The OPA is designed for the end-fire emission of a line beam with a larger beamwidth along the vertical direction. It is fully passive and incorporates arrayed waveguide delay lines (AWDLs) for wavelength-tuned line beam scanning, whose length can be varied to tailor the beam scanning rate and range. In this study, a dispersive silicon–nitride OPA performing wavelength-tuned line beam scanning is demonstrated. Hence, a line-beam scanning OPA that can realize passive beam scanning by exclusively using laser wavelength can overcome the above limitations. There are a few theoretical studies demonstrating dispersive OPAs without using grating emitters, but they incorporated multilayered waveguides, making them challenging to realize practically 14, 15. However, these OPAs still deployed grating emitters and raster-scanned the beam for each pixel in the FOV of interest, rendering slow and less efficient beam scanning. Previous studies realized dispersive OPAs which could scan a point beam in both the longitudinal and lateral directions passively without involving any active phase modulators 2, 11, 12, 13. However, these devices require active components for phase tuning to facilitate the beam scanning. The raster-scanning approach is slow, considering that the beam must be scanned through each pixel 3.Īs an alternative solution, line-beam-emitting OPAs, which do not involve diffraction grating-based emitters, resulting in higher emission efficiency, are slowly gaining attention 6, 7, 10. Furthermore, these OPAs require active components, such as phase modulators with heaters or electrodes, and require electronic driver circuitry for their control, increasing the complexity of their fabrication and operation. Although point-beam raster-scanning OPAs are widely adopted, they inevitably suffer higher excess losses owing to their grating-based emitters. Phase tuning across emitter channels using either the electro- or thermo-optic effect results in lateral beam steering. Typically, OPAs incorporate diffractive-grating-based emitters to enable longitudinal beam scanning by tuning the wavelength of the input light. Current OPA developments are towards out-of-plane emission for the two-dimensional (2D) raster scanning of a point beam covering the field-of-view (FOV) of concern by tuning the laser wavelength and phase distribution across emitter channels 1, 3, 8, 9. The emitter configuration governs the nature of the beam emission, such as end-fire emission 6, 7 or out-of-plane emission 8, 9. OPAs exploit power splitters, phase shifters, and emitters to emit and steer the beam. Although most beam scanners are pivoted on either microelectromechanical systems (MEMS) or optical phased array (OPA) technologies, the latter is more widespread owing to its complementary metal-oxide semiconductor (CMOS) compatibility, leading to a compact footprint 1, 5. The rapidly increasing demand for compact light detection and ranging (LiDAR) systems has triggered a surge in the research and development of solid-state beam-scanning mechanisms for various applications including remote sensing, surveying, and optical communications 1, 2, 3, 4. To the best of our knowledge, the embodied OPA is the first demonstration of a passive line beam scanner facilitating an adjustable beam coverage with quick operation and enhanced efficiency. The main lobe emission throughput was as small as − 2.8 dB. Combinations of different delay-length differences and taper tip-widths resulted in beam coverage (lateral × vertical) ranging from 6.3° × 19° to 23.8° × 40° by tuning the wavelength from 1530 to 1600 nm. Furthermore, adiabatic tapers that allow precise effective array aperture adjustment are used as emitter elements to flexibly realize different vertical beamwidths. To steer the line beam passively covering the two-dimensional field of view, we deployed an array of delay lines with progressive delay lengths across adjacent channels. This study proposes and demonstrates a dispersive silicon–nitride OPA that allows for passive wavelength-tuned steering of a line beam with an elongated vertical beamwidth. However, line-beam scanners require active phase shifters for beam scanning thus, they consume more power and have complex device designs. As optical phased arrays (OPAs), used as solid-state beam scanning elements, swiftly stride towards higher efficiency and faster scanning speed, the line beam scanner is emerging as a viable substitute for its counterpart relying on point-beam-incorporated raster scanning.
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