Dual-polarization Dual-parallel Mach-Zehnder Modulator Research Articles

Simple DFS and AOA simultaneous measurement scheme without directional ambiguity with co-frequency self-interference signal cancellation

A photonic method based on a dual-polarization dual-parallel Mach–Zehnder modulator (DPol-DPMZM) for the simultaneous measurement of the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals is proposed and demonstrated by simulation. The upper arm of each sub-DPMZM is driven by the echo and self-interference signals from the antenna, while the lower arm is driven by the reference signal 1 and reference signal 2. The phase and amplitude of the reference signal 1 are adjusted to match the interference signals for achieving the self-interference cancellation (SIC). At the central office (CO), the DFS and AOA can be acquired in real time without directional ambiguity by processing the two downconverted low-frequency tones in the photocurrent. The simulation results show that the presence of the SI signal will seriously interfere with the observation of the SOI frequency and waveform, and the self-interference cancellation depth of about 42 dB can be obtained after the SIC. The measurement errors of the DFS without direction ambiguity are within 0.2 Hz. After the Hilbert transformation of the intermediate frequency (IF) signal, the AOA can be measured from −87.31∘ to +87.31∘ with errors less than 3.9°. The system has a large bandwidth, excellent real-time performance, and better invisibility, and is expected to be used in modern electronic warfare systems.

Broadband Microwave Photonic Mixer with Flexibly Tunable Phase Shift and Supporting Dispersion-Induced Power-Fading-Free Fiber Transmission

A broadband microwave photonic mixer with tunable phase shift and supporting dispersion-induced power-fading-free fiber transmission is proposed and demonstrated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In this scheme, the intermediate-frequency (IF)/radiofrequency (RF) signal and the local oscillation (LO) signal are applied to the four sub-MZMs biased at their minimum transmission points via a power splitter and a 90° hybrid coupler, respectively. Through mutual beating between the IF/RF and the LO modulation sidebands in a high-speed photodetector at the remote site, high-efficiency frequency conversion is achieved. The dispersion-induced power fading over long-distance fiber transmission is eliminated through setting the biased-induced phase difference between the parent-MZMs in the two sub-DPMZMs of the DP-DPMZM to be π/2. In addition, the phase shift of the frequency-converted signal can be continuously tuned over 360° through synchronously adjusting the bias voltages of the parent-MZMs in the two sub-DPMZMs. The proposed scheme is experimentally demonstrated, where a microwave photonic mixer with a 6-dB operation bandwidth of 40 GHz and supporting dispersion-induced power-fading-free transmission over 20 km SMF is realized. Meanwhile, a continuously tunable phase shift over 360° in the frequency range of 0.1 GHz to 29.9 GHz is achieved, where the power variation during phase tuning is smaller than 4 dB.

An All-Optical Microwave Frequency Divider with Tunable Division Factors Based on DP-DPMZM

Based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved. The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers before the photodetector to increase the conversion gain. Experiment results also demonstrate that the frequency division factors can be adjusted.

Photonic Generation of Background-Free Phase-Coded Microwave Pulses with Elimination of Power Fading

We report a novel photonic scheme to generate background-free phase-coded microwave pulses with elimination of power fading by cascading a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM is driven by a radio frequency (RF) signal to generate two first-order optical sidebands with an orthogonal polarization state, while the PolM is driven by a three-level electrical coding signal. By properly adjusting the polarization state, a series of background-free frequency-doubled phase-coded microwave pulses can be generated after optical-to-electrical conversion. Benefiting from the carrier-suppressed single-sideband (CS-SSB) modulation, the proposed signal generator can suppress the chromatic-dispersion-induced power-fading effect, which has excellent potential for long-distance fiber transmission. In addition, the system can directly generate phase-coded microwave signals in pulse mode by truncating continuous wave (CW) microwave signals. Moreover, the microwave signal generator has wideband tunability since no optical filter is involved in our scheme. The proposed method was theoretically analyzed and experimentally verified. Phase-coded microwave pulses centered at 14 GHz and 19.2 GHz with a bit rate of 0.5 Gb/s were successfully generated.

Photonic-based radar for distance and velocity measurement with multiformat waveforms.

