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Lightwave Technology, Journal of

Issue 8 • Date Aug. 2000

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Displaying Results 1 - 14 of 14
  • The /spl lambda/-scheduler: A multiwavelength scheduling switch

    Publication Year: 2000 , Page(s): 1049 - 1063
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    We propose a new multiwavelength almost all-optical switch architecture called the /spl lambda/-scheduler that uses wavelength division multiplexing (WDM) internally to fold the switch architecture in both the space and time domains to reduce the hardware complexity and to improve the signal characteristics through the switch. The /spl lambda/-scheduler preserves the packet order for a given input-output pair, is consistent with virtual circuit switching, and when combined with appropriate connection and flow control protocols, provides lossless communication for bursty (or nonconstant rate) traffic, provided the traffic satisfies certain smoothness properties. The /spl lambda/-scheduler uses novel scheduling and wavelength assignment algorithms, in conjunction with a series of feed-forward delay blocks, to avoid packet collisions within the switch or at the switch outputs. We present two implementations of the /spl lambda/-scheduler when the number of internal wavelengths k equal the number of inputs (and outputs) N to the switch. In the compressed /spl lambda/-scheduler, the N internal wavelengths are used to fold the architecture in the time domain, which reduces the total number of delay blocks for the switch by 2N log N. In the collapsed /spl lambda/-scheduler, the N internal wavelengths are used to fold the architecture in the space domain, which reduces the number of delay blocks and total fiber length used for delays by a factor of N. We examine the insertion loss for both /spl lambda/-scheduler implementations and discuss the trade-offs between the reduction in overall component count and the improvement in the signal characteristics. View full abstract»

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  • Linear stability analysis of dispersion-managed solitons controlled by filters

    Publication Year: 2000 , Page(s): 1064 - 1068
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (121 KB)  

    We present a linear stability analysis of dispersion-managed (DM) solitons controlled by inline narrow-band filters. We show that the filters can destabilize the pulse if they are unsuitedly located in the dispersion map, which is contrary to the case of standard solitons in fibers with constant dispersion. We also show that for such an instability to take place the pulse energy and the dispersion-map strength should be significantly larger than those usually required for practical long-distance transmission. The filter-induced instability of DM solitons will be an issue in the operation of stretched-pulse mode-locked fiber lasers. View full abstract»

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  • Transmission performance of chirp-controlled signal by using semiconductor optical amplifier

    Publication Year: 2000 , Page(s): 1069 - 1077
    Cited by:  Papers (29)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB)  

    We examine the fiber transmission performance of the optical signal whose chirp is controlled by utilizing phase modulation in semiconductor optical amplifier (SOA) with both simulations and experiments. This chirp control technique converts a positive chirp created by electroabsorption (EA) modulator into negative chirp, which reduces the waveform degradation due to the chromatic dispersion in transmission over standard single-mode fiber (SMF). It also provides an optical gain that is sufficient to compensate the insertion loss of the EA modulator. We investigate how the chirp control is affected by the input power to the SOA and the carrier lifetime of the SOA. As the SOA input power increases, the negative chirp becomes large, while the waveform is largely distorted due to gain saturation. However, the waveform distortion at high SOA input powers can be shaped by using a frequency discriminator. The acceleration of the carrier lifetime also reduces the waveform distortion due to gain saturation. We demonstrate that the chirp control technique is effective even for a high bit rate optical signal up to 10 Gb/s, when the carrier lifetime is expedited by optical pumping. View full abstract»

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  • Influence of blanket postexposure on the thermal stability of the spectral characteristics of gratings written in a telecommunication fiber using light at 193 nm

    Publication Year: 2000 , Page(s): 1078 - 1083
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    Bragg gratings have been written in a nonhydrogenated Corning's SMF28 telecommunication fiber using ultraviolet (UV) pulses at a high power density from an ArF laser. Some of these gratings were uniformly exposed with light at 193 nm. The isothermal accelerated aging method was used to characterize the thermal decays of both pristine and postexposed grating spectral characteristics. UV postprocessing led to an increase in the stability of the Bragg grating reflectivity meanwhile the shifts in the Bragg wavelengths of the postexposed gratings proved to be higher than those of untreated gratings. It is shown that the isothermal decays of the refractive index modulation cannot be used to predict the annealing induced irreversible shifts in the Bragg wavelengths. Our observations are discussed within the Frame of the current theoretical descriptions of the links that may exist between the writing and the thermal stability of Bragg gratings. View full abstract»

