Title

Nanosecond - Cw Visible-Ir All-Optical Switching And Nonlinear Transmission With A Nonlinear Organic Optical Liquid In Bulk And Guided Wave Geometry

Abstract

Passive all-optical protection against such multiple time-scales and extremely broadband intense light sources is rather challenging due to the fact that an optical limiting mechanism that is efficient in one time scale usually become rather inefficient in another time scale. Nonlinear absorptions such as Two-Photon absorptions [TPA] and Excited State absorption [ESA] that are effective for limiting nanosecond laser pulses simply do not work in the microseconds and longer time scales as a result of the reduction in power/intensity for the same energy flux. In these time scales, a variety of approaches and materials, including dye-doped aligned nematic liquid crystals, have emerged as promising alternatives [1, 2]. In this presentation, we describe another promising organic material that enables all-optical switching in an extremely wide time scales spanning sub-nanoseconds to cw regime - a nonlinear neat organic liquid (L34) in bulk or wave-guided [fiber core] structure. In the visible spectrum [400 -700 nm], quantitative z-scan and pump-probe techniques [3,4] have shown that in the sub-nanosecond time scales, the dominant nonlinear absorption processes are two-photon coupled to excited state absorption processes characterized by an intrinsic two photon absorption coefficient of ∼5 cm/GW, and an intensity dependent effective two-photon absorption coefficient that can be over 200 cm/GW. For longer time scales, the transparency of the liquid allows doping with appropriate absorbers to generate efficient thermal/density and nonlinear scattering effects [as well as guided mode extinction in fiber geometry] for all-optical switching operations. Accordingly, one may envision single material constituent device capable of all-time scale optical switching applications. Fig. 1 and 2 illustrate the exemplary 'performance' characteristics of the liquid with visible lasers. The nonlinear absorption properties of L34 for nanosecond laser for 532 nm nanosecond lasers pulses are shown in Fig. 1; the liquid is highly transparent [over 98%] at low input energy. As a result of the multi-photon absorption, the transmission at high input intensity is severely clamped. As previously reported [3], fiber array made with L34 cores are capable of sub-μJ limiting threshold and clamped transmission below the MPE [Maximum Permissible Exposure] value of < 1 μJ. In microseconds and longer time scales optical switching exemplary results are shown in Fig. 2 for three detection configurations [Bulk: Open aperture; closed aperture. Fiber: Open aperture]. In this case, milliseconds [488 nm] laser square pulses derived from a cw laser with an electronic shutter are used. All detection configurations exhibit 'classic' limiting behavior, with differing thresholds and clamped transmission values. Lower clamped transmission and thresholds are obtained for the case where the liquid is used as the guiding core of a fiber array, or a bulk sample with 'Closed Aperture' detection. We have performed similar experiments with microsecond laser pulses [Alexandrite laser at 750 nm] and cw - microseconds 1550 nm lasers and obtained similar switching performance. With optimization of various configuration parameters and material properties, including use of appropriate dopants, one can envision several organic liquid based devices with extraordinary performance characteristics. © 2007 IEEE.

Publication Date

12-1-2007

Publication Title

LEOS Summer Topical Meeting

Number of Pages

204-205

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

DOI Link

https://doi.org/10.1109/LEOSST.2007.4288404

Socpus ID

50249128764 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/50249128764

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