Fabrication of two kinds of eight-fold photonic quasi-crystals assisted by a specially designed prism.

We demonstrate that two kinds of 2D eight-fold photonic quasi-crystals (PQCs) can be fabricated by a specially designed prism via single-exposure holographic lithography. The prism with five continuous side surfaces out of common eight symmetrical side surfaces, plus a top surface, is well designed for PQC fabrication. Compared with the traditional method of setting up eight free-space beams in the half-space for an eight-fold PQC fabrication, our specially designed prism reduces the number of beams, avoids the differences of beam-to-beam phases, and simplifies the fabrication process. The theory and computer simulation confirm the patterns of two kinds of PQCs by a single prism illumination recording. Further, these quasi-crystal patterns are successfully verified by experimental results under a scanning electron microscope. In addition, these samples show some good properties, such as uniformity over large area, the implementation of a single defect by underexposure, and symmetry break of the eight dots. Our special prism-assisted holographic lithography technique provides a base for further investigating the optical properties of these novel structures.

Anterior segment biometry during accommodation imaged with ultralong scan depth optical coherence tomography.

PURPOSE: To measure by ultralong scan depth optical coherence tomography (UL-OCT) dimensional changes in the anterior segment of human eyes during accommodation. DESIGN: Evaluation of diagnostic test or technology. PARTICIPANTS: Forty-one right eyes of healthy subjects with a mean age of 34 years (range, 22-41 years) and a mean refraction of -2.5 ± 2.6 diopters were imaged in 2 repeated measurements at minimal and maximal accommodations. METHODS: A specially adapted and designed UL-OCT instrument was used to image from the front surface of the cornea to the back surface of the crystalline lens. Custom software corrected the optical distortion of the images and yielded the biometric measurements. The coefficient of repeatability and the intraclass correlation coefficient were calculated to evaluate the repeatability and reliability. MAIN OUTCOME MEASURES: Anterior segment parameters and associated repeatability and reliability upon accommodation. The dimensional results included central corneal thickness (CCT), anterior chamber depth and width (ACD, ACW), pupil diameter (PD), lens thickness (LT), anterior segment length (ASL = ACD + LT), lens central position (LCP = ACD + 1/2LT), and horizontal radii of the lens anterior and posterior surface curvatures (LAC, LPC). RESULTS: Repeated measurements of each variable within each accommodative state did not differ significantly (P>0.05). The coefficients of repeatability (CORs) and intraclass correlation coefficients for CCT, ACW, ACD, LT, LCP, and ASL were excellent (1.2%- 3.59% and 0.998-0.877, respectively). They were higher for PD (18.90%-21.63% and 0.880-0.874, respectively) and moderate for LAC and LPC (34.86%-42.72% and 0.669-0.251, respectively) in the 2 accommodative states. Compared with minimal accommodation, PD, ACD, LAC, LPC, and LCP decreased and LT and ASL increased significantly at maximal accommodation (P<0.05), whereas CCT and ACW did not change (P>0.05). CONCLUSIONS: The UL-OCT measured changes in anterior segment dimensions during accommodation with good repeatability and reliability. During accommodation, the back surface of the lens became steeper as the lens moved forward. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Nanoscale optical reinforcement for enhanced reversible holography.

We demonstrate a nanoscale optical reinforcement concept for reversible holographic recording. The bone-muscle-like mechanism enables enhancement of holographic grating formation due to the collective alignment of liquid crystal (LC) molecules nearby photo-reconfigurable polymer backbones. The LC fluidity facilitates the ease of polymer chain transformation during the holographic recording while the polymer network stabilizes the LC collective orientation and the consequential optical enhancement after the recording. As such, the holographic recording possesses both long-term persistence and real-time rewritability.

Enhanced non-volatile and updatable holography using a polymer composite system.

Updatable holography is considered as the ultimate technique for true 3D information recording and display. However, there is no practical solution to preserve the required features of both non-volatility and reversibility which conflict with each other when the reading has the same wavelength as the recording. We demonstrate a non-volatile and updatable holographic approach by exploiting new features of molecular transformations in a polymer recording system. In addition, by using a new composite recording film containing photo-reconfigurable liquid-crystal (LC) polymer, the holographic recording is enhanced due to the collective reorientation of LC molecules around the reconfigured polymer chains.

