Study of optical losses of Nd3+ doped silicon rich silicon oxide for laser cavity

Planar and strip-loaded waveguides made of Nd3+-doped silicon rich silicon oxide (SRSO) have been fabricated by reactive magnetron sputtering and characterized, with special emphasis on the optical losses. The refractive index of Nd3+-doped SRSO layers was measured by both m-line method and reflectance spectroscopy. From these measurements, the Si volume fraction and also the Nd3+-doped SRSO index dispersion were deduced by using the Bruggeman model. At 1.06 μm, Nd3+-doped SRSO refractive index was equal to 1.543 corresponding to a Si volume fraction of 6.5%. The opto-geometrical parameters of waveguides have been studied in order to obtain single mode waveguides at 1.06 μm. The optical losses are measured as a function of wavelength and are found to be about 0.8 and 0.4 dB/cm at 1.06 and 1.55 μm, respectively. Measurements are confirmed by theoretical models showing that the losses are essentially attributed to surface scattering. From these optical loss values, a percentage value of the Nd active concentration superior of 14.5% was deduced to have a positive modal gain of waveguide.

► Nd3+-doped silicon rich silicon oxide (SRSO) as planar and strip-loaded waveguides.
► The optical losses are equal to 0.8 and 0.4 dB/cm respectively at 1.06 and 1.55 μm.
► Theoretical models attribute the losses essentially to surface scattering.
► A Nd3+ active concentration superior of 14.5% is needed for positive modal gain.