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Lightwave Technology, Journal of

Issue 3 • Date June 1984

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Displaying Results 1 - 20 of 20
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Analysis of leakage currents in 1.3-µm InGaAsP real-index-guided lasers

    Page(s): 201 - 208
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    We describe leakage current calculation in several real-index-guided laser structures using an electrical equivalent circuit model. The structures analyzed are different types of buried heterostructures in which heterojunctions are used for lateral carrier confinements. The device types are: 1) the etched-mesa buried heterostructure (EMBH); 2) the channeled-substrate buried heterostructure (CSBH); 3) the double-channel planar buried heterostructure (DCPBH); 4) the planar buried heterostructure (PBH); and 5) the buried crescent (BC). Adequate current confinement is necessary in a laser structure for both linearity and low threshold operation. Thus leakage current, i.e., the difference between the injected current and the current through the active region, should be small. We have identified the main leakage paths in these structures and the parameters (the relevant layer thicknesses and doping levels) that determine the magnitude of the leakage current. The effect of nonradiative recombination sites on junction parameters and the consequent increase in leakage current is discussed. View full abstract»

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  • An optical-fiber-based gas sensor for remote absorption measurement of low-level CH4gas in the near-infrared region

    Page(s): 234 - 237
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    A long-distance low-loss silica optical-fiber link connected to a compact absorption cell was employed to realize a fully optical highly sensitive fiber gas sensor for low-level CH4gas in conjunction with a highly radiant InGaAsP light-emitting diode (LED) at 1.66 μm. By using a dielectric interference filter which replaces a monochromator to simplify the system configuration and operation, a 2-km-long silica fiber link was demonstrated to be capable of achieving reproducibly the detection sensitivity of nearly 700 ppm for CH4gas in air, i.e., 1.3 percent of the lower explosion limit of CH4density. This high sensitivity verifies a potential for major applications to strategic points within the environment, like industrial and mining complexes as well as urban and residential areas. This result also indicates that the purely optical gas-sensor system based on ultralow loss optical-fiber networks, incorporating LED's or laser diodes, can be extensively utilized for the real-time remote measurement and surveillance of a number of dangerous, explosive, and toxic gases in the near-infrared region. View full abstract»

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  • Anisotropic fibers studied by the Green's function method

    Page(s): 284 - 291
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    The Green's function method is used to derive the fundamental mode fields of the anisotropic circularly symmetric step-profile fiber. The method is particularly simple for stress-induced birefringence. It also provides a single analytic expression for the loss of the leaky mode. generalizing the results we previously derived for some special cases using radiation modes [4], [5]. View full abstract»

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  • An experimental low-loss single-wavelength bidirectional lightwave link

    Page(s): 300 - 305
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    We describe the perofrmance of a low-loss couplerless bi-directional transmission experiment which operates at a single wavelength. The system is unique in that it employs an annular In0.53Ga0.47As/InP photodetector and has potential for use for both long-wavelength (lambda < 1.7 mum) and short-wavelength (lambda geq 0.82mum) transmission. We find that the optical crosstalk between the near-end transmitter and receiver is as low as -16.6 dB (-33.2 dB electrical) for a 200-m link: a value acceptable for use in many short haul system applications. View full abstract»

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  • Lens coupling of laser diodes to single-mode fibers

    Page(s): 305 - 311
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    This paper studied the effect of lens aberration on coupling efficiency and loss penalty due to misalignment for a laser diode to single-mode fiber couplers. The theoretical results were in very good agreement with experimental values and the validity of the present analysis was confirmed. The paper made clear that coupling loss is dominated by aberration and proposed some basic approaches to improving coupling efficiency. View full abstract»

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  • Erratum

    Page(s): 328
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    First Page of the Article
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  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE
  • Length dependence of the effective cutoff wavelength in single-mode fibers

    Page(s): 238 - 242
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    The effective cutoff wavelength of a depressed cladding single-mode fiber in either a cabled or a loose state depends upon the length of the fiber. This dependence can be accurately represented by a linear function of the logarithm of the fiber length for lengths between 1 m and 1 km. Cutoff will shift 55-66 nm per decade length for slightly and moderately depressed cladding designs, respectively. Neglecting all sources of differential mode attenuation except leaky-mode loss, the computed behavior of cutoff as a function of fiber length agrees reasonably well with the observed behavior for a moderately depressed cladding design. On the other hand, agreement is poor for a slightly depressed cladding design. A knowledge of the length dependence of cutoff is essential for establishing a production requirement for cutoff based upon the needs of the system. View full abstract»

