of magnetic field lines by a closed conducting ring. For both tuning principles, we used experimental measurements co-supported by electromagnetic simulation and analytical modelling to determine the accessible tuning range as a function of both the tuning element's characteristics and its distance to the RF coil. A maximal tuning range about 9% and 24% was achieved using the dielectric tuning principle and the inductive tuning principle, respectively. Contrarily to the dielectric tuning principle, the inductive tuning principle was found to strongly limit the quality factor of the coil. To implement the two investigated tuning principles, we have developed an automated system based on piezoelectric actuators that achieves microscopic displacements of the tuning elements. The automated system was also used to perform inductive impedance matching of the coil. For purposes of both tuning and matching, when starting from a strongly un-tuned or un-matched configuration, the automated system reaches convergence within a few tens of seconds. First MRI experiments were performed to evaluate the MRI compatibility of the automated system.

A Top-Down Design Methodology Encompassing Components Variations Due to Wide-Range Operation in Frequency Synthesizer PLLs

This paper presents a complete methodology to model, design, and implement wide tuning-range phase-locked loops (PLLs) using a top–down approach. Mathematical equations that illustrate the contribution of the different sources of noise in the PLL are presented. Behavioral models that encompass the nonidealities of the PLL components are described using Verilog-A language. The PLL components are designed, and the noise performance of each component is evaluated using transistor-level simulations. The extracted jitter from the individual blocks is used to find the overall system noise. The proposed methodology considers the variations in the loop dynamics due to changes in the voltage-controlled oscillator gain and noise, frequency divider ratio, and charge pump current. While optimizing the PLL for maximum tuning range, the methodology also considers the tradeoff between the noise, speed, and reference spurs attenuation. The design and implementation of an integer- $N$ frequency synthesizer PLL that covers a continuous frequency range from 156.25 MHz to 10 GHz using a 65-nm CMOS technology is demonstrated in this paper. Measurement results to verify the accuracy of the models and to validate the predictions made by the simulations are provided.

Impact of technology scaling on the tuning range and phase noise of mm-wave CMOS LC-VCOs

The impact of CMOS technology scaling, on the tuning range and phase noise performance of mm-wave LC voltage controlled oscillators (LC-VCOs) is presented. As a preliminary step, the fundamental LC-VCO elements (i) tank inductor, (ii) fixed and variable capacitor elements, and (iii) cross-coupled transistor pair are analytically modeled across the frequency range 10–50GHz. These models are then exploited to analyze the tuning range and phase noise revealing the ultimate performance bounds for simultaneously achieving low phase noise and wide tuning range in mm-wave CMOS LC-VCOs across the CMOS technology scaling (from 130nm down to 45nm) are explored. The analysis demonstrates the improvement of the maximum achievable tuning range, phase noise, and figures-of-merit (FoM and FoMT) with the technology down scaling. Finally, the performance trend of the mm-wave CMOS LC-VCOs implemented using both thin and thick gate cross-coupled pair is compared. The analysis indicates that thick gate cross-coupled pair VCOs achieve better phase noise at the expense of power consumption and maximum tuning range.

Fiber optic polarization beam splitter using a reduced graphene oxide-based interlayer

A fiber-optic polarization beam splitter (PBS) incorporating reduced graphene oxide (rGO) as a metallic interlayer material is proposed and demonstrated. It is experimentally shown that the polarization beam splitting function can readily be obtained using a coupler structure with a thin rGO layer embedded between two side-polished fibers due to induced transverse magnetic (TM) surface waves. The rGO layer was prepared by a simple method of dielectric GO spraying and ultraviolet irradiation-based reduction. The polarization extinction ratio of our implemented PBS was measured to be 14.5dB at a wavelength of 1550nm for both through- and cross-port. Its operating bandwidth was shown to be at least 100nm (from 1500 to 1600nm), which was limited by the maximum tuning range of the input tunable laser used.

