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A bandwidth-tunable multiband microwave photonic filter (MPF) using a strongly coupled microring resonator (MRR) with optical phase modulation is demonstrated theoretically and experimentally. Two notches of the MRR adjacent to the optical carrier break the intrinsic balance of the phase-modulated signal and then two sub-MPFs are formed thanks to the conversion from phase modulation to intensity modulation (PM-IM). The frequency responses of the two sub-MPFs are superimposed to form a passband with a fixed center frequency. Due to the periodicity of the MRR transmission spectrum, multiple passbands separated by a certain spacing appear in the frequency domain and combine to form a multiband MPF, whose bandwidth can be adjusted by tuning the wavelength of the carrier. The tunable bandwidth and shape factors ranging from 0.73 GHz to 2.73 GHz and 5.06 to 1.38 are experimentally performed. The number of passbands can be reconfigured. The proposed multiband MPF has the potential to be employed in modern multi-standard wireless communication systems.

This paper proposes a nonadaptive error demodulation technique with which to track the amplitude, the phase and the frequency information of the grid voltage for single-phase applications. A nonadaptive comb filter, Lyapunov’s estimation law, and half-cycle moving average filters are exploited in order to reconstruct the fundamental orthogonal components. The proposed nonadaptive Lyapunov filter has good bandpass filtering characteristics, thus allowing the rapid rejection of the dc-offset and the harmonics. The proposed open-loop phase angle deviation algorithm is, moreover, a rescuer as regards estimating the fundamental frequency deviation, signifying that it correctly compensates the estimated amplitude and the phase angle information through the use of a mathematical regression approach under off-nominal frequency conditions. [ABSTRACT FROM AUTHOR]

This article presents a robust single-phase phase-locked loop (PLL)-less frequency, phase, and amplitude estimation technique. The proposed scheme, unlike PLL approaches, does not require a rigorous design and tuning process in order to attain a better stability margin. It is important to note that an improved discrete-time oscillator is obtained by involving a comb filter, which helps improve the dc-offset rejection capability and transient response time. Moreover, the notch-filter-like behavior and the introduction of imaginary zeros ensure better harmonic removal ability when compared to a known nonadaptive discrete-time oscillator. The proposed scheme relies on an open-loop frequency estimation technique that does not involve an inverse trigonometric function for the estimation of fundamental frequency deviation. The feedbackless architecture of the scheme and the avoidance of inverse trigonometric function, therefore, assist in reducing the real-time implementation complexity. However, under off-nominal grid frequency deviations, the amplitude and the phase of the output of the prefilter will suffer from errors. These errors are compensated by employing a mathematical regression approach. The results are experimentally validated and compared in order to prove the robustness and usefulness of the proposed scheme for single-phase applications. [ABSTRACT FROM AUTHOR]

We demonstrate a switchable and flexible comb filter/interleaver based on ring-resonator (RR) in which the directional couplers are replaced by tunable couplers. The tunable coupler is composed of an even-arm-length Mach-Zehnder interferometer (MZI) with a micro-heater embedded in one of the arms. For the sake of discussion, we convert the heating power of the micro-heater into a pure phase shift value independent of the waveguide material and size. By changing the phase shift value, the filter can be switched between comb filter and interleaver. Meanwhile, the insertion loss (IL), full width at half maximum (FWHM), extinction ratio (ER), and the shape of the response spectrum can also be reconfigured. The switchable and flexible comb filter/interleaver may provide a potential application in dense wavelength division multiplexing (DWDM) optical communication systems. [ABSTRACT FROM AUTHOR]

This letter presents a new filter to suppress radio frequency interference (RFI) in microwave remote sensing instruments, particularly a wideband autocorrelation radiometer (WiBAR). RFI increases the noise floor and results in a decreased signal-to-noise ratio (SNR) of the WiBAR delay peak. The proposed filter operates like a Fabry–Perot interferometer (FPI) in optics and has the frequency response of a comb filter with many evenly spaced alternating pass and stop bands. The frequencies of these bands are varied with an electrically adjustable phase shifter. The design of a comb filter with an airy finesse value of 20 has been verified by simulation and measurement. [ABSTRACT FROM AUTHOR]

