This PDF file contains the front matter associated with SPIE Proceedings Volume 13502, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Benefiting from high parallelism and low latency, photonic integrated circuits (PICs) constructed from on-chip building blocks with diverse functions have emerged as a promising technology in the realm of optical neural networks (ONN). Tunable components, through the utilization of physical mechanisms such as thermo-optic effect and free-carrier plasma dispersion effect, structural motion like microelectromechanical systems (MEMS), or material properties including liquid crystal and two-dimensional materials, play a pivotal role in enabling reconfigurability within PICs. Among these reconfiguration schemes, chalcogenide phase change materials (PCMs) based photonic devices have attracted extensive attention owing to their high energy efficiency and integration density brought by huge refractive index contrasts and nonvolatility of PCMs. However, this nonvolatile modulation method meets difficulty in scalability since the process flow of integrating PCMs into silicon photonics is insupportable in the foundries. Here, we demonstrated a back-end-of-line (BEOL) integration platform for the monolithic integration of PCMs into silicon photonic devices without modification in standard process design kits (PDK). This is achieved by fabricating a low-loss oxide trench to expose the waveguide core at the functional area from the top dielectric layer, with assistance from a silicon nitride etch stop layer. On this basis, integrated photonic devices with stable switching performance and repeatable multi-bit storage capability have been developed, possessing the potential for crucial blocks of PICs in ONN applications that require infrequent reconfiguration, such as hardware error correction before training and data storage in pre-trained models.

In recent years silicon-based optoelectronic chips have great advantages in biochemical sensing due to their unique advantages. In this paper, the dispersion mechanism of a racetrack microring resonator based on a subwavelength grating waveguide is theoretically investigated, and the relationship between the electric field distributions of different parts and their parameters is studied. A highly sensitive silicon-based subwavelength grating microring resonator sensor is designed and fabricated by two-step etching photolithography process. The structure improves the sensitivity of the sensor compared with the conventional microring sensor. The resonance principle of this structure is not limited by the free spectral range due to focusing on the envelope peaks instead of individual resonance peaks. This is one of the highest refractive index sensing sensitivities reported for a microring resonator with a sensing sensitivity of 860.3 nm/RIU.

In this paper, the present research status and development of the domestic and international deep space Tracking, Telemetry and Command (TT&C) systems are summarized. Then, in terms of deep space satellite payloads and ground stations, the key technologies for China’s TT&C system are sorted out. The technical requirements include longer detection distances, larger instantaneous bandwidth, more target interconnections, and faster data transmission rate. Aiming at the technical requirements, microwave photonics technology combines the flexibility of microwave radio frequency with the photonics with strong anti-interference ability as well as large bandwidth. Based on the above analysis, active and passive photonic phase-stable transmission based on microwave photonics, ultra-fast and high peak power seed laser source, photonic frequency conversion with large bandwidth and low spurious suppression ratio, and communication link based on superconducting nanowire single-photon detectors are studied. Finally, combined with China’s current technology research techniques, some technical recommendations for China’s deep space TT&C system are discussed.

A scheme for instantaneous frequency measurement (IFM) based on carrier phase-shifted double sideband (CPS-DSB) modulation is proposed. In the proposed scheme, two CPS-DSB modulations with different phase shifts are utilized, in conjunction with a dispersion device, an amplitude comparison function (ACF) is constructed by mapping the relation between the output power ratio of two photodetectors and the unknown frequency, therefore, the frequency measurement is achieved. Simulation results indicate that a frequency measurement range of 0.1–15.7 GHz with an error of less than 80 MHz is achieved, and the larger the slope, the smaller the measured error. In addition, by adjusting two phase shifts, a two-step frequency measurement is adopted by coordinated operation of a large range rough measurement and a small range precise measurement, the measured error of the unknown frequency can be improved significantly.

A photonic approach to generate dual-chirp microwave waveform based on an improved optical frequency operation module (OFOM) is proposed and experimentally demonstrated. Without altering the existing OFOM architecture and only by expanding optical filtering and setting appropriate input radio-frequency (RF) signal parameters, two optical sidebands with opposite chirp characteristics will overlap in the frequency domain. After photodetection, a dual-chirp microwave waveform with tunable central frequency and multiplying bandwidth can be generated. Experimentally, dual-chirp signals at 13.2GHz with a tunable bandwidth from 60 MHz to 6 GHz are generated. The pulse compression ratio (PCR) and the peak-to-sidelobe ratio (PSR) of the generated signals are evaluated. In addition, the tunability of the central frequency is also investigated, which verifies the feasibility of the proposed scheme.

