M-line applications

Attenuation coefficient in planar waveguides

Principle

Figure 1 shows the instruments layout of a loss measurement equipment. Waveguide configuration and modes propagation has been achieved using the red line of a He-Ne (632.8 nm) laser by prism coupling. A videocamera recorded a picture of the light propagation streak in the waveguide, sending the image to a computer. To measure the attenuation coefficient in the NIR region (1300 and 1500 nm) light is measured by a fiber probe scanning down the length of the propagating streak directly inside the m-line measurement apparatus.

Power attenuation coefficients for waveguide a can be obtained by an exponential fit of equation:

where z is the distance in the longitudinal direction (in cm) and I(z) is the intensity along the z direction (averaged with respect to the stripe width). This method gives particularly simple and reliable measurements of waveguide loss when the sample are radiation transparent. On the contrary, when substrate reflects (such as the silica-on-silicon substrates) and/or the guide has low transmittance, interference fringes are created into the sample, then reliable data can not be simply obtained but the exponential fit must average on the interference fringes.

SiO₂-GeO₂:Er³⁺-Yb³⁺

Direct writing of grating by Excimer Laser irradiation on Er³⁺/Yb³⁺-doped SiO₂-GeO₂ planar waveguides