Linear InGaAsP edge-emitting LED's for single-mode fibercommunications

A 1.3-μm edge-emitting diode with a linear radiance and high coupled power into a fiber is described. The LED yields 60 μW of coupled power into a single-mode fiber at a driving current of 100 mA and an ambient temperature of 25°C. A V-groove structure with an optical absorption region separated from an active region is used. At active layer thicknesses below 0.14 μm, linear current-light output characteristics are obtained. The spectral modulation depth is 0% over the entire emission spectral width of 75 nm, and coherence length is 22.5 μm. LED characteristics are achieved in the range from -30 to 85°C at a driving current of 100 mA. The LEDs exhibit a cutoff frequency of 250 MHz. LED reliability is discussed using results of accelerated aging carried out at the ambient temperatures of 50, 125, and 200°C. The activation energy of degradation is determined to be 0.63 eV, and LED half-lives are estimated to be in excess of 10⁶ h     

A new edge-emitting (AlGa)As heterojunction LED for fiber-optic communications

A new edge-emitting structure designed for fiber-optical communications, in which the active area is limited to the edge of the chip, is described. Significant improvements in the quantum efficiency compared to previous emitting structures are obtained. A power emission of 2 mW for one edge is obtained at a current of 250 mA (λ = 8000 Å).     

Transmission of 140 Mbit/s signals over single-mode fibre using surface- and edge-emitting 1.3 ?m LEDs

To assess whether LEDs could be used with single-mode fibre at high bit rates, 140 Mbit/s was transmitted over 4.5 and 22.5 km using surface and edge emitters, respectively.     

A study of far-field patterns from high performance 1.3-µm InGaAsP-InP edge-emitting LED's

Liquid-phase epitaxy InGaAsP-InP 1.3-µm edge-emitting LED's are fabricated with a very simple Schottky-delineated stripe structure. With a stripe 50 µm wide and 200-250 µm long, typical characteristics of these devices include 170 µW of optical power coupled into a 60-µm core 0.2-NA graded index fiber, 600-Å spectral halfwidths, 2-5-ns risetimes. Unlike GaAs-GaAlAs edge-emitting LED's, best results of coupling efficiency are obtained with InGaAsP-InP LED's whose active layer thickness is in the range 0.12-0.15 µm, due to asymmetry in the far-field patterns. Our study of these far-field patterns shows that this asymmetry is governed by the quality of the active layer material located near the InGaAsP-nInP hetero-interface.     

LED fundamentals: Comparison of front- and edge-emitting diodes

We establish a criterion for the maximum amount of power that can be launched into an optical fiber relative to a front-emitting diode of given active layer (junction) thickness. According to this criterion it should be possible to obtain 7.5 times the amount of power from a light-emitting diode (LED) of optimum design relative to a front-emitting LED whose active layer of equal intrinsic brightness is 2.5 μm thick. We also discuss the performance of edge-emitting diodes and find that the LED's of our examples are capable of providing approximately 50 percent of the power expected from the ultimate diode configuration.     

Long-wavelength (1.3- to 1.6-µm) detectors for fiber-optical communications

A review of the current status of long-wavelength InGaAsP and AlGaAsSb quaternary alloy photodetectors for fiber-optical communications is presented. The material properties important for this application are discussed and compared for each alloy system. High-purity material necessary for low-capacitance p-n junction detectors can be routinely prepared in the InGaAsP alloy system, and techniques have been developed for the growth of compensated low-carrier-concentration AlGaAsSb alloys to satisfy this requirement. The dark current of photodiodes in both quaternary alloy systems is often limited by tunneling, and high-purity material can also be used to reduce this component of the dark current. There is some indication that tunneling current may be defect-assisted rather than band-to-band. Device structures designed to reduce the electric field in the low band-gap materials and thus reduce the tunneling dark current are also reviewed. The special enhancement of the ionization-coefficient ratio β/α in AlGaSb devices is described, and recent results of measurements of α and β in     

