Optimum Filter Bandwidth Research Articles

DEPENDENCE OF TEMPERATURE DETERMINATION ACCURACY ON THE BANDWIDTH OF THE INTERFERENCE FILTER IN OPTICAL PYROMETRY SYSTEMS

Some general issues common to all reactors for gas-phase epitaxy of A3B5 metal-organic compounds include large temperature gradients in the reactor, leading to the formation of convection loops, high gas flow rates that can result in turbulence instead of the expected laminar flow, and the need for good uniformity and precision in temperature control of the semiconductor substrate surface. Since the deposition process for many complex semiconductor devices (such as infrared laser diodes or heterojunction bipolar transistors) is highly temperature-dependent, a system for precise temperature control of the process at the substrate surface directly in the deposition zone is necessary to obtain high-quality heterostructures with reproducible parameters.
 This article describes the features of the epitaxial growth process in MOCVD reactors, as well as highlights the tasks facing the temperature control system. The feasibility of using a radiation compensation system is explored in comparison to measurement methods using a thermocouple and classical pyrometry. Transformation of the input optical signal into a proportional output current in this system is performed by a sensitive photodetector, namely a silicon photodiode. The selection of the wavelength range of the radiation is determined by the optical parameters of the semiconductor substrates and compounds used in the system. The measurement spectrum is determined by the parameters of the interference filter in the system.
 The research was conducted to determine the effect of the interference filter width on the accuracy of determining the real temperature of a pyrometric control system with radiation compensation. The dependence of the interference filter characteristic width and shape on the correction value of the temperature of pyrometric systems after calibration is analyzed. Based on the results obtained, recommendations are made for selecting the optimal working wavelength and interference filter bandwidth of the optical system as a compromise between the determination error and the magnitude of the optical signal. The results can be used for the design of modern precision pyrometric systems.

Weak fault feature extraction of rolling element bearing based on variational mode extraction and multi-objective information fusion band-pass filter

Aiming at solving the difficulty in extracting early weak fault features of rolling element bearing (REB), a feature extraction method by combing variational mode extraction (VME) with multi-objective information fusion band-pass filter (MIFBF) is proposed. This method is based on the advantage of the VME in filtering out the interference signals and the enhancement effect of the MIFBF on the impact characteristic signals. Firstly, VME is used as the signal preprocessing method to filter out the interference noise. Then, the filtered signal is taken as the target signal, and then MIFBF is used to analyze it to obtain the optimal band-pass filter parameters-center Frequency and bandwidth, thereby constructing the optimal band-pass filter. Finally, further filter the target signal based on the constructed optimal band-pass filter and apply envelope demodulation spectral (EDS) analysis on the filtered signal. At last, satisfactory fault feature extraction effect can be achieved. To obtain key parameters of the optimal band-pass filter, this paper proposes a method based on time and frequency domain fusion indexes to balance the extraction of impact characteristics and cyclostationary characteristics while REB failure occurs. Compared with the existed single index based on time domain or frequency domain, better results could be obtained. Effectiveness and superiority of the proposed method are verified through simulation and experiments.

Localization precision in chromatic multifocal imaging

Multifocal microscopy affords fast acquisition of microscopic 3D images. This is made possible using a multifocal grating optic; however, this induces chromatic dispersion effects in the point spread function, impacting image quality and single-molecule localization precision. To minimize this effect, researchers use narrow-band emission filters. However, the choice of optimal emission filter bandwidth in such systems is, thus far, unclear. This work presents a theoretical framework to investigate how the localization precision of a point emitter is affected by the emission filter bandwidth. We calculate the Cramér–Rao lower bound for the 3D position of a single emitter imaged using a chromatic multifocal microscope. Simulation results for a range of emission bandwidth systems show that in the absence of background photons and detector noise localization improves for broader emission filter bandwidth due to increased photon throughput despite a larger chromatic dispersion. When realistic background and measurement noise sources are considered in the imaging process being simulated, there is an optimal bandwidth (not the broadest emission filter bandwidth) which provides the highest localization precision. This study provides a framework for optimally designing chromatic multifocal optics and serves as a theoretical foundation for interpretting results.