Visualization of the precorneal tear film using ultrahigh resolution optical coherence tomography in dry eye.

PURPOSE: To visualize the precorneal tear film (PCTF) in dry eye patients using ultrahigh resolution optical coherence tomography (UHR-OCT). METHODS: A custom-built UHR-OCT with ultrahigh resolution (~3 µm) was used to image the PCTF at the vertical meridian. Eighteen right eyes of 18 previously diagnosed dry eye patients (9 men and 9 women, age, 47.8±20.7 years) with aqueous tear deficiency were studied. Images were taken during normal and delayed blinking. The visualized PCTF was measured directly. An indirect calculation was used to obtain the thickness in cases where the PCTF could not be visualized. RESULTS: During normal blinking, the PCTF was visualized in 5 of 18 eyes (27.8%) with an average PCTF thickness of 5.8 µm (SD, 1.3 µm). During delayed blinking, the PCTF was visualized in 11 eyes (61.1%) with a significantly increased average thickness of 7.3 µm (SD, 0.9 µm; P<0.05). The percent increase of the visualized PCTF thickness was higher during delayed blinking compared with normal blinking (χ test, P<0.05). The averaged PCTF was 4.4 µm during normal blinking, and the PCTF thickness was significantly increased to 6.6 µm (SD, 2.9 µm; P<0.05) during delayed blinking. CONCLUSIONS: We report the first visualization of PCTF in vivo in dry eye patients with UHR-OCT. Precorneal tear film can be directly visualized in some eyes during both normal and delayed blinking, and it seemed thicker during delayed blinking compared with normal blinking.

The watery eye.

The surface of the eye needs to be wet constantly to ensure its integrity in maintaining ocular comfort, clear vision, and ocular health. This article presents new findings in the tear dynamics of the human eye, with an emphasis on the tear meniscus and tear film through the day and in response to punctual occlusion and wearing of contact lenses. Recent advances in imaging technique are briefly discussed.

Wide field of view handheld smart fundus camera for telemedicine applications.

Purpose: We report that a large field-of-view (FOV) retinal image can be acquired by a smart fundus camera. Approach: This handheld system consists of a Raspberry Pi board, a touch screen display, a customized optical lens group, a ring light-emitting diode, and a Li-battery. Results: Wide FOV of ∼ 57 deg is observed with proper lens configuration and can be expanded using image stitching algorithms. Conclusions: This customized handheld fundus camera provides better image quality than cellphone-based fundus imaging solutions and offers more operational features than traditional portable fundus cameras. It may benefit field-portable ophthalmic diagnostic applications.

Entire contact lens imaged in vivo and in vitro with spectral domain optical coherence tomography.

OBJECTIVES: To demonstrate the capability of directly visualizing the entire ocular surface and the entire contact lens on the eye using spectral domain optical coherence tomography (SD-OCT). METHODS: A custom-built, high-speed, and high-resolution SD-OCT was developed with extended scan depth and width. The eye was imaged before and after wearing a toric soft contact lens (PureVision; Bausch & Lomb). A lubricant eye drop (Soothe; Bausch & Lomb) was instilled in the eye to enhance the image contrast on the lens. The same toric soft contact lens immersed in the contact lens solution was also imaged with a contrast enhancement medium (0.5% Intralipid). RESULTS: Cross-sectional OCT images of the entire ocular surface were acquired with high-resolution 2,048 x 2,048 pixels. Quantitative surface height map of the ocular surface was obtained from a radial scan data set containing 32 B-scans. With the contrast enhancement agent, the entire toric soft contact lens was clearly visualized, both in vitro and on the eye. The surfaces of the lens were detected and used to generate the thickness maps of the soft contact lens. CONCLUSIONS: Spectral domain optical coherence tomography with extended scan depth and width is a promising tool for imaging the entire ocular surface shape and soft contact lenses. This successful demonstration suggests that the extended depth SD-OCT is effective in studying ocular surface shape and its interaction with a soft contact lens. The novel method is helpful for the evaluation of contact lens fitting and lens design.

Detection of magnetic particles in live DBA/2J mouse eyes using magnetomotive optical coherence tomography.

