High-resolution aliasing-free optical beam steering
20 Aug 2016-Vol. 3, Iss: 8, pp 887-890
TL;DR: In this paper, a two-axis steerable optical phased array with over 500 resolvable spots and 80° steering in the phased array axis (measurement limited) and a record small divergence in both axes (0.14°).
Abstract: Many applications, including laser (LIDAR) mapping, free-space optical communications, and spatially resolved optical sensors, demand compact, robust solutions to steering an optical beam. Fine target addressability (high steering resolution) in these systems requires simultaneously achieving a wide steering angle and a small beam divergence, but this is difficult due to the fundamental trade-offs between resolution and steering range. So far, to our knowledge, chip-based two-axis optical phased arrays have achieved a resolution of no more than 23 resolvable spots in the phased-array axis. Here we report, using non-uniform emitter spacing on a large-scale emitter array, a dramatically higher-performance two-axis steerable optical phased array fabricated in a 300 mm CMOS facility with over 500 resolvable spots and 80° steering in the phased-array axis (measurement limited) and a record small divergence in both axes (0.14°). Including the demonstrated steering range in the other (wavelength-controlled) axis, this amounts to two-dimensional beam steering to more than 60,000 resolvable points.
Citations
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TL;DR: In this paper , a four-line selective optical phased array (FLS-OPA) with improved uniformity of radiated beam patterns is presented, where the OPA units are divided into two symmetric groups with the opposite incident directions of lights.
Abstract: We demonstrate a four-line selective optical phased array (FLS-OPA) with improved uniformity of radiated beam patterns. The FLS-OPA contains four basic OPA units, which are divided into two symmetric groups with the opposite incident directions of lights. In each group, the grating periods of the OPA units are set to 630 nm and 650 nm, respectively. Besides, a $1\times 4$ thermo-optical switch is used to select an OPA unit out of four as the beam emitting unit. Therefore, four different emitting angles in the vertical direction can be realized by only two grating periods with a fixed wavelength. By tuning the wavelength from 1530 nm to 1635 nm and switching the OPA units, the FLS-OPA achieves a scanning range of 34.2° in the vertical direction, and the corresponding tuning efficiency is 0.33°/nm. In addition, the beam steering range in the horizontal direction is 21.4°. Thus, the overall field of view is $21.4^{\circ } \times 34.2^{\circ }$ . Moreover, the symmetrical arrangement of the OPA units can improve the uniformity of the radiated beam patterns in the vertical direction.
1 citations
TL;DR: In this paper , a perimeter-controlled active metasurface for two-dimensional dynamic beam steering at mid-infrared regime is theoretically presented, which simplifies biasing architecture by allowing column-row addressing of the elements.
Abstract: Abstract The current commercially viable light detection and ranging systems demand continuous, full-scene, and dynamic two-dimensional point scanning, while featuring large aperture size to ensure long distance operation. However, the biasing architecture of large-area arrays with numerous individually controlled tunable elements is substantially complicated. Herein, inverse design of a perimeter-controlled active metasurface for two-dimensional dynamic beam steering at mid-infrared regime is theoretically presented. The perimeter-control approach simplifies biasing architecture by allowing column-row addressing of the elements. The metasurface consists of a periodic array of plasmonic patch nanoantennas in a metal-insulator-metal configuration, wherein two active layers of indium arsenide are incorporated into its building block. The metasurface profile facilitates wide phase modulation of ≈355°$\approx 355^{\circ} $ on the reflected light at the individual element level through applying independent voltages to its respective columns and rows. The multi-objective genetic algorithm (GA) for optimizing user-defined metrics toward shaping desired far-zone radiation pattern is implemented. It is demonstrated that multi-objective GA yields better results for directivity and spatial resolution of perimeter-controlled metasurface by identifying the design tradeoffs inherent to the system, compared to the single-objective optimizer. A high directivity and continuous beam scanning with full and wide field-of-view along the azimuth and elevation angles are respectively maintained.
1 citations
Dissertation•
01 Dec 2018
TL;DR: This thesis aims at refining an alternative method of non-mechanical beam steering which uses focus tunable lenses, and aims to explore this tradeoff and create a compact design which at the same time is capable of scanning over a large angle.
Abstract: LIDAR is a device used for measuring the distance of an object using laser beams to create detailed 3-D images of the object. LIDAR has numerous applications, but one of its principle applications recently has been with autonomous vehicle where it is used to map the surroundings of the vehicle so that it can detect obstacles or differentiate between roads, other vehicles and passengers etc.
For a LIDAR to capture a complete 360° surrounding view of a vehicle, the sensor must be rotated around to detect images all around the vehicle. Current autonomous cars use spinning LIDAR sensors mounted on top of the vehicle. These sensors use mechanical motors to rotate the entire device, and have the disadvantage of being bulky, expensive, and inefficient. For this reason, non-mechanical methods of steering optical beams like Optical Phased Array (OPA) technology and Micro-electromechanical systems (MEMS) is being extensively researched.
