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Showing papers on "Single-mode optical fiber published in 1985"


Patent
08 Nov 1985
TL;DR: In this article, the authors proposed to improve an S/N ratio by driving a semiconductor laser by the signal on which high-frequency current is superposed and oscillating the laser with non-single mode.
Abstract: PURPOSE:To improve an S/N ratio by driving a semiconductor laser by the signal on which high-frequency current is superposed and oscillating the laser with non-single mode. CONSTITUTION:The high-frequency current having the frequency, for example, 2.5-4GHz for returning the oscillation mode of the semiconductor laser LD to multimodes prior to lapse of the time when said mode changes to single mode is emitted from a high-frequency current source G and is superposed on the output current of a DC current source I via a capacitor C. The laser LD is thus driven by the signal on which the high frequency is superposed. The amplitude of the current source G is so set as to cut off thoroughly the threshold current of the laser LD. The characteristic having the stable S/N ratio is thus obtd. even if the optical length and the frequency of the high-frequency current vary to some extent.

271 citations


Journal ArticleDOI
TL;DR: This study predicts optimum fundamental mode oscillation in fibers with a V number of 5-25 with submilliwatt thresholds and nearly quantum-limited conversion efficiencies.
Abstract: Using the formalism of mode overlap, a theoretical analysis of optically pumped fiber laser amplifiers and oscillators is developed. The concept of normalized overlap coefficients is introduced to account for the effects of the transverse structure of the interacting signal and pump modes on the device characteristics. Simple and accurate closed-form expressions are derived for the gain of fiber amplifiers and the threshold and energy conversion efficiency of fiber laser oscillators in terms of the fiber and laser material parameters and the pump and signal modes. When applied to step-index Nd:YAG fiber lasers, this study predicts optimum fundamental mode oscillation in fibers with a V number of 5-25 with submilliwatt thresholds and nearly quantum-limited conversion efficiencies.

200 citations


Journal ArticleDOI
Leonard George Cohen1
TL;DR: In this paper, state-of-the-art techniques for characterizing dispersion in single-mode fibers are described, with special emphasis on achieving high measurement accuracy within the 1.1-1.7 \mu m wavelength region.
Abstract: This paper describes state-of-the-art techniques for characterizing dispersion in single-mode fibers. Special emphasis is placed on achieving high measurement accuracy within the 1.1-1.7 \mu m wavelength region.

196 citations


Journal ArticleDOI
TL;DR: In this paper, a method for compressing optical pulses at any wavelength in an optical fiber is described, which uses the negative dispersion property of permanent phase gratings created within the fiber.
Abstract: A method is described for compressing optical pulses at any wavelength in an optical fiber. It uses the negative dispersion property of permanent phase gratings created within the fiber. No external grating pair is required.

190 citations


Journal ArticleDOI
TL;DR: With sufficient Raman gain to compensate exactly for net fiber energy loss, distortionless propagation of 10-psec FWHM fundamental soliton pulses over a 10-km length of single-mode fiber is demonstrated.
Abstract: With sufficient Raman gain to compensate exactly for net fiber energy loss, we have demonstrated distortionless propagation of 10-psec FWHM fundamental (N = 1) soliton pulses (λ = 1.56 μm) over a 10-km length of singlemode fiber. The implications of this experiment for development of an all-optical, high-bit-rate, long-distance telecommunications system are discussed briefly.

157 citations


Journal ArticleDOI
Levenson1, Robert M. Shelby1, A. Aspect1, Margaret D. Reid2, D. F. Walls2 
TL;DR: Methods of suppressing undesired effects such as stimulated Brillouin scattering are presented as is a technique for providing the phase-shifted local oscillator wave necessary for the detection of squeezing.
Abstract: Nondegenerate four-wave mixing in a single-mode optical fiber is proposed as a method of squeezed state generation. An analysis of the near-degenerate mixing process for forward propagation in realistic fibers is presented along with the theory of an experimentally feasible detection strategy. The effects of the quantum nature of the optical nonlinearity and absorption are modeled by treating the fiber medium as a collection of anharmonic oscillators. Methods of suppressing undesired effects such as stimulated Brillouin scattering are presented as is a technique for providing the phase-shifted local oscillator wave necessary for the detection of squeezing. Preliminary experiments on fiber characterization and the detection of four-wave parametric fluorescence are described.

