Dual-drive Mach-Zehnder Modulator Research Articles

190Gbaud OOK signal generation with a sub-sampling rate of 0.63 using silicon photonic dual-drive Mach–Zehnder modulator

Intensity modulation with direct detection (IM/DD) has been served as a low-cost technology of data center optical interconnects. To achieve higher data rate, high-order partial response (PR) signaling is utilized to narrow the signal bandwidth below the Nyquist frequency of digital-to-analog converter (DAC) sampling rate. In this work, we experimentally demonstrate ultra-high speed optical interconnects based on a conventional silicon photonic traveling-wave Mach–Zehnder modulator (MZM) with a 3-dB bandwidth of 28.5 GHz. By applying PR narrowing and digital anti-aliasing brick-wall filter that serves to avoid spectral overlap, up to 190Gbaud OOK signal is generated using a 120GSa/s DAC with a sampling ratio as low as 0.63. Furthermore, a 180Gbaud OOK signal is generated and transmitted over 500 m standard single-mode fiber (SSMF) below 20% hard-decision forward error-correction (HD-FEC) threshold of 1.5 × 10−2.

Single mode fiber-free space optic based hybrid $$32\times 2~\text{Gbps}$$ WDM-PON architecture employing optical frequency comb source and polarization multiplexing

In this paper, we propose a cost-efficient single mode fiber-free space optics (SMF-FSO) based hybrid $$32 \times 2~\text{Gbps}$$ wavelength division multiplexed passive optical network (WDM-PON) employing optical frequency comb (OFC) source and polarization multiplexing. OFC source is realized at optical line terminal (OLT) by modulating a single continuous wave (CW) laser source with radio frequency (RF) sinusoidal signal and dual-drive Mach–Zehnder modulator (DD-MZM). 16 coherent optical carriers are used to split into 32 x and y-orthogonal polarization states which are used to transmit the on-off keying (OOK) data of 32 channels to remotely located optical network units (ONUs). The performance of the channels is analyzed with bit error rate (BER) plots employing Gamma–Gamma (GG) FSO channel model at different turbulence regimes and lengths of FSO link. Moreover, the effect of varying the polarization mode dispersion (PMD) on BER is also evaluated. The cost of the proposed architecture is analyzed and compared with conventional PON architecture. The cost efficiency of the proposed architecture is demonstrated by the use of a single CW laser source to transmit the data of 32 users between remote node (RN) and ONUs through FSO links having reduced installation and maintenance costs.

Filter-Free Photonic Image-Rejection Down-Conversion for Distributed Antenna Applications

Photonics-assisted frequency conversion based on cascaded modulators is an effective way to satisfy the requirements of distributed antenna array applications. A filter-free photonic image-rejection down-converter with immunity to dispersion-induced power fading is proposed and demonstrated. The radio frequency (RF) signal from the distributed antenna unit is injected into a dual-drive Mach–Zehnder modulator (DDMZM) through an electrical 90° hybrid coupler (HC), and a single-sideband (SSB) signal is realized. It is then transmitted to the center office by an optical fiber link. At the center office, the modulated RF signal is injected into a dual-polarization dual-parallel MZM (DP-DPMZM) after a polarization controller (PC). Afterwards, an LO signal remodulates it through the Y-DPMZM, and carrier-suppressed SSB modulation is fulfilled via another electrical 90° HC. After the power splitting, quadrature I and Q IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Through a combination of the I/Q IF signals with a low-frequency electrical 90° HC, a photonics image-rejection down-converter based on phase cancellation is realized. Moreover, no optical filter is required; thus, the image-rejection down-converter can work with a large bandwidth. The proposed filter-free photonic image-rejection down-converter is theoretically analyzed and experimentally verified.

