Cascaded Mach-Zehnder Modulators Research Articles

A review on photonic‐assisted dual‐chirp microwave waveform generation methods

AbstractIn recent times, photonic synthesis and processing of arbitrary microwave waveforms have gained interest due to their high frequency and huge time–bandwidth product. This study reviews methods for producing dual‐chirp microwave waveforms, focusing mostly on system topologies based on external modulation techniques, such as cascaded Mach–Zehnder modulator (MZM), dual parallel MZM, and dual polarized MZM. Other photonic approaches, like using semiconductor laser and optical heterodyne detection methods, are also discussed. These techniques are preferable because of high frequency, enhanced time–bandwidth product, greater chirp rate, and many more advantages. Additionally, the difficulties associated with integrating the systems into real‐world applications are also addressed.

Filterless Frequency Octupling Microwave Photonic Phase Shifter Based on Cascaded Mach–Zehnder Modulators

ABSTRACT In this paper, we propose a microwave photonic phase shifter (MPPS) without optical filtering to generate a frequency octupling microwave photonic (MWP) signal with 360º phase-shifting based on two cascaded Mach–Zehnder modulators (MZMs). Theoretical analysis is given to realize the high-quality frequency octupling MPPS by eliminating the undesired optical carrier and sidebands using an optical coupler (OC). Simulations show that the generated MMW signal has an electrical spurious suppression ratio (ESSR) higher than 33 dB. The impact of the non-ideal modulation index, extinction ratio, and phase drift is discussed and analyzed. Furthermore, the influence of different center frequencies, power, and linewidths of the laser is also analyzed.

Generation of arbitrary shape microwave waveform centered on two fold cascaded Mach–Zehnder modulators

Generation of arbitrary shape microwave waveform centered on two fold cascaded Mach–Zehnder modulators

Generation of frequency 16‐tupling millimeter wave without filtering based on cascaded Mach–Zehnder modulator

AbstractA scheme of generating millimeter‐wave signals with 16 times frequency using a cascaded Mach–Zehnder modulator (MZM) is proposed. Optical delay lines (ODLs) are used to place between cascaded MZMs, two MZMs work at the maximum transmission point. By controlling the modulation index of the MZM and the delay of the ODL, 0‐order, ‐order, and ‐order sidebands can be generated. The optical phase shifter and attenuator are adjusted to eliminate the 0‐order sideband, and the photodetector output generates a frequency 16‐tupling millimeter wave (MMW). In the simulation platform, a 160‐GHz MMW signal can be obtained by taking a 10‐GHz radio frequency signal as the driving signal of two MZMs. The optical sideband suppression ratio is 29.92 dB, and the radio frequency sideband suppression ratio is 24.89 dB. Further, the effect of system performance on optical devices under nonideal conditions is also discussed.

A Novel Reconfigurable Nonlinear Cascaded MZM Mixer, Amplitude Shift Key Modulator (ASK), Frequency Hopping and Phase Shifter

A novel reconfigurable Microwave Photonics (MWP) mixer is presented in this paper, which can be configured to work as a frequency hopper, ASK modulator and phase shifter. This mixer is based on a cascaded Mach–Zehnder Modulator (MZM) structure. A general nonlinear analytical model for the structure is presented. This model is platform free, which means it can be applied to several MWP and integrated MWP platforms. Based on the analytical model, the performance of the structure and output results, such as the optical and electrical spectrum of the structure, are derived in mathematical closed-form expressions. The results of the presented analytical model are compared and evaluated with the results obtained from the simulation to prove the correctness of the analytical model. The presented structure has a simple form, which can be fabricated at a low cost. In addition, according to the obtained results from the analytical model, there is no need to change the arrangement of the structure to operate in any of the mentioned configurations, and the desired function is achievable only by changing the bias voltage of the modulators at the desired frequency.

An 18-Tupled Photonic Millimeter-Wave Generation Using Cascaded Mach-Zehnder Modulators

ABSTRACT This article presents an optical generation scheme of mm-wave carriers by 18-tupling of radio frequency (RF) signal using three cascaded Mach-Zehnder modulators. The proper selection of modulation index, biasing points and phase shifts leads to generation of desired ninth-order sidebands. A thorough mathematical analysis has been performed to validate the mm-wave generation and the results obtained are also consistent with simulation findings. Moreover, the effect of variation of key system parameters from their ideal values is also investigated. The higher tupling factor and elimination of optical filtering in the proposed scheme make it promising for implementation in radio-over-fiber (RoF) transmissions.

