Photoinduced Index Research Articles

Photowritten gratings in ion-exchanged glass waveguides

The fabrication of an ion-exchanged waveguide beam deflector containing a photowritten grating is described. The planar waveguide was fabricated by thermal K(+) exchange in a borosilicate glass. The grating was written by photobleaching an absorption defect centered at 330 am, which was created by gamma-ray irradiation of the glass. The bleaching was accomplished with the 351-nm line from an argon laser. The device achieved 35% deflection efficiency at 633 nm, which corresponded to a grating with a photoinduced index change of 2.6 x 10(-5). This is to our knowledge the first demonstration of an ion-exchanged glass waveguide device containing a permanent photowritten grating.

Correlation between ultraviolet-induced refractive index change and photoluminescence in Ge-doped fiber

The refractive index change arising following the UV exposure of a Ge-doped fiber was obtained by measuring the change in the far-field width of the fiber mode in the infrared. Simultaneous measurements showed a gradual decrease in the visible photoluminescence from the fiber which can be directly correlated to the photoinduced index change.

Phase-matched second-harmonic generation in periodically poled optical fibers

Phase-matched second-harmonic generation is reported in periodically poled optical fibers for the first time. A periodic χ(2) was induced in optical fibers during phase-matched periodic-electric field-induced second-harmonic generation at a fundamental wavelength of 1064 nm. Further, it is shown that periodic poling can be achieved by photo excitation with radiation of 514.5 nm wavelength while applying a spatially periodic static field. In both cases, the mode interaction HEω11→HE2ω11 is quasi-phase matched at 1064 nm. Seeding is observed in fibers beyond the poled region. A photoinduced index change has been measured using electric field induced second-harmonic generation.

Large stable photoinduced refractive index change in a nonlinear optical polyester polymer with disperse red side groups

The photoinduced refractive index change of polyester with disperse red side groups was studied at several different wavelengths. This material exhibits a large photoinduced index change (0.3 at 633 nm) and in addition when poled has a sizable second-order nonlinear optical effect. This index change was monitored over 1000 h and long-term stability was demonstrated. Based on these results, a method using only photomasks to define channel waveguides and other patterns in such polymers was suggested and experimentally demonstrated. This photoinduced index change may have wide applications in integrated optical systems when these or other similar polymers are involved.

Modeling and analysis of fiber-optic mode transducers: single fiber with periodic perturbations

The fiber-optic LP/sub 01/ from or to LP/sub 11/ mode transducers are analyzed by a scalar coupled-mode theory with vector correction. The authors deal with fiber-optic mode transducers made of a single fiber with periodic perturbations due to microbends, acoustic waves, or a photoinduced index grating. Both the couplings caused by the index perturbations and by the vector property of the fields (polarization effect) are taken into account in the analysis. Approximate analytical solutions to the coupled-mode equations are obtained. The power exchange among the modes along the fiber and spectral properties of the mode transducers are examined. The functions of the mode transducers used as wavelength filters and polarizers are studied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Permanent Photoinduced Refractive Index Changes in Rare Earth Doped Glasses

ABSTRACTPermanent refractive index gratings were holographically photowritten into rare earth doped glasses using the 488 rn line of a Ar Ion laser. The rare earths Pr3+, Tb3+, and Eu2+ were examined. Experiments were performed to elucidate the mechanism responsible for the photoinduced index change. A model is presented in which the index change is accomplished through photoionization of the rare earth dopant and subsequent trapping of the free carrier. The viability of these materials for use in optical fiber grating devices is discussed.

Photorefractive effect in Ti-diffused channel waveguides using LiNbO3 substrates with reduced optical absorption

We report a remarkably reduced photorefractive sensitivity in Ti:LiNbO3 channel waveguides using substrates with reduced optical absorption near the absorption edge. In addition, the intensity dependence of the saturated index change was measured, which indicates that, based on the Glass model, the saturated value of photoinduced index change is independent of irradiation intensity in the high intensity limit.

Picosecond photoinduced index changes in a-Si:H and related alloys measured by transient grating experiments

We report on transient grating experiments on amorphous films as a sensitive technique to study refractive index changes due to carrier relaxation processes. The experiments are performed on a-Si:H and a-SiC:H samples at room temperature with a time resolution of 10 ps. The observed fast component of the transient grating signal is attributed to the capture of carriers from extended states into localized states within 10 ps. The slow decay component reflects carrier relaxation into deeper tail states or traps and recombination as verified by experiments on a-SiC:H films with different defect densities.

Nonlinear materials with photoinduced index change and applications

The real time generation and processing of coherent optical waves require nonlinear optical materials allowing a fast reversible index change under incident illumination. The author presents the main physical mechanisms used for this purpose, with a particular emphasis on photorefractive and semiconductor materials which require a low incident intensity. Presented applications concern optical phase conjunction, dynamic holography, bistability and self induced optical cavities.

Coherent signal beam amplification in two-wave mixing experiments with photorefractive Bi 12SiO 20 crystals

The amplification of the input signal beam in two-wave mixing experiments with photorefractive Bi 12SiO 20 crystals is achieved when an additional phase shift is established between the photoinduced index modulation (phase volume hologram) and the incident fringe pattern. This stationary phase shift is introduced by either moving the crystal or the interference fringes at a constant speed. The transferred intensity is measured versus the applied electric field, fringe spacing and crystal velocity. The crystallographic orientation and the relative displacement with respect to the applied electric field polarity determine the amplitude of the energy transfer. For the first time in this crystal, signal beam amplification is reached for an applied field E 0 > 8 kV cm −1 and a crystal or fringe displacement speed around 5 μm s −1 at the green line ( λ = 514 nm) of an argon laser.

Characterization of single-mode optical fiber filters

The fabrication of narrowband highly reflecting filters in single-mode step-index fibers was reported recently by Hill et al. [Appl. Phys. Lett. 32, 647 (1978)]. The underlying effect on which these filters are based is a photoinduced refractive-index change in the GeO(2) used as a core dopant in SiO(2) fibers. A study is reported aimed at the characterization of such optical fiber filters. A theoretical model is developed, and relevant fiber parameters are determined through intercomparison with experiment. In this way, both the magnitude of the photoinduced index change and its dependence on the writing power coupled into the fiber are determined.