Abstract
The local modification of the composition of glasses by high repetition femtosecond laser irradiation is an attractive method for producing photonic devices. Recently, the successful production of waveguides with a refractive index contrast (Δn) above 10−2 by fs-laser writing has been demonstrated in phosphate glasses containing La2O3 and K2O modifiers. This large index contrast has been related to a local enrichment in lanthanum in the light guiding region accompanied by a depletion in potassium. In this work, we have studied the influence of the initial glass composition on the performance of waveguides that are produced by fs-laser induced element redistribution (FLIER) in phosphate-based samples with different La and K concentrations. We have analyzed the contribution to the electronic polarizability of the different glass constituents based on refractive index measurements of the untreated samples, and used it to estimate the expected index contrast caused by the experimentally measured local compositional changes in laser written guiding structures. These estimated values have been compared to experimental ones that are derived from near field images of the guided modes with an excellent agreement. Therefore, we have developed a method to estimate before-hand the expected index contrast in fs-laser written waveguides via FLIER for a given glass composition. The obtained results stress the importance of considering the contribution to the polarizability of all the moving species when computing the expected refractive index changes that are caused by FLIER processes.
Highlights
Fs-laser writing of optical photonics components in dielectrics has been proven as a successful and versatile technique in many cases [1,2], it is affected by some limitations, including the relatively small index contrast accessible in most cases (∆n = nlocal − n0, typically well below 10−2 ), which is, in addition, strongly conditioned by the material itself [3]
K2 O is very different in the three samples and all components contributed to the glass polarizability
They correspond to a calculation of the material polarizability while assuming a linear constituents in phosphate-based glasses that were modified with different amounts of La2O3 and K2O, variation of the La2 O3 for the maximum and minimum local concentration of K2 O derived from the oxide ion (
Summary
Fs-laser writing of optical photonics components in dielectrics has been proven as a successful and versatile technique in many cases [1,2], it is affected by some limitations, including the relatively small index contrast accessible in most cases (∆n = nlocal − n0 , typically well below 10−2 ), which is, in addition, strongly conditioned by the material itself [3]. In this context, the use of fs-laser. FLIER has been successfully used to produce waveguides [7,8] and waveguide integrated optical amplifiers and lasers [9]
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