Large Frequency Tuning Research Articles

Dynamic characteristics control of DLC nano-resonator fabricated by focused-ion-beam chemical vapor deposition

The authors fabricated a resonant frequency-tunable diamondlike carbon (DLC) resonator by focused-ion-beam chemical vapor deposition and a wet-etching process for fabrication of a functional resonant device. The resonant frequency of the DLC resonator with a cantilever shape was controlled electrically via the electrostatic attractive force generated by the opposite electrode. As a result, we achieved an extremely large resonant frequency tuning ratio of approximately 730%. This indicates that the electrostatic attractive force, when added to the restorative force of the DLC resonator, works effectively to change the resonant frequency.

Photonic Generation of Phase-Coded Microwave Signal With Large Frequency Tunability

A photonic approach to realizing phase-coded microwave signal generation with large frequency tunability is proposed and demonstrated. Two coherent optical wavelengths are generated based on external modulation by biasing a Mach-Zehnder modulator (MZM) at the minimum transmission point to generate ±1 -order sidebands while suppressing the optical carrier. The two ±1-order sidebands are then sent to a fiber Sagnac interferometer (SI) incorporating an optical phase modulator (PM) and a broadband flat-top fiber Bragg grating (FBG), with one of the sidebands being phase modulated at the PM. A frequency tunable phase-coded microwave signal is generated by beating the two sidebands at a photodetector (PD). The proposed technique is experimentally investigated. The generation of a frequency tunable phase-coded microwave signal at 22 and 27 GHz is demonstrated.

A Varactor and FMR-Tuned Wideband Band-Pass Filter Module With Versatile Frequency Tunability

A varactor and FMR-tuned wideband band-pass filter (BPF) module with versatile frequency tunability has been devised and realized on RT/Duroid substrate. By connecting four variable capacitance diodes (varactors) to the four open-circuited stubs of an X-band passive composite-BPF and adjusting the reverse bias voltage from 2 to 22 V, the 3 dB passband of the passive composite-BPF was continuously tuned from 7.7-12.4 GHz to 11.4-17.5 GHz. The corresponding bandwidth (BW) was enlarged from 4.7 to 6.1 GHz and the upper frequency of the passband was extended from 12.4 to 17.5 GHz, namely, a total frequency span of 9.8 GHz. The BW of the passive composite-BPF was further FMR-tuned using a pair of Band-Stop Filter (BSF). By setting the reverse bias voltage at 22 V together with the bias magnetic fields at 3250 and 4200 Oe, respectively, to the two BSFs, the 6.1 GHz BW and 9.8 GHz frequency span were compressed to 1.4 GHz toward the high-end frequency. The 4.7 GHz BW and 9.8 GHz frequency span were also compressed to 1.0 GHz toward the low-end frequency with 2650 and 3500 Oe bias magnetic fields and 2 V reverse bias voltage. Thus, the combination of the varactor and FMR-tuning has facilitated versatile passband and its BW tuning covering the X-and Ku-bands with both large frequency tunability and greatly improved frequency selectivity.

Microwave and Terahertz Generation Based on Photonically Assisted Microwave Frequency Twelvetupling With Large Tunability

A novel approach to achieving photonically assisted microwave frequency twelvetupling with large frequency tunability is proposed and demonstrated. The frequency twelvetupling is realized through a joint operation of polarization modulation, four-wave mixing, and stimulated-Brillouin-scattering-assisted filtering. The key significance of the technique is that the system is capable of realizing simple frequency tuning over a wide frequency range. An experiment is performed. An electrical signal with a frequency that is tunable from 48 to 132 GHz is generated.

Highly Strained Compliant Optical Metamaterials with Large Frequency Tunability

Metamaterial designs are typically limited to operation over a narrow bandwidth dictated by the resonant line width. Here we report a compliant metamaterial with tunability of Δλ ∼ 400 nm, greater than the resonant line width at optical frequencies, using high-strain mechanical deformation of an elastomeric substrate to controllably modify the distance between the resonant elements. Using this compliant platform, we demonstrate dynamic surface-enhanced infrared absorption by tuning the metamaterial resonant frequency through a CH stretch vibrational mode, enhancing the reflection signal by a factor of 180. Manipulation of resonator components is also used to tune and modulate the Fano resonance of a coupled system.

