Dual-drive Mach-Zehnder Modulator Research Articles

Photonic generation of switchable multi-format linearly chirped signals

A compact and cost-effective photonic approach for generating switchable multi-format linearly chirped signals is proposed and experimentally demonstrated. The core component is a dual-drive Mach–Zehnder modulator driven by a coding sequence and a linearly chirped waveform. By properly setting the amplitudes of the coding sequence, a linearly chirped signal with different formats, including the frequency shift keying (FSK), phase shift keying (PSK), dual-band PSK, and FSK/PSK modulation formats, can be generated. Experiments are conducted to verify the feasibility of the proposed scheme. Linearly chirped signals with the above four formats are successfully generated. The scheme features multiple formats and high tunability based on a compact structure, which has potential applications in modern multifunctional systems.

Compact Multi-tone Microwave Photonic Frequency Measurement Based on a Single Modulator and Frequency-to-time Mapping

We propose a microwave photonic frequency measurement scheme based a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM) and frequency -to-time mapping. A compact frequency measurement system is guaranteed thanks to the use of a single modulator, and multi-tone measurement ability is achieved due to the principle of frequency-to-time mapping. In the proposed scheme, the unknown microwave signal is mixed with a linearly chirped microwave signal with the help of the DP-DDMZM, and the mixing product is selected by an electrical bandpass filter to achieve frequency-to-time mapping. Single and multi-tone microwave frequency measurement are successfully demonstrated in the experiment, and the measurement errors are less than ± 3 MHz.

Analysis of Optical Single Sideband Modulators for Radio Over Fiber Link with and without Second Order Sidebands

The analysis of Optical Single Sideband (OSSB) generation with and without second-order sidebands for Radio over Fiber (RoF) is presented. The performance of systems based on hybrid coupler with distinct phase angle and Dual-Parallel Dual-Drive Mach-Zehnder Modulator (DP-DDMZM) is compared using simulation. Impact of parameters like Single-Mode Fiber (SMF) length, Radiofrequency (RF) amplitude, and laser linewidth on Signal-to-Noise Ratio (SNR) has been investigated. It has been observed that eliminating one of the second-order sidebands with 120° hybrid coupler improves peak SNR in comparison to 90° hybrid coupler with both second-order sidebands and DP-DDMZM-based system without second-order sidebands irrespective of Continuous Wave (CW) laser linewidth.

Silicon Photonic-Based Integrated Microwave Photonic Reconfigurable Mixer, Phase Shifter, and Frequency Doubler

An integrated microwave photonic (IMWP) reconfigurable mixer, phase shifter, and frequency doubler based on the silicon photonics platform is proposed and theoretically investigated in this paper. The proposed structure consists of a novel dual-drive Mach–Zehnder modulator (DDMZM) placed in parallel with an electro-optic phase modulator (PM). The novel DDMZM is a bias-free modulator that has advantages over conventional MZMs, such as bias-free operation and tunable optical-to-carrier sideband ratio (OCSR). The proposed novel structure can be configured as an IMWP phase tunable mixer or IMWP double-balanced mixer by properly adjusting optical wavelength and choosing the proper radio frequency (RF) hybrid coupler. Besides, the proposed IMWP reconfigurable mixer has the ability to perform up-converting, down-converting, RF frequency doubling, and phase shifting. The proposed structure is theoretically analyzed and is verified by simulations.

Generalized Analysis of Dual-Output Mach-Zehnder Modulator With Applications to Photonic-Assisted Instantaneous Frequency Measurement

We propose a general and exact analytical model forintensity modulation and direct detection (IM/DD) fiber optic links using dual-output dual-drive Mach-Zehnder modulator (DO-MZM). This model extends previously published results relying on the small-signal approximation and infinite extinction ratio at the modulator outputs. In our treatment the output optical powers are calculated through analytical expressions taking into account the modulator electronic driver and directional coupler characteristics. Closed-form expressions, explicitly displaying the dependence of the link output power on the directional coupler transmission coefficients, optical modulation depth, and bias point, are obtained for output optical power, frequency chirp, extinction ratio and static characteristic MZM curves. We also propose an equivalent interferometric representation of each DO-MZM output in terms of virtual dual-drive Mach-Zehnder modulators (DD-MZMs) and show that each modulator output has distinct characteristic curves. The model is applied to a photonic-assisted instantaneous frequency measurement (IFM) based on frequency-to-power mapping, in which an amplitude comparison function (ACF) is generated by the power fading functions. We have obtained a generalized ACF through which both the frequency and amplitude of the input RF signal can be determined by a search procedure.

