Electrically driven acousto-optic devices that provide beam deflection and optical frequency shifting have broad applications from pulse synthesis to heterodyne detection. Commercially available acousto-optic modulators are based on bulk materials and consume Watts of radio frequency power. Here, we demonstrate an integrated 3-GHz acousto-optic frequency shifter on thin-film lithium niobate, featuring a carrier suppression over 30 dB. Further, we demonstrate a gigahertz-spaced optical frequency comb featuring more than 200 lines over a 0.6-THz optical bandwidth by recirculating the light in an active frequency shifting loop. Our integrated acousto-optic platform leads to the development of on-chip optical routing, isolation, and microwave signal processing.
We demonstrate a 3-GHz acousto-optic frequency shifter on a thin-film lithium niobate platform, featuring over 30 dB carrier suppression. The active frequency shifting loop generates a frequency comb with 200 lines over 5 nm optical bandwidth.
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 be strongly coupled to an external waveguide, thereby providing a large and adjustable phase shift with a small residual amplitude modulation while consuming an average power of 0.4 mW. We also introduce characterization techniques for the calibration of resonator phase shifters in the phased array. With such compact phase shifters and our calibration techniques, we demonstrate beam steering with a 1x8 PIC phased array. The small size of these resonator phase shifters will enable lowpower and ultra-large scale PIC phased arrays for long distance laser communication systems.
The required dynamic range of a practical undersea laser-based sensor is limited by its range-to-target. The dynamic range of the sensor needs to accommodate the variations in target reflectivity and specularity, water scattering and absorption, and mode of operation of the sensor at the target range. For example, the same sensor may be used to sense a diffuse flat black target and a shiny metallic mirror at normal incidence. Similarly, the same sensor may be deployed both in murky coastal waters and in clear deep oceanic waters. Since a detector used in a sensor has a limited (intrascene) dynamic range of perhaps 40 dB, methods of mitigating the required dynamic range at the sensor must be employed. Further, the required time scales of each specific dynamic range absorber must be considered. Therefore, a systematic optical budget approach considering time scales is employed.After considering maximum laser power out and minimum detectable power, the remaining available dynamic range is allocated to specific devices based on time responses matched to requirements. Devices are discussed and classified according to their parameters, and a final recommended system design is presented. The final system consists ofa continuously variable neutral density filter wheel, and a galvanometrically scanned variable neutral density filter wheel. Other devices and their merits are discussed.
We introduce silicon nanophotonic phased arrays with ultra compact and low-power resonator phase shifters for beam steering with an average applied power of 0.4 mW per phase shifter.
Photonic integrated circuit based optical phased arrays (PIC-OPAs) are emerging as promising programmable processors and spatial light modulators, combining the best of planar and free-space optics. Their implementation on silicon photonic platforms has been especially fruitful. Despite much progress in this field, demonstrating steerable two-dimensional (2D) OPAs that are scalable to a large number of array elements and operate with a single wavelength has proven a challenge. In addition, the phase shifters used in the array for programming the far-field beam are either power hungry or have a large footprint, preventing the implementation of large scale 2D arrays. Here, we demonstrate a two-dimensional silicon photonic phased array with high-speed (∼330 kHz) and ultralow power microresonator phase-shifters with a compact radius (∼3 µm) and 2π phase shift ability. Each phase-shifter consumes an average of ∼250 µW of static power for resonance alignment and ∼50 µW of power for far-field beamforming, a more than one order of magnitude improvement compared to prior OPA works based on waveguide-based thermo-optic phase shifters. Such PIC-OPA devices can enable a new generation of compact and scalable low power processors and sensors.
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