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Diffractive optics for combined spatial- and mode- division demultiplexing of optical vortices: design, fabrication and optical characterization.

Ruffato G, Massari M, Romanato F - Sci Rep (2016)

Bottom Line: During the last decade, the orbital angular momentum (OAM) of light has attracted growing interest as a new degree of freedom for signal channel multiplexing in order to increase the information transmission capacity in today's optical networks.Here we present the design, fabrication and characterization of phase-only diffractive optical elements (DOE) performing mode-division (de)multiplexing (MDM) and spatial-division (de)multiplexing (SDM) at the same time.These novel DOE designs appear promising for telecom applications both in free-space and in multi-core fibers propagation.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy 'G. Galilei', University of Padova, via Marzolo 8, 35131 Padova, Italy.

ABSTRACT
During the last decade, the orbital angular momentum (OAM) of light has attracted growing interest as a new degree of freedom for signal channel multiplexing in order to increase the information transmission capacity in today's optical networks. Here we present the design, fabrication and characterization of phase-only diffractive optical elements (DOE) performing mode-division (de)multiplexing (MDM) and spatial-division (de)multiplexing (SDM) at the same time. Samples have been fabricated with high-resolution electron-beam lithography patterning a polymethylmethacrylate (PMMA) resist layer spun over a glass substrate. Different DOE designs are presented for the sorting of optical vortices differing in either OAM content or beam size in the optical regime, with different steering geometries in far-field. These novel DOE designs appear promising for telecom applications both in free-space and in multi-core fibers propagation.

No MeSH data available.


Related in: MedlinePlus

Optical microscopy (a,b) and scanning electron microscopy (c,d) of a PMMA phase-only DOE for mode-division demultiplexing of optical vortices with OAM values in the range {−3, −2, −1, 0, +1, +2, +3}. Inner radius 300 μm, outer radius 500 μm. Pixel size: 4 × 4 μm2. Working wavelength λ = 632.8 nm. 8 step levels, nominal heights (according to equation (9)): d1 = 0 nm, d2 = 161.8 nm, d3 = 323.5 nm, d4 = 485.3 nm, d5 = 647.0 nm, d6 = 808.8 nm, d7 = 970.6 nm, d8 = 1132.3 nm.
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f5: Optical microscopy (a,b) and scanning electron microscopy (c,d) of a PMMA phase-only DOE for mode-division demultiplexing of optical vortices with OAM values in the range {−3, −2, −1, 0, +1, +2, +3}. Inner radius 300 μm, outer radius 500 μm. Pixel size: 4 × 4 μm2. Working wavelength λ = 632.8 nm. 8 step levels, nominal heights (according to equation (9)): d1 = 0 nm, d2 = 161.8 nm, d3 = 323.5 nm, d4 = 485.3 nm, d5 = 647.0 nm, d6 = 808.8 nm, d7 = 970.6 nm, d8 = 1132.3 nm.

Mentions: Phase-only diffractive optical elements are fabricated as surface-relief patterns of pixels. This 3-D structure can be realized by shaping a layer of transparent material, imposing a direct proportionality between the thickness of the material and the local phase delay. Electron beam lithography (EBL) is the ideal technique in order to fabricate 3D profiles with the required high resolution373839. By modulating the local dose distribution, a different dissolution rate is induced in the exposed polymer, giving rise to different resist thicknesses after the development process. In this work the DOE patterns were written on a polymethylmethacrylate (PMMA) resist layer with a JBX-6300FS JEOL EBL machine, 5 nm resolution, working at 100 keV with a current of 100 pA. The substrate used for fabrication is glass, coated with an ITO layer with low surface resistivity (8–12 Ω) in order to ensure a good discharge of the sample during electron beam lithography. After the exposure, the resist is developed in a temperature-controlled developer bath for 60 s. The quality of the fabricated structures has been assessed using Optical Microscopy (Fig. 5 (a,b) and 6), Scanning Electron Microscopy (SEM) (Fig. 5 (c,d)) and Atomic Force Microscopy (AFM) (see Supplementary Figure 1).


