We report the modeling and characterization of adaptive voltage controlled electro-optic microlenses. First, we utilize finite element analysis (FEA) to simulate the induced electro-optic effect in lanthanum-modified lead zirconate titanate (PLZT). FEA simulation provides microlens parameters such as phase and focal length. A simple z-scan method is developed to fully characterize the adaptive voltage controlled linear lens. Experimental z-scan results are shown to match the theoretical predictions from FEA.
We theoretically demonstrate 2-dimensional beam shaping through adaptive feedback in two adjacent and orthogonally oriented acousto-optic devices with electrical feedback using experimentally determined parameters. Cases of positive and negative feedback from undiffracted and diffracted orders are investigated. In addition, we demonstrate the dependence of the final value of the induced grating strength in the acousto-optic cell on the feedback parameters.
We here report on the modeling and characterization of adaptive microlenses. We first address device simulation with the theoretical treatment of its characterization. A follow-up paper addresses the experimental results of the focal length measurements using a simple Z-scan method. In addition, the sources of error and ways to overcome them are discussed. Previously, an adjustable electro-optic microlens with concentric electrodes was presented. The electrostatic potential was found by numerically solving Laplace's equation where the surface charge method was incorporated. The refractive index distribution within the lens aperture and the effective light path modulation was found by integration over the entire substrate thickness. We have used finite element analysis to characterize the electrostatic field distribution within the lens aperture. Unlike the previous theoretical treatment, we implement the beam propagation method to calculate the total phase delay. This will allow for accurately modeling the phase based on the optical field profile, medium inhomogeneties, and scattering and depolarization effects. Furthermore, we represent the theoretical basis for characterizing such types of lenses, and microlenses in general. In this method, we implement Fresnel diffraction and a simple Z-scan method. This technique allows for finding the lens focal length, and its sign, and study aberration effects as well.
In the second paper of two papers that address the modeling and characterization of adaptive microlenses, we report the theoretical basis for characterization of such lenses based on the z-scan method. In addition we compare the experimental measurement results with the simulated results obtained using Finite Element Analysis (FEA) utilizing FEMLABTM in the first paper. Some of the method advantages and limitations will be briefly addressed.
A simple technique for focal length measurements of adaptive micro-lenses using z-scan is reported. Focal length is one of the most important parameters of any lens. The effective focal length is measured with reference to the principal points that are not easy to find especially for micro-lenses. In addition, variable focal length microlenses pose a different challenge that makes the process of determining their exact focal length a tedious and difficult process. Classical methods such as nodal slide and magnification have been used for focal length determination. Also, advanced Interference techniques such as Talbot, Moire, Digital Speckle, Zygo and Joint Fourier Transform were used for focal length measurements. These techniques require more elaborate setups and difficult to implement, especially for microlenses. Recently a power meter was used to find the focal length of an unknown lens. Most of the techniques mentioned above proof to be not simple for microlens characterization. The z-scan technique has been implemented, for quite sometimes, to characterize the third-order effects of a nonlinear optical material. The z-scan provides information on both the sign and magnitude of the non-linear refractive index and offer advantage of simplicity. We have used a regular lens to collimate and focus light unto the lens under test. By scanning the lens under test and measuring the on-axis intensity, one can find the focal length. This is because the on-axis intensity is proportional to the phase of the lens and therefore the focal length. In the case of an adaptive lens with its focal length is a function of the applied voltage, the scanning occurs for each voltage value that will correspond to the on-axis refractive index change and therefore the far field on-axis intensity. This described technique above is easy to implement and can achieve good accuracy due to the inherent sensitivity of the z-scan.
We demonstrate beam shaping in a hybrid acousto-optic device with adaptive electronic feedback. Cases of positive and negative feedback, and from the un-diffracted and diffracted orders are investigated. We also show the dependence of the final value of the induced grating strength in the acousto-optic cell on the feedback parameters.
In this paper we present the development and characterization of Lanthanum modified Lead Zirconate Titanate (PLZT)-based Electro-optic (EO) devices for micromacined bio-photonics systems. Spatial light modulator and Dynamic programmable microlens array have been designed, fabricated and initial results have been obtained for such applications. Fully integrating light sources, detectors and dynamic filtering in recently emerging bio-photonics and Capillary Electrophoresis (CE) systems is of immediate need. An optical module that contains such devices was made using microfabrication technologies on the optically active PLZT ceramic wafer. A PLZT wafer was polished and sandwiched and bonded between 2 plastic wafers to form such optical module. Laser micromachining was implemented to etch precise, and well aligned via holes in the plastic wafers to provide windows for light sources and electrical connections to our devices. The electro-optic coefficient for the PLZT was measured in the longitudinal configuration, where light propagates in the direction of the applied field. A mathematical expression was derived for the lens effect on the far field diffraction pattern of the dynamic microlens. Such diffraction pattern can be used to measure the focal length variation with the applied voltage. Preliminary results show the variation of focal lens with the applied voltage that ranges from 50 to 300 volts.