Single-mode optical fibers for the mid-IR (λ=3-30μm) are needed for many applications such as IR fiber lasers
and spatial filtering for nulling interferometry. In the past, we have already reported the design and fabrication of stepindex
single mode fibers for the mid-IR. Index guiding photonic crystal fibers (IG-PCF) offer many advantages over
step-index fibers, such as a wide spectral range, large mode area and low bending losses. So far, only limited success has
been achieved in the development of such fibers, due to the lack of suitable materials that are transparent in this spectral
range. We report here the design, fabrication and optical characterization of single-mode IG-PCFs for the mid-IR.
Triangular and octagonal IG-PCFs were fabricated from silver halide polycrystalline materials which transmit well in the
spectral range 2-20μm. The photonic crystal fibers were characterized by near-field and far-field measurements and they
demonstrated a single-mode behavior with relatively low losses and a large mode area, in agreement with our simulations. As predicted from the simulations, the octagonal arrangement of the rods in the fiber resulted in a single mode fiber with lower losses, a better mode shape and a higher rejection of high order modes, in comparison to the
We report the design, fabrication and optical characterization of total internal reflection segmented-cladding fibers for the middle-infrared spectral range 2-20 μm. 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 10.6 μm.