Nathan Dostart, Bohan Zhang, Anatol Khilo, Michael Brand, Kenaish Al Qubaisi, Deniz Onural, Daniel Feldkhun, Kelvin H. Wagner, Miloš A. Popović
备注：
Nathan Dostart and Bohan Zhang contributed equally to this work. Main text and supplementary material in the same document. 11 pages and 11 figures total
Optical phased arrays (OPAs) implemented in integrated photonic circuits could enable a variety of 3D sensing, imaging, illumination, and ranging applications, and their convergence in new LIDAR technology. However, current integrated OPA approaches do not scale - in control complexity, power consumption, and optical efficiency - to the large aperture sizes needed to support medium to long range LIDAR. We present the serpentine optical phased array (SOPA), a new OPA concept that addresses these fundamental challenges and enables architectures that scale up to large apertures. The SOPA is based on a serially interconnected array of low-loss grating waveguides and supports fully passive, two-dimensional (2D) wavelength-controlled beam steering. A fundamentally space-efficient design that folds the feed network into the aperture also enables scalable tiling of SOPAs into large apertures with a high fill-factor. We experimentally demonstrate the first SOPA, using a 1450 - 1650 nm wavelength sweep to produce 16,500 addressable spots in a 27x610 array. We also demonstrate, for the first time, far-field interference of beams from two separate OPAs on a single silicon photonic chip, as an initial step towards long-range computational imaging LIDAR based on novel active aperture synthesis schemes.
The design, fabrication, and characterization of a 16-element optical phased array (OPA) using a high index (n = 3.1) silicon rich silicon nitride (SRN) is demonstrated. We present one-dimensional beam steering with end-fire facet antennas over a wide steering range of >115° at a fixed wavelength of 1525 nm. A spot size of 0.11° has been measured at boresight, consistent with theory. We demonstrate SRN as a viable material choice for chip-scale OPA applications due to its high thermo-optic coefficient, high optical power handling capacity due to negligible two-photon absorption (TPA), wide tra…
Photonic integrated circuit (PIC) phased arrays can be an enabling technology for a broad range of applications including free-space laser communications on compact moving platforms. However, scaling PIC phased arrays to a large number of array elements is limited by the large size and high power consumption of individual phase shifters used for beam steering. In this paper, we demonstrate silicon PIC phased array beam steering based on thermally tuned ultracompact microring resonator phase shifters with a radius of a few microns. These resonators integrated with micro-heaters are designed to …
Resonant optical phased arrays are a promising way to reach fully reconfigurable metasurfaces in the optical and NIR regimes with low energy consumption, low footprint and high reliability. Continuously tunable resonant structures suffer from inherent drawbacks such as low phase range, amplitude-phase correlation or extreme sensitivity that makes precise control at the individual element level very challenging. In order to bypass these issues, we use 1-bit (binary) control for beam steering for an innovative nano-resonator antenna and explore the theoretical capabilities of such phased arrays.…
Chip-scale optical phased arrays could enable compact beam steering and LIDAR for autonomous vehicles, precision robotics, and free-space optical communications. Because these applications demand wide angle beam steering as well as high optical power in the output beam, a natural design choice would be to space the array emitters at a half-wavelength pitch, as is common in radiofrequency phased arrays. Optical phased arrays, however, unlike RF phased arrays, have been limited by the tradeoff between field of view (i.e. angle steering) and beamforming efficiency (i.e. optical power in the outpu…
Implantable silicon neural probes with integrated nanophotonic waveguides can deliver patterned dynamic illumination into brain tissue at depth. Here, we introduce neural probes with integrated optical phased arrays and demonstrate optical beam steering in vitro. Beam formation in brain tissue was simulated and characterized. The probes were used for optogenetic stimulation and calcium imaging.
