Triangular Waveform Generation Research Articles

Photonic generation of high-accuracy triangular waveform with tunable duty cycle based on a dual-wavelength I/Q modulation

Photonic generation of high-accuracy triangular waveform with tunable duty cycle based on a dual-wavelength I/Q modulation

Photonic generation of triangular waveform with tunable symmetry based on channelized frequency synthesis.

A symmetry tunable triangular waveform photonic generator based on channelized frequency synthesis is proposed and studied. The generator adopts a multichannel system architecture and harmonic amplitude control algorithm to physically isolate each subchannel. In a single subchannel, quadrature phase shift keying modulation and coherent dual-wavelength balanced detection are used to realize optical upconversion and suppress mixing interference in the process of frequency conversion. Therefore, the model has the characteristics of a high-order Fourier series fitting tunable function waveform output. The analysis results show that the Fourier series harmonic coefficients can be adjusted flexibly by the multivariable joint regulation algorithm. The relationship between the variables is analyzed and discussed. The feasibility of the scheme is verified by optical simulation; when the rms error (RMSE)≤0.03, a 20%-80% tunable symmetry triangular waveform can be obtained.

Photonic Generation of Rectangular and Triangular Microwave Waveforms With Tunable Duty Cycle

We propose a microwave photonic scheme to generate rectangular and triangular waveforms by external modulation. Different from previous works, the duty circle of the generated waveforms in our scheme is freely tunable. The main structure is based on a Mach-Zehnder modulator and a tunable optical delay line. By power splitting and time-delay tuning on two polarization branches, triangular or rectangular waveforms can be obtained by the superposition of beating signals. Moreover, the RF modulation index in this work is unfixed, which increases the flexibility of the system. The proposed scheme is theoretically analyzed and experimentally verified. The triangular and rectangular waveforms at repetition rates of 4 and 5 GHz are successfully generated.

A Simple Photonic Generation of a Microwave Waveforms Scheme Based on a Dual-Polarization Dual-Drive Mach-Zehnder Modulator

In this paper, a simple scheme for the generation of sawtooth, triangular, and square waveforms using an integrated dual-polarization dual-drive Mach-Zehnder modulator (Dpol-DDMZM) is proposed. By properly setting the working point and the modulation index of the Dpol-DDMZM, the desired microwave waveforms are easily obtained after photodetection. The proposed scheme for the photonic generation of microwave waveforms is analyzed both by simulation and experiment. The periodical sawtooth, triangular, and square waveforms with repetition rates of 8 GHz are successfully generated. The root-mean-square errors (RMSE) are 0.190, 0.168, and 0.135, respectively. The system features flexible tunability.

Photonic generation of triangular and rectangular waveforms based on four-wave mixing effect

Photonic generation of triangular and rectangular waveforms based on four-wave mixing effect

An improved frequency-quadrupling triangular waveform generation based on external modulation and polarization control

An improved photonic generation of full-duty-cycle triangular waveforms based on external modulation and orthogonal polarization control is proposed. The external modulation configuration consists a dual-parallel Mach–Zehnder modulator (DP-MZM) and a remodulation structure. After external modulation, four main sidebands with uniform frequency interval existed in the optical spectrum. To obtain the target triangular waveform, the modulation indices of modulators need to be carefully adjusted to guarantee the amplitude ration of inner-sideband and outer- sideband is desired 9.5 dB. Subsequently, polarization control is utilized to eliminate the coherent interference of different sidebands. Based on our proposal, triangular waveforms at 10 GHz, 20 GHz, 30 GHz and 40 GHz are achieved. The proposal might be attractive since that the generated signal repetition rate is frequency-tunable and frequency-quadrupled.

Triangular-shaped waveform generation with variable symmetry based on dual-polarization modulation

Photonic generation of triangular-shaped waveform with variable symmetry based on dual-polarization modulation is proposed and demonstrated. Based on the external modulation method, a dual-polarization modulator is used to modulate the radio frequency signal to generate the needed optical signal. By setting the modulation index of the modulator and phase shift of phase shifters appropriately, the optical intensity of generated signal can equal approximately the first three terms of the Fourier series expansion of the ideal triangular-shaped waveform, so triangular-shaped waveforms with different symmetry factors can be generated. Most of previous triangular waveform generation schemes generate symmetrical triangular waveform or sawtooth waveform (sawtooth waveform can be regarded as an asymmetrical triangular waveform), and the symmetry factor is not tunable. The tunable range of symmetry factor of triangular-shaped waveform generated by this scheme can reach 0%–100%, which will greatly expand the application range of triangular-shaped waveforms. The root-mean-square error (RMSE) is introduced to measure the similarity between the generated waveform and the theoretical waveform. It can be found that theoretically the triangular-shaped waveform with a symmetry factor in a range from 14% to 86% has a good similarity to the ideal waveform (RMSE < 0.044), and the RMSE of the generated waveform in the simulation is also very close to the theoretical RMSE. Experimentally, the 4GHz triangular-shaped waveforms with different values of symmetry factor (20%–80%) are obtained by using 4GHz radio frequency signal.

