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Self-interference and chromatic dispersion are two main limiting factors that influence the recovery of the signal of interest (SOI) in in-band full-duplex (IBFD) radio-over-fiber (RoF) links. An ultrawideband photonic-assisted approach to radio-frequency (RF) self-interference cancellation (SIC) with high-speed SOI recovery and fiber transmission capability is proposed. The key to achieve the above optimum performances in a compact system is the combined use of fiber dispersion induced RF time delay and optical carrier phase-shifted double sideband (CPS-DSB) modulation. A high precision and tunable time delay matching between the reference signal and the SI signal can be achieved by dispersion induced RF time delay. Meanwhile, the equal amplitude, phase reversal, and dispersion-induced SOI power fading compensation conditions are satisfied simultaneously by manipulating the optical carrier phase of the CPS-DSB signal. For 25 km fiber transmission, 30 dB cancellation depth over 2.7 GHz bandwidth, 160 Mbit/s 16-quadrature amplitude modulation (16-QAM) SOI recovery, and good immunity to fiber dispersion are experimentally demonstrated. In addition, the proposed scheme facilitates multipath SIC by implementing an array of tunable lasers (TLs) with a shared electro-optic modulator at the reference branch.

A functional flexible photonics-assisted frequency measurement (PFM) is proposed. Owing to polarisation multiplexing, the electro-optic (O/E) conversion can be performed in a single optical path, which endows the system high stability and concise configuration. Moreover, using a specially designed functional coarse/accurate frequency measurement (C/AFM) module, a large covering range, moderate accuracy, and fast response frequency measurement results can be ensured in a radar warning receiver (RWR), whereas high accurate results can be used in an electronic countermeasures receiver (ECMR). The simulation results show that a strict monotonous amplitude comparison function (ACF) can be constructed based on the structure of a Mach – Zehnder interferometer (MZI) to map the signal frequency, with a measurement error of less than 0.2 GHz in the range of 1 – 31 GHz. This coarse measurement results can be used to perform radar warning. Based on this result, a highly accurate frequency measurement result is achieved through stimulated Brillouin scattering (SBS). The results reveal that the accuracy is improved to better than 20 MHz. Noteworthy, the C/AFM module consists of purely passive devices, which makes this system meet the potential of integration.

A novel scheme that can simultaneously measure the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals based on a single photonic system is proposed. At the signal receiving unit (SRU), two echo signals and the reference signal are modulated by a Sagnac loop structure and sent to the central station (CS) for processing. At the CS, two low-frequency electrical signals are generated after polarization control and photoelectric conversion. The DFS without direction ambiguity and wide AOA measurement can be real-time acquired by monitoring the frequency and power of the two low-frequency electrical signals. In the simulation, an unambiguous DFS measurement with errors of ±3 × 10−3 Hz and a −90° to 90° AOA measurement range with errors of less than ±0.5° are successfully realized simultaneously. It is compact and cost-effective, as well as has enhanced system stability and improved robustness for modern electronic warfare systems.

In this paper, an efficient photonics time-delayed mixer (PTDM) is proposed and demonstrated. It mainly consists of a dual-parallel Mach-Zehnder modulator (DPMZM) and a dispersion medium (DM). To eliminate the carrier component, the carrier-suppressed dual-sideband (CS-DSB) modulation is implemented without optical filters. Besides, the CS-DSB modulation is also the key to make the phase response is proportional to the converted frequency. Thanks to the controllable DC bias of the modulator, the power response of this PTDM is also tunable. Thus, this property also endows the PTDM able to resist the dispersion-induced power fading (DIPF) when considering the use of large dispersion medium. Experimental results verify the ability of wideband frequency up- and down-conversion. Moreover, a converted signal with linear phase-frequency response is also achieved, which implies the time delay capability. Time delay tuning is realized by altering the wavelength of the carrier with a stable power response. This structure is very compact and thus compresses the signal processing system volume, which is qualified to be integrated into a receiver/transmitter.

A multiple microwave frequency measurement approach based on frequency-to-time mapping (FTTM) is reported. The FTTM is constructed by optical sideband sweeping and electric-domain intermediate frequency envelope monitoring. Two optimized operations are implemented. First, the use of balanced photodetection cancels out the beat components generated by the signals under test (SUT) themselves, so as to exclude frequency misjudgment. Second, a reference signal is introduced to map the SUT frequency to a relative time difference instead of an absolute time value, avoiding the measuring bias caused by time synchronization. As a result, the proposed scheme with improved robustness could be attractive for future practical applications. An experiment is performed. Microwave frequency measurement from 16 to 26 GHz is demonstrated, with an average error of 7.53 MHz.

