Multi-target and ultra-high-speed optical wireless communication using a thin-film lithium niobate optical phased array

Domain: physics
Published: 2025-12-15
Editorial outcome: major_revision

Abstract
Optical wireless communication (OWC) effectively addresses challenges such as radio spectrum scarcity and signal attenuation by leveraging the properties of laser beams. A major advance in this field comes from the incorporation of optical phased arrays (OPAs), which enable inertial-free, high-speed beam steering with transformative potential. In this contribution, we propose and demonstrate a multi-target and ultra-high-speed OWC system based on a thin-film lithium niobate (TFLN) OPA. It enables real-time multi-target connection without mechanical components or lenses. This system can achieve OWC with a single-channel communication data rate of up to 320 Gbps in the modulation format of 16-Quadrature Amplitude Modulation (QAM), significantly exceeding the peak capabilities of 5G and current 6G proposals. System performance is further validated through the stable transmission of uncompressed high-definition video. This work establishes a new paradigm for fully solid-state, chip-scale OWC systems, combining unprecedented single-channel data throughput with dynamic multi-target support.

Introduction
Optical wireless communication (OWC) leverages the high monochromaticity, coherence, and directivity of laser sources to establish high-capacity, low-latency directional links with excellent anti-interference capabilities. It thus offers a promising solution to current challenges in modern communications, including radio frequency spectrum scarcity and signal attenuation1–3. Conventional OWC systems typically rely on point-to-point architectures, which are unable to support multicast or broadcast services from a single source to multiple users. Dynamic beam steering has emerged as a viable approach to overcome this limitation4–6. This technique provides inertia-free operation, sub-millisecond response times, and high programmability, significantly enhancing the versatility and practicality of OWC systems. These improvements show considerable potential for demanding applications, including mobile access networks, satellite communications, and emergency response systems7–10. Current dynamic beam-steering techniques mainly involve three approaches: metasurfaces11,12, mechanical beam-steering systems13–16, and optical phased arrays (OPAs)17–21. Metasurfaces employ artificially engineered subwavelength structures to achieve beam deflection, focusing, and mode conversion11,12. However, the optical responses of most metasurface devices are static once fabricated. Even those with thermal tuning often suffer from slow response speeds and limited tuning ranges. Mechanical beam-steering systems adjust the beam direction by moving optical components or transceiver modules, yet these systems often compromise reliability and integration potential13–16. In contrast, fully solid-state, miniaturized, and high-speed dynamic beam steering is a pivotal direction for next-generation OWC systems. OPAs enable non-mechanical beam steering by precisely controlling the phase of individual optical antenna elements, making them a key technology in this field17–21.

OPAs have been successfully implemented on several integrated photonic platforms, including silicon22–27, silicon nitride (Si3N4)28–30, thin-film lithium niobate (TFLN)31–34, and heterogeneous integrations of Si3N4 and TFLN35,36. Silicon-based OPAs benefit from complementary metal-oxide-semiconductor (CMOS) compatibility and high integration density. However, their thermo-optic phase shifters exhibit microsecond-scale response times and require continuous power consumption to maintain thermal stability. While Si3N4 platforms provide low propagation loss and broad optical transparency, the lack of a linear electro-optic effect limits high-speed modulation. In contrast, TFLN has emerged as a leading platform for high-performance OPAs37–40, owing to its low loss, high stability, wide transparency window, and strong Pockels effect. Furthermore, TFLN is compatible with cost-effective wafer-scale fabrication, supporting a viable path toward mass commercialization. Recent progress in TFLN-based OPAs demonstrates notable capabilities. Passive OPAs achieve wide beam steering via field-of-view (FOV) stitching, though their lack of dynamic programmability limits applicability in multi-target communication scenarios34. Active OPAs face inherent design trade-offs: larger antenna spacing improves the beam full width at half maximum (FWHM) but reduces the FOV31. Sparse arrays can narrow beam divergence and enhance pointing accuracy, albeit at the cost of limited angular coverage32,33. Additionally, a low sidelobe suppression ratio (SLSR) degrades the signal-to-noise ratio at the receiver, increasing the bit error rate (BER) in OWC links. On hybrid platforms combining Si3N4 and TFLN, OPAs using Taylor amplitude distributions achieve improved SLSR, but at the cost of longer beam-steering times. This results in communication latency and reduced real-time performance36. Despite these device-level advances, system-level demonstrations of TFLN-based OPAs for high-speed OWC remain limited. Therefore, integrating TFLN OPAs into system-level OWC architectures represents a transformative opportunity.

In this contribution, we propose and demonstrate a multi-target ultra-high-speed OWC system utilizing a TFLN OPA. The system incorporates an optimized curved coupled trapezoidal grating antenna that enables high-resolution two-dimensional beam steering across a 62°×11° FOV via independent phase and wavelength control. An SLSR as low as –13.6 dB is achieved, facilitating multi-target tracking and interference suppression. By independently manipulating the transverse phase and longitudinal wavelength dimensions, a 4×4 point-cloud matrix is generated within a 40°×10° FOV, successfully reconstructing the patterns of the letters “L”, “Z”, and “U”. Leveraging the strong Pockels effect in TFLN, the system demonstrates rapid beam steering with a record-breaking transition time of approximately 158 ps and a higher modulation efficiency of 8.73 pJ/π, compared to those reported TFLN-based OPAs. Our proposed system enables real-time multi-target communication without mechanical moving parts or external lenses. Experimental results confirm high beam direction accuracy and stability, indicating the system’s suitability for optical wireless links. Notably, OWC with a single-channel communication data rate of up to 320 Gbps is achieved using 16-Quadrature Amplitude Modulation (QAM) format at six distinct angles within the FOV of 31°×3.2°, significantly exceeding previous records and surpassing the peak rates of 5G and current 6G proposals. System reliability is further validated through the stable transmission of uncompressed high-definition (HD) video. This work establishes a fully solid-state chip-scale OWC system that combines ultra-high throughput with dynamic multi-target capability, thereby providing a foundation for next-generation satellite networks, secure drone communications, and immersive metaverse connectivity.

Results
Principles and designs
Figure 1a illustrates the working principle of an OPA-based OWC system. Information is transmitted from a data center via the OPA, which emits optical beams at specific steering angles. Each beam carries an independent data stream directed toward a receiving center. These distinct streams are subsequently distributed to end users and captured by dedicated receivers. A significant feature of the OPA is its wide FOV and high directivity, allowing each beam to establish a separate communication link. The system supports multi-target access through high-speed beam steering, while also improving channel confidentiality and security. Figure 1b presents the schematic of the core OPA device used in the OWC system. The device is fabricated on an X-cut TFLN platform, with a footprint of 10 mm × 1.1 mm. It consists of a 600-nm-thick top lithium niobate layer and a 2-μm-thick buried oxide layer. The rib waveguides are etched with a sidewall angle of approximately 67°, a width of 1 μm, a slab thickness of 300 nm, and a rib height of 300 nm (see Supplementary Note 1). Key components integrated on the chip include multimode interference (MMI) coupler trees, a voltage-controlled phase shifter array, uniformly spaced curved waveguides, and an optical antenna array. Input light at around 1550 nm is coupled into the chip via edge couplers. The MMI coupler trees splits the optical signal uniformly into 16 channels. Each channel contains an electro-optic phase shifter that can be independently adjusted to provide phase shifts from 0 to 2π. The output waveguides from the phase shifters are routed through curved sections and compressed to a pitch of 1.5 μm before connecting to trapezoidal slab antennas. The radii of adjacent curved waveguides are optimized to reduce mutual coupling. Light from each waveguide is coupled into a trapezoidal antenna and radiated into free space. The compact design and high level of integration facilitate practical deployment in OWC systems, while the optimized waveguide geometry and phase control ensure efficient and stable optical signal transmission. To validate the fabrication accuracy of the key waveguide structures in the OPA chip, Fig. 1c presents a scanning electron microscopy (SEM) image of the rib waveguide cross-section, which exhibits a well-defined geometry consistent with the designed dimensions. The OPA chip utilizes co-packaged optics, and Fig. 1d shows a micrograph of the fully assembled 16-channel device. The chip is wire-bonded to a printed circuit board (PCB), as illustrated in Fig. 1e, to enable electrical interfacing with external drive circuits for voltage application to the phase shifters and to facilitate beam control during experiments.

To address the need for flexible and efficient beam control in OWC systems, we introduce an OPA capable of independent beam steering in two dimensions. Transverse steering, controlled via phase modulation, is achieved through electro-optic phase shifters, while longitudinal steering, governed by wavelength adjustment, is facilitated using tunable lasers. In the transverse dimension, the maximum steering angle is limited by the antenna spacing. Reducing the inter-antenna spacing to half the operating wavelength permits beam steering of up to 180°. However, such narrow spacing increases inter-element coupling and crosstalk, as discussed in Supplementary Note 2. Conventional strategies often utilize a non-uniform antenna array to suppress inter-waveguide crosstalk, thereby improving the resolution of OPAs. However, achieving a wide FOV generally requires the incorporation of specialized structures fabricated through complex techniques to achieve a flattened far-field profile. To address these issues, we design and optimize a trapezoidal antenna structure22. This configuration effectively suppresses edge scattering and improves the SLSR. Additional details are provided in Supplementary Note 3. Combined with a curved coupling scheme, the trapezoidal antenna architecture enables reduced waveguide spacing and crosstalk, allowing antennas to be spaced at intervals approaching half the wavelength. Consequently, the beam steering range in the transverse dimension is substantially enhanced (see Supplementary Note 4). For the longitudinal dimension, the steering range depends primarily on two factors: the wavelength tuning range of the laser and the operational bandwidth of the passive components. Detailed specifications are provided in Supplementary Note 4.

