Dual-electrode Mach-Zehnder Modulator Research Articles

Photonic generation of frequency-doubling Nyquist pulses using external modulation.

In this paper, an approach to generate frequency-doubling sinc-shaped optical Nyquist pulses based on external modulation is proposed and demonstrated. First, four flat optical frequency comb (OFC) lines are obtained after optical carrier suppression modulation in a dual-electrode Mach-Zehnder modulator. Then an optical interleaver is introduced to split the phase-locked OFC into two paths, of which one is transmitted to a dual-parallel Mach-Zehnder modulator for quadrupling RF modulation and another is applied to the remodulated signal to acquire comb lines with equal intervals. Thus, a phase-locked 12-line flat OFC with equal frequency intervals and corresponding Nyquist pulses is finally obtained, and Nyquist pulses at 2.5GHz, 5GHz, 10GHz, and 15GHz are achieved.

Photonic-assisted generation of a frequency-octupled triangular waveform based on spectrum manipulation.

A new photonic approach for generating a triangular waveform with octupled frequency, to the best of our knowledge, is presented. The core principle is the frequency octupling technique based on two cascaded dual-parallel Mach-Zehnder modulators(MZMs). A dual-electrode MZM and a single-mode fiber are subsequently applied to manipulate the signal spectrum to satisfy the characteristics of a triangular waveform. By applying a 2GHz radio frequency signal, a full-duty-cycle triangular waveform with a repetition rate of 16GHz is obtained. The high-frequency multiplying factor shows great potential in generating a cost-effective waveform. Additionally, the phase imbalance of a hybrid coupler and bias drift of the MZM have been considered in our simulation, which further verify the feasibility and stability of our proposal.

High-performance digital-to-analog conversion based on dual-electrode Mach–Zehnder modulators

A unique high-performance digital to analog conversion (DAC) approach based on dual-electrode Mach–Zehnder modulators (DEMZMs) is proposed and experimentally demonstrated. According to the modulation transfer characteristics of DEMZM, the output waveform can be edited in-line by properly adjusting the input digital signals. In our design, a 2-bit photonic DAC module can be realized by using only one DEMZM, which is biased at the minimum transmission point. The scheme is extendable, i.e., a 4-bit DAC system can be achieved by using two parallel DEMZMs, and an 8-bit system can be obtained with four DEMZMs. As few modulators are employed and the system configuration is simplified, the proposed approach can greatly improve the bit resolution with less complexity. A proof-of-concept experiment of a 4-bit DAC system is successfully carried out, which fully verifies the feasibility of the proposed approach. Moreover, the system performance in terms of integral nonlinearity and differential nonlinearity is also discussed. The proposed scheme provides a potential solution for high-bandwidth and high-resolution photonic DAC.

Comparative analysis of microwave photonic links based on different modulators using polarizers

This paper provides an overview of linearization of two different microwave photonic links based on phase modulator and dual-electrode Mach–Zehnder modulator. It takes into account the problem of intermodulation distortion which can severely degrade the performance of the system. Spurious free dynamic range has been analyzed through numerical and simulation for both the modulator links which are linearized using mixed polarization. Improvements of 7.3 dB and 15.1 dB are found in SFDR using polarizers in phase and Mach–Zehnder modulator, respectively.

Modulation Index and Phase Imbalance of Dual-Sideband Optical Carrier Suppression (DSB-OCS) in Optical Millimeter-Wave System

This paper presents a Dual-sideband Optical Carrier Suppression (DSB-OCS) technique which is used to generate an optical millimeter-wave (mm-wave) signal in radio over fiber (RoF) systems. The proposed system employs a Dual-Electrode Mach-Zehnder Modulator (DE-MZM) and a carrier of 40 GHz mm-wave for data transmission through the RoF systems. Characteristics determining the performance of the system, among which are the modulation index, phase imbalance and dispersion parameters, are included. The performance evaluations of the system show that the mm-wave signal output power follows MZM’s transfer function when the modulation index is raised. Moreover, the generated optical mm-wave signal power is affected by phase imbalance and optical splitting ratio. It is observed that the optical fiber dispersion influences the DSB-OCS system by decreasing the amplitude of the mm-wave and the signal-to-noise ratio (SNR).

Photonic compressive sensing of sparse radio frequency signals with a single dual-electrode Mach-Zehnder modulator.