Addressing the needs for wide instantaneous bandwidth, parallel reception, and down-conversion processing in fields such as wireless communications and spectrum sensing, Radio Frequency (RF) channelization technology is receiving widespread attention. To achieve instantaneous ultra-wideband signal reception in the C, X, and Ku bands, research on 4- channel optical channelization has been conducted, with each channel having a bandwidth of 4 GHz and a 1 GHz overlap between adjacent channels. Due to the optoelectronic/electro-optic conversion losses and active optical noise present in microwave photonic links, the broadband frequency conversion link introduces significant noise figures and in-band gain fluctuations. By incorporating balanced detection technology in the coherent detection link, the relative intensity noise introduced by the laser is reduced, ensuring the signal-to-noise ratio (SNR) of the module output signal. Additionally, antialiasing filtering is performed using intermediate frequency (IF) band-pass filtering in the electrical domain, achieving high flatness, high suppression ratio, high isolation, and steep edge channel division. This effectively overcomes the poor filtering characteristics of a single optical filter, with the full IF band gain fluctuation being ±3 dB. To verify the accuracy of signal detection, the module was integrated into the system for experimental testing, achieving effective detection of signals in four channels, with a frequency measurement accuracy better than 1 MHz.

Traditional electronic radars are limited by the "electronic bottleneck", and their operating bandwidth and signal processing speed are difficult to meet the detection needs in complex environments in the future. In recent years, optical phased array systems and photon integration technology have emerged. The core of optical phased arrays is photon phase shifters. With the advantages of electro-optic(EO) effects and photonic integrated circuits, high-precision silicon-based electro-optic phase shifters have developed rapidly. The basic architecture of optical phased array systems and the basic principles of silicon-based EO phase shifters have been introduced firstly . Then, combined with photon integration technology, it focuses on the technological progress and related applications of silicon-based EO phase shifters. The article compares different silicon-based EO phase shifters with different structures. Finally ,looked forward to the future development trend of silicon-based EO phase shifters.

Delay jitter and dispersion are two important factors that impact the quality of radio over fiber transmission. In this paper, a simultaneous perception method for these two factors based on matched filtering is proposed. The proposed method effectively combines the precision of RF matched filtering process with the broadband advantages of microwave photonics technology, which can enable an accurate perception of both. The effectiveness of the proposed perception method is verified through experiments.

Metalens, a novel class of optical devices based on metasurfaces, exhibit exceptional optical properties and superior wavefront control capabilities. These characteristics have enabled the development of ultra-thin devices with broad applications in imaging, spectroscopy, optical communications, and photodetection. This paper presents the realization of a near-infrared (IR) metalens used as a beam expander. Our approach effectively achieves optical beam expansion functionality. Initially, we designed the geometric structure of the metalens on a silicon platform, leveraging its design principles. Numerical simulations confirmed that the proposed structure can achieve effective lens focusing. Subsequently, we fabricated the metalens using micro-nanofabrication techniques and validated its performance with a customized testing system. The results demonstrate that the near-IR metalens exhibits excellent focusing performance at a working wavelength of 1550 nm. It can expand and collimate the output beam of a single-mode fiber, thereby verifying the effectiveness and practicality of our design. This design can replace traditional lenses in fiber beam expansion, achieving a thinner profile. Additionally, arrayed metalenses can provide a solution for beam expansion in multi-core fibers, reducing alignment workload and enhancing alignment precision.

A low signal-to-noise ratio QAM receiving method based on optical pulse shaping is proposed in this paper. By matching the shape of the optical sampling pulses with the transmitted QAM signal and quantizing with a one-bit electrical ADC, the receiving communication signals are matched filtered. Thus, the transmitting code can be recovered even if the receiving SNR is below the demodulation threshold. In simulations, 4QAM signals with SNR of 0dB are received with the bit-error rate of 1 × 10⁻².

To address the limitations of existing polarization image fusion methods that often overlook noise interference in Degree of Linear Polarization (DoLP) images and indiscriminately fuse all source image information, we propose a novel image fusion method. Firstly, we created a polarization dataset, using DoLP images as guide and input images. For guided filtering, the filter window radius and regularization parameter were set to 2 and 0.05, respectively, to produce the output image. Subsequently, we developed an unsupervised polarization intensity image fusion network incorporating the Convolutional Block Attention Module (CBAM). This network comprises three sub-modules: feature extraction, fusion, and reconstruction. The feature extraction module employs an Attention-based Dense Block (ADB) to extract prominent features from the source images. We validated our approach using both the created dataset and a publicly available dataset, comparing it against seven advanced image fusion methods using seven quantitative evaluation metrics. Additionally, we conducted an ablation study to assess the impact of the attentional mechanism. Qualitative and quantitative results demonstrate that our proposed method effectively merges linear polarization information while suppressing noise and distortion from DoLP, preserving the significant features of the target more effectively than the other methods.

Fiber-optic transmission of broadband wireless communication signals based on source and transmission integration is proposed and experimentally demonstrated. In this scheme, a radio-over-fiber (RoF) link is employed to transmit the broadband wireless communication signal. Using the long optical fiber in the RoF link, a dual-loop optoelectronic oscillator (OEO) localized in the centralized unit (CU) can be established to up-convert the broadband wireless communication signal to a higher frequency. In such a case, the transmitted wireless communication signal can be directly emitted by the antenna, further streamlining the remote active antenna unit (AAU) structure. The proposed wireless communication system based on source and transmission integration is experimentally investigated. In the experiment, a 256-QAM signal centered at 1 GHz is transmitted by the high-power RoF link involving a spool of single-mode fiber (SMF) with a length of 1 km and then successfully up-converted to 11 GHz. In addition, the measured error vector magnitudes (EVMs) of the wireless communication signals with bandwidths of 26 MHz, 65 MHz, and 130 MHz are held below 3.5%, which satisfies the requirement of TS38.101.

