Photonic applications of rare earth-doped tetraethylorthosilicate based silica thin films and waveguides.

摘要

Materials that emit light when optically or electrically pumped have been of great interest to the high technology industry for a long time. Displays, LED's and optical amplifiers are a few of the devices that are widely desired. Until recently semiconductors and high temperature glass technologies have dominated the industry for these kinds of products. Elaborate systems like molecular beam epitaxy, vacuum sputtering and chemical vapor deposition, are examples of process that have been employed to fabricate useful thin film materials for these devices. Expensive equipment and rigorous maintenance schedules are required to keep these systems operational for the high quality films they produce. There exists, however, a process that can produce high quality thin films without the need for expensive vacuum systems and is done at low temperature and standard pressure. This is the sol gel method.; The sol gel process involves mixing of liquid chemicals, allowing a reaction to happen (usually oxidation from the addition of water), where molecules of a new material are formed and suspended within the liquid system. When solid molecules begin forming from the liquid precursors, a sol is formed. A sol is a solid solution where solid particles are suspended within a liquid medium that are not dissolved in the liquid medium. A gel is the formation of a network matrix from these solid molecules attaching to each other but still within the liquid medium. As these molecules continue to link together the matrix grows in size and compactness.; Utilizing this technology to form silicon dioxide at room temperature from liquid precursors and the ability to dope the sol gel uniformly with optically active rare earth ions is the thrust of this work.; Rare earth ions (lanthanide series of the periodic chart) are well known for their optical properties. The atoms in this series are not very interesting in their neutral state, but when these atoms are imbedded in a solid host they typically assume a triply ionized state by having three stripped off. The mechanism by which this happens is that three 4f inner shell electrons are striped off while leaving the outer 5s,d and 6s tilled shells alone. This inner shell is electrically screened from the outside and it is this mechanism by which stable optical transitions are possible.; The Er3+ ion is of particular interest due to the ability to emit light in the green, red and infrared wavelengths. Erbium doped waveguide and fiber amplifiers use this mechanism to amplify light signals in the telecommunications wavelength range (1520–1580 nm).; Erbium doped aluminosilicate symmetric waveguides were prepared by the sol gel method on SiO₂/Si substrates. Ridge channel waveguides were formed into the top SiO₂ cladding layer by ICP plasma etch with NF₃/Ar₂ gasses. Infrared and visible upconversion luminescence emission using 980 nm pump excitation was detected. Waveguide loss measurements at 980 nm and 1531 μm wavelengths yielded losses of 1.7 dB/cm and 4.93 dB/cm, respectively. Optical gain was detected over the 1.5 μm range with signal enhancement of 5.89 dB in a guide 1.1 cm long yielding 0.484 dB gain at 1531 nm wavelength.