Frequency Modulation Response Research Articles

Plasmonic electro-optic modulators on lead zirconate titanate platform

Abstract The advancement in material platforms exhibiting strong and robust electro-optic effects is crucial for further progress in developing highly efficient and miniaturized optoelectronic components with low power consumption for modern optical communication systems. In this work, we investigate thin-film lead zirconate titanate (PZT) substrates grown by a chemical solution deposition technique as a potential platform for on-chip plasmonic electro-optic modulators. A high modulation depth (>40 %) is achieved with 15 μm-long electro-optic directional coupler modulators. An unusual cutoff in the modulation frequency response at ∼200 kHz is observed and further studied with respect to possible reorientation effects. Second-harmonic generation signals are found influenced by the externally applied electric field, indicating that the domain reorientation effect can be responsible for the unusual frequency response observed.

High-precision characterization of quantum-cascade laser frequency response using wavelength modulation spectroscopy.

This paper investigates the impact of the quantum cascade laser's frequency modulation response on its tuning rate and tunability. We show a significant disparity in laser tuning rates and tunability between single and dual-frequency modulation schemes frequently used in typical direct absorption and wavelength modulation spectroscopy (WMS) techniques. We show that the DC-characterized tuning rate of a laser can be reduced significantly under a specific set of modulation frequencies of the laser injection current. We characterize these effects by simultaneous measurements of higher harmonic WMS of methane and nitrous oxide in the 7.8 µm spectral regions. We further show that WMS signal modulation broadening mechanisms and spectral structure, i.e., its zero-crossings and turning points, can be used to quantify such laser-modulation effects and validate laser frequency response under dual modulation schemes.

A conjugate frequency modulation FRM method: Applications in polyphase DFT filter bank

In this paper, we study the application of frequency response masking (FRM) technology in polyphase discrete Fourier transform (DFT) filter bank (FB). Due to the inability of FRM methods with conventional structure to simultaneously meet the needs of sharp transition band polyphase DFT FB to improve the signal-to-interference ratio of channelized signals and reduce the complexity of FBs, an improved conjugate frequency modulation frequency response masking (CFM-FRM) method is proposed. The proposed CFM-FRM method solves the problem by frequency modulation, and consumes less multipliers by taking advantage of the orthogonality between sub-filters in CFM-FRM FB. The efficient realization of CFM-FRM based polyphase DFT FB is derived and the multi-size configuration method is illustrated via coefficient decimation. We analyze the adaptability of related FRM works to polyphase DFT FB. The simulation and analysis show that the CFM-FRM method is applicable to polyphase DFT FB, the CFM-FRM based polyphase DFT FB has less multipliers than related methods in other works, and the performances of multi-size FBs meet the requirements.

Total Transfer Capacity Evaluation of HVDC Tie-Lines Considering Frequency Security Constraints

The high proportion of renewable energy access and the construction of HVDC transmission projects have led to a continuous decrease in the penetration rate of asynchronous power sources in the power system. Maintaining frequency stability and safe operation of the power system is a key issue that needs to be urgently addressed in the power grid. This article takes into account the participation of multiple types of power resources in inertia support and frequency modulation response and it also constructs an evaluation model for the total HVDC transfer capacity of the power grid. In response to the uncertainty of wind power and load power, scenario reduction methods are adopted to enhance the HVDC total transfer capacity of the power grid under frequency safety and stability constraints by the daily output of each power source. The simulation results indicate that the scheduling scheme evaluated by the proposed model has a higher frequency security level compared to traditional models.

Improve characteristics of GaN-based green mini-LEDs with double dielectric sidewall passivation

The technique of double dielectric sidewall passivation could improve the electroluminescence characteristics of green mini-LED, including the leakage current, electroluminescence intensity and external quantum efficiency (EQE). According to the analysis of EQE with ABC + f(n) model, both the increment of size and the sidewall passivation could reduce the fraction of SRH recombination. Then, the results of time-resolved photoluminescence measurement indicated that the carrier lifetime of mini-LEDs with higher surface-volume ratio and sidewall passivation would be reduced. Moreover, the communication performances such as modulation bandwidth and frequency response of green mini-LEDs could also be improved by adopting double dielectric sidewall passivation, and the smaller sized green mini-LEDs could achieve higher modulation bandwidth and frequency response.

