Active optics is an enabling technology for future large space telescopes. Image-based wavefront control uses an image-sharpness metric to evaluate the optical performance. A control algorithm iteratively adapts a corrective element to maximize this metric, without reconstructing the wavefront. We numerically study a sharpness metric in the space of Zernike modes, and reveal that for large aberrations the Zernike modes are not orthogonal with respect to this metric. The findings are experimentally verified by using a unimorph deformable mirror as corrective element. We discuss the implications for the correction process and the design of control algorithms.

PROBA3 is the first high precision formation flying (FF) mission under responsibility of the European Space Agency (ESA). It is a technology mission devoted to in-orbit demonstration of the FF techniques, with two satellites kept at an average inter-satellite distance of 144m. The guiding scientific rationale is to realize a diluted coronagraph with the telescope (ASPIICS) on one satellite and the external occulter on the other satellite to observe the inner Solar corona at high spatial and temporal resolution, down to 1.08R⊙. The two spacecraft will be orbiting in a high eccentricity geocentric trajectory with perigee at 600km and the apogee at 60000Km and with an orbital period of 19hrs. The FF acquisition and operations will last about 6 hrs around the apogee and different metrology systems will be used for realizing and controlling the FF. The alignment active most critical sub-system is the Shadow Positioning Sensors (SPS), a series of Si-PM (Silicon Photomultiplier) disposed around the ASPIICS telescope's entrance aperture and measuring the proper positioning of the penumbra generated by the occulter at the center of the coronagraph’s optical reference frame. The FF alignment measurement accuracies required to the SPS are: 500μm for lateral movements and 50mm for longitudinal movements. This paper gives an overview of the opto-mechanical and electronic design and of the software algorithm for the FF intersatellite positioning. The expected performance of the SPS metrology system are reported.

Typical sources of electronics exposure in space are the high level ionizing radiation such as the Van Allen radiation belt, cosmic radiation for spacecraft and high altitude aircraft. It causes the major problem for airspace operations and space mission. Contemporary visual CCD cameras, CMOS devises, image optical sensors are extremely vulnerable to high level ionized radiation. Radiation hardening technology for contemporary electronic devices such as image sensors and image cameras causes the loss of resolution and is expensive. Using vector-tensor algorithm and theory of self-coupling electromagnetic waves in crystal symmetry 23 we demonstrated optimization of real time image procession. The results of theory were applied to doped bismuth titanium oxide crystal which exhibits electro-optical and photorefractive effect and is not vulnerable for high level X-Ray and 2x10⁷ rad gamma radiation exposure. Under the same level radiation exposure CMOS sensor was damaged. Application potential of doped bismuth titanium oxide crystal image sensor was discussed for nondestructive, non-non-contact, in situ evaluation of the major parts of engineering constructions in space.

With the current large scale introduction of automotive LIDAR sensors, cars will enjoy new possibilities with new rising features for active safety. Nevertheless, the vehicle is turned into a laser product due to LIDARs and other laser-based technologies. LIDAR applications usually are within the spectral range of Si-detectors due to their superior price point. These wavelengths are especially dangerous for the retina since the cornea and the vitreous humor are practically transparent for them, whereas the according light is still fully focusable by the lens of the human eye. The international laser safety standard IEC 60825-1 defines situations in which worst case scenarios are applied to test systems for their laser safety classification. In this paper, different situations are discussed which might not be obvious as being a laser safety hazard. Reconstructing these situations leads to the insight that the accommodation of the eye will take a crucial role of the laser safety of such automotive LIDAR systems, especially for complex systems consisting of multiple LIDAR sensors. It is shown that the eye safety hazard can be shifting within time and space. With this information in mind, the concept of Virtual Protective Housing should be tackled and reopened. The concept is explored from the view of functional safety as it is defined in the automotive standard ISO 26262.

