When few-mode fibers are employed in mode-division multiplexing (MDM), mode coupling between the propagation modes must be suppressed. In this study, the impulse response for a two-mode fiber (TMF) ...is theoretically described to estimate the mode coupling in the fiber and at a splice point. We then propose a technique for measuring the mode-coupling coefficient in a TMF based on the impulse response technique. The mode-coupling behavior in a fiber and at splice points is measured experimentally using the proposed technique for several fabricated TMFs. We clarify the relationship between the effective-index difference Δ n eff between LP 01 and LP 11 modes and the mode-coupling coefficient h for our fabricated TMFs.
Photoluminescence provides information about the surrounding environment. In this study, aiming to develop a non-invasive deep body-temperature sensing method, we investigated photoluminescence ...properties of afterglow zirconia (ZrO
) by pulsed near-infrared (NIR) light irradiation based on the biological temperature. Pulsed light irradiation produced optically stimulated luminescence, followed by afterglow, with the property of repeating 100 times or more. Furthermore, the basic principle of temperature measurement was demonstrated through afterglow decay curve measurements. The use of harmless ZrO
as a sensing probe and NIR light, which is relatively permeable to living tissues, is expected to realize temperature measurements in the brain and may also facilitate optogenetic treatment.
Development of minimally invasive and site-selective biological temperature sensing is quite important in medical field. This study presents a novel temperature sensing technique based on afterglow ...and optically-stimulated luminescence (OSL). The dependence of afterglow photoluminescent intensity on the environmental temperature of zirconia (ZrO
) phosphor is examined to validate its use as a sensing probe. In addition, assuming the measurement in deep-part of human body, we have applied the information gathered from our validation to observe OSL from the ZrO
by irradiation with near-infrared laser through a bone sample. This study demonstrates an alternative medical application of phosphor, and introduces an elemental-technology for the temperature sensing.
We provide the differential group delay (DGD) and chromatic dispersion for the fundamental and first higher order modes traversing a large-core few-mode photonic crystal fiber (PCF). The modal ...interferometer method is used to measure the DGD and chromatic dispersion for the fundamental mode at a wavelength of ~1300 nm and in the 1450-1625-nm telecommunication band. The combined measurement of the DGD and chromatic dispersion makes it possible to obtain the chromatic dispersion of the higher order mode. The chromatic dispersion diagnosis for the two modes is discussed. In the 1450-1625-nm band, the results obtained experimentally for the two modes exactly match those obtained from the empirical relations for PCF dispersion.
A novel technique is proposed for measuring the longitudinal fiber parameters of multi-core fiber (MCF). The mode field diameter (MFD)of a fiber link composed of MCF is successfully estimated with a ...modified optical time domain reflectometer (OTDR). The measurement accuracy of the MFD distribution is revealed by simulation as a function of the mode coupling coefficient. It is also shown that the relative-index difference and chromatic dispersion of MCF can be estimated with the present technique.
In the mechanically induced long‐period fiber grating (MLPFG) fabricated by applying the periodical pressure on an optical fiber, the small bending occurs due to the periodical pressure, which ...influences the losses of the core and cladding modes. We propose the theoretical model of the MLPFG for estimating its transmittance based on the transfer matrix method and investigate the effect of the losses of the core and cladding modes in the MLPFG on the transmittance, theoretically and experimentally. We numerically clarify that the transmitted light spectrum of MLPFG shows only the main attenuation lobe, no side lobe, and the attenuation bandwidth is broadened as the cladding mode loss increases. We also clarify that the coupling coefficient, and the losses of the core and cladding modes in the fabricated MLPFG can be estimated from the measured transmitted spectrum based on our model. Moreover, we measure the transmittance of two types of MLPFGs that fabricated with a screw, weights, and metallic plates, and that fabricated with a screw and a heat‐shrinkable tube. The measured spectra show good agreements with the calculated ones using our model. Our model will be useful for designing MLPFGs applied to the sensors.
► Novel temperature-sensitive mechanical long period fiber grating (LPFG) is proposed. ► Thermal characteristics of LPFG can be controlled by using different kind of tube. ► The temperature ...characteristics of the LPFG is investigated experimentally. ► Its resonance losses and resonance wavelengths strongly depended on temperature. ► The thermal coefficients of resonance wavelength shift were more than 0.13nm/°C.
A novel temperature-sensitive mechanical long period fiber grating (LPFG) fabricated utilizing the photo-elastic effect is proposed. Our proposed LPFG consists of a telecommunication optical fiber, a metric screw, and the heat-shrinkable tube, which are commercially available. The heat-shrinkable tube and the metric screw are used to obtain the grating along the single-mode fiber. The gratings are achieved by pressing the optical fiber between the heat-shrinkable tube and the metric screw due to the contractive force of its tube. By changing the temperature, the resonance loss is tuned due to the thermal expansion of the heat-shrinkable tube. Operating mechanism of thermally tunable characteristics of our LPFG are also described from a viewpoint of the coupling coefficient.
The mode field diameter (MFD) is an essential parameter for understanding the transmission characteristics of optical fibers. A variable aperture (VA) technique is a standard test method for ...measuring the MFD of single-mode fibers. Unfortunately, the conventional one cannot measure the MFDs of some higher-order modes correctly because its measurement procedure is standardized for measuring the MFD of the fundamental mode. The conventional VA technique aligns the position of the optical fiber through a peak intensity search on the premise that the fundamental mode, whose intensity is maximum at the beam center, is measured. How to align the position of the optical fiber when measuring the MFD of higher-order modes has not yet been investigated. In this paper, we describe the principle and formulas based on the VA technique for measuring the MFD of a given higher-order mode in few-mode fibers (FMFs). Then, we propose a novel procedure for measuring the MFDs of FMFs. The test apparatus of our technique is almost the same as that of the conventional VA technique except for the use of a mode selective coupler. One can measure the MFDs of arbitrary modes in FMFs correctly by adjusting the position of the fiber under test using the fundamental mode before starting the measurement. Proof-of-principle experiments were performed for three kinds of FMFs, and the experimental results showed that our procedure is useful for characterizing the MFD of each mode.
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