Photonic Scheme for the Generation of Background-Free Phase-Coded Microwave Pulses and Dual-Chirp Microwave Waveforms

We propose a photonic scheme to generate binary phase-coded microwave pulses and dual-chirp microwave waveforms without baseband-modulated signals (background noise) based on a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM) which contains x-DDMZM and y-DDMZM at two different polarization states. A radio frequency (RF) signal from a microwave source is transferred into two differential RF signals and employed into one arm of x-DDMZM and one arm of y-DDMZM, while a baseband signal from an arbitrary waveform generator is divided by an electronic coupler and then driven into the two other arms of DP-DDMZM. By adjusting the phase differences between the x-DDMZM and the y-DDMZM, binary phase-coded pulses and dual-chirp signals without baseband-modulated signals are generated. The proposed scheme can eliminate the interference caused by baseband-modulated signals, and satisfy different radar applications for different frequency bands. Experimental results show that phase-coded signals at 15 GHz with the bit rates of 1 Gb/s and 2 Gb/s and dual-chirp signals at 10 GHz and 15 GHz with the time durations of 0.5 μs are successfully generated. The reported scheme is well analyzed in theory and verified by experiment.

Photonic approach to flexible multi-band linearly frequency modulated microwave signals generation

In this paper, a flexible multi-band linearly frequency modulated (LFM) signal generator based on a dual-polarization binary phase-shift keying (DP-BPSK) modulator is proposed and demonstrated by experiment. Two dual-drive Mach-Zehnder modulators of the DP-BPSK modulator are driven by a local oscillator (LO) signal and an LFM signal, respectively. By appropriately changing the phase difference introduced by a polarization controller, flexible multi-band LFM signals can be obtained after photoelectric conversion. The LO signal is phase modulated to eliminate self-heterodyne, which will affect the quality of the resulting signal.

Photonics Generation of Baseband-Free Arbitrary-Phase-Coded Microwave Waveform Pulse

A photonics system for baseband-free arbitrary-phase-coded microwave waveform pulse (APCMWP) generation is proposed and demonstrated. The proposed system realizes the generation of APCMWP, and further solves the baseband components problem in the pulsed process. The system uses a polarization-multiplexing dual-drive Mach–Zehnder modulator (PM-DMZM) and an optical band pass filter (OBPF) to obtain a polarization-multiplexed single-sideband modulated (SSBM) optical signal with carrier intensity-phase modulation, then uses a balanced photodetector (BPD) to properly detect the polarization-multiplexed SSBM optical signal, APCMWP with baseband components suppression can be easily generated. A detailed theoretical analysis and a proof-of-concept experiment are provided. The generations of 1.2-GBaud 9.6-GHz and 2-GBaud 12-GHz baseband-free APCMWP are verified.

Precoded OVSB-OFDM transmission system using DML with Kramers-Kronig receiver

Different from the use of IQ modulator or a dual-drive Mach-Zehnder modulator, we investigate an optical vestigial sideband orthogonal frequency division multiplexing (OVSB-OFDM) transmission system using a low-cost directly modulated laser. Precoding techniques and Kramers-Kronig (KK) algorithm are employed to enhance the bit error rate (BER) performance. The KK receiver is applied to eliminate the signal-signal beat interference caused by the square-law detection of the photodetector. Discrete Fourier transform (DFT) and orthogonal circulant matrix transform (OCT) precoding techniques can effectively average the signal-to-noise ratio over the data-carrying subcarriers and improve the BER performance. Through numerical simulation, we discuss the relationship between the order and center frequency of the optical filter and the carrier signal power ratio (CSPR). Furthermore, we study the influence of the KK algorithm and precoding techniques on receiver sensitivity under different transmission distances. The results show that both KK algorithm and precoding technologies can improve receiver sensitivity and extend the transmission distance. The performance of DFT precoding is better than that of OCT precoding. When there is no KK algorithm, the transmission distance of OCT precoding or no precoding is only 20 km at the BER of 3.8e-3; while DFT precoding can extend the transmission distance up to 60 km. With the help of the KK algorithm, OCT precoding and DFT precoding can further extend the transmission distance by up to 40 and 60 km, respectively, compared to the DFT precoding and without the KK algorithm case. The DFT precoding with the KK algorithm can improve the receiver sensitivity of more than 7 dB in terms of received optical power, compared to the no precoding and without the KK algorithm case.