Batch measurement of sheet-like product quantity is very common in manufacturing and commercial areas. Particularly, to satisfy the growing requirement of automatic and nondestructive detection, a machine vision system for stacked substrates counting is proposed in this paper. With a brief description of the system architecture and imaging module, the challenges for real data analysis are investigated. Our main contribution is to develop a robust stripe detection algorithm by combining the merits of local template matching and global frequency domain filtering. Besides the peak-valley feature across the stack profile, the collinear prior shape along the substrates is also utilized in a morphological scheme to purify the obtained ridge-line or stripe images, which, finally, benefits the statistical counting output. It is verified in experiments using a diversity of substrate media that our developed system can achieve a high counting accuracy with the detection error not more than 0.01% as the sample thickness varies between 0.05 mm and 0.5 mm. Moreover, the proposed algorithm performs much robustly with various kinds of abnormalities and interferences like irregular piling, media distortion, and foreign contamination. [ABSTRACT FROM AUTHOR]

We present an efficient implementation of brain–computer interface (BCI) based on high-frequency steady state visually evoked potentials (SSVEP). Individual shape of the SSVEP response is extracted by means of a feedforward comb filter, which adds delayed versions of the signal to itself. Rendering of the stimuli is controlled by specialized hardware (BCI Appliance). Out of 15 participants of the study, nine were able to produce stable response in at least eight out of ten frequencies from the 30–39 Hz range. They achieved on average 96±4% accuracy and 47±5 bit/min information transfer rate (ITR) for an optimized simple seven-letter speller, while generic full-alphabet speller allowed in this group for 89±9% accuracy and 36±9 bit/min ITR. These values exceed the performances of high-frequency SSVEP-BCI systems reported to date. Classical approach to SSVEP parameterization by relative spectral power in the frequencies of stimulation, implemented on the same data, resulted in significantly lower performance. This suggests that specific shape of the response is an important feature in classification. Finally, we discuss the differences in SSVEP responses of the participants who were able or unable to use the interface, as well as the statistically significant influence of the layout of the speller on the speed of BCI operation. [ABSTRACT FROM PUBLISHER]

To improve the performance of frequency-locked loops (FLLs) under distorted grid conditions, the technique of harmonic decoupling with multiple notch filters was usually employed to remove the harmonic components, which, although offering good filtering abilities, suffers from complexity, high computational burden, and deteriorated dynamics. To alleviate these problems, this letter proposes an enhanced adaptive notch-filter-based FLL, which incorporates a comb filter and improves the filtering abilities by introducing purely imaginary zeros to achieve notch peaks and harmonic cancellation. In comparison with the typical existing solutions of multiple notch-filter-based FLLs for distorted grid systems, the proposed FLL features simple structure and low computational load, and it can completely block the dc component, odd and even harmonics of the input grid voltage without sacrificing the FLL dynamics. Experimental results and comparisons are presented to validate the effectiveness of the proposed FLL. [ABSTRACT FROM AUTHOR]

A new method for remote wideband microwave frequency measurement utilizing a single-passband microwave photonic filter is proposed, theoretically analyzed, and experimentally demonstrated. The frequencies of the input microwave signals can be measured by monitoring the maximum output microwave power while scanning the central frequency of the single-passband microwave photonic filter. The parameters of the filter have also been analyzed to optimize the frequency measurement performance. The proposed frequency measurement technique is easy to implement, capable of measuring frequencies of multiple microwave signals.

A tunable and switchable multiwavelength passively mode-locked fiber laser by using a semiconductor saturable absorber mirror (SESAM) and an inline birefringence fiber filter is proposed and demonstrated. By properly rotating the polarization controllers (PCs), up to 7-wavelength mode-locked pulses in 3-dB bandwidth with 3.65-nm channel spacing are obtained. The wavelength switchable operation is determined by the characteristics of the comb filter used in the experiment. Taking advantage of an intensity-dependent loss mechanism caused by the nonlinear polarization rotation (NPR) effect, the mode competition is efficiently suppressed. In addition, the lasing locations of multiwavelength mode-locked pulses can be flexibly tuned via the wavelength-dependent loss mechanism.

