Showing papers on "Photonic-crystal fiber published in 1998"

Photonic Band Gap Guidance in Optical Fibers

Abstract: A fundamentally different type of optical waveguide structure is demonstrated, in which light is confined to the vicinity of a low-index region by a two-dimensional photonic band gap crystal. The waveguide consists of an extra air hole in an otherwise regular honeycomb pattern of holes running down the length of a fine silica glass fiber. Optical fibers based on this waveguide mechanism support guided modes with extraordinary properties.

Properties of photonic crystal fiber and the effective index model

Abstract: We report on the waveguiding properties of a new type of low-loss optical waveguide. The photonic crystal fiber can be engineered to support only the fundamental guided mode at every wavelength within the transparency window of silica. Experimentally, a robust single mode has been observed over a wavelength range from 337nm to beyond 1550nm (restricted only by available wavelength sources). By studying the number of guided modes for fibers with different parameters and the use of an effective index model we are able to quantify the requirements for monomode operation. The requirements are independent of the scale of the fiber for sufficiently short wavelengths. Further support for the predictions of the effective index model is given by the variation of the spot size with wavelength,

Group-velocity dispersion in photonic crystal fibers.

Abstract: The dispersion properties of photonic crystal fibers are calculated by expression of the modal field as a sum of localized orthogonal functions. Even simple designs of these fibers can yield zero dispersion at wavelengths shorter than 1.27 µm when the fibers are single mode, or a large normal dispersion that is suitable for dispersion compensation at 1.55 µm.

Gain characteristics of tellurite-based erbium-doped fiber amplifiers for 1.5-µm broadband amplification

Abstract: The signal-gain characteristics of tellurite-based erbium-doped fiber amplifiers are clarified based on spectroscopic properties and signal-gain measurements. The potential of tellurite-based erbium-doped fiber for use as a broadband light source is also described.

Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices

Abstract: In accordance with the invention, light is coupled from a plurality of semiconductor emitters to a cladding-pumped fiber via tapered fiber bundles fusion spliced to the cladding-pumped fiber. Individual semiconductor broad stripe emitters can be coupled to individual multimode fibers. The individual fibers can be bundled together in a close-packed formation, heated to melting temperature, drawn into a taper and then fusion spliced to the cladding-pumped fiber. Advantageously, the taper is then overcoated with cladding material such as low index polymer. In addition, a fiber containing a single-mode core can be included in the fiber bundle. This single-mode core can be used to couple light into or out of the single-mode core of the cladding-pumped fiber.

Ring-doped cladding-pumped single-mode three-level fiber laser

Abstract: We propose and theoretically analyze three-level cladding-pumped fiber lasers in which the laser-active dopant is placed in a ring around a single-mode core. A ring-doped laser can work efficiently at wavelengths with strong small-signal absorption. This is otherwise difficult in a cladding-pumped fiber. Moreover, ring doping makes the laser less sensitive to quenching of the laser-active dopant and to excited-state absorption of the lasing field. In simulations of a Yb3+-doped fiber laser, ring doping increased the slope efficiency to 62%, up from 13% for a conventional core-doped fiber.

Distributed measurement of static strain in an optical fiber with multiple bragg gratings at nominally equal wavelengths.

Abstract: The Fourier transform relationship between the reflected light froma Bragg grating and the complex spatial modulation of the Bragg grating is used to produce a distributed strain sensing system A tunable external cavity diode laser along with a reference reflector in anoptical fiber are used to produce a measurement of the phase and amplitude of the reflected light from the modulated Bragg grating as a function of wavelength The system is demonstrated with 22 Bragg gratings in a single fiber on a cantilever beam and compared with foil strain gauge readings

High-energy single-transverse-mode Q-switched fiber laser based on a multimode large-mode-area erbium-doped fiber

Abstract: We demonstrate that appropriately designed doped multimode fibers provide robust single-mode output when used within a fiber laser cavity. Using a novel large-mode-area fiber, we demonstrate what we believe to be record single-mode M2 0.5 mJ from a Q-switched fiber laser and even higher pulse energies (as high as 0.85 mJ) with slightly compromised spatial-mode quality M2<2.0. This approach offers significant scope for extending the range of single-mode output powers and energies that are achievable from fiber-laser–amplifier systems.