137 citations


Patent
18 Dec 1985
TL;DR: An optical coupler for single mode optical signals having a tunable (variable) coupling ratio, and a method of fabricating the coupler is described in this paper, where a pair of virtually identical optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, each being tapered toward the waist in such a manner as to ensure adiabatic propagation of light in the structure.
Abstract: An optical coupler for single mode optical signals having a tunable (variable) coupling ratio, and a method of fabricating the coupler. A pair of virtually identical optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, each being tapered toward the waist in such a manner as to ensure adiabatic propagation of light in the structure. An optical signal carried by one fiber first passes through a decreasing taper region and then passes through an increasing taper region of one or the other fiber (or both). The decreasing taper rate of the input portion of one fiber is such that the optical signal radiates out of the core (where V=1 locally) and into the cladding, as it approaches the waist. The increasing taper rates of the output portions of the two fibers are such that a predetermined coupling ratio is obtained. The coupler is bent in the region of the waist whereby a coupling ratio can be selected between the incoming fiber portions having the decreasing taper and the outgoing fibers having increasing tapers.

112 citations


Journal ArticleDOI
TL;DR: In this article, a simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given.
Abstract: A simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser, and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given. The dynamic spectral width of a DSM laser is determined by the modulated optical shape and the linewidth enhancement factor α. The spectral width caused by the dynamic wavelength shift is shown to be larger by ( 1 + \alpha^{2} )1/2than that caused by the sideband of the signal of the intensity modulation. Furthermore, the maximum transmission bandwidth of a conventional single-mode fiber with a DSM laser is expressed by using the parameter α and the chromatic dispersion of the fiber. The product of the maximum bit rate and the square root of the fiber length at the wavelength of 1.55 μm is estimated to be about 25 Gbit/s . km1/2.

102 citations


Patent
15 Jan 1985
TL;DR: In this article, a novel expanded beam coupling arrangement for use in association with single mode fibers is disclosed, where an appropriate length of multimode fiber is fused to the endface of an input single mode fiber, where the length of the multimode fibre is chosen to provide the desired lensing conditions of the input beam.
Abstract: A novel expanded beam coupling arrangement for use in association with single mode fibers is disclosed. An appropriate length of multimode fiber is fused to the endface of an input single mode fiber, where the length of the multimode fiber is chosen to provide the desired lensing conditions of the input beam. The multimode fiber is thus used as a lens, but provides many advantages over prior art optical connectors which use conventional quarter-pitch GRIN lenses epoxied to the fiber endfaces. In particular, the misalignment associated with the epoxied arrangement is reduced since the multimode fiber-lens connector of the present invention may be chosen to comprise the same outer diameter as the single mode fiber. Additionally, the use of a section of optical fiber as a lens allows for a fused connection to be used instead of an epoxied connection, which results in a more stable and rugged interface between the fiber and the lens.

98 citations


Journal ArticleDOI
TL;DR: In this article, the temporal behavior of stimulated Brillouin scattering (SBS) in single-mode optical fibers is investigated theoretically and experimentally, and it is shown that if external feedback exists, the SBS and the transmitted pump intensities exhibit steady oscillations with a period of twice the transit time in the fiber.
Abstract: The temporal behavior of stimulated Brillouin scattering (SBS) in single-mode optical fibers is investigated theoretically and experimentally It is shown that if external feedback exists, the SBS and the transmitted pump intensities exhibit steady oscillations with a period of twice the transit time in the fiber However, if the ratio between the SBS intensity and the input intensity is above a certain value, the oscillations decay

