Circular optical phased array for 360° constant amplitude scanning

Laser beam scanning technology has potential applications in various fields, including LIDAR, laser processing, and optical communication. However, the capability of non-mechanical beam scanning is limited by the response time of an optical element, posing challenges in achieving both high-speed scanning and reconfigurable output beams. Here we propose a new concept, to the best of our knowledge, of the frequency-encoded optical phased array (OPA) to enable high-speed reconfigurable dynamic scanning. This is achieved by employing the customized frequency deviations on the array elements of the OPA. It is turned out that, in this way, the dynamic spatiotemporal beams with continuous scanning capability can be realized. We further find that the scanning speed is linearly proportional to the frequency deviation. Moreover, we are able to give access to multi-directional and customizable structured spatiotemporal beam scanning by encoding the on-demand frequency and phase deviations. The approach proposed here might be useful for high-speed reconfigurable beam scanning with high-power output.

Large-scale optical phased arrays containing up to 64×64 nanoantennas are demonstrated on silicon photonic platform, representing the largest scale demonstrated to date. Active phase tuning is also realized for dynamic pattern generation.

Non-mechanical beam steering is required for holographic displays, free-space optical communication, and chip-scale LiDAR. Optical phased arrays (OPAs), which allow for inertia-free, high-speed beam control via electronic phase control, are an important research topic. The present study investigates the primary material platform for on-chip OPAs: Liquid crystal OPAs (LC-OPAs) employ electrically tunable refractive indices for low-voltage operation; lithium niobate OPAs (LN-OPAs) utilize high electro-optic coefficients for high-speed, low-power consumption, and large-bandwidth operation; and silicon-based OPAs (Si-OPAs) apply mature photonic integration to achieve high integration density and GHz-range steering. The paper thoroughly examines OPA basics, recent material-specific advancements, performance benchmarks, outstanding issues, and future prospects.

On-chip optical phased arrays (OPAs) are the enabling technology for diverse applications, ranging from optical interconnects to metrology and light detection and ranging (LIDAR). To meet the required performance demands, OPAs need to achieve a narrow beam width and wide-angle steering, along with efficient sidelobe suppression. A typical OPA configuration consists of either one-dimensional (1D) linear or two-dimensional (2D) rectangular arrays. However, the presence of grating sidelobes from these array configurations in the far-field pattern limits the aliasing-free beam steering, when the antenna element spacing is larger than half of a wavelength. In this work, we provide numerical analysis for 2D circular OPAs with radially arranged nano-antennas. The circular array geometry is shown to effectively suppress the grating lobes, expand the range for beam steering and obtain narrower beamwidths, while increasing element spacing to about 10 μm. To allow for high coupling efficiency, we propose the use of a central circular grating coupler to feed the designed circular OPA. Leveraging radially positioned nano-antennas and an efficient central grating coupler, our design can yield an aliasing-free azimuthal field of view (FOV) of 360°, while the elevation angle FOV is limited by the far-field beamwidth of the nano-antenna element and its array arrangement. With a main-to-sidelobe contrast ratio of 10 dB, a 110-element OPA offers an elevation FOV of 5° and an angular beamwidth of 1.14°, while an 870-element array provides an elevation FOV up to 20° with an angular beamwidth of 0.35°. Our analysis suggests that the performance of the circular OPAs can be further improved by integrating more elements, achieving larger aliasing-free FOV and narrower beamwidths. Our proposed design paves a new way for the development of on-chip OPAs with large 2D beam steering and high resolutions in communications and LIDAR systems.

