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Significance: The estimation of tissue optical properties using diffuse optics has found a range of applications in disease detection, therapy monitoring, and general health care. Biomarkers derived from the estimated optical absorption and scattering coefficients can reflect the underlying progression of many biological processes in tissues. Aim: Complex light--tissue interactions make it challenging to disentangle the absorption and scattering coefficients, so dedicated measurement systems are required. We aim to help readers understand the measurement principles and practical considerations needed when choosing between different estimation methods based on diffuse optics. Approach: The estimation methods can be categorized as: steady state, time domain, time frequency domain (FD), spatial domain, and spatial FD. The experimental measurements are coupled with models of light--tissue interactions, which enable inverse solutions for the absorption and scattering coefficients from the measured tissue reflectance and/or transmittance. Results: The estimation of tissue optical properties has been applied to characterize a variety of ex vivo and in vivo tissues, as well as tissue-mimicking phantoms. Choosing a specific estimation method for a certain application has to trade-off its advantages and limitations. Conclusion: Optical absorption and scattering property estimation is an increasingly important and accessible approach for medical diagnosis and health monitoring. [ABSTRACT FROM AUTHOR]

The use of bioluminescence as a reporter for physiology in neuroscience is as old as the discovery of the calcium-dependent photon emission of aequorin. Over the years, luciferases have been largely replaced by fluorescent reporters, but recently, the field has seen a renaissance of bioluminescent probes, catalyzed by unique developments in imaging technology, bioengineering, and biochemistry to produce luciferases with previously unseen colors and intensity. This is not surprising as the advantages of bioluminescence make luciferases very attractive for noninvasive, longitudinal in vivo observations without the need of an excitation light source. Here, we review how the development of dedicated and specific sensor-luciferases afforded, among others, transcranial imaging of calcium and neurotransmitters, or cellular metabolites and physical quantities such as forces and membrane voltage. Further, the increased versatility and light output of luciferases have paved the way for a new field of functional bioluminescence optogenetics, in which the photon emission of the luciferase is coupled to the gating of a photosensor, e.g., a channelrhodopsin and we review how they have been successfully used to engineer synthetic neuronal connections. Finally, we provide a primer to consider important factors in setting up functional bioluminescence experiments, with a particular focus on the genetic model Caenorhabditis elegans, and discuss the leading challenges that the field needs to overcome to regain a competitive advantage over fluorescence modalities. Together, our paper caters to experienced users of bioluminescence as well as novices who would like to experience the advantages of luciferases in their own hand. [ABSTRACT FROM AUTHOR]

This research paper describes the development of a low-cost reversible tandem lens mesoscope for brain imaging in rodents. The mesoscope is compact, versatile, and cost-effective, using off-the-shelf components. It offers high-resolution structural and functional imaging and can accommodate different types of samples and sample holders. The system has been successfully used to image neuronal calcium activity in rat and mouse brains in vivo. The authors provide detailed information on the system's characteristics and its application in neuroscience research. [Extracted from the article]

This document is a guest editorial from the Journal of Biomedical Optics, introducing a special section on polarimetry in biomedical optics. The special section is split into two issues, covering topics such as mathematical and statistical characterization of polarimetric signals, development of novel instrumentation, integration of AI and machine learning in analyzing polarization-sensitive data, and diverse medical applications. The editorial highlights several research papers that demonstrate the potential of polarimetric microscopy enhancements in various biomedical applications. It also mentions upcoming conferences and resources related to polarized light and optical momentum for biomedical applications. The authors acknowledge funding support and provide brief biographies of the guest editors. [Extracted from the article]

Exact aplanatic solutions of telescopic catadioptric optical system and singlet lens are presented. Details of how solutions are derived are discussed. Numerical verification carried out through geometrical optics and ray tracing simulations on specific optics geometries confirms the validity of solutions. [ABSTRACT FROM AUTHOR]

Adaptive optics (AOs) ophthalmoscopy is a powerful technique for imaging retinas of living subjects at single-cell resolution. Traditional AO ophthalmoscopes use a fixed exit pupil diameter, which is matched to the ocular pupil of a subject. A more efficient ophthalmoscope would allow for a variable exit pupil size to match the variable ocular pupil size of a subject. One method to achieve this is an optical zoom system. To make a zoom system appropriate for use in adaptive optics ophthalmoscopy, it must be simultaneously well corrected for both the field conjugate and the pupil conjugate such that the aberration correction can be successfully applied. The system must also be made of reflective optics to minimize chromatic aberration and spurious back reflections propagating through the system. Both of these factors make for an zoom system that requires tools and methods to be developed to realize successful designs. We present here our work developing a first-order starting point generator, which creates valid first-order solutions that satisfy all the constraints of the system. We then show our techniques for modeling and optimizing the simultaneous conjugates of the system throughout the process of unobscuring the system. We find that to achieve the selected specifications that freeform optics must be used. These surfaces are critical for correcting the residual aberrations introduced in the unobscuring process. [ABSTRACT FROM AUTHOR]