Adaptive algorithms for measuring low-frequency noise parameters of semiconductor devices under mass control

The solution of the problem of increasing the confidence and efficiency of quality control of semiconductor devices is considered. The analysis of conditions for measuring the power spectral density of low – frequency noise of semiconductor devices with a spectrum of the form (γ – the spectrum shape indicator) under mass quality control is presented. The error in measuring the power spectral density under the specified measurement conditions strongly depends on the value of the spectrum shape indicator. Adaptive algorithms for measuring low-frequency noise parameters are proposed for cases of a given limit error in measuring the power spectral density and a given time for a single measurement. The proposed algorithms include a preliminary estimation of the value of the spectrum shape indicator and subsequent measurement of the noise power spectral density at the optimal filter bandwidth. The optimal filter bandwidth is determined based on the results of a preliminary assessment of the spectrum shape indicator. For both cases, we obtained estimates of the gain in the sense of the average for the set (ensemble) of controlled products. The possibility of adaptive or cognitive adjustment of the measurement system parameters in the control process based on the results of evaluating sample averages in the training sample is discussed.

Optimizing Order to Minimize Low-Pass Filter Lag

This paper develops a tool kit for designing low-pass filters to exhibit the smallest possible phase drop. Based solely on the stopband requirements, it is thus possible to find the best order for a filter to be employed in a feedback loop. That is shown for two much-used filter families, Butterworth and Bessel, in cases where the filter is specified to have a minimum attenuation above a certain frequency. It is argued that the phase drop can be represented by an equivalent filter delay. Design tools are then developed, which do not depend on the precise dynamics of the application process. The tools comprise not only the means for determining the optimal filter order and bandwidth, but also formulae and tables useful for obtaining the resulting filter delay. A simple approximation is subsequently developed, which links the minimum obtainable delay directly to said requirements. The filter order need not be known to apply this expression, and the filter family is represented in it by no more than a single constant. This rule of thumb is finally adapted to the area of anti-aliasing filters and there briefly compared to approximative formulae found in existing literature.

Compressibility of Dissipative Solitons in Mode-Locked All-Normal-Dispersion Fiber Lasers

We numerically investigated the compressibility of dissipative soliton pulses in an all-normal-dispersion fiber laser which was mode-locked with a nonlinear optical loop mirror. A transition state within the area between the traditional dissipative soliton regime and dissipative soliton resonance regime was revealed to have much higher dechirped peak power and shorter dechirped pulse duration than its vicinity. This phenomenon is reported for the first time to the best of our knowledge. The peak power and pulse width of the dechirped pulse were calculated using the linear compression method. The dynamics and the distribution of the transition state were systematically analyzed in laser parameter spaces. The nonlinear frequency chirp was mainly induced by self-phase modulation and the pulse formation mechanism, which influenced the linear compressibility of the dissipative. We demonstrated that there were optimal filter bandwidth values corresponding to the best pulse compressibility under different laser parameters. The simulation results indicate that dechirped pulses with a pulse peak power of 0.5–1 MW, a pulse duration of the 100-fs level, and a pulse energy of ∼100 nJ can be obtained using the optimal parameters.

State distributions in two-dimensional parameter spaces of a nonlinear optical loop mirror-based, mode-locked, all-normal-dispersion fiber laser.

We present the results of numerical simulations of dissipative soliton generation using nonlinear Schrödinger equations in an all-normal-dispersion (ANDi) mode-locked fiber laser based on a nonlinear optical loop mirror (NOLM). Firstly, systematic and computationally intensive analysis of the pulse state distributions in two-dimensional parameter spaces of an ANDi fiber laser was conducted. In addition, we determined that unstable non-vanishing regions including pulsation and noise-like pulses are directly related to the saturable absorptions of NOLMs and that two critical filter bandwidths separate those regions from stable ones. Finally, we found that the multi-pulsing power threshold can be maximized by using an optimal optical filter bandwidth.