PARAMETRICAL SYNTHESIS OF PEAK-PHASE MODULATORS WITH THE SET QUANTITY OF IDENTICAL CASCADES OF TYPE «THE NONLINEAR PART - THE MIXED TWO-PORT NETWORK»

Combined quadripoles contain a part of two-poles, which is made only on resistive elements, while another part of two-poles is made only on reactive elements. Such class of quadripoles is widely used in construction of filters and dynamic parts of automatic control systems. Therefore, the development of algorithms for the parametric synthesis of amplitude-phase modulators with the use of combined matching quadripole networks is an urgent task. In this study, matching provides a preset dependence of the ratio of modules and phase difference of the transfer function on frequency with two states of a nonlinear element, determined by two levels of the control signal. The non-linear part is represented by three-pole non-linear feedback element. Interaction between elements of the traditional transfer matrix of combined quadripoles are established and formulas to determine resistances of two-poles they include, which are optimal for providing amplitude-phase modulation of the output signal, are obtained. The study includes data from quadripole theory, methods of matrix algebra, parametric synthesis of microwave control devices, decomposition and circuit analysis of radio devices. Comparative analysis of the theoretical results (frequency response and phase response of modulators in two states) obtained by the use of mathematical modeling in the MathCad system and experimental results obtained due to the circuit simulation in the OrCad and MicroCap systems confirm their satisfactory coincidence.

Prediction method of primary frequency modulation capability of power system based on MEA-BP algorithm

In order to accurately predict the primary frequency modulation capability of power system when frequency deviation occurs, a method for predicting primary frequency modulation performance of power system based on improved neural network with thought evolution algorithm (MEA) is presented. Nine-dimensional parameters, such as frequency deviation before and after disturbance, system backup capacity, load level, mechanical power and electrical power, are selected as input eigenvalues, and the output is the system power change curve. This paper takes CEPRI36v8 system as an example of simulation, obtains the primary frequency modulation curve of the system by setting the shear load disturbance with PSASP, uses the disturbance data and the primary frequency modulation response data as training set, test set and validation set data, trains the prediction model of primary frequency modulation capability based on MEA-BP, and finds the prediction error is about 0.5% compared with the actual data, which proves that the proposed method can accurately and quickly predict the primary frequency modulation capability after the frequency deviation of the power network. This method can assist power dispatcher to analyze the primary frequency modulation response of power grid after power disturbance.

PARAMETRICAL SYNTHESIS OF AMPLITUDE-PHASE MODULATORS WITH THE PRESET NUMBER OF IDENTICAL CASCADES OF THE «NONLINEAR PART – COMPLEX QUADRIPOLE» TYPE

Use of the complex quadripoles, each two-pole terminal of which consists of resistive and reactive elements, allows to create wideband radio devices. Therefore, the development of algorithms for the parametric synthesis of amplitude-phase modulators using complex matching quadripoles is an actual issue. In the present work the coordination provides the set dependence of the ratio of modules and phase difference of the transfer function on frequency in two states of nonlinear element, determined by two levels of the control signal. The nonlinear part represents a three-pole nonlinear feedback element. Interrelations between elements of a classical transmission matrix of two-trminal networks are established and formulas for determining the complex resistance of their two-poles, which are optimal in terms of the criterion for providing amplitude-phase modulation of the output signal are obtained. The quadripole theory, methods of matrix algebra, parametrical synthesis of SHF control devices, decomposition and circuit analysis of radio devices are used. The comparative analysis of theoretical results (frequency response and phase response of modulators in two states), obtained using mathematical modelling in the «MathCad», system and experimental results obtained by circuit simulation in «OrCad» and «MicroCap» systems, confirms their satisfactory coincidence.

Wind Turbine Load Optimization Control Strategy Based on LIDAR Feed-Forward Control for Primary Frequency Modulation Process with Pitch Angle Reservation