Photonic generation of frequency-quadrupled triangular waveform based on a DP-QPSK modulator with tunable modulation index

In this paper, a scheme for generating frequency-quadrupled triangular waveform based on a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator is proposed. The repetition rate of the generated triangular waveform is four times the frequency of radio frequency (RF) signal. In this scheme, the modulation index of modulator is no longer a fixed value, and it can be adjusted in a certain range, which increases the flexibility of the scheme. Compared with previous frequency-quadrupled triangular waveform generation schemes, the structure of this scheme is simple, and the scheme enables good repetition rate tunability. The effect of extinction ratio and DC bias drift of modulator on the scheme is analyzed by simulation.

A Simple Scheme for Photonic Generation of Microwave Waveforms Using a Dual-drive Mach–Zehnder Modulator

In this paper, a novel photonic scheme for the generation of square and triangular waveforms is proposed and experimentally demonstrated by using a dual-drive Mach–Zehnder modulator (DDMZM) without any optical signal processing. By properly setting the modulation index of the DDMZM, the square and triangular microwave waveforms could be easily achieved in conjunction with a 90° hybrid coupler. Furthermore, the modulation index of the DDMZM could be tuned for a low radio frequency (RF) signal power requirement by tuning the phase difference of the RF signals applied to the two arms of the DDMZM. The proposed scheme for the photonic generation of microwave waveforms is theoretically analyzed and experimentally demonstrated. The periodical triangular and square waveforms with repetition rates of 5 GHz, 8 GHz, and 10 GHz are successfully obtained. The root-mean-square errors between the generated and theoretical triangular and square waveforms with a repetition of 5 GHz are 0.042 and 0.053, respectively.

Photonic generation of frequency-doubled triangular waveforms based on a dual parallel Mach–Zehnder modulator

We propose a photonic approach to generating frequency-doubled triangular waveforms using a dual-parallel Mach–Zehnder modulator (DPMZM). Most previous modulator-based schemes require additional processing of optical sidebands using filters or a dispersive element. In our work, optical processing of optical components is no longer necessary. The triangular waveforms with a repetition rate twice the frequency of the applied microwave signal can be directly generated by properly setting the bias and driven signal of the DPMZM. Since there is no additional optical processing, the proposed structure is cost effective. The repetition rate of the generated waveform is freely tunable over a wide bandwidth since there is no optical or electrical filter involved. The proposed approach is theoretically analyzed and experimentally demonstrated. Triangular waveforms with the repetition rates of 6, 8, and 10 GHz are successfully generated.

Special type of current conveyor-based Schmitt trigger in novel design of triangular waveform generator

This paper introduces novel solution of triangular and square wave generator employing circuitry of interesting and unusual Schmitt trigger and specially prepared modification of lossless integrator connected in low-impedance input terminal of the comparator that allows linear charging of capacity and therefore also triangular wave generation that is not available in standard cases of applications (only relaxation generator available – exponential and square wave). Design and supposed operation of the circuit was verified not only theoretically but also experimentally with CMOS implementation of employed active elements available in form of IC device fabricated in 0.35 μm I3T ON Semiconductor process. Achieved result confirmed studied features of triangular wave generation and linear electronic tunability of its frequency between 23 and 151 kHz.

A simple and tunable photonic generation of frequency-doubled triangular waveform based on two cascaded modulators

A simple and tunable photonic approach for frequency-doubled triangular waveform generation is proposed and experimentally demonstrated. The approach is based on an intensity modulator (IM) and a cascaded polarization division multiplexing Mach–Zehnder modulator (PDM-MZM). The IM and the upper arm of the PDM-MZM are driven by the same LO signal, with the former biased at the null point and the latter at the maximum transmission point. By adjusting the modulation index of the upper arm and the direct current (DC) bias of the lower arm of the PDM-MZM, the frequency-doubled full-duty-cycle triangular waveform can be generated. The proposed approach does not use any electrical phase shifter or optical filter, it is easy to implement and exhibits the advantages of good frequency tunability. An experiment is conducted to verify the approach. Triangular waveforms with different repetition rates of 8 GHz and 10 GHz are generated.

Photonic Generation and Transmission of Frequency-Doubled Triangular and Square Waveforms Based on Two Mach–Zehnder Modulators and a Sagnac Loop

In this paper, a new photonic approach for frequency-doubled triangular and square waveforms generation is proposed and experimentally demonstrated. The scheme is based on two single-drive Mach–Zehnder modulators (MZMs) and one of them is located in a Sagnac loop. By properly setting the working points of the two MZMs and the polarization angle of the light injected into the Sagnac loop, two orthogonal-polarization optical signals with tunable amplitudes can be obtained. One of them is the carrier-suppressed first-order optical sidebands and the other is the carrier-suppressed third-order optical sidebands. After the photoelectric conversion, we can get frequency-doubled and frequency-sextupled microwave harmonics with tunable amplitudes and the desired waveforms can be obtained. In addition, the phase relationship and the amplitude of the generated second- and sixth-order electrical harmonics will remain unchanged during fiber transmission. Thus, the scheme is suitable for fiber transmission in future centralized radio-over-fiber systems.

