Solid-state beam steering enabled by optical phased arrays (OPAs) is a promising solution for compact and high-speed light detection and ranging (LiDAR). However, the vertical field of view (FOV) in conventional OPAs is fundamentally constrained by the laser tuning range, inevitably leaving forward blind spots. Existing FOV expansion strategies rely on additional optical paths or extra control channels, incurring a prohibitive complexity scaling. Here, we implement a reconfigurable silicon-based OPA that achieves orthogonal FOV reconfiguration through hardware-efficient component reuse. By dynamically routing light between two orthogonally arranged grating arrays, the OPA enables seamless switching between horizontal- and vertical-dominant scanning modes, achieving complementary FOVs of 99.7°×14.8° and 14.6°×99.4°, respectively, without duplicating the photonic circuitry. Being combined with frequency-modulated continuous-wave (FMCW) ranging, the OPA achieves dual-mode 3D imaging. Experimental results show that the dual-mode complementation effectively eliminates forward blind spots, reducing the minimum detectable near-field distance to 22 cm. Furthermore, fusion of the complementary point clouds improves sampling completeness and contour fidelity, leading to a 32% enhancement in reconstruction quality. This work provides a hardware-efficient route toward reconfigurable LiDAR systems that simultaneously improve perception coverage and spatial resolution.
Reliable trace-level detection of ammonia (NH3) in exhaled breath remains challenging because of its low concentration, high relative humidity (RH), complex gas composition, and temperature variations. In this work, a Fabry–Pérot (FP) microcavity sensor with a poly(diallyldimethylammonium chloride)/poly(acrylic acid)/reduced graphene oxide (PDDA/PAA/rGO) composite coating was developed for NH3 sensing under high-RH conditions. The PDDA/PAA network provided accessible carboxyl groups and a water-retaining environment for NH3 capture, while rGO provided abundant adsorption sites and limited excessive water uptake and swelling of the polymer network. A cascaded fiber Bragg grating was further employed for temperature monitoring and compensation. At room temperature and 90% RH, the FP sensor exhibited a linear response over 1–50 ppm NH3 with a sensitivity of approximately −0.02 nm/ppm and a detection limit of 740 ppb. The RH and NH3 responses remained nearly stable over 85–95% RH, and the response and recovery times were approximately 35 and 95 s, respectively. Furthermore, the sensor produced a distinguishable additional response to healthy exhaled breath spiked with 1 ppm NH3, supporting its potential for noninvasive breath NH3 analysis.
Due to the limitations imposed by Malus's law on the nonlinear demodulation of the Faraday rotation angle, polarization-based all-fiber current sensors (FOCS) have long faced a trade-off between dynamic range and sensitivity, and are inherently incapable of measuring high-frequency harmonic signals. To overcome this challenge, this paper proposes a FOCS based on a Faraday rotation angle–displacement mapping mechanism. This approach employs the radial-polarization detection principle to convert changes in the Faraday rotation angle into linear shifts of the light spot image, enabling linear measurement of the Faraday rotation angle by tracking the displacement of the light spot. This method breaks through the traditional limitations between measurement range and sensitivity. The demodulation mode strictly adheres to the linear superposition principle for multi-frequency input signals, thereby demonstrating the proposed FOCS with wideband measurement capability. Additionally, an imaging positioning system based on a quadrant photodetector is developed to achieve high-frequency, high-sensitivity positioning of the light spot. Experimental results demonstrate that the proposed FOCS achieves a Faraday rotation angle measurement range reaching ±45°, a measurement sensitivity of 0.0688°/A, meets the requirements of accuracy class 0.2 at the power frequency. Moreover, it is capable of measuring both high-frequency single harmonics and multi-frequency signals. The proposed sensor integrates a wide dynamic range, high measurement sensitivity, and wideband capability, all within a simple structural design.
Remote sensing applications necessitate the use of diverse microwave signals with different shapes for the purpose of signal processing, as well as the incorporation of chirp signals to facilitate energy-efficient transmission of information for moving target detection in radar system. In this work, phase tunable Mach-Zehnder modulator (MZM) based photonic technique is developed for the generation of parabolic and truncated sinc shaped waveforms in microwave frequency range. A phase shift of $\Pi /2$ in the optically modulated signal produces parabolic shaped waveform. The generated parabolic shaped waveform of 6GHz with a power level of -16.5dBm is further optically processed to get dual chirp microwave signal without seeding any external source of chirp signal. Characteristics of dual chirp microwave signal is calculated through short time Fourier transform, ambiguity function, and autocorrelation to investigate its application in dynamic radar system. An optical carrier signal split in two parts, one part is modulated by single frequency sinusoidal RF signal for the generation of parabolic or truncated sinc shaped microwave signal, and other part is modulated by the obtained parabolic shaped signal for the generation of dual chirp microwave signal. In the generation of parabolic shaped signals only two harmonics were considered, and their coefficient ratio was maintained by adjusted modulation index of external modulator by properly setting its bias voltage. Further, the same setup is used to generate truncated sinc shaped signal by tuning the phase shift to $-\Pi /2$ in the optically modulated signal after MZM. Practical generation of Infinite duration sinc pulse is not possible, however truncation leads to its practical feasibility applicable in the area of finite impulse response filter design, and high speed communication system with potential application in avoiding intersymbol interference at sampling instants.
