A common challenge in metastructure fabrication is precisely tuning of the frequency of a device’s resonance. Slight variations in device dimensions or material properties can lead to a deviation in resonance frequency in comparison to design. We present a method of tuning a dielectric metastructure’s resonance by thermally adjusting the refractive index of a chalcogenide glass (ChG) material. Several characteristics of ChGs make them good candidates for use in dielectric metastructures. They exhibit high linear refractive indices, enabling high index contrast devices; they have large optical nonlinearities, making them useful for tunable devices and nonlinear frequency conversion; and they have wide transmission windows extending from the visible through the long-wave infrared. Recently, we have carried out extensive characterization of the index tuning of arsenic selenide (As₂Se₃) ChG thin films and observed refractive index changes larger than 0.1 in some cases. We use this refractive index change to permanently shift the resonance of a Fabry-Perot filter and the cutoff wavelength for a Bragg reflector. We then demonstrate thermal tuning to shift resonance positions for a metasurface (MS). We compare finite element modeling results with measurement results and show good agreement. This tuning mechanism has potential for use in MS devices where a precise resonance frequency is required.

Abstract: In this talk I explain that enhancement of performance of almost any optical sensor in the end intimately connected to increasing the time of light-matter interaction, i.e. reducing the group velocity of light. Such similarly different phenomena as ENZ (epsilon near zero), plasmonics, micro-cavities, photonic crystals, EIT, (electro-magnetically induced transparency) Fano resonances, and PT (Parity-time) symmetry can all be characterized using the same slow light formalism indicating that their performances are in the end comparable.

This work reports on a compact and robust single-frequency laser emitting at 633 nm, for industrial metrology applications. The system integrates a miniaturized optical isolator, a single-mode fiber coupling and a vapor cell as frequency reference. The achieved absolute frequency stability is 10^-8, while the output power from the fiber is >1 mW. The system shows stable operation over an ambient temperature range between 0 and 70°C, with an electrical power consumption of <3 W. This compact laser system can replace gas lasers in industrial metrology applications, and can serve as key component in future quantum-technology devices.

Femtosecond pulse shaping, a widely used technology, enables the generation of light sources with arbitrary amplitude, phase and polarization in the ultrafast regime. This technology has seen applications in fiber and nonlinear optics, OCT, confocal microscopy, bandpass filtering etc. However, these shapers work primarily at low optical powers under the 100mW level, limited by in and out coupling optics, shaper configurations and optical design of the shaper. Recently, another exciting field of research has been high power fiber laser sources. Various high power fiber sources based on a variety of nonlinear phenomena such as high power supercontinuum sources, Raman lasers etc., have been demonstrated. However, owing to 10s of W class optical powers involved, Fourier shaping in this field has not been utilized effectively thereby limiting many potential applications. Here, we demonstrate a scalable design for a high power Fourier shaper in 4-f configuration capable of handling 20 W of CW lasers with a working bandwidth of over 450nm between 1-1.5 micron connecting the two very important Yb and Er emission windows. Our design implements a transmissive geometry thereby isolating input and output beams which is otherwise provided by fiber coupled circulators, a component unavailable at high power levels for a broadband source. Cladding mode stripping is effectively implemented to heat-sink the uncoupled laser light to ensure high power operations feasible. The design also takes accounts of modifications in fiber coupled collimators and amplitude masks to conform with the demands of high power fiber laser technology.

With the rise of Industry 4.0, smart factory is fast becoming a key concept in infrastructure. To realize the autonomous production system, it is necessary to ensure the parts are properly manufactured. 3D scanners are expected to play a vital role in quality assessment in smart factories. Especially, amplitude-modulated continuous-wave laser scanners benefit from high accuracy and high sensitivity which are suitable for industrial inspection. However, due to the limited dynamic range of receiver electronics, such laser scanners fail to obtain the data points in 3D measurement of highly reflective objects. This impairment deteriorates the performance of conversion of 3D point clouds to solid data for shape inspection, 3D modeling, reverse engineering etc. We coped with receiver saturation by adopting a high-speed polarizationindependent variable optical attenuator in our laser scanner. With such a lase scanner, we have succeeded in prevention of data loss due to receiver saturation.

As the requirements for high performance optical systems become more and more demanding it is increasingly important that every stage of the optical design process is tuned to ensure that manufactured systems meet specification. Traditionally the design steps of optimization and tolerancing have been treated separately which could result in a large divergence between the optical performance of the nominal, or unperturbed, system and that of an as-built system with realistic manufacturing and assembly errors. This divergence can lead to lower product yields or the requirements for tighter tolerances and hence increased costs. In this paper we demonstrate how including the effects of tolerance defects in the optimization step, through Zemax OpticStudio’s new High-Yield Optimization, can result in systems with higher as-built performance at potentially lower cost. We will present a case study showing the utility of this technique on a high-performance imaging system (such as may be found in medical or consumer electronics applications). The results of the High-Yield Optimization will be compared to those of a system designed to an identical set of specifications and using the same realistic tolerances with the traditional method. A detailed analysis of the resulting design forms will be performed, and the key considerations and improvements of the High-Yield Optimization discussed.