We present practical laboratory work for master's students in photonics. The laboratory session is based on the construction of a telescope, emulating the one used by Galileo Galilei and analyzing the effect of aberrations and other practical limitations on the quality of the image. Different situations and configurations are analyzed, and the recreation of historical observations is carried out to generate a debate on the limitations of real telescopes with the students. The impact on the learning procedure of the students is analyzed by means of the results they have obtained during several academic years. [ABSTRACT FROM AUTHOR]

This communication analyzes the potential for immersive virtual reality (IVR) to improve efficiency in optics education. We first critically review the common motivations to use IVR in education. Second, we highlight the two capabilities of IVR that distinguish it from the other visualization technologies that can be used in education: immersion and analysis of the learner's movement. Then, we identify four characteristics of situations in which IVR can efficiently support optics learning: large equipment, operating with distraction, security training, and feedback for motor skills. We illustrate these findings with 11 concrete examples. [ABSTRACT FROM AUTHOR]

Optics is an excellent complement to undergraduate study in fields such as mechanical, electrical, or biomedical engineering. Applications in those disciplines are also a great motivation for deeper learning in optics. One area in particular where optics and engineering intersect that is worthy of more attention is three-dimensional (3D) printing (3DP). I describe how optics concepts relevant to 3DP enhance the usual introductory discussion as well as how 3DP can be beneficial to the humbly stocked optics lab. The work concludes with some practical examples of capabilities that have been made possible in our instructional labs through 3DP. [ABSTRACT FROM AUTHOR]

There is a shortage of trained optical engineers in our industry, particularly a shortfall of optical design engineers. One way to create more optical designers is through a cultivation strategy. This work discusses the current optical design education process and describes a possible strategy to cultivate engineers into real working optical design engineers based on the mentorship program used by Hughes Aircraft Company in the 1980s. The process used by Hughes Aircraft Company is discussed and a possible structure for implementing something similar is based on today's toolset and requirements. The design process is broken into 12 blocks, each of which consists of four one hour classes with four hours of homework for each. Using a layered approach, the homework can accommodate students with diverse backgrounds and skills and can be taught using any of the existing optical design codes. The document includes a detailed structure of 48 lessons for a possible mentoring program, which can be customized as necessary for specific groups of students or companies. The mentoring program has been refined over the past five years, with more than 30 participants to date in seven countries and a dozen companies with great success. [ABSTRACT FROM AUTHOR]

Public educational outreach is critical for introducing students to the field of optics. Video-sharing platforms, including YouTube and TikTok, are powerful tools for introducing optics to young students, especially as video consumption rates continue to rise. The proliferation of short, casual videos shot vertically on a cell phone on these applications and other social media platforms has greatly reduced the barriers to entry for educating through video. This work will cover the strategies and tactics used by Edmund Optics in recent years to establish and rapidly scale up a video-based outreach program that now reaches up to 13 million views per month. While this scale may at first seem unattainable, short-form video on social media provides a low-cost, low-time-requirement method for achieving this level of reach. In addition to practical guidance for educational video creation, the benefits of such an effort to the company or institution who sponsors it and tips to get buy-in from organizational leadership will be shared. A digital video-based optics outreach program can serve as the foundation for a larger outreach effort that develops the future photonics workforce. [ABSTRACT FROM AUTHOR]

Tissues' biomechanical properties, such as elasticity, are related to tissue health. Optical coherence elastography produces images of tissues based on their elasticity, but its performance is constrained by the laser power used, working distance, and excitation methods. We develop a new method to reconstruct the elasticity contrast image over a long working distance, with only low-intensity illumination, and by non-contact acoustic wave excitation. We combine single-photon vibrometry and quantum parametric mode sorting (QPMS) to measure the oscillating backscattered signals at a single-photon level and derive the phantoms' relative elasticity. We test our system on tissue-mimicking phantoms consisting of contrast sections with different concentrations and thus stiffness. Our results show that as the driving acoustic frequency is swept, the phantoms' vibrational responses are mapped onto the photon-counting histograms from which their mechanical properties—including elasticity—can be derived. Through lateral and longitudinal laser scanning at a fixed frequency, a contrast image based on samples' elasticity can be reliably reconstructed upon photon level signals. We demonstrated the reliability of QPMS-based elasticity contrast imaging of agar phantoms in a long working distance, low-intensity environment. This technique has the potential for in-depth images of real biological tissue and provides a new approach to elastography research and applications. [ABSTRACT FROM AUTHOR]

The deformation, flicker, and drift of a light field owing to complex media such as a turbulent atmosphere have limited its practical applications. Thus, research on invariants in randomly fluctuated light fields has garnered considerable attention in recent years. Coherence is a statistical property of light, while its full and quantitative characterization is challenging. Herein, we successfully realize the orthogonal modal decomposition of partially coherent beams and introduce the application of coherence entropy as a global coherence characteristic of such randomly fluctuated light fields. It is demonstrated that coherence entropy remains consistent during propagation in a unitary system by unraveling complex channels. As representative examples, we study the robustness of coherence entropy for partially coherent beams as they propagate through deformed optical systems and turbulent media. Coherence entropy is anticipated to serve as a key metric for evaluating the propagation of partially coherent beams in complex channels. This study paves the way for a broader application scope of a customized low-coherence light field through nonideal optical systems and complex media. [ABSTRACT FROM AUTHOR]

