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Lightwave Technology, Journal of

Issue 7 • Date Jul 1994

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Displaying Results 1 - 23 of 23
  • Modeling of noise in erbium-doped fiber amplifiers in the saturated regime

    Page(s): 1198 - 1206
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    We have made a theoretical study of the noise figure of erbium-doped fiber amplifiers in the saturated regime. The noise figures of amplifiers subjected to specific gain and gain compression requirements were calculated for various amplifier lengths. The resulting noise figures together with the required pump and input signal powers map out all possible solutions given constraints on gain, compression, pump power, output signal power, and noise figure. In some cases, requirements on the output signal power prohibit any solutions. A way to solve this problem is the introduction of a post-amplifier loss. For this configuration, two possible solutions exist, which collapse into one solution at a certain critical loss, under which there exist no solutions. When the impact of amplified spontaneous emission is neglected in the model, only one solution is obtained, and the critical loss is much smaller than when the amplified spontaneous emission is included in the model. We conclude that amplified spontaneous emission generally has to be taken into account, even when the gain is as low as 10 dB, to accurately predict the noise performance of erbium-doped fiber amplifiers View full abstract»

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  • Comparison of two interactive finite-element programs for analysis of optical and microwave waveguides

    Page(s): 1112 - 1120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (788 KB)  

    This paper presents a comparison of two- finite-element programs developed for accurate cross-sectional analysis of arbitrary optical and microwave waveguiding structures. Both techniques were developed in response to the growing demand from scientists and engineers for application-specific expert systems, and employ advanced interactive pre- and post-processing facilities. They show good agreement, strongly complement one another, and could form the core of a whole library of similar “intelligent” software for computer-assisted analysis and design, with a wide range of possible applications within both supercomputer and workstation environments View full abstract»

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  • Dynamic range of coherent analog fiber-optic links

    Page(s): 1263 - 1277
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1168 KB)  

    We investigate the performance of coherent analog optical links employing amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM). The performance of these coherent links is compared to that of AM direct-detection (DD) links. The signal-to-noise ratios, nonlinearities, and-spurious-free dynamic ranges (SFDR's) of the foregoing links are evaluated. We calculate the SFDR for links using DFB and Nd:YAG lasers with typical linewidths of 10 MHz and 5 kHz, respectively. The performance of PM and FM links is dominated by phase noise above a critical value of received optical power. For a linewidth of 10 MHz, and SFDR's of PM and FM links are 30 and 31 dB, respectively, for a received optical power above -27 dBm in a 1 GHz bandwidth. For a linewidth of 5 kHz, the corresponding SFDR's above a received power level of 0 dBm are 51 and 53 dB. The performance of DD and AM links is dominated by RIN above a critical value of received optical power. For a RIN level of -155 dB/Hz, the SFDR's of DD and AM links are 49 and 47 dB, respectively, for a received optical power of 10 dBm in a 1 GHz bandwidth. The SFDR's of the DD and coherent links used for transmission of subcarrier-multiplexed (SCM) signals are also derived. We evaluate target laser parameters needed by a number of different applications. For AM video and antenna remoting applications, linewidths of <1 and <3 kHz are required to use PM and FM links, respectively. For FM video, linewidths of <150 and <350 MHz are required to use PM and FM links. For SCM digital applications, linewidths of <80 and <200 MHz are required to use PM and FM links. The paper concludes with a discussion of system implementation issues, including linearization, optical frequency modulation, balanced receivers, and IF issues View full abstract»

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  • Optimizing polarization states in a figure-8 laser using a nonreciprocal phase shifter

    Page(s): 1121 - 1128
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    The polarization states in a figure and laser are analyzed using Jones matrices. The analysis shows that a figure-8 laser in CW operation does not give enough information to allow the optimization of the birefringence for mode-locking. A switchable nonreciprocal phase shifter is proposed to provide a simple way to optimize the birefringence for a mode-locked figure-8 laser. Using this device, the mode-locking of a diode-pumped figure-8 laser was started, with a probability better than 99%, by following a sequence of predetermined mechanical adjustment. With the proposed nonreciprocal phase shifter, the optimization and starting of a figure-8 laser can easily be automated View full abstract»