Freeform optics are known for their advantages regarding optical performance and system integration. The use of additive manufacturing methods for the rapid production of freeform optics opens up new possibilities for optical metrology. By easily varying the shape and size of optical elements, optical systems specifically adapted to various applications can be fabricated cost-effectively. We present cost-effective freeform polymer optics for the application in Raman spectroscopy which combines laser focusing, Raman scattering collection and a mounting thread within one component. The aspheric surfaces of the optics were designed in a customized simulation tool and optimized regarding to Fresnel losses. The prototypes were fabricated by using a polymer-based Multi-Jet Modeling process. These prototypes were evaluated regarding their geometrical and optical properties and were successfully implemented in a compact and custom-designed Raman spectroscopy system. The system was built based on a continuous wave excitation laser emitting at 785 nm with a maximum output power of 0.5 W and a spectrometer providing a Stokes Raman shift resolution of 6.7 cm^-1.

Stellar interferometry performed in integrated photonic devices allows to increase the angular resolution of a ground-based telescope. Here we present the fabrication and characterization of a low-loss polarization insensitive photonic circuit for astrophotonics, whose geometry was engineered to combine interferometrically up to eight input beams. The employed fabrication technique consisted in the femtosecond laser micromachining followed by a thermal annealing to reduce the birefringence of the waveguides. The fabricated device was characterized to validate its functioning in terms of polarization insensitivity, good transmission and proper beam combination, thus benchmarking its suitability with real on-sky observations.

Depth-graded multilayer structures are widely used in X-ray related applications. In this paper, we propose an optimization approach using machine learning principles to accelerate depth-graded multilayer structures design. We use Monte Carlo tree search (MCTS) to find optimal thickness for each layer in the structure that achieves maximum mean reflectivity in an angular range at a specific beam energy. We obtained 0.78 mean reflectivity in an angular range 0.4~0.55° for Cu Kα radiation using this approach. For a at top structure, we could achieve a small standard deviation of 0.016 within the same range. MCTS is an iterative design method that employs tree search with guided randomization that showed exceptional performance in computer games. MCTS expands towards the promising areas of the search space making it able to search large spaces efficiently and systematically. This approach offers flexibility for multiple design purposes without the need to data availability in advance.

For many optical applications, we need more efficient ways to create complete models of the system performance, including optical, thermal, and structural effects. Current models are difficult to create and prone to error. More efficient methods would lower costs and enable new kinds of studies. We examine the ideal STOP workflow for two systems. First, we model an optical test for a light-weighted mirror with the goal of determining its on-orbit shape. Second, we inspect the workflow for a compact steering prism system with some absorption of the incident beam. We identify challenges to implementation and discuss possible solutions.

Grating array based zonal wavefront sensor (GAZWFS), using an array of gratings implemented with a liquid crystal spatial light modulator (LCSLM) to display the gratings, offers a flexible measurement approach. But the wavefront with a large slope may not accurately be sensed by the sensor like any Shack- Hartmann type sensor. In this paper, we propose a zone wise scanning method to improve the dynamic range of GAZWFS by blocking and unblocking the individual gratings. The estimation of the wavefront and expansion of the dynamic range of GAZWFS by the zone wise scanning method is demonstrated by numerical simulation and a proof-of-principle experimental implementation.

Microfluidic technologies and on-chip optical components have advanced such that on-chip sensing of minute chemical and molecular compounds is possible, e.g., detection of gases, pathogens, and DNA. Such DNA analyses require purification and amplification to maximize sensitivity. A common method for amplification of a DNA segment is polymerase chain reaction (PCR), which amplifies DNA segments through temperature changes in an assay process. As such, there is great interest in optofluidic lab-on-a-chip PCR methods. However, developments are limited due to challenges in optically driven temperature fluctuations. These challenges arise when the microfluidic samples are smaller than the optical penetration depth of the incident light and only minimal absorption is achieved. To overcome these challenges, this work presents a bio-photonic approach to the PCR method which utilizes infrared (IR) radiation with whispering gallery mode (WGM) waves. The WGM waves greatly increase the interaction length in the microdroplet, allowing smaller (and scalable) dimensions. This improved interaction length occurs because the applied IR radiation is confined along the perimeter of the microdroplet and its surrounding medium. The operation is modelled with finite-different time-domain electromagnetic simulations, comparing current optical heating with the presented technique. These simulations are validated through an experimental analysis with a thermal camera measuring temperature fluctuations. Ultimately, the presented approach is shown to greatly increase scalability in PCR lab-on-a-chip systems.