Real & Simulated QPSK Up-Converted Signals by a Sampling Method Using a Cascaded MZMs Link

This study focuses on a novel concept of transmitting of a quadrature phase shift keying (QPSK) modulation by an electro-optical frequency up-conversion using a cascaded Mach–Zehnder modulators (MZMs) link. Furthermore, we conduct and compare the results obtained by simulations using the Virtual Photonics Inc. (VPI) (Berlin, Germany) simulator and real-world experiments. The design and operating regime peculiarities of the MZM used as a sampling up-converter mixer in a radio over fiber (RoF) system are also analyzed. Besides, the simulation and experimental results of static and dynamic characteristics of the MZM have approximately the same behavior. The conversion gain of the cascaded MZMs link is simulated over many mixing frequencies and it can decrease from 17.5 dB at 8.3 GHz to −4.5 dB at 39.5 GHz. However, in real world settings, it may decrease from 15.5 dB at 8.3 GHz to −6 dB at 39.5 GHz. The maximum frequency range is attained at 78.5 GHz for up-conversion through simulations. Error vector magnitude (EVM) values have been done to evaluate the performance of our system. An EVM of 16% at a mixing frequency of 39.5 GHz with a bit rate of 12.5 Gbit/s was observed with the considering sampling technique, while it reached 19% in real-world settings with a sampling frequency of 39.5 GHz and a bit rate of 12.5 Gbit/s.

Optical frequency comb based on cascaded MZM-EAM with Gaussian-shaped pulse signal

We propose a scheme of optical frequency comb (OFC) generation based on cascaded Mach–Zehnder modulator (MZM) and electroabsorption modulator (EAM) with Gaussian-shaped pulse signal. In the proposed scheme, the MZM and the nonzero-chirp EAM are driven by a periodic Gaussian-shaped pulse signal that is controlled with binary sequences, and then an OFC is output from EAM. The theoretical model of the OFC generation is developed by improving the theory of electroabsorption modulation. The performance of OFC is investigated. The results show that the frequency spacing of the OFC can be tuned in the range of 1 to 10 GHz, the number of effective comb-lines is 35, and the power variation of comb-lines is 2.14 dB.

Photonic generation of frequency-doubled microwave waveforms based on cascaded Mach-Zehnder modulator

In this paper, a photonic method to generate frequency-doubled microwave waveforms based on cascaded Mach-Zehnder modulator were proposed and experimentally demonstrated. Cascaded modulation were used to generate the ± 1st-order sidebands with carrier suppression and ± 3rd-order sidebands with ± 1st-order sidebands suppression, which were polarization multiplexed and photodetected to generate the 2nd-order and 6th-order electrical harmonics. By properly adjusting the amplitude ratio of the 2nd-order and 6th-order harmonic signals, frequency-doubled triangle and square microwave waveforms were simulated. And a 2 GHz triangle and square waveform was realized in the experiment as a proof of concept, with RMSEs of 0.0989 and 0.3906 respectively. In addition, the effect of extinction ratio and modulation index of the modulator on RMSE were investigated. The results show that the proposed system is of such advantages as simple structure, easy implementation, low cost and flexible frequency tunability.

Filterless frequency 16-tupling millimeter-wave signal generation with cascaded Mach–Zehnder modulators

A simple scheme is proposed for generating frequency 16-tupling millimeter-wave (MMW) signal based on cascaded Mach–Zehnder modulators (MZMs) and an optical phase shifter (PS) without optical filter. Theoretical analysis is given to generate the high-quality 16-tupling MMW signal by eliminating the undesired optical carrier and sidebands. Simulations show that the generated 16-tupling optical MMW signal has the optical sideband suppression ratio higher than 29.85 dB and radio frequency (RF) spurious sideband suppression ratio higher than 23.9 dB. The impact of non-ideal modulation index, extinction ratio, and phase difference of optical PS- and RF-driven signal applied to the cascaded MZMs are discussed and analyzed. After different lengths of fiber transmission, the generated optical MMW signal shows good performance. Furthermore, the influence of different laser linewidths on the transmission performance of the generated MMW signal is also performed and analyzed.

Temporal analog optical computing using an on-chip fully reconfigurable photonic signal processor

This paper introduces the concept of on-chip temporal optical computing, based on dispersive Fourier transform and suitably designed modulation module, to perform mathematical operations of interest, such as differentiation, integration, or convolution in time domain. The desired mathematical operation is performed as signal propagates through a fully reconfigurable on-chip photonic signal processor. Although a few numbers of photonic temporal signal processors have been introduced recently, they are usually bulky or they suffer from limited reconfigurability which is of great importance to implement large-scale general-purpose photonic signal processors. To address these limitations, this paper demonstrates a fully reconfigurable photonic integrated signal processing system. As the key point, the reconfigurability is achieved by taking advantages of dispersive Fourier transformation, linearly chirp modulation using four-wave mixing, and applying the desired arbitrary transfer function through a cascaded Mach-Zehnder modulator and a phase modulator. Numerical simulations of the proposed structure reveal a great potential for chip-scale fully reconfigurable all-optical signal processing through a bandwidth of 400 GHz.

