High Speed Characterization of Spatial Light Modulators and its Applications to Optical Information Processing
E G. Paek
An experimental measurement system that allows high speed (100 nsec resolution) temporal characterization and visualization of a smart pixel or a spatial light modulator is described. The application of the measurement system for various optical information processing is proposed.Optical information processing has a great potential for future information manipulation over information superhighway including the internet. However, the practical use of the enormous computational power by light has been hampered by the rapid development in electronic counterparts that allow real-time image processing at the chip level. Fortunately, the recent advances in spatial light modulator (SLM) technologies [1,2] as well as fast two-dimensional detector arrays show promise for ultra-fast information processing that is not attainable by electronic means. To fully utilize the speed of the fast SLM's or smart pixels, it is important to accurately understand and characterize the temporal dynamics of the array devices.To characterize the temporal behavior of such ultrafast SLM's requires bulky and expensive high speed photographic instruments. Therefore, many of the current measurements are performed globally using a single detector that collects all the light through an SLM that has the same pixel value over the entire image. Such a global measurement cannot render information on local variation of fast-evolving images. The local variation includes the temporal delays among pixels of an SLM due to distances from electrodes or to the loading of an image from top to bottom or from left to right depending on the addressing scheme of a display device.A high speed stroboscopic imaging system using an acousto-optic modulator as a shutter has been used to obtain a series of high speed images[3,4]. However, the previous methods required coherent laser illumination with single wavelength and polarization and the input illuminating beam had to be highly collimated. Therefore it could not be used for self-luminous display devices such as CRT's or smart pixels. Moreover, the temporal resolution was limited to several microseconds mainly due to the limited aperture time and contrast of an acousto-optic modulator. Finally, the optical system including a laser, modulator and a driver was bulky and expensive and output image quality was poor due to the speckle effect.In this paper, we present an improved version that has higher temporal resolution (100 nsec) and can accommodate any kind of display devices or array devices including an array of smart pixels or VCSEL's. The system is based on the electronic exposure control of a CCD and is shown in Figure 1. A series of repetitive images generated by a pattern generator is presented on the display device upon receiving a triggering signal. The same triggering signal is passed through a delay generator that generates a delayed triggering signal with a certain amount of delay and width. The delayed triggering signal is used to trigger the high-sensitive cooled CCD that senses light only while the pulse is applied. The series of patterns presented on a display device under test is imaged at the CCD by a lens. The event at a certain time can be monitored by selecting the amount of delay accordingly.The high speed photography is used to monitor temporal evolution of images inside several fast SLM's. Also, a pixel-level image loading is monitored for slow speed display devices such as CRT's. The implication of the transient image evolution on optical information processing will be discussed.This work was supported by the Advanced Technology Program of U.S. Department of Commerce.
Annual Meeting Conference proceedings: LEOS
November 8-11, 1999
IEEE Lasers and Electro-Optics Society (LEOS) Conference
High Speed Characterization of Spatial Light Modulators and its Applications to Optical Information Processing, Annual Meeting Conference proceedings: LEOS
(Accessed February 21, 2024)