Showing papers on "Dispersion-shifted fiber published in 1992"

Four-wave mixing in an optical fiber in the zero-dispersion wavelength region

Abstract: Fiber four-wave mixing (FWM) in the zero-dispersion wavelength region is described. The phase-matching characteristics are studied in the wavelength region where the first-order chromatic dispersion is zero. The results show that the phase-matching condition is satisfied and FWM light is efficiently generated at particular combinations of input light wavelengths. It is also shown that the deviation of the zero-dispersion wavelength along the fiber length plays an important role in FWM behavior. >

Polarization multiplexing with solitons

Abstract: It is shown both analytically and with numerical simulation, and confirmed experimentally in transmission over distances up to approximately 10000 km, that solitons maintain a high degree of polarization over an ultra-long distance transmission system consisting of birefringent dispersion-shifted fiber segments and erbium amplifiers. Based on that fact, the authors propose a polarization/time division multiplexing technique which should allow the single-wavelength bit-rate capacity of an ultra-long distance soliton transmission system to be doubled with little or no significant increase in bit error rate. >

Wavelength conversion experiment using fiber four-wave mixing

Abstract: Wavelength conversion using fiber four-wave mixing in an optical fiber is demonstrated. Utilizing the wavelength region around the zero-dispersion wavelength of a fiber, 622 Mbt/s FSK signal light is converted from 1555.2 to 1547.6 nm with a conversion efficiency of -24 dB. >

Small signal analysis for dispersive optical fiber communication systems

Abstract: A small signal analysis for analyzing the conversion between intensity and phase modulation or noise in a dispersive fiber is given. Using this theory the small signal response of laser diodes with respect to intensity and phase modulation in dispersive optical fibers is derived. Guidelines are also given for considerably reducing the intensity noise if a fiber with a suitable dispersion is used. All analytical calculations are compared with numerical simulations and good agreement is achieved. >

Continuously tunable single-mode erbium fiber laser

Abstract: A single-mode linear-cavity fiber laser that utilizes intracore Bragg reflectors for cavity feedback has been continuously tuned, without mode hopping, when both the gratings and enclosed fiber are stretched uniformly. Continuous tuning is achieved in a 1.54-microm erbium fiber laser since the change in the reflected wavelength from a Bragg reflector tracks the change in the cavity resonance wavelength.

Dispersion compensating devices and systems

Abstract: Disclosed is a family of dispersion compensating optical fibers that are adapted for use with conventional single-mode transmission fibers that are optimized for zero dispersion operation at a wavelength in the range from 1290 nm to 1330 nm to form a transmission link suitable for low dispersion operation in the 1520-1565 nm wavelength window. The dispersion compensating fibers are capable of providing a dispersion more negative than -20 ps/nm-km and attenuation less than 1 dB/km at wavelengths in the 1520-1565 nm region. Certain of the dispersion compensating fibers also exhibit a dispersion versus wavelength relationship having a negative slope in the 1520-1565 nm region, to compensate for the dispersion versus wavelength slope of the transmission fiber. The dispersion compensating fiber can be advantageously combined with a fiber amplifier to form a compensator that is adapted to overcome attenuation introduced into the system by the dispersion compensating fiber. In one embodiment, the dispersion compensating fiber is also a distributed fiber amplifier.

Polarization effect on four-wave mixing efficiency in a single-mode fiber

Abstract: Four-wave mixing in a single-mode fiber is studied for general polarization states in input lights. A theory is developed for fiber four-wave mixing where the polarization states of input light are various and they change randomly when propagating through a fiber line. The results show that intensity beating between the propagating lights plays an important role in four-wave mixing efficiency in a fiber. Experimental results support the theoretical treatment. >

Additive-modulation-instability ring laser in the normal dispersion regime of a fiber

Abstract: A synchronously pumped modulational-instability ring laser with a nonlinear dispersive fiber can be operated in both the anomalous and the normal dispersion regimes. We obtain simple analytical expressions for the sideband gain in the cavity by using an average pulse formalism. The numerical simulations indicate that stable stationary trains of pulses may be formed in the cavity. This is independent of the sign of the dispersion.

Method of making a fiber having low polarization mode dispersion due to a permanent spin

Abstract: The presence of (typically unintended) birefringence in single mode optical fiber can severely limit the usefulness of the fiber for, e.g., high bit rate or analog optical fiber communication systems, due to the resulting polarization mode dispersion (PMD). It has now been discovered that PMD can be substantially reduced if, during drawing of the fiber, a torque is applied to the fiber such that a "spin" is impressed on the fiber. Desirably the torque is applied such that the spin impressed on the fiber does not have constant spatial frequency, e.g., has alternately clockwise and counterclockwise helicity. At least a portion of optical fiber according to the invention has a spin whose spatial frequency exceeds 4 spins/meter.

