Precision Optical Measurements Research Articles

Characteristics of metallic coated ultra-short semiconductor Fabry-Pérot lasers

Fabry-Pérot (F–P) lasers have attracted significant attention due to their extensive applications in optical communication and precision measurement fields. However, traditional F–P lasers are relatively large in size and face challenges in directly achieving single-mode lasing, which limits their applications. In this study, we employ a metallic coating layer to significantly enhance the light confinement of the F–P cavity, thereby substantially reducing the cavity length of the F–P laser. We have experimentally developed an F–P laser with a cavity length of approximately 6.8 μm, successfully achieving single-mode lasing at room temperature. The lasing mode exhibits an ultra-narrow linewidth of 0.06 nm and a relative high side-mode suppression ratio exceeding 30 dB, along with good linear polarization. Additionally, we propose a type of on-chip integrated laser based on metallic-coated F–P cavities, characterized by high coupling efficiency and large fabrication tolerances. Simulation results indicate that the coupling efficiency for double-ended and single-ended output waveguides reaches 79% and 55%, respectively. The metallic-coated ultra-short F–P lasers have great potential for applications in on-chip optical interconnects and photonic integrated chip systems.

Sr Optical Lattice Clock and Precision Optical Frequency Measurement at NIM

Sr Optical Lattice Clock and Precision Optical Frequency Measurement at NIM

Manipulating photonic spin Hall split based on nonlinear effect and surface plasmon resonance

In this work, we present a surface plasmon resonance (SPR) structure containing AuAl2 and a nonlinear Kerr medium. Based on the modulation of the refractive index of the Kerr medium by pumped light, we analyze the effects of the SPR structure and pumped light on the photonic spin Hall effect (PSHE). The numerical results indicate that the thickness of the AuAl2 exerts a profound impact on the SPR, while the intensity of the pump light (Ip) exerts a significant influence on the resonance angle. The transverse shift (TS) is very sensitive to the refractive index (RI) of the sensing layer after increasing through the SPR. Furthermore, it is observed that the sign of the TS of the PSHE can be modulated according to Ip within a specific angle of incidence. In light of these findings, we put forth a novel optical signal modulation and RI sensing scheme based on PSHE. Our study provides a new mechanism for practical applications of PSHE in optical communication and precision measurement.

Experimental analysis of failure modes depending on different loading conditions applied on cylindrical polyamide 66 gears

Abstract Engineering plastics are increasingly used for gearing systems, such as in the automotive sector, e-mobility sector, and household appliances. The basic task of the gearing system is to efficiently transfer power from the source to the application user. The use of engineering plastics for gearing applications is conditioned by the lack of tribological characteristics of material pairs which influence on fatigue and wear behaviour of the whole gearing system. The paper presents testing of the steel/Polyamide 66-gear by determining fatigue life in an infinite area, considering high precision optical measurements in the range of micro-meter accuracy of abrasion flank wear together with surface temperature in contact, providing an important database for engineers about material suitability for appropriate mechanical systems. Observing the results, gear flank wear of PA66 HT is directly proportional to the meshing temperature and torque. Thermal melting is a characteristic failure mode of the polymer gears which are exposed to higher load levels. In the middle torques, the dominant failure mode is flank fracture known as pitch point fracture. The greater impact of the gear wear mechanism occurs at lower torques where initial crack propagation starts at the pitch point and ends in the tooth root area.

Low-frequency electric field sensing via superposition orbital angular momentum light.

The polarization and orbital angular momentum (OAM) degrees of freedom carried by light have important applications in precision optical measurement and optical sensing. Here we show that the electro-optic Pockels effect of a magnesium-doped lithium niobate (MgO:LiNbO3) crystal can be used to measure a low-frequency electric field. By exploiting the rotation property of superposition OAM light, we experimentally observe that the minimum measured precision of electric field intensity is about 0.18 V/m. This study offers a method to perform low-frequency electric field sensing.

