Extraordinary stability of anisotropic femtosecond direct-written structures embedded in silica glass

Abstract

In this letter we report the different response to temperature displayed by isotropic femtosecond written structures ͑type I_fs͒, and anisotropic ones ͑type II_fs͒, which are characterized by the presence of a self-assembled subwavelength periodic structure within the irradiated volume. We observe that the anisotropic structures display an extraordinary annealing behavior, namely, their photoinduced change in refractive index increases with the annealing temperature. We explain our experimental results with a theoretical model.

Compact Birefringent Waveplates Photo-Induced in Silica by Femtosecond Laser

“…Both ¼ and ½ waveplates and combinations therefore are readily fabricated, allowing total integration of birefringent components and waveguides with unprecedented precision and resolution. These silica waveplates exhibit enormous advantages including a broad spectral range from UV to IR and high thermal stability (no decay after 2 h @ 1000 °C [30] from which an estimated lifetime of about 300 million years at room temperature) can be obtained. This is primarily due to the intrinsic structures (nanoporous silica) and the absence of glued components found in commercial waveplates, and a much higher damage threshold (25 ± 3 J/cm², at λ = 1064 nm, 3.5 ns, 10 Hz [31]).…”

Self-assembled sub-wavelength structures and form birefringence created by femtosecond laser writing in glass: properties and applications

“…20),21) It was also observed that the femtosecond laser written structures of type I-fs and type II-fs display the different response to increased temperature and in particular the structures of type II-fs demonstrate the extraordinary behavior, whose refractive index change increases with temperature. 15) An amplified, mode-locked Ti: Sapphire laser operating at a wavelength of 800 nm, with 200 fs pulse duration and 100 kHz repetition rate, was utilized to fabricate the structures to be tested. The laser beam was linearly polarized and focused with a 10 × objective.…”

“…14) The extraordinary stability of these nanogratings has also been reported. 15) Embedded micro-reflectors, 9) retardation plates, 13) and micro-fluidic channels 16) based on these nanostructures have been reported; however their optimization requires a systematic characterization of the properties of the periodic structures ver- Fig. 1.…”

Grating writing in structured optical fibers

“…However the main region of interest justifying the use of these lasers is the Type II regime since changes in this regime are significantly more stable, up to 1000 ℃ [29,30]. Type II gratings written by using energies above T2 damage threshold [31] of the glass lead to very stable gratings.…”