Two-mirror telescopes possess an agreeable tradeoff between performance and complexity that suits the needs of many scientific tasks, and recent developments in manufacturing technology have enabled unobscured two-mirror designs with freeform surfaces. We illustrate how structural aberration coefficients reveal the fundamental aberration characteristics of such systems and provide a summary table of general solutions that prescribe freeform surface shapes and tilts. Two unobscured design forms with remarkable aberration cancellation, inspired by well-known on-axis anastigmatic solutions, are presented. [ABSTRACT FROM AUTHOR]

A principle of a wavefront measurement sensor based on computer generated holograms is presented. In contrast to conventional Shack–Hartmann sensors, the wavefront is not sampled using a lens array but an array of subholograms. Each subhologram generates a multipoint pattern with unique point distribution on the camera fulfilling two tasks. First, by calculating the wavefront reconstruction for each of the multiple points, averaging improves the accuracy compared to a single point evaluation. Second, the dynamic range of the proposed sensor is enhanced due to the unique shape of each pattern. The assignment between pattern and subhologram can be achieved even for overlapping patterns by the use of digital image correlation. First results show that the averaged standard deviation is 12.5 nm, which corresponds to less than λ/50 , and the maximum angle of the incident wavefront is 8.7 deg. The sensitivity related to the aperture size is better than λ/126. [ABSTRACT FROM AUTHOR]

Optical diffractive neural networks (ODNNs) implement a deep learning framework using passive diffractive layers. Although ODNNs offer unique advantages for light-speed, parallel processing, and low power consumption, their accuracy of image reconstruction still needs to be further improved. Here, we extend ODNNs to deep optics in lensless optics by proposing an optical-electronic neural network (OENN) for multi-modality encoder design, and high-accurate image reconstruction. The OENN includes an ODNN in which a pixel-level learnable diffractive layer is included for lensless camera design and an electrical convolutional neural network for image reconstruction. And the performance of OENN is relatively comparable. For speckle reconstruction using phase information, Pearson correlation coefficient (PCC) and peak signal-to-noise ratio (PSNR) can reach to 0.929 and 19.313 dB, respectively. For speckle reconstruction using intensity information, PCC and PSNR can reach to 0.955 and 19.779 dB, respectively. For lens imaging with phase information, PCC and PSNR can reach above 0.989 and 29.930 dB, respectively. For lens imaging with intensity information, PCC and PSNR can reach above 0.990 and 30.287 dB, respectively. In the future, the proposed optoelectronics artificial intelligent framework can be further applied for "end-to-end" optics design and imaging process of lensless or computational imaging modalities. [ABSTRACT FROM AUTHOR]

Corneal thickness (CoT) is an important tool in the evaluation process for several disorders and in the assessment of intraocular pressure. We present a method enabling high-precision measurement of CoT based on secondary speckle tracking and processing of the information by machine-learning (ML) algorithms. The proposed configuration includes capturing by fast camera the laser beam speckle patterns backscattered from the corneal-scleral border, followed by ML processing of the image. The technique was tested on a series of phantoms having different thicknesses as well as in clinical trials on human eyes. The results show high accuracy in determination of eye CoT, and implementation is speedy in comparison with other known measurement methods. [ABSTRACT FROM AUTHOR]

At present, new approaches for the use of drones in high-precision optical applications are rising, especially with those known as multirotor. However, the optical turbulence effects generated by multirotor drones are not entirely understood. These optical effects can reduce the performance of the optical instruments that they transport. We present measurements of the wavefront deformation generated by the temperature fluctuations and the airflow of a drone's propulsion system. To do so, we used a single arm of a DJI S800 EVO Hexacopter (professional drone) and measured its operating temperature with a commercial infrared camera. The resulting temperature variation, between a switched-off propulsion system at room temperature and one running at its maximum performance, was 34.2°C. Later, we performed two different interferometric tests: Takeda's method and the phase-shifting technique, using a ZYGO interferometer. These tests show that the total deformation over an incident wavefront to the propeller airflow is lower than 0.074 λPV and 0.007 λRMS (HeNe laser, λ ¼ 633 nm). We determine that the optical turbulence produced by a drone propulsion system is negligible. [ABSTRACT FROM AUTHOR]

Medical imaging is very commonly described as synonymous with radiological imaging, yet optical imaging devices are widely distributed throughout many medical specialties. This delocalized nature of the technology reduces visibility and dominance as a cohesive medical technology sector. Indicators of impact of medical optical systems were examined and compared to the radiology technology sector. This study included a summary of (i) physician users, (ii) global technology valuations, and (iii) NIH funding levels. Analysis focused on comparing optical and radiological technology, comparing costs, funding, and finding differences, while tabulating strengths, weaknesses, opportunities, and threats to the field of optical imaging. The 2023 global technology revenue valuation of biomedical optical tools is $128 billion USD/year while that of radiological tools is $48 billion USD/year. A direct comparison of US NIH funding in radiology shows $8.5 billion/year, whereas optical devices are nearer to $3.6 billion USD/year. R&D investment in applications, such as endoscopy, laparoscopy, and pulse oximetry, is far below those of radiological tools when normalized by valuation. The medical optical device industry is highly fragmented but has become the largest single technology sector in medicine today. When contrasted to radiology, it appears underfunded for research, where point-of-care tools such as surgery, endoscopy, laparoscopy, ophthalmology, pulse oximetry, and monitoring have more potential for development through research investment. [ABSTRACT FROM AUTHOR]

