Showing papers on "Extinction ratio published in 1993"
TL;DR: In this article, a 1.5-mu m semiconductor optical amplifier was used for wavelength conversion at 10 Gb/s, with 0.7-3dB power penalties.
Abstract: Data at 10 Gb/s has been translated from an input signal wavelength to another wavelength, either longer or shorter, using gain compression in a 1.5- mu m semiconductor optical amplifier for wavelength conversion. To achieve operation at such high bit rates, the probe (shifted) input must be intense enough to compress the gain of the amplifier significantly. This reduces the gain recovery time of the amplifier because of probe stimulated emission. A consequence of the intense probe is an extinction ratio deduction. Using moderate input powers, wavelength conversion is achieved over a 17-nm (2-THz) range, with 0.7-3-dB power penalties. >
119 citations
TL;DR: In this paper, the first 10 Gbit/s modulation using a III-V semiconductor Mach-Zehnder interferometer is reported, which has a -3 dB bandwidth in excess of 15 GHz and is operated in a push-pull drive configuration with only 2 V peak to peak.
Abstract: 10 Gbit/s modulation using a III-V semiconductor Mach-Zehnder interferometer is reported for the first time. The modulator has a -3 dB bandwidth in excess of 15 GHz and is operated in a push-pull drive configuration with only 2 V peak to peak. 10 Gbit/s nonreturn to zero format eye diagrams with an extinction ratio>10 dB are demonstrated.
114 citations
TL;DR: In this article, a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsp multiple quantum wells was fabricated.
Abstract: The authors have fabricated a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsP multiple quantum wells. The drive voltage for 12-dB extinction ratio is 1.2 V, and the frequency response is flat within 2 dB from DC to 20 GHz. Operation at 20 Gb/s is reported. Extensive data concerning the parasitic phase modulation (chirping) are obtained as a function of applied bias acid operating wavelength. >
88 citations
TL;DR: In this paper, a glass waveguide polarization splitter for operation in the 1.3 mu m wavelength region is reported, which has a symmetric directional coupler configuration, exploits the stress-induced birefringence in K/sup +/-Na/sup +/, ion-exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations.
Abstract: A glass waveguide polarization splitter for operation in the 1.3 mu m wavelength region is reported. The device, which has a symmetric directional coupler configuration, exploits the stress-induced birefringence in K/sup +/-Na/sup +/, ion-exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations. Starting from the measured potassium concentration (refractive index) profile of the structure and utilizing a combination of the multilayer stack theory and the effective-index method, the normal mode propagation constants and mode field profiles are calculated to determine the polarization splitting length and the extinction ratio, and the results are compared with the experimental data. It is shown that in a given coupler, the splitting occurs at several wavelengths in the 1.0-1.45 mu m range. A 25 mm-long coupler, fabricated by thermal diffusion of K/sup +/ ions in BK7 glass, exhibits an extinction ratio of 18.2 dB at 1.32 mu m, in excellent agreement with the simulation results. >
86 citations
TL;DR: In this article, the rise and fall times as well as extinction ratio of optical amplifiers for efficient wavelength conversion up to 4 Gb/s were analyzed and the system performance at 4 GHz was evaluated.
Abstract: Semiconductor optical amplifiers used for efficient wavelength conversion up to 4 Gb/s are discussed. The rise and fall times as well as extinction ratio are experimentally analyzed. System performance at 4 Gb/s is evaluated showing a penalty of only 1.5 dB for the converted signal for conversion over 17 nm. >
85 citations
TL;DR: In this article, a monolithic integration of a strained-InGaAsP MQW electroabsorption modulator and a DFB laser using only two-step MOVPE growth is described.
Abstract: The monolithic integration of a strained-InGaAsP MQW electroabsorption modulator and a DFB laser using only two-step MOVPE growth is described. The extinction ratio is 20 dB with a low-driving voltage of 1.4 V for an optical power density of 102 kW/cm2.
64 citations
TL;DR: Deformable mirror devices (DMDs) have been under development at Texas Instruments for several years, primarily as spatial light modulators for free-space optical applications such as analog phase modulation and digital projection imaging.
