Self-configuring programmable silicon photonic filter for integrated microwave photonic processors

Currently, several microwave filter designs contend for use in wireless communications. Among various microstrip filter designs, the reconfigurable planar filter presents more advantages and better prospects for communication applications, being compact in size, light-weight and cost-effective. Tuneable microwave filters can reduce the number of switches between electronic components. This paper presents a review of recent reconfigurable microwave filter designs, specifically on current advances in tuneable filters that involve high-quality factor resonator filters to control frequency, bandwidth and selectivity. The most important materials required for this field are also highlighted and surveyed. In addition, the main references for several types of tuneable microstrip filters are reported, especially related to new design technologies. Topics surveyed include microwave and millimetre wave designs for 4G and 5G applications, which use varactors and MEMSs technologies.

We report on the successful fabrication and demonstration of a low loss, high performance reconfigurable bandpass filter technology. A digitally reconfigurable bandpass filter was implemented by placing the low pass and high pass reconfigurable filters in series. Reconfigurable low pass and high pass filters were implemented by combining MMICs with RF switches selecting capacitor values and off chip high Q fixed inductors. The same circuitry was implemented in both a commercial GaAs pHEMT process as well as Northrop Grumman’s GaN based SLCFET technology. The resulting reconfigurable bandpass filter operates between 1.0-2.0 GHz, with over 500 different filters selections and supporting variable center frequencies as well as variable bandwidth sizes ranging from 70 MHz to 100 MHz, all in a single device. Depending on the center frequency and bandwidth of the selected path, the SLCFET based switched reconfigurable filters demonstrated a NF and insertion loss improvement over the GaAs variant by > 2 dB, while demonstrating an P1dB <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">average</inf> of 33.6 dBm, compared to an average P1dB <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">average</inf> = 17.8 dBm power handling of the GaAs reconfigurable filter. The SLCFET based filter was measured as having 20x greater linearity than the GaAs filter, with the average two tone IIP3 for the SLCFET filter at 43 dBm, compared to 30 dBm for the GaAs design.

This paper presents a FIR Equiripple low pass filter design based on FPGA for eliminating high frequency noise from ECG signal. The filter architecture is partly serial and it is designed in MATLAB using direct form symmetric structure because implementation cost of symmetric structure is low as compared to direct form. The filter is designed using 16 bit input output precision. The filter design is synthesized on 2vp30fg676 and 5vlx50tff1136 device. Verilog Hardware Description Language (VHDL) is used for implementation of filter design on FPGA. Since coefficients are quantized in MATLAB to reduce design area and Xilinx 10.1 is used to simulate and synthesis the filter. Device utilization summary and speed comparison shows that filter design based on Virtex 5 is most speed efficient and device utilization ratio of partly serial architecture is better than fully parallel architecture.

We present a systematic photonic filter design approach by deploying pole-zero optimization. The filter transfer function is derived from its specifications by formulating closed-form optimization objective functions and subsequently translating them into optical design parameters. Two distinct filter examples, namely Chebyshev and elliptic filters, are considered for the design and validation. A compact reconfigurable three-pole photonic filter is fabricated on a silicon photonic platform to illustrate the proposed design technique including transmission tunability. Integrated thermal phase shifters coupled with micro-ring resonators are used to reconfigure filter responses. A well-matched experimental demonstration is presented to validate the proposed tuning method. We achieved a sharp out-of-band edge rejection of at least 20 and 40 dB for the elliptic and Chebyshev filter, respectively.

The design of a digitally-tunable sixth-order reconfigurable OTA-C filter in a 0.18-μm RFCMOS process is proposed. The filter can be configured as a complex band pass filter or two real low pass filters. An improved digital automatic frequency tuning scheme based on the voltage controlled oscillator technique is adopted to compensate for process variations. An extended tuning range (above 8:1) is obtained by using widely continuously tunable transcon-ductors based on digital techniques. In the complex band pass mode, the bandwidth can be tuned from 3 to 24 MHz and the center frequency from 3 to 16 MHz.

