Bidirectional high-purity structured light beams transformation based on multi-plane light conversion

Structured light beams are essential in optical communications, quantum information processing, and light-matter interactions. The generation and conversion of high-purity structured light beams are crucial for these applications. In this study, we propose a bidirectional high-purity structured light beam transformation approach based on the multi-plane light conversion (MPLC) method. This approach enables mutual conversion of arbitrary orthogonal modes and precise control of system loss and mode purity. Using the proposed method, we demonstrate the conversion of 7-modes Gaussian beams array (GBA) and perfect vortex beams (PVB), achieving a bidirectional output modes signal-to-noise ratio (SNR) exceeding 30 dB and a loss of 5.23 dB. For generation of 13-modes, an SNR above 25 dB and an insertion loss below 5.45 dB are obtained. Furthermore, the validity of methods is confirmed by generating multi-wavelength and structured light beams with more complex field distribution. The work paves the way toward structured-light-beam-based optical communications, high-dimensional quantum communications, and advancements in MPLC.