Optical Ruler Research Articles

Sensing Sound Pressure in an Anechoic Chamber Using Backscattered Laser Light

Currently standards for the measurement of the S.I. derived unit of sound pressure, the pascal, are based upon microphone reciprocity. These methods require microphones of specific geometry and performance characteristics, effectively artefacts, and are traceable through standards for electrical units. Measurement of acousto-optic interactions can provide an alternative approach to measuring sound pressure. One acousto-optic interaction is the periodic scattering of photons caused by particles moving with sinusoidal acoustic particle velocity across an optical ruler formed at the intersection of two coherent laser beams. The sequence of these scattered photons, which is collected using telescopic optics and a single photon counting device, can be auto-correlated to give the periodicity of the photon events. Through mathematical analysis of the auto-correlation function it has been shown that acoustic particle velocity is inversely proportional to the time shift of the first minima. This has effectively been shown for measurements in acoustic standing wave tubes and has been developed in to a method which can be applied in an acoustic free field chamber. This paper describes the design and implementation of such a system which allows for a comparison between optical measurements and those of a microphone.

Biosensing Using Microring Resonator Interferograms

Optical low-coherence interferometry (OLCI) takes advantage of the variation in refractive index in silicon-wire microring resonator (MRR) effective lengths to perform glucose biosensing using MRR interferograms. The MRR quality factor (Q), proportional to the effective length, could be improved using the silicon-wire propagation loss and coupling ratio from the MRR coupler. Our study showed that multimode interference (MMI) performed well in broad band response, but the splitting ratio drifted to 75/25 due to the stress issue. The glucose sensing sensitivity demonstrated 0.00279 meter per refractive-index-unit (RIU) with a Q factor of ∼30,000 under transverse electric polarization. The 1,310 nm DFB laser was built in the OLCI system as the optical ruler achieving 655 nm characterization accuracy. The lowest sensing limitation was therefore 2 × 10−4 RIU. Moreover, the MRR effective length from the glucose sensitivity could be utilized to experimentally demonstrate the silicon wire effective refractive index with a width of 0.45 μm and height of 0.26 μm.

Low-coherence interferometric fiber sensor with improved resolution using stepper motor assisted optical ruler

Low-coherence interferometric sensing is typically used to detect phase changes without simultaneous optical ruler calibration in order to by-pass light intensity fluctuations and the periodic nature of the interferometric signal. An interferogram from a two-staged optical low-coherence Mach–Zehnder interferometer is proposed to double the sensitivity improvement for fiber strain sensing. A 1310-nm wavelength distributed feedback laser implemented in an optical ruler achieved 655-nm resolved characterization from its high-coherence interferogram, which could further be enhanced to an average of 18.9nm using a stepper motor assisted optical ruler. A 2.7-nε high strain resolution was then demonstrated on a 3-m long fiber sensing arm in a Mach–Zehnder interferometer. The relative movement distances between the interferograms were utilized to experimentally show the strain and force sensitivity as 6.8μm/με and 8.5μm/mN, respectively.

Optical frequency ruler with moving fluid

A configuration consisting of a double slit and pipe in conjunction with moving fluid is proposed to manipulate a broadband light source through the interference spectrum. Theoretical analysis shows that, by varying the speed of the fluid, the scheme can act as a special dynamic frequency filter and produce regular dark lines that may serve as an optical frequency ruler.

Development of a Long-Range Surface-Enhanced Raman Spectroscopy Ruler

Optical-ruler-based distance measurements are essential for tracking biomolecular processes in a wide range of analytical biochemical applications. The normally used Förster resonance energy transfer (FRET) ruler is not useful for investigating distance-dependent properties when distances are more than 10 nm. Driven by this limitation, we have developed a long-range surface-enhanced Raman spectroscopy (SERS) optical ruler using oval-shaped gold nanoparticles and Rh6G dye-modified rigid, variable-length double-strand DNAs. The bifunctional rigid dsDNA molecule serves as the SERS-active ruler. Our experimental results show that one can tune the length of the SERS ruler between 8 and ∼18 nm by choosing the size of the oval-shaped gold nanoparticles. A possible mechanism for our observed distance-dependent SERS phenomenon is discussed using the Gersten and Nitzan model. Ultimately, our long-range SERS molecular rulers can be an important step toward understanding distance-dependent biological processes.