A radar with multiformat waveforms is proposed to measure distance and velocity. A dual-polarization, dual-parallel Mach-Zehnder modulator (DP-DPMZM) is used to realize carrier-suppressed single-sideband (CS-SSB) modulation, so the switchable down-, up-, and dual-chirp signals, and the amplitude shift keying (ASK) signal, can be generated. The central frequency and bandwidth of the signals are flexible. A Mach-Zehnder modulator (MZM) is added for an optical switch to realize the generation of a pulsed signal and suppress interference in the dechirping process. A dual-drive MZM (DDMZM) is used for the dechirping process. The key component of this radar is that there are no filters used, which can significantly extend the operation bandwidth. In our test, the interference frequency caused by the CW can be suppressed. The error of the distance measurement is less than 2cm, and the velocity error is less than 0.180m/s. In addition, the direction of the target can be distinguished.

Photonic-Assisted Reconfigurable LO Harmonic Downconverter With RF Self-Interference Cancellation and Image-Rejection

A photonic-assisted reconfigurable LO harmonic downconverter with simultaneous image-rejection and RF self-interference cancellation (SIC) for in-band full-duplex communication is proposed and experimentally investigated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The received signal from the antenna, which includes the radio frequency (RF) signal, image signal (IM) and self-interference (SI) signal, is input into one sub-MZM of the X-DPMZM. The self-reference (SR) signal is input into the other. The Y-DPMZM is used to load the LO signal and is properly biased to obtain the high-order sideband of the LO signal, which was then set as the LO signal of the reconfigurable harmonic frequency downconverter. By matching the power and delay of the SR signal and changing the main bias of the X-DPMZM, the SI signal can be eliminated directly in optical domain. With power splitting after the output of the DP-DPMZM, the quadrature IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Then, photonics image-rejection down-conversion based on phase cancellation is realized after a low-frequency electrical 90° hybrid coupler (HC) combines the quadrature IF signals. Both theoretical and experimental investigations are performed. The results show that the SIC has a cancellation depth more than 32 dB for the 10-MHz bandwidth and greater than 19 dB for the 500-MHz bandwidth, the image-rejection has an image-rejection ratio larger than 31 dB for 10-MHz bandwidth and larger than 22 dB for the 100-MHz bandwidth, both in 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> - and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order harmonic down-conversion mode. Experiments are also carried out on the reconfigurable LO harmonic downconverter with simultaneous SIC and image-rejection. A 16-quadrature amplitude modulation (16-QAM) -modulated RF signal is successfully down-converted to a 1-GHz intermediate frequency (IF) signal with self-interference and image frequency cancelled. It is verified that the RF signal can be well recovered from SI and IM signals by the proposed system.

Filter-Free Photonic Microwave I/Q Modulator for Reconfigurable Frequency Mixing

We report a simple and novel scheme to achieve the reconfigurable frequency mixing based on a filter-free photonic microwave in-phase/quadrature (I/Q) modulator. With proper photodetection configuration, four microwave frequency mixing functions are expediently reconfigured in our system: single-ended mixing, balanced mixing, I/Q mixing and image-reject mixing. The employed crucial optical modulator is a dual-polarization dual-parallel Mach–Zehnder modulator (DPol-DPMZM) driven by in-phase and quadrature intermediate frequency (IF) and local oscillator (LO) signals. The generation and switching of frequency down- and up-conversion and different mixing functions depend on the main direct current (DC) biases of the two sub-DPMZMs, instead of using additional optical hybrid, wavelength division multiplexer (WDM) or two pairs of cascaded polarization controller (PC) and polarization beam splitter (PBS) in previous reports. Our demonstrated experiment shows that the reconfigurable frequency mixer has high mixing spur suppression, frequency tunability, and image rejection ratio (IRR) of over 35 dB. The proposed simple and multifunctional structure may bring a broad potential application in radar and communication systems.

Photonic Generation of Dual-Band Microwave Waveforms with Simultaneous and Diverse Modulation Formats

A photonic method of generating dual-band microwave waveforms with simultaneous and different formats is proposed and experimentally verified using a dual-polarization dual-parallel Mach-Zehnder Modulator (DP-DPMZM). The four sub-MZMs of DP-DPMZM are driven by two independent radio frequency (RF) signals and two independent baseband signals. After photo-detection, two baseband signals are up-converted into two different higher frequency bands. The two RF signals and two baseband signals are utilized to adjust the central frequencies and modulation formats of two frequency bands, respectively. Dual-band phase-coded microwave signal with different bit rates and coding patterns at two different frequency bands, dual-band dual-chirp microwave signal with different chirp rates, and one-band dual-chirp and one-band phase-coded microwave signal are successfully generated in our experiments. The central frequencies of two frequency bands are independently tunable, and the modulation formats of waveforms at two frequency bands can also be diverse, which brings more convenience and feasibility into real-world applications. The flexible tunability in the central frequencies and modulation formats of different frequency bands can meet different requirements for radar and communication systems.

