Dual-drive Mach-Zehnder Modulator Research Articles

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.

Subcarrier multiplexed radio over fiber system with optical single sideband modulation

Abstract A subcarrier multiplexed radio over fiber (RoF) system using optical single sideband (OSSB) modulation is proposed. OSSB modulation reduces the bandwidth requirements and also combats the radio frequency (RF) power fading issue due to the dispersive effects in optical fiber. Subcarrier multiplexing (SCM) is a technique used to transmit multiple RF signals through the same optical fiber to utilize its large bandwidth. A theoretical analysis showed that OSSB generation with a number of subcarriers can be done by Hilbert transform method employing a single dual drive Mach–Zehnder Modulator (MZM). This technique is very relevant in the emerging 5G standards which require accesses of multiple standards simultaneously (5G, LTE, and Wi-Fi). This paper demonstrates a low cost solution of OSSB-RoF system and more effective utilization of the spectrum. Simulations results showing satisfactory reception of signals up to 50 km.

Multi-Frequency Phase-Coded Microwave Signal Generation With an Increased Number of Frequencies

A photonics-based approach to multi-frequency phase-coded microwave signal generation is proposed with an increased number of frequencies. Two microwave reference signals are sent to one arm of a dual-drive Mach-Zehnder modulator (DD-MZM), whereas the binary coding signal is sent to the other arm of the DD-MZM. The optical output of the DD-MZM is detected in a photodetector. Due to the nonlinearity in the electro-optic modulation, the generated photocurrent contains the nonlinear intermodulation products of the two reference signals, which are all modulated by the coding signal. An experiment is performed. Multi-frequency phase-coded microwave signals from 1 to 24 GHz with more than twelve different frequency components are generated. The performance of the generated signal including phase recovery accuracy and pulse compression capability is also verified.

Bias-Free Silicon-Based Optical Single-Sideband Modulator Without 2nd-Order Sideband

In this paper, a bias-free silicon optical single-sideband (OSSB) modulator without 2nd-order sideband is proposed and theoretically investigated. The proposed modulator is based on a dual-drive Mach-Zehnder modulator (DDMZM) and silicon photonics platform. In the proposed structure, a piece of silicon waveguide is used in one of the arms of the unbalanced DDMZM which acts as a bias for the modulator. So, the operating point of the modulator can be tuned by adjusting the optical wavelength. Analytical models for all the components in the structure are derived and closed-form expressions are found for optical transmission, optical spectrum, etc. Modulator nonlinear behavior under small and large signal modulation is discussed. Conditions on the optical wavelength to have an OSSB modulated signal with/without 2nd-order sideband are found. It has also shown that optical carrier-to-sideband ratio (OCSR) can be tuned by adjusting the applied voltage. By proper adjusting the applied voltage, suppressed carrier or equal carrier to the first sideband can be obtained in OSSB modulator without 2nd-order sideband. Analytical results are verified by simulations and previously reported measurement data. The proposed analytical model is a general model that can be used for any nonlinear electro-optic modulators such as phase and absorption modulators.

Dual-Channel Phase-Tunable Down Converter With LO Frequency Doubling

A dual-channel phase-tunable down converter with local oscillator (LO) frequency doubling is proposed by using a commercial dual-polarization dual-drive Mach-Zehnder modulator (DP-DMZM) and a specially designed dual-channel phase modulator (DP-PM). A radio frequency (RF) signal is injected to one of sub-DMZMs in the DP-DMZM, and a LO signal modulates another sub-DPMZM. An optical bandpass filter (OBPF) is used to filter out the unwanted sidebands, and only the +2nd-order LO and +1st-order RF sidebands are remained and output to the DP-PM. The DP-PM is composed by two parallel PMs with different modulation efficiency between orthogonal polarizations. Each bias voltage of the DP-PM can linearly vary the phase shift between the RF and LO modulated optical sidebands. After detected by a photodetector, the down converted signal with doubled LO frequency and dual-channel phase shift can be obtained. The principle of the proposed link is verified and the experiments are carried out. The experimental results show that the average spur suppression ratio of the down-converted signals is 29.15 dB. The spurious-free dynamic range (SFDR) of the down converter is 103.94 dB·Hz2/3. The continuous and dependent dual-channel phase shift with the full range of 360° can be experimentally achieved. The proposed down converter integrates multiple function in a link, and has the merit of high electrical purity and convenient operation.

