By Topic

Lightwave Technology, Journal of

Issue 11 • Date Nov 1997

Filter Results

Displaying Results 1 - 25 of 25
  • Skew evaluation using two-dimensional refractive-index profile in single-mode fiber ribbons

    Page(s): 2101 - 2106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    The skew of fiber ribbons must be small for high bit rate parallel optical transmission systems. Accurate skew evaluation using fiber parameters is important for this purpose. A simple method, based on the calculus of variations, is proposed for evaluating the skews of fiber ribbons. This method employs only one mode field (LP01 mode) of an ideal step-index fiber as a trial function and a two-dimensional (2-D) refractive index profile. The measured skews of a 16-fiber ribbon composed of fibers with different parameters are compared with calculated values and are found to be in good agreement. The influence on the skew of several refractive index profile deviations (including asymmetric profile deviations) are evaluated using the proposed method. It is found that the asymmetric core profile has a large influence on skew whereas that of the asymmetric core-cladding boundary is relatively small View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Learning method for neural networks using weight perturbation of orthogonal bit sequence and its application to adaptive WDM demultiplexer

    Page(s): 1997 - 2005
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    This paper proposes a novel on-chip learning method for hardware-implemented neural networks to achieve an adaptive wavelength division multiplexer (WDM) demultiplexer. The parameters of the neural network are perturbed by orthogonal bit sequences with small amplitude. The parameters are corrected based on the correlation detection result between the perturbed error signal and the corresponding perturbation signal. A learning experiment that transmits 200-Mb/s, four-channel WDM signals through a 40-km fiber and the tracking of the wavelength drift of the optical transmitter successfully demonstrate the proposed method View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Distributed grating sensors using low-coherence reflectometry

    Page(s): 2076 - 2082
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    Distributed grating sensors have recently been interrogated with low-coherence reflectometry. Initial results have been enhanced using two new and versatile configurations. The first system tracks the wavelength using a closed-loop scheme, while the second system scans the distance using an open-loop approach. Arbitrary strain and temperature profiles along gratings have been examined with 300 μm spatial resolution and 5.4 με/√Hz accuracy. A theoretical model of the interrogation technique is derived and the predicted performance limits are examined experimentally View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Estimation of waveguide phase error in silica-based waveguides

    Page(s): 2107 - 2113
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    A new estimation method is proposed in order to clarify waveguide phase error factors. Using the proposed method, it is possible to analyze such factors as core size error and refractive index error, which cause optical phase error in waveguides. This method is applied to silica-based waveguides to estimate the waveguide phase error. This revealed an average core size error of 2.1×10-3 μm and an average refractive index error of 1.9×10-6. Finally, based on the measured phase error values, the optimum arrayed-waveguide grating (AWG) configuration is considered with a view to achieving low crosstalk View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of end-pumped Nd:Ti:LiNbO3 microchip waveguide Fabry-Perot lasers

    Page(s): 2147 - 2153
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    A self-consistent analysis of end-pumped Nd:Ti:LiNbO3 microchip waveguide lasers based on the fast Fourier transform beam propagation method (FFT-BPM) has been proposed. The algorithm of the model allows one to describe the laser gain and pump absorption in terms of the complex atomic susceptibility for the case of the Nd3+ ions. Considering the interference effects between the forward and backward light waves, the population inversion longitudinal and transversal spatial effects can be simulated. The laser characteristics of the Nd:Ti:LiNbO3 waveguide laser correlate well with the experimental data and theoretical results. The design rules for the optimized microchip laser are also developed by using the proposed model View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Frequency domain detection of coherence multiplexed sensor signals by using an optical loop with a frequency shifter

    Page(s): 2069 - 2075
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    We describe a frequency domain detection scheme of coherence multiplexed sensor signals by using an optical loop with a frequency shifter. The optical path differences of the sensors are adjusted to integer-multiple of the loop length of the optical loop, and then the the sensor signals are multiplexed in the frequency domain, appearing at the integer-multiple of the working frequency of the frequency shifter. In the experiment, four Michelson-type sensors are successfully multiplexed with the sensitivities of about 2 mrad/√Hz. The sensitivities are also theoretically calculated which are in good agreement with the experimental results. The optimum design of the optical loop is also discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Statistical analysis of interferometric crosstalk: theory and optical network examples