92 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported measurements of the distribution of 90° radiation loss along the length of an optically pumped distributed feedback resonator having a second-order grating and nonreflecting ends.
Abstract: We report measurements of the distribution of 90° radiation loss along the length of an optically pumped distributed feedback resonator having a second-order grating and nonreflecting ends. The loss is strong at the ends, but nearly cancels at the center due to destructive interference of the scattered radiation from the oppositely propagating waves forming the lasing mode. This is the first observation of this interference effect, which provides an important source of single mode selection in distributed feedback lasers with second-order gratings.

Journal ArticleDOI
TL;DR: In this paper, the performance of an experimental 1.5-μm lightwave transmission system operating at 8 Gbit/s over 68.3 km of single-mode fiber is described.
Abstract: We describe the performance of an experimental 1.5-μm lightwave transmission system operating at 8 Gbit/s over 68.3 km of single-mode fiber. The dispersion penalty is limited to 1 dB through the use of external modulation and is attributable to the intrinsic information bandwidth.

Journal ArticleDOI
P. Buchmann1, H. Kaufmann
TL;DR: In this article, the fabrication and optical properties of reactive ion-etched, totally reflecting mirrors for single-mode GaAs rib waveguides are described, in order to increase packing density and to facilitate waveguide to fiber coupling.
Abstract: The fabrication and optical properties of reactive ion-etched, totally reflecting mirrors for single-mode GaAs rib waveguides are described. Low loss and orientation independance make the device useful in integrated optics, in order to increase packing density and to facilitate waveguide to fiber coupling. Results of displacement sensitivity calculations are also shown.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the spectral and modulation characteristics of injection-locked distributed feedback lasers operating at 1.5-μm wavelength and showed that the total elimination of excess chirp in directly modulated lasers by the injection locking technique has allowed them to perform transmission experiments over 82.5 km of single mode fibers at 2 Gbit/s without any measurable penalty related to dispersion.
Abstract: The spectral and modulation characteristics of injection locked distributed feedback lasers operating at 1.5-μm wavelength have been investigated. The total elimination of excess chirp in directly modulated lasers by the injection locking technique has allowed us to perform transmission experiments over 82.5 km of single mode fibers at 2 Gbit/s without any measurable penalty related to dispersion. Device design parameters for efficient chirp suppression are also given.

Journal ArticleDOI
TL;DR: Various microlenses are fabricated on the end of single-mode fibers using a photolithographic technique to measure the beam waist and beam waist position of these lenses and compared to theoretical values derived for Gaussian beams under a paraxial ray approximation.
Abstract: Various microlenses are fabricated on the end of single-mode fibers using a photolithographic technique. The radii of these lenses are in the 2.6–20-μm range. The beam waist and beam waist position of these lenses are measured and compared to theoretical values derived for Gaussian beams under a paraxial ray approximation. Beam spot sizes of <0.75 μm have been achieved at 830 nm.

Journal ArticleDOI
TL;DR: In this paper, the problem of soliton interaction in optical-fiber communication systems is investigated analytically with the assumption of incoherent SINR interaction, i.e., interaction through nonlinear intensity overlap only.
Abstract: The problem of soliton interaction in optical-fiber communication systems is investigated analytically with the assumption of incoherent soliton interaction, i.e., interaction through nonlinear intensity overlap only. This situation is found to lead to attraction forces between consecutive pulses that are weaker than those in previously investigated coherent cases. The subsequent maximum system bandwidth is correspondingly improved.

Journal ArticleDOI
P. Healey1
TL;DR: In this paper, the authors reviewed the worldwide activity on long-wavelength ( > 1.1-mu m) single-mode optical fiber reflectometry and compared and contrasted the many different approaches being taken to equipment design.
Abstract: This paper reviews the worldwide activity on long-wavelength ( >1.1-\mu m) single-mode optical fiber reflectometry and compares and contrasts the many different approaches being taken to equipment design.