A novel approach to realizing compressive sensing (CS) of sparse radio frequency (RF) signals based on photonic random demodulation (RD) is proposed. The key function of mixing the RF signal under test and the bipolar pseudo-random binary sequence (PRBS) in photonic RD is implemented with a single dual-electrode Mach-Zehnder modulator (DEMZM). By properly setting the DC bias of the DEMZM at Vπ and the voltages of the PRBS at ±Vπ/2, a pure desired multiplication term between the signal and the bipolar PRBS is obtained after an AC-coupled photodetector (PD), which not only simplifies the modeling of the CS link but also improves the recovery performance. A proof-of-concept experiment is demonstrated where a sparse signal with spectral components of 500 MHz and 950 MHz is successfully identified with a compression ratio of 20. Simulation results are also given to show the advantage of the given photonic CS scheme with bipolar random mixing.

Performance Analysis of Subcarrier Multiplexed Optical Transmission System for QPSK Data

This paper focuses on the impact of different parameters on the performance of the Subcarrier Multiplexed Optical Transmission System for the application on radio link via optical fiber. Performance results are evaluated for QPSK data format for ODSB and OSSB modulation of Microwave subcarriers with digital NRZ coded random data patterns. The four subsystems of QPSK modulators are at 400, 500, 600, 700 MHz subcarrier frequencies with frequency spacing of 100 MHz. The power of subcarriers is decreasing with increasing the link distance due to dispersion and attenuation. By using dispersion compensation fiber, the link distance has been enhanced from 100 km to 240 km successfully. The impact of chromatic dispersion has been reduced in OSSB by using dual-electrode MZM. The constellation diagram also confirms that the phase of the signal after traveling through the link is changing due to dispersion. The phase is the same for subcarrier 600 MHz & 700 MHz for ODSB and OSSB in QPSK SCM. The impact of linewidth and responsivity on SNR has also analyzed to evaluate the performance. It is concluded that the maximum SNR is decreasing with increase in the linewidth of laser source and increasing with the increase in responsivity of PIN diode for the same fiber length in SCM transmission.

Mitigating the Effects of Non-Linear Distortion Using Polarizers in Microwave Photonic Link

Abstract A scheme to suppress nonlinear intermodulation distortion in microwave photonic (MWP) link is proposed by using polarizers to compensate inherent non-linear behavior of dual-electrode Mach-Zehnder modulator (DE-MZM). Insertion losses and extinction ratio have also been considered. Simulation results depict that spurious free dynamic range (SFDR) of proposed link reaches to 130.743 dB.Hz2/3. A suppression of 41 dB in third order intermodulation distortions and an improvement of 15.3 dB is reported when compared with the conventional link. In addition, an electrical spectrum at different polarization angles is extracted and 79 ∘ 79^\circ is found to be optimum value of polarization angle.

Tunable OEO-based photonic RF receiver with image frequency rejection.

A tunable optoelectronic oscillator (OEO)-based photonic radio frequency (RF) heterodyne receiver with the capability of image frequency rejection is proposed and experimentally demonstrated. The OEO incorporating a dual-electrode Mach-Zehnder modulator (DEMZM) operates as a high quality local oscillator (LO) and a broadband mixer simultaneously, with one electrode port of the DEMZM used for the feedback of the generated LO signal and the other port for receiving external RF signals. Two channels of immediate frequency (IF) signals can be achieved in optical domain by beating the +1-order sideband of LO with the +1-order sideband of input RFs and beating the -1-order sideband of LO with the -1-order sideband of input RFs correspondingly. Through setting the bias angle of the DEMZM at π/4 or 5π/4 and quadrature combining of the two channels of the IF signal, the combined IF signal down-converted from the target RF signal gets enhanced due to the in-phase sum of two channels, while the combined IF signal down-converted from the image frequency can be rejected due to out-of-phase sum of two channels. In the experiment, the input RF signals with operating frequency range from 8.85 to 14.85GHz are successfully received with the image rejection ratio reaching 42.6dB, and the spurious free dynamic range of the system is better than 94.8 dB Hz2/3.

Direct-Detection OFDM Transmission Using Four-State Chirp Control With a Dual-Electrode MZM for Dispersion Compensation

We discuss a four-state chirp-control scheme using a dual-electrode Mach–Zehnder modulator to compensate dispersion-induced RF power fading when employing direct-detection-based orthogonal-frequency-division-multiplexed (OFDM) signals. We numerically confirm that in contrast to the previously proposed parallel transmitter employing an intensity/phase modulator, four-state chirp control can flatten frequency response and make the total performance uniform even though its structure is significantly simplified. To demonstrate this, we successfully transmitted a 20-GHz OFDM signal over an 80-km single-mode fiber using four-state chirp control, achieving a line bit rate of 78.41 Gb/s even in the presence of chromatic dispersion.