Photonic full-range phase shifter with simultaneous tunable frequency multiplying capability based on a DMZM

In this paper, a novel microwave photonic full-range phase shifter with simultaneous frequency-multiplying capability is proposed. The main device is a dual-drive Mach–Zehnder modulator (DMZM) embedded in a Sagnac loop. Under the assistance of two electrical phase shifters (EPS) and a following polarizer (Pol), the optical carrier is eliminated with desired phase tunable carrier-suppressed double-sideband (CS-DSB) signal reserved. So after photoelectric conversion, the frequency-multiplied phase tunable signals are generated. The frequency multiplication factor (FMF) switching and phase tuning operation of multiplied signals can be achieved easily by adjusting the corresponding EPS. The simulation results show that the proposed structure driven by a 10 GHz RF signal can generate a frequency-doubled signal (20 GHz) or frequency-quadrupled signal (40 GHz) that features full-phase tunable range and flat power response. What is more, the proposed phase shifter has a relatively good robustness to the non-ideal factors, large frequency operation range and good frequency tunable capability.

Microwave Photonic Mixer Using DP-DDMZM for Next Generation 5G Cellular Systems

ABSTRACT Microwave frequency down-conversion at 4.5 GHz using proposed photonic mixer is analyzed on various aspects in this manuscript. The proposed microwave photonic down-converter employs a Dual-Parallel Dual-Drive Mach–Zehnder Modulator (DP–DDMZM) that makes the system more compact than previously reported photonic mixers. Suppressed carrier modulation technique is used to increase the sideband power, which improves conversion efficiency by 20 dB as compared to dual-series modulator based mixer. To examine the performance of the proposed system for 5 G digital data transmission and reception, dispersion analysis over the length of fiber is performed. Furthermore, its performance for various digital modulation schemes is discussed.

High-Resolution Optical Microresonator-Based Sensor Enabled by Microwave Photonic Sidebands Processing

We theoretically and experimentally investigate the high-resolution performance of an optical microresonator-based sensor scheme incorporating microwave photonic sidebands processing. The optical power and phase profiles of the modulation sidebands are equalised to achieve ultrahigh-rejection RF notches with ultranarrow tip width in the electrical spectrum, where environmental changes are detected via the shift in the measurand dependent frequency of the ultradeep RF notch. The proposed structure demonstrates the ability to realise ultrahigh resolution sensing for any optical microresonator response with arbitrary coupling conditions, thus relieving strict fabrication requirements. Furthermore, factors that can disrupt the matching conditions during the dynamic sensing process are also discussed and resolved with the aid of the feedback compensation scheme which increases the resilience of the system against these interferences. As a proof-of-concept, a proposed sensing configuration comprising a dual-drive Mach–Zehnder modulator and a silicon-on-insulator microdisk resonator is demonstrated for temperature sensing. The measured temperature sensitivity is around 8.87 GHz/°C and a high rejection ratio of over 60 dB of the RF notch is successfully maintained with an ultranarrow notch tip width that makes up only 0.003% of the whole sensing operation range of 35 GHz. The temperature resolution is significantly improved by about 2500 times compared to the conventional method of direct monitoring of the optical spectrum.

