Optic Head Research Articles

Effects of Waveguide Refractive Index on Near-Field Transducer Efficiency in Heat-Assisted Magnetic Recording

In a heat-assisted magnetic recording (HAMR) system, the optical recording head is one of the essential components, where light delivered from waveguide is focused into an optical spot in the scale of tens of nanometers to heat recording media to lower coercivity temporarily and locally by a near-field optical transducer. High transducer efficiency is desired for HAMR, as large energy lost during delivery can lead to heating of the recording head, component deformation and system failure at last. Up till now, most research interest has been paid to studying transducer to improve HAMR performance. However, besides the transducer itself, the waveguide also can influence transducer efficiency, because transducer interacts with the light guided in waveguide. In waveguide, propagation mode is determined by waveguide refractive index. In this paper, effects of refractive index of the waveguide core on transducer efficiency are studied by using finite-difference time domain (FDTD) simulation. With the knowledge of waveguide refractive index effects, Si waveguide is proposed to improve HAMR performance at near infrared wavelengths.

The constrained SLAM framework for non-instrumented augmented reality

This paper addresses the challenging issue of marker less tracking for Augmented Reality. It proposes a real-time camera localization in a partially known environment, i.e. for which a geometric 3D model of one static object in the scene is available. We propose to take benefit from this geometric model to improve the localization of keyframe-based SLAM by constraining the local bundle adjustment process with this additional information. We demonstrate the advantages of this solution, called contrained SLAM, on both synthetic and real data and present very convincing augmentation of 3D objects in real-time. Using this tracker, we also propose an interactive augmented reality system for training application. This system, based on a Optical See-Through Head Mounted Display, allows to augment the users vision field with virtual information accurately co-registered with the real world. To keep greatly benefit of the potential of this hand free device, the system combines the tracker module with a simple user-interaction vision-based module to provide overlaid information in response to user requests.

Rapid regression of cystoid macular edema associated with cytomegalovirus retinitis in adult acute myeloid leukemia by intravitreal methotrexate combined with oral valganciclovir: A case report with comparison of binocular outcome

Cytomegalovirus (CMV) retinitis is a late complication of organ and hematopoietic stem cell transplant, the risk of which depends on the degree of immunosuppression. With the institution of preemptive ganciclovir therapy early after transplant, most patients survive episodes of life-threatening CMV infection during the early months (usually the first 3 months) after transplant and hence late onset of CMV disease, such as CMV retinitis, is being recognized more frequently. Direct involvement of the macula or optic head remains the leading cause of visual loss in patients with CMV retinitis, but there are few studies investigating the management of this condition.Herein, we present the case of 28-year-old man who had acute myeloid leukemia and developed CMV retinitis with bilateral cystoid macular edema and optic swelling in the right eye 6 months after bone marrow transplant. He received treatment with intravitreal methotrexate in the right eye in combination with oral valganciclovir. Visual acuity improved 1 month after four weekly injections of intravitreal methotrexate 400 μg/0.1 mL. Resolved disc swelling and regression of macular edema were also observed. By comparing binocular outcome, we present our findings and discuss the possible efficacy and safety of this treatment with respect to regression of anatomical damage and improvement in visual acuity.

Evaluation of the lamina crivosa thickness and depth, the prelaminar nerve tissue thickness and the Bruch's membrane opening‐based minimum rim width in eyes with and without primary open‐angle glaucoma: an enhanced depth imaging OCT study of the optic nerve head and the correlation between anatomy and function

