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Lightwave Technology, Journal of

Issue 1 • Date Jan. 1989

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Displaying Results 1 - 25 of 28
  • Modified optical frequency domain reflectometry with high spatial resolution for components of integrated optic systems

    Page(s): 3 - 10
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (841 KB)  

    An apparatus which allows detection of scatterers and faults as well as measurement of reflections in fiber or integrated optic devices and systems with a spatial resolution in the region of 10-100 mu m is discussed. The dynamic range is sufficient to detect reflection with a reflection coefficient down to 10/sup -10/. The system uses a modified optical frequency domain reflectometry (OFDR) technique whereby signal light and local oscillator light are coupled into the waveguide under test from opposite directions. The measurement principle requires the wavelength of the light source to be swept continuously up or down. It is shown that the experimental relationship between frequency shift and waveguide length is in fairly good agreement with the theoretical estimate. Polarization-sensitive experimental results are given for reflection factors in short, side-polished polarization-maintaining fibers.<> View full abstract»

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  • Passive equalization of semiconductor diode laser frequency modulation

    Page(s): 11 - 23
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    Optical heterodyne communication systems using direct-frequency-modulated (FM) semiconductor diode lasers often exhibit system degradation because of the nonuniform injection-current-to-FM transfer function present in most semiconductor diode lasers. In a FSK system, a nonuniform FM transfer function causes tone drift which results in increased crosstalk between time slots and a corresponding degradation in system bit-error rate (BER). Using simple passive electrical networks it is possible to equalize the nonuniform FM response and substantially reduce this transfer-function-induced BER degradation. The theory, computer optimation, construction, and test of various equalization networks and their use in realizing an FM-equalized transmitter for a 100-Mb/s binary FSK communication system is described.<> View full abstract»

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  • Real-time long range complementary correlation optical time domain reflectometer

    Page(s): 24 - 38
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1439 KB)  

    The improved performance of an optical time-domain reflectometer (OTDR) through the application of a correlation technique using codes with complementary autocorrelation properties is discussed. The theoretical foundations of the method are presented along with experimental results exhibiting the best one-way range reported to date for a practical long-haul, long-wavelength OTDR system.<> View full abstract»

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  • Measurement of mode couplings and extinction ratios in polarization-maintaining fibers

    Page(s): 45 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    Polarization mode couplings in the axial direction are evaluated for polarization-maintaining fibers using optical heterodyne detection. To verify the validity of this approach for fibers with various coupling constants, the method is applied to three fibers with modal birefringence values of 3.0*10/sup -4/, 1.1*10/sup -4/, and 1.5*10/sup -4/, respectively. The coupling constants in the 1.7*10/sup -4/ m/sup -1/ to 6.4*10/sup -7/ m/sup -1/ range are evaluated with a length resolution of 1 m. The extinction ratios are obtained from the coupling constants averaged over the fiber lengths. These values are in good agreement with the values measured directly from power ratios between the orthogonally polarized modes.<> View full abstract»

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  • Vector modes of an optical fiber in the weakly guiding approximation

    Page(s): 51 - 54
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (338 KB)  

    The authors show that starting from the appropriate linear combinations of LP modes, the weakly guiding approximation of the hybrid modes can be easily obtained without any reference to the rigorous vector modes. The analysis uses E. Snitzer's criterion (J. Opt. Soc. Amer., vol.51, p.491-8, 1961), applying it to the fields corresponding to the appropriate linear combination of LP modes.<> View full abstract»

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  • Experimental verification of microbending theory using mode coupling to discrete cladding modes

    Page(s): 55 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (693 KB)  

    The existence of discrete cladding modes in single-mode fibers is illustrated by inducing periodically repeated microbends along the fiber axis and performing spectral measurements of the loss are performed. In order to explain the results of the measurements, it is necessary to apply a microbending theory in which coupling between the guided mode and a number of discrete cladding modes is considered. Very good agreement between theory and measurement is achieved. The consequences of the existence of discrete cladding modes with regard to the proper choice of artificial microbending spectrum used for fiber characterization are also discussed.<> View full abstract»

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  • Performance degradation of APD-optical receivers due to dark current generated within the multiplication region