The interplay between active hair bundle motility and electromotility in the cochlea

The cochlear amplifier is a nonlinear active process providing the mammalian ear with its extraordinary sensitivity, large dynamic range and sharp frequency tuning. While there is much evidence that amplification results from active force generation by mechanosensory hair cells, there is debate about the cellular processes behind nonlinear amplification. Outer hair cell electromotility has been suggested to underlie the cochlear amplifier. However, it has been shown in frog and turtle that spontaneous movements of hair bundles endow them with a nonlinear response with increased sensitivity that could be the basis of amplification. The present work shows that the properties of the cochlear amplifier could be understood as resulting from the combination of both hair bundle motility and electromotility in an integrated system that couples these processes through the geometric arrangement of hair cells embedded in the cochlear partition. In this scenario, the cochlear partition can become a dynamic oscillator which in the vicinity of a Hopf bifurcation exhibits all the key properties of the cochlear amplifier. The oscillatory behavior and the nonlinearity are provided by active hair bundles. Electromotility is largely linear but produces an additional feedback that allows hair bundle movements to couple to basilar membrane vibrations.

Miniaturized Antennas and Planar Bandpass Filters With Self-Biased NiCo-Ferrite Films

Miniaturized microwave devices are realized by using magnetodielectric substrate comprising thin magnetic films that exhibit both high permittivity and high permeability at gigahertz frequency. We have fabricated and tested miniature circular patch antennas and hairpin bandpass filters with the alumina and Rogers substrate loaded with self-biased NiCo-ferrite films that exhibit excellent uniformity and low loss at frequencies exceeding 1.5 GHz. The measured results of magnetic hairpin bandpass filters have improved the central resonant frequency shift from 1.55 to 1.44 GHz, and a large resonant frequency tunability of about 23%-34% of the - 3-dB bandwidth was achieved. For the circular patch antenna, we observed an improvement of 0.8 dB in gain and a large resonance frequency tunability of 100%-320% of the antenna -10-dB bandwidth.

Circular Polarization GPS Patch Antennas with Self-biased Magnetic Films

Magneto-dielectric substrates with thin magnetic fllms show great potential in realizing electrically small tunable antennas with improved directivity and higher bandwidth than those realized on dielectric substrates. This paper introduces self-biased magnetic fllms as a practical means to tune a patch antenna by loading a commercially available dielectric substrate. Novel antenna designs with self-biased metallic magnetic fllms and ferrite fllms were investigated. These magnetic patch antennas have improved the axial ratio from 1.57dB to 0.97dB with respect to the central frequency ranging from 1.575GHz to 1.562GHz, a large radiation frequency tunability of about 40% to 80% of the i10dB bandwidth, and a signiflcantly enhanced directivity.

A modified Park-Kim voltage-controlled ring oscillator for multi-Gbps serial links

This paper proposes a new multi-stage CMOS voltage-controlled ring VCO called modified Park-Kim ring VCO for multi-Gbps serial links. An in-depth comparative study of pros and cons of Park-Kim VCO and the modified Park-Kim VCO with both single and dual delay paths is given. We show that the modified Park-Kim VCO offers an improved oscillation frequency, large output voltage swing, comparable frequency tuning range and phase noise as compared with Park-Kim VCO proposed in [1, 2]. We further show that although the modified Park-Kim VCO with single delay path and that with dual delay path offer comparable oscillation frequencies when the number of stages of the VCOs is high, the former provides a large frequency tuning range and reduced circuit complexity. To verify performance improvement, both Park-Kim VCOs and the modified Park-Kim VCOs are implemented in TSMC's-0.18 ?m, 1.8 V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3.3 device models. Simulation results are presented.

Design and development of ferroelectric tunable HTS microstrip filters for Ku- and K-band applications

In the past few years, our group has designed, fabricated and tested several ferroelectric tunable components, in collaboration with NASA Glenn Research Center. Among the components studied are microstrip tunable resonators, filters, diplexers, and couplers. Tunable filters with gold as well as YBCO high temperature superconductor (HTS) electrodes have been studied using the conductor/ferroelectric/dielectric two-layered microstrip configuration. Tunability is achieved through the non-linear dc electric field dependence of the relative dielectric constant of the ferroelectric thin film. Two pole ferroelectric tunable HTS filters using the YBCO/STO/LAO two-layered microstrip yielded low insertion loss as low as 1.5 dB, and large frequency tunability (∼2.3 GHz) at 24 K, with a peak electric field of 80 kV cm −1 for electrical tuning. The critical design issues for realizing practical tunable filters will be addressed. These include design for (i) large tunability, (ii) low insertion loss, (iii) bandwidth considerations, and (iv) dc biasing for tuning the filters. HTS filters will be compared with their gold counter parts for their performance at Ku- and K-band frequencies. Also, our current work on BSTO based room temperature tunable filters will be presented.