High-speed GaAs-(GaAl)As DH LED's with output waveguide structure for optical communications

High-speed GaAs-(GaAl)As DH edge-emitting LED's with an output waveguide structure and a reversed p-n junction for current confinement are described. A cutoff frequency of 115 MHz and a radiance of 1100 W/sr cm²at a diode current of 200 mA have been measured. The output power at the end of a fiber pigtail is about 200 µw with a driving current of 200 mA (core diameter of fiber = 60 µm and numerical aperture NA = 0.2). The coupling efficiency between the diode and a single fiber amounts to 10 percent. Factors affecting both the radiative output and the modulation characteristics are analyzed and discussed.     

High-speed high-power 1.3-µm InGaAsP/InP surface-emitting LED's for short-haul wide-bandwidth optical-fiber communications

High-speed high-power double-heterostructure 1.3-µm InGaAsP/InP LED's have been developed for use in short-haul wide-bandwidth fiber-optics systems. At 150-mA dc, devices typically launch - 11.7 dBm into a 62-µm core graded index (GI) fiber. Optical bandwidth is typically 690 MHz with a 50-mA prebias. Modulation capability was demonstrated at 1-Gbit/s NRZ with - 15.7 dBm of peak power launched into the fiber. Rise and fall times of 340 and 780 ps, respectively, were achieved. Reliability data indicates a median life of ∼ 10⁸h for anticipated operating conditions.     

A comparison of gamma-irradiation-induced degradation in amphoterically Si-doped GaAs LED's and Zn-diffused GaAs LED's

A comparison is presented of the effects of gamma irradiation on the properties of amphoterically Si-doped GaAs LED's and Zn-diffused GaAs LED's. It is shown that the light output of GaAs:Si LED's is severely degraded by irradiation, and, in addition, that the light output cannot be recovered through forward-bias-induced annealing. In contrast, commercially available dome-shaped GaAs:Zn emitters with comparable power outputs degrade much less, and the degradation that is observed can be recovered by forward-bias-induced annealing. Further, this bias-induced recovery can be achieved by applying forward-current pulses only 10 to 50 ms in width. The lack of any bias-induced recovery in the GaAs:Si devices led to an investigation of gamma-induced deep levels using the transient capacitance method of deep level transient spectroscopy (DLTS). Following irradiation, two levels with thermal activation energies of 0.21 and 0.78 eV were observed. Subsequent forward bias reduced the concentration of the 0.21-eV level but had relatively little effect on the 0.78-eV level. These results suggest that the near midgap 0.78-eV level is one of the nonradiative recombination centers responsible for light output degradation.     

Improved molecular beam epitaxial growth of AlxGa1 - xAs/GaAs high-radiance LED's for optical communications

We report some improvements made in molecular beam epitaxial growth of AlxGa1-xAs/GaAs high-radiance LED's for optical communications. These improvements have been achieved by growing these wafers in a system which includes an air-lock wafer-exchange chamber. Interfacial recombination velocity as low as6 times 10^{2}cm/s was obtained. The series resistance of the Burrus-type LED's was reduced by increasing the acceptor concentrations in the p-layers to a density as high as 10¹⁹cm^-3using Be as the dopant. CW output of 5.8 mW, or a radiance of 92 W/sr. cm², at a safe operating current of 150 mA has been obtained in these devices. The device performance is comparable to the best obtained in LPE-grown diodes of the same geometry.     

A phase-locked receiving array for high-frequency communications use

An automatically phased HF receiving array using separate RF amplifiers for each element and IF signal combination is discussed. The type of array considered corrects essentially all phase errors between the distant transmitter and the point where the received signals are combined. This includes errors due to the propagation path, array element motion, near-field obstructions, and instabilities in electronic equipment and RF cables. The array also corrects phase shifts due to changes in angle of arrival, thus giving it the highly desirable property of automatically tracking a desired signal. The effects of interference on array performance and methods for minimizing these effects are discussed. The effect of a single monochromatic interfering signal is discussed in some detail, and results showing regions of acceptable and unacceptable performance in terms of the ratio of desired-to-interfering signal strength and the difference between desired and interfering signal frequencies are presented. A six-element experimental array is described, a technique for measuring patterns is discussed, and measured array patterns are compared with calculated array patterns.     

