Entire Tuning Range Research Articles

A Novel Coupled-Line Tunable Wilkinson Power Divider With Perfect Port Match and Isolation in Wide Frequency Tuning Range

In this paper, a novel coupled-line tunable Wilkinson power divider with perfect port match and isolation in a continuously tunable passband is presented. The proposed tunable power divider consists of an isolation resistor, two coupled lines, and two types of varactors. By providing these varactors with suitable bias voltages, the operating frequency of the proposed power divider can be flexibly changed as desired. Meanwhile, perfect port match and isolation are maintained at all tunable operating frequencies. After applying the even-odd mode analysis method, the closed-form equations of the design parameters are derived to illuminate the effects on the minimum and maximum operating frequencies. These equations exhibit that the proposed power divider has a wide frequency tuning range and a high tunability (more than 110% in ideal conditions). Owing to the limitation of manufacturing process, a microstrip power divider with a tunable frequency of 0.54–1.41 GHz (89.23%) is designed and simulated based on the provided closed-form equations. The measured results show a frequency tuning range from 0.56 to 1.39 GHz (85.13%) with a more than 20-dB return loss and isolation in the entire tuning range, agreeing well with the simulation results.

Development of 6–12 GHz evanescent–mode two–pole low–loss tunable bandpass filter

ABSTRACTA very low‐loss tunable evanescent‐mode cavity bandpass filter (BPF) with one‐octave (6–12 GHz) tuning range is presented. To implement a very low‐insertion loss with wideband operation, a new coaxial‐feed structure is devised in the tunable BPF. Across the entire tuning range, the achieved insertion loss is less than 0.5 dB. The 3‐dB fractional bandwidth varies from 6.1% at 6 GHz to 12% at 12 GHz. The tenability is realized using silicon microelectromechanical systems diaphragms with slits that are electrostatically actuated. Direct comparison between a solid diaphragm and the proposed stress‐reduced diaphragm with slits is presented. The bulk of the filter is realized using physical machining of a tall printed circuit board. This article shows the upper frequency limit that is feasible using milling. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2418–2422, 2015

High power continuous-wave GaSb-based superluminescent diodes as gain chips for widely tunable laser spectroscopy in the 1.95–2.45 μm wavelength range

We present high-power single-spatial mode electrically pumped GaSb-based superluminescent diodes (SLDs) operating in the 1.95 to 2.45 μm wavelength range in continuous-wave (CW). MBE grown GaSb-based heterostructures were fabricated into single-angled facet ridge-waveguide devices that demonstrate more than 40 mW CW output power at 2.05 μm, to >5 mW at 2.40 μm at room-temperature. We integrated these SLDs into an external cavity (Littrow configuration) as gain chips and achieved single-mode CW lasing with maximum output powers exceeding 18 mW. An extremely wide tuning range of 120 nm per chip with side-mode-suppression-ratios >25 dB was demonstrated while maintaining optical output power level above 3 mW across the entire tuning range.

Tunable, high-power, continuous-wave dual-polarization Yb-fiber oscillator.

We demonstrate a high-power, dual-polarization Yb-fiber oscillator, by separately locking the two linear polarization states defined by slow and fast axis of a polarization-maintaining gain fiber with volume Bragg gratings. Dual-line lasing is achieved with a tunable wavelength separation from 0.03 to 2 THz, while exceeding output powers of 78 W over the entire tuning range, maintaining a high beam-quality with M(2)<1.2. With this laser configuration we achieve a peak-to-peak power variation of <1% for the dual-line signal and <3% for the individual signals.

High tuning stability of sampled grating quantum cascade lasers.

Predictable tuning behavior and stable laser operation are both crucial for laser spectroscopy measurements. We report a sampled grating quantum cascade laser (QCL) with high spectral tuning stability over the entire tuning range. We have determined the minimum loss margin required to suppress undesired lasing modes in order to ensure predictable tuning behavior. We have quantified power fluctuations and drift of our devices by measuring the Allan deviation. To demonstrate the feasibility of sampled grating QCLs for high-precision molecular spectroscopy, we have built a simple transmission spectroscopy setup. Our results prove that sampled grating QCLs are suitable light sources for highly sensitive spectroscopy measurements.

