There is a wide interest in single-mode optical fibers for the middle infrared range of 3–30μm. These fibers will be useful for a variety of applications such as spatial filtering and interferometry. However, many technical and theoretical problems hindered the development of such fibers. Segmented cladding fibers may make it possible to combine an extremely large core area and single mode operation over a large spectral range. The design parameters may accurately control the optical properties of such fibers. We report here the design and fabrication of segmented cladding fibers made of crystalline silver halides, which are highly transparent in the middle infrared.

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The split-step Fourier method is commonly used to simulate the propagation of radiation in a turbulent atmosphere using two-dimensional phase screens that have the desired spatial spectral content given by the atmospheric power spectrum. Using existing methodologies, isotropy of the structure function can never be achieved, mainly along the axis of propagation, for several reasons. In this paper, we introduce the sparse spectrum harmonic augmentation method that will address the lack of isotropy along the propagation axis, the limited achievable frequencies, and the limited time development possible using known approaches. Following the methodology described will produce phase screens that are transversely endless, perfectly correlated along the propagation axis, and contain the desired spectral content, including the low frequencies that even though they contain most of the energy, are usually neglected. The methodology presented can be used for many aspects of wave propagation in random media, such as atmospheric propagation, underwater acoustics, radio wave propagation in the ionosphere, and more.

We report the design, fabrication and optical characterization of total internal reflection segmented-cladding fibers for the middle-infrared spectral range 2-20µm. Segmented cladding is a novel fiber design in which the uniform core of high refractive material is surrounded by a cladding of alternating segments of high and low refractive indices. Segmented cladding fibers are capable of maintaining a single-mode operation over a wide spectral range with a large core area. The design of the fibers and the simulations were made using the radial effective index method. The fibers were extruded from silver-halide crystals by using the 'rod in tube' method. Using this method we were able to construct large core fibers which exhibited few-modes and relatively low losses at 10.6µm.

This paper introduces the concept of atmospheric channels and describes a possible approach for the coherent beam combining of lasers of an optical phased array (OPA) in a turbulent atmosphere. By using the recently introduced sparse spectrum harmonic augmentation method, a comprehensive simulative investigation was performed and the exceptional properties of the atmospheric channels were numerically demonstrated. Among the interesting properties are the ability to guide light in a confined manner in a refractive channel, the ability to gather different sources to the same channel, and the ability to maintain a constant relative phase within the channel between several sources. The newly introduced guiding properties combined with a suggested method for channel probing and phase measurement by aerosol backscattered radiation allows coherence improvement of the phased array's elements and energy refocusing at the location of the channel in order to increase power in the bucket without feedback from the target. The method relies on the electronic focusing, electronic scanning, and time gating of the OPA, combined with elements of the relative phase measurements.