Subwavelength structure enabled ultra-long waveguide grating antenna

Compact unidirectional waveguide grating emitter with enhanced wavelength sensitivity based on the hybrid plasmonic mode

Waveguide grating antennas are widely adopted in beam-steering devices, typically enabling the beam steering in longitudinal direction within a two-dimensional scanning optical array by changing the input wavelength. However, traditional waveguide grating antennas suffer from limited tuning range due to low dispersion of the gratings. In this paper, a compact silicon grating waveguide antenna array is proposed with enhanced wavelength sensitivity by introducing a periodically modulated hybrid plasmonic mode. The hybrid plasmonic mode is supported by the hybrid plasmonic waveguides (HPWs) composed of silicon waveguides and periodic subwavelength silver strips. In order to convert the guided waves to the radiated waves, a series of silicon emitting segments are deposited above the HPWs. Additionally, the horizontally arranged array of HPWs also acts as a reflector of the downward radiation, resulting in an effective unidirectional emission. Through the optimization of physical parameters, the proposed antenna array achieves a wavelength-length tuning efficiency up to 0.3°/nm within the wavelength range of 1500∼1600 nm, exhibiting a significant improvement compared with traditional ones. Moreover, an average upward emissivity exceeding 80% with a maximum value of 89% within the 100 nm bandwidth is demonstrated through the numerical simulations. The proposed compact antenna array provides an alternative solution in realizing large-scale integrated high-tuning-efficiency optical beam-steering devices.

Vertical directional coupling based grating emission engineering for optical phased arrays

In this Letter, a novel, to the best of our knowledge, vertical directional coupling waveguide grating (VDCWG) architecture is proposed to increase the length of waveguide grating antennas for large aperture on-chip optical phased arrays (OPAs). In this new architecture, the grating emission strength is engineered by the vertical directional coupler, which provides additional degrees of design freedom. Theoretical analysis and numerical simulation show that the VDCWG can adjust the grating strength in the range of more than two orders of magnitude, corresponding to an effective grating length more than a centimeter. For proof-of-concept, a VDCWG antenna with a length of 1.5 mm is experimentally demonstrated. The grating strength is measured to be 0.17 mm-1, and the far-field divergence angle is 0.061°. A 16-channel OPA is also developed based on the proposed VDCWG, which proves the potential of the new architecture for large aperture OPAs.

Silicon-based high-resolution and low-power-consumption two-dimensional beam scanner integrated with hybrid wavelength-tunable laser diode

Optical phased array (OPA) is a useful device for achieving the solid-state beam scanner required in compact light detection and ranging. However, conventional OPAs actively control the phase difference between arrays. Therefore, power consumption is extremely high in a high-resolution OPA. Herein, we fabricated a passive OPA with a 128-channel silicon arrayed waveguide and Si-dot grating antennas with large apertures. Moreover, we integrated a hybrid wavelength-tunable laser diode with a passive OPA. The field of view was 43.9° × 10.4°, and the FWHM of the beam width was 0.233° × 0.0495°. The power consumption per antenna was 0.397 mW.

Inverse-designed polarization multiplexing non-uniformly distributed gratings for one-dimensional beam steering

Non-uniformly distributed gratings on the silicon-on-insulator platform for one-dimensional beam steering are designed by direct binary search inverse-design method. The gratings exhibit good emission directionality and far-field characteristics. Within a relatively small wavelength tuning range of 1517-1577 nm, the longitudinal scanning angle for TE and TM light is 23.65° and 10.81°, respectively, both of which are much larger than their uniform counterparts. By polarization multiplexing and etching depth optimization, a remarkable longitudinal scanning angle of 32.10° and high beam steering efficiency of 0.55°/nm are obtained. This work may pave the way for the development of miniaturized optical phased arrays with excellent beam steering performance.

Ultralong waveguide grating antenna enabled by evanescent field modulation

Waveguide grating antenna (WGA) is a key component for an on-chip optical phased array. In order to form a beam with a small divergence angle, WGAs of several millimeters in length are highly desired. However, in high-index-contrast platforms such as silicon-on-insulator (SOI), such long WGAs typically require weakly modulated gratings with critical feature sizes below 10 nm. In this paper, we experimentally demonstrate a new, to the best of our knowledge, strategy to implement long WGAs. Instead of directly modulating a waveguide, we propose periodically modulating the evanescent field with subwavelength blocks. With this arrangement, weak grating strength can be achieved while maintaining a minimum feature size as large as 100 nm. For proof-of-concept, we experimentally demonstrate a 1-mm-long, single-etched WGA on a conventional 220 nm SOI platform, which achieves a far-field divergence angle of 0.095° and a wavelength scanning sensitivity of 0.168°/nm.

All-Solid-State Beam Steering via Integrated Optical Phased Array Technology

Light detection and ranging (LiDAR), combining traditional radar technology with modern laser technology, has much potential for applications in navigation, mapping, and so on. Benefiting from the superior performance, an all-solid-state beam steering realized by integrated optical phased array (OPA) is one of the key components in the LiDAR system. In this review, we first introduce the basic principle of OPA for beam steering. Then, we briefly review the detailed advances of different solutions such as micro-electromechanical system OPA, liquid crystal OPA, and metasurface OPA, where our main focus was on the recent progress of OPA in photonic integrated chips. Finally, we summarize the different solutions and discuss the challenges and perspectives of all-solid-state beam steering for LiDAR.