Optical Part Research Articles

Frequency comb with a spectral range of 0.4-5.2 µm based on a compact all-fiber laser and LiNbO3 waveguide.

This Letter presents a 0.4-5.2-µm frequency comb from a compact laser. We designed an integrated fiber device for a figure-9 laser and constructed an all-fiber laser system. The spectrum of the fiber laser was scaled to the broadband region using a chirped periodically poled lithium niobate waveguide. To use this system for gas sensing, a mid-infrared comb with a spectral range of 2.5-5.2 µm and average power of 2.1 mW was divided using an optical filter. The optical part was packaged in a 305 mm × 225 mm × 62 mm box. The comb was stabilized by locking the repetition rate and carrier-envelope offset frequency of the seed source. The system provided an ultrabroadband spectral range from 0.4 to 5.2 µm, which could be applied to spectroscopy, frequency metrology, and optical synthesizers.

Photodetectors based on chemical vapor deposition or liquid processed multi-wall carbon nanotubes

Carbon nanotubes (CNTs) have attracted great interest for applications due to their unique mechanical, electronic and optoelectronic properties. The advantages of the multiple wall carbon nanotubes for optoelectronic devices like photodetectors and photodiodes are the large effective photo-collector surface as well as the possibility to tune the band gap and absorbance by controlling the growth parameters. In this work, we demonstrate two types of hybrid Multi-Wall CNTs/Si3N4/n-Si photodetectors based on ordered (produced with Chemical Vapor Deposition – CVD) and solution processed MWCNTs and evaluate their performance in UV and visual spectrum (275 nm, 655 nm). Device parameters were obtained by comparison of I–V characteristics to Schottky barrier models and C–V characteristics to standard MIS capacitor models. The role of silicon nitride layer was also examined by comparing devices with different nitride layer thickness. Focusing on the UV part of the spectrum, the solution processed device was photosensitive in the voltage range 3V–6V giving its best performance (External Quantum Efficiency - E.Q.E. 85%@275 nm) at 5V and illumination of 5 μW. The CVD processed device showed lower EQE for the same bias voltage range. Both devices showed a low performance in optical part of the spectrum compared to the corresponding one in the UV part of the spectrum. The mean optical responsivity values obtained at the UV part of the spectrum in both cases indicate that the Visible light blind MWCNT/Si3N4/n-Si system have a potential use in UV photodetector applications. In particular, solution processed devices may pave the way for cheap production of UV sensor systems.

Vibration Measurements by Self-Mixing Interferometry: An Overview of Configurations and Benchmark Performances

Self-mixing interferometry (SMI) is suitable to sense and measure vibrations of amplitudes ranging from picometers to millimeters at frequencies from sub-Hz to MHz’s. As an optical probe, SMI has the advantage of being non-invasive with the ability to measure without any treatment of the target surface and operate from a substantial standoff distance from the target. As an additional advantage, the SMI configuration is much simpler than that of conventional interferometers as it does not require any optical part external to the laser source. After a short introduction to the basics of SMI, we review the development of configurations of SMI instruments for vibration measurements, based on both analog and digital processing, with record performance to cover the range of vibration amplitudes from 0.1 nm to 1 mm, frequencies up to MHz, and stand-off distances up to 100 m. These performances set a benchmark that is unequaled by other approaches reported so far in the literature. The configurations we describe are (i) a simple MEMS-response testing instrument based on fringe counting, (ii) a half-fringe locking vibrometer for mechanical mode analysis and transfer function measurements, with a wide linear response on six decades of amplitude, (iii) a vibrometer with analog switching cancellation for μm-to-mm amplitude of vibrations, and (iv) a long standoff distance vibrometer for testing large structures at distances up to 100 m and with nm sensitivity. Lastly, as the vibrometer will almost invariably operate on untreated, diffusing surfaces, we provide an evaluation of phase-induced speckle pattern errors affecting the SMI measurement.

