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Lightwave Technology, Journal of

Issue 11 • Date Nov 1995

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Displaying Results 1 - 21 of 21
  • Performance of optical direct receivers using noise corrupted decision threshold

    Page(s): 2202 - 2214
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1256 KB)  

    The decision threshold of digital binary detectors has to be selected in the optimum position between 0 and 1 symbol amplitudes in order to minimize the bit error rate, This optimum has to be determined by acquiring the bit amplitudes from the signal itself. In packet, or burst-mode, transmission systems the decision threshold must be rapidly acquired from a short strip of bits, and the intrinsic reception noise may have not been completely averaged. This introduces a sensitivity penalty which is shown to be given by a simple expression for the situation when additive Gaussian noise is dominant. An extension to the nonadditive Gaussian noise is given in an appendix. Special attention is devoted to the case when adaptive threshold acquisition is done by means of a peak detector and it is found that the penalty is always higher than that of the ideal integrator. The optimum decision threshold must be estimated numerically in each case and varies along the burst with the number of acquired peaks View full abstract»

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  • Design of a self-routing frequency division multiple access (SR-FDMA) network using an optical ring filter with or without gain as a router

    Page(s): 2168 - 2182
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1372 KB)  

    Self-routing frequency division multiple access (SR-FDMA) network with ASK coherent detection and dual ring topology is proposed. The router, which employs the optical ring filter, is used as a means for selecting the desired channel carrier and at the same time as a bypass of the other channel carriers. The channel capacity and the carrier-to-noise ratio are investigated with the consideration of cross talk and power budget penalty. We find that there exists an optimum coupling coefficient of the transceiver coupler and a trade-off in selecting channel number and data rate. The results show that the router with gain can suppress the cross talk, compensate the power budget penalty, and largely increase the channel number. Therefore, with this router, a self-routing, high-density FDMA network is feasible View full abstract»

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  • SSFLC optical directional coupler switch with a short device length: a proposal

    Page(s): 2236 - 2243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    A novel vertical directional coupler waveguide switch composed of ferroelectric liquid crystal (FLC) is proposed and analyzed. The surface stabilized ferroelectric liquid crystal break (SSFLC) is used as an active separation layer between passive waveguides. To decrease the switching length, the waveguide switch is based on the power crossing the separation layer rather than coupling between waveguides. The calculated results relevant to the switch parameters such as the switching length, switching time, capacitance, and extinction ratio are presented. Because of the large birefringence of FLC, a very short switching length, less than 60 μm, is possible View full abstract»

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  • Gain equalization by mitigating self-filtering effect in a chain of cascaded EDFA's for WDM transmissions

    Page(s): 2191 - 2196
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A simple method of alternatively using high-inversion and moderate-inversion erbium-doped fiber amplifiers (EDFA's) in an optical amplifier chain is presented to mitigate the self-filtering effect and equalize both signal power and signal-to-noise ratio (SNR) of multiple wavelength channels in wavelength-division multiplexing (WDM) transmission systems. The performance of the compensated system with alternatively used high- and moderate-inversion amplifiers is compared with the uncompensated ones where only moderate- or high-inversion amplifiers are employed. The result shows that the compensated system has a flatter gain profile, a lesser signal power spread, and SNR degradation View full abstract»

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  • Impact of noise and nonlinear distortion due to clipping on the BER performance of a 64-QAM signal in hybrid AM-VSB/QAM optical fiber transmission system

    Page(s): 2197 - 2201
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    Experimental BER measurements of a 64-QAM signal in a hybrid AM-VSB/QAM optical fiber transmission system are shown to be in good agreement with a corrected and reinterpreted theory of impulsive and Gaussian noise based on Middleton's class B impulsive noise model. Fiber dispersion induced distortion of the chirped laser output is also shown to adversely affect the QAM signal View full abstract»

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  • Full-wave analysis of coplanar waveguides for LiNbO3 optical modulators by the mode-matching method considering nonideal conductors on etched buffer layers

    Page(s): 2250 - 2257
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    Rigorous analysis of traveling-wave coplanar waveguide electrodes for LiNbO3 optical modulator applications is presented by using an extended full-wave mode-matching method. The microwave propagation characteristics under the composite influence of substrate anisotropy, uniform or etched buffer layers, finite electrode thickness and conductivity, and metallization undercutting are accurately assessed by employing a network equivalent formulation. Variations of the coplanar waveguide microwave effective index and the characteristic impedance at low frequencies due to finite electrode conductivity are illustrated, and are important even though the mode is quasi-TEM in nature. The effect of etching the SiO2 buffer layer is shown to be one possible method for lowering the microwave effective index while keeping the conductor loss at a fixed level View full abstract»

