Single-drive Mach-Zehnder Modulator Research Articles

Flexible Multi-Band Linearly Frequency Modulated Signal Generation Using a Single-Drive Mach–Zehnder Modulator

A photonic method for multi-band linearly frequency-modulated (LFM) signal generation is proposed and demonstrated experimentally. An intermediate-frequency (IF) LFM signal and a single-tone radio frequency (RF) signal are first coupled by an electrical coupler. Then the coupling signal is used to drive a single-drive Mach–Zehnder modulator (SDMZM). By properly setting the frequencies and corresponding modulation indices of the IF LFM signal and RF signal, the multi-band LFM signal can be generated. The number of sub-bands can be adjusted by simply controlling the direct current bias of the SDMZM. The proposed method features simple structure and flexible tunability, which is promising for modern multi-band radar systems.

Optical Frequency Comb Generator Employing Two Cascaded Frequency Modulators and Mach–Zehnder Modulator

Optical frequency combs (OFCs) are extensively used in spectroscopy, range finding, metrology, and optical communications. In this paper, we propose a novel technique to achieve a flat OFC by serially cascading two frequency modulators (FMs) followed by a single-drive Mach–Zehnder modulator (MZM). The modulators are driven by a sinusoidal RF signal of frequencies fm, fm2, and 2 fm GHz, respectively. With our proposed approach (fm), an optical spectrum of 71 subcarriers spaced at 4 GHz is realized within a power fluctuation of ∼2 dB. The proposed method is also tested for fm = 16 GHz, showing that this approach can work in all scenarios with lower power fluctuations. In addition, we also studied the impact of the phase of the RF signal on the power variation of the OFC spectrum. A theoretical investigation of the ultra-flat spectrum generated by cascaded FMs and MZM is conducted, and the results of simulations support the findings. The simulation results demonstrate good performance, allowing for the application of our proposed approach in next-generation optical networks.

Symmetry-Tunable Full-Duty Triangular-Shaped Waveform Generation Using a Simple Single-Drive Mach-Zehnder Modulator

A novel and simple photonic approach for generating symmetry-tunable full-duty triangular-shaped microwave waveforms is proposed and experimentally demonstrated. In this approach, a simple commercial single-drive Mach-Zehnder modulator (MZM) is adopted and driven by the radio frequency (RF) input. By properly presetting the RF modulation index and simply adjusting the direct current (DC) bias voltage of MZM, the full-duty triangular-shaped microwave waveforms with self-defined symmetrical coefficients can be obtained. A complete theoretical analysis on operation principle is presented and a proof-of-concept experiment is carried out. The full-duty triangular-shaped waveforms with tunable symmetrical coefficients at the repetition rate of 5 GHz are successfully generated. This approach features simple architecture, less variables, excellent reconfigurability and integrable capability, which are highly desired for the high-performance triangular-shaped waveform generator.

Flexible Microwave Waveforms Synthesis Based on Wavelength Sensitive Bias Shift of a Mach–Zehnder Modulator

A new scheme of arbitrary microwave waveform generation based on one single-drive Mach–Zehnder modulator (MZM) is proposed. Due to the characteristic of the wavelength-dependent bias shift in a MZM, two light fields with different wavelength can carry two sets of modulation components and contribute the desired waveforms through both of the Fourier synthesis and time-domain synthesis. Thanks to plentiful and controllable harmonics generation, some challenging waveforms generation, such as parabolic waveform, sawtooth waveform and frequency doubling triangular waveform, can be achieved, which are verified by the theoretical analysis and experimental results. This method exhibits not only more flexible waveform generation ability, but also the advantages of simple configuration, easy operation and high efficiency of bandwidth utilization.

Frequency-Modulated Chirp Signals for Single-Photodiode Based Coherent LiDAR System

In this paper, we investigate two categories of linear frequency-modulated chirp signals suitable for single-photodiode based coherent light detection and ranging (LiDAR) systems, namely, the frequency-modulated continuous-wave (FMCW) single-sideband (SSB) signal and the amplitude-modulated double-sideband (DSB) signal, and compare their achievable receiver sensitivity performance. The DSB signal requires a simpler transmitter design, as it is real-valued and can be generated using a single-drive Mach-Zehnder modulator (MZM), while the SSB signal, which is frequency/phase modulated, requires an in-phase and quadrature modulator (IQM)-based transmitter. A theoretical analysis of direct-detection (DD) beating interference (BI) especially the local oscillator (LO) beating with itself, known as LO-LO BI, is presented. Both Monte Carlo simulations and experimental demonstrations are carried out. Good agreement between simulations and experiments is achieved. In comparison with the SSB system, the DSB signal-based system is affected by laser phase noise-induced power fluctuation, and also suffers a significant sensitivity penalty due to nonlinear LO-LO BI. A spectral guard band for mitigating LO-LO BI is necessary for the DSB signal, achieved at the expense of requiring a larger electrical bandwidth. In system tests with a delay line of 385 m, the SSB signal outperforms the DSB signal with a 10 dB better receiver sensitivity in the case with a guard band, and 25 dB better sensitivity without a guard band.

