Electrical Filter Research Articles

A Filter-Free Photonic Microwave Single Sideband Mixer

Single-sideband mixer plays an important role in microwave and millimeter wave systems. In this letter, a novel filter-free photonic microwave single-sideband mixer based on carrier-suppressed single sideband (CS-SSB) modulation is demonstrated by using a dual-parallel Mach-Zehnder modulator (DPMZM). In the method, when the optical CS-SSB-modulated signal consists of a +1st-order sideband generated by the intermediate frequency (IF) signal and a -1st-order sideband generated by the local oscillator (LO) signal, an up-converted upper sideband (USB) RF signal can be obtained after photodetection. On the other hand, when the CS-SSB-modulated optical signal contains two +1st-order (or -1st-order) sidebands, an up-converted lower sideband (LSB) RF signal is generated at the output of the mixer. An experiment is carried out. Both the undesired sideband and the LO leakages are suppressed by more than 30 dB when the single-sideband mixer is operating in either USB or LSB mode without using an optical or electrical filter.

Design of 5 GHz‐compact reconfigurable DGS‐bandpass filter using varactor‐diode device and coupling matrix technique

ABSTRACTIn this work, a novel electrical reconfigurable second order microstrip bandpass filter is presented. The investigated filter structure consists of two neighbor coupled octagonal‐DGS resonators. The capacitor and varactor are placed on the DGS‐shape. According to the tunable characteristic of discrete lumped capacitors and varactor diode, the resonant frequencies can be tunable. The proposed filter occupies an area of 2.5 × 1.5 cm2. The coupling method has been applied and leads to an extended coupling matrix that assumes multiple couplings between both filter resonators. The measured relative tuning range of the bandpass filter is 23.5% with a fractional bandwidth of 12%. Varactors loaded on the octagonal DGS resonator allow us to control the center frequency with quasi constant bandwidth as well as to have a large tuning bandwidth. Based on the detailed analysis, the varactor‐tuned DGS bandpass filter is designed, in which the tuning bandwidth reaches 12% of the center frequency at 5 GHz. The proposed reconfigurable bandpass filter was fabricated and tested. The measured results show a variation of the center frequency from 4.3 GHz (0V) to 5.4 GHz (15V) tunable range, while the insertion loss varies from 5 to 3 dB. The measured performance of the tunable bandpass filter agrees well with the simulation results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:304–309, 2016

A Distribute Feedback Laser Diode Composed Microwave Photonic Bandpass Filter for SCM-Based Optical Transport Systems

In this paper, a distribute feedback laser diode (DFB LD) composed microwave photonic bandpass filter is proposed and experimentally demonstrated for subcarrier multiplexing (SCM)-based radio over fiber (RoF) transport systems. To realize the photonic filter, a multiwavelength laser, composed by directly modulating single-tone RF signal with a DFB LD, is developed to simultaneously generate six identical optical carriers. When these optical carriers are phase-modulated with SCM signals and communicated through optical fiber to optical network units (ONUs), a bandpass filter function is accomplished automatically due to the interaction of the accumulated chromatic dispersion and the optical interference among those transmitted optical carriers. Experimental results proof that the central frequency of the passband window of the photonic filter is not fixed, instead, it can be shifted accurately by alerting the optical channel spacing of the generated six optical carriers. By applying the proposed photonic filter for SCM-based RoF transport systems, each connected ONU will receive dedicated SCM signals only and the other SCM signals will be rejected, so no more electrical microwave filter is required to be deployed in the ONU. With the proposed scheme, the SCM-based RoF transport systems can be greatly simplified and the system transmission efficiency can be promoted and controlled centrally.

Photonic Microwave Generation With Frequency Octupling Based on a DP-QPSK Modulator

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated using a dual-polarization quadrature phase shift keying modulator. By properly setting the phase difference between the two drive signals, the working points of the modulator, and the polarization state of the light wave after the modulator, an optical signal with only ±4th order sidebands is generated. A pure 24-GHz microwave signal with low-phase noise is experimentally obtained using a 3-GHz local oscillator signal. The proposed photonic frequency octupling system also exhibits good frequency tunability as no electrical or optical filter is used.

10-Gb/s Long-Reach PON System With Low-Complexity Dispersion-Managed Coherent Receiver

We demonstrate 10-Gb/s transmission over more than 130 km of G.652 fiber using a simple directly modulated distributed feedback (DFB) laser and a new “chirp-managed” approach based on a low-complexity coherent receiver. The “chirp-managed” effect, which has been obtained in the past by optical spectral reshaping, is conveniently achieved here by means of simple electrical filtering of the received signal at the intermediate frequency. Due to coherent detection, the receiver sensitivity was $-38 \text{dBm at bit error rate (BER)} = 1.8 \times 10^{-3}$ . No colored filters and no dispersion compensation (optical or digital signal processing (DSP)-based) were used at the receiver side. We show that the coherent system presented here, based on off-the-shelf components, is robust against variations of DFB chirp, local oscillator detuning, and electrical filter bandwidth over ranges wide enough to guarantee a simple and cost-effective implementation for 10-Gb/s long-reach passive optical network applications.

