Elliot Eichen

Measurement of hole velocity in n‐type InGaAs

Hole drift velocities in n‐type In0.53Ga0.47As have been determined experimentally for the first time. Measured values of the frequency response of transit‐time‐limited InGaAs p‐i‐n photodiodes were fit with the theoretical response using hole velocity as the only free parameter. Measurements over field strengths from 54 to 108 kV/cm showed the drift velocity to be relatively constant at (4.8±0.2) 106 cm/s, indicating that velocity saturation has occurred at field levels below 54 kV/cm.

Bandwidth measurements of ultrahigh-frequency optical detectors using the interferometric FM sideband technique

A frequency modulated semiconductor laser and an interferometer are used as a source of very high frequency amplitude modulation to measure the response of optical detectors. This new technique does not require a laser with a flat, or even known, frequency response, and measures the detector response at frequencies well above the modulation frequency applied to the laser. The response of several InGaAs p-i-n detectors has been measured to 22 GHz using 1.3- and 1.55-μm semiconductor lasers modulated at only 500 MHz. These measurements were not limited by the measurement method, which may be capable of measuring bandwidths substantially in excess of 20 GHz.

Wide-bandwidth receiver photodetector frequency response measurements using amplified spontaneous emission from a semiconductor optical amplifier

The white optical noise (spontaneous-spontaneous beat noise) generated by amplified spontaneous emission from a semiconductor-optical amplifier is used to measure the frequency response of over-wide-bandwidth photodetectors and optical receivers. This technique can be used to characterize optoelectronic components of arbitrarily wide bandwidths. >

DSTS: An expert system for diagnosis of advanced digital subscriber services

While the internal networks of almost all telecommunications providers are completely digital, the services provided to end-users (customers) by telecommunications providers-voice, modem, fax, etc.-are today predominantly analog. However, the ability and demand to provide digital services-basic and primary rate ISDN, and IP over digital subscriber loop transport (xDSL) technology-is rapidly growing. Telecommunication providers are now faced with a series of operations, maintenance, and provisioning challenges to economically be able to provide these digital services. One of these challenges is the ability to remotely diagnose faults and service effecting problems. In this paper we will discuss an expert system-DSTS (Digital Services Test System) developed by GTE that provides remote diagnosis and testing of Basic and Primary Rate ISDN, IP over xDSL transport, digital service layer verification and bandwidth testing, and digital subscriber loop pre-qualification.

Configuration management of large IP telephony networks

A nationwide Internet telephony network is described that uses H.323 gateways distributed around the USA to provide customers with local telephone access to application services hosted at a central data center. A key technology that enables deployment of the network is automated configuration management. The configuration management system includes a detailed object-oriented data model of the network coupled with a collection of applications supporting configuration, auditing, testing, monitoring, and updating of network elements. The configuration management system allows the network to be administered and maintained quickly and accurately, minimizing costs in staff and service outages.

Relative intensity noise in semiconductor optical amplifiers

The spontaneous noise spectrum of high-gain semiconductor optical amplifiers is normally assumed to be dominated by spontaneous-spontaneous and signal-spontaneous beat noise, which is white over the frequency range important to fiber-optic systems. Recent measurements have shown that a strong resonance peak in the spontaneous noise spectrum appears well below the threshold current, indicating the existence of relative intensity noise. This noise term has important implications for system design, and its effect on several transmission systems is described. Relative intensity noise in semiconductor optical amplifiers is compared to the similar relative intensity noise found in semiconductor lasers.<<ETX>>

Interferometric generation of high‐power, microwave frequency, optical harmonics

A new technique for sinusoidal intensity modulation of light at microwave frequencies using a frequency modulated semiconductor laser and an interferometer is described. This technique can be more efficient than direct amplitude modulation and, since sidebands at harmonics of the modulation frequency are generated, is capable of reaching higher frequencies than direct modulation. The highest observed frequency (18 GHz) was generated by direct modulation of a laser diode at 9 GHz, and was limited by the bandwidth of available detectors. Frequencies in excess of 100 GHz can be obtained using suitable detectors.

Selective regrowth of a wide-bandwidth 1.3 mu m integrated lossless tap and optical preamplifier

The authors report the first monolithically integrated wide-bandwidth lossless tap-that is, an optical semiconductor amplifier followed by a colinear reverse-biased waveguiding photodetector with fiber-coupled input and output. The integration was achieved by using off-axis selective epitaxial growth of ridge waveguides on a patterned dielectric layer. The tilted facets produced by the off-axis growth, along with photodetector absorption, serve to reduce the effective facet reflectivity to -36 dB without any antireflection coating. By adjusting the length of the absorbing photodetector section, part or all of the amplified light may be absorbed, allowing the device to function respectively as a lossless tap or an optical preamplifier. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dB at 3 Gb/s.<<ETX>>

Subcarrier multiplexed lightwave networks for broadband distribution

Two approaches are analyzed for building low-cost subscriber distribution networks which serve many subscribers from a single transmitter and feeder. In a completely passive optical network, it is shown that 16 to 32 subscribers can be served from a single feeder. In a second approach using optical amplifiers, it is shown that several stages of amplification can be used, and that 16 to 32 subscribers can be served from each amplifier in the final stage. These results show that subcarrier multiplexing techniques (SCM) are very attractive for low-cost broadband subscriber networks. SCM enables the distribution network to combine the advantages of low-cost FM video electronics with the advantages of the passive optical network approach to subscriber distribution.<<ETX>>

Web-based expert system for automated DSL loop qualification

Digital subscriber line (DSL) uses existing standard twisted-pair copper wire to supports voice and data simultaneously and delivers high speed Internet access and multimedia services. However, DSL services cannot be carried over all twisted pair copper loops that support POTS service. It takes a lot of time and expertise to find out which lines can support DSL and which lines cannot. In this paper we describe a Web-based expert system for automated qualifying of lines on the basis of real-time electrical measurements and records stored in telephone company databases. Such a system has been operational in GTE since January 1998.