Flat frequency comb generation employing cascaded single-drive Mach–Zehnder modulators with a simple analogue driving signal

A scheme, using two-single drive Mach–Zehnder modulators (SD-MZMs) to generate flat optical frequency comb (OFC) by an analogue driving signal, is experimentally demonstrated. The modulator is used to add equidistant sidebands to an injected carrier continuous-wave laser centred at 1550 nm. The flatness of the comb lines is achieved by tuning the DC bias voltages supplied to both modulators. Five comb lines are tested for different frequency spacing of 8.5, 10, 11.5, and 12 GHz and show good frequency tunability. Also, the effect of increasing the radio frequency (RF) modulation signal power on the number of comb lines is investigated. A total of 5 comb lines are obtained with a repetition rate of 10 GHz and 0.77 dB flatness. The proposed system is simple and cost-effective due to the utilization of a simple Mach–Zehnder modulator structure driven by one RF signal generator.

Optical Field Reconstruction of Real-Valued Modulation Using a Single-Ended Photoreceiver With Half-Symbol-Rate Bandwidth

Heterodyne detection based on a single-ended photodetector is of great interest to simplify the receiver frontend complexity compared to a full coherent one, while retaining the ability of digital chromatic dispersion (CD) compensation. Nevertheless, single-ended heterodyne detection schemes typically require a transmitter, which has similar complexity as in coherent systems. Moreover, a receiver bandwidth equal to at least the symbol rate of the signal is required for the complex-valued signal recovery when using a single-ended photodetector. In this article, we study a novel heterodyne detection scheme, which allows to use a simple transmitter structure, and to reduce the receiver bandwidth to a value well below the symbol rate, while supporting digital CD compensation. In our experiment, a real-valued signal originates from a single-drive Mach-Zehnder modulator at the transmitter. A bandwidth-limited receiver suppresses one sideband of the incoming signal, however the receiver digital signal processing (DSP) reconstructs the missing sideband based on the Hermitian symmetry of a real-valued signal spectrum. A receiver bandwidth slightly larger than half of the symbol rate is required. With our novel DSP, we successfully recover 60 Gbaud PAM-4 signal after 80 km of fiber transmission in C-band, using 33 GHz electrical bandwidth at both transmitter and receiver, without optical filtering or amplification.

10-Gsymbol/s IM-based quantum noise encryption system modulated by a dual digital‐to‐analog converter

To attain secure fiber-optic transmissions at a high rate, a realizable scheme is proposed in this paper, that can achieve 10-Gsymbol/s quantum noise encryption based on intensity modulation. Specifically, a dual digital-to-analog converter (DAC) is used to drive a single-drive Mach–Zehnder modulator. Then, to demonstrate the advantage of this scheme, a trial of 10-Gsymbol/s single-channel transmissions over 30 km are confirmed at 4096 intensity levels. Furthermore, specific indicators that affect secure transmissions are analysed, such as the number of modulation levels and noise masking. Finally, experimental results show that a masking number of 370 is achieved to resist direct detection attacks at the 4096 signal levels. Multilevel optical signals are hidden in the quantum noise. It is also apparent that the proposed modulation method realizes highly secure fiber-optic transmission.

Photonic Generation of Triangular-Shaped Waveform With Tunable Symmetry Factor Based on Two Single-Drive Mach-Zehnder Modulator

An approach to generating triangular-shaped waveform with variable symmetry based on two single-drive Mach-Zehnder Modulator is proposed and analyzed. By setting the bias state of modulators, the rotation angle of polarization controller, phase shift of phase shifters and the modulation index of modulators properly, triangular-shaped waveforms with different symmetry can be synthesized in time-domain. The detailed theoretical analysis and simulation are given. Triangular-shaped waveforms with different symmetry factor (0%–100%) are obtained in simulation. Compared with previous scheme for generating triangular-shaped waveforms with different symmetry, the generated triangular-shaped waveform in this paper is more similar to the ideal waveform.

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.

