arXiv subjects

Takeshi Yasui

Publications and source records attributed to Takeshi Yasui.

At least 19 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

Jones-matrix dual-comb spectroscopic polarimetry

Spectroscopic polarimetry (SP) is a powerful tool for evaluation of thin film, optical materials, and biological samples because it can provide both polarimetric and spectroscopic characteristics of objects. However, its performance is often hampered by the mechanical instability and the limited data acquisition speed arising from the mechanical polarization modulation. Dual-comb spectroscopic polarimetry (DCSP) based on a combination of SP with dual-comb spectroscopy can acquire optical spectra of amplitude ratio and phase difference in p- and s-polarization components of the output light from simultaneous measurement of optical spectra of optical amplitude and phase in p- and s-polarization components without the need for mechanical polarization modulation. In this article, we combine the DCSP with polarization control pulse sequences (PCPS) with different polarizations and time delays for a more detailed analysis of the sample's polarization response based on Jones matrix. We obtain Jones matrix of a sample as a function of wavelength by measuring those optical spectra while multiplexing the incident light into multiple polarizations instead of a single polarization. Such Jones matrix DCSP (JM-DCSP) is applied for analysis of optical elements with known polarization property and its experimental result is in good agreement with theoretical values, indicating the validity of the proposed method. JM-DCSP will further expand the application scope of SP.

physics.optics↗

arXiv2025

All-photonic W-band terahertz receiver based on THz-to-optical carrier conversion with soliton microcomb dual carriers for high-speed OOK wireless transmission

We demonstrate an all-photonic terahertz receiver for a data-modulated signal, targeting a 106-GHz, 2.97-Gb/s OOK link. The scheme employs dual-wavelength optical carriers referenced to a soliton microcomb and performs THz-to-optical carrier conversion via nonpolarimetric electro-optic downconversion using an electro-optic polymer modulator. RF spectra and eye diagrams confirmed error-free transmission with a Q-factor of 5.78 and a bit-error rate of 3.73 x 10^-9, well below the hard-decision forward-error-correction (HD-FEC) threshold (Q = 2.67, BER = 3.8 x 10^-3). Comparative measurements using a single-wavelength optical-carrier configuration clearly revealed the superior signal-to-noise performance of the dual-wavelength scheme. System-level modeling further indicated scalability of the transmission distance beyond 100 m. These results establish soliton microcomb-referenced dual carriers as a promising platform for compact, integrated receivers enabling seamless wireless-optical convergence in future 6G networks.

physics.optics↗

arXiv2025

Beyond 350 GHz: Single-channel 112 Gbps photonic wireless transmission at 560 GHz using soliton microcombs

Sixth-generation (6G) back-haul links will require terahertz (THz) carriers above 350 GHz to escape the congested 300 GHz band and support >100 Gbps data rates. Photonic THz transmitters have so far remained below 350 GHz because high-frequency photomixing suffers from phase noise and power limits. Here we demonstrate single-channel wireless transmission at 560 GHz using a fibre-packaged silicon-nitride soliton microcomb as a compact, low-phase-noise optical reference. A high numerical aperture, UV-bonded fibre interface sustains soliton operation for more than 24 hours with 1 W pump power. We phase-lock two distributed-feedback lasers (DFBs) to adjacent comb lines and photomix them in a high-power uni-travelling-carrier photodiode, generating a 560 GHz carrier that bears in-phase and quadrature modulation. We achieve hard-decision forward-error-correction-qualified quadrature phase-shift keying and 16-quadrature amplitude modulation (16QAM) transmissions at 42 and 28 GBaud, respectively, attaining a record 112 Gbps data rate at 560 GHz. Relative to free-running DFBs, microcomb-locked photomixing cuts carrier linewidth and improves 16QAM error-vector magnitude. The results establish soliton microcombs as compact and scalable frequency references for >100 Gbps sub-THz links and chart a path toward compact 6 G back-haul radios.

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

Laser-scanning optical-frequency-comb microscopy for multimodal imaging

We introduce a novel laser-scanning optical microscopy technique that employs optical-frequency-comb (OFC) lasers. This method facilitates multimodal spectroscopic imaging by analyzing interferograms produced via a dual-comb spectroscopic approach. Such interferograms capture comprehensive light information, including amplitude, phase, polarization, frequency, and time of flight information, enabling multimodal imaging from a single measurement. We demonstrate the potential of this technique across several spectroscopic imaging applications.

