m-line spectroscopy for optical analysis of thick LiNbO3 layers grown on sapphire substrates by radio-frequency multistep sputtering

Abstract

Thick films of lithium niobate (LiNbO3) have been epitaxially grown on sapphire substrates by multistep radio-frequency magnetron sputtering. We have investigated the optical properties of the deposited layers by the m-line spectroscopy technique. The relationship between the film-substrate interface, the surface morphology of the LiNbO3 layer, and the optical measurements has been carefully established. Since this optical technique is sensitive to material defects, a detectable degradation of the optical data is observed when the microstructure of the LiNbO3 film changes. In particular, the angular width of the excited optical guided modes (Δθ) varies with the film thickness. This agrees perfectly with the evolution of the surface roughness as a function of the film thickness. We report a surface roughness rms of 2 nm corresponding to an angular width Δθ of 0.1° for the TE0 mode. The accuracy and the sensitivity of this technique can be advantageously compared to the classical tool of atomic force microscopy.

Influence of substrate temperature on the growth and optical waveguide properties of oriented LiNbO3 thin films

“…Up to now, numerous techniques have been used to deposit LiNbO 3 thin films, including sputtering [2,3], liquid-phase epitaxy (LPE) [4], sol-gel process [5,6], metal organic chemical vapor deposition (MOCVD) [7,8] and pulsed laser deposition (PLD) [9][10][11][12][13]. Among these techniques, PLD has been shown to be very appropriate for the complex oxide films deposition due to its intrinsic feature of easily transferring the target stoichiometry to the substrate.…”

Optical scattering of nanocrystalline Pb(ZrxTi1−x)O3 films

“…Similar correlation between R q values and TE 0 mode widths was also found in rf-sputtered LiNbO 3 films. 19 Sharpest β value was found for film with thickness of 500 nm post-annealed at temperature of 600 • C ( β = 0.0048), which is close to β value of epitaxial BaTiO 3 ( β = 0.0011). 6 For films with high surface roughness (R q > 20 nm) it was not possible to guide light to the film due to large surface scattering.…”

“…Both transverse electric (TE) and transverse magnetic (TM) waves can be exited depending on the crystal properties of the thin films. [17][18][19] In Fig. 3 there are TE 0 guiding modes for a film with thickness of 100 nm post-annealed at a temperature of 600 • C, 150 nm thick films post-annealed at 600 • C and 800 • C, and 500 nm films post-annealed at temperatures of 600 • C, 700 • C, and 800 • C, respectively, showing light coupling in the polycrystalline PNZT thin films.…”

Pulsed laser deposition of Er3+-doped oxyfluoride thin films

“…4(b) the measurements of the optical prism coupling of the film deposited at 10 Pa are presented for different wavelengths. It is seen that a narrowing of the minima increases with increasing wavelength, which is indicative of a reduction of the optical losses [9]. Both absorption and scattering losses decrease with wavelength, therefore it is difficult to resolve the main contribution to the losses.…”