Fabricating And Characterization Of Two-layers Buried Optical Waveguide In Glass Substrate

Ion-exchange waveguide on glass gets hot for its numerous benefits, such as low cost, low propagation loss, easily doping high concentrations of rare-earth ion, good matching with single-mode fiber, good environmental stability and capable of integrating many components on the same substrate, especially suitable for the fabrication of the large volumes and low cost integrated optical devices. Traditional Ag+/Na+ ion exchange technology has received widespread research, and lots of low cost passive and active components have been realized by this technology, such as wavelength multiplexers, optical splitter, optical amplifiers, lasers and sensors, and widely used in optical communication and sensing systems to transmit and route optical signals over distance.As technology advancing, the increasingly demanding on the integration of the devices has proposed. Nowadays the challenge is to integrate more devices or functions on one single chip. Two different paths can be used to achieve this goal:the first one consists of a reduction of the waveguides'dimensions by an increase of the refractive index change, whereas the second one, which is addressed in this paper, is based on the realization of multilayered devices. Due to the properties of ion-exchange on glass, this technology is well adapted for 3D integration. However, to realize integrated optical devices with two different layers, it is mandatory to prevent any parasitic light transfer between them. This condition can be fulfilled if the top and bottom waveguides are sufficiently separated.Based on the analysis of the traditional electric-field-assisted ion-exchanged model, we established a simple ion-exchange 3D integrated model. By simulation we verify the feasibility of multi-layer buried waveguides and analyze the interaction between the waveguides. Then double-layer waveguides have been obtained in optical glass substrate by subsequently manufacturing two layers of buried optical waveguide, each layer being manufactured by thermal Ag+/Na+ion-exchange and field-assisted ion-diffusion. Microscopic structure of the optical waveguide chips has been observed and insertion losses of the each layer are characterized. Results show that the obtained double-layer waveguide is composed of two layers of buried waveguide with their core center locates respectively at 14μm and 35μm beneath the glass surface, core dimension of top layer and bottom layer waveguide being 12μm×7μm and 9μm×8μm, respectively; waveguides in both layers are all single mode waveguide at operating wavelength of 1.55μm; there is no directional coupling is observed between different layers. Insertion loss characterizations indicate that propagation loss of both layers are 0.12dB/cm, and coupling loss with single mode fiber are 0.78dB/facet and 0.73dB/facet, for top layer and bottom layer waveguide, respectively. Test results of two structures designed in this paper show that there are some trace residues of Ag+ ions in the drift path during the formation of the bottom waveguide, which reducing the drift velocity of the upper waveguide in the electric field and the ripple effect of optical waveguide, and will be an important factor in limiting the waveguide layers.Analysis suggests that this kind of optical waveguide is promising in application of high density integration of glass-based optical chip.