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↗

arXiv2023

Wireless data transmission in a 560-GHz band using low-phase-noise terahertz wave generated by photomixing of a pair of distributed feedback lasers injection-locking to Kerr micro-resonator soliton comb

The demand for higher data rates in next-generation mobile wireless communication systems (6G) has led to significant interest in terahertz (THz) waves as a high-frequency, broad modulation bandwidth carrier wave. In this study, we propose and demonstrate a wireless data transfer in the 560-GHz band using low-phase-noise THz waves generated by photomixing of a pair of distributed feedback lasers injection-locking to Kerr micro-resonator soliton comb. Experimental results showed near-error-free on-off keying (OOK) data transfer at 1 Gbit/s in the 560-GHz band, with a Q-factor of 6.23, surpassing the error-free limit. Also, modulation formats of binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) were successfully used, showing clear constellation diagrams and relatively low root mean squared error vector magnitude (rms EVM) values of 23.9% and 23.6%, respectively. Moreover, data transfer at 0.4 Gbit/s in 16 quadrature amplitude modulation (16QAM) demonstrated clear isolated symbols and achieved a low rms EVM value of 8.1%, complying with the IEEE 802.15.3d standard amendment. These demonstrations highlight the potential of using injection-locked DFB lasers with the Kerr micro-resonator soliton comb to achieve high-quality, high-speed wireless data transfer in the 560-GHz band. These findings contribute significantly to the advancement of wireless communication technology in the THz frequency range and pave the way for the realization of 6G wireless communication systems.

physics.optics↗

arXiv2023

Coherent linking between confocal amplitude image and confocal phase image in dual-comb microscopy

This paper presents a coherent linking approach between confocal amplitude and confocal phase images acquired using dual-comb microscopy (DCM). DCM combines the advantages of confocal laser microscopy and quantitative phase microscopy, offering high axial resolution and scan-less imaging capability. By exploiting the coherence between confocal amplitude and phase images within the same DCM system, we accurately determine the number of phase unwrapping iterations, eliminating phase wrapping ambiguity. The method is demonstrated with samples having micrometer-range optical thickness and nanometer-scale surface roughness. The results showcase an expanded axial dynamic range, ranging from micrometers to millimeters, while maintaining nanometer-level axial resolution. This coherently linked DCM imaging technique enables the simultaneous acquisition of absolute phase information, enhancing its potential for high-axial-resolution imaging in a wide range of applications.

physics.optics↗

arXiv2023

Carrier conversion from terahertz wave to dual-wavelength near-infrared light injection-locking to optical comb using asynchronous nonpolarimetric electro-optic downconversion with electro-optic polymer modulator

THz waves are promising wireless carriers for next-generation wireless communications, where a seamless connection from wireless to optical communication is required. In this study, we demonstrate carrier conversion from THz waves to dual-wavelength NIR light injection-locking to an optical frequency comb using asynchronous nonpolarimetric electro-optic downconversion with an electro-optic polymer modulator. THz wave in the W band was obtained as a stable photonic RF beat signal of 1 GHz with a signal-to-noise ratio of 25 dB via the proposed THz-to-NIR carrier conversion. In addition, the results imply the potential of the photonic detection of THz waves for wireless-to-optical seamless communication.

physics.optics↗

arXiv2023

Nanometer-precision surface metrology of millimeter-size stepped objects using full-cascade-linked synthetic-wavelength digital holography using a line-by-line full-mode-extracted optical frequency comb

Digital holography (DH) is a powerful tool for surface profilometry of objects with sub-wavelength precision. In this article, we demonstrate full-cascade-linked synthetic-wavelength DH (FCL-SW-DH) for nanometer-precision surface metrology of millimeter-size stepped objects. 300 modes of optical frequency comb (OFC) with different wavelengths are sequentially extracted at a step of mode spacing from a 10GHz-spacing, 3.72THz-spanning electro-optic modulator OFC (EOM-OFC). The resulting 299 synthetic wavelengths and a single optical wavelength are used to generate a fine-step wide-range cascade link covering within a wavelength range of 1.54 um to 29.7 mm. We determine the 0.1000mm-stepped surface with axial uncertainty of 6.1 nm within the maximum axial range of 14.85 mm.

physics.optics↗

arXiv2023

Terahertz wireless communication at 560-GHz band using Kerr micro-resonator soliton comb

Terahertz (THz) waves have attracted attention as carrier waves for next-generation wireless communications (6G). Electronic THz emitters are widely used in current mobile communications; however, they may face technical limitations in 6G with upper-frequency limits. We demonstrate wireless communication in a 560-GHz band by using a photonic THz emitter based on photomixing of a 560-GHz-spacing soliton microcomb in a uni-travelling carrier photodiode together with a THz receiver of Schottky barrier diode. The on-off keying data transfer with 2-Gbit/s achieves a Q-factor of 3.4, thus, satisfying the limit of forward error correction.

physics.optics↗

arXiv2022

Low phase noise THz generation from a fiber-referenced Kerr microresonator soliton comb