Because wind power is connected to the grid on a large scale, frequency fluctuation in the power grid, which is defined as a system safety risk to the power grid, occurs from time to time. According to the grid code rules of China, wind turbines are required to be equipped with primary frequency modulation or inertia response control capability, which are used to support the safe and stable operation of the power grid. During the traditional frequency modulation process of the wind turbine, power limiting operation or pitch angle reservation is generally adopted to ensure that the reserved energy can be released at any time to support the frequency change in the power grid. However, the frequency support method leads to a large loss of power generation, and does not consider the coordination between mechanical load characteristics control and primary frequency modulation. In this paper, a mechanical load optimization control strategy for a wind turbine during the primary frequency modulation process, based on LIDAR (light detection and ranging) feed forward control technology, is proposed and verified. Through LIDAR feed forward control, the characteristics of incoming wind speed can be sensed in advance, with the consequence that the wind turbine can participate in, and actively control, the primary frequency modulation procedure. According to the characteristics of incoming wind, for instance the amplitude and turbulence, simultaneously, the size of the reserved pitch angle can be adjusted in real time. This kind of method, coordinating with the mechanical load of the wind turbine, can be used to reduce both the ultimate load and fatigue damage as much as possible. Finally, the mechanical load characteristics of the wind turbine with and without the control strategy are compared and studied through simulation. The research results show that the load optimization control strategy based on LIDAR feed-forward control technology can effectively reduce the fatigue and ultimate loads of the wind turbine while supporting the frequency change in the power grid; especially for the fatigue load of tower base tilt and roll bending moments, the reducing proportion will be about 4.3% and 6.3%, respectively.

Photonic scheme for broadband frequency response measurement of PDs.

We report a scheme to measure the broadband frequency response of photodetectors (PDs) with the capacity of self-calibration. The optical carrier at f 0 is modulated through one modulator, and this modulator is driven by a microwave signal with a fixed frequency f 1 to produce the carrier-suppressed double sideband optical signals f 0-f 1 and f 0+f 1. The frequency interval of the optical signals is 2f 1. Subsequently, the two optical signals are sent to another modulator driven by a swept microwave signal f m. Two pairs of carrier-suppressed double sideband signals with a high signal-to-noise ratio are generated. The frequencies of these signals are f 0-f 1-f m,f 0-f 1+f m, f 0+f 1-f m, and f 0+f 1+f m. After the PD under test, the frequency response can be extracted from the amplitude of the microwave signals at 2f 1, 2f 1-2f m, and 2f 1+2f m. Two PDs in our laboratory are experimentally characterized from 0.1 to 40GHz with a resolution of 100MHz. Compared with the traditional vector network analyzer swept method, the proposed method extends the measurement range from f m(max) to 2f 1+2f m(max) and has the capacity of self-calibration to eliminate the influence caused by the modulator frequency response on the measurement results.

Phase Noise Analysis of Resonator-Enhanced Electro-Optic Comb-Based Analog Coherent Receivers

We present an architecture for wavelength-division-multiplexed coherent data center links employing resonator-enhanced electro-optic frequency comb generators as both transmitter and local oscillator (LO) sources. We show that in each frequency comb, the phase noise in all comb lines is determined completely by the optical phase noise of the seed laser and the phase noise of the microwave oscillator. We propose an analog coherent receiver that performs carrier recovery on all wavelength channels using only two phase-locked loops. We use an independent cascade of phase shifters driven by marker tone detection in each channel for polarization recovery and compensation of a static optical phase shift. We study design examples for quadrature phase-shift keying and 16-ary quadrature amplitude modulation (16-QAM), determining requirements on the transmitter and LO seed laser linewidths and the LO frequency modulation (FM) response. We find that for a dual-polarization (DP) 16-QAM link with 17 wavelength channels, each operating at 56 GBaud, if the combined linewidth of the transmitter and LO seed lasers is 100 kHz, the LO seed laser requires an FM response that is flat from d.c. to several hundred MHz to maintain a phase-error penalty below 1 dB.

Multiple Tb/s Coherent Optical Transceivers for Short Reach Interconnect

This paper investigates coherent optical transceivers for short-reach interconnect, where a local oscillator laser is used to boost received optical signals for high receiver sensitivity. We review the state-of-the-art technologies and propose a miniature Mach-Zehnder modulator (mMZM) array with 3D silicon photonic-electronic integration to enable high-density, low-power multiple Tb/s coherent transceivers. For design optimization at transceiver level performances, we develop methodology and models to simulate PN junction and mMZM for high-efficiency high-speed modulation, which can be linked to system performances, including high-speed performances, receiver sensitivity, optical link budget, and coherent optical transceiver power consumption. With the optimized design and state-of-the-art technologies, we achieve highly integrated multiple Tb/s coherent transceivers with high density, high speed, and low power. Our simulation results show 3 pJ/bit for integrated driver/mMZM, 5 pJ/bit for integrated PIC/IC and 6.5 pJ/bit with transceiver optics for 6.4 Tb/s with 60 Gbaud 16QAM. Compared with conventional long phase shifter (PS) MZM (4 mm), mMZM with short PS (2.4 mm) only have an extra loss of ∼2 dB under 60 Gbaud 16QAM modulation with optimized designs. We study the scalability from 6.4 Tb/s to 12.8 Tb/s using 120 Gbaud 16QAM for intra-DC interconnect. The results show that further improvement for modulation efficiency, frequency response and laser output power are needed to enable the 12.8 Tb/s.

