Straight and curved distributed Bragg reflector design for compact WDM filters

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Semiconductor Devices

Background:

• Wavelength division multiplexing (WDM) is essential for high-capacity optical communication.
• Developing compact and efficient wavelength selective filters is critical for WDM systems.
• Grating-assisted contra-directional couplers (CDCs) are promising candidates for filter applications.

Purpose of the Study:

• To design and experimentally demonstrate grating-assisted contra-directional couplers (CDCs) as wavelength selective filters for WDM.
• To investigate two configurations: straight-distributed Bragg reflector (SDBR) and curved distributed Bragg reflector (CDBR).
• To suppress sidelobe strength and achieve stable spectral performance.

Main Methods:

• Fabrication of devices on a monolithic silicon photonics platform using a GlobalFoundries CMOS foundry.
• Apodization of grating and spacing in asymmetric waveguides to control energy exchange within the CDC.
• Experimental characterization of transmission spectrum, insertion loss, and spectral stability.

Main Results:

• Demonstration of both SDBR and CDBR configurations with suppressed sidelobe strength.
• Achieved flat-top transmission spectrum with low insertion loss (0.43 dB).
• Exhibited spectrally stable performance with a spectral shift of less than 0.7 nm across multiple wafers.
• Compact device footprints: 130 µm²/Ch (SDBR) and 3700 µm²/Ch (CDBR).

Conclusions:

• Grating-assisted contra-directional couplers are effectively demonstrated as wavelength selective filters for WDM.
• The apodization technique successfully suppresses sidelobe strength and enhances filter performance.
• The fabricated devices show excellent performance metrics, including low loss, spectral stability, and compact size, suitable for integrated photonic applications.