Optical wavelength measurement is imperative in a wide range of applications, such as optical metrology, sensing, wireless communication, and so on. In this paper, we propose and demonstrate a novel microwave photonic optical wavelength measurement method based on swept wavelength-to-time mapping, where the optical wavelength is mapped to the time domain information of a microwave photonic link with the help of a swept signal. Wavelength of the optical signal under test can therefore be measured by simply measuring the time domain information. To achieve swept wavelength-to-time mapping, a bi-directional frequency-swept optical signal for reference is first constructed. The reference optical signal and the optical signal under test is then combined and launched into a photodetector for optical-to-electrical conversion. A pair of microwave pulses can be observed, which is obtained by filtering the recovered photocurrent using an electrical bandpass filter with narrow passband. The occurrence time of the filtered pulses are related to the optical wavelength under test due to the bi-directional frequency-scanning property of the reference optical signal, thus swept wavelength-to-time mapping is enabled. Only a low-speed oscilloscope is needed for optical wavelength measurement by monitoring the time-domain information of the microwave pulses in the proposed method, which provides a cost-effective approach for microwave photonic optical wavelength measurement.

In this paper, we propose and experimentally demonstrate an approach to generate a coherent dual-frequency microwave signal based on a self-injection-locked optoelectronic oscillator (OEO). In this scheme, an electrical bandpass filter (BPF)with two passbands is used to select two oscillation modes for the final output. The key point of this scheme lies in that an electrical mixer is employed to generate the injected low-frequency signal. By passing the two initial oscillation modes through the mixer, a beating signal centered at the difference frequency between the two oscillation modes can be obtained and further injected into the OEO cavity to lock the phase relationship between the two frequency components. In such a case, a dual-frequency microwave signal with high coherence can be generated by this self-injection-locked OEO, without the assistance of any external source. A proof-of-concept experiment is carried out to demonstrate the feasibility of the proposed scheme, where a coherent dual-frequency microwave signal with frequencies of 10 GHzand10.1 GHz is obtained. The sidemode suppression ratio (SMSR) and the phase noise of the generated dual-frequency microwave signal are 38 dB and -130 dBc/Hz@10 kHz, respectively. In addition, the coherence of the generated dual frequency microwave signal is also verified.

A harmonically mode-locked optoelectronic oscillator (HML-OEO) based on injection locking is proposed to generate microwave frequency combs (MFCs) with a high supermode noise suppression ratio (SNSR) and high frequency stability. N th -order harmonic mode locking is achieved via frequency mixing of the oscillation signal and an intermediate-frequency (IF) signal with a frequency interval equal to N times the free spectral range (FSR) in the loop. The supermode noise of the HML-OEO is suppressed by the injection of a single-tone microwave signal, which is aligned with the frequency of one longitudinal mode, in order to enhance the gain competitiveness of one group of longitudinal modes. Furthermore, the correlation of the adjacent pulses can be improved by the injection-locked effect. In the numerical simulation, a microwave frequency comb with a center frequency of 10 GHz and a SNSR of 81.1 dB is generated under the condition of 3 rd -order harmonic mode locking, by injecting the microwave signal with a power of −40 dBm. Furthermore, the correlation of adjacent pulses generated in the proposed HML-OEO is superior to that before injection locking.

A novel uni-traveling-carrier photodiode (UTC-PD) array’s structure for power combining above 110GHz was designed and fabricated to extend a single PD’s power limit in the THz regime. Four identical monolithically integrated UTC-PDs’ power was combined with T-junctions connecting every 6.5µm-diameter anode of these InGaAs-InP PDs. All PDs and combiner were fabricated on a 12µm-thick InP substrate, and the fulfilled chip was then measured after flip-chip bonding on a 50µm-thick AlN-based coplanar waveguide circuit. A continuous wave output power 0.19mW was measured at an operating frequency of 112GHz with a bias voltage of -3V.

In low light conditions, color (RGB) images taken by cameras contain a lot of noise and loss of detail and color. However, multispectral images can provide spectral information, which can be fused by neural network models . In this paper, an improved U-Net model is proposed for multi-spectral image fusion to achieve color imaging in low illumination environment. The U-Net model is a symmetric convolutional neural network that helps extract and combine features at various image scales. Our improved U-Net model integrates residual blocks and attention mechanisms, utilizing multilevel feature extraction and contextual information fusion to significantly enhance imaging quality. To meet the requirements of low-light conditions, the model design incorporates a multi-scale feature fusion strategy, bolstering robustness against weak light and noise. We conducted multiple experiments at different light levels to validate the effectiveness of the model. The quality of the fused color images was evaluated with objective assessment metrics such as peak signal-to-noise ratio (PSNR), structural similarity index (SSIM) and chromatic aberration (ΔE). The experimental results demonstrated the effectiveness of the proposed method, which can generate color images with high color reproduction and rich detail under low light conditions. Compared to traditional methods, our approach shows substantial improvements in image clarity, noise suppression, and color authenticity, indicating significant practical value. In summary, this study combines deep learning with multispectral image fusion to propose an effective method for low-light color imaging. It offers new insights and technical solutions for addressing low-light imaging challenges in practical applications.

