Dual-parallel Mach-Zehnder Modulator Research Articles

Linearization and down-conversion of microwave photonics Signal based on dual-drive dual-parallel mach-zehnder modulator with eliminated 3rd intermodulation and 2nd distortions

In this paper, we propose and demonstrate a high linear analogue photonic link based on a Dual-drive Dual-parallel Mach-Zehnder Modulator (D-DPMZM) with Balanced Photo-Detector (BPD). Third order Intermodulation Distortion (IMD3) and Second-Order Distortions (SOD) products have been eliminated by controlling the phase of input RF signal and driving voltage of D-DPMZM. The proposed configuration of microwave photonic link is symmetrically single-sideband modulation in two D-DPMZM. For the proposed configuration and the purity of the system, mathematical modeling and simulations have been developed and tested by introducing additional RF signals. In addition, in the proposed configuration, a high linear down-converted signal is transmitted by changing only the operating modulator biasing point, from quadrature to maximum. The elimination of IMD3 and SOD products has been achieved simultaneously with suppressed higher order harmonic in this system. To the best of our knowledge, this is the first reported work in literature where IMD3, SOHs and second order distortion produces have been completely eliminated.

Optimized self-interference cancellation based on optical dual-parallel MZM for co-frequency and co-time full duplex wireless communication under nonlinear distortion and emulated multipath effect.

Co-frequency and co-time full duplex (CCFD) technique has the potential to further improve the capacity of the fifth-generation (5G) system. However, in a CCFD-based transceiver, the self-interference-cancellation (SIC) module is essential because the transmitted signal is also captured by the receiving antenna. In this paper, an optimized SIC technique is proposed based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In addition to the multipath effect between the transmitting and receiving antennas, the nonlinear distortion induced by the used optical and electrical components is considered and analyzed for the first time. In this scheme, one of the children MZMs is biased at 90°. The bias points of the other child MZM and the parent MZM are swept for SIC optimization. Compared to the traditional SIC scheme using DP-MZM, the power of the received signal is increased by 6 dB and the robustness to the bias point drift is improved. In our experiment, over 35 dB cancellation ratio is achieved for 200 MHz filtered orthogonal frequency division multiplexing (F-OFDM) interference signal with carrier frequency from 2.5 GHz to 6 GHz. To mitigate the influence of multipath effect and nonlinear distortion, the recursive least squared (RLS) linear equalizer and the RLS Volterra equalizer are designed and compared. Finally, 42 dB cancellation ratio is achieved for 200 MHz F-OFDM signal with carrier frequency of 4.5 GHz in the presence of nonlinear distortion and emulated multipath effect.

Photonic Image-free Mixer Based on a Dual-Parallel Mach-Zehnder Modulator and Fiber Dispersion for Radio-Over-Fiber System

In this paper, a simple image rejection mixer based on the dispersion effect in the single mode fiber is proposed and experimentally demonstrated for the radio-over-fiber (RoF) system. The key idea is to control the DC bias voltages of the dual parallel Mach-Zehnder modulator (DPMZM) to compensate for the desired components and eliminate the image induced components simultaneously during the fiber transmission. The experimental results show, the image rejection ratio (IRR) of ∼50 dB is realized, and the spurious free dynamic range (SFDR) is about 100.75 dB·Hz2/3. In addition, the results also demonstrate an image-free intermediate frequency (IF) range of 0.5 GHz–9.5 GHz. This image-free mixer can be widely employed in the radio-over-fiber (RoF) system, and greatly simplify the receiver structure in the base station.

Photonic approach to linearly chirped microwave waveform generation with large time–bandwidth product capability

Photonic approach to generating linearly chirped waveforms with large time–bandwidth product (TBWP) is proposed and demonstrated. In the approach, a dual-output dual-parallel Mach–Zehnder modulator (DPMZM) is employed to generate dual-tone wavelengths in the two output ports. The polarization modulator (PolM) is employed to conduct complementary phase modulation of the dual-tone wavelengths. After driving PolM with parabolic signal, frequency-doubled chirped microwave waveform will be obtained from photodetector (PD). To enlarge the TBWP, parabolic waveform is split into time domain and convolved with binary sequences to increase the bandwidth and temporal duration of the generated signal simultaneously. Simulation results show that linearly chirped microwave waveforms with carrier frequency of 40 GHz, bandwidth of 12.5 GHz, time duration of 819.2 ns are generated. After splitting and code-convolving with binary sequence, TBWP of the generated signal is enlarged to 10,240. Pulse compression performances of the generated signal are analyzed, and structure stability is also investigated.