基于硅基微环的光双二进制

A silicon-based microring modulator and a narrow-band optical Gaussian filter were employed to generate optical duobinary at 10Gbit/s.Performance of the optical duobinary signal was analyzed in terms of laser linewidth,laser operating wavelength,fiber length,and filter bandwidth using Optisystem and Matlab.Simulation results show the optical duobinary signal is sensitive to laser linewidth and wavelength.At the BER of 10-9,the maximum transmission distance of the optical duobinary format can be up to 60km with the optimal Gaussian filter bandwidth of 8GHz.

基于硅基微环的光双二进制

A silicon-based microring modulator and a narrow-band optical Gaussian filter were employed to generate optical duobinary at 10Gbit/s.Performance of the optical duobinary signal was analyzed in terms of laser linewidth,laser operating wavelength,fiber length,and filter bandwidth using Optisystem and Matlab.Simulation results show the optical duobinary signal is sensitive to laser linewidth and wavelength.At the BER of 10-9,the maximum transmission distance of the optical duobinary format can be up to 60km with the optimal Gaussian filter bandwidth of 8GHz.

Moment Generating Function for the Rigorous Performance Assessment of Direct-Detection Baseband OFDM Communication Systems

A new moment generating function (MGF) is proposed to assess rigorously the performance of optically preamplified receivers with direct-detection employing baseband orthogonal frequency division multiplexing (OFDM). By comparison with Monte Carlo simulation, the proposed MGF-based method shows very good accuracy when predicting the bit error probability for arbitrary optical and electrical filters, different numbers of OFDM subcarriers, and double sideband and single sideband optical OFDM signals. Its good accuracy when estimating the bit error probability in each individual subcarrier is also demonstrated. The new MGF-based method exhibits a significant improvement of accuracy when compared to the MGF-based method previously reported in the literature, especially for filter bandwidths not exceeding the OFDM signal bandwidth, which is the range corresponding to the optimum filter bandwidth.

Impact of filter shape and bandwidth on terabit polarization-multiplexed quadrature phase-shift keying transmission with baud-rate spacing

The impact of the optical multiplexing/demultiplexing filter on ultradense wavelength-division multiplexing transmission based on polarization-multiplexed quadrature phase-shift keying (PM-QPSK) modulation at the Nyquist spectral efficiency limit is studied through simulations. We analyze 10×111 Gbit/s PM-QPSK systems with baud-rate channel spacing for both back-to-back and long-haul nonlinear transmission cases. We show that, although a higher-order filter generally leads to better system performance at the optimal filter bandwidth, this benefit comes at the cost of reduced tolerance to variations in filter bandwidth and center-frequency shifts.

Optimal filter bandwidth for pulse oximetry

Pulse oximeters contain one or more signal filtering stages between the photodiode and microcontroller. These filters are responsible for removing the noise while retaining the useful frequency components of the signal, thus improving the signal-to-noise ratio. The corner frequencies of these filters affect not only the noise level, but also the shape of the pulse signal. Narrow filter bandwidth effectively suppresses the noise; however, at the same time, it distorts the useful signal components by decreasing the harmonic content. In this paper, we investigated the influence of the filter bandwidth on the accuracy of pulse oximeters. We used a pulse oximeter tester device to produce stable, repetitive pulse waves with digitally adjustable R ratio and heart rate. We built a pulse oximeter and attached it to the tester device. The pulse oximeter digitized the current of its photodiode directly, without any analog signal conditioning. We varied the corner frequency of the low-pass filter in the pulse oximeter in the range of 0.66-15 Hz by software. For the tester device, the R ratio was set to R = 1.00, and the R ratio deviation measured by the pulse oximeter was monitored as a function of the corner frequency of the low-pass filter. The results revealed that lowering the corner frequency of the low-pass filter did not decrease the accuracy of the oxygen level measurements. The lowest possible value of the corner frequency of the low-pass filter is the fundamental frequency of the pulse signal. We concluded that the harmonics of the pulse signal do not contribute to the accuracy of pulse oximetry. The results achieved by the pulse oximeter tester were verified by human experiments, performed on five healthy subjects. The results of the human measurements confirmed that filtering out the harmonics of the pulse signal does not degrade the accuracy of pulse oximetry.