    Page(s): 62 - 67
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    General expressions for the effective gain and effective excess noise factor associated with dark current generated within the high-field region of an avalanche photodiode (APD) are given. The influence of this background current on the performance of a uniformly multiplying APD receiver is evaluated and compared with that due to a dark current component generated outside the multiplication region (diffusion current). The results indicate clearly that the former dark current component has less effect on receiver performance than the latter, especially when hole and electron ionization rates are very different.<> View full abstract»

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  • A simple interferometric method for monitoring mode hopping in tunable external-cavity semiconductor lasers

    Page(s): 68 - 76
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    The mode-hopping events in a 1.3- mu m grating-tuned external-cavity laser are analyzed on the basis of interferometric measurements. The average frequency of mode hopping for a 7.5-cm external-cavity laser is estimated and is expressed as f/sub c/=2.7*10/sup 6/*exp (-1.7/(I/I/sub th/-1)) (hertz) for 0.07> View full abstract»

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  • Wideband frequency-response measurement of optical receivers using optical heterodyne detection

    Page(s): 92 - 98
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    Measurements have been carried out using 1.3- mu m distributed-feedback laser diodes (DFB-LDs). The frequency difference of the LDs is continuously varied with temperature changes of a few degrees and the spectral linewidth of one of the LDs is narrowed by optical feedback using a grating. Wideband, highly sensitive measurement has been achieved for a p-i-n photodiode and a Ge avalanche photodiode from DC to 20 GHz. The result is compared with that of the pulse spectrum analysis (PSA) method. Although the finite pulsewidth in the PSA method causes roll-off in the frequency response, the optical heterodyne method has the advantage for very wideband frequency response measurement. The S/N ratio in the optical heterodyne method can be made as high ( approximately 40 dB) as that of the PSA method by narrowing the spectral linewidth of DFB-LDs.<> View full abstract»

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  • Deterioration of taper lens performance due to taper asymmetry

    Page(s): 99 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (869 KB)  

    The influence of rotationally asymmetrical, i.e. bent drawn, fiber tapers on the coupling performance of taper lenses used for laser diode- or LED-to-single-mode-fiber coupling is investigated. It is found by experiments that the lateral offset of the taper tip with respect to the fiber axis should be below approximately=6 mu m if a significant increase in coupling loss is to be avoided. The experimental results are interpreted by numerical simulations applying the beam propagation method.<> View full abstract»

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  • Tuned front-end design for heterodyne optical receivers

    Page(s): 105 - 114
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    A theoretical analysis of the noise performance of optical receivers with front-end tuning, suitable for wideband coherent systems, is presented. An algorithm for choosing the values of the tuning components in the front end so as to minimize the thermal noise output power has been developed. This theory is applied to the well-known simple parallel and serial tuning configurations and also to three more advanced designs. It is shown that any tuning is better than none in the wide-bandwidth designs considered and that the more advanced designs yield up to 12-dB reduction in thermal noise power. Two of the designs can be implemented with discrete components and should yield shot-noise-limited detection with 50-100 mu W of local oscillator power in receivers with 5-GHz bandwidth. The practical problem of equalizing the front-end response is considered, and it is shown that good performance can be expected using realizable components.<> View full abstract»

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  • Optical fiber drawing method with gas flow controlling system

    Page(s): 115 - 121
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (777 KB)  

    A method for reducing the diameter variation of optical fibers during fiber drawing is described. The method is based on the control of gas flow and drawing speed. Rapid fluctuations in diameter are suppressed by adjusting the gas flow rate, and slower ones are controlled by changing the drawing speed. The efficiency of this method has been tested by applying stepwise disturbance of +or-63% in preform feeding speed. Fluctuations of fiber diameter are controlled within +or-1 mu m despite the forced disturbance. By applying this method to high-speed drawing (30 m/min), a high-tensile-strength fiber, with diameter fluctuations within +or-1 mu m and transmission losses near the 0.85- mu m wavelength region of approximately 3 dB/km, is achieved.<> View full abstract»

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  • Optical fiber up-tapers modeling and performance analysis

    Page(s): 131 - 137
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (645 KB)  

