| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
1.Brillouin gain spectrum measurement
The output light from a DFB LD operating at 1.55 μm was divided into two light waves with an optical fiber coupler. We shifted the optical frequency of one of them by 10 GHz with a LiNbO_3 optical phase modulator to use it as pump light for Brillouin amplification. Then we modulated the power of the shifted light with an acousto-optic modulator, amplified it by using an erbium-doped fiber amplifier, and launched it into a silica-based optical waveguide under test from its input end. We used the other of the divided light waves as the Stokes light and launched it into the waveguide from its output end. By setting the repetition frequency of the pump pulses at f_P =200 KHz, we could measure the Brillouin gain spectrum of the waveguide, where the ratio of the peak value to the background level in the spectrum was S/N=43.
We irradiated CO_2 laser light onto a 3 mm-long part of the waveguide through the use of a cylindrical lens, where the light was chopp
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ed at f_L=100 Hz. By using a heterodyne detection, we succeeded in measuring the temperature change of the waveguide part during the laser irradiation to be 100℃. Since the increase in temperature changed the Brillouin frequency shift to around 100 MHz while the gain width of the Brillouin amplification was around 10 MHz, we concluded that the induced temperature change was enough to switch the Brillouin amplification on and off at the waveguide part.
We measured the change of Stokes light power at the frequency of f_P + f_L while irradiating the CO_2 laser light onto the waveguide. Although the detected output had a peak at a particular frequency of the LiNbO_3 phase modulator, we could not conclude that we could measure the Brillouin gain spectrum at the irradiated waveguide part only. This was because the peak frequency was varied at repetitive measurements of the gain spectra.
2.Rayleigh backscattering measurement
We constructed a high-sensitivity optical low coherence reflectometer (OLCR) using three optical fiber couplers and an ASE light source. To increase the OLCR sensitivity, we reduced endreflection of the silica-based waveguide under test by polishing its two endfaces at an angle of 8. As the stage of the OLCR translated, we observed the Rayleigh backscatter beat signal so clearly that the S/N was increased to 50. Due to the reduction in endreflection, however, the S/N of the beat signal from a coherent laser operating at 1.3 μm was reduced drastically. Therefore we incorporated a balanced detection circuit operating at 1.3 μm into the OLCR interferometer. The circuit reduced the intensity noise of the laser light so effectively that the S/N of the beat signal at 1.3 μm was increased at 100. Less
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