Microwave Photonic Link Research Articles

TFLN-based nondegenerate optical parametric amplifier with high gain, high saturated optical power and linear wavelength tunability

Optical parametric amplifier (OPA) utilizing thin-film lithium niobate (TFLN) is a cornerstone in integrated microwave optics and high-speed optical communication due to its outstanding properties, including high gain, low noise figure, and high integration. Here, we proposed a pump-depletion nondegenerate amplifier to discuss the saturated optical power. This OPA exhibits a good performance with high gain (over 30 dB) and high saturated optical power (over 15 dBm). The signal frequency is well separated from idle which reduces the difficulties of separation. Meanwhile, we found that the quasi-phase-matching wavelength can be regulated by temperature to achieve a linear adjustable OPA. Detailed design strategies are provided in this paper to underpin the fabrication of high-performance OPA in integrated optics. This theoretical analysis creates opportunities for performance enhancement in microwave photonic links.

Performance study of microwave photonic links by considering the effect of phase shifters and bias conditions on dual-drive dual parallel Mach–Zehnder modulator

Abstract This paper presents the performance analysis of different schemes for generating linearized photonic signal by varying phase shifter arrangements of a dual-drive dual parallel Mach–Zehnder modulator (DD-DPMZM). The RF signals at the electrodes of sub-modulators of DD-DPMZM are fed using different phase angles to generate optically modulated signals in the output. The proposed system consists of a DD-DPMZM and phase shifters. Spurious free dynamic range (SFDR) is evaluated for different configurations of sub modulators in upper and lower arm of DD-DPMZM. SFDR of 135.6 dB Hz4/5 is obtained for quadrature and optical carrier suppression modulation in upper and lower submodulators by suppressing third order intermodulation distortion completely. It is found to be high performance configuration for dual parallel Mach–Zehnder modulator based linear microwave photonic link.

A Wideband LFMCW Radar Jamming System Based on Microwave Photonic Link

A Wideband LFMCW Radar Jamming System Based on Microwave Photonic Link

Adaptive Non-Iterative Linearization Technique for Broadband Multi-Carrier Microwave Photonic Link

Adaptive Non-Iterative Linearization Technique for Broadband Multi-Carrier Microwave Photonic Link

Optical frequency comb assisted reconfigurable broadband spread spectrum signal generation.

A photonic-assisted scheme for spread spectrum communication signals generation is proposed and demonstrated in this article. The spreading sequence and the baseband data codes are modulated on the photonic link by electro-optic modulators, and the spread spectrum process is completed through stream processing on the analog microwave photonic link. By combining optical frequency comb and injection locking technologies, the carrier frequency of the communication signals can be tuned over an ultra-broadband range of 3-39 GHz. In the proof-of-concept experiments, spread spectrum signals at 3 GHz and 6 GHz are obtained with a spread factor of 31. The analysis results indicate that the generated signals possess excellent reconfiguration, anti-interference, and anti-interception properties. Overall, our proposed scheme offers a flexible photonic architecture with significant potential in the application of ultra-broadband covert communication systems.

Comparison of Polarization Fading Compensation Methods for Broadband Microwave Photonic Links by Introduced Noise and Achievable Dynamic Range

Comparison of Polarization Fading Compensation Methods for Broadband Microwave Photonic Links by Introduced Noise and Achievable Dynamic Range

Time-delay signature suppression of the chaotic signal in a semiconductor laser based on optoelectronic hybrid feedback.