Evaluation of advanced cleaning processes for sensitive surfaces in optical instrumentation

Contamination has become a major issue in all high-tech industries, with increasingly stringent cleanliness requirements. It is the case for sensitive parts of space flight hardware, such as optics or other embedded equipment for which surface cleanliness is a critical topic, since even a thin layer of contaminant can adversely affect performance. Sometimes, cleaning may be needed to reach a specified cleanliness surface level at different integration phases of instrument or satellite, or as a corrective action in case of anomaly. Thus it is recommended to consider cleaning techniques without direct contact with the sensitive or fragile surface to prevent any damage after treatment. Five processes or techniques among those described for instance in the ECSS standard dedicated to ultracleaning of flight hardware (laser, vacuum bakeout, carbon dioxide (CO2) snow, supercritical CO2 and plasma) have been chosen for a test campaign to assess their efficacy on representative samples of sensitive optical parts (e.g.: glasses, mirrors, treatments, coatings, etc.). The study has been focused on the removal of molecular residues from substrates intentionally contaminated by a mixture of typical chemical contaminants. After a description of the selected cleaning techniques and their pros and cons, this paper will present the methodology adopted for the process validation using analytical chemistry and the comparative results of the performance of each cleaning technique. The impact on materials and the ease of implementation have been evaluated as well. In fine, the objective of this study is to provide some guidance to choose one or several non-contact processes suitable for cleaning sensitive space hardware, in order to guarantee contamination-free surfaces before flight and limit any risk of failure.

Modeling of a dielectric vibration sensor

The article presents a numerical analysis of the possibility of creating a dielectric amplitude oscillation sensor and selecting its optimal parameters. The sensor consists of a quartz sensing element with a mirror attached to it, which is attached to the body with an elastic suspension, and two optical fibers. The study is divided into two main stages: modeling the mechanical part of the sensor and determining its optimal geometry and developing a model of the optical component of the sensor. A mechanical study of the vibration sensor was carried out in order to determine its resonant frequency and determine the optimal length of the elastic jumper. The optical part of the study focused on the selection of optimal parameters for the configuration of the location of optical fibers. The results showed that the sensor has a natural oscillation frequency above 2000 Hz, and there is a weak dependence of the sensor sensitivity on the oscillation frequency with a jumper length of 1 mm. The study presents an analytical solution for choosing the optimal parameters of the optical component of the sensor. The research contributes to the development of fiber-optic accelerometers for measuring and analyzing vibration in various applications.

Quantum Efficiency Measurement of Single-Particle Phosphor by Proximity Method

In this study, a technique for measuring the quantum efficiency of single-particle phosphors was developed. For this purpose, a proximity measurement technique capable of measuring the photoluminescence of a single particle with a high signal-to-noise ratio was adopted. Single optical fibers were combined with a commercially available spectrofluorometer to directly measure the light distribution near the phosphor. The number of photons absorbed by the phosphor can be evaluated by focusing the Xe light down to 18 μm, which is equivalent to the particle diameter. By eliminating the optical parts as much as possible and performing spectral sensitivity calibration over a wide wavelength range, an internal quantum efficiency evaluation similar to a powder measurement was established.

Laser Bioprinting with Cell Spheroids: Accurate and Gentle.

Laser printing with cell spheroids can become a promising approach in tissue engineering and regenerative medicine. However, the use of standard laser bioprinters for this purpose is not optimal as they are optimized for transferring smaller objects, such as cells and microorganisms. The use of standard laser systems and protocols for the transfer of cell spheroids leads either to their destruction or to a significant deterioration in the quality of bioprinting. The possibilities of cell spheroids printing by laser-induced forward transfer in a gentle mode, which ensures good cell survival ~80% without damage and burns, were demonstrated. The proposed method showed a high spatial resolution of laser printing of cell spheroid geometric structures at the level of 62 ± 33 µm, which is significantly less than the size of the cell spheroid itself. The experiments were performed on a laboratory laser bioprinter with a sterile zone, which was supplemented with a new optical part based on the Pi-Shaper element, which allows for forming laser spots with different non-Gaussian intensity distributions. It is shown that laser spots with an intensity distribution profile of the "Two rings" type (close to Π-shaped) and a size comparable to a spheroid are optimal. To select the operating parameters of laser exposure, spheroid phantoms made of a photocurable resin and spheroids made from human umbilical cord mesenchymal stromal cells were used.

