George C. Valley

The Aerospace Corporation

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

George A. Sefler

The Aerospace Corporation

Arthur L. Smirl

University of Iowa

Thomas F. Boggess

University of Iowa

T. Justin Shaw

The Aerospace Corporation

Mordechai Segev

Technion – Israel Institute of Technology

M. B. Klein

Los Alamos National Laboratory

Marvin B. Klein

Intelligent Optical Systems (United States)

K. Bohnert

ABB (Switzerland)

Ruth Ann Mullen

Bellevue Hospital Center

Amnon Yariv

California Institute of Technology

Cooperative Institutions

HRL Laboratories (United States)

K Lab (United States)

The Aerospace Corporation

University of Southern California

California Institute of Technology

University of California, Los Angeles

Massachusetts Institute of Technology

Stanford University

Lawrence Livermore National Laboratory

University of Arkansas at Fayetteville

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

High Brightness Diode Lasers for Blue-Green Applications

Ruth Ann Mullen D. J. Vickers George C. Valley D. M. Pepper R. C. Lind

Abstract : The threshold for self-pumped optical phase conjugation via stimulated photorefractive scattering has been dramatically lowered by inserting a diffusely retroreflecting screen in the path of the beam exiting the crystal. Stable reflectivities of up to about 60% have been demonstrated in a crystal having too low a gain-length product to exhibit unseeded backward stimulated scattering. The phase-conjugate fidelity is also very good. This conjugator offers many practical advantages over previous photorefractive phase conjugators. The threshold of the device can be precisely controlled by adjusting the attenuation of the seed. The device operates both in the visible and at the infrared diode laser wavelengths. The conjugator's reflectivity and fidelity have been experimentally characterized as a function of the following parameters: pump and seed intensity, crystal angle with respect to the incident beam direction, crystal interaction length, crystal-lens separation, and aberration strength.

Green laser

10.21236/ada360081

Cite

Citations (0)

Ultrafast photorefractive effects in GaAs

Conference on Lasers and Electro-Optics (1987)

Arthur L. Smirl George C. Valley M. B. Klein K. Bohnert Thomas F. Boggess

Ultrafast optics

Source

Cite

Citations (0)

Photonic Analog-to-Digital Converters A Tutorial

George C. Valley

Each new bit of ADC resolution requires an increase in signal-to-noise-and-distortion ratio (SNDR) of 6 dB ENOB without noise bandwidth is meaningless Decreasing the noise bandwidth by a factor of 4 increases ADC resolution by 1 ENOB – e.g. the Tektronix 50 GS/s digital oscilloscope has 5 ENOB over 16 GHz 7 ENOB over 1 GHz Every time you sneeze, you lose a few 1/10's of an ENOB Optical photons are very energetic compared to RF photons – Shot noise is irrelevant for electronic ADCs – Shot noise is a fundamental limit in photonic ADCs Photonic ADCs usually contain a microwave photonic link – Standard analysis gives the SNR/CNR – Max ENOB over a given noise bandwidth readily estimated If commercialized, photonic ADCs will resemble data conversion modules and digital oscilloscopes rather than single chip ADCs

10.1364/ofc.2009.omi1

Cite

Citations (2)

Characterization of Band-Edge Photorefractive Effect in Compound Semiconductors

Afshin Partovi Alan Kost E. Garmire George C. Valley Marvin B. Klein

We have recently shown that at optical wavelengths near the band-edge, non-electrooptic gratings can be used for two beam coupling energy transfer [1]. By combining these gratings with conventional electrooptic gratings, very large gain coefficients can be achieved. We will present measurements of the wavelength dependence of the two-beam-coupling gain in compound semiconductors. A large increase in the amount of energy transfer is observed near the band edge, as compared with values at longer wavelengths. We will discuss the relative magnitude and origins of the mechanisms involved and compare the beam coupling results with direct measurements of the nonlinearities. We will discuss possible applications.

Characterization

10.1364/pmed.1990.c1

Cite

Citations (1)

Isoplanatic degradation of tilt correction and short-term imaging systems

Applied Optics (1980)

George C. Valley

A MTF is derived that includes isoplanatic effects of tilt correction or short-term imaging systems. The MTF is used to predict degradation in Strehl ratio or resolution due to tilt decorrelation on offset paths for long horizontal paths through constant turbulence and for space-to-earth paths through a path-dependent structure constant Cn2.

Strehl ratio

Decorrelation

Optical transfer function

Point spread function

10.1364/ao.19.000574

Cite

Citations (116)

Laser Speckle in Multimode Waveguides for Random Projections in Compressive Sensing and Reservoir Computing

2022 IEEE Photonics Conference (IPC) (2019)

George A. Sefler Uttam Paudel T. Justin Shaw Daniele M. Monahan Adam C. Scofield

Detection of wideband RF signals has applications in sensing and communications. When the signals of interest are sparse, compressive sensing (CS) provides a sub-Nyquist sampling strategy with potential size, weight, and power savings. The critical element in a CS receiver is the device that produces the wideband CS measurement matrix (MM), a MxN matrix with M <; <; N satisfying certain properties [1]. We have shown that passive optical speckle in multimode waveguides provides excellent MMs for CS. The M rows of the MM are obtained from M photodetectors placed at different locations within the output speckle pattern. A range of algorithms can be used to recover the sparse input signal from the resulting measurement vector. We have experimentally demonstrated two speckle-based CS systems: (1) a real-time system with M = 16 implemented using multimode fiber (MMF) that recovers RF frequency, amplitude, and phase, and (2) a simplified spectrometer system implemented using a multimode planar waveguide on a silicon photonic chip that detects only RF frequency and amplitude.

