Catalin Florea

Stimulated Brillouin scattering in single-mode As 2 S 3 and As 2 Se 3 chalcogenide fibers

Stimulated Brillouin scattering was investigated for the first time in As(2)S(3) single-mode fibers, and also in As(2)Se(3). The propagation loss and numerical aperture of the fibers at 1.56 mum, along with the threshold intensity for the stimulated Brillouin scattering process were measured. From the threshold values we estimate the Brillouin gain coefficient and demonstrate record figure of merit for slow-light based applications in chalcogenide fibers.

Reduced Fresnel losses in chalcogenide fibers by using anti-reflective surface structures on fiber end faces.

We demonstrate microstructuring of chalcogenide fiber end faces in order to obtain enhanced transmission due to the antireflective properties of the microstructured surfaces. A variety of molding approaches have been investigated for As(2)S(3) and As(2)Se(3) fibers. Transmission as high as 97% per facet was obtained in the case of As(2)S(3) fiber, compared to the native, Fresnel-loss limited, transmission of 83%. The potential for hydrophobic character was also demonstrated by increasing the contact angle of water droplets to greater than 120°.

Anti-reflective surface structures for spinel ceramics and fused silica windows, lenses and optical fibers

Anti-reflective surfaces structures (ARSS) have been successfully fabricated on fused silica windows, lenses and fibers, and spinel ceramics. The reflection loss for spinel was reduced from 7% per surface to 0.9%. For fused silica with ARSS, the reflection loss was reduced to 0.02% near 1 µm. Pulsed laser damage thresholds at 1.06 µm were measured and thresholds as high as 100 J/cm2 were obtained for fused silica windows of up to 10 cm in diameter with ARSS and 850 J/cm2 for silica fibers with ARSS on the end faces. Spinel samples with ARSS showed damage thresholds more than two times higher than that of spinel with traditional AR coatings.

Reduced Fresnel losses in chalcogenide fibers obtained through fiber-end microstructuring

We demonstrate microstructuring of chalcogenide fiber facets in order to obtain enhanced transmission due to the antireflective properties of the microstructured surfaces. A variety of molding approaches have been investigated for As(2)S(3) and As(3)Se(3) fibers. Transmission as high as 97% per facet was obtained in the case of As(2)S(3) fiber, compared to the native, Fresnel-loss limited, transmission of 83%.

Broadband beam steering using chalcogenide-based Risley prisms

In this paper, we propose using chalcogenide glasses for improved, large-angle, beam steering of infrared radiation, with minimal spectral dispersion and improved thermal performance over wavelength intervals covering the 2 to 12-μm range. For example, we evaluate that full-angle dispersion in the 2 to 5 μm region for LiF/As 2 S 3 combination should be three times smaller than in the case of LiF/ZnS combination. We also evaluate that using the ZnSe/As 2 Se 3 combination will provide twice as small thermal walk-off than a similar ZnS/Ge system in the 8 to 12-μm region.

Laser oscillation from Ho 3+ doped Lu 2 O 3 ceramics

We report, for the first time, the laser oscillation from 2% Ho3+:Lu2O3 hot pressed ceramic. We have synthesized optical quality Lu2O3 nano-powders doped with concentrations as high as 5% Ho3+. The powders were synthesized by a co-precipitation method beginning with nitrates of holmium and lutetium. The nano-powders were hot pressed into optical quality ceramic discs. The optical transmission of the ceramic discs is excellent, nearly approaching the theoretical limit. The optical, spectral and morphological properties as well as the preliminary lasing performance from highly transparent ceramics are presented.

Recent advancements in anti-reflective surface structures (ARSS) for near- to mid-infrared optics

Fused silica, YAG crystals, and spinel ceramics substrates have been successfully patterned through reactive ion etching (RIE). Reflection losses as low as 0.1% have been demonstrated for fused silica at 1.06 microns. Laser damage thresholds have been measured for substrates with ARSS and compared with uncoated and/or thin-film anti-reflection (AR) coated substrates. Thresholds as high as 100 J/cm2 have been demonstrated in fused silica with ARSS at 1.06 microns, with ARSS substrates showing improved thresholds when compared with uncoated substrates.

Irradiance enhancement and increased laser damage threshold in As₂S₃ moth-eye antireflective structures.

It has been experimentally observed that moth-eye antireflective microstructures at the end of As2S3 fibers have an increased laser damage threshold relative to thin-film antireflective coatings. In this work, we computationally study the irradiance enhancement in As2S3 moth-eye antireflective microstructures in order to explain the increased damage threshold. We show that the irradiance enhancement occurs mostly on the air side of the interfaces and is minimal in the As2S3 material. We give a physical explanation for this behavior.

Dynamics of photoinduced refractive index changes in As2S3 fibers.

We investigate the dynamics of photoinduced index changes in chalcogenide As(2)S(3) fibers. Using a novel phase sensitive technique for measuring the photoinduced index change, we find that the index evolution is a two-stage process: it consists of a fast reduction and a subsequent slow increase in the refractive index. We show that the index change depends strongly on the beam intensity with both positive and negative changes possible. These findings can have application in design and fabrication of photoinduced devices such as Bragg gratings and photonic cavities.

Progress of Chalcogenide Glass Fibers

High nonlinearity and large IR transparency make these fibers well suited for compact Raman amplifiers, supercontinuum generation and other mid-IR sources. As2S3 fiber has record high theoretical gain compared with silica fiber for slow-light applications.