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Lightwave Technology, Journal of

Issue 1 • Date Jan 2003

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Displaying Results 1 - 25 of 39
  • Accurate noise characterization of wavelength converters based on XGM in SOAs

    Page(s): 182 - 197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (923 KB) |  | HTML iconHTML  

    Wavelength conversion (WCR) has recently emerged as an important technique that can be used to manage the spectacular increase in traffic in dense wavelength division multiplexing (DWDM) networks. WCR is extremely useful to solve contention, reduce wavelength blocking and a wide range of WCR methods have been reported. The optimum placement of these devices within a network remains an unexplored area and accurate models to measure the performance of the system are becoming vital. Therefore, this paper presents an original noise characterization of a class of WCRs based on cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) when the components from spontaneous emission of the SOAs at the receiver are dominant over thermal and shot noise terms. A new and simple expression for the error probability (Pe) is presented offering considerable additional accuracy in sensitivity assessment compared with the Gaussian approach when ASE noise is dominant. Simulation comparisons are presented in different scenarios for a standard system working at 2.5 Gb/s in a metropolitan area network taking into account the key parameters when such systems are designed. View full abstract»

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  • High-output-power polarization-insensitive semiconductor optical amplifier

    Page(s): 176 - 181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (386 KB) |  | HTML iconHTML  

    A high-output-power 1550 nm polarization-insensitive semiconductor optical amplifier (SOA) was developed for use as a compact in-line optical amplifier. A very thin tensile-strained bulk structure was used for the active layer and active width-tapered spot-size converters (SSCs) were integrated on both input and output sides. The SOA module exhibited a high saturation output power of +17 dBm together with a low noise figure of 7 dB, large gain of 19 dB, and low polarization sensitivity of 0.2 dB for optical signals of 1550 nm wavelength. For the amplification of optical signals modulated at 10 Gb/s in the nonreturn-to-zero (NRZ) format, a good eye pattern without waveform distortion due to the pattern effect was obtained at an average output power of up to +12 dBm. Additionally, good amplification characteristics were demonstrated for the signal wavelength range corresponding to the C-band. View full abstract»

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  • Investigation of electromagnetic field in a layer with time-varying medium by Volterra integral equation method

    Page(s): 305 - 314
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (980 KB) |  | HTML iconHTML  

    The application of the Volterra integral equation method for investigations of the interaction of electromagnetic fields with a one-dimensional time-varying dielectric layer is considered. The medium permittivity inside the layer may change in time owing to a nonlinearity as well as to extrinsic sources. Original software for the computer modeling of such an interaction is developed. Numerical results are presented and a comparison made between the accuracy and stability of integral equation method and the finite-difference time-domain (FDTD) method. View full abstract»

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  • Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-to-phase optical conversion

    Page(s): 127 - 131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (281 KB) |  | HTML iconHTML  

    A technique for interrogating multiplexed FBG sensors using all-fiber low-cost devices is demonstrated. It is based on spectral filtering employing a fused biconical wavelength-division multiplexer and on amplitude-to-phase optical conversion to perform power referencing. Four FBG sensors are wavelength multiplexed in the network, and a 3-nm-wide tunable optical filter is employed at the detection block for sensor demultiplexing. With this technique an operation range of more than 2 nm is demonstrated for the sensors with achievable wavelength static resolution ranging from 1.9 to 13.4 pm/Hz12/ with no observable hysteresis. As for power referencing, the system is proven to be unaffected by power variations as high as 75% of the total power launched by the source. Finally, output-phase variations due to crosstalk are shown to be under 1% of the total output phase range, with more than 29-dB optical isolation between channels. View full abstract»

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  • Improved techniques for the measurement of phase error in waveguide based optical devices

    Page(s): 198 - 205
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (687 KB) |  | HTML iconHTML  

    Phase-error measurement using an incoherent light source and information in the resulting interferograms is an effective technique for characterizing waveguide-based optical devices. We propose a new analysis scheme that utilizes Hilbert transformation along with an increased data sampling rate of the interferogram. The higher data sampling rate makes the measurement more noise tolerant and improves the accuracy of the resulting phase determination to 0.2°. This technique enables a "windowing" analysis method that is capable of testing waveguides with very small path length differences. We also present a new analysis tool for device characterization by creating a "phase trend" plot that detects different optical modes propagating within the waveguide. View full abstract»

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  • Measured temporal and spectral PMD characteristics and their implications for network-level mitigation approaches

    Page(s): 79 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (667 KB) |  | HTML iconHTML  