Broadband dispersion compensation by using the higher-order spatial mode in a two-mode fiber

Abstract: A fiber-optic technique for compensating both first- and second-order group-velocity dispersion in single-mode fiber spans is demonstrated by using the large waveguide dispersion that occurs for the higher-order (LP11) spatial mode in a two-mode fiber near cutoff. Complete restoration of 7-ps pulses that had been dispersed by a factor of 10 in 5 km of single-mode fiber is demonstrated over a 20-nm-wavelength window. First-order dispersion as large as −228 ps/(nm km) is observed for the LP11 mode at 1560 nm in the two-mode fiber.

High power laser - optical fiber connection system

Abstract: A system for coupling laser radiation at a high power to an optical fiber while dissipating heat from scattered laser and optical pump radiation, including an optical fiber, a protective ferrule surrounding a portion of the optical fiber extending from the input face of the optical fiber and welded to the fiber in the region of the input face and otherwise separated from the fiber by an air space, and a holder surrounding the ferrule to absorb scattered radiation and dissipate heat.

Low noise high power optical fiber amplifier

Abstract: A rare earth doped optical fiber amplifier is pumped at a first wavelength selected to provide a low noise figure, and at a second wavelength selected to provide a high power efficiency. An erbium-doped fiber amplifier is illustrated, in which the first wavelength is about 980 nm and the second wavelength is about 1480 nm. The amplifier is forward pumped with the 980 nm wavelength adjacent the amplifier input to provide a low noise figure. Backward pumping at the 1480 nm wavelength is provided adjacent the amplifier output to achieve a high power efficiency.

Stimulated Brillouin threshold dependence on fiber type and uniformity

Abstract: The effects of fiber uniformity on stimulated Brillouin scattering thresholds have been measured, and the theory for stimulated Brillouin scattering in uniform fibers has been extended to the case of nonuniform fibers. This theory enables the, design of long fiber spans with ten times higher stimulated Brillouin scattering thresholds. >

Fluorometer and tapered fiber optic probes for sensing in the evanscent wave

Abstract: To develop an improved fiber optic biosensor both the optical component selection and the signal coupling efficiency were investigated. The emission filter and fiber connectors were carefully chosen to reduce their contribution to noise in the system. We used long, fused silica fibers that had several centimeters of cladding removed along the distal end. This exposed core is coated with the recognition molecules that bind analyte-fluorophore complexes from the sample solution. A fluorescent signal generated in the evanescent wave region of the unclad, immersed portion of the probe is lost as it enters the cladded portion of the fiber because of a V-number mismatch. To minimize the mismatch, the core radius is reduced along the uncladded region to form a continuous taper. An assay using the tapered fiber and the described optical configuration is presented that demonstrates instantaneous signal generation in response to nanogram amounts of a toxic material.

Microlenses for coupling optical fibers to elliptical light beams

Abstract: An asymmetric hyperbolic microlens on the end of a single-mode optical fiber enhances the fiber's coupling to elliptical laser beams The lenses, with controlled eccentricity ratios, are made by micromachining the end of the fiber with a pulsed CO₂ laser as the fiber is directed, preferably by computer control, about the focused laser beam Coupling efficiencies of 90 percent (-075 dB) have been realized with single transverse mode lasers at a wavelength of 098 µm having an approximately 3 to 1 beam ellipticity With multimode lasers at 148 µm having similar elliptical beams, the asymmetric lenses demonstrate an almost 2 dB increase in coupling efficiency over symmetric hyperbolic microlenses Such lasers are useful to pump erbium-doped fiber amplifiers About 120 mw was coupled from such a laser into single-mode fiber

Optical fiber amplifier and laser with flattened gain slope

Abstract: An in-fiber Bragg grating is used to flatten the gain slope of a fiber optical amplifier or optical fiber laser. The grating can be formed using photorefractive techniques, and is placed within a guided wave portion of a doped optical fiber. The grating is oriented at a nonperpendicular angle with respect to a longitudinal axis of the fiber, and has an interaction wavelength that is selected to flatten the gain slope of the device by diverting excess spontaneous emission therefrom. The interaction wavelength is preferably selected to correspond to a wavelength at or near that at which the spontaneous emission produced by the fiber peaks.