Hundred megahertz microwave photonic filter based on a high Q silicon nitride multimode microring resonator

Narrowband microwave photonic filters based on a microring resonator are difficult to achieve because low cavity loss and low coupling loss should be satisfied simultaneously. Here, a high Q (∼2.6×106) multimode microring resonator is proposed to achieve an ultra-narrow band tunable microwave photonic filter. Combining the ultra-low loss of the silicon nitride waveguide and the ultra-low coupling coefficients of the multimode ring resonator, very narrow optical bandwidths between 72.5 MHz to 275 MHz were obtained for different order modes, which match the simulation results well. Furthermore, by introducing the two switchable modulation methods supported by the dual-drive Mach–Zehnder modulator, we achieved a narrowband passband/stopband switchable microwave photonic filter, whose 3 dB bandwidths are 180 MHz and 120 MHz, respectively. The filter frequency can be tuned from 2 ∼ 18 GHz by altering the laser wavelength, and a high out of band RF rejection ratio about 27 dB was obtained for the passband filter due to the high-quality factor. Besides, a high RF rejection ratio of about 51 dB was achieved for the stopband filter by using the RF cancellation technology.

Ultra-wideband doublet signal generation with tunable notch band based on delay-line filter

ABSTRACT A novel and simple scheme to generate Ultra-wideband (UWB) doublet signal with tunable notch band based on a tunable delay-line filter is presented. The first-order differentiation is realized by a dual-drive Mach–Zehnder modulator (DD-MZM), which differentiates the Gaussian pulses to the monocycle pulses. Subsequently, the UWB monocycle pulses are transmitted to an optical delay-line filter implemented by a balanced photo-detector and a tunable delay line for both differentiation and photodetection. Consequently, the desired UWB doublet signal can be obtained with a 10-dB bandwidth of 8.75 GHz. Besides, the polarity reversibility of the generated doublet signal is demonstrated by changing the bias voltage of the DD-MZM. Moreover, the desired notch can be introduced in the generated frequency spectrum to eliminate the interference between the existing narrowband systems and the UWB systems. And the tunability of the band-notched position is implemented by simply adjusting the delay time of the delay-line filter. The feasibility of the presented scheme is investigated by mathematical models and simulations.

A Photonic-Based Wideband RF Self-Interference Cancellation Approach With Fiber Dispersion Immunity

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity is proposed. A dual-drive Mach–Zehnder modulator (DD-MZM) in a dual-polarization binary phase-shift keying (DP-BPSK) modulator is used as an optical interference canceller, which cancels the self-interference from the received signal and generates two optical sidebands of the signal of interest (SOI) in the received signal. Another DD-MZM in the DP-BPSK modulator is used to provide a pure optical carrier. By combing the optical signals from the two DD-MZMs and beating them at a photodetector, the SOI can be recovered. In addition, if the SOI needs to be transmitted in optical fiber, the power fading effect caused by fiber dispersion can be overcome by simply introducing a proper phase shift to the pure optical carrier. An experiment is performed. RF self-interference cancellation (SIC) with a bandwidth up to 2 GHz is experimentally demonstrated and a cancellation depth of more than 20 dB is achieved even if the bandwidth of the self-interference is about 2 GHz. The SIC with 25-km fiber transmission and the RF power of the SOI after 25-km fiber transmission are also demonstrated, which proves that the SIC has very good immunity to fiber dispersion and the SOI can be transmitted without power fading.

Photonic Generation of Dual-Chirp Microwave Waveforms Based on a Tunable Optoelectronic Oscillator

We propose a photonic scheme to generate dual-chirp microwave waveforms based on a widely tunable optoelectronic oscillator (OEO) using a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM). The upper DDMZM is properly biased to serve as a phase modulator and further constructs OEO loop to generate radio frequency (RF). The lower DDMZM injected by the combination of the RF and a single-chirp signal is utilized to generate a dual-chirp microwave waveform with an arbitrarily tunable central frequency. The RF from the OEO replaces external millimeter-wave source in our scheme, which improves the phase noise performance of RF in high-frequency range, alleviates the complexity of the system, and increases the possibility of integration. Dual-chirp microwave waveforms centered at 10 GHz with a bandwidths of 0.4 GHz and 1 GHz, and centered at 15 GHz with a bandwidth of 0.4 GHz are successfully generated. The proposed scheme is theoretically analyzed and experimentally demonstrated.