To assess the stability of transverse beam steering in the proposed OPA at a fixed wavelength, Fig. 2a presents the far-field beam spots at transverse steering angles of ±31°, ±24°, ±18°, ±12°, ±6°, and 0°. These measurements are conducted at a wavelength of 1550 nm. The beam profiles remain distinct and well-defined across all angles, confirming that the OPA maintains consistent transverse steering performance without significant degradation. This stability is critical for reliable signal transmission in OWC systems, as it minimizes beam quality deterioration during angular adjustments. To investigate the influence of transverse steering angles on the optical field distribution at various wavelengths within the C-band, Fig. 2b displays the normalized optical field distributions for several steering angles at wavelengths of 1530 nm, 1550 nm, and 1565 nm. The beam is calibrated using a gradient descent algorithm (see Supplementary Note 5). The optical field distributions exhibit uniform profiles across all wavelength and angle combinations, indicating that the calibration process effectively compensates for variations induced by fabrication imperfections and other disturbances. This consistency underscores the suitability of the OPA for multi-wavelength OWC applications, where stable field distribution is essential for maintaining signal integrity. Figure 2c characterizes the FWHM of the far-field beam profile, a key parameter for evaluating beam collimation. The measured FWHM values are 3.8° in the transverse direction (θ) and 1.72° in the longitudinal direction (φ). The inset depicts the corresponding far-field beam profile after phase calibration. The narrow FWHM values demonstrate the capability of the OPA to generate highly collimated beams, which reduces signal divergence and enhances energy concentration in OWC links. The calibrated beam profile further confirms that phase correction significantly improves beam quality by reducing phase-related distortions. To evaluate the SLSR during transverse beam steering, a parameter pertinent to crosstalk in multi-beam systems, Fig. 2d shows the SLSR across a range of transverse steering angles. The SLSR reaches a peak value of –13.6 dB and remains below –7.8 dB throughout the angular range tested. This consistently low SLSR indicates effective suppression of sidelobe energy, thereby reducing interference among adjacent beams. In multi-target OWC systems, this characteristic is vital for minimizing signal crosstalk and ensuring communication reliability.

To validate the longitudinal beam-steering performance of the OPA via wavelength tuning, Fig. 2e displays far-field beam spots at wavelengths of 1500 nm, 1530 nm, 1560 nm, 1590 nm, and 1620 nm. The beam spots shift monotonically with increasing wavelength, demonstrating clear longitudinal steering. Complementing the steering analysis, Fig. 2f shows the corresponding normalized optical field distributions at the same wavelengths. The profiles maintain a consistent Gaussian shape under wavelength variation, aligning with the stable beam spots observed in Fig. 2e. This uniformity ensures that the optical field quality remains unaffected during steering, which is essential for preserving signal integrity across the operating range. For quantitative analysis of wavelength-dependent steering efficiency, Fig. 2g presents a linear fit of beam-steering angle versus wavelength. Over a 120 nm bandwidth, the OPA achieves a steering range of 11°. The fit yields a steering efficiency of –0.091°/nm. The linear relationship between wavelength and steering angle simplifies control and enables precise beam positioning via laser tuning. To verify the multi-target connectivity of the OPA, two laser beams at 1530 nm and 1630 nm are simultaneously injected into the device. The appearance of two distinct far-field spots on the screen confirm the OPA’s ability to generate stable beams for multi-target operation. Figure 2h shows far-field beam spots at wavelengths of 1530 nm and 1630 nm for transverse steering angles of ±20°, ±10°, and 0°. The spots retain well-defined shapes across all angles, demonstrating that the OPA maintains stable beam quality while facilitating multi-target connectivity. To further demonstrate its practical utility, the OPA generates a 4×4 point-cloud matrix across a 40°×10° FOV, as shown in Fig. 2i. This matrix is configured to form the characters “L”, “Z”, and “U”, shown in Fig. 2j. This ability to project user-defined patterns confirms independent control over both transverse and longitudinal steering dimensions, supporting applications such as multi-target free-space communication or structured light imaging. Additional details on OPA performance are provided in Supplementary Note 6. Notably, we report two distinct FOV values for the same OPA device. The maximum device-level FOV of 62°×11° is characterized from far-field scans under combined phase and wavelength control. The demonstration of pattern reconstruction is conducted within a 40°×10° FOV, which is selected as it provides the necessary angular area to project a clearly defined 4×4 point-cloud pattern.

Performance characterization of OPA
The half-wave voltage (Vπ) is a key parameter for evaluating the performance of OPA phase shifters, as it dictates the driving voltage required to achieve a π-phase shift. This parameter is measured using the experimental setup shown in Fig. 3a. Through a polarization controller (PC), a 1550 nm laser source is coupled into a Mach–Zehnder interferometer (MZI) modulator, which incorporates two target OPA phase shifters. One arm of the MZI modulator is driven by a 10 MHz triangular wave signal generated by an arbitrary function generator (AFG). The modulated optical signal is detected by a photodetector (PD), and the PD output is recorded using an oscilloscope. Figure 3b plots the measured normalized optical intensity versus driving voltage. For the OPA phase shifter with an 8 mm electrode length, the measured Vπ is 4.7 V. The corresponding power consumption, calculated based on this Vπ, is 8.73 pJ/π. Detailed derivations of the power consumption are provided in Supplementary Note 7. A Vπ of 4.7 V is beneficial for practical OPA deployments, as it reduces the demand for high-voltage drive electronics. Furthermore, the low power consumption of 8.73 pJ/π contributes to energy-efficient operation of OPA systems, which is an essential characteristic for portable and power-sensitive optical communication devices.

Steering speed represents another critical performance metric for OPA phase shifters, as it directly determines the dynamic response of the overall OPA. A higher steering speed enables faster adjustments of the beam direction, which is essential for dynamic OWC applications. To evaluate this parameter, the rise and fall times of the MZI modulator are measured using the setup illustrated in Fig. 3c. In this experiment, a 1550 nm laser source is employed, and light is coupled into the MZI modulator via a PC to maintain a stable polarization state. One arm of the modulator is driven by a 1 GHz square-wave voltage signal generated by an arbitrary waveform generator (AWG). The time-domain response of the optical output is recorded using a digital communication analyzer (DCA). Figure 3d presents the waveform acquired from the time-domain response measurement in Fig. 3c. From this waveform, the rise and fall times of the MZI modulator are determined to be 170 ps and 146 ps, respectively. These short transition times reflect a fast dynamic response of the OPA phase shifter. In high-speed OWC systems, such as those used for real-time dynamic beam tracking or multi-target switching, such rapid responsiveness ensures that the OPA can adapt promptly to varying communication requirements, thereby enhancing the stability and reliability of the optical link.

The OPA can function as either a transmitter or a receiver owing to the reciprocity principle. To characterize its transmission performance across different distances, the OPA chip is employed as the transmitter, and a collimator serves as the receiver. Detailed experimental procedures are provided in Supplementary Note 8. Figure 3e presents the total link efficiency as a function of transmission distance, revealing a decline in efficiency with increasing distance. A linear fit yields an attenuation rate (k) of approximately –1.48 dB/m. In practical implementations, this attenuation can be compensated for by achieving more precise beam divergence control at the OPA output. The beam directivity of the OPA under wavelength shifts is also evaluated. Measurements indicate a 3 dB attenuation in power with a wavelength shift of only 2.2 nm, corresponding to an angular deviation of approximately ±0.1°. These results affirm the device’s excellent beam directivity and precise beam-steering capability, both essential for OWC systems. To assess operational stability in OWC scenarios, tests are conducted at a fixed distance of 1 m. Figure 3f shows the stability measurement results, demonstrating a gradual decrease in received optical power over time, with 3 dB attenuation occurring after 174 min. This confirms that the OPA maintains high stability, which is crucial for reliable OWC applications.

High-speed OWC system based on OPA
To validate the high-speed communication performance of the OPA, a coherent detection-based measurement system is employed. This system forms the basis of the experimental setup illustrated in Fig. 4a, which is designed to evaluate two key functionalities of the OPA: optical beam steering and high-speed signal transmission. In this configuration, the OPA directs optical beams towards six distinct angles (θ=0°, φ=1.6°; θ=0°, φ=3.4°; θ=0°, φ=4.8°; θ=31°, φ=1.6°; θ=31°, φ=3.4°; θ=31°, φ=4.8°) while transmitting 320-Gbps 16-QAM signals for analysis. Since the OPA’s far-field divergence is symmetric in the transverse direction, performance is characterized over half of the full angular span. The longitudinal range is limited to 3.2° due to the experimental setup optimized for the C-band in high-speed coherent transmission, which represents an instrumentation constraint and not a fundamental limitation of the OPA. By integrating beam steering with high-speed data transmission tests, this approach provides a comprehensive assessment of OPA performance under realistic communication conditions. Such evaluation is essential to verify whether the OPA can maintain reliable high-speed communication during beam steering, a fundamental requirement for practical OWC systems. The detailed experimental procedure is as follows. A laser source operating at 1550 nm emits a continuous wave optical signal, which is amplified using an erbium-doped fiber amplifier (EDFA). A PC adjusts the polarization state before an optical splitter divides the signal into two paths: one for electro-optic modulation and the other serving as the local oscillator (LO) at the receiver. A digital-to-analog converter (DAC) operating at 100 GSa/s generates a 320-Gbps 16-QAM electrical signal. These I/Q parts are amplified by two electrical amplifiers (EAs) before driving a 35 GHz in-phase/quadrature modulator (IQM). The IQM is biased at the transmission null to suppress the carrier component, thereby enabling efficient modulation of the optical signal in the signal arm41. The modulated light is further amplified by another EDFA and then injected into the OPA for beam steering at predefined angles. After 93 cm of free-space propagation, the beam is collected by a collimator and coupled back into a fiber. At the receiver, the EDFA is employed for compensating the transmission loss. The received carrier-suppressed modulated signal is detected with a single-polarization coherent receiver. To meet the polarization-matching requirement in a coherent receiver, two PCs ensure precise alignment between the signal and the LO relative to the optical hybrid. Finally, the output photocurrents are captured using a digital storage oscilloscope (DSO) with a sampling rate of 160 GSa/s.