Broadband Optical Frequency Comb Generation With Flexible Frequency Spacing and Center Wavelength

A broadband optical frequency comb with a flexible frequency spacing and a center wavelength is proposed and experimentally demonstrated. The proposed scheme consists of a single continuous-wave laser, cascaded Mach–Zehnder modulator (MZM) and phase modulator (PM), two-stage dispersion-flattened highly nonlinear fibers (DF-HNLFs), and a single-mode fiber in between. A narrow-band frequency comb is generated in the MZM and PM, and a broadband frequency comb is achieved by a self-phase modulation based spectral broadening in the DF-HNLFs. Since the DF-HNLF has low dispersion over a wide wavelength range, the central wavelength of the generated frequency comb can be tuned from 1535 to 1564 nm. In addition, the central wavelength of frequency comb has a potential to be extended to L-band according to the dispersion profile of the DF-HNLF and the operation bandwidths of the MZM and PM. By tuning the driving radio-frequency signal, the frequency spacing of the generated frequency comb can be tuned. In the experiment, the frequency spacing of 25 and 40 GHz has been achieved.

A tunable frequency-decuple optoelectronic oscillator based on frequency comb and stimulated Brillouin scattering

An optically tunable frequency-decuple optoelectronic oscillator based on optical frequency comb (OFC) and stimulated Brillouin scattering has been proposed and theoretically analyzed. In the proposed structure, the OFC is generated using a cascaded Mach–Zehnder modulator and a dual-parallel Mach–Zehnder modulator (DPMZM), and multi-pump lights could be obtained instead of one pump. A quintuple Brillouin frequency shift oscillation signal generated by using Brillouin gain-loss compensation principle and carrier phase-shifted double sideband modulation is realized by using the DPMZM to double the oscillation frequency. As a consequence, a decuple frequency shift microwave signal is achieved. Profit from the wavelength-dependent nature of Brillouin frequency shift, a frequency-decuple signal at 10 $$f_{b}$$ which could be tunable from 87.9750 to 94.4750 GHz by simply tuning the wavelength of the tunable laser source is obtained in theory.

Generation of Low Phase-Noise Frequency-Sextupled Signals Based on Multimode Optoelectronic Oscillator and Cascaded Mach–Zehnder Modulators

We have demonstrated a scheme to realize the generation of frequency-sextupled signals with low phase noise (PN). The structure is based on a multimode optoelectronic oscillator (OEO) and two cascaded Mach–Zehnder modulators (MZMs). A drive source signal is modulated by the MZM1, which is biased at the minimum transmission point (MITP); the generated first-order sidebands are injected into the multimode OEO, which is contributed by the MZM2, the single-mode fiber, the photodetector, and the amplifier. The third-order sidebands are generated by the MZM2, which is also biased at the MITP. The modulated signal is then divided into reflection components and transmission components by a fiber Bragg grating (FBG). The reflection components, including the first-order sidebands, are sent to the photodetector and fed back to the MZM2 to form an optoelectronic hybrid loop. The transmission components, including the third-order sidebands, are heterodyned by another photodetector to generate a frequency-sextupled signal. Compared with the drive signal, the generated signal has a lower PN due to the selection of the oscillation mode. In the experiment, a frequency-sextupled signal from 15 to 24 GHz is generated by a drive signal, which is tuned from 2.5 to 4 GHz. The PN of the generated signal at 24 GHz is −103.6 dBc/Hz@10 kHz; 14.6 dB PN reduction is realized.

Research of dual-band microwave photonic filter for WLAN based on optical frequency comb.

This paper presents a dual-band microwave photonic filter for a wireless local area networks with independently tunable passband center frequencies and bandwidths. The two bands of the filter were 2.4 GHz and 5.725 GHz, respectively. The filter was based on a stimulated Brillouin scattering and an optical frequency comb (OFC) scheme. We created this filter using OFC pumps instead of a single pump. The OFC scheme consists of a cascaded Mach-Zehnder modulator (MZM) and a dual-parallel MZM (DPMZM) hybrid modulation that generated seven and 11 lines. The experimental results show that the two passbands of the filter were 80 and 130 MHz.

