Reflective liquid crystal hybrid beam-steerer

We report on efficient optical beam-steering using a hot-embossed reflective blazed grating in combination with liquid crystal. A numerical simulation of the electrical switching characteristics of the liquid crystal is performed and the results are used in an FDTD optical simulator to analyze the beam deflection. The corresponding experiment on the realized device is performed and is found to be in good agreement. Beam deflection angles of 4.4° upon perpendicular incidence are found with low applied voltages of 3.4V. By tilting the device with respect to the incoming optical beam it can be electronically switched such that the beam undergoes either total internal reflection or reflection with a tunable angle

Proof-of-concept demonstration of free-form optics enhanced confocal Raman spectroscopy in combination with optofluidic lab-on-chip

Raman spectroscopy is a powerful optical and non-destructive technique and a well-known method for analysis purposes, especially to determine the molecular fingerprint of substances. Traditionally, such analyses are done in a specialized lab, with considerable requirements in terms of equipment, time and manual sampling of substances of interest. In this paper we take a step from bulky Raman spectroscopy laboratory analyses towards lab-on-chip (LOC) analyses. We present an optofluidic lab-on-chip for confocal Raman spectroscopy, which can be used for the analysis of liquids. The confocal detection suppresses the unwanted background from the polymer material out of which the chip is fabricated. We design the free-form optical reflector using non-sequential ray-tracing combined with a mathematical code to simulate the Raman scattering behavior of the substance under test. We prototype the device in Polymethyl methacrylate (PMMA) by means of ultraprecision diamond tooling. In a proof-of-concept demonstration, we first show the confocal behavior of our Raman lab-on-chip system by measuring the Raman spectrum of ethanol. In a next step, we compare the Raman spectra measured in our lab-on-chip with spectra measured with a commercial Raman spectrometer. Finally, to calibrate the system we perform Raman measurements on urea solutions with different concentrations. We achieve a detection limit that corresponds to a noise equivalent concentration of 20mM. Apart from strongly reducing the background perturbations, our confocal Raman spectroscopy system has other advantages as well. The reflector design is robust from a mechanical point of view and has the potential for mass-manufacturing using hot embossing or injection molding

Active optical beam shaping based on liquid crystals and polymer micro-structures

Emerging applications requiring light beam manipulation, such as high-efficiency sunlight concentrators for solar cells, switchable micro-lens arrays for autostereoscopic displays, tunable lenses for augmented reality goggles, auto-focusing spectacles, and smart contact lenses, mostly depend on one or more active optical components with the desired and controllable beam modifying functionalities, preferably manufactured at relatively low cost. Recent progress in research on components based on the combination of liquid crystals (LCs) and various polymer micro-structures is reviewed in this paper. It is found that such components can address the demands appropriately and have the potential of paving the way for large-scale applications of active optical beam shaping components

SINPHOS - SINgle PHOton spectrometer for biomedical application

In the last decades several experiments have clearly demonstrated that, once illuminated, all biological systems emit for some time a very weak flux of photons, called Delayed Luminescence (DL). Some recent results have shown the possibility of using the DL as a diagnostic tool in the field of optical biopsy or of multi-dimensional diagnostics. Following such indications we decided to start developing SINPHOS, a monolithic micro-device, capable of measuring simultaneously the time distribution and the spectrum of photons coming from a weak source. Two important innovative aspects will characterize this spectrometer: the optical part, realized by means of the Deep Lithography with Particles (DLP), and SPAD (Single Photon Avalanche Diode) detectors under development along with ST-Microelectronics

Light-modulating pressure sensor with integrated flexible organic light-emitting diode

Organic light-emitting diodes (OLEDs) are used almost exclusively for display purposes. Even when implemented as a sensing component, it is rarely in a manner that exploits the possible compliance of the OLED. Here, it is shown that OLEDs can be integrated into compliant mechanical micro devices making a new range of applications possible. A light-modulating pressure sensor is considered, whereby the OLED is integrated with a silicon membrane. It is shown that such devices have potential and advantages over current measurement techniques. An analytical model has been developed that calculates the response of the device. Ray tracing numerical simulations verify the theory and show that the design can be optimised to maximise the resolution of the sensor

Comprehensive numerical design approach for refractive laser beam shapers to generate annular irradiance profiles

A refractive laser beam shaper typically consists of either two plano-aspheric lenses or one thick lens with two aspherical surfaces. Ray mapping is a general optical design technique for irradiance reshaping based on geometric optics. Although ray mapping, in principle, allows generating any rotational-symmetric irradiance profile, in the literature this technique is mainly used to transform a Gaussian irradiance profile to a uniform rotational-symmetric profile. For more complex profiles, especially with low intensity in the inner region (such as annular profiles), a high sampling rate is required to ensure an accurate calculation of the surfaces. In practice, the high sampling rate increases the numerical effort to calculate the aspherical surfaces and the simulation time to verify the design considerably. In this work, we evaluate different sampling approaches and surface construction methods. This allows us to propose and demonstrate a comprehensive numerical approach to efficiently design refractive laser beam shapers to generate rotational-symmetric collimated beams with annular irradiance profiles. Ray tracing analysis for several annular irradiance profiles demonstrates the excellent performance of the designed lenses and the versatility of our design procedure.status: publishe

OLED integrated silicon membranes for light-modulation devices

Organic light-emitting diodes (OLEDs) are most frequently used for display purposes and while they have also been utilized in sensing applications, their innate compliance has not previously been exploited for these applications. However, in this manuscript it is shown that OLEDs are compatible with microfabrication methods used in the production of micro mechanical devices. In particular it is shown that the compliance of OLEDs can be utilized in, and not limited to, a new generation of opto-mechanical pressure sensors. A fabrication process for a light-modulating pressure sensor is described. Prototypes were fabricated and tested and the response compared to an analytical theory developed by the authors. It is shown with simple circuitry, a resolution of 11.4 Pa up to 350 kPa is attainable using this technology