FS-laser irradiation at high repetition pulse rate enables producing high-performance passive waveguides in different glasses through the local modification of the glass composition. In this paper, we show that this mechanism can similarly be used to produce high-performance waveguide amplifiers and lasers. Furthermore, we show the feasibility of producing active waveguides with different optical gains in the same phosphate glass sample by changing the laser writing parameters. The lanthanides present in the glass composition (Er ³⁺ , Yb ³⁺ , and La ³⁺ , the refractive index carrying element) experience similar local concentration changes upon fs-laser writing, enabling to determine the concentration of La ³⁺ and thus the refractive index contrast of the guiding region by measuring its absorption at 1534 nm. The produced waveguide lasers show slope efficiencies (respect to the absorbed pump power) above 38%, which could reach up to 42% by further optimization of the waveguide laser cavity configuration. The active waveguides produced are thermally stable for temperatures up to at least 450 °C.

The design and performance of borate glass samples compositionally pre-designed to be femtosecond laser writable via laser-induced ion migration is reported in this Letter. It is demonstrated that borate glasses modified on purpose with small amounts of ${\mathrm{La}}_2{\mathrm{O}}_3$ and ${\mathrm{Na}}_2\mathrm{O}$ can be straightforwardly used to produce high-index contrast ($\mathrm{\Delta }n$) waveguides by femtosecond-laser-assisted ion migration. The positive $\mathrm{\Delta }n$ of the waveguides is caused by the local enrichment of ${\mathrm{La}}_2{\mathrm{O}}_3$ in the guiding region with a slope of $8·{10}^{-3}{(\mathrm{mol}.\%)}^{-1}$. The value of this is consistent with numerical aperture measurements of the waveguides and local compositional measurements at the guiding region performed by energy-dispersive x-ray micro-analysis. The maximum achievable $\mathrm{\Delta }n$ values can be controlled through the initial ${\mathrm{La}}_2{\mathrm{O}}_3$ content of the glass. Maximum $\mathrm{\Delta }n$ values $>{10}^{-2}$ for samples with just 5.5 mol. % of ${\mathrm{La}}_2{\mathrm{O}}_3$ have been produced. This compositional design approach could be potentially used to produce highly efficient femtosecond laser writeable glasses in other glass families.

Here in we present the fabrication and performance of waveguide tapers produced by femtosecond laser induced element redistribution in modified phosphate glasses. More particularly, it is demonstrated that by controlling the scan velocity during the writing process it is possible to adequately tune both the size of the modified area and the refractive index contrast to produce waveguides that can cope with mode field diameters in the range of 7-16 μm. In addition, we fabricated tapered structures through the induction of an acceleration in the laser scanning velocity, resulting in a device that can efficiently convert a wide range of mode fields. The fine control achieved over the index contrast in the range of 10 ^-3 and 10 ^-2 would allow the production of a wide variety of tapers that could potentially be used to couple numerous photonic devices.

Non-steady-state photoelectromotive force effect in the presence of periodical and linear phase shift was investigated both theoretically and experimentally. It was shown that superposition of oscillating and linear movements of the interference pattern leads to the appearance of the sharp peak in the frequency dependence of the photoelectromotive force output current when the frequency of periodical modulation matches the frequency of the linear phase shift. We demonstrated experimentally that this effect can be used for determination of a Doppler frequency shift between signal and reference beam.

The local modification of the composition of glasses by high repetition femtosecond laser irradiation is an attractive method for producing photonic devices. Recently, the successful production of waveguides with a refractive index contrast (Δn) above 10⁻² by fs-laser writing has been demonstrated in phosphate glasses containing La₂O₃ and K₂O modifiers. This large index contrast has been related to a local enrichment in lanthanum in the light guiding region accompanied by a depletion in potassium. In this work, we have studied the influence of the initial glass composition on the performance of waveguides that are produced by fs-laser induced element redistribution (FLIER) in phosphate-based samples with different La and K concentrations. We have analyzed the contribution to the electronic polarizability of the different glass constituents based on refractive index measurements of the untreated samples, and used it to estimate the expected index contrast caused by the experimentally measured local compositional changes in laser written guiding structures. These estimated values have been compared to experimental ones that are derived from near field images of the guided modes with an excellent agreement. Therefore, we have developed a method to estimate before-hand the expected index contrast in fs-laser written waveguides via FLIER for a given glass composition. The obtained results stress the importance of considering the contribution to the polarizability of all the moving species when computing the expected refractive index changes that are caused by FLIER processes.

Fs-laser induced element redistribution (FLIER) has been a subject of intensive research in recent years. Its application to various types of glasses has already resulted in the production of efficient optical waveguides, tappers, amplifiers and lasers. Most of the work reported on FLIER-based waveguides refers to structures produced by the cross-migration of alkali (Na, K) and lanthanides (mostly La). The latter elements act as refractive index carrying elements. Herein, we report the production of Ba-based, FLIER-waveguides in phosphate glass with an index contrast > 10⁻². Phosphate glasses modified with the same amount of Na₂O and K₂O, and variable amounts of BaO and/or La₂O₃ were used to produce the FLIER-waveguides with Ba and or La acting as index carriers. Ba-only modified glasses show a waveguide writing threshold and light guiding performance comparable to that of La-based structures. However, mixed Ba-La glasses show a much higher element migration threshold, and much smaller compositionally modified regions. This behavior is consistent with a competition effect in the cross-migration of both elements (Ba and La) against the alkalis. Such an effect can be applied to inhibit undesired element redistribution effects in fs-laser processing applications in multicomponent glasses.