D-Band mm-Wave SSB Vector Signal Generation Based on Cascaded Intensity Modulators

We proposed and experimentally demonstrated a novel and simple method to realize D-band millimeter-wave (mm-wave) single-sideband (SSB) vector signal generation using cascaded one single-drive Mach-Zehnder modulator (MZM) and one push-pull MZM. After the first MZM driven by a radio frequency (RF) signal of 20-GHz, an optical frequency comb (OFC) with six flat carriers was successfully generated. Using the subsequent push-pull MZM driven by 10-GHz SSB vector signals and a photodiode (PD) for detection, we finally generated D-band SSB vector mm-wave signals at frequencies of 130-GHz and 150-GHz, respectively. The experimental results are well consistent with theoretical and simulation analysis. Based on the proposed scheme, 4-Gbaud generated D-band quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16QAM) mm-wave signals were transmitted over 10-km/25-km single-mode-fiber (SMF) and 1-m wireless links. The bit-error-rate (BER) performance can reach less than 7% hard-decision forward-error-correction (FEC) threshold of 3.8 × 10−3.

Tunable microwave sawtooth waveform generation based on one single-drive Mach-Zehnder modulator.

A photonic method of sawtooth waveform generation by using one single-drive Mach-Zehnder modulator is proposed and experimentally demonstrated. Depending on the polarization-sensitive characteristic of the modulator, the modulation sidebands and optical carrier can independently exist on two orthogonal polarization directions. Therefore, the required Fourier components can be manipulated on two polarization dimensions separately, and the superposition of the orthogonal optical envelopes synthesize a sawtooth waveform in time domain. The feasibility of the scheme is theoretically analyzed. In the experiment, sawtooth waveforms with full duty cycle at 3, 5, and 8 GHz are obtained, which agree with the simulation results well.

Photonic generation of triangular-shaped waveform signal with adjustable symmetrical coefficient

ABSTRACTA configuration for triangular-shaped microwave signal generator is proposed and analysed. In the proposed model, a single-drive Mach–Zehnder modulator operated under the push–pull mode is firstly driven by a sinusoid signal. The lightwave is then split into two branches and converted by a balanced photodetector. According to the analysis, the output photocurrent contains infinite sinusoidal harmonics of the driven frequency. By adjusting three variables (modulation index, bias state and optical time delay), the power of the first three harmonics can be arbitrarily controlled. Such a property can be used in triangular-shaped microwave generation with adjustable symmetrical coefficient δ. The theory and discussion are proposed in this work. A fitting error η is defined to evaluate the waveform quality. With a defined η < 6%, the symmetrical coefficient can be adjusted within a range of 20% ≤ δ ≤ 80%.

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.

A RoF system based on polarization multiplexing and carrier suppression to generate frequency eightfold millimeter-wave

Abstract In this paper, we propose and demonstrate a RoF system based on polarization multiplexing and carrier suppression to generate frequency eightfold millimeter-wave. The proposed scheme is based on one single drive Mach-Zehnder modulator and a polarization control system. By adjusting the modulation index, two-forth sidebands can be obtained. By controlling the polarization direction, our system can generate 80 GHz frequency eightfold millimeter-wave or recover optical carrier at the base station (BS). Finally, we verified the bit error rate (BER) of received optical power in the uplink and downlink. The received power penalty of uplink and downlink via 15 km single mode fiber (SMF) are 0.13 dBm and 0.34 dBm at the BER of 1 × 10 - 9 respectively. This technology opens a new path for developments in microwave photonics.

Photonic microwave waveform generation based on dual-wavelength time domain synthesis technology

&lt;sec&gt;Microwave waveforms, such as square waveforms, sawtooth waveforms and triangle waveforms are widely used in radar communication, electronic measurement and medical imaging and so on. Using photonic microwave technology to generate arbitrary microwave waveforms has been a research hotspot.&lt;/sec&gt;&lt;sec&gt;In this paper, a photonic microwave waveform generation scheme based on dual-wavelength time domain synthesis is proposed and experimentally demonstrated. Used in this scheme mainly are two lasers, two single-drive Mach-Zehnder modulators, a wavelength division multiplexer and a tunable optical delay line. The two Mach-Zehnder modulators are respectively biased at different operating points. When two beams with different wavelengths are superimposed in the time domain, different microwave waveform outputs can be generated. Therefore, by adjusting the bias voltage and modulation depth of the modulator, the phase and amplitude of the modulated optical signal can be controlled, and finally the photonic microwave waveform is generated.&lt;/sec&gt;&lt;sec&gt;At first, the generation mechanism of square waveform, sawtooth waveform and triangle waveform are analyzed, and the comparisons among ideal square waveform, sawtooth waveform, triangle waveform and their third-order waveforms are made through the simulation analysis. It is verified that third-order waveforms become close to the ideal waveforms. Since the proposed scheme produces higher-order components, and the waveforms of the first three orders are the same as the ideal waveforms, so the scheme has good waveform generation capability. And then square waveform, sawtooth waveform and triangle waveform with a repetition rate of 2.5 GHz are successfully generated experimentally. Thus, experimental results are well consistent with the theoretical analyses. In addition, the system also has good tunable characteristics. By changing the modulation frequency of the modulator, the frequency tuning of the output photonic microwave waveforms can be realized, and square waveform, sawtooth waveform and triangular waveform with a repetition rate of 5 GHz are also experimentally achieved. The repetition rate of the generated microwave waveform is mainly limited by the bandwidth of modulator and electrophotonic detector, so the devices with higher bandwidth can be used to generate arbitrary waveform with a higher repetition rate. Therefore, the scheme has good application prospects.&lt;/sec&gt;