In this paper, a novel and efficient photonic-assisted remote frequency measurement (RFM) system with a significantly simplified structure and flexible operation range is proposed. By simply changing the dispersion coefficient or length of the dispersion medium in the central station (CS), the microwave frequency measurement range in the remote antenna unit (RAU) can be tuned. In this system, the RAU and the CS is separated to ensure the concealment and safety of the signal processing unit. The measurement range of the RFM system can be tuned easily during the measurement process without system reconstruction, and different RAUs located at different places can be controlled to work at the same measurement range. The simulation results show that a frequency measurement over the high frequency range (>18 GHz) can be achieved with a measurement error better than ±0.2 GHz. Noteworthy, the impact of the non-ideal factors such as bias drift, intensity noise, phase noise, the equivalent deviation of the polarization beam splitter (PBS), and the dispersion value of the single mode fiber (SMF) is also discussed. It has been proved that they have little influence on the system performance over the high frequency range.

In recent years, chest X-ray (CXR) imaging has become one of the significant tools to assist in the diagnosis and treatment of novel coronavirus pneumonia. However, CXR images have complex-shaped and changing lesion areas, which makes it difficult to identify novel coronavirus pneumonia from the images. To address this problem, a new deep learning network model (BoT-ViTNet) for automatic classification is designed in this study, which is constructed on the basis of ResNet50. First, we introduce multi-headed self-attention (MSA) to the last Bottleneck block of the first three stages in the ResNet50 to enhance the ability to model global information. Then, to further enhance the feature expression performance and the correlation between features, the TRT-ViT blocks, consisting of Transformer and Bottleneck, are used in the final stage of ResNet50, which improves the recognition of complex lesion regions in CXR images. Finally, the extracted features are delivered to the global average pooling layer for global spatial information integration in a concatenated way and used for classification. Experiments conducted on the COVID-19 Radiography database show that the classification accuracy, precision, sensitivity, specificity, and F1-score of the BoT-ViTNet model is 98.91%, 97.80%, 98.76%, 99.13%, and 98.27%, respectively, which outperforms other classification models. The experimental results show that our model can classify CXR images better.

A high-accuracy photonics-assisted frequency measurement with rough-accurate compensation based on Mach-Zehnder interfering and power cancellation is proposed. A polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is employed to mix the unknown RF signal and sweep signal to optical field. The rough measurement is firstly performed by the interference of a Mach-Zehnder interferometer (MZI) to realize fast frequency estimation. Then, based on the rough measurement result, the accurate measurement based on power cancellation is implemented in a much narrower range, which greatly improves the efficiency of frequency measurement. The simulation results show that the amplitude comparison function (ACF) established by interference can achieve a measurement error of less than 0.3 GHz over 0.5 ~39 GHz. Moreover, thanks to the rough-accurate compensation, the accuracy can be further improved to 4 MHz. Additionally, the multiple frequency identification with a resolution of 10 MHz can also be achieved based on this system.

The Sagnac effect is an important factor that leads to nonreciprocity in long-haul fiber-optic time and a frequency transfer system. For high-precision time transfer, correction must be performed to eliminate the time difference based on the trajectory of the path. However, the routing information may be not detailed enough to guarantee sufficient precision for Sagnac correction. Thus, nodes along the path must be surveyed with a certain sparsity. We provide a practical method for estimating the average distance of these nodes. Six simulated paths are generated to validate the method for different uncertainties.

The combined use of carrier suppression single sideband (CS-SSB) modulation and photonic microwave phase shift is described and analyzed to realize microwave frequency down-conversion with image re...

A novel photonic approach to generate frequency and bandwidth multiplying dual-chirp microwave for application in dual-band radar system is proposed using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. The proposed approach is based on optical frequency multiplying and polarization selection. In the approach, the baseband signal and RF signal are injected into the DP-QPSK modulator to generate optical broad spectra and sidebands respectively. By adjusting the bias points of the DP-QPSK modulator, after polarization selection and optical to electrical conversion, frequency-quadrupling bandwidth-octupling and frequency-double bandwidth-quadrupling or frequency-tripling bandwidth-sextupling and frequency-fundamental bandwidth-doubling dual-chirp signals can be generated in the single structure respectively. The proposed approach is verified by simulations. Dual-chirp microwaves with central frequency–bandwidth of 32 GHz-8 GHz, 16 GHz-4 GHz or 24 GHz-6 GHz, 8 GHz-2 GHz are generated in the two ports respectively. Their autocorrelation results manifest good pulse compression capabilities. The central frequency, bandwidth, chirp rate and time duration can be tuned independently. The generated dual-chirp signals show good performance on the range-Doppler coupling and can significantly improve the range-Doppler resolution in dual-band radar system.

