By Topic

Lightwave Technology, Journal of

Issue 12 • Date Dec. 1997

Filter Results

Displaying Results 1 - 18 of 18
  • 1997 Index

    Page(s): 0_5 - 0_45
    Save to Project icon | Request Permissions | PDF file iconPDF (1753 KB)  
    Freely Available from IEEE
  • A transparent, all-optical, metropolitan network experiment in a field environment: the “PROMETEO” self-healing ring

    Page(s): 2206 - 2213
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    In this paper, we present an optical network demonstrator realizing a wavelength division multiplexing (WDM) metropolitan self-healing ring. The network integrate three optical add-drop multiplexer (OADM) nodes, designed by two manufacturing companies adopting different architectures and technological solution. It is so demonstrated that transversal compatibility among optical network entities produced by different companies is possible at the state of the art of the technology. A complete transmission performance characterization of the network has been carried out demonstrating that, in nominal operating conditions and on the most critical path, the error probability is lower that 10-14. The reconfiguration times in case of failure has been measured too, demonstrating that this network architecture provide fast self-healing mechanism, in line with the requirements of ITU-T recommendations for very high capacity networks View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Sensitivity improvement of an optical current sensor with enhanced Faraday rotation

    Page(s): 2246 - 2252
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    A sensitivity improvement technique is proposed for a class of bulk-glass optical current sensors that employ a ferromagnetic field concentrator. The total effective optical path length is demonstrated theoretically to be an invariant regardless of the bulk glass thickness and consequently independent of the size of the concentrator gap opening. Thus, if the magnetic field is increased by reducing the gap size, the eventual Faraday rotation for a given electric current can be increased proportionally, leading to an improved device sensitivity. The dependence of the gap magnetic field on gap size is calculated with an equivalent circuit model, and this analytical treatment is compared with a dedicated finite element computer package. By taking account of various types of optical power losses present in the bulk glass, the above formulated gap dependence of magnetic field is used to aid a realistic assessment of device sensitivity and this serves as a tool to design and analyze practical bulk-glass optical current sensors. A detailed experimental study to confirm the proposed sensitivity improvement technique is also reported View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High packing density 2.5 THz true-time-delay lines using spatially multiplexed substrate guided waves in conjunction with volume holograms on a single substrate

    Page(s): 2253 - 2258
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    A 3-bit true-time-delay lines device having a packing density of 5 lincs/cm2 with a minimum delay step of ~100 ps is designed, fabricated and demonstrated. This device is based on substrate guided wave propagation combined with slanted photopolymer volume phase gratings. In this paper, we report the delay and bandwidth measurements for the 3-bit delay lines fabricated on BK-7 glass substrates with a substrate bouncing angle of 45°. The power fluctuation among the outputs due to the cascading fanout effect (a serious drawback for real system applications) is experimentally investigated as well. A power fluctuation controlled to within ±10% is achieved. A femtosecond laser pulse is sent through the device and a bandwidth measurement of up to 2.5 THz is obtained. The delay step is measured by employing an ultrafast photodetector together with a sampling scope. The true-time-delay device presented herein has the potential to be integrated with photodetector arrays due to its planar structure on a single substrate together with the surface normal fan-in and fan-out features View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical beamsteering using integrated optical modulators

    Page(s): 2259 - 2263
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB)  

    A device has been designed and fabricated to demonstrate the principle of using the interference pattern of a number of coherent optical sources to form and steer an optical beam. Steering of the beam can be accomplished by varying the relative phase of the constituent sources. The effect of relative source phase variation and source separation variation has beers considered and optimized using a multiple source interference model. In this case the constituent sources are the outputs of integrated optical waveguides, excited by a common optical source to maintain relative coherence. In order to demonstrate the principle of beamsteering, a device with two constituent sources (waveguides) has been fabricated, and the resultant output interference pattern has been laterally translated by varying the phase of the output of one waveguide with respect to the other, via a novel optical phase modulator View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical frequency domain differential phase shift keying in femtosecond-pulse spectral modulation systems

    Page(s): 2214 - 2222
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    We propose a novel scheme of differential phase shift keying (DPSK) in the optical frequency domain. We take advantage of the intrinsic coherence among spectral elements derived by spectrum slicing a femtosecond optical pulse, introducing differential phase modulation between adjacent spectral elements with a femtosecond-pulse shaper. Detection of the differential phase is achieved by a Mach-Zehnder (MZ) or Sagnac interferometric receiver without requirement of any external phase reference View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fused taper infrared optical fiber couplers in chalcogenide glass

    Page(s): 2242 - 2245
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (56 KB)  