A laser based soldering technique – Solderjet Bumping – using liquid solder droplets in a flux-free process with localized thermal impact demonstrates the all inorganic, adhesive free attachment of optical components and support structures made of heterogeneous materials for a high-resolution optical filter under harsh environmental conditions. Space applications demand an attachment technology which maintains the precise alignment of bonded components and overcomes challenges of common adhesives such as being more radiation resistant and appropriate for vacuum environments. Besides, stress and strain induced into optical components can deteriorate the wavefront of passing light and therefore reduce the system performance significantly. The presented case study shows the mandatory changes in the design of an optical filter instrument according to the boundary conditions of Solderjet Bumping for different bonding issues. First, a filter window made of N-BK10, covering the optical sensor beneath, is soldered into a frame of DilverP1®. Second, this sub-assembly is aligned w.r.t. to fiducials on a support structure and is attached in this state by soldering as well. The process chain of Solderjet Bumping including cleaning, wettable metallization layer, handling, soldering and inspection is discussed. This multi-material approach requires well-defined reflow energies to melt the spherical shaped solder preforms to create a media-fit joint and to prevent damages on the fragile filter window simultaneously. The findings of process parametrization and environmental testing are presented. The optical performance with respect to stress/strain before and after soldering as well as the alignment state are evaluated using non-contact optical techniques.

A new, simple and highly efficient approach for tunable wavelength filtering is evaluated with a motorized angle dependent tunable filter. This new device combines the flexibility of a monochromator with the imaging functionality of a thin-film interference filter, and is ideal for use in both illumination and image acquisition in optical microscopes. The main features include independent tuning of center wavelength and bandwidth, high transmission efficiency and circular round aperture with high damage threshold.

For the past 25 years, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center’s Photonics Group in the Engineering Directorate has been substantially contributing to the flight design, development, production, testing and integration of many science and navigational instruments. The Moon to Mars initiative will rely heavily upon utilizing commercial technologies for instrumentation with aggressive schedule deadlines. The group has an extensive background in screening, qualifying, development and integration of commercial components for spaceflight applications. By remaining adaptable and employing a rigorous approach to component and instrument development, they have forged and fostered relationships with industry partners. They have been willing to communicate lessons learned in packaging, part construction, materials selection, testing, and other facets of the design and production process critical to implementation for high-reliability systems. As a result, this successful collaboration with industry vendors and component suppliers has enabled a history of mission success from the Moon to Mars (and beyond) while balancing cost, schedule, and risk postures. In cases where no commercial components exist, the group works closely with other teams at Goddard Space Flight Center and other NASA field centers to fabricate and produce flight hardware for science, remote sensing, and navigation applications. Summarized here is the last ten years of instrumentation development lessons learned and data collected from the subsystems down to the optoelectronic component level.

In this paper, the development of a novel picosecond pulsewidth direct detection lidar for velocimetry and hard target imaging applications is discussed. The lidar system comprises of a high-speed fiber coupled laser, novel interleaved three-dimensional (3D) scanner, fiber coupled receiver with optical pre-amp module and a high-speed digitizer. The laser is a pulsed Erbium-doped fiber laser that operates at 1.55 microns wavelength, 10 MHz PRF, 60 picosecond pulse width and 8 W of output average power. The scanner is a multi-faceted polygon type that operates at scan speeds of 10000 lines per second. The system utilizes a state-of-the art 40 GS/s digitizer. The picosecond lidar allows high resolution volumetric measurement of temporally and spatially resolved 3D airspeeds in wind tunnels for capturing a 3D time-accurate map of aerosols or other seeding particles in the airflow using elastic backscatter from a rapidly scanned lidar beam with a narrow field-of-view. Preliminary testing inside wind tunnel has generated promising results for aerodynamic applications including visualizing flow characteristics around test targets. The lidar provided dynamic measurements of complex flow, including the downstream evolution of a wing tip vortex. A 3D image processing algorithm was used to correlate the motion of aerosol features between successive frames and to extract 3D airflow profiles. In this paper, details of lidar instrumentation configuration is discussed followed by results of high-speed 3D hard target imaging of various test targets.

The size and cost of astronomical instruments for extremely large telescopes (ELTs), are pushing the limits of what is feasible, requiring optical components at the very edge of achievable size and performance. Operating at the diffraction-limit, the realm of photonic technologies, allows for highly compact instruments to be realized. In particular, Integrated Photonic Spectrographs (IPSs) have the potential to replace an instrument the size of a car with one that can be held in the palm of a hand. This miniaturization in turn offers dramatic improvements in mechanical and thermal stability. Owing to the single-mode fiber feed, the performance of the spectrograph is decoupled from the telescope and the instruments point spread function can be calibrated with a much higher precision. These effects combined mean that an IPS can provide superior performance with respect to a classical bulk optic spectrograph. In this paper we provide a summary of efforts made to qualify IPSs for astronomical applications to date. These include the early characterization of arrayed waveguide gratings for multi-object injection and modifications to facilitate a continuous spectrum, to the integration of these devices into prototypical instruments and most recently the demonstration of a highly optimized instrument directly fed from an 8-m telescope. We will then outline development paths necessary for astronomy, currently underway, which include broadening operating bands, bandwidth, increasing resolution, implementing cross-dispersion on-chip and integrating these devices with other photonic technologies and detectors such as superconducting Microwave Kinetic Inductance Detector arrays. Although the focus of this work is on IPS applicability to astronomy, they may be even more ideally suited to Earth and planetary science applications.