Fiber nonlinearity compensation for CO-OFDM transmission with 10.7-Gb/s NRZ-OOK neighbors

Fiber nonlinearity limits the use of coherent optical orthogonal frequency division multiplexing (CO-OFDM) to upgrade wavelength-division multiplexing (WDM) systems using legacy non-return-to-zero-on-off-keying (NRZ-OOK) channels. This letter proposes to compensate for the fiber nonlinearity of CO-OFDM with NRZ-OOK neighbors by combining digital signal processing (DSP)-based self-phase modulation (SPM) post-compensation with pilot-tone-based cross-phase modulation (XPM) compensation. The simulation results demonstrate that the optimum low-pass filter bandwidth for pilot-tone-based XPM compensation depends on the pilot-to-signal ratio value and launch optical power. Our method allows a 4-dB increase in the launch power for a 40-Gb/s single polarization CO-OFDM channel placed in the middle of six 10.7-Gb/s NRZ channels in a 50-GHz space and 1 200-km WDM system.

Optimizing the FEC Overhead in a 100 GbE PDM-QPSK Digital Coherent Transmission System

The finite electrical bandwidth of digital coherent transceivers together with limited wavelength division multiplexing (WDM) channel spacing constrains the maximum forward error correction (FEC) overhead that can be advantageously applied to fiber optic transmission systems. We investigate through simulations of a 100 GbE system employing coherent polarization division multiplexed quaternary phase shift keying, the impact of these bandwidth constraints on the optimal code rate thereby minimizing the required optical signal-to-noise ratio (OSNR) at the receiver. The optimum FEC overhead is found to increase linearly with available bandwidth and the required OSNR is found to reduce for lower order transponder filters. Fabrication of transmitters with a broader spectral response than their receiver counterpart is found to be advantageous. The optimum electrical bandwidth is found to be approximately half the WDM channel spacing for nonreturn to zero (NRZ) transmission and slightly less for return to zero (RZ). There is shown to be no performance advantage in using RZ over NRZ modulation formats when the optimum FEC overhead and filter bandwidth is employed in each case. Nonlinear simulations demonstrate that transpacific transmission is attainable with a margin that increases as the spectral efficiency is relaxed.

Pulse shortening and quality improvement based on spectral filtering in a stretched-pulse mode-locked fiber laser with large third-order dispersion

We demonstrate a passively mode-locked ring fiber laser operating in the stretched-pulse regime. The ring cavity model is constructed with standard single-mode fiber and dispersion delay line for dispersion management. Here, all-solid Yb-doped photonic bandgap fiber is used as the dispersion delay line and provides laser gain simultaneously. As the all-solid Yb-doped photonic bandgap fiber has large third-order dispersion, it is necessary to study its impact on the stretched-pulse operation. The presence of the third-order dispersion reduces pulse quality because of the relatively small group velocity dispersion. To improve the pulse quality, a spectral filter is employed in the model. The simulation results show that spectral filtering could improve the pulse quality and shorten the pulse duration. Meanwhile, the optimum filter bandwidth is studied.

