Chitrarekha Chaudhari

Ultrabroadband supercontinuum generation from ultraviolet to 6.28 μm in a fluoride fiber

Ultrabroadband supercontinuum light expanding from ultraviolet to 6.28 μm is generated in a centimeter-long fluoride fiber pumped by a 1450 nm femtosecond laser. The spectral broadening in the fluoride fiber is caused by self-phase modulation, Raman scattering and four-wave mixing. The experimental and simulated results show that fluoride fiber is a promising candidate for generating the midinfrared supercontinuum light up to 8 μm.

Tellurite microstructure fibers with small hexagonal core for supercontinuum generation

Tellurite glass microstructure fibers with a 1 microm hexagonal core were fabricated successfully by accurately controlling the temperature field in the fiber-drawing process. The diameter ratio of holey region to core (DRHC) for the fiber can be adjusted freely in the range of 1-20 by pumping a positive pressure into the holes when drawing fiber, which provides much freedom in engineering the chromatic dispersion. With the increase of DRHC from 3.5 to 20, the zero dispersion wavelengths were shifted several hundred nanometers, the cutoff wavelength due to confinement loss was increased from 1600 nm to 3800 nm, and the nonlinear coefficient gamma was increased from 3.9 to 5.7 W(-1)/m. Efficient visible emissions due to third harmonic generation were found for fibers with a DRHC of 10 and 20 under the 1557 nm pump of a femtosecond fiber laser. One octave flattened supercontinuum spectrum was generated from fibers with a DRHC of 3.5, 10 and 20 by the 1064 nm pump of a picosecond fiber laser. To the best of our knowledge, we have for the first time fabricated a hexagonal core fiber by soft glass with such a small core size, and have demonstrated a large influence of the holey region on the dispersion, nonlinear coefficient and supercontinuum generation for such fiber.

Fabrication and characterization of a chalcogenide-tellurite composite microstructure fiber with high nonlinearity

A highly nonlinear composite fiber, which has a 1.5 microm chalcogenide glass core surrounded by a tellurite glass microstructure cladding, has been fabricated by the method of stack and draw. A tellurite glass capillary containing a As(2)S(3) rod was sealed with negative pressure inside. Then this capillary and other empty capillaries were stacked into a tellurite glass tube, and elongated into a cane. This cane was then inserted into another tellurite glass jacket tube and drawn into the composite microstructure fiber. The fiber has a flattened chromatic dispersion together with a zero dispersion wavelength located in the near infrared range. The propagation losses at 1.55 microm were 18.3 dB/m. The nonlinear coefficient at 1.55 microm was 9.3 m(-1)W(-1). Such a high nonlinear coefficient counteracts the high propagation losses to a large extent. A supercontinuum spectrum of 20-dB bandwidth covering 800-2400 nm was generated by this composite microstructure fiber.

A highly non-linear tellurite microstructure fiber with multi-ring holes for supercontinuum generation

We have fabricated a highly nonlinear complex microstructure tellurite fiber with a 1.8 micron core surrounded by four rings of holes. The cane for the fiber was prepared by combining the methods of cast rod in tube and stacking. In the process of fiber-drawing a positive pressure was pumped into the holes of cane to overcome the collapse of holes and reshape the microstructure. The correlations among pump pressure, hole size, surface tension and temperature gradient were investigated. The temperature gradient at the bottom of the preforms neck region was evaluated quantitatively by an indirect method. The chromatic dispersion of this fiber was compared with that of a step-index air-clad fiber. It was found that this fiber has a much more flattened chromatic dispersion. To the best of our knowledge this is the first report about a soft glass microstructure fiber which has such a small core together with four rings of holes for the dispersion engineering. The SC generation from this fiber was investigated under the pump of a 1557 nm femtosecond fiber laser. Infrared supercontinuum generation, free of fine structure, together with visible third harmonic generation was obtained under the pump of a femtosecond fiber laser with a pulse energy of several hundred pJ.