A Radio Over Fiber System Compatible With 3G/4G/5G for Full Spectrum Access and Handover With Multi-Scenarios

A Radio over Fiber system based on optical frequency multiplication and multiplexing compatible with 3G/4G/5G systems for full spectrum access and handover with multiple scenarios is proposed and analyzed theoretically as well as simulated numerically. By combining a dual-drive Mach-Zehnder Modulator in Push-Pull modulation-mode with optical frequency multiplication and multiplexing technology, the simultaneous transmission of multiple radio frequency signals in optical carrier is realized. It can be also switchable for full spectrum access of different scenarios and user terminals with Multi-Input Multi-Output wireless capability, based on frequency diversity technology. The BER and eye diagram for the transmission performances have been presented by the simulation experiment. Meanwhile, the feasibility of the scheme has been demonstrated by lots of numerical simulations and accurate theoretical analyses. The method could meet the requirements for communication capacity and transmission rate in both continuous-wide-area coverage and hot-spot high-capacity transmission of 5G system, and for full spectrum access and handover.

Reconfigurable Photonic generation and transmission of multi-format radar signals

In this paper, photonic generation and transmission technique for multi-format microwave waveform is proposed. In the center office, a broadband optical source (BOS) is utilized as optical carrier. And the main component is a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM) followed by a polarization division multiplexed emulator (PDME). The DPol-DDMZM consists of two sub-DDMZMs to generate two orthogonally polarized optical signals. The system we proposed is conveniently reconfigured to generate different waveforms. By applying phase modulation (PM) to the orthogonal polarization states, a polyphase-coded microwave waveform with a tunable center frequency multiplication factor can be generated. By tuning the differential group delay (DGD) of the two polarizations by the PDME, the multiplication factor can be easily adjusted. In addition, if the carrier is suppressed at the upper and lower DDMZM, broadband dual-chirp microwave signal can be generated, transmitted over fiber and detected at a base station. The chromatic dispersion induced power fading is eliminated. The approach is investigated by simulations. Polyphase-coded signal with a repetition rate of 4 Gbit/s is demonstrated. And dual-chirp signal with a bandwidth of 8 GHz is carried out. Besides, the practical feasibility of the system is further studied by analyzing the power of the BOS, the relative time delay of PDME and the photonic integrated circuit (PIC) replica of the generator.

Photonic-Enabled Doppler Frequency Shift Measurement for Weak Echo Signals Based on Optical Single-Sideband Mixing Using a Fixed Low-Frequency Reference

A simplified photonic-enabled Doppler frequency shift (DFS) measurement approach is proposed based on a single dual-polarization binary phase-shift keying (DP-BPSK) modulator with the help of a fixed low-frequency reference. The low-frequency reference and the transmitted signal are combined and then single-sideband mixed in the upper dual-drive Mach-Zehnder modulator (DD-MZM) in the DP-BPSK modulator to generate an optical sideband of the transmitted signal and a mixed optical sideband of the two signals, which is combined with the optical sideband of the echo signal from the other DD-MZM. The combined optical signal is detected in a low-speed photodetector. Both the direction and the value of the DFS can be measured by analyzing the frequency of the generated photocurrent. An experiment is performed. DFS from -100 to 100 kHz is measured for microwave signals from 6.9 to 16.1 GHz with a measurement error of less than ±0.04 Hz. The stability of the system is also studied, and the change of the measurement error is less than ±0.04 Hz in 30 minutes.

Experimental demonstration of secure 100 Gb/s IMDD transmission over a 50 km SSMF using a quantum noise stream cipher and optical coarse-to-fine modulation.