Controlling the phase and amplitude of light emitted by the elements (i.e., pixels) of an optical phased array is of paramount importance to realizing dynamic beam steering for LIDAR applications. In this paper, we propose a plasmonic pixel composed of a metallic nanoantenna covered by a thin oxide layer, and a conductive oxide, e.g., ITO, for use in a reflectarray metasurface. By considering voltage biasing of the nanoantenna via metallic connectors, and exploiting the carrier refraction effect in the metal-oxide-semiconductor capacitor in the accumulation and depletion regions, our simulatio…
Beam steering device such as optical phased array (OPA) is a key component in applications of solid-state Lidar and wireless communication. The traditional single-layer optical phased array (OPA) results in a significant energy loss due to the substrate leakage caused by the downward coupling from the grating coupler structure. In this work we have investigated a structure based on multi-layers Si3N4/SiO2 platform that can form a 3-D OPA to emit the light from the edge of the device with high efficiency, a 2-D converged out-coupling beam will be end-fired to the air. The high efficiency and wi…
Transition metal dichalcogenides (TMDCs) exhibit high second harmonic (SH) generation in the visible due to their non-centrosymmetric crystal structure in odd-layered form and direct bandgap transition when thinned down to a monolayer. In order to emit the SH radiation into a desired direction one requires a means to control the phase of the in-plane nonlinear polarization. Here, we couple the SH response of a monolayer MoS$_{\text{2}}$ to an optical phased array antenna and demonstrate controllable steering of the nonlinear emission. By exploiting the intrinsic SH generation by the phased arr…
High-performance integrated optical phased arrays (OPAs) are crucial for building up energy-efficient solid-state beam steering systems on a chip. This work demonstrates a first heterogeneous III-V/Si phase-shifter based OPA that utilizes III-V multiple quantum well (MQW) structures to provide superior performance. Demonstrated phase shifters have Vpi of only 0.45 V and residual amplitude modulation (RAM) of only 0.15 dB at 1550 nm for 2pi phase shift with low power consumption of less than 3 nW, which are, to the best our knowledge, the state-of-the-art performance with a record low operating…
Optical phased arrays are of strong interest for beam steering in telecom and LIDAR applications. A phased array ideally requires that the field produced by each element in the array (a pixel) is fully controllable in phase and amplitude (ideally constant). This is needed to realize a phase gradient along a direction in the array, and thus beam steering in that direction. In practice, grating lobes appear if the pixel size is not sub-wavelength, which is an issue for many optical technologies. Furthermore, the phase performance of an optical pixel may not span the required $2π$ phase range, or…
Optical phased array (OPA) is a promising beam-steering device for various applications such as light detection and ranging (LiDAR), optical projection, free-space optical communication and switching. However, the previously reported OPAs suffer from either an insufficiently small number of resolvable points, or a complicated control requirement due to an extremely large number of phase shifters. This work introduces a novel array configuration for OPA devices based on the non-redundant array (NRA) concept. Based on this design, we can realize high-resolution OPA whose number of resolvable poi…
Optical phased arrays (OPA) with high integration, fast speed, low power consumption, and high steering resolution are critical components in the emerging photonic integrated circuit (PIC), LiDAR, free space optical communication, 3D printing, and so on. According to the OPA working principle, its function is generally achieved by independently controlling the phase of the array elements. In practice, this presents a major challenge to overcome critical trade-offs of the element numbers, the control electronics, and the power consumption. Here, we give an alternative OPA solution to overcome t…
We demonstrate an optical phased-array (OPA) equipped with a 3D-printed facet-attached element for shaping and deflection of the emitted beam. The beam shaper combines freeform refractive surfaces with total-internal-reflection (TIR) mirrors and is in-situ printed to edge-emitting waveguide facets using high-resolution multi-photon lithography, thereby ensuring precise alignment with respect to on-chip waveguide structures. In a proof-of-concept experiment, we achieve a grating-lobe free steering range of $\pm 30°$ and a full-width-halfmaximum (FWHM) beam divergence of approximately $2°$. The …
The ability of photonic crystal waveguides (PCWs) to confine and slow down light makes them an ideal component to enhance the performance of various photonic devices, such as optical modulators or sensors. However, the integration of PCWs in photonic applications poses design challenges, most notably, engineering the PCW mode dispersion and creating efficient coupling devices. Here, we solve these challenges with photonic inverse design, and experimentally demonstrate a slow-light PCW optical phased array (OPA) with a wide steering range. Even and odd mode PCWs are engineered for a group index…
