Refractive-index changes in fused silica produced by heavy-ion implantation followed by photobleaching

The changes in refractive index, optical absorption, and volume of synthetic fused silica resulting from the implantation of germanium and silicon ions at energies of 3 and 5 MeV are reported. Implantation changes the density and generates ultraviolet color centers in the silica, which increases the refractive index at visible wavelengths by ∼1%. Irradiation of the implanted samples with 249-nm light from a KrF excimer laser photobleaches the color centers and reduces the index by more than 0.1%. Photobleaching is used to write a 4.3-μm pitch diffraction grating in the implanted silica

Unbalanced dissimilar-fibre Mach-Zehnder interferometer: application as filter

An unbalanced Mach-Zehnder interferometer made using dissimilar-fibre fused taper couplers is proposed for filtering applications. The all-fibre device is compact, rugged, simple to make and provides extended control and flexibility for the design of various types of filters

Ultraviolet light photosensitivity in Ge-doped silica fibers: wavelength dependence of the light-induced index change.

A novel technique is reported for detecting permanent and transient light-induced refractive-index changes (photosensitivity) in optical fibers. The index change is detected by irradiating one arm of an unbalanced Mach–Zehnder fiber interferometer with UV light, thereby changing its optical path length. From a measurement of the change in the spectral response of the Mach–Zehnder interferometer, the change in the fiber core index as a function of wavelength can be determined. The equilibrium change in the core index is found to have an almost constant value of approximately 2.3 × 10−5 over the measured wavelength range of 700 to 1400 nm

Apodization technique for fiber grating fabrication with a halftone transmission amplitude mask

Experimental results of fiber Bragg gratings fabricated with halftone amplitude transmission masks and 10-cm-long phase masks are presented for the first time to our knowledge. The performance of the devices is evaluated in terms of their spectral characteristics and deviation from linear group delay. Good out-of-band sidelobe suppression of -27 dB and group-delay ripple of ?9.5 ps is achieved for fully apodized grating devices

High-g accelerometer based on an in-fiber bragg grating sensor

An accelerometer based on an in-fiber Bragg grating sensor has been fabricated and demonstrated. The grating sensor operates linearly up to accelerations of 170,000gn. The design, testing and performance of the accelerometer are discussed

Variable-spectral-response optical waveguide Bragg grating filters for optical signal processing

A simple method is described that permits the spectral response (spectral width, shape, and center resonant wavelength) of an optical waveguide Bragg grating to be controlled accurately in a prescribed manner. The control methodology consists of bonding the Bragg grating along the length of a mechanical support structure, which is then loaded with an appropriate force distribution. The function of the support structure is to transfer the strain induced by loading to the grating, thus modifying the grating’s spectral response in accordance with the variation in effective optical pitch induced by the strain transfer. We design and demonstrate a support structure that provides independent control over the spectral width and center wavelength of a Bragg grating

Photosensitivity in Ge-doped silica optical waveguides and fibers with 193-nm light from an ArF excimer laser

Photosensitivity in optical fibers and waveguides has been associated with the bleaching of an absorption band located near 5.0 eV (or 242 nm). We present new results for Bragg grating formation and UV bleaching experiments carried out using 193-nm light from an ArF excimer laser instead of the usual laser sources operating near 242 or 248 nm

Dichroism in the absorption spectrum of photobleached ion-implanted silica

The optical absorption spectrum of ion-implanted silica is shown to become dichroic when it is photobleached with polarized 248-nm light. The dichroism is modeled by a photobleaching process that bleaches color centers preferentially depending on their local orientation with respect to the polarization of the photobleaching light. A similar photobleaching process may occur in photosensitive fiber, thus providing a possible explanation for the birefringence that is observed in the photoinduced index change

Bragg gratings in defect-free germanium-doped optical fibers.

Bragg gratings have been written in germanium-doped optical fibers that have been treated to remove the UV absorption bands associated with oxygen-deficient defects. When one is using high-intensity 193-nm light from an ArF excimer laser to fabricate the gratings, the refractive index increases and the grating transmission spectra are similar to those obtained in standard (untreated) fiber