Full-vector analysis of a realistic photonic crystal fiber

Abstract: We analyze the guiding problem in a realistic photonic crystal fiber using a novel full-vector modal technique, a biorthogonal modal method based on the nonselfadjoint character of the electromagnetic propagation in a fiber. Dispersion curves of guided modes for different fiber structural parameters are calculated along with the 2D transverse intensity distribution of the fundamental mode. Our results match those achieved in recent experiments, where the feasibility of this type of fiber was shown.

Miniaturization of fiber optic surface plasmon resonance sensor

Abstract: A novel design of surface plasmon resonance (SPR) sensor is reported which leads to a highly miniaturized optical fiber sensing element with high sensitivity A surface plasmon wave is excited on a thin metal film on a side-polished single-mode optical fiber and variations in the refractive index of analyte are detected by measuring changes in the intensity of the light back-reflected from a mirrored end face of the fiber The operation range of the sensor is tuned toward aqueous media by using a thin tantalum pentoxide overlayer It is demonstrated that the sensor is capable of detecting changes in the refractive index below 4×10 −5

Effects of Random Perturbations in Plastic Optical Fibers

Abstract: REVIEW The most important feature of an optical fiber waveguide is its bandwidth, which defines its information-carrying capacity. A major limitation on the bandwidth of multimode glass and plastic optical fibers is modal dispersion, in which different optical modes propagate at different velocities and the dispersion grows linearly with length. However, in plastic optical fibers, experimental and theoretical results indicate that the modes are not independent but are highly coupled, which leads to a characteristic square-root length dependence and an unanticipated large enhancement of the bandwidth to gigahertz levels. The ever increasing demands for low-cost, high-bandwidth communications media for voice, video, and data transmission in short- and medium-distance applications are generating a new assessment of multimode optical fibers to serve as high-speed fiber links.

Influence of nonideal chirped fiber grating characteristics on dispersion cancellation

Abstract: The effect of nonideal dispersion and reflection characteristics of chirped fiber gratings on the performance of 10-Gb/s nonreturn-to-zero-transmission systems operating over standard fiber is investigated. The system penalty for different amplitude and period ripples are quantified. Analyses of an experimental grating confirm that current fabrication technology can meet the requirements for <1-dB-penalty operation.

All-fiber zero-insertion-loss add-drop filter for wavelength-division multiplexing.

Abstract: We developed and fabricated an all-fiber add–drop filter by recording a Bragg grating in the waist of an asymmetric mode converter–coupler formed by adiabatic tapering and fusing of two locally dissimilar, single-mode optical fibers. The insertion loss of the device was ~0.1 dB. A narrow spectral bandwidth ( 90%) were also demonstrated. In addition, the filter was polarization independent.

Dispersion-free fiber transmission for femtosecond pulses by use of a dispersion-compensating fiber and a programmable pulse shaper.

Abstract: We demonstrate nearly distortionless 2.5-km fiber transmission of sub-500-fs pulses, using a combination of standard single-mode fiber, dispersion-compensating fiber, and a programmable pulse shaper for simultaneous quadratic and cubic dispersion compensation. The dispersion-compensating fiber corrects the bulk of the quadratic and the cubic phases for the single-mode fiber, and the fiber-pigtailed programmable pulse shaper exactly compensates the residual dispersion terms. Together these elements permit complete recompression of pulses, which first broaden by ?400 times in the single-mode fiber.

Fiber optical Bragg grating refractometer

Abstract: We have demonstrated an evanescent field refractive index fiber sensor comprising a 42-mm Bragg grating in an etched fiber together with a tunable Distributed Bragg Reflector (DBR) laser. Characterization of different aqueous sucrose solutions resulted in a resolution of roughly 10 mM sucrose. The sensor in the presented form has a theoretical sensitivity of higher than 10 -5 refractive index unit (riu) in a refractive index region close to the cladding index of the fiber. However, the technique allows for an even higher sensitivity than 10 -6 riu with a proper signal processing scheme.

Analysis of phase-shifted long-period fiber gratings

Abstract: Phase-shifted long-period fiber gratings (LPFG's) are analyzed by the coupled-mode theory together with the fundamental-matrix method. The effects of introducing multiple phase shifts at various locations along a LPFG are highlighted. The results compare well with published experimental data.