Design of low power low phase noise negative resistance Ku‐band VCO using planar resonator pair

ABSTRACTNew negative resistance voltage‐controlled oscillator (VCO) at Ku‐band is designed. The proposed topology uses packaged NPN Silicon Germanium RF transistor and two parallel resonator structures connected to the device emitters. Novel active open ended planar structure is proposed as a resonator for the VCO. Resonator is analyzed in terms of required reflection coefficient and input impedance. Resonator's quality factor varies in between 159 and 235 as a function of tuning voltage. VCO microwave IC is fabricated on TMM10i soft substrate with 17.5μm Cr‐Cu‐Au metallization process. VCO can be tuned for 180MHz by varying resonators’ varactors from 0 to 22 V. Measured output power remains in between 4.2 and 8.06 dBm for the entire tuning range. Measured phase noise is −145 dBc/Hz at 1 MHz offset with 8 V tuning voltage. Normalized phase noise figure of merit for the VCO is −214.4 dBc/Hz. The circuit has low power consumption of 25.5 mW and high DC to RF conversion efficiency (ηDC‐RF). © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1938–1941, 2015

Dynamic Polarization Control

Dynamic polarization control (DPC) is the method of setting the polarization of the far-field electric field generated by a radiating antenna entirely electronically in order to maintain polarization matching with the receiving antenna regardless of its polarization or orientation in space. This work implements a fully integrated 2 × 1 phased array radiator in 32 nm CMOS SOI at 105.5 GHz with DPC. The system consists of a central locking oscillator that phase locks oscillators within the core of each antenna followed by three amplification stages with variable gain that drive the antennas. By controlling the amplitude and phase of two orthogonal polarized subparts of each multi-port antenna, various far-field polarizations can be realized. The array is capable of beam steering, controlling the polarization angle across the entire tuning range of 0° to 180° while maintaining axial ratios above 10 dB, and controlling the axial ratio from 2.4 dB (near circular) to 14 dB (linear) in various directions of radiation. It radiates a maximum EIRP of 7.8 dBm with a total radiated power of 0.9 mW. To the best of the authors' knowledge, this work presents the first integrated radiator with dynamically controllable polarization.

A Low Phase-Noise Wide Tuning-Range Quadrature Oscillator Using a Transformer-Based Dual-Resonance Ring

This paper presents a dual-band quadrature voltage-controlled oscillator (QVCO) using a transformer-based high-order LC-ring resonator, which inherently provides quadrature signals without requiring noisy coupling transistors as in traditional approaches, thereby achieving low phase-noise performance. Moreover, the proposed resonator shows two possible oscillation frequencies, which are exploited to realize a wide-tuning range QVCO employing a mode-switching transistor network. Due to the use of transformers, the oscillator has a minimal area penalty compared to the conventional designs. The implemented prototype in a 65-nm CMOS process achieves a continuous tuning range of 77.8% from 2.75 to 6.25 GHz while consuming from 9.7 to 15.6 mA current from a 0.6-V supply. The measured phase-noise figure-of-merit at 1-MHz offset ranges from 184 to 188.2 dB throughout the entire tuning range. The QVCO also exhibits good quadrature accuracy with 1.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> maximum phase error and occupies a relatively small silicon area of 0.35 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\hbox{mm}}^{2}$</tex> </formula> .

A Matrix-Grating Equivalent Phase Shifted Laser Array With 25-nm Wavelength Tuning Range

A matrix-grating equivalent phase shifted (MG-EPS) eight-wavelength distributed-feedback (DFB) semiconductor laser array is experimentally demonstrated. This device contains eight index-coupled DFB semiconductor laser diodes with a V-junction combiner, which have wavelength channel spacing of ~3.37 nm, with quarter-wave EPS structures. 25-nm continuous wavelength tuning range is achieved by changing the temperature, with side mode suppression ratios >42 dB within the entire tuning range. Meanwhile, because of the quarter-wave equivalent phase shift structures, no mode-hopping problems have been observed and good single-longitudinal mode operation is achieved. This device is promising for cost-effective applications of wavelength division multiplexing systems.

A Low Phase Noise and Wide Tuning Range Millimeter-Wave VCO Using Switchable Coupled VCO-Cores

This work presents a millimeter-wave (mm-wave) dual-mode voltage-controlled oscillator (VCO) topology with switchable coupled VCO-cores for wide frequency tuning range and low phase noise application. By taking advantage of the different parasitic capacitance of cross-coupled pair when the VCO-core operates in ON and OFF states, the dual-mode operation of VCO can be realized, and the oscillations for both modes can be excited at the lower resonant frequency of tank, such that tank Q and phase noise performance could be improved for both modes. Strongly coupled transformer with large coupling coefficient (k) is utilized to increase the oscillation stability at the desired resonant frequency for both modes. The large k transformer will also facilitate the enhancement of tank Q at the lower resonant frequency. Frequency tuning range of the VCO is increased by properly designing the VCO-cores and combining the frequency bands of the two modes. In addition, the cross-coupled pair of VCO-core at OFF state is able to act as high Q active capacitor, which can further increase the tank Q and thus reduce the phase noise. Fabricated in a 0.18 μm BiCMOS process, the VCO exhibits a wide tuning range of 17.2% from 55.7 GHz to 66 GHz, and low phase noise from -87.5 dBc/Hz to -93.5 dBc/Hz at 1 MHz offset over the entire tuning range.

