We experimentally demonstrate a microwave frequency measurement scheme using a heterogeneous multicore fiber (MCF). Taking advantage of the inherently different differential group delays (DGDs) among four cores of the heterogeneous MCF, two individual 2-tap microwave filters with different free spectral ranges (FSRs) are constructed and the power ratio between their frequency responses is used as the amplitude comparison function (ACF). Since the DGD among the cores and the FSR of the filters are wavelength-dependent, by tuning the operational wavelength over a set of different values, we can obtain a set of different ACF traces. The collective information provided by these ACFs is then used to estimate the unknown frequency. Compared to many previous microwave frequency measurement approaches using dispersive elements, this scheme offers higher flexibility, tunability and compactness, along with higher measurement resolution (±71 MHz) over a broader radiofrequency range (0.5–40 GHz).
Multi-static SARs from low earth orbits (LEO) allow single-pass high-resolution imaging and detection of moving targets. A coherent MIMO approach requires the generation of multi-band orthogonal signals, the fusion of which increases the system resolution. Up to now the synchronization capability of SAR signals of different satellites is critical. Here we propose the use of photonics to generate, receive and distribute the radar signals in a coherent multi-static SAR constellation. Photonics overcomes issues in implementation of MIMO SAR, allowing for flexible multi-band signals generation and centralized generation in a primary satellite with coherent distribution to all the secondary satellites of the SAR signals through FSO links. The numerical analysis shows the proposed system has noise equivalent sigma zero (NESZ) <−31.6 dB, satisfying the SAR system requirements. An experimental proof of concept based on commercial bulk devices, for both radar signal up and down conversion is implemented, demonstrating the system functionality.
We present an ultra-stable wideband signal distribution system via a star-like fiber network. By inserting a 26 GHz probe signal and precisely measuring its round-trip delay variation with double optical mixing, the link length variation has been accurately compensated, leading to a distributed transmission network with stability on the order of femtosecond. Experimentally, a wideband signal ranging from 8 GHz to 12 GHz is distributed from a local end to 2 remote ends via 20 km fiber links. The root-mean-square delay jitters of the transmitted wideband signals are between 10 to 20 femtoseconds within an hour. The proposed wideband signal transfer scheme is highly desired for distributed systems with high stability and strict coherence requirements.
We present experimental results of Power-over-Fiber (PoF) impact on 5G New Radio Analog Radio over fiber transmission. Different ARoF links are implemented with approximate lengths of 6km, 10km, 14km, and 25 km, using QPSK modulations, with a bandwidth of 5MHz and with RF carriers within the range from 10 GHz to 20 GHz. The high power laser (HPL) output is set up to +33 dBm. In the experiment, the power fading, and the critical frequency shift as a consequence of the power injected by the HPL are analyzed. A maximum shift of 250 MHz was experimentally obtained at a length of 25.2 km for a HPL optical power of 33 dBm.
Synthesis of low-noise microwaves is desirable in a wide variety of scientific and engineering fields. Optical frequency division with frequency combs has been a key part in the realization of ultrastable microwave signals. However, fully self-referenced frequency combs are complex and involve several nonlinear processes for implementation of the f-2f interferometer. In this paper, we provide a novel approach for generation of ultrastable microwaves by stabilizing the comb spacing, while the offset frequency of the comb is free-running. This is achieved by mixing the beats of a frequency comb with two continuous wave (cw) lasers separated by 1.3 THz, which are PDH locked to a single reference cavity. We demonstrate the generation of stable 10 GHz microwaves with −140 dBc/Hz phase noise at 10 kHz Fourier frequency and 5·10 −13 level Allan deviation instability at 0.3 s. This work projects the potential of future compact microwave generation with low power consumption.
Thanks to the development of high power uni-travelling-carrier photodiodes, we studied optoelectronic oscillators architectures with optical gain. We compared the phase noise performances with two different optical amplifiers, based on erbium-doped fiber or semiconductor. Optical intensity noise is the main limitation for the phase noise, both at low and high offset frequencies. With a semiconductor optical amplifier, ultra-low phase noise is reached with equivalent performances from 8 to 15 GHz.
