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Defect free direct bonding of rigid and large area glass samples, such as prisms, becomes increasingly important for the manufacturing of modern optical and optomechanical components. Typically, in order to apply a static load during the annealing step, specialized heat-resistant pressure mountings are required. This makes manufacturing effortful and cost-intensive. In this paper, we present plasma activated bonding experiments conducted on fused silica plates where residual stress has been introduced prior to the contacting step and where annealing is performed with and without a static load. We find that in case of a sufficiently smooth surface, bonding strength is insensitive towards residual stress or static load, or more precisely, towards the interface stress. Furthermore, the residual Fresnel reflection losses of the realized bonding interface were optically measured and they amount to only $$10^{-6}$$ 10 - 6 . We propose that a consideration of the change in Gibbs free energy, dG, allows qualitatively predicting the resulting bonding strength and its spatial distribution, where dG is determined by surface energy and interface stress. At the end of this article, conceivable applications are discussed.

Here, we report on the approach of realizing an all-fused-silica PGP disperser (prism + grating + prism) by low temperature direct bonding. A surface relief grating with period 660nm and overall depth of approximately 2000nm is sandwiched between two equal prisms. Direct bonding of glass relies on the formation of covalent bonds between hydrophilic silicon-oxide surfaces. Compared to other joining technologies, like adhesive bonding or optical contacting, the established connection is stiff, shows no outgassing, is highly resistant against chemical and radiative degradation and the established optical interface is intrinsically impedance-matched. In summary, two prototypes were realized, optically characterized and successfully underwent environmental testing. The overall diffraction efficiency of the PGP is larger than 90%.

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For the manufacturing of space-qualified spectrometric applications, the benefits of direct bonding are highly promising. While there are some recent spectrometric design concepts which rely on the usage of optical coatings, the direct bonding of optical glasses with added optical coatings is still challenging. This work presents investigations on plasma-activated direct bonding of optical glasses without and with added optical coatings. As a result, it is highly beneficial to add an additional SiO 2 final layer onto the coating and to perform an additional chemical-mechanical polishing process prior to direct bonding in order to achieve high bonding strengths.