The blossoming of artificial intelligence technologies demands greater computational power. Optical computing, with its ultra-fast operation and inherent parallel processing capabilities, is considered promising for high-performance computing tasks. However, there is no evidence that optical computing outperforms classical neural networks in machine learning tasks. In this work, we explored this issue by evaluating the expressive and trainable capabilities of optic propagation processes. This evaluation was based on the Fisher information and the effective dimension theories. Practical machine learning experiments were conducted to validate our theoretical findings. The results revealed that optical-propagation-based computing exhibited a superior effective dimension and quicker training speed than classical feedforward neural networks, underscoring optical computing’s benefits in machine learning applications.

We present an on-chip optical matrix operator designed for multichannel 1×1 optical convolution, which is deployed in a deep residual U-Net for biomedical image segmentation. The integrated optical matrix operator is fabricated on a silicon-on-insulator (SOI) chip that supports fully reconfigurable 5×5 matrix operation and is used in a deep residual U-net that requires 3-channel 1×1 convolution operation. The multichannel optical 1×1 convolution operation is experimentally validated by using the deep residual U-Net to achieve precise segmentation of pneumonia lesion region in lung CT images. The on-chip optical matrix operator features high scalability and large-scale parallel operation and may find great application in future optical neural networks.

With the explosive growth of data volume, the computational complexity of using digital signal processing methods to compensate for optical fiber dispersion and nonlinear effects is rising rapidly. This paper proposes using a support vector machine (SVM) algorithm to address this challenge in QPSK systems. For nonlinear compensation, Particle Swarm Optimization (PSO) is utilized instead of the traditional grid search method to optimize parameters. The performance of the PSO-SVM method is compared with Dispersion Compensation and Digital Backpropagation (DBP) algorithms. Results indicate that PSO-SVM outperforms both alternatives, providing a more effective solution for managing nonlinear effects in optical communication systems.

An active mode-locking optoelectronic oscillator (OEO) based on a dual-drive Mach-Zehnder modulator (DDMZM) is proposed and experimentally demonstrated. The kernel of this scheme is that an electro-optic DDMZM driven by a lowfrequency sine signal whose period is equal to the OEO loop delay is employed to periodically regulate the loop gain for achieving mode locking. By adjusting the bias voltage of the DDMZM, the gain curve of the OEO cavity can be changed accordingly, resulting in the generation of different microwave pulse waveforms. Compared to the reported active modelocking OEO, the repetition frequency or the period of the microwave pulse train generated by the proposed scheme can be varied just by changing the bias voltage of the DDMZM, rather than the frequency of the driving low-frequency signal. An experiment is carried out to demonstrate the feasibility of this DDMZM-based active mode-locking OEO. In the experiment, under the condition of a 1.1-km cavity length and fixed driving frequency of 180 kHz, microwave pulse waveforms with repetition frequencies of 180 kHz and 90 kHz are generated by setting the bias voltage of the DDMZM to be different values. In addition, the autocorrelation result of the microwave pulse train with a repetition frequency of 90 kHz illustrates that there is a certain phase relationship between four pulses within a period, leading to the achievement of a phase-coded microwave pulse, which is beneficial for solving the problem of distance ambiguity in the radar system.

We report a dual-wave microwave comb signal generation system based on an active mode-locked optoelectronic oscillator (AML-OEO), with the output signal being a dual-center frequency microwave comb signal. We utilize an equivalent dual-band filter based on parallel filters, where both parallel filters are narrow-band filters. When the optoelectronic oscillator loop is running freely, the output signal is a single-frequency signal with a frequency equal to the bandwidth of one of the narrow-band filters in the equivalent dual-frequency filter. When an excitation signal with a frequency equal to the difference between the two filters is injected through the mixer, the oscillation mode of the loop changes and the output signal becomes a dual-frequency signal with a frequency equal to the center frequency of each of the two narrow-band filters. The mode intervals of the optoelectronic oscillator are calculated from the spectrogram, and after injecting an active mode-locked signal with the same frequency and mode interval size, it can be observed that multimode oscillations occur at two frequencies. Replacing different optical fibers to change the loop length and thus the mode interval, a dual-frequency microwave comb signal with a larger number of combs can be generated when an active mode-locked signal at the fundamental frequency is injected. The center frequency can be tuned by replacing the filter with a narrower center frequency and has a narrower bandwidth and lower price compared to commercial dual band filters.

