Single mode fibers are being installed in nearly all communication lines. For the purpose of maintenance and observation of line, data of the installed fiber condition is needed. Distributed temperature sensing for single mode fiber is expected in this field. Special wavelength light sources are necessary to measure the temperature distribution by Raman ratiomelry because of avoiding the single mode fiber's cut-off wavelength Distributed temperature sensing of the single mode fiber is perceived using fiber Raman laser. Fiber Raman laser is pumped by the LD pumped solid state laser source. l400nm pulse light is coupled into a single mode fiber, and the 1320 Anti-Stokes and l500nm Stokes light are detected to calculate the temperature. Temperature accuracy is with the average time of 3mm and maximum measurable range is 3 km.

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The Ti diffusion method is well known for making low-loss waveguides. However, the coupling and bending loss must be reduced for small-scale integration. These losses are mainly attributed to the asymmetric spot of waveguide.1 A symmetric waveguide spot is appropriate for reducing both the coupling and the bending loss. To achieve this, several proposals such as MgO/Ti double diffusion have been made.2 However, there is a trade off between reduction of loss and other switching performances.2

A MgO/Ti bilaterally diffused optical waveguide is proposed. It features controlling the waveguide spot size and strengthening the optical confinement. It is experimentally shown that the coupling loss with single-mode fiber is reduced to 0.6 dB/facet. The bending loss is also suppressed from 2.2 dB of the Ti diffused waveguide to 0.2 dB at a 30-mm bending radius. The performance of the switch using this method is demonstrated. Total insertion loss is 2.6 dB. Driving voltage is 5.6 V with no degradation of the EO effect.

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