Showing papers on "Zero-dispersion wavelength published in 1993"

Optical and mechanical properties of single-crystal sapphire optical fibers

Abstract: Single-crystal sapphire fibers are produced by the laser heated pedestal growth technique The fibers have attenuation coefficients of less than 2 dB/m at the Er:YAG laser wavelength of 294 μm and are used to deliver over 600 mJ of Er:YAG laser energy Mechanical testing of these fibers and the sapphire fibers produced by the edge-defined, film-fed growth technique results in a measured 04% strain to failure when testing is done under a 4-point load Teflon-FEP (perfluorinated ethylene propylene) is applied to sapphire fibers as a cladding The cladding is extremely effective in preventing leakage of energy from the fibers into absorbing environments that may surround the fiber

Dispersion-compensating single-mode fibers: efficient designs for first- and second-order compensation.

Abstract: Single-mode dispersion compensating fiber designs with absolute dispersion values of greater than 100 ps/(nm km) are described. A multiclad fiber with a triangular refractive-index profile in the core gives a dispersion of −250 ps/(nm km), resulting in a 15:1 compensation scheme. All fiber designs use only the fundamental LP01 mode for dispersion compensation and can account for first- and second-order dispersion effects.

Enhanced self-phase modulation in tapered fibers

Abstract: Fiber tapering reduces the effective area and increases the Kerr nonlinear phase shift of the fundamental mode. A significant nonlinear effect was observed in a micrometer-diameter centimeter-long section of tapered fiber at a wavelength of 1550 nm. The numerical simulation of a second-order soliton entering the taper gives a spectral widening that matches the observed spectrum.

Saturable absorber modelocked polarisation maintaining erbium-doped fibre laser

Abstract: Using a polarisation-maintaining erbium-doped fibre near the zero dispersion wavelength and a bulk InGaAsP saturable absorber, the authors passively modelock a fibre laser to generate nearly transform-limited 320 fs pulses with 40pJ energy. The laser produces a stable state of linear polarisation and the semiconductor, which acts both as a slow and fast saturable absorber, self-starts the laser.

Tapered Fabry-Perot waveguide optical demultiplexer

Abstract: We describe a novel waveguide spectrometer for use in wavelength division multiplexing (WDM) systems. A high refractive index resonator is coupled to a waveguide and extracts light from the waveguide at its resonance frequency. A taper in the thickness of the resonator allows light of different wavelengths to be extracted at different positions. A structure is fabricated for use at 750 nm with a measured dispersion of 29 nm/cm and a wavelength resolution of 1 nm. The device operation is in good agreement with first-order coupled-mode calculations. >

An optical communications system for transmitting information signals having different wavelengths over a same optical fiber

Abstract: An optical communications system provides optical signals of different wavelengths over an optical fiber (1, 2) having a zero dispersion wavelength. Electrical dispersion compensating elements (36-39) independently compensate optical signals having wavelengths different than the zero dispersion wavelength for dispersion in the optical fiber. Limiting radio frequency signals for modulating a light emitting device or laser (21-24) outputting signals at a wavelength different than the zero dispersion wavelength to less than one octave of frequency permits second order harmonic distortion resulting from dispersion in the fiber to be filtered at a receiving location. The optical communications system may include a reverse transmission path.

System for optically transmitting digital communications over an optical fiber with dispersion at the operating wavelength

Abstract: When digital signals are transmitted over optical fibers (3), which have a considerable chromatic dispersion at the wavelength being used, the length of the transmission path is very limited when the digital signal to be transmitted is converted into an optical signal by means of intensity modulation. If frequency modulation (also called FSK = Frequency Shift Keying) is used instead of the intensity modulation, the bridgeable path can be greatly increased, but requires a suitable optical receiver at the receiving end. The invention utilizes a simple optical receiver (4), which is not sensitive to frequency modulation, but to intensity modulation. This is possible, because an intensity variation is created, due to the chromatic dispersion of the optical fiber (3) and the resulting running time differences of signal portions at different wavelengths (.lambda.0, .lambda.1) from the initial frequency modulation during the transmission over the optical fiber (3), which process is contained in the digital signal.

