Design of dual-core optical fibers with NEMS functionality.

An optical fiber with nano-electromechanical functionality is presented. The fiber exhibits a suspended dual-core structure that allows for control of the optical properties via nanometer-range mechanical movements. We investigate electrostatic actuation achieved by applying a voltage to specially designed electrodes integrated in the cladding. Numerical and analytical calculations are preformed to optimize the fiber and electrode design. Based on this geometry an all-fiber optical switch is investigated; we find that optical switching of light between the two cores can be achieved in a 10 cm fiber with an operating voltage of 35 V.

Halo-tellurite glass fiber with low OH content for 2-5µm mid-infrared nonlinear applications.

We report the fabrication of new dehydrated halo-tellurite glass fibers with low OH content (1ppm in weight) and low OH-induced attenuation of 10dB/m in 3-4 µm region. It shows halo-tellurite glass fibers a promising candidate for nonlinear applications in 2-5µm region.

Laser-induced crystalline optical waveguide in glass fiber format.

We report on the first fabrication of a glass fiber based laser-induced crystalline waveguide. The glass and crystal are based on the stoichiometric composition of (La,Yb)BGeO(5). A laser induced waveguide has been fabricated on the surface of a ribbon glass fiber using milliwatt-level continuous wave UV laser radiation at a fast scanning speed. Evidence of crystallinity in the created structure was observed using micro-Raman spectroscopy and scanning electron microscopy. Preliminary investigations on the waveguiding behavior and the nonlinear performance in the crystalline waveguide are reported.

Phase regeneration of DPSK signals in a highly nonlinear lead-silicate W-type fiber.

We experimentally demonstrate phase regeneration of a 40-Gb/s differential phase shift keying (DPSK) signal in a 1.7-m long highly nonlinear lead silicate W-type fiber using a degenerate two-pump phase-sensitive amplifier (PSA). Results show an improvement in the Error Vector Magnitude (EVM) and a reduction of almost a factor of 2 in the phase noise of the signal after regeneration for various noise levels at the input.

Phase sensitive amplification in a highly nonlinear lead-silicate fiber.

We experimentally demonstrate phase-sensitive amplification in a highly nonlinear and low-dispersion lead-silicate W-type fiber. A phase-sensitive gain variation of 6 dB was observed in a 1.56-m sample of the fiber for a total input pump power of 27.7 dBm.

Nanomechanical optical fiber.

Optical fibers are an excellent transmission medium for light and underpin the infrastructure of the Internet, but generally after fabrication their optical properties cannot be easily modified. Here, we explore the concept of nanomechanical optical fibers where, in addition to the fiber transmission capability, the internal core structure of the fiber can also be controlled through sub-micron mechanical movements. The nanomechanical functionality of such fibers is demonstrated in the form of dual core optical fibers, in which the cores are independently suspended within the fiber. The movement-based optical change is large compared with traditional electro-optical effects and we show that optical switching of light from one core to the other is achieved through moving one core by just 8 nm.

Continuously tunable optical buffer with a dual silicon waveguide design.

We propose a design for an optical buffer that comprises two coupled silicon waveguides, which is capable of generating a large continuously tunable change in the propagation delay time. The optical delay can be varied by more than 100% through varying the spacing between the waveguides.

All-solid highly nonlinear singlemode fibers with a tailored dispersion profile.

We investigate a novel approach to obtain highly nonlinear fibers with a tailored group velocity dispersion around a desired wavelength region of interest. Rather than exploiting longitudinal holes to control the average refractive index of the cladding and hence the fiber's waveguide dispersion, as in holey fibers, we propose using an all-solid cladding with a suitably chosen refractive index difference relative to the core. We demonstrate numerically that this solution allows a large freedom in the manipulation of the overall fiber dispersive properties, while enabling, in practice, a much more accurate control of the fiber's structural properties during fabrication. Effectively single mode guidance over a broad wavelength range can be achieved through the use of a second outer cladding forming a W-type index profile. We derive simple design rules for dispersion controlled fibers, based on which an algorithm for the automatic dispersion optimization is proposed, implemented and used to design various nonlinear fibers for all-optical processing and supercontinuum generation. Fabrication of a lead silicate fiber with flattened dispersion at telecoms wavelengths confirms the potential of these new fibers.

Near-zero dispersion, highly nonlinear lead-silicate W-type fiber for applications at 1.55 microm.

We report the design, fabrication and characterization of a lead-silicate glass highly nonlinear W-type fiber with a flattened and near-zero dispersion profile in the 1.55 microm region. The fiber was composed of three types of commercial lead silicate glasses. Effectively single-mode guidance was observed in the fiber at 1550 nm. The nonlinear coefficient and the propagation loss at this wavelength were measured to be 820 W(-1)km(-1) and 2.1 dB/m, respectively. Investigations of the Brillouin threshold revealed no evidence of stimulated Brillouin scattering for continuous wave signal powers up to 29 dBm in a 2m sample of the fiber. A broadband dispersion measurement confirmed the near-zero dispersion values and the flat dispersion profile around 1550 nm, in good agreement with our simulations. Efficient four-wave-mixing, tunable across the whole C-band, was demonstrated in a 2.2m length of the fiber.