In this paper, we experimentally demonstrate a secure 100 Gb/s 214-level intensity modulation and direct detection transmission over a 50 km standard single-mode fiber (SSMF) using a quantum noise stream cipher (QNSC) technique and 8-bit digital to analog converters. Optical coarse-to-fine modulation (CTFM) has been proposed to simultaneously enhance the security and overcome the weakness of low modulation depth in the traditional CTFM scheme. The optical power instead of the radio-frequency signal power is adjusted to satisfy the required peak-to-peak relation for CTFM, and thus the coarse and fine modulation has the same modulation depth. Two optical CTFM schemes based on an optical coupler and a polarizing beam combiner (PBC) are proposed and their pros and cons are analyzed and compared. Considering the trade-off of transmission performance and security performance, the optical CTFM scheme based on PBC is preferred in our experiment. 214-level pulse amplitude modulation (PAM) is achieved using two dual-drive Mach-Zehnder modulators (DD-MZM). Simultaneously, each DD-MZM is also used to achieve single-sideband (SSB) modulation to eliminate the power fading induced by fiber dispersion. By these means, 100 Gb/s 214-level PAM-QNSC signal transmission over 50 km SSMF with the bit error rate below the 7% overhead hard-decision forward error correction threshold of 3.8×10-3 is achieved. The results validate that the proposed scheme is effective to realize low-cost, high-speed, and highly secure optical transmission in the data center.

Stable Radio Frequency Transmission of Single Optical Source Over Fiber Based on Passive Phase Compensation

In this paper, we propose a stable radio frequency(RF) transmission scheme for optical link based on Dual drive Mach-Zehnder modulator(DDMZM). By frequency mixing, the phase jitter of the output signal caused by environment variation has been automatically compensated. Different from other passive compensation schemes, the reference signal and the pre-compensation signal are modulated on one optical carrier by a DDMZM, and the crosstalk of two RF signals can be depressed by using dispersion compensation and adjusting the bias voltage of DDMZM, without multiple frequency multiplications and divisions. Meanwhile, the noises induced by Rayleigh scattering can be suppressed by using acousto-optic modulator. Our scheme is featured by single laser diode employed and no extra phase jitter induced by wavelength differences, with the advantages of simple structure and cost-effectiveness. In the experiment, we demonstrate 10 GHz RF signal stability transmission over 50 km single mode fiber, the phase jitter mean square error is 0.82 ps during 10 hours.

An ultra-dense spacing-based PON by incorporating dual drive Mach–Zehnder modulator for comb generation

Abstract Wavelength division multiplexed passive optical is promising technique to achieve a high data rate and large number of user. The notable advantages of WDM PON is the combination of reliability, cheap in cost, accessible bandwidth, high security, large optical reach and it can support large number of ONU. There are multiple approaches to achieve high-speed WDN PON using different transmission techniques. In WDM, multiple lasers are required which increase the cost of the system. To reduce cost, an optical multicarrier generation system is proposed. An economical multiple carrier generation with the incorporation of sine generator and Mach–Zehndar modulator is demonstrated. Utmost work of sine generator and dual drive modulator was to attain low cost functioning of passive optical networks. Multicarrier generation was done and replacement of laser carriers with optical multicarrier generator. Carriers were generated with the frequency spacing of 20 GHz and these carriers were used in the passive optical networks with the tone-to-noise ratio of 40 dB, amplitude difference of 1.4 dB. For the transmission of downstream in the PON, differential phase shift keying was employed at 10 Gbps data speed. Transmission distance achieved was 30 km using single-mode fiber and this was a part of optical distribution network. Optical network unit was next part after ODN and signals were received with balanced receiver. Moreover, half signal was given to intensity modulator for the signal re-modulation. Bit error rate of 10–9 was achieved at all channels in the downstream. An upstream of 10 Gbps was accomplished in the passive optical network.

Broadband Optoelectronic Frequency Response Measurement Utilizing Frequency Conversion

A broadband optoelectronic (O/E) frequency response measurement method utilizing photonics-based frequency conversion is proposed and experimentally demonstrated. It is characterized by a sub-kilohertz frequency resolution and a doubled measurement bandwidth compared with the RF frequency sweeping range and the working bandwidth. A carrier-frequency-shifted optical double-sideband (ODSB) signal is produced by employing a dual-drive Mach-Zehnder modulator (DD-MZM) and stimulated Brillouin scattering (SBS). Then, a photodetector (PD) under test receives and converts the optical signal into a photocurrent. By detecting the frequency up- and down-conversion components generated by the two first-order sidebands and the optical carrier, the O/E frequency responses in the low- and high-frequency regions are achieved. After stitching the two measured responses together, an O/E frequency response with a frequency range that is twice the bandwidth of the input microwave signal is obtained. In an experiment, the O/E frequency response of a commercial high-speed PD is precisely characterized with a frequency resolution up to 5.55 MHz. A frequency bandwidth of 66.8 GHz (0.1–66.9 GHz) is achieved by using a 25-GHz DD-MZM. The measured O/E frequency response is coincident with that measured by a commercial instrument.

