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We develop a framework for two advanced trapped-ion cooling schemes, polarization-gradient and electromagnetically-induced-transparency cooling, for 88Sr+ ions using a visible-wavelength integrated-photonics platform and present the design of the key integrated devices.

I discuss MIT Lincoln Laboratory’s development of integrated photonics and detectors for trapped-ion-array optical clocks, as well as compact, narrow-linewidth lasers to serve as clock oscillators. These technologies will help enable liter-scale, high- performance optical clocks.

Integrated photonic technologies for quantum applications are discussed with emphasis on those supporting trapped-ion-based systems. A long-term vision of a fully integrated trapped- ion chip and current work towards its realization are presented.

Many spectroscopic techniques today rely on time-resolved measurements under short excitation pulses. Instead of using a chopped pump excitation, or ultrafast optical pulses, we expand on and apply the previously developed set of frequency domain methods to analyze the population level dynamics in rare-earth-doped media. By identifying the full frequency response of the gain medium, this method can accurately yield excited state lifetimes and can also be used to estimate transition cross-sections. The accuracy of the frequency domain methods are verified with ${\rm Er}^{3+}$ - and ${\rm Tm}^{3+}$ -doped fibers, and an ${\rm Al}_{2}{\rm O}_{3}{:}{\rm Tm}^{3+}{}$ waveguide, recovering similar results as reported by time-resolved techniques. The complete frequency domain model presented here can be used in characterization of novel optical gain media, and can provide insights into population dynamics in solid state amplifiers and lasers.

Conference on Lasers and Electro-Optics : [Proceedings] - OSA Washington, D.C., 2018. - ISBN 978-1-943580-42-2 - doi:10.1364/CLEO_SI.2018.SM3L.1 Conference on Lasers and Electro-Optics, CLEO, San Jose, California, USA, 13 May 2018 - 18 May 2018; Washington, D.C. : OSA 2 pp. (2018). doi:10.1364/CLEO_SI.2018.SM3L.1, We demonstrate silicon-photonics-based octave spanning optical frequency combs phase coherently locked to a microwave oscillator for optical frequency synthesis. This system offers capability for precision optical synthesis of CW laser over the entire C-band., Published by OSA, Washington, D.C.

Silicon Photonics: From Fundamental Research to Manufacturing : [Proceedings] - SPIE, 2018. - ISBN 97815106189859781510618992 - doi:10.1117/12.2318010 Silicon Photonics: from Fundamental Research to Manufacturing, SPIE.Photonics Europe, Strasbourg, France, 22 Apr 2018 - 26 Apr 2018; SPIE, 11 pp. (2018). doi:10.1117/12.2318010, Mode-locked lasers provide extremely low jitter optical pulse trains for a number of applications ranging from sampling of RF-signals and optical frequency combs to microwave and optical signal synthesis. Integrated versions have the advantage of high reliability, low cost and compact. Here, we describe a fully integrated mode-locked laser architectureon a CMOS platform that utilizes rare-earth doped gain media, double-chirped waveguide gratings for dispersion compensation and nonlinear Michelson Interferometers for generating an artificial saturable absorber to implement additive pulse mode locking on chip. First results of devices at 1.9 µm using thulium doped aluminum-oxide glass and operating in the Q-switched mode locking regime are presented., Published by SPIE

We present a CMOS-compatible, Q-switched mode-locked integrated laser at 1.9µm with a compact footprint of 23.6×0.6×0.78mm, a Q-switched rate of 720kHz, a mode-locked rate of 1.2GHz, and pulse durations of 215fs.

We demonstrate holmium-doped DFB lasers monolithically integrated on silicon. Single mode lasing at wavelength from 2.02 to 2.10 μm with 15 mW maximum output power are reported. This work extends silicon-photonic microsystems beyond 2 μm.