Dispersion-shifted all-solid high index-contrast microstructured optical fiber for nonlinear applications at 1.55 microm.

We report the fabrication of an all-solid highly nonlinear microstructured optical fiber. The structured preform was made by glass extrusion using two types of commercial lead silicate glasses that provide high index-contrast. Effectively single-moded guidance was observed in the fiber at 1.55 microm. The effective nonlinearity and the propagation loss at this wavelength were measured to be 120 W(-1)km(-1) and 0.8 dB/m, respectively. Numerical simulations indicate that the fiber is dispersion-shifted with a zero-dispersion-wavelength of 1475 nm and a dispersion slope of 0.16 ps/nm(2)/km respectively at 1.55 microm. These predictions are consistent with the experimentally determined dispersion of + 12.5 ps/nm/km at 1.55 microm. Tunable and efficient four-wave-mixing based wavelength conversion was demonstrated at wavelengths around 1.55 microm using a 1.5m-length of the fiber.

Loosening the DNA wrapping around single-walled carbon nanotubes by increasing the strand length.

In this study, we discuss the influence of DNA strand length on DNA wrapping of single-walled carbon nanotubes under high-shear sonication and find that different strand length results in changed DNA-nanotube interaction, which is sensitively probed by the upshift extent of the Raman radial breathing mode bands of nanotubes due to DNA wrapping. The difference in the interaction between nanotubes and DNA strands of various length results in apparently different degrees of wrapping compactness, revealed by atomic force microscopy observations, and nanotube selectivity in wrapping, indicated by both Raman and photoluminescence spectroscopy results. The above findings can be utilized to precisely control the nanotube diameter distribution and modulate the physicochemical properties of the nanotube wrapped by DNA without any direct functionalization of nanotubes. This finding is of considerable interest from both theoretical and practical standpoints.

Modification of the Er3+ radiative lifetime from proximity to silicon nanoclusters in silicon-rich silicon oxide.

The lifetime of Er3+ in silicon-rich silicon oxide has been reported with quite widely varying values ranging from 9 ms to 2 ms. In this work, we consider the direct impact of silicon nanoclusters on the erbium radiative lifetime, and show that it is a function of the silicon nanocluster size, and also the erbium proximity to the nanocluster.

Comment on the reported fiber attenuations in the visible regime in "Fabrication of glass photonic crystal fibers with a die-cast process".

We comment on the recent paper by Zhou et al. [Appl. Opt.45, 4433 (2006)APOPAI0003-693510.1364/AO.45.004433], in which transmission losses of 0.2-0.3 dB/m were claimed across the wavelength range 420-900 nm in a high-index (n(d)=1.80518 at 587.6 nm) SF6 glass-based photonic crystal fiber fabricated by novel die-cast technique. If confirmed, these losses are at least 1 order of magnitude lower than previous reported losses of SF6 photonic crystal fibers from other fabrication approaches. Here we present a statistic survey on the relationship between the refractive index and the bulk material attenuation, based on a large number of commercial Schott optical glasses with the n(d) ranging between 1.40 and 2.05. It shows that the loss of a high-index (n(d)=1.80) glass optical fiber should be at the levels of 10-50 dB/m at 420 nm and 1-10 dB/m at 500 nm, respectively. Moreover, the material attenuation of such a high-index glass fiber should intrinsically show a large decay, from 10-50 dB/m at 420 nm to the level of 1 dB/m at 700 nm, which arises from the tail on the UV absorption edge of the high-index glass extending to the visible region. Therefore, we conclude that: (1) the low loss of 0.2-0.3 dB/m reported in the cited paper is abnormally one or two magnitudes lower than the material attenuation that a high-index (n(d)=1.80) glass optical fiber should have in the range between 420 and 500 nm and that (2) the flat loss curve between 420 and 700 nm in the cited paper deviates greatly from the intrinsic behavior of a high-index (n(d)=1.80) glass fiber.

Single-mode tellurite glass holey fiber with extremely large mode area for infrared nonlinear applications.

We report the fabrication of a large mode area tellurite holey fiber from an extruded preform, with a mode area of 3000microm(2). Robust single-mode guidance at 1.55microm was confirmed by both optical measurement and numerical simulation. The propagation loss was measured as 2.9dB/m at 1.55microm. A broad and flat supercontinuum from 0.9 to 2.5microm with 6mW output was obtained with a 9cm length of this fiber.

On the delayed self-heterodyne interferometric technique for determining the linewidth of fiber lasers.

The delayed self-heterodyne interferometric technique, first proposed in the context of semiconductor lasers, has been commonly used for over 20 years in the determination of the optical linewidth of lasers. We examine this technique in the light of recent work on fiber lasers, and point out further constraints in the applicability of these measurements. An approximate but simple and intuitive expression is provided for assessing the self-heterodyne technique when applied to fiber lasers.