Femtosecond writing of active optical waveguides with astigmatically shaped beams

Abstract

We describe a novel approach for the fabrication of optical waveguides by focused lowrepetition-rate femtosecond laser pulses. This approach overcomes the main limitation of the technique, i.e., the strong asymmetry of the waveguide profile. By use of an astigmatic beam and suitably controlling both beam waist and focal position in tangential and sagittal planes, it is possible to shape the focal volume in such a way as to obtain waveguides with a circular transverse profile and of the desired size. This technique is applied to the fabrication of active waveguides in Er:Yb-doped glass substrates. The waveguides are single mode at 1.5 m and exhibit propagation losses of 0.25 dB/cm and an internal gain of 1.4 dB at 1534 nm.

Femtosecond laser microstructuring: an enabling tool for optofluidic lab‐on‐chips

“…For focused diameters of the order of a few micrometers, this results in a large difference in waveguide sizes in the two directions. This problem can be overcome [58,59] by introducing a focusing geometry in which the femtosecond writing beam is astigmatically shaped by changing both the spot sizes in the tangential and sagittal planes and the relative positions of the beam waists. This shaping allows one to modify the interaction volume in such a way that the waveguide cross section is circular and with arbitrary size.…”

“…The results were achieved with an amplified Ti:sapphire laser (800-nm wavelength, 1-kHz repetition rate, 100-fs pulsewidth) using 4-μJ pulse energy, mild focusing (20× objective, 0.3 NA) and 20-μm/s translation speed [64]. The astigmatic beam shaping technique [58,59] was employed to obtain circular waveguide cross section. Figure 3 shows a top view (Fig.…”

Femtosecond Fabrication of Waveguides in Ion-Doped Laser Crystals

“…Ellipticity is high for low rep rate inscription. Special beam shaping is applied in order to make waveguide with a circular cross section at low rep rate laser systems (Osellame, 2003;Moh, 2005;Marshall, 2006). High rep rate lasers provide circular waveguide cross section even without beam shaping due to strong cumulative heating effect (Eaton, 2005).…”

Optical Amplifiers from Rare-Earth Co-Doped Glass Waveguides

“…This technique has an unique advantage in fabricating of 3-D waveguides inside glass substrates, which is not easy from conventional ion-exchange and photolithographic processes. Channel waveguides written using ultrafast lasers in erbium-doped phosphate glasses for integrated amplifiers and lasers operating in the C-band have been already demonstrated (Osellame, 2003). Among all, ion-exchange has been the most popular technique for rare earth doped waveguides in glass.…”