The aim of this study was to test the feasibility and the additional value of time-resolved computed tomography angiography (CTA) of the aorta, using multiple low-dose phases. Twenty-two consecutive patients underwent a time-resolved CTA protocol (TR-CTA) of the aorta, either for follow-up of endovascular aneurysm repair (EVAR) or aortic dissection, using a CT scanner with the possibility of bidirectional table movements for dynamic CT imaging (Siemens Definition AS+; 12 phases, temporal resolution 2.5 s/scan, 80 kVp, 120 mAs/rot, scan range 27 cm, 60 mL; Imeron 400, flow 5.0 mL/s). The patients had previously undergone standard CTA (120 kVp, 100 mL contrast agent). Standard CTA after EVAR and aortic dissection were triphasic and biphasic protocols, respectively. Effective radiation dose and maximum Hounsfield unit values were compared between the TR-CTA and standard CTA. Image quality was rated for TR-CTA. Fifteen patients underwent TR-CTA for follow-up after EVAR; 4 were examined for follow-up after dissection and 3 for both, that is, aortic dissection treated with an endovascular stent. Mean effective dose of TR-CTA for the scan range of 27 cm (15.3+/-1.1 mSv) was comparable with the biphasic standard CTA protocols (16.2+/-2.4 mSv; P=0.29). Triphasic protocols resulted in 23.7+/-4.9 mSv (P<0.0001). Hounsfield unit values were not significantly different. Most of the examinations (91%) were fully evaluable, whereas 9% were of limited evaluability because of high image noise. None of the examinations was nondiagnostic. TR-CTA consisting of multiple low-dose phases leads to a clear depiction of the angiographic information and is feasible for follow-up after EVAR and aortic dissection. Considering the limited scan range, radiation dose is comparable with the standard biphasic CTA protocol, but dynamic information may provide additional information.

A microelectromechanical systems (MEMS) mirror with large vertical displacement has been developed for Fourier transform microspectrometers, but there exists a large tilting during the large-stroke scanning of the MEMS mirror, which greatly compromises the usable range. In this paper, a closed-loop control method has been established to minimize the tilting of the MEMS mirror. According to experimental results, the tilting motion of the mirror plate can be modeled as a fourth-order system. A feedback controller consisting of a phase-lag compensator, a low-pass filter and a notch filter utilized to stabilize the closed-loop tilt system. A gain scheduling approach is also used to compensate the bias-dependent loop gain and thereby provide more consistent tilting rejection over a wide scan range. Compared with the open-loop drive approach, the closed-loop system offers a stable scan operation with much faster dynamic response and improved overall robustness. The experiments show that the residual tilting is reduced to below ±0.0015° during the full range scan of the MEMS mirror. With this control method, the MEMS mirror achieved a stable scan range up to 356.4 μm, so the measured spectral resolution reached 28 nm at 532 nm in a microspectrometer. The mirror tilting can be reduced dramatically by the proposed active control scheme, and thereby, the usable vertical scan range is increased significantly.

A new type of circularly polarized printed periodic leaky-wave antenna (LWA) structure with a wide scanning range and reduced sidelobe level (SLL) is presented. Fifteen matched unit cells (UCs) are cascaded along the direction of propagation to provide seamless frequency scanning from 20 to 29 GHz with a scanning range of 95° from backward to forward quadrant. The open-stopband has been suppressed around the broadside region by matching the input impedance of the UC to the characteristic impedance of the transmission line. Two empirical transmission line models are presented to describe the behavior of the periodic LWA. Parametric study using full-wave simulation is used to improve the SLL and minimize the axial ratio of the circular polarization leading to a fully optimized periodic leaky LWA.

Nonmechanical laser steering was presented. Associated steering effeciency and scanning range was improved for 2-D and 14° range steering. The effect of laser steering by optical phased array on laser communication was studied.

We present a highly compact integrated silicon nitride optical phased array (OPA) for laser beam steering fabricated in a CMOS-compatible silicon photonic platform. The basic components to form the OPA are optimized separately, including low-loss waveguide, multi-mode interference splitter, thermo-optic phase shifter, and grating emitter array. The demonstrated OPA with 16 channels exhibits continuous thermo-optic steering in free space of $\sim 12 ^{\circ}$ with beam divergence of $\sim 1.1 ^{\circ}$ and speed of $\sim 8$ kHz. The approaches for further performance improvement are discussed.

We design and integrate four optical phased arrays (OPAs) in a single chip. Each OPA possesses different output grating period. Furthermore, we use optical switches to select one or more OPAs for beam scanning. We demonstrate the longitudinal scanning by tuning the laser wavelength. The experimental results show that the scanning range of the four-lines chip reaches 28.54° when the wavelength ranges from 1520 nm to 1570 nm, and the eight-lines one reaches 19.04° with wavelength range of 1520 nm-1540 nm. We greatly improve the wavelength tuning efficiency for longitudinal scanning.