The continued scaling of deep neural networks (DNNs) is driving accelerator architectures toward chiplet-based integration. However, conventional fixed and workload-level optimized topologies do not track fine-grained, time-varying communication during DNN inference, resulting in multi-hop latency and link congestion. To address this challenge, we propose R$^{2}$PIAC, a runtime-reconfigurable photonic interconnect architecture for chiplet-based DNN accelerators. R$^{2}$PIAC uses an electro-optic Mach–Zehnder interferometer (EO-MZI) switching fabric to establish high- bandwidth, single-hop lightpaths on demand. To enable runtime reconfiguration, R$^{2}$PIAC adopts a two-stage heuristic scheduler. The scheduler combines capacity-aware topology matching with utility-driven holding-time selection and uses a cost-aware static fallback to avoid low-benefit reconfigurations for long-tail traffic. We validate R$^{2}$PIAC through cross-layer hardware–software co-design using a custom $8\times 8$ EO-MZI switch controlled by a field-programmable gate array (FPGA) and optimized receiver alignment and header qualification. Parallel all-offset alignment and 32-header qualification restore Ethernet packet service within $2.0352~\mu \mathrm{s}$ after an optical-circuit reconfiguration. Across five DNN workloads on a four-board, eight-chiplet FPGA prototype, R$^{2}$PIAC reduces mean aggregate inter-chiplet service time by 28.22%–63.43% relative to three baselines. The corresponding mean reduction in end-to-end inference latency is 6.14%–18.89%.
As passive optical networks evolve toward very-high-speed operation, future access systems must simultaneously provide higher per-wavelength capacity, longer reach, and flexible service tiers. Although coherent PON can satisfy the above requirements and support user tiering through coherent transceivers with different levels of simplification, simplified coherent ONUs still rely on optical-field-sensitive coherent reception and the associated optical front-end and signal-processing functions. In contrast, IM/DD ONUs directly detect optical intensity and can therefore eliminate these coherent-specific receiver functions, providing a lower-complexity solution for users with lower performance requirements. Therefore, enabling coherent and IM/DD ONUs to operate under the same OLT architecture can further broaden the cost-performance range of next-generation PONs and allow users to select the ONU type according to their service requirements. So far, however, no work has demonstrated a single OLT supporting both coherent and IM/DD operation within one network, except for coexistence schemes based on different OLTs and different wavelengths. In this work, a hybrid access architecture with a unified coherent OLT is demonstrated. A zero-flip encoding method is proposed, which enables intensity modulation using a null-biased IQM and allows DSP-only switching between coherent and IM/DD operation. Moreover, the IQM can be exploited to mitigate the chromatic-dispersion problem of C-band IM/DD transmission. The scheme is experimentally validated over 20- and 50-km SSMF links using 50-Gb/s OOK, 100-Gb/s PAM-4, 200-Gb/s QPSK, and 400-Gb/s 16-QAM, enabling interoperability between coherent and IM/DD ONUs without changing OLT hardware. In downstream transmission over 20-km SSMF, OPBs of 46.1 dB, 32.1 dB, 47.6 dB, and 35.6 dB are achieved for 50-Gb/s OOK, 100-Gb/s PAM-4, 200-Gb/s QPSK, and 400-Gb/s 16-QAM, respectively. In upstream transmission, the corresponding 20-km OPBs are 47.5 dB, 34.2 dB, 43.8 dB, and 29.5 dB. These results establish a practical unified OLT framework for flexible hybrid access in next-generation PONs.
