The present invention describes a system and method for communicating voice and data over a packet-switched network that is adapted to coexist and communicate with a legacy PSTN. The system permits packet switching of voice calls and data calls through a data network from and to any of a LEC, a customer facility or a direct IP connection on the data network. The system includes soft switch sites, gateway sites, a data network, a provisioning component, a network event component and a network management component. The system interfaces with customer facilities (e.g., a PBX), carrier facilities (e.g., a LEC) and legacy signaling networks (e.g., SS7) to handle calls between any combination of on-network and off-network callers. The soft switch sites provide the core call processing for the voice network architecture. The soft switch sites manage the gateway sites in a preferred embodiment, using a protocol such as the Internet Protocol Device Control (IPDC) protocol to request the set-up and tear-down of calls. The gateway sites originate and terminate calls between calling parties and called parties through the data network. The gateway sites include network access devices to provide access to network resources. The data network connects one or more of the soft switch sites to one or more of the gateway sites. The provisioning and network event component collects call events recorded at the soft switch sites. The network management component includes a network operations center (NOC) for centralized network management.

Voice over data telecommunications network architecture

The properties of hot electrons in systems where electrons and phonons experience quantum confinement are reviewed. The modifications to the behaviour of electrons and phonons brought about by confinement are described, particularly with reference to the principal scattering mechanism. The latter include the interaction with longitudinal optical phonons and plasmons, along with carrier-carrier effects. Some conflict in the literature concerning Fuchs-Kliewer polaritons is discussed. Low-temperature interactions with acoustic phonons are described. A central topic is that of energy relaxation, and the experimental and theoretical data relating to this form a large part of the review. Energy relaxation mechanisms in the femtosecond to nanosecond regimes, including intersubband and well-capture processes, are eventually summarized. An equally large section deals with hot-electron transport; in which negative differential resistance and other instabilities associated with parallel transport are discussed before turning to ballistic transport and impact ionization.

https://iopscience.iop.org/article/10.1088/0034-4885/54/2/001/pdf

Hot electrons in low-dimensional structures

Plasmons and magnetoplasmons in semiconductor heterostructures

Taking into account the discrete nature of the quantum‐well intersubband infrared detectors, we construct a model to calculate the photoconductive gain. It is shown that the photoconductive gain is inversely proportional to the number of quantum wells and that the detector‐current responsivity is independent of the number of wells.

Photoconductive gain mechanism of quantum‐well intersubband infrared detectors

We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasi-continuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path; net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

We have measured the electron intersubband relaxation time due to the emission of longitudinal-optical (LO) phonons in GaAs-AlGaAs quantum wells using time-resolved anti-Stokes Raman scattering. When the energy separation of the subbands is greater than the LO phonon energy we find the lifetime of electrons in the n=2 level to be \ensuremath{\le}1 ps which is in excellent agreement with theoretical calculations of two-dimensional electron-phonon interactions.

Time-resolved Raman measurements of intersubband relaxation in GaAs quantum wells.

A packet carried on an optical network is routed by carrying out a logic operation on an address word carried in a packet header, and a predetermined discriminator word. A binary routing decision is made in accordance with the product of the logic operation. The operation may be a bit-wise Boolean AND operation. An additional logic operation may be carried out with an additional discriminator word to determine whether the packet is destined for a remoter region of the network. In this case the packet may be steered directly to the remote region.

Optical telecommunications network

Raman scattering from electronic excitations in periodically δ-doped GaAs

A systematic investigation is presented into the frequency response and differential gain in both strained and unstrained InGaAs/InGaAsP 1.5 mu m quantum well lasers. Both the differential gain and damping in strained devices were found to be similar in magnitude to comparable unstrained devices. In addition, the differential gain was found to increase and the damping to decrease with increasing numbers of quantum wells. >

Frequency response and differential gain in strained and unstrained InGaAs/InGaAsP quantum well lasers

We describe recent developments in time-resolved optical measurements of electron-phonon interactions in quantum wells which reveal the fundamental two-dimensional properties of the process. Picosecond photoluminescence experiments show enhanced energy relaxation in narrow quantum wells. Time-resolved Raman measurements of inter- and intra-subband relaxation of electrons reveal the participation of confined optical phonons; in narrow quantum wells there is strong coupling to interface phonons.

M.C. Tatham

Papers

Time-resolved Raman measurements of intersubband relaxation in GaAs quantum wells.

Optical telecommunications network

Raman scattering from electronic excitations in periodically δ-doped GaAs

Frequency response and differential gain in strained and unstrained InGaAs/InGaAsP quantum well lasers

Picosecond optical studies of 2D electron - 2D phonon dynamics