All-Optical Pulsed Signal Doppler Frequency Shift Measurement System

A simple and all-optical Doppler frequency shift (DFS) measurement system is presented. It is based on a dual-drive Mach Zehnder modulator (DDMZM) driven by a transmitted signal and an echo signal received by an antenna. A low-frequency sawtooth wave is applied to the DDMZM DC port to frequency shift the carrier and sidebands generated by the transmitted signal. Beating of a frequency-shifted transmitted signal sideband and an echo signal sideband at the photodetector produces a low-frequency electrical signal. The DFS, and consequently the speed and moving direction of a target, can be obtained from the frequency of this low-frequency electrical signal. The DDMZM used in the proposed DFS measurement system does not need to be operated at a specific point in the transfer function and hence it has no bias drift problem. The proposed DFS measurement technique can be used in both CW and pulsed radar systems. Experimental results demonstrate the proposed DFS measurement system has a wide operating frequency range of 10 GHz to 19.95 GHz, small DFS measurement error of less than ±0.6 Hz and long-term stable performance. Results also demonstrate, for the first time, DFS measurement of a pulsed signal using a microwave photonic technique.

Dual-function measurement system for Doppler-frequency-shift and angle-of-arrival of microwave signals

A photonic method for simultaneously measuring the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signal is proposed and verified by simulation. The echo signals are applied to a dual-parallel dual-drive Mach–Zehnder modulator for modulating the lightwave with carrier-suppressed double-sideband pattern. The lightwave carrying the echo signals is coupled with the lightwave carrying the local oscillator signal, and their upper and lower sidebands are separated by an interleaver. Then, the optical signals are converted into low-frequency electrical signals by two identical photodiodes, and the parameters of DFS and AOA are obtained by processing two low-frequency photocurrents. In the simulation, the measurements of the DFSs in the range of ± 1 MHz with errors < ± 9 × 10 − 4 Hz and the AOAs from 1.82 deg to 90 deg with errors <0.9 deg are realized, and the orientation of DFS can also be distinguished by comparing the phase difference of two electrical signals.

Photonics-assisted wideband RF self-interference cancellation with digital domain amplitude and delay pre-matching

A photonics-based digital and analog self-interference cancellation approach for in-band full-duplex communication systems and frequency-modulated continuous-wave radar systems is reported. One dual-drive Mach-Zehnder modulator is used to implement the analog self-interference cancellation by pre-adjusting the delay and amplitude of the reference signal applied to the dual-drive Mach-Zehnder modulator in the digital domain. The amplitude is determined via the received signal power, while the delay is searched by the cross-correlation and bisection methods. Furthermore, recursive least square or normalized least mean square algorithms are used to suppress the residual self-interference in the digital domain. Quadrature phase-shift keying modulated signals and linearly frequency-modulated signals are used to experimentally verify the proposed method. The analog cancellation depth is around 20 dB, and the total cancellation depth is more than 36 dB for the 2-Gbaud quadrature phase-shift keying modulated signals. For the linearly frequency-modulated signals, the analog and total cancellation depths are around 19 dB and 34 dB, respectively.

Optical Analog Noise Encryption With Adaptive Recovery of Two-Dimensional Keys

An optical analog noise encryption system with adaptive recovery of two-dimensional keys is proposed and demonstrated using regular triangle (RT)adaptive algorithm in an optical self-interference cancellation system at the designated receiver. Analog noise encryption and data modulation are performed in a single dual-drive Mach-Zehnder modulator at the transmitter, while decryption is performed in an electro-absorption modulated laser based adaptive cancellation system at the receiver. The weight and delay of the analog noise form the two-dimensional orthogonal encryption keys. Two sets of fingerprints are securely pre-shared for only once between the transmitter and designated receiver and stored before real transmission to ensure that both sides are legitimate users and facilitate adaptive key recovery when using RT adaptive algorithm at the legitimate receiver for retrieving the orthogonal keys. Without receiving the keys from the transmitter, the legitimate receiver is able to adaptively find the two orthogonal keys even under dynamic key changing scenario. In the experiment, a 3.5 GHz wideband analog noise is used to encrypt a 10 Gbps 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) signal at 1.75 GHz. By recovering the orthogonal keys using RT algorithm and the unique pre-shared fingerprints, the designated receiver has successfully decrypted the encrypted signal by removing the analog noise as wide as 3.5 GHz, 28 dB stronger than the sensitive signal, which is by far the best performance in an optical analog noise encryption system.