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  • Equivalent optical waveguides

    Page(s): 268 - 276
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    We develop a comparison method which identifies a waveguide with properties that are well known and are very similar to the one under investigation. It has a very simple mathematical basis which allows a trivial derivation of the moment method for circular cross-sectional fibers includingW-fibers, and an extension to noncircular optical waveguides. We first use the scalar approximation, and then extend to the full vector theory which accounts for polarization. Our concern is with fundamental mode propagation constants and higher mode cutoffs. View full abstract»

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  • Partition fluctuations in nearly single-longitudinal-mode lasers

    Page(s): 209 - 216
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    A simple model of mode partition noise is developed, which is valid for semiconductor lasers operating CW, having a single active region and oscillating primarily in one dominant mode. It is shown that the intensity fluctuations in the nonlasing modes occur with characteristic times of a few nanoseconds and have exponential probability distributions. We show that the lasing mode is able to follow adiabatically fluctuations in the nonlasing modes in such a way that the total intensity remains constant. Our model quantitatively accounts for the observations of Linke et al. that the frequency of "dropouts" in the lasing-mode intensity decreases exponentially with the ratio of average intensities of the lasing and nonlasing modes, and that in digital communication applications a ratio of about 50 is required to reduce the resulting bit-error probability tolsim 10^{-9}. We also account for the probability distribution of the lasing-mode intensity, which was observed by Liu et al to be exponential at low intensity and Gaussian at high intensity. The exponential fluctuations constitute partition noise induced in the lasing mode by large Gaussian fluctuations in the field amplitude of the nonlasing mode. Additional noise sources associated with the carrier density and the lasing-mode field produce Gaussian behavior at high intensities plus a negligible broadening of the low-intensity exponential tail. View full abstract»

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  • Progress in monomode optical-fiber interconnection devices

    Page(s): 217 - 227
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    We review recent progress in coupling devices for monomode fiber systems, with an eye towards practical performance limits in the near future. Emphasis is placed on key subjects such as laser-to-fiber coupling and packaging, connectors, and splicing. In addition, we also discuss planar lenses which are being developed for various applications. View full abstract»

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  • Electrooptic leaky anisotropic waveguides using nematic liquid crystal overlays

    Page(s): 292 - 295
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    This paper describes the experimental results on two types of electrooptically controllable leaky anisotropic waveguides using nematic liquid crystal (LC) overlayers. In these constructions the conversion of a guiding structure into a leaky one or a reverse operation is feasible by applying an electric field. They showed a switching of millisecond order with an extinction ratio of 20 dB at 30-V peak-to-peak (p-p) applied. View full abstract»

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  • Fundamental mode size and bend sensitivity of graded and step-index single-mode fibers with zero-dispersion near 1.55 µm

    Page(s): 312 - 316
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    Single-mode fibers, for near 1.55-μm operating system wavelength with triangular (alpha = 1), parabolic (alpha = 2), and step-index (alpha=infty) profiles were fabricated by the modified chemical vapor deposition (MCVD) technique. Optical transmission losses under zero-tension and with the basket weave under 10, 40, and 70 gm tensions were measured, respectively. Fundamental mode size was obtained as a function of wavelength by using the transverse offset technique. The triangular-profile fiber shows lower loss (≃0.25 dB/km at 1.55μm) under zero-tension and a larger spot size than the other fibers. However, the basket weave test showed the triangular-profile fiber incurred higher loss with tension than the other profiles. View full abstract»

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  • Measurement of stress profiles in the preform of a polarization-holding fiber with stress-applying parts

    Page(s): 228 - 233
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    Stress difference distribution, principal stress trajectories, and surface stress profiles are measured for the preform of a polarization-holding fiber with stress-applying parts. Experimentally evaluated stresses are compared with stresses computed by a finite element method. Experimental results are well explained by the calculated ones. Contour maps for stress difference and principal stress are presented. Surface stress is found to be compressive for the entire boundary of the fiber. Tensile test is carried out for the fiber drawn from the same preform rod. The result reveals that the strength of the polarization-holding fiber is comparable with that of a usual fiber without a stress-producing structure. View full abstract»

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  • Receiver design for high-speed optical-fiber systems