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  • A multilevel WDM access protocol for an optically interconnected multiprocessor system

    Page(s): 2152 - 2167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1744 KB)  

    Scalable, hierarchical, all-optical WDM networks for processor interconnection in multiprocessor systems have been recently considered. The principal objective of this paper is to introduce an access protocol for this type of network which supports a distributed shared memory (DSM) environment. The objectives of the protocol are reduced average latency per packet, support of broadcast/multicast, collisionless communication, and exploitation of inherent DSM traffic characteristics. The protocol is based on a hybrid approach that combines reservation access and preallocated reception channels for a WDM system. The proposed approach trades maximum capacity for reduced communication latency to improve system response. The performance of the protocol is analyzed through semiMarkov analytic and simulation models with varying system parameters such as number of nodes and channels. The performance of the new protocol is compared to a TDM-based protocol and their relative merits are examined View full abstract»

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  • Optimum optical power splitting ratio of decision driven phase-locked loop in BPSK optical homodyne receiver

    Page(s): 2183 - 2190
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    In a BPSK optical homodyne receiver that utilizes a decision-driven phase-locked loop, the splitting ratio of the received power and that of the local oscillator power are very important parameters in achieving high receiver sensitivity. This paper determines the optimum setting of these parameters considering the influence of the relative intensity noise of the local oscillator and the thermal noise of the preamplifier. The optimum splitting ratio of the local oscillator power to the Q-arm is found to be 0.5. The splitting ratio of the received power to Q-arm is obtained as a function of laser linewidth. The optimum setting of the received power and the local oscillator power Is independent of the relative intensity noise of the local oscillator, the thermal noise of the preamplifier and the bit rate, At the optimum splitting ratios, required beat linewidth is obtained as 1.3×10 -3/Tb(τ/Tb≪1) and 2.99×10 -3/τ(τ/Tb≫1), where Tb is the bit duration and τ is the loop propagation delay time. We show that the total power penalty of 0.8 dB from the shot noise limit can be realized with the relative intensity noise of -170 dB/Hz and equivalent input noise current of 10 pA/√(Hz), even if an imperfect balanced receiver is utilized; quantum efficiency ratio of the twin-photodetector is 0.96, propagation time difference T/Tb is 0.01. To confirm the theoretical model, a BPSK homodyne detection experiment is performed and good agreement is found between theoretical and experimental results View full abstract»

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  • Photonic access concentrator for ATM gigabit switching fabrics

    Page(s): 2142 - 2151
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1124 KB)  

    In future broadband communication networks the interest for purely photonic switches is due to the bandwidth mismatch between optical transmission networks and electronic switching nodes. Photonic ATM switching fabrics mainly based on wavelength-switching stages are therefore being studied, to implement high capacity switches with also concentration, multiplexing and demultiplexing functions, using state-of-the-art photonic technology. The architecture of an ATM photonic access concentrator is described in this paper, illustrating the design and implementation of its basic subsystems, the traffic concentrator and the cell multiplexer. The design guidelines are outlined in detail referring to an example, where 128 user lines at 622 Mb/s are given access to 4 outlets at 2.488 Gb/s. The corresponding implementation, based on the systematic use of cell wavelength encoding, makes use either of well-known photonic components, such as Fabry-Perot filters, fiber delay lines, splitters and combiners, either of recently developed devices, like high-speed optical gates and tunable filters and lasers. Finally, the system feasibility is demonstrated presenting the results obtained on a reduced size and speed experimental setup of the cell multiplexer View full abstract»

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  • Three-dimensional method for simulation of multimode interference couplers

    Page(s): 2296 - 2299
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A three-dimensional (3-D) method for modeling multimode interference devices based on a finite element formulation is presented as an alternative to models having one-dimensional cross-sections only. The method is tested for couplers with two different strongly confined waveguides structures. The results show that full treatment of two-dimensional cross-section is of special importance for design and simulation of waveguide devices for which the effective index approximation is no longer valid. For deep rib waveguide geometries, excess loss greater than 15 dB can be obtained if the 3-D method is not used in the design of the couplers View full abstract»

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  • Optical beat-induced crosstalk of an acousto-optic tunable filter for WDM network application

    Page(s): 2224 - 2235
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1012 KB)  