In addition to achieving a desired freeform profile, ensuring a superb micro-roughness finish is a key factor for successful freeform optics manufacturing. We present a pseudorandom orbiting stroke-based postprocessing technique that maintains freeform optic forms, while improving small-scale surface quality. The full-aperture tool can avoid subaperture effects, and the small stroke pseudorandom tool path guarantees the match of freeform profiles while preventing the directionality of the final surface profiles. Three independent experimental studies are designed, conducted, and presented for a wide range of optics, including magnetorheological finishing-polished BK7 glass, single-point diamond turned (SPDT) poly(methyl methacrylate), and SPDT Al6061 optics. The comparison of direct measured maps on the initial and final smoothed optics verifies the form maintenance capability of the freeform optics postprocessing technology. Surface roughness measurement highlights improvements in local surface roughness and periodic toolmark errors left by the previous polishing method. [ABSTRACT FROM AUTHOR]

The application of microlaser assisted machining of precision optical components made of optical grade single-crystal Si is reviewed. An optical raytracing model is developed and used for predicting the laser interaction with the workpiece. Optical characterization of the system is shown to be in good agreement with that predicted by the model. Using the information from the simulation and experimental validation, the laser-assisted diamond turning of single-crystal Si samples is shown to have exhibited little to no brittle fracture on the surface and the potential of extending the diamond tooling life by 150%. [ABSTRACT FROM AUTHOR]

Metal mirrors are used for spaceborne optical systems, such as telescopes and spectrometers. In addition to the optical performance, the mechanical needs and the mass restrictions are important aspects during the design and manufacturing process. Using the additive manufacturing process, optimized internal lightweight structures are realized to reduce the weight of the system while keeping the mechanical stability. A mass reduction of ≈60.5% is achieved. Using the aluminum silicon alloy AlSi40, the thermal mismatch of the mirror base body to a necessary electroless nickel-polishing layer is minimized. Based on an exemplary mirror design, the optimization of the interior lightweight structure is described, followed by the manufacturing process from additive manufacturing to diamond turning, plating, and polishing. Finally, the results of surface metrology and light scattering measurements are presented. A final form deviation below 80 nm p: − v: and a roughness of ∼1 nm rms could be demonstrated. [ABSTRACT FROM AUTHOR]

We acquired multiphoton images of normal and lung adenocarcinoma cell lines in three dimensions. Image stacks of the cells were then processed to obtain nucleusto-cytoplasm (N/C) ratios in two and three dimensions. While N/C ratios in three dimensions can be unambiguously determined from the volumetric ratios of the nucleus and cytoplasm, two-dimensional (2-D) N/C can vary depending on the axial plane selected for N/C ratio determination. We determined 2-D N/C ratios from three criteria: (1) axial position at which the nuclear area is the largest; (2) the largest 2-D N/C ratio value; and (3) axial position at the midpoint of nuclear axial position. We found that different definitions of 2-D N/C ratio will significantly affect its value. Furthermore, in general, larger variance was found in 2-D rather than three-dimensional (3-D) N/C ratios. Lack of ambiguity in definition and reduced variance suggest that 3-D N/C ratio is a better parameter for characterizing tumor cells in the clinical setting. [ABSTRACT FROM AUTHOR]

Active optics technology eases the requirements for the fabrication and stability of mirrors. Optical replication techniques make it possible to fabricate a mirror of optical quality rapidly and inexpensively. Combining the advantages of these two methods, we designed a lightweight unimorph mirror with a diameter of 160 mm based on an Al-SiC passive layer. A finite element model was established to predict the performance of this mirror and to optimize relevant parameters. A spherical prototype mirror was fabricated and tested to measure its shape-correction capability, thermal stability, and surface roughness; this prototype has been used in an innovation project on lightweight active mirrors from the Chinese Academy of Sciences. [ABSTRACT FROM AUTHOR]

Retarders or waveplates are tools for polarization modification in bulk optical systems. These devices usually have a strong wavelength dependence in their performance, making them suitable for use over a wavelength band on the order of a few percent of the center wavelength for which they are made. Display and tunable laser applications are examples that can require consistent polarization modification over a much broader wavelength range. We discuss new methods and designs for dramatically increasing range of performance and review older methods as well. We show examples of achievable performance using modern polymer and liquid crystal materials. [ABSTRACT FROM AUTHOR]

Spatial domain multiplexing (SDM) offers a degree of photon freedom to optical fibers. One variant of SDM utilizes ring-like output profiles, created through specific oblique input angles, and shows high-performance gains. Conventional modeling of this system utilizes Laguerre-Gaussian based models; however, these models are more suitable for free-space environments as opposed to fiber propagation. Therefore, a diffraction-based approach to deriving a Bessel-Gaussian beam solution is presented that adheres well to experimental data while maintaining continuity requirements. The derived model shows an input angle to azimuthal index relationship proportional to the transverse wave number of the carrier optical fiber region of SDM architectures. [ABSTRACT FROM AUTHOR]