PurposeTo evaluate the lamina crivosa (LC)thickness (LCT), depth (LCD), prelaminar thickness (PLTT) and Bruch's membrane opening‐based minimum rim width (BMO‐MRW) in primary open‐angle glaucoma (POAG) and normal eyes (NE) and their correlation with function (MD).MethodsThis observational study included 45 eyes (25 eyes with POAG; 20 normal eyes),which were evaluated clinically, by applanation tonometry, pachymetry, Octopus perimetry and by enhanced depth imaging‐optical coeherence tomography (EDI‐OCT). A grid scan of the optic herve head (ONH), averaged 80 scans, to image the LCT, LCD and PLTT in center, mid‐inferior (I‐ONH), and superior positions and a nerve fiber layer (NFL) scan were done. LCT was the distance between borders of the LC. LCD was the distance between BMO reference line‐anterior LC border. BMO‐MRW was the shortest distance between BMO and internal limiting membrane. All values were compared between both groups and correlations between variables were tested.ResultsGlobal LCT was lower in POAG (132.9 ± 40.1 µm) than in control group (235.9 ± 36.8 µm, p < 0.05). Mean LCD was higher in POAG (572.2 ± 195.2 µm). Mean PLTT was lower in POAG (91.9 ± 49.9 µm, p < 0.05), as occurred with BMOMRW. In all eyes, the global LCT was correlated to NFLT (R = 0.61) and BMOMRW (R = 0.67; p < 0.001). In POAG eyes, global NFL was correlated to BMOMRW (R = 0.67) and the PLTT (R = 0.386). In I‐ONH scan, PLTT was correlated with LCD (R = −0.502) and inferior‐temporal (IT)‐NFLT(R = 0.479, p = 0.015). MD was correlated with PLTT(R = −0.597) and MBOMRW (R = −0.670, p < 0.01).ConclusionsGlaucoma can cause a decrease in LCT, PLTT, BMOMRW and increase in LCD, being potential markers of glaucomatous damage. Some ONH‐OCT parameters correlated with function, as measured by the MD. ONH EDI‐OCT imaging with automatic segmentation would be useful in glaucoma evaluation.

Fiber torsion sensor based on a twist taper in polarization-maintaining fiber.

A novel optical fiber torsion sensor head is proposed. A section of polarization-maintaining fiber (PMF) is spliced between single mode fiber (SMF), and a twist taper is fabricated by a commercial electric-arc fusion splicer in the middle of the PMF. The asymmetric characteristics are obtained by the twist taper so that a fiber torsion sensor with directional discrimination is fabricated. Due to the characteristics of the asymmetric structure, the torsion sensitivity for the twist rate from 0 rad/m to -8 rad/m reaches 2.392 nm/rad·m-1, and for the twist rate from 0 rad/m to 8 rad/m reaches 1.071 nm/rad·m-1 respectively.

An ultra-low noise optical head for liquid environment atomic force microscopy.

The design considerations and eventual performance of a new, ultra-low noise optical head for dynamic atomic force microscopy (AFM) are presented. The head, designed specifically for the study of hydration layers and ion organization next to solid surfaces and biomolecules, displays an integrated tip-sample distance noise below 3 pm. The sensitivity of the optical beam deflection sensor, operating at frequencies up to 8.6 MHz (3 dB roll-off), is typically below 10 fm/√Hz, enabling utilization of high frequency cantilevers of low thermal noise for fundamental and higher mode imaging. Exceptional signal stability and low optical noise are achieved by replacing the commonly used laser diode with a helium-neon laser. An integral photothermal excitation of the cantilever produces pure harmonic oscillations, minimizing the generation of higher cantilever modes and deleterious sound waves characterizing the commonly used excitation by a piezoelectric crystal. The optical head is designed to fit on top of the widespread Multimode(®) (Bruker) piezo-tube and accommodate its commercial liquid cell. The performance of the new AFM head is demonstrated by atomic resolution imaging of a muscovite mica surface in aqueous solution.

Efficient estimation of tissue thicknesses using sparse approximation for Gaussian processes.

Highly accurate localization of the human skull is vital in cranial radiotherapy. Marker-less optical head tracking provides a fast and accurate way to monitor this motion. Recent research has given evidence that marker-less tracking of the forehead benefits from tissue thickness information in addition to the 3D surface geometry. Using Gaussian Processes (GPs) tissue thickness is determined from optical backscatter of a sweeping laser. However, the computational complexity of the GPs scales cubically with the number of training samples. A full head scan contains 1024 points, whereas scans from several perspectives may be required for a comprehensive model for each subject. In five subjects, we thus evaluate sparse approximation methods to reduce the computational effort. We found a better - computation time versus root mean square error (RMSE) - tradeoff for a simple subset of data (SoD) technique. The increase of RMSE when dropping data was not found steep enough to justify the computational overhead of a better approximation by inducing point methods (namely FITC). Promising results were, however, obtained when clustering the training data before selecting the subset.

