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

TL;DR

This paper presents an on-chip active wavelength division multiplexer for THz frequencies, utilizing inverse design topology optimization to achieve a compact, broadband device integrated with a quantum cascade laser, enabling advanced on-chip THz signal processing.

Contribution

It introduces a novel inverse-designed, subwavelength THz WDM device integrated with a quantum cascade laser, advancing on-chip THz photonic components.

Findings

Operates at 2.2-3.2 THz with 330 GHz bandwidth

Achieves a normalized volume of about 0.5 λ^3

Maximum crosstalk of -6 dB

Abstract

The development of photonic integrated components for terahertz has become an active and growing research field. Despite its numerous applications, several challenges are still present in hardware design. We demonstrate an on-chip active wavelength division multiplexer (WDM) operating at THz frequencies. The WDM architecture is based on an inverse design topology optimization, which is applied in this case to the active quantum cascade heterostructure material embedded within a polymer in a planarized double metal cavity. Such an approach enables the fabrication of a strongly subwavelength device, with a normalized volume of only $V/\lambda^3 \simeq 0.5$. The WDM input is integrated with a THz quantum cascade laser frequency comb, providing three broadband output ports, ranging from 2.2 THz to 3.2 THz, with $\approx$ 330 GHz bandwidth and a maximum crosstalk of -6 dB. The three ports are outcoupled via integrated broadband patch array antennas with surface emission. Such a device can be also function as a stand-alone element, unlocking complex on-chip signal processing in the THz range