Abstract: Deformable Mirror Devices (DMDs) have been under development at Texas Instruments for several years, primarily as spatial light modulators for free-space optical applications such as analog phase modulation and digital projection imaging. A DMD consists of one or more electrostatically deflectable micromechanical aluminum mirror elements, including both micromirrors suspended from thin flexible hinges and membranes. These devices are fabricated using low temperature silicon-compatible semiconductor processing techniques, and thus can be monolithically fabricated over any addressing circuitry. In the last few years DMDs have been integrated into optical fiber switching systems, and efforts are underway to integrate them as routing switches onto optical waveguides. The DMDs used for optical fiber switching are torsion-hinged devices similar to those used for projection imaging. These devices have been integrated with multimode fibers to construct a 4 X 4 multimode optical fiber cross-bar switch with a 19 dB optical (80:1) extinction ratio for all 16 channels. Extinction ratios of 73 dB optical (20 X 106) have been achieved for single point single mode switches. The waveguide switches currently under development are deformable membranes which are monolithically fabricated on silicon wafers with phosphosilicate glass (PSG) waveguide directional couplers to form optical time delay path selection switches. In this paper we describe the fabrication of deformable mirrors, their integration with optical fibers and waveguides, and the resulting system performance.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
49 citations
Proceedings Article•
02 May 1993
TL;DR: In this article, the authors reported the operation of a diode-pumped monolithic self-Q-switched CR,Nd:YAG laser in which the codoped ions create saturable absorption for Nd" laser emission at 1064 nm.
Abstract: We report the operation of a diode-pumped monolithic self-Q-switched Cr,Nd:YAG laser in which the codoped ions create saturable absorption for Nd" laser emission at 1064 nm. With a 70-/um beam diameter in the gain medium, the Q-switched pulse has a duration of 3.5 ns and a peak power of 2 kW. The output is linearly polarized with an extinction ratio of 600:1. The pulse-to-pulse intensity fluctuation is less than the instrument resolution of 0.25%. A 5-mm-long KTP crystal butted against the with a peak power-conversion efficiency of 30%.
42 citations
TL;DR: In this paper, the polymer-dispersed liquid crystal light valve (PDLCLV) was used for large screen displays, which has high transmittance (72 to 78%) and high extinction ratio (146:1 to 178:1) in the entire visible wavelength.
Abstract: We describe the polymer-dispersed liquid crystal light valve (PDLCLV) using a polymer-dispersed liquid crystal (PDLC) film and a Bi12SiO20 (BSO) photoconductive crystal. The PDLCLV has many features suitable for large screen displays, such as no polarizer requirement, a high transmittance (72 to 78%) and high extinction ratio (146:1 to 178:1) in the entire visible wavelength, short rise/decay times (3/5 to 14/15 ms), and a high resolution (34 lp/mm). We discuss the light scattering and modulation characteristics of the PDLC film; photoconductive characteristics of the BSO crystal; and the design, fabrication method, and optical input/output characteristics of the PDLCLV. We also describe the configuration and image display characteristics of a monochrome projection-type display consisting of the PDLCLV as an image converter, an active matrix liquid crystal panel with thin film transistors as an image source, and a 1-kW xenon arc lamp as a reading light source.
25 citations
TL;DR: In this article, a 10 mu m thick LAMIPOL was obtained having an insertion loss of 0.15 dB and an extinction ratio of greater than 60 dB at the wavelength of 1.3 mu m.
Abstract: Techniques for fabricating laminated polarizers (LAMIPOLs), which consist of alternating laminated layers of aluminum and silica, for the wavelength region lambda >1 mu m, are investigated. The oxidation of Al films is prevented by a suitable choice of deposition conditions. The surfaces of SiO/sub 2/ films are smoothed by bias sputtering. A 10 mu m thick LAMIPOL was obtained having an insertion loss of 0.15 dB and an extinction ratio of greater than 60 dB at the wavelength of 1.3 mu m. These characteristics can be estimated from the attenuated constants of the fundamental modes even when higher modes are considered. >
22 citations
TL;DR: In this article, an 8-tap finite impulse response (FIR) fiber filter module was fabricated using optical amplifiers and polymer-dispersed liquid-crystal (PDLC) shutters.