Tuning for Resonances

AbstractDue to a very distinct spectrum of resonant frequencies, the characterization of optical microcavities calls for widely tunable sources of continuous wave laser light, offering suitably narrow linewidths and single‐mode operation over the entire tuning range. This is why external cavity diode lasers, which allow for mode‐hop free wavelength tuning, often over more than a hundred nanometers, have matured to a fundamental tool of the optical microresonator research apparatus.

All-periodically poled, high-power, continuous-wave, single-frequency tunable UV source.

We report on experimental demonstration of an all-periodically poled, continuous-wave (CW), high-power, single-frequency, ultra-violet (UV) source. Based on internal second-harmonic-generation (SHG) of a CW singly resonant optical parametric oscillator (OPO) pumped in the green, the UV source provides tunable radiation across 398.94-417.08 nm. The compact source comprising of a 25-mm-long MgO-doped periodically poled stoichiometric lithium tantalate (MgO:sPPLT) crystal of period Λ(SLT)=8.5 μm for OPO and a 5-mm-long, multi-grating (Λ(KTP)=3.3, 3.4, 3.6 and 3.8 μm), periodically poled potassium titanium phosphate (PPKTP) for intra-cavity SHG, provides as much as 336 mW of UV power at 398.94 nm, corresponding to a green-to-UV conversion efficiency of ∼6.7%. In addition, the singly resonant OPO (SRO) provides 840 mW of idler at 1541.61 nm and substantial signal power of 108 mW at 812.33 nm transmitted through the high reflective cavity mirrors. UV source provides single-frequency radiation with instantaneous line-width of ∼18.3 MHz and power >100 mW in Gaussian beam profile (ellipticity >92%) across the entire tuning range. Access to lower UV wavelengths requires smaller grating periods to compensate high phase-mismatch resulting from high material dispersion in the UV wavelength range. Additionally, we have measured the normalized temperature and spectral acceptance bandwidth of PPKTP crystal in the UV wavelength range to be ∼2.25°C·cm and ∼0.15 nm·cm, respectively.

Four-Pole Narrowband Superconducting Tunable Filter at VHF-Band

This paper presents a narrowband superconducting tunable filter at very high frequency (VHF)-band with a fractional bandwidth of 1.4%. The effect of the resonator structure on the unloaded quality factor and frequency tuning range is analyzed and simulated. A shorted spiral resonator, with the inner end loaded with a gallium arsenide (GaAs) varactor through air bridges, is chosen for compact size, wide tuning range, and high quality factor. The interstage and external couplings of this resonator remain almost unchanged with the varactor capacitance. Thus, the filter keeps a constant fractional bandwidth in the entire tuning range. The four-pole tunable filter at VHF-band is successfully designed with a compact size of 30 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\times$</tex></formula> 14.6 mm. The measured results match well with the simulated results. The tuning range of the filter is 17%, from 193.9 to 229.8 MHz. The variation of the fractional bandwidth is within (1.40 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex></formula> 0.01)%. The insertion loss at 229.8 MHz is 0.32 dB, with a reverse bias voltage of 9 V. The unloaded quality factor of the resonators in the four-pole filter is estimated to be 5600 at 229.8 MHz.

A 1.7–2.2 GHz Compact Low Phase-Noise VCO Using a Widely-Tuned SIW Resonator

A 1.7-2.2 GHz low phase-noise voltage controlled oscillator (VCO) based on a widely-tuned substrate integrated waveguide (SIW) cavity resonator is presented. The frequency of the SIW resonator is tuned based on loading the cavity with three via posts and thus changing the field distribution inside the cavity. The widely-tunable SIW resonator is employed inside a reflective-type VCO structure resulting in a tuning range of 1.7-2.2 GHz ( ~ 26%) and a phase noise better than -109 dBc/Hz at a 100 kHz offset over the entire tuning range.

High‐power VHF tunable filters with high selectivity

A tunable helical bandpass filter with high selectivity designed for 30-88 MHz operation is presented. The two-pole tunable filter is discretely tuned by connecting PIN switched capacitor banks at the terminal ends of the helix. The filter schematic provides two finite transmission zeros located in the lower and upper stopbands, respectively. The experimental filter has an insertion loss between 1.65 and 2.75 dB with its return loss better than 13 dB. The 3-dB fractional bandwidth of the filter is 3.3%-3.7% and the shape factor (BW 30 dB /BW 3 dB ) is smaller than 5.5 over the entire tuning range. The input power handling capability is greater than 45 dBm. The measured results show good agreement with the simulated ones.