Gas-line absorption (GLA), especially due to residual CO$_{2}$, has emerged as a key impairment in deployed hollow-core fiber (HCF) links, where narrow absorption notches can introduce strong, frequency-selective OSNR penalties that vary with HCF links and operating conditions. Accurate and efficient in-field estimation of these penalties is essential for GLA-aware quality-of-transmission (QoT) estimation in deployed HCF networks. In this paper, we present a shift-invariant superposition model for GLA-induced OSNR penalties, established from VPI simulations and validated experimentally using commercial 800 Gbps/140GBaud coherent transponders over 100 km HCF. We extended the prior linear depth-to-penalty mapping to a power-law form, reducing the full-band reconstruction RMSE from 0.118 dB to 0.077 dB, while retaining the homogeneous scaling property that enables one-shot in-field calibration. We further show through half-band cross-validation that a model trained on only half the measured spectrum remains sufficient for reliable field calibration. One-shot validation across 80 km and 130 km HCF spans achieves RMSEs of 0.053 dB and 0.169 dB, confirming that a single laboratory characterization model combined with one field measurement provides a reusable OSNR-penalty model across HCF links with different residual gas concentrations. Our modeling approaches are helpful for supporting more reliable QoT estimation, link provisioning/optimization in large-scale HCF deployed networks, as well as future dynamic and low-latency AI network infrastructure.
Dynamic beam manipulation devices are crucial for applications in free-space optical communication and switching in artificial intelligence (AI) data centers. As a mechanical beam steering device, rotation-enabled cascaded diffractive layers can achieve low cost, large steering angles, and precise optical manipulation, but conventional design methods have difficulties either in realizable interlayer spacings or in flexible rotation output relationships. The challenges are able to be solved by inverse design method. Whereas the optimization algorithm would still fall in a poor performance when the excessive constraints imposed by the targeted functionality severely curtail the design freedom. Here, the widely used wavefront matching (WFM) algorithm for designing cascaded light modulation was modified to gain two capabilities: 1. the design of mechanically tunable phase masks; 2. the design of arbitrarily tunable intensity distributions and much simpler rotation controls by adjusting unrestricted phase profiles. The flexible customization and easy implementation of the modified algorithms facilitate the application of tunable cascaded diffractive layers in beam steering, optical communication and switching in AI data centers.
A new variant of staircase codes, termed block-wise staircase codes, is proposed for high-throughput hard-decision forward error correction in optical communication systems. By incorporating block-wise concatenation into the staircase structure, the proposed construction enables the use of stronger component codes with larger error-correcting capability, thereby significantly reducing the probability of miscorrections and improving overall error-rate performance. The block-wise structure also preserves an error-confinement property, which enables an odd-even One-Step-Ahead-aided (OSA-aided) iterative hard-decision decoding algorithm to further suppress dominant stall events without a noticeable increase in decoding complexity. Closed-form analytical expressions are derived to characterize the error-floor behavior of the proposed codes, enabling accurate error-floor estimation without time-consuming Monte Carlo simulations. Performance evaluations show that, at a target output bit error rate of 10$^{-15}$, the proposed block-wise staircase code achieves a net coding gain of 9.54 dB, corresponding to a 0.13 dB improvement over the conventional staircase code, while the proposed odd-even OSA-aided decoding algorithm further increases the net coding gain to 9.60 dB. In addition, the proposed scheme exhibits a steeper waterfall region and a lower error floor than conventional staircase codes, while maintaining comparable decoding complexity and latency.
A polarization-maintaining Yb-doped crystal-derived silica fiber (PM-YCDSF) was fabricated, exhibiting a gain coefficient exceeding 5.5 dB/cm at 1030 nm, a birefringence of 6.31×10−5, and a polarization extinction ratio (PER) variation of only 2.1 dB during the temperature range of 20–200 °C. Using only 0.6 cm of active fiber, a short-cavity distributed Bragg reflector (DBR) single-frequency fiber laser (SFFL) was constructed. The laser achieved a slope efficiency of 65% and a PER of 31.5 dB. Its output power is up to 672 mW. To the best of our knowledge, this is the first DBR SFFL exceeding 670-mW linearly polarized output with only 0.6-cm active fiber. Furthermore, the laser exhibited a threshold power as low as 3 mW and an optical signal-to-noise ratio exceeding 80 dB. The power fluctuation in the mode-hop-free operation was below 0.17% (RMS) over 570 min, and the relative intensity noise stabilized at approximately −159.8 dBc/Hz above 8.8 MHz. Additionally, by employing a homemade all-fiber quarter-wave plate, a circularly polarized light with an ellipticity angle of approximately 43.58° could be maintained during the 120 min. And its output power also reached 583 mW. These results show that the PM-YCDSF is a promising gain medium for the compact and high-power-density SFFL sources applied in atomic physics, quantum sensing, biomedical imaging, precision measurement, and beyond.