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  • A directional coupler acoustooptic filter with reduced sidelobe levels

    Page(s): 1144 - 1151
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    A two-waveguide directional coupler filter with an acoustically induced grating structure is proposed. The directional coupler filter has the advantage that it does not require input and output polarizers and does not require specific birefringent material properties. Since multiple acoustic waves could be applied simultaneously, this property could be used to couple both TE and TM polarizations from one waveguide to the other. This allows for filtering the required optical wavelength from both polarizations simultaneously. A notable weakness of acoustooptical filters and all mode-coupling filters is the high sidelobe levels in their optical transmission spectrum. A technique to suppress these high sidelobe levels in the proposed acoustooptic filter is presented. It is based on simultaneous application of several acoustic waves on the optical waveguide. This technique could be applied to any existing configuration of acoustooptic filters View full abstract»

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  • Amplified double recirculating delay line using a 3×3 coupler

    Page(s): 1136 - 1143
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    We propose the use of a 3×3 coupler as a signal divider to implement an amplified double recirculating delay line. We describe the circuit layout and provide a subsequent analysis leading to the computation of its transfer function under general arbitrary conditions. The different conditions in which the structure can be operated, their effect on the overall transfer function, and stability conditions are also addressed. The use of the amplified double recirculating delay line as a building block to implement more complex filters is also considered View full abstract»

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  • An efficient transmission scheduling algorithm for a wavelength-reusable local lightwave network

    Page(s): 1278 - 1290
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    Although single-hop star networks based on wave-length division multiplexing (WDM) are attractive owing to their all-optical communication features, the throughput of such lightwave networks is limited due to the small number of available wavelengths. In this paper, a wavelength-reusable local lightwave network that consists of two interconnected WDM star networks is proposed. Based on this architecture, the lower bounds for the problems of minimizing the switching duration and the number of switching modes are derived. A transmission scheduling algorithm for this architecture to efficiently reuse the wavelengths is also proposed. The analytical result shows that the proposed scheduling algorithm always produces solutions close to the lower bounds. Simulation results show that given the same number of users and available wavelengths, the solutions (in terms of the average switching duration and the average number of switching matrices) obtained by the proposed scheduling algorithm on the interconnected WDM networks are better than the optimal solution on a single-star WDM network. In most cases, the performance improvement achieves 20 to 45% View full abstract»

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  • Terahipas: a modular and expandable terabit/second hierarchically multiplexing photonic ATM switch architecture

    Page(s): 1307 - 1315
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    A terabit/second hierarchically multiplexing photonic asynchronous transfer mode (ATM) switch network architecture, called Terahipas, is proposed. It combines the advantages of photonics (a large bandwidth for transport of cells) and electronics (advanced logical functions for controlling, processing, and routing). It uses a hierarchical photonic multiplexing structure in which several tens of channels with a relatively low bit rate, say 2.4 Gb/s, are first time-multiplexed on an optical highway by shrinking the interval between optical pulses, then a number of optical highways are wavelength-multiplexed (or space-division multiplexed). As a result, the switch capacity can be expanded from the order of 100 Gb/s to the order of 10 Tb/s in a modular fashion. A new implementation scheme for cell buffering is used for eliminating the bottleneck when receiving and storing concurrent optical cells at bit rates as high as 100 Gb/s. This new architecture can serve as the basis of a modular, expandable, high-performance ATM switching system for future broad band integrated service digital networks (B-ISDN's) View full abstract»

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  • Wavelength selective optical fiber couplers based on longitudinal Fabry-Perot structures

    Page(s): 1129 - 1135
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    A new approach for the development of wavelength selective optical fiber couplers is proposed. It is based on a standard polished fiber coupler in which an intermediate planar multilayer structure, which acts as a transversal optical filter, is included between the two fibers. The simplest multilayer structure, with interesting potential applications, is constituted by high refractive index single-layer Fabry-Perot filters. Experimental results for several single-layer Fabry-Perot filters, as well as a phenomenological model that provides accurate predictions about the wavelength selective coupling ratio, are presented View full abstract»

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  • All-fiber compound ring resonator with a ring filter