Journal ArticleDOI
TL;DR: The results support the model of the coupling mechanism as a beat phenomenon between modes guided by a glass core with a dumbbell cross section and an external refractive index.
Abstract: It is demonstrated that through control of the refractive index surrounding a fused biconical-taper single-mode coupler the coupling coefficient can be changed from 0% to 96%. Data are also presented that show the coupling mechanism cannot be attributed to power transfer between the modal fields guided by the fiber cores in the taper-waist region. The results support the model of the coupling mechanism as a beat phenomenon between modes guided by a glass core with a dumbbell cross section and an external refractive index.

Journal ArticleDOI
TL;DR: In this paper, the authors show that laser sources with a large spectrum of narrow longitudinal modes may cause high speckle contrast and important modal noise over more than 1-km length in graded-index multimode fibers.
Abstract: The speckle contrast for multimode fibers, and thus the modal noise, is essentially given by the impulse response of the fiber and the power spectrum of the source. Theoretical and experimental results show that laser sources with a large spectrum of narrow longitudinal modes may cause high speckle contrast and important modal noise over more than 1-km length in graded-index multimode fibers.

Journal ArticleDOI
TL;DR: In this article, the phase and amplitude fluctuations of a single-mode laser were compared with the same total average power of a mode-locked single-modal laser, and it was shown that the linewidth of each of the locked modes is the same as that of the single mode.
Abstract: Comparisons are made of the phase and amplitude fluctuations of a laser when it operates single mode and when it is mode locked with the same total average power. Despite the much lower signal-to- (spontaneous emission) noise ratio of the mode-locked laser, the linewidth of each of the locked modes is the same as that of the single mode. The fluctuation of the total intensity of the mode-locked laser, and the linewidth enhancement factor due to intensity fluctuation as recently analyzed by Henry, are the same in both cases.

Patent
09 Oct 1985
TL;DR: In this paper, an improved fiber optic magnetometer is presented for use in environments having large magnetic field ranges and gradients, such as space-based applications, where the magnetometer includes a laser which generates a coherent beam of light which is split by a beam splitter into first and second beams.
Abstract: The present invention provides an improved fiber optic magnetometer having particular application for use in environments having large magnetic field ranges and gradients, such as space based applications. The magnetometer includes a laser which generates a coherent beam of light which is split by a beam splitter into first and second beams. The first beam is passed through a single mode fiber optic having a short metallic conductor attached to it. This fiber is referred to as the "sensor arm" of the magnetometer. The second beam is passed through another single mode fiber which is wrapped around a modulator that is coupled to a feedback circuit. This adjusts the magnetometer such that ambient system noise is filtered and the device is maintained at maximum sensitivity. The output of the two fibers is combined forming a Mach-Zehnder interferometer. A current I is passed through the conductor in the sensor arm. If this fiber is in the vicinity of a magnetic field, displacement of the current carrying conductor will cause the fiber to bow. The resulting stretching of the fiber increases the pathlength for the light beam traversing through the sensor arm. The subsequent phase change measured by the Mach-Zehnder is related to the force exerted by the magnetic field on the conductor. The direction in which the fiber bows is dependent upon the magnetic field direction. The present invention also discloses an improved modulator for maintaining the present invention at the point of optimum operation.

Journal ArticleDOI
TL;DR: In this paper, a low-loss dispersion-shifted single-mode fiber with a segmented-core profile was developed for long-haul high-data-rate operation utilizing multilongitudinal mode lasers.
Abstract: The development of a low-loss dispersion-shifted single-mode fiber with a segmented-core profile is reported. The combination of low dispersion in the 1550-nm window, 0.21-dB/km median attenuation at 1550 nm, excellent bend resistance ( \lambda_{c} = 1200 nm), and good splicing behavior make this fiber an economically viable alternative for long-haul high-data-rate operation utilizing multilongitudinal mode lasers. System experiments have demonstrated bit rates as high as 1.3 Gbit/s over 107 km and repeaterless spans of up to 233 km.

