Large-Scale Optical Phased Arrays Enabled by Silicon Photonics

The on-chip nano-integration of large-scale optical phased arrays (OPAs) is a development trend. However, the current scale of integrated OPAs is not large because of the limitations imposed by the lateral dimensions of beam-splitting structures. Here, we propose an ultra-compact and broadband OPA beam-splitting scheme with a nano-inverse design. We employed a staged design to obtain a T-branch with a wavelength bandwidth of 500 nm (1300–1800 nm) and an insertion loss of −0.2 dB. Owing to the high scalability and width-preserving characteristics, the cascaded T-branch configuration can significantly reduce the lateral dimensions of an OPA, offering a potential solution for the on-chip integration of a large-scale OPA. Based on three-dimensional finite-difference time-domain (3D FDTD) simulations, we demonstrated a 1 × 16 OPA beam-splitter structure composed entirely of inverse-designed elements with a lateral dimension of only 27.3 μm. Additionally, based on the constructed grating couplers, we simulated the range of the diffraction angle θ for the OPA, which varied by 0.6°–41.6° within the wavelength range of 1370–1600 nm.

A high-speed phase calibration method for large-scale silicon-based optical phased arrays (OPAs) is proposed, integrating the Hadamard parallel gradient descent (HPGD) algorithm and a dedicated hardware architecture. Deterministic, orthogonal Hadamard matrices generate perturbation sequences, enabling efficient optimization. The architecture consists of an FPGA, a DSP, and a high-speed avalanche photodiode (APD), employing the APD to acquire objective functions. Simulations show that, compared with the stochastic parallel gradient descent algorithm, HPGD reduces convergence iterations for a 512-element OPA from 4929 to 2285, and a variant with adaptive gain (adaHPGD) further reduces iterations to 1480 (70.0% reduction). For OPAs with 1024 to 4096 elements, HPGD reduces iterations by 31.8% to 41.3%. Experimentally, on a 512-element OPA, each iteration takes 6.7 ms, with a convergence time of 12.8 s. After calibration, the beam achieves a peak sidelobe ratio of 12.93 dB and a full width at half maximum of 0.110°, matching simulations.

Since the power of continuous wave laser sources have reached one kilowatt, beam shaping is an important topic in the sector of laser material processing. The high intensity allows the increase of process speed, but the extreme local overheating often decreases the quality. Typically beam shaping solutions use a static beam adaptation by optical elements. For laser cutting for example, the increase of sheet thickness requires larger Rayleigh length what will be achieved by adapting the conditions of the incident ray at the focalization element. In this case the cutting quality increases but the cutting speed decreases. The advantage of high intensity gets lost. The dynamic beam shaping is known from the electron beam, and already applied in laser hardening and welding applications using galvanometer scanners. While the galvo-systems reached the physical limitations, the frequency is not high enough to achieve the desired effects. Resonance galvanometer scanners are limited by the atmosphere damping, too.This paper will introduce a new possibility of dynamic beam shaping, using MEMS technology in a low pressure atmosphere. It describes the reached steps to transfer the technology from display and sensor applications with low apertures and laser power to laser material applications with large apertures and high laser power. Finally, the technology possibilities are disclosed for the complete field of laser application.Since the power of continuous wave laser sources have reached one kilowatt, beam shaping is an important topic in the sector of laser material processing. The high intensity allows the increase of process speed, but the extreme local overheating often decreases the quality. Typically beam shaping solutions use a static beam adaptation by optical elements. For laser cutting for example, the increase of sheet thickness requires larger Rayleigh length what will be achieved by adapting the conditions of the incident ray at the focalization element. In this case the cutting quality increases but the cutting speed decreases. The advantage of high intensity gets lost. The dynamic beam shaping is known from the electron beam, and already applied in laser hardening and welding applications using galvanometer scanners. While the galvo-systems reached the physical limitations, the frequency is not high enough to achieve the desired effects. Resonance galvanometer scanners are limited by the atmosphere damping, too.T...

Optical phased arrays (OPAs) have received considerable attention as solid-state beam scanners. However, conventional OPAs that actively control the phase difference between arrays are characterized by excessive power consumption for high-precision beam emission. In this study, we fabricated an OPA comprising Bragg grating and arrayed waveguide grating (AWG). Multi-mode waveguide is used in AWG to reduce the effect of manufacturing error. This device realizes wide and high-resolution two-dimensional beam steering only by sweeping wavelength. FWHM of the emitted beam is 0.534° × 2.27°, and the steering range is 43.9° × 13.5° with 1/64 of the power consumption of conventional OPA.