Vast tunable optical components are realized based on dynamic reconfigurations of the incident wavefronts, such as beam steering and tunable lens. However, the dominant paradigm of current wavefront reconfiguration technologies relies on complex control systems with degrees of freedom much larger than output wavefronts, e.g. beam steering based on spatial light modulator or phased array antennas. Here, we propose a new paradigm for dynamic reconfiguration of arbitrary output wavefronts using control systems with the same degrees of freedom. As an example, a wavefront transformer is demonstrate…
Here, we experimentally demonstrate an Indium Tin Oxide (ITO) Mach-Zehnder interferometer heterogeneously integrated in silicon photonics. The phase shifter section is realized in a novel lateral MOS configuration, which, due to favorable electrostatic overlap, leads to efficient modulation (VπL = 63 Vum). This is achieved by (i) selecting a strong index changing material (ITO) and (ii) improving the field overlap as verified by the electrostatic field lines. Furthermore, we show that this platform serves as a building block in an endfire silicon photonics optical phased array (OPA) with a hal…
A two-dimensional optical-phased array is demonstrated by using a multiple-input star coupler, compatible with FMCW LiDAR. Previous approach using a single-input design achieves two-dimensional beam-steering by relying on a tunable laser source, taking advantage of grating coupler radiation angle wavelength dependance and variation of the waveguide refractive index. While implementing a convenient way to distribute power in a single step, star coupler architecture is inefficient in terms of employed waveguide length and thus, optical loss and footprint. Multi-input approach partially alleviate…
Ever growing pixel acquisition rates in the fields of augmented reality, autonomous driving and robotics have increased interest in solid state beam scanning without moving parts. Modern photonic integrated laser ranging advances towards passive beam steering solutions. Recently demonstrated imagers based on focal plane arrays, nanophotonic metasurfaces, and optical phased arrays enable unprecedented pixel resolution and measurement speed. However, parallelization of >100 lasers and detectors - successfully implemented in commercial time-of-flight sensors - has not been widely adopted for pass…
We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, w…
Highly integrated active nanophotonics addressing both device footprint and operation speed demands is a key enabling technology for the next generation optical networks. Plasmonic systems have proven to be a serious contender to alleviate current performance limitations in electro-optic devices. Here, we demonstrate a plasmonic optical phased array (OPA) consisting of two 10-$μ$m-long plasmonic phase shifters, utilized to control the far-field radiation pattern of two subwavelength-separated emitters for aliasing-free beam steering with an angular range of $\pm5^\circ$ and flat frequency resp…
Optical beamforming networks (OBFNs) based on optical true time delay lines (OTTDLs) are well-known as the promising candidate to solve the bandwidth limitation of traditional electronic phased array antennas (PAAs) due to beam squinting. Here we report the first monolithic 1x8 microwave photonic beamformer based on switchable OTTDLs on the silicon-on-insulator platform. The chip consists of a modulator, an eight-channel OBFN, and 8 photodetectors, which includes hundreds of active and passive components in total. It has a wide operating bandwidth from 8 to 18 GHz, which is almost two orders l…
Electro-optic modulators transform electronic signals into the optical domain and are critical components in modern telecommunication networks, RF photonics, and emerging applications in quantum photonics and beam steering. All these applications require integrated and voltage-efficient modulator solutions with compact formfactors that are seamlessly integratable with Silicon photonics platforms and feature near-CMOS material processing synergies. However, existing integrated modulators are challenged to meet these requirements. Conversely, emerging electro-optic materials heterogeneously inte…
Optical antennas are a fundamental element in optical phased arrays (OPA) and free-space optical interconnects. An outstanding challenge in optical antenna design lies in achieving high radiation efficiency, ultra-compact footprint and broad radiation angle simultaneously, as required for dense 2D OPAs with a broad steering range. Here we demonstrate a fundamentally new concept of a nanophotonic antenna based on near-field phase-engineering. By introducing a specific near-field phase factor in the Fraunhofer transformation, the far-field beam is widened beyond the diffraction limit for a given…