Patent
02 Oct 1985
TL;DR: In this article, a super-radiant light source having an output with a low temporal coherence was presented. But the output was not suitable for optical inertial sensor applications, such as optical optical waveguide.
Abstract: 57 A super-radiant light source having an output with a low temporal coherence well suited, for example, to optical inertial sensor applications, includes a single mode optical waveguide such as an optical fiber having its core doped with an active laser material, such as neodymium. Pump light is coupled into the optical fiber at an intensity sufficient to produce a significant amplification of the spontaneous emission. The reflectivity at the exit end of the fiber is low enough so that even with a high gain for the light in one traverse through the fiber, the fiber is operated well below threshold for laser oscillation. The resulting emission is of high intensity, but has a low temporal coherence. In one form, the pump light is coupled into one end of the fiber and a dichroic filter is interposed in the light path between the pump light and the optical fiber to pass pump light into the core and reflect the spontaneous emission of the active material back into the core and toward the output.

Patent
12 Nov 1985
TL;DR: In this article, a method of fabricating a single mode fiber optic multiplexer/demultiplexer is described, where the first and second lights are fused together to form a coupler.
Abstract: A single mode fiber optic multiplexer/demultiplexer has first and second optical fibers, each having an input and an output end. The first and second optical fibers are single mode fibers each having a core of a predetermined diameter and a cladding about the core of a predetermined diameter. Along a predetermined length two fibers are placed in juxtaposition and the claddings are fused together to form a fiber optic coupler. Previous to being fused, the claddings are reduced by etching. The coupling of the fiber optic device is such that a first light having a first predetermined wavelength and a second light having a second predetermined wavelength enter together on an input of one of the fibers and are substantially split such that substantially only the first light will appear on an output of one of the fibers and substantially only a second light will appear on an output of the other fiber. When the first and second lights enter on the input end of the first and second fibers, the novel device combines the first and second lights onto one of the output ends of the fibers. In this configuration the device operates as a multiplexer. A method of fabricating the multiplexer/demultiplexer is disclosed.

Journal ArticleDOI
TL;DR: In this article, the effect of polarization on fiber-waveguide insertion loss is discussed and the first measurements of waveguide-mode position as a function of polarization are presented. And the authors report on coupling arrays of SM fibers in silicon V grooves to waveguides with an average excess loss of 0.3 dB per interface.
Abstract: We report on coupling arrays of SM fibers in silicon V - grooves to waveguides. Arrays with up to 12 fibers have been permanently attached to waveguides with an average excess loss of 0.3 dB per interface. We discuss a subtle, heretofore unreported effect of polarization on fiber-waveguide insertion loss and we describe the first measurements of waveguide-mode position as a function of polarization. In general, the modes of a Ti:LiNbO 3 waveguide peak at different positions. This results in different optimum positions for coupling and thus leads to an unavoidable excess loss when attaching fibers. For low-loss waveguides, we predict a minimum excess loss of 0.25 dB per interface.