New classification of acute papilledema in children with severe malaria

Raised intracranial pressure is a feature of cerebral malaria in children living in Africa. We investigated specific clinical optic disc features of papilledema to establish their prognostic significance in this encephalopathy. We developed a classification of acute papilledema and tested it against disease outcome. Kenyan children admitted with severe falciparum malaria (cerebral or impaired consciousness) underwent dilated fundal examination using direct and indirect ophthalmoscopy. Clinical features of the optic disc were systematically recorded and compared to the child's outcome. Poor outcome defined as death or neurological impairment on discharge was used to construct and test a clinical classification of papilledema. Forty-five children were examined (26 cerebral malaria, 17 severe malaria with an impaired conscious level or prostration) of whom seven had a poor outcome (three died, four had residual neurological impairment). Loss of the optic disc cup and marked optic disc elevation were significantly correlated with a poor outcome (P < 0.05). Increasing severity in the proposed classification of acute papilledema was positively correlated with a poor outcome (P < 0.05, chi-square test for trend). Loss of the optic disc cup and marked elevation of the optic disc head appear to be correlated with poor outcome in children with severe malaria whereas the presence of dilated veins suggests a good outcome. The proposed classification of acute papilledema is useful as a prognostic indicator and may be applicable to other encephalopathies with raised intracranial pressure.

Cell depth imaging by point laser scanning fluorescence microscopy with an optical disk pickup head

A compact, cost-effective, and position-addressable digital laser scanning microscopy (DLSM) instrument is made using a commercially available Blu-ray disc read-only memory (BD-ROM) pickup head. Fluorescent cell images captured by DLSM have resolutions of 0.38 µm. Because of the position-addressable function, multispectral fluorescence cell images are captured using the same sample slide with different excitation laser sources. Specially designed objective lenses with the same working distance as the image-capturing beam are used for the different excitation laser sources. By accurately controlling the tilting angles of the sample slide or by moving the collimator lens of the image-capturing beam, the fluorescence cell images along different depth positions of the sample are obtained. Thus, z-section images with micrometer-depth resolutions are achievable.

Low-cost ultrahigh areal density optical disc system towards 400 Gbyte/disc

We introduce a new 400 Gbyte disc system, which has twice as much areal density as BDXL™ does, retaining the use of the conventional optical head and disc technology. Our proposal is based on the application of code modulations with enlarged minimum run length (d) and land/groove (L/G) geometry to increase linear recording density and track density by 1.5 and 1.33 times, respectively. Also, saw tooth wobble (STW) was introduced for a multilayered L/G disc system to suppress readout signal fluctuations. Here, we demonstrated that the linear recording density increased to 45.5 Gbyte/layer by applying d = 3 to a commercially available BDXL™. Also, we checked that crosstalk, which is a major concern in an L/G disc with a track pitch of 240 nm, was suppressed to below −30 dB by choosing the proper groove depth. Moreover, the investigation of the effect of track width modulation on the write/read performance demonstrated that an adverse influence can be suppressed by employing STW.

PRECISE HEAD TRACKING IN HEARING APPLICATIONS

Abstract. The paper gives an overview about two research projects, both dealing with optical head tracking in hearing applications. As part of the project “Development of a real-time low-cost tracking system for medical and audiological problems (ELCoT)” a cost-effective single camera 3D tracking system has been developed which enables the detection of arm and head movements of human patients. Amongst others, the measuring system is designed for a new hearing test (based on the “Mainzer Kindertisch”), which analyzes the directional hearing capabilities of children in cooperation with the research project ERKI (Evaluation of acoustic sound source localization for children). As part of the research project framework “Hearing in everyday life (HALLO)” a stereo tracking system is being used for analyzing the head movement of human patients during complex acoustic events. Together with the consideration of biosignals like skin conductance the speech comprehension and listening effort of persons with reduced hearing ability, especially in situations with background noise, is evaluated. For both projects the system design, accuracy aspects and results of practical tests are discussed.

