Contradirectional couplers in silicon-on-insulator rib waveguides

Area of Science:

• Photonics and Waveguide Engineering
• Integrated Optics
• Semiconductor Device Fabrication

Background:

• Developing efficient and compact optical filters is crucial for wavelength-division multiplexing (WDM) systems.
• Existing add-drop filters often face limitations such as narrow fabrication tolerances and limited free spectral range.
• Silicon-on-insulator (SOI) technology offers a promising platform for integrated photonic devices due to its high refractive index and CMOS compatibility.

Purpose of the Study:

• To demonstrate contradirectional couplers in silicon-on-insulator rib waveguides.
• To achieve narrow-bandwidth add-drop filters with high fabrication tolerances.
• To overcome the free spectral range limitations of conventional filter designs.

Main Methods:

• Fabrication of contradirectional couplers using CMOS-compatible technology on silicon-on-insulator.
• Introduction of periodic dielectric perturbation in the coupling region between different-sized rib waveguides.
• Utilizing commercially available deep-ultraviolet lithography for device fabrication.
• Experimental characterization and validation using coupled-mode theory and mode-profile calculations.

Main Results:

• Successful demonstration of contradirectional couplers in SOI rib waveguides.
• Achieved narrow optical bandwidth of 0.35 nm.
• Obtained low insertion loss of less than 1 dB.
• Demonstrated high fabrication tolerances suitable for mass production.

Conclusions:

• The proposed contradirectional coupler design offers a viable solution for high-performance add-drop filters.
• CMOS-compatible fabrication and high tolerance make the technology suitable for scalable photonic integrated circuits.
• The device achieves excellent performance metrics, including narrow bandwidth and low loss, without free spectral range limitations.