An approach to generating chaotic signals with low time-delay signatures (TDSs) from a semiconductor laser (SCL) is proposed and demonstrated based on optoelectronic hybrid feedback. Through using a chirped fiber Bragg grating (CFBG) to provide distributed feedback, a chaotic signal with a low TDS is generated from the SCL. With the assistance of the nonlinear optoelectronic feedback provided by a microwave photonic link, the relaxation oscillation effect in the SCL is effectively suppressed, and the periodicity of the oscillation is greatly weakened. Hence, the TDS of the generated chaotic signal from the SCL is further suppressed, and the effective bandwidth is enlarged. Both simulation and experiment are carried out to verify the feasibility of the proposed scheme to suppress the TDS. In the experiment, a chaotic signal with a large effective bandwidth of 12.93 GHz, an extremely high permutation entropy (PE) of 0.9983, and a low TDS of 0.04, is generated by using a CFBG with a dispersion coefficient of 22.33 ps/nm. This TDS value is at the same level as that obtained by using the SCL-based scheme relying solely on distributed feedback in a CFBG with a dispersion coefficient of 2000 ps/nm.

Investigation of modified uni-traveling carrier photodiode for cryogenic microwave photonic links

Quantum devices present the potential for unparalleled computing and communications capabilities; however, the cryogenic temperatures required to successfully control and read out many qubit platforms can prove to be very challenging to scale. Recently, there has emerged an interest in using microwave photonics to deliver control signals down to ultracold stages via optical fiber, thereby reducing thermal load and facilitating dense wavelength multiplexing. Photodetectors can then convert this optical energy to electrical signals for qubit control. The fidelity of the quantum operations of interest therefore depend heavily upon the characteristics of the photodiode, yet experimental demonstrations of fiber-coupled photodetection systems at low temperatures are relatively few in number, leaving important open questions regarding how specific detectors may perform in real-world cryogenic settings. In this work, we examine a highly linear modified uni-traveling carrier photodiode (MUTC-PD) under C-band illumination (1530–1565 nm) at three temperature regimes (300 K, 80 K, and ∼4 K) and multiple bias conditions. Our findings of reduced responsivity but preserved bandwidth are consistent with previous studies, while our saturation tests suggest a variety of potential applications for MUTC-PDs in cryogenic microwave photonics with and without electrical bias. Overall, our results should provide a valuable foundation for the continued and expanding use of this detector technology in quantum information processing.

MMW Signal Gain in DML-Based Microwave Photonic Links Under Large Signal Regime

This paper presents a theoretical and experimental analysis of the millimeter wave (mmW) signal gain observed in photonically generated signals by using carrier suppressed (CS) external modulation in a centralized network architecture while the data is transmitted over a directly modulated laser (DML) operating under different signal regimes. Measurements of the frequency response under small and large signal regimes are presented for the sake of comparison. Moreover, the mmW signal gain has been measured for different standard single mode fiber (SSMF) lengths in order to identify the conditions and impact of large signal regime operation. The results are also validated by the experimental transmission of a 25 MHz QPSK signal transmitted over 40 GHz since the error-vector-magnitude (EVM) is measured for different input electrical power values as well as several received optical power (RoP) levels. Moreover, the spurious-free dynamic range (SFDR) ratio is measured to compare the third-order intermodulation distortion (IMD3) between small and large signal regime. The quantitative results demonstrate that proper system conditions allow the exploitation of the mmW signal gain towards the future deployment of high energy efficient networks.

Sagnac Loop Based Broadband Self-Interference Cancellation and Down-Conversion for Distributed Antenna Systems

Focusing on distributed antenna systems, we propose a photonics-assisted self-interference cancellation and down-conversion method based on a Sagnac loop structure. Two inversely cascaded modulators form a Sagnac loop through polarization multiplexing. To support in-band full duplex (IBFD) communication, a double parallel Mach–Zehnder modulator (DPMZM) operated in a clockwise direction is used as a self-interference canceller (SIC) to achieve the phase conversion in the optical domain. Another MZM modulator working in the counterclockwise direction is used to modulate the local oscillation (LO) signal for frequency down-conversion. The adjustment of bias voltage is analyzed to optimize the conversion efficiency of the system. The power fading effect generated by fiber dispersion is compensated by a polarization-sensitive phase modulator (PS-PM). The experimental results show that the average cancellation depth is 56.4 dB at a single frequency in the operating frequency range of 6–22 GHz, and 29.1 dB and 23.7 dB for 20 MHz and 100 MHz bandwidth signals, respectively. In addition, the error vector map is improved from 16.50% to 6.26% after dispersion compensation. The self-interference cancellation, down-conversion and dispersion compensation are integrated in a microwave photonics link. Two cascaded modulators are equivalent to a parallel structure by the Sagnac loop, simultaneously ensuring high LO isolation and conversion efficiency. The proposed method provides an alternative for IBFD-based distributed antenna communication applications.

