arXiv subjects

Takeo Minamikawa

Publications and source records attributed to Takeo Minamikawa.

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↗

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

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↗

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↗

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↗

arXiv2022

Plasmon-molecule remote coupling via column-structured silica layer for enhancing biophotonic analysis

We demonstrated remote plasmonic enhancement (RPE) by a dense random array of Ag nanoislands (AgNIs) that were partially gold-alloyed and attached with column-structured silica (CSS) overlayer of more than 100 nm in thickness. The physical and chemical protection of the CSS layer could lead to reducing the mutual impact between analyte molecules and metal nanostructures. RPE plate was realized just by sputtering and chemical immersion processes, resulting in high productivity. We found a significant enhancement on the order of 10$^7$-fold for Raman scattering and 10$^2$-fold for fluorescence by RPE even without the proximity of metal nanostructures and analyte molecules. We confirmed the feasibility of RPE for biophotonic analysis. RPE worked for dye molecules in cells cultured on the CSS layer, enabling the enhanced fluorescence biosensing of intracellular signaling dynamics in HeLa cells. RPE also worked for biological tissues, enhancing Raman histological imaging of esophagus tissues with esophageal adventitia of a Wistar rat attached atop the CSS layer. We also investigated the wavelength dependency of RPE on the on- or off-resonant with the dye molecular transition dipoles with various molecular concentrations. The results suggested that the RPE occurred by remote resonant coupling between the localized surface plasmon of AgNIs and the molecular transition dipole of the analyte via the CSS structure. The RPE plate affords practical advantages for potential biophotonic analyses such as high productivity and biocompatibility. We thus anticipate that RPE will advance to versatile analytical tools in chemistry, biology, and medicine.

physics.optics↗

arXiv2020

Computationally image-corrected dual-comb microscopy with a free-running single-cavity dual-comb fiber laser

Dual-comb microscopy (DCM), an interesting imaging modality based on the optical-frequency-comb (OFC) mode and image pixel one-to-one correspondence, benefits from scan-less full-field imaging and simultaneous confocal amplitude and phase imaging. However, the two fully frequency-stabilized OFC sources requirement hampers DCM practicality due to the complexity and costs. Here, a bidirectional single-cavity dual-comb fiber laser (SCDCFL) is adopted as a DCM low-complexity OFC source. Computational image correction reduces the image blur caused by the SCDCFL residual timing jitter. Nanometer-order step surface profilometry with a 14.0 nm uncertainty highlights the image-corrected DCM effectiveness. The proposed method enhances the DCM versality and practicality.

physics.optics↗

arXiv2020

Scan-less full-field fluorescence-lifetime dual-comb microscopy using two-dimensional spectral mapping and frequency multiplexing of dual-optical-comb beats

Fluorescence lifetime imaging microscopy (FLIM) is a powerful tool for quantitative fluorescence imaging because fluorescence lifetime is independent of concentration of fluorescent molecules or excitation/detection efficiency and is robust to photobleaching. However, since FLIM is based on point-to-point measurements, mechanical scanning of a focal spot is needed for forming an image, which hampers rapid imaging. In this article, we demonstrate scan-less full-field FLIM based on a one-to-one correspondence between two-dimensional (2D) image pixels and frequency-multiplexed RF signals. A vast number of dual-optical-comb beats between dual optical frequency combs is effectively adopted for 2D spectral mapping and high-density frequency multiplexing in radio-frequency region. Bimodal images of fluorescence amplitude and lifetime are obtained with high quantitativeness from amplitude and phase spectra of fluorescence RF comb modes without the need for mechanical scanning. The proposed method will be useful for rapid quantitative fluorescence imaging in life science.

physics.optics↗

arXiv2020

Optical image amplification in dual-comb microscopy by use of optical-fiber-amplified interferogram

Dual-comb microscopy (DCM), based on a combination of dual-comb spectroscopy (DCS) with two-dimensional spectral encoding (2D-SE), is a promising method for scan-less confocal laser microscopy giving an amplitude and phase image contrast with the confocality. However, signal loss in a 2D-SE optical system hampers increase in image acquisition rate due to decreased signa-to-noise ratio. In this article, we demonstrated optical image amplification in DCM with an erbium-doped fiber amplifier (EDFA). Combined use of image-encoded DCS interferogram and EDFA benefits from not only the batch amplification of amplitude and phase images but also significant rejection of amplified spontaneous emission (ASE) background. Effectiveness of the optical-image-amplified DCM is highlighted in the single-shot quantitative nanometer-order surface topography and the real-time movie of polystyrene beads dynamics under water convection. The proposed method will be a powerful tool for real-time observation of surface topography and fast dynamic phenomena.

physics.optics↗

arXiv2019

Comb-mode-resolved adaptive sampling terahertz dual-comb spectroscopy with a free-running single-cavity fiber laser

