Finite-difference time-domain modeling and experimental characterization of planar waveguide fluorescence sensors

Journal ArticleThe finite-difference time-domain method (FDTD) is a powerful numerical technique for solving Maxwell's equations in a discretized space and time grid. Its applications have up to now been in the analysis of electrically large structures in the microwave domain, and the scope of investigations has been extended to the optical region only recently. Because of computer memory limitations, the method is generally restricted to configurations which extend to the order of tens of wavelengths in three dimensions, or hundreds of wavelengths in two dimensions. Optical sensor structures are therefore of suitable size to be modeled with FDTD, and e. g. fluorescence sensor design can benefit from the use of FDTD in optimization of the waveguide structures. In general, the integration of chemical and optical design is difficult, but FDTD can bring the two design approaches closer together. One of the main advantages of FDTD is its ability to include near-field effects, such as distribution of protein molecules on the active surface of optical sensors in the model, which has been shown to be important in estimating the fluorescent excitation and collection efficiencies of molecules on surfaces. In addition, for planar structures, two-dimensional models are adequate for studying many aspects of sensor design. We applied FDTD to design of planar fluorescence sensors. Excitation and emission models were analyzed for planar waveguide structures with side collection of emitted light in mind. Planar waveguides were fabricated on fused silica substrates, and the characteristics of the waveguides were compared to the model. Good agreement was found with the FDTD modeling to the physical model, and based on this knowledge, an FDTD sensor model was prepared predicting good fluorescence excitation and emission side collection efficiencies

Visual performance with small concave and convex displays

Peer reviewe

Live delivery of neurosurgical operating theater experience in virtual reality

A system for assisting in microneurosurgical training and for delivering interactive mixed reality surgical experience live was developed and experimented in hospital premises. An interactive experience from the neurosurgical operating theater was presented together with associated medical content on virtual reality eyewear of remote users. Details of the stereoscopic 360-degree capture, surgery imaging equipment, signal delivery, and display systems are presented, and the presence experience and the visual quality questionnaire results are discussed. The users reported positive scores on the questionnaire on topics related to the user experience achieved in the trial.Peer reviewe

Orthogonally coupled geometrical constraints in optics design

Modern optical multi-camera systems require integrating many camera modules in a small volume. A new space-saving concept for such imaging systems is presented, based on intersecting optical paths that utilize one or more common elements for the respective optical paths. The principles for the optimization for such systems is examined, providing the theory for geometric optimization constraints. These principles can become useful in designing e. g. spatially challenging 360-degree imaging systems for surveillance and consumer applications

Studies on Diffractive Mobile Display Backlights

The digital convergence has brought about a new class of mobile devices that allows a compelling, visually rich multimedia experience to the user in a handheld product, such as a mobile telephone. The display in these “smart phones”, “feature phones”, or “multimedia computers”, is a strategically important component that defines the user experience for a great part. While the visual user experience provided by the display can be very good, the power dissipation in the display is the limiting factor in the length of the user interaction with the mobile multimedia content. As the proportion of time of interacting with the visually rich content increases over that of simple voice-driven communication, such commonly used techniques for reducing the overall energy consumption of the device as power-saving modes or time outs cannot be used during a multimedia session without compromising the quality of service to the user.The conventional mobile liquid-crystal display structure consists of a backlight unit with the associated light sources, the display panel itself, and various optical films that control the state of polarization and viewing characteristics of the display. The backlight unit itself has evolved in the last fifteen years to become a very efficient component to provide uniform illumination to the electro-optic spatial light modulator comprised by the liquid-crystal pixel array. In the conventional structure, the color filter array embedded in the liquid-crystal display panel limits the light throughput in the display system. The backlight unit itself in the conventional configuration is difficult to improve any further, and a system redesign is required to make the display system perform more efficiently than what is currently possible.One possible way to redesign a display system more effectively is to direct the appropriate primary bands of light through the respective subpixels in the display panel, instead of having these filter white light into the primary colors. This can be done by diffractive means, i. e. by placing a grating structure on the light guide plate of the backlight unit. Significant improvement in energy efficiency of a mobile display system can be achieved by this approach, and at the same time, cost savings can be expected due to the elimination of many beam-shaping films in the backlight unit, as compared to the conventional mobile liquid-crystal display configuration. Further cost savings can be achieved by removing the color filter array, provided that the color purity of outcoupled light is good.This thesis presents a new pixelated color-separating grating array concept that diffracts the light from red, green, and blue light-emitting diodes in the backlight unit through a subpixel array in a prospective mobile display module. A literature review was conducted and key research studies in the area of diffractive mobile display backlights were reviewed. Experimental studies to verify various constituent elements of this concept are presented, and conclusions are drawn on how the display industry could benefit from this new concept, and what should be taken into account when adopting a new display manufacturing paradigm based on diffractive backlights