Dynamic phase-only beam shaping with a liquid crystal spatial light modulator is a powerful technique for tailoring the intensity profile or wave front of a beam. While shaping and controlling the light field is a highly researched topic, dynamic nonlinear beam shaping has hardly been explored so far. One potential reason is that generating the second harmonic is a degenerate process as it mixes two fields at the same frequency. To overcome this problem, we propose the use of type II phase matching as a control mechanism to distinguish between the two fields. Our experiments demonstrate that distributions of arbitrary intensity can be shaped in the frequency-converted field at the same quality as for linear beam shaping and with conversion efficiencies similar to without beam shaping. We envision this method as a milestone toward beam shaping beyond the physical limits of liquid crystal displays by facilitating dynamic phase-only beam shaping in the ultraviolet spectral range.

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.

Silicon photonics has become the key enabling technology in many sensor applications including light detection and ranging (LiDAR) systems because of its high integration, chip-scale footprint and CMOS-compatible process. Thanks to these advantages, optical phased array (OPA) based on silicon photonics has emerged as a solid-state LiDAR solution to replace mechanical LiDAR counterpart. In such a system, optical loss from each component of the OPA devices should be minimized, while the radiation efficiency from the radiators of the OPA devices should be maximized for extending the power budget of the LiDAR system. These components can improve their performances through the recently emerged inverse design method. In this study, we designed a novel grating structure which is one of the components of OPA and allows wide-band and high coupling efficiency of light using inverse design approach with the particle-swarm-optimization method. Considering Silicon-On-Insulator (SOI) platform with 220 nm thickness, the configuration of the grating structure is determined by the finite number of particles so that the height and width of the corrugations are optimized based on the objective of boosting the out-of-plane radiated power amount. Highly efficient and vertical emission was obtained using finite-difference-time-domain calculation in telecommunication window centered at around 1550 nm. Including additional constraints in the inverse design will allow the realization of multitude spatial field profiles of the radiated light that may have an important contribution for OPA, sensing, imaging, lasers and optical interconnection.

Many components for free space optical communication systems have shrunken in size over the last decade. However, the steering systems have remained large and power hungry. Non-mechanical beam steering offers a path to reducing the size of these systems. Optical phased arrays can allow integrated beam steering elements. One of the most important aspects of an optical phased array technology is its scalability to a large number of elements. Silicon photonics can potentially offer this scalability using CMOS foundry techniques. In this paper a small-scale silicon photonic optical phased array is demonstrated for both the transmitter and receiver functions in a free space optical link. The device using an array of thermo-optically controlled waveguide phase shifters and demonstrates one-dimensional steering with a single control electrode. Transmission of a digitized video data stream over the link is shown.

Integrated optical phased arrays (OPAs) based on arrayed waveguide gratings (AWGs) enable two-dimensional (2D) beam steering through wavelength tuning. Achieving a high vertical resolution for practical applications remains challenging due to the waveguide phase errors associated with the large AWG required. Here, we present a high-resolution 65-channel AWG-assisted OPA with 5 inputs. Ultra-low loss silicon nitride waveguide technology and transverse magnetic mode operation are employed for waveguide-phase-error mitigation. A vertical resolution of 0.32° using a single input is attained with a beam width of 0.55° × 0.07° and an alias-free horizontal field of view (FOV) of 30°. By utilizing all 5 inputs, the vertical resolution can be enhanced to 0.06°. Real-time 2D beam steering over a 25° × 5° FOV is demonstrated. To our best knowledge, this work demonstrates the highest vertical resolution reported for an AWG-based OPA.

We present high-performance integrated optical phased arrays along with first-of-their-kind light detection and ranging (LiDAR) and free-space data communication demonstrators. First, record-performance optical phased array components are shown with low-power phase shifters and high-directionality waveguide grating antennas. Then, one-dimensional (1-D) 512-element optical phased arrays are demonstrated with record low-power operation ( $ 1 mW total), large steering ranges, and high-speed two-dimensional (2-D) beam steering ( $ 30 $\mu$ s phase shifter time constant). Next, by utilizing optical phased arrays, we show coherent 2-D solid-state LiDAR on diffusive targets with simultaneous velocity extraction at a range of nearly 200 m. In addition, the first demonstration of 3-D coherent LiDAR with optical phased arrays is presented with raster-scanning arrays. Finally, lens-free chip-to-chip free-space optical communication links up to 50 m are shown, including a demonstration of a steerable transmitter to multiple optical phased array receivers at a 1 Gb/s data rate. This paper shows the most advanced silicon photonics solid-state beam steering to date with relevant demonstrators in practical applications.