FRF Smoothing to Improve Initial Estimates for Transfer Function Identification

Good initial values are crucial to obtain solutions of nonconvex optimization problems. When estimating the transfer function of physical systems from measured noisy data, obtaining good initial parameter estimates is therefore a primordial step. In this paper, it is shown that smoothing the measured frequency response function of a linear time-invariant system enhances the construction of initial estimates significantly, resulting in the optimization schemes to converge to a better optimum. This is achieved with minimal user interaction. Two smoothing techniques, the time-truncated local polynomial method and the regularized finite impulse response, are compared with the existing generalized total least squares and the bootstrapped total least squares initial estimates. The improvement attributable to smoothing is demonstrated by a simulation and by measurements of an electrical filter. The results ultimately show that the parametric models obtained using the proposed starting values are much more likely to give a good description of the measured system and hence lead to more useful models.

Frequency tunable optoelectronic oscillator based on a directly modulated DFB semiconductor laser under optical injection.

A frequency tunable optoelectronic oscillator based on a directly modulated distributed-feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Through optical injection, the relaxation oscillation frequency of the DFB laser is enhanced and its high modulation efficiency can enable the loop oscillation with a RF threshold gain of less than 20 dB. The DFB laser is a commercial semiconductor laser with a package of 10 GHz, and its packaging limitation can be overcome by optical injection. In our scheme, neither a high-speed external modulator nor an electrical bandpass filter is required, making the system simple and low-cost. Microwave signals with a frequency tuning range from 5.98 to 15.22 GHz are generated by adjusting the injection ratio and frequency detuning between the master and slave lasers. The phase noise of the generated 9.75 GHz microwave signal is measured to be -104.8 dBc/Hz @ 10 kHz frequency offset.

Narrow-linewidth microwave generation using AlGaInAs/InP microdisk lasers subject to optical injection and optoelectronic feedback.

Narrow-linewidth and low phase noise photonic microwave generation under sideband-injection locking are demonstrated using an 8-μm-radius AlGaInAs/InP microdisk laser subject to optical injection and optoelectronic feedback. Microdisk laser subject to external optical injection at the period-one state provides the microwave subcarrier seed signal, and the optoelectronic feedback serves as direct current modulation to stabilize and lock the generated microwave signal without using the electrical filter. High-quality photonic microwave signals are realized with the 3-dB linewidth of less than 1 kHz and the frequency tunable range from 8.8 to 17 GHz. Single sideband phase noise of -101 dBc/Hz is obtained at a frequency offset of 10 kHz for the generated 14.7 GHz signal. Furthermore, the dependences of photonic microwave signal on the optical injection and optoelectronic feedback parameters are investigated.

Selectively plated stretchable liquid metal wires for transparent electronics

This paper presents an innovative and versatile selective liquid-metal plating (SLMP) process to realize a transparent stretchable circuit board (TSCB) with the capability of large deformation and self-healing. The TSCB consists of polydimethylsiloxane (PDMS) thin films and non-toxic liquid-metal patterns that are embedded into the PDMS substrate. Complex liquid-metal patterns with various aspect ratios are achieved by using the selective wetting behavior of the reduced liquid metal on the Au/Cr patterns of the PDMS substrate. The smallest liquid-metal pattern is approximately 3μm in width. The TSCB integrated with a light-emitting diode exhibit stable performance, even though it is twisted more than 180° or is stretched up to ∼60% 6000 times. To evaluate the feasibility of the SLMP process, an electrical filter was fabricated on the PDMS substrate and the current–voltage (I–V) characteristics are successfully demonstrated under various conditions. The experimental results reveal that the proposed idea has the potential to enable advanced electronics such as wearable computers, wall-scale displays, electronic paper, and other stretchable electronics.

Analog Electric Circuits Synthesis using a Genetic Algorithm Approach

hardware is a hardware that depends on evolutionary algorithms (EAs) for performing electrical circuit synthesis and evolving its electrical circuit architecture, furthermore it depends on EAs for making the necessary adaptations to this architecture while working on line. This paper presents a new approach for solving the electrical circuit synthesis problem using genetic algorithms as an automated design technique, the proposed approach offers a new coding style for the chromosome representing the electric circuit, and also minimizes the chromosome size in an attempt to solve the scalability problem associated with evolvable hardware. This approach is tested upon the synthesis of low pass electrical filter and has proved to be efficient and capable of handling more complex circuit design tasks with minor future changes. Keywordsdesign, Artificial Intelligence, electric circuit synthesis, Genetic algorithms.