This thesis aims at refining an alternative method of non-mechanical beam steering which uses focus tunable lenses. Focus tunable lenses have a variable focal length that can be controlled by applying appropriate electrical signals. By using two such lenses one after the other, the direction and focus of a laser beam can be controlled. The tunable lenses, along with other optical elements can be used to create a wide-angle scan. Past research on this method is limited, and the device size was too large for practical applications. This can be attributed to the long optical path lengths present between adjacent elements in the design, which is required for the beam scan angle to be as large as possible. So ultimately a tradeoff between device size and the scan angle exists. This work aims to explore this tradeoff and create a compact design which at the same time is capable of scanning over a large angle. Zemax software was used to model the elements, design the systems, and trace the rays to detect their exact position for different values of focal length of the tunable lenses.
The first design aimed at observing the effect of reducing the optical path length between the adjacent elements in the design. The design elements were placed close to each other to reduce the physical length (and consequently the optical path length) between them. The total length of the device was only 114 mm, but reducing the optical path resulted in a very low scan angle of 16°.
In the second design, instead of removing a big part of the optical path between the relay lens and the diffuser all together, it was replaced with two 90° prisms with their bases facing each other. With this arrangement, a total optical path of 224 mm was created within a physical length of 48mm. The focal length of the objective lenses placed after the diffuser were reduced from 50mm to 25mm. The results from the final design show a total beam scan angle of 52° for a device only 119mm in length.
The third design incorporated a third prism to further increase the optical path length to create a larger scan. The scan angle from this design was found to be 60°. The total size of the device however, increased due to the addition of a third prism.
Measurements were made of the RMS beam radius at different distances from the device, and the beam divergence was calculated to be 0.45°.
1 citations
Cites background or methods from "High-resolution aliasing-free optic..."
...In an effort to increase the steering angle range of OPA architecture, Hutchison et al [29] proposed a new emitter architecture which uses non-uniform emitter spacing and wide angle emitters to suppress grating lobes which limit the steering angle range in traditional OPA devices....
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...6 Simulation of the OPA from [29] showing beam steering using (a) uniform emitter spacing, and (b) non uniform emitter spacing....
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21 Jan 2018
TL;DR: In this article, a novel two-dimensional (2D) optical phased arrays with 25,600 addressable phase shifters made of diffraction gratings with in-plane movement is presented.
Abstract: We report on a novel two-dimensional (2-D) optical phased arrays with 25,600 addressable phase shifters made of diffraction gratings with in-plane movement. The phase shift is independent of wavelength, and only depends on the displacement of the grating. The large optical aperture 3.2×3.1mm2 produces a narrow beam (0.028°×0.029°) steerable over a field-of-view of 4.4°×4.6° at 1550nm wavelength, with a maximum response time of 4.2μs.
1 citations
Cites background from "High-resolution aliasing-free optic..."
...Optical phased arrays (OPAs) are key enabling elements for solid-state LiDAR (light detection and ranging) and three-dimensional (3-D) imaging without bulk mechanical moving parts [1]....
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TL;DR: In this paper , a monolithic frequency-modulated continuous-wave (FMCW) lidar chip with an integrated transceiver array based on lens-assisted beam steering (LABS) technology is demonstrated.
Abstract: We demonstrate a monolithic frequency-modulated continuous-wave (FMCW) lidar chip with an integrated transceiver array based on lens-assisted beam steering (LABS) technology. It enables beam emitting, steering, receiving, and coherent detecting on a single chip with simultaneous distance and velocity detection. An integrated transceiver is designed with a composite structure of a Bragg grating in the middle and a U-shaped photodetector (PD) surrounding it. For a proof-of-concept demonstration, a chip with 2 × 2 switchable transceiver array is fabricated. A monolithic coherent LABS lidar system with a scanning angle of 2.86° and a scanning speed of 5.3 µs is implemented for 5 m ranging and 0.45 m/s velocity detection.
1 citations
References
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TL;DR: This work demonstrates that a robust design, together with state-of-the-art complementary metal-oxide–semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips and therefore extends the functionalities of phased arrays beyond conventional beam focusing and steering, opening up possibilities for large- scale deployment.
