In order for Terahertz (THz) technology to enter the forefront of the industry, technology to generate THz wave with simple structure and low cost is required. This paper suggests compact and portable THz imaging system by the use of Single Mode Fabry-Perot Laser Diodes (SMFPLD). The existing THz system has a disadvantage that it is bulky, complicated, expensive, and difficult to use. To compensate for this, we use an inexpensive and simple FPLD combined with an external cavity to construct a THz imaging system. SMFPLD shows a steady longitudinal mode state through self-injection locking by means of a built-in aspherical lens. The position of the dominant mode changes as the current and temperature are controlled, and the dual mode is also generated under certain conditions. This characteristic is a great advantage in the photomixing method that requires two lasers. Because a laser alone can create a THz wave, and it creates two frequencies in a single family, it is not necessary to consider polarization or phase differences. Based on these advantages, we have constructed a laser module and combined with PCA to create a THz imaging system. A THz imaging systems demonstrated in this paper are superior to ordinary systems due to their inexpensive and compact structure.
In this paper, a surface plasmon resonance sensor for the detection of refractive index variation is presented. A novel waveguide type surface plasmon resonance sensing configuration with focal length variable liquid lens is introduced. The method of surface plasmon resonance sensor is based on the waveguide type with incident angle variation. The incident angle is varied by using an electrowetting liquid lens which is possible to actively change focal length as applying voltage. The optical system, which is adapted to electrowetting lens can continuously change the incident angle of light from 73 to 78 degrees with compact size. The surface plasmon waves are excited between metal and dielectric interface. The sensing surfaces are prepared by a coating of gold metal above high refractive index glass substrate. The incident light which is 532nm monochromatic light source passes through a noble metal coated substrate to detect intensity with incident angle variation. An analysis to distinguish the contribution of light with various incident angle is focused on the angular characteristics of the surface plasmon sensor under wavelength interrogation. The resonance angle is determined corresponding to sensing material refractive index with high sensitivity. The result suggests that the performance of surface plasmon resonance sensor can be improved by real time varying incident angle. From this presented study, it provides a different approach for angular interrogation surface plasmon resonance sensor and can be miniaturized for a portable device.
Surface plasmon resonant (SPR) phenomenon is widely researched for various purposes, among which biomedical sensing is getting more attentions as they are suitable for surface functionalization acting as a bio recognition element to detect different biological infections. The common method of surface resonant is propagating SPR such as reflection method. Another method which is widely used for SPR is localized SPR which use nanostructures in thin metal. Various structures such as slit only, slit- groove and slit-multiple groove are used for generation of SPR and obtaining the optimum optical transmittance through the structure. The number and position of slits and grooves affect transmittance through the structure. In this paper we propose a new structure of cross slit-grooves structure, which includes slit-groove structure in grid form. The slit-grooves structures are arranged in such a way that it forms symmetrical structure in two dimension with slit and groove and hence the transmittance with cross slit-grooves structure increases significantly. The cross slit-grooves structure takes the advantage of symmetrical slit and groove by using both dimensional structures for generating SPR which increases the transmittance through the structure. A comparison of proposed slit-grooves grid structure with straight slit-grooves structure is carried out to show the increase in transmittance through the cross slit-grooves grid structure. Plane wavelength of 400 nm to 900 nm is used for the analysis of transmittance through the Ag slit-grooves grid structures with glass substrate. We also measure the change in transmittance with change in refractive index, which can be helpful for measuring different chemical analytes, and hence can be used for different chemical and biosensors applications.
In this research, electrowetting liquid lens array on curved substrates is developed for wide field of view image sensor. In the conventional image sensing system, this lens array is usually in the form of solid state. However, in this state, the lens array which is similar to insect-like compound eyes in nature has several limitations such as degradation of image quality and narrow field of view because it cannot adjust focal length of lens. For implementation of the more enhanced system, the curved array of lenses based on electrowetting effect is developed in this paper, which can adjust focal length of lens. The fabrication of curved lens array is conducted upon the several steps, including chamber fabrication, electrode & dielectric layer deposition, liquid injection, and encapsulation. As constituent materials, IZO coated convex glass, UV epoxy (NOA 68), DI water, and dodecane are used. The number of lenses on the fabricated panel is 23 by 23 and each lens has 1mm aperture with 1.6mm pitch between adjacent lenses. When the voltage is applied on the device, it is observed that each lens is changed from concave state to convex state. From the unique optical characteristics of curved array of liquid lenses such as controllable focal length and wide field of view, we can expect that it has potential applications in various fields such as medical diagnostics, surveillance systems, and light field photography.