One kilometer balanced analog photonic link based on a single multicore fiber

A one kilometer balanced microwave photonic link based on a single four core multicore optical fiber is demonstrated for the first time, to the best of our knowledge. The radio frequency gains and differential phase stabilities over temperature were measured and compared to a conventional balanced link based on two spans of single mode fiber. Both the multicore fiber link and the single mode fiber balanced link exhibited differential phase fluctuations of |Δφ|≤13° at 25 GHz (corresponding to a differential delay or skew, |Δt|, of ≤1.4ps) under identical periodic temperature oscillations of ±13°C over a 60 min period. In contrast, previous studies have shown that two single mode fiber spans should have exhibited up to an order of magnitude greater Δφs compared to the multicore fiber. Our different results can be attributed to how the fibers are arranged; the previous works kept the two single mode fiber spans separate, on different spools, whereas in this work the two single mode fiber spans were co-located as close as possible together by spooling them ‘side-by-side’ onto a single mandrel, more representative of a balanced link in application. In addition, the radio-frequency crosstalk between the multicore fiber’s cores were measured, exhibiting acceptable levels at least 60 dB below the signal for all core combinations. The crosstalk is shown to be dominated by occurrences at localized points, e.g. at the multiplexers (fan-in/fan-outs) and splices, rather than during propagation. Regardless of the single mode fiber link’s performance, the measurements here demonstrate that multicore fiber-based balanced links are a viable single fiber alternative to conventional dual single mode fiber-based balanced links.

A broadband integrated microwave photonic mixer based on balanced photodetection

An integrated microwave photonic mixer based on silicon photonic platforms is proposed, which consist of a dual-drive Mach–Zehnder modulator and a balanced photodetector. The modulated optical signals from microwave photonic links can be directly demodulated and down-converted to intermediate frequency (IF) signals by the photonic mixer. The converted signal is obtained by conducting off-chip subtraction of the outputs from the balanced photodetector, and subsequent filtering of the high frequency items by an electrical low-pass filter. Benefiting from balanced detection, the conversion gain of the IF signal is improved by 6 dB, and radio frequency leakage and common-mode noise are suppressed significantly. System-level simulations show that the frequency mixing system has a spurious-free dynamic range of 89 dB·Hz2/3, even with deteriorated linearity caused by the two cascaded modulators. The spur suppression ratio of the photonic mixer remains higher than 40 dB when the IF varies from 0.5 to 4 GHz. The electrical-electrical 3 dB bandwidth of frequency conversion is 11 GHz. The integrated frequency mixing approach is quite simple, requiring no extra optical filters or electrical 90° hybrid coupler, which makes the system more stable and with broader bandwidth so that it can meet the potential demand in practical applications.Graphical

Ultrahigh-linearity dual-drive scheme using a single silicon modulator.

Here, a high-linearity dual-drive scheme using a single silicon dual-drive Mach-Zehnder modulator is presented. The bias voltages and RF amplitudes of the two driving arms are adjusted such that the nonlinearity of the transfer function of the Mach-Zehnder interferometer cancels out the nonlinear response of the arms. Using the proposed scheme, the spurious-free dynamic range of the third-order intermodulation distortion is 123.4 dB Hz6/7, which is believed to be a record-breaking value for silicon modulators. In comparison, the result obtained using a conventional single-drive scheme is 102.6 dB·Hz2/3. The proposed scheme could simplify the design of modulators and promote high-performance microwave photonic links.