Generation of an ultraflat and power efficient optical frequency comb by cascading of electroabsorption and single-drive Mach–Zehnder modulator

We have investigated the theoretical and principal analysis of cascaded electroabsorption modulators (EAMs) and Mach–Zehnder modulator (MZM). We have proposed a technique to generate an ultraflat and power efficient optical frequency comb (OFC) by the serial cascading of two EAMs and one single-drive MZM. Continuous wave (CW) light source is modulated and spectrum broadened by two EAMs and MZM, respectively. Here, EAMs in cascaded mode produce ultrashort pulses followed by MZM, which is introduced to perform intensity modulation and tuned the power variation of even and odd order sidebands at the same level for obtaining a flat optical spectrum at the output. The first EAM acts as a subcarrier generator and the latter one acts as a subcarrier enhancer, which is followed by the MZM acting as subcarrier flatter. By this proposed technique, we have generated 63 subcarriers with 10-GHz spacing and within 2-dB power fluctuation. The generated OFC has a bandwidth of 630 GHz. This technique generates OFC with an appreciable power level and flattened optical spectrum, which is very much essential in dense wavelength division multiplexing and elastic optical networks.

Optical Single Sideband Modulator Without Second-Order Sidebands

An optical single sideband modulator without generating both the −2nd- and +2nd-order sidebands is presented. It is based on a parallel operation of two dual-drive Mach–Zehnder modulators (DDMZMs) where one is operated as a conventional single sideband (SSB) modulator and the other is operated as a single-drive Mach–Zehnder modulator (MZM) biased at the maximum transmission point. The 2nd-order sidebands generated by the SSB modulator and the maximum-biased MZM can be cancelled by controlling the sideband amplitude and phase. Canceling the 2nd-order sidebands eliminates the second-order harmonic component presented at the output of a long-reach fiber optic link. The new SSB modulator can be implemented using standard off-the-shelf components and has a wide bandwidth. Experimental results show >20 dB 2nd-order sidebands suppression for different modulation indexes and 22.6 dB reduction in the fiber optic link output second-order harmonic component, compared to using a conventional SSB modulator formed by a DDMZM and a 90° hybrid coupler. Results also demonstrate that the performance of the new SSB modulator is insensitive to the optical carrier frequency and the input RF signal frequency.

Photonic microwave waveforms generation based on two cascaded single-drive Mach-Zehnder modulators.

A new photonic scheme for various waveforms generation has been proposed and demonstrated. In the scheme, two cascaded single-drive LiNbO3 Mach-Zehnder modulators serve as pulse shaper and the polarization-dependent character of the modulators is fully exploited and utilized. By arranging the polarization states of the incident light, two different spectra are achieved on two orthogonal polarization components respectively. Finally, the desired waveforms can be obtained by superimposing the photocurrents of the two orthogonal signals on a photodetector. The detailed theoretical analyses and simulations are given. In the experiment, square-shaped waveform, triangular waveform and sawtooth (or reversed-sawtooth) waveform are obtained successfully. Furthermore, an approach to smoothing the sawtooth waveform with fewer harmonics is suggested and verified.

Ultrahigh-resolution and wideband optical vector analysis for arbitrary responses.

An ultrahigh-resolution and wideband optical vector analyzer (OVA) with the simplest architecture, to the best of our knowledge, is proposed and demonstrated based on chirped optical double-sideband (ODSB) modulation in a single-drive Mach-Zehnder modulator (MZM). To distinguish the magnitude and phase information carried by the two sidebands in the ODSB signal, a two-step measurement, in which biasing, respectively, the MZM at two different points is applied. Because no optical filtering is required in the scheme, the optical carrier can be located at any wavelength that is suitable for accurate measurement, e.g., close to the notch of a notch response or within the passband of a bandpass response, so the proposed OVA has the capability to measure an arbitrary response. An experiment is carried out, which achieves the magnitude and phase responses of a programmable optical processor with bandpass, notch, or falling-edge responses. The measurement bandwidth is 134GHz, and the measurement resolution is 1.12MHz.