    Page(s): 2006 - 2019
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    General, statistical properties of accumulation of interferometric crosstalk due to a number of interfering signals are analyzed. The probability density function of the total crosstalk is derived as function of the sum of the incoherent crosstalk contributions associated with the interfering signals, Because the total crosstalk level can be expected to vary only slowly as compared to the time duration of one bit, the probability p that the total crosstalk exceeds a maximum tolerable value is introduced as a parameter in the crosstalk and bit error rate analysis of optical networks. General computations show that the crosstalk requirement on optical network elements may be significantly relaxed if it can be accepted that it is possible, although most unlikely, that the total crosstalk may exceed this maximum tolerable value. The statistical crosstalk model is then illustrated by investigation of optical network examples with respect to their crosstalk and transmission properties, and, finally, compared with previous crosstalk models View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Stresses in a partially coated optical glass fiber subjected to the ends off-set

    Page(s): 2091 - 2094
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB)  

    A simple formula based on the elementary beam theory is obtained for the evaluation of the maximum bending stress in an optical glass fiber whose ends are clamped and experience lateral off-set. We consider a situation when the fiber is partially coated and/or partially metallized, and therefore its flexural rigidity is not constant along its span. The obtained formula can be helpful in the analysis and design of optical glass fibers and optical interconnects structures of the type in question View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • FDTD microcavity simulations: design and experimental realization of waveguide-coupled single-mode ring and whispering-gallery-mode disk resonators

    Page(s): 2154 - 2165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    We investigate the properties of high-Q, wide free-spectral-range semiconductor microcavity ring and disk resonators coupled to submicron-width waveguides. Key optical design parameters are characterized using finite-difference time-domain (FDTD) solutions of the full-wave Maxwell's equations. We report coupling efficiencies and resonant frequencies that include the effects of waveguide dispersion and bending and scattering losses. For diameters of 5 μm, the microcavity resonators can have Q's in the several thousands and a free spectral range of 6 THz (50 nm) in the 1.55 μm, wavelength range. Studies of the transmittance characteristics illustrate the transition from single-mode resonances to whispering-gallery-mode resonances as the waveguide width of the microring is increased to form a solid microdisk. We present nanofabrication results and experimentally measured transmission resonances of AlGaAs/GaAs microcavity resonators designed in part with this method View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Numerical simulation of avalanche breakdown within InP-InGaAs SAGCM standoff avalanche photodiodes

    Page(s): 2137 - 2140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The breakdown location within a planar InP/In0.53Ga0.47As (InGaAs) separate absorption, grading, charge sheet, and multiplication (SAGCM) avalanche photodiode (APD), using the standoff breakdown suppression design to replace guard rings, depends on the two-dimensional (2-D) geometry of the Zn diffused well. Since the geometry of this p+ diffusion is dependent upon the surface etch, the effects of varying the etch depth (tstandoff) and length of the sloped etch edge (wslope ) are studied using a two-dimensional drift-diffusion simulator. It is determined that the etch depth brackets a region where center breakdown dominance is possible. To ensure center breakdown within this region it is concluded that there is a maximum value that the slope of the etch walls must not exceed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Gain temperature dependence of erbium-doped silica and fluoride fiber amplifiers in multichannel wavelength-multiplexed transmission systems

    Page(s): 2083 - 2090
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    The temperature dependence of the gain of aluminosilica and fluoride based erbium-doped fiber amplifiers are theoretically and experimentally examined and compared. As expected from the larger temperature dependence of erbium-doped fluoride fibers (EDFB) cross sections, the single channel gain of EDFF amplifiers presents larger wavelength-dependent temperature sensitivity. The implications of this large and nonuniform temperature dependence of the gain on wavelength-division multiplexing (WDM) are theoretically analyzed and discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Narrow linewidth operation of an erbium fiber laser containing a chirped Bragg grating etalon

    Page(s): 2130 - 2136
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    A numerical model is presented which shows that a control signal suitable for preventing longitudinal mode hops can be derived by sensing changes in the polarization state of the light reflected from an intracavity etalon. This is verified experimentally by including a continuous fiber etalon formed from chirped Bragg reflectors in a unidirectional erbium ring fiber laser. Mode hop free operation is observed with resolution limited linewidths of 170 kHz View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Formation of the refractive index profile in the graded index polymer optical fiber for gigabit data transmission

    Page(s): 2095 - 2100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    Bandwidth characteristics of the large core graded index polymer optical fiber (GI-POF) are theoretically and experimentally clarified. The refractive index profile of the GI-POF was controlled by interfacial-gel polymerization to investigate the relation between the index profile and the bandwidth characteristics. It was experimentally confirmed that the maximum bandwidth of the poly methyl methacrylate (PMMA) base GI-POF is at most 3 GHz for 100 m transmission using a typical laser diode emitting at 650-nm wavelength (3 nm source spectral width) when its refractive index profile is optimized. The maximum bandwidth theoretically estimated by considering both modal and material dispersions is approximately 3 GHz which is exactly the same as the measured value, while higher than 10 GHz for 100 m was expected if only modal dispersion was taken into account. The optimum refractive index profile of the PMMA base GI-POF is theoretically and experimentally clarified by considering the profile dispersion further View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Beam propagation analysis for tapered waveguides: taking account of the curved phase-front effect in paraxial approximation