Patent
06 Nov 1985
TL;DR: In this article, a quasi-resonant coupling of the guided mode LP 01 to an appropriate tunneling leaky (TL) mode, e.g., LP 11, is proposed.
Abstract: Optical radiation can be efficiently removed from, or injected into, single mode optical fiber at an intermediate point along the fiber, by causing quasi-resonant coupling of the guided mode LP 01 to an appropriate tunneling leaky (TL) mode, e.g., LP 11 . Such coupling is caused by means of a "grating" in the fiber, with the grating being formed by impressing a periodic (or pseudo-periodic) modulation on the fiber, or by causing a periodic (or pseudo-periodic) variation of the refractive index of the fiber by means of the photoelastic or the photorefractive effect. The nominal grating spacing Λ(z) is chosen such that Ω o =(2π/Λ)>β 01 -2πn cl /λ o , where Λ is the average grating spacing, β 01 is the propagation constant of the LP 01 mode, n cl is the refractive index of the fiber cladding, and λ o is the wavelength of the radiation to be coupled from or into the fiber. Furthermore, Λ(z) is to be chosen such that Ω o ˜β 01 -β rs , where β rs is the propagation constant of the selected TL mode. In order for the coupling to be quasi-resonant, it is necessary that α rs , the attenuation constant of the selected TL mode, be relatively small, typically <1 dB/cm. By appropriately choosing Λ(z) and/or the amplitude function of the grating, it is possible to increase the coupling efficiency above what is possible with a constant spacing, constant amplitude grating. Devices according to the invention can be advantageously used not only as radiation couplers but also as filters and, if they are of the photorefractive type, as amplitude modulators.

Patent
29 Oct 1985
TL;DR: An optical fiber comprising a core and cladding having different refractive indices and forming a singlemode guiding region, the core having a non-circular cross-section defining two transverse orthogonal axes which, in combination with the different as mentioned in this paper indices, permit the de-coupling of waves polarized along the axes.
Abstract: An optical fiber comprising a core and cladding having different refractive indices and forming a single-mode guiding region, the core having a non-circular cross-section defining two transverse orthogonal axes which, in combination with the different refractive indices, permit the de-coupling of waves polarized along the axes. The guiding region is located sufficiently close to the surface of the fiber along a selected length of the fiber, to allow coupling to a guided wave. The outer surface of the fiber has a non-circular cross-section with a predetermined geometric relationship to the guiding region and the orthogonal transverse axes so that the location of the guiding region and the orientation of the axes can be ascertained from the geometry of the outer surface.

Patent
19 Sep 1985
TL;DR: In this paper, the power from a single cw laser is divided over a plurality of single mode optical fibers to transmit information from the central office to the user stations, each user station includes a directly modulated LED for transmitting information to the central station.
Abstract: An optical communications network which connects a central office with a plurality of user stations is disclosed. In the central office, the power from a single cw laser is divided over a plurality of single mode optical fibers to transmit information from the central office to the user stations. Each user station includes a directly modulated LED for transmitting information to the central office.

Journal ArticleDOI
TL;DR: In this paper, optical amplification of signals from laser diodes in the first and second optical transmission windows is reported for 1.32 um laser diode light at the rate of 11 dB/W in a 2.5 km long SMF.
Abstract: In this paper, fibers and transmission system designs using nonlinear optical amplification and frequency conversion in single-mode fibers (SMF) are discussed. Optical amplification of signals issued from laser diodes in the first and second optical transmission windows is reported. Raman gains of 40 dB have been obtained for 1.32 um laser diode light at the rate of 11 dB/W in a 2.5 km long SMF. Parametric amplification of laser diode signals at 1.57µm in a 30 m long SMF pumped in the low dispersion region at 1.32 um is presented. Gain values in excess of 30 dB are measured. Up and down frequency conver-sions using stimulated four-photon mixing experiments are also demonstrated.

Patent
29 Apr 1985
TL;DR: A fiber optic saturable absorber for processing optical signals is characterized by an optical fiber (20) from which a portion (40) of the cladding (36) is removed to form a facing surface (28), such that a portion of the optical signal energy is transferred from the fiber to the substance (30) where it is absorbed as mentioned in this paper.
Abstract: A fiber optic saturable absorber for processing optical signals is characterized by an optical fiber (20) from which a portion (40) of the cladding (36) is removed to form a facing surface (28). A light-absorbing substance (30) having non- linear light-absorbing characteristics is applied to the facing surface (28) such that a portion of the optical signal energy is transferred from the fiber (20) to the substance (30) where it is absorbed. The device selectively attenuates the optical signal and noise, and can be used to reduce pulse waveform distortion caused by pulse broadening and by amplification of system noise.