Digital twin (DT) technology has emerged as a cornerstone for autonomous optical networks; however, its predictive fidelity is critically dependent on the accuracy of the underlying physical parameters—particularly the fiber attenuation, component insertion losses (ILs), and amplifier gain profiles. These parameters are often impractical to measure directly in field-deployed systems. To address this challenge within practical constraints, we propose a two-stage, data-driven multi-parameter self-refinement framework for C+L-band transmission systems, capable of jointly refining fiber parameters and erbium-doped fiber amplifier (EDFA) gain spectra without requiring additional monitoring hardware, intrusive link reconfigurations, or service disruption. In the first stage, a neural network is constructed to learn the mapping between variations in fiber parameters (attenuation coefficient and ILs) and the corresponding changes in stimulated Raman scattering (SRS)-induced band powers measured by built-in photodetector at each EDFA, enabling fiber parameter refinement. The second stage extracts an equivalent optical multiplex section (OMS)-level EDFA gain spectrum via a bisection-based iterative process, utilizing the received power profile (RPP) difference monitored by optical channel monitor (OCM) at the reconfigurable optical add-drop multiplexer (ROADM) node. Comprehensive simulations on an OMS C+L-band system are conducted, and the results show that the proposed method reduces the generalized signal-to-noise ratio (GSNR) estimation error to a mean absolute error (MAE) of 0.10 dB and a maximum absolute error of 0.14 dB. The calibrated DT model demonstrates strong generalization capability, maintaining accuracy across 100 heterogeneous test links with diverse parameter sets, under varying launch power profiles, and in dynamic loading scenarios including partial channel cuts and full L-band shutdowns. Furthermore, experimental validation on a three-span C+L-band transmission system confirms the method's practical effectiveness, achieving GSNR MAE of 0.18 dB and a maximum absolute error of 0.23 dB after full refinement. The proposed framework established a viable pathway toward self-calibrating DT that maintain high fidelity throughout the network lifecycle. By achieving accurate parameter estimation using only existing measurement infrastructure, it proved potential applicability in current optical networks within measurement contraints.
Fiber Kerr nonlinearity remains a major factor limiting the transmission performance of long-haul coherent optical communication systems. Although digital subcarrier multiplexing (DSCM) provides improved processing flexibility and enhanced tolerance to transmission impairments, effective nonlinear equalization is still required in long-haul wavelength-division-multiplexed (WDM) systems, where both compensation capability and computational complexity are critical concerns. In this paper, we propose a DSCM-oriented staged nonlinear equalization framework, termed Synergistic SAGE, for long-haul coherent optical transmission. The proposed scheme combines a first-stage subcarrier-aware gated equalizer (SAGE) for dominant structured nonlinear compensation with a second-stage selective-update decision-directed least-mean-square (SU-DDLMS) equalizer for adaptive tracking of residual slowly varying impairments. Experimental results in a seven-channel 64-GBaud 16-QAM WDM system over 1600-km standard single-mode fiber show that the proposed framework consistently outperforms conventional DBP-based baselines under 2-, 4-, and 8-subcarrier configurations. Among the investigated subcarrier configurations, the 4-subcarrier case provides the best overall performance, achieving a 0.56-dB $Q^{2}$-factor improvement over chromatic-dispersion compensation (CDC) at 1600 km and extending the transmission reach by up to 700 km relative to the single-carrier baseline at the 20% forward error correction threshold. In addition, Synergistic SAGE surpasses DBP-32 while reducing the computational complexity by 98.4%. These results indicate that the proposed staged framework provides an effective and low-complexity solution for nonlinear equalization in future long-haul DSCM coherent optical systems.
Two dimensional (2D) optical wireless communications (OWC) with a large-angle coverage are eagerly being pursued by wireless and mobile applications of internet of things, high-resolution image/video transmission, 6G/beyond wireless communications and network, remote conference and diagnosing, etc. Silicon photonics based optical phased array (OPA) can provide the large-angle beam scanning for OWC, benefitting from the near-half-wavelength OPA antenna spacing. However, the coupling loss of the laser source to the OPA chip is too high, meanwhile the sensitivity for state-of-the-art OWC receiver is too poor to meet the practical requirements for OPA-based OWC. The additional optical amplification is inevitably required to enhance the transmitted power and the received power of the OWC system. In this work, we present the large beam-scanning angle of OPA by simultaneously phase-controlling multi-wavelength beams. A compact wavelength-division-multiplexing (WDM) emitter provides an efficient and broadband source of 1270 nm-1610 nm to trigger parallel emissions off the OPA grating antennas, covering the whole optical communication band. Furthermore, we enhance the sensitivity to -40 dBm for OWC using a highly sensitive avalanche photodiode without additional optical amplification. Finally, the 2D OPA-based OWC with the coverage angle of 48°×50° is achieved by actively controllable phase tuning of WDM-radiated 18 beams.