Robot-guided laser ablation for surgical applications potentially offers many advantages compared to by-hand mechanical tissue cutting. However, given that tissue can be rough and/or uneven, ablation quality can be compromised if the beam waist deviates significantly from the target tissue surface. Therefore, we present a method that uses optical coherence tomography (OCT) for dynamic refocusing of robot-guided surgical laser ablation. A 7-DOF robotic manipulator with an OCT-equipped optical payload was used to simulate robotic guided laser osteotomy. M-mode OCT feedback is used for continuous surface detection to correct for axial deviations along the ablation path due to surface nonuniformity. We were able to show that such a correction scheme could maintain the beam waist within the depth of focus for surface variation as aggressive as 45 deg with feed rates up to 1 mm/s. Strategies for implementation in surgical and nonsurgical applications are examined. [ABSTRACT FROM AUTHOR]

We describe the design and ground-based performance of the two-color calibration lamp for the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) instrument on the NASA Ionospheric Connection (ICON) satellite. The calibration lamp assembly contains radio frequency excited krypton and neon lamps, which generate emission lines at 557 and 630 nm, respectively, and which are used to monitor thermal drifts in the two MIGHTI Doppler asymmetric spatial heterodyne interferometers. The lamps are coupled to two mixed optical fiber bundles that deliver the calibration signals to the two MIGHTI optical units. The assembly starts reliably, consumes <8 W, and has passed environmental testing for the ICON satellite. The total mass of the lamp assembly is 1.8 kg. Special features of the assembly and its implementation are described along with results of life tests. [ABSTRACT FROM AUTHOR]

A computational method is proposed to measure the aberration of a lens using an extended ptychographic iterative engine. By reconstructing the entering wavefront φin and exiting wavefront φex of the lens under detection from two sets of diffraction patterns iteratively, the lens aberration can be easily extracted by subtracting the phase of φin and theoretical lens phase from the phase of φex. Since it needs no extra reference beam and high quality optics, this suggested method has advantages of simplicity in structure, high accuracy, and low requirement on working environment, and it is free of the aberration of other optical elements in the experimental system, indicating it can find lots of applications in lens evaluation. [ABSTRACT FROM AUTHOR]

High on the list of desired capabilities for warfighters noted at the 2008 Fort Benning "Lab Day" was the development of combat protective eyewear with lenses that would instantly change the amount of light they transmit, based on incident lighting conditions. We reviewed the investigation regarding the effect of four different protective spectacle lens designs [clear, standard sunglass, step filter (SF), and electro-optical (EO)] on a soldier's ability to rapidly transition from bright to dim environments. The dependent measures were selected to specifically permit the findings to be evaluated in both clinical and operational terms. A multifactorial analysis of variance revealed global statistically significant interactive effects regarding the viewing lenses, subject marksmanship, and subject visual acuity. The subjective preference ratings indicated a clear preference for the SF and the EO eyewear over no eyewear, the Authorized Protective Eyewear List (APEL) clear eyewear, and the APEL sun eyewear. Operational performance results while wearing either of these two optical devices (the SF eyewear and the electronic eyewear) are equally effective. Consequently, the fielding of either transition strategy provides equal acceptance and utility by the soldiers using this transitional gear. [ABSTRACT FROM AUTHOR]

Cerebral endovascular neurosurgery has transformed the way we manage cerebrovascular disease. Several landmark trials have demonstrated the effectiveness of endovascular techniques leading to continued technological development and applications for various diseases. The utilization of optical technologies and devices is already underway in the field of endovascular neurosurgery. We discuss the contemporary paradigms, challenges, and current optical applications for the most common cerebrovascular diseases: carotid atherosclerotic disease, cerebral aneurysms, intracranial atherosclerosis, and dural arteriovenous fistulas. We also describe needs-based opportunities for future optical applications, with the goal of providing researchers a sense of where we feel optical technologies could impact the way we manage cerebral disease. [ABSTRACT FROM AUTHOR]

A software for fast rendering the visual appearance of a blood vessel located in human skin was developed based on a numerical solution of the radiative transfer equation. The user can specify geometrical properties, such as the depth and the diameter of the vessel, and physiological properties, such as the oxygen saturation of the vessel or the blood concentration in the skin. From these data, the spatially and spectrally resolved reflectance from the skin containing the blood vessel is calculated via Monte Carlo simulations, by which a two-dimensional image is generated. The short calculation time of about a second is achieved by precalculating and storing the spatially resolved reflectance for a variety of combinations of the optical and geometrical properties. This concept gives the user the opportunity to rapidly explore the influence of the physiological and geometrical properties of the investigated blood vessel on its visual appearance. The correctness of the lookup table was validated by comparison with independent Monte Carlo simulations. Rendering examples of different blood vessels in human skins are given. [ABSTRACT FROM AUTHOR]