This letter presents a reconfigurable active bandpass filter based on a controllable slope parameter. The proposed filter has reconfigurable bandwidths and center frequencies, and both can be continuously changed using varactor diodes as the tuning elements. The wide tuning range of the bandwidth is achieved by adjusting the slope parameter of the resonators. This letter describes the design and testing of a two-pole reconfigurable filter with tuning ranges in the center frequency of 2.0-2.6 GHz and 3 dB bandwidth of 127-598 MHz at the center frequency of 2.15 GHz.

Microresonators with a high Kerr nonlinearity show great potential to generate optical frequency combs with ultrabroad spectra, high repetition rate, and high coherence between comb lines. The compact size and possibility of chip-level integration make the Kerr combs attractive for many applications, especially including photonic radiofrequency (RF) filters. In this paper we report the first demonstration of a programmable photonic RF filter based on the Kerr comb from a silicon nitride microring. A novel scheme enabled by the large frequency spacing of the Kerr comb is introduced in order to suppress unwanted RF passbands including the image and periodic passbands. As a result, a single passband is achieved. To the best of our knowledge, this is the first demonstration of a single-bandpass photonic RF filter employing a discrete-wavelength comb source.

This paper proposes a new approach for tuning microwave filters, which are tunable in a certain frequency range. An Artificial Neural Network (ANN) is used to build a filter inverse model, which maps scattering parameters into tuning elements deviations. Once the model is built, it may be applied for tuning filters of the same type on different center frequencies provided that the filter design allows to shift its band. Described considerations showed that a transformation of phase has to be performed on working signal. Five different types of phase compensation methods are proposed based on experiments performed on 4 th order filter. Such compensation modifies scattering parameters in a way that the filter can be tuned for different frequencies using the same inverse model. Experiments performed on 7 th order filter verified this approach.

We demonstrated the application of optical frequency combs in the realization of programmable microwave photonic filters. A reconfigurable high-order PF filter based on a wide-bandwidth optical frequency comb was designed, and the increasing of the tap (comb tooth) numbers results in the increasing of the order of the microwave photonic filter. In this article, the repetition frequency of the optical frequency comb is 12.5 GHz, and the optical spectral coverage reaches 25.6 nm. The order of the RF filter obtained in the experiment reaches 256, the free spectrum range (FSR) reaches 11 GHz, the 3dB-passband width is from 300 MHz to 2.6 GHz, and the sidelobe suppression is as high as 26 dB. A progressive optical pulse shaper was used to program the tap weights, which allow us to shape the bandpass of the filter. In addition, by adjusting the spectral distribution of the optical frequency comb, two types of RF filters with different passband shapes can be realized, namely, Gaussian and Sinc filters.

A reconfigurable silicon-photonic filter stage for the processing and monitoring of input signals is demonstrated and employed. The device consists of a balanced Mach-Zehnder interferometer with two ring resonators nested in each arm and built-in germanium photodetectors at its output ports. The transfer function of the device is adjustable through thermo-optic tuning of optical phase delays within each of the four resonators and between the two interferometer arms. Response examples include bandpass filters of variable bandwidth, as well as narrow bandpass and narrow band-stop shapes. The device is used in the wavelength division demultiplexing of a 16 Gbit/s on-off-keying data channel, with spacing of only 26 GHz between adjacent channels. A basic optical spectrum analyzer is realized by scanning the transmission wavelength of a narrowband filter response and reading the output from the on-chip detector. The device supports agile processing and monitoring input signals.

A study on the design, simulation and characterization of a reconfigurable terahertz (THz) filter, composed of two frequency-selective surfaces (FSSs) with applications on sensor devices in general and highly sensitive stress sensors, is presented in this paper. Using the developed theoretical model, we found out that by careful tuning the wire parameters, it is possible to control the filter sensitivity and also the energy transmission and reflection that passes through the structure. Numerical modelling of both the mechanical and electromagnetic components (using the elasticity equation and Maxwell’s equations, respectively) has been undertaken for two types of the device assemblies based on different thermoplastic polymers transparent to the THz radiation, namely: high-density polyethylene (HDPE) and polytetrafluoroethylene (PTFE), operating in a THz window from 395 to 455 GHz. The numerical results allowed us to characterize the relation between the reflectance/transmittance and the amount of force required to obtain a specific frequency shift along that window. It was found that the device assembled with HDPE presents a more linear response and it is able to pass from a full transparency to almost full opacity using only its linear operating zone. Due to its characteristics, this THz filter might be an interesting solution not only for THz sensors based on reconfigurable filters but also for optical modulators for the THz domain.