PVDF/Al2O3/Gd2O3 layers splitter with first-order suppression functionality

In the realm of optical component design, the proposed multilayer grating splitter represents a significant breakthrough. For the triple-layered grating in this paper, it combines the outstanding optical properties of polyvinylidene fluoride (PVDF), aluminum oxide (Al2O3), and gadolinium oxide (Gd2O3) to achieve high-efficiency outputs for both the 0th and −2nd orders under secondary Bragg angle incidence conditions. The diffraction efficiencies for both TE and TM polarizations exceed 97%, with energy uniformity surpassing 99%. These results highlight the potential of this design in precision beam control applications. The splitter's performance benefits from the intrinsic material properties and optimally designed structural dimensions, which enhance transparency and thermal stability under operational conditions. Through rigorous design and optimization, including modal methods and simulated annealing algorithms, the device achieves exceptional uniformity in diffraction efficiency, which is crucial for high-resolution spectroscopy and precision optical measurement applications.

National standards of optical density units: principles of optical scheme design, constructive and metrological characteristics

The current state of metrological support for precision optical density measurements is described. In order to analyze the principles of building optical schemes, structural, constructive and functional features of the blocks included in the standards, and metrological characteristics of national standards of optical density units, high-precision optical density measuring instruments developed by national metrological institutes of Russia, Germany, China, and the USA are considered. The equations of optical density measurements are presented, which are a mathematical model of the process of measuring the optical transmittance density of materials. The principles of operation of optical transmittance density unit standards based on light fl fi ration are described. The data of studies of geometric and spectral characteristics of fi national standards of optical density units of four countries are presented, as well as optical schemes and characteristics of standards in the following areas are analyzed: compliance with international standards; features of optical schemes; methods of fi the luminous fl and creating scattered radiation; features of object positioning; type of radiation receiver; metrological characteristics. Information is provided on the participation of national standards in international comparisons. The metrological characteristics of these national standards are summarized in a table. Taking into account and using the considered features of optical schemes, design solutions in conjunction with the metrological characteristics of the described devices contributes to an increase in the level of development while improving the State primary standard of the unit of optical density GET 206-2016.

High sensitivity dual-mode ratiometric optical thermometry based on Ce3+/Mn2+ co-doped LiYF4 single crystal

Serial dual-emitting single crystals LiYF4: 0.5Ce3+/αMn2+ (α = 0, 0.05, 0.1, 0.3, 0.5, and 1.0) samples were synthesized by a reformative Bridgman technique. A comprehensive investigation was carried out to systematically analyze the crystal structure, energy transfer mechanism, luminescence properties, and temperature-dependent sensing capabilities. The single crystal exhibits distinct dual broadband emissions, with peaks at 373 nm attributed to the transition from 5d to 4f of Ce3+ ions and 555 nm assigned to the transition from 4T1g(4G) to 6A1g(4S) level of Mn2+ ions. The optical properties of the Ce3+/Mn2+ co-doped LiYF4 single crystal were studied in relation to temperature, with a focus on enabling precise optical temperature measurements. The research revealed a relative sensitivity of 0.995 % K−1 at 498 K and temperature resolution of 0.03 K at 498 K, indicating the potential of LiYF4: Ce3+/Mn2+ single crystals for use in highly sensitive optical thermometry applications. These findings highlight the crystal suitability for the development of temperature sensing devices with enhanced sensitivity and resolution.

Investigating the influence of solvent type and pH on protein adsorption onto silica surface by evanescent-wave cavity ring-down spectroscopy.

