Ryozo Yamauchi

A novel temperature-insensitive long-period fiber grating using a boron-codoped-germanosilicate-core fiber

Long-period fiber gratings are promising components as gain equalizers for erbium-doped fiber amplifiers, band rejection filters and sensors. It has been reported that these devices have a high temperature sensitivity, typically 0.05 nm//spl deg/C at room temperature. Judkins et al., showed a method to eliminate the temperature sensitivity by optimizing the refractive-index profile of the host fiber. In this paper, we show a novel method to compensate the temperature sensitivity using a boron codoped germanosilicate core fiber as a host fiber.

Novel long-period fiber grating using periodically released residual stress of pure-silica core fiber

Summary form only given. Long-period fiber gratings (LPFGs) are promising components in optical fiber communications. The LPFG is usually fabricated by photo-refractive effect using an UV-laser or by fiber deformation by local heating methods. In this report, we propose a new technique for fabricating an LPFG by local heating of a pure-silica core fiber to release residual stress of a core without fiber deformation.

Polarization-independent quantum-confined Stark effect in an InGaAs/InP tensile-strained quantum well

We present a theoretical analysis and experimental studies on the control of the polarization-dependent characteristics of the refractive index change and the absorption change due to the quantum-confined Stark effect in an InGaAs/InP quantum-well structure. The polarization dependency which arises from the energy level splitting of heavy-hole and light-hole states in the quantum well can be controlled by inducing an appropriate amount of tensile strain in the quantum well. Measurements were carried out on the polarization dependency of the refractive index change and the absorption change in unstrained, 0.15, 0.3, and 0.45% tensile-strained 11.5-nm-thick InGaAs quantum-well structures through the whole spectral range, i.e., near and below the transition energy. We found that by inducing a 0.3% tensile strain in the 11.5-nm quantum well, the spectral profiles for the transverse electric and the transverse magnetic modes are brought closer to each other, with the peaks of the negative index changes corresponding to both modes occurring at the same wavelength with a slight difference in their absolute values. Moreover, in the long wavelength region, the refractive index change for both modes coincides in the wavelength as well as the absolute value. Based on these results, we have fabricated an absorption modulator and controlled the modulation characteristics with respect to the incident light polarization. >

Polarimetric Strain And Pressure Sensors Using Temperature-Independent Polarization Maintaining Optical Fiber

A polarimetric fiber sensors stabilized against the ambient temperature change has been developed by cancelling the temperature dependence of the intrinsic fiber birefringence with the thermal stress of a multi-layer plastic jacket.

Observation of polarization independent electric field effect in InGaAs/InP tensile strained quantum well and its proposal for optical switch

We have experimentally observed the polarization independent electric field induced absorption coefficient variation in an InGaAs/InP tensile strained quantum well (QW) structure for the first time. We have also found that the field induced absorption coefficient/refractive index variation of strained QW for the transverse electric (TE) mode does not change appreciably from that of an unstrained one. Based on these results, we propose tensile strained QW for polarization independent optical switch/modulator.

Length dependence of bandwidth for fibers with random-axial profile fluctuations

Length dependence of bandwidth for graded-index optical fibers with random-axial profile fluctuations is investigated theoretically in connection with optical equalization in long spliced fibers. Based on the statistical approach, a simple analytical formula is derived on the assumption that the profile fluctuation does not cause mode coupling. At a short distance, the bandwidth has been found to be inversely proportional to square root of distance due to the profile fluctuation. The length dependence presents a remarkable contrast to that of the mode-coupling case showing the same dependence at a long distance.

Effect of spectral-hole burning on multi-channel EDFA gain profile

We show that a spectral gain profile of a multichannel erbium-doped fiber amplifier (EDFA) changes associated with the change in multichannel location, which is well described by a summation of hole burning caused by each signal.

Design and performance of Gaussian-profile dispersion-shifted fibers manufactured by VAD process

Design and manufacturing of dispersion-shifted fibers with a Gaussian profile, which is compatible to the VAD process, are studied. From the viewpoint of stable cabling, the parametric analysis is made with emphasis on the bending loss. To make the bending sensitivity of the Gaussian core fibers comparable with the conventional 1.3- μm zero-dispersion fibers, an 0.8 percent or higher index difference is required. In the experiment, the achieved loss at the 1.55-μm dispersionless wavelength is 0.21 dB/km. The effects of a ring profile around the Gaussian core on the fiber transmission characteristics also are examined. While the cutoff wavelengths are greatly lengthened by the ring, the bending sensitivity is not so affected. It is found that the index difference of the main core still dominates the bending loss of the fiber.

Bending loss evaluation of single-mode fibres with arbitrary core index profile by far-field pattern

An evaluation of the bending loss of single-mode fibers based on the measured mode field is described. The field decay constant and the normalized field intensity in the cladding are determined. Experimental results verified the validity of this method. Its accuracy is determined by the accuracy of field measurement. The mode field is calculated from the far-field distribution measured with finite dynamic range of more than 50 dB. Far-field measurement with finite dynamic range limits the accuracy of field evaluation. Dispersion shifted fibers are easier for evaluation because of the wider far-field distribution. Bending loss and mode field diameter can be measured simultaneously, and the method is applicable to any single-mode fibers with a matched clad structure. A microbending loss formula is also determined by the decay constant and the normalized field intensity in the cladding as well as uniform bending loss. >

Thin Film Magneto-Impedance Sensor Integrated Into

A linear magneto-impedance (MI) sensor integrated into a FePt thin film bias magnet which has in-plane isotropic magnetic property was investigated. The maximal bias field of 13.1 Oe was obtained after magnetizing a 1.3-mum thick FePt film in longitudinal direction of the sensor element. The bias field changed with the magnetizing angle. By controlling the angle in the magnetizing direction of the bias magnet and sensing direction, it was shown to be able to adjust the effective bias field after fabrication of the sensor element.