Eran Rave

Silver halide single-mode fibers for the middle infrared

There is an interest in single-mode fibers that are highly transparent in the middle infrared. Such fibers would be valuable for spectroscopy, interferometry, fiber lasers, and heterodyne detection. We developed core-clad fibers made of crystalline silver halides, with external diameter 900 μm, small core diameters (50–60 μm) and an extremely small difference (∼0.004) between the indices of refraction of the core and the clad. These fibers behaved as single-mode fibers at the wavelength 10.6 μm.

Silver halide photonic crystal fibers for the middle infrared.

Photonic crystal fibers are normally holey silica fibers, which are opaque in the mid- and far-infrared. We have fabricated novel fibers by multiple extrusions of silver halide crystalline materials, which are highly transparent in the mid-infrared. These fibers are composed of two solid materials; The core consists of pure AgBr, and the cladding includes AgCl fiberoptic elements arranged in two concentric hexagonal rings around the core. Flexible fibers of outer diameter 1 mm and length of approximately 1 m were fabricated, and their optical properties were measured. These fibers exhibited core-clad behavior and would be extremely useful for IR laser power transmission, IR radiometry, and IR spectroscopy.

Ordered bundles of infrared transmitting silver halide fibers: attenuation, resolution and crosstalk in long and flexible bundles

Flexible ordered bundles of infrared transmitting silver-halide fibers were fabricated by multiple extrusions from single crystals. We have developed flexible bundles of outer diameter 1 mm and lengths up to 2 m, which included 30 to 100 individual elements and the diameters of each element were between 40 to 70 ?m. The transmission losses of individual elements in the bundles were of the order of a few decibels per centimeter. The modulation transfer function of the bundles was determined and the resolution was found to be a few lines per millimeter. The crosstalk was of the order of 30%. Such thin, long, and flexible bundles would be extremely useful for fiber-optic thermal imaging in science, medicine, and industry.

Thermal imaging through ordered bundles of infrared-transmitting silver-halide fibers

Ordered bundles of infrared-transmitting silver-halide (AgClxBr1−x) fibers were fabricated by extrusion. Bundles of total area 5–20 mm2 and lengths 5–50 cm included 100–2500 individual fibers and the packing fraction was 0.2–0.3. Each of the individual fibers was transparent in the spectral range 3–30 μm, and therefore, the whole bundle was suitable for thermal imaging. The modulation transfer function was studied using the “bar chart” and the “knife-edge” methods. The resolution was found to be 4–5 lines/mm for a 900 fiber bundle. Thermal images of objects at room temperature were transmitted from the entrance ends to the exit ends of the bundles.

Infrared photonic crystal fiber

An infrared photonic crystal fiber has been made by multiple extrusions of silver halide (AgClxBr1−x) crystalline materials. The core of the fiber consisted of pure AgBr, and the cladding area included fiberoptic elements made of AgCl (with lower refractive index). Fibers of outer diameter 1 mm and length of the order of 1 m were flexible and transparent in the spectral range 3–20 μm. Measurements of the power distribution and the transmission losses in the fibers indicated that they behave like core-clad structures, with an effective core diameter 200 μm. These fibers will be extremely useful for many applications in the middle- and far-infrared.An infrared photonic crystal fiber has been made by multiple extrusions of silver halide (AgClxBr1−x) crystalline materials. The core of the fiber consisted of pure AgBr, and the cladding area included fiberoptic elements made of AgCl (with lower refractive index). Fibers of outer diameter 1 mm and length of the order of 1 m were flexible and transparent in the spectral range 3–20 μm. Measurements of the power distribution and the transmission losses in the fibers indicated that they behave like core-clad structures, with an effective core diameter 200 μm. These fibers will be extremely useful for many applications in the middle- and far-infrared.

Few modes in infrared photonic crystal fibers

Photonic crystal fibers guide light by trapping it in a periodic array of elements in the cladding area. We fabricated photonic crystal fibers by multiple extrusions of silver halide (AgClxBr1−x) crystals which are highly transparent in the middle infrared. The core of such a fiber consisted of pure silver bromide AgBr (n=2.16 at 10.6μm), and the cladding area consisted of concentric rings of fiber-optic elements made of pure silver chloride AgCl (n=1.98 at 10.6μm), which lowered the refractive index of the clad. Two types of photonic crystal fibers were fabricated, one with two concentric rings and one with five concentric rings of fiber-optic elements around the core. The characterization of the fibers, such as the power distribution, the attenuation, and the numerical aperture were measured. Both fibers behaved like regular core-clad structures. Simulations on these structures showed that each of these fibers guided a small number of modes and that adding rings to the structure lowered the number of bo...

Thermal imaging through infrared fiber/waveguides bundles

Trans-endoscopic Infrared Imaging (IRI) relates the possibility to conduct IRI diagnosis of internal body surfaces under minimal invasiveness. It may also be utilized to control and to optimize the thermal interactions and the potential side effects during Minimally Invasive Surgeries (MIS). However, transferring the thermal images transendoscopically requires the usage of IR imaging bundles, which are neither yet mature nor commercially available. In our setup we have used two basic types of recently-developed imaging bundles: Ag/AgI-coated Hollow Glass Waveguide (HGW) bundles and Silver Halide (AgClBr) core-clad fiber bundles. The optical setup system was consisted of IR optics (e.g. ZnSe lenses, reflective objectives) and a thermal IR camera. We have succeeded to image objects through the bundles, such as various shapes of electrically heated wires, ex-vivo biological phantoms (samples of porcine stomach) and in-vivo phantom models (mice) irradiated by CO2 laser. Measurements were conducted for both - static and dynamic object states.

Toward the realization of a single-mode photonic crystal fiber in the middle infrared

Photonic crystal fibers confine light within a periodic array of elements. We used multiple extrusions of silver halide (AgClxBr1-x) crystalline materials to fabricate photonic crystal fibers, which are transparent in the middle infrared (mid-IR) in the spectral range 2-20 μm. The cores of these fibers consisted of pure silver bromide (AgBr) of refractive index n=2.16, and the cladding area included concentric rings of tens of fiberoptic elements made of pure silver chloride (AgCl), of a lower refractive index n=1.98. Simulations on photonic crystal structures showed that all the fabricated fibers guide a small number of modes. Furthermore, adding rings to such a structure should lower the number of bound modes in the core. We measured the attenuation and the output power distribution of these fibers and carried out spectroscopic measurements in the mid-IR. Good correlation was found between the experimental and the theoretical results. These findings will pave the way for the fabrication of single-mode fibers in the mid-IR range.

AgClBr photonic crystal fibers for the middle infrared

Photonic crystal fibers (PCFs) are normally holey fibers, made of silica glass, which is opaque in the mid- and far-infrared spectral range 3-20 μm. We have fabricated novel PCFs by multiple extrusions of silver halide (AgClxBr1-x) crystalline materials, which are highly transparent in this spectral range. These PCFs are composed of two solid materials: the core consists of pure AgBr (n=2.16), and the cladding includes small diameter fiberoptic elements, made of AgCl (n=1.98). These AgCl fiberoptic elements are arranged in two concentric hexagonal rings around the core. This structure gives rise to a cladding region of lower refractive index, thus ensuring total internal reflection. Flexible PCFs of outer diameter 1mm and length of about 1m were fabricated, and their optical properties were measured. Measurements of numerical aperture, laser power transmission and evanescent wave spectroscopy indicated that the PCFs behave like a core-clad structure. There was a good agreement between the results and those obtained by theoretical simulations. Silver halide PCFs would be extremely useful for IR laser power transmission, for IR radiometery and for IR spectroscopy.