F. Bilodeau

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.

An all-fiber dense wavelength-division multiplexer/demultiplexer using photoimprinted Bragg gratings

A wavelength multiplexing/demultiplexing device is fabricated and used to drop/insert a single wavelength channel from/into a multiple wavelength transmission link with 100 GHz channel-spacing at 1550 nm. The device consists of an all-fiber Mach-Zehnder interferometer with photoinduced Bragg gratings. The following performances were measured: extraction/coupling efficiency =99.4%, excess loss <0.5 dB, adjacent channel-isolation >20 dB, and return loss >23 dB.<<ETX>>

Comparison of one‐photon and two‐photon effects in the photosensitivity of germanium‐doped silica optical fibers exposed to intense ArF excimer laser pulses

The growth rate of fiber Bragg gratings written using 193 nm light from an ArF excimer laser is linearly proportional to the laser pulse energy density for fibers with high germanium doping but proportional to the square of the pulse energy density for standard telecommunications fibers with low germanium concentration. The two‐photon process in standard fibers yields refractive index increases that saturate around 10−3, an order of magnitude improvement over previous results in this type of fiber without sensitization treatment. The two types of photoinduced refractive index gratings have comparable thermal stability and preserve about 50% of their initial magnitude after 30 min at 600u2009°C.

High-return-loss narrowband all-fiber bandpass Bragg transmission filter

An all-fiber narrowband transmission filter (FWHM=0.25 nm) that is compact and exhibits high return loss (30 dB or better) is demonstrated using simultaneously written matched-pair, side-by-side Bragg gratings in a Michelson interferometer configuration.<<ETX>>

PHOTOSENSITIVITY IN PHOSPHORUS-DOPED SILICA GLASS AND OPTICAL WAVEGUIDES

Irradiation of hydrogen loaded or flame brushed phosphorus doped, germanium free silica glass with a 193‐nm ArF excimer laser changes the optical absorption at ultraviolet wavelengths by 40–140 dB/mm and the refractive index by more than 2×10−4. Bragg gratings with 90%–95% reflectivity are photoinduced in channel optical waveguides made from this glass. The thermal stability of the photosensitivity is measured by annealing up to 700u2009°C.

Minimization of phase errors in long fiber Bragg grating phase masks made using electron beam lithography

Centimeter-long fiber Bragg grating phase masks having several thousand periods are fabricated using electron beam lithography and require the stitching together of many electron beam writing fields. Two techniques are used to minimize the effect of phase errors arising from the stitching process. Fiber Bragg gratings with more than 99.9% reflectivity are photoimprinted using the phase masks and near perfect spectral response is obtained in spite of stitching errors.

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.

Comparison of fiber Bragg grating dispersion-compensators made with holographic and e-beam written phase masks

Experimental results of time delay ripples in dispersion compensating fiber Bragg gratings fabricated with either holographic or electron-beam written 10-cm-long phase masks are presented. Deviations from linear phase delay are dependent upon UV exposure uniformity and phase mask errors.

Wavelength division multiplexer with photoinduced Bragg gratings fabricated in a planar-lightwave-circuit-type asymmetric Mach-Zehnder interferometer on Si

A planar-lightwave-circuit (PLC)-type wavelength division multiplexer with photoinduced Bragg gratings is successfully fabricated on Si. The Bragg gratings are formed in the arms of an asymmetric four-port Mach-Zehnder interferometer (MZI). We demonstrate that signals with three wavelengths can be demultiplexed to three output ports. Heaters are used to compensate for the phase error in the MZI and to switch the output ports. An insertion loss at a Bragg wavelength of 1534.78 nm can be changed from 1.5 to about 19 dB by controlling the heater, indicating that photoinduced Bragg gratings are useful for expanding PLC functions.

Maskless writing of submicrometer gratings in fused silica by focused ion beam implantation and differential wet etching

Surface relief gratings with submicrometer periods have been fabricated in silica by ion implantation with a focused ion beam, followed by etching in diluted hydrofluoric acid. Implanted silica etches three times faster than unimplanted silica and groove depths of the order of 300 nm have been achieved. The method does not require photolithography or masking layers, allows arbitrary patterns to be defined, and may be used to fabricate diffractive optical elements or grating filters in optical waveguides.