Optics letters 42(6), 1181 - 1184 (2017). doi:10.1364/OL.42.001181, Mid-infrared laser sources are of great interest for various applications, including light detection and ranging, spectroscopy, communication, trace-gas detection, and medical sensing. Silicon photonics is a promising platform that enables these applications to be integrated on a single chip with low cost and compact size. Silicon-based high-power lasers have been demonstrated at 1.55 μm wavelength, while in the 2 μm region, to the best of our knowledge, high-power, high-efficiency, and monolithic light sources have been minimally investigated. In this Letter, we report on high-power CMOS-compatible thulium-doped distributed feedback and distributed Bragg reflector lasers with single-mode output powers up to 267 and 387 mW, and slope efficiencies of 14% and 23%, respectively. More than 70 dB side-mode suppression ratio is achieved for both lasers. This work extends the applicability of silicon photonic microsystems in the 2 μm region., Published by Soc., Washington, DC

Conference on Lasers and Electro-Optics : [Proceedings] - OSA Washington, D.C., 2017. - ISBN 978-1-943580-27-9 - doi:10.1364/CLEO_SI.2017.STu4J.7 CLEO: Science and Innovations, CLEO, San Jose, California, USA, 14 May 2017 - 19 May 2017; Washington, D.C. : OSA, OSA technical digest (online), 2 pp. (2017). doi:10.1364/CLEO_SI.2017.STu4J.7, We demonstrate an octave spanning coherent supercontinuum generated in a silicon waveguide covering the near to shortwave IR (SWIR) region. The measured -20 dB SC span ranges from 1.124 μm to 2.4 μm., Published by OSA, Washington, D.C.

An integrated artificial fast saturable absorber at 1.9 μm is demonstrated in a CMOS-compatible process. It is based on the Kerr effect in a nonlinear Mach-Zehnder Interferometer using silicon nitride waveguides embedded in SiO 2 .

A fully-integrated Q-switched laser is demonstrated at 1.9μm using thulium-doped aluminum oxide waveguides, with the potential for achieving an on-chip passively mode-locked laser. All components of the laser are fabricated in a CMOS-compatible silicon photonics process.

The spontaneous emission lifetime in Al 2 O 3 :Tm3+ waveguides is measured to be 568 ± 48 μs, using a frequency-domain method. The method is studied and verified in Er3+-doped silica fiber, yielding a measured lifetime of 9.73 ± 0.08 ms.

We report a high power CMOS-compatible thulium-doped distributed feedback laser with single-mode output power up to 267 mW, 14% slope efficiency, and >70dB side mode suppression ratio.

This paper presents the design and experimental analysis of a system architecture for 60-GHz broadband wireless communications. The architecture uses a dual-wavelength photonic signal source based on stimulated Brillouin scattering to generate the millimeter-wave carrier signal through photomixing. Data is encoded onto the optical signals and is upconverted directly to the millimeter-wave carrier through a photonic upconversion process, which does not require electronic upconversion. The data is encoded onto one optical wavelength in a single-sideband fashion, which affords significant dispersion tolerance over long remoting distances compared with standard double-sideband modulation. The prototype architecture was tested at ranges of 2-30 m indoors and 78 m outdoors, demonstrating a building-to-building link. Binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation formats were tested, with BPSK data rates up to 3 Gb/s and QPSK data rates up to 2.64 Gb/s. Good bit-error ratios are demonstrated as a function of received power and range for a fixed transmit power.

An in-depth analysis of the phase noise of a microwave oscillator based on dual-wavelength stimulated Brillouin scattering is presented. The system is investigated under the influence of injection-locking and also in a regenerative-frequency configuration. Measurements from 1 to 25 GHz demonstrate the invariance of the phase-noise spectrum with respect to carrier frequency. Phase noise of -90 dBc/Hz at 1-kHz offset is shown, and is compared to the best reported performance of optical heterodyne sources. The frequency stability of the oscillator is also discussed.

Double-chirped Bragg gratings for use in dispersion compensation are demonstrated using silicon nitride waveguides, on a silicon photonics platform that allows for 3-D integration of photonic devices with CMOS electronics.

