arXiv subjects

Masayuki Higaki

Publications and source records attributed to Masayuki Higaki.

4 recordsLinked to original sources

arXiv2026

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

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.

physics.optics↗

arXiv2025

Microcomb-referenced photonic stabilization of resonant tunneling diode terahertz oscillators

We demonstrate a compact stabilization scheme for terahertz (THz) sources by exploiting the complementary advantages of microresonator-based optical frequency combs (microcombs) and resonant tunneling diodes (RTDs). A microcomb-driven photomixing THz signal is employed as the master for injection locking of an RTD, enabling faithful transfer of the microcomb stability into the RTD. Using this approach, the free-running RTD linewidth of 50 MHz was narrowed to 165 Hz, while the single-sideband phase noise reached -80 dBc/Hz at a 10 kHz offset with a locking range of 80 MHz. Compared with conventional electronic frequency multiplier or fiber-comb-based schemes, this method avoids high-order frequency multiplication and associated noise penalties, offering a compact and practical alternative. The dual functionality of linewidth narrowing and power scalability highlights the potential of microcomb-assisted injection locking as a route toward chip-scale, spectrally pure THz sources for beyond-5G/6G wireless communication and radar, with prospects for future extension to time-frequency metrology and precision sensing.

physics.optics↗

arXiv2025

Direct fiber-coupled soliton microcomb system with enhanced stability and reproducibility via high numerical-aperture polarization-maintaining single-mode fibers and temperature control

We propose a compact and robust system architecture for soliton microcomb generation, based on two key techniques: direct fiber coupling using high numerical-aperture polarization-maintaining single-mode fibers (high-NA PMFs) and active temperature control of the microresonator. These complementary strategies address two major challenges in microcomb implementation: environmental sensitivity and resonance instability. Building on prior work using single-mode fiber (SMF)-based direct coupling, which demonstrated device miniaturization and partial suppression of thermal drift in coupling efficiency, our PMF-based approach offers enhanced thermal stability and significantly greater robustness to environmental disturbances such as temperature fluctuations and vibration. In our system, precision alignment using microscopes or multi-axis stages is no longer required, enabling a simplified optical setup and stable long-term operation. The direct coupling scheme achieved a coupling efficiency of 57.7% and maintained soliton operation for over 24 hours under external perturbations. In parallel, active temperature control of the microresonator was quantitatively evaluated, reducing the wavelength variation of the pump and auxiliary lasers by 79% and 97%, respectively. This stability enables reproducible soliton generation even in thermally dynamic environments. Comparative experiments with SMF-based direct coupling and lensed-SMF-based free-space coupling systems confirmed the superior performance of the PMF-based design in terms of coupling stability, soliton lifetime, and immunity to environmental noise. The architecture developed in this study lays a strong foundation for future integration into compact modules, paving the way for portable and robust microcomb sources in real-world photonic systems.

physics.optics↗

arXiv2024

Reduction of temperature drift in refractive-index-sensing optical frequency comb by active-dummy compensation of dual-comb configuration

Refractive-index (RI) sensing plays a pivotal role in various domains, encompassing applications like glucose sensing, biosensing, and gas detection. Despite the advantages of optical fiber sensors, such as their compact size, flexibility, and immunity to electromagnetic interference, they are often plagued by temperature-induced drift, which adversely impacts the accuracy of RI measurements. This study introduces an innovative approach to alleviate temperature-induced drift in RI-sensing optical frequency combs (OFCs) by employing active-dummy compensation. The central idea revolves around the utilization of a dual-comb setup, comprising an active-sensing OFC that monitors both sample RI and environmental temperature, and a dummy-sensing OFC that exclusively tracks environmental temperature. The disparity between these sensor signals, denoted as delta_frep, effectively nullifies the effects of temperature variations, yielding a temperature-independent sensor signal for precise RI measurements. This investigation delves into the relationship between active-dummy temperature compensation and delta_frep. It becomes evident that diminishing delta_frep values enhance temperature compensation, thereby diminishing fluctuations in delta_frep caused by environmental temperature shifts. This compensation technique establishes a direct link between delta_frep and sample RI, paving the way for absolute RI measurements based on delta_frep. The findings of this research are a valuable contribution to the advancement of accurate and temperature-compensated RI sensing methodologies using dual-comb setup. The insights gained regarding delta_frep dependency and the strategies proposed for enhancing measurement precision and stability hold significant promise for applications in fields of product quality control and biosensing.

physics.optics↗