Hyperspectral image acquisition is challenging due to its three-dimensional dataset consisting of two spatial and one spectral dimensions. Available spectral imagers are either based on spatial or spectral scanning or they sacrifice spatial and spectral resolution for snapshot imaging. Compressive Sensing techniques have already been applied to spectral imaging to enhance the image acquisition, but they still rely on multiple consecutive measurements. We utilize several diffraction orders of a novel diffractive optical element whose diffraction efficiency has been optimized for a broad wavelength range. Based on this diffractive optical element we design and compare novel compressive snapshot spectral imaging systems and present experimental results.

Optical fiber distributed acoustic sensor (DAS) and distributed temperature sensor (DTS) are considerably desirable for many important applications including oil and gas industry. Simultaneous measurements of vibration and temperature will exclude the need for two separate DAS and DTS systems, reduce overall cost, and ensure continuous real-time monitoring of these two important sensing parameters. We here devise a hybrid DAS-DTS system using a few-mode fiber (FMF). Although the system requirements for DAS and DTS are quite different, FMF is considered an ideal compromise to satisfy the requirements of the two systems.

We present our latest advances in the field of miniature optical particulate matter sensors. By illuminating a single particle in an air channel, one can record the light scattering signature with a CMOS image sensor and then classify particles. This signature is optically pre-processed with an advanced, millimeter-sized, monolithic, refracto-reflective optical system. It performs notably a Fourier transform with very wide field of view of scattering angles, and includes as well integrated fluidics and alignment. Functional prototypes were fabricated using laser micro machining on glass, selective polishing, and were replicated with epoxy resin using a molding process.

A highly sensitive optical transduction system suitable for photoacoustic trace gas detection is presented. The system includes a thin deformable hinged cantilever assembled on an optical fiber to form a Fabry-Perot cavity, whose length varies according to the acoustic pressure disturbance. Consequently, the optical power of the reflected light fluctuates at acoustic frequencies around the working point, which is stabilized to prevent from environmental drift of the interference fringes. The resonant mechanical structure proposed in this study shows a spectral response in good agreement with FEM simulation, good linearity and stability, with a noise equivalent pressure of 12 μPa/√Hz.

Gas weak absorption in near-infrared is considered as inherent limit hinder the achievement of the miniaturized gas sensor. Thus, cavity enhanced absorption spectroscopy (CEAS) techniques are used to enhance the sensitivity by improving light-matter interaction length. In this work, a novel cavity enhanced technique is proposed based on the detection of the optical signal beating on RF analyzer to enhance the signal to noise performance by eliminating the flicker noise. Besides, enhancing the effective interaction length. The source consists of a fiber drum, a directional coupler, a tunable filter with FWHM of 1 nm and a semiconductor optical amplifier pumped above the laser threshold. The ring length is 1004 m leading to an FSR of 199 kHz. The gas cell is inserted into another ring, which consists of two directional couplers. The ring length is 6 m leading to an FSR of 33 MHz. The large ratio between the lengths of the two rings eliminates the need for a mode-locking technique. The acetylene gas cell is measured around 1535 nm. The novel technique capable of enhancing measurement sensitivity, providing experimental sensitivity and flicker noise immunity.

In this paper, the phase-sensitive optical time-domain reflectometry (Φ-OTDR) system is experimentally demonstrated using a Rayleigh enhanced AcoustiSens optical fiber to improve the acoustic sensing performance. The AcoustiSens optical fiber made of continuous gratings over the fiber, which significantly enhances the backscattered signal by 15 dB compared to the standard single-mode silica fiber. In addition, a simple and cost-effective self-mixing demodulation technique has been employed in coherent Φ-OTDR system to eliminate the frequency offset between the electrical local oscillator and the beat signal. The acoustic sensing performance with various acoustic frequencies are experimentally demonstrated in the proposed system using a 2 km sensing fiber with 1 m spatial resolution.

The Semiconductor industry’s evolution towards 7, 5 and 3 nm nodes at higher throughputs, poses a challenge on motion systems. Motion systems are expected to yield a sub nanometer accuracy and velocity higher than 500 mm/sec, fast move and settle, low drift and minimal thermal load on the system, especially in vacuum. Ultrasonic piezo-motors have many benefits to fulfill these requirements. This paper reports on the development of a novel piezo motor, characterized by high velocity, high stiffness, low thermal load and ultra-high precision. The use of six motors, in parallel, on a single motion axis can yield a 200N of thrust force and a 60 N/μm stiffness. The motor is driven by a new driver having a noise equivalent position of better than 60 pico-meter. This paper reviews the motor design considerations, performance capabilities in stiffness, duty cycle, sub-nanometer convergence and ultra-low drift. Robustness is demonstrated by long term run. An example of a motion axis driven by the novel motor is shown.

