Bragg gratings fabricated in monomode photosensitive optical fiber by UV exposure through a phase mask

A photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass. A KrF excimer laser beam (249 nm) at normal incidence is modulated spatially by the phase mask grating. The diffracted light, which forms a periodic, high-contrast intensity pattern with half the phase mask grating pitch, photoimprints a refractive index modulation into the core of photosensitive fiber placed behind, in proximity, and parallel, to the mask; the phase mask grating striations are oriented normal to the fiber axis. This method of fabricating in-fiber Bragg gratings is flexible, simple to use, results in reduced mechanical sensitivity of the grating writing apparatus and is functional even with low spatial and temporal coherence laser sources

Effective index drift from molecular hydrogen diffusion in hydrogen-loaded optical fibres and its effect on Bragg grating fabrication

When hydrogen loading is used to enhance the photosensitivity of silica-based optical waveguides and fibres, the presence of molecular hydrogen dissolved in the glass matrix changes the effective index of propagation of guided optical modes by as much as 0.05%. Real-time monitoring of the reflectivity spectrum of Bragg gratings written in such conditions shows that the centre wavelength follows the changes in hydrogen concentration due to diffusion and reaction with glass defects

Coherent Crosstalk of an Optical Add/Drop Filter with Bragg Gratings in a PLC Mach-Zehnder Interferometer for Optical LAN

The coherent crosstalk of an add/drop filter with Bragg gratings written in a planar lightwave circuit Mach-Zehnder interferometer is investigated experimentally and theoretically. The filter is used to design an optical local area network without any optical amplifiers, based on the coherent crosstalk limitation

Apodised in-fibre Bragg grating reflectors photoimprinted using a phase mask

An apodized in-fibre Bragg grating reflector is fabricated using the phase mask photoimprinting technique. The reflector has a centre wavelength of 1550 nm, a bandwidth of 0.22 nm and a peak reflectivity of 90%. At 0.4 nm (50 GHz) from the centre wavelength the reflectivity is 40 dB lower than the peak reflectivity; this is an improvement of more than 20 dB over an unapodized Bragg grating reflector with similar bandwidth and peak reflectivity

Enhanced photosensitivity in lightly doped standard telecommunication fibre exposed to high fluence ArF excimer laser light

The core refractive index of Corning SMF-28 optical fibre exposed to ArF laser pulses increases with the square of the fluence per pulse. Bragg gratings with a refractive index modulation amplitude higher than 10 -3 have been obtained. This is an order of magnitude improvement over previously reported values for this type of fibre in the absence of treatment to enhance the photosensitivity

Low-Loss Planar Lightwave Circuit OADM with High Isolation and No Polarization Dependence

A passive optical add-drop multiplexer with 1 dB of insertion loss and 36 dB of isolation is fabricated by writing Bragg gratings in a waveguide Mach-Zehnder interferometer using ArF excimer laser light. The spectral properties and bit-error-rate performance of the device are fully characterized using polarized light

Temperature-insensitive UV-induced Bragg gratings in silica-based planar lightwave circuits on Si

A novel technique is proposed to realise temperature-insensitive Bragg gratings in silica-based lightwave circuits on Si using a bimetal plate. A wavelength shift < 0.15nm is successfully demonstrated between -40 and 80°C in the Bragg gratings written in a Mach-Zehnder interferometer