Theoretical insight of stabilities and optoelectronic properties of double perovskite Cs2CuIrF6: Ab-initio calculations

In this study, we predict the stability, elastic, electronic and optical properties of double perovskite (DP) Cs2CuIrF6. The detailed investigation of electronic structure and optical properties to find the suitability of DP Cs2CuIrF6 for device applications. From the structural optimization results, the stability of DP (Cs2CuIrF6) is in cubic order and belongs to the Fm-3m space group (#225) with a nonmagnetic (NM) state. Additionally, the elastic results show that this DP is mechanically stable in a cubic and ductile manner. Further, we explain in detail the semiconducting nature of the proposed DP with the help of electronic structure and density of states (DOS). The electronic band gap of DP Cs2CuIrF6 is 0.72eV (LV-XC). The optical part discussion, like the dielectric function ε, reflectivity R, refractive index n, absorption coefficient α and optical conductivity σ up to 13.00eV. The studied compound is explored as a potential candidate for optoelectronic applications. The density functional theory (DFT) within generalized gradient approximation (GGA) scheme of Perdew, Burke and Ernzerhof (PBE) as implemented in Wien2k computational code is utilized to achieve stable structure, elastic, electronic and optical properties of this material. The dynamic stability of this material was studied using the finite displacement method implemented in the CASTEP computational code. The elastic results have been computed by the IRelast package implemented in the Wien2k computational code.

APPLICATION FEATURES OF GLASS-CERAMIC SO-115M IN MANUFACTURING OF OPTICAL PARTS FOR RING He-Ne-LASERS

The results of an investigations into the effect of filamentous striae with birefringence from 3 to 15 nm/cm in SO-115M glass-ceramic on the manufacturing quality of optical parts for ring lasers and the exact characteristics of laser gyroscopes based on them are presented. It is shown that the presence of striaes with stresses of no more than 15 nm/cm in SO-115M glass-ceramic does not depend on the speed of manufacturing the resonator optical circuit and the quality of its assembly. The presence of striaes in the output mirror additional backscattered of a ring laser may have the destination of lock-in zone. Correct adjustment of the output mirror allows to reduce scattering and reveal the growth of the lock-in zone in laser gyroscope. It is shown that the accuracy of the laser gyroscope improves by the quality mirror substrates, the geometry of the resonator body, and increases the accuracy of scattering inside the resonator.

Environmental Stability Design of the Aerial Mapping Camera Based on Multi-Dimensional Compound Structure.

Environmental stability technology plays an important role in improving the adaptive range, image resolution and ensuring the stability of geometric parameters of aerial mapping camera. Traditional environmental stability methods directly implement active and passive thermal design to optical systems, which is easy to lead to radial temperature difference of optical components, and cannot eliminate the influence of pressure change. To solve the above problem, a method of environment stability design based on multi-dimensional structure is proposed. Firstly, the aerial mapping camera is designed as imaging system component (core) and sealing cylinder (periphery), and a sealed air insulation sandwich is formed between the two parts to realize the sealing design. A thermal interface is reserved outside the seal to avoid the radial thermal stress caused by direct heating of the optical parts, and a multi-dimensional Environmental stability structure is formed. Secondly, the core and the external thermal environment of aerial mapping camera in complex aviation environment are modeled and theoretically analyzed. Finally, the effectiveness and stability of the multi-dimensional structure method is verified by the thermal simulation and the flight. The results show that the thermal control power is 240 W, the thermal gradient of the optical system is less than 5 °C, the radial temperature difference is less than 0.5 °C. High quality image and ground measurement accuracy are obtained. Compared with tradition thermal control methods, the proposed method has the advantages of accuracy and low power consumption, which can effectively reduce the power consumption and difficulty of the thermal control.