Coherent-detection radio-over-fiber link with high spectral efficiency based on digital phase noise cancellation.

A radio-over-fiber (RoF) link with high spectral efficiency using digital phase cancellation is proposed and experimentally verified. The link can be utilized to transmit four microwave vector signals. The four microwave vector signals are modulated on optical signals by using a dual-polarization dual-parallel Mach-Zehnder modulator at the transmitter. The optical signals subsequently pass through a spool of single-mode fiber (SMF) and are sent into a coherent receiver. A digital signal processing (DSP) algorithm is proposed to eliminate the phase noise and frequency difference caused by two free-running lasers at transmitter and receiver. Two 16-quadrature amplitude modulation (16-QAM) vector signals at 6GHz and another two 16-QAM vector signals at 7GHz transmit over a 10-km SMF and are successfully recovered after a DSP algorithm. In order to evaluate the transmission performance of the RoF link, error vector magnitudes and bit error rates are also estimated.

Stimulated Brillouin Scattering Based Image-Reject Microwave Signal Harmonic Down-Converter

We propose and demonstrate a photonic microwave signal harmonic down-converter with image rejection capability via stimulated Brillouin scattering (SBS). A dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is driven by a radio frequency/image (RF/IM) signal and a local oscillation (LO) signal to realize equivalent phase modulation and 4th-order double sideband modulation respectively. The optical carriers from the two arms of the DP-DPMZM can cancel out each other after polarization combining, thereby increasing the useful optical signal power in photodetection. Since the beating notes between the IM-modulated signals and LO-modulated 4th-order sidebands interfere destructively, the down-converted IM signals disappear naturally, which makes the down-converted image parts be suppressed in optical domain. By using an SBS-based dual-band microwave photonic filter to suppress the RF modulated -1st-order sideband and amplify the +1st-order sideband, destructive interference can be broken. Therefore, the RF signal over frequency range of 21-28 GHz can be down-converted to intermediate frequency (IF) band, and the image rejection ratio (IRR) can be also improved to more than 55 dB. Under -160 dBm/Hz noise floor, the SFDR is 105.1 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .

Single-modulator Based Multi-Format Switchable Signal Generator Without Background Noise

A photonic multi-format background-free binarily modulated microwave signal generator using a single dual-polarization dual-parallel Mach–Zehnder modulator is proposed and demonstrated. The proposed generator features good reconfiguration and switchability. By simply adjusting the direct current biases of the modulator, amplitude shift keying (ASK), phase shift keying (PSK) and frequency-shift keying (FSK) microwave signals can be generated. Benefiting from the complementary intensity modulation, there is no residual baseband modulated signal in the generated binarily modulated signals. The system does not involve any optical or electrical filters, which ensures good tunability of the generator. By changing the frequency of the driven microwave carrier and bit rate of the electrical coded signal, the frequency and rate of the generated multi-format signals can be adjusted accordingly. The multi-format switchable signal generator has great potential in multi-functional communication and radar systems.

Photonic Generation of Reconfigurable Ternary Modulated Microwave Signals with a Large Frequency Range

A photonic scheme generating ternary modulated signals, which include amplitude, phase, and frequency modulated signals, has been proposed and demonstrated. This scheme is based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), where the X-DPMZM is used to generate an optical frequency comb (OFC), and the Y-DPMZM is utilized to accomplish ternary modulation. The key feature of this scheme is that ternary modulated signals with eight wavebands can be obtained by using only the DP-DPMZM in situations of different input signals. In the simulation, a 2.5 Gbit/s amplitude shift keying (ASK), phase shift keying signal (PSK), or an 8 GHz bandwidth linearly frequency modulated (LFM) signal are obtained. The generated signals have eight wavebands with a large frequency range from 10 GHz to 80 GHz. Moreover, the recovery and pulse compression performances of the generated signals are evaluated.

