The multifunctional interface allows manipulation of light waves in free space

May 24, 2023

(Nanowerk News) Recent technological advancements have given us the extraordinary ability to manipulate and control light waves, opening up many applications in areas such as optical communications, sensing, imaging, energy, and quantum computing. Central to these advances are photonic structures that can control light waves, either at the chip level in the form of photonic integrated circuits (PICs) or in free space as meta-optics. Combining these structures allows the creation of compact optical systems. PICs can be used to make subtle changes to light waves, such as manipulation of their phase and intensity to achieve a desired output, which can then be guided in free space with meta-optics. Such a combined system could control qubits for quantum computing and power light detection, as well as range systems such as those used for autonomous vehicle navigation and mapping.

Because PICs use nanometer-scale waveguides to limit and direct light, connecting their light to and from larger devices, such as optical fibers, is complicated. Grating couplers are usually used for this purpose because of their lattice structure which can bend light into or out of the PIC waveguide. However, these devices can only form light waves to a certain degree, limiting their applicability.

Given these drawbacks, meta-optics capable of manipulating optical wavefronts of arbitrary shape have been suggested to couple the light from the PIC. Although this approach is promising, no multifunctional coupling between PIC and free space has been reported yet. Photonic integrated circuits guide the input light received from the optical fiber to a separate meta-optical chip, which bends the light to the desired shape in free space. (© Nexus Advanced Photonics)

Now, in a study published in Advanced Photonic Nexus (“A multifunctional interface between integrated photonics and free space”), researchers from the University of Washington, have demonstrated a chip-scale hybrid PIC/meta-optical platform consisting of photonic integrated circuits with a grid under a separate meta-optical chip. The PIC consists of 16 identical lattices arranged in a two-dimensional array, each with an aperture size of 300 micrometers and coupled to the optical fiber by a lattice coupler. This grating acts as a waveguide and directs light from the fiber to the meta-optical chip which forms and emits light into the empty space, parallel to the input light.

“Using a range of low-loss meta-optics, we have developed a flexible and interchangeable interface between photonic integrated circuits and free space,” said senior author Associate Professor Arka Majumdar of the University of Washington in Seattle.

Using this platform, researchers can simultaneously pass light through 14 PIC gratings and then form a beam that fits 14 different meta-optics, such as meta-lens, vortex beam generator, extended depth of focus lens, and holograms.

“Meta-optics has the ability to shape optical wavefronts to create multifunctional interfaces between free-space optics and integrated photonics. This study exploits that. All the light beams coming out of the PIC are identical, but by placing a different meta-optic over each grating, we can manipulate the beams simultaneously,” explained Majumdar.

In their experiments with different meta-optics, the researchers found that the device operated with high accuracy and reliability, even without prior knowledge of the input light or the need for precise alignment between the two chips. In particular, they achieved a diffraction-limited spot of three micrometers and holographic images with a peak signal-to-noise ratio of greater than 10 decibels.

The outstanding feature of the proposed device is its ability to change its function by simply switching the meta-optics connected to the PIC. This allows a wide range of possibilities to control and modify the light beam with a high degree of fault tolerance. Potential applications of this interface are manifold, and include beam steering, structured light generation, optical trapping, and manipulation of cold atomic qubits.

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