Study on millimeter-wave photonic generator scheme with tunable multiplication factors

In this paper, we propose and demonstrate a prototype of millimeter-wave (MMW) generator with tunable multiplication factors. A dual-parallel Mach-Zehnder modulator and a remodulation structure are used to effectively excite higher-order optical sidebands and a programmable filter contributes to changing multiplication factors. In our work, frequency-quadrupling (20GHz), frequency-12-tupling (60GHz) and frequency-20-tupling (60 GHz) MMW signals were generated, transmitted and detected. Benefited from the satisfactory unwanted mode suppression ratio, the generated signals show anti-power fluctuation capability along the fiber length, which helps to reduce the power penalty in signal transmission.

Generation of tunable frequency-multiplication factor signal with full range phase shift based on a DPMZM

In this paper, a novel photonic phase shifter with full range phase shift and tunable frequency-multiplication factor based on a simple configuration is proposed. The main devices are a dual-parallel Mach–Zehnder modulator (DPMZM) and a FBG-based Sagnac loop. The DPMZM is employed to generate two optical sidebands with multiplied frequency spacing and a FBG-based Sagnac loop is applied to make the two sidebands orthogonally polarized. A following polarization controller (PC) is employed to tune the phase continuously from −180°to 180°. The simulation results show the frequency multiplication factors (FMF) can be two, four, and eight. A RF signal with the frequency of 5 GHz can be converted to 10 GHz, 20 GHz and 40 GHz with their phases continuously tuned from −180°to 180°. The results emerge that the power response is flat for different phase shift. Furthermore, the proposed structure may feature large frequency tuning range since no optical filter and 90°electrical hybrid coupler are used. The effect of non-ideal factors, i.e., DC drifting, RF signal power variation and extinction ratio on the performance of the unwanted signal suppression ratio (USSR) and the conversion efficiency (CE) are also studied. In addition, the polarization isolation performance of the FBG-based Sagnac loop and the bandwidth of the whole structure is clarified. The influence on the multiplied signals due to the unsatisfactory phase and power response of the FBG are also discussed.

A general analytical method for suppressing the third-order intermodulation in microwave photonic link based on dual-parallel Mach–Zehnder modulator

A general analytical method by adjusting the phases of the signals applied to the four electrodes of a dual-parallel Mach–Zehnder modulator (DPMZM) is proposed to suppress the third-order intermodulation (IMD3) in microwave photonic link. Through the detailed theoretical and numerical analysis, all the signal combinations for the four electrodes of the DPMZM are found and classified into three groups according to the IMD3 cancellation mechanism. In this process, a new group of the four electrodes’ setting to suppress the IMD3 is found. The simulation and experiment are carried out to verify our discovery. It is found that this newly found group can also suppress IMD3 by about 30 dB and improve the spurious free dynamic range (SFDR) by 11.5 dB⋅Hz2∕3.

Photonic phase shifter with full tunable range and multi-band frequency-conversion feature based on a PDM-DPMZM

In this paper, a novel photonic phase shifter with − 180° to 180° phase-tunable range and multi-band frequency-conversion feature is proposed. The main device is a single polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM). The PDM-DPMZM is employed to generate an optical frequency comb (OFC) and a carrier-suppressed single sideband (CS-SSB) in two mutually orthogonal polarizations. Simultaneously, an electrical phase shifter is adopted to control the initial phase of the CS-SSB. The simulation results show, a RF signal with the frequency of 4.3 GHz (C-band) can be down-converted to 1.4 GHz (L-band). Meanwhile, it can also be up-converted to 5.7 GHz (C-band), 10 GHz (LO signal), 14.3 GHz (Ku-band) and 18.6 GHz (K-band) with their phases continuously tuned from − 180° to 180°. Furthermore, the proposed structure features flat power response, frequency-independent operation, simple configuration, easy phase tuning, better ability to cope with DC drift and wide operation bandwidth. The unwanted signal suppression ratio (USSR) and the spurious free dynamic range (SFDR) of the phase shifter are also studied.