Tip, Tilt, Z mechanisms are required in a diversity of applications including Semicon and Life-Science. A challenge is to realize a long travel design. Using Ultra Sonic Piezo motors, two long travel designs are demonstrated and analyzed. The challenges of achieving high stiffness and fast response are discussed. Accuracies in the nanometer linearly or micro radian angularly are attained. The stage design is modular and robust. Both vacuum and ambient pressure versions could be implemented. Experimental results are presented on positioning and scanning. The mechanism benefits further from previously developed capabilities with these motors: Vibration suppression by the motor itself, zero drift and fast response.

The measurement of optical components using Experimental Ray Tracing (ERT) has proven its abilities in numerous applications. In this paper, we show how the measurement speed can be boosted by using a position sensitive detector (PSD). The results are compared with the measurement results using a camera. The idea of ERT is based on the linear propagation of a beam’s centroid through a homogenous medium. Therewith, detecting the centroid position of a beam in two parallel planes with a known distance leads to the beams direction. By introducing narrow laser beams at known positions and directions into an optical component or system and measuring the direction of the beams behind the component or systems as described above, the optical function of the component or system can be determined. To get this measurement technique working accurately, we used a movable camera chip as detector in two parallel planes. This brings the advantage of a good linearity and repeatability of the centroid detection. However, in contrast with a PSD, a camera chip is slow due to the generation and processing of many unused data. A PSD can achieve a measurement rate 20 times faster than a camera chip. Although, a good calibration is needed to achieve the same linearity and repeatability as a camera chip. In this paper we show the advantages and disadvantages of the use of a camera chip and a PSD in ERT. By measuring the same optical component, the detectors characteristics can be compared.

In this paper we show that Wave Front Phase Imaging (WFPI) has high lateral resolution and high sensitivity enabling it to measure nanotopography and roughness on a silicon wafer by simply acquiring a single image of the entire wafer. WFPI is achieved by measuring the reflected light intensity from monochromatic uncoherent light at two different planes along the optical path with the same field of view. We show that the lateral resolution in the current system used for these experiments is 24μm but can be pushed to less than 5μm by simply adding more pixels to the image sensor, and that the amplitude resolution limit is 0.3nm. Three 2-inch unpatterned silicon wafers were measured, and the nanotopography and roughness was revealed by applying a double Gaussian high pass filter to the global topography data.

We propose and demonstrate a new class of LIDAR technique based on optical frequency comb, named frequency-modulated comb LIDAR (FMcombLIDAR), to realize both high resolution and long distance measurement, overcoming the trade-off between the scan range and the coherence length. In FMcomb LIDAR, the multiple carriers from an optical frequency comb are used, enabling the coherent stitching of the multiple carriers. FMcomb LIDAR allows for a resolution equivalent to scanning by many comb modes while scanning only by the comb mode spacing.

Lock-in amplifiers are a powerful tool for signal detection within a noise environment. Commercial Lock-in amplifiers are bulky and disqualified for handheld operation. We report recent progress on FPGA based lock-in real-time detection scheme with the application in Quartz-Enhanced-Photo-Acoustic Spectroscopy (QEPAS). The new QEPAS configuration is tested and verified on a fast Methane detection scheme in the 1650 nm spectral regime. The novel FPGA detection scheme can be easily transferred into other spectral regimes and offers the opportunity of multi-species real-time measurements.

Artificial adaptive structures are systems which react on different environmental conditions. Bridges may dampen oscillations caused by heavy wind load, while high buildings may react to static loads from snow or much more dynamic ones, such as earthquakes. To interact, adaptive systems need control systems which control the actuators by measuring sensory input parameters (length, stress, deformation etc.). We realize a system where the sensory input comes from an image based optical camera system feeding the control system. We show first results for a holographic multipoint-based system for obtaining fast and highly accurate position measurement / deformation analysis with high accuracy at multiple spatial positions.

Hyperspectral imaging (HSI) technology has become prominent, with a wide range of applications: food quality control, crop monitoring, and medical diagnostics. As HSI is able to capture spatial and spectral data, it is highly desirable, but highly complex. However, this functionality presents a challenge for data acquisition as three-dimensional HSI images must be acquired by an image sensor of one less dimension. Thus, HSI systems are often pushbroom systems, with twodimensional images being successively constructed over time from line scans. Additionally, HSI is expensive and difficult to operate. A snapshot HSI system is developed to address these challenges, whereby the additional image dimension is encoded onto an occupied dimension on the image sensor. Additionally, the snapshot HSI system is constructed from low cost, readily available components. The presented snapshot HSI system consists of a transparent diffraction optical disc bonded to an aperture mask, with alternating transparent and opaque regions, acting as an optical chopper when rotated by a DC brushless motor. This allows separation of the spectra of overlapped pixels on the HSI image sensor. When an incident beam passes through this optical chopper, many frequencies (corresponding to spatial channels) are imposed by the binary mask, while undergoing diffraction across the visible spectrum. Overlapped spectra are directed at a charge coupled device, where Fourier analyses distinguish each spatial channel. System geometry is used to transform the Fourier amplitude spectra into functions of wavelength for each spatial pixel. The design is experimentally validated through comparison to a commercially available spectrometer.