Abstract: We demonstrate the application of optical amplifiers and polymer-dispersed liquid-crystal (PDLC) shutters to electrically reconfigurable fiber optic delay line signal processors. Two 8-tap finite impulse response (FIR) fiber filter modules were fabricated. These two modules can also be interconnected in a cascaded or parallel configuration to implement a 16-tap fiber FIR filter. An erbium-doped fiber amplifier with a peak gain of about 20 dB was used to compensate for the large optical losses involved in the filters due to the large tap numbers. The relatively inexpensive PDLCs were used to realize electrically reconfigurable analog tap weights. The individual fiber filters were then evaluated for their impulse and frequency responses. The fabricated filters used single-mode fibers and fiber components and were polarization independent to within 0.5 dB. The sampling frequency was about 200 MHz, which can easily be upgraded into the gigahertz range. The tapping extinction ratio was about 13 dB with subkilohertz tunability speed. The amplified spontaneous emission noise can limit the filtering performance unless appropriate spectral filtering is included before detection. These optically amplified electrically reconfigurable fiber signal processors have the potential to lead to the realization of complex programmable and adaptive optical systems.
TL;DR: An InGaAsP-InP 2*2 laser amplifier gate switch matrix operating at 1.5 mu m with a fiber-to-fiber insertion loss of 3 dB is reported in this article.
Abstract: An InGaAsP-InP 2*2 laser amplifier gate switch matrix operating at 1.5 mu m with a fiber-to-fiber insertion loss of 3 dB is reported. The switch consists of passive waveguides for branching and recombining, monolithically integrated with laser amplifiers. The passive waveguides perform the signal routing, and the amplifiers provide gain/absorption in each path for on/off switching, achieving gain in the on state to compensate the losses. Dry-etched total internal reflection mirrors are employed as 90 degrees waveguide corner mirrors and also incorporated in the splitters in order to give a compact design. The on/off extinction ratio is >45 dB and the crosstalk is >
TL;DR: In this paper, a two-channel ground-based high spectra resolution Rayleigh-Mie lidar (553.7 nm) was used to obtain vertical profiles of atmospheric parameters including temperature, potential temperature, pressure and density.
Abstract: A two-channel ground-based high spectra resolution Rayleigh-Mie lidar (553.7 nm) and its operation is described. Inversion of data collected with this unique lidar system yields vertical profiles of atmospheric parameters including temperature, potential temperature, pressure and density, as well as aerosol parameters including backscatter ratio, extinction ratio, aerosol volume extinction cross section, and backscatter phase function. The results of the lidar temperature profiles (within 10 K) are compared with those measured by a nearby balloonsonde. Although present accuracies are not acceptable for routine measurements, the concept has been demonstrated. Use of a more stable filter will significantly improve the accuracy of the temperature measurements. This technique makes accessible a fairly complete set of simultaneous measurements of thermodynamic and aerosol properties of the atmosphere.
TL;DR: In this paper, an analytical closed-form expression for the receiver sensitivity of an optically preamplified direct-detection transmission system and the system power penalties arising from excess electrical and optical filter bandwidths and finite extinction ratio are presented.
Abstract: Novel analytical closed-form expressions for the receiver sensitivity of an optically preamplified direct-detection transmission system and the system power penalties arising from excess electrical and optical filter bandwidths and finite extinction ratio are presented. An explicit analytical expression covering the combined effects of APD noise, receiver circuit noise, finite extinction ratio, electrical and optical filter bandwidths, amplifier noise, and input coupling loss is given. These results form a useful basis for the design of high sensitivity optically preamplified transmission systems. >
TL;DR: In this article, a highly efficient (2V peak to peak for 22dB extinction ratio) and extremely low-chirp (< 64 pm) integrated electroabsorption modulator/DFB laser is demonstrated by reducing both electrical and optical crosstalk between the modulator and the laser.
Abstract: A highly efficient (2V peak to peak for 22dB extinction ratio) and extremely low-chirp (< 64 pm) integrated electroabsorption modulator/DFB laser is demonstrated by reducing both electrical and optical crosstalk between the modulator and the laser. The device allowed 2.5 Gbit/s penalty-free transmission over a repeatcrless 200km-long 1.3μm-optimised singlemode fibre.
TL;DR: In this article, an electroabsorption modulator and an optical amplifier have been monolithically integrated by using nonplanar MOVPE, and a bandgap shift of more than 60 nm was obtained with atmospheric pressure MoVPE of GaInAs/GaInAsP strained QWs on 10 μm wide ridges.
