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

Abstract

We have investigated the direct fabrication of subsurface waveguide amplifiers in Er-Yb zinc polyphosphate glass by utilizing the relationship between the initial glass composition and the resulting changes to the network structure after modification by fs laser pulses. Waveguides, exhibiting internal gain of 1 dB∕cm at 1.53 μm when pumped with 500 mW at 976 nm, were directly fabricated using a regenerative amplified Ti:sapphire 1 kHz, 180 fs laser system. Optical properties as well as insertion losses and internal gain are reported. [14]. Of all these active glasses, phosphate glass systems offer the best RE solubility without RE clustering and are ideal for the fabrication of compact waveguide amplifiers that operate in the telecommunications window [15,16]. 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. We have recently reported [21] that fs-laser modification in an undoped zinc polyphosphate glass with an O∕P ratio of 3.25 (molar composition 60ZnO-40P 2 O 5 ) always results in a change to the refractive index that is positive and ideal for the fabrication of optical waveguides over a wide range of fs-laser writing conditions. Using this result, it is possible to design an Er-Yb doped zinc polyphosphate glass with the same O∕P ratio in order to fabricate subsurface single-pass waveguide amplifiers. Optimization of the material composition results in an enhanced degree of flexibility with regards to waveguide processing conditions inside Er-Yb doped phosphate glass systems. In this letter we demonstrate the fabrication of a single-pass 1534 nm signal waveguide amplifier with fslaser inscription inside an Er-Yb doped phosphate glass 0.65Er 2 O 3 -1.30Yb 2 O 3 -56.05ZnO-42.00P 2 O 5 mol% using a 1 kHz repetition rate system. The Er-Yb doped zinc polyphosphate glass used in this study may be a more suitable material for directly fabricating waveguides under single-scan writing conditions over an expanded modification range. Such a unique property makes this glass an attractive substrate to use for fs-laser micromachining of active three-dimensional (3-D) photonic devices.An Er-Yb codoped zinc polyphosphate glass with molar composition of 0.65Er 2 O 3 -1.30Yb 2 O 3 -56.05ZnO-42.00P 2 O 5 (from here on referred to as Er-Yb ZnP) was prepared using reagent-grade ZnO, Er 2 O 3 , Yb 2 O 3 , and NH 4 H 2 PO 4 . A detailed melting procedure is described elsewhere [22]. Annealed samples, approximately 15 mm × 5 mm × 5 mm in size, were polished using SiC paper and diamond pastes to a finish of 0.25 microns.Optical waveguides 1.5 cm in length were fabricated using linearly pola...

Effects of rare-earth doping on femtosecond laser waveguide writing in zinc polyphosphate glass

“…22,23 These absorption and emission properties are well-suited for fabricating compact waveguide devices that operate with a relatively high gain bandwidth over most of the telecommunications window (1530 nm-1565 nm). We have carried out gain experiments, described in more detail elsewhere, 24 in waveguides that were fabricated with the following optimized writing parameters: sample translation speed of 5 lm/s, a pulse fluence of 10 J/cm 2 , writing with a 300 lm wide slit placed before a 0.55 NA focusing objective. By optically pumping the waveguides with a maximum 500 mW of 976 nm pump power, a total 1534 nm signal enhancement of approximately 10 dB was measured over a 1.5 cm length, resulting in an internal gain of close to 1 dB/cm.…”

Femtosecond-laser writing of photonic structures in zinc phosphate glasses

“…In the Er-Yb doped glass we have demonstrated the successful fabrication of subsurface waveguide amplifiers exhibiting internal gain of 1 dB⁄cm at 1.53 µm when pumped with 500 mW at 976 nm [3]. The ZnMgP composition was used to create waveguide Bragg gratings employing a single pass technique in which a waveguide that has a periodic refractive index profile is produced.…”

“…After fs-laser modification the modified regions were tested for optical guiding and characterized with confocal fluorescence (FL) and Raman spectroscopy. Detailed descriptions about the experimental procedures can be found elsewhere [1][2][3][4].…”

“…Phosphate glasses, which are of interest as host materials for active devices since they allow incorporation of high concentrations of rare earth ions, typically produce negative refractive index changes in the laser-exposed regions. We have recently found that good quality waveguides can be fabricated in zinc polyphosphate glass compositions with an O/P ratio close to 3.25 [1][2][3][4]. This paper summarizes the effects of glass composition on fs-laser induced structural modification as well as the fabrication of active devices in zinc phosphate glasses.…”

The influence of femtosecond laser wavelength on waveguide fabrication inside fused silica

“…[9][10][11][12] The effect of the laser processing parameters such as pulse duration, polarization, pulse energy, writing speed, and repetition rate has been thoroughly investigated and extensively reported in the literature for a variety of glasses with different compositions. [12][13][14][15][16] Furthermore, the use of laser beam shaping techniques has been exploited (a) to find potential advantages for laser micromachining and (b) to study the influence of the temporal and spatial distribution of the laser on the balance of the ionization mechanisms. 17,18 However, the influence of the laser wavelength on the fabrication of optical waveguides has not been fully understood nor systematically investigated, although several commercially available laser wavelengths and their frequency doubled counterparts have been independently used for direct laser writing.…”