We describe a tunable liquid crystal lens based on Fresnel optics that enables variable focus of virtual images displayed by a head-worn VR or AR device. This lens has been fabricated using ultra-thin, light bioplastic film instead of glass, uniquely enhancing visual comfort whilst reducing weight and thickness compared to glass-based approaches.

This paper provides a new method to implement substrate integrated defected ground structure (SIDGS)-based bandpass filter (BPF) with adjustable frequency and controllable bandwidth. Compared with previous literature, this method implements a new SIDGS-like resonator capable of tunable frequency in the same plane as the slotted line using a varactor diode, increasing the design flexibility. In addition, the method solves the problem that the tunable BPF constituted by the SIDGS resonator cannot control the bandwidth by introducing a T-shaped non-resonant unit. The theoretical design method and the structural design are shown. Moreover, the configured structure is fabricated and measured to show the validity of the design method in this paper.

This paper demonstrates that a 360° radio-frequency phase detector consisting of a combination of symmetrical mixers and 45° phase shifters with tunable devices can achieve a low phase-detection error over a wide frequency range. It is shown that the phase detection error does not depend on the voltage gain of the 45° phase shifter. This allows the usage of tunable devices as 45° phase shifters for a wide frequency range with low phase-detection errors. The fabricated phase detector having tunable low-pass filters as the tunable device demonstrates phase detection errors lower than 2.0° rms in the frequency range from 3.0 GHz to 10.5 GHz.

This paper presents a theoretical analysis of a tunable resonator using a coupled line and switches for the first time. The tunable resonator has the capability to tune its resonant frequency and bandwidth. The resonator has two suitable features on its tunable capability. The first feature is that the resonator retains its resonant frequency during bandwidth tuning. The second feature is that the on-state switch for tuning the bandwidth does not affect the insertion loss at the resonant frequency. These features are theoretically confirmed by its mathematically derived input impedance. The results from electromagnetic simulation and measurement of the fabricated tunable resonator also confirm these features. The fabricated tunable resonator changes the resonant frequency from 2.6 GHz to 6.4 GHz and bandwidth between 9% and 55%.

This paper presents a theoretical analysis and experimental confirmation of a tunable ring resonator that can independently change its resonant frequency and bandwidth. The tunable ring resonator comprises a ring resonator, three tunable capacitors, and switches. The resonant frequency changes according to the capacitance of tunable capacitors, and the bandwidth varies by changing the state of the switches. The unique feature of the resonator is that the resonant frequency remains steady when the bandwidth is changed. The fundamental characteristics are shown based on linear circuit simulation and electromagnetic simulation results. The resonator is fabricated using GaAs FET single-pole single-throw switches. The fabricated resonator changes the resonant frequency from 1.5 GHz to 2.0 GHz and the fractional bandwidth from 5% to 30%.

A design method of the differential N-path filter with sampling computation is proposed. It enables the scale of the whole filter to be reduced by approximately half for easier realization. On top of that, the proposed method offers the ability to eliminate the harmonic passbands of the clock frequency and an increase of harmonic rejection. By using the proposed method, previous work involving an 8-path filter can be reduced to 5-path. The proposed differential 5-path filter reduces the scale of the circuit and at the same time has the performance of a 10-path filter from previous work. An example of differential 7-path filter using the same proposed design method is also stated in comparison of the differential 5-path filter. The differential 7-path filter offers the ability to eliminate all the passbands below 10 times the clock frequency with a tradeoff of an increase in circuit scale.

In this study, a plasma loop tube is presented as a tunable VHF-UHF band plasma antenna. In plasma medium, wave radiation mechanism is due to ionized gas instead of metal. Meanwhile, the most important advantage of plasma elements is electronic tunability rather than the rigid and fixed features of metals. Here, we employ an external magnetic field as a background to affect the plasma without any shape, gas or source manipulation. Finite difference time domain (FDTD) is performed for plasma antenna analysis. The FDTD formulation should be adapted to fluid modeling of plasma in the anisotropic zone in the presence of an external magnetic field. The bandwidth coverage of 700MHz is obtained by designing correctly. Parametric study in return loss, gain and radiation pattern are studied here and other new points are presented as well.

This invited paper aims to present an overview of our recent research and development (R&D) of advanced microwave planar filters, in particular with miniaturization and/or electronically tunable/ reconfigurable functionalities, which are in demand for future communication/radar systems as well as emerging wireless applications.

