Abstract: A grating is induced in the core of a hydrogen-loaded high-germanium-content optical fiber using near-UV (275 nm-390 nm) laser light. An interference pattern is generated at the core using a molded polymer phase mask with a square wave surface relief pattern. The light is directed through the phase mask, through a protective fiber coating, through the cladding, and into the core. The phase mask generates an interference pattern with a period half that of the surface relief pattern. Index of refraction changes occur at the bright fringes of the interference pattern--thus creating the grating. Advantages over existing mid-UV technology include lower fabrication costs for phase masks, simplified grating induction since fiber coatings do not need to be removed, and reduced infrared absorption caused by grating formation in the fiber.

Abstract: An optical amplification system directs a diffraction-limited signal beam through a series of crossings, at substantially less than 90.degree. crossing angles, with a number of non-diffraction-limited pump beams in a photorefractive medium. The pump beams are e-polarized while the signal beam travels down the crystal medium's c-axis and is polarized in the same plane as the pump beam polarization, resulting in an energy transfer from the pumps to the signal beam while leaving the signal beam diffraction-limited. The photorefractive medium is preferably a series of BaTiO.sub.3 :Rh crystals that are aligned parallel to the angled edge of a wedged-shape prism through which the pump beams are transmitted, with the crystals cut so that their C-axes are parallel to the signal beam.

Abstract: An optical amplification system directs a diffraction-limited signal beam through a series of approximately 90.degree. crossings with a number of non-diffraction-limited pump beams in a photorefractive medium. All of the beams are s-polarized, resulting in an energy transfer from the pumps to the signal beam while leaving the signal beam diffraction-limited. The photorefractive medium is preferably a series of BaTiO.sub.3 :Rh crystals that receive the pump and signal beams through orthogonal faces, with their C-axes at approximately 45.degree. to both beams. A binary tree optical distribution network is used to minimize waveguide splits in forming a large number of pump beams.

Abstract: A laser system includes a linear array of broad area lasers. Such a laser source produces a beam that has a polarization axis in the direction in which the array extends and a coherency axis orthogonal to that. The laser is injection locked by phase conjugating a portion of the array's light output. The phase conjugator has a conjugation axis. The coherency axis is aligned with this conjugation axis. External cavity optics include a polarization rotator to align the polarization axis with the coherency axis before the beam reaches the phase conjugator. Thus, the polarization, coherency, and conjugation axes are all aligned, optimizing the action of the phase conjugator. The approach works in both a single-beam and a dual-beam phase conjugation mode. The result is a laser system output of higher intensity, greater coherence, and a narrower frequency range.

Abstract: In a conventional hologram, a photographic film records the interference pattern of monochromatic light, scattered from an object (20) to be imaged, with a reference beam of unscattered light. Illumination of the developed film with a replica of the reference beam then creates a virtual image of the original object. Molecular resonance may be used to record an interference pattern between light signals that arrive at different times, and with this technique create a hologram (10') with time resolution. Using a time reference pulse (16) as a "light shutter", holographic images may be recorded selectively, according to the time taken by light travelling from the object to the hologram. This method may be used to image an object obscured by a light-scattering medium.

Abstract: A microscope that preferentially displays either moving or stationary objects. This all-optical device operates in real-time using the coupling of optical beams in suitable nonlinear medium such as a photorefractive crystal of barium titanate. A holographic image is continuously written and compared with the real image. For the transient detection microscope any discrepancy between the two images is immediately visible. In the stationary object enhancing microscope stationary objects are enhanced and preferentially displayed.

Abstract: A phase-conjugate optical communication system includes a first source of coherent radiation for producing a first beam having a nominal wavelength .lambda. and a first modulator for temporally modulating the first beam. A second source of coherent radiation, mutually incoherent with the first source, produces a second beam having the nominal wavelength .lambda., while a second modulator temporally modulates the second beam. A mutually pumped phase conjugator is positioned such that the first and second beams fan in the conjugator and produce a set of shared fanning holograms, the holograms causing a third beam, which is the phase conjugate of the first beam and on which is imposed the temporal modulation of the second beam, to be diffracted in a direction opposite to the first beam and causing a fourth beam, which is the phase conjugate of the second beam and on which is imposed the temporal modulation of the first beam, to be diffracted in a direction opposite to the second beam.

Abstract: Changes in an image are detectable by a tracking novelty filter while an incorporated holographic medium is in disequilibrium. A suitably doped single-domain barium titanate crystal can serve as the holographic medium. Image information is imposed on a laser beam in the form of a spatially varying polarization across the beam cross section spatial position. The modulated beam is directed to the crystal, which cooperates with a polarizing beam splitter and a half wave plate to define a polarization conjugator. The conjugated beam is passed through the modulator a second time and then operated on by a beam splitter. When the crystal is in equilibrium with the incident laser light, the beam splitter directs minimal light to a detector. However, when an image change causes a change in the applied modulation, the changed image elements are intensified at the detector while the holographic medium is in disequilibrium. In alternative embodiments, phase is the variable modulated.