Simple Optical System Research Articles

Simple retinal imaging system using a MEMS scanning mirror

We have fabricated a simple and compact scanning laser optical system using microelectromechanical system (MEMS) scanner that can be incorporated into portable health monitoring devices. The two-dimensional (2-D) MEMS scanner used in this system is much smaller and light in weight compared to galvanometer scanners and polygon scanners used in the commercially available ophthalmic devices. MEMS scanners have many advantages and also limitations compared to galvanometer and polygon scanners. An easy to use and compact device is more useful for rapid alignment for measurement and data acquisition. Sensitivity of the system was quantified by measuring signal-to-noise ratio (SNR) for both high and low reflectivity materials. SNR was 10 for the high reflectance materials and about 4 for low reflectance materials, which is sufficient for biological imaging. Distortion generated using large scanning angle of 2-D MEMS scanner was corrected in real time by custom made LabVIEW program. Ocular safety is important to consider when using a laser for ophthalmic devices. We calculated the maximum permissible beam power for thermal damage and photochemical damage considering the specification of our system such as visual angle and wavelength of the laser beam. The measured laser intensity in the front of model eye was 6 μW, which is much smaller than the maximum permissible beam power recommended by the American National Standards Institute.

LED-Based Portable Optical Biosensor for Measurement of Serum Urea Levels Using Urease Immobilized Agarose-Guar Gum Composite Film

A simple, reliable, low cost, and portable biosensor has been developed for direct measurement of urea levels in serum samples. It is based on hydrolysis of urea by immobilized urease, generating ammonia that is estimated by modified Berthelot method using simple optical detection system. The immobilization of urease was achieved in agarose guar-gum composite film for the first time which offered an excellent retention of enzyme activity (90%–95%) with negligible leaching and good operational stability. The optical detection system involving LED light, optical fiber, and phototransistor provides simple and portable measurement system. The sensor shows linear response in the wide range of urea concentration from 0.025 to 10 mM with reusability for 10 cycles and superior storage stability of 180 days. The fabricated biosensor was successfully employed for measurement of normal and abnormal urea levels in serum samples with accuracy of 96% using very small sample volume ( $15~\mu \text{l}$ ). It showed an excellent correlation ( $r^{2}=0.99$ ) for determination of urea levels with that of using Siemens autoanalyzer.

Online 3D Displacement Measurement Using Speckle Interferometer with a Single Illumination-Detection Path.

Measurement systems for online nondestructive full-field three-dimensional (3D) displacement based on the single-shot and multiplexing techniques attract more and more interest, especially throughout the manufacturing industries. This paper proposes an accurate and easy-to-implement method based on an electronic speckle pattern interferometer (ESPI) with single illumination-detection path to realize the online nondestructive full-field 3D displacement measurement. The simple and compact optical system generates three different sensitivity vectors to enable the evaluation of the three orthogonal displacement components. By applying the spatial carrier phase-shifting technique, the desired information can be obtained in real time. The theoretical analysis and the measurement results have proven the feasibility of this ESPI system and quantified its relative measurement error.

Low-cost single-pixel 3D imaging by using an LED array.

We propose a method to perform color imaging with a single photodiode by using light structured illumination generated with a low-cost color LED array. The LED array is used to generate a sequence of color Hadamard patterns which are projected onto the object by a simple optical system while the photodiode records the light intensity. A field programmable gate array (FPGA) controls the LED panel allowing us to obtain high refresh rates up to 10 kHz. The system is extended to 3D imaging by simply adding a low number of photodiodes at different locations. The 3D shape of the object is obtained by using a non-calibrated photometric stereo technique. Experimental results are provided for an LED array with 32 × 32 elements.