    Acousto-optic tunable filters (AOTF) using TE-TM mode conversion are attractive for wavelength routers, such as WDM add/drop multiplexers or WDM cross-connect switching fabrics, due to their multichannel selectivity. However, their multichannel selection creates optical beat-induced crosstalk, the so called “coherent crosstalk”, due to the interaction of the lightwave with several acoustic waves. This paper evaluates the transmission characteristics of WDM systems employing AOTF's. First, we develop an analytical model of coherent crosstalk based on the coupled mode theory. Next, we examine coherent crosstalk induced BER degradation both theoretically and experimentally for optical WDM systems and show that the analytical studies well support the experimental results. Finally, maximum AOTF cascade number is estimated based on these results for WDM based wavelength routing networks View full abstract»

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  • Second-order distortion of amplified intensity-modulated signals with chirping in erbium-doped fiber

    Page(s): 2129 - 2135
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    Second-order distortion produced in an erbium-doped fiber amplifier (EDFA) is investigated theoretically and experimentally. Rate equations for intermodulation products are led by the perturbation method. From numerical calculation, it is shown that optimum combinations of input power to EDFA and signal wavelength exist that give a distortion-free condition, Improvement of the composite second-order (CSO) distortion, which results from the cancellation of the laser distortion and the gain tilt induced distortion, was confirmed for VHF multichannel transmission. Furthermore, CSO distortion-free transmission in cascaded EDFA's has been demonstrated for a 42-channel AM-SCM signal by experimentally determining the optimum operating condition of the EDFA such that each amplifier generates no additive distortion View full abstract»

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  • H1(curl) tangential vector finite element method for modeling anisotropic optical fibers

    Page(s): 2290 - 2295
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    For the purpose of modeling anisotropic optical fibers, accurate and efficient description of how electromagnetic waves propagate in these structures of arbitrary geometry is required. This paper presents a full-wave analysis of anisotropic waveguides which are characterized simultaneously by both off-diagonal second rank symmetric [ε] and [μ] tensors. By using the H1(curl) tangential vector finite element method, electromagnetic characteristics of propagating modes in the fibers are obtained without the occurrence of spurious modes. In this procedure, a formulation in terms of vector and scalar potentials is adopted and the eigenvalue of the final matrix equation corresponds to the propagation constant itself. Furthermore, the direct matrix solution technique with minimum degree of reordering has been combined with the modified Lanczos algorithm to solve for the resultant sparse generalized eigenmatrix equation efficiently. To demonstrate the strength of the present method, numerical results are verified and agreements with other published results are achieved View full abstract»

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  • Back-reflexion from fused biconic couplers

    Page(s): 2282 - 2289
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    Several theories are investigated to account for the origin of back-reflexions from fused biconic couplers. Amongst the effects causing such variation are those considered in this paper, namely, tapering, surface roughness on the cladding-air interface, fiber bends and twists and, finally, stress arising from bending and packaging. The basic investigative tool is the coupled local mode equations solution for the coupling between the forward- and backward-propagating modes arising in response to these effects. Theoretical analysis shows the stress optic effect to be the most likely reflexion origin and experimental results support this assertion, as well as ruling out tapering and surface roughness as likely causes View full abstract»

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  • Optimizing driving conditions of a MQW EA modulator for soliton generation

    Page(s): 2215 - 2223
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    A detailed analysis of the pulses generated with a multiple quantum well (MQW) electroabsorption (EA) modulator used as a soliton source is performed. The pulse temporal and spectral shape are simulated and a good agreement is obtained with the experimental results. An irregular holed spectrum shape is observed under certain operating conditions and its existence is attributed to parasitic phase modulation. This type of spectrum could be observed even for pulses having a time bandwidth τΔν product below 0.4 which makes them usually considered as nearly transform limited. However it is not the case. The influence of the pulse spectral shape on transmission performances is investigated by means of a realistic simulation of soliton pulse propagation at 10 Gb/s. It is shown that for 9000 km propagation distance and for pulses presenting this irregular spectral shape a signal degradation occurs as the timing jitter is above 10 ps and the quality factor Q is below 2, which results in an increase of the transmission bit error rate. In order to avoid the generation of this kind of pulses when operating a MQW modulator as a soliton source, a mapping is realized giving the adequate voltages to apply to the diode for acceptable soliton generation View full abstract»

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  • Elimination of clock recovery and framing by transporting clock, data and synchronization pulse for OC-192 using WDM

