Paul Blazkiewicz

Modification of thermal poling evolution using novel twin-hole fibers

Thermal poling current and electrooptic evolution were studied for a standard twin-hole fiber and two novel design twin-hole fibers. The poling characteristics were modified in the novel fibers, which had a trap or donor region inside the anode hole. Modifications of the poling characteristics were observed in both the current evolution and the electrooptic evolution. The novel fiber designs can facilitate the tailoring of poled fiber device characteristics.

Silica Fiber Poling Technology

Silica fiber poling technology is used to induce a second-order nonlinearity or linear electro-optic coefficient into silica fiber, an amorphous centrosymmetric material without intrinsic second-order nonlinearity. This paper reports on three poling techniques used for silica fiber: thermal poling, CO2 laser-assisted poling, and ultraviolet (UV) poling. The characteristics, mechanisms, and latest research results for each poling technique are addressed.

Mechanism for thermal poling in twin-hole silicate fibers

Thermal poling and depoling current for twin-hole fibers was measured. The current’s evolution was compared with electro-optic evolution. The thermally stimulated discharge efficiency was measured to be 5%. Atomic-force microscopy was used to study the HF-etched transverse sections of thermally poled twin-hole fiber. Thermal poling modified the etch rate in two rings about the anode hole. The outer ring was found to move with time, whereas the inner ring’s position was stationary. Results are explained by use of a space-charge model that comprises two components: movement of impurity ions and charge injection in which the charge injection component dominates the poling characteristics.

Carbon dioxide laser-assisted poling of silicate-based optical fibers.

A novel poling method, carbon dioxide laser-assisted poling (CLAP), is demonstrated. Localized heating during CLAP is achieved through silicate absorption of the CO>(2) laser radiation. Electro-optic coefficients of 0.2 pm/V are achieved within a 55-s scan of a twin-hole fiber. It is shown that there is a range of CO>(2) laser powers for which the residual electro-optic coefficient is maximized.

Optimum parameters for CO/sub 2/ laser-assisted poling of optical fibers

CO/sub 2/ laser-assisted poling is a new technique that potentially allows rapid poling and spatially selective poling. The effect of scan-rate, multiple scans, and power fluctuations on CO/sub 2/ laser-assisted poling were investigated. For a beam irradiance of 52 W /spl middot/ cm/sup -2/ the minimum necessary dwell time was 0.55 s; multiple scans have no effect unless the poling conditions are changed. CO/sub 2/ laser-assisted poling was found to be sensitive to perturbations such as laser power fluctuations, which were detrimental. Under optimized conditions the maximum electrooptic coefficient achieved was 0.4 pm/V. Fiber devices up to 90 cm in length have been poled.

Modification of the third-order nonlinearity in poled silica fibers

Silica glass can be poled either thermally or with UV exposure during application of a strong electric field. Such treatment allows electret formation. So normally isotropic glass can become anisotropic via formation of a frozen-in field. This produces non-zero second-order nonlinearity in glass. After such poling treatment a change in the third- order nonlinearity has been observed. In this paper we examine if modification of the third-order nonlinearity is real or some artifact. To do this the DC third-order nonlinearity was measured before poling, after poling and then after erasure of the second-order nonlinearity. It was found that modification of the third-order nonlinearity remains after erasure of the frozen-in field. The reason for modification of the third-order nonlinearity is still not understood. It may be due to some kind of structural modification of the glass. It is known that impurity ionic species are moved through the glass during poling. This movement of ions under the high field may be sufficient to modify the glass structure. From our results, it is clear that the second-order nonlinearity is predominantly caused by formation of a frozen-in field. The increase of the third-order nonlinearity is independent of existence of a frozen-in field after poling.

Electrically Tunable Thermally-Poled Bragg Gratings

Electrically tunable fibre Bragg gratings are demonstrated based on the thermal poling induced linear electro-optic effect. Fabrication process, device characterization, and performance improvement are addressed.

Effects of ultraviolet and thermal pretreatment on the formation of self-written χ(2) gratings and optical damage

In this article we report the effects of thermal and ultraviolet light pretreatments of a variety of optical fibers with different core dopants. Except for fibers codoped with phosphorus, a negative correlation was found between the onset of optical damage to the fibers and the formation of seeded second-harmonic generation (SHG). From our results and from those of other workers, we conclude that there is a link between susceptibility to optical damage and the formation of seeded SHG in germanosilicate optical fibers.

Thermally stimulated poling and depoling current in thermally poled silica fiber

This paper presents an analysis and comparison of the poling and depoling current evolution with the electro-optic coefficient evolution for positively poled twin-hole fiber, where the anode is closer to the core. The current discharge efficiency was measured to be 5% suggesting that the poling mechanism is due to movement of space charge. During thermal poling we have observed a current peak which corresponds to formation of the shielding field. After formation of the shielding field the electro-optic coefficient begins to grow due to a second poling mechanism. The second poling mechanism occurs during the decay component of the current evolution. The second poling mechanism causes the depletion region to move into the fiber and obtain better overlap with the core. The activation energy for charges in the current peak are of the order of 0.5 eV. In addition, the activation energy was measured to be 30% higher for depoling than for poling of the same device.

Experimental Demonstration of Carbon-Dioxide Laser-Assisted Poling of Optical Fibers

A carbon-dioxide laser is used as a rapid heat source to thermally pole optical fibers. Significant electrooptic coefficients are achieved within seconds.