Calculation and research of contact ophthalmic dual application lenses

Subject of research. Algorithm for calculation of contact ophthalmic lenses for dual application has been suggested based on unified approach for their calculation. The algorithm has been tested on the composition of Goldmann ophthalmic lenses and Panfundoscope lens optical systems. Method. The condition of mutual unambiguous orientation of patient’s eye and instruments is performed at the initial calculation step by face mounting and movement of coordinate table with optical head. Then such type of patient's eye optical system model is selected that the lens would be combined with the front surface of eye cornea optical system. Pupil of patient eye is under anesthesia. At the final calculation step we determine the functions of optical lens image quality and their values based on medical and technical requirements for the components of the complex system. Main results. The algorithm for ophthalmic lenses calculation has been suggested and its correctness has been proved practically on the example of two basic models in the group of such type lenses being applied in practice as a part of complex system with ophthalmic laser coagulators. Optical calculation of Goldmann ophthalmic contact lenses and Panfundoscope is presented. The method of neutralization is optimal for Goldmann lenses. The first component in Panfundoscope operates the position of object planes whereas the second component operates the position of complex system with ophthalmocoagulator's pupils. Computer modeling of complex system "Computer model of eye-ophthalmic lens" in ZEMAX confirmed the correctness of calculation algorithm in which the criteria of diffraction image quality has been used. Application possibility of simplified computer eye model called "Reduced eye" by Verbitskiy has been demonstrated. Practical relevance. The general scientific approach to the problem of synthesis, calculation and research of complex system with contact ophthalmic lenses for diagnostics and laser intervention on the eyeground has been found and confirmed. The results obtained have practical significance for the further development of optical calculation method and optical ophthalmologic instruments such as the fundus camera, wavefront analysers, opthalmoscopes and systems of vision optical correction.

Parallel micro manipulator for optical spot array alignment of maskless lithography

Photolithography is the one of the core processes in micro-nano fabrication that includes micro electro mechanical system devices, flat panel displays, and various semiconductor chips. Since manufacturing of masks takes major portion of overall cost structure for the typical lithography procedure, elimination of the masks from the process will make a great impact on cost reduction. In addition, the maksless lithography generally provides a great flexibility for product design and verification. Firstly, In the present work, it was introduced that a point array method applied to Digital Micro mirror Device (DMD)-based optical head system in maskless digital exposure process. Secondly, it was shown the design of a redundant 4-[PP]PS parallel mechanism and analysed kinematic characteristic of the parallel manipulator. An array error model of the system is defined and application of genetic algorithm to the alignment spot array position error correction is presented. Finally, the system is tested and analyzed with a 10 by 10 optical array setup.

Optical head alignment method using serial manipulators for maskless lithography system

As the cost of photomasks for lithography processes becomes prohibitive especially for large size panel displays, researchers have been developing maskless alternatives using various physical wave sources. Despite the prominent overall manufacturing cost reduction benefit, the maskless lithography system has drawbacks in some respects. These issues include productivity, size of the system, and lithography hardware cost efficiency. One of the well accepted solutions is massive parallel exposure using multioptical heads. In order to implement the multi heads option, securing accurate alignment of the heads is essential. In this paper, an alignment algorithm of a spot array manipulated with serial mechanism is suggested. The suggested method enables to reduce the overall error using the genetic algorithm. Defining spot array error as fitness function of the algorithm is introduced. And correlation with kinematics of the optical system and spot array error will be represented. In addition, 4 DOF serial manipulator design and its kinematic analysis is presented. Finally, the developed system is tested and evaluated. The suggested algorithm allows spot array error to be reduced about 80 % with regards to random error. This paper contributes to accurate alignment of the heads by suggesting an alignment algorithm of a spot array manipulated with a serial mechanism.

English

English

Feasibility of bit patterned media for HAMR at 5 Tb/in2

We have investigated the feasibility of BPM for HAMR via Finite Difference Time Domain and atomistic simulation and we have substantiated the feasibility of 5 Tb/in2 with two filling factors 25% and 56% even when the maximum on-track bit temperature is below the Curie temperature. The success of this underheated switching is attributed to sufficiently low anisotropy instead of reduction of Curie temperature. The temperature gradient in the cross-track direction is almost doubled if the optical head width is reduced by half, indicating the possibility of higher areal densities. Moreover, contrary to continuous media, we also found that the power absorption peaks at the bottom of the bit patterned FePt when the media is illuminated from above, which is probably due to stronger coupling there between FePt and the surrounding materials.