Broadband multi-frequency microwave photonic up-conversion with tunable phase shift

A broadband multi-frequency microwave photonic up-conversion scheme with a tunable phase shift is proposed and demonstrated based on a cavity-less ultrashort optical pulse source and a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In this scheme, the intermediate-frequency (IF) signal is loaded onto the optical frequency comb from a cavity-less ultrashort pulse source via carrier-suppressed double-sideband (CS-DSB) modulation by using a DP-DPMZM and a 90° electric hybrid coupler (HC). Through mutual beating between multi-groups of optical modulation sidebands and multi-tone optical carrier at the photodetector (PD), multi-frequency up-converted microwave signals are obtained after coherent superposition. Meanwhile, the phase of the generated signals can be continuously tuned through varying the bias voltages of the DP-DPMZM. Simulation results show that the multi-frequency up-conversion is with a 3-dB operation bandwidth of 36 GHz and a phase shift tuning range over 360°. Hence, this scheme is a potential candidate to simultaneously realize broadband multi-frequency operation and generate the large-scale tunable phase shift in modern radar systems.

Photonics-assisted joint communication-radar system based on a QPSK-sliced linearly frequency-modulated signal.

A photonics-assisted joint communication-radar system is proposed by introducing a quadrature phase-shift keying (QPSK)-sliced linearly frequency-modulated (LFM) signal. An LFM signal is carrier-suppressed single-sideband modulated onto the optical carrier in one dual-parallel Mach-Zehnder modulator (DPMZM) of a dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM). The other DPMZM is biased as an IQ modulator to implement QPSK modulation on the optical carrier. The polarization orthogonal optical signals from the DPol-DPMZM are further combined and detected in a photodetector to generate the QPSK-sliced LFM signal. The QPSK-sliced LFM signal is used to realize efficient data transmission and high-performance radar functions including ranging and imaging. An experiment is performed. Radar range detection with an error of less than 4 cm, inverse synthetic aperture radar imaging with a resolution of 14.99cm×3.25cm, and communication with a data rate of 105.26 or 210.52 Mbit/s are successfully verified.

Switchable down-, up- and dual-chirped microwave waveform generation with improved time–bandwidth product based on polarization modulation and phase encoding

A switchable down-, up- and dual-chirped microwave waveform generation technique with improved time–bandwidth product (TBWP) is proposed and demonstrated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) cascaded with a polarization modulator (PolM). By properly controlling the phase shifts of the radio frequency signals applied to the DP-DPMZM, switchable down-, up- and dual-chirped waveforms with simultaneous frequency and bandwidth doubling can be generated. To enlarge the TBWP further, splitting parabolic signal and phase-encoding splitting parabolic signal are used to drive the PolM for the enhancement of bandwidth and time duration. Numerical results demonstrate the generation of down-, up- and dual-chirped microwave waveform with TBWP of 8, 160 and 10240. The proposed method may find applications in future multifunction radar systems due to the high performance and flexibility.

Brillouin-assisted frequency-tuning-range-extended and passband-selected microwave photonic filter based on DPol-DPMZM

A frequency-tuning-range-extended and passband-selected microwave photonic filter (MPF) based on dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM) is proposed and experimentally demonstrated. The upper DPMZM is biased to serve as an equivalent phase modulator, while the lower DPMZM is selectively biased to generate different modulated sideband for pump wave, and then different passband frequency response is selectively realized based on the stimulated Brillouin scattering effect. By using the upper and lower sidebands of carrier-suppression single sideband for pump wave successively, the frequency tuning range of the single-passband MPF can be extended by a value of Brillouin frequency shift, comparing with only one sideband is used. A single-passband MPF with a frequency tuning range of 1.43–19.43 GHz is experimentally obtained, while only a single-tone RF with a frequency range of DC-9 GHz is used. The double-passband MPF with equal passband magnitude and frequency interval tuned is also experimentally achieved.