Active tuning of all-dielectric metasurfaces.

All-dielectric metasurfaces provide a powerful platform for highly efficient flat optical devices, owing to their strong electric and magnetic dipolar response accompanied by negligible losses at near-infrared frequencies. Here we experimentally demonstrate dynamic tuning of electric and magnetic resonances in all-dielectric silicon nanodisk metasurfaces in the telecom spectral range based on the temperature-dependent refractive-index change of a nematic liquid crystal. We achieve a maximum resonance tuning range of 40 nm and a pronounced change in the transmittance intensity up to a factor of 5. Strongly different tuning rates are observed for the electric and the magnetic response, which allows for dynamically adjusting the spectral mode separation. Furthermore, we experimentally investigate the influence of the anisotropic (temperature-dependent) dielectric environment provided by the liquid crystal on both the electric and magnetic resonances. We demonstrate that the phase transition of the liquid crystal from its nematic to its isotropic phase can be used to break the symmetry of the optical metasurface response. As such, our approach allows for spectral tuning of electric and magnetic resonances of all-dielectric metasurfaces as well as switching of the anisotropy of the optical response of the device.

Transmission characteristics of photonic crystal fibers based on filling different kinds of liquid crystals

The transmission characteristics of full-filled photonic liquid crystal fibers (PLCFs) which are filled with five kinds of liquid crystals (LCs) are experimentally studied and theoretically analyzed. The influences of temperature and external electric field on the transmission characteristics of PLCFs are also discussed in this paper. The transmission spectra of PLCFs show obvious bandgaps, and the number and the central wavelengths of the bandgaps depend on the average value of the refractive indices of LCs. By changing the temperature from 20 ℃ to 80 ℃, a blue shift in the bandgap is observed, and the maximum tuning range of the bandgap is 41 nm. Then, with the voltage turning from 0 V to 250 V, the output power of the transmission spectrum decreases, while the central wavelength of the bandgap is almost unchanged. Finally, the transmission spectrum keeps a good stability, even if the polarization state of the input light changes.

Single passband microwave photonic filter with high selectivity and large tunable range

A tunable single passband microwave photonic filter with high selectivity and flexible tunability based on stimulated Brillouin scattering (SBS) is theoretically analyzed. The passband is generated due to phase to amplitude modulation conversion by mapping the Brillouin gain spectrum induced by SBS process. Typically the linewidth of Brillouin gain spectrum for a given fiber is a constant, which restricts the filtering performance in terms of selectivity. In order to alleviate this restriction, spectrum narrowing technique is applied to reduce filter bandwidth by superimposing the gain spectrum with two loss spectra. In addition, the technique based on gain-loss compensation is used to broaden the filter tunable range. In theory, near 60 % filter bandwidth reduction and maximum tuning range of \(2\nu _{B}\) are achieved.

Mechanism and characteristics of a fast-tuning Brillouin/erbium fiber laser.

A fast-tuning Brillouin/erbium fiber laser (BEFL) is investigated on its mechanism and characteristics in detail, in which a 4 m erbium-doped fiber (EDF) as both the Brillouin gain and linear gain media is coiled on a piezoelectric transducer (PZT) for laser frequency modulations. We demonstrate the fast-tuning mechanism theoretically and experimentally that only the lasing cavity mode is modulated, instead of the previous presumption that the Brillouin frequency shift of the EDF is modulated synchronously with the lasing mode. And the maximum tuning range (~60 MHz) is limited by the bandwidth of the Brillouin gain spectrum. The frequency tuning amplitude is direct proportional to the voltage on the PZT. The tuning rates reach up to 48 kHz. The BEFL keeps high-coherence property under fast frequency modulation. Its phase noise remains about -124 dB/Hz1/2 (normalized to 1 m optical path difference) at 1 kHz under 32 kHz modulations. This fast-tuning BEFL presents a wide range of applications in fiber sensors, optical fiber communications, and so forth.