Mechanical polygon mirror (PM) based spectral filters provide a low-cost, alternative method of tuning through broadband spectra. Their application is predominantly in Swept Source Optical Coherence Tomography (SS-OCT) whereby large bandwidths and narrow laser linewidths are essential for producing high resolution images with adequate depth range. Whilst higher scanning speeds are possible from commercially available sources, PM spectral filters retain distinct advantages. They are versatile, capable of operating in any wavelength range and have the ability to run several sources from the same PM, thereby reducing their cost. These aspects make them suitable for experimenting with different settings for OCT imaging in the laboratory. Although a number of different experimental configurations have been reported, the exact method that achieves optimum performance still requires more research. This investigation examines a free space, PM spectral filter with a two-lens telescope arranged in a Littman configuration, utilising a transmission grating as the spectral dispersive element. Research has shown that the parameters of this optical system, such as the focal lengths used in the telescope, have a significant effect on the bandwidth and linewidth, as well as the maximum power throughput. The system’s overall performance can easily be diminished if careful attention is not given to their operation with respect to the other components. This study is a comparison of overall system performance between telescope designs of different lens numerical apertures and diameters and we examine the factors that lead to higher power transmission and more uniform spectral power distribution, by reducing aberration and vignetting effects. An analysis of the spectral power distribution carried out on 1-inch and 2-inch diameter telescope designs shows that the wider diameter telescope provides superior performance across the selected wavelength range.

We illustrate a modular numerical approach that allows for the prediction of laser-generated optoacoustic signals in melanin doped PVA-H (polyvinyl alcohol hydrogel) tissue phantoms, geared towards experiments with dominantly absorbing, acoustically homogeneous media. We apply the numerical procedure to predict signals observed in the acoustic farfield and complement numerical simulations and laboratory measurements for an exemplary layered source volume configuration. Further, we address the inverse OA problem that facilitates the reconstruction of optical properties from measured OA signals for sufficiently facile problem setups.

In a previous work we have demonstrated a novel numerical model for the point spread function (PSF) of an optical system that can efficiently model both experimental measurements and lens design simulations of the PSF. The novelty lies in the portability and the parameterization of this model, which allows for completely new ways to validate optical systems, which is especially interesting for mass production optics like in the automotive industry, but also for ophtalmology. The numerical basis for this model is a non-linear regression of the PSF with an artificial neural network (ANN). In this work we examine two important aspects of this model: the spatial resolution and the accuracy of the model. Measurement and simulation of a PSF can have a much higher resolution then the typical pixel size used in current camera sensors, especially those for the automotive industry. We discuss the influence this has on on the topology of the ANN and the final application where the modeled PSF is actually used. Another important influence on the accuracy of the trained ANN is the error metric which is used during training. The PSF is a distinctly non-linear function, which varies strongly over field and defocus, but nonetheless exhibits strong symmetries and spatial relations. Therefore we examine different distance and similarity measures and discuss its influence on the modeling performance of the ANN.

High-order statistical properties of wavefield had been proven to have great influences in the realm of optics. For example, the speckle pattern induced by multi-interference of a coherent light source could be utilized to reconstruct the speckle flowgraphy either in ocular or cerebral blood flow. Such speckle pattern could also be used in depth estimation or optical positioning system. Recently, Kondakci et al. proposed a far-field lensless identification system based on measuring the complex coherence factor (the second-order phenomenon of light) of the field scattering off an obstructive object, which developed another possibility in optical imaging. However, their measurement was based on digital micro-mirror device, which restricted the flexibility of such optical system. Therefore, in this work, we designed an optical system to dynamically measure the complex coherence factor of a Schell-model and quasi-homogeneous beam via spatial light modulator. By analyzing the pixelated structure in theoretically and numerically, it was found that the fill factor of spatial light modulator would not affect the second-order characteristics of incident field even if its first-order characteristics were different. Our experimental results showed this system indeed had a good performance in the measurement of complex coherence factor. We believe the proposed optical system can help the lensless identification. Moreover, this system can be further improved by replacing the reflective-type spatial light modulator with transmitted-type, which will significantly increase the flexibility of optical instrument and will definitely have a great impact on other optical technologies.

Modelling of quadruple asymmetrical micro optical ring resonator is carried out in this paper and its performance as optical filter is analysed. Unit delay signal processing technique is implemented to model the proposed the proposed configuration in z-domain. MATLAB software is used to determine the free spectral range (FSR), group delay and dispersion characteristic of proposed configuration. Coupler design of the proposed configuration is done using Finite Difference Time Domain (FDTD) method.