We propose and demonstrate a multiwavelength switchable fiber ring laser by employing a simple but novel polarization beam splitter (PBS)-based Mach-Zehnder (M-Z) comb filter. The proposed comb filter consists of a rotatable polarizer, a PBS, and a 3-dB fiber coupler. By adjusting the polarization state of the lasing light launched into the PBS, the multiwavelength switchable operation can be easily achieved. When the proposed comb filter was incorporated into the laser cavity, up to 11 multiwavelength switchable lasing lines with a channel spacing of 1.2 nm were obtained. In addition, the lasing locations and the number of the lasing lines can be flexibly tuned by exploiting the wavelength-dependent loss mechanism.

Based on a sampled fiber Bragg grating (FBG) with simultaneous utilization of two amplitude-assisted phase sampling functions and a phase-only sampling (POS) function, a novel comb filter that has a high channel count and an excellent channel uniformity is first proposed. With the proposed method, an ultra-narrow FBG-based filter with consecutive 1377 channels, a channel bandwidth of 1.5 GHz, and a channel spacing of 25 GHz is theoretically demonstrated. [ABSTRACT FROM PUBLISHER]

An all-optical clock recovery (CR) scheme with wide locking range is demonstrated, based on a silicon microring resonator (MRR) and a semiconductor optical amplifier (SOA). The MRR with a free spectral range of 40 GHz works as a comb filter, which removes the modulation information, whereas the SOA operating in the saturation regime performs amplitude equalization to achieve a good optical clock signal. The design of the MRR is investigated according to the tolerance of the subsequent equalizer. Based on the fabricated MRR, single and dual channels CR from 40 Gb/s input data streams can be achieved successfully with root mean square time jitter of ~ 900 fs. Because of the moderate finesse of the MRR, the CR can be achieved with a wide range of several gigahertz. [ABSTRACT FROM PUBLISHER]

This paper deals with fundamental properties of the least-squares-based estimation algorithms of power frequency, such as immunity and insensitivity to harmonics and noise. This paper is motivated by a recent study that dealt with an optimal case of the distance between equidistantly spaced samples. This paper extends and generalizes that approach by decoupling of task of canceling dc component from the least-squares estimation task. Two different algorithms derived as particular cases of this generalized approach are investigated. In addition, besides the basic least-squares (LS) method, the Prony-based method previously formulated by Lobos and Rezmer has also been investigated. The task of estimation frequency from a pure sine signal without dc component presence is also considered. Finally, the third method is derived and its basic properties are shown. [ABSTRACT FROM PUBLISHER]

A polarization-independent, multifunctional all-fiber comb filter by using variable ratio coupler (VRC)-based dual-pass Mach-Zehnder interferometer is newly proposed and demonstrated. Depending on the dynamic settings of coupling ratios of the fiber couplers, the comb filter provides the channel spacing tunable, multiwavelength switchable, and flat-top spectral responses. Theoretical calculations are verified by the experimental results. Experimentally, a comb filter with the channel spacing tunable from 0.4 to 0.8 nm was obtained. Meanwhile, when the comb spacing was tuned to 0.8 nm, the multiwavelength switchable operation with both the sinusoid and flat-top spectral responses was achieved. The proposed comb filter may find applications in optical communication systems and tunable multiwavelength fiber lasers. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate a multiwavelength switchable fiber ring laser by employing a simple but novel polarization beam splitter (PBS)-based Mach–Zehnder (M–Z) comb filter. The proposed comb filter consists of a rotatable polarizer, a PBS, and a 3-dB fiber coupler. By adjusting the polarization state of the lasing light launched into the PBS, the multiwavelength switchable operation can be easily achieved. When the proposed comb filter was incorporated into the laser cavity, up to 11 multiwavelength switchable lasing lines with a channel spacing of 1.2 nm were obtained. In addition, the lasing locations and the number of the lasing lines can be flexibly tuned by exploiting the wavelength-dependent loss mechanism. [ABSTRACT FROM PUBLISHER]

A tunable and switchable multiwavelength passively mode-locked fiber laser by using a semiconductor saturable absorber mirror (SESAM) and an inline birefringence fiber filter is proposed and demonstrated. By properly rotating the polarization controllers (PCs), up to 7-wavelength mode-locked pulses in 3-dB bandwidth with 3.65-nm channel spacing are obtained. The wavelength switchable operation is determined by the characteristics of the comb filter used in the experiment. Taking advantage of an intensity-dependent loss mechanism caused by the nonlinear polarization rotation (NPR) effect, the mode competition is efficiently suppressed. In addition, the lasing locations of multiwavelength mode-locked pulses can be flexibly tuned via the wavelength-dependent loss mechanism. [ABSTRACT FROM PUBLISHER]