Large mode area photonic crystal fiber

Abstract: formed by a polarization doublet. The transverse inten­ sity distribution of these guided modes for a wavelength of λ = 632.8 nm was also calculated and the result for one of the polarizations is shown in Figure la. Our work proves that electromagnetic propagation in a realistic PCF can support a robust single-mode structure nearly at all wavelengths for certain fiber para­ meters. It is notable that this approach is based on a full-vector method, so that polarization effects are in­ corporated in an exact manner. Our results for both dis­ persion curves and intensity distributions completely agree with those experimentally measured. This method provides a powerful tool for a better understanding of the PCF's properties because it allows us to fully determine the dispersion curves of their guided modes, as well as their electro­ magnetic field and in­ tensity distributions. The flexibility of our approach also permits the simula­ tion of a great variety of fiber designs. By analyzing the disper­ sion curves of these different fibers, we have already discov­ ered a richer modal structure in some of them. In the example shown in Figure lb there exists, besides the fundamental dou­ blet, two other polar­ ization doublets. Sim­ ilarly, we can use this tool to optimize the design of PCFs with unconventional dis­ persion relations, of potential interest for pulse propagation.

Tunable fiber fabry-perot surface-emitting lasers

Abstract: This invention provides compact, fixed-wavelength and tunable fiber-optic lasers comprising a gain medium, for example a semiconductor, half-cavity VCSEL, or an organic light emitting polymer, within a Fabry-Perot cavity wherein one of the mirrors forming the cavity is a mirror integral with a fiber, for example a mirror (metallic or dielectric, for example) deposited at a fiber end, a reflective tap within an optical fiber, a fiber Bragg Grating (FBG), or a fiber loop mirror. Semiconductor gain material can be bulk semiconductor material or comprise a semiconductor multiple quantum well region. The gain medium itself is not confined to a fiber. The FP cavity of these lasers typically contains a thin active medium ranging up to about 10 μm in length, but more preferably about 1 to about 21 μm in thickness

Generation of ultra-broad-band supercontinuum by dispersion-flattened and decreasing fiber

Abstract: It has been made clear through model simulations that dispersion-flattened and decreasing fiber (DFDF) is one of the most suitable fibers for broad-band supercontinuum (SC) generation. SC generation In a bandwidth of 280 nm with intensity fluctuation less than 15 dB has been experimentally observed by using the DFDF designed and manufactured with an optimized dispersion profile.

A novel fiber-optic gas-sensing configuration using extremely curved optical fibers and an attempt for optical humidity detection

Abstract: A novel configuration for optochemical sensors is proposed using a single optical fiber which is extremely curved at an angle of 180° and turned back. Although the curvature of optical fiber caused some loss in the transmission of the incident light, this loss was not very large. To examine the utility of a sensor head using the curved fiber, all or part of the curved region was coated with a Rhodamine B/hydroxypropyl cellulose humidity sensing film instead of the normal cladding. When the curved fiber was used instead of a straight fiber, the modulation of the incident light by the sensing film was dramatically enhanced, and the change with humidity in the transmission of the incident light through the sensor became much larger. The light signal of the humidity sensor using the curved fiber exhibited a short response time, a high reproducibility, and a smooth dependence on humidity with little hysteresis effect in a wide humidity range.

In-fiber photonic crystals and systems

Abstract: One or more photonic crystals 11, 22, 40, 58, 59 are formed directly in the path of light within an optical fiber 13, 23, 42, 56. Light processed by the photonic crystal may be transmitted out of the fiber by means of a lens 48 or it may be measured by a photoresistive device 51, 60. The photonic crystal may be formed in a trench 12 as an array of dielectric rods 16 having one or more selective defects 17, or the crystal may be formed by providing holes 20 directly in the optical fiber. Filling the interstices between rods 16 with non-linear optical material, and subjecting the crystal to a varying electric field applied by electrodes or to a varying optical radiation can produce a tunable photonic crystal within an optical fiber.

Highly sensitive hydrogen sensors using palladium-coated fiber optics with exposed cores and evanescent field interactions

Abstract: Here we propose and report a novel fiber optic hydrogen sensor which is constructed by depositing palladium over an exposed core region of a multimode fiber. Since the length, thickness, and composition of the palladium patch can be controlled independently of each other, it is possible to increase the speed of our sensor at lower temperatures while maintaining its sensitivity. This is not possible in so called micromirror sensors due to a restriction imposed on their active area of interaction by the fiber optic cross- sectional area. Micromirror fiber optic sensors, studied in the past, take advantage of the reflection/absorption of a palladium film deposited at the end of a fiber and it is only possible to have one sensor per a fiber optic strand. On the other hand, since many evanescent field-based sensors can be deposited over a single fiber optic strand, multiplexing can be easily accomplished using both time- domain and wavelength-domain methods. Using a 100 angstroms thick palladium with 1.5 cm interaction length, we could detect hydrogen in the 0.2% to 0.6% range with corresponding response times of 30 s to 20 s at room temperature. At -10 degree(s)C, these response times increased by a factor of only 2 which is impressive.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Single mode optical fiber

