Flat-focal-field integrated spectrometer using a field-flattening lens

Area of Science:

• Photonics
• Integrated Optics
• Waveguide Devices

Background:

• Arrayed-waveguide gratings (AWGs) are crucial for wavelength-division multiplexing (WDM) in optical communication systems.
• Minimizing crosstalk, especially at the edges of the channel spectrum, is essential for maintaining signal integrity.
• Existing AWG designs face challenges in achieving optimal field distribution, leading to increased crosstalk in high-channel-count devices.

Purpose of the Study:

• To introduce a novel flat-focal-field AWG design incorporating an integrated field-flattening lens.
• To investigate the effectiveness of a silicon nitride (SiN) layer in a silicon oxynitride environment for creating the lens.
• To experimentally validate the performance improvements offered by the lens in 81-channel AWGs.

Main Methods:

• A new AWG design featuring an integrated field-flattening lens in the second star coupler was developed.
• The effective index difference for the lens was achieved using a SiN layer within a silicon oxynitride environment.
• Two distinct lens designs were implemented, and 81-channel AWGs with and without the lens were fabricated and characterized.

Main Results:

• Adjacent crosstalk at peripheral channels was improved by 2 dB in AWGs with the integrated lens.
• The lens introduced only an additional 0.4 dB of excess loss.
• Performance improvements are projected to be more significant for AWGs with a higher number of output waveguides, with an estimated ~16 dB improvement for 200-channel devices.

Conclusions:

• The integrated field-flattening lens is an effective method for reducing crosstalk in AWGs.
• The proposed SiN/silicon oxynitride approach provides a viable way to implement the field-flattening lens.
• This design offers a promising solution for enhancing the performance of future high-density WDM systems.