Abstract: A new structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed by using a full-vector finite element method with anisotropic perfectly matched layers. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM-PCF within the wavelengths ranging from 1.48 to 1.6 /spl mu/m, where only the slow-axis mode exists and the confinement loss is less than 0.1 dB/km.

Abstract: Subthreshold measurements of a photonic crystal (PC) microcavity laser operating at 1.3 μm show a linewidth of 0.10 nm, corresponding to a quality factor (Q)∼1.3×104. The PC microcavity mode is a donor-type mode in a graded square lattice of air holes, with a theoretical Q∼105 and mode volume Veff∼0.25 cubic half-wavelengths in air. Devices are fabricated in an InAsP/InGaAsP multi-quantum-well membrane and are optically pumped at 830 nm. External peak pump power laser thresholds as low as 100 μW are also observed.

Abstract: Sub-threshold measurements of a photonic crystal (PC) microcavity laser operating at 1.3 microns show a linewidth of 0.10 nm, corresponding to a quality factor Q ~ 1.3x10^4. The PC microcavity mode is a donor-type mode in a graded square lattice of air holes, with a theoretical Q ~ 10^5 and mode volume Veff ~ 0.25 cubic half-wavelengths in air. Devices are fabricated in an InAsP/InGaAsP multi-quantum well membrane and are optically pumped at 830 nm. External peak pump power laser thresholds as low as 100 microWatts are also observed.

Abstract: We report the results of our recent investigation on the properties of a highly birefringent photonic crystal fiber including modal birefringence, mode field diameter, divergence angle, and polarization mode dispersion, which are important for sensing and communication applications.

Abstract: We report the experimental generation, simply by use of a subnanosecond microchip laser at 532 nm and a conventional dispersion-shifted fiber, of a supercontinuum that spans more than 1100 nm. We show by detailed spectral analysis that this supercontinuum originates from a preliminary four-wave mixing process with multimode phase matching and subsequent double-cascade stimulated Raman scattering and is transversely single mode as a result of Raman-induced mode competition. This technique is believed to be the simplest configuration that allows one to generate a stable supercontinuum.

Abstract: A frequency comb spanning more than one octave has been achieved by injecting the second-harmonic generation (780 nm) of a mode-locked fiber laser (1.56 μm) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency of the frequency comb. Frequency noise has been observed on the measured carrier-envelope offset frequency, which has been confirmed to be generated in the photonic crystal fiber by comparing the measured beat frequencies between cw lasers and frequency combs before and after the photonic crystal fiber. The mode-locked fiber laser is considered to be an important candidate for the light source used in realizing a compact optical frequency measurement system including applications in the telecommunication bands.

Abstract: A polarization-selective photonic stop band is demonstrated in a new chiral fiber structure with double-helix symmetry. The stop band exists for only circularly polarized radiation with the same handedness as the structure and is centered at a wavelength in the fiber equal to the fiber pitch. When one part of the chiral fiber is twisted about its axis, a localized mode is produced, which can be tuned across the gap by changing the twist angle. Observations in single-mode fibers are in good agreement with one-dimensional simulations of a dispersive cholesteric material. At higher frequencies, however, we find a sharp onset of a broad polarization-selective scattering band, which is not present in one-dimensional simulations.

Abstract: We numerically calculate the equivalent mode-field radius of the fundamental mode in a photonic crystal fiber (PCF) and show that this is a function of the V parameter only and not the relative hole size. This dependence is similar to what is found for graded-index standard fibers, and we furthermore show that the relation for the PCF can be excellently approximated with the same general mathematical expression. This is to our knowledge the first semianalytical description of the mode-field radius of a PCF.

Abstract: If a single optical fiber is used for both delivery and collection of light, two major factors affect the measurement of collected light: (1) the light transport in the medium that describes the amount of light that returns to the fiber and (2) the light coupling to the optical fiber that depends on the angular distribution of photons entering the fiber. We focus on the importance of the latter factor and describe how the efficiency of the coupling depends on the optical properties of the medium. For highly scattering tissues, the efficiency is well predicted by the numerical aperture (NA) of the fiber. For lower scattering, such as in soft tissues, photons arrive at the fiber from deeper depths, and the coupling efficiency could increase twofold to threefold above that predicted by the NA.