A 50-100-GHz Highly Integrated Octave-Bandwidth Transmitter and Receiver Chipset in &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;${\hbox{0.35-}}\mu{\hbox {m}}$&lt;/tex&gt;&lt;/formula&gt; SiGe Technology

This work presents a highly integrated transmitter (TX) and receiver (RX) chipset operating from 50 to 100 GHz. The local oscillator (LO) is realized using a high output power millimeter-wave integrated frequency synthesizer with an octave output frequency range. The proposed low-complexity discrete tuned synthesizer architecture employs a single wide-tuning range voltage-controlled oscillator core and a single-sideband mixer, which can be switched to operate as a LO amplifier. An ultra broadband variable gain amplifier, with a gain control range > 25 dB, is used at the output of the synthesizer to provide a tunable output power. A maximum output power from +7 to +12 dBm and an output phase noise from -83 to -96 dBc/Hz at 1-MHz offset are measured over the complete output frequency range. Moreover, a spurious suppression > 22 dB is achieved over the entire synthesizer's tuning range. The RX shows a conversion gain > 19 dB and a noise figure from 50 to 100 GHz. The TX's measured saturated output power is from +6 to -1 dBm over the entire frequency range. The complete chipset is realized in a commercial low-cost SiGe:C technology with an ft/fmax of 170/250 GHz. Each of the TX and RX chips including the frequency synthesizers draw a current of 370 mA from a 3.3-V supply.

Autocorrelation measurement of femtosecond laser pulses based on two-photon absorption in GaP photodiode

Semiconductor materials which exhibit two-photon absorption characteristic within a spectral region of interest can be useful in building an ultra-compact interferometric autocorrelator. In this paper, we report on the evidence of a nonlinear absorption process in GaP photodiodes which was exploited to measure the temporal profile of femtosecond Ti:sapphire laser pulses with a tunable peak wavelength above 680 nm. The two-photon mediated conductivity measurements were performed at an average laser power of less than a few tenths of milliwatts. Its suitability as a single detector in a broadband autocorrelator setup was assessed by investigating the nonlinear spectral sensitivity bandwidth of a GaP photodiode. The highly favourable nonlinear response was found to cover the entire tuning range of our Ti:sapphire laser and can potentially be extended to wavelengths below 680 nm. We also demonstrated the flexibility of GaP in determining the optimum compensation value of the group delay dispersion required to restore the positively chirped pulses inherent in our experimental optical system to the shortest pulse width possible. With the rise in the popularity of nonlinear microscopy, the broad two-photon response of GaP and the simplicity of this technique can provide an alternative way of measuring the excitation laser pulse duration at the focal point of any microscopy systems.

A 0.9- to 8-GHz VCO With a Differential Active Inductor for Multistandard Wireline SerDes

This study demonstrates a wide frequency tuning range LC voltage-controlled oscillator (LC-VCO) with an active inductor in a 90-nm CMOS process. As the proposed LC-VCO is intended to be extremely flexible without redesign for several new-generation SerDes interfaces, a wide operating frequency makes the phase-locked loop (PLL) applicable to the multistandards. To demonstrate a highly competitive design, a quality (Q) factor enhancement technique has been also demonstrated to reduce the loss from the active inductor, leading to an appropriate phase noise over the entire tuning range. At a supply of 1.2 V, the fabricated LC-VCO provides a frequency tuning range of 0.9-8 GHz (160%) with power consumption of 3.2-19.1 mW. The measured phase noise is from -105 to -118 dBc/Hz at a 1-MHz offset. Realized in a fully integrated PLL chip, it occupies an active area of 0.08 × 0.16 mm 2 .

A 248–262 GHz InP HBT VCO with Interesting Tuning Behavior

A fundamental-mode common-base voltage-controlled oscillator (VCO) based on 250-nm InP heterojunction bipolar transistor (HBT) technology is reported. The VCO, which employs varactors implemented by connecting the base and emitter of npn transistors as tuning components, shows a tuning range of 247.8-262.2 GHz. The output power is greater than 0 dBm over the entire tuning range, and dissipated dc power is around 85 mW. An unexpected tuning behavior was observed, which was shown to arise from the internal parasitic base inductance of the transistors used for varactors in this work.

A 3.01–3.82 GHz CMOS LC voltage-controlled oscillator with 6.29% VCO-gain variation for WLAN applications

A wideband low-phase-noise LC voltage-controlled oscillator (VCO) with low VCO gain (KVCO) variation for WLAN fractional-N frequency synthesizer application is proposed and designed on a 0.13-μm CMOS process. In order to achieve a low KVCO variation, an extra switched varactor array was added to the LC tank with the conventional switched capacitor array. Based on the proposed switched varactor array compensation technique, the measured KVCO is 43 MHz/V with only 6.29% variation across the entire tuning range. The proposed VCO provides a tuning range of 23.7% from 3.01 to 3.82 GHz, while consuming 9 mA of quiescent current from a 2.3 V supply. The VCO shows a low phase noise of −121.94 dBc/Hz at 1 MHz offset, from the 3.6 GHz carrier.