On-chip, inverse-designed active wavelength division multiplexer at THz frequencies

Area of Science:

• Photonics
• Terahertz (THz) technology
• Integrated optics

Background:

• Terahertz (THz) spectral range offers numerous applications but faces hardware design challenges.
• Development of photonic integrated components for THz frequencies is an active research area.
• On-chip signal processing in the THz range requires advanced component design.

Purpose of the Study:

• To demonstrate an on-chip, active wavelength division multiplexer (WDM) operating at THz frequencies (> 1 THz).
• To enable advanced on-chip signal processing in the THz range.
• To overcome hardware design challenges in THz photonic components.

Main Methods:

• Utilized inverse design topology optimization for WDM architecture.
• Embedded an active quantum cascade heterostructure in a double metal cavity, planarized with a polymer.
• Integrated the WDM with a THz quantum cascade laser (QCL) frequency comb.
• Outcoupled signals via integrated broadband patch array antennas for surface emission.

Main Results:

• Fabricated a strongly subwavelength device with a normalized volume of V/λ³ ≃ 0.5.
• Achieved three broadband output ports (2.2 THz-3.2 THz) with 330 GHz bandwidth each.
• Demonstrated a maximum crosstalk of -6 dB between output ports.
• Device operates as a stand-alone element for THz signal processing.

Conclusions:

• The developed on-chip THz WDM is a significant advancement in photonic integrated components.
• The device enables efficient THz signal processing and multiplexing.
• This technology unlocks new possibilities for applications in the terahertz spectral range.