Water is always at risk of accidental or intentional pollution that would consist of introducing a harmful chemical into a drinking water reservoir. Fiber-optics evanescent wave sensing has been shown to be an efficient sensor scheme for direct in-water sensing. Here we demonstrate a system for the detection of chemicals dissolved in water by using quantum cascade lasers (QCLs) coupled into a silver halide fiber. The study was performed over two frequency ranges: short wavelength (i.e. 3µm and 5µm) and long wavelength (between 8µm and 10µm) and using two different types of QCL source: pulsed and continuous wave.

The wide spectral range, compactness, low cost and high measurement speed of the MEMS FTIR spectrometers enable their use in real-time in-line gas analysis. They have the potential of identifying and quantifying several gases simultaneously compared to other infrared technologies such as the NDIR. However, the challenge of real-time spectral background removal from the measured spectrum has to be tackled first. In fact background removal is a common problem to spectroscopic applications relaying on the spectral shape and strength of the absorption lines. In this work, two of the most recent background correction algorithms, namely iterative averaging and morphological weighted penalized least squares, are adapted and applied on the MEMS FTIR spectrometer for gas mixture analysis. These algorithms don’t require prior knowledge about the background or the peaks position and don’t involve any manual selection of a suitable local minimum value. A 10-cm gas cell that contains known concentrations of SO₂, C₂H₄, N₂O and N₂ was measured using the MEMS FTIR spectrometer. The presence of several spectral absorption lines of these gases in the mid-infrared (MIR) region is considered a challenging case for automatic background correction algorithms. The spectra are measured in the MIR range of 1.6 μm - 4.9 μm with a resolution down to 33 cm^-1. The corrected spectra are compared with spectra measured with a standard bench-top spectrometer and the RMS error and Pearson’s correlation coefficient are calculated and good values of 0.8 % and 98 %, respectively, are obtained. Overcoming the spectral background removal paves the way for the use of MEMS FTIR spectrometer in real-time monitoring of multiple gases simultaneously.

Silicon Avalanche Photodiodes (APDs) are used in NASA’s Global Ecosystem Dynamics Investigation (GEDI) that was launched in December 2018 and is currently measuring the Earth’s vegetation vertical structure from the International Space Station. The APDs were specially made for space lidar with a much lower hole-to-electron ionization coefficient ratio (k-factor ~0.008) than that of commercially available silicon APDs in order to reduce the APD excess noise. A silicon heater resistor was used under the APD chip to heat the device to 70°C to improve its quantum efficiency at the 1064-nm laser wavelength while maintaining a low dark current such that the overall signal to noise ratio is optimized. Special APD protection circuits were included to raise the overload damage threshold to prevent device damage from strong laser returns from specular surfaces, such as still water bodies, and space radiation events. The APD and a hybrid transimpedance amplifier circuit were hermetically sealed in a TO-8 type metal package with a sufficiently low leak rate to ensure a multi-year operation lifetime in space. The detector assemblies underwent a series of pre-launch tests per NASA Goddard Environmental Verification Standard for space qualification. The APDs have performed exactly as expected in space. A detailed description of the GEDI detector design, signal and test results are presented in this paper.

Narrow bandwidth linear variable filters (NB-LVF) bring hyperspectral imaging to a wide range of applications in a compact, low weight, rigid structure. The center wavelengths of the narrow bandpass of a linear variable filter changes smoothly in one dimension and are constant in the orthogonal dimension along the surface of the filter. The filter, which is the size of the camera’s detector, is placed directly ahead of the detector and successive frames are acquired as the camera skews or as the camera platform moves across a scene. The full width, half maximum bandwidth of the filter used is 0.8% of the center wavelength and the spectral range is 400 to 900 nm with a wavelength gradient of 50 nm/mm. Examples using the LVF camera for emission spectroscopy, absorption spectroscopy, machine vision, and industrial process control and hyperspectral imaging are presented.

We demonstrate an intelligent multispectral system for various applications. The multispectral camera is handheld ideal for high resolution (5 Mpixel) applications, the system has 16 bands from 365 to 1020 nm that works at 40 fps, and can collect a hyperspectral cube in less the 500 milliseconds. The system uses deep convolution neural networks trained in a supervised learning fashion to characterize up to 7 skin conditions including skin cancer. Given a specific skin image the system characterizes the underline condition along with a confidence score.

We present an innovative optical particulate matter sensor. This optical sensor ‘on-a-chip’ combines a visible fibered light source and a custom-made CMOS image sensor chip. By illuminating a single particle in an air channel, we can record the light scattering signature on the photodiode matrix. A piece realized in 3D printing achieves fiber alignment and an efficient stray light protection.

A specific scattering pattern occurs from the interaction of light with a single particle. Unlike traditional optical PM sensors based on a single photodiode detection, we measure a lens-free projection of the scattering signature on the nearby image sensor (1.5mm projection distance). This allows us to count particles and determine their size and refractive index. These parameters are retrieved through image processing and by comparison with a radiometric model that calculates the projection of a Lorenz-Mie’s scattering pattern.
We describe the sensing technique, the architecture and fabrication of this sensor as well as the characterization results, which are in good agreement with our theory-based predictions. In particular, we show that it is possible to differentiate calibrated particulates of different sizes (monodisperse polystyrene-latex spheres). The sensor is sensitive enough to detect single particle and smallest than 1μm.

