Microstructured waveguides in z-cut LiNbO_3 by high-repetition rate direct femtosecond laser inscription

Abstract

Abstract:We report on the operational parameters that are required to fabricate buried, microstructured waveguides in a z-cut lithium niobate crystal by the method of direct femtosecond laser inscription using a highrepetition-rate, chirped-pulse oscillator system. Refractive index contrasts as high as −0.0127 have been achieved for individual modification tracks. The results pave the way for developing microstructured WGs with low-loss operation across a wide spectral range, extending into the mid-infrared region up to the end of the transparency range of the host material.

High-repetition-rate femtosecond-laser micromachining of low-loss optical-lattice-like waveguides in lithium niobate

“…The immersion oil layer (RI = 1.523) between the lenses and the sample was checked regularly during the experiment to prevent any formation of air-bubbles or dust that could affect the inscription results. A detailed description of our laser inscription system can be found in Dubov et al 25 . Figure 1b shows an example of a waveguide cross-section, where the circle array represents the track positions programmed into the translational stage controller and the inset shows the actual track positions and shapes after fabrication.…”

“…In this work, a fixed energy increase rate (∆Ed) of approximately 0.3 nJ (corresponding to 3-mW optical power) per distance between two consecutive track rows was chosen after investigating some try-out fabrications. While the induced RI change of a track increases linearly with the inscribing pulse energy 25 , which is crucial for obtaining strongly confining depressed-cladding waveguides, increased pulse energy is liable to induce structural defects and micro-crack generations along the track. These high-laser-energy driven non-uniformities would result in a reduction of the waveguide performance due to effects such as scattering, absorption, and so on.…”

Comparative analysis of ways for femtosecond laser formation of optical waveguides

“…Прямая фемтосекундная запись является перспективной безмасочной и ши-роко распространенной технологией создания оптических волноводов в объеме стекол и кри-сталлов [1][2][3][4][5][6][7]. Оптические стекла и кристаллы могут быть разделены на три группы на осно-ве знака постоянно изменяющегося показателя преломления (ПП): 1) материалы, ПП которых увеличивается при фемтосекундной микрообработке; 2) материалы, ПП которых понижается;…”

High-repetition-rate femtosecond-laser inscription of low-loss thermally stable waveguides in lithium niobate

“…This is especially advantageous to the fabrication of complex structures and large-scale commercial production. It is also noteworthy that the energy efficiency of HRR systems can be twice as large as that of LRR systems owing to the heat accumulation effect [18]. Recently, Bhardwaj et al demonstrated depressed-cladding waveguides based on the usual circular packing geometry in a x-cut LN crystal with impressively low losses of 0.56 dB/cm and 0.51 dB/cm for TE (perpendicular to optical axis) and TM (parallel to optical axis) polarized light, respectively, at 1550 nm [17].…”