Post-Silicon Tunable (PST) buffers are widely adopted in high-performance integrated circuits to fix timing violations introduced by process variations. In typical optimization procedures, the statistical timing analysis of the circuits with PST clock buffers will be executed more than 2000 times for large scale circuits. Therefore, the efficiency of the statistical timing analysis is crucial to the PST clock buffer optimization algorithms. In this paper, we propose a stochastic collocation based efficient statistical timing analysis method for circuits with PST buffers. In the proposed method, we employ the Howard algorithm to calculate the clock periods of the circuits on less than 100 deterministic sparse-grid collocation points. Afterwards, we use these obtained clock periods to derive the yield of the circuits according to the stochastic collocation theory. Compared with the state-of-the-art statistical timing analysis method for the circuits with PST clock buffers, the proposed method achieves up to 22X speedup with comparable accuracy.

This paper presents a simple-structured tunable resonator employing semiconductor switches that can change its resonant frequency discretely but precisely. The tunable resonator comprises a transmission line with a comb-shaped pattern and multiple single-pole single-throw (SPST) switches placed between the teeth of the comb-shaped pattern. The resonator changes its resonant frequency according to the switch states, by controlling the path length carrying a high frequency current. The characteristics of the proposed resonator are evaluated through both method of moment electromagnetic simulation and fabrication, using GaAs FET SPST switches. The fabricated resonator changes its resonant frequency from 1.63,GHz to 1.85,GHz. This paper also introduces two circuit designs based on the proposed resonator that expands the tuning range of the resonant frequency or the number of resonant frequencies to be obtained.

We describe wavelength-routed switching technology for 25-Gbit/s optical packets using a tunable transmitter that monolithically integrates a parallel-ring-resonator tunable laser and an InGaAlAs electro-absorption modulator (EAM). The transmitter provided accurate wavelength tunability with 100-GHz spacing and small output power variation. A 25-Gbit/s burst-mode optical-packet data was encoded onto the laser output by modulating the integrated EAM with a constant voltage swing of 2 V at 45$^{circ}$C. Clear eye openings were observed at the output of the 100 GHz-spaced arrayed-waveguide grating with error-free operation being achieved for all packets. The tunable transmitter is very promising for realizing a high-speed, large-port-count and energy-efficient wavelength-routing switch that enables the forwarding of 100-Gbit/s optical packets.

We demonstrate an all-optical non-return-to-zero differential phase shift keying (NRZ-DPSK) to return-to-zero differential phase shift keying (RZ-DPSK) format conversion with wavelength-shift-free and pulsewidth tunable operations by using a semiconductor optical amplifier (SOA)-based switch. An NRZ-DPSK signal is injected into the SOA-based switch with an RZ clock, and is converted to RZ-DPSK signal owing to the nonlinear effects inside the SOA. In this scheme, the wavelength of the converted RZ-DPSK signal is maintained as the original wavelength of the input NRZ-DPSK signal during the format conversion. Moreover, the pulsewidth of the converted signal is tunable in a wider operating range from 30 to 60 ps. The format conversion with pulsewidth tunability is based on cross-phase modulation (XPM) and cross-gain modulation (XGM) effects in the SOA. The clear eye diagrams, optical spectra and the bit-error-rate (BER) characteristics show high conversion performance with the wide pulsewidth tuning range. For all cases of the converted RZ-DPSK signal with different pulsewidths, the receiver sensitivities at a BER of 10$^{-9}$ for the converted RZ-DPSK signal were 0.7 to 1.5 dB higher than the receiver sensitivity of the input NRZ-DPSK signal.

Parasitic antenna elements with tunable terminations can be used for interference suppression in multi-antenna systems without using the degrees of freedom. The authors have proposed a fast non-iterative algorithm for optimizing the termination conditions. However, this method cannot be used for suppressing the interference from unknown systems since it requires the channel state information. In this paper, a fast non-iterative algorithm based on the correlation matrix, which can be obtained even from unknown interference sources, is proposed for the multi-antenna system with parasitic antenna elements. The correlation matrix including both receiving and parasitic antennas can be estimated from a few observations of the signals even without receiving signals at the parasitic antenna. By using this correlation matrix, the power of the interference with the arbitrary termination conditions can be easily estimated. Therefore, the termination condition, which minimizes the interference power, can be calculated without knowledge of the channel state information or additional estimations. The results of a numerical analysis indicate that proposed method works well in suppressing the interference without the perfect channel state information.

The quantum dot optical frequency comb laser (QD-CML) is an attractive photonic device for generating a stable emission of fine multiple-wavelength peaks. In the present paper, 1.0-GHz and 10-ps-order short optical pulsation is successfully demonstrated from a hybrid mode-locked QD-CML with an ultrabroadband wavelength tuning range in the T+O band. In addition, 10-GHz high-repetition intensity-stable short optical pulse generation with a high S/N ratio is successfully demonstrated using an external-cavity QD-CML with a 10th-harmonic mode-locking technique.