With the improved abilities in the manufacturing of optical components, including spherical, aspherical and freeform optics, measurement systems with high potential in accuracy and repeatability are required. In this work, enhanced improvements and abilities of the new measurement technique based on a variation of experimental ray tracing (ERT), recently introduced at the “SPIE – Optifab 2017”, are presented. The idea of ERT is to detect the direction of a ray, deflected by the device under test (DUT), by measuring its location in two known planes. Originally, this has been proposed to measure the function of lenses in transmission. The potential of this original idea is demonstrated in several papers considering the measurement of imaging lenses, objectives and progressive additional lenses. Relying on the experiences from these works, a variation of the original ERT is shown in this work. Therefore, a setup has been created using a ray, represented by a narrow laser beam, introduced into the measurement system under a certain angle. This ray is directed on the DUT. After the ray has been reflected from the specular surface, a camera chip catches this ray and determines its position. By moving the camera chip along a linear axis, the direction of the reflected ray is calculated. Performing this test for a high number of points on the DUT, the surface can measured completely. The advantage of this technique is the simplicity of the measurement principle. In contrast to other non-contact surface measurement techniques, no optical components are needed between the DUT and the measurement sensor. Thus, no errors can be introduced to the measurement results from defective optics in the measurement setup. Furthermore, using only the principle of reflection leads to the advantage, that no reference for the detection of the surface data is needed. Furthermore, the principle of single rays propagated through the measurement system opens up the area of computer vision. High efficient algorithms make the representation of the measurement data in the evaluation process fast and easy. With this measurement setup, the measurement of a huge variety of surfaces is possible. Spheres, aspheres and freeform optics can be measured all in the same way. However, certain limits are given from the measurement setup. The results are compared to the results of commercially available measurement systems.

This paper highlights two examples of the use of full surface metrology to allow for functional tolerancing of components in the areas of EUV lithography (reticle characterization) and DUV precision lens manufacturing (lens holder metrology). For both examples, the measurement of the full surface is a key enabler to understanding the critical characteristics to control and tolerance for functionality or performance. Interferometric techniques are used to provide high resolution and accurate measurements for both examples. Subsequently, this data can be used to identify the surface characteristics that contribute to the end functionality and provide a means for deterministic correction or compensation.

A new demodulation method for sinusoidal frequency/phase modulation (SFM/SPM) interferometers, which can be suitable for displacements/3D profiles of targets, is proposed in the paper. Utilizing a laser diode (LD) as the light source and an electric optic modulator (EOM), frequency/phase modulations of the LD light can be achieved by modulating the LD injection current or the EOM. The SFM/SPM interference signal for the displacement measurement is composed by a series of harmonics of the modulation frequency. The two adjacent (2nd and 3rd) harmonics include the displacement information. By using the two harmonics, a Lissajous diagram can be drawn to obtain the displacements. Normally, the two harmonics can be demodulated by two lock-in amplifiers. In this paper, we propose a signal demodulation method to acquire the 2nd and 3rd harmonics without any lock-in amplifiers, for reducing a cost of lock-in amplifiers. In the proposed method, the data acquisition system is synchronized to the modulation frequency such that the sampling points are exactly at the maximum and minimum points of the 2nd and the 3rd harmonics, respectively. By addition/subtraction calculations of the data at the maximum/minimum points, the 2nd and 3rd harmonics can be obtained for drawing the Lissajous diagram. We first show displacement measurements of the target mirror in the SFM interferometer with 20 kHz modulation frequency. Secondly, we show 3D profile (=2D displacement) measurements of the moving target in the modified SFM interferometer using the high speed camera with 128*128 pixels and 180k frames/s. Thirdly, we discuss the feasibility of the proposed method. The authors will introduce experimental results of SPM interferometers at the oral presentation.