Optical polarization division multiplexing fiber-wireless integration system at Ka-band based on a low-cost dual-drive MZM.

In this paper, a low-cost dual-drive Mach-Zehnder modulator (DDMZM) based 40 Gbit/s polarization division multiplexing (PDM) fiber-wireless-integration system at Ka-band is experimentally demonstrated. Since the DDMZM is biased at the quadrature point for electro-to-optical (E/O) conversion, a high-power direct current (DC)/radio frequency (RF) component will appear within the received signal bandwidth. This high-power component becomes a narrowband interference due to the phase noise of lasers, which will lead to the incorrect convergence of the constant-modulus algorithm (CMA) during equalization at the receiver side. In order to deal with the broadened DC component, twin-single-sideband (twin-SSB) signal with bandwidth interleave and RF-pilot based phase noise compensation scheme are adopted. Enabled by the combination of optical PDM technique and heterodyne coherent detection, a 40 Gbit/s PDM twin-SSB Nyquist-shaped quadrature-phase-shift-keying (QPSK) signal transmitting over 20-km single mode fiber (SMF) and 1-m 2×2 multiple-input multiple-output (MIMO) wireless distance is achieved with the bit error rate (BER) below the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10-3.

All-Optical In-Phase/Quadrature Microwave Mixer for Antenna Remoting Applications

A new microwave photonic signal processing structure for realising in-phase/quadrature (I/Q) mixing is presented. It is based on a dual-drive Mach Zehnder modulator (DDMZM) and an optical phase modulator inside a Sagnac loop interferometer. Two output IF signals with a quadrature phase difference are obtained by using two photodetectors to detect the upper and lower sidebands of the optical signal at the Sagnac loop output. A quadrature phase difference in the two IF signals is realised by biasing the DDMZM at the quadrature point. This has the advantage of very little quadrature phase errors as a standard modulator bias controller can accurately lock the DDMZM bias point. The optical phase modulator driven by an RF signal can be placed in a remote location for antenna remoting. Theoretical analysis and simulation show using the proposed I/Q mixer for image rejection can overcome the modulation index dependent image rejection ratio problem in the reported I/Q mixers based on a cascaded modulator structure. The Sagnac loop based I/Q mixer is experimentally verified with results show only ±1° quadrature phase error and more than 50 dB image rejection ratio over the operating frequency range of 6 to 20 GHz.

A High Spectral Efficiency Radio Over Fiber Link Based on Coherent Detection and Digital Phase Noise Cancellation

An approach to transmitting two independent microwave vector signals on a single optical carrier with one polarization state based on coherent detection and digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, two independent microwave vector signals are modulated on an optical carrier via a dual-drive Mach-Zehnder modulator (DD-MZM). The modulated optical signals are transmitted over a single-mode fiber (SMF) and sent to a coherent receiver. At the receiver, the optical signals are detected where a local oscillator (LO) optical wave generated by a second free-running laser source is also applied. To recover the two microwave vector signals, a novel digital signal processing (DSP) algorithm is developed and applied to eliminate the joint phase noise terms from the transmitter and the LO laser sources as well as the unstable offset frequency between the two laser sources. An experiment is performed. The transmission of two independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals at 4 GHz with a symbol rate of 1 GSymb/s over a 9-km SMF is demonstrated. The transmission performance in terms of error vector magnitudes (EVMs) and bit error rates (BERs) is also evaluated.

Hybrid-integrated high-performance microwave photonic filter with switchable response