Photonic generation of frequency-decupled microwave signal based on cascaded Mach-Zehnder modulators

In order to effectively solve the generation problem of high frequency microwave signal, a frequency-decupled signal generation system based on two cascade Mach-Zehnder modulators (MZMs) is proposed. The RF drive signal is modulated by the first MZM, by adjusting the bias voltage, it is biased at the minimum transmission point (MITP). The generated signal is partly sent to the photoelectric detector (PD1) to heterodyne the first-order sidebands. With an optical coupler, the generated first-order sidebands are also used as the optical source for the second modulation. The generated frequency-doubled signal is modulated by the second MZM which is biased at the maximum transmission point (MATP), then the fifth-order sidebands signal are separated by a fiber Bragg grating from the generated sidebands. With the EDFA and PD2, the generation of a frequency-decupled microwave signal is realized. The structure is also verified by experiments, a frequency-decupled signal from 15 to 27GHz is generated by the drive source signal which is tuned from 1.5 to 2.7GHz.

Generalized study of microwave frequency multiplication based on two cascaded MZMs

A comprehensive analysis of photonically assisted microwave frequency multiplication based on two cascaded Mach–Zehnder modulators (MZMs) is presented. The expressions, including all harmonics, are entirely general in terms of the extinction ratio (EXT) of MZM. A theoretical derivation that induces operating conditions is developed to achieve frequency quadrupling, sextupling, and octupling. The impact of an imperfect EXT of MZM on optical sideband suppression ratio and RF spurious suppression ratio is investigated. The improvement of system performance through MZM modulation index optimization is also analyzed. Simulation verifications are provided for the microwave frequency multiplication schemes.

Optical frequency comb generation based on chirping of Mach–Zehnder Modulators

A new approach for the generation of an optical frequency comb, based on chirping of modulators, is proposed and numerically demonstrated. The setup includes two cascaded Mach–Zehnder Modulators (MZMs), a sinusoidal wave oscillator, and an electrical time delay. The first MZM is driven directly by a sinusoidal wave, while the second MZM is driven by a delayed replica of the sinusoidal wave. A mathematical model of the proposed system is formulated and modeled using the Matlab software. It is shown that the number of the frequency lines is directly proportional to the chirp factor. In order to achieve the highest number of frequency comb lines with the best flatness, the time delay between the driving voltages of the two MZMs is optimized. Our results reveal that at least 51 frequency lines can be observed at the output spectrum. In addition, 27 of these lines have power fluctuations of less than 1dB. The performance of the proposed system is also simulated using a split-step numerical analysis. An optical frequency comb, with tunable frequency spacing ranging from 5 to 40GHz, is successfully generated.

Simplified optical millimeter-wave generation configuration based on frequency octupling

In this paper, a tunable, wideband, with simple configuration to generate frequency octupled millimeter (mm)-wave signal for radio-over-fiber systems is theoretically analyzed and experimentally demonstrated. The proposed system consists of two cascaded Mach–Zehnder modulators (MZMs). The first one is working at optical carrier suppression modulation that is used for the first-order optical harmonic generation. The second one is dual-parallel MZM which utilized the first-order optical harmonic to generate frequency octupled mm-wave signal. The experiments show that without any filter, a wideband frequency octupled optical mm-wave signals with the frequency varying from 4 to 80GHz and the undesired sideband suppression ratios of higher than 34dB can be obtained. The phase noise performance and the transmission performance of the radio-over-fiber downlink system are also demonstrated. The single-sideband phase noise of the generated 80GHz signal is −88dBc/Hz at 10kHz offset. The power penalty is less than 3dB at the bit error rate of 10−10 after 50km single-mode fiber transmission. Furthermore, it is proved to be valid that the proposed scheme is insensitive to the RF signal phase drift and the MZM bias drift, which demonstrates a relatively higher stability.

Simultaneous clock recovery and demultiplexing of a 320 Gb/s OTDM system using an optoelectronic oscillator based on cascaded MZM and PolM

An improved optoelectronic oscillator scheme for an optical time division multiplexing (OTDM) system based on cascaded Mach-Zehnder modulator (MZM) and polarization modulator (PolM) is experimentally investigated. The system can simultaneously realize clock recovery and demultiplexing. With the MZM working at peak point to generate return-to-zero-33 optical pulses and the PolM working as an equivalent intensity modulator, a high-quality clock signal with 35-fs timing jitter is extracted from the 160-GBaud OTDM-differential quaternary phase-shift keying signal. Narrow short optical switch gates (4 ps) are also generated to demultiplex 160-GBaud signals to 40-GBaud signals. Error-free performance is achieved with 2.4-dB power penalty in the worst case.