This paper presents the experimental demonstrations of LFMCW radar system based on microwave photonics generated radar signal and electronic receiving link. In the transmitting section of the radar, the seed signal given by DDS with relative low frequency and relative narrow bandwidth is designed with tunable signal wave forms, which can afford the system with different time-width and bandwidth. After the microwave photonics electro-optic modulation and photoelectric transformation system, the seed signal will be transformed into the radar signal by 4 times with the frequency carried and instantaneous bandwidth. In the receiving part of the radar, the electronic dechirping method is carried out to down convert the radar echo signal instead of microwave photonics approach. After electronic ADC, the ranging data is processed. The experiments towards to the cooperative UAV target are carried out in urban background. The true data about the longitude, latitude and the flight height of the UAV is sent to the radar from the UAV, and the data is used to guide the radar to detect the UAV’s range. A typical radar wave forms 4GHz bandwidth and 20ms pulse width is operated through the system. The experimental demonstration by protocol type has been shown, and the experimental results show that the range of frequency modulated continuous wave radar based on this system can reach 1 km for target with RCS 0.01m² (DJI).

Frequency hopping communication is a type of spread spectrum communication. It has the advantages of strong anti-interference ability, low interception probability, good confidentiality performance, and random access of multiple users. It has been widely used in military communications, electronic countermeasures, navigation, measurement and other fields. This technology controls the change of carrier frequency within a certain bandwidth through pseudo-random code, so as to disperse the enemy's interference power, thereby improving the system's anti-interference ability. Therefore, increasing the frequency hopping bandwidth is an important means to improve the performance of the frequency hopping communication system. Traditional military anti-interference satellite communication systems usually use microwave technology for on-board signal processing and forwarding. They are limited by the communication frequency band in terms of processing speed and transmission bandwidth, making it difficult to achieve multi-band, large bandwidth, and multi-granularity data transmission while taking into account the weight, volume and power consumption of the payload. This has become the biggest bottleneck for improving the anti-interference ability of the frequency hopping system[1]. Microwave photonics integrates the two major technologies of microwave and photon, and has the characteristics of wide working frequency band, large instantaneous bandwidth, no electromagnetic interference, flexible access, small size, and light weight. It is particularly suitable for ultra-wideband signal processing of satellite payloads. In the frequency hopping communication system based on the microwave photon , optical means are used to overcome the electronic bottleneck of the limited bandwidth of traditional microwave technology, which greatly improve the anti-interference performance of the frequency hopping communication system with multi-band and large bandwidth transmission, and provide a new idea for satellite communication anti-interference. In view of the limitations of the traditional microwave frequency hopping communication system, this paper explores the future new ultra-wideband frequency hopping anti-interference communication system based on microwave photons. First, the article analyzes the mechanism of improving the anti-interference and anti-interception performance of the frequency hopping system by the cross-band and ultra-wideband characteristics of microwave photon technology, and analyzes the impact of the broadband characteristics of microwave photon technology on communication signal processing. Then, this paper studies the architecture of the frequency hopping anti-interference satellite communication system based on microwave photons, and adopts a hybrid optoelectronic two-level ultra-wideband frequency hopping scheme to realize a multi-dimensional joint anti-interference architecture. On this basis, an adaptive anti-interference technology based on ultra-wideband spectrum measurement and interference avoidance is proposed, and the key adaptive anti-interference technologies adapted to ultra-wideband systems are explained in detail, including the key technologies of ultra-wideband satellite anti-interference system payload design, ultra-wideband interference prediction technology based on deep learning, adaptive interference avoidance technology, waveform design technology adapted to microwave photon ultra-wideband system, and ultra-wideband channel characteristic compensation technology. Finally, the development route of ultra-wideband frequency hopping technology based on microwave photons and the key and difficult problems to be solved are summarized and prospected, providing important theoretical reference and key technical support for the design of cross-band, ultra-wideband frequency hopping anti-interference communication systems.

A phase-stable transmission system is proposed based on high accuracy and fast measurement of optical transfer delay(OTD). Only 4 frequency points are required to solve the optical transfer delay, which can greatly reduce the time spent on continuous multi-frequency sweeping during the phase-derived process to enhance the robustness of an active phase stabilization system. The system achieved an OTD measurement accuracy of ±0.08 ps in the proof-of-concept experiment. We also measured the link delay stability of the two 2 km optical fiber links with and without phase stabilization for 2 hours. During the measurement, the fluctuation between the phase-stable link delay and the set delay was within ±0.18 ps, while the delay difference without phase stabilization was over 200 ps.

A novel ultra-wideband microwave photonic circulator scheme is proposed and demonstrated. In this scheme, the microwave photonic circulator is composed of a laser diode, a specially-designed thin-film lithium niobate modulator and a photodetector. Benefited from the large modulation index difference between the forward modulation and the counter modulation in the MZM, the microwave photonic circulator is with a high isolation. In the experiment, the isolation of the proposed circulator is larger than 10 dB in the frequency range from 6.3 GHz to 50 GHz, while the maximum isolation of the circulator is 30.1 dB at 8.7 GHz. The measured frequency response curves agree well with those obtained in the simulation. This circulator is employed in a simultaneous transmission and reception experimental system. The low EVM values and crosstalk in the operation frequency range from 8.0 GHz to 9.4 GHz can verify that the proposed microwave photonic circulator has large application potential in the wideband full-duplex wireless communications.

