Analysis and optimization of propagation losses in LiNbO3 optical waveguides produced by swift heavy-ion irradiation

Abstract

The propagation losses (PL) of lithium niobate optical planar waveguides fabricated by swift heavy-ion irradiation (SHI), an alternative to conventional ion implantation, have been investigated and optimized. For waveguide fabrication, congruently melting LiNbÜ3 substrates were irradiated with F ions at 20 MeV or 30 MeV and fluences in the range 10 13 -10 14 cm . The influence of the temperature and time of post-irradiation annealing treatments has been systematically studied. Optimum propagation losses lower than 0.5 dB/cm have been obtained for both TE and TM modes, after a two-stage annealing treatment at 350 and 375°C. Possible loss mechanisms are discussed.

Phase transformations inLn2O3materials irradiated with swift heavy ions

“…This highly transient, nanometric energy deposition can produce unique structural changes in insulating materials, including the formation of defects 7,8 , polymorphic phase transformations 9,10 , amorphization 11,12 , chemical decomposition 13,14 , and irreversible deformations 15,16 . These irradiation-induced modifications are useful for the engineering of nanostructures [17][18][19][20] , the tailoring of optoelectronic properties 21 , and the simulation of damage to materials from particles of similar mass and energy, such as nuclear fission fragments 22 and cosmic rays 23 .…”

Low loss optical waveguides fabricated in LiTaO3 by swift heavy ion irradiation

“…Unfortunately, we have found at this stage the somehow surprising result that, increasing the annealing temperature above some 250-300 °C, produces worse results, due to the appearance of some cracks, probable due to the relaxation of accumulated strains. This does not happens in the equivalent LN waveguides produced by F ion irradiation where annealing in the range 300-350 °C still reduced optical losses [19,20]. It is timely to cite here various works on damage induced in LT by low energy Ar implantation (i.e.…”

“…Interestingly, the use of buried damaged layers produced by ion implantation have been found to be good for producing easier, better and smaller domain reversal patterning in LN with nanometer sizes [16][17][18] Recently, the use of irradiations with heavier ions (i.e. A > 10) at higher energies (≥ 1 MeV/amu, also called swift heavy ions or SHI) such that the maximum electronic energy loss (or stopping power, Se) takes place some microns underneath the surface, has been proposed for fabricating good and novel optical waveguides in LiNbO 3 [19][20][21] and other oxides [22,23] with the pragmatic benefit of using fluences several orders of magnitude lower than those used with light ion implantation. The defects and damage generation of SHI and the final structural changes that cause the useful refractive index modification are strongly related to the high electronic energy density deposited along the ions tracks.…”

“…Several regimes of damage creation and accumulation have been studied in LN. For medium mass ions (like F) moderate damage is created per ion track that accumulates, after track overlapping given enough fluence, to finally create buried thick amorphous layers with sharp boundaries and high refractive index change (decrease >10%) that allows for high optical confinement [19,20]. This method of waveguide fabrication has been applied for the fabrication of demanding devices like micro-rings resonators [24] or in innovative applications such as nanoparticle trapping and patterning [25].…”

Characterization and inhibition of photorefractive optical damage of swift heavy ion irradiation waveguides in LiNbO_3

“…The guides support ordinarily and extraordinarily polarized modes and, unlike other nonlinear LiNbO 3 waveguides, they show for both polarizations step-like, high-jump index profiles (Δn e 0.1, Δn o 0.2). Initially, the guides presented moderate/high propagation losses (1-10 dB∕cm) [17,18], but very recently, using higher temperature annealing treatments (350°C-375°C) and thick enough amorphization barriers, propagation losses were reduced to below 0.5 dB∕cm [20]. Furthermore, good nonlinear optical (χ 33 ) and electro-optic (r 33 ) coefficients have been reported [19,21], so that the novel waveguides have become good candidates for nonlinear devices.…”