We propose and experimentally demonstrate a photonics-aided 2 × 2 multiple-input multiple-output (MIMO) wireless Terahertz-wave (THz-wave) signal transmission system, which realizes 6 × 20-Gb/s six-channel polarization division multiplexing quadrature-phase-shift-keying THz-wave signal delivery over 10-km wireline single-mode fiber- link and 142-cm wireless 2 × 2 MIMO link with a bit-error ratio under the hard-decision forward-error-correction threshold of 3.8 × 10−3. Our employed multi-carrier frequencies are located within the range of 375 GHz to 500 GHz. To the best of our knowledge, this is the first experimental demonstration of 2 × 2 MIMO wireless transmission of multi-channel THz-wave signal. Here, it is worth noting that our wireless 2 × 2 MIMO link, which offers point-to-point straight transmission and brings neither interference nor gain, is different from the traditional MIMO link defined in the field of wireless communications.

A method for photonic generation of arbitrary microwave binary digital modulation signal based on polarization switch is proposed and investigated. A polarization modulator is utilized to switch the direction of a linearly-polarized optical signal between two orthogonal axes. Then, a polarization-dependent modulation structure is employed to modulate an external RF signal to the two optical carriers with different polarization directions respectively. The modulation structure consists of a polarization beam splitter, two parallel placed dual-drive Mach–Zehnder modulators and an optical combiner. By adjusting the parameters of the two modulators, different optical sidebands can be obtained in two polarization directions. After optical-to-electrical conversion, a microwave amplitude shift keying (ASK), frequency shift keying (FSK) or phase shift keying (PSK) signal can be achieved. The modulation format, bit-rate and carrier frequency of the generated signal can be tuned independently and flexibly. A simulation is demonstrated to verify the proposed scheme, a 2-Gbit/s 40-GHz ASK signal, a 2-Gbit/s FSK signal with carrier frequencies of 20 and 40 GHz, and a 2-Gbit/s 20-GHz PSK signal are obtained. The scheme has good tunability.

To generate boiling water beyond 100 °C via heat pump technology, the prototype of an ultra-high temperature air source heat pump water heater (ASHPWH) based on a single-stage compression cycle of R134a was established, and an experimental investigation on it was conducted under an environment temperature of 25 °C. Then, thermodynamic analyses were carried out on the basis of the experimental results, especially when the prototype produced 95.9 and 100.3 °C water. The experimental and analytical results indicate that water beyond 100 °C was achieved through the prototype. When producing 100.3 °C water, the discharge temperature and compression ratio of the compressor of the prototype are only 108.4 °C and 4.07, respectively, which are in moderate levels. Correspondingly, the work input of the compressor is 0.622 kW, the heating capacity is 2.786 kW, and the heating coefficient of performance is 4.48. In addition, when producing 95.9 and 100.3 °C water, the system exergy efficiencies of the prototype are 50.76% and 49.73%, which are larger than those of the existing ASHPWHs, demonstrating that dividing the condensing process into two parts of high-grade exergy and low-grade exergy and utilizing them separately is effective. That is the essential reason of generating boiling water beyond 100 °C as expected only through the single-stage compression cycle.

A photonic microwave hybrid frequency and phase shift keying (FPSK) signal generator is proposed and demonstrated. In the scheme, a parallel structure is constructed to functions as an optical sidebands selector, in which a single-drive Mach-Zehnder modulator (MZM) is placed in parallel with another MZM and a phase modulator (PM). After the parallel structure, a following PM is employed to realize phase modulation. The output signal of the PM is combined with a local oscillator at the receiver after 6-km fiber transmission, and then a hybrid FPSK signal can be obtained after photodetection. The feasibility of the proposed scheme is verified by simulation through a transmission test in a radio over fiber (ROF) system, and a hybrid FPSK signal with frequencies of 5/15 GHz and phase shift of 𝜋 is successfully generated. The scheme features the advantages of polarization independence and good frequency tunability since no polarization multiplexing devices or frequency-dependent devices are applied.