Laser sources in the mid-infrared are of great interest due to their wide applications in detection, sensing, communication and medicine. Silicon photonics is a promising technology which enables these laser devices to be fabricated in a standard CMOS foundry, with the advantages of reliability, compactness, low cost and large-scale production. In this paper, we demonstrate a holmium-doped distributed feedback laser monolithically integrated on a silicon photonics platform. The Al2O3:Ho3+ glass is used as gain medium, which provides broadband emission around 2 µm. By varying the distributed feedback grating period and Al2O3:Ho3+ gain layer thickness, we show single mode laser emission at wavelengths ranging from 2.02 to 2.10 µm. Using a 1950 nm pump, we measure a maximum output power of 15 mW, a slope efficiency of 2.3% and a side-mode suppression ratio in excess of 50 dB. The introduction of a scalable monolithic light source emitting at > 2 µm is a significant step for silicon photonic microsystems operating in this highly promising wavelength region.

Light 7(1), 17131 (2018). doi:10.1038/lsa.2017.131, Efficient complementary-metal-oxide-semiconductor-based nonlinear optical devices in the near infrared are in strong demand. Due to two-photon absorption in silicon, however, much nonlinear research is shifting towards unconventional photonics platforms. In this work, we demonstrate the generation of an octave-spanning coherent supercontinuum in a silicon waveguide covering the spectral region from the near- to shortwave-infrared. With input pulses of 18 pJ in energy, the generate d signal spans the wavelength range from the edge of the silicon transmission window, approximately 1.06 μm to beyond 2.4μm, with a −20 dB bandwidth covering 1.124 - 2.4μm. An octave-spanning supercontinuum was also observed at the energy levels as low as 4 pJ (-35 dB bandwidth). We also measured the coherence over an octave, obtaining $|g_{12}^{(1)}(\lambda)|$ in good agreement with the simulations. Additionally, we demonstrate optimization of the third-or der dispersion of the waveguide to strengthen the dispersive wave and discuss the advantage of having a soliton at the long wavelength edge of an octave-spanning sign al for nonlinear applications. This research paves the way for applications, such as chip -scale precision spectroscopy, optical coherence tomography, optical frequency metrology, frequency synthesis and wide-band wavelength division multiplexing in the telecom window., Published by Nature Publishing Group, London

Integrated components necessary for a mode-locked laser are demonstrated on a platform that allows for monolithic integration with active silicon photonics and CMOS circuitry. CW lasing and Q-switched mode-locking are observed in the full structures.

Long-term stable timing distribution over a 3.5-km polarization maintaining (PM) fiber link using balanced optical cross-correlators (BOC) for optical-to-optical synchronization is demonstrated. Remote laser synchronization over 40 hours showed a residual timing jitter and drift of 2.5 fs for the whole locking period and only 1.1 fs integrated from 100 μHz to 1 MHz. This result corresponds to the lowest jitter and drift achieved to date for a multi-km fiber link and remote timing synchronization operating continuously over multiple days.

Long-term stable, sub-femtosecond timing distribution over a 1.2-km polarization-maintaining (PM) fiber-optic link using balanced optical cross-correlators for link stabilization is demonstrated. Novel dispersion-compensating PM fiber was developed to construct a dispersion-slope-compensated PM link, which eliminated slow timing drifts and jumps previously induced by polarization mode dispersion in standard single-mode fiber. Numerical simulations of nonlinear pulse propagation in the fiber link confirmed potential sub-100-as timing stability for pulse energies below 70 pJ. Link operation for 16 days showed ~0.6 fs RMS timing drift and during a 3-day interval only ~0.13 fs drift, which corresponds to a stability level of 10(-21).

We present here key technologies for an all-optical timing distribution system with sub-femtosecond precision. Timing distribution over a 1.2-km polarization-maintaining, fiber-optic link using balanced optical cross-correlators (BOC) for link stabilization was demonstrated for 16 days with 0.6 fs RMS timing drift and during a 3-day interval only 0.13 fs drift. Jitter characterization of two identical commercial femtosecond lasers using the BOC method verified sub-100-as timing jitter for frequencies above than 1 kHz. Preliminary operation of a fiber-coupled, hybrid-integrated BOC using periodically-poled KTiOPO4 (PPKTP) waveguides indicate great potential for improved BOC timing sensitivities and overall system efficiency and robustness.