Ultraflat and broadband optical frequency comb generator based on cascaded two dual-electrode Mach–Zehnder modulators

A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM). The first DE-MZM can generate a four-comb-line OFC, then the OFC is injected into the second DE-MZM as a carrier, which can increase the number of comb lines. Our modified scheme finally can generate a broadband OFC with high flatness by simply modifying the electrical power and the bias voltage of the DE-MZM. Theoretical analysis and simulation results reveal that a 16-comb-line OFC with a frequency spacing that two times the frequency of the RF signal can be obtained. The power fluctuation of the OFC lines is 0.48 dB and the unwanted-mode suppression ratio (UMSR) can reach 16.5 dB. Additionally, whether the bias drift of the DE-MZMs has little influence on the power fluctuation is also analyzed. These results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness.

An 80 Gbps multi-band access radio over fiber link with single side band optical millimeter-wave dispersion-tolerant transmission without FBG and optical filter

We are presenting a new low-cost Single Sideband (SSB) modulated Radio-over Fiber (RoF) communication system for millimeter (mm)-wave multiband wireless communication at the frequencies of 40 GHz, 80 GHz and 120 GHz. Its principle lies in the Carrier Suppressed modulation through a nested dual electrode Mach–Zehnder Modulator (MZM) and product modulator based baseband signal decomposition. In this novel method, the optical signal is decomposed into different SSB signals using a power splitter and product modulators at the base station. This proposed method uses a different technique for a baseband signal decomposition from the existing method. The proposed signal decomposition technique has reduced the nonlinearities due to the FBGs. The proposed method is compared with the existing method in terms of BER, data rate and OSNR. The simulation results disclose that our proposed scheme outperforms the existing methods at a higher data rate of 80 Gbps with a minimum BER and privileged Q factor.

Optical Nyquist pulse generation by using a dual-electrode Mach-Zehnder modulator.

We demonstrate a simple and efficient optical Nyquist pulse generation by using a dual-electrode Mach-Zehnder modulator (MZM) driven by a combination of fundamental and second-harmonic RF signals. The method is based on a raised-cosine-shaped time filter and time lens created in the MZM under operation conditions given by a simple equation. Optical Nyquist pulses with a roll-off factor of 0.52 and intrinsic conversion efficiency of 37% are experimentally confirmed. Numerical analyses indicate that the roll-off factor can be moderately controlled down to ∼0.3 by increasing relative strength of fundamental RF signals.

Full-duplex hybrid PON/RoF link with 10-Gbit/s 4-QAM signal for alternative wired and 40-GHz band wireless access based on optical frequency multiplication

A novel full-duplex hybrid passive optical network/radio over fiber (PON/RoF) link with 10-Gbit/s 4-ary quadrature amplitude modulation (4-QAM) signal for alternative wired and wireless converged access is proposed. In the central station (CS), optical frequency multiplication (OFM) is implemented to generate millimeter- wave (mm-wave) band optical carrier with three tones via a dual-electrode Mach-Zehnder modulator (DE-MZM). The downlink QAM baseband signal is modulated on one sideband via an optical I/Q modulator. At the hybrid optical network unit (HONU), the downlink converged signal is routed into different receiver modules to achieve wired or wireless access. Moreover, the centralized lightwave separated from the downlink is reused as the uplink optical carrier for either wired or wireless access, and modulated by the baseband or mm-wave data of the uplink alternatively. Since the HONU is free from the laser source, the system complexity and cost are reduced. The simulation results show that our proposed full-duplex hybrid PON/RoF link for the alternative wired and wireless access maintains good performance even when the transmission link with standard single mode fiber (SSMF) is extended to 30km.