Simultaneous photonic generation of multiple chirp and unchirp microwave waveform with frequency multiplying capability for optical beam forming system

A photonic technique based on the Mach–Zehnder Modulator and the dual parallel Mach–Zehnder modulator is proposed for the simultaneous generation of multiple chirp and unchirp microwave waveform with frequency multiplying capability for efficient beam steering applications. There is provision to obtain a single chirp signal of a particular center frequency and chirp rate from a multiple chirp signal without any alternation in the experimental setup. In the proposed methodology, the PIN photodetector is used for the detection of 12 GHz unchirp microwave waveform showing the frequency doubling characteristics and the balance photodetector is used for the detection of multiple chirp signal with frequency components 6, 12, and 18 GHz. The same experimental setup is used to generate dual linear chirp microwave signal of 12 GHz center frequency. This can be achieved by adjusting the bias voltage of the phase modulator. Time bandwidth product and bandwidth of the signal are 18.33 and 410 MHz, respectively. This technique is tunable in frequency, but the generation of higher frequency microwave signals is limited by the speed and bandwidth of the Mach–Zehnder Modulator and photodetector. The novelty of our proposed scheme is that we are going to drive MZM by chirp RF signal to multiply the chirp rate in manifold. To the best of our knowledge the effect of chirp microwave signal on photonic highly steerable beam forming system has not yet been studied experimentally in past, which we are targeting under this paper. It is expected that the range of beam steering performance should be improved substantially as compared to previously reported results.

Filter-free photonic microwave upconverter with frequency quadrupling.

A novel method, to the best of our knowledge, of frequency upconversion with frequency quadrupling is presented and experimentally demonstrated. The scheme is based on an integrated polarization-division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) and an intensity modulator (IM). Polarization-multiplexed second-order sidebands are obtained by properly adjusting the bias voltage of the PDM-DPMZM. By adjusting the polarization controller, the +2-order sideband is aligned with the IM's slow axis to be modulated by the intermediate frequency (IF) signal, and the -2-order sideband is aligned with the IM's fast axis with a much lower modulation efficiency. An upconverted signal with frequency quadrupling is generated at the photodetector. The experiment result shows that the working bandwidth range is 6-40GHz, the spur suppression ratio of the upconverted signals is 37.5dB, and the conversion efficiency is -32 dB. 100MSym/s quadrature phase shift keying (QPSK) or a 16QAM signal at 26GHz is generated using a 6GHz local oscillator signal and transmitted through 25km SMF.

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.

Low-Power RF Signal Detection Using a High-Gain Tunable OEO Based on Equivalent Phase Modulation

A novel photonic method for low power radio-frequency (RF) signal detection by a tunable optoelectronic oscillator (OEO) with high gain based on equivalent phase modulation (EPM) is proposed and experimentally demonstrated. A dual-parallel Mach-Zehnder modulator is utilized to generate the EPM signal with a controllable optical carrier to sideband ratio, by which the gain to the RF signal by the OEO loop can be enhanced. A phase-shifted fiber Bragg grating (PS-FBG) with a narrow-band notch in its reflection band implements the phase modulation to intensity modulation conversion by removing one sideband of the EPM signal. The gain and noise performance of the detection system are theoretically analyzed and simulated. In the experiment, the maximum gain of 10.4 dB is obtained at 8 GHz, and the detection sensitivity for RF signals from 2 to 18 GHz are within the range of −87.7 to −84.3 dBm by using the developed detection system. Compared to normal phase modulation based scheme, the EPM-based system offers 9.1 dB higher gain. Utility of the proposed approach for detecting modulated RF signal is also investigated and an optimization scheme is discussed.

Anti-chromatic dispersion transmission of frequency and bandwidth-doubling dual-chirp microwave waveform.