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  • Cladding-mode-resonances in air-silica microstructure optical fibers

    Publication Year: 2000 , Page(s): 1084 - 1100
    Cited by:  Papers (64)  |  Patents (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (863 KB)  

    We present a comprehensive study of mode propagation in a range of different air-silica microstructured fibers. The inscription of both Bragg and long-period gratings (LPGs) into the photosensitive core region of microstructured air-silica fibers has allowed us to generate complex transmission spectra from a range of fibers with various fill fractions and with increasing air-clad hole diameters. The spectral characteristics for typical air-hole geometry's are explained qualitatively and modeled using beam propagation simulations, where the numerical modeling corroborates the experimental measurements. Specifically, the data reveal the propagation of higher order leaky modes in fibers with periodically spaced air-holes, and relatively small air-fill fraction. And as the air-hole diameter increases, spectra show cladding modes defined solely by the inner air-clad region. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures. View full abstract»

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  • Fiber Bragg grating interrogation and multiplexing with a 3/spl times/3 coupler and a scanning filter

    Publication Year: 2000 , Page(s): 1101 - 1105
    Cited by:  Papers (18)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (97 KB)  

    We present a new technique for fiber Bragg grating (FBG) sensor interrogation and multiplexing. The technique combines a scanning bandpass filter used to multiplex by wavelength multiple gratings in a single fiber, and an unbalanced Mach-Zehnder fiber interferometer made with a 3/spl times/3 coupler to detect strain-induced wavelength shifts. A demonstration system interrogates four gratings in a single fiber at a sampling rate up to 20 kHz, with a noise floor measured at less than 10 n/spl epsiv///spl radic/(Hz) above 0.1 Hz. View full abstract»

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  • A composite optical waveguide-based polarimetric interferometer for chemical and biological sensing applications

    Publication Year: 2000 , Page(s): 1106 - 1110
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (103 KB)  

    A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)/sub 0/ and transverse magnetic (TM)/sub 0/ modes in a composite optical waveguide (OWG). The composite OWG consists of a single-mode potassium ion-exchanged planar waveguide overlaid with a high-index thin film that has two tapered ends and supports only the TE/sub 0/ mode. Applying tapered velocity coupling theory, we found that the TE/sub 0/ and TM/sub 0/ modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE/sub 0/ mode was coupled into the thin film while the TM/sub 0/ mode was confined in the potassium ion-exchanged layer. Interference occurs between TE- and TM-polarized output components when a single output beam is passed through a 45/spl deg/-polarized analyzer. The phase difference /spl phi/ between both orthogonal output components is very sensitive to the superstrate index n/sub c/ in the thin film region. Our experimental results indicate that a slight change of /spl Delta/n/sub c/=3.71/spl times/10/sup -6/ results in the phase-difference variation of /spl Delta//spl phi/=1/spl deg/ for a 5-mm-long TiO/sub 2//K/sup +/ composite OWG with a 34-nm-thick TiO/sub 2/ film. Such a simple polarimetric interferometer can be applied to chemical or biological sensors by modifying the upper film surface of the composite OWG with a chemically or biologically active substance. View full abstract»

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  • Pulsed injection locking dynamics of passively mode-locked external-cavity semiconductor laser systems for all-optical clock recovery

    Publication Year: 2000 , Page(s): 1111 - 1120
    Cited by:  Papers (26)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (622 KB)  

    The performance characteristics of a pulse injection locked, passively mode-locked (PML) external-cavity semiconductor laser system for all-optical clock recovery are investigated in detail. It is important to characterize the clock recovery dynamics to understand the fundamental capabilities and limitations of the clock recovery system. It is experimentally shown that these devices offer robust clock recovery with low phase and amplitude noise, low injected data power requirements, large frequency locking bandwidth, large phase tracking bandwidth, short lockup time, long dephasing time and immunity to bit-pattern-effects. Harmonic clock generation and subharmonic clock generation are demonstrated for data-rate conversion applications. View full abstract»