Tunable Optoelectronic Oscillator Using FWM Dynamics of an Optical-Injected DFB Laser

A wideband frequency-tunable optoelectronic oscillator using four-wave mixing nonlinear dynamics of an optical-injected distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. Utilizing the wavelength-selective optical gain of the DFB laser under optical injection, a frequency-tunable microwave photonic filter is realized, which is used as the desired oscillation frequency selector. Therefore, the electrical bandpass filter is not required in the proposed scheme. An optoelectronic oscillating signal with a frequency tuned from 9.63 to 19.11 GHz is obtained by changing the injection parameters. The single sideband phase noise of the generated 13.74-GHz microwave signal is measured to be −103.19 dBc/Hz at 10-kHz offset.

Modulation-format-independent OSNR monitoring insensitive to cascaded filtering effects by low-cost coherent receptions and RF power measurements.

Optical signal-to-noise ratio (OSNR) monitoring is indispensable for ensuring robust and flexible optical networks that provide failure diagnosis, dynamic lightpath provisioning and modulation format adaptation. We propose and experimentally demonstrate a low-cost, modulation-format-independent OSNR monitoring scheme utilizing reduced-complexity coherent receptions, electrical filtering and radio frequency (RF) power measurements. By measuring the RF power of the coherently received baseband signals at three different frequency components, the proposed OSNR monitor is also insensitive to spectral narrowing induced by cascaded wavelength selective switches (WSSs). We experimentally demonstrate accurate data-format-transparent and filtering-effect-insensitive OSNR monitoring for 25-Gbaud dual-polarization (DP-) transmissions with QPSK, 16-QAM and 64-QAM signals over various distances with different amount of filtering effects by cascaded WSSs. We further characterize the influence of different system parameters, such as the bandwidth of the electrical low-pass filter, the laser frequency offset and laser linewidth on the accuracy of the proposed OSNR monitor. The robustness of the proposed OSNR monitoring scheme to fiber nonlinearities, calibration parameter mismatches and variations of WSS parameters are also investigated.

Power supply and impedance matching to drive technological radio-frequency plasmas with customized voltage waveforms.

We present a novel radio-frequency (RF) power supply and impedance matching to drive technological plasmas with customized voltage waveforms. It is based on a system of phase-locked RF generators that output single frequency voltage waveforms corresponding to multiple consecutive harmonics of a fundamental frequency. These signals are matched individually and combined to drive a RF plasma. Electrical filters are used to prevent parasitic interactions between the matching branches. By adjusting the harmonics' phases and voltage amplitudes individually, any voltage waveform can be approximated as a customized finite Fourier series. This RF supply system is easily adaptable to any technological plasma for industrial applications and allows the commercial utilization of process optimization based on voltage waveform tailoring for the first time. Here, this system is tested on a capacitive discharge based on three consecutive harmonics of 13.56 MHz. According to the Electrical Asymmetry Effect, tuning the phases between the applied harmonics results in an electrical control of the DC self-bias and the mean ion energy at almost constant ion flux. A comparison with the reference case of an electrically asymmetric dual-frequency discharge reveals that the control range of the mean ion energy can be significantly enlarged by using more than two consecutive harmonics.

Analysis the electrical parameters of a high-frequency coreless induction furnace

The paper analyzes the most important electrical parameters of a coreless induction furnace, having a capacity of 7 kg molten iron (i.e. 2.5 kg aluminum). The furnace is supplied by a high-frequency (HF) static converter ITS2 12K20, with the output frequency 5...12 kHz, 600...1200 Vac rated HF voltage, and 20 kW rated HF power. Monitoring of electrical parameters was done for an aluminum charge, using a power quality analyser CA8334. The measurement results showed that induction furnace operation causes unbalance and harmonics in three-phase currents absorbed from the distribution network. Harmonics in the line currents are caused mainly by static converter, and to a lesser extent by furnace load and interaction of eddy currents induced in the charge and the magnetic field of the inductor. To reduce the negative impact of the current harmonics on the distribution network is necessary the design and achievement of electrical filters for odd-order harmonics (5th, 7th, 11th, 13th, 17th, 19th, 23th, 25th).

Microwave generation with photonic frequency octupling using a DPMZM in a Sagnac loop

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a π/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability.