Synthesis of full Poincaré beams by means of uniaxial crystals

A simple optical system is proposed to generate full-Poincaré beams (FPBs), i.e. beams presenting all possible states of (total) polarization across their transverse section. The method consists in focusing a uniformly polarized laser beam onto a uniaxial crystal having its optic axis parallel to the propagation axis of the impinging beam. A simple approximated model is used to obtain the analytical expression of the beam polarization at the output of the crystal. The output beam is then proved to be a FPB. By changing the polarization state of the input field, full-Poincaré beams are still obtained, but presenting different distributions of the polarization state across the beam section. Experimental results are reported, showing an excellent agreement with the theoretical predictions.

Calculation of vectorial diffraction in optical systems.

A vectorial diffraction theory that considers light polarization is essential to predict the performance of optical systems that have a high numerical aperture or use engineered polarization or phase. Vectorial diffraction integrals to describe light diffraction typically require boundary fields on aperture surfaces. Estimating such boundary fields can be challenging in complex systems that induce multiple depolarizations, unless vectorial ray tracing using 3×3 Jones matrices is employed. The tracing method, however, has not been sufficiently detailed to cover complex systems and, more importantly, seems influenced by system geometry (transmission versus reflection). Here, we provide a full tutorial on vectorial diffraction calculation in optical systems. We revisit vectorial diffraction integrals and present our approach of consistent vectorial ray tracing irrespective of the system geometry, where both electromagnetic field vectors and ray vectors are traced. Our method is demonstrated in simple optical systems to better deliver our idea, and then in a complex system where point spread function broadening by a conjugate reflector is studied.

A recovered friend: the afocal system

The basic properties of a simple afocal optical system, namely a two-lens Keplerian telescope, are reviewed and compared with measurements that can be easily performed with instrumentation available in a university optical laboratory. The object–image conjugation, along with the Lagrangian invariant of the systems, are made clear by the comparison between theory and experiments, highlighting also the limits of the Gaussian approximation in the chosen experimental realization.

Volume holographic spatial mode demultiplexer with a dual-wavelength method.

Volume holographic demultiplexers (VHDMs) provide spatial mode demultiplexing using simple optical systems. However, applying VHDM to practical optical communication systems is difficult, as typical holographic media have no sensitivity in the infrared region, which includes optical transmission bands. In this paper, we propose a VHDM scheme combined with a dual-wavelength method (DWM). Using the DWM, VHDMs are able to perform mode demultiplexing in the optical transmission bands. We experimentally demonstrated the basic operation of our proposal using experiments performed at an 850-nm wavelength. In addition, we performed numerical simulations to investigate the application of VHDM to the C-band.

Integration of multiple theories for the simulation of laser interference lithography processes

The periodic structure of laser interference lithography (LIL) fabrication is superior to other lithography technologies. In contrast to traditional lithography, LIL has the advantages of being a simple optical system with no mask requirements, low cost, high depth of focus, and large patterning area in a single exposure. Generally, a simulation pattern for the periodic structure is obtained through optical interference prior to its fabrication through LIL. However, the LIL process is complex and combines the fields of optical and polymer materials; thus, a single simulation theory cannot reflect the real situation. Therefore, this research integrates multiple theories, including those of optical interference, standing waves, and photoresist characteristics, to create a mathematical model for the LIL process. The mathematical model can accurately estimate the exposure time and reduce the LIL process duration through trial and error.

Development of a small telescope like PZT and effects of vibrations of mercury surface and ground noise

A PZT type telescope for observations of gravity gradient and lunar rotation was developed, and a Bread Board Model (BBM) for ground experiments was completed. Some developments were made for the BBM such as a tripod with attitude control system, a stable mercury pool and a method for collecting the effects of vibrations. Laboratory experiments and field observations were performed from August to September of 2014, in order to check the entire system of the telescope and the software, and the results were compared to the centroid experiments which pursue the best accuracy of determination of the center of star images with a simple optical system. It was also investigated how the vibrations of mercury surface affect the centroid position on Charge Coupled Device (CCD). The results of the experiments showed that the effects of vibrations are almost common to stars in the same view, and they can be corrected by removing mean variation of the stars; and that the vibration of mercury surface can cause errors in centroid as large as 0.2 arcsec; and that there is a strong correlation between the Standard Deviation (SD) of variation of the centroid position and signal to noise ratio (SNR) of star images. It is likely that the accuracy of one (1) milli arcsecond is possible if SNR is high enough and the effects of vibrations are corrected.

