Dual terahertz frequency combs for photonic RF readout of refractive index sensing with frequency multiplication and active-dummy temperature compensation

TL;DR

This paper introduces a dual terahertz frequency comb system that enhances refractive index sensing by amplifying signal shifts and suppressing temperature noise, achieving high sensitivity, stability, and rapid measurement.

Contribution

It combines THz frequency multiplication with dual-comb temperature compensation to improve RI sensing performance beyond traditional trade-offs.

Findings

Sensitivity of 5.05 * 10^7 Hz/RIU achieved

High linearity with R^2 = 0.9979 demonstrated

Resolution improved to 1.07 * 10^-4 RIU

Abstract

We present a unified refractive index (RI) sensing platform that integrates THz-comb-based frequency multiplication with dual-comb active-dummy temperature compensation. In conventional RI-sensing optical frequency combs (OFCs), sensitivity, stability, and measurement speed are fundamentally coupled, limiting overall performance. In the proposed system, RI-induced shifts in the repetition frequency are amplified in the terahertz domain, while temperature-induced fluctuations are suppressed through common-mode rejection in a dual-comb configuration. Experimental results demonstrate a sensitivity of 5.05 * 10^7 Hz/RIU, high linearity (R^2 = 0.9979), improved resolution (1.07 * 10^-4 RIU), and high accuracy (5.50 * 10^-5 RIU). The RI-induced frequency shift is expanded from tens of hertz to hundreds of kilohertz, enabling rapid and precise readout with short gate times. This approach overcomes the conventional trade-off between sensitivity and stability. More fundamentally, it establishes orthogonal control of signal scaling and noise suppression as a design principle for high-performance RI sensing.