    Signal degradation due to polarization-mode dispersion (PMD) effects may become significant for signaling rates of 10 Gb/s, 40 Gb/s, and beyond. To assess the utility of various PMD mitigation schemes, temporal and spectral measurements of differential group delay (DGD) were made on 95 km of buried standard single-mode fiber over an 86-d period to determine the distribution and rate of change of high-DGD events. As expected, statistical analysis of variations in DGD indicate that excursions from the mean DGD by factors of 3.7 or higher have very low probability. For this link, the DGD varied slowly with time (having a drift time of about 3.4 d) and rapidly with wavelength. The DGD data agree well with results of similar experiments reported in the literature. Statistical analysis of the measured DGD data shows that high-DGD episodes will be exceedingly rare and short-lived. The impact of PMD on network operations is explored and approaches to ensure network reliability are reviewed for network operators given the task of transporting high-bit-rate channels over fiber links with known PMD characteristics. View full abstract»

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  • Fabrication and characterization of photonic devices directly written in glass using femtosecond laser pulses

    Page(s): 246 - 253
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1001 KB) |  | HTML iconHTML  

    Both straight and curved waveguides are written in a variety of silicate glasses using near-IR femtosecond laser pulses. Writing parameters are identified that produce waveguides that support only a single mode and yield smooth-mode profiles. The laser pulse-induced refractive index change is reconstructed from near-field mode profile data using the scalar wave equation and by refractive near-field profiling. Waveguide propagation losses are determined by throughput and Fabry-Perot resonator measurements. Both coarse and fine period gratings are written and characterized, and the thermal stability of these gratings is investigated. The utility of the femtosecond writing technique is demonstrated by fabricating an optical interleaver. View full abstract»

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  • Space mapping technique for design optimization of antireflection coatings in photonic devices

    Page(s): 281 - 285
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (422 KB) |  | HTML iconHTML  

    Space-mapping (SM) technique is applied for design optimization of antireflection (AR) coatings for photonic devices such as the semiconductor optical amplifiers (SOA). The approximate and efficient transfer matrix method (TMM) serves as the coarse model for design optimization, whereas the time-intensive and accurate finite-difference time-domain (FDTD) method is used as the fine model for model calibration. A mapping is established between the parameter spaces of the coarse and the fine models so that the fine model design becomes the inverse mapping of the optimized coarse model design. Remarkable performance of the SM technique in terms of efficiency and accuracy in the design optimization is demonstrated by way of examples. It is shown that, in the context of multilayer coating design, the desired broadband ultralow reflectivities can be obtained within three fine model (FDTD) calculations. View full abstract»

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  • Closed WKB formulas for weakly guiding optical fibers

    Page(s): 286 - 292
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    This paper proposes closed WKB formulas for cutoff frequencies and the propagation constant of weakly guiding optical fibers. For the sake of simplicity, only nondecreasing refractive profiles are taken into consideration. The formulas arise from an approximation of the WKB integral, which preserves the general validity requirements of the method. View full abstract»

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  • Analysis of a racetrack microring resonator with MMI coupler

    Page(s): 206 - 210
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    The static spectral characteristic response of a ring resonator in the form of racetrack with a multimode interference (MMI) coupler has been numerically simulated and investigated. The generalized multimode transmission matrix of the MMI has been evaluated with beam-propagation method simulation and furthermore, the effect of the excitation of higher order modes in the ring resonator on the device-transmission characteristic has been analyzed. View full abstract»

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  • Design of grating-assisted codirectional couplers with discrete inverse-scattering algorithms

    Page(s): 254 - 263
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (539 KB) |  | HTML iconHTML  

    We present a flexible and accurate approach for the design of grating-assisted codirectional couplers. The design method is based on a discrete coupling model. The two spectral responses of the coupler are chosen according to certain physical constraints. We prove necessary and sufficient conditions for realizability and demonstrate how they can be applied for determining an optimal coupler response. The ambiguity when designing a coupler with a specified cross-coupling response is also discussed in detail. Once the realizable responses have been found, they can be applied as input to a layer-peeling inverse-scattering method which computes the required coupler structure. The layer-peeling algorithm is implemented in the time domain for increased efficiency and clarity. Since the algorithm is tailored to the special case of codirectional coupling, divergence problems for strong coupling is avoided. Numerical design examples are shown in order to illustrate the performance of the method. Various realizations of square passband filters with high power transfer and a long-period fiber grating filter for EDFA gain flattening within the entire C-band have been designed. View full abstract»

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  • A broadcast-and-select OADM optical network with dedicated optical-channel protection

    Page(s): 25 - 31
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (799 KB)  