Several studies have explored the adsorption of various proteins onto solid-liquid interfaces, revealing the crucial role of buffer solutions in biological processes. However, a comprehensive evaluation of the buffer's influence on protein absorption onto fused silica is still lacking. This study employs evanescent-wave cavity ring-down spectroscopy (EW-CRDS) to assess the influence of buffer solutions and pH on the adsorption kinetics of three globular proteins: hemoglobin (Hb), myoglobin (Mb), and cytochrome c (Cyt-C) onto fused silica. The EW-CRDS tool, with a ring-down time of and a minimum detectable absorbance of , enabled precise optical measurements at solid-liquid interfaces. The three heme proteins' adsorption behavior was investigated at pH 7 in three different solvents: deionized (DI) water, tris(hydroxymethyl)-aminomethane hydrochloride (Tris-HCl), and phosphate buffered saline (PBS). For each protein, the surface coverage, the adsorption and desorption constants, and the surface equilibrium constant were optically measured by our EW-CRDS tool. Depending on the nature of each solvent, the proteins showed a completely different adsorption trend on the silica surface. The adsorption of Mb on the silica surface was depressed in the presence of both Tris-HCl and PBS buffers compared with unbuffered (DI water) solutions. In contrast, Cyt-C adsorption appears to be relatively unaffected by the choice of buffer, as it involves strong electrostatic interactions with the surface. Notably, Hb exhibits an opposite trend, with enhanced protein adsorption in the presence of Tris-HCl and PBS buffer. The pH investigations demonstrated that the electrostatic interactions between the proteins and the surface had a major influence on protein adsorption on the silica surface, with adsorption being greatest when the pH values were around the protein's isoelectric point. This study demonstrated the ability of the highly sensitive EW-CRDS tool to study the adsorption events of the evanescent-field-confined protein species in real-time at low surface coverages with fast resolution, making it a valuable tool for studying biomolecule kinetics at solid-liquid interfaces.

Optical measurement of glutamate release robustly reports short-term plasticity at a fast central synapse.

Recently developed fluorescent neurotransmitter indicators have enabled direct measurements of neurotransmitter in the synaptic cleft. Precise optical measurements of neurotransmitter release may be used to make inferences about presynaptic function independent of electrophysiological measurements. Here, we express iGluSnFR, a genetically encoded glutamate reporter in mouse spiral ganglion neurons to compare electrophysiological and optical readouts of presynaptic function and short-term synaptic plasticity at the endbulb of Held synapse. We show iGluSnFR robustly and approximately linearly reports glutamate release from the endbulb of Held during synaptic transmission and allows assessment of short-term plasticity during high-frequency train stimuli. Furthermore, we show that iGluSnFR expression slightly alters the time course of spontaneous postsynaptic currents, but is unlikely to impact measurements of evoked synchronous release of many synaptic vesicles. We conclude that monitoring glutamate with optical sensors at fast and large central synapses like the endbulb of Held is feasible and allows robust quantification of some, but not all aspects of glutamate release.

Back action evasion in optical lever detection

The optical lever is a centuries old and widely used detection technique employed in applications ranging from consumer products and industrial sensors to precision force microscopes used in scientific research. However, despite the long history, its quantum limits have yet to be explored. In general, any precision optical measurement is accompanied by optical force induced disturbance to the measured object (termed as back action) leading to a standard quantum limit (SQL). Here, we give a simple ray optics description of how such back action can be evaded in optical lever detection. We perform a proof-of-principle experiment demonstrating the mechanism of back action evasion in the classical regime, by developing a lens system that cancels extra tilting of the reflected light off a silicon nitride membrane mechanical resonator caused by laser-pointing-noise-induced optical torques. We achieve a readout noise floor two orders of magnitude lower than the SQL, corresponding to an effective optomechanical cooperativity of 100 without the need for an optical cavity. As the state-of-the-art ultralow dissipation optomechanical systems relevant for quantum sensing are rapidly approaching the level where quantum noise dominates, simple and widely applicable back action evading protocols will be crucial for pushing beyond quantum limits.

Simulation analysis and collaborative optimization of key components of the precision detection platform for high precision encoder

To realize the error detection of the high-precision photoelectric encoder, the optical small-angle precision measurement principle of the photoelectric autocollimator and single-sided mirror, and the 360° full circle measurement principle of angle inversion of the compound biaxis turntable are used to establish the precision detection platform of the encoder. The error model of the biaxial structure in the photoelectric coding error detection platform is established by introducing the error sources of the biaxial structure, such as the coaxiality error, angular position error, and installation error. At the same time, the biaxis structure and error models are used to optimize the compound biaxis structure system. By analyzing the natural frequency and vibration characteristics of the structure, the rationality and reliability of the compound biaxis system of the high-precision encoder precision detection platform are verified.

