Acousto-optic and opto-acoustic modulation in piezo-optomechanical circuits

Acoustic wave devices provide a promising chip-scale platform for efficiently coupling radio frequency (RF) and optical fields. Here, we use an integrated piezo-optomechanical circuit platform that exploits both the piezoelectric and photoelastic coupling mechanisms to link 2.4 GHz RF waves to 194 THz (1550 nm) optical waves, through coupling to propagating and localized 2.4 GHz acoustic waves. We demonstrate acousto-optic modulation, resonant in both the optical and mechanical domains, in which waveforms encoded on the RF carrier are mapped to the optical field. We also show opto-acoustic modulation, in which the application of optical pulses gates the transmission of propagating acoustic waves. The time-domain characteristics of this system under both pulsed RF and pulsed optical excitation are considered in the context of the different physical pathways involved in driving the acoustic waves, and modeled through the coupled mode equations of cavity optomechanics.Comment: 8 pages, 6 figure

Stably accessing octave-spanning microresonator frequency combs in the soliton regime

Microresonator frequency combs can be an enabling technology for optical frequency synthesis and timekeeping in low size, weight, and power architectures. Such systems require comb operation in low-noise, phase-coherent states such as solitons, with broad spectral bandwidths (e.g., octave-spanning) for self-referencing to detect the carrier-envelope offset frequency. However, stably accessing such states is complicated by thermo-optic dispersion. For example, in the Si3N4 platform, precisely dispersion-engineered structures can support broadband operation, but microsecond thermal time constants have necessitated fast pump power or frequency control to stabilize the solitons. In contrast, here we consider how broadband soliton states can be accessed with simple pump laser frequency tuning, at a rate much slower than the thermal dynamics. We demonstrate octave-spanning soliton frequency combs in Si3N4 microresonators, including the generation of a multi-soliton state with a pump power near 40 mW and a single-soliton state with a pump power near 120 mW. We also develop a simplified two-step analysis to explain how these states are accessed in a thermally stable way without fast control of the pump laser, and outline the required thermal properties for such operation. Our model agrees with experimental results as well as numerical simulations based on a Lugiato-Lefever equation that incorporates thermo-optic dispersion. Moreover, it also explains an experimental observation that a member of an adjacent mode family on the red-detuned side of the pump mode can mitigate the thermal requirements for accessing soliton states

Single-molecule fluorescence measurement of local polymer properties

The composite interphase is a vital region whose properties are notoriously difficult to measure. Fluorescent molecules can act as uniquely sensitive probes of their local environment, displaying changes in fluorescence lifetime, polarization anisotropy, and spectral shifts, all of which could provide useful information about this region. A prerequisite to making use of this information is the ability to determine the positions and orientations of single molecules accurately and precisely so that molecular behavior can be correlated with material structure. Here, we show the ability to determine the position and orientation of single molecules with an uncertainty of approximately 9 nm and a few degrees, respectively, allowing us to resolve features as small as 20 nm. Another challenge is to introduce probe fluorophores with a sufficient density to capture local material property variations in detail, but without perturbing the property of interest. We solve this problem by means of lithographically-fabricated test structures. These enable us to produce thousands of essentially identical replicas of a feature, the image data from which can be overlaid and integrated. In this way, a sparse fluorophore distribution can still yield a spatially-dense data set. Additional complications involve the interaction of fluorophore emission with variations in the local refractive index of the sample. We address these by fabricating and measuring nanoscale test structures that vary fluorophore environments in a precisely-controlled fashion. In this talk, I will describe our unique, wide-field, single-molecule fluorescence microscope, that allows us to measure the position, orientation, lifetime, and spectrum of fluorescent probes distributed within lithographically-fabricated analogs of real composite structures, and our progress in correlating single-molecule behavior with local material properties Please click Additional Files below to see the full abstract

Subnanometer traceability of localization microscopy

In localization microscopy, subnanometer precision is possible but supporting accuracy is challenging, and no study has demonstrated reliable traceability to the International System of Units (SI). To do so, we measure the positions of nanoscale apertures in a reference array by traceable atomic-force microscopy, creating a master standard. We perform correlative measurements of this standard by optical microscopy, correcting position errors from optical aberrations by a Zernike calibration. We establish an uncertainty field due to localization errors and scale uncertainty, with regions of position traceability to within a 68 % coverage interval of +/- 1.0 nm. These results enable localization metrology with high throughput, which we apply to measure working standards, validating the subnanometer accuracy of lithographic pitch

A lateral nanoflow assay reveals nanoplastic fluorescence heterogeneity

Colloidal nanoplastics present technological opportunities, environmental concerns, and measurement challenges. To meet these challenges, we develop a lateral nanoflow assay from sample-in to answer-out. Our measurement system integrates complex nanofluidic replicas, super-resolution optical microscopy, and comprehensive statistical analyses to measure polystyrene nanoparticles that sorb and carry hydrophobic fluorophores. An elegant scaling of surface forces within our silicone devices hydrodynamically automates the advection and dominates the diffusion of the nanoparticles. Through steric interaction with the replica structure, the particle size distribution reciprocally probes the unknown limits of replica function. Multiple innovations in the integration and calibration of device and microscope improve the accuracy of identifying single nanoparticles and quantifying their diameters and fluorescence intensities. A statistical model of the measurement approaches the information limit of the system, discriminates size exclusion from surface adsorption, and reduces nonideal data to return the particle size distribution with nanometer resolution. A Bayesian statistical analysis of the dimensional and optical properties of single nanoparticles reveals their fundamental structure-property relationship. Fluorescence intensity shows a super-volumetric dependence, scaling with nanoparticle diameter to nearly the fourth power and confounding basic concepts of chemical sorption. Distributions of fluorescivity - the product of the number density, absorption cross section, and quantum yield of an ensemble of fluorophores - are ultrabroad and asymmetric, limiting ensemble analysis and dimensional or chemical inference from fluorescence intensity. These results reset expectations for optimizing nanoplastic products, understanding nanoplastic byproducts, and applying nanoplastic standards

An Integrated-Photonics Optical-Frequency Synthesizer

Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify that the fractional-frequency instability of the integrated photonics synthesizer matches the $7.0*10^{-13}$ reference-clock instability for a 1 second acquisition, and constrain any synthesis error to $7.7*10^{-15}$ while stepping the synthesizer across the telecommunication C band. Any application of an optical frequency source would be enabled by the precision optical synthesis presented here. Building on the ubiquitous capability in the microwave domain, our results demonstrate a first path to synthesis with integrated photonics, leveraging low-cost, low-power, and compact features that will be critical for its widespread use.Comment: 10 pages, 6 figure

Released micromachined beams utilizing laterally uniform porosity porous silicon

© 2014, Sun et al.; licensee Springer. Abstract: Suspended micromachined porous silicon beams with laterally uniform porosity are reported, which have been fabricated using standard photolithography processes designed for compatibility with complementary metal-oxide-semiconductor (CMOS) processes. Anodization, annealing, reactive ion etching, repeated photolithography, lift off and electropolishing processes were used to release patterned porous silicon microbeams on a Si substrate. This is the first time that micromachined, suspended PS microbeams have been demonstrated with laterally uniform porosity, well-defined anchors and flat surfaces. PACS: 81.16.-c; 81.16.Nd; 81.16.R