We observed residual stress relaxation by ${\mathrm{CO}}_2$ laser irradiation in the cores of optical fibers by direct stress measurement. It was demonstrated that the mechanical stress was fully relaxed by ${\mathrm{CO}}_2$ laser irradiation and that the remaining stress in the core was thermal stress that was due to a mismatch of the thermal expansion coefficients of the fiber core and cladding. The net core stresses after relaxation were 17, 68, and 203 MPa in Ge–B-codoped fibers drawn at 0.53, 1.38, and 3.48 N, respectively. Changes in the refractive indices of the cores as a result of residual stress relaxation were also estimated.

The large temperature sensitivity of the Sagnac loop interferometer based on the birefringent holey fiber filled with metal indium was experimentally demonstrated. The temperature sensitivities of the wavelength shift of the interferometer and the birefringence the fiber with indium were measured to be -6.3 nm/K and -3.3×10^-6 /K, respectively. The large temperature sensitivity of the fiber was explained by introduction of the fiber birefringence change originated from the large thermal expansion property of the metal indium at the elevated temperature.

We have experimentally developed a highly sensitive and a compact size current sensor by using the CdSe quantum dots-doped bend insensitive optical fiber, operating in the visible band of wavelength. The modified sensitivity of this sensor was about 675 μrad/(Turn.A.m) for the loop radius of just 10 mm, which is more than 16 times larger than that of the single mode optical fiber current sensor.

The effect of CO₂ laser irradiation on the refractive-index change in optical fibers is investigated by measuring the interference fringe shift formed by a long-period fiber grating pair. The refractive-index decrease on CO₂ laser irradiation was due to relaxation of the residual stress, which was formed in optical fibers during the drawing process, and the refractive-index decrease was found to increase linearly with the drawing force. The effect of the CO₂ laser output power on residual-stress relaxation, and fiber elongation was also studied.

Er³⁺-doped K-Ca-Al fluorophosphate glasses were prepared by melt quenching technique and their thermal and optical properties were studied. The thermal stability factor was obtained to be 131 °C. The gain bandwidth, lifetime and quantum efficiency of the ⁴I_13/2→⁴I_15/2 transition were found to be 96.14 × 10⁻²⁷ cm³, 5.41 ms and 61%, respectively for 1.0 mol% Er₂O₃-doped glass. The quenching concentration has been evaluated (Q = 2.30 mol%) and found to be higher compared to other reported glasses. These results clearly indicate that present glasses are suitable for laser as well as optical amplifiers in the 1.53 μm region.

We firstly report on the fabrication of Cu²⁺ -doped germano-silicate glass fiber for nonlinear optical devices application by using modified chemical vapor deposition and solution doping processes. Broadband absorption near 700nm due to the 3d-shell electron transitions of Cu²⁺ ions from the ground state to the excited states was observed. The resonant nonlinearity of the Cu²⁺-doped fiber was estimated to be 5.5×10^-17m²/W by measuring the phase shift of the fringes obtained from the long-period fiber grating pair upon pumping with a laser diode at 980nm and non-resonant nonlinearities were also measured to be 4.114×10^-21m²/W by the continuous wave self-phase modulation method.