A photonic approach to realizing anti-chromatic dispersion transmission for a frequency and bandwidth-doubling dual-chirp microwave waveform is proposed and experimentally demonstrated. The system has no requirement on polarization devices or optical filters for only the integrated dual-drive dual-parallel Mach-Zehnder modulator employed. To overcome chromatic dispersion, the carrier frequency suppression approach is proposed. The anti-chromatic dispersion process is accomplished in a central station and independent to carrier frequency, fiber length, and dispersion coefficients. An experiment is conducted to verify the analysis. Dual-chirp waveforms at 13GHz with a bandwidth of 0.8GHz and time duration of 1μs are obtained. After 25km fiber transmission, the proposed approach shows a relatively flat curve in a frequency-power diagram, while the normally carrier-suppressed double-sideband modulation method experiences a significant power fading for fiber dispersion.

Highly flat optical frequency comb generation based on pulse carving and sinusoidal phase modulation

We investigate the relationship between an optical pulse shape and a time lens implemented by means of sinusoidal phase modulation. Based on this investigation, two schemes are proposed to obtain an optical frequency comb (OFC) with exceptionally high flatness and a large number of spectral lines by carving an optical pulse shape to result in a quasilinear chirp via a simple sinusoidal phase modulation technique. The first scheme utilizes an intensity modulator with a single-drive port or with dual-drive ports to carve a narrow pulse. The experimental results show very good spectral profiles with 38 OFC lines at 1.2-dB flatness and 53 lines at 1.5-dB flatness when the intensity modulator is combined with two and three phase modulators for sinusoidal phase modulation, respectively. The second scheme is implemented by replacing the intensity modulator by a dual-parallel Mach–Zehnder modulator (DP-MZM). In this case, we obtain 35 OFC lines at nearly perfect flatness of less than 1 dB and 53 lines at 1.5-dB flatness after combining the DP-MZM with two and three phase modulators, respectively.

All-optical generation of binary phase-coded microwave pulses without baseband components based on a dual-parallel Mach-Zehnder modulator.

In this paper, we propose an all-optical system for the generation of binary phase-coded microwave pulses without baseband components. The scheme is based on a dual-parallel Mach-Zehnder modulator (DPMZM). By properly applying the coding signals and the microwave signals to the precisely biased DPMZM, accurate π phase shift binary phase-coded microwave pulses without baseband components can be generated. The proposed system has an extremely simple and stable all-optical structure, leading to a large frequency tuning range and a high signal quality. The operation of the system is very easy. The generation of the 2-Gbit/s 14-GHz and 4-Gbit/s 16-GHz binary phase-coded microwave pulses under different coding signal amplitudes and microwave carrier powers are experimental verified. The results show that the proposed binary phase-coded microwave pulses generation system has high quality and performance.

Photonic angle-of-arrival measurement without direction ambiguity based on a dual-parallel Mach–Zehnder modulator

A novel scheme based on a dual-parallel Mach–Zehnder modulator (DPMZM) is proposed for angle-of-arrival (AOA) measurement without direction ambiguity. The signals received by two antennas are modulated on the two sub-MZMs of a DPMZM. When the main bias of the DPMZM is properly set, the positive and negative side bands will produce two different phase differences. We can obtain two different power curves and achieve AOA measurement without ambiguity by measuring the power. The phase measurement range of the system is about 330 degrees (the AOA measurement range is 165 degrees) and the measurement error is less than 2.24 degrees (0.68% of the full phase measurement range).

Multi-IF-Over-Fiber System With Adaptive Frequency Transmit Diversity for High Capacity Mobile Fronthaul

