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Author

Shuji Taue

Other affiliations: Okayama University
Bio: Shuji Taue is an academic researcher from Kochi University of Technology. The author has contributed to research in topics: Optical fiber & Fiber optic sensor. The author has an hindex of 9, co-authored 36 publications receiving 176 citations. Previous affiliations of Shuji Taue include Okayama University.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a simple, high-sensitivity optical-fiber temperature sensor based on multimode interference (MMI) was developed. But it is not suitable for outdoor applications.
Abstract: We have developed a simple, high-sensitivity optical-fiber temperature sensor based on multimode interference (MMI). The fabricated MMI structure comprises three segmented fibers: a single-mode fiber (SMF); a large-core multimode fiber (MMF), whose outer surface is coated with a temperature-sensitive material; and another SMF. Fluoroacrylate and silicone rubber are tested as temperature-sensitive cladding materials. The silicone rubber coating exhibits a large shift in interference wavelength with temperature, producing a very fine temperature resolution as low as 0.01 °C.

26 citations

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TL;DR: In this article, a fiber-based multimode interference phenomenon in the wavelength domain was investigated by using a white light source and an optical spectrum analyzer, where the interference wavelengths were blue-shifted and the interference signals were sharpened with an increase in the length of the larger core fiber.
Abstract: We investigated a fiber-based multimode interference phenomenon in the wavelength domain by using a white light source and an optical spectrum analyzer. This phenomenon was produced by a larger-core optical fiber joined at both ends with smaller-core optical fibers. We examined the variation of interference wavelength with changes in the length of the larger-core fiber. The interference wavelengths were blue-shifted and the interference signals were sharpened with an increase in the length of the larger-core fiber. The calculated results agreed well with the measured results. Next, we investigated how the input and output fibers with a small core influence the interference signal characteristics. By comparing the amplitude differences of the interference signal we find the conditions of input and output (I/O) fibers for higher sensitivity. In addition, an interference-signal shift was observed by changing the medium surrounding an multimode interference (MMI) structure. The amount of shift increased at a longer wavelength. This leads to the sensitive detection of the refractive index. Finally, a demonstration of the optical fiber refractometer with a multimode interference structure was given by refractive-index measurements of ethanol/water solutions.

25 citations

Journal ArticleDOI
TL;DR: In this paper, a coherent link between the optical and radio frequencies is proposed to enable high-precision refractive index measurement based on frequency measurement in radio-frequency (RF) region.
Abstract: Optical frequency combs (OFCs) have attracted attention as optical frequency rulers due to their tooth-like discrete spectra together with their inherent mode-locking nature and phase-locking control to a frequency standard. Based on this concept, their applications until now have been demonstrated in the fields of optical frequency metrology. However, if the utility of OFCs can be further expanded beyond their application by exploiting new aspects of OFCs, this will lead to new developments in optical metrology and instrumentation. Here, we report a fiber sensing application of OFCs based on a coherent link between the optical and radio frequencies, enabling high-precision refractive index measurement based on frequency measurement in radio-frequency (RF) region. Our technique encodes a refractive index change of a liquid sample into a repetition frequency of OFC by a combination of an intracavity multi-mode-interference fiber sensor and wavelength dispersion of a cavity fiber. Then, the change in refractive index is read out by measuring the repetition frequency in RF region based on a frequency standard. Use of an OFC as a photonic RF converter will lead to the development of new applications in high-precision fiber sensing with the help of functional fiber sensors and precise RF measurement.

24 citations

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TL;DR: In this article, the authors theoretically and experimentally studied the change in the bandwidth and amplitude of the signal response of an optically pumped atomic magnetometer, considering the effect of the attenuation of a pump beam inside a cell.
Abstract: Recently developed ultrasensitive optically pumped atomic magnetometers are promising for biomagnetic measurements such as magnetoencephalograms and magnetocardiograms. The magnetometer's bandwidth and amplitude of signal response are important factors for biomagnetic measurements. These factors depend on various operating parameters such as power density and wavelengths of laser beams. By focusing on the transverse spin relaxation time, we theoretically and experimentally studied the change in the bandwidth and amplitude of the signal response. By considering the effect of the attenuation of a pump beam inside a cell, we showed good agreement between theoretical and experimental results. Furthermore, the magnetometer's integrated performances for the factors were evaluated by changing the power density of the pump beam. Measured data indicated that the bandwidth of signal response depended on the power density of the pump beam and that the bandwidth could be tuned to a desirable frequency range.

19 citations

Journal ArticleDOI
TL;DR: In this paper, a coherent frequency link between the optical and radio-frequency regions, enabling high-precision refractive index measurement of a liquid sample based on frequency measurement in radio frequency region is presented.
Abstract: Optical frequency combs have attracted attention as optical frequency rulers due to their tooth-like discrete spectra together with their inherent mode-locking nature and phase-locking control to a frequency standard. Based on this concept, their applications until now have been demonstrated in the fields of optical frequency metrology and optical distance metrology. However, if the utility of optical combs can be further expanded beyond their optical-frequency-ruler-based application by exploiting new aspects of optical combs, this will lead to new developments in optical metrology and instrumentation. Here, we report a fibre sensing application of optical combs based on a coherent frequency link between the optical and radio-frequency regions, enabling high-precision refractive index measurement of a liquid sample based on frequency measurement in radio-frequency region. Our technique encodes a refractive index change of a liquid sample into a radio-frequency comb by a combination of an intracavity multi-mode-interference fibre sensor and wavelength dispersion of a cavity fibre. Then, the change in refractive index is read out by measuring the repetition frequency of the radio-frequency comb with a frequency counter and a frequency standard. Use of an optical comb as a photonic radio-frequency converter will lead to the development of new applications in high-precision fibre sensing with the help of functional fibre sensors and precise radio-frequency measurement.