Abstract: Monolithic vertical external cavity surface emitting lasers of cavity mode volume 350 mW in a TEM00 mode was obtained at 850 nm. Output power >2.5 W was obtained at 980 nm.

Abstract: The performance of plastic optical fiber is greatly influenced by the related but distinct effects of mode coupling and differential modal attenuation (DMA). We establish a method for estimating the matrix that governs both of these effects and allows us to distinguish the two. We obtain partial quantitative estimates of this matrix for a particular graded-index plastic optical fiber (GI-POF). The sample we studied exhibited strong but incomplete mode coupling over 100-m lengths, while DMA was largely limited to a centerline defect. We show that much of the loss of the fiber can be attributed to mode coupling between mode groups with similar effective indexes.

Abstract: The acousto-optic mode coupling from core to LP11cl mode of a dispersion-compensating fiber excited by two acoustic waves with orthogonal perturbations is studied by use of a novel composite piezoelectric transducer. Highly polarization-dependent mode-selective spectra are observed that are due to coherent acousto-optic coupling between the core and various constituent cladding modes. Potential applications for implementing an all-fiber wavelength-tunable polarization analyzer are also discussed.

Abstract: The demonstration of an optical fiber based probe for efficiently exciting the waveguide modes of high-index contrast planar photonic crystal (PC) slabs is presented. Utilizing the dispersion of the PC, fiber taper waveguides formed from standard silica single-mode optical fibers are used to evanescently couple light into the guided modes of a patterned silicon membrane. A coupling efficiency of approximately 95% is obtained between the fiber taper and a PC waveguide mode suitably designed for integration with a previously studied ultra-small mode volume high-Q PC resonant cavity [1]. The micron-scale lateral extent and dispersion of the fiber taper is also used as a near-field spatial and spectral probe to study the profile and dispersion of PC waveguide modes. The mode selectivity of this wafer-scale probing technique, together with its high efficiency, suggests that it will be useful in future quantum and non-linear optics experiments employing planar PCs.

Abstract: We demonstrate simultaneous mode locking of more than 24 wavelengths at 3 GHz in an actively mode-locked erbium-doped fiber laser operating at room temperature. The multiwavelength operation is achieved when a frequency shifter and an all-fiber 50-GHz periodic filter are inserted into a ring cavity. Active mode locking is performed with an amplitude modulator, and pulses with a FWHM of 30 ps are obtained.

Abstract: We demonstrate 10 Gb/s, 5-channel, wavelength multiplexed transmission over four 80-km standard fiber spans using polarization invariant spectral inversion provided by a broadband fiber parametric amplifier using orthogonally-polarized pumps having synchronized phase modulation for stimulated Brillouin suppression.

Abstract: We have theoretically and experimentally investigated an optical fiber with circular polarization modes on one end and linear polarization modes on the other end. We call this fiber a polarization-transforming fiber because the local modes, or polarization states they represent, are converted from linear to circular, and visa versa, in the fiber. We have developed and implemented a postdraw process for making polarization-transforming fiber samples 30 mm long with losses less than 1 dB and a polarization-mode conversion from circular to linear greater than 20 dB. Also, we have modeled and measured the dependence on wavelength and temperature of polarization-transforming fiber samples. The measured normalized wavelength dependence of a sample fiber 30 mm long was approximately 1.4 x 10(-4) nm(-1), and the measured normalized temperature dependence was approximately 6 x 10(-4) degrees C(-1). These values are better in some cases than values for conventional high-birefringent fiber quarter-wave plates.

Abstract: We introduce a formalism that provides a unified solution for the gain spectrum of fiber optical parametric amplifiers (OPAs) using either linearly or circularly polarized waves. There are 12 basic types, including five that have not been previously investigated to our knowledge. We provide a simple method for calculating the maximum gain and nonlinear phase mismatch for such OPAs. All these OPAs have similar elliptical graphs for parametric gain versus propagation constant mismatch, with a width equal to four times the height. This implies that, when fiber dispersion is taken into account, any two-pump OPA can be used to obtain the same gain spectrum as any other OPA in the same fiber, provided that the pump power is adjusted for equal maximum gain and that real solutions exist for the resulting equation for the required pump spacing. In that sense, all these fiber OPAs form an equivalence class.