Abstract: An electroabsorption modulator and an optical amplifier have been monolithically integrated by using nonplanar MOVPE. A bandgap shift of more than 60 nm was obtained with atmospheric pressure MOVPE of GaInAs/GaInAsP strained QWs on 10 μm wide ridges. A chip gain of 9 dB and an extinction ratio of 17 dB were obtained for the monolithic electroabsorption modulator/amplifier. The integration of an optical amplifier enables the use of a wavelength close to the bandgap of the modulator, resulting in low voltage and low chirp operation
TL;DR: An AlGaAs/GaAs ridge directional coupler electro-optic modulator with a voltage-length (VL) product of only 70 V mm (L=35 mm, V=2 V) is reported in this article.
Abstract: An AlGaAs/GaAs ridge directional coupler electro‐optic modulator with a voltage‐length (VL) product of only 70 V mm (L=35 mm, V=2 V) is reported The low VL product has resulted from the efficient electrode configuration as well as the large overlap between the optical and electrical fields in the waveguides Propagation loss of 34 dB/cm and the measured I‐V characteristics confirm that the contributions from the Franz–Keldysh, charge‐carrier, and thermal effects are small To our knowledge, this is the lowest VL product ever reported for an electro‐optic directional coupler modulator utilizing the Pockels effect An extinction ratio of 13 dB was measured for the modulator at 083 μm wavelength
Patent•
08 Jan 1993TL;DR: In this article, the driver circuit simultaneously sets the relative magnitude of the signal current with respect to a bias current such that a sufficient extinction ratio is achieved in an output optical beam and further sets a relative magnitude for the bias current to achieve a sufficiently small oscillation delay in the laser diode.
Abstract: A semiconductor light source system includes a laser diode that is operated in a variable temperature environment and a driver circuit, wherein the driver circuit sets a magnitude of a signal current supplied to the laser diode below an upper limit level that corresponds to a maximum operational temperature of the laser diode. The driver circuit simultaneously sets a relative magnitude of the signal current with respect to a bias current such that a sufficient extinction ratio is achieved in an output optical beam and further sets a relative magnitude of the signal current with respect to the bias current such that a sufficiently small oscillation delay is achieved in the laser diode.
TL;DR: Results of a study on the use of synthesized light sources in white-light interferometry are presented and the optimum wavelength combination with a pair of multimode laser diodes used to generate a synthetic wavelength source was simulated theoretically and verified experimentally.
Abstract: Results of a study on the use of synthesized light sources in white-light interferometry are presented. The optimum wavelength combination with a pair of multimode laser diodes used to generate a synthetic wavelength source was simulated theoretically and verified experimentally. Using the best wavelength combination, we found that the lowest signal-to-noise ratio required by the system was 18.1 dB in theory and 22.1 dB from experiment. The relationships between the wavelengths of the two diodes used, their coherence lengths, and the signal-to-noise ratio required by the system are shown and discussed.
TL;DR: In this paper, the InGaAsP semiconductor laser amplifier was used as a detector at a received optical power of -27 dBm with simultaneous cavity gain of 16 dB.
Abstract: Multifunctional properties of an InGaAsP semiconductor laser amplifier have been evaluated. A bit error rate of 10/sup -9/ at 100 Mb/s was obtained using the amplifier as a detector at a received optical power of -27 dBm with simultaneous cavity gain of 16 dB. The bandwidth of the amplifier detector was 300 MHz and the maximum responsivity was 30 V/W. The amplifier had a maximum gain of 29 dB and a very large optical on/off ratio of 50 dB. When the amplifier was used as a switch the cavity gain was 19 dB and the extinction ratio was 22 dB. >
IBM1
TL;DR: In this article, the performance of a DC-coupled fully-differential interconnect is analyzed in terms of the deterministic vertical and horizontal eye closure at Gb/s for different optical power levels and extinction ratios in the two complementary arms.