To illustrate the operational principles of signal generation and recovery in our high-capacity transmission system, Fig. 4b depicts the digital signal processing (DSP) flowchart for the 320 Gbps 16-QAM system. At the transmitter, the data stream is upsampled and pulse-shaped using a root-raised cosine (RRC) filter with a roll-off factor of 0.01. These steps precede DAC and optical modulation. On the receiver side, coherent detection is first applied. The captured signal is then resampled and subjected to a series of digital compensation steps, including frequency offset correction, matched filtering, and equalization based on a multiple-input multiple-output feed-forward equalizer (MIMO-FFE). After the linear equalization-enhanced noise following these compensations, carrier phase recovery is conducted. Additional noise suppression is achieved through a post-filter (PF) combined with maximum likelihood sequence detection (MLSD), enhancing BER performance. This comprehensive DSP workflow ensures high-quality generation and accurate recovery of the 320 Gbps 16-QAM signals, which is essential for sustaining the reliability of our high-capacity transmission system. Further details on the complete DSP procedure are provided in Supplementary Note 9.

To characterize the spectral evolution of the transmitted signal and evaluate link-induced impairments, Fig. 4c presents high-resolution spectral measurements (1.12 pm) of the 320 Gbps 16-QAM signal acquired at different stages of the transmission link. The fine spectral resolution enables clear visualization of changes introduced during modulation, amplification, and transmission. These measurements provide direct evidence for assessing signal integrity and link-induced losses. To evaluate system stability under multi-angle beam steering via the OPA, Fig. 4d shows the BER measured at different wavelengths for transverse angles θ=0° and θ=31°, respectively. The BER remains consistently below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8×10−3 for every angle, with a maximum observed value of only 1.1×10−3. This confirms robust system stability during OPA operation at various steering angles, indicating that beam steering does not introduce significant signal degradation and attests to the system’s reliability in dynamic beam control scenarios. To further assess signal quality across steering angles, Fig. 4e displays recovered 16-QAM constellation diagrams obtained at different angles. These constellations consistently demonstrate high signal integrity across all channels. Further enhancements in transmission capacity may be pursued through several strategies. Increasing the performance data rate of the signal source can alleviate the DAC and DSO current rate limitation, thereby boosting overall transmission capacity. Incorporating an optical bandpass filter (OBPF) after the second EDFA could suppress amplified spontaneous emission (ASE) noise, improving signal quality and facilitating higher data rates or extended reach. Furthermore, lithium niobate exhibits marked optical anisotropy, enabling independent propagation and manipulation of distinct polarization states. Exploiting defined polarization states such as transverse magnetic (TM) mode significantly expand the scanning range of OPA, thereby increasing the channel capacity in OWC systems (see Supplementary Note 10).

Wireless video transmission based on OPA
After characterizing the optical properties and validating the communication performance of the core device, we construct an OWC system based on the OPA. This system is employed to perform point-to-point HD video transmission experiments. To illustrate the system design and experimental configuration, Fig. 5a, b present the schematic diagram and the actual experimental setup, respectively. The specific experimental procedure is as follows. A computer controls an optical module (electrical-to-optical conversion) to convert the electrical signal from an HD video stream on the source monitor into an optical signal. This signal is coupled into a single-mode fiber for transmission. The optical signal is then directed through an EDFA for power amplification before being coupled into the OPA chip. Under active control, the OPA emits the optical signal directionally at a steering angle of 0°. After 93 cm of free-space propagation, the optical signal is collected by a collimator at the receiver. The collected signal is delivered to another optical transceiver module (optical-to-electrical conversion), which reconstructs the original analog electrical signal. This process ultimately results in stable, undistorted HD video output on the output monitor, confirming that the OPA-based OWC system supports high-quality signal transmission.

To evaluate the reliability of the OWC system, we conduct tests of HD video transmission. Experimental results demonstrate that the HD video stream remains stable and uninterrupted when the beam pointing angle of the transmitter aligns with that of the receiver (see Supplementary Movie 1). This finding confirms that precise beam alignment between the transmitter and receiver is essential for maintaining a stable communication link. Conversely, the communication link is immediately interrupted when the free-space channel between the OPA transmitter and the receiver is obstructed (see Supplementary Movie 2). Notably, the OPA device employed in this study enables dynamic beam steering to any specified angle through wavelength or phase control. This capability facilitates direct parallel signal transmission in multiple directions without the need for additional multiplexing or demultiplexing components, thereby simplifying the system architecture and reducing hardware complexity. It also allows flexible coverage of any designated communication area, enhancing the system’s adaptability for practical OWC applications such as multi-user communication or dynamic coverage adjustment.

Methods
Simulation and fabrication of the OPA chip
The near-field and far-field distributions of the OPA antenna are simulated using the finite-difference time-domain (FDTD) method. These simulations are carried out with the commercial software Lumerical FDTD Solutions. Boundary conditions are applied in three-dimensional space, specifically along the x, y, and z directions, to accurately model the periodic grating antenna array structure shown in Fig. 1b.

Lithium niobate on insulator (LNOI) wafers are used as the substrate for fabricating the chip. Waveguide structures are patterned by means of deep ultraviolet (DUV) lithography and then precisely transferred into the TFLN via dry etching. The sidewalls of the waveguides exhibit an inclination angle of approximately 67°. The measured transmission loss of the fabricated waveguide is below 0.5 dB/cm.

Chip packaging is implemented through optoelectronic hybrid integration. The fabricated chips are mounted onto custom-designed metal substrates using conductive silver adhesive. Electrical connections between on-chip pads and external printed circuit boards are established with gold wire bonding. For optical interfacing, a polarization-maintaining fiber array with a small mode field diameter is selected. The polarization direction of the fiber is carefully aligned with the transverse electric (TE) mode of the chip waveguide. This alignment minimizes mode mismatch loss and preserves the polarization state. Low-loss optical coupling between the fiber array and the on-chip optical ports is achieved through active alignment. The output of the fiber array is terminated with a standard FC/APC connector to ensure low insertion loss and low back reflection. The electrical interface employs a dual-row pin header with a 2.54 mm pitch, which offers versatile and plug-compatible connectivity to external drive and control systems.

Experimental setup
Beam characterization of the fabricated OPA is performed using a tunable laser (Santec TSL 570), a PC (Thorlabs FPC561), an optical screen, and an infrared camera (Xenics Bobcat 640). For subsequent measurements, a triangular wave signal generated by an AFG (Tektronix AFG3102C) is applied to determine the Vπ of the phase shifter. The output signal is detected by a PD (Finisar XPDV3120R, 70 GHz) and displayed on an oscilloscope (Tektronix TDS2012C, 100 MHz). The device response time is evaluated using a square-wave signal from an AWG (Keysight M8199B, 224 GSa/s), and the resulting waveform is analyzed with a DCA (Keysight N1000A). The OPA transmitter, driven by a voltage source controlled by a field programmable gate array (FPGA), is coupled to a fiber collimator (Thorlabs F810APC1550). This setup is used to characterize the relationship between the received optical power, measured with a power meter (Thorlabs PM100D), and the transmission distance, as well as to assess temporal stability. Before coupling, beam steering is carried out using a plano-convex lens (Jcoptix OLC320166 T4M) and a plano-concave lens (Jcoptix OLE240136T4M) to ensure a collimated input beam to the collimator.

In the high-speed coherent communication experiment, the output from a tunable laser (Keysight 8190A) is divided into two separate paths. One path function as the optical carrier, while the other undergoes electro-optic modulation. An IQM (FTM7992HM), driven by a 100 GSa/s DAC (Micram DAC4), generates a 16-QAM signal. The DAC output is first amplified by an EA before driving the IQM. A collimator (Thorlabs F810APC1550) collects the free-space optical signal transmitted from the optical power amplifier. Both the modulated signal and the optical carrier are then fed into a coherent receiver. The final output is captured using a 160 GSa/s DSO (LeCroy 36ZiA).