Convex optical freeforms using fringe Zernike overlay approach for two-mirror and three-mirror telescopes for space applications

The challenge in manufacturing and testing of convex optical parts is well known in comparison to its concave counterpart and an optimized imaging system invariably features a combination of both. Of late, freeform mirrors find lot of interest in space applications as the optical systems remain compact within the allocated envelope. As is well known, these freeform mirrors are difficult to manufacture and test due to their lack of rotational or translational symmetry and poses additional challenges if it has convex profile. In the current investigations, two new convex freeform optical surfaces are proposed which is based on fringe Zernike overlay technique. The first convex freeform envisaged is for a two-mirror off-axis telescope where the secondary mirror is an off-axis freeform and the second convex freeform for a three-mirror anastigmat telescope where the secondary mirror is an on-axis convex freeform. Substitution of these convex freeform surfaces in the two-mirror and three-mirror telescope systems aid in the correction of asymmetrical aberrations to a wider view field, thereby enhancing the performances of the de-centred and tilted systems in the respective configurations. The procedure adopted for the manufacturing of these convex freeform surfaces using bonnet polishing methods and the interferometric tests using modified-Hindle null corrector and subaperture-stitching techniques for evaluation are described in detail.

Development of runner reservoir and its effect on optical properties of small high-precision plastic injection molded parts

ABSTRACT Adding reservoirs as extensions to a multi-cavity runner-system to regulate cavity fill-rate within small, high-precision optical parts during filling and fill-to-pack switch-over (F/P) was studied with the aid of simulations. This work aimed for a constant melt-front velocity inside the cavities with varying geometries. Three methods of reservoir designs were considered: first, using engineering intuition, second and third, using mass balance and mass and momentum balance equations, respectively. Eight reservoirs were designed and compared to two no-reservoir cases. For each case, 27 runs covering three levels of fill-rate, F/P, and packing pressure were simulated, resulting in 270 simulation runs. The quality variables of flow and thermally induced retardation and the average and standard deviation of volumetric shrinkage were considered and for each parameter, the minimum, best cases, occurred with a reservoir case. Thus, this study offers a proof-of-concept design for using reservoirs to improve molding of small, high-precision optical parts.

Using a dynamic Mueller matrix in modeling of retinal birefringence scanning systems

Polarization modeling by means of the Mueller matrix formalism is widely used for representation and optimization of the performance of complex polarization-sensitive systems. Yet, this turns out to be a challenge, as soon as such systems become dynamic, as is the case with scanning systems using polarized light. This work explores the possible use of dynamic Mueller matrices, in order to enable modeling of the optical system at any given moment, regardless of the position or orientation of any moving part. To achieve this, first the dynamic optical part (or a whole optical module) is measured using ellipsometry, to obtain several Mueller matrices characterizing the part at different moments in time. Then, all transitional matrices are calculated by means of interpolating their elements. This method is particularly useful when modeling scanning systems employing a scanning mirror. The author demonstrates its performance on a retinal birefringence scanning system. It was shown that the system itself is changing polarization quite significantly. It was determined how the six degenerate states can be changed by the dynamic system alone, and which Stokes vector elements are most prone to matrix element fluctuations. It is also suggested that a dynamic Mueller matrix can facilitate precise polarization modeling, and accelerate system optimization.