A numerical investigation on the melting process of paraffin wax RT44 under supergravity (5–20 g) was conducted to evaluate the effect of supergravity on the melting heat transfer characteristics. The simulations were conducted in a horizontally placed container with a constant heat flux of 5–50 kW/m2 maintained on the bottom wall under both supergravity and the earth gravity (1 g). The numerical data under supergravity are compared with those under the Earth gravity for all circumstances. The results indicate that the melting heat transfer characteristics of the phase change material (PCM) are affected by supergravity significantly (around 30%) within 20 g. With the increase of supergravity, the heating wall temperature decreases, and the liquid fraction as well as the melting rate increases. Meanwhile, the variation amplitudes of these melting characteristics decrease gradually until less than 2% at 20 g. The effect of supergravity can be attributed to the intensification of the natural convection due to buoyancy, yielding vortexes in internal flow and fluctuations of solid–liquid interface and temperature field.

In this Letter, we demonstrate a ${{\rm Si}_3}{{\rm N}_4}$Si

We controlled the phase matching for four-wave mixing (FWM) in a chalcogenide waveguide by Brillouin-induced phase shift. Over 2n phase shift was realized and a 6-dB improvement in FWM conversion efficiency was obtained.

A photonic approach for the generation of microwave hybrid frequency/phase shift keying (FSK/PSK) signal based on an integrated polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is proposed and demonstrated. In the scheme, the polarization modulator is employed to modulate the linearly polarized lightwave to generate an optical polarization-shift keying (PolSK) signal. Then the PolSK signal is sent to the PDM-DPMZM via a polarization controller to generate optical PSK signal. After photo-detection, a microwave hybrid FSK/PSK signal can be obtained. Simulations are conducted to verify the proposed scheme. As bit rate is set to 1 Gbit/s, a hybrid FSK/PSK signal with frequency of 10/15 GHz and phase shift of $$\pi$$ is successfully demonstrated. Hybrid signals with 2-Git/s frequency shift and 1-Git/s phase shift are also implemented. The compression ratio of the generated signal is 25.5 and the main-to-sidelobe ratio is 11.2 dB. The generations of ASK, PSK and FSK signals are discussed, and the impact of the polarization extinction ratio is also analyzed.

Photonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed....

In this paper, a single, flexible and stable optical frequency conversion scheme with tunable phase shift is proposed. It mainly consists of a dual-parallel binary phase shift keying (DP-BPSK) modu...

A method for photonic generation of a linearly chirped microwave waveform using a frequency-sweeping laser and a dual-polarization modulator is proposed and investigated. A frequency-sweeping continuous-wave light is generated from the laser and then sent to the modulator. In the modulator, one part of the light is modulated with an RF signal to generate a frequency-shifting optical signal, while another part of the light is passed through a polarization rotator to rotate the polarization to an orthogonal direction. At the output of the modulator, the two optical signals are combined with orthogonal polarizations, and then injected into a polarization delay device to introduce a time delay. After combining the two optical signals for heterodyning, a linearly chirped waveform can be generated. The bandwidth, time duration, chirp rate and sign, central frequency of the generated waveform can be tuned independently and flexibly, furthermore, frequency doubling for the central frequency can be achieved in the waveform generation. A simulation is demonstrated to verify the proposed scheme, a linearly chirped microwave pulse with up or down chirp, central frequency of 20 or 40 GHz, bandwidth of 20 GHz, time duration of 500 ns, time-bandwidth product (TBWP) of 10000 is obtained.

Photonic microwave frequency down-conversion with independent multichannel phase shifting and zero-intermediate frequency (IF) receiving is proposed and demonstrated by simulation. By combined use of a phase modulator (PM) in a sagnac loop and an optical bandpass filter (OBPF), orthogonal polarized carrier suppression single sideband (CS-SSB) signals are obtained. By adjusting the polarization controllers (PCs) to introduce the phase difference in the optical domain and using balanced detection to eliminate the direct current components, the phase of the generated IF signal can be arbitrarily tuned. Besides, the radio frequency (RF) vector signal can be also frequency down-converted to baseband directly by choosing two quadrature channels. In the simulation, high gain and continuously tunable phase shifts over the 360 degree range are verified. Furthermore, 2.5 Gbit/s RF vector signals centered at 10 GHz with different modulation formats are successfully demodulated.

