Science and Technology with Optical Frequency Combs

1. Introduction Frequency combs have been investigated in the laboratory over the course of the last 25 years in a wide range of implementations and applications including but not limited to precision metrology, optical atomic clocks, LIDAR, low-phase-noise RF generation, and precision spectroscopy [1]. While the Nobel prize winning technology of frequency combs have shown their usefulness in a variety of applications, there have been few demonstrations of this technology in real-world applications [2, 3]. Here we present a mode-locked oscillator that has been designed to be environmentally robust and low cost, while maintaining suitability for use in frequency comb applications. Vescent Photonics is designing and manufacturing fiber mode-locked oscillators and frequency combs for government customers whose application deployments include satellites and terrestrial moving platforms. These designs allow for repetition rate matching at the time of manufacture, which is an important consideration for integration of this technology into optical atomic clocks, dual comb spectroscopy, and low-phase-noise radio frequency generation. Vescent currently is manufacturing oscillators at 100 and 200 MHz repetition rates, and these designs could be modified to give repetition rates between 80 and 250 MHz. While performance and environmental robustness are necessary metrics for real-world applications of frequency combs, the cost of these devices can also be a barrier to wide-spread deployment. Vescent Photonics is diligently working on optimizing all three parameters (performance, environmental robustness, and cost) to bring a deployable mode-locked laser and frequency comb solution to market. 2. Mode-locked oscillator performance The compact mode-locked oscillators presented here have been designed to be low-cost, low-volume, highperformance, and environmentally robust for field-deployed applications. Figure 1a shows the mechanical enclosure for the fiber oscillator measuring 0.12 L (10.75 cm x 6.35 cm x 1.72 cm) in volume; it should be noted that pump diodes have not been included in this packaging due to thermal considerations. An enclosure for a frequency comb system (optic only) has also been designed with a volume of 0.62 L (19.05 cm x 11.30 cm x 2.86 cm). Two length actuators are included in this design; a fast PZT with >200 kHz bandwidth that allows 150 Hz of tuning on a 100 MHz repetition rate, and slow temperature control of the fiber with a ~10 s thermal time constant and >40 kHz of tuning on a 100 MHz repetition rate. The oscillator optical spectrum is included in Figure 1b. Average optical powers out of the oscillators are on the order of a few milliwatts, and pulses are close to transform limited (~250 fs). Erbium-doped fiber amplifiers and pulse compression stages are routinely added to the oscillator outputs to achieve average powers >200 mW and pulse durations <100 fs. While these parameters are useful for a wide range of mode-locked laser applications, it also allows the detection of the carrier envelope offset frequency ( , a fundamental comb parameter) in an f-2f interferometer with greater than 40 dB SNR in 300 kHz resolution bandwidth (Figure 1c). To show suitability of these fiber mode-locked oscillators in frequency comb applications, fractional Allan Deviations of the in-loop stabilized signals have been included in Figure 1d where the absolute frequency deviations have been divided by the distance between the frequency comb lock points. Typical optical clock performance has also been plotted, where the performance of the locks is more than suitable for this application. 3. Summary A compact, low-cost, environmentally robust mode-locked oscillator has been shown to be suitable for frequency comb experiments. Detection and stabilization of the fundamental comb parameters is suitable for optical atomic clocks, as well as a host of real-world frequency comb applications including dual comb spectroscopy, low phase noise RF generation, and optical metrology.