Abstract: We present a rigorous analysis methodology of fundamental to higher order mode converters in step index few mode optical fibers. We demonstrate experimental conversion from a fundamental LP01 mode to the higher order LP11 mode utilizing a multiple mechanical bend mode converter.We perform a quantitative analysis of the measured light intensity, and demonstrate a modal decomposition algorithm to characterize the modal content excited in the fiber. Theoretical modelling of the current mode converter is then performed and compared with experimental findings.

Abstract: A finite deformation theory of elasticity and a theory of nonlinear photoelasticity are applied to describe the wavelength shifts of cladding-mode resonance in corrugated long-period fiber gratings under torsion. The deformation of fiber is found by use of the Murnaghan model of a solid elastic body. The quadratic photoelastic effect that is proportional to the second-order displacement gradient is investigated and compared with the classical photoelastic effect. The electromagnetic field in the twisted corrugated structure is presented as a superposition of circularly polarized modes of the etched fiber section. The wavelength shift is found to be proportional to the square of the twist angle. As predicted by our theory, a wavelength shift of the same nature has been found in a conventionally photoinduced long-period fiber grating.

Abstract: A strong resonance and extremely short length long-period grating (LPG) has been fabricated in a large-mode-area photonic crystal fiber (PCF) by use of a CO2 laser heat source. We believe that such a longperiod grating in pure silica PCF is the first example of a point-by-point technique. The fabrication method is simple and repeatable. The resulting LPG has been developed with eight periodic collapses within a 2.8-mmlong period of the fiber, which gives the strong resonance of core-cladding mode coupling. The lowest mode of LP01 is at a 1529.2-nm wavelength with a full width at half-maximum of ~0.7 nm and a resonance strength of -31.5 dB. The principal advantages of this LPG are that (1) it is temperature insensitive and stable, (2) the device is compact when it is packaged, and (3) it provides practical, low-cost all-fiber filters and PCF-based devices for optical fiber communications and sensing systems.

Abstract: When optical fibers are used for delivery and collection of light, two major factors affect the measurement of collected light: 1) light transport in the medium from the source to the detection fiber and 2) light coupling to the optical fiber (which depends on the angular distribution of photons entering the fiber). This paper studies the latter factor, describing how the efficiency of the coupling depends on the optical properties of the sample. The coupling dependence on optical properties is verified by comparing experimental data to a simple diffusion model and to a Monte Carlo (MC)-corrected diffusion model. Mean square errors were 7.9% and 1.4% between experiments and the diffusion, and experiments and the MC-corrected models, respectively. The efficiency of coupling was shown to be highly dependent on the numerical aperture (NA) of the optical fiber. However, for lower scattering, such as in soft tissues, the efficiency of coupling could vary two- and threefold from that predicted by fiber NA. The collection efficiency can be used as a practical guide for choosing optical fiber-based systems for biomedical applications.

Abstract: Stimulated Brillouin scattering in optical fibers is described by a theoretical model and numerical analysis. The results showed that, for an optical fiber pumped by a laser beam with ns-order-pulse width and kW-order peak-power, SBS reflectivity tends to saturate when the fiber length exceeds a limit, named “effective fiber length”. Using small core-diameter and long enough fiber, the SBS reflectivity level could be raised but is limited by optical damage of the entrance surface of the fiber. Therefore, just a small dynamic range can be obtained.

Abstract: An apparatus for producing a low-PMD optical fiber, comprises a furnace (6) for melting a lower portion of an optical preform (3); a traction device (8) for pulling an optical fiber (4) from said lower portion of an optical preform; a spinning device (20) for imparting a substantially constant and unidirectional spin to the optical fiber as it is pulled, which causes the fiber to undergo an elastic torsion; a winding device (9) for winding the optical fiber onto a reel (10); and a twisting device (40) for imparting to the spun optical fiber a unidirectional twist in a direction opposite said elastic torsion, so as to control the residual twist in the optical fiber. A process for producing the fiber, the optical fiber and a cable comprising the optical fiber are also claimed.