Rapid fluorometric determination of ammonium in exhaled breath condensate based on digital image of a windowless falling drop cell via a low-cost digital microscope

Measurement of ammonia in exhaled breath is of interest in medical and health sciences. The fluorometric determination of NH3 in exhaled breath condensate (EBC) was developed based on a digital image of a windowless falling drop (WFD) cell at the end of tube via a sensitive and selective reaction of NH3-OPA-sulfite in flow injection analysis system (FIA). A low-cost USB microscope as a facile instrumentation without expensive optical parts, an amplifier circuit, and a data acquisition unit, was used as a fluorescence light detector for the WFD cell via instant reporting temporal profile of digital value. A linear calibration graph of NH4+ in the range of 0.5–10 µmol L−1 can be obtained with a limit of detection of 0.5 µmol L−1 NH4+, and repeatability of 5.5% RSD (n = 11). The fluorescence (FL) signal obtained from the low-cost USB microscope was not different from that using the photodiode detector via a cross-shape flow cell. The proposed device was successfully applied for NH4+ determination in EBC and air absorbing solution samples with the recovery of 98–110%. The approach for instant reporting of a temporal profile of digital image value from a camera shows a potential to be applied for rapid chemical analysis in other microfluidics systems.

Triple Color Image Encryption Using Hybrid Digital/Optical Scheme Supported by High-Order Chaos

Image security has attracted increasing interest, wherein image encryption is an effective and direct method that can be implemented using digital, optical, or hybrid techniques. The challenge is how to design a high-speed, and high-security level multiple color image encryption scheme which makes use of advanced techniques such as chaotic system and deep learning. This issue is addressed in this paper where a nine-dimensional (9D) chaotic-based Hybrid Digital/Optical Encryption (HDOE) scheme is proposed for triple color images. The scheme consists of cascading digital and optical encryption parts controlled separately by the chaotic sequences. The nine chaotic sequences are grouped into three sets, and each set is responsible for the encryption of one of the RGB channels independently. The digital part uses fusion, XOR operation, and scrambling. The optical part uses two independent chaotic phase masks in the optical Fourier transforms domain. A Denoising Convolution Neural Network (DnCNN) is designed to assist the robustness of the decrypted images against Gaussian noise. The simulation results reveal that the proposed triple-image HDOE scheme offers entropy of 7.9991, 7.9987, and 7.9991 bits for R, G, and B channels, respectively,  and infinite Peak Signal-to-Noise Ratio (PSNR) for the decrypted images.

All-fiber-device-coupled compact, transportable ultra-stable laser.

In response to the demand for operation in non-laboratory environments, there has been a trend toward the development of compact, transportable ultra-stable lasers. This paper reports on this sort of laser system assembled in a cabinet. The whole optical part utilizes fiber-coupled devices to simplify the integration. In addition, spatial beam collimation and alignment into the high-finesse cavity are realized by a five-axis positioner and a focus-adjustable fiber collimator, which significantly relax the alignment and adjustment. A theoretical analysis is performed on how the collimator adjusts the beam profile and coupling efficiency. The support structure of the system is specially designed as well so that it features robustness and transportation without performance degradation. The observed linewidth is 1.4Hz within a duration of 1s. After subtracting the linear drift of 70 mHz/s, the fractional frequency instability is better than 4 × 10-15, for the averaging time ranging from 1 to 100s, which is close to the thermal noise limit of the high-finesse cavity.

Quantitative analysis of the effects of incorporating laser powder bed fusion manufactured conformal cooling inserts in steel moulds over four types of defects of a commercially produced injected part

The introduction of additively manufactured conformal cooling inserts in steel moulds for plastic injection is becoming a recommended standard. Fine adjustment of the temperatures in the mould has demonstrated potential to reduce cycle times and to increase production volumes. Within this context, the present article explores the historical production data of a commercially produced part, before and after the incorporation of an L-PBF conformal cooling insert, to analyse what is the quantitative real effect on the efficiency of the production runs. The article analyses the change in the global rejection rates, and its effect over four different product defect types, i.e.: optical (surface), part integrity (bubbles, transparency, geometry), incomplete fill-in (interior), and breakages during extraction. The results demonstrate a specific decrease on the average appearance (from 20.53% to 13.48%; reduction of 7.05%) and variability (standard deviation from 14.16% to 6.81%; reduction of a 7.35%), of the global scrap rates, and a significant decrease in the scrap rates generated by optical defects and extraction part breakages. The article also characterises the former and the new processes by adjusting two distribution functions (Pareto Type-I and Weibull) and compares different estimates for the global expected scrap rates in past and future production runs.