    Page(s): 1256 - 1262
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    The new all-fiber compound ring resonator has two rings: a primary one that serves as a resonator, and a secondary one that serves as a filter. The main contribution of this resonator is to increase the free spectral range by choosing the fiber lengths in the compound ring cavity. This resonator with a large free spectral range can be readily used as a doped fiber laser. The optimum resonant conditions of the resonator are discussed by using an equivalent model and by the transfer matrix method. The frequency responses of the output and of the circulating intensities are given. Mode suppression by the vernier effect is demonstrated. Comparison with a fiber Fox-Smith resonator is also presented View full abstract»

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  • A high-density, four-channel, OEIC transceiver module utilizing planar-processed optical waveguides and flip-chip, solder-bump technology

    Page(s): 1185 - 1191
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    An optoelectronic transceiver module is described consisting of a four-channel AlGaAs integrated laser/monitor transmitter and a four-channel GaAs MESFET integrated detector/preamp receiver. The optoelectronic chips are flip-chip, solder-bump bonded to a substrate containing electrical wiring and planar-processed optical waveguides. The optical waveguide layer serves two purposes: the routing of optical signals, as well providing mechanical registrations for the optoelectronic chips and fiber-optic ribbon connector. The work described here demonstrates one approach to high-density, optoelectronic array packaging compatible with existing high-performance electronic packaging technology View full abstract»

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  • Architectural framework for optical frequency division multiplexing systems based on regular space-frequency interconnections

    Page(s): 1291 - 1306
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    The paper describes a multistage interconnection network (MIN) with regular interconnections in three dimensions (two space dimensions and the third dimension is the frequency) and dimension-dependent switches. (Regular interconnections mean that the same interconnection principles are applied throughout the stages of the MIN.) The frequency domain is organized by introducing artificial dimensions. The architecture is interpreted as an optical frequency division multiplexing (OFDM) system with multidimensional interconnections and switches where the dimension is an additional design parameter. The multidimensional interconnections may be implemented using a combination of space and frequency channels. The frequency interconnections (data movements between channels) are expressed by the Kronecker product (KP) of permutation matrices. In this case the number of frequency conversion (FC) operations and the number of frequency channels crossed during the generation of interconnections and switching decreases. The architectural principles presented are of general interest for the study of transmission and processing in arbitrary large scale interconnection systems implemented in the 3-D physical space View full abstract»

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  • Optical information processing by synthesis of the coherence function

    Page(s): 1247 - 1255
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    We propose an optical parallel information processing technique adopting synthesis of the optical coherence function by using direct frequency modulation of a laser diode. The optical coherence function having a delta-function-like shape can be synthesized by modulating the laser frequency with an appropriate waveform. In this optical parallel information processing system, selective extraction of two-dimensional information from a three-dimensional semitransparent object, and other operations between two-dimensional information, can be carried out. This manner has no mechanical moving part, and there is no need for calculation by combining with holographic method. In this paper, the method to synthesize the optical coherence function is studied in detail. The manner to improve the suppression ratio of unnecessary subpeaks in the delta-function-like coherence function is studied both in theory and experiments. Moreover, notch-shaped optical coherence function is also studied. Selective extraction and selective masking of a two-dimensional information from a three-dimensional object was successfully performed in basic experiments View full abstract»

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  • Analysis of relative intensity noise in semiconductor lasers and its effect on subcarrier multiplexed lightwave systems

    Page(s): 1159 - 1166
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    It is found that the presence of the asymmetric nonlinear gain causes the longitudinal modes of a Fabry-Perot laser as well as a nearly single-mode laser to couple such that the low-frequency relative intensity noise is greatly enhanced. For the first time we have included this asymmetric mode coupling to adequately model the translation of the enhanced low-frequency noise to the signal band of a subcarrier multiplexed transmission system in the presence of both modulation and fiber dispersion. This effect, which is crucial in determining the system's signal-to-noise ratio, is also verified experimentally. Theoretical and experimental investigations of system impairment caused by noise translation and fiber dispersion are also performed. Excellent agreement between the theoretical predictions and the experimental results is obtained View full abstract»

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  • Improvements to the standard theory for photoreceiver noise