With the goal of evaluating connectivity, we propose a novel method to measure the rotation angles of multi-core fibers (MCFs) based on the guide hole (GH) centers at the end faces of a multi-fiber push-on (MPO) connector. The proposed method derives the rotation angle by processing the image of the fiber core as captured by a microscope. We first clarify the angular resolution required to adequately evaluate the connectivity of MCF connectors and then describe the procedure for obtaining the rotation angle using image processing. To capture the two GH centers and fiber cores with high resolution and high accuracy in an MPO connector with an oblique end face, we use focus stacking and image concatenation. We calculate the rotation angles by core recognition utilizing template matching. The results of measuring the relative rotation angle of paired MPO connectors holding 12 weakly coupled 4-core fibers through repeated experiments confirm that our proposed method attains the required measurement accuracy of 0.1 degrees. We also show that our approach is effective for connector inspection in terms of connection loss and for ensuring reliable connectivity among multi-fiber MCF connectors.
Spectral beam combining is an effective approach to overcome the single-fiber output power limitation of fiber lasers. For spectral beam combining systems, high-performance narrow-linewidth fiber laser sources play a crucial role in determining the output power, combining efficiency, beam quality, thermal management, and compactness. In spectral beam combining systems, a widely adopted scheme for narrow-linewidth fiber lasers is to broaden the spectrum of a single-frequency seed through phase modulation, followed by power amplification of the phase-modulated seed. This approach offers strong capability in spectral control while maintaining a narrow linewidth. In this work, the modulation waveform is optimized to reduce the spectral power density. In addition, a low-NA large-mode-area gain fiber is adopted in the main amplifier stage to further mitigate stimulated Brillouin scattering. Experimentally, a 5 GHz-level narrow-linewidth fiber laser with an output power of 3 kW is achieved. The beam quality reaches M2 = 1.26/1.21, and no transverse mode instability is observed. To the best of our knowledge, this represents the highest output power reported for a 5 GHz-level narrow-linewidth fiber laser within the full gain bandwidth of ytterbium-doped fiber. The results of this work are expected to provide a higher performance laser source for spectral beam combining systems.
As passive optical networks (PONs) evolve toward 200 Gb/s to support bandwidth-intensive services, intensity modulation with direct detection (IM-DD) faces challenges from limited optoelectronic bandwidth and chromatic dispersion. While coherent detection offers superior performance, its high hardware complexity is not suitable for cost-sensitive optical network units (ONUs). In this paper, we propose and experimentally demonstrate a linear phase-diverse direct detection (LPD-DD) receiver architecture without signal-signal beat interference (SSBI) for 200G PON. The proposed scheme employs three carrier phase-switching branches with a narrowband phase-shift configuration (i.e., θ, 0, and -θ). We experimentally demonstrate that LPD-DD receiver achieves a 35-dB optical power budget over 20-km standard single-mode fiber (SSMF) with 240-Gb/s 16-QAM signals at the 15% soft-decision forward error correction (SD-FEC) threshold. The proposed receiver requires only low-complexity linear DSP and operates at an optimal CSPR of 0 dB. Furthermore, to facilitate the practical implementation of low-cost ONUs, we theoretically investigate feasibility of realizing narrowband phase shifts using integrated silicon photonic all-pass filters (APFs) based on racetrack resonators and Mach-Zehnder interferometer (MZI)-coupled micro-ring resonators (MRRs). The LPD-DD architecture provides a high-speed and cost-effective solution for next-generation very-high-speed PON (VHSP) evolution.
We propose two fully digital frequency offset estimation (FOE) techniques, a frequency-window method and a pilot-tone approach, for coherent time-division multiplexing (TDM) passive optical networks (PONs), enabling ultra-wide carrier frequency offset (CFO) estimation and compensation. The proposed methods support CFOs up to ±20 GHz, significantly exceeding the ±3 GHz limit of conventional 4th-power-based FOE. Experimental demonstrations using super-rated 30 GBd DP QPSK and DP-16QAM signals confirm stable downstream continuous-mode and upstream burst-mode transmission over a 50 km optical distribution network with minimal performance penalty under large CFO conditions. Both methods operate entirely in the digital domain and require no additional hardware, facilitating the use of low-cost, frequency-unstable lasers and providing a practical pathway toward cost-efficient high-speed coherent PON deployment.