In this paper, we present and experimentally demonstrate a broadband intermediate frequency-over-fiber (IFoF) system with adaptive frequency transmit diversity for the next generation mobile fronthaul (MFH) applications. We propose to employ an integrated dual-parallel Mach-Zehnder Modulator (DPMZM) with adaptive dc-bias voltage setting for a simplified, efficient, and flexible IFoF communication system. The DPMZM is utilized to compensate the chromatic dispersion (CD) induced deep RF power fading impact, by taking advantage of the frequency transmit diversity of the two parallel modulators and optical paths. Using probe signals and the supervised machine learning (ML) technique, an accurate frequency response of the system is generated and utilized to design a dynamic allocation of IF channels to each DPMZM port. This ML-based link frequency response can capture the accumulated CD-induced power fading frequency region, as well as the random degradation caused by the used RF and optical devices characteristics and bandwidth limitation. Applying our proposed system, we successfully transmitted 15 IF channels with 1.2 GHz bandwidth and 64-QAM-OFDM modulated signals over 20-km fiber length, leading to about 1.18 Tbps CPRI-equivalent data rate. If we assume the maximum spectral efficiency of the LTE-A systems (i.e., 3.75 bit/s/Hz), the user throughput can be higher than 67 Gb/s. The obtained results show the potentials of DPMZM-based multi-IFoF system to satisfy the high capacity requirement of 5G mobile network and beyond.

Reconfigurable microwave photonic frequency upconverter with local oscillator doubling or local oscillator quadrupling

A reconfigurable microwave photonic frequency upconverter with local oscillator (LO) doubling or LO quadrupling is proposed based on two cascaded dual-parallel Mach–Zehnder modulators (DPMZMs) and a fiber Bragg grating (FBG) with a wide bandwidth (0.4 nm). The first DPMZM is used to generate the ±1st-order or ±2nd-order sidebands of the LO signal. The FBG is inserted to separate the positive and negative sidebands. Only the transmitted LO sideband is sent to the second DPMZM, and the carrier-suppressed single-sideband (CS-SSB) modulation of the intermediate frequency (IF) signal is realized by using an electrical 90 deg hybrid coupler. The reflected LO sideband via FBG and the −1st-order IF sideband are combined. Then, the upconverted signal with the frequency of 2ωLO + ωIF or 4ωLO + ωIF can be generated by a photodetector. The experimental results show that the spur suppression ratios of the upconverter with LO doubling and quadrupling are 21.3 and 11.3 dB, respectively. The proposed approach greatly reduces the frequency requirement of the LO signal. The purity of electrical spectrum is largely improved in both the LO doubling and LO quadrupling upconversion benefiting from the CS-SSB modulation. Furthermore, these two upconversion modes can be easily switched by tuning the DC biases of the first DPMZM.

Microwave Photonic Phase Shifter Based on an Integrated Dual-polarization Dual-parallel Mach-Zehnder Modulator without Optical Filter

ABSTRACTA frequency-doubled microwave photonic phase shifter (MPPS) without optical filter is proposed. The MPPS is based on an integrated dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM with a 90° polarization rotator in one arm is used to generate an optical carrier suppressed double sideband (OCS-DSB) signal with orthogonal polarization, and the PolM with two modes opposite phase modulation is used to introduce the optical phase shift between the two orthogonally polarized tones. Simulations show that the MPPS can realize a continuously tunable phase shift of 360° with only one DC bias voltage, and is not sensitive to the optical carrier wavelength and microwave signal frequency since no optical filter is used.

Microwave Photonic Link With Flexible Even-Order and Third-Order Distortion Suppression

A microwave photonic link with flexible suppression of the even-order and third-order distortions is proposed by using a single integrated polarization-multiplexing dual parallel Mach-Zehnder modulator (PM-DPMZM). A 180° electric hybrid is applied to introduce a phase shift of 180° between the even and odder modulation sidebands of the radio frequency (RF) signal. One DC bias voltage of the PM-DPMZM is adjusted to implement not only the optimal suppression of the even-order or third-order distortions but also a simultaneous suppression of these two distortions. The experimental system is carried out. In the best suppression points for the second or third intermodulation distortions (IMD2 or IMD3), the spurious-free dynamic range (SFDR) of IMD2 and IMD3 is improved by 17.1 and 17.7 dB, comparing with the conventional MZM based MPL. In the case of the simultaneous suppression, the SFDR values of IMD2 and IMD3 are enhanced by 10.6 and 6.4 dB. The proposed link has great flexibility, simple structure, and convenient operation, and it can be applied in both the single-octave and multi-octave communication systems.