Ultrashort pulsed lasers represent unique tools for the processing of micro-optical components. Pulse durations around 1 ps and corresponding extreme peak intensities lead to interaction processes with all conceivable materials. As parts of almost every optoelectronic device, transparent materials represent a particularly challenging example for processing. Here, a controlled energy deposition at the surface or inside the volume is required while maintaining optical properties or implemented functionalities of adjacent areas. The talk will review strategies for the micro-processing of transparent materials that become possible by spatiotemporal beam shaping. Here, the beneficial use of non-diffracting beams is discussed as well as 3D-beam splitting approaches.

If a zonal wavefront sensor such as the Shack-Hartmann wavefront sensor is used to measure the surface profile, the sensing scheme apart from the test wavefront requires a reference wavefront. In order to switch between the two there is a need to replace the test surface by a reference surface such as a mirror. This often introduces inaccuracies in the measurement. In this paper, we introduce an experimental arrangement comprising wave plates and polarizing beam splitters where both the reference and the test wavefronts can be simultaneously present or one can easily switch from reference wavefront to test wavefront.

An innovative approach, based on hyperspectral imaging (HSI) coupled with chemometrics, allowing the detection of arsenic (As) in the hyper-accumulator fern Pteris Vittata L., is presented in this study. The aim of this work was to investigate the possibility of monitoring by HSI the As sequestration capacity of plants grown on As-contaminated soils, in order to perform soil remediation. The proposed approach is based on the acquisition by HSI in the SWIR range (1000-2500 nm) of fern leaves, followed by the implementation of a classification model based on Partial Least Square Discriminant Analysis (PLS-DA). Following this procedure, false color maps, representative of the chemical elements distribution on the leaves were obtained, where As is clearly detected without performing any chemical analysis. The proposed approach is not invasive and not destructive. Comparative evaluations were carried out analyzing Pteris Vittata L. leaves collected from plants grown on natural soils containing different As concentrations. To evaluate reliability, robustness and analytical correctness of the proposed HSI approach, micro X-ray fluorescence (μXRF) analyses were carried out on the same samples in order to quantitatively and topologically assess As presence in the leaves of the plants. The achieved results are very promising for monitoring the phytoremediation process by detecting and controlling the uptake of As plants growing on contaminated soils.

Questions of the necessity and ways of creating a photometric sensor for the express determination of impurities of light hydrocarbon fractions in wastewater and industrial waters, which are ultimately pollutants of the world's oceans, are posed. The results of studies of luminescence spectra using LEDs as a source of UV stimulation show the possibility of creating a luminescent small-sized highly sensitive sensor for monitoring the presence of light hydrocarbon impurities in wastewater and industrial waters. Achieving greater sensitivity is possible for a real sensor with a specific design.

Wavelength-tuning interferometry has been widely used for measuring the thickness variation of optical devices used in the semiconductor industry. However, in wavelength-tuning interferometry, the nonlinearity of phase shift causes a spatially uniform error in the calculated phase distribution. In this study, the spatially uniform error is formulated using Taylor series. A new 9-sample phase-shifting algorithm is proposed, with which the uniform spatial phase error can be eliminated. Finally, optical-thickness variation of transparent plate is measured using the proposed algorithm and wavelength-tuning Fizeau interferometer.

An innovative system structure was proposed including a linear probes device, an automatic optical registration system, a chamber-based gas supply system, a chuck table integrated with a heating device to efficiently evaluate the quality of sensors chips. The chamber-based gas supply system provided required gas concentration at the probing region. A chuck table integrated with a heating device to provide required uniform temperature was integrated to motion stage platform. An AOR system was implemented for registration of wafer automatically and adjustment of a linear probes device. Developed equipment had several advantages:(1) Registration process of wafer could be completed automatically within 50 seconds; (2) Required gas concentration could be quickly achieved within 60 seconds at testing region to save a lot of time and gas consumption; (3) Measurement could be finished within 30 minutes for a 6”-wafer with chip size of 1x1 mm under the condition of 10 chips probed for each time. The measuring efficiency was at least up to 10 times greater than the one of testing one by one for packaged sensors.

In the high-end optical instrument application, aspherical lenses have replaced spherical lenses and became a key component owing to the aberration correction characteristic it benefits. Though aspherical lenses truly provide multiple advantages, as long as the uncertainty and time-taking issue remain unsolved in CNC polishing process, the term “mass production” will still be far from realization. In this paper, we have developed a method based on Preston’s equation and the Hertz-Contact theorem (HCT) to construct the tool influence function (TIF), hoping to increase the convergence of the process result. We will also discuss how different tool offsets affect the polishing force against the workpiece. We firstly obtained velocity distribution between bonnet and workpiece from dynamics in polar coordinates, then applied the equivalent contacting-Young’s modulus in Hertz-Contact theorem to calculate the pressure distribution model. Subsequently, we conducted a series of experiments under IRP1000 by Zeeko Ltd. and avoided unstable outcomes caused by both machine vibration and deficient tool offset. We modified the parameters into five different feed rates while remaining the equivalent dwelling time, to create more observable features of material removed and further proved the linearity relationship between the dwell time and the removal depth. We applied LP66 as the polishing pad and fused silica as the workpiece to acquire the experiment result.