Stimulated Raman scattering in a multimode optical fiber: evolution of modes in Stokes waves

Abstract: Stimulated Raman scattering in a 50-μm multimode graded-index optical fiber was studied with a pulsed dye laser as the pump source. With 30 m of the fiber, the scattered waves (the Stokes waves) in the fiber could be made to propagate predominantly in one of the low-order modes of the fiber by careful adjustment of the light-launching conditions. The observed phenomenon is believed to be the result of nonuniform excitation of the modes by the pump. The experimental results are presented and discussed.

Sapphire-fiber-based intrinsic Fabry-Perot interferometer.

Abstract: A sapphire optical fiber intrinsic Fabry–Perot interferometric sensor is demonstrated. A length of multimode sapphire fiber that functions as a Fabry–Perot cavity is spliced to a silica single-mode fiber. The interferometric signals of this sensor are produced by the interference between the reflection from the silica–sapphire fiber splice and the reflection from the free end face of the sapphire fiber. This sensor has been demonstrated for temperature measurement. A resolution of 0.2°C has been obtained over a measurement range of 310°C to 976°C.

Optical fiber amplifier with flattened gain

Abstract: An apparatus and method for flattening the gain of an optical fiber amplifier (18) doped with an ion such as erbium and which is pumped by a pump laser (20). Optical couplers (32, 34) inserted before and after the fiber amplifier couple the main optical path to an optical ring passing through the fiber amplifier so as to form a ring laser. An optical isolator (32) placed in the ring causes the lasing light to only counterpropagate relative to the optical signal being amplified. When the fiber amplifier primarily exhibits inhomogeneous broadening and the ring lases, the lasing light clamps the gain to a value determined by the loop loss, and the value of the clamped gain is relatively uniform across a wide bandwidth.

Wavelength multiplexed two dimensional image transmission through single mode optical fiber

Abstract: An apparatus and method are provided for transmitting two-dimensional images through a single mode optical fiber. Light from a broadband source is dispersed into component wavelengths, spatially modulated to contain an image, collected for multiplexing in a single mode optical transmission fiber, transmitted through the single mode fiber, and demultiplexed into its component wavelengths to reproduce the transmitted image. The two-dimensional dispersing and collecting elements may be realized using thin film channel waveguides having arrays of optical gratings. Because the dispersive element at the receiving (output) end of the transmission fiber must reproduce the dispersal pattern used at the source, the information transmitting device may be used for data encryption and decryption.

Sensitized erbium fiber optical amplifier and source

Abstract: An optical fiber for amplifying or sourcing a light signal in a single transverse mode The fiber comprises a host glass doped with erbium (Er) and a sensitizer such as ytterbium (Yb) or iron (Fe) Preferably the host glass is doped silicic glass (eg, phosphate or borate doped) Electrical energy is provided to diode lasers that pump the Nd laser rod, which in turn pumps the fiber Such a configuration for pumping the fiber provides a high energy transfer from the diodes to the Nd laser rod, which in turn enables high pumping powers to be coupled into the single-mode co-doped fiber Based on the amplification characteristics of the co-doped fiber and the efficient coupling of power from the laser diodes, the amplifier provides power and small signal gains comparable to the best observed, while requiring only conventional and readily available diode-based pump sources

Grating compensation of third-order fiber dispersion

Abstract: Subpicosecond optical pulses propagating in single-mode fibers are severely distorted by third-order dispersion even at the fiber's zero-dispersion wavelength ( lambda /sub 0/). Using cross-correlation techniques, the authors measured the broadening of a 100-fs pulse to more than 5 ps after passing through 400 m of fiber near lambda /sub 0/. The measured asymmetric and oscillatory pulse shape is in agreement with calculations. A grating and telescope apparatus was configured to simultaneously equalize both third- and second-order dispersion for wavelengths slightly longer than lambda /sub 0/. Nearly complete compensation has been demonstrated for fiber lengths of 400 m and 3 km of dispersion-shifted fiber at wavelengths of 1560-1580 nm. For the longer fibers, fourth-order dispersion due to the grating becomes important. >

Optical fiber pressure sensor based on photoelasticity and its application

Abstract: An optical fiber pressure sensor based on the photoelastic effect using a novel compensation technique is described. Two optical sources and a polarization-splitting prism are incorporated into a sensor system to minimize output drifts. The four major factors-the optical source power, the fiber loss, the optical coupling loss, and the modal power distribution in fibers-are well compensated. The measurement range of 0-147 kPa has been obtained with accuracies of 0.2% within the temperature range of -10 degrees C to 42 degrees C and a resolution of 10 Pa has been achieved. Compensation for fiber loss has been observed up to -30 dB. This sensor system has been successfully put into practical operation for oil storage measurement in a tank. >

Gain equalization multiwavelength lightwave systems using acoustooptic tunable filters

Abstract: An acoustooptic tunable filter is used to compensate for the gain spectrum variations in multiwavelength lightwave systems containing cascaded fiber amplifiers. Demonstrations of such systems using a circulating loop containing a fiber amplifier and an acoustooptic tunable filter have shown that differential gain compensations of up to 14 dB can be achieved for two arbitrary injected wavelengths. >

Soliton propagation in an optical fiber with third-order dispersion.