19 citations


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TL;DR: In this article, the authors present a comprehensive textbook on general relativity with a focus on more advanced and modern subjects that will prepare the student to start doing research in the area of general relativity.
Abstract: radar echo delay, black holes and gravitational waves. It is worth pointing out that even here the author goes beyond a mere introduction, for example in the analysis of the phase diagram of cosmological parameters, the calculation of the first acoustic peak in the spectrum of the cosmic microwave background, the discussion of the precession of gyroscopes, the utilisation of Penrose diagrams to understand the causal structure of spacetime and the study of rotating black holes. Gravitational lensing, despite its important role in modern astronomy, is not covered at all. After just under 600 pages, the reader is already well versed in general relativity and many of its most important applications. Where many other textbook authors would have stopped, Zee goes on and continues with more advanced and modern subjects that will prepare the student to start doing research in the area. Maximally symmetric spaces, the vielbein formalism, conformal algebra, de Sitter and anti de Sitter spacetime, Kaluza– Klein theory, brane worlds, topological field theory and twistors are some of the more exotic topics the author addresses. These chapters make Zee’s book incredibly worthwhile, since treatments at the undergraduate level of these subjects hardly exist. All in all, Zee succeeded to write a unique textbook on general relativity. His narrative is exciting and well structured, but he also does not shy away from computations when they are necessary. The logical steps in attacking a problem are always presented very transparently, making it easier for the novice to become familiar with the material. The book is beautifully typeset and richly illustrated. It contains exercises at the end of each chapter and solutions to selected exercises in the appendix, together with a detailed index and a collection of important formulae. I strongly recommend this book to anyone interested in understanding general relativity.

299 citations

Journal ArticleDOI
TL;DR: A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion-spliced between two SMS fibers as mentioned in this paper.
Abstract: A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion- spliced between two SMS fibers. The mechanism underpinning the operation of an SMS fiber structure is multimode interference and associated self-imaging. SMS structures can be used in a variety of optical fiber systems but are most commonly used as sensors for a variety of parameters, ranging from macro-world measurands such as temperature, strain, vibration, flow rate, RI and humidity to the micro-world with measurands such as proteins, pathogens, DNA and specific molecules. While traditional SMS structures employ a short section of standard multimode fiber, a large number of structures have been investigated and demonstrated over the last decade involving the replacement of the multimode fiber section with alternatives such as a hollow core fiber or a tapered fiber. The objective of replacing the multimode fiber has most often been to allow sensing of different measurands or to improve sensitivity. In this paper, several different categories of SMS fiber structures, including traditional SMS, modified SMS and tapered SMS fiber structures are discussed with some theoretical underpinning and reviews of a wide variety of sensing examples and recent advances. The paper then summarizes and compares the performances of a variety of sensors which have been published under a number of headings. The paper concludes by considering the challenges faced by SMS based sensing schemes in terms of their deployment in real world applications and discusses possible future developments of SMS fiber sensors.

80 citations

Journal ArticleDOI
TL;DR: In this article, an optically pumped atomic magnetometer (OPAM) with a pump-probe arrangement and potassium used as the sensing atom was used to measure human magnetocardiograms (MEGs).
Abstract: In the field of biomagnetic measurements, optically pumped atomic magnetometers (OPAMs) are expected to be alternative sensors to magnetometers based on superconducting quantum interference devices (SQUIDs). In addition, miniaturized OPAMs are required for practical use. To address this issue, we developed a compact module of a high-sensitivity OPAM with a pump–probe arrangement and potassium used as the sensing atom. Because the noise spectrum density of the OPAM reached 21 fTrms/Hz1/2 at 10 Hz, we attempted to use it to measure human magnetocardiograms (MEGs). Compared with the results obtained with SQUID-based magnetometers, we could successfully observe distinct features of event-related desynchronization in the 8–13 Hz band associated with eye opening. The results demonstrate the feasibility of using the OPAM module for neuromagnetic field measurements.

58 citations

Journal ArticleDOI
TL;DR: In this paper, an optically pumped atomic magnetometer using a hybrid cell of potassium and rubidium atoms was demonstrated to yield high sensitivity to magnetic fields and the dependence of the sensitivity on the power densities of the pump and probe beams and the wavelength of the probe beam.
Abstract: An optically pumped atomic magnetometer using a hybrid cell of potassium and rubidium atoms was demonstrated to yield high sensitivity to magnetic fields. We operated the magnetometer with the four possible combinations of optically pumped and optically probed atoms and found that the combination of optically pumped potassium and optically probed rubidium showed the highest sensitivity among the four combinations because the rubidium atoms were denser than those of potassium. Furthermore, we investigated the dependence of the sensitivity on the power densities of the pump and probe beams and the wavelength of the probe beam. The magnetometer using the hybrid cell required higher pump-beam power and had narrower magnetic linewidth than those of the single alkali-metal cell. However, the magnetic linewidth was larger than the theoretical value, ignoring the spin relaxation caused by the spin-exchange collisions. By adjusting the laser conditions, the highest sensitivity approached 30 fTrms/Hz1/2.

49 citations