    Page(s): 2183 - 2189
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    A novel equivalent waveguide theory based on the conformal mapping method is employed to investigate the tapered waveguide with curved phase fronts. By using the theory, the curved phase fronts of a tapered waveguide would be transformed into the planar ones of its equivalent straight-liked structure. Therefore, the paraxial beam propagation method can be used to analyze the equivalent structures of tapered waveguides (even for wide-angle tapers). Two kinds of popular tapered waveguides, including the cross-sectional dimension tapering and the constant V-number tapering, are used to analyze by our combination of conformal mapping method and beam propagation method (BPM) View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Numerical simulation of a silicon-on-insulator waveguide Fabry-Perot interferometer for intensity light modulators at 1.3 μm

    Page(s): 2124 - 2129
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    We present a new silicon-on-insulator (SOI) integrated optics structure to be used as an intensity light modulator at 1.3 μm. The device consists of a waveguide Fabry-Perot interferometer. In association with a grating coupler this device could function as a spatial light modulator or a reflective-mode modulator. The Fabry-Perot reflectivity is tuned by free-carrier injection from a forward-biased lateral P+/N-/N+ diode. Consequently, the reflected back guided-mode has an intensity that is a function of the effective index modulation in the central waveguide of the Fabry-Perot. Our numerical simulation reveals that such a structure could function for current densities not exceeding 500 A/cm2 with a cutoff frequency of 100 MHz. This new type of device is compatible with the mature silicon technology and could replace in applications the standard liquid-crystal spatial light modulators or for fiber-to-the-home intensity modulators View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Planar optical waveguides with arbitrary index profile: an accurate method of analysis

    Page(s): 2179 - 2182
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    We present here an improvement of the existing modified Airy function (MAF) method. The results of our study show that the improvement gives extremely accurate propagation constants and also the modal fields for planar waveguides with arbitrary index profile View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improved demodulation scheme for fiber optic interferometers using an asymmetric 3×3 coupler

    Page(s): 2059 - 2068
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Problems associated with the demodulation of the signal produced by a fiber optic interferometer which employs a 3×3 fiber coupler are investigated both theoretically and experimentally. It is shown that existing demodulation methods do not work well, especially when the 3×3 coupler is asymmetric, as is often the case. Modifications to improve the performance of a previously proposed method are suggested. Furthermore, an alternative demodulation circuit is presented which is simple and which works well even when the 3×3 coupler is asymmetric View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analytical performance evaluation of nonreturn-to-zero transmission systems operating in normally dispersive nonlinear fibers

    Page(s): 2038 - 2050
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    An analytical theory for the evaluation of the performance of a nonreturn-to-zero (NRZ) transmission system operating in weakly normally dispersive nonlinear fibers is presented. Explicit expressions are given to compute an estimate of the transmission bit error rate, and those are compared with results obtained through numerical simulations. A good agreement is found, both for systems having fibers with a constant dispersion value, and for systems encompassing dispersion management technique View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modeling of noncollinear multifrequency acoustooptic interaction in guided-wave Bragg cells

    Page(s): 2114 - 2123
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    We present an original detailed theoretical modeling of guided-wave noncollinear acoustooptic (AO) interaction produced by a multifrequency surface acoustic wave (SAW) in planar guided-wave structures. The modeling of the multifrequency AO interaction is based on a modified version of the coupled-mode theory. The first- and third-order diffraction efficiency and optimum dynamic range of the Bragg cell have been calculated as a function of acoustic power, acoustic radiofrequency, and optical waveguide parameters in Y-cut Ti:LiNbO3 planar waveguides. Polynomial approximations, describing the first and third order diffraction efficiency versus normalized acoustic power in the cases of two- and three-frequency interactions, are derived and presented for the first time for arbitrarily large RF signals View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Low distortion 1.3 μm strained-layer MQW-DFB laser for AM-SCM transmission systems with large channel capacity