Linearization of a Dual-Parallel Mach-Zehnder Modulator Using Optical Carrier Band Processing

The linearization of a microwave photonic link based on a dual-parallel Mach-Zehnder modulator is theoretically described and experimentally demonstrated. Up to four different radio frequency tones are considered in the study, which allow us to provide a complete mathematical description of all third-order distortion terms that arise at the photodetector. Simulations show that a complete linearization is obtained by properly tuning the DC bias voltages and processing the optical carrier band. As a result, a suppression of 17 dB is experimentally obtained for the third-order distortion terms, as well as a SDFR improvement of 3 dB. The proposed linearization method enables the simultaneous modulation of four different signals without the need of additional radio frequency components, which is desirable to its implementation in integrated optics and makes it suitable for several applications in microwave photonics.

High-Performance Microwave Photonic Transmission Enabled by an Adapter for Fundamental Mode in MMFs

Microwave photonic links (MPLs) have long been considered as an excellent way for radio frequency (RF) transmission due to their advantages such as light weight, high bandwidth, low cost and large spurious-free dynamic range (SFDR). However, the effective mode-field area (Aeff) of the single-mode fiber (SMF) used in the traditional MPL is not large, so the MPL based on SMF have relatively strong nonlinearity, which limits the processing power of SMFs to a level of few milliwatts. Few-mode fibers (FMFs) have been applied in MPL as an alternative due to the larger Aeff, and photonic lanterns are used simultaneously to excite the high-order mode of FMFs for RF signal transmission. However, the photonic lantern could bring additional insertion loss, and the production cost of FMFs is high, so we propose an MPL based on multimode fibers (MMFs) with mode field adapters (MFAs). Since MMFs have larger Aeff, the nonlinearity of the link can be greatly reduced. And matched MFAs realized by reverse tapering, to excite only the fundamental mode in MMFs to reduce the crosstalk, which are very stable. As a result, the stimulated Brillouin scattering threshold and SFDR are improved by 5 dB and 14.5 dB, respectively.

A ‘DOMZM–Filter–BPD’-Based Microwave Photonic Link for Eliminating Even Harmonics Distortion

The ‘Mach-Zehnder modulator (MZM)–wavelength division demultiplexer (WDM)–photodetector (PD)’ structure in photonic analog-to-digital converters (PADCs) may result in residual even harmonics after photodetection. In this paper, we build the model for the ‘Dual-output MZM (DOMZM)–filter–balanced PD (BPD)’-based microwave photonic link, where the amplitude and the phase responses of the filter can be arbitrary. It is proved that this link can eliminate the aforementioned even harmonics. Theoretical analysis is verified by the simulation and experimental results. By using this structure, the spur-free dynamic range (SFDR) limited by the even harmonics can be improved and the sampling frequency range can be expanded for the PADCs. As the spectrum contains only odd harmonics, the inverse cosine transform for calibrating the nonlinearity of the MZM can be applied to further improve the SFDR.

Highly linear lithium niobate Michelson interferometer modulators assisted by spiral Bragg grating reflectors.

Highly linear electro-optic modulators are key components in analog microwave photonic links, offering on-chip direct mixing of optical and RF fields. In this work, we demonstrate a monolithic integrated Michelson interferometer modulator on thin-film lithium niobate (LN), that achieves linearized performance by modulating Bragg grating reflectors placed at the end of Michelson arms. The modulator utilizes spiral-shaped waveguide Bragg gratings on Z-cut LN with top and bottom electrodes to realize extensive reflectors, essential for linearized performance, in a highly integrated form. Optical waveguides are realized using rib etching of LN with precisely engineered bottom and top cladding layers made of silicon dioxide and SU-8 polymer, respectively. The compact design fits a 3 mm long grating in an 80 µm × 80 µm area, achieving a broad operating bandwidth up to 18 GHz. A spurious free dynamic range (SFDR) of 101.2 dB·Hz2/3 is demonstrated at 1 GHz, compared to 91.5 dB·Hz2/3 for a reference Mach-Zehnder modulator fabricated on the same chip. Further enhancement in SFDR could be achieved by reducing fiber-to-chip coupling loss. The proposed demonstration could significantly improve the linearity of analog modulator-based integrated optical links.