A novel approach to the generation of an optical frequency comb with a widely tunable center wavelength and comb spacing based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The OEO is implemented using a polarization modulator (PolM), a phase-shifted fiber Bragg grating (PS-FBG), and a photodetector (PD). The PolM is a special phase modulator that supports phase modulation along the two principal axes with opposite modulation indexes. The joint operation of the PolM, the PS-FBG, and the PD corresponds to a frequency-tunable microwave photonic bandpass filter. When the output from the PD is fed back to the PolM, the OEO starts to oscillate and the oscillation frequency can be tuned by tuning the center frequency of the microwave photonic bandpass filter through tuning the optical wavelength. The optical comb is then generated by tapping part of the optical signal from the PolM and sending it to a second PolM. The joint operation of the two PolMs generates an optical comb with the comb spacing tunable by tuning the center frequency of the microwave photonic filter. Through introducing a second wavelength into the OEO, a duplicated optical comb at the second wavelength is generated. An experiment is performed. An optical frequency comb with tunable frequency spacing from 6.6 to 15.3 GHz and a tunable center wavelength from 1500 to 1580 nm is generated.

The Clean Air Mercury Rule (CAMR) which was published in the Federal Register on May 18, 2005, requires that calibration of mercury continuous emissions monitors (CEMs) be performed with NIST-traceable standards. Western Research Institute (WRI) is working closely with the Electric Power Research Institute (EPRI), the National Institute of Standards and Technology (NIST), and the Environmental Protection Agency (EPA) to facilitate the development of the experimental criteria for a NIST traceability protocol for dynamic elemental mercury vapor generators. The traceability protocol will be written by EPA. Traceability will be based on the actual analysis of the output of each calibration unit at several concentration levels ranging from about 2-40 ug/m{sup 3}, and this analysis will be directly traceable to analyses by NIST using isotope dilution inductively coupled plasma/mass spectrometry (ID ICP/MS) through a chain of analyses linking the calibration unit in the power plant to the NIST ID ICP/MS. Prior to this project, NIST did not provide a recommended mercury vapor pressure equation or list mercury vapor pressure in its vapor pressure database. The NIST Physical and Chemical Properties Division in Boulder, Colorado was subcontracted under this project to study the issue in detail and to recommend a mercury vapormore » pressure equation that the vendors of mercury vapor pressure calibration units can use to calculate the elemental mercury vapor concentration in an equilibrium chamber at a particular temperature. As part of this study, a preliminary evaluation of calibration units from five vendors was made. The work was performed by NIST in Gaithersburg, MD and Joe Rovani from WRI who traveled to NIST as a Visiting Scientist.« less

A Look at its Past Decade and a Gaze towards its Future. As the National Metrology Institute (NMI) for the United States, the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards, has provided measurement services, both calibrations and reference materials, for more than 100 years. Through these services, our customers have benefitted from our measurement capabilities and expertise in many areas, including amount of substance; dimensional metrology; electricity and magnetism; ionizing radiation; mass and related quantities; photometry and radiometry; thermodynamics; and time and frequency. NIST’s customers have also had access to some of the lowest measurement uncertainties available and a dependable way to establish traceability to the International System of Units (SI) [http://www.nist.gov/pml/wmd/metric/si-units.cfm].In response to the signing of the International Committee for Weights and Measures (CIPM) Mutual Recognition Arrangement (MRA), NIST first established an institution-wide quality system for the measurement services 10 years ago [http://www.bipm.org/en/cipm-mra/objectives.html]. NIST’s Quality System for Measurement Services has advanced the quality of service and measurements we provide our customers by fostering an environment in which NIST management and staff work towards continual improvement in the development and delivery of NIST measurement services. This paper describes NIST’s Quality System for the Measurement Services and its relevance to international standards of quality, such as the International Organization for Standardization and the International Electrotechnical Commission (ISO/IEC) 17025 standard and ISO Guide 34 [http://www.nist.gov/nistqs/]. It also provides a history of this quality system and a glimpse of future goals for improving its implementation.