THz oscillators generated via frequency-multiplication of microwaves are facing difficulty in achieving low phase noise. Photonics-based techniques, in which optical two tones are translated to a THz wave through opto-electronic conversion, are promising if the relative phase noise between the two tones is well suppressed. Here, a THz ($\approx$ 560 GHz) wave with a low phase noise is provided by a frequency-stabilized, dissipative Kerr microresonator soliton comb. The repetition frequency of the comb is stabilized to a long fiber in a two-wavelength delayed self-heterodyne interferometer, significantly reducing the phase noise of the THz wave. A measurement technique to characterize the phase noise of the THz wave beyond the limit of a frequency-multiplied microwave is also demonstrated, showing the superior phase noise of the THz wave to any other photonic THz oscillators (> 300 GHz).

physics.optics↗

arXiv2022

Rapid, high-sensitivity detection of biomolecules using dual-comb biosensing: application to the SARS-CoV-2 nucleocapsid protein

Rapid, sensitive detection of biomolecules is important for improved testing methods for viruses as well as biomarkers and environmental hormones. For example, testing for SARS-CoV-2 is essential in the fight against the COVID-19 pandemic. Reverse-transcription polymerase chain reaction (RT-PCR) is the current standard for COVID-19 testing; however, it is hampered by the long testing process. Shortening the testing process while achieving high sensitivity would facilitate sooner quarantine and thus presumably prevention of the spread of SARS-CoV-2. Here, we aim to achieve rapid, sensitive detection of the SARS-CoV-2 nucleocapsid protein by enhancing the performance of optical biosensing with a dual-comb configuration of optical frequency combs. The virus-concentration-dependent optical spectrum shift is transformed into a photonic RF shift by frequency conversion between the optical and RF regions, facilitating mature electrical frequency measurements. Furthermore, active-dummy temperature-drift compensation enables very small changes in the virus-concentration-dependent signal to be extracted from the large, variable background signal. This dual-comb biosensing technique has the potential to reduce the COVID-19 testing time to 10 min while maintaining sensitivity close to that of RT-PCR. Furthermore, this system can be applied for sensing of not only viruses but also various biomolecules for clinical diagnosis, health care, and environmental monitoring.

q-bio.QM↗

arXiv2021

Thermal control of Kerr microresonator soliton comb via an optical sideband

We report the thermal control of a dissipative Kerr microresonator soliton comb via an optical sideband generated from an electro-optic modulator. Same as the previous reports using an independent auxiliary laser, our sideband-based (S-B) auxiliary light also enables to access a stable soliton comb and to reduce the phase noise of the soliton comb, greatly simplifying the setup with an auxiliary laser. More importantly, because of the intrinsically high frequency/phase correlation between the pump and S-B auxiliary light, the detuning between the pump and resonance frequency is automatically almost fixed, allowing the 18 times larger "effective"soliton existence range than the conventional method using an independent auxiliary laser, as well as the scanning of the soliton comb of more than 10 GHz without using microheaters.

physics.optics↗

arXiv2021

Generation of a microresonator soliton comb via current modulation of a DFB laser

Dissipative Kerr-microresonator soliton combs (hereafter called soliton combs) has been rapidly progressing as compact frequency combs. Comb mode scanning of the soliton combs with a large range and fast speed is of paramount importance for applications such as LiDAR and spectroscopy, requiring large and rapid frequency scanning of a pump continuous-wave (CW) laser as well as resonance frequency of a microresonator. Here, we demonstrate the generation of a soliton comb by a distributed feedback (DFB) laser toward the comb mode scanning with a large range and fast speed. Compared with conventional pump CW lasers (i.e. external cavity diode lasers: ECDLs), DFB lasers can be frequency-scanned more largely and rapidly without mode-hopping. In addition, because of the fast scan speed of the DFB laser, a single soliton comb is generated simply by controlling the injection current of the DFB laser, greatly simplifying the system without having any additional optical modulators such as a carrier-suppressed single-sideband modulator (CS-SSB modulator), acousto-optic modulator (AOM), and auxiliary CW laser.

physics.ins-det↗

arXiv2021

Frequency-scanned microresonator soliton comb with the tracking of the frequency of all comb modes

Rapid and large scanning of a dissipative Kerr-microresonator soliton comb with the characterization of all comb modes along with the separation of the comb modes is imperative for the emerging applications of the frequency-scanned soliton combs. However, the scan speed is limited by the gain of feedback systems and the measurement of the frequency shift of all comb modes has not been demonstrated. To overcome the limitation of the feedback, we incorporate the feedback with the feedforward. With the additional gain of > 40 dB by a feedforward signal, a dissipative Kerr-microresonator soliton comb is scanned by 70 GHz in 500 $μ$s, 50 GHz in 125 $μ$s, and 25 GHz in 50 $μ$s (= 500 THz/s). Furthermore, we propose and demonstrate a method to measure the frequency shift of all comb modes, in which an imbalanced Mach-Zehnder interferometer with two outputs with different wavelengths is used. Because of the two degrees of freedom of optical frequency combs, the measurement at the two different wavelengths enables the estimation of the frequency shift of all comb modes.

physics.optics↗