An adaptive multipath optical self-interference cancellation scheme based on deep reinforcement learning is proposed and investigated. The simulation results demonstrate that the proposed scheme can adaptively achieve multipath self-interference cancellation using deep neural networks, where the multipath SI is successfully eliminated to the noise floor and a cancellation depth of 33.4 dB over 2 GHz bandwidth at a center frequency of 2 GHz is achieved within 5 steps. The proposed scheme may provide a promising solution for future in-band full-duplex systems.
In this paper, we present a theoretical framework for investigating losses and thermal fluctuations in a Josephson traveling-wave parametric amplifier (JTWPA). Our model is based on a discrete-mode Hamiltonian which includes a four-wave-mixing process and system-reservoir interactions. From this Hamiltonian, we derive a quantum master equation that describes the lossy Josephson-junction-embedded transmission line. The resulting equation of motion for the reduced density operator is applied for evaluating the average photon number in the signal mode. We present an analytic solution for the case of a dispersionless transmission line, where the phase-modulation effects can be neglected, and evaluate the photon number spectrum of a JTWPA structure with parameters from the literature. The quantum master equation is especially advantageous for a direct treatment of the expectation values of the photon number, in comparison to other strategies.
Deep learning is a powerful tool for enhancing performance and increasing the functionalities of a system. However, it is challenging to use deep learning to enhance hardware-based photonic systems because a large dataset that covers the whole operation range of each device is needed for achieving an accurate model. However, not all devices in a system can be controlled automatically, making the data collection process challenging and time consuming. In this letter, we use an instantaneous microwave frequency measurement (IFM) system to demonstrate the use of generative adversarial network (GAN) in deep learning platform for data augmentation. With GAN, only 75 sets of experimental data are needed to collect manually from the IFM system. The GAN augments the 75 sets of experimental data into 5000 sets of data for training the model, effectively reduces the amount of experimental data needed by 98.75%, and reduces frequency estimation error by 10 times.
We experimentally demonstrate a duplex millimeter-wave-over-fiber (MMWoF) link for duplex wireless communications using a free-running InAs/InP quantum-dash passively-mode-locked laser (QD-MLL) as a light source. The QD-MLL is able to generate a frequency comb with a comb spacing of 0.2 nm (25.08 GHz). In the downlink, a microwave vector signal at 3 GHz is modulated on one comb line and transmitted with an adjacent comb line to a remote radio unit over a 10-km single-mode fiber. After detection at a photodetector, a microwave vector signal at an up-converted frequency of 28 GHz is generated and radiated to achieve 2-m wireless transmission. In the uplink, a microwave vector signal at 28 GHz is down converted to 3 GHz and modulated on a reused comb line and transmitted to the central office over the same fiber link. The performance in terms of the error vector magnitudes and bit error rates is evaluated experimentally.
High-resolution imaging of near field targets is experimentally demonstrated using a broadband microwave photonic array radar that is implemented by photonic frequency quadrupling and de-chirping. A scanning time delay (STD) compensated digital beam forming (DBF) method is adopted to deal with the beam squint and broadening problem in broadband radar imaging. In the experiment, a 1×16 microwave photonic array radar having a bandwidth of 8 GHz is implemented. By using the STD-compensated DBF method, high-resolution imaging of near-field targets is achieved with obvious suppression of grating lobes and accurate beam correction.
Biomimicry offers effective solutions to critical challenges in our society by learning and mimicking the strategies used by living organisms. In this paper, biomimicry in microwave photonics and soft robotics will be introduced. Bio-inspired approaches has been used to provide promising solutions to the field of microwave photonic such as localization, jamming avoidance, and steganography. The analog solution provided by bio-inspired approaches does not propose a bandwidth limitation because there is no need for digitization. In recent years, soft robotics has been a promising alternative to conventional robots by offering safer robot-to-human interaction. Unique embedding configurations allow fiber optic sensor to be used in soft robotic to provide feedback for precise control. The second part of this paper will introduce several bio-inspired soft robots with embedded fiber optic sensors. Fiber optics provide flexible and light weight sensing solution, making it a promising candidate for sensing in soft robotics.