Enhancement of optical-amplifier noise by nonlinear refractive index and group-velocity dispersion of optical fibers

Abstract: The influence of the nonlinear refractive index and the group-velocity dispersion of optical fibers on optical-amplifier noise is studied. A new method is used to calculate the spectrum of the amplified spontaneous emission. The result shows that the positive dispersion is favorable for suppressing the enhancement of the amplifier noise. >

Survivability of optical fibers in space

Abstract: The survivability of optical fibers for data bus and gyroscope applications in the natural space radiation environment has been analyzed using radiation-induced loss data of single mode, multimode, and polarization-maintaining fibers. Since it is virtually impossible to simulate the dynamic conditions of space, extrapolations have been made from measurements at dose rates, temperatures, and total doses different from those onboard spacecraft. The anticipated degradation of most Ge-doped silica core fibers and all pure silica core fibers appears to be well within allowable margins in fibers for data bus applications, while the radiation sensitivity of polarization-maintaining fibers could result in a significant decrease in fiber gyro performance.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Simultaneous compensation of laser chirp, Kerr effect, and dispersion in 10-Gb/s long-haul transmission systems

Abstract: The effects of chirp and fiber nonlinearity in a directly modulated 10-Gb/s intensity-modulated direct-detection (IM-DD) fiber transmission system are investigated by simulation, and a simple and flexible technique for compensating these effects is discussed. Self-phase-modulation (SPM) in optical fiber can be equalized by an anomalous dispersion fiber, whereas pulse broadening caused by laser transient chirp can be compensated by normal dispersion. Using these characteristics, laser transient chirp, SPM, and fiber dispersion can be simultaneously compensated by equalizing fibers inserted within certain intervals. Optimum compensation is always realizable for such fixed equalizing fibers, since the magnitude of SPM can be controlled by changing the optical power in the fiber. Simulation suggests that this technique enables 10-Gb/s, 100-km fiber transmission by direct modulation. >

Method and apparatus for chromatic dispersion measurements

Abstract: A chromatic dispersion measuring method and apparatus are disclosed which permit highly accurate measurements of the wavelength dispersion characteristic of an optical transmission such as an optical fiber or an optical amplifier repeater system. Measurements are made on the propagation time of a first optical signal of a fixed wavelength through an optical transmission line to be measured and the propagation time through the same optical transmission line of a second optical signal whose wavelength can be arbitrarily set over the measuring wavelength band. By obtaining a difference between the both propagation times, it is possible to obtain only a change in the propagation time of each signal which is caused by a change in the wavelength of the second optical signal. That is, the elongation or shrinkage of the optical fiber has an equal influence on both of the first optical signal and the second optical signal, and hence does not induce an error in the detection of the above-said time difference.

Triple-clad single-mode fibers for dispersion shifting

Abstract: A design procedure for triple-clad dispersion-shifted single-mode fibers is developed. Following this procedure, fibers are identified which have low dopant concentrations in the core compared to those of the previous dispersion-shifted fiber designs, a second-mode cutoff wavelength close to the operating wavelength, zero dispersion at 1550 nm, a small bending loss at 1550 nm (for a bend radius of 3.75 cm), and a spot size that is large enough not to compromise the splice loss. A significant advantage of these fibers is that low-dispersion is available over a wide wavelength band about the wavelength of zero dispersion. >

Optical fiber bendable coupler/switch device

Abstract: A 1×N fiber optic switch is disclosed for selectively coupling light from a first fiber to any one of a plurality of output fibers. The switch includes a coupler in which the first optical fiber and the plurality of optical fibers are elongated in a narrowed coupling region. The coupling region can be bent in various directions to cause the radius of curvature of the input fiber to differ from that of at least one of the output fibers, whereby light propagating in the input fiber can be coupled to only one of the output fibers or to more than one of those fibers.

Low bend loss singlemode optical waveguide fiber

Abstract: An optical waveguide fiber with improved bend loss performance while maintaining cutoff wavelength, λc, and zero dispersion wavelength, λ0, in practical operating ranges. The fiber includes an inner core region with a refractive index delta higher than the rest of the core and a reduced diffusion tail at the core/cladding interface. Optionally, a ring at the outer portion of the core is provided to compensate for increased λ0 which results from the higher inner core refractive index delta. This ring also contributes to the reduced diffusion tail at the core/cladding interface.

A new design arrangement of transmission fiber dispersion for suppressing nonlinear degradation in long-distance optical transmission systems with optical repeater amplifiers

Abstract: The invention of the erbium-doped fiber amplifier has opened the possibility of constructing long-distance optical transmission systems with 1.5-mm zero-dispersion wavelength shifted fibers. In such systems, nonlinear degradation due to four-wave mixing and self-phase modulation strictly limits the total span of systems and the length of the optical repeater spacing. There are proposals to use slightly normal group velocity dispersion fibers (D >