Novel system for modulated lidar parameter optimization

We present a novel system for parameter design and optimization of modulated lidar. The system is realized by combining software simulation with hardware circuit. This method is more reliable and flexible for lidar parameter optimization compared with theoretical computation or fiber-simulated system. Experiments confirm that the system is capable of optimizing parameters for modulated lidar. Key parameters are analyzed as well. The optimal filter bandwidth is 200 MHz and the optimal modulation depth is 0.5 under typical application environment.

Evaluation of Band-Pass Filters Influence on NRZ Signal in HDWDM Systems

In this paper we demonstrate performance of three different optical filter transfer functions: Lorentzian, Raised Cosine and Supergaussian, and their influence on non-return-to-zero (NRZ) coded optical signal in high density WDM (HDWDM) systems. The effect of filter bandwidth at -3 dB influence on NRZ and spectral narrowing on signal quality has been studied extensively. We foresee that for 10 Gbit/s data transmission speed NRZ coded optical signal optimal filter bandwidth at -3 dB level referred to full width half maximum (FWHM) value must be greater than 0.1 nm or 12.5 GHz. Ill. 9, bibl. 9 (in English; abstracts in English, Russian and Lithuanian).

Improved nonlinearity precompensation for long-haul high-data-rate transmission using coherent optical OFDM

We show that the performance of precompensation of fiber nonlinearity in coherent optical OFDM systems operating at up to 60 Gbps/polarization can be improved by electrical filtering the precompensation signal. The optimal filter bandwidth is related to the FWM efficiency spectrum when dispersion is considered.

Studies of Thermal Diffusion in Planar Absorber Designs for the Micro-X Rocket

We have studied a potential design for a transition-edge sensor (TES) microcalorimeter array for the Micro-X High Resolution Microcalorimeter X-ray Imaging Rocket. Diffusion simulations of a design that places a small TES in the center of the pixel with a large in-plane absorber around the TES demonstrate that with high-quality gold films (RRR >6) 2 eV resolution is attainable in a 700 μm pixel, meeting the Micro-X requirement. X-ray hits directly on the TES, however, create a non-gaussian high energy tail to the device response. This high energy tail contains 5% of incident photons and cannot be removed by lowering the optimal filter bandwidth.

Externally Modulated Optical Minimum Shift Keying Format

This paper presents the generation and the performance evaluation of optical minimum shift keying (MSK) for high-speed and high-spectral-efficiency wavelength-division multiplexing systems. The detailed principle on optical MSK generation and detection is derived and analyzed. Optical MSK data (10.7 Gb/s) are successfully generated by an experiment using the proposed scheme. The results show that the optical MSK signal exhibits a very compact optical spectrum. The performance of the optical MSK modulated system is evaluated and compared with those of 50% duty-cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty-cycle return-to-zero on-off keying (RZ-OOK) modulated systems, via both simulation and experiment, in terms of dispersion tolerance, linear crosstalk, self-phase modulation (SPM) tolerance, stimulated Brillouin scattering (SBS) threshold, optimal receiver filter bandwidth, and optimal link launch power into single-mode fibers and dispersion compensation fibers. Experimental and simulation results show that the MSK signal exhibits the largest tolerance against fiber dispersion and SPM effect as compared with RZ-DPSK and RZ-OOK. Experimental results also confirm the negative penalty against the SPM effect. The SBS threshold of both the MSK and RZ-DPSK systems is more than 10 dB higher than that of the RZ-OOK system. The MSK that is generated with conventional carrier-suppressed return-to-zero (CSRZ) pulses exhibits a narrower optimal optical filter bandwidth but a wider electrical filter bandwidth compared with those of RZ-OOK and RZ-DPSK. The MSK signal that is generated with pure dual-mode pulses has a similar optimum range to RZ-OOK and RZ-DPSK at a high optical signal-to-noise ratio (OSNR) but has a narrower optimal optical filter bandwidth at a low OSNR. The optimum fiber launch power study shows that the MSK signal that is generated using the conventional CSRZ pulses exhibits higher optimum launch power, which agrees with the SPM tolerance study.