This work is reporting the concept of photomixer arrays for multiple 100 Gbit/s THz communications, as a technology enabler towards Tbit/s transmitters. Initial 4-UTC-PD array is shown and characterization of a single UTC-PD used as 100 Gbit/s data source.
Heterogeneous integration provides the capability of integrating III-V gain material with ultra-low-loss silicon photonic circuits on a monolithic silicon substrate. This integration results in the dramatic reduction of optical loss of the laser cavity and thus extends the photon lifetime and narrows the linewidth of semiconductor lasers beyond what is achieved with monolithic III-V integration. Recent progress includes widely-tunable III-V/silicon lasers with ultra-wide tuning range and lasers on silicon nitride with narrow linewidth that is comparable with fiber lasers. These lasers will play a critical role in ultra low noise microwave photonics.
We develop and experimentally demonstrate a microwave photonic-based directional phased antenna array using quantum dash mode-locked laser. Thanks to the 25 GHz free spectral range, this system has higher band utilization. With these comb lines, two types of directional antenna arrays, uniform linear array (ULA) and uniform circular array (UCA), are designed and simulated. It is found that these two structures have directivity up to 14 dBi. Moreover, the end-fire ULA system shows less sensitivity to the phase error. Although UCA is more sensitive, it also has wider RF bandwidth compared to ULA.
In this paper, investigations of a novel photonic measurement technique for scaled microwave structures have been further explored. Results of this new technique are promising in linking microwave scattering of large electromagnetic structures to those of near-infrared (NIR).
We present a phase-stable receiving system for signals transmitted via a 25 km fiber optic link. The timing jitter of the signal induced by the transmission link is precisely eliminated after the signal is digitized with a dithered sample clock. The dithered clock is generated from the phase of a voltage-controlled oscillator, introducing the same transmission timing jitter of the link. Therefore, it can withstand an unlimited range of transmission delay variations without using any optical or electrical delay lines. Experimentally, a binary phase-shift keying signal is transmitted and received by the proposed system. The calculated timing jitter of the received signal with a bandwidth of 400 MHz is decreased from 650 ps to merely 1.6 ps. The simple remote end and immunity to environmental perturbations of the proposed scheme make it an ideal candidate for a large-scale distributed antenna system.
In this paper, a new microwave photonic (MWP) sensing scheme, which is based on interrogating microresonator sensors with fast speed and improved resolution by adopting a broadband linear frequency-modulated pulse (LFMP) in the MWP sideband processing, is presented. The LFMP modulates the interrogation light, creating the optical sideband that sweeps through the resonance rapidly. By using the optimized DC bias point, the resonance spectral dip with arbitrary characteristics can be transformed into the zero point in the temporal envelope of the transmitted LFMP, hence providing improved interrogation resolution of the resonance shifts caused by environmental changes. The proposed scheme was implemented with a microdisk resonance for temperature sensing, where up to 20-fold interrogation resolution improvement was demonstrated by tuning the DC bias voltage to the optimum. The interrogation speed is 500 kHz, which can be further improved by using a shorter repetition period and pulse width.
Covert wireless communication assisted by optical frequency comb (OFC) has already been presented, but its denoise capacity is restricted by the OFC properties. A novel, low-cost covert wireless communication system is proposed and demonstrated. In the proposed approach, original data are spread and buried by the noise to ensure high covertness, and then are effectively recovered by analog frequency convolution using the OFC and the cloned OFC generated by an optical frequency shifter. A same signal to noise ratio (SNR) enhancement can be achieved by employing half of the optical comb lines, which alleviates the requirement of OFC generator. 400 comb lines provide 800 comb channels, so that 29 dB SNR rise is achieved for the microwave signal with a 16 GHz bandwidth and a 20 Mbit/s data rate, which is hidden below the in-band noises by 20 dB or even 29 dB in both the frequency and time domains.