A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM). The first DE-MZM can generate a four-comb-line OFC, then the OFC is injected into the second DE-MZM as a carrier, which can increase the number of comb lines. Our modified scheme finally can generate a broadband OFC with high flatness by simply modifying the electrical power and the bias voltage of the DE-MZM. Theoretical analysis and simulation results reveal that a 16-comb-line OFC with a frequency spacing that two times the frequency of the RF signal can be obtained. The power fluctuation of the OFC lines is 0.48 dB and the unwanted-mode suppression ratio (UMSR) can reach 16.5 dB. Additionally, whether the bias drift of the DE-MZMs has little influence on the power fluctuation is also analyzed. These results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness.

A novel photonic dual-frequency phase-coded signals generator based on the optical carrier phase shifting and polarisation selection techniques is proposed by using an integrated dual-polarisation quadrature phase shift keying (DP-QPSK) modulator. The key feature of the scheme is the capability to generate dual-frequency phase-coded signals with reconfigurable frequency multiplication factors. In the upper QPSK modulator, an optical binary phase shift keying (BPSK) signal and a carrier-suppressed double-sideband optical signal are generated, while in the bottom QPSK modulator, another carrier-suppressed double-sideband optical signal is generated. Thanks to the dual-polarisation property of the integrated modulator, the optical BPSK signal and different optical sidebands can be selected by using polarisation selection. As a result, two phase-coded signals with different frequencies can be achieved simultaneously. By adjusting the bias phases of the submodulators, dual-frequency phase-coded signals with frequencies of one and three, or two and four times the frequency of the RF carrier can be generated. The generation of 2.5 Gbps dual-frequency phase-coded signals with frequencies of 20 and 40 GHz, or 10 and 30 GHz are verified. The proposed scheme is simple, compact, and promising to find applications in future multi-band and multi-functional radars.

A photonic approach to generate frequency-doubled microwave waveforms using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator driven by a sinusoidal radio frequency (RF) signal is proposed. By adjusting the dc bias points of the DP-QPSK modulator, the obtained second-order and six-order harmonics are in phase while the fourth-order harmonics are complementary when the orthogonal polarized outputs of the modulator are photodetected. After properly setting the modulation indices of the modulator, the amplitude of the second-order harmonic is 9 times of that of the six-order harmonic, indicating a frequency-doubled triangular waveform is generated. If a broadband 90° microwave phase shifter is attached after the photodetector (PD) to introduce a 90° phase shift, a frequency-doubled square waveform can be obtained after adjusting the amplitude of the second-order harmonic 3 times of that of the six-order harmonic. The proposal is first theoretically analyzed and then validated by simulation. Simulation results show that a 10 GHz triangular and square waveform sequences are successfully generated from a 5 GHz sinusoidal RF drive signal.

A simple photonic microwave image-reject mixer (IRM) using two parallel phase modulators is proposed. First, a photonic microwave mixer with phase shift ability is achieved using two parallel phase modulators (PMs), an optical bandpass filter, three polarization controllers, three polarization beam splitters and two balanced photodetectors. At the output of the mixer, two frequency downconverted signals with tunable frequency difference can be obtained. By adjusting the phase difference as 90° and utilizing an electrical 90° hybrid, the useless components can be eliminated, and the image reject operation is realized. The key advantage of the proposed scheme is the usage of PM, which avoid the DC bias shifting problem and make the system simple and stable. A simulation is performed to verify the proposed scheme, a relative − 90° or 90° phase shift can be obtained between the two output ports of the photonic microwave mixer, at the output of the IRM, 60 dB image-reject ratio is obtained.

We propose and demonstrate a simple, flexible and stably operated multi-band frequency conversion approach based on a dual-polarization quadrature phase shift keying modulator (DP-QPSK). The modulator incorporating two dual parallel Mach–Zehnder modulators (DPMZMs) which perform as OFC generator and +1st carrier suppressed single sideband generator, respectively, to achieve the purpose of frequency conversion. The theoretical analysis indicates that by properly adjusting six DC bias points in the integrated modulator and two modulation indices, a frequency of received RF signal can be directly converted into different frequencies that cover different bands simultaneously. The simulation results verified the possibility. For example, the received C band frequency of 3.8 GHz can be converted into X, Ku, K and Ka bands. An X band frequency of 9.6 GHz can be down-converted to C band and up-converted to Ku, K, Ka band. In addition, the simulation also focuses on how the adjustable parameters (such as DC bias points and modulation index) influence the conversion results. It demonstrates stable conversion efficiency against the DC drafting.