Stable tunable narrow-linewidth fiber laser based on random distributed feedback

Stable narrow linewidth fiber lasers with relatively high output power have broad application prospects in optical communication, sensing and precision measurement, due to their high coherence and low noise characteristics, which are the main requirements to increase the detection range and accuracy of these systems. Obtaining narrow linewidth laser output with improved performance has been one key topic in the field of laser science and technology. Here, we propose a combination of transmission and reflection of randomly distributed Bragg grating arrays to compress the linewidth of laser emission in an Erbium-doped fiber system at the 1550 nm band, thereby providing a selective reflection-transmission channel effect without too many feedback points. A stable narrow linewidth fiber laser with a linewidth of 570 Hz (output power of 6 mW) and 830 Hz (output power amplified to 25 mW), a maximum signal-to-noise ratio (SNR) greater than 63 dB, and a wavelength adjustable in the range of 445 pm is realized.

Optical Measurement of Ligament Strain: Opportunities and Limitations for Intraoperative Application.

A feasible and precise method to measure ligament strain during surgical interventions could significantly enhance the quality of ligament reconstructions. However, all existing scientific approaches to measure in vivo ligament strain possess at least one significant disadvantage, such as the impairment of the anatomical structure. Seeking a more advantageous method, this paper proposes defining medical and technical requirements for a non-destructive, optical measurement technique. Furthermore, we offer a comprehensive review of current optical endoscopic techniques which could potentially be suitable for in vivo ligament strain measurement, along with the most suitable optical measurement techniques. The most promising options are rated based on the defined explicit and implicit requirements. Three methods were identified as promising candidates for a precise optical measurement of the alteration of a ligaments strain: confocal chromatic imaging, shearography, and digital image correlation.

A new method for precise optical measurements of the sub-micron height of levitation of droplet clusters

Droplet clusters levitating over the locally heated water surface are considered a very promising phenomenon of microfluidics for the potential use of the droplets as unique microreactors for microbiological experiments. A new optical method is suggested for precise measurements of the sub-micron levitation height of single droplets. The method is based on the analysis of variable colors of the interference halo around the droplet. For the first time, it is possible to measure the extremely low downward velocity of droplets, which grow due to steam condensation. This velocity was found to be 5–8 nm/s. The height of the levitation of various droplets just before their coalescence with a layer of water was also determined. Such measurements might be used for the verification of sophisticated models for the droplet levitation to be developed for a very thin layer of humid air under the droplet when the Knudsen effect should be taken into account.

Estimation of a parameter encoded in the modal structure of a light beam: a quantum theory

Quantum light is described not only by a quantum state but also by the shape of the electromagnetic modes on which the state is defined. Optical precision measurements often estimate a “mode parameter” that determines properties such as frequency, temporal shape, and the spatial distribution of the light field. By deriving quantum precision limits, we establish the fundamental bounds for mode parameter estimation. Our results reveal explicit mode-design recipes that enable the estimation of any mode parameter with quantum enhanced precision. Our approach provides practical methods for optimizing mode parameter estimation with relevant applications, including spatial and temporal positioning, spectroscopy, phase estimation, and superresolution imaging.

Intrinsic Spectrum Analysis of Laser Dynamics Based on Fractional Fourier Transform

The intrinsic spectrum that results from the coupling of spontaneous emission in a laser cavity can determine the energy concentration and coherence of lasers, which is crucial for optical high-precision measurements. To date, it has been difficult to analyze the intrinsic spectrum in high-speed laser dynamics processes, especially under the condition of fast wavelength sweeping. In this work, a new method to analyze the laser intrinsic spectrum is proposed with laser energy decomposition into a series of chirp-frequency signals, which is realized by fractional Fourier transform (FRFT) of the coherently reconstructed laser waveform. The new understanding of the energy distribution of lasers contributes to accurate characterization of laser dynamic parameters in the time-frequency domain. In a proof-of-concept experiment, the time-frequency dynamic process of a commercial wavelength-swept laser is tested for different wavelength-scanning speeds, and the most suitable measurement time window width required for the narrowest FRFT-based spectrum is also explored. The proposed analysis method of laser dynamic parameters will promote the understanding of laser dynamics and benefit optical precision measurement applications.

