Tunable SNAP Microresonators via Internal Ohmic Heating

We demonstrate a thermally tunable Surface Nanoscale Axial Photonics (SNAP) platform. Stable tuning is achieved by heating a SNAP structure fabricated on the surface of a silica capillary with a metal wire positioned inside. Heating a SNAP microresonator with a uniform wire introduces uniform variation of its effective radius which results in constant shift of its resonance wavelengths. Heating with a nonuniform wire allows local nanoscale variation of the capillary effective radius, which enables differential tuning of the spectrum of SNAP structures as well as creation of temporary SNAP microresonators that exist only when current is applied. As an example, we fabricate two bottle microresonators coupled to each other and demonstrate differential tuning of their resonance wavelengths into and out of degeneracy with precision better than 0.2 pm. The developed approach is beneficial for ultraprecise fabrication of tunable ultralow loss parity-time symmetric, optomechanical, and cavity QED devices

Crowdsourcing Coordination: A Review and Research Agenda for Crowdsourcing Coordination Used for Macro-tasks

Crowdsourcing has become a widely accepted approach to leveraging the skills and expertise of others to accomplish work. Despite the potential of crowdsourcing to tackle complex problems, it has often been used to address simple micro-tasks. To tackle more complex macro-tasks, more attention is needed to better comprehend crowd coordination. Crowd coordination is defined as the synchronization of crowd workers in an attempt to direct and align their efforts in pursuit of a shared goal. The goal of this chapter is to advance our understanding of crowd coordination to tackle complex macro-tasks. To accomplish this, we have three objectives. First, we review popular theories of coordination. Second, we examine the current approaches to crowd coordination in the HCI and CSCW literature. Finally, the chapter identifies shortcomings in the literature and proposes a research agenda directed at advancing our understanding of crowd coordination needed to address complex macro-tasks.National Science Foundation grant CHS-1617820Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150620/1/Kim and Robert 2019 Preprint Chapter 2.pdfDescription of Kim and Robert 2019 Preprint Chapter 2.pdf : Preprint Versio

Crowdsourcing Controls: A Review and Research Agenda for Crowdsourcing Controls Used for Macro-tasks

Crowdsourcing—the employment of ad hoc online labor to perform various tasks—has become a popular outsourcing vehicle. Our current approach to crowdsourcing—focusing on micro-tasks—fails to leverage the potential of crowds to tackle more complex problems. To leverage crowds to tackle more complex macro tasks requires a better comprehension of crowdsourcing controls. Crowdsourcing controls are mechanisms used to align crowd workers’ actions with predefined standards to achieve a set of goals and objectives. Unfortunately, we know very little about the topic of crowdsourcing controls directed at accomplishing complex macro tasks. To address issues associated with crowdsourcing controls formacro-tasks, this chapter has several objectives. First, it presents and discusses the literature on control theory. Second, this chapter presents a scoping literature review of crowdsourcing controls. Finally, the chapter identifies gaps and puts forth a research agenda to address these shortcomings. The research agenda focuses on understanding how to employ the controls needed to perform macro-tasking in crowds and the implications for crowdsourcing system designers.National Science Foundation grant CHS-1617820Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150493/1/Robert 2019 Preprint Chapter 3.pdfDescription of Robert 2019 Preprint Chapter 3.pdf : PrePrint Versio

Nonlinear propagation of a-few-optical-cycle pulses in a photonic crystal fiber-experimental and theoretical studies beyond the slowly varying-envelope approximation

The evolution of spectral and temporal profiles of 4.5 optical-cycle pulses propagating near zero-dispersion wavelength (ZDW) in a photonic crystal fiber is investigated experimentally and theoretically beyond the slowly varying-envelope approximation. The excellent agreement between the experimental and theoretical results suggests that the observed gap in the spectral profile, the most distinctive feature, originates from the self-steepening effect. This effect intensifies the spectral component shorter than the ZDW with the decay of higher order solitons and consequently induces the intrapulse four-wave mixing (FWM). As a result, the anti-Stokes and Stokes components produced by the FWM enables us to generate a supercontinuum from 480 to 1020 nm

Ultrahigh-resolution optical coherence tomography by broadband continuum generation from a photonic crystal fiber.

We have developed an ultrahigh-resolution optical coherence tomographic system in which broadband continuum generation from a photonic crystal fiber is used to produce high longitudinal resolution. Longitudinal resolution of 1.3-microm has been achieved in a biological tissue by use of continuum light from 800 to 1400 nm. The system employed a dynamic-focusing tracking method to maintain high lateral resolution over a large imaging depth. Subcellular imaging is demonstrated

Amplitude noise on supercontinuum generated in microstructure fiber: Measurements and simulations

Supercontinua generated in microstructure fiber can exhibit significant excess amplitude noise. We present experimental and numerical studies of the origins of this excess noise and its dependence on the input laser pulse parameters.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Experimental studies of the coherence of microstructure-fiber supercontinuum

Abstract: The phase coherence of supercontinuum generation in microstructure fiber is quantified by performing a Young's type interference experiment between independently generated supercontinua from two separate fiber segments. Analysis of the resulting interferogram yields the wavelength dependence of the magnitude of the mutual degree of coherence, and a comparison of experimental results with numerical simulations suggests that the primary source of coherence degradation is the technical noise-induced fluctuations in the injected peak power

Soliton generation via intrapulse stimulated Raman scattering in photonic crystal fibers: Experimental and numerical investigations

We investigate femtosecond pulse propagation in photonic crystal fiber, reporting the generation of tunable femtosecond soliton pulses. For sufficiently broad spectral content, stimulated Raman scattering transfers energy from the higher frequency spectral components to lower frequencies, resulting in a continuous self-frequency shift to longer wavelengths. Power dependent spectral analysis reveals a well-formed soliton at peak powers exceeding 100 W. Background-free intensity autocorrelation measurements confirm soliton formation with a duration of < 90 fs and with an energy conversion efficiency of 60%. Numerical solutions were performed based on a generalized nonlinear Schrödinger equation that included the effects of dispersion, self-steepening, optical shock formation, self-phase modulation and stimulated Raman scattering. The resulting spectra from the simulations are in excellent agreement with the measured spectra, and are consistent with the intensity autocorrelation measurements.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis

We stabilized the carrier-envelope phase of the pulses emitted by a femtosecond mode-locked laser by using the powerful tools of frequency-domain laser stabilization. We confirmed control of the pulse-to-pulse carrier-envelope phase using temporal cross correlation. This phase stabilization locks the absolute frequencies emitted by the laser, which we used to perform absolute optical frequency measurements that were directly referenced to a stable microwave clock. Progress in femtosecond pulse generation has made it possible to generate optical pulses that are only a few cycles in duration (1–4). This has resulted in rapidly growing interest in controlling the phase of the underlying carrier wave with respect to the envelope (1, 5–7). The absolute carrier phase is normally not important in optics; however, for such ultrashort pulses, i