Relative frequency response measurement of Mach-Zehnder modulators utilizing dual-carrier modulation and low-frequency detection.

A self-calibrated approach is proposed to measure the relative frequency response of Mach-Zehnder modulators (MZMs) based on dual-carrier modulation and low-frequency detection. In this scheme, a dual-carrier is generated by combining a continuous-wave light from a distributed feedback laser diode with its frequency-shifted replica. Through modulating the dual-carrier by a frequency-scanned single-tone microwave signal via the MZM under test biased at its minimum transmission point, a fixed low-frequency heterodyne signal carrying the electro-optic modulation response information is generated after photodetection, from which the relative frequency response of the MZM can be obtained. In the experiment, the relative frequency response of a commercial MZM is measured by using the proposed method, where the result fits in with those obtained by using the conventional optical spectrum analysis method and the microwave network analysis method. The proposed method features self-calibration, high frequency resolution, low-frequency detection, and usage of only a single frequency-scanned microwave source, which is favorable for characterizing the microwave performance of MZMs in backbone optical communication and microwave photonic systems.

Frequency Response of Thermo-Optic Phase Modulators Based on Fluorinated Polyimide Polymer Waveguide.

Polymer waveguide phase modulators exhibit stable low-power phase modulation owing to their exceptional thermal confinement and high thermo-optic effect, and thus, have the merit of thermal isolation between channels, which is crucial for an optical phased array (OPA) beam scanner device. In this work, a waveguide phase modulator was designed and fabricated based on a high-refractive-index fluorinated polyimide. The propagation loss of the polyimide waveguide and the temporal response of the phase modulator were characterized. Moreover, the transfer function of the phase modulator including multiple poles and zeros was obtained from the measured frequency response. The polyimide waveguide modulator device demonstrated a fast response time of 117 μs for 1 kHz input signal, however, for 1 mHz step-function input, it exhibited an additional 5% phase change in 5 s.

Self-referenced electro-optic response measurement of dual-parallel Mach-Zehnder modulators employing single-tone level control and low-frequency bias swing.

A self-referenced method is proposed to characterize the electro-optic frequency response of dual-parallel Mach-Zehnder modulators (DPMZMs) based on single-tone level control and low-frequency bias swing. The single-tone driving signal and the low-frequency bias signal of the DPMZM mix with each other after photodetection, and a low-frequency beat note is generated in the electrical domain. The functional relationship between the desired low-frequency amplitude and the single-tone driving level is investigated and established, from which the modulation depth and half-wave voltage are extracted with the help of regression analysis. We experimentally demonstrate the feasibility of the proposed method and compare it with the conventional ones to check the consistency. The self-referenced method features single-tone modulation and low-frequency detection for measuring high-speed DPMZMs, which avoids the use of a broadband photodetector (PD) and the influence of the uneven response of the PD.

Multi-clad optical fiber design for ultra-wideband modulation instability

Developments of electro-optic (EO) modulators do not have a satisfactory pace and bandwidth restrictions are still limited to several hundred GHz, thus, obtaining methods that enable using broadband optical channels are key factors in high-speed optical communications. In this paper, Modulation Instability (MI) as an approach in order to improve the performance of EO modulators, is investigated in the anomalous and zero-dispersion regimes of proposed optical fiber. In present conventional optical fibers, MI is observed over a few hundred gigahertz bandwidths at low pump power. In order to obtain ultra-wideband (a few Terahertz) bandwidths and maximum gain in the MI process at low pump power, a new structure for optical fiber is proposed. The genetic algorithm is utilized for performance optimization in optical fiber design. It is shown that the proposed optical fiber is able to support MI for a few Terahertz bands at low pump power (100 mW). Furthermore, in this analysis, it is demonstrated that higher-order dispersion terms have a strong impact on modulation instability. Finally, it is concluded that the geometrical and optical parameters of optical fiber are key factors to control modulation instability parameters (gain and bandwidth). The proposed optical fiber can be used as an optical booster in order to compensate frequency response of EO modulators, which is a considerable step forward in high-speed optical communication.