In the past few years, a new type of camera has been emerging on the market: a digital camera capable of capturing both the intensity of the light emanating from a scene and the direction of the light rays. This camera technology called a light-field camera uses an array of lenses placed in front of a single image sensor, or simply, an array of cameras attached together. An optical device is proposed: a four minilens ring that is inserted between the lens and the image sensor of a digital camera. This device prototype is able to convert a regular digital camera into a light-field camera as it makes it possible to record four subaperture images of the scene. It is a compact and cost-effective solution to perform both postcapture refocusing and depth estimation. The minilens ring makes also the plenoptic camera versatile; it is possible to adjust the parameters of the ring so as to reduce or increase the size of the projected image. Together with the proof of concept of this device, we propose a method to estimate the positions of each optical component depending on the observed scene (object size and distance) and the optics parameters. Real-world results are presented to validate our device prototype. [ABSTRACT FROM AUTHOR]

Background: Many MEMS and optical sensor devices can benefit from layers that block transmission and suppress reflection of light across the visible spectrum. Because these devices can include complicated topography, many existing methods for depositing antireflective layers are difficult, impractical, or unusable. Aim: To create a light-blocking antireflective layer that works well with complicated MEMS and sensor devices, a layer should be made that is cheap, simple, and can be deposited and patterned with high resolution at low temperatures. Approach: Light blocking is achieved using an aluminum layer. Suppressing reflection is achieved by mixing aluminum oxide nanoparticles in photoresist to create a layer that partially absorbs and partially scatters light. Results: The combination of a layer of metal and a layer of nanoparticles and photoresist completely blocks transmission of light and significantly reduces reflections across the visible spectrum, particularly for shorter wavelengths. The layer is also patternable to sizes as small as a few microns with high resolution. Conclusion: By combining a metal layer and a layer of nanoparticles in photoresist, a simple, cheap, and effective light-blocking antireflective layer can be created that is compatible with planar devices with complex topography. [ABSTRACT FROM AUTHOR]

X-ray and optical technologies are the two central pillars for human imaging and therapy. The strengths of x-rays are deep tissue penetration, effective cytotoxicity, and the ability to image with robust projection and computed-tomography methods. The major limitations of x-ray use are the lack of molecular specificity and the carcinogenic risk. In comparison, optical interactions with tissue are strongly scatter dominated, leading to limited tissue penetration, making imaging and therapy largely restricted to superficial or endoscopically directed tissues. However, optical photon energies are comparable with molecular energy levels, thereby providing the strength of intrinsic molecular specificity. Additionally, optical technologies are highly advanced and diversified, being ubiquitously used throughout medicine as the single largest technology sector. Both have dominant spatial localization value, achieved with optical surface scanning or x-ray internal visualization, where one often is used with the other. Therapeutic delivery can also be enhanced by their synergy, where radiooptical and optical-radio interactions can inform about dose or amplify the clinical therapeutic value. An emerging trend is the integration of nanoparticles to serve as molecular intermediates or energy transducers for imaging and therapy, requiring careful design for the interaction either by scintillation or Cherenkov light, and the nanoscale design is impacted by the choices of optical interaction mechanism. The enhancement of optical molecular sensing or sensitization of tissue using x-rays as the energy source is an important emerging field combining x-ray tissue penetration in radiation oncology with the molecular specificity and packaging of optical probes or molecular localization. The ways in which x-rays can enable optical procedures, or optics can enable x-ray procedures, provide a range of new opportunities in both diagnostic and therapeutic medicine. Taken together, these two technologies form the basis for the vast majority of diagnostics and therapeutics in use in clinical medicine. [ABSTRACT FROM AUTHOR]

We report the design, fabrication, and measurement of waveguide lattice filters for use in integrated Raman- or fluorescence-based spectroscopy and sensing systems. The filters consist of a series of broadband directional couplers and optical delay sections that create an n-stage unbalanced Mach-Zehnder interferometer specifically designed to segregate pump light and redshifted signal light in the two output ports. We first report the design criteria for optimal filter performance. Then, we use these criteria with numerical beam propagation methods to design specific broadband couplers. The filters were fabricated by a photonic integrated circuit foundry and measured using white-light spectroscopy. We report both four-stage and eight-stage filters, with the eight-stage filter demonstrating a 190-nm-wide signal passband (1100 cm-1) on the "through" port with <1.5 dB of ripple and a 17-nm-wide, 20-dB extinction band at the filter resonance. [ABSTRACT FROM AUTHOR]

We present the design of a varifocal freeform optics consisting of two lens bodies each with a helicaltype surface structure of azimuthally varying curvatures. This arrangement allows for tuning the optical refraction power by means of a mutual rotation of the lens bodies around the optical axis. Thus, the refraction power can be tuned continuously in a defined range. The shape of the helical-type surfaces is formed by a change in curvature subject to the azimuthal angle α. At the transition of the azimuthal angle from α = 2π to α = 0, a surface discontinuity appears. Since this discontinuity will seriously affect the imaging quality, it has to be obscured. In the initial state, i.e., zero-degree rotation, the curvatures of the opposing surfaces result in a specific refraction power, which is constant over the entire circular aperture. Rotating one of the lens bodies by an angle φ around the optical axis will change the opposing curvatures and result in a change of refraction power. Two circular sectors with different tunable optical refraction powers are formed, thus resulting in a tunable bifocal optics. Obscuring the minor sector will result in a tunable monofocal rotation optics. In contrast to conventional tunable lens systems, where additional space for axial or lateral lens movement has to be allocated in design, rotation optics allowing for a more compact design. A performance analysis of the rotation optics based on simulations is presented in dependence on aperture size as well as approaches to compensate for spherical aberrations. [ABSTRACT FROM AUTHOR]