Abstract: For pt.I see ibid., vol.11, no.7, p.1234-49 (1993). The performance of a DC-coupled fully-differential interconnect is analyzed in terms of the deterministic vertical and horizontal eye closure at Gb/s for different optical power levels and extinction ratios in the two complementary arms. Two types of transmitters are investigated, one based on an ideal optical modulator switch (IOMS) and the other based on conventional modulation of two separate lasers. In general, it is found that the timing jitter increases when the imbalance between the power levels in the two arms increases, when the difference between the laser turn-on delay in the two arms increases, and when the receiver and transmitter bandwidth is reduced. To achieve low latency and to accept a maximum power imbalance of 4-5 dB at the receiver, the IOMS and the lasers should be modulated to produce an extinction ratio of at least 10 dB, and the lasers should be biased above threshold. If low latency is not the main concern, an improvement in the maximum tolerable imbalance can be obtained with regular laser modulation by biasing the lasers below threshold. The fitter can be reduced and the maximum tolerable imbalance be increased if faster receivers and transmitters are employed. >
TL;DR: In this paper, the effects of loss and gain on the filter spectral responses were investigated for a novel resonator filter made of two closely coupled asymmetric waveguides with phase-shifted exchange-Bragg grating.
Abstract: Novel resonator filters made of two closely coupled asymmetric waveguides with phase-shifted exchange-Bragg grating, are investigated. Coupled-mode theory based on the normal modes is used to examine the effects of loss and gain on the filter spectral responses. The filter exhibits a total transmission at central wavelength and a rejection to the adjacent waveguide with high extinction ratio for other signals in the absence of loss and gain. Material loss reduces the transmitted power level and increases the filter bandwidth. With a certain amount of optical gain, good transmission can still be maintained in the presence of material loss. Proper control of the optical gain can lead to the amplification of both the transmitted and reflected powers at the central wavelength. >
28 Jun 1993
TL;DR: In this paper, an optical beam shifter module consisting of liquid-crystal cells and a birefringent plate is investigated for a 1024-input-port switching network.
Abstract: An optical beam shifter module consisting of liquid-crystal cells and a birefringent plate is investigated for a 1024-input-port switching network. High extinction ratio (> 20 dB) and low insertion loss (0.5 dB) are achieved by optimal device design. Precise optical alignment is obtained without any adjustment mechanism by using assembly baseplate and an optical assembly bench.
TL;DR: In this paper, the properties of multiple-quantum-well waveguide modulators on strained InGaAs/GaAs layers are analyzed using a tunable Ti-sapphire-laser.
Abstract: Detailed experimental results on the properties of multiple-quantum-well waveguide modulators on strained InGaAs/GaAs layers are presented. Transmission and photocurrent measurements are performed using a tunable Ti-sapphire-laser. The spectra reveal an absorption edge shift as large as 60 nm at 5 V reverse bias. Optimum performance is achieved around a wavelength of 1 mu m, where an extinction ratio of up to 20 dB is obtained with an absorption loss of less than 2 dB/cm. The overall insertion loss of the modulator approaches a constant value of 6.5 dB at higher wavelengths ( lambda >or=980 nm) which is shown to be mainly affected by coupling losses. >
Patent•
3M1
TL;DR: In this article, a multi-branch digital optical switch with three branch waveguides through which light may exit is described, which has an extinction ratio of 700:1 (28 dB) between its two side branches.
Abstract: A multi-branch digital optical switch (10) having three branch waveguides through which light may exit. The multi-branch digital optical switch includes a main waveguide (12), two side branch waveguides (16, 18), and one center branch waveguide (14). The two side branch waveguides diverge symmetrically from the center branch waveguide at angles which are sufficiently small to allow modal evolution through the switch to be substantially adiabatic. Electric fields are used to raise the index of refraction of one side branch waveguide above the index of the center branch waveguide and to lower the index of refraction of the other side branch below the index of the center branch waveguide. The switch has an extinction ratio of 700:1 (28 dB) between its two side branches.
TL;DR: In this article, a stress-induced birefringent polarization-maintaining fiber and an elliptical core fiber are wound under two different winding configurations to experimentally study thermally-induced nonreciprocity in small interferometric fiber optic gyroscope coils.
Abstract: An experimental investigation is conducted to study the effect of alternate winding techniques in reducing fiber optic gyroscope sensitivity to environmental perturbations caused by time- varying temperature and stress. A stress-induced birefringent polarization-maintaining fiber and an elliptical core fiber are wound under two different winding configurations to experimentally study thermally-induced nonreciprocity in small interferometric fiber optic gyroscope coils. The spools, designed to permit temperature control throughout the fiber pack, are constructed with a thermally-insulating material. Fiber extinction ratio and radial temperature gradient data for the coils are obtained in an environmental control chamber. The experimental data are discussed in this paper. Our results indicate that alternating of the winding configuration has no notable effect on the extinction ratio as expected, however proper winding techniques and efficient coil designs can improve the overall performance of the coil over temperature.