    A metro-area optical-ring network based on a novel optical add-drop multiplexer (OADM) architecture using a wavelength blocker is proposed. We demonstrate experimentally the performance of the OADM and capability of optical channel dedicated protection in a two-fiber ring network with 24×10 Gb/s dense wavelength division multiplexing traffic capacity. The channel-by-channel optical protection of the network is enabled by using a liquid crystal-based wavelength-selective switch as the protection switch and erbium-doped fiber amplifiers (EDFAs) with fast transient-gain control. The bit-error rate performance of the network is studied for the normal operation and for the transition to the protection state from a failure. The network protection for all channels is provided within 5 ms on a cable-cut failure. Importance of transient-gain control during protection switching to reduce the network transients is also discussed. View full abstract»

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  • Determining PML modes in 2-D stratified media

    Page(s): 293 - 298
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (930 KB) |  | HTML iconHTML  

    A contour-integration method is presented to determine the eigenmodes in a layered structure closed with PML layers at the boundaries of the computational window. Improvements are provided to ensure the accuracy of contour integration and to assure that all the encircled eigenvalues are determined. Numerical examples are presented to test the accuracy of the method. View full abstract»

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  • Calculation of APD impulse response using a space- and time-dependent ionization probability distribution function

    Page(s): 155 - 159
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (634 KB) |  | HTML iconHTML  

    A new approach is described for calculating the current impulse response of an avalanche photodiode, allowing for an arbitrary model for carrier transport and also for an arbitrary distribution of ionization events in space and time, following carrier injection. The technique can evaluate both the mean current response and its variance. We find that while the effects of diffusion on mean current are small, the enhanced speed to early ionization can speed up the avalanche process significantly. View full abstract»

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  • Design of double-coated optical fibers to minimize long-term tensile-force-induced delamination of polymeric coatings from glass fibers

    Page(s): 106 - 110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (531 KB) |  | HTML iconHTML  

    The design of double-coated optical fibers to minimize long-term tensile-force-induced delamination of polymeric coatings from glass fibers is investigated using viscoelastic theory. To prevent the delamination of polymeric coatings from glass fibers, the tensile-force-induced interfacial shear stress between the glass fiber and primary coating should be always smaller than its interfacial shear strength in the long term. The tensile-force-induced interfacial shear stress can be minimized by properly selecting physical properties of polymeric coatings and their thicknesses. The method for the minimization of the long-term tensile-force-induced delamination of polymeric coatings from glass fibers in double-coated optical fibers is proposed. View full abstract»

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  • Fabrication and characteristics of GaP-AlGaP tapered waveguide semiconductor Raman amplifiers

    Page(s): 170 - 175
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (578 KB) |  | HTML iconHTML  

    We have fabricated GaP-AlGaP tapered waveguide semiconductor Raman amplifiers, and analyzed the effect of tapering in pulse-pumped high-gain operation. The finesse measurement and 80-ps pulse pumped Raman amplification experiment were performed. Although the tapering has caused additional optical loss, the highest gain of 23 dB has been obtained for a tapered waveguide with input facet of 6.0 μm2 and back facet of 2.9 μm2 at averaged input power of 170 mW (peak power 26 W). It is shown that the optical loss of the pump light is more severe than the linear optical loss of the signal light when the gain is higher than 20 dB. View full abstract»

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  • Tree-shared multicast in optical burst-switched WDM networks

    Page(s): 13 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (566 KB) |  | HTML iconHTML  

    In this paper, we propose a new multicast scheme called tree-shared multicasting (TS-MCAST) in optical burst-switched wavelength-division-multiplexing networks, taking into consideration overheads due to control packets and guard bands (GBs) associated with data bursts. In TS-MCAST, multicast traffic belonging to multiple multicast sessions from the same source-edge node to possibly different destination-edge nodes can be multiplexed together in a data burst, which is delivered via a shared multicast tree. To support TS-MCAST, we propose three tree-sharing strategies based on equal coverage, super coverage, and overlapping coverage, and present a simple shared multicast tree-construction algorithm. For performance comparison, we consider two other multicast schemes: separate multicasting (S-MCAST) and multiple unicasting (M-UCAST). We show that TS-MCAST outperforms S-MCAST and M-UCAST in terms of bandwidth consumed and processing load (i.e., number of control packets) incurred for a given amount of multicast traffic under the same unicast traffic load with static multicast sessions and membership. View full abstract»

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  • Fast optical wavelength interrogator employing arrayed waveguide grating for distributed fiber Bragg grating sensors