    Page(s): 2136 - 2141
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    Using the least dispersed wavelengths in a wavelength division network (WDM) system to transport the clock and synchronization pulse as data signals along with byte wide data is proposed for OC-192 and higher rates. This scheme eliminates the clock recovery, scrambling and descrambling functions. A behavioral model of the WDM-based communication network using a hardware description language is described View full abstract»

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  • Wavelength-selective fiber loop mirrors and their wavelength tunability by twisting

    Page(s): 2276 - 2281
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    Wavelength characteristics and the wavelength tunability of the fiber loop mirror constructed by a fused taper coupler are studied for elongation and twisting. The difference between the reflected and the transmitted wavelengths decreases exponentially with the number of minimal transmissions of the monitored light during fiber mirror fabrication. The fiber loop mirror twisted the constituent coupler can be realized as a fiber coupler and an equivalent waveplate for a theoretical study. The measured spectrum transmission agrees well with the theory. The reflected and the transmitted wavelengths can be tuned by twisting fiber mirrors without significant degradation. The wavelength change due to twisting is reversible and repeatable View full abstract»

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  • Maximum achievable throughputs for uncoded OPPM and MPPM in optical direct-detection channels

    Page(s): 2121 - 2128
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    Tight upper and lower bounds on the maximum throughputs for both overlapping and multipulse pulse position modulation (OPPM and MPPM) in optical direct-detection channels are derived. The corresponding pulse-position multiplicities are estimated. Simple lower bounds for the maximum achievable throughput (with the error rate not exceeding a certain threshold) are obtained for OPPM. A comparison between the maximum achievable throughputs for both OPPM and MPPM is also considered. Our results suggest using MPPM for high efficient transmission and OPPM for low efficient transmission. Namely, MPPM should be used when the transmission efficiency exceeds 0.027 nats/photon View full abstract»

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  • Flip-chip planar GaInAs/InP p-i-n photodiodes-fabrication and characteristics

    Page(s): 2270 - 2275
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    New flip-chip planar GaInAs/InP p-i-n photodiodes have been fabricated as an array. We describe the structure of the photodiode, the design of a microlens, the fabrication processes, characteristics, and the optical fiber-coupled modules. This photodiode satisfied the requirements for a small junction capacitance and low dark current, good optical fiber coupling, and easy fabrication. We obtained a low dark current with good reproducibility by using two layer polyimide and SiN passivation films. A microlens with a 50 μm φ to 120 μm φ aperture could easily be fabricated with an InP-substrate. By electroplating, flip-chip metal bumps were directly formed on the active region of the photodiode for the first time View full abstract»

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  • Recursive simulation models of the semiconductor laser modulation characteristics for accurate performance evaluation of coherent optical CPFSK systems

    Page(s): 2258 - 2269
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    Modeling of the semiconductor laser nonuniform FM response and residual IM modulation is essential for the computer-aided design of coherent optical communication systems. This paper presents an accurate simulation model, in which the FM and IM responses are represented by recursive digital filters derived directly from measurements. A comparison with previous models of the bibliography reveals the advantages of the current approach. The proposed modeling procedure is applied in the case of a single-electrode DFB laser. This DFB model, in combination with a semi-analytical technique for the evaluation of the error probability, is used to study the influence of the modulation characteristics on the performance of a coherent heterodyne CPFSK system with differential receiver operating at 1 Gb/s. Theoretical and experimental results are in excellent agreement View full abstract»

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  • Integrated optical polarization-discriminating receiver in glass

    Page(s): 2244 - 2249
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    We have successfully demonstrated an integrated optical TE-TM mode discriminator using waveguide polarizers and guided-wave photodetectors for use in polarimetric optical sensor and positioning systems. The photonic integrated circuit consists of a Y-branch waveguide splitter formed by potassium-sodium ion exchange in silicate glass. Hydrogenated amorphous silicon claddings were deposited on each branch of the splitter to act as polarizers. One output cladding was trimmed to a thickness which attenuated the TE polarization, while the other cladding was trimmed to attenuate light having TM polarization. The thickness trimming was accomplished using a process of localized plasma etching which allows in situ extinction optimization by monitoring transmitted light. Optical extinction ratios of up to 27 dB were demonstrated on Y-branch waveguides for polarizers with claddings 1.2 mm in length. The integrated receiver was completed with the deposition of metal-semiconductor-metal photodetectors on each of the output waveguide branches following the polarizers. Amorphous silicon claddings were contacted with chrome-gold interdigitated Schottky contacts to form the waveguide detectors 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