Standards provide critical benefits across a wide variety of contexts, including safety and health, environmental protection, and quality of products and services. However, while these benefits are generally acknowledged, estimating the social and economic value of standards and determining how specific entities and activities influence their development require careful analysis. In October of 2018, the National Institute of Standards and Technology (NIST) asked the RAND Corporation to estimate the benefit of NIST’s research contributing to particular fire safety standards. The original objectives of the project were to (1) document the role of the NIST in the standards development process, (2) estimate the value these standards provide to society, and (3) thereby inform the economic value of NIST’s contribution to these standards. This report presents results for the first two objectives. Given that NIST’s contribution is one of several inputs combining to create these standards, NIST’s share of the credit for their value could not be quantified. Our analysis focused on case studies in standards for home smoke alarms and for protecting structures at the wildland-urban interface (WUI). Our analysis draws on a wide variety of qualitative and quantitative methods to holistically describe the impacts of these standards and NIST’s role in their development. The intended audience of this report includes those who work on fire safety research, fire safety standards, building codes, and technology transfer. The conclusions presented here may also be of interest for broader resource allocation and federal budget justification purposes. Finally, this report was written to be accessible to any interested members of the general public.

Optical frequency combs have been explored in different applications from optical frequency measurements to optical communications. OFCs can be formed using numerous techniques such as optical modulation, laser mode locking and optical fiber recirculating loops. An optical frequency comb generator based on an optical fiber recirculation loop operating with a Mach-Zehnder modulator was experimentally investigated using different types of amplifiers as gain media. The idea is to compare the use of semiconductor optical amplifiers (SOAs) and erbium-doped fiber amplifiers (EDFAs) and their efficiency in aiding or contributing on the generation of spectral lines. The process efficiency associated with nonlinear effects, specially four-wave mixing, is the main advantage of using SOAs over EDFAs. Under the best operational conditions, an optical comb with up to 30 lines and spacing around 20 GHz was obtained by a SOA-based loop, where an ultralong SOA was used for the first time in such an application.

We show, both experimentally and theoretically, that a slave laser injected with an optical frequency comb can undergo two distinct locking mechanisms, both of which decrease the output optical comb's frequency spacing. We report that, for certain detuning and relative injection strengths, slave laser relaxation oscillations can become undamped and lock to rational frequencies of the optical comb spacing, creating extra comb tones by nonlinear dynamics of the injected laser. We also study the frequency locking of the slave laser at detunings in between the injected comb lines, which add the slave laser's frequency to the comb. Our results demonstrate the effect of the α parameter and stability of the locked states and indicate how the frequency of the relaxation oscillations affect both of these locking mechanisms. These optical locking mechanisms can be applied to regenerate or multiply optical combs.

In this paper, we report on the polarization dynamics of a 1550 nm vertical-cavity surface-emitting laser (VCSEL) under gain switching regime. We focus our analysis on the resulting optical frequency combs associated with the main and suppressed polarization modes. Measurement of the parameters characterizing the polarization behavior of our single-transverse mode VCSEL is performed from the analysis of high-resolution optical spectra. An extension of the spin-flip rate model to include nonlinear carrier recombination is developed. An analysis of polarization-resolved dynamics is performed by using the previous model with the measured VCSEL parameters. We show that two orthogonally polarized combs are generated that combine to produce a wider overall optical comb. We analyze the dependence of combs on the amplitude and frequency of the modulation. Our results are in agreement with experiments reported by Prior et al. We also analyze the dependence of the combs on the linear dichroism of the VCSEL We show that the change of this dichroism results in bistability between the two orthogonally polarized combs.