We present a novel design of wholly fiber-based mode scrambler. The device consists of two multimode fibers with halfball microlens finish, being at some distance and connected via liquid of a certain refractive index. The prototype was made using standard components. The laser output profile was proved to be stable and almost entirely independent of input conditions, i.e. varying positions and angles of input laser beam. Moreover, the mode scrambler of the new design shows a very good power throughput, reaching as much as 90% of the light power compared to a single multimode fiber.

The optical thickness is an important property of transparent plates when fabricating critical components. Spatially nonuniform errors, which are major factors in the measurement of the absolute optical thickness, can be brought about by phase errors related to the nonlinear error term. In this study, equations and a new sampling window for suppressing spatially uniform errors were constructed. Using these equations and new sampling amplitudes, we designed a new phase-shifting algorithm with 17 samples. Herein, the characteristics and advantages to the measurement of highly reflective surfaces when applying this new 17-sample algorithm are presented based on a Fourier representation. In addition, the superiority of the new algorithm in terms of its error control is demonstrated by comparing the errors occurring from a varying object phase, as well as root mean square errors, with those from different conventional algorithms.

CMOS image sensor (CIS) is used in various applications such as surveillance cameras, automobile cameras, mobile phones and digital single lens reflex (DSLR). The photodetectors used in the CIS are p-n junction photodiodes, pinned photodiodes, MOSFET-type photodetectors, and bipolar junction transistor-type photodetectors. A CMOS active pixel sensor (APS) with adjustable sensitivity is presented which uses MOSFET-type photodetector with a built-in transfer gate. The sensitivity of the APS using the MOSFET-type photodetector is much higher than that of the APS using the pn junction photodiode, since the MOSFET-type photodetector is composed of a floating-gate tied to an n-well and the photocurrent is amplified by the MOSFET. Although the APS using conventional MOSFET-type photodetector cannot control the current flowing through the channel, the APS using MOSFET-type photodetector with a built-in transfer gate can control the photocurrent by adjusting the pulse level of the transfer gate. Since the transfer gate controls the amount of electric charge that is transferred from the drain of the MOSFET to the integration node, the sensitivity of the APS can be adjusted by controlling the pulse level of the transfer gate. Using the high sensitivity characteristic of MOSFETtype photodetector and the function of transfer gate, the APS maintains high sensitivity under low intensity of illumination and adjusts to low sensitivity under high intensity of illumination. These results might be useful for extending the dynamic range of the APS using the MOSFET-type photodetector. The CMOS APS was designed and fabricated using 2-poly 4-metal 0.35 μm standard process and its performance was evaluated.

Topography becomes more important in quality assurance for manufacturing. This regards the characterization of macro-sized to medium optics and the optimization of a manufacturing process using a coherence scanning interferometer, e.g., the measurement of touch points that directly relate to the polishing process and how to better optimize the manufacturing. Profiles or simple flatness measurements are not sufficient and areal measurements by line profiler or microscope-based systems are time consuming. Quality assurance in manufacturing is cost sensitive, especially, when a 100% control and optimization is needed. A macro lens optical metrology tool can overcome these disadvantages. We investigated the use of a large area coherence scanning interferometer for manufacturing, including measurements. Depending on the tolerances of parameter and the given cycle-time, solutions are presented on how to provide important measurement feedback to the manufacturing process.

Engineers and more specifically surveyors frequently choose optical interferometry techniques for high precision metrology applications, as they offer a very good resolution and traceability of the measured distances. Nowadays, multiple interferometric solutions and interferometer configurations are available on the market. Part of them, typically single wavelength ones, offer a relative displacement measurement capability, with the advantage of a very high (even picometre) resolution, but are impractical in applications where distance tracking is needed after the reboot of the interferometer unit. Other solutions are absolute interferometers, usually based on Frequency Sweeping Interferometry (FSI), which offer true distance measurement. For such solutions, the measurement accuracy is worse than for relative ones and is of the order of the micrometer, mainly due to vibrations causing an optical path length change during the laser scan. At CERN, a range of new alignment solutions using Fourier based FSI is under development and qualification. This FSI technique allows the simultaneous measurements of absolute distances to multiple targets and is less sensitive to variations of intensity from the reflected optical signal, hence predisposing it for the harsh environment of accelerators. One advantage of this measuring technique is its simplicity to distribute hundreds channels over large-scale alignment installations. Its main disadvantage comes from potential variations of distance during the laser sweep. Such variations are typically caused by vibration or displacements of the reflector.
Multiple tests were performed to characterize the impact of reflective target vibration on the measurement uncertainty of Fourier-based FSI solutions. This paper describes the results of these tests and the lessons learnt.

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