TL;DR: In this paper, a new polarisation-insensitive and robust all-fibre-optic interferometer is outlined and demonstrated, which consists of a polarisation maintaining (PM) 3 dB coupler and a PM fibre in a simple Sagnac configuration.
Abstract: A new polarisation-insensitive and robust all-fibre-optic interferometer is outlined and demonstrated. The interferometer consists of a polarisation maintaining (PM) 3 dB coupler and a PM fibre in a simple Sagnac configuration. An insertion loss of 1.2 dB +0.1 dB and an extinction ratio better than 28 dB is obtained for an interferometer designed to have a free spectral range (FSR) of 16 GHz. Exploiting the interferometer for FM to AM conversion has high potential for overcoming dispersion limitations in long distance and highspeed optical communication systems.
TL;DR: In this paper, a panel-type (or surface-illuminated-type) semiconductor optical modulator based on absorption control by electron depletion around the p-n junctions is demonstrated.
Abstract: Operation of a newly proposed panel-type (or surface-illuminated-type) semiconductor optical modulator based on absorption control by electron depletion around the p-n junctions is demonstrated. Performance of a 61% on/off extinction ratio for 5.5 V variation of the applied voltage was obtained in a device having 39 p-n junctions.
Patent•
22 Jun 1993TL;DR: In this article, a junction of a 2-input/2-output directional coupler and a 1-input, 2-output (1-input) or 1-1-output DSC is formed by successively optically connecting, from the input side to the output side, a front-stage partial junction, front-stage partial junction with electrode, central partial junction (CPJ), rear-staged partial junction(RSJ), and rear-stage PSJ, each having a predetermined length.
Abstract: A directional coupler type optical function element with a high extinction ratio, in which a junction of a 2-input/2-output directional coupler or 1-input/2-output directional coupler, formed of a semiconductor or dielectric, is formed by successively optically connecting, from the input side to the output side, a front-stage partial junction, front-stage partial junction with electrode, central partial junction, rear-stage partial junction with electrode, and rear-stage partial junction, each having a predetermined length. The connection state at the front-stage partial junction and an incidence-side lead section optically connected thereto and the connection state at the rear-stage partial junction and an emergence-side lead section optically connected thereto cancel each other, thereby equivalently providing a symmetrical connection state and preventing the extinction ratio for a cross mode from lowering. Moreover, by forming the central partial junction with a proper length, the extinction ratio for a through mode can be kept high enough. Thus, high extinction ratio characteristics can be enjoyed for both of the cross and through modes.
21 Feb 1993
TL;DR: In this paper, the authors present the capability of NRZ WDM ultralong distance transmission with the demonstration of 5Gbit/s NRZ 2-channel WDM signals over 4,500km straight-line transmission, together with the discussion of the method to reduce the degradation due to FWM.
Abstract: Er-doped fiber amplifiers (EDFAs) are attractive for longdistance optical communication systems, because they can amplify optical signals independently of bit-rate, modulation schemes, number of optical channels and so on. Among these features, the use of IM-DD wavelength- division multiplexed (WDM) technology in the EDFA systems is thought to be a candidate for the deployment of the future multi-destination optical communication networks. Although several experiments show the capability of EDFAs for long distance optical communication systems with IM-DD WDM technique1 >2.3, the system length was limited to less than 1,500km3 because of the fiber nonlinearity (four wave mixing, FWM). However, the use of optical soliton pulse can remove the effect of FWM, more than 10,000km WDM transmission by using recirculating loop was demonstrated4. In this paper, we present the capability of NRZ WDM ultralong distance transmission with the demonstration of 5Gbit/s NRZ 2- channel WDM signals over 4,500km straight-line transmission, together with the discussion of the method to reduce the degradation due to FWM. Description of the Experiments Fig.l shows a schematic diagram of the experimental setup. Two DFB-LDs emitting at 1557nm (channel 1) and 1559nm (channel 2) were used as optical light sources and two electroabsorption (EA) modulators were employed to produce 5Gbit/s 215-1 pseudorandom NRZ bit-streams. An extinction ratio of 20dB was obtained at a driving voltage of 3.8V. The two signals were multiplexed with a 3dB fiber coupler. To compensate the insertion loss of the EA modulator modules and the fiber coupler, a booster Er-doped fiber amplifier was used.