A Flexible Multi-Format Signal Generation Method Based on Optically Coupled Selector Switch

An approach for microwave signal generation with adjustable formats including ASK, PSK, FSK and FPSK (FSK-PSK) is proposed and demonstrated in this paper. In the proposed scheme, a phase modulator (PM) and an optical coupler form optically coupled selector switch (OCSS), which transmit the optical signal on specified path by adjusting its driving signal. Two parallel-placed Dual-Drive Mach-Zehnder modulators (DD-MZM) and a followed photodetector (PD) are employed to generate the multi-format microwave signals. From a theoretical analysis, the microwave signals with tunable formats can be obtained by properly adjusting the amplitude of the coding signals. The simulation and experimental results show that the ASK, PSK, FSK and FPSK signals are successfully generated, and the modulation format can be switched simply by adjusting the system parameters. In addition, the frequency and bit rate of generated signal can be adjusted according to the demand, so flexible tunability can be realized easily.

A Robust Sparse RLS-Volterra Nonlinear Equalizer Using ℓ₀-Regularization for 4 × 150 Gbit/s IMDD-Based Optical Interconnect

Volterra equalizer (VE) is a well-known and effective algorithm to deal with the linear and nonlinear distortions in optical interconnect, but the high computational complexity hinders its practical application. Generally, sparse VEs based on ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> - or ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -regularization are good ways to reduce the complexity by discarding some inessential taps. However, a tap threshold needs to be chosen in these sparse VEs like the threshold-based pruned retraining VE (TR-VE) to decide the discarded taps. And this tap threshold should be adjusted fine to balance the reduced complexity and equalization performance, especially when the testing environments alter. Thus, the reduced complexity in these sparse VEs may fluctuate. To address this issue, a robust and stable complexity reduced sparse VE using ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -regularization (ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -SR-VE) is proposed in this paper. The recursive least square (RLS) algorithm is used to replace the least mean square algorithm for the faster convergence speed and better equalization performance. The complexity of this equalizer depends on its parameters but not the tap threshold. Once the equalizer parameters are determined, the complexity would not change with the system characteristics, contributing to higher practicability. In our experiment, a 150 Gbit/s PAM8 signal transmission system based on intensity modulation and direct detection (IMDD) is achieved, and a dual-drive Mach-Zehnder modulator for optical single-sideband signal generation is used to mitigate the power fading effect. The experimental results show that with the help of ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -SR-VE, the reduced complexity percentage is stable at 66.18% compared with the RLS-based VE, even after 75 km standard single-mode fiber (SSMF) transmission. By using this equalizer, 4×150 Gbit/s PAM8 signals have also been successfully transmitted over 30 km SSMF at C-band. The reduced complexity variation of ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -TR-VE is >20%, but the reduced complexity of the proposed ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -SR-VE is stable at 60% even after 30 km SSMF for all four lanes.

Photonics-Based Serrodyne Microwave Frequency Translator With Large Spurious Suppression and Phase Shifting Capability

A Serrodyne microwave frequency translator implemented using a microwave photonic technique is presented. It is based on two dual-drive Mach-Zehnder modulators connected in parallel where one of the modulators is operated as an optical phase modulator driven by a sawtooth wave. It is capable of simultaneously shifting the frequency and phase of an input microwave signal. The frequency translator is designed to largely suppress the undesired carrier and sidebands and to minimise the frequency translation loss. Results on the frequency translator demonstrate -1 to 1 MHz frequency translation of multiple microwave signals with a large spurious suppression ratio of 34 to 41 dB and a wide bandwidth of 2 to 18 GHz. Simultaneous frequency and phase shifting operation is also demonstrated.

