The authors show that micron size fibers comprised of semiconductor and metallic materials can be purified or doped, recrystallized or have the constituents rearranged into a variety of structures with device prospects. The molten core drawing method allows scalable fabrication of novel core fibres with kilometre lengths. With metal and semiconducting components combined in a glass-clad fibre, CO2 laser irradiation was used to write localised structures in the core materials. Thermal gradients in axial and transverse directions allowed the controlled introduction, segregation and chemical reaction of metal components within an initially pure silicon core, and restructuring of heterogeneous material. Gold and tin longitudinal electrode fabrication, segregation of GaSb and Si into parallel layers, and Al doping of a GaSb core were demonstrated. Gold was introduced into Si fibres to purify the core or weld an exposed fibre core to a Si wafer. Ga and Sb introduced from opposite ends of a silicon fibre reacted to form III-V GaSb within the Group IV Si host, as confirmed by structural and chemical analysis and room temperature photoluminescence.

High speed optical modulation of THz radiation is of interest for information processing and communications applications. In this paper infrared femtosecond pulses are used to generate free carriers that reduce the THz transmission of silicon based waveguides over a broad spectral range. Up to 96 6 70 modulation is observed from 0.5 to 7 THz in an optical fiber with a 210 mu m diameter gold-doped silicon core. The observed carrier recombination time of 2.0 +/- 0.2 ns makes this material suitable for high speed all-optical signal processing. These results show both enhanced modulation depth and reduced carrier lifetime when compared to the performance of a high resistivity float zone silicon rectangular guide with comparable cross sectional area.

Stimulated Raman amplification is observed for the first time in the silicon core fiber (SCF) platform. The SCFs were tapered to obtain sub-micrometer core dimensions and low optical transmission losses, facilitating efficient spontaneous scattering and stimulated Raman amplification using a continuous-wave pump source with milliwatt power levels. A maximum on-off gain of 1.1 dB was recorded at a pump power of only 48 mW with our numerical simulations, indicating that gains up to 6dB are achievable by increasing the fiber length. This work shows that the SCF platform could open a route to producing compact and robust all-fiber integrated Raman amplifiers and lasers across a broad wavelength region.

Hair-thin strands of glass, intrinsically transparent and strong, of which many millions of kilometers are made annually, connect the world in ways unimaginable 50 years ago. What could another 50 years bring? That question is the theme of this Perspective. The first optical fibers were passive low-loss conduits for light, empowered by sophisticated sources and signal processing; a second advance was the addition of dopants utilizing atomic energy levels to promote amplification, and a third major initiative was physical structuring of the core-clad combinations, using the baseline silica material. Recent results suggest that the next major expansions in fiber performance and devices are likely to utilize different materials in the core, inhomogeneous structures on different length scales, or some combination of these. In particular, fibers with crystalline cores offer an extended transparency range with strong optical nonlinearities and open the door to hybrid opto-electronic devices. Opportunities for future optical fiber that derive from micro- and macro-structuring of the core phase offer some unique possibilities in 'scattering by design'.

Silicon core fibers represent a versatile platform for all-fiber integrated nonlinear optical applications. This paper describes the state of the art in four-wave mixing-based parametric amplification, and wavelength conversion in silicon fibers that have been tapered to improve the material quality, and engineer the dispersion profile. Fibers with submicron core dimensions have been fabricated, and used to demonstrate high gain parametric amplification in the C-Band, and broadband wavelength conversion extending out to the S-, and L-bands. The potential to use these fibers for all-optical signal processing of 20 Gbit/s data signals has also been demonstrated, with a robust all-fiber coupling scheme presented to improve the efficiency, and practicality of these devices. These results highlight the potential of silicon core fibers for use in nonlinear signal processing within future telecommunication systems.

Novel core fibers have a wide range of applications in optics, as sources, detectors and nonlinear response media. Optoelectronic, and even electronic device applications are now possible, due to the introduction of methods for drawing fibres with a semiconductor core. This review examines progress in the development of glass-clad, crystalline core fibres, with an emphasis on semiconducting cores. The underlying materials science and the importance of post-processing techniques for recrystallization and purification are examined, with achievements and future prospects tied to the phase diagrams of the core materials. The application space for optical fibers is growing, enabled by fibers built using special materials and processes. In this Review, the authors discuss the materials science behind producing crystalline core fibers for diverse applications and progress in the field.

Silicon waveguide structures are a viable alternative for the transmission of signals over a wide range of frequencies, and new fabrication methods are key to increased applications. In this work, THz transparency of silicon-core, silica clad fibers, refined using a traveling solvent method, is demonstrated. The approximate to 200 mu m core of these fibers is shown to have good transmission from 4.8-9 mu m and 1-7 THz. Fibers were drawn on a conventional optical fiber tower using the scalable molten core technique and CO2 laser annealed, resulting in large-grain crystalline cores with broadband transmission. The spectral properties are comparable to those of rectangular guides of similar cross-sectional area cut from high resistivity float zone silicon wafers.

CO2 laser annealing of SiGe core, glass-clad optical fibers is a powerful technique for the production of single-crystal cores with spatially varying Ge concentrations. Laser power, laser scan speed and cooling air flow alter the Ge distribution during annealing. In this work, near-single crystal fibers exhibiting a central axial feature with peak Ge concentration similar to 15 at% higher than the exterior of the semiconductor core have been prepared. Preferential transmission of near infrared radiation through the Ge-rich region, and spectral data confirm its role as a waveguide within the semiconductor core. This proof-of-concept step toward crystalline double-clad structures is an important advancement in semiconductor core optical fibers made using the scalable molten core method.

The waveguiding properties of high-resistivity float zone silicon slab waveguides are characterized over the spectral range from 0.5 to 7.5 THz. Waveguide modes and dispersion are observed for lengths of 1.2 cm and silicon thicknesses from 40 to 300 mu m. The influence of core thickness and cladding glass attenuation is characterized, and modeled transmitted pulse shapes compare well to the measured signals. Fused silica cladding allows propagation in the 40 mu m thick wafer, demonstrating the feasibility of developing flexible semiconductor core fibers for THz transmission.

An all-fiber integrated nonlinear silicon photonic wavelength converter has been proposed and fabricated using the silicon core fiber platform. The silicon fiber was spliced directly to a conventional single mode fiber, facilitated via an inverse tapered nano-spike that helped to reduce the mode mismatch between the different core materials. Four-wave mixing-based wavelength conversion with an efficiency as high as -22.1 dB has been achieved for selected wavelengths across the C-band in a device length of only similar to 1 cm. Successful conversion of quadrature phase-shift keying signals at a 20-Gb/s bitrate, with a 1 to 2 dB penalty level at the bit error ratio (BER) = 3.8 x 10(-3), was used to demonstrate the suitability of the silicon fiber device for the construction of ultra-compact, all-fiber-based optical signal processing systems.