OBJECTIVES: To demonstrate in vivo molecular imaging of the eye using spectral-domain magnetomotive optical coherence tomography (MMOCT). METHODS: A custom-built, high-speed, and high-resolution MMOCT was developed for imaging magnetic particle-coupled molecules in living mouse eyes by applying an external dynamic magnetic field gradient during optical coherence tomography (OCT) scanning. The magnetomotive signals were tested in vitro by scanning magnetic beads embedded within an agarose gel (1.5%) and in vivo in the anterior segment of a mouse eye. RESULTS: Cross-sectional OCT images of the gel and the anterior segment of the eye were acquired by regular OCT structural scanning. Magnetomotive optical coherence tomography signals were successfully captured in the agarose gel with embedded magnetic beads. The signals were captured in the anterior segment of the mouse eyes after injecting the beads. The signal was overlaid successfully onto the structural OCT image. CONCLUSIONS: We demonstrated the ability to detect particles injected into the anterior chamber of the mouse eye using MMOCT. This suggests that MMOCT is effective for future live detection of molecular (protein) targets in various ocular diseases in mouse models.

Agile dual-channel spectral imaging with spectral zooming.

A dual-channel spectral imaging system with agile spectral band access and spectral bandwidth tuning capability is presented. A diffractive grating and an acousto-optic tunable filter (AOTF) are respectively used as spectral dispersion and spectral filtering elements for the two channels. A 4f spectral filtering channel using an adjustable slit is set up at the first diffraction order of the grating to realize coarse spectral band selection. The AOTF selectively filters the spectrum of the nondispersed zero order to realize fine spectral imaging. The spectral zooming function is achieved without increasing spectral frame number facilitating real-time spectral imaging operation. Feasibility of the spectral imaging has been demonstrated through preliminary experiments. Minimum 6 nm spectral resolution and 1.2 degrees field of view have been achieved. The real-time spectral imaging capable of wide spectral band operation without loosing desired fine spectral capability is particularly useful for a variety of defense, medical, and environmental monitoring applications.

Wavelength-multiplexed submicron holograms for disk-compatible data storage.

By using a hybrid diffractive and refractive achromat with extended depth of focus, we have successfully recorded a micro-hologram array with diffraction-limited individual spot size maintained throughout the thickness of recording medium. An electrically programmable wavelength combiner was constructed in which a white light source was adopted. By modifying on a commercial CD readout head, we configured a compact micro-hologram recording/readout system that is compatible to existing disk storage technology. Base on the wavelength combiner and recording/readout system, wavelength-multiplexed micro-holograms were recorded and recovered. The presented results demonstrate the practicality of our novel storage architecture.

Improving lateral resolution and image quality of optical coherence tomography by the multi-frame superresolution technique for 3D tissue imaging.

The multi-frame superresolution technique is introduced to significantly improve the lateral resolution and image quality of spectral domain optical coherence tomography (SD-OCT). Using several sets of low resolution C-scan 3D images with lateral sub-spot-spacing shifts on different sets, the multi-frame superresolution processing of these sets at each depth layer reconstructs a higher resolution and quality lateral image. Layer by layer processing yields an overall high lateral resolution and quality 3D image. In theory, the superresolution processing including deconvolution can solve the diffraction limit, lateral scan density and background noise problems together. In experiment, the improved lateral resolution by ~3 times reaching 7.81 µm and 2.19 µm using sample arm optics of 0.015 and 0.05 numerical aperture respectively as well as doubling the image quality has been confirmed by imaging a known resolution test target. Improved lateral resolution on in vitro skin C-scan images has been demonstrated. For in vivo 3D SD-OCT imaging of human skin, fingerprint and retina layer, we used the multi-modal volume registration method to effectively estimate the lateral image shifts among different C-scans due to random minor unintended live body motion. Further processing of these images generated high lateral resolution 3D images as well as high quality B-scan images of these in vivo tissues.

Tear film measurement by optical reflectometry technique.