Flexible Multi-band Dual-chirped Microwave Waveforms Generation with Double Bandwidth

ABSTRACT A multi-band dual-chirp linearly frequency modulated (LFM) signal-generation scheme with doubled chirp bandwidth and flexible center frequency and band numbers is proposed. In the scheme, the polarization multiplexed multi-tone optical signals with chirped phases are generated via a dual-polarization dual-parallel Mach–Zehnder modulator (DPMZM) cascaded with a polarization modulator. The two polarization multiplexed lightwaves are recombined as two linearly polarized beams by a polarization beam splitter and are detected by a balanced photodiode with a photocurrent that includes the multi-band dual-chirp LFM signal with doubled bandwidth and multiplied central frequencies but does not have a dc component. Since the orders and numbers of the generated optical sidebands are changed by adjusting the bias voltages of a DPMZM, we can obtain the multi-band dual-chirp LFM signal flexibly. Based on simulation, four-band, six-band and two seven-band dual-chirp LFM signals are generated with four groups of bias voltage configurations. For each case, every dual-chirp LFM signal of the generated multi-band dual-chirp LFM signal has a 5-GHz bandwidth and a time-bandwidth product of 512. The auto-correlations and ambiguity function of the generated LFM signal show good performance of pulse compression and range-Doppler resolution.

Multi-Functional Microwave Photonic Radar System for Simultaneous Distance and Velocity Measurement and High-Resolution Microwave Imaging

A photonic-assisted multi-functional radar system for simultaneous distance and velocity measurement and high-resolution microwave imaging is proposed and experimentally demonstrated by using a composite transmitted microwave signal of a single-chirped linearly frequency-modulated (LFM) signal and a single-tone microwave signal. In the system, the transmitted signal is generated via photonic frequency up-conversion based on a single integrated dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM), while the echo signals scattered from the target are de-chirped to two low-frequency signals using a microwave photonic frequency mixer. By using the two low-frequency de-chirped signals, the real-time distance and radial velocity of the moving target can be measured accurately according to the round-trip time of the echo signal and its Doppler frequency shift. Compared with the previously reported distance and velocity measurement methods, where two LFM signals with opposite chirps are used, these parameters can be obtained using only a single-chirped LFM signal and a single-tone microwave signal. Meanwhile, high-resolution inverse synthetic aperture radar (ISAR) imaging can also be realized using ISAR imaging algorithm. An experiment is performed to verify the proposed multi-functional microwave photonic radar system. An up-chirped LFM signal from 8.5 to 12.5 GHz and an 8.0 GHz single-tone microwave signal are used as the transmitted signal. The results show that the absolute measurement errors of distance and radial velocity are less than 5.9 cm and 2.8 cm/s, respectively. ISAR imaging results are also demonstrated, which proves the high-resolution and real-time ISAR imaging ability of the proposed system.

Photonic generation of quadruple bandwidth dual-band dual-chirp microwave waveforms with immunity to power fading.

A photonic method to generate and transmit quadruple bandwidth dual-band dual-chirp microwave waveforms with immunity to fiber chromatic dispersion induced power fading is proposed and experimentally demonstrated, which is suitable for Doppler blind-speed elimination, small target detection, and multiband detection in multiband radar systems. A dual-polarization dual-parallel Mach-Zehnder modulator is utilized to realize carrier-suppressed harmonic single-sideband modulation of a radio frequency carrier and carrier-suppressed DSB modulation of a baseband single-chirped waveform at two orthogonal polarization states. After photoelectronic conversion, dual-band bandwidth-quadrupling dual-chirp waveforms are generated. Moreover, different from traditional DSB-based dual-chirp signal generation, the generated dual-chirp microwave waveforms can be transmitted over fiber without power fading, which is significant in dual-band radars for one to multiple base station transmissions.

Photonic Generation and Transmission of Dual-Band Dual-Chirp Microwave Waveforms at C-Band and X-Band With Elimination of Power Fading

We propose a photonic method to generate and transmit dual-band dual-chirp microwave waveforms based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). The key novelty of this work is the generation of dual-band dual-chirp waveforms with flexible central frequency relationship to meet the requirement of the dual-band radar system, and transmission of the generated waveforms with elimination of power fading. In the proposed method, dual-band dual-chirp microwave waveforms are generated by applying two different RF signals and a parabolic coding signal to the DP-DPMZM. By properly adjusting the DC biases of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -DPMZM and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -DPMZM, dispersion-induced power fading effect in the transmission of the generated waveforms can be compensated. A proof-of-concept experiment is conducted to generate and transmit dual-band dual-chirp microwave signals at C-band and X-band (centered at 7 GHz and 10 GHz) with tunable bandwidth. The proposed system has a simple structure and good reconfigurability, which has great potential in applications such as dual-band radar systems.