Optical frequency combs are commonly utilized for generating reconfigurable linearly-frequency-modulated (LFM) signals with a large operating frequency range in radar systems. However, traditional systems employing cascade delectro-optic modulators and relying on external electronic signal sources often suffer from high power consumption and bulky size. In contrast, chip-scale microcombs offer inherent advantages in terms of power efficiency and compactness. In this study, we propose and experimentally demonstrate a microcomb-based system for generating reconfigurable LFM signals. By self-injection locking a commercial distributed feedback laser chip through the backscattering of a micro resonator chip, a coherent microcomb state is achieved. Additionally, we utilize the wideband injection locking technique to enhance the signal-to-noise ratio, resulting in a significant power gain for the modulated sideband. The center frequency of the generated signals can be flexibly reconfigured by adjusting the selected comb line numbers and the frequency of the modulation signals. This enables the achievement of LFM signals with a large tunable range spanning from X- to W-bands. Furthermore, we analyze the characteristics of the produced LFM signal at Ka-band. Our measurements indicate a linearity of approximately 0.01% and a pulse compression ratio of approximately 2.1×10⁵. These results validate the effectiveness and potential of the proposed approach.

In 6G mobile communication technology, accurately perceiving channel state information can significantly improve communication performance, enabling spatial multiplexing and more accurate beamforming. Intelligent holographic radio imaging technology can precisely perceive the electromagnetic space of communication users in complex environments, obtaining interferograms with extremely high spatial resolution and fine spectral resolution. Reconstruction of the K-space can yield information such as the central frequency and azimuth of the incident radio frequency signals. This paper proposes a target detection method based on wavelet packet transform, which can accurately and rapidly detect the center frequency, azimuth, and other information of targets in the reconstructed K-space images obtained from holographic radio imaging. Moreover, hardware acceleration is implemented on FPGA to provide an efficient solution for target detection in channel state information perception.

An adaptive delay calibration method for optical beamforming networks (OBFN) based on wideband sweep and windowed FFT spectrum analysis is proposed and demonstrated by simulation. With the FFT spectrum analysis of the wideband sweep signal, the delay difference between different channels in OBFN can be obtained continuously, and can be canceled adaptively by controlling variable optical delay lines(VODL), resulting in fast and high precision calibration for an OBFN. Furthermore, assisted by pilot carriers with multiple frequencies, the phase unwrapping can be achieved, and phase difference beyond 2π can be compensated. In order to demonstrate such method, a 16-arrayoptical beamforming simulation system is presented in this paper. Simulation results show that delay calibration range reaches467.1ps with the frequency range of 6-18 GHz. The delay calibration accuracy is increased by 50 times from5ps to 0.1ps. In addition, the number of simultaneous beamformer achieves to be 3, which covers the airspace from-30° to +30°.

In phase interferometer direction finding methods, the angle of arrival (AOA) is calculated by measuring the phase difference generated by the propagation of microwave signals between antenna array elements. In the direction finding technique based on the power-phase mapping relationship of microwave photons, there exists a mapping relationship between the power of the output optical sidebands and the phase difference, allowing the AOAto be obtained by measuring the power of the carrier waveform or sidebands. To address the technical challenges of small antenna array spacing, this work proposes a novel approach where it greatly improves direction finding accuracy. The two beams of optical carriers carry the differential-mode component and the common-mode component of the phase difference of the microwave signals, respectively, i.e.. After they are converted to electrical signals by the PD respectively, the power ratio (PR) of the two electrical signals is calculated. PR exhibits a mapping relationship with the AOA ,thus it can be derived by calculating the angle of arrival. Based on this method, MATLAB simulation software is employed to investigate antenna array spacings of λ/8, λ/12, λ/16, λ/20, and λ/50, where λ is the wavelength of the microwave signals. The simulated direction finding accuracies are ±0.42°, ±0.63°, ±0.83°, ±1.1°, and ±2°, respectively. The simulation results demonstrate that the proposed microwave photon direction finding system can meet the demand for high-precision direction finding with small antenna array element spacing.