In the point-to-point HD video transmission experiment, a computer-driven optical module (Huawei, 10G 1550nm 80km SM SFP+) encodes video data into optical signals. These signals are coupled into a single fiber within a fiber array. The light emitted from the fiber facet is deflected by the OPA at programmed angles and propagates through free space over a predetermined distance. A receiver collimator (Thorlabs F810APC1550) collects the optical signal. This signal is then routed to a second optical transceiver, where it undergoes photoelectric conversion, ultimately reconstructing the original video signal for display on an HD monitor.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This work presents a TFLN-based OPA for beam steering and high-speed optical wireless communications. Key results include 16-channel configuration, wide FOVs, fast steering speed, low sidelobe level, 320 Gbps OWC transmission, and HD video demonstration. The paper is very well written and the experimental works are solid. While I am very impressed by the achieved results, I do have a few major concerns regarding its novelty and significance, considering the standard of the targeted journal.\n1. Compared with silicon-based OPAs, the biggest concern for TFLN-based OPAs is the compactness and scalability in channel counts. SiP based OPAs have demonstrated up to 1000 channels (e.g. https://arxiv.org/abs/2508.19977), thus can achieve wide FOV and fine resolution simultaneously. Also the demonstrated sidelobe level is even lower than this work within the same FOV range. Comparably, the 16-channel TFLN device presented in this work is not that impressive. The authors should critically discuss the challenges and solutions to scale up the channel numbers of TFLN-based OPAs to a few hundred or even thousand. The energy efficiency of the overall OPA also correlates with the channel numbers. Otherwise, the steering speed merit alone brought by TFLN is not enough to justify its feasibility.\n2. There are three difference values of FOVs presented in the paper, i.e., 62° × 11°, 40° × 10°, 31° × 3.2°, all coming from the same device. This is a bit confusing to follow. I understand that the performance of the pattern reconstruction and high-speed transmission limit the operational range of FOV. The authors are suggested to make it clear in the beginning regarding the reasons of such limitations, and discuss them in details in corresponding sections.\n3. Using curved waveguides to address the different pitch mismatch between the phase shifter section and the optical antenna section is indeed a viable design. What's the maximum time delays induced by the different waveguide lengths in this design? And please also discuss how much it impacts high speed signal transmission.\n4. Three EDFAs are used for the transmission experiment, yet the transmission distance is only 1m. In the discussion section, the authors repeatedly suggest that extending the distance should rely on more amplifications, either EDWAs or fiber amplifiers. In my opinion this is not exactly where the issue is and shouldn't be considered as the way forward. Considering the atmospheric loss in this wavelength should be well below 1 dB/km once the beam is properly collimated, a more precise beam divergence control at the output of the OPA should be the key issue to solve for practical deployment.\n5. There is a typo in Fig. 4a, 'DCA' should be 'DAC'.", "reviewer_2": "This manuscript presents a multi-target, ultra-high-speed optical wireless communication system based on a thin-film lithium niobate optical phased array. The system demonstrates impressive performance, including high-speed multi-target beam steering across a wide field of view, low sidelobe levels, and a record single-channel data rate of 320 Gbps using 16-QAM modulation. The work highlights significant advantages in integration, power efficiency, and dynamic reconfigurability, supported by comprehensive experimental data such as high-definition video transmission. The results are clearly presented and address a highly relevant research direction with considerable potential for next-generation wireless networks. The manuscript is well-structured, exhibits strong originality, and the data are systematically organized, providing robust support for the conclusions. This work is likely to attract broad interest from the photonics and communications communities. In my view, the paper merits publication after the authors address the following points:\n1. The current vertical beam steering range is 11°. The authors should discuss potential strategies or design modifications to further expand the vertical field of view in future implementations.\n2. The manuscript does not explicitly clarify the parameters governing the horizontal and vertical beam resolution, nor the ultimate factors limiting these resolutions. A discussion on these aspects would help readers better understand the system's performance constraints.\n3. For multi-wavelength parallel beam control scenarios, could the authors comment on whether the SPGD algorithm requires separate objective functions for each wavelength? If a unified objective function is used, how is convergence stability maintained? Additionally, is sequential calibration necessary for the dual-wavelength operation demonstrated in the experiments?\n4. Prior to operation, does the SPGD algorithm require calibration at each beam steering angle? If so, could this initialization process limit the overall communication speed or target switching rate?\n5. The discussion mentions a \"transition time of approximately 158 ps\", while the measured rise and fall times are 170 ps and 146 ps, respectively. The calculation or definition of the 158 ps value should be clarified for consistency.\n6. On page 13, first paragraph, \"tcoherent detection\" appears to be a typographical error. This should be corrected to \"coherent detection\".\n7. Please verify the angle units in Figure 4d and ensure consistent capitalization of units in Table 1 (e.g., 'mW' vs. 'mw')."}, "author_response": "Response to the reviewers’ comments\nTo Reviewer #1’s comments:\nRecommendation: This work presents a TFLN-based OPA for beam steering and\nhigh-speed optical wireless communications. Key results include 16-channel\nconfiguration, wide FOVs, fast steering speed, low sidelobe level, 320 Gbps OWC\ntransmission, and HD video demonstration. The paper is very well written and the\nexperimental works are solid. While I am very impressed by the achieved results, I do\nhave a few major concerns regarding its novelty and significance, considering the\nstandard of the targeted journal.\nAuthor Response:\nThank you for your positive evaluation and constructive feedback. We are grateful\nfor the opportunity to further clarify the novelty and significance of our work.\nTo our knowledge, compared with silicon, lithium niobate exhibits a strong linear\nelectro-optic effect (Pockels effect), which enables pure phase modulation of light with\nhigher speed and lower consumption by applying a traveling-wave electrode along\nboth sides of the lithium niobate waveguide, without requiring carrier injection or\nthermo-optic effects. For example, our fabricated OPA demonstrates a switching\nspeed of 158 ps and a modulation efficiency of 8.73 pJ/π, all of which are among\nthe best performances reported for OPAs to date, whether lithium niobate-,\nsilicon- or MEMS-based. These results pave the way for high-speed, low-power\noptical wireless communication (OWC) systems.\nIn this work, we also introduce a new integrated OPA architecture on the TFLN\nplatform, which incorporates curved couplers and trapezoidal grating antennas\nto mitigate phase discontinuity. Thanks to this novel design, the fabricated 16-channel\nOPA device can achieve two-dimensional beam steering with a 62° × 11° FOV and a\nlow sidelobe level of -13.6 dB. Notably, previously reported systems with comparable\nperformance typically require 32 or more phase channels, underscoring the superior\ncompactness of our device.\nThis work also presents the first-ever experimental demonstration of a 320\nGbps optical wireless link using 16-state quadrature amplitude modulation\ntogether with OPA-based beam steering. This data rate substantially exceeds the\nthroughputs of current 5G systems and the projected capabilities of early 6G proposals.\nSystem robustness is validated by real-time transmission of uncompressed high-\ndefinition video. The approach enables multi-beam control without moving parts and\nsupports real-time multi-target tracking and communication.\nIn summary, the combined contributions in device architecture, record-setting\nperformance metrics, and system-level demonstration represent a substantive\nbreakthrough in integrated lithium niobate photonics. The results open immediate\nopportunities in secure mobile links, LiFi, and free space optical communication, and\nthey create clear avenues for future applications in advanced LiDAR and computational\nimaging. We believe these clarifications address the reviewer’s comments and convey\nthe high novelty and academic value of the work. Thank you again for the careful\nreview and helpful suggestions.\nComment 1:\nCompared with silicon-based OPAs, the biggest concern for TFLN-based OPAs is the\ncompactness and scalability in channel counts. SiP based OPAs have demonstrated up\nto 1000 channels (e.g. https://arxiv.org/abs/2508.19977), thus can achieve wide FOV\nand fine resolution simultaneously. Also the demonstrated sidelobe level is even lower\nthan this work within the same FOV range. Comparably, the 16-channel TFLN device\npresented in this work is not that impressive. The authors should critically discuss the\nchallenges and solutions to scale up the channel numbers of TFLN-based OPAs to a\nfew hundred or even thousand. The energy efficiency of the overall OPA also correlates\nwith the channel numbers. Otherwise, the steering speed merit alone brought by TFLN\nis not enough to justify its feasibility.\nReply and modifications:\nWe sincerely thank the reviewer for their insightful and constructive comments\nregarding the scalability and feasibility of our TFLN OPA. We greatly appreciate the\nopportunity to address these important points and further clarify the strengths and\npotential of our proposed approach.