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.

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.

Improving the spatial resolution of volume Bragg grating two-dimensional monochromatic images.

Higher spatial resolution indicates sharper recognition ability in applications. To improve the spatial resolution of volume Bragg grating spectral imagers, quantitative wave vector theory is used to elucidate the formation mechanism of diffraction blur, and the corresponding optimal design approaches are put forward. The simulation results show that the main factors for the spectral image blur are the chromatic blur and diffraction aberration, while the central wavelength deviation further deteriorates these. To deal with these factors, one must optimize the grating period, thickness, slant angle, and refractive index, as well as compress the divergence angle of the incident beam. After optimization under the guidance of the newly defined integrated merit functions, the experimental results show that the optimized smeared point-spread function is reduced by about an order of magnitude. The horizontal spatial resolution of the recorded two-dimensional monochromatic images is improved to 14.3 lines/mm under diffuse reflection illumination.

A Study on the Surface Quality and Damage Properties of Single-Crystal Silicon Using Different Post-Treatment Processes.

Detecting subsurface defects in optical components has always been challenging. This study utilizes laser scattering and photothermal weak absorption techniques to detect surface and subsurface nano-damage precursors of single-crystal silicon components. Based on laser scattering and photothermal weak absorption techniques, we successfully establish the relationship between damage precursors and laser damage resistance. The photothermal absorption level is used as an important parameter to measure the damage resistance threshold of optical elements. Single-crystal silicon elements are processed and post-processed optimally. This research employs dry etching and wet etching techniques to effectively eliminate damage precursors from optical components. Additionally, detection techniques are utilized to comprehensively characterize these components, resulting in the successful identification of optimal damage precursor removal methods for various polishing types of single-crystal silicon components. Consequently, this method efficiently enhances the damage thresholds of optical components.