A high-speed, tunable silicon photonic ring modulator integrated with ultra-efficient active wavelength control.

We report the first complete 10G silicon photonic ring modulator with integrated ultra-efficient CMOS driver and closed-loop wavelength control. A selective substrate removal technique was used to improve the ring tuning efficiency. Limited by the thermal tuner driver output power, a maximum open-loop tuning range of about 4.5nm was measured with about 14mW of total tuning power including the heater driver circuit power consumption. Stable wavelength locking was achieved with a low-power mixed-signal closed-loop wavelength controller. An active wavelength tracking range of > 500GHz was demonstrated with controller energy cost of only 20fJ/bit.

A 105-GHz VCO With 9.5% Tuning Range and 2.8-mW Peak Output Power in a 65-nm Bulk CMOS Process

To demonstrate high tuning range and large output power, we propose a loop of coupled oscillators in this work. Two different tuning mechanisms are simultaneously exploited. First, each core oscillator is tuned using a variable capacitor. Next, by controlling the phase/delay between the coupled oscillators, the entire loop dynamics, and hence, its frequency is tuned. In this paper, we analyze a loop of “n” coupled oscillators using Adler's equation and derive the expression for the maximum tuning range. Perturbation analysis is used to study the stability conditions of the loop of coupled system. The analysis is extended toward a nested loop of coupled oscillators. The activity condition from two-port theory is used to squeeze maximum power out of active devices. The proposed system is designed and implemented using four coupled Colpitts voltage-controlled oscillators (VCOs) in a 65-nm bulk CMOS process. The VCO achieves continuous tuning range of 9.5% at the center frequency of 105 GHz with the peak output power of 2.8 mW. The circuit consumes 54 mW from a 1.2-V supply. To the best of our knowledge, this VCO has the highest output power and tuning range among all the CMOS oscillators at or above 100 GHz.

On the Influence of Spatial Dispersion on the Performance of Graphene-Based Plasmonic Devices

We investigate the effect of spatial dispersion phenomenon on the performance of graphene-based plasmonic devices at terahertz (THz). For this purpose, two different components, namely a phase shifter and a low-pass filter, are taken from the literature, implemented in different graphene-based host waveguides, and analyzed as a function of the surrounding media. In the analysis, graphene conductivity is modeled first using the Kubo formalism and then employing a full-k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ρ</sub> model that accurately takes into account spatial dispersion. Our study demonstrates that spatial dispersion upshifts the frequency response of the devices, limits their maximum tunable range, and degrades their frequency response. Importantly, the influence of this phenomenon significantly increases with higher permittivity values of the surrounding media, which is related to the large impact of spatial dispersion in very slow waves. These results confirm the necessity of accurately assessing nonlocal effects in the development of practical plasmonic THz devices.

Widely Tunable Fiber Bragg Grating and its Application in Fiber Lasers

ABSTRACTThe article describes a simple design to make a widely tunable fiber Bragg grating (FBG) filter with a minimum tuning range of 0.02 nm, and its application to develop a widely tunable, single‐longitudinal‐mode, medium‐power fiber laser. The tunable grating was developed using a commercially available FBG. The maximum tuning range of the laser was 35 nm, which was due to the available gain from the laser gain medium. The laser was operating at room temperature. The laser was free from mode hopping and produced more than 300 mW output power at room temperature. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2824–2826, 2013

Laser micropen integrated direct writing for fabrication of thick film gap-tuning capacitor

With a fixed base-electrode and a movable upper-electrode structure, the electrostatic actuated parallel plate tuning capacitors have the advantages of no DC power consumption, high efficiency and easy to implement. We propose a novel approach of laser micropen integrated direct writing for fabrication of the thick film electrostatic-controlled gap-tuning capacitors. Adopting commercial gold paste (Au) as the material of structural electrodes and polyimide colloid as the material of sacrificial layer, the thick film gap-tuning capacitor arrays are successfully fabricated on the fused silica glass substrate. The electrical analysis shows that the maximum tuning range (MTR) of the thick film gap-tuning capacitor is 30.35% with the practical pull-in voltage of 39V, and the Q value is 50 under the frequency of 1GHz.