Application of the Improved Grinding Technology to Freeform Surface Manufacturing

In order to meet the manufacturing requirements of modern space remote sensors for high-precision freeform optical parts, the grinding technology and its application were studied. The objective of this paper was to improve the application effect of traditional grinding technology in the processing of hard and brittle materials, and then apply it in specific fields. Therefore, the influence of key process factors such as cutting speed and removal depth on subsurface damage (SSD) was studied based on orthogonal experiments, and an improved grinding technology characterized by low SSD and high surface shape accuracy was formed. Then, the effect of this grinding technology was further verified by the high-precision manufacturing of freeform surfaces. A surface of a 130 mm diameter freeform surface was machined by improved grinding technology and combined polishing technology, the final root mean square of surface shape reached 12.1 nm. The improved grinding technology can reduce SSD from 20 μm to 10 μm, and improve the manufacturing efficiency of freeform surfaces above 30% when the cut speed is 20 m/s and the remove depth is 10 μm. The proposed technology can be applied to the extreme manufacturing of hard and brittle materials.

Portable TDLAS Sensor for Online Monitoring of CO2 and H2O Using a Miniaturized Multi-Pass Cell.

We designed a tunable diode laser absorption spectroscopy (TDLAS) sensor for the online monitoring of CO2 and H2O concentrations. It comprised a small self-design multi-pass cell, home-made laser drive circuits, and a data acquisition circuit. The optical and electrical parts and the gas circuit were integrated into a portable carrying case (height = 134 mm, length = 388 mm, and width = 290 mm). A TDLAS drive module (size: 90 mm × 45 mm) was designed to realize the function of laser current and temperature control with a temperature control accuracy of ±1.4 mK and a current control accuracy of ±0.5 μA, and signal acquisition and demodulation. The weight and power consumption of the TDLAS system were only 5 kg and 10 W, respectively. Distributed feedback lasers (2004 nm and 1392 nm) were employed to target CO2 and H2O absorption lines, respectively. According to Allan analysis, the detection limits of CO2 and H2O were 0.13 ppm and 3.7 ppm at an average time of 18 s and 35 s, respectively. The system response time was approximately 10 s. Sensor performance was verified by measuring atmospheric CO2 and H2O concentrations for 240 h. Experimental results were compared with those obtained using a commercial instrument LI-7500, which uses non-dispersive infrared technology. Measurements of the developed gas analyzer were in good agreement with those of the commercial instrument, and its accuracy was comparable. Therefore, the TDLAS sensor has strong application prospects in atmospheric CO2 and H2O concentration detection and ecological soil flux monitoring.

Proposal of a PIT-based pressure sensor using high pairing of MoS2 monolayer and graphene

In this paper, design and numerical simulation of a new proposed plasmonic pressure sensor based on Plasmon-Induced Transparency (PIT) is introduced. One of the most sensitive methods in using of plasmonic structures is PIT-phenomena that we used in this sensor. Two-dimensional (2D) molybdenum disulfide (MoS2) and graphene are used in the proposed structure because of their high sensitivity to pressure and suitable resonance conditions. The system consists of two parts: mechanical and optical parts. Applying any pressure to the mechanical part, causes a compression in the sensor structure, which results in a change in the resonant frequency of the optical output spectrum. Ultra-high sensitivity, nanoscale, simple structure, integration capability and suitable range of pressure measurement from 1 MPa to 50 GPa are the advantages of the proposed sensor. Finite Element Method (FEM) and Finite Difference Time Domain (FDTD) methods have been used for simulation of mechanical and optical parts, respectively.