\nLithium niobate waveguides exhibit weaker optical confinement than silicon\nwaveguides, primarily due to the lower refractive index contrast between their cladding\nand core regions. This results in a lower integration level for lithium niobate photonics\ncompared to silicon photonics. Nevertheless, lithium niobate has a unique advantage\nin its strong linear electro-optic effect, known as the Pockels effect. This effect\nallows pure phase modulation with higher speed and lower power consumption\nwhen traveling-wave electrodes are used alongside the waveguides, without\nrelying on carrier injection or thermal effects. In our proof-of-concept\ndemonstration, the fabricated OPA achieves a switching speed of 158 ps and a\nmodulation efficiency of 8.73 pJ/π phase shift. These performance metrics are\namong the best reported for lithium niobate-, silicon- or MEMS-based OPAs,\nwhich highlights the potential of our device for applications requiring extreme speed\nand precision, such as high-speed OWC, quantum information processing, high-\nresolution lidar, and real-time holographic displays. The comparative analysis in Table\n1 confirms the advantages in switching speed and power consumption for high-speed\nOWC system, showing how this work opens new pathways for developing high-speed,\nlow-power OWC system.\nTable 1 Comparison of representative works in high-speed OWC system.\nSingle-\nRepresentative Switching Modulation\nMethod FOV SLSR channel Applications\nworks speed efficiency\nspeed\nSilicon-\nC1 based 60°×14° NA 24.4 µs 20 mW/π Signal/Image\n(OOK)\nOPA\nSiN- Si-\n3 4\n96°×14.4\nC2 based -6 dB NA 32.26 µs 1.33 W/π Image\n°\nOPA\nSilicon-\n25.6°×8. 40 Gbps\nC3 based -7.2 dB NA 1.92 W (total) Signal\n1° (OOK)\nOPA\nTFLN- 320\n–13.6\nThis work based 62°×11° Gbps (16 158 ps 8.73 pJ/π Signal/Video\ndB\nOPA QAM)\nNote: NA indicates not measured.\nOur study also introduces a novel integrated OPA architecture on the TFLN\nplatform, which uses curved couplers and trapezoidal grating antennas to effectively\nsuppress phase discontinuities. With this innovative design, the fabricated 16-channel\nOPA device achieves a two-dimensional beam steering range of 62°×11° and a low\nsidelobe level of -13.6 dB. Table 2 provides a comprehensive performance comparison\nwith other representative TFLN OPAs reported to date. This comparison clearly\ndemonstrates significant advancements in key parameters, including FOV, beam width,\nsidelobe suppression ratio, power consumption, and scanning speed. It is noteworthy\nthat achieving similar performance in existing reports usually requires 32 or more\nphase channels, indicating that our device maintains excellent performance while\nachieving higher integration density.\nTable 2 TFLN OPA system performance comparison.\nRepresentative Power\nPlatform Channels FOV Beamwidth SLSR Speed\nworks Consumption\nRef. C4 TFLN 16 50°×8.6° 0.73°×2.8° 5.1 dB 330 pJ/π 0.4 ns\nRef. C5 TFLN 16 24°×8° 2°×0.6° 10 dB 13.5 pJ/π 0.23 ns\nRef. C6 TFLN 32 62.2°×8.8° 2.4°×1.2° 7.4 dB 1.11 nJ/π 14.4 ns\nRef. C7 TFLN 8 50° 8° 10 dB NA NA\nRef. C8 TFLN-SiN 16 22°×5° 1.2°×0.2° NA 3.2 pJ/π 0.83 ns\nRef. C9 TFLN-SiN 16 62°×7.6° 3.2°×1.4° 20.3 dB 41.6 pJ/π 26 ns\nThis Work TFLN 16 62°×11° 3.8°×1.72° 13.6 dB 8.73 pJ/π 158 ps\nWe fully agree that scaling the channel count to hundreds or thousands is essential\nfor future high-performance systems to achieve superior angular resolution and larger\neffective apertures, especially in applications requiring wide FOV and high resolution.\nOur proposed TFLN OPA is also well suited for such scaling. In terms of fabrication\nand material properties, recent progress in deep ultraviolet lithography for TFLN has\nachieved excellent waveguide uniformity with propagation losses below 0.042 dB/cm\n[C10]. This level of precision is critical for maintaining phase consistency in large-scale\narrays. Moreover, the same deep ultraviolet equipment used for high-channel-count\nsilicon photonic devices can be directly applied to lithium niobate on insulator wafers,\nmeaning there are no fundamental physical barriers to fabricating hundreds to\nthousands of channels. Regarding electronic control, both silicon-based and TFLN\nOPAs face common challenges in control circuit complexity and cost when scaling to\nthousands of channels. Reducing the number of electronic components is important to\nsimplify design and lower system costs. Future systems will need to adopt innovative\nelectronic driving architectures, such as row-column addressing combined with pulse-\nwidth modulation, to address these limitations [C11]. In terms of energy efficiency, the\ntotal power consumption of an OPA includes contributions from electro-optic phase\nshifters, thermal tuning, and drive circuits. Our TFLN electro-optic phase shifters\nachieve high efficiency at 8.73 pJ/π, with energy consumption primarily occurring\nduring switching events. This differs from silicon thermal phase shifters, which require\ncontinuous power. When scaling to thousands of channels, the total modulation power\nincreases linearly with the number of channels, but the per-channel picojoule-level\npower consumption of TFLN remains significantly lower than the typical milliwatt-\nlevel consumption of silicon-based OPAs. System-level energy efficiency will still\nneed to address drive circuit power and thermal management. Silicon-based OPAs\nbenefit from CMOS driver integration but suffer from high static power consumption\ndue to their modulation mechanisms, whereas thermal tuning in TFLN is mainly used\nfor operational stability and requires very low power.\nWe are currently exploring multiple technical pathways to enable high-channel-\ncount scaling for TFLN OPAs. Hybrid integration techniques, which combine the high-\nspeed phase shifting of TFLN with the low-loss power distribution of silicon or silicon\nnitride, offer a viable solution to increase channel density without sacrificing\nmodulation performance [C12, C13]. To manage layout complexity, advanced\narchitectures under development, such as multilayer interconnects and folded routing,\ncan optimize the electro-optic footprint [C11, C14]. Additionally, monolithic or co-\nintegration strategies that directly integrate CMOS drivers with TFLN modulators are\ncrucial for achieving ultimate system-level energy efficiency and scalability [C15]. Co-\ndesign of custom CMOS drivers for TFLN modulators is also progressing to address\nchallenges in high-voltage, high-speed driving for large arrays.\nIn summary, while this study focuses on demonstrating the high-speed and system-\nlevel capabilities of TFLN OPAs, the material properties, maturity of fabrication\nprocesses, and compatibility with advanced integration schemes together outline a clear\nand feasible path toward scaling to large-scale, high-efficiency OPAs with hundreds to\nthousands of channels for next-generation communication and sensing applications.\nIn the revised manuscript, we have added the following sentences:\n“While the present work demonstrates a 16-channel OPA as a proof of concept,\nwe\nrecognize that scaling the channel count to several hundred or more is essential for\napplications demanding both wide FOV and fine angular resolution. Compared with\nsilicon photonics, lithium niobate waveguides exhibit a lower refractive index contrast,\nwhich historically has limited integration density. However, the strong Pockels effect\nin lithium niobate enables high-speed, low-power phase modulation without free-\ncarrier absorption or thermal crosstalk burdens, offering a distinct pathway for scalable,\nenergy-efficient systems. Fabrication processes such as deep ultraviolet lithography\nhave already achieved low propagation loss in TFLN, confirming the feasibility of\nmaintaining phase uniformity across large arrays [65]. Furthermore, hybrid integration\nwith low-loss passive waveguides and innovative electronic driving architectures,\nincluding row-column addressing [66], can alleviate layout and control complexity in\nfuture large-scale implementations. With continued development in co-integration\ntechniques and custom CMOS drivers, TFLN OPAs are positioned to achieve channel\ncounts comparable to silicon-based systems while retaining superior switching speed\nand power efficiency.” (Paragraph 4, section 3)\nIn the revised manuscript, we have added the following references:\n“65. Liu, J. et al. High-precision propagation-loss measurement of single-mode optical\nwaveguides on lithium niobate on insulator. Micromachines 10, 612 (2019).\n66. 1000-channel integrated optical phased array with 180° field of view, high\nresolution and high scalability. (https://doi.org/10.48550/arXiv.2508.19977)”\n(References)\nReferences:\n[C1] Yang, S. et al. Fast-beam-switching optical phased array for moving objects in\nwireless optical communication networks. Opt. Lett. 49, 1961-1964 (2024).\n[C2] Li, Y. et al. Integrated communication and sensing system based on Si-SiN dual-\nlayer optical phased array. Opt. Express 32, 33222-33231 (2024).\n[C3] Jiao, W. et al. Two-dimensional multi-beam steering for parallel free-space optical\ncommunication based on a silicon nitride optical phase array. APL Photon. 10,\n056110 (2025).\n[C4] Li, W. et al. High-speed 2D beam steering based on a thin-film lithium niobate\noptical phased array with a large field of view. Photonics Res. 11, 1912-1918\n(2023).\n[C5] Yue, G. Li, Y. Integrated lithium niobate optical phased array for two-dimensional\nbeam steering. Opt. Lett. 48, 3633-3636 (2023).\n[C6] Wang, Z. et al. Fast-speed and low-power-consumption optical phased array based\non lithium niobate waveguides. Nanophotonics 13, 2429-2436 (2024).\n[C7] Li, Y. et al. Design of optical phased array with low-sidelobe beam steering in thin\nfilm lithium niobate. Optics & Laser Technology 171, 110432 (2024).\n[C8] Lee, W., Kwon, Y., Kim D., Sunwoo, Y., Lee, S. Hybrid integrated thin-film\nlithium niobate-silicon nitride electro-optical phased array incorporating silicon\nnitride grating antenna for two-dimensional beam steering. Opt. Express 32,9171-\n9183 (2024).\n[C9] Liu, J. et al. Taylor amplitude distribution for low sidelobe in thin-film lithium\nniobate optical phased array. J. Lightwave Technol. 43, 8286-8292 (2025).