The lens is a very familiar optical element, which belongs to the passive optical elements, used to converge and diverge light radiation in the optical system. Usually lenses are relatively large in size, visible to the human eye, and are refractive optical elements that follow the laws of refraction, and their optical properties can be well studied with the knowledge of geometric optics. Identical lenses arranged in a certain period of time in a plane will constitute a lens array, the optical properties of the lens array composed of ordinary lenses is the synthesis of the function of a single lens.
However, with the progress of science and technology, the current instrumentation has been toward the trend of optical, mechanical and electrical integration development trend. The use of traditional methods of manufacturing out of optical components is not only complex manufacturing process, and manufacturing out of optical components of large size and weight, has been unable to meet the needs of today's scientific and technological development. At present, people have been able to produce a very small diameter lenses and lens arrays, such lenses and lens arrays usually can not be recognized by the human eye, only with microscopes, scanning electron microscopes, atomic force microscopes and other equipment can be observed, which is the microlens and microlens arrays.
The microlenses and microlens arrays made by micro-optics technology have become a new direction of scientific research development with its advantages of small size, light weight, easy integration and arraying. With the trend of miniaturization of optical components, many new technologies have been developed to reduce the size of lenses and lens arrays, and it is now possible to produce microlenses and microlens arrays with diameters of millimeters, micrometers and even nanometers.
In the 1980s, a new type of tiny optical array device self-focusing planar microlens arrays developed, which used the then-advanced photolithography process, the production of aligned, structurally homogeneous microlens arrays, and microlens arrays, the surface of the plane, easy to coupled with other planar components connected, and has a better focusing, collimation, routing, imaging, wavelength division multiplexing, switching, isolation and other three-dimensional functions. In addition, due to the small diameter of a single lens, the lens density is high, which can realize the large capacity of information, multi-channel parallel processing. Therefore, it has gained important applications in optical sensing, optical computing, fiber optic communication and other optoelectronic devices.
In 1992, Sony of Japan reported the integration of microlens arrays with CCD monoliths to produce highly sensitive CCD devices. Microlens array and CCD integration can improve the fill factor of the CCD and thus improve the sensitivity and signal-to-noise ratio of the CCD. the CCD consists of a number of light-sensitive elements, light-sensitive elements will be obtained by the conversion of optical signals into electrical signals, and then transferred out. Due to the existence of shift registers and transfer gate, there are obvious gaps between the photosensitive elements, falling on the CCD signal light about 2 / 3 and can not be picked up by the photosensitive elements.CCD fill factor is only 20.30%, resulting in the CCD lower photosensitivity. This is incident to the CCD other areas of the signal light will be wasted, the signal light utilization is very low. Therefore, the main role of the microlens array is to make the original fall into the dielectric layer on the photons due to the role of the microlens to make the deflection falls into the photosensitive area, to improve the filling factor of the CCD. Through the use of microlens arrays on CCDs, light is focused on the CCD photosensitive element, which can make CCDs get a substantial increase in sensitivity, and the quantum efficiency of CCDs in the visible spectral range of an average increase of two times.
In 1994, Philip R & D Center successfully produced a two-dimensional large-area image sensing microlens array. The diameter of the microlens is 190um, the spacing is 200um, and the focal length of the microlens is from 200-450um. the microlens arrays improve the response speed of the sensor device without affecting the image resolution.
In 1997, the United States Massachusetts Institute of Technology (MIT) Lincoln Laboratory researchers used the mass transfer method, successfully produced a refractive non-spherical microlens arrays, used for beam collimation of tapered resonant cavity lasers, so that the diffraction-limited beam divergence angle of only 0.43. And to achieve the coupling with single-mode fiber.
In 2002, researchers at the University of Osaka used microlens arrays integrated with a second harmonic generation microscope (second harmonic generation microscopy) to propose a multifocal scanning technique, which, compared with the traditional single-focal scanning method, enabled a tens of-fold improvement in the detection efficiency of the second harmonic generation and the image acquisition rate. This technique has improved the detection efficiency and image acquisition rate of second harmonic generation tens of times compared with the traditional single-focus scanning method.
In 2005, researchers in South Korea reported that microlens arrays were used in very large-size 3D imaging displays, and that the microlens arrays were able to increase the field-of-view of the displays, while displaying images that were very clear and free of distortion.
In 2006, researchers at Stanford University in California successfully utilized microlens arrays to replace the single lens imaging in digital cameras, greatly increasing the depth of focus and field of view of the camera. Cameras equipped with microlens arrays are not only able to make distant and near images clear, even the background is also very clear, while the general camera can only get near or far images.
In 2007, researchers at South Korea's LG reported the use of high fill factor microlens arrays to enhance the light output efficiency of OLEDs. They utilized a micromechanical fabrication process of trench molding and polymer layered vapor deposition to create high fill factor microlens arrays on the surface of the OLED device, increasing the output efficiency of the OLED by 48%.
In China, researchers have also carried out in-depth studies on the theory and fabrication process of microlens arrays, which have been widely used. For example, the Chengdu Institute of Optoelectronics has successfully used it in practical systems such as wavefront measurement, laser beam diagnosis, laser beam shaping and quality evaluation of optical components; Zhejiang University has conducted in-depth research on its application in dense multicarrier wavelength-division multiplexers; and the Diffractive Micro-Optics Laboratory of the Institute of Optics at Nankai University has conducted in-depth research on the fabrication process of microlenses.
Since microlens arrays have important and extensive applications in micro-optical systems, such as optical information processing, optical computing, optical interconnect, optical data transmission, generation of two-dimensional point light sources, but also for copiers, image scanners, fax machines, cameras, and medical and health care devices. In addition, microlens array devices have been miniaturized and integrated, making them highly adaptable and widely used in communication, display and imaging devices. Elliptical refractive microlens arrays for semiconductor lasers can achieve focusing and collimation of lasers, beam shaping of laser diodes (LDs), which can also be used in optical fibers, optical integration circuits, to achieve effective coupling of optical devices. In fiber optic communications, elliptical microlenses will come from free space light coupled into the optical fiber, and calibrate the light out of the fiber. At present, microlens arrays have been used in the field of atomic optics, the use of microlens arrays made of atomic waveguides, beamsplitters, Mach a Z?ndel interferometer or use it to capture atoms or neutral atoms for quantum information processing. Therefore, it is necessary to study the materials used in microlens arrays, the production process and the use of the research.