A 1.2-km timing-stabilized, polarization-maintaining fiber link based on balanced optical cross-correlation was demonstrated with ∼0.9 fs RMS timing jitter over 16 days and ∼0.2 fs RMS timing jitter over 3 days.

A hybrid integrated balanced optical cross-correlator using continuous PPKTP channel waveguides and dielectric coatings is demonstrated for use in femtosecond and sub-femtosecond timing applications.

In this work, an analog-to-digital converter architecture utilizing the precision timing and wide bandwidth capability of photonics technology and the versatility and efficient data processing of compressive sampling techniques is explored. The generation, control and transfer of the precision timing and sampled resolution to the final digitization stage is a key technical challenge to realizing the potential of the architecture; involving significant component, sub-system and interface developments as well as optimizations to capitalize on the unique benefits of compressive sampling techniques. Concept demonstration experiments, device and subsystem requirements and potential applications will be discussed.

We discuss the potential benefits of combining the high speeds, broad modulation bandwidths and precision timing of photonic sampling techniques with recent advances in the theory and algorithms of compressive sampling.

A frequency-independent low-phase-noise microwave source is demonstrated via frequency division of a photonic frequency sythesizer.

A 60 GHz free-space communication system is demonstrated with broadband data encoding and a novel photonic millimeter-wave carrier generator. A 60.8 GHz carrier signal is generated by photomixing two optical subcarriers sourced from a dual-wavelength laser based on stimulated Brillouin scattering in optical fiber. Data is baseband encoded onto a single optical subcarrier using an optical phase modulator and photonically upconverted to the 60.8 GHz RF carrier. Data rates of 1.65 Gbps are demonstrated, with the goal of facilitating wireless personal area networking based on a fiber-distributed network architecture. The implemented encoding scheme is intrinsically dispersion tolerant, enabling remoting of signals over long distances between a base station and wireless access nodes. The prototype link was tested in an indoor setting at ranges up to 30 m using a low-gain transmitter antenna and high-gain receiver antenna. Good bit-error ratios are demonstrated as a function of range. A building-to-building communication link, with long-distance fiber distribution to the wireless transmitter, is demonstrated at a range of 78 m.

Frequency downconversion is an essential part of many RF systems and is particularly important in microwave to digital systems. Photonic technology offers numerous potential benefits including very broad bandwidths, low loss signal transport over optical fiber, and various physical advantages related to fiber transport including electromagnetic interference immunity and signal multiplexing. The key to realizing these advantages is the efficient conversion from the electrical-to-optical and optical-to-electrical domain. In this paper, system design issues are discussed to take full advantage of recently available photonic technology including photonic downconversion and downsampling. These concepts are discussed and demonstrated within the context of two promising photonic microwave to digital architectures.

The use of phase modulation in lieu of the typical amplitude modulator in an optoelectronic oscillator (OEO) has not yet been extensively investigated. In this paper we present the first experimental demonstration of a phase-modulated OEO using a fiber delay-line demodulator with balanced detection. Preliminary phase noise and frequency stability measurements are also demonstrated.

Free -space transport of 60 GHz band RF signals is demonstrated. The RF carrier is generated from the beat frequency in a dual -wavelelength fiber laser. Optical phase modulation data is photonically converted to RF phase modulation data for transport.

We demonstrate suppression of relative intensity noise by >25 dB for the primary output of a stimulated Brillouin fiber laser by operating above the threshold for second-order stimulated Brillouin scattering.

We present phase-noise measurements of microwave signals generated by our dual-wavelength Brillouin fiber laser that approach the performance of commercially available frequency synthesizers. We demonstrate the invariance of the phase-noise spectrum with respect to carrier frequency. Methods for further improving performance are also discussed.