Wideband

10.1109/ipcon.2019.8908273

Cite

Citations (0)

Calibration of a speckle-based compressive sensing receiver

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2017)

George A. Sefler T. Justin Shaw Andrew Stapleton George C. Valley

Optical speckle in a multimode waveguide has been proposed to perform the function of a compressive sensing (CS) measurement matrix (MM) in a receiver for GHz-band radio frequency (RF) signals. Unlike other devices used for the CS MM, e.g. the digital micromirror device (DMD) used in the single pixel camera, the elements of the speckle MM are not known before use and must be measured and calibrated. In our system, the RF signal is modulated on a repetitively pulsed chirped wavelength laser source, generated from mode-locked laser pulses that have been dispersed in time or from an electrically addressed distributed Bragg reflector laser. Next, the optical beam with RF propagates through a multimode fiber or waveguide, which applies different weights in wavelength (or equivalently time) and space and performs the function of the CS MM. The output of the guide is directed to or imaged on a bank of photodiodes with integration time set to the pulse length of the chirp waveform. The output of each photodiode is digitized by an analog-to-digital converter (ADC), and the data from these ADCs are used to form the CS measurement vector. Accurate recovery of the RF signal from CS measurements depends critically on knowledge of the weights in the MM. Here we present results using a stable wavelength laser source to probe the guide.

Digital micromirror device

Photodiode

SIGNAL (programming language)

Waveguide

Chirp

10.1117/12.2250660

Cite

Citations (2)

High-resolution broadband RF spectrometer based on laser speckle imaging

Matthew W. Kelley Matthew N. Ashner Radhika Bhuckory T. Justin Shaw George C. Valley

Photonic measurement of microwave signals promises broader bandwidth, higher resolution, and increased resilience to electromagnetic interference relative to conventional electronic instruments for the same size, weight and power (SWaP). Here we demonstrate a microwave photonic spectrometer based on laser speckle pattern imaging. We modulate the RF signal on a frequency-stabilized CW laser using an electro-optic intensity modulator. The modulated CW laser travels through a 100-meter long high-NA multimode optical fiber before collection and recording on a low noise, high dynamic range silicon camera. An RF tone generator is stepped over the desired operational range of the spectrometer with frequency step size on the order of the desired frequency resolution to record the associated speckle pattern. An unknown signal under test is then generated and recovered from the recorded speckle patterns using regression analysis techniques. The spectrometer has been demonstrated over a 17-GHz frequency range with single tone resolution of better than 5-MHz using a penalized ℓ¹ norm (lasso) regression.

Arbitrary waveform generator

Photodiode

10.1117/12.2631396

Cite

Citations (5)

Characterization of imaging threshold detectors employing a phase-conjugate resonator

Conference on Lasers and Electro-Optics (1986)

G. J. Dunning M. B. Klein George C. Valley

We have previously reported resolution of 40 Ip/mm in an imaging threshold detector using a phase conjugate resonator (PCR),1 This device, which is a combination of the conventional BaTiO3 PCR2 with the incoherent-to-coherent spatial light modulator concept3,4, is intended to produce an output when one element of an n × n pixel array is above a preset threshold. This performance is obtained by using a separate spatially encoded erase beam to erase all transverse modes of the resonator except those of the desired element. Since the erasure is not complete, but only sufficient to keep undesirable pixels from resonating, it is necessary to avoid crosstalk, i.e., partial reflections from one element assisting the oscillation of another, for the device to operate as intended.

Spatial light modulator

Crosstalk

10.1364/cleo.1986.fp5

Cite

Citations (0)

Classification of time-domain waveforms using a speckle-based optical reservoir computer

Optics Express (2019)

Uttam Paudel Marta Luengo-Kovac Jacob Pilawa T. Justin Shaw George C. Valley

Reservoir computing is a recurrent machine learning framework that expands the dimensionality of a problem by mapping an input signal into a higher-dimension reservoir space that can capture and predict features of complex, non-linear temporal dynamics. Here, we report on a bulk electro-optical demonstration of a reservoir computer using speckles generated by propagating a laser beam modulated with a spatial light modulator through a multimode waveguide. We demonstrate that the hardware can successfully perform a multivariate audio classification task performed using the Japanese vowel speakers public data set. We perform full wave optical calculations of this architecture implemented in a chip-scale platform using an SiO 2 waveguide and demonstrate that it performs as well as a fully numerical implementation of reservoir computing. As all the optical components used in the experiment can be fabricated using a commercial photonic integrated circuit foundry, our result demonstrates a framework for building a scalable, chip-scale, reservoir computer capable of performing optical signal processing.

Reservoir computing

Spatial light modulator

SIGNAL (programming language)

Waveguide

10.1364/oe.379264

Cite

Citations (22)