Abstract: We compare the eye-opening penalty from a first-order polarization mode dispersion (PMD) model with that from an all-order PMD model in optical fiber transmission systems. Evaluating the performance by taking into account only first-order PMD produces a good approximation of the true eye-opening penalty of uncompensated systems when the penalty is low. However, when the penalties are high, this model overestimates the penalty for outage probabilities in the range of interest for systems designers, which is typically approximately 10-5 to 10-6.

Abstract: We demonstrate a novel fused-type directional coupler that couples the LP/sub 01/ mode in one fiber and the LP/sub 02/ mode in another using a few-mode fiber. The phase-matching condition was satisfied in the coupler waist by initially etching and prepulling portions of the fibers based on simple numerical calculation. A coupling efficiency of about 70% was maintained over 1515-1595-nm wavelength range, and the mode extinction ratios with LP/sub 01/, LP,/sub 11/, and LP/sub 21/ modes were measured to be 35,20, and 7 dB, respectively.

Abstract: A sensor measures temperature in stationary components of electrical machines using fiber optics. An optical fiber is embedded in a non-metallic ribbon. Notches are cut in the ribbon to effect bends that accommodate a shape of a stationary component. The ribbon and optical fiber are attached to the stationary component. A series of laser pulses can be injected from at least one end of the optical fiber, and the stationary component temperature can be monitored by interrogation of reflections from the series of laser pulses.

Abstract: A discussion of the dispersion relation of the modes guided by an annular core fiber is done in order to prove that the fundamental mode has a zero cutoff. It also gives the inequalities satisfied by the cutoff frequencies of the first lower modes. A relation is established between the propagation constants of two modes with the same radial order but different azimuthal orders. It allows us to precisely set the conditions for these constants to be almost similar. Numerical results are shown to confirm these assertions. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 249–254, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11029

Abstract: An Yb3+-doped optical fiber with a refractive index profile that distributes the intensity of light uniformly across the core of the fiber has been designed. A >2X decrease in stimulated Raman scattering was measured. 02003 Optical Society of America OCIS Codes: (060.2320) Fiber optics amplifiers and oscillators; (140.3510) Lasers, fiber Femtosecond, chuped-pulse, fiber lasers with pulse energies greater than 1m.I have been demonstrated [l]. This output power was limited by the onset of stimulated Raman scattering. A common approach for scaling the output power and pulse energy of these fiber lasers is to increase the core size of the fiber and selectively excite only the fundamental mode [2]. The core size to which the fiber can be scaled before output beam quality begins to degrade is around 30-50pm. In this paper we pursue an alternative and complimentary approach which is to reduce the intensity of light propagating in the core by distributing it more evenly across the core area via careful design of the refractive index profile [3]. In figure 1, we show one such refractive index profile for creating a flat-topped fiber mode on the left hand side. On the right hand side of figure 1, we show the intensity distribution of a large flattened mode fiber design (LFM) and a standard step index profile fiber normalized such that the total power contained in the two modes is the same. (i.e. The two intensity distributions contain the same total power after the integmtion over the full cross sectional area is performed.) We see the LFM design decreases the peak intensity on axis by a factor of 2.46, which should lead to a sigrufkant decrease in the amount of stimulated Raman scattering for a given pulse energy, while not compromising the power handling capability. Fundamental Mode Intensity Profile and Index Normalized Intensity Profile of Fundamental Profile LFM Fiber I I 1.4520 1.4515 =

Abstract: The beam quality of large-mode-area fiber amplifiers was investigated at the 10 W power level using a tunable ring cavity, that is also used in the laboratory system of GEO600 as a pre-mode-cleaner for mode filtering. More than 98% of the overall output power were contained within the polarized (200:1) TEM00 mode with an appropriate choice of coiling diameter. With the high sensitivity ring cavity analysis, the beam quality improvement caused by decreasing the coiling diameter was verified, while this could not be seen within conventional M2-measurements. The results are compared with the properties of single-mode fibers.