Measuring the distance between two mercapto groups with an optical molecular ruler on the nanometer scale

We have developed an absorption spectrum based molecular ruler that measures the distance between two mercapto groups. The conformation of the molecular rulers changes with the distance, which induces an absorption spectrum change. DFT calculation has been carried out to elucidate the relation between the molecular conformation and the absorption spectrum. With this simple method, we can estimate the distance between two mercapto groups on the scale of 0.4-1 nm. This method can also be used to monitor conformation transition, which is demonstrated by a silver ion titration experiment.

Nanometrology optical ruler imaging system using diffraction from a quasiperiodic structure

This work demonstrates wafer-scale, path-independent, atomically-based long term-stable, position nanometrology. This nanometrology optical ruler imaging system uses the diffraction pattern of an atomically stabilized laser from a microfabricated quasiperiodic aperture array as a two-dimensional optical ruler. Nanometrology is accomplished by cross correlations of image samples of this optical ruler. The quasiperiodic structure generates spatially dense, sharp optical features. This work demonstrates new results showing positioning errors down to 17.2 nm over wafer scales and long term stability below 20 nm over six hours. This work also numerically demonstrates robustness of the optical ruler to variations in the microfabricated aperture array and discretization noise in imagers.

Nanometrology Using a Quasiperiodic Pattern Diffraction Optical Ruler

This paper presents a nanometrology optical ruler imaging system to enable rapid wafer-scale nanometrology, particularly for scanning probe microscopes. The ruler is generated by the diffraction of a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> stabilized laser by a metal thin-film pattern. Microfabrication techniques create a high-count quasiperiodic aperture array in the film which generates a translationally asymmetric feature-dense optical diffraction pattern well suited for the nanometrology application. An imager array samples the optical ruler and calculates its position by Fourier transform cross-correlation methods. Numerically, it is found that improving the imager by pixel count and size can reduce positioning errors down to 1/120th of the pixel size, after which further improvements yield no reduction in error. Experiments using a modest complementary metal-oxide-semiconductor imager demonstrate a positioning accuracy of 1/124th of the pixel size, or 29 nm. This system will enable high-precision high-throughput metrology and fabrication of nano- and microelectromechanical systems.

Tracking Spatial Disorder in an Optical Ruler by Time-Resolved NSET

For biomolecular applications, potential interactions between newly developed dye molecules and the biomolecule of interest can dramatically influence the accuracy of optical ruler techniques. By utilizing nanometal surface energy transfer (NSET), an optical technique is developed that allows the nature of interactions between dyes and a biomolecule, namely DNA, to be directly assessed. To demonstrate the method, interactions between well-known molecular dyes based on carboxyfluorescein (FAM, noninteracting) and Cy5 (known intercalator) with DNA is probed. The results demonstrate that FAM exhibits no interactions with the DNA backbone and is adequately represented as a solvent exposed dye, while the commonly used near-IR dye Cy5 exhibits two discrete interactions that depend on the site of appendage and the length of the linker arm. The exact population and nature of Cy5 interaction with the DNA indicates a 37% ratio of intercalation for the internal C(6), a 42% ratio for an internal C(3) spacer length, and no evidence of interaction for terminal labeling. The results allow quantitative assignment of the site occupation of donors to be analyzed providing a powerful set of information for use of dyes in FRET based optical ruler technologies without the need of single molecule methods or the assumption of an averaged site occupation for the donor.

Optimum algorithm for WDM channel allocation for reducing four-wave mixing effects

A novel channel allocation method, based on optical Golomb ruler (OGR), that allows reduction of the FWM effect while maintaining bandwidth efficiency along with the algorithms has been presented in this paper. Very high-capacity, long-haul optical communication systems can be designed by wavelength division multiplexing (WDM) of high-bit-rate channels and by using erbium-doped fiber amplifiers (EDFAs) to periodically compensate the fiber loss. In such all-optical systems, the effects of chromatic dispersion and nonlinearities accumulate during light propagation, imposing limits on the achievable performance. Chromatic dispersion at 1.55 pm can be effectively reduced by using dispersion-shifted fiber (DSF). The use of very-low-dispersion fiber, however, enhances the efficiency of generation of four-wave mixing (FWM) waves by reducing the phase mismatch naturally provided by the fiber dispersion. For this reason, crosstalk due to FWM is the dominant nonlinear effect in long-haul WDM systems using DSFs. To reduce four-wave-mixing crosstalk in high capacity long-haul repeater less WDM light wave systems, the use of the channel allocation method that involves unequal spaced channels has been proposed.