Nyquist 4-ary pulse amplitude modulation scheme based on electrical Nyquist pulse shaping and fiber Bragg grating filter

Intensity modulation and direct detection signal are sensitive to power fading and nonlinear intersymbol interference (ISI) induced by modulator chirp, fiber dispersion, and square-law photo-detection. We propose and experimentally demonstrate a Nyquist 4-ary pulse amplitude modulation and direct detection scheme relying on pulse-shaping with an electrical filter and optical equalization with a vestigial-sideband (VSB) filter in the transmitter. The power fading could be eliminated by using the VSB filter. Compared with conventional 4-ary pulse amplitude modulation, the Nyquist signal has a stronger resistance to nonlinear ISI.

Calculation of Bit Error Rates in Optical Systems With Silicon Photonic Wires

A theoretical approach to calculate the bit error rate (BER) in optical systems containing silicon photonic wires (Si-PhWs) is presented. Specifically, the optical link consists of a single-mode silicon-on-insulator strip waveguide followed by a direct-detection optical receiver containing an optical filter, an ideal square-law photodetector, and an electrical filter. We assume that the optical input consists of a superposition of a nonreturn-to-zero ON–OFF keying modulated optical signal and an additive white Gaussian noise, the BER of the transmitted optical signal being calculated using the time domain Karhunen–Loève expansion method. The propagation of the optical signal in the Si-PhW is described by employing both a rigorous theoretical model that incorporates all relevant linear and nonlinear optical effects and the mutual interaction between the free carriers and the optical field, as well as a linearized model valid in the low-noise power regime. These analytical and computational tools are then used to comprehensively investigate the influence of the parameters characterizing the waveguide and optical signal on the transmission BER.

Theoretical analysis and modeling of a photonic integrated circuit for frequency 8-tupled and 24-tupled millimeter wave signal generation.

A photonic circuit design for implementing frequency 8-tupling and 24-tupling is proposed. The front- and back-end of the circuit comprises 4×4 MMI couplers enclosing an array of four pairs of phase modulators and 2×2 MMI couplers. The proposed design for frequency multiplication requires no optical or electrical filters, the operation is not limited to carefully adjusted modulation indexes, and the drift originated from static DC bias is mitigated by making use of the intrinsic phase relations of multi-mode interference couplers. A transfer matrix approach is used to represent the main building blocks of the design and hence to describe the operation of the frequency 8-tupling and 24-tupling. The concept is theoretically developed and demonstrated by simulations. Ideal and imperfect power imbalances in the multi-mode interference couplers, as well as ideal and imperfect phases of the electric drives to the phase modulators, are analyzed.

Electrical filter-based and low-complexity DPSK coherent optical receiver.

Direct-detection of differential phase shifted keying (DPSK) optical signals is implemented either by ad hoc optical filtering or one-bit delayed optical interferometers. We show a coherent receiver where the filtering is performed in the electrical domain after down-converting the incoming signal to the baseband or to an intermediate frequency. This can be particularly advantageous whenever optical filters cannot be used or when extremely narrow filtering (sub-GHz) would be required [for example ultra-dense wavelength division multiplexing (WDM) passive optical networks]. Electrical filters can be realized more accurately than their optical counterpart. In addition, in a coherent receiver, this operation is colorless and avoids digital signal processing. We show experimentally this reduced complexity receiver and compare it with the classical one based on the delay and multiply block.

Experimental noise filtering by quantum control

Instabilities due to extrinsic interference are routinely faced in systems engineering, and a common solution is to rely on a broad class of $\textit{filtering}$ techniques in order to afford stability to intrinsically unstable systems. For instance, electronic systems are frequently designed to incorporate electrical filters composed of, $\textit{e.g.}$ RLC components, in order to suppress the effects of out-of-band fluctuations that interfere with desired performance. Quantum coherent systems are now moving to a level of complexity where challenges associated with realistic time-dependent noise are coming to the fore. Unfortunately, standard control solutions involving feedback are generally impossible due to the strictures of quantum mechanics, and existing error-suppressing gate constructions generally rely on unphysical bang-bang controls or quasi-static error models that do not reflect realistic laboratory environments. In this work we use the theory of quantum control engineering and experiments with trapped $^{171}$Yb$^{+}$ ions to demonstrate the construction of novel $\textit{noise filters}$ which are specifically designed to mitigate the effect of realistic time-dependent fluctuations on qubits \emph{during useful operations}. Starting with desired filter characteristics and the Walsh basis functions, we use a combination of analytic design rules and numeric search to construct time-domain noise filters tailored to a desired state transformation. Our results validate the generalized filter-transfer function framework for arbitrary quantum control operations, and demonstrate that it can be leveraged as an effective and efficient tool for developing novel robust control protocols.