A reference-free dual-comb spectroscopy calibrated by passive devices

Dual-comb spectroscopy has enabled new approaches for optical precision measurements. Although Doppler-limited resolution can be achieved over long-time scales across a large bandwidth, the development of dual-comb spectroscopy is hindered by strict demands for light source stability. Typically, expensive and complex self-reference systems are required to lock the carrier-envelope offset frequency (fceo) of the laser. Additionally, simply locking the repetition frequency (frep) to a radio frequency reference source still results in residual relative timing jitter between light sources. Here we extracted the relative fceo fluctuation between the frep-locked lasers from the high-precision passive notch filtering characteristics of the phase-shifted fiber Bragg grating and then eliminated it through online phase calibration. By introducing a passive broadband Fabry–Perot cavity with excellent thermal wavelength stability, we subsequently corrected residual relative timing jitter with online wavelength calibration, and the standard deviation of the relative wavelength drift was reduced to less than 0.4 pm within the full operating range. The spectral profile can also be extracted and removed by the Fabry–Perot cavity through intensity calibration. By calibrating these three dimensions, we built a reference-free post-calibration dual-comb spectroscopy and used this powerful tool to measure the Fabry–Perot cavity resonance peaks, the notch filtering narrow band of phase-shifted fiber Bragg gratings, and the absorption characteristics of hydrogen cyanide gas. The system achieves a spectral resolution of 0.8 pm over a bandwidth of more than 100 nm. This low-cost and convenient scheme provides new ideas for the application of dual-comb spectroscopy systems.

High throughput screening system for engineered cardiac tissues.

Introduction: Three dimensional engineered cardiac tissues (3D ECTs) have become indispensable as in vitro models to assess drug cardiotoxicity, a leading cause of failure in pharmaceutical development. A current bottleneck is the relatively low throughput of assays that measure spontaneous contractile forces exerted by millimeter-scale ECTs typically recorded through precise optical measurement of deflection of the polymer scaffolds that support them. The required resolution and speed limit the field of view to at most a few ECTs at a time using conventional imaging. Methods: To balance the inherent tradeoff among imaging resolution, field of view and speed, an innovative mosaic imaging system was designed, built, and validated to sense contractile force of 3D ECTs seeded on a 96-well plate. Results: The system performance was validated through real-time, parallel contractile force monitoring for up to 3 weeks. Pilot drug testing was conducted using isoproterenol. Discussion: The described tool increases contractile force sensing throughput to 96 samples per measurement; significantly reduces cost, time and labor needed for preclinical cardiotoxicity assay using 3D ECT. More broadly, our mosaicking approach is a general way to scale up image-based screening in multi-well formats.

Helical Long-Period Fiber Grating-Based OAM Interferometer and Its Application to Fiber Sensing

Orbital-angular-momentum (OAM) beams-based interferometers have recently been attracted significant interest and found various applications in the field of optical precision measurement. Whereas all-fiber OAM interferometers featured with the superior characteristics of the compact size, low cost, extremely-low insertion-loss, and the inherent compatibility with other fiber devices, have less been studied and especially demonstrated in experiment. In this study, we proposed and experimentally demonstrated an all-fiber OAM beams-based interferometer, where the two conjugated OAM beams generated by helical long-period fiber gratings (HLPGs) but with opposite helicities, were particularly utilized as the tested and referenced beams, respectively. The resulted interferograms are of the polarization independence, robust, and particularly suitable for phase-demodulation in azimuthal angle domain. As application examples of the proposed all-fiber OAM beams-based interferometer, changes in temperature ranging from 30 °C to 60 °C and changes in the strain ranging from 0 to 100 μϵ were measured, respectively. The obtained maximum sensitivity in temperature and strain are 26.585 rad/°C and 2.130 rad/μϵ, respectively. The accuracies for temperature and strain measurements are estimated to be 0.0016 °C and 0.0195 μϵ, respectively, which are about 2–3 order higher than those obtained from the conventional optical fiber-based sensors. It is believed that the proposed all-fiber OAM beams-based interferometer would find potential applications to ultra-high precision and sensing measurements.