Evaluation of tear film is performed by an optical reflectometer system with alignment guided by a galvanometer scanner. The reflectometer system utilizes optical fibers to deliver illumination light to the tear film and collect the film reflectance as a function of wavelength. Film thickness is determined by best fitting the reflectance-wavelength curve. The spectral reflectance acquisition time is 15 ms, fast enough for detecting film thickness changes. Fast beam alignment of 1 s is achieved by the galvanometer scanner. The reflectometer was first used to evaluate artificial tear film on a model eye with and without a contact lens. The film thickness and thinning rate have been successfully quantified with the minimum measured thickness of about 0.3 µm. Tear films in human eyes, with and without a contact lens, have also been evaluated. A high-contrast spectral reflectance signal from the precontact lens tear film is clearly observed, and the thinning dynamics have been easily recorded from 3.69 to 1.31 µm with lipid layer thickness variation in the range of 41 to 67 nm. The accuracy of the measurement is better than ±0.58% of the film thickness at an estimated tear film refractive index error of ±0.001. The fiber-based reflectometer system is compact and easy to handle.

Micrometer-scale contact lens movements imaged by ultrahigh-resolution optical coherence tomography.

PURPOSE: To dynamically evaluate contact lens movement and ocular surface shape using ultrahigh-resolution and ultralong-scan-depth optical coherence tomography (OCT). DESIGN: Clinical research study of a laboratory technique. METHODS: Four different types of soft contact lenses were tested on the left eye of 10 subjects (6 male and 4 female). Lens edges at primary gaze and temporal and nasal gazes were imaged by ultrahigh-resolution OCT. Excursion lag was obtained as the distance between the lens edge at primary gaze and immediately after the eye was quickly turned either nasally or temporally. The inferior lens edges were imaged continuously to track vertical movements during blinking. Ultralong-scan-depth OCT provided quantifiable images of the ocular surface, and the contour was acquired using custom software. RESULTS: Excursion lag at the horizontal meridian was 366 ± 134 µm at temporal gaze and 320 ± 137 µm at nasal gaze (P > .05). The lens uplift at the vertical meridian was 342 ± 155 µm after blinking. There were significant differences in horizontal lags and vertical movements among different lenses (P < .05). Horizontal lags were correlated with radii of curvatures and sagittal heights at 6-mm and 14-mm horizontal meridian (P < .05). The blink-induced lens uplift first lowered by 104 ± 8 µm, and then lifted 342 ± 155 µm after the blink. CONCLUSIONS: Ultrahigh-resolution and ultralong-scan-depth OCT can assess micrometer-scale lens movements and ocular surface contours. Both lens design and ocular surface shape affected lens movements.

Ultra-high resolution optical coherence tomography for monitoring tear meniscus volume in dry eye after topical cyclosporine treatment.

PURPOSE: This study was designed to determine the ability of ultra-high-resolution optical coherence tomography (UHR-OCT) to monitor tear meniscus volume after dry eye treatment with Restasis(®) (0.05% cyclosporine). METHODS: UHR-OCT was used to image the upper and lower tear menisci (height and volume) in 14 consecutive dry eye patients at baseline. The treatment group was initiated on daily Restasis and measurements were repeated at 1 and 2 months while on treatment. All measurements were performed immediately after a blink. RESULTS: The baseline tear meniscus volumes were 0.40 ± 0.19 µL (upper) and 0.43 ± 0.18 µL (lower). In the treatment group, tear meniscus heights showed significant increases of both upper (post-hoc test with Bonferroni correction: P = 0.003) and lower (P = 0.0003) tear menisci, after 1 month on Restasis. The tear meniscus volumes in the treatment group after 1 month of Restasis showed significant increases of both upper (P = 0.007) and lower (P = 0.007) tear menisci. At 2 months, the increase of the tear meniscus was still evident in all measured variables compared with baseline (P < 0.05). CONCLUSION: UHR-OCT offers a promising tool for monitoring dry eye treatment. With this method, a measurable increase in tear meniscus volume was evident after 1 month of treatment with Restasis in dry eye patients.

Extended scan depth optical coherence tomography for evaluating ocular surface shape.

Spectral domain optical coherence tomography (SD-OCT) with extended scan depth makes it possible for quantitative measurement of the entire ocular surface shape. We proposed a novel method for ocular surface shape measurement using a custom-built anterior segment SD-OCT, which will serve on the contact lens fitting. A crosshair alignment system was applied to reduce the misalignment and tilting of the eye. An algorithm was developed to automatically segment the ocular surface. We also described the correction of the image distortion from the segmented dataset induced by the nontelecentric scanning system and tested the accuracy and repeatability. The results showed high accuracy of SD-OCT in measuring a bicurved test surface with a maximum height error of 17.4 µm. The repeatability of in vivo measurement was also good. The standard deviations of the height measurement within a 14-mm wide range were all less than 35 µm. This work demonstrates the feasibility of using extended depth SD-OCT to perform noninvasive evaluation of the ocular surface shape.