Abstract: A large core photonic crystal fiber for transmitting radiation having a core comprising a substantially transparent core material and having a core diameter of at least 5 μ. The fiber also comprises a cladding region surrounding the length of core material, wherein the cladding region comprises a first substantially transparent cladding material, having a first refractive index, and wherein the first substantially transparent cladding material has embedded along its length a substantially periodic array of holes, wherein the holes are filled with a second cladding material having a second refractive index less than the first refractive index, such that radiation input to the optical fiber is transmitted along the length of the core material in a single mode of propagation. In a preferred embodiment, the core diameter may be at least 20 μ, and may be as large as 50 μ. The fiber is capable of transmitting higher power radiation than conventional fibres, whilst maintaining propagation in a single mode. The core material may be doped with a material capable of providing amplification under the action of pump radiation input to the fiber. The invention also relates to a fiber amplifier and a fiber laser comprising a doped large core photonic crystal fiber. The fiber may also be used in a system for transmitting radiation comprising a plurality of lengths of large core photonic crystal fiber, separated by large core photonic crystal fiber amplifiers, such that the power of radiation transmitted through the system is maintained above a predetermined threshold power.

Broadband square-pulse operation of a passively mode-locked fiber laser for fiber Bragg grating interrogation

Abstract: A long-cavity, passively mode-locked erbium fiber laser operated in the square-pulse regime is demonstrated as a useful light source for interrogating fiber Bragg grating arrays. Output pulses with 4-W peak-power, 10-ns pulse widths, and bandwidths greater than 60nm were used successfully to interrogate 2% fiber Bragg gratings.

Demonstration of Long-Period-Grating Efficient Couplings with an External Medium of a Refractive Index Higher than that of Silica.

Abstract: We discuss the behavior of the transmission spectra of a long-period grating (LPG) with an external medium of refractive index higher than that of silica. We studied the evolution of the features of LPG’s surrounded by several liquid media for several kinds of fiber. The study demonstrated that the behavior depends strongly on the fiber type. Efficient couplings (efficiency greater than 50%) have been obtained with an external medium of a refractive index larger than that of silica. This result indicates that a LPG can operate with surrounding materials of a refractive index higher than that of silica, promising new applications for LPG’s as active optical filters.

Multicore glass optical fiber and methods of manufacturing such fibers

Abstract: A glass optical fiber includes multiple cores fused into a single fiber. The new optical fiber is coherent, in the sense that the cores maintain their relative position with respect to each other within the fiber throughout the length of the fiber. That is, a core having specific radial and angular positions at one end of the fiber will have the same radial and angular positions throughout the fiber, including at the fibers opposite end. In one aspect of the invention the fiber presents a circular cross section, in another it presents an elliptical cross section of greater eccentricity to ease the task of orienting the cores within the fiber for connection to signal sources, other fibers, integrated optic devices, receivers and other optical components. An orienting core may suitably be included in the fiber to further assist in orienting the fiber end. In manufacturing the new optical fiber, a silica tube is stuffed with core canes. The resultant assembly is then melted or fused, preferably while being drawn under vacuum, to produce an integrated multicore fiber blank which then can be drawn down to a standard diameter fiber using standard fiber drawing techniques. Alternatively, fusing and drawing can be combined in a single step process.

Amplified spontaneous emission of an Nd3+-doped poly(methyl methacrylate) optical fiber at ambient temperature

Abstract: Polymer optical fibers have received much attention in recent years as they can replace silica glass fibers in local area nets in the future. A neodymium ion (Nd3+)-doped poly(methyl methacrylate) (PMMA) fiber has been made from Nd3+ containing PMMA as a core and silica resin as claddings. Fluorescence of the fiber results from the transition of 4G5/2 to 4I9/2 in a three energy level system. Amplified spontaneous emission (ASE) at 575 nm has also been observed and the critical power at a pump wavelength of 514.5 nm for the onset of ASE has been found to be 85 mW.