In this paper, a microstrip reconfigurable wideband filtering power divider (FPD) with tunable center frequency (CF), bandwidth (BW), and power division is presented. The proposed structure consists of two trimode stub-loaded resonators, a three-line coupled structure loaded two varactor diodes, and two output parallel-coupled lines loaded a lumped capacitor. The CF and BW of wideband filtering response can be tuned by controlling the varactor diodes loaded onto the open end of trimode resonators. Meanwhile, the power division ratio (PDR) is controlled by tuning the coupling strength between the center line and sidelines of three-line coupled structure. Compared with the conventional wideband FPDs, the capacitor loaded onto the parallel-coupled line of two output ports is to enlarge the coupling, which can increase the return loss (RL), and thus relieve the limitation of the line space between two coupled lines. A complete design procedure with analytical design equations for driving parameters of the structure is described. The measured results show that the CF can be tuned from 0.86 to 1.32 GHz with RL better than 16 dB, while the 1-dB BW can be tuned from 180 to 710 MHz. The measured isolation is better than 21 dB from dc to 2.5 GHz. Then, the achieved PDR can be tuned from 1:1 to 3:1. The proposed circuit can be also utilized as a switchless bandstop filter, where the isolation is better than 20 dB from dc to 19 GHz. The proposed tunable wideband FPD exhibits good RL, wide range of frequency and BW control, wide harmonic suppression, high isolation, and multifunctional application.

A novel type of dual-mode microstrip bandpass filter using degenerate modes of a dual-mode microstrip square loop resonator with capacitively loaded open-loop arms is proposed. Such a dual-mode bandpass filter with a 0.75% bandwidth at the center frequency of 1.603 GHz is designed and fabricated to demonstrate the design of reduced-size microstrip filters. It is shown that the proposed filter has a size reduction of about 59% at the same center frequency, as compared with the dual-mode bandpass filters such as microstrip patch, cross-slotted patch, square loop and ring resonator filter.

In this study, the construction of the hybrid, with the crossed strips, is presented. The hybrid is designed as a broadside-coupled suspended strip-line coupler, with the crossed strips, for the frequency range from 150 MHz to 200 MHz, with the central frequency at 175 MHz. The strips made of brass, with the Teflon substrate between them, are placed inside the aluminum casing filled with air. The hybrid has to direct the sum of the two input signals, ports 1 and 4, towards an output port (port 2 or 3), leaving nothing at the second output port (port 3 or 2). The input signals have 16 KW of power each, while the output signal has 32 KW of power. Knowledge of the conditions, which must be satisfied by the hybrid, enables the acquisition of dimensions of the hybrid, through the process of EM simulation. The values of the S-parameters of the simulated coupler are being compared, to the values of the S-parameters of the produced coupler to validate the design process.

We present a new approach to teaching filter design. In the classroom, students see graphical design methods emphasizing relationships between poles/zeros and frequency response (e.g., Chebyshev pole locations, low-pass to band-pass mapping, and bilinear transformation). In lab, each student develops a MATLAB <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> program, capable of designing analog or digital, low-pass/high-pass/band-pass/notch, and Butterworth or Chebyshev filters. Using a ¿bottom-up¿ approach, students write individual functions as topics are covered in class, thereby creating ¿student toolboxes¿ that make no use of inherent MATLAB filter design functions. Students then craft a ¿main program¿ to implement filter design logic by calling their (tested) lower level functions. Finally, students use their programs to filter individually corrupted music files. Students design a digital filter to remove that band-limited noise, while preserving music fidelity, in an iterative process, exploring tradeoffs between maximum passband attenuation, minimum stopband attenuation, filter type, passband and stopband cutoffs, filter order and fidelity. Using graphical techniques, along with bottom-up program development, provides significant insight into fundamental tradeoffs in the filter design process not attainable through design by table lookup or inherent MATLAB function calls. Furthermore, feedback suggests the final design project is very gratifying and unites theory and real world design.