Abstract: A simple model is described that correctly explains numerically observed resonance features on the soliton spectrum when the perturbative effects of third-order dispersion are present.

Resonator fiber optic gyro employing a polarization-rotating resonator

Abstract: A novel fiber optic resonator employing a 90 degree polarization rotation was developed to reduce polarization related bias errors of the resonator fiber optic gyro. For the first time, we have fabricated and tested a nearly all guided-wave gyro having a polarization-rotating fiber resonator. Bias stability better than 0.4 deg/hr, random walk of 0.1 deg/root-hr, and day to day absolute bias stability of 10 deg/hr are reported. The major error mechanism of bias instability and other error sources are discussed.

Chromatic dispersion compensated optical fiber communication system

Abstract: An optical fiber communication system according to the invention comprises, in addition to conventional single mode (SM) optical fiber, dispersion compensating (DC) optical fiber. The DC fiber is selected such that its chromatic dispersion (DDC (λ)) and first derivative of the chromatic dispersion with respect to wavelength (D'DC (λ)) at a wavelength λ=λop have opposite sign from those of the SM fiber. Advantageously, the DC fiber is selected such that LDC ·DDC (λ)+L·D(λ) is approximately zero at λ=λop, and such that D'DC (λ) is approximately equal to --(L/LDC)·D'(λ) at λ=λop, where LDC and L are appropriate lengths of DC and SM fiber, respectively. Typically, L is much greater than LDC, and λop typically is about 1.5 μm, e.g., about 1.56 μm. Preferred embodiments of the invention have low chromatic dispersion over a substantial wavelength region (e.g., dispersion less than 1.5 ps/nm·km over at least 50 nm) that includes λo, facilitating wavelength division multiplexing.

System of very-long-distance digital transmission by optical fiber with compensation for distortions at reception

Abstract: A system for very-long-distance transmission of a digital signal between a transmitter station and a receiver station, wherein the transmitter and receiver stations are connected by a monomode optical fiber with negative chromatic dispersion at the operating wavelength of the system, having a length of at least one thousand kilometers. The receiver station comprises device to compensate for the distortions due to the non-linear effects and to the chromatic dispersion introduced by the transmission line, the compensation device carrying out a positive chromatic dispersion of the received signal, the amplitude of the positive chromatic dispersion being a function notably of the amplitude of the negative chromatic dispersion induced by the optical fiber as well as of the mean on-line optical power of the signal transmitted on the optical fiber.

Optical signal source for overcoming distortion generated by an optical amplifier

Abstract: An amplified signal source is provided for transmitting modulated information signals over a fiber optic communication link, which may have high fiber dispersion. A continuous wave laser produces an optical carrier at a wavelength λ1. The optical carrier is intensity modulated to provide a substantially chirp free output signal. The output signal is amplified in an optical amplifier and coupled for transmission over a link fiber that can have a minimum dispersion at a wavelength λ2 that is different than λ1. The nonzero gain slope of the optical amplifier does not significantly degrade the substantially chirp free output signal.

The Effect of Tapering the Optical Fiber on Evanescent Wave Measurements

Abstract: Optical biosensors are analytical tools employed in environmental, biotechnology and clinical fields. For remote evanescent wave detection with optical fibers, the majority of the fiber remains cladded while only a small portion of the core is exposed to perform the analysis. To improve the sensitivity of this type of fiber optic biosensor, tapering the sensing region of the fiber was investigated. Silica fibers were tapered into two geometries: step and continuous tapers. To determine the effect of tapering on detection levels, a fluoroimmunoassay was performed on fibers with nontapered, step-tapered and continuously tapered geometries. Solutions containing a fluorescent analyte were circulated over an antibody-coated fiber and the fluoresence signal measured The minimum detection limit for fibers with 10 cm sensing region was 1.56 nM, 0.31 nM and 0.16 nM for nontapered, step-tapered and continuously tapered fibers, respectively. Continuous tapering of the sensing region of an optical fiber offe...