Robert J. Carpenter

Programmable instrumentation and gigahertz signaling for single-photon quantum communication systems

We discuss custom time-tagging instrumentation for high-speed single-photon metrology, focusing particularly on implementations that can tag and process detection events from multiple single-photon detectors with sub-nanosecond timing resolution and at detection rates above 100 MHz. The systems we present view the detector signal as if it were a serial data stream, tagging events according to the bit period in which a rising edge from the detector occurs. We achieve sub-nanosecond resolution with serial data receivers operating up to 10 Gb s−1. Data processing bottlenecks are avoided with pipelined algorithms and controlled data flow implemented in field-programmable gate arrays.

Serving users with a local area network

Abstract The NBS local data network, NBSNET, emphasizes serial, asynchronous service at speeds up to 9600 bauds to terminal users and small computers. Network-wide conventions have been adopted so servers need not be aware of the detailed characteristics of user terminals or computers. These conventions have been implemented in software which resides in the individual network nodes. This software does all of the necessary translation to generate the correct control and escape sequences required by the attached equipment. Nodes attached to terminals handle the following characteristics: speed, echoing, parity, flow control, within-line editing, cursor positioning, delay after format characters, and line-at-a-time or character-at-a-time transmission mode. Each network node has the correct variants of these characteristics for a single specified terminal type, but most of them may be varied under local and/or remote control. Another variant of the node software supports connections to computers acting as either servers or users of the network. Cooperating software in the attached computer can implement both TELNET (simulated terminal) connections, and a file transfer protocol. Full end-to-end flow control is provided in three stages; user-to-node, node-to-node, and node-to-user. This prevents needless lost data packets when output has been suspended by a user, and is required for speed conversion to be done correctly. By segmenting the flow control, a device need not know all the various ways that other devices do flow control. An interrupt feature allows data buffers to be flushed and supporting processes to be notified. A software rotary has been incorporated in all nodes to provide automatic sequencing of connection attempts to a computer acting as a server which has multiple nodes attached to it.

Regulation of Ionization Gauge Emission Current to Better than 0.05

A control system is described for regulating the temperature‐limited emission current from the filament of an ionization gauge tube. A dc transistor circuit is used with a lamp and a photosensitive resistor to provide electrical isolation between the control and the controlled circuits. Emission currents from 10 to 0.5 mA can be maintained with a stability of better than 0.05% with the system.