Mourou and co-workers have proposed that femtosecond laser pulses can be used to induce localized refractive index increase in a wide variety of glasses. Thermally stable optical waveguides were produced  in silicate, borosilicate, chalcogenide and fluoride glasses and, also, more complex structures such as a Y-junction splitter  and long period gratings  have been reported.
We report for the first time, to the best of our knowledge, an active waveguide device directly written using near-IR femtosecond laser pulses. The device is a waveguide amplifier in a Nd-doped silicate glass.
Experimental Details and Discussion:
The material used in this study was a commercially available Nd-doped silicate glass rod. From the measured absorption coefficient of the glass we estimate the Nd doping level to be around 2 x 1020 ions/cm3.
For waveguide fabrication, a Clark-MXR femtosecond workstation operating at 775-nm was used. From throughput measurements of waveguides of lengths varying between 2mm and 10mm we estimate the waveguide propagation losses to be well below 0.5dB/cm. Gain measurements were performed using an Argon-ion pump laser as a source at 514-nm and a signal at 1054-nm provided by a continuous-wave laser. The data on the gain of the amplifier at a signal of 1054-nm is presented in Figure 14.1. (The gain was measured as the ratio between the signal power with the pump turned on and the signal power with the pump turned off.)
Figure 14.1: Small signal gain versus launched pump power
Fluorescence data indicate that the emission cross-section at 1054-nm is only half as large as that at the 1062-nm the peak. Thus this device should provide a peak unsaturated gain of about 3dB/cm for launched pump power levels of about 140 mW.
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