Recent advancements in technology have granted us an incredible capability to manipulate and control light waves, opening up numerous opportunities in various fields like optical communication, sensing, imaging, energy, and quantum computing. Central to this progress are photonic structures that can effectively control light waves, whether at the chip level as photonic integrated circuits (PICs) or in free space using meta-optics.
By combining these structures, compact optical systems can be created. PICs enable precise modifications to the light wave, such as manipulating its phase and intensity, to achieve desired outputs. Meta-optics, on the other hand, guide and shape the light wave in free space. This combined approach allows for the control of qubits in quantum computing, light detection for power, as well as ranging systems used in autonomous vehicle navigation and mapping.
However, coupling the light between nanometer-scale waveguides in PICs and larger devices like optical fibers poses challenges. Grating couplers are commonly employed for this purpose due to their ability to diffract light entering or exiting the waveguides. Nevertheless, their limitations in shaping light waves restrict their applicability.
To address this limitation, researchers at the University of Washington have proposed a chip-scale hybrid PIC/meta-optical platform, as reported in a study published in Advanced Photonics Nexus. This platform consists of a photonic integrated circuit with gratings positioned beneath a separate meta-optics chip. The PIC comprises 16 identical gratings arranged in a two-dimensional array, each with an aperture size of 300 micrometers, coupled to an optical fiber using a grating coupler. These gratings act as waveguides, directing light from the fiber to the meta-optics chip which then shapes and outputs the light to free space, parallel to the input light.
Associate Professor Arka Majumdar from the University of Washington in Seattle, the senior author of the study, explains, “Using an array of low-loss meta-optics, we have developed a flexible and interchangeable interface between a photonic integrated circuit and free space.”
Using this platform, the researchers successfully passed light through 14 PIC gratings simultaneously, shaping each corresponding beam with 14 different meta-optics. These meta-optics include meta-lenses, vortex beam generators, extended depth of focus lenses, and holograms.
Majumdar elaborates, “Meta-optics has the ability to shape optical wavefronts to create a multifunctional interface between free-space optics and integrated photonics. This study exploits that. All the light beams that come out of the PIC are identical, but by placing different meta-optics on top of each grating, we were able to simultaneously manipulate the beams individually.”
In their experiments with various meta-optics, the researchers observed that the device exhibited high accuracy and reliability. Importantly, it achieved a diffraction-limited spot of three micrometers and a holographic image with a peak signal-to-noise ratio greater than 10 decibels. Notably, the device operated effectively without prior knowledge of the input light or the need for precise alignment between the two chips.
The remarkable aspect of this device is its ability to change its functionality by simply replacing the meta-optics connected to the PIC. This opens up a wide range of possibilities for controlling and modifying light beams with a high level of error tolerance. The potential applications of this interface are diverse, including beam steering, structured light generation, optical trapping, and manipulation of cold atom qubits.