In view of the fact that the weak laser damage resistance of HfO2/SiO2 coatings at 355 nm hinders the observation of the fatigue effect, nanosecond single and multiple pulse laser damage studies on Al2O3/SiO2 high-reflective coatings were performed at 355 nm. Relative to that at the long wavelength, the fatigue effect at 355 nm is very weak and complicated. The damage probability curves and the evolution of the laser-induced damage threshold under multiple irradiations reveal that the fatigue effect is affected by both laser fluence and shot number. As the laser fluence or number of shots increases, the fatigue effect becomes more apparent. The damage morphologies induced by single and multiple irradiations both manifest as micrometer-scale pits without plasma scalding around, with the characteristics of a high defect density and high absorption coefficient. In particular, the accumulation damage mechanism at 355 nm may be reflected not only in the newly created defects but also in the modification of the coating material around the damage precursors. Thus, the coatings at 355 nm "seem to" have no damage growth threshold, no matter what the laser fluence is; once damage occurs, the damage site will grow sharply under subsequent pulses finally resulting in catastrophic damage. [ABSTRACT FROM AUTHOR]

Continuous noninvasive measurement of intraocular pressure (IOP) is an important tool in the evaluation process for glaucoma. We present a methodology enabling high-precision, noncontact, reproducible, and continuous monitoring of IOP based on the value of the damping factor of transitional oscillations obtained at the surface of the eye after terminating its stimulation by a sound wave. The proposed configuration includes projection of a laser beam and usage of a fast camera for analyzing the temporal–spatial variations of the speckle patterns backscattered from the iris or the sclera following the above-mentioned sound waves external stimulation. The methodology was tested on an artificial eye and a carp fish eye under varying pressure as well as on human eyes. [ABSTRACT FROM AUTHOR]

We propose a phase imaging method that combines the Fourier ptychography and compressive sensing theories using single-pixel detection in the spatial spectrum plane. Specifically, the spatial Fourier spectrum is shifted based on the Fourier ptychography theory, and the compressive sensing theory is applied to reduce the amount of acquired data. Further, an algorithm has been developed to reconstruct the phase images and an asymmetric mask introduced to eliminate ghost interference. The feasibility of the proposed method was verified through simulation and evaluated in terms of the compressive sensing theory realized. The results show that a two-dimensional image can be restored at a low sampling rate of 5% using the proposed method. [ABSTRACT FROM AUTHOR]

Beam confinement or “no free-space optics” via fiber transmission can achieve improved reliability, lower cost, and reduced component count for active sensing systems. For midinfrared delivery, mechanically robust chalcogenide (arsenic sulfide) single-mode fibers are of interest. A 12-μm core diameter fiber is shown to transport >10 W at 2053 nm, and a 25-μm core diameter fiber enables single-mode beam transport from a 4550-nm quantum cascade laser. As midinfrared sources continue to increase their output power capabilities, chalcogenide fibers will eventually be limited in their power-handling capacity due to optical nonlinearities or thermal failure. These limitations are discussed and analyzed in the context of single-mode chalcogenide fibers in order to provide a framework for power transmission limitations in various operating regimes. [ABSTRACT FROM AUTHOR]

Fluorescence guided surgery (FGS) has demonstrated improvements in decision making and patient outcomes for a wide range of surgical procedures. Not only can FGS systems provide a higher level of structural perfusion accuracy in tissue reconstruction cases but they can also serve for real-time functional characterization. Multiple FGS devices have been Food and Drug administration (FDA) cleared for use in open and laparoscopic surgery. Despite the rapid growth of the field, there has been a lack standardization methods. This work overviews commonalities inherent to optical imaging methods that can be exploited to produce such a standardization procedure. Furthermore, a system evaluation pipeline is proposed and executed through the use of photo-stable indocyanine green fluorescence phantoms. Five different FDA-approved open-field FGS systems are used and evaluated with the proposed method. The proposed pipeline encompasses the following characterization: (1) imaging spatial resolution and sharpness, (2) sensitivity and linearity, (3) imaging depth into tissue, (4) imaging system DOF, (5) uniformity of illumination, (6) spatial distortion, (7) signal to background ratio, (8) excitation bands, and (9) illumination wavelength and power. The results highlight how such a standardization approach can be successfully implemented for inter-system comparisons as well as how to better understand essential features within each FGS setup. Despite clinical use being the end goal, a robust yet simple standardization pipeline before clinical trials, such as the one presented herein, should benefit regulatory agencies, manufacturers, and end-users to better assess basic performance and improvements to be made in next generation FGS systems. [ABSTRACT FROM AUTHOR]

The editorial introduces the JBO Special Section on Short Wave Infrared Techniques and Applications in Biomedical Optics. [ABSTRACT FROM AUTHOR]

We propose a technique for additive manufacturing of polymer step-index (STIN) optics. The process is composed of aerosol jet multi-material deposition followed by laser-assisted stereolithography in an alternating fashion to fabricate multi-material three-dimensional objects. The layer-wise dynamic tuning of the refractive index provides the possibility to fabricate optics with tailored index profiles. The index range achieved by the presented approach is considerably higher than the common index tuning techniques. Using this technique, a planar multilayer STIN lens is fabricated. The index profile of the fabricated lens has similar progression to the designed profile. In addition, through simulation and also optical characterization, the lensing functionality of the structure is observed. [ABSTRACT FROM AUTHOR]