In this study, an integrated optical beam-forming network (OBFN) with multiple channel optical true time delay lines (OTTDLs) based on silicon-on-insulator (SOI) platform is designed and fabricated. The optical carriers in C-band are with a frequency space of 100 GHz and designed to meet the ITU standard. 1×32 arrayed waveguide grating (AWG) is applied to achieve dense wavelength division multiplexing(DWDM). The OTTDLs are single-mode strip waveguide for TE mode. The nominal delay step between the OTTDLs is 21 ps. To achieve a compact footprint and low loss photonics circuit, spiral routing strategy and Euler bendings are employed. The insertion loss of such waveguide is estimated to be 1.5 dB/cm. A Mach-Zehnder interferometer (MZI) based variable optical attenuator (VOA) array is designed in order to adjust the uniformity of optical power in each OTTDL, which can employ an attenuation of more than 30 dB. Due to the wavelength dependent loss of the grating coupler, AWG, and prapagation loss difference of OTTDLs, the output spectrum shows that the optical power fluctuation is less than ±2 dB before VOA tuning. The group delay is examined by a microwave transmission response measurement in the frequency range of 6∼18 GHz, which is derived from the frequency derivative of the phase. The average delay step of 21.3 ps is achieved, and no significant fluctuation of group delay among such frequency range. It denotes the broadband feature of OBFN, which is promising for application in microwave photonics (MWP) radar and other related scenarios.

We designed a novel compact micro-ring electric field sensor based on the thin-film lithium niobite on insulator (LNOI) platform. By leveraging the method of inverse design based on topology-optimized algorithm, a remarkable micro-ring detector with a bending radius of 6 μm has been achieved, resulting in an order of magnitude reduction in loss compared to conventional bends. The designed detector achieves an ultra-compact footprint of 13.22 μm × 22 μm with a relatively flat frequency response across the 50 Hz - 1.95 GHz. At the wavelength of 1550.75 nm, the detector achieves an impressive maximum detectable electric field of 4×10^7 V/m, with a minimum detectable electric field value of 4 kV/m when the maintaining a linear dynamic range of 80 dB for the system. The compact size and electrode-free design of the proposed sensor enable seamless integration into chips and wearable devices, catering to the growing demands of high-field strength electric field measurements in smart power equipment and grid operations. Furthermore, this work represents a pioneering effort in developing a micro-ring electric field sensor using inverse design methodology and opens up new method for advanced sensing applications, paving the way for extensive utilization in future modern photonic integrated circuits.

A novel on-chip programmable photonic processor based on an arrayed Mach-Zehnder interferometer (MZI) with a forward transmission structure is proposed and demonstrated for real-time multipath interference and self-interference cancellation of wireless microwave communication signals. The proposed technique is experimentally validated, showing its capability to mitigate the multipath interference in an amplitude-shift keying (ASK) signals to achieve error-free transmission. In addition, the programmable photonic processor can also be configured to achieve self-interference cancellation between transmitting and receiving antennas for up to 9 dB with signal bandwidth from 6.2 to 7.0 GHz. These experimental results confirm the feasibility of the on-chip signal processor and provide new insights for future communication signal processing research.

In recent years, the propagation delay in optical transmission systems has received increasing attention. Including precise time synchronization protocol, optically controlled distributed coherent radar and other technical fields. The traditional optical time domain reflectometer (OTDR) measures the propagation delay of optical fibers from a single end, using several nanosecond pulses with measurement accuracy of the same magnitude. Meanwhile, as an ultrafast pulse light source with multiple equidistant optical modes, optical frequency combs have shown significant advantages in many precision measurement scenarios such as long-distance ranging, spectroscopy and frequency modulation radar due to their excellent time-frequency characteristics. In this article, a measurement method of propagation delay in fiber based on dual microcombs at the sub-femtosecond is proposed. Based on the principle of linear optical sampling(LOS), the interval of the signal pulses can be stretched in the time domain, and high-precision measurement is carried out. In order to improve the coherence of the dual-comb in the system, we use the same continuous-wave laser source to pump the dissipative Kerr soliton (DKS) comb in two microcavities with slightly different free spectral ranges of~25GHz. In the end, we achieved a femtosecond level accuracy of 8.04fs at single LOS measurement. Moreover, due to a high update rate exceeding 1MHz, we obtained a sub femtosecond level measurement accuracy of 0.744fs with an average processing time of 0.1 milliseconds. This method has unique advantages of fast measurement speed and high accuracy, and has broad application potential in various fields such as optical communication and optical distributed sensing.

In this paper, a photonic dual-band radar receiving and processing technique based on a Stepped Linear Frequency Modulation (SLFM) signal has been proposed, achieving high-resolution radar detection driven by a low-rate signal source. The generation of dual-band radar signal with GHz-level bandwidth from SLFM sub-pulse signals with MHz-level bandwidth is utilized, significantly conserving the bandwidth resources of the radar driving signal source. Subsequently, a photonics-assisted dual-channel radar de-chirper cascaded with two electro-optic modulators is employed to realize wideband radar pulse compression processing covering both the X-band and Ku-band. Finally, the coherent fusion processing algorithm for dual-band radar is utilized, not only accomplishing an equivalent high-resolution radar ranging and Inverse Synthetic Aperture Radar (ISAR) imaging but also facilitating an anti-jamming radar detection. In simulation experiments, this paper has achieved the reception of dual-band SLFM radar signals with a sub-pulse number of 100 and a frequency coverage range of 8GHz-16GHz. Due to the coherent fusion processing algorithm, the radar target ranging and ISAR imaging with a resolution of ~2cm (equivalent bandwidth of 8GHz) successfully have been achieved.