The accurate collection and assessment of information contained in the electromagnetic (EM) environment is crucial to the success of a variety of avionic systems. The nature of the information to be collected and platform demanding multi-functionality requires these systems to simultaneously cover many RF and microwave bands and to deliver accurate (post-processed) information. Additionally, the increasing demands for higher system performance and increased versatility result in the reliance on digital signal processing (DSP) and consequently the high fidelity conversion of the analog microwave input signals to digital representations. In this paper, we seek to classify input waveforms representing the key classes of analog signals and identify desired output information classes. We will also provide guidance for matching recently demonstrated photonic microwave-to-digital architectures to the input waveform/output time-spectra reconstruction scenarios. In addition, we will cover the performance parameters and the crucial microwave-optical-electrical-digital interface issues.

We demonstrate the generation of microwave and millimeter-wave frequencies from 26 to 100 GHz by heterodyning the output modes of a dual-wavelength fiber laser based on stimulated Brillouin scattering. The output frequency is tunable in steps of 10.3 MHz, equal to the free spectral range of the resonator. The noise properties of the beat frequency indicate a microwave linewidth of

We discuss recently developed techniques for photonic analog-to-digital conversion based on nonuniform sampling. We have experimentally validated this approach, demonstrating high resolution, alias-free signal reconstruction at carrier frequencies up to 20 GHz.

We report recent progress made in a complete fiber-optic, high-precision, long-term stable timing distribution system for synchronization of next generation X-ray free-electron lasers. Timing jitter characterization of the master laser shows less than 170-as RMS integrated jitter for frequencies above 10 kHz, limited by the detection noise floor. Timing stabilization of a 3.5-km polarization-maintaining fiber link is successfully achieved with an RMS drift of 3.3 fs over 200 h of operation using all fiber-coupled elements. This all fiber-optic implementation will greatly reduce the complexity of optical alignment in timing distribution systems and improve the overall mechanical and timing stability of the system.

We present a fiber-coupled balanced optical cross-correlator using waveguides in periodically-poled KTiOPO4 (PPKTP). The normalized conversion efficiency of the waveguide device is measured to be η0 = 1.02% / [W·cm2], which agrees well with theory and simulation. This result represents an expected improvement of a factor of 20 over previous bulk-optic devices. The sensitivity of the cross-correlator is characterized and shown to be comparable to the free-space bulk-optic version, with the potential for significant performance enhancements in the future.

This article presents the underlying rationale for a theory of foreign policy dynamics, and is the second part of a two‐part series which specifies a theoretical perspective for explaining the exchanges between nations. The task of the first paper was to discuss the substantive thrust of the research, and to give a view of the Monte Carlo simulation which lies at its core. The theory deals with the relevance of such concepts as reciprocity, uncertainty, third party effects, bureaucratic politics and domestic events for explaining foreign policy. This article provides the axioms which structure our theory and formal theorems that follow from these axioms.

This article is the first of a two‐part series on the development of a theoretical perspective for explaining foreign policy exchanges between nations. The first paper discusses the substantive thrust of the research, and presents an overview of the Monte Carlo computer simulation which lies at its core. The theory largely built on the body of research on events data analysis, attempts to assimilate the set of findings arising from this research into a single integrated theory. Basic assumptions of the theory derived from cybernetics and information theory are outlined, and the simulation rules used in the research are presented. These provide the basis for a later paper (to appear in Vol. 2, No. 2, 1975) that presents a formal mathematical theory which seeks to explain foreign policy exchanges.

This paper is part of a research project attempting to develop long range forecasting models for foreign policy planning. An attempt will be made to analyze the goals of five nations: Iraq, Iran, Algeria, Libya and Saudi Arabia. The relevance of this enterprise to foreign policy planning is that the goals of a state determine what it would be willing to give up in negotiations and what kind of bait can be used to strike bargains with that state. A goal will be understood to mean a desired state of affairs. A nation's goals are those of the top decision-making elite in the nation. It is assumed that to some extent the elite is a coherent group and the goal set is uniform for all members. The desired states may be either those which can be attained only with some change or those which are already achieved and only need to be preserved. Goals may be either specific or general quantitative targets or open-ended growth desires. Goals may be either ends in themselves or means to other goals or both.