NOnlinear Optical Devices: Relative Status of Polymeric Materials
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NONLINEAR OPTICAL DEVICES:
George I.
RELATIVE STATUS OF POLYMERIC MATERIALS
Stegeman
Center for Research in Electro-Optics and Lasers University of Central Florida Orlando, FL 32826
INTRODUCTION Nonlinear optical phenomena have been investigated over the last three decades in many different materials and a great deal of progress has been made in both the basic science and device applications.(1] Although interest in nonlinear organic materials dates back to the early days of nonlinear optics, it is only in the last five years that progress has been sustained and rapid. The purpose of this paper is to examine progress in developing new nonlinear organic materials and in their application to devices for comparison with current state-of-the-art devices using other material systems. A compact, long-lived source of a few milliwatts power in the blue spectral region has recently become an urgent need for optical data storage and xerography.[2] The reliability of semiconductor lasers operating in the blue has not been established and the efficient doubling of semiconductor diode lasers operating in the near infrared has emerged as the most viable approach. A key development has been the discovery of new waveguide phase-matching techniques.[3,4] As a result many of the largest nonlinear coefficients, for example d 33 = 35 pm/V in LiNbO3 [4], can now be used in waveguiaing geometries. Furthermore, new second-order active organic materials have been synthesized and coefficients measured up to an order of magnitude larger than those in the best dielectrics such as lithium niobate. [5-8] Already the reports of organics in waveguide second harmonic doubler geometries make it clear that these materials should ultimately outperform other materials. (8-11] The main problems reside not in finding materials with yet higher nonlinearities, but instead in tailoring other properties of the material for suitable device fabrication and stability. The fact that poled polymers with second order activity are being independently developed for electro-optic applications will accelerate their development for SHG.[12] Materials with an intensity-dependent refractive index have been slower in being adopted for devices. Bistability, logic gates, nonlinear grating coupling, all-optical switching, optical limiting etc. have all been successfully demonstrated.[13-20] Although the large nonlinearities associated with organic materials were pointed out in the 1970s, the detailed investigation of the physics of organic nonlinearities and their application in device demonstrations has lagged behind that of other materials, semiconductors for example. [21] Although large nonlinearities have been reported in organics, in many cases the degree of resonance enhancement was not clear and in some cases the nonlinearities were possibly thermal in origin. Despite such limitations, optical bistability and logic gates have been reported in Fabry-Perot Mat. Res. Soc. Symp. Proc. Vol. 228. V1992 Materials Research Society
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