The traditional electric field reception technology has the contradiction between the measurement bandwidth, speed, and accuracy. The under-sampling electric field measurement system of the optical frequency comb can down convert all signals within a wide frequency band to a low frequency for reception and measurement, thus solving the above contradiction. Due to the use of undersampling reception, the original carrier frequency of the signal was lost. For this purpose, a dual frequency pulse light source is used for electric field sampling, and the residual matching method is used to recover the signal frequency information. However, when there are two or more different signals in the test signal, it is difficult to pair the down conversion components, resulting in a sharp increase in the error rate of the system's frequency recovery. In response to the above issues, this article proposes a frequency recovery method based on signal feature matching. By extracting features from dual channel signals, accurate grouping of down converted signals can be achieved. Then use the remainder matching method to accurately recover the frequency. The simulation results demonstrate that when the system receives four different signals simultaneously, the frequency recovery error rate is about 0.4%, which is about 1/3 of the original.

The Ritchey-Chretien (RC) optical system contains an aspheric primary mirror and secondary mirror, as well as a refractive corrector lens. This flexible structure allows for a wide range of applications. The assembly process for a RC optical system differs from traditional refractive lens systems, as the aspheric reflective primary and secondary mirrors require high centering precision, which necessitates further adjustments during the assembly process. This paper discusses the assembly process for a Ø300mm RC optical system, analyzing the centering precision of the aspheric reflective primary and secondary mirrors. By adjusting the relative position of the primary and secondary mirrors based on the wavefront aberration, the final RMS wavefront aberration of the RC optical system was reduced to 0.054, and the full-field modulation transfer function (MTF) exceeded 0.68. Finally, the paper discusses the manufacturing techniques to improve the centering precision of the aspheric reflective mirrors and enhance the assembly efficiency.

The new microwave photonic receiver system employs spatial light processing to enable multi-beam imaging within its field of view. This system uses fiber optic links for transmission, where the optical phase is sensitive to environmental disturbances, potentially affecting imaging quality. This paper aims to design and implement an efficient phase consistency control system for multi-channel optical fiber links. The system ensures the coherence of optical signals during transmission by precisely locking the phase in each channel's fiber optic link. Additionally, a serial digital-to-analog conversion scheme is proposed to address the pin count limitations of FPGA. Precise optical phase consistency control was achieved in single-channel experiments, and the serial digital-to-analog conversion scheme was validated on a 24- channel microwave photonic receiver, where stable image points were observed on the camera.

Microwave photonic (MWP) radars based on radio-frequency orbital angular momentum(RF-OAM) beams have been extensively researched recently, for their potential to provide high-azimuth and high-range resolution for radar imaging at the same time. However, the inherent divergence effect of RF-OAM beams limits the effective detection distance, which has become the main technical bottleneck of the long-distance MWP OAM radar. In this paper, the mathematical model of the MWP-controlled circular antenna array (CAA) is constructed, and the basic transmission properties of generated RF-OAM beams are investigated. Then each factor in the model is extracted for numerical simulation to explore its influence on the generation of RF-OAM beams, and the Bessel function term is found to be the factor leading to beam-divergence. Within the Bessel function term, the role that each physical element plays is analyzed, which is just consistent with our experimental experience and previous research results. Finally, the quantization equation of the RF-OAM beam divergence angle is fitted based on the properties of the Bessel function.

In this paper, we propose a fiber link delay mismatch detection method for the fiber-optic phase-aligned transmission system of broadband microwave signals. Different from the conventional pulse time-of-flight method to solve the problem of periodic ambiguity for a sine signal, an adjustable frequency signal is adopted as the reference in the process of phase discrimination. The main frequency is employed to extract the fiber delay difference and its fluctuation within the corresponding period. Meanwhile, the auxiliary frequency is introduced to deal with the periodic ambiguity for the delays beyond one period. A proof of principle system with an equivalent 5 km outdoor transmission length is implemented to verify the feasibility and effectiveness of the proposed method. Broadband microwave signals received at eight antenna ends are transmitted to the central station through wavelength division multiplexing. At the central station, each link delay is obtained in turn from the incorporated reference frequency signal. Then, the phases of each broadband microwave signals are set in line by the corresponding adjustable optical delay lines. According to the experimental demonstration, the phase consistency is better than 8.68° for a 10 GHz transmitted frequency.

Radio frequency (RF) signals with extraordinary low phase noise can be produced by long-fiber optoelectronic oscillators (OEOs). These signals have wide applications, including modern communication systems, radar technology, and radio astronomy. However, the phase noise of the RF signals is primarily limited by the double-Rayleigh scattering (DRS) and the nonlinear effects in long-distance optical fibers. Based on experimental demonstration, we observe the dominated fiber noises and corresponding suppression mechanism in the open optoelectronic loop. By utilizing the methods of coherent multi-carrier and frequency modulation, a 10 GHz OEO with phase noise of -151 dBc/Hz at 10 kHz offset frequency is successfully achieved.