Controlled dopant diffusion for fiber optic coupler

Abstract: Uniformity of optical coupling of optical elements such as couplers and splitters is improved by heat treatment which causes dopants in the core of an optical fiber to diffuse into material from the cladding layer of the optical fibers from which the optical element is formed, resulting in a substantially homogeneous interior region of the star coupler or splitter Increased lossiness of the optical element thus formed may be limited by termination of the heat treatment before dopant diffusion reaches equilibrium throughout the fibers so that a portion of the cladding layer of the fibers remains surrounding the substantially homogeneous region where the fibers have been fused together Dopant diffusion is constrained to a substantially radial direction in each fiber by uniformity of heating over a region where at least two fibers are twisted together Thus dopant diffusion is highly repeatable and can be readily regulated to provide highly selective, wavelength-dependent coupling between fibers, particularly for multiplexing and demultiplexing applications

Optical passive component assembly

Abstract: An optical fiber amplifier suited for use in optical fiber transmission systems includes a plurality of optical passive components. The optical passive components are integrated into an assembly including a birefringent crystal, a first lens, a magneto-optic crystal, an optical filter, and a second lens, all of which are axially aligned in this order, with a half-wave plate interposed between the birefringent crystal and the first lens. The birefringent crystal is opposed to end faces of first and second optical fibers and separates incident light into two linearly polarized light beams having respective polarized light planes generally perpendicular to each other. The half-wave plate allows light emitted from the second optical fiber to pass therethrough and rotates a polarized light plane of incident light. The first lens converts incident light into a generally collimated ray, and the magneto-optic crystal rotates a polarized light plane of incident light by an angle of π/8+Nn/4 (N=0, 1, 2, . . .) under the influence of a magnetic field. The optical filter reflects light having a specific wavelength and allows light having a wavelength other than this specific wavelength to pass therethrough, and the second lens are opposed to end faces of third and fourth optical fibers and converges a collimated ray introduced thereinto. By this construction, an optical coupling system is constituted between the first and second optical fibers and between the third and fourth optical fibers and one of the first and second optical fibers.

Pulse propagation in optical fibers near the zero dispersion point

Abstract: The problem of nonlinear pulse propagation in optical fibers near the zero dispersion point is investigated. It is shown, both analytically and numerically, that stable double:-humped solitary-wave solutions potentially can be used for transmission. The results clarify previous problems with the existence of single-humped localized solitary waves, i.e., fundamental solitons, which are forbidden in the strict mathematical sense

Optical wavelength shifting by traveling-wave electrooptic modulation

Abstract: Optical wavelength shifting of 1.054-nm laser pulses in excess of +or- 10 wavenumbers (+or- 300 GHz) was demonstrated. The wavelength shifter consists of synchronous microwave and optical waveguides fabricated monolithically on LiNbO/sub 3/. An optical pulse experiences a constant refractive index gradient that travels with the pulse and causes the wavelength shift. >

Article comprising a rare earth or transition metal doped optical fiber

Abstract: We have discovered that silica-based optical fibers (e.g., 33) that are doped with Ge, Al and a rare earth (e.g., Er) can be very susceptible to hydrogen-induced attenuation change. For instance, such fiber can exhibit loss increase rates that are, at 20°C, 106 times larger than those of a standard single mode fiber. We also believe that transition metal-doped silica-based fibers can exhibit large hydrogen-induced attenuation change. In many circumstances- (e.g., amplifier fiber, attenuator fiber) significant attenuation change of optical fiber is undesirable. We disclose that such change can be substantially eliminated by provision of hydrogen gettering material and/or a "hermetic" fiber coating. It is currently preferred to provide silica cladding material that is a hydrogen getter, and also provide a "hermetic" fiber coating. Containment of the fiber, together with a quantity of a gettering material (e.g., ErFe2) in an essentially hermetic enclosure is also disclosed.

Fiberoptic couplers having spacer fibers that have no optical cores

Abstract: The invention is a fiberoptic coupler formed by multiple optical fibers each having a core and a surrounding cladding and at least one spacer fiber having the refraction index substantially matched to the refraction index of the cladding of at least one adjacent optical fiber. The optical and spacer fibers are arranged, over a region extending axially through a limited length coupling region, in a side-by-side configuration wherein each fiber touches neighboring fibers. The coupling region is created by laterally fusing all fibers and is adapted to couple propagating modes of light between the optical fibers. Various configurations of the coupler include an arrangement of seven equal diameter fibers with a center fiber surrounded by six fibers, or an arrangement of nineteen equal diameter fibers with a center fiber surrounded by a first ring of six close-packed fibers and a second ring of twelve close-packed fibers. The number of the optical fibers and spacer fibers and their relative arrangements are selected to achieve desired properties of the coupler such as a number of optical input and output fibers, the coupling ratio or wavelength dependent coupling.