    An extensive CRAY-computer-based simulator using the propagating beam method for the accurate evaluation of the performance of optical fiber up-tapers is discussed. Up-tapers with and without straight tips and with arbitrary index profiles and tapering functions can be evaluated. Results of the evaluation of various 1.5-cm-long optical up-tapers followed by a straight tip and drawn from special preforms with various index profiles are quite encouraging. They show that beam expansion ratios in the range of 5-10 are feasible with a corresponding insertion loss per taper of less than 0.01-0.025 dB. Tapers shorter than 1.5 cm with insertion loss in the same range are also feasible but have slightly smaller beam expansion ratios.<> View full abstract»

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  • Dependence of optical receiver sensitivity, in a 147-Mbit/s heterodyne DPSK system, as a function of optical and electrical parameter variations

    Page(s): 138 - 150
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    Measurements of the changes in optical receiver sensitivity are described. They are caused by (a) the effect of bandpass and low-pass filtering, (b) the dependence on integer and noninteger values of the intermediate-frequency-to-bit-rate ratio, (c) the influence of the local oscillator power, and (d) the impact of deviation from ideal pi phase-shift modulation. The studies were conducted at lambda =1.523 mu m and at a bit rate of 147.75 Mb/s, using external-cavity lasers with negligible phase noise. The results demonstrate the conditions for optimum DPSK system performance in the absence of laser phase noise. The receiver degradation observed for deviations from optimal electrical and optical conditions have been measured and found to be in good agreement with earlier theoretical calculations of microwave phase modulated schemes.<> View full abstract»

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  • Infrared optical fibers with vapor-deposited cladding layer

    Page(s): 158 - 162
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    Core-cladding structures constructed for KRS-5 polycrystalline and As/sub 2/S/sub 3/ glass infrared fibers by means of vapor deposition are discussed. In order to obtain high-numerical-aperture fibers, KRS-6 and AsS/sub 3/, respectively, have been used as cladding materials. A CO/sub 2/ laser beam of 15-20 W has been successfully transmitted through the KRS-5 fiber. For the As/sub 2/S/sub 3/ fiber an absorption loss due to Teflon coating has been reduced, and a loss of 0.13 dB/m has been achieved.<> View full abstract»

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  • Performance of packaged near-traveling-wave semiconductor laser amplifier with multilongitudinal mode input

    Page(s): 163 - 170
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    The results for a packaged 1.30- mu m InP/InGaAsP optical amplifier used to switch broadband multilongitudinal modes signals are presented. Despite the absence of optical isolators and even with the introduction of additional external reflections (R approximately=1.0%), the optical fiber-to-fiber gain is stable over a large temperature range at resonance ( Delta G> View full abstract»

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  • Stimulated Brillouin scattering excited by a modulated pump wave in single-mode fibers

    Page(s): 171 - 174
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    The effects of modulation on the gain of stimulated Brillouin scattering (SBS) are discussed. Three different modulation techniques, i.e. frequency shift keying (FSK), amplitude shift keying (ASK), and phase shift keying (PSK) are considered. The results show that the SBS threshold depends on the ratio between the spontaneous Brillouin linewidth and the bit rate. The SBS threshold for ASK and FSK is 6 dB higher at high bit rates, whereas the SBS threshold for PSK increases by 10dB for each factor of 10 increase in the bit rate.<> View full abstract»

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  • Prism-coupling of light into narrow planar optical waveguides

    Page(s): 175 - 180
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    The efficiency and selectivity of the prism-coupler for exciting single modes in narrow planar optical waveguides is investigated both theoretically and experimentally. A previously published calculation of the coupling efficiency between a plane input wave with finite cross section and a number of waveguide modes, as a function of both the incidence angle and the skew angle, is extended to include the effects of diffraction, which are shown to play a dominant role for small focal widths of the input beam. The theoretical predictions are compared with experimental results obtained at 633 nm on an embedded ridge-type waveguide structure. A number of mechanisms reducing coupling selectivity and stability are discussed, and some practical rules are given for obtaining good stability and selectivity.<> View full abstract»

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  • Optical feedback in offset-structure optoelectronic integrated devices

    Page(s): 181 - 185
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (470 KB)  