    Page(s): 2172 - 2178
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    1.3-μm strained-layer multiquantum-well distributed-feedback (SL-MQW-DFB) lasers with extremely low distortion and low noise characteristics up to high output-power as well as over wide frequency range were successfully fabricated. This was achieved by both the high relaxation oscillation frequency (fr) characteristics of the laser with the optimized SL-MQW active structure and the suppression of nonradiative current with relatively long laser cavity length. By using the SL-MQW laser with a 400-μm long cavity as a light source for CATV transmission system, high quality AM-SCM transmissions with the largest channel capacity (151 channel) was demonstrated due to low distortion characteristics at high output power. Also, for the laser with 300 μm long cavity, extremely low bias-current operation (17 mA above threshold) is realized in high quality 100 channel AMSCM transmissions, due to high fr at low bias-current View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A DC to multigigabit/s polarization-independent modulator based on a Sagnac interferometer

    Page(s): 2166 - 2171
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    A broadband, electrically controlled polarization-independent intensity modulator (PLM) based on a Sagnac interferometer is presented. Influences from asymmetric modulation and traveling wave effects are analyzed and methods to eliminate these effects are proposed. Compared to Mach-Zehnder interferometer-based modulators, this modulator is independent of the input polarization state and less sensitive to ambient perturbations due to its reciprocity property. A prototype modulator operating at 1 and 2.488 Gb/s modulation rates is demonstrated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fiber four-wave mixing demultiplexing with inherent parametric amplification

    Page(s): 2051 - 2058
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    We present an all-optical time-division demultiplexer with 22 dB conversion efficiency, using four-wave mixing (FWM) at 1550 nm in a single-mode dispersion-shifted fiber. Error-free demultiplexing of 20 Gb/s data to 10 Gb/s is obtained, with 1.4 dB power penalty at BER=10 -9. We also derive theoretical expressions for the conversion efficiency, the maximum bit rate that is possible to demur and the shape of the switching window. In particular we emphasize the importance of phase-matching in order to achieve a flat switching window. Furthermore the pump must remain undepleted to avoid a detrimental reduction of the extinction ratio due to instantaneous parametric gain saturation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modulation characteristics of high speed (f-3 dB=20 GHz) tunneling injection InP/InGaAsP 1.55 μm ridge waveguide lasers extracted from optical and electrical measurements

    Page(s): 2141 - 2146
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    High-performance multiquantum-well 1.55 μm InP-based tunneling injection lasers are fabricated using a conventional single mode ridge waveguide fabrication process and characterized. The lasers consist of an eight quantum-well strain-compensated gain region and a 30-Å InP tunneling barrier. The bandwidth of these lasers is measured to be 20 GHz with a damping limited bandwidth extracted from the K-factor (determined from optical modulation measurements) of 26 GHz. To our knowledge, this is the highest measured bandwidth recorded for an InP-based simple ridge waveguide structure. The differential gain is measured to be as high as 1×10-15 cm2, with a measured gain compression coefficient ε of 5×10-17 cm3. It is shown that the K-factor can also be extracted solely from measurements of the small signal electrical impedance. The carrier escape time τesc is determined to be 0.5 ns, independent of bias. This high frequency performance is achieved with a very simple device structure at room temperature under constant drive currents View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New wavelength interchangeable cross-connect architectures with reduced complexity

    Page(s): 2029 - 2037
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    We present several new optical cross-connect structures capable of wavelength conversion. The new structures use fewer wavelength converters than previous structures. We describe an effective approach to best use wavelength converters when the input/output fibers of an optical cross-connect do not carry an identical number of wavelength division multiplexed (WDM) data channels. It is shown that the hardware complexity of the new structures can he further reduced if a small but acceptable blocking probability is allowed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Synchronization of passively mode-locked erbium-doped fiber lasers and its application to optical communication networks

    Page(s): 2020 - 2028
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    We synchronized two passively mode-locked erbium-doped fiber lasers using a phase lock loop with a large dynamic range and bandwidth, which is realized by using a novel acoustooptic-modulator-grating scheme. Cross-correlation of the two lasers shows the interlaser jitter is under 2 ps (same as the laser pulse width) for period as long as hours. To prove the quality of phase locking, we apply synchronized lasers in two all-optical network applications, one of which requires the lasers to have the same wavelength and the second requires the lasers to be at different wavelengths. In the single wavelength application, the synchronized lasers drive a cascade of two low-birefringence, polarization maintaining, optical logic gates with switching timing window of 4 and 5 ps, respectively. We obtain nonlinear transmission of ~50% at a switching energy of 8 pJ and contrast ratio of 16 dB, which are comparable performance as that obtained using a single laser. In the different wavelength application, we use 0.8 ps pulses to switch 2 ps pulses in a two-wavelength nonlinear optical loop mirror demultiplexer with timing window of 5.5 ps. Stable switching is reached at a efficiency as high as 90% at switching energy of 0.8 pJ, and a contrast ratio of 20 dB. Excellent agreement is found between the experimental data and the simulated results, which exclude the timing jitter View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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