Conventionally, poly (dimethylsiloxane) lens array is fabricated by replica molding. In this paper, we describe simple method for fabricating lens array with expanding property of PDMS. The PDMS substrate is prepared by spin coating on cleaned glass. After spin coating PDMS, substrate is treated with O2 plasma to promote adhesion between PDMS substrate and photoresist pattern on it. Positive photoresist az-4330 and AZ 430K developer is used for patterning on PDMS. General photolithography process is used to patterning. Then patterned PDMS substrate is dipped to 1- Bromododecane bath. During this process, patterned photoresist work as a barrier and prevent blocked PDMS substrate from reaction with 1-Bromododecane. Unblocked part of PDMS directly react with 1-Bromododecane and results in expanded PDMS volume. The expansion of PDMS is depends on absorbed 1-Bromododecane volume, dipping time and ratio of block to open area. The focal length of lens array is controlled by those PDMS expansion factors. Scale of patterned photoresist determine a diameter of each lens. The expansion occurs symmetrically at center of unblocked PDMS and 1-Bromododecane interface. As a result, the PDMS lens array is achieved by this process.
In this paper, we present a depth enhancing technique for integral imaging (II) system using a varifocal lens array. Expressible depth range of II is restricted in a specific region. If the image gets out of the region, displayed image becomes distorted and broken. The center of the region which called central depth plane (CDP) is defined by the focal length of lens array. In our experiment, liquid lens array is used for II system instead of ordinary solid lens array. The focal length of lens array varies depending on the applied voltage across. As a result, the proposed II system enables control of the location of image planes electrically. With this depth plane controllable system, time multiplexed II system is implemented. For this purpose, two objects of different positions and appropriate voltage level for each object are chosen. In display panel, elemental images for each object are alternately displayed with high frame rate and appropriate voltage levels are applied to the liquid lens array. Because the time period between two sequences is very short, both objects are seems to appear simultaneously. Hence the depth range of the constructed image is enhanced.
Generally, volumetric 3D display panel produce volume-filling three dimensional images. This paper discusses a volumetric 3D display based on periodical point light sources(PLSs) construction using a multi focal lens array(MFLA). The voxel of discrete 3D images is formed in the air via construction of point light source emitted by multi focal lens array. This system consists of a parallel beam, a spatial light modulator(SLM), a lens array, and a polarizing filter. The multi focal lens array is made with UV adhesive polymer droplet control using a dispersing machine. The MFLA consists of 20x20 circular lens array. Each lens aperture of the MFLA shows 300um on average. The polarizing filter is placed after the SLM and the MFLA to set in phase mostly mode. By the point spread function, the PLSs of the system are located by the focal length of each lens of the MFLA. It can also provide the moving parallax and relatively high resolution. However it has a limit of viewing angle and crosstalk by a property of each lens. In our experiment, we present the letter ‘C’, ‘O’, ‘DE’ and ball’s surface with the different depth location. It could be seen clearly that when CCD camera is moved to its position following as transverse axis of the display system. From our result, we expect that varifocal lens like EWOD and LC-lens can be applied for real time volumetric 3D display system.
Electrowetting has been widely studied for various optical applications such as optical switch, sensor, prism, and display. In this study, vari-focal liquid lens array is developed using electrowetting principle to construct integral 3-dimensional imaging. The electrowetting principle that changes the surface tension by applying voltage has several advantages to realize active optical device such as fast response time, low electrical consumption, and no mechanical moving parts. Two immiscible liquids that are water and oil are used for forming lens. By applying a voltage to the water, the focal length of the lens could be tuned as changing contact angle of water. The fabricated electrowetting vari-focal liquid lens array has 1mm diameter spherical lens shape that has 1.6mm distance between each lens. The number of lenses on the panel is 23x23 and the focal length of the lens array is simultaneously tuned from -125 to 110 diopters depending on the applied voltage. The fabricated lens array is implemented to integral 3-dimensional imaging. A 3D object is reconstructed by fabricated liquid lens array with 23x23 elemental images that are generated by 3D max tools. When liquid lens array is tuned as convex state. From vari-focal liquid lens array implemented integral imaging system, we expect that depth enhanced integral imaging can be realized in the near future.