Efficient frequency doubling in femtosecond laser-written waveguides in lithium niobate

Abstract

Optical waveguides in lithium niobate have been fabricated with a femtosecond laser. Different types of modifications depending on the laser parameters were observed and discussed. In these waveguides, frequency doubling of 1064nm radiation was demonstrated utilizing birefringent phase matching. A conversion efficiency of 49% was obtained in a 9.3mm long sample.

Femtosecond Fabrication of Waveguides in Ion-Doped Laser Crystals

“…In this design waveguide core is the stressed area which is not exposed by the femtosecond beam. An identical scheme was implemented earlier in x-cut LiNbO 3 single crystal (Burghoff, 2006), and z-cut PPLN (Thomas, 2007) and then in YVO 4 :Nd single crystal (Silva, 2010). Refractive index alteration was found in Al 2 O 3 :Ti 3+ single crystal under irradiation with 1 kHz rep rate Ti:sapphire laser.…”

“…Positive refractive index change in the exposed crystal area was observed only under certain restricted conditions. Refractive index change is positive in LiNbO 3 crystal for extraordinary axis under low pulse energy (Burghoff, 2006;. Second harmonic generation in a waveguide written in this regime in z-cut PPLN crystal was demonstrated (Lee, 2006).…”

Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

“…Waveguides can also be inscribed in crystalline and ceramic media [28], where typically only optical damage, that is, Type II modifications, can be induced. Thus waveguiding is achieved by creating a stress-field between two damage lines resulting in a waveguide in between [29] (see Figure 2C) or by fabricating a depressed cladding from Type II damages [30], as shown in Figure 2D. Type I modifications have only been observed in a handful of crystals, such as lithium fluoride [31], lithium niobate [32], strontium barium niobate [33], lithium tantalite [34], yttrium aluminium garnet [35], yttrium calcium oxoborate (YCOB) [36] and bismuth germanate crystals [37,38].…”

Control of waveguide properties by tuning femtosecond laser induced compositional changes

“…This result further confirms the feasibility of generating efficient, integrated optics elements via spatially selective modification of the glass composition. Femtosecond (fs) laser writing 1 has been proven a versatile method for producing optical waveguides inside both glassy 2 and crystalline dielectrics, 3 including highly nonlinear ones. 4 Yet, one of its present limitations is imposed by the maximum refractive index contrast accessible, which is given by the refractive index modification mechanism involved.…”