    Page(s): 243 - 267
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    The technology of optical-fiber systems is advancing rapidly. Parallel to the development of long-haul telecommunication systems in the gigabits per second data rates operating in the long-wavelength region is the wide penetration of optical-fiber systems in local area networks, video trunking and distribution, sensors, etc. These diversified applications impose different and often conflicting constraints on the optical receiver. This paper re-examines the optical receiver design in view of these different requirements, namely, high receiver sensitivity, wide dynamic range, transparent to the operating bit rate, unrestricted data format, and fast acquisition time. Design tradeoffs between conflicting receiver requirements are considered in detail. In particular, the sensitivity of high-capacity long-wavelength transmission systems is emphasized. The state-of-the-art performance of photodetectors and low-noise amplifiers is discussed. We show that dark current of avalanche photodiodes (APD's) is the main factor limiting the sensitivity of long-wavelength optical receivers. In addition, as an example, we report on the design and experimental performance of a hybridized low-noise optical receiver amplifier capable of more than 2-Gbits/s operation. The input noise spectral density achieved is 9 pA/sqrt{Hz}with a noise corner frequency of 920 MHz, corresponding to an equivalent noise resistance of 120 Ω. View full abstract»

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  • Coated optical fibers for high-strength fusion splices

    Page(s): 295 - 299
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    Suitable fiber-coated structures and a practical splice technique which are superior in both long-term reliability and splice operation efficiency in the field are required. A splice technique without using any dangerous chemical acids to remove the primary coat and coated fiber structures are proposed in this paper. With these techniques, an average strength of 0.88 GPa for bare fusion spliced fibers is obtained in the field, which is more than double the value compared with the average strength of 0.4 GPa obtained by the conventional splicing technique, which is used practically in the field. In addition, the splice time decreases to about one-third of the conventional splice time. The splice operation efficiency improvement is recognized for not only coated mono-fibers but for fiber ribbons. View full abstract»

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  • Optical microscope observation method of a single-mode optical-fiber core for precise core-axis alignment

    Page(s): 277 - 283
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    A new method is presented for observing a single-mode optical-fiber core by the use of an optical microscope to achieve precise core-axis alignment. The formation mechanism of a core image and its observation condition have been investigated using a ray tracing method. Simulation results show good accordance with practical observed results. Precise alignment of cores can be achieved when the dimension of a core image becomes equal to the core diameter multiplied by the magnification of the observation system. In the core aligning experiment for a single-mode fiber with a large core eccentricity of 3.4 μm, the average misalignment was 0.6 μm. View full abstract»

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  • Description and application of the fiber SLC carrier system

    Page(s): 317 - 322
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    The Fiber SLC1Carder System is a repeaterless digital loop carrier that employs lightwave features for the transmission of voice and data from a telephone central office to a remote location. This paper describes the development and application of this 1.3-μm LED/p-in based system. Experience with first applications is reported along with current developments intended to increase its capacity and bring digital capability close to the customer at the DS3 bit rate (44.736 Mbits/s). Services to the customer include DS1 port capability (1.544 Mbits/s), DS2 optical paths (6.312 Mbits/s), voice, and data. View full abstract»

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  • Transmission characteristics of a single-mode fiber in the 1.3-µm wavelength region

    Page(s): 322 - 327
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    Transmission characteristics of 1.3-μm-band single-mode optical fibers were studied experimentally and theoretically. OH-ion content dependence of optical loss in the 1.3-μm region was investigated on single-mode fibers fabricated by the VAD method. The optical loss was evaluated for OH-ion content by calculating correlation factors between the optical loss and 1.39-μm OH-peak absorption loss. It was clarified that the optical loss calculated by correlation factors agreed approximately with the loss given by Lorentzian absorption in case of 0.0253-μm absorption half width, Next, the relationship between chromatic dispersion and fiber parameters was studied for step-index single-mode fibers. It was found that the zero-dispersion wavelength and the incline at the wavelength was expressed as simple functions of effective cutoff wavelength and relative index difference. Experimentally obtained zero-dispersion wavelengths on single-mode fibers fabricated by the VAD method were found to be in excellent agreement with the calculated values. View full abstract»

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Aims & Scope

The Journal of Lightwave Technology contains articles on current research, applications and methods used in lightwave technology and fiber optics.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Peter J. Winzer
Alcatel-Lucent Bell Labs