Abstract
We report on fabrication of an optical waveguide-mode-field compressor in glass using a femtosecond laser. Our approach is based on building up a stress field within the waveguiding area which is realized by sandwiching the waveguide between a pair of laser-induced-modification-tracks. To induce an adiabatic conversion of the optical mode in the waveguide, the tracks are intentionally designed to be tapered along the waveguide. We show that our technique can allow for reducing the mode field size in a single mode waveguide from more than 10 μm to around 7 μm.
Highlights
A femtosecond laser has been used for writing optical waveguides in various types of materials such as glass, crystals, semiconductors and polymers [1,2,3,4,5,6,7,8,9]
The waveguides are produced by space-selectively modifying the refractive index in the laser-irradiated areas which has enabled to produce either type I waveguides by inducing positive refractive changes to form the waveguide cores [1,2,3] or type II waveguides by inducing negative refractive changes to form the waveguide claddings [10,11]
The transmission optical microscopy structures images of the femtosecond laser direct writing waveguides and the tapered mode field modulation structures with μm are shown in Figure are the crossfield sections of the waveguides without with modification and the2a,b tapered mode modulation structures with 6 μm arethe shown in Figurestructures, 2, where
Summary
A femtosecond laser has been used for writing optical waveguides in various types of materials such as glass, crystals, semiconductors and polymers [1,2,3,4,5,6,7,8,9]. Speaking, writing optical waveguides in transparent materials with femtosecond laser pulses provides extreme flexibility in terms of the choice of substrate materials, the geometry of the mode field profile, and the configuration of three-dimensional (3D) optical circuits [3,8,20,21,22,23]. One difficulty in the application of laser-written waveguides is to connect the waveguides with external photonic components such as optical fibers or waveguides produced with other technologies. For this purpose, modification of the mode field profiles of the laser-written waveguides is frequently required which can be realized by gradually tuning the laser parameters during the waveguide writing process [21,24]. We provide an alternative solution to achieve smooth mode field
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