An amplitude-modulated (AM) ultrasonic range finder using an online parameter estimation procedure is presented, which uses the sliding discrete Fourier transform (SDFT) algorithm for extracting the sinusoidal envelope from the received reference and ultrasonic signals. The received ultrasonic envelope contains an additive noise, which resembles another sine wave whose frequency is very close to that of the envelope. This gives rise to a low-frequency beat in the phase shift between the transmitted and received envelopes. Consequently, the estimated phase shows an equivalent phase jitter. The desired sinusoidal envelope signal cannot easily be separated from the noise signal, even by sharply tuned SDFT filters with phase-locked loops (PLLs). A parameter estimation procedure has been applied to remove these interharmonic signals with the help of comb filters. The PLL was strengthened by a cosine lookup table (LUT). By locating the envelope frequency far away from the interharmonic noise frequency, the convergence time could greatly be reduced. Simulation studies were conducted in the Matlab--Simulink--DSP builder environment, and ideas were implemented in a Cyclone-II field-programmable gate array (FPGA)-based range finder fabricated in the laboratory. The test results of the AM ultrasonic range finder are presented to show its performance for static and slowly moving objects. [ABSTRACT FROM AUTHOR]

An extension to the analytical design of digital equiripple comb FIR filters is presented here. The filters are optimal in Chebyshev sense. The design runs from the filter specification through the degree formula to the impulse response coefficients, which are evaluated by an extremely efficient recursive algorithm. The proposed design method outperforms the standard procedures in terms of speed and robustness. [ABSTRACT FROM AUTHOR]

We propose an adaptive, low-complexity, blind carrier tracking algorithm that takes advantage of the in-band ripple of the orthogonal frequency-division multiplexing (OFDM) power spectral density (PSD). With the aid of a comb filter, the proposed algorithm tracks the location of the ripple peaks and provides an estimate of the carrier offset. Analytical results are presented that predict the expected performance and show the consistency and robustness of the proposed algorithm in environments characterized by time-varying carrier offsets and frequency-selective fading channels. Computer simulations that corroborate the theoretical analysis are also presented. [ABSTRACT FROM PUBLISHER]

Recently, we proposed using Capon's minimum variance principle to find the fundamental frequency of a periodic waveform. The resulting estimator is formed such that it maximizes the output power of a bank of filters. We present an alternative optimal single filter design and then proceed to quantify the similarities and differences between the estimators using asymptotic analysis and Monte Carlo simulations. Our analysis shows that the single filter can be expressed in terms of the optimal filterbank and that the methods are asymptotically equivalent but generally different for finite length signals. [ABSTRACT FROM AUTHOR]

In the encoder of the national television system committee (NTSC) system, a composite video burst signal (CVBS) is generated using the luminance (Y) signal and the quadrature amplitude modulation (QAM) modulated chrominance (C) signal. In the decoder, it is important that the CVBS be accurately separated into luminance and chrominance signals by a Y/C separation filter. Otherwise, various artifacts, such as dot crawl, rainbow effect, and color bleeding, appear in a decoded video, degrading the quality of the decoded video. In addition, modern high-definition television (HDTV) system suffers from outdated analog decoding artifacts when HDTV compression techniques were applied to the not ideally decoded former standard-definition format video images. This paper proposes artifact reduction methods of dot crawl and rainbow effect using the characteristics of the CVBS video. The proposed artifact reduction algorithms use two successive frames, in which the decoded video images are divided into not moving (stationary) and moving regions. The stationary regions are filtered by a temporal filter whereas the moving regions are further classified into three subdivided regions of different types of artifacts to apply them into temporal or spatial filters because inappropriately temporally filtered moving region delivers jitters on the edge. In the proposed algorithms, considering characteristics of the NTSC decoded image, a block matching algorithm based on 4×4 non-overlapping blocks is used for motion estimation and compensation. Computer simulations with various simulated and real videos containing NTSC artifacts show the effectiveness of the proposed artifact reduction methods. [ABSTRACT FROM AUTHOR]