    An optical feedback mechanism in offset-structure integrated optoelectronic devices which exhibit light amplification, optical bistability, and regenerated oscillation is discussed. The amount of optical feedback was evaluated by adding a third electrode which allowed each of the integrated devices to be operated separately. Optical feedback control by an additional layer for the absorption of feedback light was demonstrated.<> View full abstract»

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  • Optoelectronic integrated four-channel transmitter array incorporating AlGaAs/GaAs quantum-well lasers

    Page(s): 186 - 197
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    A four-channel optoelectronic integrated transmitter array which is fabricated on a single GaAs substrate and operates at 834 nm is described. Each of the circuits incorporates a laser, a photodiode for laser power monitoring, and a laser driver circuit consisting of three GaAs field-effect transistors and a resistor. Laser threshold current of 15-21 mA, transmitter conversion efficiency of approximately 6 mW/V and high-speed operation at a bit rate of more than 1.5-Gb/s NRZ with allowable crosstalk have been demonstrated. A preliminary aging test of the lasers indicated that their stability is comparable to that of discrete devices. The results have demonstrated the feasibility of applying the transmitter array to optical components that process multichannel optical signals at high speed.<> View full abstract»

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  • Mathematical analysis of optically powered quartz resonant structures in sensor applications

    Page(s): 202 - 208
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (781 KB)  

    A mathematical analysis of quartz resonant structures used in fiber optic sensor systems and driven optically is undertaken using analytical and finite-element methods. Photothermal excitation of the structure was simulated in order to study important parameters relating to heat flow, the input optical duty cycle, the maximum displacement and the frequency-load relationship. Comparisons are made with the results of experimental investigations. The extension of such work to other materials used in resonant sensor devices is discussed.<> View full abstract»

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  • Statistical design of long optical fiber systems

    Page(s): 209 - 217
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (773 KB)  

    A design strategy is proposed to minimize the most likely overall system cost, that is, the sum of the equipment installation cost and the repair cost over the lifetime of the system. By choosing a repeater spacing larger than that dictated by a worst-case design, the possibility of system failure due to negative system margin is admitted. However, for a correctly chosen repeater spacing, the most likely cost of repairing these failures, when added to the reduced installation cost, is significantly less than the system cost of a worst-case design. This statistical design strategy is applied to a 565-Mb/s single-mode optical fiber system operating at 1.3 mu m. Several different failure modes which can occur in such an optical fiber system are identified, and the probability density function for each type of failure is calculated. It is shown that the design strategy leads to significant savings compared with worst-case design. For typical device parameters, a saving of about 30% in equipment installation and repair costs over the lifetime of the system is reported.<> View full abstract»

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  • Influence of lens imperfection with LD and LED to single-mode fiber coupling

    Page(s): 77 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A method which allows numerical calculations of aberration-induced coupling loss with arbitrary coupling optics for single-mode fibers is discussed. It makes use of standard ray-tracing procedures and is applicable to coherent sources, like laser diodes (LDs), and partially coherent sources, such as light-emitting diodes (LEDs). Good agreement between calculated and measured coupling loss is found for LDs and edge-emitting LEDs. Some consequences of lens aberrations for coupling-lens design are discussed View full abstract»

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  • Variational analysis of anisotropic graded-index optical fibers

    Page(s): 87 - 91
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    The variational principle for nonstandard eigenvalue problems recently introduced and used for step-index optical fiber analysis by the present authors is extended to anisotropic graded-index optical fibers. It is seen through an example of a round parabolic-index fiber that the choice of trial functions is more delicate than for the step-index fiber because of the more complicated field function. Certain two-parameter approximants, however, appear accurate enough and can be optimized with a simple calculator or desk computer analysis View full abstract»

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  • Analysis of a novel optical fiber interferometer with common mode compensation

    Page(s): 151 - 157
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    An optical fiber interferometer formed when the unused output of a fiber Mach-Zehnder interferometer is fed back through a length of fiber to the unused input port is discussed. For sensor applications, the resulting optical circuit combines many features of a Mach-Zehnder with the high measured sensitivity of a resonant fiber recirculating delay line. This analysis shows that suitable choice of path lengths preserves high measurand sensitivity, yet it permits complete common-mode compensation in which the effects of all perturbations which uniformly affect the interferometer vanish 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