Diffractive optics for combined spatial- and mode- division demultiplexing of optical vortices: design, fabrication and optical characterization.

Ruffato G, Massari M, Romanato F - Sci Rep (2016)

Optical microscopy (a,b) and scanning electron microscopy (c,d) of a PMMA phase-only DOE for mode-division demultiplexing of optical vortices with OAM values in the range {−3, −2, −1, 0, +1, +2, +3}. Inner radius 300 μm, outer radius 500 μm. Pixel size: 4 × 4 μm2. Working wavelength λ = 632.8 nm. 8 step levels, nominal heights (according to equation (9)): d1 = 0 nm, d2 = 161.8 nm, d3 = 323.5 nm, d4 = 485.3 nm, d5 = 647.0 nm, d6 = 808.8 nm, d7 = 970.6 nm, d8 = 1132.3 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837364&req=5

f5: Optical microscopy (a,b) and scanning electron microscopy (c,d) of a PMMA phase-only DOE for mode-division demultiplexing of optical vortices with OAM values in the range {−3, −2, −1, 0, +1, +2, +3}. Inner radius 300 μm, outer radius 500 μm. Pixel size: 4 × 4 μm2. Working wavelength λ = 632.8 nm. 8 step levels, nominal heights (according to equation (9)): d1 = 0 nm, d2 = 161.8 nm, d3 = 323.5 nm, d4 = 485.3 nm, d5 = 647.0 nm, d6 = 808.8 nm, d7 = 970.6 nm, d8 = 1132.3 nm.
Mentions: Phase-only diffractive optical elements are fabricated as surface-relief patterns of pixels. This 3-D structure can be realized by shaping a layer of transparent material, imposing a direct proportionality between the thickness of the material and the local phase delay. Electron beam lithography (EBL) is the ideal technique in order to fabricate 3D profiles with the required high resolution373839. By modulating the local dose distribution, a different dissolution rate is induced in the exposed polymer, giving rise to different resist thicknesses after the development process. In this work the DOE patterns were written on a polymethylmethacrylate (PMMA) resist layer with a JBX-6300FS JEOL EBL machine, 5 nm resolution, working at 100 keV with a current of 100 pA. The substrate used for fabrication is glass, coated with an ITO layer with low surface resistivity (8–12 Ω) in order to ensure a good discharge of the sample during electron beam lithography. After the exposure, the resist is developed in a temperature-controlled developer bath for 60 s. The quality of the fabricated structures has been assessed using Optical Microscopy (Fig. 5 (a,b) and 6), Scanning Electron Microscopy (SEM) (Fig. 5 (c,d)) and Atomic Force Microscopy (AFM) (see Supplementary Figure 1).

Bottom Line: During the last decade, the orbital angular momentum (OAM) of light has attracted growing interest as a new degree of freedom for signal channel multiplexing in order to increase the information transmission capacity in today's optical networks.Here we present the design, fabrication and characterization of phase-only diffractive optical elements (DOE) performing mode-division (de)multiplexing (MDM) and spatial-division (de)multiplexing (SDM) at the same time.These novel DOE designs appear promising for telecom applications both in free-space and in multi-core fibers propagation.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy 'G. Galilei', University of Padova, via Marzolo 8, 35131 Padova, Italy.

ABSTRACT
During the last decade, the orbital angular momentum (OAM) of light has attracted growing interest as a new degree of freedom for signal channel multiplexing in order to increase the information transmission capacity in today's optical networks. Here we present the design, fabrication and characterization of phase-only diffractive optical elements (DOE) performing mode-division (de)multiplexing (MDM) and spatial-division (de)multiplexing (SDM) at the same time. Samples have been fabricated with high-resolution electron-beam lithography patterning a polymethylmethacrylate (PMMA) resist layer spun over a glass substrate. Different DOE designs are presented for the sorting of optical vortices differing in either OAM content or beam size in the optical regime, with different steering geometries in far-field. These novel DOE designs appear promising for telecom applications both in free-space and in multi-core fibers propagation.

No MeSH data available.


Related in: MedlinePlus