    We have fabricated low loss, high coupling ratio bidirectional optical couplers for infrared light using multimode step-index chalcogenide fiber. Using a fusion technique similar to that commonly employed with silica fibers, we have found a temperature regime where fusion can occur while interdiffusion of the core and cladding materials will not. The resultant device has a roughly 3:1 coupling ratio, less than 0.3 dB of excess insertion loss, and preserves the guided modes of the fiber intact View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The influence of nonstationary carrier transport on the bandwidth of p-i-n photodiode

    Page(s): 2270 - 2277
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    The influence of nonstationary carrier transport on the bandwidth and the bandwidth quantum efficiency product of p-i-n photodiodes is analyzed using the complete phenomenological model for two-valley semiconductors. The analysis has been made for various submicron and micron dimensions, for different bias voltages and for several energies of incident pulse excitation, including the variation of the active area of the p-in photodiode. The analysis shows that, as the thickness of the absorption layer varies, the bandwidth could have more than one maximum, especially for smaller bias voltages. The optimal thickness of the absorption layer versus bias voltage and device area is determined, providing maximal bandwidth and maximal bandwidth-quantum efficiency product View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Signal extraction with frequency arrangement (SEFA) and superimposed subcarrier modulation (SSM) schemes in fiber-oriented wireless access systems

    Page(s): 2223 - 2231
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    This paper describes technologies for the improvement of the noise and nonlinearity characteristics of wireless access systems based on subcarrier optical transmission. First, the superimposed subcarrier modulation (SSM) technique is proposed to reduce the reflection noise induced by fiber connectors. We experimentally confirmed that the proposed method reduces this noise, and we found the optimum frequency and power of the superimposed subcarrier, SSM design methodology is also presented, taking both noise and nonlinearity into account. Second, signal extraction with frequency arrangement (SEFA) is proposed for increasing the optical modulation index, because the third-order intermodulation distortion (IM3) produced by the optical devices can be ignored. Simulation results show that SEFA greatly improves the transmission performance in terms of both the ratio of desired-to-undesired signal and the receiver sensitivity under Rayleigh fading. Combining the SSM and SEFA is also considered, for use with FP-LDs or DFB-LDs. These technologies will enable cheaper FP-LD implementation in fiber-oriented wireless access systems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transmission capacity of optical path overhead transfer scheme using pilot tone for optical path network

    Page(s): 2197 - 2205
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    Photonic networks based on the optical path concept and wavelength division multiplexing (WDM) technology require unique operation, administration, and maintenance (OAM) functions. In order to realize the required OAM functions, the optical path network must support an effective management information transfer method. The method that superimposes a pilot tone on the optical signal appears very interesting for optical path overhead transfer. The pilot tone transmission capacity is determined by the carrier to noise ratio which depends on the power spectral density of the optical signal. The pilot tone transmission capacity of an optical path network employing WDM technology is elucidated; 4.5 kb/s transmission can be realized when the pilot tone modulation index is set at 3% View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vector modal solution of evanescent coupler

    Page(s): 2316 - 2324
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    We present a vector modal solution for the evanescent coupler comprising an optical fiber and a slab waveguide. We identify the normal vector ridge modes of the device for different configurations. The dispersion characteristics and the power transmission properties of these modes are presented. Also, the effect of the proximity between the waveguides on the ridge modes is investigated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Volterra series transfer function of single-mode fibers

    Page(s): 2232 - 2241
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A nonrecursive Volterra series transfer function (VSTF) approach for solving the nonlinear Schrodinger (NLS) wave equation for a single-mode optical fiber is presented. The derivation of the VSTF is based on expressing the NLS equation In the frequency domain and retaining the most significant terms (Volterra kernels) in the resulting transfer function. Due to its nonrecursive property and closed-form analytic solution, this method can excel as a tool for designing optimal optical communication systems and lumped optical equalizers to compensate for effects such as linear dispersion, fiber nonlinearities and amplified spontaneous emission (ASE) noise from optical amplifiers. We demonstrate that a third-order approximation to the VSTF model compares favorably with the split-step Fourier (recursive) method in accuracy for power levels used in current optical communication systems. For higher power levels, there is a potential for improving the accuracy by including higher-order Volterra kernels at the cost of increased computations. Single-pulse propagation and the interaction between two pulses propagating at two different frequencies are also analyzed with the Volterra method to verify the ability to accurately model nonlinear effects. The analysis can be easily extended to include inter-channel interference in multi-user systems like wavelength-division multiple-access (WDM), time-division multiplexed (TDM), or code-division multiplexed (CDM) systems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Characterization of metal-clad TE/TM mode splitters using the finite element method

