We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable to compensate DMD in wide wavelength range. All fabricated TMFs composed of a graded index core and a depressed inner claddings have low DMD slopes of less than |0.15| ps/km/nm, low optical loss of less than 0.21 dB/km for LP<sub>01</sub> and LP<sub>11</sub> modes respectively and low mode coupling ratio of less than -35 dB at the wavelength of 1550 nm. All TMFs have the similar effective area of 120 μm<sup>2</sup> for LP<sub>01</sub> mode and 160 μm<sup>2</sup> for LP<sub>11</sub> mode at 1550 nm. Moreover, it is clarified that a DMD compensation transmission line composed of the fabricated TMFs can successfully achieve the DMD of below |4.0| ps/km in the C+L band and mode conversion ratio of less than -30 dB at splice points.
We propose a new structure of optical fiber temperature sensor with cascaded long-period fiber gratings (LPFGs) and
investigate the temperature dependent loss of cascaded LFPGs. Each of the cascaded LPFGs has the same resonance
wavelength with the same temperature change, because the cascaded LPFGs are made of a heat-shrinkable tube and a
screw. The total resonance loss of proposed cascaded LPFGs shows higher temperature sensitivity than that of a single
LPFG. The thermal coefficient of 4-cascaded LPFG also shows more than 4 times larger than that of a single one.
We propose a compact water depth sensor with a long period fiber grating (LPFG) using a heat-shrinkable tube. The
pressure property of the LPFG is investigated experimentally to confirm the feasibility of the water depth sensor.
Moreover, the water depth in the 2m long water-filled pipe is successfully estimated by the proposed water sensors.
We propose a fiber-optic temperature sensing method based on a long period fiber grating induced by a heat-shrinkable
tube and a metric screw. Our proposed technique employs the relationship between temperature and LPFG insertion loss,
and we estimate the loss change using an OTDR.
Simple technique is proposed for measuring distributed Raman gain efficiency spectrum in a single-mode fiber based on
the bidirectional OTDR. The Raman gain efficiency spectra are successfully estimated easily from the relative-index
difference and wavelength dependence of the mode field radius (MFR).
A simple technique for measuring fiber parameter distribution of the pure silica core fiber using a conventional OTDR is
proposed. This technique is based on the relationships among fiber parameters and the bidirectional OTDR technique.
The fiber parameter distributions are successfully evaluated for a silica core fiber link.