\n[C10] Liu, J. et al. High-precision propagation-loss measurement of single-mode\noptical waveguides on lithium niobate on insulator. Micromachines 10, 612\n(2019).\n[C11] 1000-channel integrated optical phased array with 180° field of view, High\nResolution and High Scalability. (https://doi.org/10.48550/arXiv.2508.19977)\n[C12] Lee, W., Kwon, Y., Kim D., Sunwoo, Y., Lee, S. Hybrid integrated thin-film\nlithium niobate-silicon nitride electro-optical phased array incorporating silicon\nnitride grating antenna for two-dimensional beam steering. Opt. Express 32,\n9171-9183 (2024).\n[C13] Liu, J. et al. Taylor amplitude distribution for low sidelobe in thin-film lithium\nniobate optical phased array. J. Lightwave Technol. 43, 8286-8292 (2025).\n[C14] Liu, M., Wu, J., Fu, Z., Zheng, S., Hou, Y. Low-cost and easy-to-embed 7-bit\n360° phase shifter with transitions for large-scale phased arrays. Microw. Opt.\nTechnol. Lett. 66, 34243 (2024).\n[C15] Tan, Y. et al. Micro-transfer printed thin film lithium niobate (TFLN)-on-silicon\nring modulator. ACS Photonics 11, 1920–1927 (2024).\nComment 2:\nThere are three difference values of FOVs presented in the paper, i.e., 62° × 11°, 40° ×\n10°, 31° × 3.2°, all coming from the same device. This is a bit confusing to follow. I\nunderstand that the performance of the pattern reconstruction and high-speed\ntransmission limit the operational range of FOV. The authors are suggested to make it\nclear in the beginning regarding the reasons of such limitations, and discuss them in\ndetails in corresponding sections.\nReply and modifications:\nWe sincerely thank the reviewer for this insightful comment and for highlighting\nthe potential confusion regarding the different FOV values presented in our manuscript.\nWe appreciate the opportunity to clarify this important aspect and have carefully\nrevised the manuscript to address these points in a more comprehensive and accessible\nmanner.\nThe three FOV values (62° × 11°, 40° × 10°, and 31° × 3.2°) indeed originate from\nthe same OPA device, but they correspond to distinct operational scenarios and\nexperimental demonstrations. We acknowledge that the initial presentation may be\nunclear, and we now provide explicit explanations from the beginning of the manuscript\nto elucidate the reasons for these variations.\nSpecifically, the differences arise from the following considerations:\n1．The full device-level FOV of 62° × 11° represents the maximum beam steering\ncapability of our OPA, as determined through extensive far-field scanning under\ncombined phase and wavelength control, as presented in Figure 2. This value defines\nthe fundamental steering range governed by the antenna pitch and the wavelength\ntuning range.\n2．The pattern reconstruction FOV of 40° × 10° is selected for the point cloud\nreconstruction experiment because this specific angular area is necessary to project a\nrecognizable and coherent 4×4 pattern, such as the \"LZU\" image. The choice is driven\nby the spatial requirements of the demonstration itself.\n3．The high-speed communication FOV of 31° × 3.2° is constrained by\nexperimental setup limitations. Due to the symmetric far-field divergence distribution\nof the OPA in the transverse direction (as shown in Figure C1), we adopt a methodology\nconsistent with previous research [C16], evaluating performance only within half of the\nfull angular span during these tests. The longitudinal extent is limited to 3.2° because\nour high-speed coherent transmission experiments are conducted within the C-band,\nwhere our external amplifier chain and coherent receiver are specifically optimized.\nThis limitation stems from instrumentation constraints and is not an inherent restriction\nof the OPA device.\nFigure C1. Far-field beam spots measured at transverse steering angles of ±31°, ±24°,\n±18°, ±12°, ±6°, and 0° at a wavelength of 1550 nm.\nIn the revised manuscript, we have added the following sentences:\n“Notably, we report two distinct FOV values for the same OPA device. The\nmaximum device-level FOV of 62° × 11° is characterized from far-field scans under\ncombined phase and wavelength control. The demonstration of pattern reconstruction\nis conducted within a 40° × 10° FOV, which is selected as it provides the necessary\nangular area to project a clearly defined 4 × 4 point cloud pattern.” (Paragraph 4,\nSection 2.1)\n“Since the OPA’s far-field divergence is symmetric in the transverse direction,\nperformance is characterized over half of the full angular span. The longitudinal range\nis limited to 3.2° due to the experimental setup optimized for the C-band in high-speed\ncoherent transmission, which represents an instrumentation constraint and not a\nfundamental limitation of the OPA.” (Paragraph 1, Section 2.3)\nReferences:\n[C16]. Li, Y. et al. High-data-rate and wide-steering-range optical wireless\ncommunication via nonuniform-space optical phased array. J. Lightwave\nTechnol. 41, 4933-4940 (2023).\nComment 3:\nUsing curved waveguides to address the different pitch mismatch between the phase\nshifter section and the optical antenna section is indeed a viable design. What's the\nmaximum time delays induced by the different waveguide lengths in this design? And\nplease also discuss how much it impacts high speed signal transmission.\nReply and modifications:\nWe sincerely thank the reviewer for this insightful comment and for highlighting\nthe importance of the curved waveguide design in our OPA. The reviewer's question\nregarding the maximum time delay and its impact on high-speed signal transmission is\nhighly valuable, as it allows us to further clarify a key aspect of our device performance.\nIn our design, the curved waveguides address the pitch mismatch between the\nphase shifter section and the optical antenna section by enabling adiabatic compression\nof the channel pitch to approximately 1.5 µm. This approach is essential for maintaining\ndevice compactness and minimizing optical crosstalk between adjacent channels. The\nsymmetrical configuration of these curved waveguides introduces a maximum\ndifferential optical path length of about 300 µm between the outermost and innermost\nchannels. With a group index of 2.2 for our TFLN waveguides, this corresponds to a\nmaximum time delay of approximately 2.2 ps.\nWe have thoroughly investigated the impact of this delay on high-speed signal\ntransmission, particularly for the 320 Gbps 16-QAM signals demonstrated in our work.\nThe symbol period for this data rate is 12.5 ps. The 2.2 ps delay represents a small\nportion of the symbol period (17.6 percent), and it is critical to emphasize that this delay\nis static and fixed for a given device configuration. This static nature leads to two\nconsiderations. First, since the delay is less than one full symbol duration, it does not\ncause inter-symbol interference by overlapping adjacent symbols in time. Second, as\nall channels operate coherently under a common optical carrier, the sub-picosecond\ndelay differences result only in fixed phase offsets. These offsets are fully compensated\nduring the initial beam calibration process, as described in Supplementary Note 5, and\nare further mitigated by standard digital signal processing algorithms implemented in\nour coherent communication system. Therefore, the delay does not introduce\nmeasurable signal distortion or phase misalignment in high-speed operation.\nOur experimental results strongly support this analysis. The bit-error-rate\nperformance presented in Figure 4d remains well below the hard-decision forward error\ncorrection threshold across all beam steering angles, confirming that the curved\nwaveguide design has no observable adverse effect on communication performance.\nTo provide additional clarity in the manuscript, we have included the following\nsentences in the revised Supplementary Information:\n“The curved interconnection waveguides, essential for pitch matching, introduce\na maximum static path length difference of approximately 300 µm, corresponding to a\ntime delay of about 2.2 ps. This delay is about 17.6% of a symbol duration for the 320\nGbps 16-QAM signal and therefore does not induce inter-symbol interference by\noverlapping adjacent symbols in time. Furthermore, the fixed phase offsets arising from\nthese path differences are effectively calibrated out during the initial beam-forming\nprocess and are compensated by standard digital signal processing in the coherent\nreceiver, ensuring they have no measurable impact on communication performance.”\n(Paragraph 3, Supplementary Note 9, Supplementary information)\nComment 4:\nThree EDFAs are used for the transmission experiment, yet the transmission distance\nis only 1m. In the discussion section, the authors repeatedly suggest that extending the\ndistance should rely on more amplifications, either EDWAs or fiber amplifiers. In my\nopinion this is not exactly where the issue is and shouldn't be considered as the way\nforward. Considering the atmospheric loss in this wavelength should be well below 1\ndB/km once the beam is properly collimated, a more precise beam divergence control\nat the output of the OPA should be the key issue to solve for practical deployment.\nReply and modifications:\nWe sincerely thank the reviewer for their insightful and constructive comments,\nwhich have greatly helped us improve the discussion on extending transmission\ndistance in OWC systems based on OPAs. We fully agree with the reviewer that the\nkey challenge for practical long-range deployment lies in achieving precise beam\ndivergence control at the OPA output, rather than relying solely on amplification. This\nperspective is crucial, and we have carefully revised the manuscript to reflect this\nemphasis.\nIn our experimental setup, the three EDFAs are used primarily to compensate for\ninsertion losses from external components, such as the in-phase/quadrature modulator,\noptical splitters, and fiber coupling interfaces, not to overcome free-space attenuation.\nAs the reviewer correctly points out, atmospheric loss at 1550 nm is well below 1\ndB/km with proper beam collimation. The 1 m transmission distance in our study was\nselected to validate high-speed modulation and coherent detection performance in a\ncontrolled laboratory setting, not to maximize link range. We acknowledge that for real-\nworld applications, reducing beam divergence is essential.