Ferroelectric single crystal fibers for high frequency electrooptic modulation and optical frequency shift

It is demonstrated in this thesis work that the pulse frequency and pulse profile of an optical wave propagating through an electrooptic single crystal fiber inside a microwave cavity are tuned or modulated by interaction with driving microwave field through nonlinear crystal medium. The approach provides a possible solution to the bandwidth demands and channel definition in optical communications systems. Ferroelectric crystals are of significant interests in electrooptic modulator devices due to their exceptionally high electrooptic coefficients. Ferroelectric single crystal fibers of strontium barium niobate (Sr0.61Ba0.39Nb2O6: SBN) grown by laser heated pedestal growth (LHPG) technique are employed to investigate the relevant properties and the characteristics of this bulk modulator in the microwave range.;Grown from the congruent Sr0.61Ba0.39Nb2O 6 ceramics by LHPG, the phase component changing is monitored by XRD from ceramics to single crystal fibers. The corresponding dielectric properties are measured and compared with each other as function of temperature at low frequency range. Two dielectric anomalies are observed in dielectric spectroscopy at distinct temperature range and the mechanism is investigated to explain the difference of dielectric behavior. The dielectric property of SBN single crystal fiber is also measured at X band microwave frequency by perturbation method using the microwave resonant cavity. It is found that the dielectric constant is in the vicinity of &egr;r =40 (c-axis) in X band of microwave frequency and is relatively constant, deviating from the dramatic decrease trend of low frequency, and can be attributed to the combination of dipole reorientation and electronic polarizability at microwave frequency.;The frequency dependent electrooptic (EO) coefficient of SBN crystal is investigated in this thesis using Senermont method at low frequency and a novel dynamic measurement at high frequency. The EO coefficient increases near the piezoelectric resonant frequency, which may be attributed to the harmonic contribution of piezoelectric resonances. The formula and new mechanism of measuring the EO coefficient at 10GHz is deduced and explored using a standing mode microwave cavity. It is found that SBN61 crystal possesses smaller electrooptic coefficient (r33 ∼200pm/V) at 10GHz compared to low frequency (rc ∼300pm/V) at 1kHz. This method can be easily extended to measure EO property at other frequency ranges using corresponsive cavity across the wide frequency scope without the requirement of electric contact on the specimen.;Ferroelectric single SBN crystal fiber is evaluated for optical pulse engineering in terms of frequency shifting and pulse compression/expansion at microwave frequencies. The microwave-photonic interaction is investigated experimentally in a TE103 microwave cavity at 10GHz. The theoretical consideration and potential experimental solution in traveling wave mode are also studied in order to accumulate the modulating effect and to make full use of crystal length. It is shown that the frequency component of an optical pulse can be controlled effectively using the SBN single crystal in microwave cavity without the need of contact electrodes or any interruption to the optical system. The technique is of utility in several aspects of optical communications such as channel definition and security encoding of the signal, and of potential to a range of optoelectronic applications.