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  • All-optical wavelength conversion and signal regeneration using an electroabsorption modulator

    Publication Year: 2000 , Page(s): 1121 - 1127
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (131 KB)  

    All-optical wavelength conversion and signal regeneration based on cross-absorption modulation in an InGaAsP quantum well electroabsorption modulator (EAM) is studied at different bit rates. We present theoretical results showing wavelength conversion efficiency in agreement with existing experimental results, and the signal regeneration capability of the device is investigated. In particular, we demonstrate the dependence of the extinction ratio of both the converted signal and the control signal on the device length and on the power level of the control signal. We also show how the sweep-out dynamics influences the results. View full abstract»

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  • Control of widely tunable SSG-DBR lasers for dense wavelength division multiplexing

    Publication Year: 2000 , Page(s): 1128 - 1138
    Cited by:  Papers (15)  |  Patents (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2067 KB)  

    This paper presents a general discussion on the control of widely tunable super structure grating distributed Bragg reflector (SSG-DBR) lasers. A feedback control scheme is presented that ensures frequency stability and accuracy (better than /spl plusmn/0.5 GHz), as well as high side mode suppression ratio (>35 dB). The active section voltage is monitored to maintain mode stability and a highly stable Fabry-Perot etalon is used as a reference to lock the laser frequency to a specific ITU channel. It is shown that stability can even be maintained when directly modulating the laser at 1.244 Gb/s. Furthermore, a characterization scheme is demonstrated that uses the voltage monitoring to generate a look-up table of operation points very efficiently and accurately. For all operation points, the frequency accuracy is better than /spl plusmn/0.5 GHz and the side mode suppression ratio is above 35 dB. View full abstract»

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  • Performance analysis of a dispersion compensator using arrayed-waveguide gratings

    Publication Year: 2000 , Page(s): 1139 - 1147
    Cited by:  Papers (8)  |  Patents (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (198 KB)  

    We have developed a dispersion compensator that uses arrayed-waveguide gratings (AWGs) and a spatial filter. The compensator using AWGs with 380 waveguides in each array and the diffraction order of 53, can compensate a total second-order dispersion of 260 ps/nm with an eye-closure penalty of 1 dB for a 40-Gb/s nonreturn-to-zero (NRZ) signal. It is shown that the required spatial resolution of the spatial phase filter for compensation is 2.55 /spl mu/m for silica AWGs of usual design. The acceptable fluctuation in the refractive index of the waveguides in the AWGs is as large as 5/spl times/10/sup -5/. View full abstract»

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  • Efficient approach for modeling collision-induced timing jitter in WDM return-to-zero dispersion-managed systems

    Publication Year: 2000 , Page(s): 1148 - 1154
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    A semi-analytical approach that allows us to create an efficient numerical algorithm to accurately evaluate collision-induced timing jitter in wavelength-division-multiplexing (WDM) systems with return-to-zero (RZ) modulation format is developed. The approach agrees well with full numerical simulations. The computational time is reduced by two orders of magnitude compared to full numerical simulations. View full abstract»

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  • Complex propagators for evanescent waves in bidirectional beam propagation method

    Publication Year: 2000 , Page(s): 1155 - 1160
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB)  

    Existing algorithms for bidirectional optical beam propagation proposed to simulate reflective integrated photonic devices do not propagate evanescent fields correctly. Thus inaccuracy and instability problems can arise when fields have significant evanescent character. We propose complex representations of the propagation operator by choosing either a complex reference wave number or a complex representation of Pade approximation to address this issue. Therefore correct evolution of both propagating waves and evanescent waves can be simultaneously realized, significantly reducing the inaccuracy and instability problems. Both test problems and practical problems are presented for demonstration. View full abstract»

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  • WKB analysis of bend losses in optical waveguides

    Publication Year: 2000 , Page(s): 1161 - 1166
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (130 KB)  

    A more complete Wentzel-Kramers-Brillouin (WKB) analysis of bend losses is given for a circularly curved waveguide. Using the WKB approximation with a conformal transformation of a curved optical waveguide, is shown to give more accurate bend loss results. 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.

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Meet Our Editors

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