Abstract: Annealing a planar wave guide layer is critical because small structural imperfections lead to optical problems. Chemical vapor deposition of the layer tends to leave gaseous substances bonded to the deposit, which on being driven off by initial annealing warm-ups leave cavities requiring densification. Traditional annealing methods take several hours. This invention proposes a rapid heating of the layer to a temperature below the flow temperature, maintaining this temperature for about 30 to 300 seconds, then rapidly heating up further to a temperature close to or above the flow temperature, maintaining this temperature for about 30 to 300 seconds, then allowing the substrate and layer to cool rapidly to room temperature.

Abstract: A planar optical waveguide comprises at least two cladding layers on a substrate with at least one core layer disposed between the cladding layers. The overcladding layer of the two layers is doped in order to produce a thermal coefficient of expansion close to or equal to that of the substrate in order to reduce the polarisation sensitivity of the device.

Abstract: A cladding layer on the core of an optical waveguide is subjected to a rapid thermal annealing process preferably either: in a multi-stage furnace in which the waveguide substrate can be transported rapidly on a carriage between stages at different temperatures; or in a quartz chamber adjacent a bank of quartz halogen lamps of low thermal inertia and easily switched rapidly between different intensities of thermal radiation through the chamber.

Abstract: An optical circuit device having a core supported on a substrate incorporates a wave guide being in a layer of the core. The structure is provided with a cladding layer by depositing by means of a PECVD process a cladding material on the wave guide core and maintaining a negative bias between the substrate or the core and earth while the deposition is proceeding.