    Page(s): 132 - 139
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (595 KB) |  | HTML iconHTML  

    A new type of interrogator for distributed fiber Bragg grating (FBG) sensors that employs an arrayed waveguide grating (AWG) is proposed and its operating features are in detail investigated both theoretically and experimentally. The remedy for achieving the linear characteristics of wavelength detection as well as for insuring the reliable and environmentally stable operation of interrogation is proposed and its usefulness is demonstrated in good agreement with the experimental results. The developed interrogator consists of a fully passive, small, all-solid, rugged optical IC and can detect wavelengths of a great number of FBG sensors with high precision better than 0.5 pm and high speed. View full abstract»

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  • A new spot-size converter concept using fiber-matched antiresonant reflecting optical waveguides

    Page(s): 269 - 274
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    We report on a new concept for InGaAsP-InP 1.55-μm lasers with integrated spot-size converters (SSCs) based on antiresonant reflecting optical waveguides (ARROW). The mode expanders consist of a laterally tapered active region on top of a fiber-matched passive slab waveguide. The large slab mode is laterally confined by an antiresonant configuration of a couple of lateral waveguides defined in the same fabrication process as the active ridge. This feature makes the presented spot-size transformer as simple to fabricate as a standard waveguide, only requiring a planar growth step and a single conventional etch process. The fabricated tapers exhibit a low transformation loss and reduce the coupling loss to standard single-mode fibers from 8 to 4 dB. We also analyze by simulation two variants of the concept proposed in this work, including a taper structure for a buried waveguide, which are expected to show better performance. Simulation results show fiber-coupling efficiencies as low as 2.4 and 1.1 dB for both variants. View full abstract»

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  • Transmission characteristics of long-period fiber gratings having arbitrary azimuthal/radial refractive index variations

    Page(s): 218 - 227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (867 KB) |  | HTML iconHTML  

    A numerical method is presented for determining the transmittance of long-period (LP) fiber-gratings having arbitrary azimuthal/radial refractive index variations. The method uses coupled-mode theory and includes both the sine and cosine character of the LP modes. The model treats interactions between the fundamental LP01 mode and high-azimuthal-order cladding modes. The method utilizes the transfer matrix method to model cylindrical layers both in the core and the cladding regions. View full abstract»

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  • High-speed directly modulated Fabry-Perot and distributed-feedback spot-size-converted lasers suitable for passive alignment, unisolated operation, and uncooled environments up to 85°C

    Page(s): 69 - 78
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (867 KB)  

    Semiconductor lasers with narrow far fields are highly desirable because they can be directly coupled to fiber with high-coupling efficiency, eliminating the cost of lenses and extra packaging. Because of their smaller size, they facilitate more compact transmitters, and since they can be used unpackaged, they enable complex integrated optoelectronic devices. We describe the design, fabrication, and performance characteristics of our family of spot-size-converted (SSC) devices with narrow far fields designed for directly modulated (2.5 and 10 Gb/s) uncooled (85°C) use. The design consists of a conventional active region buried heterostructure laser coupled to an expander region (consisting of a loosely confining waveguide) through a laterally tapered etch of the active layers. This basic design achieves far fields of ∼16×10 degrees, suitable for coupling ∼50 percent of the emitted light into a flat cleaved fiber. Distributed feedback (DFB) 1.3- and 1.5-μm devices, and 1.3-μm Fabry-Perot (F-P) lasers have been implemented in this technology. The devices have dc thresholds from 8-12 mA at 25°C and 35-45 mA at 85°C, with peak power of >15 mWs over temperature, all similar to non-SSC devices with the same active regions. Both SSC F-Ps and DFBs demonstrate bandwidths of >7 GHz and wide-open eyes at 85°C, and reliability suitable for uncooled use. With the DFB device, we also demonstrate a wide open 10-Gb/s eye pattern at room temperature. The laser on a submount demonstrates coupling to a fiber in a v-groove of ∼25% using passive alignment, and sufficient tolerance to back reflection to enable transmission over at least 15 km with typical drive circuitry. Analysis shows that these lasers also have a factor of two improvements in alignment tolerance compared to standard devices in a typical lensed system. The expander impacts the dc and dynamic characteristics of the SSC F-P through the increase in cavity size. The dc and dynamic characteristics of SSC DFBs and standard DFBs are very similar, demonstrating that expander-related absorption and mode transition loss has been almost eliminated in this structure. The SSC-DFBs are, thus, the preferred device for high-speed applications. To ou- r knowledge, the 1.3-μm lasers described are the first SSC devices fully suited for use as an uncooled 2.5-Gb/s transmitters up to 85°C. The combination of a tailored narrow far field with an edge emitting structure rivals vertical cavity lasers in alignment tolerance for low-cost packaging with superior dynamic and thermal performance. View full abstract»

