In situ assessment and minimization of nonlinear propagation effects for femtosecond-laser waveguide writing in dielectrics

Abstract

The effect of nonlinear propagation on the shape of the focal volume has been assessed by in situ plasma emission imaging during the subsurface processing of a commercial phosphate glass. The sample was processed with an elliptically shaped femtosecond-laser beam at 1 kHz repetition rate and scanned transversely with respect to the writing beam axis. As a consequence, optimal conditions for minimizing undesirable nonlinear propagation effects during the production of optical waveguides by direct laser writing have been determined. Under these conditions, it is possible to induce structural transformations and still preserve the focal volume shape associated with the linear propagation regime. While at low pulse energy a single scan laser-written structure does not support a guided mode, the use of multiple scans with minimized nonlinear propagation effects enables the production of optical waveguides. The latter show a significantly improved performance in terms of the refractive index change and propagation losses when compared to single scan waveguides.

Direct femtosecond laser waveguide writing inside zinc phosphate glass

“…As a consequence, high quality single-mode waveguides cannot be easily fabricated by direct waveguide writing techniques. Femtosecond laser writing in commercially available phosphate glasses, such as Schott IOG-1 or Kigre Er-Yb QX and MM2a glass, has demonstrated that both the magnitude and the sign of the induced net refractive index change inside the focal volume is highly sensitive to the fs-laser writing conditions [13][14][15][16][17][18][19]. The resulting micro-structure changes, induced by femtosecond laser inscription, result in complex refractive index profiles that can be used for waveguiding only when very specific combinations of laser processing parameters are used, thus limiting the effectiveness of these glasses as substrates for direct fs-laser waveguide writing.…”

Single-pass waveguide amplifiers in Er-Yb doped zinc polyphosphate glass fabricated with femtosecond laser pulses

“…In many of these glasses, particularly phosphate glasses, the type of refractive index change that can be induced using the direct-write technique is determined by a combination of the laser processing conditions and the initial glass composition [8,10,[17][18][19][20][21]. While commercially purchased QX phosphate glass has been engineered to function as a short-gain, solid-state laser medium that operates in the C band, it is not necessarily the optimal material for fs-laser waveguide writing.…”

Metallic nanoparticles grown in the core of femtosecond laser micromachined waveguides

“…7,8,[14][15][16] In this direction, the purpose of this paper is to encompass the interesting nonlinear optical properties of tungsten lead-pyrophosphate glass and femtosecond laser micromachining to produce waveguides containing metallic nanoparticles in its core, using one-step laser processing material. …”