\nTo address this, we have expanded the discussion in the revised manuscript to\nclearly state that future improvements should focus on beam control over amplification.\nSpecifically, we now highlight the following approaches as effective pathways for\noptimization:\n1．Antenna engineering for narrower beam divergence: Refining grating\ngeometries, including apodized or chirped gratings [C17, C18], and improving phase\nuniformity across channels can significantly enhance far-field beam confinement.\n2．Hybrid optical packaging: Integrating on-chip microlenses or low-loss\ndielectric metasurfaces enables pre-collimation directly at the chip facet, reducing\ndependence on bulk optics [C19, C20].\n3．Dynamic beam-shape control: Techniques such as adaptive phase distribution\nor amplitude apodization can help maintain a constant spot size over extended distances\n[C21, C22].\nIn the revised manuscript, we have modified the following sentences to emphasize\nbeam divergence control:\n“In practical implementations, this attenuation can be compensated by achieving\nmore precise beam divergence control at the OPA output.” (Paragraph 3, Section 2.2)\n“Meanwhile, on-chip integrated erbium-doped waveguide amplifiers (EDWAs)\ncan effectively compensate for link loss and enhance output optical power [55,56]. In\npractical deployment of OPAs, the primary factor limiting transmission distance is the\nbeam divergence at the optical power output. Therefore, optimizing antenna design and\noutput coupling schemes, such as apodized gratings [57,58], metasurface pre-collimators\n[59], integrated microlens arrays [60], and dynamic beam shaping control [61,62],\nwill\nachieve tighter beam confinement and higher far-field collimation efficiency, thereby\nenabling long-range, low-power optical links.” (Paragraph 4, Section 3)\nIn the revised manuscript, we have added following references:\n“57. Yu, L. et al. Adoption of large aperture chirped grating antennas in optical phase\narray for long distance ranging. Opt. Express 30, 28112-28120 (2022).\n58. Huang, Y., Yu, C., Chen, C. Sidelobe-suppressed silicon waveguide gratings\nthrough asymmetrically-apodized corrugations. IEEE Photonics T. 36, 629-632\n(2024).\n59. Wang, Z. et al. Metasurface empowered lithium niobate optical phased array with\nan enlarged field of view. Photonics Res. 10, B23-B29 (2022).\n60. Im, C. et al. Hybrid integrated silicon nitride–polymer optical phased array for\nefficient light detection and ranging. J. Lightwave Technol. 39, 4402-4409 (2021).\n61. Zhao, S., Lian, D., Li, W., Chen, J., Dai, D. & Shi, Y. Low sidelobe silicon optical\nphased array with chebyshev amplitude distribution. Nanophotonics 13, 263-269\n(2024).\n62. Sharma, A. et al. Optimization of a programmable λ/2-pitch optical phased array.\nNanophotonics 13, 2241-2249 (2024).” (References)\nReferences:\n[C17] Yu, L. et al. Adoption of large aperture chirped grating antennas in optical phase\narray for long distance ranging. Opt. Express 30, 28112-28120 (2022).\n[C18] Huang, Y., Yu, C., Chen, C. Sidelobe-suppressed silicon waveguide gratings\nthrough asymmetrically-apodized corrugations. IEEE Photonics T. 36, 629-632\n(2024).\n[C19] Wang, Z. et al. Metasurface empowered lithium niobate optical phased array with\nan enlarged field of view. Photonics Res. 10, B23-B29 (2022).\n[C20] Im, C. et al. Hybrid Integrated silicon nitride–polymer optical phased array for\nefficient light detection and ranging. J. Lightwave Technol. 39, 4402-4409\n(2021).\n[C21] Zhao, S., Lian, D., Li, W., Chen, J., Dai, D. & Shi, Y. Low sidelobe silicon optical\nphased array with chebyshev amplitude distribution. Nanophotonics 13, 263-269\n(2024).\n[C22] Sharma, A. et al. Optimization of a programmable λ/2-pitch optical phased array.\nNanophotonics 13, 2241-2249 (2024).\nComment 5:\nThere is a typo in Fig. 4a, 'DCA' should be 'DAC'.\nReply and modifications:\nWe sincerely thank the reviewer for their meticulous review and for identifying\nthe typographical error in Figure 4a. We have corrected “DCA” to “DAC” in the figure.\nFigure 4. Experimental results of a high-speed OWC system utilizing the OPA. a Schematic of the 320\nGbps data transmission link.\nTo Reviewer #2’s comments:\nRecommendation: This manuscript presents a multi-target, ultra-high-speed optical\nwireless communication system based on a thin-film lithium niobate optical phased\narray. The system demonstrates impressive performance, including high-speed multi-\ntarget beam steering across a wide field of view, low sidelobe levels, and a record\nsingle-channel data rate of 320 Gbps using 16-QAM modulation. The work highlights\nsignificant advantages in integration, power efficiency, and dynamic reconfigurability,\nsupported by comprehensive experimental data such as high-definition video\ntransmission. The results are clearly presented and address a highly relevant research\ndirection with considerable potential for next-generation wireless networks. The\nmanuscript is well-structured, exhibits strong originality, and the data are\nsystematically organized, providing robust support for the conclusions. This work is\nlikely to attract broad interest from the photonics and communications communities. In\nmy view, the paper merits publication after the authors address the following points:\nAuthor Response:\nWe sincerely thank the reviewer for their positive assessment of our work and for\nraising these insightful points. We have carefully considered the comments and provide\nthe following responses.\nComment 1:\nThe current vertical beam steering range is 11°. The authors should discuss potential\nstrategies or design modifications to further expand the vertical field of view in future\nimplementations.\nReply and modifications:\nWe thank the reviewer for this insightful suggestion. In the present design, the\nOPA achieves a vertical beam steering range of 11°. The steering efficiency is\ndetermined to be -0.091°/nm based on our experimental data. The current limitation in\nthe vertical FOV is primarily due to the bandwidth constraints of passive devices and\nthe wavelength tuning range of the external laser source.\nVertical steering angle control is achieved through wavelength tuning. The output\ncoupling angle is determined by the grating equation and can be expressed as:\nΛn -λ\neff 0\nsinφ=\nn Λ\n0\nwhere Λ is the antenna period, n is the effective refractive index of the waveguide\neff\nmode, λ is the wavelength, and n is the background refractive index. Therefore, for a\n0 0\nfixed grating geometry, the achievable vertical field of view is directly proportional to\nboth the laser tuning span and the effective refractive index difference.\nTo further expand the vertical steering range in future implementations, we\npropose three potential strategies. First, introducing a linearly chirped or apodized\ngrating profile can broaden the effective radiation bandwidth, enabling a larger angular\nsweep over the same wavelength tuning range, as demonstrated in references [C1, C2].\nSecond, utilizing both TE and TM modes [C3, C4], made possible by the optical\nanisotropy of TFLN, can produce distinct vertical steering ranges, thereby significantly\nexpanding the accessible FOV. Our simulations in Supplementary Material 10 confirm\nthat this approach can at least double the FOV. Third, implementing a multi-period\nOPA design allows for the generation of diverse steering angles from gratings with\ndiffering periodicities, leading to an enlarged FOV, as supported by references [C5].\nTo provide additional clarity in the manuscript, we have included the following\nsentences in the revised Supplementary Information:\n“The current vertical beam steering range of 11° is mainly limited by the spectral\nresponse of the bandwidth of passive devices and the wavelength tuning range of the\nexternal laser. Future designs could substantially extend this range by employing\napodized or chirped gratings to increase radiation bandwidth [1,2], and exploiting\npolarization diversity [3,4] or multi-period [5] OPA in the thin-film lithium niobate\n(TFLN) platform. These strategies, combined with the integration of widely tunable on-\nchip lasers, are expected to expand the vertical FOV well beyond 20°, enabling more\nflexible beam steering for next-generation optical wireless communication (OWC)\nsystems.” (Paragraph 4, Supplementary Note 3, Supplementary information)\nIn the revised Supplementary Information, we have added following references:\n“[1] Yu, L. et al. Adoption of large aperture chirped grating antennas in optical phase\narray for long distance ranging. Opt. Express 30, 28112-28120 (2022).\n[2] Huang, Y., Yu, C., Chen, C. Sidelobe-suppressed silicon waveguide gratings\nthrough asymmetrically-apodized corrugations. IEEE Photonics T. 36, 629-632\n(2024).\n[3] Zhao, S., Chen, J., Shi, Y. Dual polarization and bi-directional silicon-photonic\noptical phased array with large scanning range. IEEE Photonics J. 14, 6620905\n(2022).\n[4] Zhao, S. et al. Polarization multiplexing silicon photonic optical phased array with\na wide scanning range. Opt. Lett. 48, 6092-6095 (2023).\n[5] Zhang, L. et al. Large-scale integrated multi-lines optical phased array chip. IEEE\nPhotonics J. 12, 6601208 (2020).” (References)\nReferences:\n[C1] Yu, L. et al. Adoption of large aperture chirped grating antennas in optical phase\narray for long distance ranging. Opt. Express 30, 28112-28120 (2022).\n[C2] Huang, Y., Yu, C., Chen, C. Sidelobe-suppressed silicon waveguide gratings\nthrough asymmetrically-apodized corrugations. IEEE Photonics T. 36, 629-632\n(2024).\n[C3] Zhao, S., Chen, J., Shi, Y. Dual polarization and bi-directional silicon-photonic\noptical phased array with large scanning range. IEEE Photonics J. 14, 6620905\n(2022).\n[C4] Zhao, S. et al. Polarization multiplexing silicon photonic optical phased array with\na wide scanning range. Opt. Lett. 48, 6092-6095 (2023).\n[C5] Zhang, L. et al. Large-scale integrated multi-lines optical phased array chip. IEEE\nPhotonics J. 12, 6601208 (2020).\nComment 2:\nThe manuscript does not explicitly clarify the parameters governing the horizontal and\nvertical beam resolution, nor the ultimate factors limiting these resolutions. A\ndiscussion on these aspects would help readers better understand the system's\nperformance constraints.