Progress toward absolute frequency measurements of the /sup 127/I/sub 2/-stabilized Nd:YAG laser at 563.2 THz/532 nm

Progress on the development of a frequency chain devoted to the absolute frequency measurement of /sup 127/I/sub 2/-stabilized lasers around 563.2 THz/532 nm is reported. The aim of this work is the improvement of the accuracy-by at least one order of magnitude-of the absolute frequency of this standard. The scheme is based on the frequency combination of two well-known optical frequency standards, namely a CO/sub 2/ laser stabilized on OsO/sub 4/, and a 778-nm diode laser stabilized on Rb measured, at BNM-LPTF, against a cesium primary standard with 2/spl times/10/sup -13/ and 2/spl times/10/sup -12/ relative uncertainty respectively. This last value gives the ultimate accuracy of the reported chain.

A 2-1600-MHz CMOS clock recovery PLL with low-Vdd capability

A general-purpose phase-locked loop (PLL) with programmable bit rates is presented demonstrating that large frequency tuning range, large power supply range, and low jitter can be achieved simultaneously. The clock recovery architecture uses phase selection for automatic initial frequency capture. The large period jitter of conventional phase selection is eliminated through feedback phase selection. Digital control sequencing of the feedback enables accurate phase interpolation without the traditional need of analog circuitry. Circuit techniques enabling low Vdd operation of a PLL with differential delay stages are presented. Measurements show a PLL frequency range of 1-200 MHz at Vdd=1.2 V linearly increasing to 2-1600 MHz at Vdd=2.5 V, achieved in a standard process technology without low threshold voltage devices. Correct operation has been verified down to Vdd=0.9 V, but the lower limit of differential operation with improved supply-noise rejection is estimated to be 1.1 V.

Frequency tunable monomode diode laser at 670 nm for high resolution spectroscopy

The frequency tuning behaviour of four diode lasers manufactured by Toshiba is investigated using an external-cavity diode-laser system with optical feedback from a diffraction grating in Littrow configuration. Continuous frequency tuning up to 90 GHz is achieved in the spectral region around 670 nm without antireflection (AR) coating of the laser facets. The largest frequency tuning is observed for external cavity length equal to an integer multiple of the effective diode laser length. An explanation of the experimental results is proposed based on the steady-state solutions for the threshold gain and the lasing frequency of the grating-tuned external-feedback diode laser. The theoretical model has been expanded by considering the grating reflectivity profile. The I 2 ro-vibrational absorption spectrum was measured around 673.1 nm.

CW MIR optically pumped ammonia laser with large frequency tunability

We have studied the frequency tunability of two 15NH 3 emission lines pumped by a CW CO 2 laser operating at the 10 R(42) line. We report a 550 MHz frequency tunability for the aP(4, 0) emission line at 11.76 μm (directly pumped), and 430 MHz for the aP(5, 3) emission line at 12.06 μm (collisionally pumped). The results are compared to numerical calculations which predict a frequency tunability above 1.5 GHz for many emission lines of the ammonia laser.

Demonstration of multilevel multichannel optical frequency shift keying (FSK) with cleaved-coupled-cavity (C 3 ) semiconductor lasers

We report the first demonstration of multilevel multichannel (4-level, 2-channel) optical frequency shift keying (FSK) using a newly developed cleaved-coupled-cavity (C3) GaInAsP semiconductor laser operating at ~1.3 μm. This is made possible because of the very large frequency tuning rate (~10 A/mA) and frequency tuning range (~150 A) achievable with these new lasers. In addition, such a laser is also shown to operate in a highly stable single-longitudinal mode even under high-speed direct frequency modulation.

Stark effect on CH3OH and CH3F FIR lasers: Large frequency tuning and resolved structures

The operation of a cw FIR laser in the presence of a strong electric field is described. A hybrid metal-dielectric waveguide is used and the cavity length is scanned to study how the frequency and power of the laser depend on the field strength. The results have also been checked by heterodyning with a conventional reference laser. We report the results obtained for the 496 μm line of CH3F and the 70.5 μm and 119 μm lines of CH3OH. A large frequency tunability of almost ±40 MHz is obtained in the best case with power levels in the mW range. A very simple theoretical model accounts for the experimental results. We also report the appearance of a new FIR line at about 204 μm when CH3OH is pumped by the 9 μmP(34) of CO2 in the presence of an electric field larger than 1.2 KV/cm.