One of the largest challenges for optical systems is eliminating stray light generated by reflections off the walls and other optical elements of the device. Most black coatings are not sufficiently effective at grazing angles. Acktar’s black coatings exhibit particularly low residual reflectance and have been implemented in various instruments. The new proposed material exhibits particularly low hemispherical and specular reflectance – especially at grazing angles.

Mass-production of optical and opto-electronic devices is very critical to the number of the elements, their shape and type. Physical prototyping for this optical system depends not only on the lens quality and quantity, but also on the camera housing and the sensor. In our research we’ve studied the reasons of optical systems’ complexity and found out that it depends on optical system structure. After that a lens is optimized, tolerances are calculated and physical prototyping is implemented. In our case physical prototyping means a trial lot production. It was found, that virtual prototyping for different starting points can help to find the solution for mass-production, which will be then used for its manufacturing. This approach includes calculation of all elements of the camera lens from the first surface of a lens to the sensor, including 3D environment model. Depending on the type of the designed optical system, the virtual prototype modeling is included into a merit function for further optimization in the automatic lens design software. We can estimate a reduction of visual contrast of the image of the camera lens in the conditions similar to the conditions of the real device operation or show dependence of the contrast reduction in time of the operation. We implemented such an approach as a virtual parametric model of the lens camera device. We show a plot of the dependence on the cost of mass production of the mobile phone camera from the number of components. The cost information is valid for China.

The prototype of compact light-weighted hyperspectral imager based on the compact Offnerspectrometer is introduced. Two curved prisms are designed to disperse the incident light in the optical system with the benefits of low smile, keystone and lateral distortion. It has 148 spectral bands covering spectral range from 420 to 1000nm, the ground sampling distance is 50m@700km, and the swath width is 100km. But the weight is only 12.8kg, the outer dimensions are 362mm (X)* 343mm (Z)*139 mm (Y). As prisms are used for imaging spectrometer, the spectral sampling distance varies with wavelength. The width of the spectral response function varies from 1nm to 12nm. The mean bandwidth is less than 5nm. The sensor has achieved high performance levels in terms of signal to noise ratio(SNR), spectral calibration and image quality. It can be used for environmental and disaster monitoring.

Multi-oscillator ring laser gyro has no moving part in comparing with dither biased ring laser gyro, thus it is very suitable for wide band vibration measurement. Random noise in the output of ring laser gyro will constrain its performance dramatically. The random noise can be typically divided into quantization noise, white rate noise, bias instability (1/f or flicker rate), rate random walk and flicker rate ramp etc.. Allan variance method is a powerful tool in the time domain for the analysis of random noise, but because different noise has different correlation time, the Allan Variance need long test time such as more than a few hours. A noise analysis method of multi-oscillator ring laser gyro based on power spectral density (PSD) is put forward which need very short test time than Allan Variance method. the analyze is carried out in frequency domain other than time domain, curve fitting method is then used to get noise coefficients. Contrast experiments with the Allan variance analysis method are carried out. The results show that the noise coefficients calculated by the PSD method in which the test time is a few seconds are in good agreement with the coefficients calculated by Allan variance method in which the test time is 16384 seconds. Thus, it is feasible to calculated angle random walk coefficient by the PSD method. Moreover, due to less test time, the trend of the noise coefficients can also be observed by this new method.

Current paper presents the results of the optical neurosystem research for intracranial implantation targeted on phototheranostics of deep-lying brain tumors. Brain tumors treatment is a complicated multistage process, and currently there is a need for the user-friendly fiber optic toolkit that could allow carrying out multiple diagnostics and therapy of such neoplasms type without additional surgical intervention. The optical neurosystem developed in the framework of this study is based on the scaffold with the internal optical fiber structure placed into the tumor bed and designed for diagnostic and therapeutic laser radiation delivery. Such neurosystem, along with specific photosensitive agent application will provide malignant cells diagnostics by the fluorescent signal and permanent monitoring of processes occurring in the probed area by means of fiber optic probe with emitting and receiving fibers connected with laser source and spectrometer, respectively. The created neurosystem could be used to direct the growth of randomly proliferated deep lying brain tumor cells along the scaffold fibers towards the extracranial surface where malignant cells could be registered, identified and therapeutically affected by photodynamic action. A set of preliminary experiments devoted to spectral-optical evaluation of brain tissue properties was performed. The research of the scaffold and its inner fiber optical structure was carried out on the model samples of brain tissue phantom and in vitro on C6 glioblastoma cell line. Obtained results are being discussed.