Beam scanning technology based on optical phased arrays has great potential for applications in the fields of LIDAR, space optical communication, and optical switching. Among them, the microlens array optical phased array can modulate the tilted phase of multiple beams simultaneously through the relative displacement of micrometer scale between microlens arrays, so as to achieve large angle beam scanning, with the advantages of large emitting aperture, simple structure, small size, micro-inertia, etc. Several well-known institutions at home and abroad have conducted research on the microlens array optical phased array. This paper first introduces the scanning principle of microlens array optical phased array, then elaborates on its development status and application, and finally gives an outlook on the trend of its development.

A novel optical phased array is experimentally demonstrated with high speed (0.577 MHz) beam steering, which consists of 8×8 tunable 1550-nm all-pass filters with ultrathin high-contrast grating as the micro-electro-mechanically actuated reflector for fast tuning.

The nitrogen-vacancy center in diamond serves as a nanoscale multi-sensor for precise magnetic and electric field measurements in optically detected magnetic resonance (ODMR) experiments. The ODMR system at cryogenic temperatures can be employed for the exploration of significant physical phenomena, such as two-dimensional ferromagnetism and current transport dynamics. Conventional systems, however, suffer from limited scanning range, low load capacity, and instability due to their reliance on cryogenic scanning mechanisms to manipulate samples, objective, and magnetic components. Here, we present a cryogenic ODMR platform utilizing all room-temperature scanning systems, enabling stable operation from 300 to 10.6 K. Our design achieves a positioner motion range of &amp;gt;5 cm and makes it possible to range from 50 to 5000 G, addressing critical challenges in applications requiring large-scale magnetic field scanning and broad temperature range experiments, such as quantum relaxometry studies. The system exhibits high robustness (vibrations &amp;lt;50 nm), high load capacity, cost-effectiveness, and ease of maintenance. Furthermore, our approach can also be directly applied to other promising quantum bit platforms, such as solid-state spin defects in silicon carbide (SiC) and so on.

High-resolution, large-angle optical beam scanning methods are sought to meet the ever-increasing demands of free-space laser communication, medical imaging and treatment, printers, scanners, and laser radar. We present a precise steering method with high angular resolution and a wide scanning range. The proposed beam-steering device is also lightweight and compact, which are significant advantages in many applications. The scanning is implemented by means of a pair of diffraction gratings, which can be translated relative to one another, and a tunable-wavelength laser. Thus the beam is steered by the combined effect of two independent mechanisms. The agility of wavelength tuning enhances the performance of a grating-based device, while the sensitivity to chromatic aberrations is minimized by performing the coarse steering with the diffraction grating. The system performance is demonstrated experimentally, and the results are reported. To the best knowledge of the authors, We present for the first time a scanning system that includes a combination of a pair of diffraction gratings and a tunable-wavelength laser.

Microcirculation imaging is a key parameter for studying the pathophysiological processes of various disease conditions, in both clinical and fundamental research. A full-range spectral-domain correlation mapping optical coherence tomography (cm-OCT) method to obtain a complex-conjugate-free, full-range depth-resolved microcirculation map is presented. The proposed system is based on a high-speed spectrometer at 91 kHz with a modified scanning protocol to achieve higher acquisition speed to render cm-OCT images with high-speed and wide scan range. The mirror image elimination is based on linear phase modulation of B-frames by introducing a slight off-set of the probe beam with respect to the lateral scanning fast mirror's pivot axis. An algorithm that exploits the Hilbert transform to obtain a complex-conjugate-free image in conjunction with the cm-OCT algorithm is used to obtain full-range imaging of microcirculation within tissue beds in vivo. The estimated sensitivity of the system was around 105 dB near the zero-delay line with ∼20 dB roll-off from ±0.5 to ±3 mm imaging-depth position. The estimated axial and lateral resolutions are ∼12 and ∼30 μm, respectively. A direct consequence of this complex conjugate artifact elimination is the enhanced flow imaging sensitivity for deep tissue imaging application by imaging through the most sensitive zero-delay line and doubling the imaging range.