Direct modulation of electrically pumped coupled microring lasers.

We demonstrate how the presence of gain-loss contrast between two coupled identical resonators can be used as a new degree of freedom to enhance the modulation frequency response of laser diodes. An electrically pumped microring laser system with a bending radius of 50 μm is fabricated on an InAlGaAs/InP MQW p-i-n structure. The room temperature continuous wave (CW) laser threshold current of the device is 27 mA. By adjusting the ratio between the injection current levels in the two coupled microrings, our experimental results clearly show a bandwidth improvement by up to 1.63 times the fundamental resonant frequency of the individual device. This matches well with our rate equation simulation model.

Frequency response measurement of electro-optic phase modulators using the time-frequency analysis method

We propose a novel method for the frequency response measurement of electro-optic phase modulators by time-frequency analyzing the instantaneous frequency of a sinusoidal frequency-modulated (SFM) signal. The SFM signal is generated by a frequency-shifting loop (FSL) in which the electro-optic phase modulator under test generates a dual-sideband frequency shift per roundtrip. And the bandwidth of the generated SFM signal is dozens of times of the input radio-frequency (RF), which makes it a precise method to measure the frequency response of electro-optic phase modulators at lower cutoff frequencies. Based on the previously proposed time-delayed interference model [H. Yang et al., J. Lightwave Technol. 39, 3112 (2021)10.1109/JLT.2021.3059875], we establish the relationship between the “peak-to-peak” frequency of the SFM waveforms and the modulation index of the phase modulators. And a short-time Fourier transformation (STFT) is adopted to characterize the time-frequency properties of output waveforms. Experimental results are well supported by the simple theoretical model. Finally, the accuracy of the half-wave voltage measurement is discussed.

Quantifying a frequency modulation response biomarker in responsive neurostimulation

Objective. Responsive neurostimulation (RNS) is an effective treatment for controlling seizures in patients with drug-resistant focal epilepsy who are not suitable candidates for resection surgery. A lack of tools for detecting and characterizing potential response biomarkers, however, contributes to a limited understanding of mechanisms by which RNS improves seizure control. We developed a method to quantify ictal frequency modulation, previously identified as a biomarker of clinical responsiveness to RNS. Approach. Frequency modulation is characterized by shifts in power across spectral bands during ictal events, over several months of neurostimulation. This effect was quantified by partitioning each seizure pattern into segments with distinct spectral content and measuring the extent of change from the baseline distribution of spectral content using the squared earth mover’s distance. Main results. We analyzed intracranial electroencephalography data from 13 patients who received RNS therapy, six of whom exhibited frequency modulation on expert evaluation. Patients in the frequency modulation group had, on average, significantly larger and more sustained changes in their squared earth mover’s distances (mean = 13.97 × 10−3 ± 1.197 × 10−3). In contrast, those patients without expert-identified frequency modulation exhibited statistically insignificant or negligible distances (mean = 4.994 × 10−3 ± 0.732 × 10−3). Significance. This method is the first step towards a quantitative, feedback-driven system for systematically optimizing RNS stimulation parameters, with an ultimate goal of truly personalized closed-loop therapy for epilepsy.

High-Performance Optical Frequency-Domain Reflectometry Based on High-Order Optical Phase-Locking-Assisted Chirp Optimization

We present optical frequency-domain reflectometry with high performance in terms of an ultralong range window, high spatial resolution, and precision enabled by a high-order optical phase-locked loop (OPLL)-assisted commercial fiber laser. Due to elaborate loop designs that allow matching with the nonlinear frequency modulation response of the laser, the potential tuning capability can be fully exploited, leading to efficient optimization of the frequency chirp range and rate in addition to chirp linearization and an enhancement of the dynamic coherence. A nearly Fourier-transform-limited spatial resolution is realized over multiples of the intrinsic coherence length. Practically, a cm-level spatial resolution is demonstrated along the entire fiber link. We achieved a spatial resolution of ∼3.2 cm and ∼4.3 cm for backscatter no more than 130 km and reflections at 242 km, respectively, corresponding to a high range resolution factor of up to 1.78 × 10−7 in the latter case. The precision of the backscatter measurement is verified to be at least 0.5 dB throughout the entire measurement range. Moreover, the limiting factors resulting in a degeneration of the spatial resolution are carefully investigated. The proposed approach can be readily applied to other lasers, offering a powerful tool for a variety of applications.