The laser and optical system for the RIBF-PALIS experiment

This paper describes the laser and optical system for the Parasitic radioactive isotope (RI) beam production by Laser Ion-Source (PALIS) in the RIKEN fragment separator facility. This system requires an optical path length of 70 m for transporting the laser beam from the laser light source to the place for resonance ionization. To accomplish this, we designed and implemented a simple optical system consisting of several mirrors equipped with compact stepping motor actuators, lenses, beam spot screens and network cameras. The system enables multi-step laser resonance ionization in the gas cell and gas jet via overlap with a diameter of a few millimeters, between the laser photons and atomic beam. Despite such a long transport distance, we achieved a transport efficiency for the UV laser beam of about 50%. We also confirmed that the position stability of the laser beam stays within a permissible range for dedicated resonance ionization experiments.

An optical dustbin made by the subwavelength-induced super-black carbon aerogels

Abstract

Physical realization of Schell‐model sources using a fast steering mirror

AbstractA simple optical system is built to quickly realize partially coherent sources for directed energy applications. The apparatus implements a recently developed technique in which any uniformly correlated or Schell‐model source can be generated by summing many statistically independent randomly tilted beams. This result means that only a tip‐tilt or fast steering mirror (FSM) is needed to realize Schell‐model sources, which in contrast to existing synthesis techniques, is both fast and flexible. A brief review of the theory necessary to understand and implement the tilt‐only synthesis technique is presented. The FSM apparatus is then described. Lastly, experimental results of a Schell‐model source are compared with theoretical predictions to validate both the synthesis technique and FSM apparatus.

Shape measurement with modified phase-shift lateral shearing interferometry illumination and radial basis function.

Three-dimensional shapes of objects were evaluated with modified phase-shift lateral shearing interferometry illumination and radial basis function. A simple optical system was developed to create the fringe pattern based on the Murty interferometer. The phase shift was generated only by moving a plane-parallel plate along an in-plane parallel direction. A novel moving radial basis function method was presented to improve the quality of fringe patterns. And the proper calculation window size was given based on numerical simulation. Three-dimensional shapes of two kinds of objects were determined to verify the feasibility and effectiveness of the proposed method, and the reconstructed height distributions were in good accordance with the referenced data.

Low-cost and large-size nanoplasmonic sensor based on Fano resonances with fast response and high sensitivity.

We have developed a low-cost, fast and sensitive plasmonic sensor with a large-size for easy handling. The sensor is formed by a Au nanobelt grating fabricated by soft lithography with a period of 780 nm and a width of 355 nm in an even and uniform area of ~2 × 2 cm2. The sensor uses the Fano-shaped third order mode localized plasmon resonance of the Au nanobelts, which appears in the visible part of the transmission spectrum. We have found a detection resolution of 1.56 × 10-5 refractive index units with a temporal resolution of 1 s in a sensing area of 0.75 × 0.75 mm2. The high uniformity and size of the sensor permit the detection using a simple optical system, which provides the device with the potential to be used as an easy to handle, portable and disposable sensor.

Proposal of a simple optical coherence tomography-based scoring system for progression of age-related macular degeneration.