Characterization of one-dimension edge roughness from far-field irradiance at subwavelength-scale precision

It is proposed and numerically verified that the one-dimensional edge roughness of test sample can be characterized by far-field irradiance measurement at subwavelength-scale precision with a constructed aperture playing as an optical ruler. The precision of the proposed scheme of measurement could be better than 3%, even when the edge roughness is in subwavelength-scale. The influence of sample thickness on the proposed measurement scheme is also investigated and considered.

A New Approach to Improve the Performance of Phase Laser Range Finder

Present phase laser range finder system mostly adopts the phase detection methods of fixed optical ruler and constant mixing frequency. However, its phase detection accuracy is comparatively low when the measuring range varies continuously and its operational speed is also slow. Being directed against this situation, the thesis proposes a new phase detection system on the basis of adaptive frequency conversion. The experiments show that the phase detection accuracy of this new system is superior to 1/1000, and the operational speed is twice as before.

Ultrahigh-resolution multicolor colocalization of single fluorescent probes.

An optical ruler based on ultrahigh-resolution colocalization of single fluorescent probes is described in this paper. It relies on the use of two unique families of fluorophores, namely energy-transfer fluorescent beads (TransFluoSpheres) and semiconductor nanocrystal quantum dots, that can be excited by a single laser wavelength but emit at different wavelengths. A multicolor sample-scanning confocal microscope was constructed that allows one to image each fluorescent light emitter, free of chromatic aberrations, by scanning the sample with nanometer scale steps with a piezo-scanner. The resulting spots are accurately localized by fitting them to the known shape of the excitation point-spread function of the microscope. We present results of two-dimensional colocalization of TransFluoSpheres (40 nm in diameter) and of nanocrystals (3-10 nm in diameter) and demonstrate distance-measurement accuracy of better than 10 nm using conventional far-field optics. This ruler bridges the gap between fluorescence resonance energy transfer, near- and far-field imaging, spanning a range of a few nanometers to tens of micrometers.

Performances of an optical ruler based on one-dimensional hydrogenated amorphous Si position-sensitive detectors produced using different metal contacts

Abstract The aim of this work is to determine the role of different metal contacts on the performances of one-dimensional thin-film position-sensitive detectors produced by plasma-enhanced chemical vapour deposition, to be used in optical rulers for alignment applications. The device consists on an indium tin oxide/p-i-n structure where the metal contacts used were based on Al, Al + Cu and Ag. The results achieved show that the contact mainly influences the final sensor range by limiting the magnitude of the analogue signals recorded. In spite of soldering problems the Al contact was the contact that lead to better discrimination of the sensor, with a nonlinearity of ± 0.8% and a fall-off parameter of 3.2 × 103 cm−1. The Al + Cu contact also exhibits good performances (nonlinearity, of ±1.1%; fall-off parameter, 1.4 × 10−2cm−1) and should be chosen since it is much easier to solder but requires protection against oxidation. The integration of these sensors on the optical ruler lead to the production of a ...

Performances of an optical ruler based on one-dimensional hydrogenated amorphous Si position-sensitive detectors produced using different metal contacts

Performances of an optical ruler based on one-dimensional hydrogenated amorphous Si position-sensitive detectors produced using different metal contacts

USE OF AN OPTICAL DENSITY RULER IN MEASUREMENTS OF DYE-DILUTION CURVES.

The inapplicability of Beer's law to densitometry of dyes in whole blood or other nonhomogeneous media has been long known. When using a densitometer whose output is directly proportional to the light transmitted, a simple transformation— log X = log (x – x0)—can be employed to allow rapid, accurate estimation of dye concentration. This is facilitated by use of an optical density ruler. The transformation, X = x – x0, can be made mechanically, by shifting the infinity position of the ruler with reference to the zero light transmission position, or electrically, by appropriate use of zero suppression in the densitometer circuit. The transformation results in an exponential (logarithmic) relationship between light transmitted and concentration of the dye (indocyanine green). Readings of relative optical density obtained by use of the ruler are multiplied by a calibration constant to calculate dye concentration. The principles of the transformation have been applied to the determination of the optimal zero suppression required for maintenance of constant sensitivity of the densitometer in the presence of various levels of background dye. densitometer calibration; indocyanine green densitometer; calibration of dye-dilution curves; correction of dye-dilution curves Submitted on September 13, 1963