\nReply and modifications:\nWe thank the reviewer for raising this important point regarding the parameters\ngoverning horizontal and vertical beam resolution, and the factors limiting these\nresolutions. We appreciate the opportunity to clarify these aspects, as they are critical\nfor understanding the performance boundaries of our OPA system.\nThe horizontal beam resolution, often characterized by its full width at half\nmaximum (FWHM), is primarily determined by the overall aperture size, which is the\nproduct of the number of antenna elements (N) and their pitch (d). According to the\n0.886λ\nrelation θ = , a larger aperture leads to a narrower beam, thereby improving\nFWHM\nNdcosθ\nthe horizontal resolution. In our 16-channel OPA design with a 1.5 μm antenna pitch\noperating at a 1550 nm wavelength, the theoretical horizontal beamwidth is\napproximately 3.72°. This closely matches the measured FWHM of 3.8° shown in\nFigure 2c, confirming the consistency between experiment and theory.\nThe vertical beam resolution is mainly governed by the radiation characteristics of\nthe trapezoidal grating antennas. The effective grating length defines the beam\ndivergence in the vertical direction. In our device, the measured vertical FWHM is\n1.72°, which aligns well with simulations based on the designed grating length.\nTo provide additional clarity in the manuscript, we have included the following\nsentences in the revised Supplementary Information:\n“The horizontal and vertical resolutions of the OPA are governed by distinct\nparameters. The horizontal beam resolution, characterized by its full width at half\nmaximum (FWHM), is primarily determined by the overall aperture size, which is the\nproduct of the number of antenna elements (N) and their pitch (d). According to the\n0.886λ\nrelation θ = , a larger aperture yields a narrower beam, thus enhancing the\nFWHM\nNdcosθ\nhorizontal resolution. Conversely, the vertical beam resolution is chiefly dictated by the\nradiation properties of the trapezoidal grating antennas. The effective grating length\nsets the vertical beam divergence.” (Paragraph 6, Supplementary Note 2,\nSupplementary information)\nComment 3:\nFor multi-wavelength parallel beam control scenarios, could the authors comment on\nwhether the SPGD algorithm requires separate objective functions for each wavelength?\nIf a unified objective function is used, how is convergence stability maintained?\nAdditionally, is sequential calibration necessary for the dual-wavelength operation\ndemonstrated in the experiments?\nReply and modifications:\nWe sincerely thank the reviewer for raising this important question regarding\nmulti-wavelength parallel beam control. In our experimental setup, we assign a separate\nobjective function for each wavelength, defined based on diffraction efficiency, to\naddress the specific requirements of individual wavelengths. To manage the complexity\nof the multi-wavelength optimization, we employ a weighted sum method that reduces\nthe problem dimensionality effectively.\nThe convergence stability in the presence of multiple wavelengths is ensured by\nthe physical properties of the OPA and the weighted optimization approach.\nSpecifically, the phase shifters in the OPA control the beam direction, and when\ndifferent wavelengths are incident simultaneously, the radiation direction for each\nwavelength shifts independently due to dispersion effects, as described in reference\n[C6]. This independence allows the beams to operate without mutual interference. We\ndefine an objective function for each wavelength and optimize all beams concurrently\nusing a weighted method applied across the targets, which balances the optimization\nprocess and maintains convergence stability, as supported by prior work [C7].\nFor the dual-wavelength operation in our experiments, we do not use sequential\ncalibration. Instead, we implement a parallel optimization strategy to avoid disrupting\nthe voltage settings that might occur in a step-by-step approach. This ensures that the\noptimization for one wavelength does not compromise the results for others, leading to\nmore robust performance.\n[C6] Chen, J. et al. Single soliton microcomb combined with optical phased array for\nparallel FMCW LiDAR. Nat. Commun. 16, 1056 (2025).\n[C7] Marler, R.T., Arora, J.S. The weighted sum method for multi-objective\noptimization: new insights. Struct. Multidisc. Optim. 41, 853–862 (2010).\nComment 4:\nPrior to operation, does the SPGD algorithm require calibration at each beam steering\nangle? If so, could this initialization process limit the overall communication speed or\ntarget switching rate?\nReply and modifications:\nWe thank the reviewer for raising this pertinent question regarding the\ninitialization process of the SPGD algorithm. The reviewer is correct to note that initial\nphase calibration is essential for high-resolution OPAs, primarily to compensate for\ninherent phase errors introduced during device fabrication.\nIn our system, once an initial calibration is performed at a reference angle (for\ninstance, at the diffraction null), the obtained phase map effectively captures the static\nfabrication-derived errors. For any subsequent beam steering angle, the required phase\npattern is generated by superimposing the ideal gradient phase for that angle onto the\npre-calibrated error phase. Therefore, repeated full recalibration at each individual\nsteering angle is not necessary.\nWhile environmental perturbations can introduce minor dynamic phase shifts, our\nexperiments confirm that the SPGD algorithm compensates for these efficiently,\ntypically converging within only a few iterations. Furthermore, the final voltage\nconfigurations corresponding to various steering angles are stored in the memory of the\nhost computer or FPGA. During operation, these pre-calculated values can be loaded\nonto the phase shifters almost instantaneously. As a result, the calibration process does\nnot impose a bottleneck, and the overall communication speed and target switching rate\nremain unaffected.\nComment 5:\nThe discussion mentions a \"transition time of approximately 158 ps\", while the\nmeasured rise and fall times are 170 ps and 146 ps, respectively. The calculation or\ndefinition of the 158 ps value should be clarified for consistency.\nReply and modifications:\nWe thank the reviewer for highlighting this point. We agree that the original\ndescription of the transition time was not sufficiently clear, and we apologize for any\nconfusion caused. The value of 158 ps is calculated as the arithmetic mean of the\nmeasured rise time (170 ps) and fall time (146 ps), which provides a representative\nestimate of the overall switching performance.\nIn the revised manuscript, we have clarified this point in the text as follows:\n“The phase shifters exhibit measured rise and fall times of 170 ps and 146 ps,\nrespectively, yielding an average transition time of 158 ps, and a modulation efficiency\nof 8.73 pJ/π. ” (Paragraph 1, Section 3)\nComment 6:\nOn page 13, first paragraph, \"tcoherent detection\" appears to be a typographical error.\nThis should be corrected to \"coherent detection\".\nReply and modifications:\nWe sincerely thank the reviewer for bringing this typographical error to our\nattention. The reviewer is correct that \"tcoherent detection\" is inadvertently misspelled\nand should read as \"coherent detection.\"\nIn the revised manuscript, we have carefully corrected this error:\n“On the receiver side, coherent detection is first applied.” (Paragraph 2, Section\n2.3)\nComment 7:\nPlease verify the angle units in Figure 4d and ensure consistent capitalization of units\nin Table 1 (e.g., 'mW' vs. 'mw').\nReply and modifications:\nWe sincerely thank the reviewer for highlighting these important details and for\ntheir thorough review, which has significantly improved the quality of our manuscript.\nWe have addressed both points as follows.\nRegarding Figure 4d, we have carefully verified the angle units and confirm that\nall angles are correctly represented in degrees (°). We apologize for any oversight in\nthe initial presentation and have ensured that the units are clearly and consistently\nlabeled.\nIn the revised manuscript, we have carefully corrected the errors:\n“Figure 4. Experimental results of a high-speed OWC system utilizing the OPA. a\nSchematic of the 320 Gbps data transmission link. b DSP flowchart implemented at the\ntransmitter and receiver. c Optical spectra of the 16-QAM signal recorded at different\npoints within the system. d BERs measured at different wavelengths for transverse\nangles θ = 0° and θ = 31°, respectively. e Recovered constellation diagrams\ncorresponding to each angle.” (Figure 4, Section 2.3)\nTable 1 Comparison of representative works in high-speed OWC.\nDynamic\nOn- SLS Single-channel Switching Modulation\nYear Method beam FOV Applications\nchip R speed speed efficiency\nscanning\n(ref. 42)\n2018 35 Gbps (OOK)\nAWGR No No 18.6°×18.6° NA NA NA Signal/Video\n(ref. 43) 112 Gbps (PAM 4)\n(ref. 44)\nNo No 35° NA 20 Gbps (OOK) NA NA Signal\n(ref. 45) & AWGR\n(ref. 46)\n(ref. 47)\nMetasurface\n2023\n& LCoS- No Yes 20°×20° NA 10 Gbps (OOK) ~ms NA Signal\n(ref. 48)\nSLM\nMetalens &\n(ref. 49)\nstage\n(ref. 11)\n(ref. 21) beamformer\nYes Yes 60°×14° NA 12 Gbps (OOK) 24.4 µs 20 mW/π Signal/Image\n(ref. 9) based OPA\nYes Yes 96°×14.4° NA 32.26 µs 1.33 W/π Image\n(ref. 50) based OPA dB\nYes Yes 25.6°×8.1° 40 Gbps (OOK) NA Signal\n(ref. 51) based OPA dB (total)\n–\nThis TFLN- 320 Gbps (16\nYes Yes 62°×11° 13.6 158 ps 8.73 pJ/π Signal/Video\nwork based OPA QAM)\ndB\nNote: NA: not measured, MEMS: micro-electrical mechanical system, AWGR: arrayed waveguide grating router, LCoS SLM: liquid crystal\non silicon spatial light modulator."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I have carefully gone through the authors' response and the revisions to the manuscript. In my opinion, the revised manuscript has convincingly addressed my previous comments and concerns. I don't have more suggestions and would like to recommend accepting it for publication.", "reviewer_2": "The authors have addressed all my concerns and I recommend the publication of the manuscript."}, "author_response": ""}]

Decision letter