Parabolic dielectric reflector for extreme on-chip spot-size conversion with broad bandwidth

Area of Science:

• Photonics
• Optoelectronics
• Waveguide Optics

Background:

• Spot-size converters (SSCs) are crucial for efficient light coupling between waveguides of varying sizes.
• Adiabatic tapers are impractical for large expansion factors (e.g., ×100) required for integrated optics to free-space coupling.
• Existing solutions like evanescent couplers and Bragg deflectors have limited operational bandwidth.

Purpose of the Study:

• To propose and demonstrate a novel spot-size converter design using a parabolic dielectric interface.
• To achieve a large expansion factor (×570) for efficient light coupling.
• To overcome the bandwidth limitations of conventional spot-size converters.

Main Methods:

• Design of a parabolic dielectric interface for coupling light between a 0.5 μm and a 285 μm waveguide.
• Experimental demonstration of the parabolic spot-size converter's performance.
• Derivation of analytical expressions for designing parabolic spot-size converters for various expansion factors.

Main Results:

• Experimental demonstration of a spot-size converter with an expansion factor of ×570.
• Achieved an unprecedented operational bandwidth exceeding 380 nm.
• Insertion losses were measured to be below 0.35 dB.

Conclusions:

• The proposed parabolic dielectric interface offers a highly effective solution for large-ratio spot-size conversion.
• This technology provides a broad bandwidth and low insertion loss, surpassing existing methods.
• Analytical design expressions enable versatile application of parabolic spot-size converters for diverse photonic integration needs.