Performance evaluation of optical OFDM in direct detected systems based on MZM bias and drive voltages

The impact of DC bias and the RF drive voltage of the dual electrode Mach Zehnder Modulator (DE-MZM) on the transmission performance of optical orthogonal frequency division multiplexing (O-OFDM) direct detected systems is analyzed theoretically and verified by simulation. Selection of optimum bias and drive voltage is necessary to minimize the optical signal to noise ratio (OSNR) requirements and the non-linear distortions in the fiber transmission. In this paper, we compare MZM modulation techniques such as double sideband full carrier and single sideband (SSB) [biased at quadrature and minimum power transmission (MPT) point] with a novel modified SSB OFDM technique. To the best of our knowledge for the first time, a mathematical model for above modified SSB technique is developed to evaluate the OSNR requirement, chromatic dispersion of the fiber, spectral efficiency and the receiver sensitivity against other modulation techniques. Our results show that the modified SSB technique provides high spectral efficiency, receiver sensitivity and low chromatic dispersion against other the modulation techniques, while the one biased at MPT minimizes the OSNR requirements.

SFDR evaluation for multi-user single side band RoF system including intermodulation effect

A single sideband (SSB) radio-over-fiber (RoF) system based on a dual-electrode Mach–Zehnder modulator has been studied including the effects of third-order intermodulation distortion (IMD3) to measure the spurious-free dynamic range (SFDR) of the RoF system. A theoretical analysis is given and simulation has also been carried out. SNDR fluctuates within 6.2 dB range for high input power values due to fiber dispersion. Also, the power of intermodulation product terms increases greatly at high input RF power. The results show the SFDR of 124.854 dB Hz2/3 for the considered system.

High flatness optical frequency comb generator based on the chirping of modulators

A novel scheme for generation of an optical frequency comb (OFC) based on the chirping of two cascaded modulators is proposed. The first modulator is a dual-electrode Mach–Zehnder modulator (MZM), while the other modulator is an integrated MZM composed of two parallel MZMs that increases the number of comb lines. Our modified scheme can generate a large number of frequency lines with excellent flatness by simply modifying the chirp factor, and it is shown that up to 54 frequency lines could be observed. Theoretical analysis and simulation results show that under the variety of conditions that can be used in this scheme, the power fluctuations of the OFC lines are less than 0.5 dB in all cases; these results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness. Additionally, our modified scheme has the merit of tunable frequency spacing, which is practical for experimental realization of the OFC.

Selective delivery of broadband wireless and wired services in an integrated ROF-PON system using dual-sideband optical carrier suppression

Selective delivery of gigabit-per-second wireless and wired services is demonstrated in an integrated fiber-wireless access network using the millimeter-wave (mm-wave) radio-over-fiber (RoF) system employing the dual-sideband optical carrier suppression technique. A dual-electrode Mach-Zehnder modulator is used in this technique to generate 40 GHz carrier to distribute 1.25 Gbps data via direct modulation (DM) over a 20 km RoF system. The results show that selective signal delivery can be achieved using a low-cost DM laser diode drive current of 20 mA. The advantage of the proposed system is that it provides versatility to control the gigabit-per-second (Gbps) signal delivery in an integrated ROF-PON system with a common high frequency oscillator shared for the whole system. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1768–1773, 2016

Efficient Photonic Microwave Mixer With Compensation of the Chromatic Dispersion-Induced Power Fading

The conversion gain of a photonic microwave mixer is often limited by the large carrier of the modulated optical signal, and may be further deteriorated by the chromatic dispersion-induced power fading after transmission over fiber. To solve this problem, an efficient photonic microwave mixer based on a dual-electrode Mach–Zehnder modulator is proposed in this paper. The carrier of the modulated optical signal is suppressed by bidirectional use of the modulator in a Sagnac loop, and a 21.9-dB improvement of the conversion gain is achieved in the experiment. In addition, the frequency response of the mixer after transmission over fiber can be tuned by simply adjusting the direct current bias of the modulator. This feature is applied to compensate the dispersion-induced power fading of the mixing product. In the proof of concept experiment, a vector signal centered at 2.4 GHz is up-converted to 16 GHz and transmitted over 25-km single mode fiber. After power compensation, the constellation diagram, error vector magnitude and receiver sensitivity are significantly improved, and are almost as good as that without fiber transmission.

Simultaneous generation of 3G and millimeter-wave signals using a dual-electrode MZM in ROF systems

A novel radio-over-fiber (ROF) scheme to simultaneously generate and transmit the 3rd generation telecommunication (3G) and millimeter-wave (MMW) signals by using a single dual-electrode Mach-Zehnder modulator (MZM) is proposed. There is no apparent nonlinearity induced by the ROF system. By employing this analog ROF signal transmission technique, highly transparent fiber-wireless convergence networks can be realized, which are ideal for multi-standard wireless system operation.