Chalcogenide Core Tellurite Cladding Composite Microstructured Fiber for Nonlinear Applications

We present detailed design of a highly nonlinear chalcogenide core tellurite cladding composite microstructured fiber and dispersion tailoring in it. The fabrication procedure for the microstructured fiber is explained. Its applications to nonlinear phenomena are described with the experimental demonstration of the supercontinuum generation and the simulation of the parametric gain. It is observed that a supercontinuum spectrum of 20 dB bandwidth covering 0.80-2.40 μm is generated by this composite microstructure fiber when 1.85 μm pump is used. The simulation results show that the bandwidth over which the calculated parametric gain is more than 10 dB is 1680 nm, ranging from 1.04 to 2.72 μm.

Second and third harmonics and flattened supercontinuum generation in tellurite microstructured fibers

We report what we believe to be the first demonstration of the second and third harmonics in tellurite microstructured fibers pumped by a 1557 nm femtosecond fiber laser. The intensities of the second and third harmonics are enhanced by increasing the nonlinear coefficient of the tellurite microstructured fiber. By using tellurite microstructured fiber with a core diameter of approximately 2.7 microm, supercontinuum light expanding from 470 nm to 2400 nm could be achieved. The effects of the fiber-core diameter on the flatness of the supercontinuum light are also investigated when pumped at 1557 nm.

Design of Zero Chromatic Dispersion Chalcogenide As

We design a nonlinear air-clad chalcogenide As2S3 subwavelength diameter fiber, referred to as nanofiber or nanowire, and calculate the chromatic dispersion in it. The zero dispersion is achieved at the core size of 500 nm for this nanofiber at the telecommunication wavelength of 1.5 mum. We further present the flattening of the zero dispersion in the telecommunication window by cladding the As2S3 core with borosilicate glass, the thermal properties of which match with those of the As2S3 glass. Zero-flattened dispersion centered at 1.408 mum wavelength can be tailored for the nanofiber with this new structure when the nanofiber core diameter is 724 nm.

_{2}

We report what we believe to be the first demonstration of supercontinuum generation spanning over three octaves from UV (at least approximately 350 nm) to 3.85 microm in a 2.5-cm-long fluoride fiber pumped by a 1450 nm femtosecond laser. The spectral broadening in the fluoride fiber is caused primarily by self-phase modulation. Its performance is also compared with that of a 2.5-cm-long silica fiber pumped by the same laser.

S

For a suspended core nanofiber, the holey region is expected to be as large as possible to propagate the light at wavelengths as long as possible. Additionally, a large holey region is significant for its applications in sensors. However, the fabrication of nanofiber with large holey region is still a challenge so far. In this paper a method, which involves pumping positive pressure of nitrogen gas in both the cane fabrication and fiber-drawing processes, was proposed. A suspended core nanofiber, with a core diameter of around 480 nm and an unprecedented diameter ratio of holey region to core (DRHC) of at least 62, was fabricated in the length of several hundred meters. Owing to the large holey region, the confinement loss of the suspended core nanofiber is insignificant when the wavelength of light propagated in it is 1700 nm. For this fabrication technique, the nanowire length, fabrication efficiency, and the uniformity in the diameter are much superior to those of the nanowires fabricated in other ways. Finally, single mode third harmonic generation was observed by this nanofiber under the pump of a 1557 nm femtosecond fiber laser. This work shows the prospect of fabrication of nanostructured waveguide in glass materials by an inflation technique.

_{3}

We design air cladding tellurite (TeO2), bismuth oxide (Bi2O3) based, and chalcogenide (As2S3) nanofibers, and calculate the chromatic dispersions. For each material, wavelength dependent propagation constants of the nanofiber are obtained from the exact solutions of the Maxwells equations, and from the propagation constants the chromatic dispersion is calculated. We tailor the dispersion to zero at the communication wavelength, 1.5 μm, by proper selection of the core diameter of the nanofiber for all the above materials. We further explain the technique for flattening the zero dispersion in telecommunication window, using glass instead of air, as the cladding of the nanofiber structure. Using the glass cladding has the advantage of easy handling, specially, for the communication purposes. Further, the glass cladding causes larger effective index difference between various modes of the nanofiber, thus reducing the mode coupling. We present the numerical results of the dispersion flattening technique by assuming the borosilicate glass cladding to the chalcogenide As2S3 glass core nanofiber. With the borosilicate cladding the dispersion characteristics of the nanofiber change drastically and flattening of the zero dispersion is achieved at 1.408 μm wavelength, when the core diameter is 724 nm.