Fig. 1. Compact OAM multiplexing and demultiplexing via laser-processed glass chips. (a) Schematic illustration of the OAM multiplexing and demultiplexing using a reciprocal arrangement of two glass chips interfaced with fiber bundles. (b) Photograph of a fabricated glass chip encased in a metal housing for protection.

Fig. 2. Optical performance of four laser-inscribed single-mode waveguides. (a) Schematic diagram of laser-inscribed glass waveguides. The gray lines denote the four inscribed single-mode waveguides, and the inset shows the corresponding transverse magnetic (TM) mode profile at the waveguide output facet. The dashed blue rectangle indicates the spatial arrangement of the four waveguide outputs. (b) Measured mode profiles of the four fabricated single-mode waveguides at the end-face of the glass chip. The dashed black circles denote the area for the OAM (de)multiplexing hologram in a later stage. (c) Transmission loss analysis of the four waveguides (the black line is the loss of sample 1, and the red line is the loss of sample 2).

Fig. 3. Design and experimental characterization of an OAM-multiplexing hologram. (a) Illustration of the OAM-multiplexing hologram design. (b) Optical and SEM (inset) images of the fabricated hologram device (scale bars: 150 μm for the optical image, 200 nm for the SEM image). (c) Experimental characterization of the hologram (scale bar: 2 μm). Top right: the astigmatic transformation patterns induced by a tilted spherical lens (scale bar: 2 μm). The number of dark fringes indicates the OAM order, while their orientation indicates a positive or negative OAM order.

Fig. 4. All-on-glass OAM multiplexing and demultiplexing. (a) Optical setup used for aligning the OAM multiplexing glass chip with the OAM demultiplexing glass chip. The blue box indicates the alignment imaging setup, which can be removed after alignment. (b) Experimental characterization of the OAM output signals from the OAM demultiplexing glass chip based on the OAM input signals from the OAM multiplexing glass chip. (c) Multiplexing crosstalk presented as the OAM mode matrix.

Fig. 5. Design of single-mode waveguides with tilted tips. (a), (c) Schematic diagrams of light propagating from the glass chip with straight (a) and tip-tilted (c) waveguides. (b), (d) Wave vector analysis of the cases in (a) and (c), respectively. (e) Schematic diagram of light propagating in the reciprocal process in (c) with tilted waveguides. (f) Wave vector analysis of light propagating during the OAM demultiplexing process.

Fig. 6. Simulation results of an OAM multiplexing hologram. (a) Schematic illustration of the OAM multiplexing. (b) Simulated four different OAM outputs after passing a plane-wave beam through the designed OAM multiplexing hologram.

Fig. 7. Optical imaging setup for characterizing the OAM generation from a planar substrate sample. An objective lens with a numerical aperture of 0.25 and a tube lens with a focal length of 200 mm were used in the experiment.

Fig. 8. Optical imaging setup for characterizing a glass chip. A Fourier lens (left) with a focal distance of 25 mm was used to perform the Fourier transform of the laser-written hologram. An objective lens with a numerical aperture of 0.25 and a tube lens with a focal length of 200 mm were used to collect the Fourier imaging results.

Fig. 9. OAM mode outputs from the OAM multiplexing glass chip during the multiplexing stage. Spurious diffraction orders with different OAM modes appear off-axis and can be removed using a Fourier pinhole in Fig. 4(a). (a)–(d) Imaging results from the OAM multiplexing hologram based on the fiber-waveguide channels 1 to 4.

Fig. 10. (a), (b) Simulation and experimental results of the OAM demultiplexing holograms fabricated on a planar silica substrate. From left to right, the selected incident OAM modes were +2, −2, +4, and −4. (c) Optical setup used for characterizing OAM demultiplexing on a planar silica substrate.

Fig. 11. Misalignment analysis between the end-face nanoprinted meta-structures and single-mode waveguide center. (a), (b) Fourier plane distribution of the demultiplexing stage under perfect alignment and misalignment conditions. (c) Effect of misalignment on the coupling efficiency of matched modes.