Flat optical frequency comb generation employing cascaded dual-drive Mach-Zehnder modulators

The generation of flat optical frequency comb lines (OFCL) of 10 GHz frequency spacing is proposed and demonstrated theoretically employing Dual-Drive Mach Zehnder modulators (DD-MZMs). A theoretical analysis is carried out for ultra flat spectra due to single stage and cascading of DD-MZMs, which is confirmed by simulative results. Employing single DD-MZM, 19 OFCL with flatness 0 dB and 39 OFCL with flatness ≤ 1 dB have been generated at 11.16 Vπ−11.66 Vπ modulation voltages. 37 comb lines are obtained with 0 dB flatness and 49 OFCL with flatness ≤ 0.5 dB using two cascaded dual drive MZMs at 5.61 Vπ–6.11 Vπ–5.61 Vπ, 6.11 Vπ modulation voltages. Combining four DD-MZMs, 34 & 54 OFCL with flatness 0 dB and ≤ 0.5 dB is generated at modulation voltages 2.78 Vπ and 3.33 Vπ. Large numbers of OFCL with very high flatness are achieved by applying low RF voltage.

Dual-Drive Mach-Zehnder Modulator-Based Single Side-Band Modulation Direct Detection System Without Signal-to-Signal Beating Interference

Kramers-Kronig (KK) receiver based optical single sideband (SSB) direct detection (DD) systems have been extensively investigated to cope with signal-to-signal beating interference (SSBI) for long-reach optical interconnect and 400G ZR. In this paper, we analyze the principle of dual-drive Mach-Zehnder modulator (DDMZM)-based SSB modulation due to its low cost compared with IQ modulator. We find that SSBI does not exist in back-to-back (BTB) after square-law direct detection, and electrical dispersion compensation (EDC) cannot be realized at the transmitter due to the nonlinear modulation of DDMZM. In our proposed scheme, Cartesian to Polar conversion (CPC) is used to achieve the linear modulation of DDMZM, then pre-EDC is achievable. Signal construction operation is applied to generate a target signal avoiding SSBI in DDMZM-based SSB modulation with direct detection, thus KK algorithm is not necessary both in BTB and after fiber transmission with pre-EDC, and the computation complexity of the receiver can be effectively reduced. In the simulation results of 25 GHz SSB Discrete Fourier transform spread discrete multi-tone (DFT-S DMT), the BER of our proposed scheme and conventional DDMZM scheme with optical signal-to-noise ratio (OSNR) of 26 dB are 1.2 × 10−3 and 1.7 × 10−2, respectively, after 80 km standard single mode fiber (SSMF) transmission with pre-EDC. The simulation results show that our proposed scheme is better than conventional DDMZM scheme. Although it is still inferior to the conventional IQ scheme with KK algorithm, the computation complexity of CPC is much lower than KK algorithm as it saves the numbers of adders and multipliers by the factors of 119 and 62, respectively, and reduces the memory size by a factor of 4.3.

High-Performance Fully Integrated Silicon Photonic Microwave Mixer Subsystems

We experimentally demonstrate two silicon photonic based mixer subsystems for applications in next gen fronthaul networks, defense, and communications for space, avionics, and vehicles. The mixer subsystems leverage emerging integrated microwave photonics technology through the AIM Photonics foundry. Our work demonstrates the potential for full integration of spectrally agile functions to enable seamless upconversion and downconversion over wide instantaneous bandwidths. Characterization of the frequency converting architectures focuses on analog metrics including gain, linearity, and noise figure. The first architecture represents the simplest architecture for practical frequency conversion on-chip using a single dual-drive Mach–Zehnder modulator and single photodetector. The second architecture, using dual parallel single-drive Mach–Zehnder modulators and balanced detection, represents the first silicon photonic downconverter with electrical-in, electrical-out frequency conversion fully on-chip; additionally, this architecture demonstrates the widest bandwidth reported among mixers of similar integration level on any material platform. Simulations using characterized parameters of components are performed and demonstrate accurate prediction of analog metrics for both mixer architectures. Using these simulations, we predict the performance of improved, fully integrated implementations of the characterized architectures using state-of-the-art platforms, demonstrating that high performance integrated microwave photonic frequency conversion is achievable.