This work presents a highly sensitive hybrid-integrated optical receiver with a custom designed linear transimpedance amplifier (TIA). The choice of the circuit and diode technology, considering the impact of process parameters on the optical sensitivity and the input referred noise current, are elaborated. The TIA has been designed in a 55-nm complementary metal oxide semiconductor process and was combined with a commercial InGaAs/InP PIN-diode. Measurements resulted in a transimpedance of 9.2 kΩ and a bandwidth of 1.4 GHz. The optical sensitivity of the hybrid receiver is −27.45 dBm for 2 Gbps, with a wavelength of 1550 nm and a bit error rate of 10 − 9. The input referred root mean square (RMS) noise current results in 110 nA. The fabricated chip has an area of 410 μm × 410 μm and a power consumption of 31 mW at a 1 V supply voltage. The performance of the designed TIA is able to match other designs used in high sensitivity applications such as continuous variable quantum key distribution or optical wireless communication, while consuming significantly less power and having a smaller chip area. [ABSTRACT FROM AUTHOR]

An optical imaging system's image quality can deteriorate due to uncorrected astigmatism and defocus. An approach to correct these issues is proposed, which involves a non-mechanical, electronically adjustable system. This system consists of three liquid crystal-based cylindrical lenses, which adjust optical power depending on applied voltage values. The advantages of this system include a simple and low-cost structure, large aperture size, low-voltage drive, and compact design. This non-mechanical solution has great potential for various applications, such as wavefront correction for large telescopes, microscopy, augmented reality/virtual reality, and prescription eyeglasses. Design, fabrication, and optical characterization of the proposed device are discussed. [ABSTRACT FROM AUTHOR]

We used intravital multiphoton microscopy to study the recovery of hepatobiliary metabolism following carbon tetrachloride (CCl4) induced hepatotoxicity in mice. The acquired images were processed by a first order kinetic model to generate rate constant resolved images of the mouse liver. We found that with progression of hepatotoxicity, the spatial gradient of hepatic function disappeared. A CCl4-induced damage mechanism involves the compromise of membrane functions, resulting in accumulation of processed 6-carboxyfluorescein molecules. At day 14 following induction, a restoration of the mouse hepatobiliary function was found. Our approach allows the study of the response of hepatic functions to chemical agents in real time and is useful for studying pharmacokinetics of drug molecules through optical microscopic imaging. [ABSTRACT FROM AUTHOR]

Optical technologies may be applied to multiple facets of spinal surgery from diagnostics to intraoperative image guidance to therapeutics. In diagnostics, the current standard remains cross-sectional static imaging. Optical surface scanning tools may have an important role; however, significant work is required to clearly correlate surface metrics to radiographic and clinically relevant spinal anatomy and alignment. In the realm of intraoperative image guidance, optical tracking is widely developed as the current standard of instrument tracking, however remains compromised by line-of-sight issues and more globally cumbersome registration workflows. Surface scanning registration tools are being refined to address concerns over workflow and learning curves, and allow real-time update of tissue deformation; however, the line-of-sight issues plaguing instrument tracking remain to be addressed. In therapeutics, optical applications exist in both visualization, in the form of endoscopes, and ablation, in the form of lasers. Further work is required to extend the feasibility of laser ablation to multiple tissues, including disc, bone, and tumor, in a safe and time-efficient manner. Finally, we postulate some of the short- and long-term opportunities for future growth of optical techniques in the context of spinal surgery. Particular emphasis is placed on intraoperative image guidance, the area of the authors’ primary expertise. [ABSTRACT FROM AUTHOR]

We present a technique to record refreshable holographic stereograms continuously. We eliminated the translation stage that shifts the recording beams back and forth and replaced it with an uninterrupted transparent belt holding holographic lenses. The belt is driven along a perimeter, shifting the lens laterally in front of a photorefractive screen without reversing direction. The holographic lenses focus the object beam onto holographic pixels and are permanently recorded in a thin photopolymer. The photopolymer material is flexible enough for the lenses to follow the curvature of the belt when it goes around the tensioning rollers. The hogel data are uploaded sequentially onto a spatial light modulator to form the object beam. The rotation of the belt in one single direction allows for a continuous operation and a much faster recording speed than with a translation stage that needs to reverse direction at the end of its travel span. [ABSTRACT FROM AUTHOR]

We present an overview of the applications of self-mixing interferometer (SMI) to tasks of interest for mechanical engineering, namely high-resolution measurement of linear displacements, measurements of angles (tilt, yaw, and roll), measurements of subnanometer vibrations, and absolute distance, all on a remote target--representative of the tool-carrying turret of a tool-machine. Along with the advantages of SMI--compactness, low cost, minimum invasiveness, ease of use, and good accuracy, we illustrate the typical performance achieved by the basic SMI sensors, that is, the versions requiring a minimum of signal processing and discuss special features and problems of each approach. [ABSTRACT FROM AUTHOR]