A novel approach to developing efficient, high-precision 3D light shaping

Modern technologies such as optical computing, integrated photonics, and digital holography require light signals to be manipulated in three dimensions. To achieve this requires the ability to shape and guide the light stream according to the desired application. Since the flow of light in the medium is regulated by the index of refraction, special adjustment of the index of refraction is required to control the path of light in the medium.

To this end, scientists have developed so-called “aperiodic photonic volume elements” (APVEs), microscopic voxels with a specific index of refraction that are located at predetermined positions to direct a stream of light in a controlled manner. However, sculpting these elements requires a high degree of precision, and most light-forming materials are limited to a 2D configuration or ultimately lower the output beam profile.

In a recent study published in Advanced Photonic Nexus (APNexus), researchers led by Alexander Jesacher of the Medical University of Innsbruck in Austria proposed a simple approach to fabricate highly precise APVEs for various applications. This method uses a technique called “direct laser writing” for 3D voxel setting of a specific refractive index in borosilicate glass.

In their study, the researchers devised an algorithm that stimulates the flow of light through the media to determine the optimal voxel placement to achieve the required precision. Based on this, they are capable of producing between 154,000 and 308,000 voxels, each occupying a volume of about 1.75 Mm × 7.5 Mm × 10 Mm, in just 20 minutes. Additionally, they employ dynamic wavefront control to compensate for any spherical aberration (beam profile distortion) during laser focusing on the substrate. This ensures consistency of each voxel profile at all depths in the medium.

The team developed three types of APVE to demonstrate the application of this method: an intensity shaper to control the intensity distribution of the input beam, an RGB multiplexer that manipulates the transmission of the red-green-blue (RGB) spectrum of the input beam. , and a Hermite–Gaussian (HG) mode sorter to increase data transfer rates.

The team used an intensity shaper to convert the Gaussian beam into a microscopic distribution of light in the shape of a smiley, followed by a multiplexer to represent different parts of the smiley distribution in different colors, and finally an HG mode sorter to convert some of the Gaussian mode input sent by the optical fiber into an HG mode. In all cases, the device is capable of transmitting the input signal without significant loss and achieving the highest diffraction efficiency of up to 80 percent, setting a new benchmark for the APVE standard.

“The results reported in this paper greatly advance the field of ultrafast laser direct writing. The new method can open the door to a low-cost platform that is ideal for rapid prototyping of highly integrated 3D light-shaping,” said APNexus Editorial Board Member Paulina Segovia-Olvera of the Center for Scientific Research and Higher Education at Ensenada (CICESE). “The demonstration of a solid method for generating consistent, reproducible and reliable APVEs not only adds to current knowledge in the field but also enables new avenues in applied photonics,” he added.

This method, apart from simplicity, low cost and high precision, may also be extendable to other substrates, including nonlinear materials. “The flexibility of our method can make it feasible to design a wide range of 3D devices for applications in information transport, optical computing, multimode fiber imaging, nonlinear photonics and quantum optics,” concludes Jesacher.

Read the Open Access Gold article by N. Barré et al., “Direct laser writing aperiodic photonic volume elements for high-efficiency complex light generation: reverse design and fabrication,” Photo continued. Communications 2(3) 036006 (2023), doi 10.1117/1.APN.2.3.036006.