Abstract: A large-scale silicon nanophotonic phased array with more than 4,000 antennas is demonstrated using a state-of-the-art complementary metal-oxide–semiconductor (CMOS) process, enabling arbitrary holograms with tunability, which brings phased arrays to many new technological territories. Nanophotonic approaches allow the construction of chip-scale arrays of optical nanoantennas capable of producing radiation patterns in the far field. This could be useful for a range of applications in communications, LADAR (laser detection and ranging) and three-dimensional holography. Until now this technology has been restricted to one-dimensional or small two-dimensional arrays. This paper reports the construction of a large-scale silicon nanophotonic phased array containing 4,096 optical nanoantennas balanced in power and aligned in phase. The array was used to generate a complex radiation pattern—the MIT logo—in the far field. The authors show that this type of nanophotonic phased array can be actively tuned, and in some cases the beam is steerable. Electromagnetic phased arrays at radio frequencies are well known and have enabled applications ranging from communications to radar, broadcasting and astronomy1. The ability to generate arbitrary radiation patterns with large-scale phased arrays has long been pursued. Although it is extremely expensive and cumbersome to deploy large-scale radiofrequency phased arrays2, optical phased arrays have a unique advantage in that the much shorter optical wavelength holds promise for large-scale integration3. However, the short optical wavelength also imposes stringent requirements on fabrication. As a consequence, although optical phased arrays have been studied with various platforms4,5,6,7,8 and recently with chip-scale nanophotonics9,10,11,12, all of the demonstrations so far are restricted to one-dimensional or small-scale two-dimensional arrays. Here we report the demonstration of a large-scale two-dimensional nanophotonic phased array (NPA), in which 64 × 64 (4,096) optical nanoantennas are densely integrated on a silicon chip within a footprint of 576 μm × 576 μm with all of the nanoantennas precisely balanced in power and aligned in phase to generate a designed, sophisticated radiation pattern in the far field. We also show that active phase tunability can be realized in the proposed NPA by demonstrating dynamic beam steering and shaping with an 8 × 8 array. This work demonstrates that a robust design, together with state-of-the-art complementary metal-oxide–semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips. In turn, this enables arbitrary radiation pattern generation using NPAs and therefore extends the functionalities of phased arrays beyond conventional beam focusing and steering, opening up possibilities for large-scale deployment in applications such as communication, laser detection and ranging, three-dimensional holography and biomedical sciences, to name just a few.
1,065 citations
01 Aug 1998
TL;DR: The digital display engine (DDE) as discussed by the authors is based on a single DMD device having array dimensions of 800/spl times/600 elements, illuminated by a metal halide arc lamp through a compact optics train.
Abstract: A period of rapid growth and change in the display industry has recently given rise to many new display technologies. One such technology, the Digital Micromirror Device/sup TM/ (DMD), developed at Texas Instruments, represents a unique application of microelectromechanical systems to the area of projection displays. In this paper, we describe a representative example of a DMD-based projection display engine, the digital display engine (DDE). The DDE is based on a single-DMD device having array dimensions of 800/spl times/600 elements, illuminated by a metal halide arc lamp through a compact optics train. The engine is designed for portable and fixed conference-room graphics and video display applications, and many design decisions were made to tailor the engine for its intended venue. The design of the projection engine optics and electronics is discussed, along with the basic operation, manufacture, and reliability of the DMD itself.
642 citations
TL;DR: A 16-channel, independently tuned waveguide surface grating optical phased array in silicon for two dimensional beam steering with a total field of view of 20° x 14° and full-window background peak suppression of 10 dB is demonstrated.
Abstract: We demonstrate a 16-channel, independently tuned waveguide surface grating optical phased array in silicon for two dimensional beam steering with a total field of view of 20° x 14°, beam width of 0.6° x 1.6°, and full-window background peak suppression of 10 dB.
373 citations
TL;DR: An integrated approach is followed in which a 1D optical phased array is fabricated on silicon-on-insulator in which continuous thermo-optical steering of 2.3 degrees and wavelength steering of 14.1 degrees is reported.
Abstract: Optical phased arrays are versatile components enabling rapid and precise beam steering. An integrated approach is followed in which a 1D optical phased array is fabricated on silicon-on-insulator. The optical phased array consists of 16 parallel grating couplers spaced 2 mum apart. Steering in one direction is done thermo-optically by means of a titanium electrode on top of the structure using the phased array principle, while steering in the other direction is accomplished by wavelength tuning. At a wavelength of 1550 nm, continuous thermo-optical steering of 2.3 degrees and wavelength steering of 14.1 degrees is reported.
299 citations
TL;DR: The photonic integrated circuit (PIC) consists of 164 optical components including lasers, amplifiers, photodiodes, phase tuners, grating couplers, splitters, and a photonic crystal lens and exhibited steering over 23° x 3.6°.
Abstract: In this work we present the first fully-integrated free-space beam-steering chip using the hybrid silicon platform. The photonic integrated circuit (PIC) consists of 164 optical components including lasers, amplifiers, photodiodes, phase tuners, grating couplers, splitters, and a photonic crystal lens. The PIC exhibited steering over 23° x 3.6° with beam widths of 1° x 0.6°.
283 citations