This paper presents a novel isolator that employs a varactor that tunes the operating frequency for use in future multi-band mobile handsets. The proposed isolator employs only one varactor for compactness and has a three-fold symmetric structure to reduce the parasitic reactance at each port. Analytical and experimental results clarify the tuning range of the proposed isolator. This paper presents the fundamental characteristics of the proposed isolator such as the insertion loss, isolation, and adjacent channel leakage ratio (ACLR) using a W-CDMA signal. The impact of the proposed isolator on the system performance is described based on experimental evaluation of the ACLR with a multi-band transmission system consisting of a power amplifier and the proposed isolator.

L-band SiGe HBT frequency-tunable differential amplifiers with dual-bandpass or dual-bandstop responses have been developed for the next generation adaptive and/or reconfigurable wireless radios. Varactor-loaded dual-band resonators comprised of series and parallel LC circuits are employed in the output circuit of differential amplifiers for realizing dual-bandpass responses as well as the series feedback circuit for dual-bandstop responses. The varactor-loaded series and parallel LC resonator can provide a wider frequency separation between dual-band frequencies than the stacked LC resonator. With the use of the varactor-loaded dual-band resonator in the design of the low-noise SiGe HBT differential amplifier with dual-bandpass responses, the lower-band frequency can be varied from 0.58 to 0.77 GHz with a fixed upper-band frequency of 1.54 GHz. Meanwhile, the upper-band frequency can be varied from 1.1 to 1.5 GHz for a fixed lower-band frequency of 0.57 GHz. The dual-band gain was 6.4 to 13.3 dB over the whole frequency band. In addition, with the use of the varactor-loaded dual-band resonator in the design of the low-noise differential amplifier with dual-bandstop responses, the lower bandstop frequency can be varied from 0.38 to 0.68 GHz with an upper bandstop frequency from 1.05 to 1.12 GHz. Meanwhile, the upper bandstop frequency can be varied from 0.69 to 1.02 GHz for a lower bandstop frequency of 0.38 GHz. The maximal dual-band rejection of gain was 14.4 dB. The varactor-loaded dual-band resonator presented in this paper is expected to greatly contribute to realizing the next generation adaptive and/or reconfigurable wireless transceivers.

This paper presents a multi-band WCDMA receiver consisting of a multi-band low noise amplifier (LNA), a multi-band mixer and an inter-stage tunable notch filter. The notch filter is used to suppress Tx leakage, and 0.8–1.5 GHz (66%) of tuning range is achieved. The receiver achieves 33 and 30 dB conversion gain, 6.4 and 8 dB NF, 50 and 35.5 dBm IIP2, and -6 and -4.7 dBm IIP3 at 0.8 and 1.5 GHz, respectively. The power consumption is 121 mW from a 1.8-V power supply. The receiver is implemented in a 0.18-µm CMOS process.

A hybrid buffer structured optical packet switch and its scheduling algorithm are presented for a limited number of tunable wavelength convertors (TWCs) and internal wavelengths. The hybrid buffer consists of the fiber delay line (FDL) buffer and the electronic buffer. With the proposed algorithm, it could lead realizable packet loss reduction that the LAUC-VF algorithm with only the FDL buffer does not reach. Also, we optimized the number of TWCs and internal wavelengths of the hybrid buffer structured OPS. For the fully shared TWC structure, the optimum number of TWCs and internal wavelengths to guarantee minimum packet loss is evaluated to prevent resource waste under the hybrid buffer.

We propose a novel 13 planar optical switch using aspheric lenses and carrier-induced tunable prisms on InP. An input light beam is collimated by the aspheric lenses in a slab waveguide. The tunable prism, whose refractive indices are tuned by the carrier plasma effect, deflect the collimated light beam and guide it to the output ports. The switching operations of the 13 optical switch that consists of five lenses and eight prisms with a footprint of 5003500 µm are performed by three-dimensional beam propagation methods. A static switching operation with a 5-dB insertion loss and a 13-dB extinction ratio is obtained with 70-mA current injection for each prism. This device has a simple structure and low power consumption and may be useful for optical packet switching systems.

This paper presents three CMOS power amplifiers (PA) which realize wide-tunable output impedance matching. For realization of multi-standard and single-chip transceiver, the prototypes were fabricated by 0.18 µm CMOS process. The proposed PAs can achieve a tunable impedance matching within a wide frequency range by utilizing a resistive feedback and parallel resonator with an inductor and capacitor array. Therefore, the proposed PA has a realization possibility of isolator-less PA which contributes to decrease die area including external component. In other words, the PAs have tunable impedance matching function at their output ends. With a 3.3-V supply, three power amplifiers can cover frequency ranges of 0.9–3.0 GHz, 2.1–5.8 GHz, and 5.7–9.7 GHz, respectively. The PAs realize P1 dB of 21 dBm, Psat of 22 dBm, and PAEpeak of larger than 23%. The proposed PAs present a potential to realize multi-band transceivers without isolators.