Larry R. Eaton

Coherent operation of injection-locked monolithic surface-emitting diode laser arrays

A row of six surface‐emitting GaAlAs laser diode arrays was locked in a coupled resonator configuration by means of interconnecting waveguides. An external master oscillator was injected into the first array in order to achieve single longitudinal mode operation and wavelength tunability. Spectral data show all six devices were locked in a single longitudinal mode, with tunable operation of over 60 A. Far‐field fringe visibilities greater than 60% were achieved at 100 mW output powers.

Design of a 10 K NbN A/D converter for IR focal plane array sensors

We are implementing a 12 bit SFQ counting ADC with parallel-to-serial readout using our established 10 K NbN capability. This circuit provides a key element of the analog signal processor (ASP) used in large infrared focal plane arrays. The circuit processes the signal data stream from a Si:As BIB detector array. A 10 mega samples per second (MSPS) pixel data stream flows from the chip at a 120 megabit bit rate in a format that is compatible with other superconductive time dependent processor (TDP) circuits being developed. We will discuss our planned ASP demonstration, the circuit design, and test results.<<ETX>>

Improved performance of a superconductive optical detector with planar antennas

A significant improvement in performance of an ultrathin-film NbN superconductive infrared detector was demonstrated by using a planar antenna concept. The output signal voltage is increased through improved optical coupling and the detector noise is decreased by reducing the total area of the NbN detector element. An enhancement in the signal-to-noise ratio by 32 dB was observed when comparing antenna-coupled detectors to area detectors (e.g., meandering lines). In addition, the authors observed a polarization selectivity of about 13 dB to linearly polarized light, which can provide additional discrimination. The primary noise mechanism in these films is confirmed to be voltage shot noise due to fluctuations in the motion of flux quanta in the film. This is a precise dual to current shot noise.<<ETX>>

Superconductive digital readout for IR FPA sensors

We have built and demonstrated an all superconductive digital readout for use in an IR focal plane array sensor. High performance, ultralow power superconductive circuits perform the functions of low noise preamplification and analog to digital conversion. The superconductive readout was tested with a variety of detectors, including InSb, Si:As, and a thin film NbN superconducting detector. Light sources included a HeNe laser (0.6 micron), a CO2 laser (10 microns), and a blackbody (400 to 900 K). In each case, the detector and readout circuitry was assembled into a 2 inch diameter, 6 inch long test package cooled in a single dewar. We demonstrated the functionality of the detector/readout channel from input photons to output digital signal. The superconductive readout reported here used Nb-based circuits operating at 4 K. An NbN squid amplifier and detector have subsequently been demonstrated above 10 K. We discuss the extension of the entire digital readout to operating temperatures above 10 K.

Optimization of NbN MVTL logic gates for 10 K operation

We have systematically studies designs for Modified Variable Threshold Logic Gates (MVTL) in NbN within the framework of factorial analysis. Our goal is to attain optimized margin and fanout for 10 K operation. Significant parasitic inductances, associated with current crowding at junction vias, were measured and are found to affect the operating margin. We report the progression of designs, margin measurements and yield data for our 10 K circuits.<<ETX>>

Enhanced optical detection in a Josephson junction

Shifting of the energy gap of a Nb Josephson junction under direct optical illumination was measured. The response is linear with optical input power over more than five orders of magnitude and is nearly independent of temperature from 4 to 8 K. The rise time of this signal is faster than the 2- mu s rise time of the chopped light signal. These direct signals are 500 to 1500 times larger than those obtained when the same optical power is focused elsewhere on the substrate. This enhanced direct response is interpreted as resulting from thermal isolation of the Josephson junction from the substrate due to thermal boundary resistance.<<ETX>>

Potential architectures for superconductive IR focal plane sensors

Extremely low power superconductive electronics (SCE) (low noise preamplifier, analog to digital converter, multiplexer, etc.) for very large focal plane arrays can significantly reduce the overall sensor system power, hence its weight and volume, thus reducing overall mission cost. The general architecture for a Z-plane, all-superconducting technology focal plane signal processor is presented illustrating the functional elements and their general configurations. The low noise and speed of the TRW developed SCE permits unique solutions to focal plane array signal processing issues such as in-line gamma suppression and digital signal integration.