Optimization of Low-Loss AL2O3AL_{2}O_{3} Waveguide Fabrication for Application in Active Integrated Optical Devices

In this paper we will present the fabrication and properties of reactively co-sputtered $AL_{2}O_{3}$ layers, being a very promising host material for active integrated optics applications such as rare-earth ion doped laser devices. The process optimization towards a reactive co-sputtering process, which resulted in stable, target condition-independent deposition of $AL_{2}O_{3}$ with high optical quality will be discussed in detail. The loss value of as-deposited optical waveguides sputtered by the optimized process has been measured. The loss in the near infrared wavelength range was 0.3 dB/cm. Furthermore $AL_{2}O_{3}$ material hosts fabricated by sputtering techniques are compatible with Si-based integrated optical technology and allow for uniform deposition over a large substrate area

Metal mask free dry-etching process for integrated optical devices applying highly photostabilized resist.

Photostabilization is a widely used post lithographic resist treatment process, which allows to harden the resist profile in order to maintain critical dimensions and to increase selectivity in subsequent process steps such as reactive ion etching. In this paper we present the optimization of deep UV-curing of 0,3-3.3 μm thick positive resist profiles followed by heat treatment up to 280 °C. The effectiveness of this resist treatment allows for metal mask free reactive ion etching with selectivity up to 6 for silicon structures, thermal silicon oxide and silicon oxynitride. This procedure is demonstrated by the results obtained in etching of various integrated optical structures

Influence of phosphorus doping on hydrogen content and optical losses in PECVD silicon oxynitride

PECVD Phosphorus-doped silicon oxynitride layers (n=1.5) were deposited from N2O, 2%SiH4/N2, NH3 and 5%PH3/Ar gaseous mixtures. Chemical bonds were determined by Fourier transform infrared spectroscopy. N–H bond concentration of the layers decreased from 3.29×10-21 to 0.45×10-21 cm−3, as the 5%PH3/Ar flow rate increased from 0 to 60 sccm. A simultaneous decrease of O–H related bonds was also observed within the same phosphine flow range. The optical loss of slab-type waveguides at λ=1505 nm was found to decrease from 14.1 to 6.2 dB/cm as the 5%PH3/Ar flow rate increased from 0 to 30 sccm, respectively. Moreover, the optical loss values around λ=1400 and 1550 nm were found to decrease from 4.7 to below 0.2 dB/cm and from 1.8 to 1.0 dB/cm respectively. These preliminary results are very promising for applications in low-loss integrated optical devices

Silicon oxynitride based photonics

Silicon oxynitride is a very attractive material for integrated optics. Besides possessing excellent optical properties it can be deposited with refractive indices varying over a wide range by tuning the material composition. In this contribution we will summarize the key properties of this material class and discuss several application examples. Preliminary results on novel processes, which will lead to largely reduced hydrogen incorporation and enable reflow of SiON material, are being presented

Low-threshold laser in a high-index-contrast double tungstate waveguide

The paper reports the laser emission from an enhanced-index-contrast KYW waveguide fabricated by co-doping the active layer with Lu and Gd ions. Both, Lu3+ and Gd3+ possess higher electron densities than Y3+, thus increasing the refractive index. The emission wavelength varied from 1010 nm to 1040 nm, strongly depending on the alignment, which was probably caused by the etalon effects of the gaps between the mirrors and the endfaces

Lattice matching and microstructuring of Gd3+, Lu3+ co-doped KY(WO4)2:Tm3+ channel waveguide lasers

Lattice-matched KY(WO4)2:Gd3+,Lu3+,Tm3+ layers with a thickness of 6 μm have been grown onto pure KY(WO4)2 substrates. Channel waveguides of 7.5 μm to 12.5 μm width have been microstructured to a depth of 1.5 μm using Ar+ beam milling. Laser experiments with buttcoupled mirrors demonstrate laser oscillation near 1844 nm while pumping at 792 nm

Gd3+, Lu3+ co-doped KY(WO4)2:Yb3+ planar waveguide lasers at 1025 and 980 nm

Single-crystalline layers of KY(WO4)2:Yb3+ co-doped with Gd3+ and Lu3+ have been grown onto pure (010) oriented KY(WO4)2 (KYW)substrates by vertical liquid phase epitaxy. The Yb3+ concentration is optimized to 1.2-2.4at.% for application of these layers as planar waveguide lasers near 1 μm, yielding a refractive index contrast between layer and\ud substrate of 6×10-4. Both co-dopants, Gd3+ and Lu3+, are optically inert but possess higher electron densities than Y3+, thus co-doping a total of 40% of these ions significantly increasing the refractive index contrast by an order of magnitude to 7.5×10-3 without affecting the optical properties of the layer.\ud This allows for a significant reduction of the layer thickness to 2-4 μm for single-mode guiding, thus facilitating micro-structuring and making the layer\ud suitable for active integrated optical devices. Two main advantages of this method are its nearly constant refractive index contrast over a wide range of Yb3+ doping level, because Yb3+ can now replace Lu3+, and the ability to\ud engineer good lattice matching by adjusting the amounts of Gd3+ and Lu3+ ions in the KYW:Yb3+ layer. The grown layers resulted in a planar waveguide laser with butt-coupled mirrors operating at 1025 nm with a record-high slope\ud efficiency of 82.3% versus absorbed pump power, and an output power of 195 mW. Another laser experiment without the use of an outcoupling mirror revealed laser emission at the zero-phonon line at 981 nm, with a slope efficiency of 71% versus absorbed pump power