Today the most important problem of a transplantation is a rejection of healing skin tissue. The reason of a skin rejection is a high level of inflammation reaction and a slow rate of neoangeoginesis. A lot of methods exist for imaging of tissue healing extent, unfortunately, all of them have some drawbacks. Laser induced fluorescence is a non-invasive method which provides ambulatory and fast diagnosis. The concept was created and optimal parameters of spectral device were selected based on the experiment results. The non-invasive spectral device will allow determining a state of a healing skin and rate of skin tissue engraftment or rejection by its spectroscopic properties analysis using aluminum phthalocyanine nanoparticles (nAlPc). These nanoparticles are spectroscopically sensitive to inflammation reactions and begin to fluoresce while interacting with immune cells in inflamed tissue. The operation principle of developed device based on analysis of diffuse reflected light from a skin area. The device consists of the six red laser diodes. The red range laser irradiation allows dedicating autofluorescence of biological tissue components such as lipopigments, porphyrins. The fluorescence intensity of exogenous fluorophores helps identifying the degree of transplant engraftment because it is correlate with the inflammatory reactions intensity in a skin. End users will be burn centers, medicine facilities for monitoring of a postoperative sutures engraftment. It can also be used at home to assess the healing of small wounds.

Rapid rates of technologies development allow humanity to take a look at new opportunities. Development of 3Dprinting is a great example, which more actively comes into everyday life. Despite tempestuous development of 3D-printing, there is a big amount of problems connected with accuracy, quality, reliability, economy and safety of manufacturing. The technological process of three-dimensional printing requires control over the accuracy of the product, identifying defective parts in the printing process, as well as adjusting the print parameters during operation. In this work we propose the solution of problems by using systems of visual control. A system of solutions that allows to reliably detect problems that occur during printing, to form a feedback system that react to events happening in the area of printing in the real time. For example, the creation of a visual feedback system will help improve accuracy. Controlling defective parts can be done by comparing the detail that is in the process of printing with its three-dimensional model. By equipping the system with additional sensors, for example, a thermal imager, it is possible to analyze the model overheating zones and change the print parameters directly during the manufacturing of the part. The creation of such a tool is the development of hardware and software acquisition and maintenance of additional parameters in the 3D-printing. From the point of view of optics, it is possible to solve such a problem in several ways, which will be describe in this report.

Nowadays, fast development of laser based material processing technology and additive manufacturing requires highly efficient high-power laser diode modules with a sub kW level output optical power. Such modules are also used for pumping of solid-state and fiber lasers. One option for obtaining a high-power laser beam is the spatial combination of the radiation of single laser emitters using polarization elements. The second way is manipulation of radiation from stack of laser bars. Both ways have advantages and disadvantages: in the first case, the failure of one emitter is not so crucial, but it is necessary to align a large number of optical elements with high accuracy, which also put stringent requirements to manufacturing tolerance. The second is more compact, but the solution of the thermal problem is much more difficult and bulky complex shapes optical elements emerge. In this paper, several approaches for design of optical scheme of high-power laser diode module are considered. The efficiency of optical schemes and sensitivity to misalignments are analyzed. Recommendations on the choice of schemes depending on necessary power are given.

We investigate the application of optical feedback interferometry (OFI) for balance adjustments of rotating mechanical gyroscopes that are used in many areas such as aeronautics industry. We compare our results with the industrial balancing machine which measures the amount and position degree of horizontally rotating gyroscope disk. Measurement results show that OFI can be used as an alternative for balance checking. Optical feedback interferometry is based on the mixing of laser light in the cavity with the portion of light which is reflected back to the cavity. Self-mixing interferometric effect occurring in the cavity carries the information about the object movement with high precision such as fluctuations from the ideal value. In this work, we report that OFI offers promising results for measuring unbalance of high precision spinning gyroscopes or rotors used in industry.