    Page(s): 1174 - 1184
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    The standard theory for photoreceiver noise unrealistically defines the system transfer function solely in terms of the input and output pulse shapes, based on the assumption that equalization is provided at the receiver output. Most photoreceivers reported in the literature, however, are only front ends and do not include equalizers, making direct application of the conventional noise expressions inappropriate. Even if equalization is provided, a signal-dependent definition of the transfer function will be accurate only under certain limited conditions. Furthermore, it is unrealistic to assume a given pulse shape at the input. In this paper we consider the effect of incorporating a more realistic transfer function into the conventional noise theory. We choose the transimpedance amplifier for our analysis due to its widespread popularity; however, our approach is general and can he applied to a broad class of photoreceivers. Since our transfer function is based on a physical circuit, our results can be used to estimate photoreceiver noise performance without making any assumptions on the input or output pulse shapes View full abstract»

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  • Polarization-independent integrated optical, acoustically tunable double-stage wavelength filter in LiNbO3

    Page(s): 1192 - 1197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    We report a polarization-independent integrated acousto-optical double-stage wavelength filter in X-cut, Y-propagating LiNbO3. The device consists of a combination of four acousto-optical mode converters, a TE- and a TM-pass polarizer, and two polarization splitters; their specific design and properties are discussed. The filter has a bandwidth of 1.4 nm and a tuning range of 76 nm around λ1.55 μm. Maximum filter transmission is achieved with a RF drive power of only 80 mW; it excites via a single unidirectional transducer a guided surface acoustic wave driving the four polarization converters of both stages. Fiber-to-fiber insertion loss is 4.6 dB for TM- and 4.8 dB for TE-polarized waves. Multiwavelength filtering has been demonstrated View full abstract»

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  • Multilevel signaling and pulse shaping for spectrum efficiency in subcarrier multiplexing transmission

    Page(s): 1239 - 1246
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    Subcarrier multiplexing (SCM) transmission has been widely used for analog video transmission in CATV systems. As digital video technology rapidly advances, there is a strong need to transmit digital video over the same SCM system. Since digital video such as HDTV requires a much larger bandwidth, multilevel signaling becomes an important approach. As the number of levels increases, however, the noise margin decreases and the system is more subject to adjacent channel interference (ACI). In this paper, we analyze the spectrum efficiency and power penalty of multilevel SCM transmission. We found that using pulse shaping can make multilevel signaling attractive. Depending on the ACI that can be tolerated, results show that multilevel amplitude-shift keying (ASK) of 5-7 b/symbol can give the optimum spectrum efficiency using the raised-cosine pulse. The price paid is a slight power penalty of 0.4 dB to reduce intersymbol interference (ISI) to zero View full abstract»

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  • The effect of modulator nonlinearity on measurements of chirp in electroabsorption modulators

    Page(s): 1152 - 1158
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    Traditional techniques for measuring the chirp in external modulators assume that the optical intensity output of the modulator is a faithful representation of the applied voltage. For electroabsorption modulators, which can have highly nonlinear transmission- vs voltage characteristics, this is a poor approximation, especially when they are operated at high modulation indices. We demonstrate a new technique that makes use of the actual measured T(V) for the device under test, and show that this new technique permits measurement of chirp in modulators generating either NRZ signals or soliton pulses. We apply this technique to both bulk and MQW electroabsorption modulators, and show that traditional measurements significantly underestimate the α values of these devices View full abstract»

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  • Three-wave envelope solitons: possibility of controlling the speed of light in fiber

    Page(s): 1101 - 1111
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    Theory predicts that three-wave envelope solitons (TWES) can he generated in dual-mode optical fibers by simultaneous injection of two copropagating optical modes. The mechanism of the three-wave interaction is the recently observed intermodal forward stimulated Brillouin scattering (FSBS). The dynamics of soliton generation depends on the duration of the injected pulses, the pump power, and the attenuation time constant. For the adiabatic modulation of injected optical waves, a new type of generation has been analyzed: an acoustical wave structure that scatters the incident pump into the Stokes wave is formed in the fiber prior to and after the soliton generation. This structure appears as a result of FSBS and serves as a TWES “launcher.” We identify this type of generation in earlier soliton experiments in stimulated Raman scattering. The TWES velocity depends on the pump power. For a typical dual-mode fiber, the speed of TWES can be adjusted over four orders of magnitude by adjusting the pump power between 0.01 and 200 mW. The duration of the soliton is <3 ms due to the acoustic attenuation. The length of the fiber can be shorter than the length of the soliton while preserving the same TWES characteristics. Both Ar+ and Nd:YAG lasers are suitable for TWES generation View full abstract»