We propose a new method to segregate concurrent speech sounds using an auditory version of a channel vocoder. The auditory representation of sound, referred to as an "auditory image," preserves fine temporal information, unlike conventional window-based processing systems. This makes it possible to segregate speech sources with an event synchronous procedure. Fundamental frequency information is used to estimate the sequence of glottal pulse times for a target speaker, and to repress the glottal events of other speakers. The procedure leads to robust extraction of the target speech and effective segregation even when the signal-to-noise ratio is as low as 0 dB. Moreover, the segregation performance remains high when the speech contains jitter, or when the estimate of the fundamental frequency F0 is inaccurate. This contrasts with conventional comb-filter methods where errors in F0 estimation produce a marked reduction in performance. We compared the new method to a comb-filter method using a cross-correlation measure and perceptual recognition experiments. The results suggest that the new method has the potential to supplant comb-filter and harmonic-selection methods for speech enhancement. [ABSTRACT FROM AUTHOR]

A tunable multiwavelength fiber laser based on a semiconductor optical amplifier (SOA) is newly proposed. The proposed fiber laser employs a fiber comb filter based on a polarization-diversity loop configuration (PDLC) for the multiwavelength selection. The spectral characteristic of the comb filter is graphically explained by tracing the state of polarization (SOP) of the light propagating through the filter on the Poincare sphere. Particularly, the method of adjusting the filter characteristics is established with the help of the Poincare-sphere representation. The experimental results show that 18 laser lines oscillate with the signal to amplified spontaneous emission noise ratio over 25 dB. Particularly, all of the laser lines with a fixed channel spacing of ∼ 0.8 nm can be continuously shifted by adjusting only a wave plate contained within the filter. [ABSTRACT FROM PUBLISHER]

A low-cost video decoder for NTSC signals is described in this paper. The proposed NTSC video decoder design employs a 2D2L comb filter, and a DDFS (Direct Digital Frequency Synthesizer) -based DCO (digital control oscillator) based on a trigonometric quadruple angle formula in a digital PLL to track and lock the demodulation clocks. The complexity of the digital video decoder is consequently drastically reduced. The overall cost of the proposed design is 7.22 mm² (26 K gates). The maximum power dissipation is 109.2mW at the highest clock rate which is 21.48 MHz. [ABSTRACT FROM AUTHOR]

The authors recently proposed the multiple-phase-shift (MPS) technique, in which multiple phase shifts are introduced in sampled fiber Bragg gratings (SFBGs) to realize dense channel spacing. In this paper, the MPS technique is studied in detail, and it is shown that it can densify SFBGs both spectrally and spatially. Then, the paper presents that the MPS technique is applicable to densify the spectra of not only simple SFBGs but also various kinds of complex SFBGs, such as apodized, sinc-, and chirped SFBGs. [ABSTRACT FROM PUBLISHER]

A new approach for eliminating aberration effects through introduction of elliptical grating facets in optical comb filters is presented. Simulation results show remarkable improvements of comb filter performance for aberration-free elliptical facets compared to traditional flat facet designs. The proposed theory was validated through design and fabrication of 100-GHz-period planar silica-on-silicon comb filters for use in multiwavelength optical sources. Multimode interference structures were used to achieve both flat-top and Gaussian spectral comb filter responses. All devices showed high extinction ratio, low nonuniformity in insertion loss, and high degree of passband shape control. [ABSTRACT FROM PUBLISHER]

A novel analytical design method for highly selective digital optimal equiripple comb finite-impulse response (FIR) 111- ten is presented. The equiripple comb FIR filters are optimal in the Chebyshev sense. The number of notch bands, the width of the notch bands and the attenuation in the passbands can be independently specified. The degree formula and the differential equation for the generating polynomial of the filter is presented. Based on the differential equation, a fast simple algebraic recursive procedure for the evaluation of the impulse response of the filter is described. Its arithmetic robustness outperforms, by far, the known analytical design method. Highly selective equiripple comb FIR filten with thousands of coefficients can be designed. One example demonstrates the efficiency of the filter design. [ABSTRACT FROM AUTHOR]