Compact photonic triangular waveform generator with wideband tunability

A compact triangular waveform generator, consisting of a laser diode, a single dual-output Mach–Zehnder modulator (DOMZM), a variable optical delay line and a balanced photodetector (BPD), is proposed and experimentally demonstrated, using a single-frequency RF signal as the input. The DOMZM is biased at the quadrature point, so that no even-order harmonics of the RF frequency would be generated after the BPD. Then, the modulation index is properly selected to let the generated electrical first- and third-order harmonics approximately equal those of the triangular waveform. The use of the balanced detection not only increases the output power by 6 dB but also removes the DC component and the common-mode noise. No optical filtering is required, which guarantees the simplicity and wide frequency range of the system. A proof-of-concept experiment is carried out. Triangular waveforms with repetition rate tuning from 1 to 13 GHz are successfully generated, with the even-order harmonics suppressed by more than 54 dB.

A simple photonic method to generate square and triangular microwave waveforms

We report a simple photonic method to generate square and triangular microwave waveforms. Previous works normally need complicated processing of optical signals for the generation of these waveforms. Actually we find that the simplest microwave photonic link can do the same thing without any optical signal processing which is the key advantage of our method compared with previous works. The proposed signal generator only consists of a sinusoidal radio-frequency (RF) source, a conventional Mach–Zehnder modulator (MZM), and a photodetector (PD). The intensity modulated optical signal is directly coupled to a PD for square-law detection without any signal processing. By properly setting the modulation index of the MZM to 1.15 rad, a square waveform can be easily obtained. For triangular waveform generation, a 90° hybrid coupler is attached after PD to compensate the phase mismatch. Besides, neither optical nor electrical filters are needed in our link which can ensure a wide frequency range. The proposed scheme is theoretically analyzed and experimentally verified. Square and triangular waveforms at repetition rates of 3, 4, and 5 GHz are successfully generated.

Photonic Generation and Transmission of Triangular and Square Waveforms With a Large Repetition Rate Tunable Range

A photonic approach to generate and transmit triangular and square-shaped microwave waveforms with a large repetition rate tunable range is proposed and experimentally demonstrated using a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) integrated in the DP-QPSK modulator, which is driven by a microwave signal, is properly biased to serve as an optical carrier-suppressed single-sideband modulator to generate a first-order optical sideband and an opposite third-order optical sideband. The lower DP-MZM in the DP-QPSK modulator, driven by dc voltage, functions as an optical phase shifter to tune the phase of the optical carrier. By properly controlling the phase of the optical carrier and the amplitude of the optical sidebands, a triangular or a square microwave waveform can be generated. In addition, the influence of the fiber dispersion on the shape of the waveform can be overcome by properly adjusting the phase of the optical carrier, so the generated microwave waveforms can be transmitted over an optical fiber. An experiment is performed. Triangular waveforms with a repetition rate from 3 to 13 GHz and square waveforms with a repetition rate from 3 to 7 GHz are generated. The compensation of the dispersion-induced distortion is also evaluated in the experiment.

A Simple Technique for Triangular Waveform Generation based on a Dual-Polarisation Modulator

A new microwave photonic topology for generating a triangular waveform is presented. The concept is based on incoherent summation of two intensity modulated optical signals to generate the first- and third-order harmonic frequency components with the same amplitude and phase as that of an ideal triangular waveform. The proposed triangular waveform generator has a very simple and low-cost structure as it only requires the Mach Zehnder modulator in a conventional fiber optic link to be replaced by an integrated dual-polarization modulator driven by two 90° phase difference RF signals. It also has a widely tunable repetition rate, low insertion loss, and a stable performance. Experimental results demonstrate a triangular waveform with a tunable microwave-frequency repetition rate and a root mean square error value of <;0.049 when comparing with an ideal triangular waveform. The stability of the proposed triangular waveform generator is also examined experimentally.

基于光电微波振荡器的三角波和正弦信号发生器

基于光电微波振荡器的三角波和正弦信号发生器

基于注入锁定和时域综合的倍频三角波产生技术

基于注入锁定和时域综合的倍频三角波产生技术

Simultaneous Triangular Waveform Signal and Microwave Signal Generation Based on Dual-Loop Optoelectronic Oscillator

A self-starting triangular waveform and microwave signal generator based on a dual-loop optoelectronic oscillator (OEO) is proposed. In this scheme, two continuous waves (CWs) with different wavelength are emitted from two laser diodes (LDs) to form two feedback loops in an OEO system. When the oscillation is established and the modulation index of the Mach–Zehnder modulator (MZM) is set to be 0.752, a triangular waveform could be generated by the superposition of the two oscillation signal envelopes on photodetector with appropriate time delay between two wavelength channels. Although the proposed system is similar to a traditional dual-loop OEO and no more devices are required, it is not only a microwave signal source with high side-mode suppression ratio (SMSR) but a triangular waveform generator simultaneously as well. The operation principle is theoretically analyzed and stimulated. In experimental demonstration, the full-duty-cycle triangular waveform signal and high-quality microwave signal at 5 GHz can be achieved simultaneously. In addition, the experiment result shows that the variety of the modulation depth for triangular waveform generation does not influence the quality of the generated microwave signal.