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  • The performance limit of coherent OTDR enhanced with optical fiber amplifiers due to optical nonlinear phenomena

    Page(s): 1230 - 1238
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    This paper theoretically and experimentally clarifies the limit of incident optical pulse power in coherent optical time-domain reflectometry (C-OTDR) enhanced with optical fiber amplifiers. The critical pulse power, at which the performance of C-OTDR is degraded by the effect of optical nonlinear phenomena in a single-mode optical fiber, depends on the amplified optical pulse waveform and the pulse width. For a pulse width of 1 μs or longer, the incident pulse power is limited by the effect of self-phase modulation (SPM). When an optical pulse having a power gradient within the pulse width is incident to a single-mode optical fiber, the optical frequency of the backscattered signal is shifted by SPM, and the center frequency of the signal moves outside the receiver band, so the sensitivity of C-OTDR is degraded. For a pulse width of 100 ns, the incident optical pulse power is limited by four-wave mixing (FWM) which transfers the energy from the incident optical pulse to Stokes and anti-Stokes light as a result of the interaction between the incident optical pulse and amplified spontaneous emission. This paper also demonstrates the high performance of C-OTDR enhanced with EDF A's with 48, 44, 39, and 29 dB single-way dynamic ranges for pulse widths of 10 μs, 4 μs, 1 μs, and 100 ns, respectively, limited by the effect of SPM or FWM. These results are believed to be the best performance of C-OTDR with EDFA's View full abstract»

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  • High-performance Mach-Zehnder modulators in multiple quantum well GaAs/AlGaAs

    Page(s): 1167 - 1173
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    We demonstrate Mach-Zehnder interferometric waveguide intensity modulators which employ electrorefraction due to the quantum-confined Stark effect in multiple quantum well (MQW) GaAs/AlGaAs. These devices exhibit average half-wave voltage-length products as low as 3.0 V·mm and extinction ratios greater than 23.8 dB, which are superior to any MQW devices of this type. An effective index based model is developed to extract linear and quadratic electro-optic coefficients from the modulation data. Also, the power handling limitations of MQW modulators are discussed in terms of device performance and catastrophic electrical failure View full abstract»

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  • Bit-error-rate analysis of optically preamplified receivers using an eigenfunction expansion method in optical frequency domain

    Page(s): 1224 - 1229
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    An accurate method of analysis is presented for optically preamplified receivers using an eigenfunction expansion technique in the optical frequency domain. Excluding three conventional simplifying assumptions on optical filters, electrical circuits, and amplified spontaneous emission, our method can give accurate predictions to the bit-error probabilities in real systems where the amplified spontaneous emission is the dominant noise View full abstract»

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  • Coherent homodyne optical communication receivers with photorefractive optical beam combiners

    Page(s): 1207 - 1223
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1576 KB)  

    The principles of operation and the results of performance measurements are reported of a new type of coherent optical receiver that used a dynamic volume index of refraction grating formed inside a photorefractive material to coherently combine signal and local oscillator light prior to photodetection. Because the refractive index grating is formed by the interference pattern generated where mutually coherent optical beams overlap, the receiver can automatically adjust to changes in angle of arrival or optical wavefront profiles which occur on time scales longer than the grating formation time. The grating appears stationary to high-speed phase modulation imposed on the signal beam and coherently diffracts local oscillator light into the signal beam direction. Performance measurements are reported for a prototype system that used two independent Nd:YAG lasers at 1.064 μm, an iron-doped indium phosphide photorefractive crystal, and a four-slot phase modulation signal format. A receiver BER of 10-6 was obtained at received signal powers that corresponded to an average of 70 detected signal photons per bit at a source data rate of 50 Mb/s, 130 detected signal photons/bit at 220 Mb/s, and about 400 detected signal photons/bit at a 325 Mb/s source data rate. Quantum-limited operation corresponds to an average of six detected signal photons per transmitted information bit for this signal format 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