The integrated microwave photonic filter (MPF), as a compelling candidate for next-generation radio-frequency (RF) applications, has been widely investigated for decades. However, most integrated MPFs reported thus far have merely incorporated passive photonic components onto a chip-scale platform, while all necessary active devices are still bulk and discrete. Though few attempts to higher photonic integration of MPFs have been executed, the achieved filtering performances are fairly limited, which impedes the pathway to practical deployments. Here, we demonstrate, for the first time to our knowledge, an all-integrated MPF combined with high filtering performances, through hybrid integration of an InP chip-based laser and a monolithic silicon photonic circuit consisting of a dual-drive Mach–Zehnder modulator, a high- Q ring resonator, and a photodetector. This integrated MPF exhibits a high spectral resolution as narrow as 360 MHz, a wide-frequency tunable range covering the S-band to K-band (3 to 25 GHz), and a large rejection ratio of &gt; 40 dB . Moreover, the filtering response can be agilely switched between the bandpass and band-stop function with a transient respond time ( ∼ 48 μs ). Compared with previous MPFs in a similar integration level, the obtained spectral resolution in this work is dramatically improved by nearly one order of magnitude, while the valid frequency tunable range is broadened more than twice, which can satisfy the essential filtering requirements in actual RF systems. As a paradigm demonstration oriented to real-world scenarios, high-resolution RF filtering of realistic microwave signals aiming for interference rejection and channel selection is performed. Our work points out a feasible route to a miniaturized, high-performance, and cost-effective MPF leveraging hybrid integration approach, thus enabling a range of RF applications from wireless communication to radar toward the higher-frequency region, more compact size, and lower power consumption.

Wideband Doppler frequency shift measurement and direction discrimination based on optical single sideband modulation with a fixed low-frequency reference signal

A wideband Doppler frequency shift (DFS) measurement and direction discrimination method based on optical single sideband (OSSB) modulation with a fixed low-frequency reference signal is proposed and experimentally demonstrated. In the proposed approach, the transmitted signal and the fixed low-frequency reference signal are applied to the lower and upper Mach–Zehnder modulators (MZMs) of a dual-drive dual-parallel MZM (DD-DPMZM) respectively, for realizing OSSB modulation independently. The echo signal is applied to a conventional MZM for optical double sideband (ODSB) modulation. A low-speed photodetector (PD) is used to implement optical-to-electrical conversion and generate three low-frequency beating signals. Both the value and direction of the DFS can be simply obtained by analyzing the frequencies of the three low-frequency beating signals. The proposed scheme has a simple structure, a wideband operating frequency range, and a low requirement of the receiving circuit. Experiments demonstrate that wideband DFS measurement and direction discrimination within 5∼18 GHz with a measurement error of less than ±0.06 Hz are achieved by using a 20 MHz reference signal.

Research on Ultra-Fast Optical Vector Analysis Based on Microwave Photonic Frequency Sweeping

An ultra-fast and high-resolution optical vector analysis scheme has been proposed and experimentally demonstrated. In the scheme, a broadband optical frequency-sweeping signal is generated by injecting a linearly frequency-modulated signal into one radio-frequency (RF) port of a dual-drive Mach-Zehnder electro-optic modulator, which is used to achieve fast scanning of the frequency response characteristic of the device under test (DUT). A single-tone microwave signal is injected into the other RF port of the modulator to realize down-conversion of the frequency-sweeping signal. The down-converted signal is then digitized by an analog-to-digital converter, and is processed through Hilbert transform to extract the amplitude- and phase-frequency response of the DUT. In the proof-of-concept experiment, the amplitude- and phase-frequency response of the Brillouin gain in a section of non-zero dispersion shifted fiber with a length of 3 km is accurately measured, where the measurement time is only 20 μs, and the frequency resolution reaches 20 kHz.

Rapid optical tomographic vibrometry using a swept multi-gigahertz comb.

We propose a rapid tomographic vibrometer technique using an optical comb to measure internal vibrations, transient phenomena, and tomographic distributions in biological tissue and microelectromechanical system devices at high frequencies. This method allows phase-sensitive tomographic measurement in the depth direction at a multi-MHz scan rate using a frequency-modulated broadband electrooptic multi-GHz supercontinuum comb. The frequency spacing was swept instantaneously in time and axisymmetrically about the center wavelength via a dual-drive Mach-Zehnder modulator driven by a variable radio frequency signal. This unique sweeping method permits direct measurement of fringe-free interferometric amplitude and phase with arbitrarily changeable measurement range and scan rate. Therefore, a compressive measurement can be made in only the depth region where the vibration exists, reducing the number of measurement points. In a proof-of-principle experiment, the interferometric amplitude and phase were investigated for in-phase and quadrature phase-shifted interferograms obtained by a polarization demodulator. Tomographic transient displacement measurements were performed using a 0.12 mm thick glass film and piezo-electric transducer oscillating at 10-100 kHz with scan rates in the range 1-20 MHz. The depth resolution and precision of the vibrometer were estimated to be approximately 25 µm and 1.0 nm, respectively.

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.