In the fall of 2019, the National Institute of Standards and Technology (NIST) funded threes studies to better understand equity and inclusivity. This report documents phase two of a three phased sequential, exploratory mixed methods study designed to provide an in-depth look at the population of NIST federal employees to identify factors, attitudes, and processes that might result in gender- specific barriers at NIST. Phase 1 analyzed human resources demographic data, compensation data, and performance data of NIST federal employees from 2011 to 2019 to determine any relevant trends. Phase 1 informed the development of an in-depth interview protocol designed to identify the differences, if any, in the ways in which men and women experience work at NIST. A total of 40 (36 female and 4 male) participants were interviewed. Three interconnected themes emerged in the data: 1) a culture at NIST that creates a Chilly Climate for women; 2) gendered experiences that contribute to and are outcomes of that chilly climate; and 3) gendered outcomes that influence women s experiences in the organization. The culture has evolved from NIST s scientific roots, scientific excellence, a strong belief in meritocracy, and as a Federal agency. Each of these characteristics contribute to a gendered social structure and the perception that change is not needed. This backdrop sets the stage for the characterizations of NIST from the interviews as a Boys Club and an Elitist environment. The radically different perspectives of men and women based in the culture result in experiences and outcomes that provide advantages and opportunities for men while erecting barriers to survival for women, including isolation and possibly exclusion. These barriers result in consequences of discrimination as well as lack of trust and resignation. Participant quotes are used as exemplars to provide details related to each of these themes. Overall, the interviews demonstrate that women and men experience a very different NIST.

The National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards, was established by the U.S. Congress in 1901 and charged with establishing a measurement foundation to facilitate U.S. and international commerce. NIST provides reference materials and reference instruments that are used to ensure the accuracy, metrological traceability, and comparability of measurement results in many diverse fields of science, industry, and technology. This document provides and explains the vocabulary used at NIST to describe the reference materials and reference instruments available to NIST s customers. This document also describes the methods used in developing NIST reference materials. The definitions and descriptions provided supersede those used in the original versions of this publication, NIST SP260-136 and SP260-136-2020.

This paper presents a summary of the strategies and activities underway at the National Institute of Standards and Technology (NIST) in electronics packaging, interconnection and assembly (P/I/A). In addition, a sampling of collaborations involving these works is included. The overall NIST effort in P/I/A is composed of targeted programs conducted by the NIST laboratories and by the NIST Advanced Technology Program (ATP). A dominant aspect of the laboratory-based P/I/A program focuses on the metrology and data needed to support the product technologies envisioned within industry roadmaps. A significant aspect of the work includes efforts in metrology, materials, complex material assemblies, and microelectronic components and circuits. In parallel, the NIST ATP is supporting on a cost-share basis a variety of industry-based development projects of high-risk enabling technologies for new or improved products, manufacturing, and processes in P/I/A.

On September 5–8, 2023, the National Institute of Standards and Technology (NIST) held the second Standards and Performance Metrics for On‐Road Automated Vehicles Workshop. This four‐day virtual event provided updates on NIST’s recent work in automated vehicles (AVs) and gave stakeholders an opportunity to provide feedback and input on current and future NIST research. The workshop included high‐level keynote presentations, a series of industry keynote presentations, and NIST presentations on its current AV activities. The industry keynotes and NIST presentations were paired with breakout sessions that discussed NIST’s progress, community challenges, and stakeholder research needs in six key areas: systems interaction, perception, cybersecurity, communications, artificial intelligence, and digital infrastructure. There was general agreement that developing standards allows for better comparisons and evaluations of emerging technologies. Other key themes included: 1) Digital technologies for automation and related security/privacy concerns, including artificial intelligence, machine learning, and smart communication technologies (i.e., vehicle‐to‐vehicle (V2V), vehicle‐to‐infrastructure (V2I), and vehicle‐to‐everything (V2X)), 2) Need for standardized or common language to improve information sharing, 3) Open data sets to support and validate technical advances and standardization across system components and areas (i.e., standards evolving in parallel with technology), and 4) Pivotal role for NIST as a convener to bring diverse stakeholders together for knowledge exchange and cross‐industry dialogue.