C band 112 Gb/s PAM4 signal transmission over 320 km with a quasi-linear double-side electro-absorption modulated laser (DS-EML)

The growing traffic demand in data center interconnections (DCIs) requires high-speed and low-cost transceivers that can flexibly adapt to different transmission distances up to 80 km or further. In this paper, based on the double-side electro-absorption modulated laser (DS-EML), we propose a transmitter with a fixed 90-degree phase rotation on one side of the DS-EML that can realize quasi-linear complex modulation. We verify the application of the quasi-linear DS-EML for a 112 Gb/s CD pre-compensation 4-level pulse amplitude modulation (PAM4) signal transmission over 320 km by simulation. Compared with the LiNbO3 in-phase quadrature (IQ) modulator and the dual-drive Mach-Zehnder modulator (DDMZM), our proposed transmitter has several obvious advantages, such as low cost, small footprint, ease of integration and reduced power consumption.

Optical single sideband modulation with tunable optical carrier-to-sideband ratio using DP-BPSK modulator

In this paper, a novel approach to achieving optical single sideband modulation with tunable carrier-to-sideband ratio (OCSR) is proposed and demonstrated. The key of the scheme is a DP-BPSK (Dual Polarization BPSK) modulator. The DP-BPSK modulator is integrated and consists of two parallel dual-drive Mach-Zehnder modulator, an optical power splitter, a 90° polarization rotator, and a polarization beam combiner. The upper modulator of the DP-BPSK modulator is set to single sideband modulation and the lower modulator of DP-BPSK modulator is not modulated by radio frequency, then we can achieve a single sideband modulation signal with tunable OCSR by adjusting the angle of PC2. The scheme uses only one light source, one signal generator, one 90° hybrid coupler, one DP-BPSK modulator, two polarization controllers, one DC power supply and one linear polarizer. Compared with optical filter, optical grating, multiple modulators or other devices used in the previous schemes, the proposed structure is much simpler. The proposed approach is first theoretically analyzed and then verified by experiment. The single sideband modulation signals are obtained with a wide OCSR range of −20 dB to 38 dB in the experiment, and the performance of the scheme in the transmission link is also verified by simulation.

Asymmetric Carrier Divider with an Irregular RF Phase on DD-MZ Modulator for Eliminating Dispersion Power Fading in RoF Communication

The main problem of intensity modulation (IM) in radio-over-fiber (RoF) communication is dispersion power fading (DPF), which occurs when the signal is transmitted through a dispersive link that causes a sideband cancelation effect. The DPF level of the RoF link is determined by the deviation factor (DF). The optical single-sideband (OSSB) modulation scheme, which is generated by driving one of the dual-drive Mach–Zehnder modulators (DD-MZMs), is usually used to overcome DPF. The DF value of OSSB modulation at modulation index m = 0.1 increases from 0.008 to 0.930 at m = 1. It can be said that this method is only effective at reducing DF at low m. However, as well-known information of the DD-MZM system, high-efficiency optic–electric conversions can be obtained at high m values, but DF will increase. Therefore, reducing the DPF value for high m ≥ 0.1 is interesting. It is known that in wireless communication, to reduce the impact of fading, direct signals are amplified and signals with irregular phases are used. Moreover, this paper proposes the DD-MZM with an asymmetric carrier divider as a direct signal and combines it with an irregular radio frequency (RF) phase to reduce the DPF at high m. The carrier that is generated by laser diode (LD) power (PIN) is divided asymmetrically as power modulation (PDD-MZM) and carrier arm (CA) power (PCA). Furthermore, the minimum DF is obtained when the PIN is separated as 75% for PCA and 25% for PDD-MZM with an irregular RF signal of θ = 48° and a bias point value of γ = ¾. As a result, with the same power as OSSB, this proposed structure produces DF at m = 0.1 and m = 1 with values of 0.008 and 0.03, or it can reduce DF of 96.7% at m = 1. The mathematical model and simulation model have very good agreement, which validates the proposed method.