We report a simple concept to implement a single-wavelength beam steering based on a liquid-cladded one-dimensional (1D) optical phased array (OPA). The beam steering was realized by modifying the waveguide mode effective index through replacing the liquid upper claddings. A prototype of a 32-channel liquid-cladded OPA was fabricated and characterized. Owing to the high refractive index range of liquids (>0.625), a maximum steering angle of >10∘ was achieved with the liquid range from 1.0 to 1.63 at a wavelength of 940 nm. Moreover, the liquid-cladded OPA reveals a quasi-continuous beam steering range of >29∘ by combining the liquid cladding tuning and discrete wavelength tuning of λ=785nm, 852 nm, and 940 nm. Further integration with optofluidic systems offers the OPA potential for low power consumption and all-fluidic beam steering operating at a single wavelength.

We present an indoor free space, line-of-sight optical communication system with gigabit bandwidth using an ultra-low power VCSEL diode, which is enhanced by dynamic beam steering and beam shaping for rapid user acquisition.

An optically addressable light valve is used for high repetition rate dynamic laser beam shaping used in a unique metal additive manufacturing process [1]. The resulting Area Printing™ delivers high power pulses - each with an individually controlled shape - to a metal powder bed that locally sinters and melts to consolidate into a fully dense metal part. This technology and device enable scaling cheaper additive manufacturing with high spatial resolution, while capable of printing part features beyond reach of conventional manufacturing, and with greater efficiency and minimal spatter defects. We address here the unique optoelectronic properties needed from the optically addressable photoresistor that controls the dynamic beam shaping for high density, high-resolution laser 3D printing. Further description is presented of the device-level thermomechanical analysis from parasitic absorption of the laser at kW to MW power levels. We thus highlight key areas of semiconductor properties challenging the performance capabilities in optically addressed light valves used in high power switching applications. [1] https://www.seurat.com/area-printing

Phase change materials (PCMs) are attracting more and more attentions as enabling materials for tunable nanophotonics. They can be processed into functional photonic devices through customized laser writing, providing great flexibility for fabrication and reconfiguration. Lithium Niobate (LN) has excellent nonlinear and electro-optical properties, but is difficult to process, which limits its application in nanophotonic devices. In this paper, we combine the emerging low-loss phase change material with LN and propose a new type of high Q resonant metasurface. Simulation results show that the -LN metasurface has extremely narrow linewidth of 0.096 nm and high quality (Q) factor of 15,964. With LN as the waveguide layer, strong nonlinear properties are observed in the hybrid metasurface, which can be employed for optical switches and isolators. By adding a pair of Au electrodes on both sides of the LN, we can realize dynamic electro-optical control of the resonant metasurface. The ultra-low loss of , and its combination with LN, makes it possible to realize a new family of high Q resonant metasurfaces for actively tunable nanophotonic devices with widespread applications including optical switching, light modulation, dynamic beam steering, optical phased array and so on.

Silicon photonics enables the development of optical components on a chip with the potential for large-scale optical integrated circuits that can be fabricated at the wafer-scale using foundries similar to those used in the electronics industry. Although silicon is a passive optical material with an indirect bandgap, reconfigurable devices have been demonstrated using thermo-optic effects (large phase shifts, but relatively slow with large power consumption) and carrier plasma dispersion effects (high-speed, but small phase shifts). We recently demonstrated a low-power approach for inducing large phase shifts (>2π) using a technique that we call micro-opto-electro-mechanical index perturbation (MOEM-IP). In this initial work we characterized silicon nitride waveguides in which the propagating optical mode’s evanescent field is vertically coupled to silicon nitride microbridges. This interaction leads to an effective index tuning that is a strong function of the waveguide-microbridge separation. We now extend our MOEM-IP approach to different configurations (i.e. in-plane coupling) and material systems (i.e. silicon-oninsulator). Mode perturbation simulations indicate that the MOEM-IP approach is widely applicable to many configurations and material systems enabling large effective index tuning (Δneffective>0.1) requiring microbridge displacements of only a few hundred nanometers. We also examine several device applications that take advantage of MOEM-IP. These include tunable optical filters using high-Q microring cavities and optical phased arrays that enable chip-scale beam steering in two-dimensions using low-power phase shifting enabled by MOEM-IP.