In consultation with ASTM and other stakeholders in Tissue-Engineered Medical Products (TEMPs) industry, the National Institute of Standards and Technology (NIST) initiated a project designed to produce Reference Material scaffolds for tissue engineering. The rationale for Reference Material scaffolds was developed through several NIST/Industry workshops. In brief, Reference Material scaffolds have multiple uses: facilitating the development and the validation of new test methods that measure interactions among various components of a TEMP; comparison with other scaffolds and scaffold materials in terms of cellular responses, biodegradation, and releases of growth factors; and comparisons of responses among various cell lines. The primary customers for Reference Material scaffolds are expected to be the TEMPs industry, academic researchers, regulators, and standards developing organizations. There are many properties of a TEMP that warrant development of multiple Reference Material scaffolds. Currently, NIST is defining a set of Reference Material scaffolds based on geometric descriptors such as permeability, pore volume, pore size distribution, interconnectivity, and tortuosity. In consultation with ASTM, NIST is testing three candidate scaffolds produced by: three dimensional (3-D) printing, stereolithography, and fused deposition modeling (FDM). Scaffolds made by these methods have been obtained from Mayo Clinic (Rochester, MN), Case Western Reserve University (CWRU) (Cleveland, OH), and Osteopore International (Singapore), respectively, for structural characterization. These prototype scaffolds, with well-defined architectures, have been selected to address the following items of interest: 1) establishment of useful functional definitions of porosity content, interconnectivity, and pores; 2) evaluation of testing methods listed in the Standard Guide for the Porosity of Polymeric Scaffolds for Use in Tissue-Engineered Medical Products, which is being drafted by ASTM. Currently, NIST and the Center for Devices and Radiological Health of the Food and Drug Administration, as well as other groups from US and foreign laboratories, are actively carrying out cross-validation test of these prototype scaffolds.

As cybersecurity issues surge, it highlights the pressing need for increased awareness. In our digitally interconnected world, where information technology underpins the lives of individuals, businesses, and even national security, the threat of cyberattacks looms large. To enhance national cybersecurity preparedness, there is a critical call to action: we must promote public awareness of cybersecurity issues and bolster the ranks of trained cybersecurity professionals. This research introduces a novel cybersecurity awareness model based on the National Institute of Standards and Technology (NIST). Its primary goal is to make NIST accessible to secondary school students pursuing ICT courses and their invaluable resource, the school counselling units. The model aims to instil cybersecurity awareness in secondary school students and guide them in choosing the most suitable higher education paths, particularly in the ICT and cybersecurity fields. The study comprises three phases. In the first phase, a systematic literature review (SLR) examines globally applicable cybersecurity education models. The second phase investigates the implementation of cybersecurity education for secondary school students in Malaysia. This includes interviews with school counselling units responsible for guiding students toward higher education and surveys of students in grades four and five enrolled in ICT courses. The third and pivotal phase focuses on developing the proposed model. It involves analysing and implementing the results of the SLR, mapping them to the NIST framework, and incorporating themes from interviews and surveys. As a tangible representation of the model, a mobile application prototype has been developed. The Cybersecurity Awareness Model empowers school counselling units to seamlessly integrate career exploration with career decision-making for secondary students at any stage of their development. Moreover, it offers a means to create strategies for after-school programs, particularly in the dynamic field of cybersecurity. This model is expected to guide students in exploring academic majors and careers, preparing for higher education post-high school, initiating internships or job searches, and adapting to a world in constant flux. In doing so, it not only empowers individuals but also strengthens the nation's resilience in the face of cybersecurity challenges.

Optical frequency combs have been widely used in spectrum analysis, coherent optical communication, and accurate distance measurement. We propose a straightforward method to improve the flatness of optical frequency combs. First, we derived the output of the optical signal for the configuration of a cascaded MZM and two PMs. Second, we identified the parameter value when the flatness was optimal after traversing different parameter spaces. The optimal flatness conditions could be automatically determined from an existing sample dataset by using neural networks and Bayesian optimization, which significantly reduced the calculation cost. Furthermore, a broad spectrum and low power consumption were also achieved. Finally, the generated optical frequency comb signal was divided into eight carriers with 50 GHz intervals, and the optical transmission system was verified by applying a 16-QAM modulation of 40 GBaud/s to each channel. The constellation diagram proved the feasibility of this optical comb generation scheme.