Researchers have developed a universal photonic processor for spatial mode decomposition, a technique crucial for information storage and processing using light’s various degrees of freedom. This technology accurately measures and decomposes arbitrary spatial modes into their orthogonal components using a reconfigurable photonic integrated circuit. By identifying and quantifying the relative contributions of constituent modes in a Laguerre-Gaussian basis, this device can provide both the relative weights and phases of these modes, offering a novel approach to optical information processing.
With applications ranging from advanced optical communications to microscopy, this photonic processor represents a significant advancement in integrated photonics. The device’s input interface allows for the decomposition of input beam polarization into circular polarization basis, enhancing its capabilities for vector beam analysis. The processor’s potential scalability and compatibility with existing technologies make it a promising tool for future applications in high-resolution microscopy and optical communication systems.
Constructed on a silicon-on-insulator platform, the photonic processor features a mesh architecture for field processing. It consists of an input interface, a processing unit with Mach-Zehnder interferometers, and an output interface with surface grating couplers for light detection. The measurement procedure involves calibrating the on-chip elements, such as phase shifters and beam splitters, and measuring the complex amplitudes of the incoming light at the input interface. The data acquisition process is carried out in stages to optimize thermal management and ensure stable operation.
Using the photonic processor, researchers successfully decomposed various spatial modes, such as Laguerre-Gaussian modes, Hermite-Gaussian modes, and mixed modes with different weightings and relative phases. The device demonstrated its ability to distinguish up to six constituting modes in a beam, resolving phase degeneracy and accurately reconstructing the input field. Additionally, the processor showcased its polarization resolving capability by decomposing linearly and circularly polarized Gaussian beams.
Compared to existing techniques like Shack–Hartmann sensors and spatial light modulators, the on-chip mode-decomposition device offers advantages in mode resolution, polarization discrimination, scalability, and data acquisition time. While the current implementation resolves nine modes, future iterations could potentially increase the number of resolvable modes while maintaining the benefits of on-chip integration. Overall, the universal photonic processor for spatial mode decomposition represents a significant advancement in integrated photonics technology with broad applications in optical communications, microscopy, and beyond.
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