Characterization of soft contact lens edge fitting using ultra-high resolution and ultra-long scan depth optical coherence tomography.

PURPOSE: To characterize the edge fitting of soft contact lenses using ultra-high resolution optical coherence tomography (UHR-OCT) and ultra-long scan depth optical coherence tomography (UL-OCT). METHODS: A total of 20 participants (11 men, 9 women; mean age, 32.3 years) were recruited. Four different types of soft contact lenses were randomly fitted to both eyes of each subject on two separate visits. After 30 minutes, the horizontal meridians of the corneal center, midperiphery, and limbus were imaged by UHR-OCT. UL-OCT imaged each lens in vitro and the ocular surface of a physical model eye. RESULTS: Angle-edged lenses had significantly less conjunctival buildup than did round-edged lenses (P = 0.008). Limbal post-lens tear film gaps were present in 42% of the eyes, with the round-edged lenses having the most at 68%. Similarly, post-lens tear film gaps at the corneal mid-periphery were present in 47% of all eyes, with the round-edged lens having the most at 75%. Mismatches between the lens and the ocular surface were simulated based on UL-OCT images of the in vitro lenses and the model eye. The existence of tear film gaps and touching points were predicted in the simulation. CONCLUSIONS: The soft contact lens edge fitting was characterized by the conjunctival buildup and tear film gaps. Different types of contact lenses presented different levels of conjunctival buildup as well as different frequencies of tear film gaps. The findings by UHR-OCT were predicted in the simulation by UL-OCT. The application of these new technologies may open new ways of designing lenses and evaluating their fit.

Broadband superluminescent diode-based ultrahigh resolution optical coherence tomography for ophthalmic imaging.

Spectral domain optical coherence tomography (SD-OCT) with ultrahigh resolution can be used to measure precise structures in the context of ophthalmic imaging. We designed an ultrahigh resolution SD-OCT system based on broadband superluminescent diode (SLD) as the light source. An axial resolution of 2.2 µm in tissue, a scan depth of 1.48 mm, and a high sensitivity of 93 dB were achieved by the spectrometer designed. The ultrahigh-resolution SD-OCT system was employed to image the human cornea and retina with a cross-section image of 2048 × 2048 pixels. Our research demonstrated that ultrahigh -resolution SD-OCT can be achieved using broadband SLD in a simple way.

SD-OCT with prolonged scan depth for imaging the anterior segment of the eye.

An 840-nm wavelength spectral domain optical coherence tomography (SD-OCT) with prolonged scan depth was developed and mounted onto a conventional slit lamp for imaging the anterior segment of the eye. X-Y cross aiming was applied to align the SD-OCT scanning position during imaging. An internal fixation target displayed on a miniature LCD monitor was provided. The SD-OCT instrument had an axial resolution of 6 µm and a prolonged scan depth of 7.2 mm. High-quality SD-OCT images, consisting of 2,048 × 2,048 pixels, were acquired of the entire anterior chamber and entire crystalline lens from a healthy subject. The entire cornea, anterior chamber angle, limbus, and iris were clearly visible. Additionally, the internal structure of crystalline lens, including anterior and posterior surfaces of the crystalline lens, capsule, nucleus, and cortex, were clearly imaged with the instrument. The system was also tested in imaging accommodation of the same eye, demonstrating the feasibility of the novel approach for evaluating presbyopia/accommodation.

Array waveguide evanescent ribbon coupler for card-to-backplane optical interconnects.

A flexible array waveguide evanescent coupler for card-to-backplane optical interconnects is presented. The proposed technique eliminates traditional 90 degrees out-of-plane turns and local waveguide termination of multidrop bus architectures that hinder conventional card-to-backplane optical interconnections. Evanescent coupling between array waveguide ribbons has been successfully demonstrated. Further experiments have been performed to quantify array waveguide coupling length versus transfer efficiency and waveguide misalignment tolerance. Preliminary optical interconnect testing has demonstrated 2.5GHz operation of the coupler ribbons. The successful high-speed coupling confirms the effectiveness of the proposed method for high-speed computing systems.