Novel RF-source-free reconfigurable microwave photonic radar.

A novel reconfigurable microwave photonic (MWP) radar has been proposed and experimentally demonstrated. At a transmitting end, a microwave signal with a large bandwidth and ultra-low phase noise is generated by a Fourier domain mode locking optoelectronic oscillator. At a receiving end, photonics-based de-chirp processing is implemented by phase-modulating light waves in a dual-drive Mach-Zehnder modulator and mixing the modulated light waves at a photodetector. Without the requirement of external RF sources, the developed photonics-assisted programmable radar is capable of generating and processing microwave signals with adjustable format, bandwidth and central frequency. The proposed radar working from X to Ku band with an instantaneous bandwidth of 2 GHz is demonstrated. The reconfiguration of the radar is theoretically analyzed. The tunability of radar bandwidth and central frequency is investigated. Microwave imaging of a pair of trihedral corner reflectors based on the developed MWP radar is achieved.

High-speed SSB transmission with a silicon MZM and a soft combined artificial neural network-based equalization.

We experimentally demonstrate high-speed metro-scale optical transmission of a single sideband (SSB) 4-ary pulse amplitude modulation (PAM-4) signal based on a silicon photonic dual-drive Mach-Zehnder modulator (MZM). We propose a novel, to the best of our knowledge, artificial neural network (ANN) structure of soft combined ANN (SC-ANN) to compensate for both linear and nonlinear impairments of the signal. SC-ANN obtains the enhanced performance by averaging the outputs of conventional ANN with different sizes. With the help of the SC-ANN, we achieve a 320 km standard single-mode fiber (SSMF) transmission of 184 Gb/s (92Gbaud) PAM-4 with a bit-error rate (BER) below the 20% soft-decision forward error-correction (SD-FEC) threshold of ${2.4} \times {{10}^{ - 2}}$2.4×10-2, and the optical signal-to-noise ratio (OSNR) penalty is only 0.3 dB compared to the back-to-back (BTB) results.

Angle-of-arrival estimation of a microwave signal based on optical interference and stimulated Brillouin scattering

We propose an optical approach to estimate the angle of arrival (AoA) of a microwave signal. The microwave signal and its phase-shifted replica received from separated antenna elements are applied to a null-biased dual-drive Mach–Zehnder modulator. An optical loss resonance at the optical carrier is introduced by stimulated Brillouin scattering in optical fiber. By measuring the resultant optical power, we can obtain the phase difference, from which the AoA of the incoming microwave signal can be determined. An experiment is carried out, which exhibits that phase measurement errors are <1.86 deg with a phase difference from 9 deg to 162 deg.

Photonics-Based CW/Pulsed Microwave Signal AOA Measurement System

A new microwave photonic system for determining the angle of arrival (AOA) of a continuous wave (CW) or pulsed microwave signal is presented. It is based on a dual-polarisation dual-drive Mach–Zehnder modulator followed by an optical notch filter for carrier suppression. Two orthogonal-polarised carrier- suppressed optical signals are detected by low-frequency photodetectors that generate two DC voltages. An incoming microwave signal AOA can be obtained from the ratio of the two DC voltages, without the need of a calibration procedure or measuring the incoming microwave signal power level, which are required in previously reported structures. The proposal system can be incorporated with a conventional radar receiver front end consists of mixers and filters, for measuring the AOA of a pulsed microwave signal. Experimental results demonstrate 0°–63° AOA measurement with less than 2° errors for an input microwave signal having different frequencies and different power levels.

High-speed frequency-hopping signal generator with a stimulated Brillouin scattering-based optoelectronic oscillator

We propose and demonstrate an approach to generating a frequency-hopping (FH) microwave signal using an optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS). An SBS-based OEO is utilized to generate pure microwave signals as local frequency signal, and a dual-drive Mach–Zehnder modulator is employed to generate the FH signal. During the experiment, the local frequency generated by the OEO is 9.2 GHz with a power of 0 dBm and the FH signal hopping between 9.2 and 18.4 GHz is generated with FH speed up to 2 GHz.