Volume grating preferential-order focusing waveguide coupler.

Area of Science:

• Optoelectronics
• Waveguide Optics
• Holographic Gratings

Background:

• Integrated optical devices require efficient methods for coupling light out of waveguides.
• Existing outcoupling techniques can suffer from low efficiency or poor beam quality.
• Volume gratings offer potential for advanced optical control and manipulation.

Purpose of the Study:

• To design, fabricate, and test a volume grating focusing waveguide coupler.
• To achieve efficient, normal-incidence light outcoupling from a single-mode waveguide.
• To focus the outcoupled light into a line with high spatial resolution.

Main Methods:

• Holographic recording of a slanted-fringe volume grating using two coherent ultraviolet beams.
• Focusing the ultraviolet beams with a cylindrical lens to create a chirped grating structure.
• Fabrication of a 1-mm-long volume grating coupler integrated with a polyimide waveguide.
• Testing the coupler's preferential-coupling ratio, coupling efficiency, and focal line quality.

Main Results:

• The volume grating coupler preferentially couples light into the air cover with a ratio of 0.98.
• Achieved a high coupling efficiency of 95%.
• Generated an almost diffraction-limited focal line with a full width at half-maximum of 10.49 micrometers.

Conclusions:

• The designed volume grating waveguide coupler demonstrates highly efficient and precise light outcoupling.
• The holographic fabrication method enables the creation of complex grating structures for optical control.
• This technology holds promise for applications requiring focused light delivery from waveguides.