    Page(s): 2264 - 2269
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    A metal-clad directional coupler-based polarizer with two-dimensional (2-D) modal confinement has been designed and its performance has been rigorously computed by using the accurate vector H-field finite element method after taking into consideration the polarization-dependent coupling lengths, phase mismatchings and losses due to metal-cladding of the system involved View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of grating-assisted directional couplers using the Floquet-Bloch theory

    Page(s): 2301 - 2315
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The Floquet-Bloch theory is used to develop a theory for grating-assisted directional couplers which predicts the coupled power and coupling lengths and is applicable to lossy waveguides. This theory views grating-assisted directional couplers as conceptually similar to conventional synchronous (nongrating) couplers. In the Floquet-Bloch analysis of the directional coupler, it is necessary to include both proper and improper space harmonics. The determination of which space harmonics are improper is critical to the understanding of the coupler performance. The choice of the improper space harmonics used for the analysis of the coupler is different from that used in contemporary papers View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of carrier heating on static linearity of MQW InGaAsP/InP lasers

    Page(s): 2284 - 2286
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (80 KB)  

    Carrier heating can degrade the linearity of the light-current (L-I) characteristics of a laser diode, which is a critical parameter for devices used in cable television (CATV) systems. On the basis of experimental estimation of the carrier heating rate above threshold, we consider the contributions of different mechanisms through which carrier heating can cause static nonlinearity. Comparison with measured L-I characteristics shows that the contribution of carrier heating to L-I nonlinearity is considerably less than previously estimated. We conclude that the carrier heating effect is not a dominant mechanism in producing the intermodulation distortions View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Inline quantum-well waveguide photodetectors for the measurement of wavelength shifts

    Page(s): 2278 - 2283
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    A two-segment GaAs-InGaP-InGaAs p-i-n quantum-well waveguide photodiode has been fabricated and demonstrated to function as a sensitive wavelength monitor. The ratio of the two segments' photocurrents varies linearly with wavelength in a region near the absorption band edge. A wavelength sensitivity on the order of 1 pm was measured for input optical power levels above 30 μW and signal averaging times of 0.2 s. An operating range from 980 to 1020 nm was achieved using electroabsorption tuning of the band edge. The intended application for this detector is wavelength demodulation of Bragg grating fiber optic strain sensors. A strain sensor with resolution of ±6 με was demonstrated using a superluminescent diode and the inline detectors to monitor strain-induced changes in the reflection wavelength of an in-fiber grating View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A numerical study of erbium doped active LiNbO3 waveguides by the beam propagation method

    Page(s): 2294 - 2300
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    A numerical investigation of active waveguides realized on lithium niobate crystals using erbium as active element is presented. A software package is implemented to simulate the propagation of electromagnetic waves in graded-index active waveguides using an active vectorial beam propagation method (ABPM), which enables to calculate the optical field evolution along the propagation axis. A comparative study of the optical signal gain evolution as function of erbium concentration profiles obtained by various doping methods is presented. The optimal doping method, leading to the maximum gain, is determined View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design of double-pass electroabsorption modulators with low-voltage, high-speed properties for 40 Gb/s modulation

    Page(s): 2287 - 2293
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    We discuss device design for electroabsorption (EA) modulators using a double-pass (DP) configuration to attain low-voltage, high-speed operation for wide-wavelength 40 Gb/s optical intensity modulation. It is important to suppress residual antireflective-coated facet reflectivity R1 for the input-output port and on-state propagation loss Abs, on in the waveguide for reducing level change variation Δ caused by the interference effect. As a result, R1<0.5% and Abs, on<1.5 dB are required to obtain Δ less than 1 dB. The most interesting features-reduced drive voltage and improved a figure of merit (bandwidth to drive voltage)-are found theoretically compared to those of conventional a single-pass (SP) configuration. Drive voltage reduction by introducing a DP configuration is clarified: the degree of the reduction is decided by nonlinearity “n” of absorption increase, assuming voltage dependence on increase of the absorption coefficient is proportional to the applied voltage to the n power (V11). For the same device length, the drive voltage is decreased to 2-1n/ leading up to an improvement of a figure of merit up to 21n/. We then present experimental results for fabricated devices having an InGaAsP bulk absorption layer showing small interference effect and large improvement of characteristics. Drive voltages reduced to 52-60% are achieved over a SP configuration with the same waveguide length, which is in good agreement with the theoretical expectation of 2-1n/. Design window for 40 Gb/s modulation appears by introducing a DP configuration even for devices with a bulk absorber. Proper waveguide length design provides high performance with a low drive voltage ~1.2 V, a modulation bandwidth over 30 GHz (showing a figure of merit of ~25 GHz/V), an insertion loss below 8 dB, and a small variation of on-state loss less than 1 dB for wide wavelength range of input light from 1.545 to 1.558 μm. An almost twice larger modulation index is confirmed even under a dynamic condition 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