Low-loss waveguides fabricated in BK7 glass by high repetition rate femtosecond fiber laser

Abstract

For the first time femtosecond-laser writing has inscribed low-loss optical waveguides in Schott BK7 glass, a commercially important type of borosilicate widely used in optical applications. The use of a variable repetition rate laser enabled the identification of a narrow processing window at 1 MHz repetition rate with optimal waveguides exhibiting propagation losses of 0.3 dB/cm and efficient mode matching to standard optical fibers at a 1550 nm wavelength. The waveguides were characterized by complementary phase contrast and optical transmission microscopy, identifying a micrometer-sized guiding region within a larger complex structure of both positive and negative refractive index variations.

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

“…The observations and results described here serve to support our numerical studies in [10,11]. HRR fs lasers have become the preferred laser source for fast writing of low-loss WGs in glasses [12][13][14][15][16][17], enabling RI contrasts between exposed and unexposed areas of up to five times higher than those of standard optical fibers [14,15]. However the application of this approach to crystals has received less attention in the literature [18].…”

“…However the application of this approach to crystals has received less attention in the literature [18]. We would also like to note that the energy efficiency of HRR laser systems can be twice as large as that of low-repetitionrate (LRR) systems owing to the heat accumulation effect [12,13]. At HRRs, the time between successive laser pulses is shorter than the heat dissipation or cooling time, resulting in an accumulation of heat in the focal volume that melts the material.…”

Inscription and characterization of waveguides written into borosilicate glass by a high-repetition-rate femtosecond laser at 800 nm

“…These procedures result in low processing cost along with good chemical stability and high transmission in the visible and near-infrared spectrum. Some researchers have reported the fabrication of waveguides in borosilicate glasses, but with relatively high attenuation coefficients of around 1 dB cm −1 and above at 1300 nm [4][5][6][7][8], with only a few research groups demonstrating low-loss optical waveguides in BK7 glass possessing attenuations of around 0:3 dB cm −1 at 1550 nm [9]. The low-loss waveguides were produced using a 1 MHz repetition rate laser, but the reports lack detail of the induced index.…”

“…The low-loss waveguides were produced using a 1 MHz repetition rate laser, but the reports lack detail of the induced index. Reference [9] also implies that high-repetition-rate systems produce lossy waveguidelike structures. In this paper we investigate the operational parameters that are required to fabricate low-loss waveguides using an 11 MHz repetition rate 800 nm femtosecond laser and obtain minimal propagation losses of 0:2 dB=cm at a wavelength of 633 nm and 0:6 dB=cm at a wavelength of 1550 nm.…”

Waveguide fabrication in lithium-niobo-phosphate glasses by high repetition rate femtosecond laser: route to non-equilibrium material’s states

“…For example, some glasses allow precipitation of nano-particles or nano-crystals formation in two-stage process, like in photo-thermo-refractive glasses [7] the NaF nano-crystals grow in silica matrix. One can expect that intensive heating and high pressures, produced by direct fs inscription at high-repetition rate [8][9][10], can trigger similar transformations but in a single-stage process, which may be an advantage. Laser-induced crystallization under HRR fs irradiation has not been widely explored yet, but it could result in a stronger nonlinear response of the media.…”