Comparison of optical back propagation schemes for fiber-optic communications

Optical back propagation techniques that utilize two highly nonlinear fibers to compensate for transmission fiber nonlinear effects are analyzed. When the step-size is equal to the amplifier spacing, inline compensation of fiber nonlinearity without inline dispersion compensation provides the best performance.     

Effective use of wireless data communications

This article summarizes the various wireless data network technologies and describes the underlying data communication elements necessary for effective application deployment. © 1998 John Wiley & Sons, Ltd.     

前向纠错码在高速光纤通信系统中的应用

介绍了前向纠错（FEC）技术在高速光通信系统中应用的必要性、特点、实现方式、以及其对系统性能的改善。     

连续相位FSK在电缆电视网络中的数据通信

介绍一种ＣＰＦＳＫ调制解调在电缆电视网络中数据通信的实现方法。该电路实用性强，通信可靠性高，并给出了调测方法。     

Power and modulation bandwidth of gaAs-AlGaAs high-radiance LED's for optical communication systems

We present an analytical model for GaAs-AlGaAs double heterostructure high-radiance LED's intended for use in optical communication systems. This model takes all the important device and material parameters, such as self absorption, heterointerfacial recombination, doping concentration, active-layer width, injection carrier density, and carrier confinement into account. A theoretical discussion of the effect of these parameters on LED output power and modulation bandwidth is given along with experimental results which are in good agreement with the model. The best high-output 50-μm LED's (biased near saturation) emitted 15 mW into the air with a radiance of 200 W/cm². sr (highest ever reported for a surface emitter LED) and a modulation bandwidth of 17 MHz; the highest bandwidth obtained was 170 MHz at 2-mW output.     

Joint use of DFT filter banks and modulated transmultiplexers for multicarrier communications

In this paper, new procedures for performing multicarrier modulation (MCM) are presented, based on using IFFT/FFT embedded in a filter bank-based transmultiplexer system. The IFFT/FFT blocks, along with the use of cyclic prefix or zero-padding strategies, enable easy equalization of the transmission channel. Additionally, the transmultiplexer system provides improved spectral discrimination, which can increases the transceiver robustness against mainly narrow-band interferences. Moreover, one of the proposed procedures presents an IDFT as the final stage of the MCM transmitter, and a DFT as the first stage of the receiver. This front-end is similar to standardized systems, enabling its compatibility. As it is illustrated by means of several examples, given a signal to noise ratio and comparing the new procedures to DFT-based MCM adopted in several digital communications standards, the following attractive features can be found: (a) greater spectral separation in the information transmitted over each subcarrier and (b) the robustness of the systems in noisy environments, mainly when narrow-band interferences appear, can be increased, allowing a reduction in the bit error probability.     

Impact of pump OSNR on noise figure for fiber-optical parametric amplifiers

Electrical measurements of the noise figure of a fiber-optical parametric amplifier are presented and compared with optical measurements. The transfer of pump noise by four-wave mixing was clearly demonstrated. A numerical model was developed to simulate the transfer of pump noise and validated by these measurements. Using this model, we determine, for practical systems, a minimum required pump optical signal-to-noise ratio of 65 dB.     

光学双稳态在光纤传感器的应用

光强调制型光纤传感器，已得到了广泛的应用，它的测量灵敏度，精度和稳定性，主要取决于光源输出功率的稳定性，传统的办法是采用引入参考光路，利用光电补偿方法，来减小光源波动造成的影响，我们提出采用光学双稳装置来稳定光源输出功率，并将它用於折射率调制型光纤传感器测量液体浓度的实验中，本文详细报导了该装置的原理，内容和测量结果，并指出进一步研究方向。