Mode-resolved dual-comb spectroscopy (DCS) is an emerging spectroscopic tool with the potential to simultaneously achieve a broad spectral coverage and ultrahigh spectral resolution in terahertz (THz) spectroscopy. However, the need for two independently stabilized ultrafast lasers significantly hampers the potential application of DCS techniques. In this article, we demonstrate mode-resolved DCS in the THz region based on a free-running single-cavity dual-comb fiber laser with adaptive sampling. Low-pressure spectroscopy of acetonitrile gas with absorption features approaching the Doppler limit is demonstrated by comb-mode-resolved measurements with a spectral sampling spacing of 48.8 MHz, a spectral resolution of less than 5 MHz and a signal-to-noise ratio of ~50 dB. The successful demonstration of the proposed method clearly indicates the great potential for the realization of low-complexity, MHz-resolution THz spectroscopy instrumentation.

physics.ins-det↗

arXiv2019

Refractive index sensing with temperature compensation by a multimode-interference fiber-based optical frequency comb sensing cavity

We proposed a refractive index (RI) sensing method with temperature compensation by using an optical frequency comb (OFC) sensing cavity employing a multimode-interference (MMI) fiber, namely, the MMI-OFC sensing cavity. The MMI-OFC sensing cavity enables simultaneous measurement of material-dependent RI and sample temperature by decoding from the comb spacing frequency shift and the wavelength shift of the OFC. We realized the simultaneous and continuous measurement of RI-related concentration of a liquid sample and its temperature with precisions of 1.6*10^-4 RIU and 0.08 degree. The proposed method would be a useful means for the various applications based on RI sensing.

physics.app-ph↗

arXiv2019

Lock-in-detection dual-comb spectroscopy

Dual-comb spectroscopy (DCS) is useful for gas spectroscopy due to high potential of optical frequency comb (OFC). However, fast Fourier transform (FFT) calculation of a huge amount of temporal data spends significantly longer time than the acquisition time of an interferogram. In this article, we demonstrate frequency-domain DCS by a combination of DCS with lock-in detection, namely LID-DCS. LID-DCS directly extracts an arbitrary OFC mode from a vast number of OFC modes without the need for FFT calculation. Usefulness of LID-DCS is demonstrated in rapid monitoring of transient signal change and spectroscopy of hydrogen cyanide gas.

physics.optics↗

arXiv2018

Multicascade-linked synthetic wavelength digital holography using an optical-comb-referenced frequency synthesizer

Digital holography (DH) is a promising method for non-contact surface topography because the reconstructed phase image can visualize the nanometer unevenness in a sample. However, the axial range of this method is limited to the range of the optical wavelength due to the phase wrapping ambiguity. Although the use of two different wavelengths of light and the resulting synthetic wavelength, i.e., synthetic wavelength DH, can expand the axial range up to a few tens of microns, this method is still insufficient for practical applications. In this article, a tunable external cavity laser diode phase-locked to an optical frequency comb, namely, an optical-comb-referenced frequency synthesizer, is effectively used for multiple synthetic wavelengths within the range of 32 um to 1.20 m. A multiple cascade link of the phase images among an optical wavelength (= 1.520 um) and 5 different synthetic wavelengths (= 32.39 um, 99.98 um, 400.0 um, 1003 um, and 4021 um) enables the shape measurement of a reflective millimeter-sized stepped surface with the axial resolution of 34 nm. The axial dynamic range, defined as the ratio of the maximum axial range (= 0.60 m) to the axial resolution (= 34 nm), achieves 1.7*10^8, which is much larger than that of previous synthetic wavelength DH. Such a wide axial dynamic range capability will further expand the application field of DH for large objects with meter dimensions.

physics.app-ph↗

arXiv2018

Label-free evaluation of myocardial infarct in surgically excised ventricular myocardium by Raman spectroscopy

Understanding the viability of the ischemic myocardial tissue is a critical issue in determining the appropriate surgical procedure for patients with chronic heart failure after myocardial infarction (MI). Conventional MI evaluation methods are; however, preoperatively performed and/or give an indirect information of myocardial viability such as shape, color, and blood flow. In this study, we realize the evaluation of MI in patients undergoing cardiac surgery by Raman spectroscopy under label-free conditions, which is based on intrinsic molecular constituents related to myocardial viability. We identify key signatures of Raman spectra for the evaluation of myocardial viability by evaluating the infarct border zone myocardium that were excised from five patients under surgical ventricular restoration. We also obtain a prediction model to differentiate the infarcted myocardium from the non-infarcted myocardium by applying partial least squares regression-discriminant analysis (PLS-DA) to the Raman spectra. Our prediction model enables identification of the infarcted tissues and the non-infarcted tissues with sensitivities of 99.98% and 99.92%, respectively. Furthermore, the prediction model of the Raman images of the infarct border zone enabled us to visualize boundaries between these distinct regions. Our novel application of Raman spectroscopy to the human heart would be a useful means for the detection of myocardial viability during surgery.

physics.med-ph↗