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  • Wavelength-interleaved OADMs incorporating optimized multiple phase-shifted FBGs for fiber-radio systems

    Page(s): 32 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (417 KB) |  | HTML iconHTML  

    We demonstrate that a single fiber Bragg grating (FBG)-based optical add-drop multiplexer can be used to improve the optical spectral efficiency in a mm-wave WDM-fiber wireless network. The technique employs wavelength interleaving in conjunction with optical single-sideband modulation, together with a single multiphase-shifted fiber Bragg grating. Wavelength optical add-drop features are also demonstrated using the grating, and our results show the performance of the novel grating in terms of channel isolation and add-drop functionality. We perform simulations to optimize placement of the phase shifts when an apodization profile is applied to the grating, in an attempt to minimize in-band and out-of-band transmission-amplitude ripples. Experiments are performed using cascade configurations both with the apodized gratings with optimal phase-shift positions and with the original unoptimized gratings. The experimental results demonstrate how these novel gratings can be used in fiber-radio networks incorporating multiple optical add-drop multiplexers. View full abstract»

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  • Rapidly tunable optical add-drop multiplexer (OADM) using a static-strain-induced grating in LiNbO3

    Page(s): 236 - 245
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB) |  | HTML iconHTML  

    A rapidly tunable, polarization-independent, low-loss optical add-drop multiplexer (OADM) for the 1550-nm wavelength regime is reported. The four-port device consists of two input waveguides, a polarization beam splitter (PBS), two polarization conversion/electrooptic tuning waveguide sections, a second PBS and two output waveguides. The waveguides, which are single mode for both TE and TM polarizations, are fabricated on a LiNbO3 substrate by Ti diffusion. Spectral selection is based on phase-matched polarization conversion due to shear strain induced by a dielectric grating overlay film. An applied voltage tunes the device by changing the waveguide birefringence and hence the optical wavelength at which most efficient polarization conversion occurs. Tuning of 0.1 nm/V with a maximum range of 24 nm has been obtained. A tuning speed of 50 ns, corresponding to a rate of 0.128 nm/ns, has been achieved. Channel isolation is better than 24 dB. Fiber-to-fiber insertion loss <5.4 dB has been obtained and polarization independent loss (PDL) of 0.24 dB for both drop and through ports have been realized over the tuning range. Thermal tuning has also been demonstrated. View full abstract»

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  • Optical packet switching and buffering by using all-optical signal processing methods

    Page(s): 2 - 12
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (706 KB) |  | HTML iconHTML  

    We present a 1 × 2 all-optical packet switch. All the processing of the header information is carried out in the optical domain. The optical headers are recognized by employing the two-pulse correlation principle in a semiconductor laser amplifier in loop optical mirror (SLALOM) configuration. The processed header information is stored in an optical flip-flop memory that is based on a symmetric configuration of two coupled lasers. The optical flip-flop memory drives a wavelength routing switch that is based on cross-gain modulation in a semiconductor optical amplifier. We also present an alternative optical packet routing concept that can be used for all-optical buffering of data packets. In this case, an optical threshold function that is based on a asymmetric configuration of two coupled lasers is used to drive a wavelength routing switch. Experimental results are presented for both the 1 × 2 optical packet switch and the optical buffer switch. View full abstract»

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  • Variational analysis of matched-clad optical fibers

    Page(s): 96 - 105
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (747 KB) |  | HTML iconHTML  

    A variational analysis of weakly guiding optical fibers is described. A series expansion of Laguerre-Gauss functions and a modified Bessel function have been used to describe the field in the fiber core and in the uniform cladding, respectively. A numerical procedure optimizing the field parameters (the expansion coefficients, the Gaussian spot-size and the normalized transverse propagation constant) has been developed which allowed highly accurate field representations to be obtained through few-term expansions. Low-order LP modes have been analyzed for refractive index profiles with a power-law variation in the core for which reference solutions (either exact or approximate) are available. A modified profile exhibiting a high index ring around the core has also been analyzed. For power-law profiles, the results are in excellent agreement with the reference solutions and show that the proposed variational analysis also appears to be appropriate for determining the field at wavelengths near to cutoff. Moreover, the comparison with other field representations which use series expansions, shows that our solution needs a noticeably lower number of terms. The analysis of the modified profile, for which only numerical solutions are available, highlights that the developed method provides very accurate field representations. 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