To develop a simple, clinically practical, optical coherence tomography (OCT)-based scoring system for early age-related macular degeneration (AMD) to prognosticate risk for progression to late AMD. We retrospectively reviewed OCT images (512×128 macular cube, Cirrus) from 138 patients diagnosed of early AMD in at least one eye and follow-up of at least 12months. For patients with early AMD in both eyes, only the right eye was chosen as the study eye for longitudinal assessment. Scans were graded on four SD-OCT criteria associated with disease progression in previous studies: drusen volume within a central 3-mm circle ≥0.03mm3, intraretinal hyperreflective foci (HRF), hyporeflective foci (hRF) within a drusenoid lesion (DL), and subretinal drusenoid deposits (SDD). Each criterion was assigned one point. For risk assessment of the study eye, the baseline status of the fellow eye was also considered, and thus these four features were also assessed in the fellow eye. The number of risk factors were summed for both eyes, yielding a total score (TS) of 0 to 8 for each patient. A fellow eye with evident choroidal neovascularization (CNV) or atrophy automatically received 4 points. Scores were then grouped into four categories to facilitate comparative analysis: I. (TS of 0, 1, 2), II. (TS of 3, 4), III. (TS of 5, 6) and IV. (TS of 7, 8). Correlation of baseline category assignment with progression to late AMD (defined as the presence of atrophy or CNV on OCT) by the last follow-up visit was evaluated with logistic regression analysis. The rate of progression to late AMD was 39.9% (55/138). Progression rates by category (I to IV) were 0, 14.3, 47.5, and 73.3%, respectively. Logistic regression analysis showed risk of progression to late AMD was 3.0 times (95% CI: 1.2-7.9) higher for an eye assigned to category IV than for an eye in category III and 16.4 (95% CI: 4.7-58.8) times higher than for an eye in category II. A simple scoring system relevant to prognosis for early AMD, and practical for use in a busy clinic, can be developed using SD-OCT criteria alone.

Multimodal Imaging Based on Digital Holography

Digital holography provides a method of the 3-D recording and numerical reconstruction by a simple optical system and a computer. Quantitative measurement and numerical refocusing are major characteristics. So far, many physical parameters such as amplitude, phase, polarization, fluorescence, and spectra can be obtained independently. Recently, multimodal imaging that can obtain simultaneously two or more physical parameters by combining digital holographic microscope and other optical microscopes such as a fluorescence optical microscope and a Raman scattering microscope has emerged. In this review, physical parametric imaging techniques based on digital holography are presented and then these techniques are enhanced to develop multimodal imaging based on digital holography.

Conservation of extremal ellipticity and analytical expressions for astigmatism and asymmetry in Gaussian beam transformations.

A Gaussian beam with initial astigmatism, waist, and M2 asymmetry propagates through a simple optical system consisting of a single thin, aberration-free lens. We derive simple analytical expressions for the asymmetry, astigmatism, and ellipticity of the beam after the lens, and show that the maximal ellipticity of the beam is a conserved quantity that is solely dependent on these input parameters. This appears to still hold for general astigmatic Gaussian beams. Our simple, analytical results conveniently determine the trade-off between astigmatism and asymmetry of a laser for a given output maximum ellipticity requirement pre- or post-lenses.

Coating Qualities Deposited Using Three Different Thermal Spray Technologies in Relation with Temperatures and Velocities of Spray Droplets

Three guns based on different thermal spray technologies—namely, gas flame spray, wire arc spray, and wire plasma spray—were operated at each best cost–performance condition, and the resulting spray droplets and deposited coating qualities were investigated. For the former, a simple optical monitoring system was used to measure temperatures and velocities of spray droplets ejected from the guns. On the other hand, for the latter, qualities of coating layers on substrates—namely, surface roughness, atomic composition, hardness, adhesive strength, and porosity—were characterized. Then, these coating qualities were discussed with respect to the measured temperatures and velocities of spray droplets, which revealed novel features in the coatings that have not been seen before, such as atomic composition and hardness strongly dependent on temperature and environments of droplets towards the substrates, and porosity on velocity of droplets impinging onto the substrates.

A Passive Authentication System Based on Optical Variable Nano/Micro-Structures

A new optical authentication and security system using optical variable nano/micro-structures (OVNs) is presented. The proposed design features a passive authentication method using a simple optical system found in common fabrication facilities. The passive authentication is obtained by insertion of an OVN image directly on a processing layer or divided between multiple layers of the fabrication process. Authentic fabrication process is validated when the proper alignment (reconstructed image, for example) at the end of the fabrication is achieved. Simple proof-of-concept devices with the OVN-based authentication system are presented along with the optical images of the resulting authentication patterns.