Tunable Zeroth-Order Resonance in Metamaterial-Inspired Transmission Lines Based on Electrowetting on Dielectric

A new approach for tuning the resonant frequency of metamaterial-inspired transmission lines (TLs) by using electrowetting on dielectric (EWOD) is presented. Coplanar Waveguide (CPW) metamaterial-inspired TLs were designed and used as digital microfluidic platforms, where tunable resonance frequency was demonstrated for RF/microwave applications. A repeatable tuning mechanism was realized by exploiting the interface deformation of a liquid metal (mercury) droplet by an applied voltage. The maximum tuning range achieved is around 400 MHz (from 3.51 GHz to 3.92 GHz) with a dc actuation voltage of 110 V.

Active Frequency Tuning for Magnetically Actuated and Piezoresistively Sensed MEMS Resonators

This letter, for the first time, reports an active frequency tuning for a magnetically actuated and piezoresistively sensed MicroElectroMechanical Systems resonator. Magnetic transduction is used to drive the device into the resonance. Piezoresistive transduction is used as resonance sensing technique and to tune the device's frequency by the Joule heating generated in the Wheatstone bridge without fabricating additional electrothermal heaters. The experiments are performed in air at room temperature and atmospheric pressure. The measurements shows that, by increasing the DC bias current of Wheatstone bridge from 0.5 to 5 mA, a maximum tuning range of -3403 ppm is achieved with a device resonating at 25.77 kHz.

Frequency Tuning Range Extension in LC-VCOs Using Negative-Capacitance Circuits

We present an experimentally validated capacitance cancellation structure to increase the tuning range (TR) of LC voltage-controlled oscillators (VCOs) with minimal phase noise or power impact. The cancellation is based on an ultrawideband differential active negative-capacitance (NC) circuit. An NC scheme suitable for bottom-biased VCOs is analyzed and combined with a CMOS VCO to cancel the fixed capacitance in the LC tank. The NC structure is further modified to be tunable, enabling additional expansion of the VCO TR. By manipulating the quality factor (Q) of the NC tuning varactor pair, a prototype VCO achieves a maximum TR of 27% in a 130-nm technology, while dissipating 13 mA from a 0.9-V supply. The TR is the highest reported at Q-band, covering from 34.5 GHz to 45.4 GHz. Compared to the reference VCO without an NC circuit, the TR is increased by 38%. The measured worst case phase noise is -95 dBc/Hz at 1-MHz offset, and the FOMT is -184.9 dBc/Hz.

Fast tunable and broadband microwave sweep-frequency source based on photonic technology

A high-speed broadband tunable microwave source utilizing the wavelength tunable characteristics of distributed Bragg reflector (DBR) laser is proposed and demonstrated. The wavelength tuning of the laser is achieved instantaneously by controlling the voltage of the phase section of the DBR laser. By means of optical delay self-heterodyne technology, the microwave signal with the property of frequency broadband tuning is generated. Sweep speeds of 5 and 40 μs of the sweep-frequency source prototype were achieved and the maximum tuning range was up to 38.45 GHz.

Fully-tunable microwave photonic filter with complex coefficients using tunable delay lines based on frequency-time conversions

A fully electrically tunable microwave photonic filter is realized by the implementation of delay lines based on frequency-time conversion. The frequency response and free spectral range (FSR) of the filter can be engineered by a simple electrical tuning of the delay lines. The method has the capability of being integrated on a silicon photonic platform. In the experiment, a 2-tap tunable microwave photonic filter with a 3-dB bandwidth of 2.55 GHz, a FSR of 4.016 GHz, a FSR maximum tuning range from -354 MHz to 354 MHz and a full FSR translation range is achieved.