William R. Christian

Volume holographic memory systems: techniques and architectures

Although the concept of using multiplexed holography for data storage has been considered for some time, recent advances in several critical device technologies along with developments in storage materials have greatly enhanced the likelihood of successful implementations. We review several basic architectural concepts along with various multiplexing options and associated techniques for holographic data storage.

Two-wave mixing and phase conjugation at 830 nm in BaTiO 3

We report two-wave mixing and self-pumped phase-conjugation measurements for GaAlAs laser-diode radiation at 830 nm in BaTiO(3). At 11 degrees C, two-wave mixing gain coefficients as large as 18 cm(-1) and response times of the order of 1 min have been observed by using an optimized mixing geometry. Phase-conjugate reflectivities as large as 56% with 10-sec response times have also been measured using BaTiO(3) in a passive ring conjugator when the source laser is optically isolated from the conjugator. These results represent significant improvements over corresponding values previously reported.

Energy transfer between injection-locked single-mode diode lasers by two-beam coupling in BaTiO(3).

Two-beam coupling in photorefractive BaTiO(3) is used to combine beams coherently from two injection-locked single-mode diode lasers operating at 830 nm. We are able to transfer more than 70% of the power in one beam to the other beam with this method.

Picosecond pulsed diode ring-laser gyroscope.

We have demonstrated a novel solid-state ring-laser gyroscope, which utilizes as the gain media a pair of semiconductor diodes in an external ring cavity. The use of homogeneously broadened gain media is made possible by actively mode locking the laser. We observe no evidence of frequency locking between the counterpropagating optical pulse trains generated in the cavity to within the limit of our experimental resolution.

Pulsed diode ring laser gyroscope

We have demonstrated a novel solid-state ring laser gyroscope by actively modelocking a pair of InGaAsP diodes in an external ring cavity. We observe no evidence of gain competition or frequency locking between the counterpropagating optical pulse trains circulating in the cavity to within the limit of our experimental resolution.

Picosecond-pulsed diode ring laser gyroscope

An external ring cavity containing as its active medium a pair of InGaAsP diodes is modelocked to produce picosecond pulses. In such a laser, a small frequency difference proportional to the nonreciprocal phase shift (resulting from, e.g., the Sagnac effect) can be observed by beating together the counterpropagating laser arms; the device therefore acts as a rotation sensor. In contrast to a conventional (cw) ring laser gyroscope, the pulsed gyroscope can avoid gain competition, thereby enabling the use of homogeneously broadened gain media like semiconductor diodes. Temporal separation of the pulses within the cavity also discriminates against frequency locking of the lasers. The picosecond pulsed diode ring laser gyroscope is reviewed. Both active and passive modelocking are discussed.

Nonlinear optical techniques for obtaining high brightness from diode lasers

How nonlinear optics can be used to obtain high brightness from diode lasers is described. The use of two-wave mixing to combined and clean up the output of any frequency-locked high-power device is addressed. The application of phase conjugation for coupling to lock lasers is considered.

Theoretical and experimental results for 1550-nm light scattering in clouds and their predictions for pulse broadening effects on high-throughput optical communications

We present theoretical and experimental results for the expected impact on high-throughput optical communication systems of pulse broadening effects from scattered light propagating through water-based clouds. Existing analytical models are compared with experimental results. A preferred Monte Carlo model is developed and validated from field measurements of off-axis scattering through clouds, using a low-power continuous wave laser source at 1550 nm wavelength. This model is used in the time domain to examine the effects of pulse broadening for Gigabit and higher systems with practical apertures and fields of view. Results indicate that, for most current scenarios, pulse stretching may not cause significant inter-symbol interference.

Photorefractive Optics At Near-Infrared Wavelengths

Measurements of two-wave mixing gain and phase-conjugate response in barium titanate using GaAlAs diode laser sources emitting at 830 nm are discussed. Gain coefficients as large as 18 cm-1 have been obtained with optimized mixing geometries. With an optically isolated barium titanate ring passive phase-conjugate mirror we have obtained phase-conjugate reflectivities as large as 56% (uncorrected for Fresnel reflection losses) and response times on the order of tens of seconds. These results represent significant improvements over corresponding values previously reported in the literature.