A Microwave Photonic Link With Quadrupled Capacity Based on Coherent Detection and Digital Phase Noise Cancellation

A microwave photonic link (MPL) with quadrupled capacity based on coherent detection and digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, a continuous-wave (CW) light wave is intensity modulated by four independent microwave vector signals with two having an identical center microwave frequency at a dual-parallel Mach-Zehnder modulator (DPMZM) consisting of two dual-drive MZMs (DEMZMs) with the sub-DEMEMs biased at the quadrature transmission point. Four intensity-modulated optical signals are generated and transmitted over a single-mode fiber (SMF) to a coherent receiver. To perform coherent detection, a second CW laser source as a local oscillator (LO) is also applied to the coherent receiver. To recover the microwave vector signals, a novel digital phase noise cancellation algorithm is developed and applied to eliminate the joint phase noise from the transmitter laser source and the LO laser source as well as the unstable offset frequency between the two laser sources. A theoretical analysis is performed to show the recovery of the microwave vector signals which is verified by an experiment. For four independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals with a symbol rate of 0.5 GSymbol/s, error-free transmission over a 9-km SMF is achieved when the received optical power at the coherent receiver is higher than −18 dBm with forward error correction (FEC).

Linearization for Microwave Photonic OFDM Transmission Systems Using an Iterative Algorithm Based on FEC Mechanism

A digital linearization algorithm is proposed to reduce the third-order intermodulation distortion (IMD3) for the microwave photonic (MWP) orthogonal frequency-division multiplexing (OFDM) transmission system with intensity modulation and direct detection. Forward error correction (FEC) is added to the OFDM signal to suppress the IMD3 in conjunction with an iterative operation. The distorted OFDM signal from the MWP system goes through iterative operations including fast Fourier transform, demodulation, error correction, signal reconstruction, and interference cancellation until the output converges. Compared with the non-iterative method and the iterative method without FEC mechanism, the proposed method has a significant advantage in linearizing signals with large nonlinearity and low signal-to-noise ratio. 200-Msym/s 64 quadrature-amplitude modulation (64-QAM) OFDM signals with a large peak-to-peak voltage of 650 mV are amplified by a power amplifier and then input to the MWP link and linearized by the FEC-based iterative method. The results show that the error vector magnitudes (EVMs) of the OFDM signals can be optimized from 13.1% to 2.9% and from 13.4% to 6.3% when the output <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_b/N₀</i> from the MWP link is about 35 dB and 13.5 dB, respectively. Besides, a 3-GHz 64-QAM OFDM signal is successfully transmitted through a 25-km standard single-mode fiber with an EVM of 3.9% after linearization.

Polymer modulators in silicon photonics: review and projections

Abstract Optical modulators are vital for many applications, including telecommunication, data communication, optical computing, and microwave photonic links. A compact modulator with low voltage drive requirement, low power, high speed, and compatibility with CMOS foundry process is highly desirable. Current modulator technologies in Si suffer from trade-offs that constrain their power, performance (speed, drive voltage), and area. The introduction of additional materials to the silicon platform for efficient phase shift promises alternatives to relax those trade-offs. Si-organic-hybrid (SOH) devices demonstrate large modulation bandwidth leveraging the electro-optic (EO) effect and smaller drive voltage or footprint owing to a strong EO coefficient. In this study, we review various SOH modulators and describe their path towards integration to silicon, including their challenges associated with aging and temperature. We also briefly discuss other high-performance modulators such as plasmonic-organic-hybrid (POH), photonic-crystal-assisted SOH, and LiNbO3.