A novel moiré-based optical scanning head for high-precision contouring

This paper is devoted to the design and implementation of a novel moire-based optical head mounted on the robotic arm of a coordinate measuring machine. The optical components of the recently developed two-projector moire setup were miniaturized and integrated in the optical head. Special care was taken in minimizing the weight of the resulting structure so as to reduce as much as possible the forces acting on the robotic arm. The prototype of the optical head was tested by contouring the shape of different objects and measuring the displacements of a metallic bar subjected to compression loading. Measurements conducted with the proposed optical head were consistent with those obtained via a coordinate measuring machine (CMM). The values of the dimensions found fell always within the average ± standard deviation interval measured with the CMM. The optical head appears very suited for contouring the shape of objects and for determining the out-of-plane displacement field of mechanical components subjected to specific boundary and loading conditions. Furthermore, the system can be easily implemented inline in an industrial context to perform measurements as a product is being manufactured.

3D direct laser writing of Petabyte Optical Disk

Abstract We report novel results for 3D recording of an optical disk with ultra-high density. Multilayer 5 nm nanomarks were experimentally obtained by using fluorescent photosensitive glass-ceramics and an optical head with λ =650 nm and NA=0.60. The distance between adjacent 5 nm nanomarks has been reduced to 10 nm. Ultra-high density optical data is recorded by focusing laser beam of a CW laser diode operating at low power ( P max =10 mW).

INFLUENCE THE STRUCTURE OF THE ROAD SURFACE ON THE MEASUREMENT OF DISTANCE AND SPEED USING OPTICAL HEAD

The optical head is a linear vehicle speed sensor. Its action is based on image analysis of the moving road surface. A special algorithm converts it on the speed signal. Because the image of a road is analyzed, therefore the change in structure of the road surface causes change of the signal from the optical head. Therefore, for each type of surface, it is necessary to calibrate the optical head. Calibration consists of measuring, using an optical head, the length of the measurement distance, which was previously precisely measured with another reference device. Based on these two values the calibration factor is calculated, and entered afterwards in the optical head control software. This optical head is used in several the road tests, and its speed measurement function is used in the measurement of vehicle acceleration, braking distance, the total vehicle road load. This device, connected to the recorder, is also used in research on motion parameters of vehicle under real driving conditions. During these tests may occur the change of the road surface, therefore it is particularly important to know the influence of road surface structure on the signal from the optical head. This paper presents the results of optical head tests on the road with different structure and surface quality.

Differences between Non-arteritic Anterior Ischemic Optic Neuropathy and Open Angle Glaucoma with Altitudinal Visual Field Defect.

PurposeTo investigate the differences in retinal nerve fiber layer (RNFL) change and optic nerve head parameters between non-arteritic anterior ischemic optic neuropathy (NAION) and open angle glaucoma (OAG) with altitudinal visual field defect.MethodsSeventeen NAION patients and 26 OAG patients were enrolled prospectively. The standard visual field indices (mean deviation, pattern standard deviation) were obtained from the Humphrey visual field test and differences between the two groups were analyzed. Cirrus HD-OCT parameters were used, including optic disc head analysis, average RNFL thickness, and RNFL thickness of each quadrant.ResultsThe mean deviation and pattern standard deviation were not significantly different between the groups. In the affected eye, although the disc area was similar between the two groups (2.00 ± 0.32 and 1.99 ± 0.33 mm2, p = 0.586), the rim area of the OAG group was smaller than that of the NAION group (1.26 ± 0.56 and 0.61 ± 0.15 mm2, respectively, p < 0.001). RNFL asymmetry was not different between the two groups (p = 0.265), but the inferior RNFL thickness of both the affected and unaffected eyes were less in the OAG group than in the NAION group. In the analysis of optic disc morphology, both affected and unaffected eyes showed significant differences between two groups.ConclusionsTo differentiate NAION from OAG in eyes with altitudinal visual field defects, optic disc head analysis of not only the affected eye, but also the unaffected eye, by using spectral domain optical coherence tomography may be helpful.