Danny Wong

Large electrooptic modulation in a thermally-poled germanosilicate fiber

A large linear electro-optic phase shift observed in a germanosilicate fiber has been induced by thermal poling at about 250/spl deg/C for 20-60 min with an electric field of >8/spl times/10/sup 5/ V/cm and a 3.3-cm electrode length. Polarization dependence of the V/sub /spl pi//L product in a birefringent germanosilicate fiber has been found, and the lowest V/sub /spl pi//L product has been measured for TE-polarization of 224 V/cm at 633 nm. Furthermore, it has been found that the electrical resistance between the electrodes is reduced by thermal poling.<<ETX>>

Stress-birefringence reduction in elliptical-core fibers under ultraviolet irradiation.

It is found that the temperature sensitivity of a fiber polarimeter can be significantly reduced by UV irradiation of the fiber. A stress-relief model is proposed to explain the mechanism, which is proposed to be a consequence of the breakage of oxygen-deficient bonds (wrong bonds) in the glass network through single-photon or multiphoton absorption, with a subsequent relaxation of the tensile stresses in the fiber core.

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.

Evidence of space-charge effects in thermal poling

The in situ thermal poling processes in germanosilicate fibers for positive and negative poling voltages are significantly different. Thermal poling of silica fibers consists of two processes: the faster linear process of charge migration and the subsequent single exponential process of charge ionization. Both the shielding electrical field due to charge migration and the ionization electrical field due to charge ionization are able to be frozen-in at room temperature and lead to the residual linear electrooptic effects. The observations support that the mechanism of the induced electrooptic effects is based on space charge electrical fields instead of dipole/bond orientation.

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.

Ultraviolet photolytic-induced changes in optical fibers: the thermal expansion coefficient

We show that recent experimental results of Wong et al. [Opt. Lett. 17, 1773 (1992)] on the effect of UV photolytic processing on the birefringence of elliptical-core fibers arise from a 15-30% reduction of the coefficient of thermal expansion of the germanosilicate core. An explanation based on reconfiguration of the glass network to minimize the stress energy during UV processing is proposed.

Growth and decay of the electrooptic effect in thermally poled B/Ge codoped fiber

Using an in situ technique for measuring the induced electrooptic effect during poling, we have studied the growth and decay characteristics of thermally poled twin hole B/Ge codoped fiber devices. The decay characteristic measured at elevated temperatures were best fitted with a stretched exponential function, indicating a distribution of relaxation times is present in this material. Using the Arrhenius relation, we calculate an activation energy for the stability of the electrooptic effect with this material and poling geometry in the range from 25 to 28 kJ/mol (0.28-0.31 eV), corresponding to a lifetime at 298 K of approximately 45 days.

Eliptically polarizing optical fiber

Elliptically polarizing optical fiber has been fabricated. Measurements show an extinction of the lossy mode relative to the transmitted mode of around 10 dB/m. The preform is spun during drawing and the ellipticity of the transmitted polarization state is as expected from the measured beat length of the unspun fiber and the pitch length of the spun fiber. This fiber is expected to be useful for interferometric or laser-based electric-current sensing, and perhaps in other applications for an in-line polarizer.

Positive and negative thermal poling of germanosilicate fibres

In situ measurements of thermal poling of germanosilicate fibers under positive and negative poling voltages show different dynamics of a linear electro-optic effect induced into fibers. The mechanism for the induced electro-optic effect is addressed.

Charge dynamics and distributions in thermally poled silica fiber

Silica glass plays a key role in photonic systems because of its excellent optical properties, such as low loss, low fabrication cost and high photo-refractive damage threshold. Unfortunately, silica, being centrosymmetric, has no intrinsic linear electro-optic (LEO) coefficient or second-order nonlinearity (SON). However, thermal poling has been demonstrated to produce a LEO coefficient and SON of approximately 1 pm/V in silica glass and fiber. It is necessary to understand the mechanism of thermal poling in order to achieve a larger, stable and reliable LEO effect. A series of thermal poling experiments on silicate fiber was carried out. The in situ measurements of the total LEO coefficients (the sum of the poling field induced LEO coefficient and the thermal poling induced residual LEO coefficient) suggest movement of charges. Thermal poling induced residual LEO coefficients are measured in situ during prolonged negative thermal poling. Both the shielding field and the ionization field are frozen-in at room temperature and lead to LEO effect. The time evolution of the residual LEO coefficients shows that the competition between the shielding and ionization fields is a linear process. Using this new understanding, a specialty optical fiber was developed for the production of thermally poled optical fiber devices.