Radiation-induced coloring of erbium-doped optical fibers

Abstract: The radiation-induced coloring of erbium-doped optical fibers (EDF's) is reported. The radiation hardness of the EDF's is observed to be strongly dependent on composition. The implications for erbium-doped fiber amplifier (EDFA) performance is modelled.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Transverse strength of composites containing optical fibers

Abstract: The effect of embedded optical fibers on the transverse strength of an AS4/3501-6 composite is experimentally evaluated. The test data are compared with an existing analytical model where applicable. Parametric studies reported on include varying the optical fiber's physical size, coating thickness, and adhesion between the optical fiber and the composite. Results demonstrate that for certain cases the transverse strength can be degraded as much as 50%, however for small diameter optical fibers the strength reduction is negligible. Furthermore, polyimide coated optical fibers appear to have less of an effect on transverse strength than do uncoated optical fibers. It is suggested, both analytically and experimentally, that an optimal coating thickness exists to minimize the degradation in transverse strength.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Emission source spectrum stabilizer

Abstract: A spectrum stabilizer for stabilizing the wavelength of light emitted by a source for use in an optical system where the source can have that wavelength altered by varying one or more source parameters, such as source current, temperature and/or alignment of the output end of the source with an optical fiber of the optical system, and wherein light from a selected point in the optical system is coupled to a double mode waveguide for wavelength sensing

Complete compensation for the soliton self-frequency shift and third-order dispersion of a fiber

Abstract: The conditions of complete compensation for both the soliton self-frequency shift and the third-order dispersion are given. These forces, which are destructive to femtosecond pulse propagation, can be completely compensated for by the proper choice of the optical gain spectrum and the dispersion parameters of the optical fiber. This result is significant for achieving ultrahigh-bit-rate (>100 Gbits/s) optical transmission systems.

Optical communication system compensating wavelength dispersion and phase conjugate light generator applicable to this system

Abstract: PURPOSE:To enable the compensation of wavelength dispersion by generating the phase conjugate light to the signal light from a first optical transmission line and having a second optical transmission line for transmitting this phase conjugate light. CONSTITUTION:A light signal transmitter 1 supplies the signal light modulated in accordance with an input signal to the optical transmission line 2. The signal light transmitted by the optical transmission line 2 is supplied to a phase conjugate light generating means 3. This phase conjugate light generating means 3 generates the phase conjugate light to the received signal light. The optical transmission line 4 transmits the phase conjugate light generated by the phase conjugate light generating means 3 and supplies this light to a light receiver 5. This light receiver 5 reproduces a demodulation signal corresponding to the input signal of the light transmitter 1. The optical transmission lines 2, 4 of such a case are optical fibers of, for example, a quartz system with which the wavelength dispersion arises inevitably. The optical transmission lines 2, 4 are subjected to the compensation of the wavelength dispersion. The wavelength dispersion is effectively compensated if the wavelength dispersion generated in the optical transmission line 2 is nearly equal to the wavelength dispersion generated in the optical fiber 4.

Minimization of the chromatic dispersion over a broad wavelength range in a single-mode optical fiber.

Abstract: The effective refractive index as a function of vacuum wavelength is approximated by Lagrange interpolation polynomials. The rms value of the chromatic dispersion is then calculated analytically. It is demonstrated that use of fourth-degree polynomials is far more efficient than the use of second-degree polynomials. The rms value of the chromatic dispersion over the wavelength range (1.25 μm, 1.60 μm) is calculated and minimized for step-index fibers, triangular index fibers, and α-power fibers. The full vector solution of Maxwell’s equations is used. The error induced by the approximate refractive-index model is found to be negligible at the point of minimum dispersion.

Dispersion compensating fibers and systems

Abstract: A silica based dispersion compensating optical waveguide fiber includes a core region and a surrounding clad layer. The core region has a refractive index profile which includes a central core region doped with an index raising dopant having a positive central core region index of refraction with a positive Delta %, surrounded by a core moat region having a negative moat region index of refraction with a negative Delta %. The clad layer has a clad index of refraction, said central core region index of refraction being greater than said clad index of refraction which is greater than said core moat region index of refraction. The fiber has a dispersion Ddcf more negative than -20 ps/nm-km at a given wavelength in the range of 1520nm to 1565nm, an attenuation at the given wavelength in the range of 1520nm to 1565nm less than 1 dB/km with a negative average dispersion slope Sdcf (ps/nm2) in the wavelength range of 1520nm to 1565nm, and the dispersion at the given wavelength in the range of 1520nm to 1565nm divided by the attenuation at the given wavelength in the range of 1520nm to 1565nm is more negative than -120 ps/nm-dB.